U.S. patent application number 11/697568 was filed with the patent office on 2007-08-02 for vehicle having twin transmissions for driving respective wheels.
Invention is credited to Koji Irikura.
Application Number | 20070175676 11/697568 |
Document ID | / |
Family ID | 33489930 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070175676 |
Kind Code |
A1 |
Irikura; Koji |
August 2, 2007 |
Vehicle Having Twin Transmissions For Driving Respective Wheels
Abstract
A vehicle comprises a vehicle frame, a prime mover mounted on
the vehicle frame, a laterally turnable wheel disposed at one side
of the vehicle frame, a pair of drive wheels disposed at the other
side of the vehicle frame, a steering operation device, a traveling
operation device for setting the traveling speed and direction of
the vehicle, and a pair of transmissions for controlling the rotary
speed and direction of the respective drive wheels. The
transmissions are operationally connected with the steering
operation device so as to create a difference of rotary speed
between the drive wheels according to operation of the steering
operation device. The transmissions are operationally connected
with the traveling operation device so as to drive the drive wheels
in a common rotary direction from their stationary state according
to operation of the traveling operation device. A clutch is
interposed between the transmissions so as to connect the drive
wheels with each other when the steering operation device is set in
a straight traveling position. Based on setting of a switching
device for switching the traveling direction of the vehicle between
forward and rearward, a reverser decides the rotational direction
of the drive wheels.
Inventors: |
Irikura; Koji; (Hyogo,
JP) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX P.L.L.C.
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Family ID: |
33489930 |
Appl. No.: |
11/697568 |
Filed: |
April 6, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11327415 |
Jan 9, 2006 |
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11697568 |
Apr 6, 2007 |
|
|
|
10455306 |
Jun 6, 2003 |
7004268 |
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11327415 |
Jan 9, 2006 |
|
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Current U.S.
Class: |
180/6.24 |
Current CPC
Class: |
B62D 11/005 20130101;
B60K 17/10 20130101; B60K 17/356 20130101; B60K 17/36 20130101;
B62D 7/09 20130101; B62D 3/02 20130101; B62D 11/24 20130101; B62D
11/006 20130101 |
Class at
Publication: |
180/006.24 |
International
Class: |
B62D 11/24 20060101
B62D011/24 |
Claims
1. A vehicle comprising: a prime mover; a pair of left and right
steerable wheels; a steering operation device for steering the pair
of left and right steerable wheels; a pair of left and right gear
assemblies interposed between the steering operation device and the
respective left and right steerable wheels, wherein, in each of the
gear assemblies, a first non-circular gear operatively connected to
the steering operation device meshes with a second non-circular
gear operatively connected to each of the left and right steerable
wheels; a pair of left and right unsteerable driving wheels; a
speed control operation device for controlling rotational speeds of
the unsteerable driving wheels; and a pair of continuously variable
transmissions driven by the prime mover so as to drive the
respective unsteerable driving wheels, wherein the speed control
operation device is operatively connected to the continuously
variable transmissions so as to substantially evenly control output
rotational speeds of the continuously variable transmissions, and
wherein the steering operation device is operatively connected to
the continuously variable transmissions so that a differential
rotational speed of the unsteerable driving wheels is increased
according to increase of an operation degree of the steering
operation device.
2. The vehicle according to claim 1, wherein the speed control
operation device is a foot pedal, and wherein the steering
operation device is a steering wheel.
3. The vehicle according to claim 1, wherein the continuously
variable transmissions are operatively connected to the speed
control operation device and the steering operation device so that
a turning direction of the vehicle coincides to an operation
direction of the steering operation device regardless of whether
the speed control operation device is operated for forward
traveling of the vehicle or for backward traveling of the
vehicle.
4. A vehicle comprising: a prime mover; a pair of left and right
steerable wheels; a steering operation device for steering the pair
of left and right steerable wheels; a pair of left and right gear
assemblies interposed between the steering operation device and the
respective left and right steerable wheels, wherein, in each of the
gear assemblies, a first non-circular gear operatively connected to
the steering operation device meshes with a second non-circular
gear operatively connected to each of the left and right steerable
wheels; a pair of left and right unsteerable driving wheels; a
speed control operation device for controlling rotational speeds of
the unsteerable driving wheels; and a pair of hydrostatic
continuously variable transmissions driven by the prime mover so as
to drive the respective unsteerable driving wheels, wherein the
speed control operation device is operatively connected to the
hydrostatic continuously variable transmissions so as to
substantially evenly control output rotational speeds of the
hydrostatic continuously variable transmissions, and wherein the
steering operation device is operatively connected to the
hydrostatic continuously variable transmissions so that a
differential rotational speed of the unsteerable driving wheels is
increased according to increase of an operation degree of the
steering operation device.
5. The vehicle according to claim 4, wherein the speed control
operation device is a foot pedal, and wherein the steering
operation device is a steering wheel.
6. The vehicle according to claim 4, wherein the hydrostatic
continuously variable transmissions are operatively connected to
the speed control operation device and the steering operation
device so that a turning direction of the vehicle coincides to an
operation direction of the steering operation device regardless of
whether the speed control operation device is operated for forward
traveling of the vehicle or for backward traveling of the
vehicle.
7. A vehicle comprising: a prime mover; a pair of left and right
steerable wheels; a steering operation device for steering the pair
of left and right steerable wheels; a pair of left and right gear
assemblies interposed between the steering operation device and the
respective left and right steerable wheels, wherein, in each of the
gear assemblies, a first non-circular gear operatively connected to
the steering operation device meshes with a second non-circular
gear operatively connected to each of the left and right steerable
wheels; a pair of left and right unsteerable driving wheels; a
speed control operation device for controlling rotational speeds of
the unsteerable driving wheels; and a pair of hydraulic units for
driving the respective unsteerable driving wheels, each of the
hydraulic units including a variable displacement hydraulic pump
driven by the prime mover and a fixed displacement hydraulic motor
fluidly connected to the hydraulic pump so as to drive the
corresponding unsteerable driving wheel, wherein the speed control
operation device is operatively connected to the hydraulic pumps so
as to substantially evenly control output rotational speeds of the
hydraulic motors, and wherein the steering operation device is
operatively connected to the hydraulic pumps so that, as an
operation degree of the steering operation device is increased, a
displacement of one hydraulic pump is increased, and
simultaneously, a displacement of the other hydraulic pump is
reduced, so as to increase a differential rotational speed of the
unsteerable driving wheels.
8. The vehicle according to claim 7, wherein the speed control
operation device is a foot pedal, and wherein the steering
operation device is a steering wheel.
9. The vehicle according to claim 7, wherein the hydraulic pumps
are operatively connected to the speed control operation device and
the steering operation device so that a turning direction of the
vehicle coincides to an operation direction of the steering
operation device regardless of whether the speed control operation
device is operated for forward traveling of the vehicle or for
backward traveling of the vehicle.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is continuation of U.S. application
Ser. No. 11/327,415, filed Jan. 9, 2006, which is a divisional of
U.S. application Ser. No. 10/455,306, filed Jun. 6, 2003, now U.S.
Pat. No. 7,004,268, the entire disclosures of which are
incorporated in their entirety herein by reference thereto.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a vehicle equipped with a
pair of transmissions, e.g., a pair of hydrostatic transmissions
(HSTs), a pair of belt type continuous variable transmissions
(CVTs), or a pair of electric motors, for driving respective left
and right drive wheels, wherein the pair of transmissions, which
surely drive the vehicle straight when they are set so, are
operated for left and right turning of the vehicle so that one of
the left and right drive wheels is accelerated and the other is
decelerated, and wherein each of the left and right turning
directions of the vehicle always coincides with the manipulated
leftward or rightward direction of a steering operation device
whether the vehicle travels forward or rearward.
[0004] 2. Related Art
[0005] There is a well-known vehicle having twin parallel
transmissions, such as HSTs, for driving respective left and right
drive wheels. For left and right turning of the vehicle, one of the
transmissions accelerates the corresponding drive wheel (on an
outside of turning), and the other decelerates the other drive
wheel (on an inside of turning). For example, if a steering wheel
serving as a steering operation device of the vehicle is turned
left, one transmission decelerates the left drive wheel, and the
other accelerates the right drive wheel, whereby the vehicle turns
left.
[0006] Incidentally, if the deceleration force applied on the
inside drive wheel becomes relatively larger than the traveling
force thereof, the rotational direction of the inside drive wheel
is reversed. Then, the deceleration force becomes an acceleration
force for the rotationally reversed inside drive wheel.
[0007] Also, unless the steering wheel is operated for turning, the
traveling speed and direction of the vehicle can be changed by
operation of a speed change operation device such as a pedal or a
lever so that both the transmissions drive both the drive wheels at
equal rotary speed. If the steering wheel is turned for turning,
the rotary speed of one drive wheel becomes higher than the equal
rotary speed, and that of the other drive wheel becomes lower than
the equal rotary speed.
[0008] However, the vehicle having the twin transmissions still has
such a problem as follows: When it is assumed that the left drive
wheel is decelerated and the right wheel accelerated by turning the
steering wheel leftward during the forward traveling of the
vehicle, the steering wheel must be turned rightward for left
turning during the rearward traveling of the vehicle because the
acceleration force for a forwardly rotating wheel serves as a
deceleration force for a rearwardly rotating wheel. Such an
operation of the steering wheel is so illusional as to cause the
vehicle to turn to a wrong side.
[0009] As means for coincidence of turning side of a vehicle with a
steering direction whether the vehicle travels forward or rearward,
Japanese Laid Open Gazette No. 2000-25,637 discloses mechanical
means interposed among a transmission, a steering operation device
and a speed changing operation device, and Japanese Patent No.
3,176,237 discloses a hydraulic switching valve provided in an HST
for steering. However, while each of the two Japanese documents
discloses a pair of HSTs for driving two rotors, one of the HSTs is
provided for traveling so as to rotate both the rotors at various
equal speeds, and the other HST is provided for steering so as to
accelerate one rotor and decelerate the other rotor. Therefore,
each of the above-mentioned disclosed means does not correspond to
the vehicle driving system comprising a pair of transmissions for
driving respective right and left drive wheels. Furthermore, while
the rotors disclosed in Japanese Laid Open Gazette No. 2000-25,637
are drive wheels, those disclosed in Japanese Patent No. 3,176,237
are sprockets.
[0010] For another problem of the vehicle comprising the twin
transmissions for driving respective drive wheels, even if the
vehicle is provided with a driving direction changing system which
ensures that one drive wheel on inside of the turning vehicle is
decelerated and the other on outside thereof is accelerated in
correspondence to the turning side of the steering operation device
such as a steering wheel whether the vehicle travels forward and
rearward, the performances of the parallel transmissions must be
strictly equal to each other so as to ensure a straight traveling
when the steering wheel is set in the straight traveling position.
If there is a slight performance difference between the
transmissions, the drive wheels rotate at different speeds so as to
turn the vehicle while the steering wheel is in the straight
traveling position, or a complicated and troublesome adjustment of
a linkage from the steering wheel to the transmissions must be
performed. Moreover, the differential driving of left and right
drive wheels is not requested in such a case where the vehicle
travels on a rough road or one of the drive wheels slumps into
mud.
[0011] For solving this kind of problem, U.S. Pat. No. 5,590,737
discloses a crawler vehicle equipped with a driving system
comprising a pair of HSTs for driving respective right and left
sprockets, wherein a differential-locking clutch is provided so as
to lock the sprockets with each other at need.
[0012] However, this U.S. Patent does not disclose a pair of
transmissions for driving respective right and left drive
wheels.
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a vehicle
including a prime mover, left and right drive wheels, and twin
parallel transmissions for driving the respective drive wheels,
wherein the vehicle is made user-friendly by such a driving
direction changing system as to ensure that each of left and right
turning directions of the vehicle corresponding to the manipulated
direction of the steering operation device is constant whether the
vehicle travels forward or rearward.
[0014] To achieve the object, the vehicle according to the present
invention comprises a traveling operation device for setting a
traveling speed of the vehicle and selecting a traveling direction
of the vehicle between forward and rearward, which is operationally
connected with the pair of transmissions so as to drive the drive
wheels at a common speed and in a common direction, and a steering
operation device for turning the vehicle leftward or rightward,
wherein the steering operation device is operationally connected
with the pair of transmissions so as to accelerate one of drive
wheels at outside of the turning vehicle and to decelerate the
other drive wheel at inside of the turning vehicle. The vehicle
further comprises switching means for switching the traveling
direction of the vehicle between forward and rearward selected by
the traveling operation device, and reversing means provided to the
pair of transmissions so as to reverse driving directions of the
respective drive wheels in correspondence to the switching
operation of the switching means.
[0015] As an aspect for arrangement of the reversing means, in case
that the vehicle includes a common input shaft shared between the
transmissions to receive power of the prime mover, the reversing
means is preferably interposed among the common input shaft and the
pair of input shafts of the respective transmissions.
[0016] As another aspect for arrangement of the reversing means,
the reversing means may be interposed between each of output shafts
of the respective transmissions and each of the drive wheels.
[0017] Assuming that a vehicle includes (1) a prime mover, left and
right drive wheels, and twin parallel transmissions for driving the
respective drive wheels, (2) a traveling operation device for
setting a traveling speed of the vehicle and selecting a traveling
direction of the vehicle between forward and rearward, which is
operationally connected with the pair of transmissions so as to
drive the drive wheels at a common speed and in a common direction,
and, (3) a steering operation device for turning the vehicle
leftward or rightward, which is operationally connected with the
pair of transmissions so as to accelerate one of the drive wheels
at outside of the turning vehicle and to decelerate the other drive
wheel at inside of the turning vehicle whether the vehicle travels
forward or rearward, a second object of the present invention is to
ensure both the drive wheels rotate at the same speed for exact
straight traveling of the vehicle when the steering operation
device is set so the vehicle travels in a straight direction, in
spite of some performance differences between the
transmissions.
[0018] To achieve the second object, the vehicle according to the
present invention comprises a differential locking clutch for the
drive wheels. The differential locking clutch is engaged to lock
the drive wheels with each other when the steering operation device
is set to make the vehicle travel straight, and wherein the
differential locking clutch is disengaged to unlock the drive
wheels from each other when the steering operation device is set to
make the vehicle travel leftward or rightward.
[0019] These, further and other objects, features and advantages
will appear more fully from the following description taken in
connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0020] FIG. 1 is a schematic plan view of a six-wheel vehicle
according to the present invention, including a steering wheel, two
front casters, two middle drive wheels, and two rear drive wheels,
wherein the middle and rear drive wheels are not steerable.
[0021] FIG. 2 is a schematic plan view of another six-wheel vehicle
according to the present invention, including a steering wheel, two
steerable front driven wheels, two middle drive wheels, and two
rear drive wheels, wherein the middle and rear drive wheels are not
steerable.
[0022] FIG. 3 is a schematic plan view of a four-wheel vehicle
according to the present invention, including a steering wheel, two
front drive wheels, and two rear drive wheels, wherein the four
drive wheels are not steerable.
[0023] FIG. 4 is a schematic plan view of another four-wheel
vehicle according to the present invention, including a steering
wheel, two front drive wheels which are not steerable, and two
steerable rear drive wheels.
[0024] FIG. 5 is a diagram of a wheel driving system for a vehicle
according to the present invention, including twin transmissions
for driving respective left and right drive wheels independently,
wherein a differential-locking clutch is provided so as to connect
the left and right drive wheels to each other when a steering wheel
is set in a straight traveling position.
[0025] FIG. 6 illustrates a perspective view of a mechanical
linkage for controlling left and right speed control levers of the
respective twin transmissions, together with a diagram of hydraulic
and electric circuit for controlling the speed control levers and
the differential locking clutch, wherein the linkage and the
hydraulic and electric circuit are provided for the wheel driving
system shown in FIG. 5.
[0026] FIG. 7 is a diagram of another wheel driving system for a
vehicle according to the present invention, including twin
transmissions for driving respective left and right drive wheels
independently, wherein a differential-locking clutch is provided so
as to connect left and right drive wheels to each other when a
steering wheel is set in a straight traveling position, and a
reversing mechanism (a reverser) is provided among a primary input
shaft and respective input shafts of the twin transmissions.
[0027] FIG. 8 is a diagram of another wheel driving system for a
vehicle according to the present invention, including twin
transmissions for driving respective left and right drive wheels
independently, wherein a differential-locking clutch is provided so
as to connect left and right drive wheels to each other when a
steering wheel is set in a straight traveling position, and a
reverser is interposed between an output shaft of each transmission
and each drive wheel.
[0028] FIG. 9 is a perspective view of a mechanical linkage for
controlling left and right speed control levers of the respective
twin transmissions, together with a diagram of hydraulic and
electric circuit for controlling the speed control levers, the
differential locking clutch and the reverser, wherein the linkage
and the hydraulic and electric circuit are provided for any of the
wheel driving systems shown in FIGS. 7 and 8.
[0029] FIG. 10 is a perspective view of the mechanical linkage of
FIG. 9, having an alternative reverser control system.
[0030] FIG. 11 is a diagram of the wheel driving system of FIG. 7,
having an alternative reverser clutch formation.
[0031] FIG. 12 is a diagram of the wheel driving system of FIG. 8,
having an alternative reverser clutch formation.
[0032] FIG. 13 is a perspective view of a mechanical linkage for
controlling left and right speed control levers of the respective
twin transmissions, together with a diagram of hydraulic and
electric circuit for controlling the speed control levers and the
differential locking clutch, wherein the linkage and the hydraulic
and electric circuit are provided for any of the wheel driving
systems shown in FIGS. 11 and 12.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Referring to FIG. 1, a six-wheel vehicle has a vehicle frame
1, on which a vertical crankshaft engine 2, a transmission housing
3 and left and right axle casings 4L and 4R are mounted. Left and
right drive wheels 5L and 5R are disposed on left and right sides
of transmission housing 3, respectively. Left and right drive
wheels 6L and 6R are disposed behind respective drive wheels 5L and
5R. Left and right casters 7 are supported (alternatively, only one
caster 7 or more than two casters 7 may be supported) by a front
portion of vehicle frame 1 so as to serve as laterally turnable
driven wheels, which are free from driving power of engine 2 and
turn to a lateral side coinciding with a turning side of a steering
wheel 14 serving as a steering operation device. Thus, in this
vehicle, casters 7 serve as front wheels, drive wheels 5L and 5R as
middle wheels, and drive wheels 6L and 6R as rear wheels. However,
positions of these wheels may be changed in the longitudinal
direction of the vehicle, e.g., drive wheels 6L and 6R may serve as
front wheels, and casters 7 as rear wheels.
[0034] A belt 8 is interposed between an engine output pulley 9 of
vertical crankshaft engine 2 and a primary input pulley 10 fixed on
a primary input shaft 11 projecting from transmission housing 3 so
as to transmit power from engine 2 to a transmission system in
transmission housing 3. Additionally, belt 8 is looped over a
tension pulley 12 to be tensioned.
[0035] The transmission system in transmission housing 3 comprises
left and right power take-off portions which transmit power to left
and right axle casings 4L and 4R through respective propeller
shafts 13, thereby driving drive wheels 6L and 6R.
[0036] Left and right speed control levers 17L and 17R are pivoted
on transmission housing 3. Steering wheel 14 is operationally
connected to speed control levers 17L and 17R through a power
steering system 15 and respective links 16L and 16R.
[0037] Referring to FIG. 2, left and right steerable driven wheels
60, serving as the laterally turnable wheels as mentioned above,
mechanically interlock with steering wheel 14. A pivot (a king pin)
of each driven wheel 60 is connected to a pivot 61c of each of two
small sector gears 61. Each small sector gear 61 has a front edge
61a and a shorter rear edge 61b. Pivot 61c is disposed extremely
adjacent to an end of gear 61 where both edges 61a and 61b are
gathered. On the other hand, an axle housing for supporting both
driven wheels 60 is provided at each of left and right ends thereof
with each of two large sector gears 62 supported rotatably around
respective vertical pivots. Each large sector gear 62 has a front
edge 62a and a longer rear edge 62b. An end of gear 62 where both
edges 62a and 62b are gathered is pivotally connected to each of
left and right ends of a tie rod 63 interlocking with steering
wheel 14.
[0038] Large sector gears 62 serving as drive gears mesh with
respective small sector gears 61 serving as follower gears. A
distance of a serrated periphery of each gear 61 from pivot 61c
(hereinafter, the distance is referred to as a "radius") gradually
decreases while it passes from front edge 61a to rear edge 61b. As
compensating for the decrease of the radius of gear 61, a distance
of a serrated periphery of each gear 62 from the end of gear 62
pivotally connected to tie rod 63, i.e., a radius of gear 62
gradually increases while it passes from front edge 62a to rear
edge 62b.
[0039] As each driven wheel 60 laterally turns so as to turn its
front end to the proximal side of the vehicle, meshing gears 61 and
62 are rotated so that front edges 61a and 62a approach each other,
whereby a gear ratio of small sector gear 61 to large sector gear
62 increases. On the contrary, as the rear end of driven wheel 60
turns proximally, rear edges 61b and 62b approach each other so as
to decrease the gear ratio of gear 61 to gear 62. Consequently,
during the turning of the vehicle, driven wheel 60 on lateral
inside of the turning vehicle is turned at a larger angle than
driven wheel 60 on lateral outside of the turning vehicle. Thus,
similarly to a vehicle having a caster, the vehicle can turn on a
small circle swiftly even if the angle of steering wheel 14 is not
very large. Moreover, the vehicle is more advantageous than a
vehicle having a caster in that a driver can comprehend the
direction of driven wheels 60 and stably operate the vehicle on a
slope because steering wheel 14 is always connected to driven
wheels 60.
[0040] Referring to FIG. 3, a skid steering type four-wheel vehicle
has left and right front drive wheels 5L and 5R and left and right
rear drive wheels 6L and 6R, wherein none of the four wheels are
steerable. Steering wheel 14 serving as a steering operation device
is manipulated so as to locate left and right speed control levers
17L and 17R. The vehicle selectively travels straight or turns left
or right, depending upon whether or not the rotary speed of left
drive wheels 5L and 6L determined by the location of left speed
control lever 17L coincides with that of right drive wheels 5R and
6R determined by the location of right speed control lever 17R.
[0041] Referring to FIG. 4, a four-wheel vehicle has left and right
front drive wheels 5L and 5R and left and right steerable rear
drive wheels 6L and 6R. Steering wheel 14 is operationally
connected to drive wheels 6L and 6R through a linkage which is
similar with that of FIG. 2.
[0042] Referring to FIG. 5, in transmission housing 3, left and
right HSTs 18L and 18R are disposed oppositely to each other. Each
of HSTs 18L and 18R comprises a hydraulic pump 19 including a
movable swash plate 19a, and a hydraulic motor 20 including a fixed
swash plate 20a. Hydraulic pump 19 and hydraulic motor 20 are
fluidly connected with each other through a center section 21.
Speed control levers 17L and 17R interlock with respective movable
swash plates 19a (See FIG. 4).
[0043] Pump shafts 19b of both hydraulic pumps 19 are extended
toward each other. Bevel gears serving as HST input gears 19c are
fixed onto ends of pump shafts 19b facing each other, respectively.
An upper wall of transmission housing 3 rotatably supports primary
input shaft 11 vertically. Above-mentioned primary input pulley 10
is fixed onto the outer end of primary input shaft 11. A bevel gear
22 is fixed onto the other inner end of primary input shaft 11 and
meshes with both HST input gears 19c. Incidentally, primary input
shaft 11 penetrates charge pump 23 so as to serve as a drive shaft
of charge pump 23.
[0044] Alternatively, if an engine has a horizontal crankshaft,
primary input shaft 11 is supported horizontally by transmission
housing 3. An outer end of horizontal primary input shaft 11
penetrating charge pump 23 may be extended outward from
transmission housing 3 so as to serve as a PTO shaft for driving a
working machine attached to the vehicle.
[0045] Motor shafts 20b of both HSTs 18L and 18R are extended
toward each other and connected/disconnected through a differential
locking clutch 24. Oppositely to differential locking clutch 24,
each motor shaft 20b projects from center section 21 so as to be
provided thereon with a brake 25. Differential locking clutch 24 is
a spring-loaded hydraulic clutch, which is engaged by spring force
and disengaged by hydraulic pressure overcoming the spring force.
The hydraulic pressure for disengaging differential locking clutch
24 is applied by fluid supplied by a later-discussed electric and
hydraulic circuit.
[0046] Each of drive wheels 5L and 5R is fixed to each of left and
right drive axles 27 rotatably supported by transmission housing 3.
Motor shafts 20b engage with respective counter shafts 26 through
deceleration gears 20c and 26a. Counter shafts 26 engage with
respective drive axles 27 through deceleration gears 26b and 27a.
Left and right drive axles 27 project laterally outward from
transmission housing 3 oppositely to each other and are provided on
their outer ends with respective drive wheels 5L and 5R.
[0047] Each counter shaft 26 is extended outward in transmission
housing 3 so as to be fixedly provided on its distal end with a
bevel gear 26c, which meshes with a bevel gear 29a fixed on an
inner end of each of left and right PTO shafts 29. Each PTO shaft
29 projects rearward from transmission housing 3 so as to be joined
to propelling shaft 13 through a universal joint.
[0048] In each of axle casings 4L and 4R, a horizontal input shaft
31 and a horizontal drive axle 32 are rotatably supported mutually
perpendicularly and engage with each other through bevel gears 31a
and 32a fixed onto respective shafts 31 and 32. Input shaft 31
projects outward from each of axle casings 4L and 4R so as to be
joined to propelling shaft 13 through a universal joint. Drive
axles 32 project laterally outward from respective axle casings 4L
and 4R oppositely to each other and are provided on their outer
ends with respective drive wheels 6L and 6R.
[0049] Each PTO shaft 29 is intermediately provided with a clutch
30. Clutches 30 are engaged or disengaged so as to put the vehicle
into either a four-wheel drive (4WD) mode or a two-wheel drive
(2WD) mode.
[0050] Referring to FIG. 6, a structure of power steering system 15
(see FIG. 1) for controlling speed control levers 17L and 17R will
be described. A forward traveling shift pedal 33 and a rearward
traveling shift pedal 34 (together, the traveling operation device)
are juxtaposed above a footboard on the vehicle. A pressure-sensing
switch 35F is disposed on forward traveling shift pedal 33 so as to
be switched on by a driver's foot when pedal 33 is depressed. A
pressure-sensing switch 35R is disposed on rearward traveling shift
pedal 34 so as to be switched on by a driver's foot when pedal 34
is depressed.
[0051] A support shaft 36 is disposed horizontally and fixed to a
vehicle body such as vehicle frame 1. A sleeve 37 is relatively
rotatably disposed around support shaft 36. A shaft 38 is fixedly
extended upward from sleeve 37 radially about shaft 36. A sleeve 39
is relatively rotatably provided around shaft 38. A top of shaft 38
projects upward from sleeve 39.
[0052] An arm 33a fixedly projects upward from a boss of forward
traveling shift pedal 33 serving as a pivot of pedal 33. A link 45
is connected at one end thereof to arm 33a so as to be pulled by
depression of pedal 33. An arm 34a fixedly projects downward from a
boss of rearward traveling shift pedal 34 serving as a pivot of
pedal 34. A link 46 is connected at one end thereof to arm 34a so
as to be pushed by depression of pedal 34. Links 45 and 46 are
joined at the other ends thereof to the top of shaft 38.
[0053] When neither pedal 33 nor 34 is depressed, sleeve 37 is
biased by neutral-returning springs (not shown) interposed in
respective links 45 and 46 so as to locate shaft 38 at a neutral
position N. By depressing pedal 33, link 45 pulls the top of shaft
38 so as tilt shaft 38 forward from neutral position N to a maximum
forward traveling speed position Fm in forward traveling range F in
correspondence to the depth of depressed pedal 33. By depressing
pedal 34, link 46 pushes the top of shaft 38 so as to tilt shaft 38
rearward from neutral position N to a maximum rearward traveling
speed position Rm in rearward traveling range R in correspondence
to the depth of depressed pedal 34. Thus, by depressing either
pedal 33 or 34, shaft 38 is rotated forward or rearward together
with sleeve 37 around shaft 36.
[0054] A pair of opposite traverse bars 39a are fixedly extended
from sleeve 39 radially about shaft 38. Bars 39a are connected at
utmost ends thereof to respective links 16L and 16R extended from
speed control levers 17L and 17R. Consequently, either pedal 33 or
34 is depressed so as to tilt sleeve 39 together with shaft 38
forward or rearward and move the utmost ends of traverse bars 39a
with links 16L and 16R forward or rearward, thereby rotating speed
control levers 17L and 17R to an equal degree.
[0055] By depressing forward traveling shift pedal 33, both levers
17L and 17R are pulled and rotated from their neutral positions
through links 16L and 16R, thereby rotating movable swash plates
19a of HSTs 18L and 18R so as to accelerate drive wheels 5L and 5R
forward. On the contrary, by depressing rearward traveling shift
pedal 34, both levers 17L and 17R are pushed and rotated from their
neutral positions through links 16L and 16R, thereby rotating
movable swash plates 19a of HSTs 18L and 18R so as to accelerate
drive wheels 5L and 5R rearward.
[0056] A double-acting hydraulic cylinder 40 is disposed
horizontally in parallel to shaft 36, and its cylinder casing is
fixed to sleeve 37. A piston rod 40a of cylinder 40 is connected to
sleeve 39 through an arm 39b extended radially (perpendicularly to
bars 39a) from sleeve 39. Sleeve 39 is rotated in relative to shaft
38 by telescopic motion of piston rod 40a. Consequently, one bar
39a pulls corresponding one of levers 17L and 17R, and the other
bar 39a pushes the other lever 17R or 17L, so that one of drive
wheels 5L and 5R is accelerated, and the other decelerated.
However, if one drive wheel 5L or 5R is rotated forward and the
other rearward, both drive wheels 5L and 5R are accelerated in
respective forward and rearward directions.
[0057] Hereinafter, the movement of piston rod 40a pushing arm 39b
is defined as extension movement increasing the stroke thereof, and
the movement of piston rod 40a pulling arm 39b as contraction
movement decreasing the stroke thereof.
[0058] By a later-discussed steering valve 41, the stroke of piston
rod 40a is controlled to correspond to a set rotational position of
steering wheel 14. However, the corresponding position of steering
wheel 14 differs due to whether the vehicle travels forward or
rearward, i.e., whether pedal 33 or 34 is depressed.
[0059] When steering wheel 14 is set at a straight traveling
position S14, the stroke piston rod 40a becomes a neutral stroke.
At this time, bars 39a are oriented in a direction S for straight
traveling of the vehicle relative to shaft 38 at any place.
[0060] When piston rod 40a is extended from the neutral stroke to
increase the stroke thereof, sleeve 39 is rotated so that bars 39a
are rotated in shown ranges LT to respective maximum rotational
positions. LTm symmetrically with respect to shaft 38. That is,
left bar 39a rotates rearward from direction S so as to push left
speed control lever 17L rearward, and right bar 39a rotates forward
from direction S so as to pull right speed control lever 17R
forward.
[0061] If shaft 38 is disposed in forward traveling range F where
both swash plates 19a of left and right hydraulic pumps 19 are
tilted in their ranges for forward traveling, rearwardly pushed
left lever 17L reduces the tilt angle of swash plate 19a linked
therewith so as to reduce the capacity of left hydraulic pump 19,
thereby decelerating left drive wheel 5L. Simultaneously, forwardly
pulled right lever 17R increases the tilt angle of swash plate 19a
linked therewith so as to increase the capacity of right hydraulic
pump 19, thereby accelerating right drive wheel 5R. Therefore, the
vehicle turns left.
[0062] If shaft 38 is disposed in rearward traveling range R where
both swash plates 19a of left and right hydraulic pumps 19 are
tilted in their ranges for rearward traveling, rearwardly pushed
left lever 17L increases the tilt angle of swash plate 19a linked
therewith so as to increase the capacity of left hydraulic pump 19,
thereby accelerating left drive wheel 5L. Simultaneously, forwardly
pulled right lever 17R reduces the tilt angle of swash plate 19a
linked therewith so as to reduce the capacity of right hydraulic
pump 19, thereby decelerating right drive wheel 5R. Therefore, the
vehicle turns right.
[0063] When piston rod 40a is contracted from the neutral stroke to
decrease the stroke thereof, sleeve 39 is rotated so that bars 39a
are rotated in shown ranges RT to respective maximum rotational
positions RTm symmetrically with respect to shaft 38. That is, left
bar 39a rotates forward from direction S so as to pull left speed
control lever 17L forward, and right bar 39a rotates rearward from
direction S so as to push right speed control lever 17R
rearward.
[0064] If shaft 38 is disposed in forward traveling range F where
both swash plates 19a of left and right hydraulic pumps 19 are
tilted in their ranges for forward traveling, forwardly pulled left
lever 17L increases the tilt angle of swash plate 19a linked
therewith so as to increase the capacity of left hydraulic pump 19,
thereby accelerating left drive wheel 5L. Simultaneously,
rearwardly pushed right lever 17R reduces the tilt angle of swash
plate 19a linked therewith so as to reduce the capacity of right
hydraulic pump 19, thereby decelerating right drive wheel 5R.
Therefore, the vehicle turns right.
[0065] If shaft 38 is disposed in rearward traveling range R where
both swash plates 19a of left and right hydraulic pumps 19 are
tilted in their ranges for rearward traveling, forwardly pulled
left lever 17L reduces the tilt angle of swash plate 19a linked
therewith so as to reduce the capacity of left hydraulic pump 19,
thereby decelerating left drive wheel 5L. Simultaneously,
rearwardly pushed right lever 17R increases the tilt angle of swash
plate 19a linked therewith so as to increase the capacity of right
hydraulic pump 19, thereby accelerating right drive wheel 5R.
Therefore, the vehicle turns left.
[0066] A steering valve 41 connects each of ports 40b and 40c of
cylinder 40 to either pump 42 or tank 43. Steering valve 41 is an
electro-magnetically controlled hydraulic (servo) valve having
oppositely active solenoids 41a and 41b, which is switched among
three positions, i.e., a neutral position N41, an extension
position E41 and a contraction position C41. In this regard, if a
detected value about an actual position (stroke) of piston rod 40a
is different from a value corresponding to its requested position,
steering valve 41 is set to either extension position E41 or
contraction position C41, and if it becomes no further different,
steering valve 41 is returned to neutral position N41 by
springs.
[0067] By exciting solenoid 41a, steering valve 41 is located at
extension position E41, where port 40b is connected to pump 42, and
port 40c to tank 43, thereby extending piston rod 40a. By exciting
solenoid 41b, steering valve 41 is located at contraction position
C41, where port 40c is connected to pump 42, and port 40b to tank
43, thereby contracting piston rod 40a. When neither solenoid 41a
nor 41b is excited, steering valve 41 is set at neutral position
N41 so as to block both ports 40b and 40c, thereby stopping piston
rod 40a.
[0068] Steering wheel 14 is manually turned from a straight
traveling position S14 either rightward in a right turning range
RT14 or leftward in a left turning range LT14. A switch 14a inputs
a detected positional signal of steering wheel 14 to controller 44.
An actual stroke of piston rod 40a or another actual value
corresponding to an actual stroke of piston rod 40a, e.g., an
actual rotational angle of sleeve 39, is detected. Based on a
difference of actual stroke of piston rod 40a from a stroke of
piston rod 40a corresponding to the detected rotational position of
steering wheel 14, controller 44 outputs an exciting signal to one
of solenoids 41a and 41b of steering valve 41 and stops the output
so as to switch steering valve 41 between neutral position N41 and
either position E41 or C41, thereby telescoping and stopping piston
rod 40a. Therefore, in correspondence to the rotational position of
steering wheel 14, sleeve 39 is rotationally located together with
levers 17R and 17L so as to locate swash plates 19a of right and
left hydraulic pumps 19 to appropriate slant angles and
directions.
[0069] It is temporarily assumed that a signal value with respect
to a stroke of piston rod 40a is zero when the stroke is a neutral
stroke corresponding to the rotational position of steering wheel
14 in straight traveling position S14, that the signal value is
increased in a positive range from zero when piston rod 40a is
extended from the neutral stroke, and that the signal value is
decreased in a negative range from zero when piston rod 40a is
contracted from the neutral stroke. When forward traveling sensing
switch 35F is turned on and steering wheel 14 is rotationally
located at a position, controller 44 calculates a positive signal
value in correspondence to the position of steering wheel 14. On
this assumption, if rearward traveling sensing switch 35R is turned
off and steering wheel 14 is rotationally located at the same
position, controller 44 calculates a negative signal value of the
same volume with the positive signal value calculated when forward
traveling sensing switch 35F is turned on. In other words, piston
rod 40a, which is extended to a degree from the neutral stroke
during forward traveling of the vehicle, is contracted to the same
degree from the neutral stroke during rearward traveling of the
vehicle. Similarly, in correspondence to a rotational position of
steering wheel 14, piston rod 40a, which is contracted to a degree
from the neutral stroke during forward traveling of the vehicle, is
extended to the same degree from the neutral stroke during rearward
traveling of the vehicle.
[0070] Movement of speed control levers 17L and 17R will now be
remarked. When setting forward straight traveling of the vehicle,
shaft 38 and sleeve 39 are located at any position in forward
traveling range F, and both bars 39a are extended laterally in
direction S so as to locate speed control levers 17L and 17R
fowardly slantwise in the same angle. At this time, left and right
drive wheels 5L and 5R rotate forward at equal speed. Next, assume
that steering wheel 14 is turned to a certain rotational position
in left turning range LT14. The stroke of piston rod 40a is
increased to a certain degree from the neutral stroke so as to
rotate sleeve 39 counterclockwise around shaft 38 and rotate bars
39a in ranges LT, whereby left speed control lever 17L is rotated
rearward, and right speed control lever 17R forward, that is, they
are symmetrically rotated from their above-mentioned initial
position set for forward straight traveling when viewed along the
common pivot of levers 17L and 17R. Accordingly, forward rotating
left drive wheel 5L is decelerated, and forward rotating right
drive wheel 5R is accelerated so as to compensate for the reduced
speed of left drive wheel 5L, whereby the forward traveling vehicle
turns left.
[0071] On the other hand, when setting rearward straight traveling
of the vehicle, shaft 38 and sleeve 39 are located at any position
in rearward traveling range R, and both bars 39a are extended
laterally in direction S so as to locate speed control levers 17L
and 17R rearwardly slantwise in the same angle. At this time, left
and right drive wheels 5L and 5R rotate rearward at equal speed.
Next, assume that steering wheel 14 is turned to the certain
rotational position in left turning range LT14, which is the same
with the above-mentioned certain position of steering wheel 14 when
setting forward traveling. The stroke of piston rod 40a is reduced
from the neutral stroke to a certain degree as much as the
above-mentioned increased degree thereof when setting forward
traveling so as to rotate sleeve 39 clockwise around shaft 38 and
rotate bars 39a in ranges RT, whereby left speed control lever 17L
is rotated forward, and right speed control lever 17R rearward,
that is, they are symmetrically rotated from their above-mentioned
initial position set for rearward straight traveling when viewed
along the common pivot of levers 17L and 17R. Accordingly, rearward
rotating left drive wheel 5L is decelerated, and rearward rotating
right drive wheel 5R is accelerated so as to compensate for the
reduced speed of left drive wheel 5L, whereby the rearward
traveling vehicle turns left.
[0072] In this way, by rotating steering wheel 14 leftward from
straight traveling position S14, the vehicle turns left whether the
vehicle travels forward or rearward. The same is true when steering
wheel 14 is rotated rightward from straight traveling position S14.
Consequently, the rotational direction of steering wheel 14 from
straight traveling position S14 agrees with turning direction of
the vehicle whether the vehicle travels forward or rearward.
[0073] Hydraulic pump 42 serves as a common hydraulic pressure
source for hydraulic cylinder 40 and differential-locking clutch
24. On a hydraulic oil circuit between hydraulic pump 42 and
differential-locking clutch 24 is provided a two-positioned
spring-loaded electromagnetic differential-locking valve 60 which
is switched between positions I and II. Controller 44 controls the
location of differential-locking valve 60 in association with
operation of steering wheel 14.
[0074] When steering wheel 14 is set in straight traveling position
S14, differential-locking valve 60 is automatically located in
position I so as to engage differential-locking clutch 24, thereby
rotating right and left drive wheels 5R and 5L at the perfectly
same speed, whereby the vehicle accurately travels straight. Even
if the vehicle is on a slope and such an unexpected accident as
engine or electric power failure occurs, right and left drive
wheels 5R and 5L are locked together so as to keep the vehicle in
safety.
[0075] When steering wheel 14 is rotated right or left from
straight traveling position S14 so as to turn the vehicle,
controller 44 excites a solenoid of differential-locking valve 60
so that differential-locking valve 60 is located at position II to
disengage differential-locking clutch 24, thereby enabling right
and left drive wheels 5R and 5L to rotate differentially.
Preferably, in consideration of such a case that the vehicle is
mired at one of drive wheels 5R and 5L in a ditch,
differential-locking valve 60 may be optionally held at position I
by manual operation so as to engage differential-locking clutch 24
whether steering wheel 14 is located at straight traveling position
S14 or not, thereby enabling the vehicle to escape from the
ditch.
[0076] FIG. 7 illustrates that transmission housing 3 contains a
modification of the transmission system of FIG. 5. A reverser 50 is
constituted among primary input shaft 11 and pump shafts 19b. Each
of bevel gears 51 and 52 is relatively rotatably provided on
primary input shaft 11 and meshes with both HST input gears 19c
fixed on proximal ends of respective pump shafts 19b. A
hydraulically controlled reversal clutch 53 for selecting either
normal or reversed rotation of pump shafts 19b is disposed on
primary input shaft 11 between bevel gears 51 and 52. Clutch 53 is
supplied with oil so as to fix either bevel gear 51 or 52 to
primary input shaft 11. Which direction pump shafts 19b are rotated
in depends upon which bevel gear 51 or 52 is fixed to primary input
shaft 11 by reversal clutch 53. When oil is not supplied to clutch
53, hydraulic pumps 19 of both right and left HSTs 18R and 18L are
stopped.
[0077] Incidentally, brake 25 is provided on each motor shaft 20b
between fixed swash plate 20a and gear 20c. Alternatively, such an
arrangement of brakes 25 as shown in FIG. 5 may be employed.
[0078] FIG. 8 illustrates that transmission housing 3 contains a
further modification of the transmission system of FIG. 5,
comprising a pair of reversers 50, each of which is interposed
between motor shaft 20b of each of HST 18L and 18R and each of
drive axles 27 (drive wheels 5L and 5R). Primary input shaft 11 and
input shafts 19b interlock with one another through bevel gear 22
and HST input gears 19c so that the rotational direction of pump
shafts 19b is fixed.
[0079] Left and right counter shafts 26 are extended toward each
other so as to be mutually connected or disconnected through
differential-locking clutch 24, which is not interposed between
left and right motor shafts 20b but interposed between left and
right counter shafts 26.
[0080] An idler shaft 54 is interposed between each motor shaft 20b
and each counter shaft 26. Idler shaft 54 always engages with motor
shaft 20b through gears 20c and 54a. Gears 26d and 26e are
relatively rotatably provided on counter shaft 26. Hydraulically
controlled reversal clutch 53 is disposed on each of left and right
counter shafts 26 between gears 26d and 26e so as to selectively
engage either gear 26d or 26e with counter shaft 26. Gear 26d
always meshes with gear 20c fixed on motor shaft 20b. Gear 26e
always meshes with another gear 54b fixed on counter shaft 54.
Gears 20c and 26d constitute a normal gear train for rotating
counter shaft 26 in one of opposite directions, i.e., a normal
direction. Gears 20c, 54a, 54b and 26e constitute a reversing gear
train for rotating counter shaft 26 in the other direction, i.e., a
reversed direction.
[0081] Basically, left and right clutches 53 opposed with respect
to differential-locking clutch 24 are operated simultaneously so
that, between both HSTs 18L and 18R and both drive axles 27, both
the normal gear trains are selected simultaneously, or
alternatively, both the reversing gear trains are selected
simultaneously. By stopping oil supply to reversal clutch 53, left
and right drive wheels 5L and 5R are stopped even if left and right
HSTs 18L and 18R actuate.
[0082] Incidentally, brake 25 is disposed on each counter shaft 26.
Further, in each of HSTs 18L and 18R, hydraulic motor 20 with fixed
swash plate 20a is mounted to one surface of center section 21
which is opposite to another surface of center section 21 for
mounting hydraulic pump 19 thereon. Thus, a space for arranging
reverser 50 and the normal and reversing gear trains is ensured
among motor shaft 20b and counter shafts 26 and 54.
[0083] In any of reversers 50 shown in FIGS. 7 and 8, each reversal
clutch 53 includes an oil chamber 53a for normal rotation and an
oil chamber 53b for reversed rotation, as shown in FIG. 9.
Regarding reversal clutch 53 shown in FIG. 7, oil chamber 53a is
supplied with pressure oil to fix one of bevel gears 51 and 52 to
primary input shaft 11 so as to rotate pump shafts 19b in the
normal direction corresponding to forward traveling of the vehicle.
Oil chamber 53b is supplied with pressure oil to fix the other of
bevel gears 51 and 52 to primary input shaft 11 so as to rotate
pump shafts 19b in the reversed direction corresponding to rearward
traveling of the vehicle. Regarding clutches 53 shown in FIG. 8,
oil chambers 53a are supplied with pressure oil to engage bevel
gears 26e with respective counter shafts 26 so as to transmit
output power of HSTs 18L and 18R to the normal gear trains. Oil
chambers 53b are supplied with pressure oil to engage bevel gears
26d with respective counter shafts 26 so as to transmit output
power of HSTs 18L and 18R to the reversing gear trains.
[0084] Such arrangement of reverser 50 or reversers 50 on the
upstream or downstream of twin transmissions for respective drive
wheels represented by left and right HSTs 18L and 18R is applied
for combination of the twin transmissions with a transmission,
whose output rotation is nonreversible, such as a variable electric
motor or a frictional mechanical continuous variable transmission
(CVT) having a toroidal belt or another means. Furthermore, the
vehicle may have means for unclutching the reverser or reversers 50
so as to stop right and left drive wheels 5R and 5L simultaneously
at need.
[0085] Description will be given of a control system of HSTs 18L
and 18R shown in FIG. 9, which is adapted to the respective
transmission systems shown in FIG. 7 and FIG. 8. As the system of
FIG. 9 serves as a modification of the control system of HSTs 18L
and 18R shown in FIG. 6, description of parts and devices shown in
FIG. 9, which are identical with those in FIG. 6 and marked with
the same reference numerals of those in FIG. 6, will be
omitted.
[0086] Referring to FIG. 9, a steering valve 41, a reverser valve
55 and differential-locking valve 60 are supplied in parallel with
oil from pump 42. Steering wheel 14 is mechanically linked with
steering valve 41, through which ports 40b and 40c of cylinder 40
are fluidly connected to pump 42 and tank 43. Therefore, the
different point from the case with steering valve 41 of FIG. 6 is
that the stroke of piston rod 40a, i.e., the rotational direction
of sleeve 39 around shaft 38 is constant in relation to the left or
right rotational direction of steering wheel 14 from the straight
traveling position S14 whether the vehicle travels forward or
rearward. That is, whether the vehicle travels forward or rearward,
steering valve 41 alters the leftward rotation of steering wheel 14
from straight traveling position S14 into proportional extension of
piston rod 40a from the neutral stroke causing bars 39a to rotate
in ranges LT so as to push left lever 19L rearward and pull right
lever 19R forward, and it alters the rightward rotation of steering
wheel 14 from straight traveling position S14 into proportional
contraction of piston rod 40a from the neutral stroke causing bars
39a to rotate in ranges RT so as to pull left lever 19L forward and
push right lever 19R rearward.
[0087] Furthermore, both pedals 33 and 34 have respective upwardly
projecting arms 33a and 34a, to which links 45 and 46 extended from
shaft 38 are connected. Therefore, whichever pedal 33 or 34 is
depressed, shaft 38 and sleeve 39 are tilted only forward in
forward traveling range F from neutral position N to maximum
forward traveling speed position Fm, that is, swash plates 19a of
both hydraulic pumps 19 are rotated in only their ranges which are
essentially provided for forward traveling of the vehicle.
[0088] Consequently, the leftward rotation of steering wheel 14
from straight raveling position S14 necessarily reduces the
capacity of left hydraulic pump 19 so as to decelerate left drive
wheel 5L, and increases the capacity of right hydraulic pump 19 so
as to accelerate right drive wheel 5R, thereby causing a left turn
of the vehicle. The rightward rotation of steering wheel 14 from
straight traveling position S14 necessarily increases the capacity
of left hydraulic pump 19 so as to accelerate left drive wheel 5L,
and reduces the capacity of right hydraulic pump 19 so as to
decelerate right drive wheel 5R, thereby causing a right turn of
the vehicle. Therefore, whether the vehicle travels forward or
rearward does not depend upon positional control of swash plates
19a of hydraulic pumps 19 but needs to depend upon other means for
switching the rotational direction of drive wheels 5L and 5R
between forward and rearward directions.
[0089] As means for changing the rotational direction of drive
wheels 5L and 5R, reverser valve 55 is a three-positioned
electromagnetic solenoid valve, which has opposite directive
solenoids 55a and 55b and is switched among a neutral position N55
and other two positions F55 and R55, and interposed between pump 42
and oil chambers 53a and 53b of reversal clutch 53.
[0090] Description will now be given of the case where the
transmission system shown in FIG. 7 is associated with the control
system shown in FIG. 9. For forward straight traveling of the
vehicle, forward traveling shift pedal 33 is depressed together
with switch 35F and steering wheel 14 is located in straight
traveling position S14. Controller 44 receives the depression
signal from switch 35F and excites solenoid 55a so as to locate
reverser valve 55 to position F55, thereby connecting chamber 53a
to pump 42 and connecting chamber 53b to tank 43, whereby bevel
gear 51 is fixed to primary input shaft 11 so as to rotate pump
shafts 19b in the normal direction. Therefore, hydraulic motors 20
are rotated in one direction such as to drive the vehicle
forward.
[0091] For rearward straight traveling of the vehicle, rearward
traveling shift pedal 34 is depressed together with switch 35R and
steering wheel 14 is located in straight traveling position S14.
Controller 44 receives the depression signal from switch 35R and
excites solenoid 55b so as to locate reverser valve 55 to position
R55, thereby connecting chamber 53b to pump 42 and connecting
chamber 53a to tank 43, whereby bevel gear 52 is fixed to primary
input shaft 11 so as to rotate pump shafts 19b in the reversed
direction. Therefore, hydraulic motors 20 are rotated in the
opposite direction such as to drive the vehicle rearward.
[0092] As shown in FIG. 9, shaft 38 is tilted only forward in
forward traveling range F whichever pedal 33 or 34 is depressed.
That is, movable swash plate 19a of each hydraulic pump 19 can be
tilted to only one side for forward traveling from its neutral
position so that each hydraulic motor 20 is essentially rotated in
only one direction for forward traveling at variable speed.
However, when pedal 34 is depressed, reverser 50 is changed so as
to reverse the flow of fluid between pump 19 and motor 20, thereby
reversing the rotational direction of motor 20 for rearward
traveling.
[0093] Incidentally, if neither pedal 33 nor 34 is depressed,
controller 44 locates reverser valve 55 to shown neutral position
N55 so as to drain oil from both chambers 53a and 53b in reversal
clutch 53 to tank 43, whereby left and right HSTs 18L and 18R do
not actuated and power transmission to left and right drive wheels
5L and 5R is perfectly shut down.
[0094] When steering wheel 14 is rotated rightward or leftward from
straight traveling position S14, switch 14a sends controller 44 a
signal meaning that steering wheel 14 is rotated apart from
straight traveling position S14. Therefore, controller 44 switches
differential valve 60 to position II so as to disengage
differential-locking clutch 24, similarly with that of FIG. 6, so
that right and left hydraulic motors 20 are allowed to rotate
freely from each other.
[0095] In this embodiment, steering valve 41 is a spring-center
hydraulic change-over valve mechanically linked with steering wheel
14. Then, according to rotation of steering wheel 14 from straight
traveling position S14, steering valve 41 is changed from a neutral
position N41 to either an extension position E41 or a contraction
position C41 so as to telescope piston rod 40a. When the stroke of
piston rod 40a of hydraulic cylinder 40 becomes correspondent to
the rotational position of steering wheel 14, steering valve 41
returns to neutral position N41 by springs. Therefore, speed
control levers 17R and 17L are rotated in mutually opposite
directions so as to differentially rotate right and left drive
wheels 5R and 5L.
[0096] By returning steering wheel 14 to straight traveling
position S14, the stroke of piston rod 40a becomes the neutral
stroke. At this time, bars 39a are oriented in direction S so as to
equalize directions and angles of speed control levers 17L and 17R,
thereby equalizing rotational directions and speeds of hydraulic
motors 20. Furthermore, switch 14a sends controller 44 a signal
meaning that steering wheel 14 is set in straight traveling
position S14, so that controller 44 switches differential locking
valve 60 to position I so as to engage differential-locking clutch
24. Therefore, the vehicle travels perfectly straight.
[0097] It is assumed that steering wheel 14 is rotated leftward in
left turning range LT14 from straight traveling position S14. In
this case, steering valve 41 connects port 40b to pump 42, and
connects port 40c to tank 43 so as to rotate sleeve 39 clockwise
around shaft 38 and rotate bars 39a in ranges LT, whereby left link
16L pushes left speed control lever 17L, and right link 16R pulls
right speed control lever 17R. At this time, when forward traveling
shift pedal 33 is depressed so as to fix bevel gear 51 to primary
input shaft 11, pulled right lever 17R causes right HST 18R to
accelerate forwardly rotating right drive wheel SR, and pushed left
lever 17L causes left HST 18L to decelerate forwardly rotating left
drive wheel 5L. On the contrary, if rearward traveling shift pedal
34 is depressed in the assumed leftward rotated state of the
steering wheel 14, switch 35R is switched on so as to fix bevel
gear 52 to primary input shaft 11. Therefore, right lever 17R is
pulled so as to cause right HST 18R to accelerate rearwardly
rotating right drive wheel 5R, and left lever 17L is pushed so as
to cause left HST 18L to decelerate rearwardly rotating left drive
wheel 5L. Consequently, when steering wheel 14 is rotated leftward
from straight traveling position S14, right drive wheel 5R is
accelerated, and left drive wheel 5L is decelerated, so that the
vehicle turns left whether it travels forward or rearward. When
steering wheel 14 is rotated rightward in right turning range RT14
from straight traveling position S14, vise versa. In this case,
steering valve 41 contracts piston rod 40a from the neutral stroke
so as to pull left lever 17L forward and push right lever 17R
rearward.
[0098] Description will now be given of the case where the
transmission system shown in FIG. 8 is associated with the control
system shown in FIG. 9. For straight traveling of the vehicle,
forward traveling shift pedal 33 is depressed together with switch
35F, and steering wheel 14 is located at straight traveling
position S14. Based on depression of switch 35F, controller 44
excites solenoid 55a of reverser valve 55 so as to locate reverser
valve 55 at position F55 for setting each of reversal clutches 53
into a state where chamber 53a is connected to pump 42 and chamber
53b is connected to tank 43, thereby fixing gears 26d to respective
counter shafts 26, i.e., selecting the normal gear trains for
rotating counter shafts 26 opposite to respective motor shafts
20b.
[0099] When rearward traveling shift pedal 34 is depressed together
with switch 35R, controller 44 excites solenoid 55b of reverser
valve 55 based on the depression of switch 35R so as to locate
reverser valve 55 at position R55 for setting each of reversal
clutches 53 into a state where chamber 53a is connected to tank 43
and chamber 53b is connected to pump 42, thereby fixing gears 26e
to respective counter shafts 26, i.e., selecting the reversing gear
trains for rotating counter shafts 26 in the same rotational
direction with respective motor shafts 20b.
[0100] Whether pedal 33 or 34 is depressed, shaft 38 and sleeve 39
are tilted only forward in forward traveling range F so that, in
each of HSTs 18L and 18R, movable swash plate 19a of pump 19 is
rotated to only one side from its neutral position so as to
accelerate or decelerate output rotation of motor 20 in a constant
direction for essential forward rotation of drive wheels 5R and 5L.
However, by depressing rearward traveling shift pedal 34, reversers
50 actuate to rotate drive wheels 5R and 5L rearward while the
output rotational direction of motors 20 is still constant.
[0101] When none of pedals 33 and 34 is depressed, controller 44
sets reverser valve 55 at neutral position N55 so as to drain oil
from both chambers 53a and 53b of reversal clutch 53 to tank 43.
Therefore, both right and left drive wheels 5R and 5L are perfectly
isolated from power transmission even if neutral location of at
least one HST 18R or 18L is inaccurately adjusted and a slight
output arises from the HST 18R or 18L.
[0102] It is assumed that steering wheel 14 is rotated leftward in
left turning range LT14 from straight traveling position S14. At
this time, steering valve 41 connects port 40b to pump 42, and
connects port 40c to tank 43, thereby extending piston rod 40a from
the neutral stroke, whereby left link 16L pushes left lever 17L
rearward and right link 16R pulls right lever 17R forward. When
pedal 33 is depressed, switch 35F is switched on so as to fix gears
26d to respective counter shafts 26, pulled right lever 17R makes
right HST 18R accelerate forwardly rotating right drive wheel 5R,
and pushed left lever 17L makes left HST 18L decelerate forwardly
rotating left drive wheel 5L. When pedal 34 is depressed, switch
35R is switched on so as to fix gears 26e to respective counter
shafts 26, pulled right lever 17R makes right HST 18R accelerate
rearwardly rotating right drive wheel 5R, and pushed left lever 17L
makes left HST 18L decelerate rearwardly rotating left drive wheel
5L.
[0103] Consequently, when steering wheel 14 is turned left from
straight traveling position S14, right drive wheel 5R is
accelerated and left drive wheel 5L is decelerated, or if left
drive wheel 5L is rotated opposite to right drive wheel 5R, left
drive wheel 5L is accelerated, so that the vehicle turns left
whether it travels forward or rearward. The same is true when
steering wheel 14 is turned rightward in right turning range RT14
from straight traveling position S14. In this case, steering valve
41 contracts piston rod 40a from the neutral stroke so as to pull
left lever 17L forward and push right lever 17R rearward.
[0104] An operation system shown in FIG. 10 is adapted for a
vehicle transmission system having any of reversers 50 shown in
FIGS. 7 and 8, which is not operated based on turning of a switch
provided on a traveling shift pedal as shown in FIG. 9, but is
manually operable with a mechanical link. A reverser valve 55 is
mechanically linked with a reverser lever (not shown) provided in a
driver's portion of a vehicle. Accordingly, only a single pedal 33
serves as an operation device for changing traveling speed of the
vehicle. A pressure-sensing switch 35 is provided on a depressed
surface of pedal 33.
[0105] A clutch valve 61, which is electro-magnetically controlled
by controller 44 based on ON/OFF signal from switch 35, is
interposed among reverser valve 55, pump 42 and tank 43. When pedal
33 is not depressed and switch 35 is turned off, clutch valve 61 is
located at a shown position 161 so that any reversal clutch 53
having oil chambers 53a and 53b, from which oil is drained to tank
43, is unclutched wherever reverser valve 55 is located. If pedal
33 is depressed, reverser valve 61 is shifted to a position II 61
so as to be applied for supplying oil to either oil chamber 53a or
53b in any reversal clutch 53 through reverser valve 55.
[0106] According to setting the above-mentioned reverser lever to
either a forward traveling position or a rearward traveling
position, reverser valve 55 is set to either forward traveling
position F55 or rearward traveling position R55. The forward tilt
angle of sleeve 39 is changed according to depression of pedal 33
so as to equally change the capacities of both left and right
hydraulic pumps 19, thereby changing the traveling speed of a
vehicle.
[0107] When steering wheel 14 is rotated rightward or leftward from
straight traveling position S14, hydraulic cylinder 40 telescopes
piston rod 40a so as to rotate sleeve 39 around shaft 38.
Therefore, the capacity of hydraulic pump 19 on one side of the
vehicle corresponding to the rotational direction of steering wheel
14 is reduced so as to reduce the output power of hydraulic motor
20 fluidly connected thereto, thereby decelerating corresponding
drive wheel 5L or 5R. Simultaneously, the capacity of hydraulic
pump 19 on the other side of the vehicle opposite to the rotational
direction of steering wheel 14 is relatively increased so as to
increase the output power of hydraulic motor 20 fluidly connected
thereto, thereby accelerating corresponding drive wheel 5R or
5L.
[0108] Reverser (or reversers) 50 maintains the relation of
deceleration and acceleration of drive wheels 5L and 5R to
rotational direction of steering wheel 14 so as to coincide turning
direction of the vehicle to the rotational direction of steering
wheel 14 whether the vehicle travels forward or rearward.
[0109] Referring to FIG. 11, reverser 50 is interposed between
primary input shaft 11 and pump shafts 19b, similarly with FIG. 7.
However, reverser 50 shown in FIG. 11 is provided with a mechanical
reversal dog clutch 53' instead of hydraulic reversal clutch 53.
Clutch 53' is provided with a clutch slider 53'a, which is not
relatively rotatably but axially slidably disposed on primary input
shaft 11 so as to selectively engage with one of opposite bevel
gears 51 and 52 freely rotatably provided on primary input shaft
11. Clutch slider 53'a is mechanically linked with a reverser lever
(with reference to a reverser lever 72 shown in FIG. 12) provided
in a driver's portion of a vehicle.
[0110] By manual operating the reverser lever, clutch slider 53'a
of reversal clutch 53' slides on primary input shaft 11 and engages
with one of bevel gears 51 and 52 so as to rotate pump shafts 19b
in either one direction for forward traveling or the other
direction for rearward traveling. In addition, clutch slider 53'a
may be disengaged from both bevel gears 51 and 52 so that reversal
clutch 53' may be unclutched to isolate both pump shafts 19b from
rotational force of primary input shaft 11.
[0111] A main clutch 71, which may be integrally provided on output
pulley 9 as shown in FIG. 11, is temporarily disengaged to isolate
primary input shaft 11 from power of engine 2 before switching
reversal clutch 53'. Main clutch 71 may be electro-magnetically
controlled so as to be automatically switched depending upon
whether later-discussed traveling shift pedal 33 is depressed or
not, for example.
[0112] Referring to FIG. 12, reversers 50 are provided on
respective counter shafts 26 on the downstream of respective
hydraulic motors 20, similarly with FIG. 8. However, reversers 50
shown in FIG. 12 are provided with respective mechanical reversal
dog clutches 53' instead of hydraulic reversal clutches 53. Each
reversal clutch 53' is provided with a clutch slider 53'a, which is
not relatively rotatably but axially slidably disposed on counter
shaft 26 so as to selectively engage with one of opposite gears 26d
and 26e freely rotatably provided on counter shaft 26. Both clutch
sliders 53'a are engaged to a common fork shaft 53'b through
respective forks 53'c. Fork shaft 53'b is mechanically linked with
a reverser lever 72 provided in a driver's portion of a
vehicle.
[0113] By manual operating reverser lever 72, both clutch sliders
53'a of reversal clutches 53' slide on respective counter shafts 26
and engage with either gears 26d or 26e so as to rotate counter
shafts 26 in either one direction for forward traveling or the
other direction for rearward traveling. In addition, each clutch
slider 53'a may be disengaged from both gears 26d and 26e so that
both reversal clutches 53' may be unclutched to isolate counter
shafts 26 from rotational force of motor shafts 20b.
[0114] Main clutch 71, which may be integrally provided on output
pulley 9 as shown in FIG. 12, is temporarily disengaged to isolate
primary input shaft 11 from power of engine 2 before switching
reversal clutches 53'. Main clutch 71 may be electro-magnetically
controlled so as to be automatically switched depending upon
whether later-discussed traveling shift pedal 33 is depressed or
not, for example.
[0115] FIG. 13 illustrates a structure with electric and hydraulic
circuits for controlling tilt angles of swash plates 19a of left
and right hydraulic pumps 19, which is adapted for each of the
transmission systems of FIGS. 11 and 12, and functions similarly
with the structure of FIG. 10. When pressure-sensing switch 35
detects depression of single traveling shift pedal 33, controller
44 electro-magnetically controls main clutch 71 to engage. Either
forward or rearward traveling direction of the vehicle is
determined by setting mechanical reverser 50. While the vehicle
travels in the set forward or rearward direction, the forward tilt
angle of sleeve 39 with shaft 38 is changed according to depression
of pedal 33 so as to change the capacities of left and right
hydraulic pumps 19, thereby changing traveling speed of the
vehicle.
[0116] When steering wheel 14 is rotated leftward or rightward from
straight traveling position S14, piston rod 40a of hydraulic
cylinder 40 is telescoped so as to rotate sleeve 39 around shaft
38, whereby the capacity of hydraulic pump 19 on one side of the
vehicle corresponding to the rotational direction of steering wheel
14 is reduced so as to decelerate corresponding drive wheel 5L or
5R, and the capacity of hydraulic pump 19 on the other side of the
vehicle opposite to the rotational direction of steering wheel 14
is increased so as to accelerate corresponding drive wheel 5R or
5L. Reverser (or reversers) 50 maintains the relation of
deceleration and acceleration of drive wheels 5L and 5R to
rotational direction of steering wheel 14 so as to coincide turning
direction of the vehicle to the rotational direction of steering
wheel 14 whether the vehicle travels forward or rearward.
[0117] Although the invention has been described in its preferred
form with a certain degree of particularity, it is understood that
the present disclosure of the preferred form has been changed in
the details of construction and the combination and arrangement of
parts may be resorted to without departing from the spirit and the
scope of the invention as hereinafter claimed.
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