U.S. patent application number 10/681226 was filed with the patent office on 2004-04-22 for vehicle improved steering.
Invention is credited to Abend, Robert, Andrews, Keith J., Hasegawa, Toshiyuki, Irikura, Koji, Ishii, Norihiro, Kawada, Hirohiko, Ohashi, Ryota, Shimizu, Hiroaki, Takada, Kenichi.
Application Number | 20040074678 10/681226 |
Document ID | / |
Family ID | 27280813 |
Filed Date | 2004-04-22 |
United States Patent
Application |
20040074678 |
Kind Code |
A1 |
Irikura, Koji ; et
al. |
April 22, 2004 |
Vehicle improved steering
Abstract
A vehicle is installed with an integral transaxle apparatus
constructed so that a single housing contains left and right axles,
a driving hydrostatic transmission (HST) having a variable
displacement first hydraulic pump and a first hydraulic motor
fluidly connected with each other, a steering HST having a variable
displacement second hydraulic pump and a variable displacement
second hydraulic motor fluidly connected with each other, and a
differential unit differentially connecting the axles with each
other so as to be driven regularly or reversely by the output of
the driving HST and to differentially drive the axles while
receiving the output of the steering HST, wherein the first
hydraulic pump receives power of a prime mover and has a first
movable swash plate, and the second hydraulic pump receives power
of the prime mover independently of the first hydraulic pump and
has a second movable swash plate. The vehicle is also provided with
driving operating means for slanting operation of the first movable
swash plate for switching the travelling direction between forward
and backward and for changing the travelling speed, and steering
operating means for slanting operation of the second movable swash
plate so as to determine the leftward and rightward cornering
angle. The second hydraulic motor has a third movable swash plate
interlocking with the driving operating means so that the slanting
direction of the third movable swash plate is changed oppositely
with respect to its neutral position according to the travelling
direction switching operation of the driving operating means,
whereby the vehicle turns laterally in the same direction of
leftward and rightward steering operation of the steering operating
means whether the vehicle travels forward or backward.
Inventors: |
Irikura, Koji;
(Amagasaki-shi, JP) ; Ishii, Norihiro;
(Amagasaki-shi, JP) ; Ohashi, Ryota;
(Amagasaki-shi, JP) ; Takada, Kenichi;
(Amagasaki-shi, JP) ; Kawada, Hirohiko;
(Amagasaki-shi, JP) ; Abend, Robert; (Morristown,
TN) ; Andrews, Keith J.; (Morristown, TN) ;
Hasegawa, Toshiyuki; (Morristown, TN) ; Shimizu,
Hiroaki; (Morristown, TN) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX PLLC
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Family ID: |
27280813 |
Appl. No.: |
10/681226 |
Filed: |
October 9, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10681226 |
Oct 9, 2003 |
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10122396 |
Apr 16, 2002 |
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6659216 |
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10122396 |
Apr 16, 2002 |
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09489680 |
Jan 24, 2000 |
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6397966 |
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Current U.S.
Class: |
180/6.48 ;
180/305 |
Current CPC
Class: |
A01D 69/03 20130101;
B62D 11/04 20130101; B60K 17/105 20130101; B62D 11/006 20130101;
B62D 11/24 20130101; F16H 39/14 20130101; B62D 11/18 20130101 |
Class at
Publication: |
180/006.48 ;
180/305 |
International
Class: |
B62D 011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 22, 1999 |
JP |
HEI. 11-014919 |
Jan 22, 1999 |
JP |
HEI. 11-014920 |
Jun 21, 1999 |
JP |
HEI. 11-174647 |
Claims
What is claimed is:
1. A vehicle comprising: an integral transaxle apparatus for
driving and steering a vehicle, including; a housing, a driving
hydrostatic transmission having a variable displacement first
hydraulic pump and a first hydraulic motor fluidly connected with
each other, said driving hydrostatic transmission being disposed in
said housing, wherein said first hydraulic pump receives power of a
prime mover and has a first movable swash plate, a steering
hydrostatic transmission having a variable displacement second
hydraulic pump and a second hydraulic motor fluidly connected with
each other, said steering hydrostatic transmission being disposed
in said housing, wherein said second hydraulic pump receives power
of said prime mover independently of said first hydraulic pump and
has a second movable swash plate, a pair of axles disposed
co-axially with each other and supported in said housing, and a
differential unit differentially connecting said axles with each
other, said differential unit being disposed in said housing,
wherein said differential unit is driven regularly or reversely by
the output of said driving hydrostatic transmission and
differentially drives said axles while receiving the output of said
steering hydrostatic transmission; manually operable driving
operating means disposed on said vehicle apart from said transaxle
apparatus for slanting operation of said first movable swash plate
for switching the travelling direction between forward and backward
and changing the travelling speed; and manually operable steering
operating means disposed on said vehicle apart from said transaxle
apparatus for slanting operation of said second movable swash plate
so as to determine the leftward and rightward cornering angle,
wherein said vehicle turns laterally in the same direction of
leftward and rightward steering operation of said steering
operating means whether said vehicle travels forward or
backward.
2. The vehicle as set forth in claim 1, wherein said second
hydraulic motor is of a variable displacement type and has a third
movable swash plate, said third movable swash plate interlocking
with said driving operating means so that the slanting direction of
said third movable swash plate is changed oppositely with respect
to its neutral position according to the travelling direction
switching operation of said driving operating means.
3. The vehicle as set forth in claim 2, wherein said first movable
swash plate is kept in a neutral position while said driving
operating means is operated for forward travelling or for backward
travelling to some degree from a neutral position.
4. The vehicle as set forth in claim 3, wherein said third movable
swash plate is slanted to a certain degree in a direction
corresponding to forward travelling when said driving operating
means is located in its own neutral position.
5. The vehicle as set forth in claim 4, wherein said third movable
swash plate is changed in its slanting direction from that for
forward travelling to that for backward travelling according to the
operation of said driving operating means from its own neutral
position into its range for backward travelling while said first
movable swash plate is kept in its own neutral position.
6. The vehicle as set forth in claim 4, wherein said third movable
swash plate is kept at said certain degree while said driving
operating means is operated for forward travelling within the range
to keep said first movable swash plate in its own neutral
position.
7. The vehicle as set forth in claim 1, wherein said second
hydraulic motor is of a variable displacement type and has a third
movable swash plate, said first hydraulic motor is of a variable
displacement type and has a fourth movable swash plate, and said
driving operating means comprises manually operable
forward/backward travelling direction switching means and manually
operable speed changing means, said forward/backward travelling
direction switching means interlocking with both of said third
movable swash plate and said fourth movable swash plate so as to
change the slanting directions of said third and fourth movable
swash plates oppositely with respect to their neutral positions,
according to the switching operation of said forward/backward
travelling direction switching means, and said speed changing means
interlocking with said first movable swash plate so as to vary the
slanting angle of said first movable swash plate according to the
operational degree of said speed changing means.
8. The vehicle as set forth in claim 7, wherein said first movable
swash plate is kept in a neutral position while said speed changing
means is operated to some degree from a neutral position.
9. The vehicle as set forth in claim 8, wherein said third movable
swash plate is slanted to a certain degree in a direction
corresponding to forward travelling when said speed changing means
is located in said neutral position.
10. The vehicle as set forth in claim 8, wherein said third movable
swash plate is changed in its slanting direction from that for
forward travelling to that for backward travelling according to the
switching operation of said forward/backward travelling direction
switching means for backward travelling and the operation of said
speed changing means from said neutral position to some degree,
while said first movable swash plate is kept in a neutral
position.
11. A vehicle comprising: manually operable steering operating
means, and a caster interlocking with said steering operating means
so as to be swivelled in relation to said vehicle by operation of
said steering operating means, wherein said caster is restricted in
its range where it can be freely swivelled.
12. The vehicle as set forth in claim 11, further comprising: a
caster guide interposed between said caster and said vehicle,
wherein said caster guide interlocks with said steering operating
means so as to be swivelled in relation to said vehicle by
operation of said steering operating means, wherein said caster is
laterally rotatably supported to said caster guide while being
restricted in its range of free swivelling in relation to said
caster guide.
13. The vehicle as set forth in claim 11, further comprising: a
transaxle apparatus supporting a pair of driving axles, wherein
said driving axles are differentially driven by operation of said
steering operating means.
14. A vehicle comprising: an integral transaxle apparatus for
driving and steering a vehicle, including; a housing, a driving
hydrostatic transmission having a variable displacement first
hydraulic pump and a first hydraulic motor fluidly connected with
each other, said driving hydrostatic transmission being disposed in
said housing, wherein said first hydraulic pump receives power of a
prime mover and has a first movable swash plate, a steering
hydrostatic transmission having a variable displacement second
hydraulic pump and a second hydraulic motor fluidly connected with
each other, said steering hydrostatic transmission being disposed
in said housing, wherein said second hydraulic pump receives power
of said prime mover independently of said first hydraulic pump and
has a second movable swash plate, a pair of axles disposed
co-axially with each other and supported in said housing, and a
differential unit differentially connecting said axles with each
other, said differential unit being disposed in said housing,
wherein said differential unit is driven regularly or reversely by
the output of said driving hydrostatic transmission and
differentially drives said axles while receiving the output of said
steering hydrostatic transmission; manually operable driving
operating means disposed on said vehicle apart from said transaxle
apparatus for slanting operation of said first movable swash plate
for switching the travelling direction between forward and backward
and for changing the travelling speed; manually operable steering
operating means disposed on said vehicle apart from said transaxle
apparatus for slanting operation of said second movable swash plate
so as to determine the leftward and rightward cornering angle; and
a caster interlocking with said steering operating means so as to
be swivelled in relation to said vehicle by operation of said
steering operating means, wherein said caster is restricted in its
range where it can be freely swivelled.
15. The vehicle as set forth in claim 14, further comprising: a
caster guide interposed between said caster and said vehicle,
wherein said caster guide interlocks with said steering operating
means so as to be swivelled in relation to said vehicle by
operation of said steering operating means, wherein said caster is
laterally rotatably supported to said caster guide while being
restricted in its range of free swivelling in relation to said
caster guide.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a vehicle, especially a
working vehicle like a tractor, improved in its steering. Firstly,
the improvement is provided for the vehicle installed with an
integral transaxle apparatus comprising a hydrostatic and
mechanical axle driving and steering system including two
hydrostatic transmissions (hereinafter, each hydrostatic
transmission is called an "HST"); one for driving left and right
axles, and the other for steering the axles, wherein the input of
the HST for steering is independent of the output of the HST for
driving. Secondly, the improvement is for the vehicle having a
caster in addition to its driving wheels.
[0003] 2. Related Art
[0004] A well-known conventional system for driving and steering
left and right axles for wheels or sprockets of tracks, which
employs a pair of HSTs provided for the respective axles, is
disclosed in U.S. Pat. No. 4,782,650 or Japanese Laid Open Gazette
No. Hei 2-261,952, for example. Output rotary speeds of the two
HSTs are equalized for straight driving of a vehicle and made
different from each other for steering of it.
[0005] The conventional system has the problem that the
equalization of output rotary speeds between the two HSTs must be
precise and if there is difference of capacity between the two
HSTs, a vehicle was steered differently whether leftward or
rightward.
[0006] The present axle driving and steering system includes two
HSTs and two differentials, wherein one (a driving HST) of the HSTs
interlocks with a speed changing operation means like a lever or a
pedal and transmits power from a prime mover like an engine into
one differential connecting left and right axles for driving them.
The other HST (a steering HST) interlocks with a steering operation
means like a steering wheel and transmits its output rotational
force corresponding to the direction and degree of the steering
operation means into the other differential, and a pair of
differential output shafts of the latter differential are drivingly
connected to the respective axles through two drive trains which
are opposite in their output rotational directions.
[0007] Furthermore, two types of such an axle driving and steering
system have been provided. One is a dependent steering type,
wherein the steering HST receives the driving power for its
hydraulic pump from the output of the hydraulic motor of the
driving HST. The other is an independent steering type, wherein the
steering HST receives the driving power for its hydraulic pump from
the prime mover independently of the output of the driving HST.
[0008] In comparison with the dependent steering type system, the
independent type system has some advantages as follows:
[0009] Firstly, the steering HST can be driven while the speed
changing operating means is in neutral so as not to drive the
driving HST, so that both the left and right axles are rotated
oppositely to each other at an equal speed, whereby a vehicle
installed with the system can swivel in place.
[0010] Secondly, the volume of the driving HST can be reduced
because it does not have to drive the steering HST.
[0011] Thirdly, while the steering HST of the dependent steering
type must have so large volume as to compensate the low efficiency
of rotation of its input shaft (a pump shaft), the volume of the
independent steering type one, which has a pump shaft independently
driven by a prime mover, does not have to be so large. However, a
vehicle installed with the independent steering type system has the
following disadvantage:
[0012] If a vehicle employing the independent steering type system
is instituted so that the lateral direction of the steered vehicle
coincides with that of an operated steering operating means (like a
steering wheel) during forward travelling, the vehicle comes to be
steered oppositely to the operational direction of the steering
operating means during backward travelling. For example, when a
steering wheel is rotated leftward during backward travelling, the
vehicle turns rightward. Such a situation confuses an operator
accustomed to driving a normal car.
[0013] Also, there has never been disclosed a compact integral
construction employing the above mentioned system comprising two
axles, two HSTs; one for driving a vehicle and the other for
steering; and a differential receiving the output of both HSTs,
whether the system is of the dependent steering type or of the
independent steering type.
[0014] Otherwise, it is well-known that the vehicle installed with
the above mentioned system is provided with a caster or casters in
addition to the above mentioned driving axles for improvement of
its capacity of steering, that is, so as to enable the vehicle to
turn left or right easily and swiftly.
[0015] Conventionally, the caster attached to the vehicle has been
able to swivel in all horizontal directions in relation to the
vehicle body independently of operation of the steering operating
means. The steering operating means merely applies difference in
rotary speed between left and right driving axles. The caster is
laterally swivelled by its following-up the differential rotation
of the both axles and is rotated in the direction where it is
oriented after the swivelling.
[0016] The axis of the caster's own rotation is longitudinally
offset from the axis of its lateral swivelling in relation to the
vehicle. The caster rotates around its own rotational axis for
travelling in such a situation that the swivelling axis and the
rotational axis are disposed front and rear. In this regard, the
longitudinal direction of the caster is oriented to the travelling
direction of the vehicle after the caster has been laterally
swivelled. Since the caster is independent of the steering
operating means, the lateral swivelling of caster is not performed
while the vehicle is stationary but must be performed while the
vehicle travels.
[0017] Such a construction of caster causes the problem that, while
the travelling direction of the vehicle is reversed between forward
and backward, the portion of the vehicle to which the caster is
attached meanders laterally because the caster is swivelled
approximately to an angle of 180.degree. in relation to the vehicle
body so as to be longitudinally reversed. Furthermore, the vehicle
which has stopped while turning leftward stays in the situation
that its caster is oriented leftward to some degree. If the vehicle
which has stayed in such a situation starts travelling while
turning rightward, the vehicle also meanders laterally because the
caster oriented for leftward cornering is laterally swivelled to
the direction for rightward cornering for a little while.
[0018] Such meandering of the vehicle confuses an operator. Also,
while laterally swivelling, the caster is oriented perpendicularly
to the travelling direction of the vehicle in a moment so that the
resistance of the ground surface against rotation of the caster is
maximized, thereby making the volume of the steering HST
insufficient to effect its output. Also, in this moment, the caster
is dragged without rotation thereby being damaged by the ground
surface.
[0019] Moreover, since the caster, which is conventionally disposed
under the vehicle body, even if it is attached as a front wheel, is
invisible to an operator sitting on the seat, the operator feels
uneasy especially in such a case supposing the above mentioned
meandering of the vehicle.
SUMMARY OF THE INVENTION
[0020] An object of the present invention is to provide a vehicle
installed with a compact integral transaxle apparatus employing the
above described axle driving and steering system of the independent
steering type, so as to save its manufacturing cost and to ease its
maintenance, wherein the vehicle can be steered in the same
direction with that of operated steering operating means whether
the vehicle travels forward or backward.
[0021] To achieve the object, the vehicle according to the present
invention is installed with an integral transaxle apparatus for
driving and steering a vehicle so constructed that a driving HST
including a variable displacement first hydraulic pump and a first
hydraulic motor fluidly connected with each other, a steering HST
including a variable displacement second hydraulic pump and a
variable displacement second hydraulic motor fluidly connected with
each other, a pair of axles disposed co-axially with each other,
and a differential unit differentially connecting the axles with
each other are disposed together in a housing, wherein the first
hydraulic pump receives power of a prime mover and has a first
movable swash plate, the second hydraulic pump receives power of
the prime mover independently of the first hydraulic pump and has a
second movable swash plate, and the differential unit is driven
regularly or reversely by the output of the driving HST and
differentially drives the axles while receiving the output of the
steering HST.
[0022] On a portion of the vehicle apart from the integral
transaxle apparatus are provided driving operating means for
slanting operation of the first movable swash plate so as to
switching the travelling direction between forward and backward and
to change the travelling speed, and steering operating means for
slanting operation of the second movable swash plate so as to
determine the leftward and rightward cornering angle.
[0023] For the purpose of enabling the vehicle to turn laterally in
the same direction of leftward and rightward steering operation of
the steering operating means whether the vehicle travels forward or
backward, the second hydraulic motor is of a variable displacement
type and has a third movable swash plate. The third movable swash
plate interlocks with the driving operating means so that the
slanting direction of the third movable swash plate is changed
oppositely with respect to its neutral position according to the
travelling direction switching operation of the driving operating
means.
[0024] Additionally, the second hydraulic motor is of a variable
displacement type and has a third movable swash plate, the first
hydraulic motor is of a variable displacement type and has a fourth
movable swash plate, and the driving operating means comprises
forward/backward travelling direction switching means and speed
changing means. The forward/backward travelling direction switching
means interlocks with both the third movable swash plate and the
fourth movable swash plate so as to change the slanting directions
of the third and fourth movable swash plates oppositely with
respect to their neutral positions. The speed changing means
interlocks with the first movable swash plate so as to vary the
slanting angle of the first movable swash plate according to the
operational degree of the speed changing means.
[0025] For providing a play to the driving operating means or the
speed changing means, the first movable swash plate is kept in its
own neutral position while the means is operated to some degree
from its own neutral position whether forward travelling or
backward travelling.
[0026] Also, for enabling the vehicle employing the apparatus to
swivel in place, the third movable swash plate is slanted to a
certain degree in a direction corresponding to forward travelling
when the driving operating means or the speed changing means is
located in its own neutral position.
[0027] In this construction, for avoiding the problem that the
vehicle is steered oppositely to the expected direction, the third
movable swash plate is changed in its slanting direction from that
for forward travelling to that for backward travelling according to
the operation of the driving operating means from its own neutral
position into its range for backward travelling (or according to
the switching of the forward/backward travelling direction
switching means to its backward travelling position and the
operation of the speed changing means from the neutral position)
while the first movable swash plate is kept in its own neutral
position.
[0028] Also, for making the steering response to the operation of
the steering operating means gentle during slow travelling, the
third movable swash plate is kept at the certain degree while the
driving operating means is operated for forward travelling (or
while the forward/backward travelling direction switching means is
switched to its forward travelling position and the speed changing
means is operated from the neutral position) within the range to
keep the first movable swash plate in its own neutral position.
[0029] Another object of the present invention is to provide a
vehicle having a caster in addition to its driving wheels, wherein
the caster can nicely follow the driving wheels so as to ensure
expected cornering.
[0030] To achieve the object, the caster interlocks with the
steering operating means so as to be swivelled in relation to the
vehicle by operation of the steering operating means, wherein the
caster is restricted in its range where it can be freely
swivelled.
[0031] Additionally, a caster guide is interposed between the
caster and the vehicle so as to interlock with the steering
operating means thereby being swivelled in relation to the vehicle
by operation of the steering operating means, and to laterally
rotatably support the caster while restricting the caster in its
range of free swivelling in relation to the caster guide.
[0032] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE FIGURES
[0033] FIG. 1 is an entire side view of a mid-mount type lawn
tractor 1 employing an integral transaxle apparatus 2 according to
the present invention;
[0034] FIG. 2 is an entire side view of an alternative mid-mount
type lawn tractor 1a employing the same;
[0035] FIG. 3 is an entire side view of a front-mount type lawn
tractor 1b employing the same;
[0036] FIG. 4 is a plan view partly in section of the interior of
an integral transaxle apparatus 2 which is of an independent
steering type;
[0037] FIG. 5 is a perspective plan view of the same from which a
housing 23 is removed;
[0038] FIG. 6 is a cross-sectional view taken on line vi-vi of FIG.
4;
[0039] FIG. 7 is a perspective view of a charge pump casing
301;
[0040] FIG. 8 is an exploded view in perspective of a strainer 306
and a charge relief valve 330 being attached to charge pump casing
301 and parts of charge pump 300 including casing 301 being
attached to center section 51 as they appear during assembly
thereof;
[0041] FIG. 9 is a perspective view partly in section of casing 301
illustrating its inner oil passages;
[0042] FIG. 10 is a perspective view partly in section of the same
illustrating charge relief valve 330 disposed therein;
[0043] FIG. 11 is a sectional plan view of center sections 51 and
75 of twin HSTs 21 and 22;
[0044] FIG. 12 is a cross sectional view taken on line xii-xii of
FIG. 4;
[0045] FIG. 13 is a cross sectional view taken on line xiii-xiii of
FIG. 4;
[0046] FIG. 14 is a sectional fragmentary side view, on an enlarged
scale, of a control shaft 59 for rotating a movable swash plate 76
of a hydraulic pump 52 of driving HST 21 and its surroundings;
[0047] FIG. 15 is a sectional fragmentary plan view, on an enlarged
scale, of the same;
[0048] FIG. 16 is a sectional fragmentary plan view, on an enlarged
scale, of a brake 110 and its surroundings;
[0049] FIG. 17 is a fragmentary side view of apparatus 2
illustrating a control arm 60 rotated so as to push a first link
rod 211 of a linkage 210 which interlocks a movable swash plate 85
of a hydraulic motor 72 of a steering HST 22 with movable swash
plate 76;
[0050] FIG. 18 is a perspective view of axles 40L and 40R and parts
of differential gear unit 5 as they appear during assembly
thereof;
[0051] FIG. 19 is a perspective view partly in section of a
transmission mechanism illustrating arrows as the directions of
power transmitted from motor shafts 54 and 77 of HSTs 21 and 22 to
axles 40L and 40R through differential gear unit 5;
[0052] FIG. 20 is a diagram illustrating hydraulic circuits and
gear mechanisms of independent-steering type apparatus 2, wherein
hydraulic motor 72 of steering HST 22 is of a variable displacement
type whose swash plate 85 interlocks with swash plate 76 through
linkage 210;
[0053] FIG. 21 is a perspective plan view of apparatus 2;
[0054] FIG. 22 is a perspective right side view of the same;
[0055] FIG. 23 is a perspective front view of the same;
[0056] FIG. 24 is a perspective left side view of the same;
[0057] FIG. 25 is a perspective rear view of the same;
[0058] FIG. 26 is a perspective bottom view of the same;
[0059] FIG. 27 is a schematic side view of linkages for steering
wheel 14 and speed change pedal 15 to be connected to movable swash
plates 57, 76 and 85 of hydraulic pumps 52 and 71 and motor 72 in
HSTs 21 and 22 of the independent steering type, wherein both
steering wheel 14 and speed change pedal 15 are located in their
neutral positions;
[0060] FIG. 28 is a side view of speed change pedal 15 for the
linkage shown in FIG. 27;
[0061] FIG. 29 is a schematic side view of the same shown in FIG.
27, wherein speed change pedal 15 is trod down to some degree for
forward travelling and steering wheel 14 is rotated leftward to
some degree;
[0062] FIG. 30 is a schematic side view of the same, wherein speed
change pedal 15 is trod down to some degree for backward travelling
and steering wheel 14 is rotated leftward to some degree;
[0063] FIG. 31 is a graph of angles of slanted swash plates 57 and
85 in relation to the position of speed change pedal 15 by use of
the linkages shown in FIG. 27;
[0064] FIG. 32 is a schematic side view of the modified linkages
shown in FIG. 27, wherein swash plate 85 is slanted to a certain
degree for forward travelling while speed change pedal 15 is in
neutral;
[0065] FIG. 33 is a graph of the same shown in FIG. 31 by use of
the linkages shown in FIG. 32;
[0066] FIG. 34 is a graph of the same by use of the further
modified linkage shown in FIG. 32;
[0067] FIG. 35 is a schematic side view of linkages for steering
wheel 14, speed change pedal 15' and forward/backward travelling
direction switching lever 205 to be connected to swash plates 57,
65', 76 and 85 of hydraulic pumps 52 and 71 and motors 53 and 72 in
HSTs 21 and 22 of the independent steering type, wherein steering
wheel 14 and speed change pedal 15' are located in their neutral
positions and lever 205 is located at its forward travelling
position;
[0068] FIG. 36 is a schematic side view of a linkage for connecting
steering wheel 14 to a control arm 193' of swash plate 76 through a
slide guide 312 so as to change the response of swash plate 76 to
operation of steering wheel 14 according to the change of angle of
operated steering wheel 14, when steering wheel 14 is in neutral
and slide guide 312 is disposed at the top position of its slidable
range;
[0069] FIG. 37 is a schematic side view of the same linkage when
steering wheel 14 is rotated from its neuttal position and slide
guide 312 is disposed at the top position of its slidable
range;
[0070] FIG. 38 is a schematic side view of the same linkage when
slide guide 312 is positioned at the intermediate position of its
slidable range, when steering wheel 14 is in neutral and slide
guide 312 is disposed at the intermediate position of its slidable
range;
[0071] FIG. 39 is a schematic side view of the same linkage when
steering wheel 14 is rotated from its neutral position and slide
guide 312 is disposed at the intermediate position of its slidable
range;
[0072] FIG. 40 is a schematic side view of linkages including that
shown in FIG. 36 wherein speed change pedal 15' is connected to
slide guide 312 through another linkage;
[0073] FIG. 41 is a schematic side view of alternative linkages
including that shown in FIG. 36 wherein speed change pedal 15' is
connected to slide guide 312 through an alternative linkage
replacing that shown in FIG. 40;
[0074] FIG. 42 is a schematic perspective view of an alternative
linkage for connecting steering wheel 14 to swash plate 76 so as to
change the response of swash plate 76 to operation of steering
wheel 14 according to the change of angle of operated steering
wheel 14 by use of a cam plate 144 and a slide link 145;
[0075] FIG. 43 is a graph of an angle of slanted swash plate 76 in
relation to the angle of rotated steering wheel 14 by use of the
linkage shown in FIG. 42;
[0076] FIG. 44 is a schematic side view of small speed-reduction
gear 108b provided with an engaging member 130 for restriction of
the motion of transmission shaft 93;
[0077] FIG. 45 is a side view of a caster 16 together with a
schematic plan view of the same, caster 16 being provided with a
caster angle P for improvement of its following driving wheels
43;
[0078] FIG. 46 is a side view of a conventional caster 16' having
no caster angle;
[0079] FIG. 47 is a schematic plan view of vehicle 1 having two
front driving wheels 43 and two rear casters 16, wherein vehicle 1
is traversing a slope;
[0080] FIG. 48 is a schematic plan view of vehicle 1 having two
front driving wheels 43 and two rear casters 16, wherein a king pin
of each driving wheel 43 is laterally offset outwardly from the
pivot point of caster 16 on the same side;
[0081] FIG. 49 is a side view of a vehicle 1.times. having two
front casters 16 which can be steered by steering wheel 14;
[0082] FIG. 50 is a side view of caster 16 provided with a caster
guide 400 and a caster hanger 404 to be supported to chassis
12;
[0083] FIG. 51 is a front view of the same;
[0084] FIG. 52 is a plan view of the same;
[0085] FIG. 53 is a sectional plan view of the same;
[0086] FIG. 54 is a sectional plan view of the same, wherein caster
16 is swivelled in relation to caster guide 400;
[0087] FIG. 55 is a plan view of the same, showing a range of
swivelling of caster 16, and
[0088] FIG. 56 is a diagram of linkages for steering wheel 14 to be
connected to both caster guides 400 and to be connected to
hydraulic pump 71 in apparatus 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0089] At first, description will be given on some embodiments of a
lawn tractor serving as a vehicle employing the present invention.
Referring to a lawn tractor 1 shown in FIG. 1, a front column 13
erected on the forward portion of chassis 12 is provided thereabove
with a steering wheel 14 serving as a steering operation tool, and
beside the foot thereof with a speed change pedal 15 serving as a
speed changing operation tool and a brake pedal (not shown).
[0090] Speed change pedal 15 shaped like a seesaw is pivoted at its
intermediate portion and is provided at its front and rear ends
with pedal surfaces. The front pedal surface is trod down so as to
drive the vehicle forwardly, and the rear pedal surface is to drive
it backwardly. The travelling speed of the vehicle, corresponds to
the degree of downward movement of each pedal surface. Pedal 15 is
biased toward its neutral position by a spring (not shown).
[0091] A pair of casters 16 serving as front wheels are provided on
respective left and right sides of the forward bottom portion of
chassis 12. Alternatively, only one caster 16 may be provided on
the lateral middle thereof, or more than two casters 16 may be
provided.
[0092] An engine 11 is mounted on the forward portion of chassis 12
and is covered with a bonnet. A seat 17 is disposed above the
rearward portion of chassis 12. A mower 9 is suspended downwardly
from the longitudinally intermediate portion of chassis 12, thereby
defining lawn tractor 1 as a mid-mount type. Mower 9 comprises a
casing 19 containing at least one rotary blade which is driven by
power from engine 11 transmitted through means like a shaft,
pulleys and a belt (not shown). A linkage is provided so as to
enable mower 9 to move vertically.
[0093] An integral transaxle apparatus 2 of the invention is
disposed at the rearward portion of chassis 12. Apparatus 2
receives rotational power of a vertically downward output shaft 11a
of engine 11 through pulleys and a belt (not shown), and drives
left and right axles 40 supported by the rearward portion of
chassis 12. Left and right driving wheels 43 serving as rear wheels
are fixedly mounted onto utmost ends of axles 40.
[0094] Referring to FIG. 2, an alternative lawn tractor 1a has a
chassis 12' forming a platform 12s at the top of forward portion
thereof, on which front column 13 provided there above with
steering wheel 14 is erected and speed change pedal 15 and the
brake pedal are provided. Chassis 12' is provided on the bottom of
rearward portion thereof with left and right casters 16 serving as
rear wheels.
[0095] Engine 11 having vertically downward output shaft 11a is
mounted on the rearward portion of chassis 12' and is covered with
a bonnet. Mower 9 which is similar to that of FIG. 1 is suspended
downwardly from the longitudinally intermediate portion of chassis
12' (behind driving wheels 43), thereby defining lawn tractor la as
a mid-mount type. Transaxle apparatus 2 disposed at the forward
portion of chassis 12' receives rotational power of output shaft la
through pulleys and a belt (not shown) and drives left and right
axles 40 supported by the forward portion of chassis 12'. Left and
right driving wheels 43 serving as front wheels are fixedly mounted
onto utmost ends of axles 40.
[0096] Referring to FIG. 3, a further alternative lawn tractor 1b
is similar to lawn tractor 1a with the exception that mower 9 is
disposed below the forward portion of chassis 12' (before driving
wheels 43), thereby defining lawn tractor 1b as a front-mount
type.
[0097] Next, description will be given on the internal system of
internal transaxle apparatus 2 for driving and steering a vehicle
such as lawn tractor 1, 1a or 1b in accordance with FIGS. 4-20,
with some references to the external configuration thereof shown in
FIGS. 21-26.
[0098] As shown in FIG. 4, apparatus 2 comprises a driving HST 21
for driving a vehicle forwardly and rearwardly, a steering HST 22
for steering the vehicle, left and right axles 40L and 40R, a
differential gear unit 5 including planetary gears for
differentially connecting axles 40L and 40R, and some drive trains
(gear trains) interlocking component elements 21, 22 and 5 with one
another.
[0099] A housing 23 contains all of elements 21, 22 and 5, axles
40L and 40R and the above said driving trains. As best shown in
FIG. 6, housing 23 consists of an upper half 23t and a lower half
23b joined with each other along a horizontal surrounding joint
surface 23j. Bearing port ions for a support shaft 105 and a
transmission shaft 93 as discussed below are formed by halves 23t
and 23b, whereby resulting shafts 105 and 93 journalled
therethrough are horizontally disposed with their axes on surface
23j, as shown in FIGS. 12 and 13. Bearing portions for axles 40L
and 40R are formed by upper half 23t above surface 23j, as shown in
FIGS. 6 and 13.
[0100] Housing 23 is full of a predetermined amount of oil. A
magnet M as a filter is properly disposed in housing 23, as shown
in FIG. 4 and 6. Metallic dust which has floated in the oil sump
within housing 23 sticks to magnet M, thereby cleaning the oil in
housing 23.
[0101] Referring to the interior of housing 23 as shown in FIGS. 4
and 5, a center section 51 is disposed along the inner right side
wall of housing 23, and a center section 75 is disposed along the
inner rear wall thereof perpendicular to center section 51.
[0102] Center sections 51 and 75 shaped like flat plates may be
identical with each other, so as to save manufacturing costs. They
are both oriented horizontally. A hydraulic pump 52 and a hydraulic
motor 53 are mounted onto the top surface of center section 51,
thereby constituting driving HST 21. Hydraulic pump 52 and motor 53
of driving HST 21 are aligned in a row along the inner right side
wall of housing 23. A hydraulic pump 71 and a hydraulic motor 72
are mounted onto the top surface of center section 75, thereby
constituting steering HST 22. Hydraulic pump 71 and motor 72 are
aligned in a row along the inner rear side wall of housing 23.
Pumps 52, 71 and motors 53, 72 all have vertical rotary axes.
[0103] Axles 40L and 40R are differentially connected to each other
through differential gear unit 5 including planetary gears. Utmost
ends of axles 40L and 40R project laterally outwardly from housing
23, as shown in FIG. 4. In plan view as shown in FIG. 4,
differential gear unit 5 is laterally opposed to center section 51,
and is disposed before center section 75.
[0104] The positional relationship among HSTs 21 and 22 and
differential gear unit 5 best shown in FIG. 4 is an example.
Alternatively, HST 21 and differential gear unit 5 may be exchanged
and HST 22 laterally reversed (pump 71 and motor 72 are exchanged).
Further alternative configurations may be utilized without
departing from the spirit of the invention.
[0105] Referring to FIGS. 5 and 11, each of center sections 51 and
75 is provided therein with two horizontally parallel oil passages
51a or 75a for fluidly connecting corresponding hydraulic pump and
motor to each other. Vertical oil passages 51b are downwardly
extended from respective oil passages 51 a so as to be open at the
bottom of center section 51. Similarly, vertical oil passages 75b
which are extended from respective oil passages 75a are open at the
bottom of center section 75. Corresponding to respective oil
passages 51b and 75b, two draining holes 176 and two draining holes
177 are bored through the bottom of housing 23, as shown in FIG.
26. As shown in FIGS. 5, 6 and 11, each of two vertical draining
pipes 171 is interposed between the bottom opening of each passage
51b and each hole 176, and each of two vertical draining pipes 172
between the bottom opening of each passage 75b and each hole 177,
thereby enabling the oil in center sections 51 and 75 to be drained
downwardly from housing 23. The bottom opening of each of pipes 171
and 172 is regularly plugged.
[0106] In vertically opposite to the hydraulic pumps and motors for
two HSTs 21 and 22, gear trains, which interlock motor shafts 54
and 77 of hydraulic motors 53 and 72 to differential gear unit 5,
are disposed below center sections 51 and 75.
[0107] As shown in FIGS. 6, 17 and 21-25, a pump shaft 25 of
hydraulic pump 52 projects upwardly from the top of housing 23
(upper half 23t) so as to serve as a first input shaft, which is
provided thereon with a first input pulley 27 and a cooling fan 42
(omitted in FIGS. 21-25). As shown in FIG. 20, a belt is interposed
between first input pulley 27 and an output pulley fixed on output
shaft 11a of engine 11.
[0108] Similarly, as shown in FIGS. 6 and 21-25, a pump shaft 26 of
hydraulic pump 71 projects upwardly from the top of housing 23 so
as to be provided thereon with a second input pulley 28 and another
cooling fan 42 (omitted in FIGS. 21-25), thereby serving as a
second input shaft. As shown in FIG. 20, a belt is interposed
between second input pulley 28 and another output pulley fixed on
output shaft 11a.
[0109] Pump shaft 26 of hydraulic pump 71, in steering HST 22 may
be alternatively driven by the output of motor shaft 54 of
hydraulic motor 53 in driving HST 21 through something mechanical
like gears. In other words, there can be provided two types for
integral transaxle apparatus 2 including driving HST 21 and
steering HST 22. One is named an independent steering type, wherein
pump shaft 26 is driven by a prime mover (in this embodiment,
engine 11) independently of the output of motor shaft 54. The other
is named a dependent steering type, wherein pump shaft 26 is driven
by motor shaft 54. However, the present invention is provided for
solving the problem involved in the independent steering type, so
that the shown embodiments and the above and below descriptions
thereof refer to only the independent steering type.
[0110] As shown in FIG. 6, pump(input) shaft 25 projects downwardly
through center section 51 so as to transmit power into a charge
pump 300 attached onto the bottom surface of center section 51.
Charge pump 300 driven by pump shaft absorbs oil in housing 23
through a strainer 306, so as to compensate for leak of operating
oil in two HSTs 21 and 22.
[0111] Detailed description will now be given on charge pump 300.
Center section 51 is provided on the bottom surface thereof with a
charge pump mounting surface onto which a pump casing 301 is
attached. As shown in FIG. 7, casing 301 is provided at the top
portion thereof with a seat 301d having a horizontal surface to be
stuck to the bottom surface of center section 51, and also with a
downwardly recessed rotor chamber 301a for containing rotors, an
inner rotor 302 and an outer rotor 303. Casing 301 is extended
downwardly and bent laterally so as to integrally form retainers
301b and 301c for strainer 306 and a charge relief valve 330,
respectively.
[0112] As shown in FIGS. 6 and 8, inner rotor 302 and outer rotor
303 are disposed within rotor chamber 301a. The lower end of pump
shaft 25 is also disposed vertically in rotor chamber 301a so as to
pass through an axial throughout hole of inner rotor 302 as shown
in FIGS. 6 and 8, and fixed to inner rotor 302 as shown in FIG. 6,
thereby transmitting its rotational force to inner rotor 302. Inner
rotor 302 is torochoidal at its surrounding outer side surface. The
outer rotor 303 has a torochoidally shaped internal gear which is
diametrically larger than the torochoid outer surface of inner
rotor 302. Outer rotor 303 is rotatably retained by casing 301 so
as to be disposed off center of inner rotor 302, so that the
internal gear of outer rotor 303 engages with the external gear of
inner rotor 302. As a result, outer rotor 303 is rotated according
to rotation of inner rotor 302 driven by pump shaft 25.
[0113] During the rotation of rotors 302 and 303, there appear an
expanding space and a reducing space between rotors 302 and 303. In
casing 301 is bored a suction port 321 which is open toward the
reducing space in rotor chamber 301a. As shown in FIG. 9, in casing
301 is bored an oil passage 350 vertically extending from suction
port 321 and an oil passage 340 horizontally extending between oil
passage 350 and tile interior of retainer 301b.
[0114] As shown in FIG. 7, retainer 301b is formed in a circular
shape at the lower side portion of casing 301 and is slantingly cut
away at its inner peripheral edge so as to form a guide surface
315. As shown in FIG. 8, retainer 301b is disposed co-axially with
an opening of the side wall of lower half 23b. Cylindrical strainer
306 is inserted at the inward end thereof along guide surface 315
into retainer 301b. As shown in FIGS. 6, 9, 25 and 26, a discoid
lid 307 is removably plugged into the opening of lower half 23b. A
projection 307a inwardly extending from the inner surface of lid
307, as shown in FIG. 6, is inserted into a spring 308 provided on
the outward end of strainer 306. As a result, strainer 306 is
fixedly interposed between lid 307 and retainer 301b, as shown in
FIG. 6.
[0115] A discharge port 322 is bored in casing 301 so as to be open
toward the expanding space in rotor chamber 301a. A charge relief
valve 330 is provided into retainer 301c. In casing 301 is bored an
oil passage 351 extending between discharge port 322 and the
interior of retainer 301c, and a drain port 331 outwardly extending
from the interior of retainer 301c.
[0116] Charge relief valve 330 comprises a spool 332 and a spring
333. Charge relief valve 330 limits the charge pressure of charge
pump 300. If the pressure in discharge port 322 is increased beyond
the predetermined degree, spool 332 pushed against spring 333 by
the oil discharged from charge pump 300 makes drain port 331
communicate with the interior of retainer 301c, so that the
excessively discharged oil is drained through drain port 331,
thereby keeping the charge pressure equal to or lower than the
predetermined.
[0117] In center section 51, an oil supplying passage 295 is
interposed between two oil passages 51a, as shown in FIG. 11, and
oil passages 287 and 288 are extended from the intermediate portion
of passage 295, so as to be connected to a charge port 390 which is
open at the bottom surface of center section 51, as shown in FIGS.
6 and 8.
[0118] Charge port 290 is open toward the expanding space between
two rotors 302 and 303 in rotor chamber 301a. Oil passages 51a are
charged therein with the operating oil pressurized by the pumping
action of rotors 302 and 303 through charge port 290 and oil
passages 287, 288 and 295 within center section 51. Each passage
51a is provided therein with ball check valve 291, as shown in FIG.
11, which is made open during the oil charging and checks the oil
from passage 51a to passage 295. Passages 51a are thereby prevented
from lack of hydraulic pressure.
[0119] A neutral returning member 261, as shown in FIG. 11, is
slidably disposed in the side wall of housing 23 for making a short
path between two valves 291 through passage 295. Member 261
projects outwardly from housing 23 so as to provide an operating
portion 262, as shown in FIGS. 6, 11, 22, 23, 25 and 26, and is
provided at the inward end thereof with two spools 263, as shown in
FIG. 11, which are inserted into respective passages 51a so as to
be disposed adjacently to balls of valves 291.
[0120] In such a case that a vehicle which has apparatus 2 is drawn
by another vehicle, operating portion 262 is pushed so as to make
neutral returning member 261 slide inwardly so that both spools 263
push balls of valves 291 against springs, whereby oil is drained
from one passage 51a which is pressurized higher than the other.
Thus, motor shaft 54 of driving HST 21 is made freely rotatable, so
that wheels 43 fixed on axles 40L and 40R drivingly connected with
motor shaft 54 are freely rotated without resistance during the
traction.
[0121] Oil in passage 295 can be extracted from housing 23 through
a joint J1. Similarly to center section 51 having passage 295 and
check valves 291, center section 75 involves oil supplying passage
289 interposed between two check valves 291 disposed in respective
passages 75a. Passage 289 is fluidly connected with a joint J2
projecting from housing 23. As shown in FIGS. 11, 21, 23-26, an
external conduit P is interposed between joints J1 and J2
surrounding the bottom portion of housing 23, so as to make the oil
in passage 295 flow into corresponding passage 75a through passage
289 and valve 292, thereby compensating for lack of oil in steering
HST 22. While flowing through conduit P, the oil is cooled by the
atmosphere. Additionally, conduit P may be provided therearound
with fins F for enhancing the cooling effect as drawn in phantom
lines in FIG. 11.
[0122] Also, similarly to neutral returning member 261 for driving
HST 21, two oil passages 75a of steering HST 22 can be equal to
each other in hydraulic pressure by neutral returning member 264,
whose external portion projecting outwardly from housing 23 is
provided thereon with all operation portion 265.
[0123] Due to the above mentioned construction, both HSTs 21 and 22
are compensated for lack of oil by the pumping action of charge
pump 300.
[0124] Detailed description will now be given on driving HST 21
which is so constructed that hydraulic pump 52 and hydraulic motor
53 are mounted on the top of center section 51 as mentioned above.
Referring to variable displacement hydraulic pump 52 as shown in
FIG. 6, a cylinder block 44 is rotatably and slidably mounted on
the pump mounting surface at the top of center section 51. Vertical
pump shaft 25 is axially and is not relatively rotatably disposed
in cylinder block 44. A plurality of pistons 45 are reciprocally
slidably inserted with respective biasing springs (not shown) into
cylinder block 44. The heads of pistons 45 abut against a movable
swash plate 57 which is operated slantwise so as to control the
amount and direction of oil discharged from hydraulic pump 52.
[0125] A control shaft 59 is supported by the wall of housing 23 in
parallel to axles 40 so as to operate swash plate 57 slantwise, as
shown in FIGS. 4, 13-15 and 17. An arm member 271 is fixed onto the
inward end of control shaft 59 in housing 23.
[0126] Referring to FIG. 14, a swash plate arm 272 as an integral
part of arm member 271 is extended from a boss 280 of arm member
271 fixed around control shaft 59 so as to engage at the utmost end
thereof with swash plate 57.
[0127] Referring to FIG. 15, a neutral holding arm 273 as another
integral part of arm 271 is extended backwardly from boss 280. An
inward projection 275 is provided on the inner side wall of housing
23 behind control shaft 59. A neutral biasing spring 277 is
provided around boss 280. Both end portions 278 and 279 of spring
277 are extended backwardly so as to sandwich projection 275 up and
down. A projection 276 is integrally provided on the utmost end of
arm 273. The utmost end of projection 276 is disposed between end
portions 278 and 279 of spring 277.
[0128] As shown in FIGS. 4, 13-15, 21, 24 and 25, a control arm 60
is fixed onto control shaft 59 outside housing 23. As best shown in
FIG. 24, control arm 60 is integrally provided with a boss 60a, an
arm 60b, a projection 60c and a push edge 60d. Boss 60a is fixed
onto control shaft 59 with a pin 25t. Arm 60b projects upwardly
from boss 60a, so as to interlock with a speed change operating
tool (in this embodiment, speed change pedal 15) through a linkage
or the like. Projection 60c projects downwardly from boss 60a. Push
edge 60d projects backwardly from boss 60a.
[0129] As shown in FIG. 14, a limiter 173 is fixed onto the
external side surface of housing 23 below control shaft 59, so as
to limit the rotational range of control arm 60. Projection 60c of
control arm 60 is disposed between two projections 174 and 175 as
integral parts of limiter 173. Either of projections 174 and 175
abuts against projection 60c rotated to a certain degree.
[0130] Due to the above construction, when speed change pedal 15 is
trod down, control arm 60 interlocking with pedal 15 is rotated
together with control shaft 59, so that swash plate 57 connected to
control shaft 59 through arm 272 is rotated slantwise, thereby
controlling the amount and direction of oil discharged from
hydraulic pump 52.
[0131] As shown in FIGS. 5, 13-15 and 20, pressure oil discharged
from hydraulic pump 52 is circulated between pump 52 and motor 53
through two oil passages 51a.
[0132] Hydraulic motor 53 in this embodiment is of a fixed
displacement type, however, that shown in FIG. 35 in another
embodiment as discussed below is of a variable displacement
type.
[0133] Referring to fixed displacement hydraulic motor 53 of this
embodiment, center section 51 forms a motor mounting surface on the
top thereof so as to be disposed behind axle 40R opposite to the
pump mounting surface thereof, as shown in FIGS. 4 and 6. Cylinder
block 63 is rotatably and slidably mounted onto the motor mounting
surface, as shown in FIGS. 6 and 12. Similarly to hydraulic pump
52, a plurality of pistons 64 with respective biasing springs are
reciprocally slidably inserted into cylinder block 63 and abut at
the heads thereof against a fixed swash plate 65. Vertical motor
shaft 54 is axially and not relatively rotatably disposed in
cylinder block 53.
[0134] As shown in FIGS. 6 and 12, motor shaft 54 penetrates center
section 51 and projects downwardly so as to be fixedly provided
thereon with a bevel gear 61. Bevel gear 61 engages with a bevel
gear 62 fixed on driving transmission shaft 93 rotatably disposed
in parallel to axles 40 in housing 23, as shown in FIG. 12. Shaft
93 forms a driving gear 69 which engages with a center gear 94 of
differential gear unit 5.
[0135] Detailed description will now be given on a brake 110
disposed on shaft 93. As shown in FIGS. 12 and 16, a brake disk 195
is not relatively rotatably but slidably provided on an end of
shaft 93. A brake pad 196 is disposed adjacently to brake disk 195,
and a brake pad 199 is caught in the inner wall of housing 23 so as
to be disposed adjacently to brake disk 195 in opposite to brake
pad 196. A brake control shaft 197 integrally forming a cam 197a is
vertically disposed in contact with brake pad 196. Brake control
shaft 197 projects upwardly from housing 23 so as to be fixedly
provided thereon with a brake control lever 198, as shown in FIGS.
12, 22 and 23. Lever 198 interlocks with the above-mentioned brake
pedal through a linkage or the like. When the brake pedal is trod
down, shaft 197 is rotated so that cam 197a of shaft 197 presses
brake pad 196 against brake disk 195.
[0136] Brake disk 195 is pushed outwardly by cam 197a through pad
196 and is pressed against brake pad 199. Thus, brake disk 195,
sandwiched between pads 196 and 199, and shaft 93 are braked.
[0137] Next, detailed description will be given on steering HST 22
comprising hydraulic pump 71 and hydraulic motor 72 mounted on
center section 75. In this embodiment described hereinafter, center
section 75 of steering HST 22 is separate from center section 51 of
driving HST 21. Alternatively, a single center section may be
disposed so as to be shared between both HSTs 21 and 22.
[0138] Referring to variable displacement hydraulic pump 71,
vertical pump shaft 26 rotatably penetrates center section 75 and
projects downwardly so as to be fixedly provided thereon with an
input gear 161, as shown in FIGS. 4 and 20. Input gear 161 engages
with steering driving gear 160 fixed on motor shaft 54 of driving
HST 21, so that the rotational force of motor shaft 54 is
transmitted to pump shaft 26.
[0139] Pump shaft 26 projects upwardly axially from the pump
mounting surface formed at the top of center section 75, so as to
be axially and not relatively rotatably disposed in a cylinder
block 46 which is rotatably slidably mounted on the pump mounting
surface, as shown in FIG. 6.
[0140] A plurality of pistons 47 with respective biasing springs
are reciprocally slidably inserted into cylinder block 46 so as to
abut at the heads thereof against a movable swash plate 76. Swash
plate 76 is operated slantwise so as to control the amount and
direction of oil discharged from hydraulic pump 71.
[0141] A control shaft 73 is vertically supported by the ceiling of
housing 23 so as to operate swash plate 76, as shown in FIGS. 4 and
6. An arm 191 projects from control shaft 73 in housing 23, so as
to engage at the utmost end thereof with swash plate 76, as shown
in FIG. 6. A control lever 193 is fixed onto control shaft 73
through a pin 252 above housing 23, as best shown in FIGS. 6 and
23. Control lever 193 is connected with a steering operating means
(steering wheel 14 in this embodiment) through a linkage (not
shown).
[0142] Swash plate 76 is biased toward the neutral position. The
biasing force and the neutral position may be adjustable. In
housing 23, a limiter 192, shaped like a sector in plan view as
shown in FIG. 4 and 6, is fixed onto shaft 73. When lever 193 is
rotated to some degree, one of the two radial edges of limiter 192
comes to abut against the internal wall of housing 23, so as to
limit the rotational range of lever 193.
[0143] Due to the above construction, steering wheel 14 is rotated
so as to rotate control lever 193 and control shaft 73, thereby
moving swash plate 76 slantwise through arm 191 for changing the
direction and volume of operating oil discharged from hydraulic
pump 71.
[0144] As shown in FIGS. 11 and 20, the oil is circulated between
hydraulic pump 71 and motor 72 through both of second oil passages
75a.
[0145] According to the preferred embodiment, hydraulic motor 72 is
of a variable displacement type. In this regard, a cylinder block
80 is rotatably and slidably mounted onto the motor mounting
surface which is formed on the top of center section 75 leftward of
the pump mounting surface on the same. Cylinder block 80 is
provided therein with a plurality of reciprocally movable pistons
82 and springs for biasing them. A movable swash plate 85 abuts
against the heads of pistons 82. A vertical motor shaft 77 is
axially disposed in cylinder block 80 so as to fixedly engage
therewith. Swash plate 85 is so operated as to change the rotary
speed of shaft 77.
[0146] As shown in FIG. 13, a control shaft 86 is horizontally
journalled by the side wall of housing 23 for operating swash plate
85 slantwise. A swing arm 281 is fixed at the basic end thereof
onto the inward end of shaft 86 in housing 23. The utmost end of
arm 281 engages with swash plate 85.
[0147] As shown in FIGS. 4, 13, 27-29 and 32, a control lever 87
fixed onto shaft 86 outside housing 23 interlocks through a linkage
210 with control arm 60 which operates swash plate 57 of hydraulic
pump 52 in driving HST 21.
[0148] Hydraulic motor 72 may be replaced with that of a fixed
displacement type. In this case, linkage 210 is unnecessary.
[0149] Description will now be given on linkage 210 in accordance
with FIGS. 4, 13, 15, 17, and 21-26. A first link rod 211 is
disposed along the outside of housing 23 and is slidably supported
by a supporter 213 fixed onto housing 23. A head 212 of rod 211 is
disposed adjacently to push edge 60d of control arm 60.
[0150] An L-like shaped arm 220 is pivoted at the intermediate
position thereof onto a rearward outside corner of housing 23.
First link rod 211 is pivotally connected to one end of arm 220. A
second link rod 220 is pivotally interposed along the rear outside
end of housing 23 between the other end of arm 220 and control
lever 87. Rods 211 and 220 are substantially perpendicular to each
other.
[0151] When an operator treads down speed change pedal 15, control
arm 60 is rotated so as to change the position of swash plate 57 of
hydraulic pump 52 in driving HST 21. Simultaneously, whether arm 60
is rotated regularly or reversely, edge 60d of rotated arm 60 is
pressed against head 212 of first link rod 211, as shown in FIG.
17, so as to thrust rod 211 toward arm 220, so that arm 220 is
rotated to pull control level 87 through second link rod 221,
thereby tilting swash plate 85 of hydraulic motor 72 in steering
HST 22. As a result, the rotary speed of motor shaft 77 is reduced
as the rotary speed of motor shaft 54 is increased whether the
rotational direction of shaft 54 is regular or reverse. Thus, the
faster the vehicle employing apparatus 2 travels, the more the
steering response to operation of steering wheel 14 becomes dull,
thereby preventing the vehicle from the fear of hard cornering
during its fast travelling.
[0152] A turnbuckle 222 is interposed at the intermediate portion
of second link rod 221 for adjusting the length thereof, thereby
enabling the relationship between the driving speed and the
steering response to be changed within a certain range.
[0153] As shown in FIG. 13, motor shaft 77 passes through center
section 75 and projects downwardly so as to be fixedly provided on
the bottom end thereof with a bevel gear 104. Shaft 105 is disposed
below bevel gear 104 in parallel to axles 40. As shown in FIG. 4,
both ends of shaft 105 are fixedly inserted into sleeves 190 fixed
in two opposed bosses formed by lower half 23b. A pair of adjacent
sleeves 111 are rotatably provided on shaft 105. Bevel gears 106
are fixed onto respective sleeves 111, so that both bevel gears 106
are laterally symmetrically disposed with respect to motor shaft
77, so as to engage with bevel gear 104.
[0154] The output power of hydraulic motor 72 is shared between
left and right bevel gears 106 which are rotated in opposite
directions.
[0155] As shown in FIG. 4, two sleeves 111 are also fixedly
provided thereon with respective gears 107. Shaft 93 is provided
thereon with two laterally juxtaposed speed-reduction gears 108,
each of which consists of a diametrically large gear 108a and a
diametrically small gear 108b. Both gears 108b are rotatably
provided on shaft 93 so as to be disposed laterally oppositely to
each other with respect to driving gear 69. Each gear 108a engages
at the inner periphery thereof with the outer periphery of each
gear 108b, so that gears 108a and 108b engaging with each other are
not relatively rotatable. Both gears 108a engage with respective
gears 107. Differential gear unit 5, as discussed below, includes a
pair of ring like shaped internal gears 98 which form gears 99 at
their outer peripheral surfaces. Gears 108b engage with gears
99.
[0156] Description will now be given on differential gear unit 5
which differentially connects left and right axles 40L and 40R in
accordance with FIGS. 4, 13, 18-20. As shown in FIG. 4, a sun gear
95 is rotatably provided on the abutting proximal ends of axles 40L
and 40R so as to integrally engage with the inner peripheral teeth
of a center gear 94. Driving gear 69 fixed on shaft 93 engages with
center gear 94.
[0157] Left and right carriers 97 are fixed onto respective axles
40L and 40R, and fixedly provided at the outer peripheries thereof
with respective internal gears 98. A plurality of planet gears 96
are rotatably supported by each carrier 97 so as to lie interposed
between sun gear 94 and each internal gear 98.
[0158] If internal gears 98 were directly supported onto axles 40L
and 40R apart from carriers 99, differential gear unit 5 would be
laterally wide along the axes of axles 40L and 40R. Internal gears
98 according to the preferred embodiment are provided on the outer
peripheries of carriers 99, thereby compacting differential gear
unit 5 which is actually made laterally narrow along axles 40L and
40R.
[0159] In FIG. 19, a bold arrow describes the power transmission
from motor shaft 54 of hydraulic motor 53 in driving HST 21 to sun
gear 94 of differential gear unit 5 through bevel gears 61 and 62,
shaft 93, gear 69 and center gear 94.
[0160] Also in FIG. 19, a hollow arrow describes the power
transmission from motor shaft 77 of hydraulic motor 72 in steering
HST 22 to left and right internal gears 98 of differential gear
unit 5, wherein two bevel gears 106 sharing the rotary power of
bevel gear 104 are rotated in opposite directions so as to rotate
internal gears 98 in opposite directions through speed-reduction
gears 108.
[0161] Accordingly, one of the two sets of planet gears 96 opposed
with respect to center gear 94 receive the rotational force of
corresponding internal gear 98 in addition to that of sun gear 95,
and the other set of gears 96 receive the rotational force of sun
gear 95 reduced by that of corresponding gear 98.
[0162] As a result, left and right carriers 97 become different
from each other in rotary speed, so that axles 40L and 40R are
differentially rotated so as to steer the vehicle.
[0163] Hitherto discussed apparatus 2 of the independent steering
type has the problem that, if the rotational direction of steering
wheel 14 is set to coincide with the cornering direction of a
vehicle during its forward travelling, the vehicle, when backward
travelling, turns in the opposite direction to the rotation of
steering wheel 14. For example, the rightward rotation of steering
wheel 14 during the backward travelling of vehicle causes the
vehicle to turn leftward. Therefore, steering the vehicle is
difficult for an operator who is accustomed to steering a regular
type car.
[0164] If the vehicle is to turn leftward when steering wheel 14 is
rotated leftward, left axle 40L (close to the corner) must be
decelerated and right axle 40R (away from the corner) must be
accelerated whether the vehicle travels forward or backward.
[0165] The force of decelerating and accelerating axles 40L and 40R
for cornering is caused by rotation of motor shaft 77 of steering
HST 22. Each axle 40 is rotated oppositely between the case of
forward travelling and of backward travelling, therefore, the
slanting direction of motor shaft 77 must be opposite between the
cases of forward travelling and of backward travelling.
[0166] For solving the problem, the present invention provides some
alternative linkages replacing the above-mentioned linkage 210,
each of which makes three movable swash plates 57, 76 and 85
interlock with one another as discussed below, wherein swash plate
85 is slanted oppositely between the cases of forward travelling
and of backward travelling.
[0167] Firstly, referring to FIG. 27, an arm 200 interlocking with
a stem of steering wheel 14 through gears and the like (not shown)
further interlocks with control arm 193 for operating swash plate
76 of hydraulic pump 71 of steering HST 22. Also, an arm 201
projecting from the pivotal shaft of speed change pedal 15
interlocks with control arm 87 of hydraulic motor 72 of steering
HST 22, and an arm 202 projecting from the same interlocks with
control arm 60 of hydraulic pump 52 of driving HST 21.
[0168] Arm 201 shaped like a sector is bored by an elongated hole
203 along the peripheral edge thereof, as shown in FIG. 28. An end
of a link for connecting to control arm 60 is slidably inserted
into hole 203, so that the end is located substantially in the
middle of hole 203 when swash plate 57 is in the neutral position.
Due to such a construction, even if the above-mentioned spring for
biasing pedal 15 to the neutral has a slight error causing the
vehicle to drive unexpectedly, swash plate 57 can be located in
neutral when pedal 15 is not trod down, whereby the vehicle is safe
from the unexpected travelling.
[0169] FIG. 27 shows that both steering wheel 14 and speed change
pedal 15 are in neutral, thereby positioning both swash plates 57
and 76 in neutral. In this condition, both hydraulic pumps 52 and
71 in HSTs 21 and 22 are not driven, so as to make the vehicle free
from travelling and cornering.
[0170] FIG. 29 shows that pedal 15 is trod down for forward
travelling and steering wheel 14 is leftward rotated for
left-cornering. The link interposed between arm 202 and control arm
60 is pushed toward control arm 60 because arm 202 rotated
integrally with pedal 15 pushes the end of the link in contact with
the end of hole 203 thereof, so that swash plate 57 is slanted so
as to make hydraulic pump 52 perform its pumping action for driving
hydraulic motor 53 in one direction, thereby making the vehicle
travel forwardly.
[0171] Also, arm 200 is tilted by leftward rotation of steering
wheel 14 so as to slant swash plate 76 through control arm 193 and
a link, thereby making hydraulic pump 71 perform its pumping action
in one direction. Simultaneously, arm 201 of pedal 15 is tilted so
as to slant swash plate 85 in one direction from its neutral
position through control arm 87 and a link. The association between
the direction of pumping action of pump 71 and the direction of
slanted swash plate 85 results in motor shaft 77 rotating in one
direction so as to make the forward travelling vehicle turn
leftward.
[0172] In turn, FIG. 30 shows that pedal 15 is trod down for
backward travelling and steering wheel 14 is rotated leftward. Arm
202 is tilted oppositely to that shown in FIG. 29 while the end of
the link is in contact with the other end of hole 203, whereby the
link is pulled away from control arm 60. Swash plate 57 is slanted
oppositely to that in the case of FIG. 29, thereby causing
hydraulic motor 53 to drive in the other direction for making the
vehicle travel backwardly.
[0173] Also, arm 200 is tilted by leftward rotation of steering
wheel 14 so as to slant swash plate 76 through control arm 193 and
the link, thereby making hydraulic pump 71 perform its pumping
action in the same direction. Simultaneously, arm 201 of pedal 15
trod down for backward travelling is tilted so as to slant swash
plate 85 slantwise in the other direction. The association between
the direction of pumping action of pump 71 and the direction of
slanted swash plate 85 results in motor shaft 77 rotating in the
other direction so as to make the backward-travelling vehicle turn
leftward.
[0174] In addition to the solution of the problem as its essential
purpose, the linkage shown in FIGS. 27-30 has such an advantage as
follows:
[0175] The angle of slanted swash plate 85 is increased in
proportion to the degree of tread of pedal 15, thereby causing
motor shaft 77 to be decelerated in spite of the constant pumping
action of hydraulic pump 71. FIG. 31 shows graphs A and B of
slanting angles of both swash plates 57 and 85 in relation to the
position of pedal 15. Graph A is drawn in a solid line, and graph B
in a dotted line. The angle in the slant direction of swash plate
85 when speed change pedal 15 is trod down for forward travelling
is marked "+", and the angle thereof for backward travelling is
marked "-". The same is true in FIGS. 33, 34 and 43. If steering
wheel 14 is rotated to a certain degree, the rotary speed of motor
shaft 77 during fast travelling is smaller than that during slow
travelling, thereby avoiding hard-cornering during fast
travelling.
[0176] In FIG. 31, graph B has a constant level range "b" which
means that swash plate 57 is hold in the neutral position when
pedal 15 is in vicinity of the neutral position because of the play
of hole 203 in arm 202. Even if steering wheel 14 is rotated
leftward or rightward while pedal 15 is in neutral, motor shaft 77
is not rotated by the pumping action of hydraulic pump 71 because
swash plate 85 is placed horizontally (in neutral). In this
condition, the operating oil discharged from pump 71 is drained
into charge pump casing 301 through charge relief valve 330.
[0177] If motor shaft 77 can be rotated while speed change pedal 15
is in the neutral position so as to keep hydraulic motor 53 in
neutral, the vehicle is enabled to spin-turn (to swivel in place).
This can be achieved by the further modified construction as shown
in FIGS. 32 and 33.
[0178] Referring to FIG. 32, swash plate 85 is slanted to an angle
Z in the forward travelling direction white pedal 15 is located in
neutral. The forward travelling direction means the slant direction
of swash plate 85 when pedal 15 is trod down for forward
travelling, which is marked by "T" in FIG. 33 as discussed below.
Additionally, the slant direction of swash plate 85 when pedal 15
is trod down for backward travelling is named a backward travelling
direction (marked by "-" in FIG. 33). Angle Z of swash plate 85 can
be adjusted by adjustment of the spring for biasing it to the
neutral position, and by that of the length of link interposed
between arm 201 and control arm 87. The other construction is
identical with that of FIG. 27.
[0179] The construction shown in FIG. 32 causes graphs A and B of
slanting angles of both swash plates 57 and 85 in relation to the
position of pedal 15 as shown in FIG. 33, wherein graph B displays
that the angle of swash plate 85, when pedal 15 is located in the
neutral position, is Z in the forward travelling direction (marked
by "+"). Therefore, if steering wheel 14 is rotated leftward or
rightward when pedal 15 is in the neutral position, the pumping
action of hydraulic pump 71 is applied to hydraulic motor 72 so as
to rotate motor shaft 77, so that left and right axles 40L and 40R
are rotated in opposite directions, thereby making the vehicle
spin-turn.
[0180] There appears that swash plate 85 is not slanted in the
backward travelling direction (marked by "-") while pedal 15 is
trod down in a shown range "a". However, range "a" is within that
"b" wherein swashplate 57 is held in the neutral position by the
play of hole 203, whereby, while steering wheel 14 is rotated,
there is no problem such that motor shaft 77 is unexpectedly
rotated so as to make the vehicle turn oppositely to the rotational
direction of steering wheel 14 and that motor shaft 77 is not
rotated so as to make the vehicle travel unexpectedly in
straight.
[0181] Arm 201 of speed change pedal 15 is provided therein with an
elongated hole similarly to arm 202 of the same, thereby providing
a play for the operation of swash plate 85 of steering HST 22. As a
result, swash plate 85 remains in the slanting condition at angle Z
while pedal 15 is trod down to some degree for forward travelling.
This construction causes graphs A and B of slanting angles of both
swash plates 57 and 85 in relation to the position of pedal 15 as
shown in FIG. 34, wherein a flat level range "c" of graph B
preferably substantially coincides with a part "bf" of the flat
level range "b", so that the range where swash plate 85 is slanted
at angle Z substantially coincides with that where swash plate 57
is kept in neutral while pedal 15 is trod down for forward
travelling.
[0182] Swash plate 85 of FIG. 34, in comparison with that of FIG.
33, is slanted at a smaller angle while speed change pedal 15 is
trod down within a range "d" for slow forward travelling. Thus,
motor shaft 77 of FIG. 34 can be rotated faster than that of FIG.
33 while steering wheel 14 is rotated to the same degree in the
case of forward travelling. The resulting vehicle can turn in
almost spin-turning condition during slow forward travelling.
[0183] Alternatively, referring to FIG. 35, hydraulic motor 53 of
driving HST 21 is provided with a movable swash plate 65', thereby
being defined as a variable displacement pump. Apparatus 2 is
provided with a control arm 112 for operating swash plate 65'.
Also, vehicle 1 is provided with a forward/backward travelling
switching lever 4 and a speed change pedal 15' both which replace
speed change pedal 15. For example, lever 4 is disposed beside
front column 13 or seat 17. Pedal 15' has only one pedal surface
for treading.
[0184] An arm 204, which is identical with arm 202 of pedal 15,
projects from a pivotal shaft of pedal 15', so as to interlock with
swash plate 57 of hydraulic pump 52 in driving HST 21 through
control arm 60.
[0185] An arm 205 projects from a pivotal shaft of lever 4, so as
to interlock with swash plates 65' and 85 of both hydraulic motors
53 and 72 through control arms 112 and 87, respectively.
[0186] Due to the association between lever 4 and swash plate 65',
the pumping action of hydraulic pump 52 caused by treading of pedal
15' is applied to hydraulic motor 53, so that motor shaft 54 is
rotated regularly when lever 4 is located in a forward travelling
position F, and is rotated reversely when lever 4 is in a backward
travelling position R.
[0187] Also, due to the association between lever 4 and swash plate
85, the pumping action of hydraulic pump 71 caused by rotation of
steering wheel 14 is applied to hydraulic motor 72, so that motor
shaft 77, when lever 4 is located in position F, is rotated
oppositely to that when lever 4 is in position R while steering
wheel 14 is rotated in the same direction. Thus, the rotation of
motor shaft 77 is reversed between the cases of forward travelling
and of backward travelling.
[0188] In this construction, even if pedal 15' is located in the
neutral position, swash plate 85 of hydraulic motor 72 is not
neutral but slanted to some degree. Therefore, if steering wheel 14
is rotated while pedal 15' is neutral, motor shaft 77 is rotated,
thereby enabling the vehicle to spin-turn. This is different from
the construction shown in FIG. 27, but is similar with that shown
in FIG. 32.
[0189] Referring to FIG. 36, a modified linkage is constructed
between steering wheel 14 and swash plate 76 of hydraulic pump 71
in steering HST 22. A control arm 193' having a straight elongated
hole 310 along its longitudinal direction replacing control arm 193
is provided for operating swash plate 76. Additionally, a slide
guide 312 having an elongated hole 311 substantially in parallel to
hole 310 is provided. Slide guide 312 can slide substantially in
parallel to hole 310 when control arm 193' is in the neutral
position.
[0190] A link 215 is interposed between arm 200 interlocking with
steering wheel 14 and arm 193'. A first end of link 215 is
pivotally connected to arm 200. A second end of link 215 is
slidably inserted into both hole 310 of control arm 193' and hole
311 of slide guide 312. If guide 312 slides vertically in FIG. 36,
the second end of link 215 slides along hole 310 according to the
movement of guide 312.
[0191] When guide 312 is located in an upper position within its
slide range, the second end of link 215 is close to the upper end
of hole 310, thereby being near the basic end of control arm 193'.
In this condition, if steering wheel 14 is rotated to a certain
degree, arm 193' is rotated to an angle "An" as shown in FIG.
37.
[0192] Meanwhile, when guide 312 is located in a lower position,
the second end of link 215 is close to the lower end of hole 310,
thereby being away from the basic end of arm 193'. In this
condition, if steering wheel 14 is rotated to the same degree with
that of FIG. 37, arm 193' is rotated to an angle "Af" as shown in
FIG. 38, which is smaller than angle "An" shown in FIG. 37.
[0193] In brief, the vertical sliding motion of guide 312 enables
swash plate 76 to differ in its slanting angle while the rotational
angle of steering wheel 14 is the same. Hole 311 of guide 312,
which is gently arcuate in FIG. 36, is not limited in its shape.
Various kinds of relationships between both angles of rotated
steering wheel 14 and slanted swash plate 76 can be provided by
modification of hole 311. For example, it may be directly
proportional, quadratic, or higher dimensional. Also, the width of
hole 310 may be changed so that swash plate 76 is kept in neutral
when steering wheel 14, is in vicinity of the neutral position,
that is, steering wheel 14 is provided with an enlarged play.
[0194] FIG. 40 shows a mechanism for making guide 312 slide.
Control arm 60 for operating swash plate 57 of hydraulic pump 52
is, when being in neutral, oriented perpendicularly to the sliding
direction of guide 312. Guide 312 is connected with control arm 60
through a link 216. A link 225 and a wire 226 are extended from arm
204 of pedal 15'. Link 225 is connected to an arm 227 which is
integral with control arm 60. Wire 226 is connected to control arm
60 through a pulley 228. A pair of springs 218 bias guide 312 so as
to return guide 312 to its neutral position when the treading force
applied onto pedal 15' is released.
[0195] Due to such a construction, when pedal 15' is trod down, arm
204 is rotated so as to rotate control arm 60, thereby making guide
312 slide through link 216 so as to change the rate of angle of
slanted swash plate 76 to the angle of rotated steering wheel
14.
[0196] As a result, guide 312 interlocks with pedal 15' so that the
cornering response to operation of steering wheel 14 is gentle
during fast travelling, and is sharp during slow travelling,
thereby enabling the vehicle to change the rate of cornering angle
to the operational angle of steering wheel 14 according to the
travelling speed.
[0197] Control arm 60 may be removed from the linkage between pedal
15' and guide M. It is enough for guide 312 to interlock with pedal
15' or another part of driving system for driving HST 21.
[0198] Referring to FIG. 41, for modification of the construction
shown in FIG. 40, link 216 is replaced with a link 216' having an
elongated hole 219 into which a joint pin of control arm 60 is
slidably inserted, thereby applying a play for the motion of guide
312 in relation to treading of pedal 15'.
[0199] With regard to the construction shown in FIG. 27, the
linkage between steering wheel 14 and control arm 193 may be
replaced with that shown in FIG. 42. Referring to FIG. 42, a cam
plate 144 having a cam groove 144a is fixed onto stem 14a of
steering wheel 14. A first end of groove 144a is nearest to stem
14a, and a second end thereof is farthest from stem 14a. Groove
144a is so curved that the distance between groove 144a and stem
14a is generally larger and larger while advancing from the first
end to the second end. A slide link 145 is disposed so as to
slidably pass through slide guide 146. A cam follower 145a is
provided on an end of slide link 145 so as to be slidably inserted
into groove 144a. The other end of slide link 145 is pivotally
connected to control arm 193 for operating swash plate 76 of
hydraulic pump 71.
[0200] Due to such construction, when steering wheel 14 is rotated,
cam plate 144 is integrally rotated. The position of cam follower
145a in groove 144a of rotated cam plate 144 is changed so as to
change the distance between cam follower 145a and stem 14a, thereby
making guide 145 slide so as to rotate control arm 193 for slanting
swash plate 76.
[0201] The displacement of slanting response of swash plate 76 to
the rotational angle of steering wheel 14 can be varied by changing
the shape of groove 144a. Referring to FIG. 43, for example, the
graph of slant angle of swash plate 76 in relation to the
rotational position of steering wheel 14 has a flat level range "e"
which means that swash plate 76 is held in neutral when steering
wheel 14 is in vicinity of its neutral position. As a result,
vehicle 1 can travel in straight steadily even if steering wheel 14
is rotated from its neutral position (for straight travelling) to a
slight angle to be considered as an error.
[0202] When being apart from range "e", the graph is curved at an
increasing tempo. If the rotational position of steering wheel 14
is in either of shown ranges "ff" and "fr", the displacement of
slanting angle of swash plate 76 is small. Therefore, the cornering
response to operation of steering wheel 14 is gentle when steering
wheel 14 is rotated to a small degree leftward or rightward, so
that vehicle 1 can travel steadily along a gentle winding course.
At a large rotational angle of steering wheel 14, the angle of
slanted swash plate 76 is increased dramatically. As a result,
within the whole of normally limited rotational range of steering
wheel 14, vehicle 1 is provided with a variety of steering
responses which enables vehicle 1 to select various cornering types
from meandering to hard cornering.
[0203] For restriction of slanting of swash plate 76 when steering
wheel 14 is in vicinity of its neutral position, a steering
transmission system in apparatus 2 may be provided at a suitable
portion thereof with something to check the motion of swash plate
76 instead of such a limited slip mechanism as shown in FIG. 42.
For one of such checking means, a normal brake is applied when
steering wheel 14 is in vicinity of the neutral position.
[0204] Referring to another of the check means as shown in FIG. 44,
there is provided an engaging member 130 adjacent to diametrically
small gear 108b of each of left and right speed reduction gears
108. Engaging member 130 has teeth 131 for engaging with gear 108b.
Both engaging members 130 interlock with steering wheel 14 through
linkage, so that, when steering wheel 14 is in vicinity of the
neutral position, both engaging members 130 engage with left and
right gears 108b, thereby stopping both speed-reduction gears 108,
whereby the vehicle can be kept in the condition of straight
travelling even if steering wheel 14 is slightly rotated leftward
or rightward as an operational error.
[0205] Moreover, if the volume of HST 21 or 22 is large, the
movable swash plate or plates thereof, generally require a large
force to be operated. Thus, each of the movable swash plates may be
of a trunnion type, which requires a smaller force, thereby
enabling an operator to operate steering wheel 14 or speed change
pedal 15 by small force regardless of the large volume of HST 21 or
22.
[0206] Next, description will be given on improvement of caster 16
in accordance with FIGS. 45 to 56.
[0207] A conventional caster 16' is, as shown in FIG. 46, supported
by a vertically oriented supporter 16a' so that caster 16' abuts
against the ground surface through a caster trail W', which is a
distance between a phantom vertical shaft VS crossing a pivot of
caster 16' and an extension of an axis of supporter 16a' on the
ground. Referring to FIG. 45, a supporter 16a for caster 16 is
tilted to a caster angle P from a phantom vertical shaft VS so that
a caster trail W becomes smaller than that W'.
[0208] Such small caster trail W can reduce the torque for rotating
caster 16, thereby enabling caster 16 to follow the driving of
wheels 43 nicely. Preferably, such caster 16 or casters 16 are
disposed on the rear portion of a vehicle (behind driving wheels
43). Such a vehicle has an advantage especially in traversing a
slope. As illustrated in FIG. 47, when vehicle 1 having left and
right driving wheels 43 as front wheels and left and right casters
16 as rear wheels traverses a slope, a component force Fc of
gravity downwardly along the slope surface is applied onto each of
wheels 43 and casters 16 in perpendicular to the travelling
direction of the vehicle. Driving wheels 43 have rotational force
for advancing as resistance against component force Fc of gravity.
However, casters 16 have only follow rotational force in the
travelling direction. Component force Fc is increased in proportion
of the area of caster 16 abutting against the slope surface, that
is, caster trail W. In this embodiment, caster trail W is so small
as to restrict component force Fc so that casters 16 can follow
wheels 43 without dragging downwardly on the slope.
[0209] Also or alternatively, referring to FIG. 48, on each of left
and right sides of vehicle 1, a king pin of driving wheel 43 is
laterally outwardly offset from the pivotal point of caster 16 at a
distance L, thereby reducing the torque required to rotate caster
16. This results in the vehicle having the same advantages with a
vehicle using casters 16 as shown in FIG. 45.
[0210] Detailed description will now be given on disposal of
casters 16 on a vehicle in accordance with FIGS. 49 to 56.
[0211] Referring to FIG. 49, a lawn tractor (vehicle) 1.times. is
provided with a pair of left and right caster wheels 16 as front
wheels. Both caster wheels 16 are supported onto vehicle 1.times.
with the same supporting construction. As shown in FIGS. 50 to 52,
left and right bosses 12a are formed on the front portion of
chassis 12. A first swivel shaft 401 of a caster guide 400 is
vertically disposed so as to rotatably pass through each boss
12a.
[0212] Caster guide 400 integrally comprises first swivel shaft
401, limiter 402 and a swivel shaft casing 403. Limiter 402 is
fixed onto the bottom end of shaft 401. Casing 403 is integrally
extended downwardly from limiter 402 while being downwardly
open.
[0213] A wheel hanger 404 integrally comprises a second swivel
shaft 405, a supporting plate 406 and a wheel shaft 407. Second
swivel shaft 405 is disposed vertically so as to be laterally
rotatably inserted into casing 403. Supporting plate 406, which is
fixed onto the bottom end of second swivel shaft 405, is extended
horizontally above caster wheel 16 and bent at a right angle so as
to further extend downwardly along one side surface of caster 16.
Shaft 407 integrally projects horizontally from the lower end
portion of plate 406. Caster wheel 16 is rotatably provided on
shaft 407, thereby being defined as an overhung wheel. A pair of
projections 408 integrally project downwardly from limiter 402 so
as to be opposed to each other with respect to plate 406. In front
view as shown in FIG. 51, projections 408 overlap with plate
406.
[0214] On the assumption that caster 16 is normally oriented, that
is, projections 408 are disposed before and behind plate 406, if
caster wheel 16 is swivelled leftward in relation to caster guide
400, that is, if caster wheel 16 is rotated leftward with respect
to second swivel shaft 405, the right side of front end of plate
406, which is swivelled integrally with caster wheel 16, comes to
abut against front projection 408, thereby limiting the leftward
swivelling of caster wheel 16.
[0215] On the same assumption, if caster wheel 16 is swivelled
rightward in relation to caster guide 400, the left side of rear
end of plate 406 comes to abut against rear projection 408, thereby
limiting the rightward swivelling of caster wheel 16.
[0216] As a result, as shown in FIG. 55, the swivellable range of
caster wheel 16 in relation to caster guide 400 is limited to that
between "-A" and "A". For example, caster wheel 16 may be so
constructed as to be able to swivel both leftward and rightward to
an angle 25.degree. from its regular position.
[0217] As shown in FIGS. 50 and 52, caster guide 400 is integrally
provided with a projecting joint tab 409 (which is backwardly
extended in this embodiment). As shown in FIG. 56, tabs 409 of left
and right caster guides 400 are connected with each other through a
tie rod 457. Tie rod 457 is connected to a pitman arm 459 which
interlocks with stem 14a of steering wheel 14 through gears or the
like.
[0218] Steering wheel 14 is connected to control arm 193 for
operating swash plate 76 of hydraulic pump 71 of steering HST 22
through pitman arm 459 and a link 460.
[0219] Due to such a construction, the rotational operation of
steering wheel 14 causes swash plate 76 to be slanted for
differential driving of axles 40L and 40R, and simultaneously,
causes first swivel shafts 401 to be swivelled in bosses 12a to an
angle "B" for steering casters 16. Each of leftward and rightward
angles "B" of shaft 401 (which is an integral part of caster guide
400) swivelled in relation to boss 12a is limited, for example, to
65.degree.. Each caster 16 can be swivelled between both angles
"-A" and "A" in relation to caster guide 400 which is swivelled to
angle "B". As mentioned above, if angle A is predetermined
25.degree., each caster 16 can be leftward and rightward swivelled
to 90.degree. as the maximum in relation to vehicle 1.times..
However, within all the swivelling range thereof in relation to
vehicle 1.times., the range for casters 16 to swivel perfectly
freely is rather small. In most of the all, casters 16 are
restrictedly swivelled by rotation of steering wheel 14 through
caster guides 400.
[0220] Such restriction of casters 16 has some advantages as
follows:
[0221] For example, in the precondition that vehicle 1.times. stays
and left and right caster guides 400 and casters 16 are oriented
leftward, in order to start vehicle 1.times. while turning
rightward, all that has to be done is rotate steering wheel 14
rightward before starting, thereby swivelling caster guides 400 and
casters 16 so as to be expectedly oriented rightward. As a result,
vehicle 1.times. can turn rightward smoothly at the beginning of
its driving without meandering of casters 16.
[0222] Also, caster guides 400 and casters 16 are oriented forward
while vehicle 1.times. drives forward. If the travelling direction
of vehicle 1.times. is to be changed from forward to backward,
vehicle 1.times. must once be stopped. A conventional caster, which
can freely swivel in all directions in relation to a vehicle body,
comes to swivel to such a large angle as 180.degree. during such a
change of travelling direction, thereby causing the vehicle to
meander. Shown casters 16 are restricted in their free swivelling
by caster guide 400, which is swivelled in relation to vehicle
1.times. by rotation of steering wheel 14, so that they are not
swivelled to such a large angle as 180.degree. during the same
situation, thereby enabling vehicle 1.times. to change its
travelling direction between forward and backward smoothly.
[0223] Additionally, on vehicle 1.times. may be provided means to
make an operator on seat 17 know the orientation of casters 16
easily. In this embodiment as shown in FIG. 56, an indicator 410 is
extended forwardly from pitman arm 459 so as to project forwardly
from the front end of vehicle 1.times. so that the operator sitting
on seat 17 can see indicator 410 beyond front column (see FIG. 49).
Indicator 410 may be alternatively provided on tie rod 457 or
caster guide 400.
[0224] 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 can be changed in the
details of construction and the combination and arrangement of
parts may be changed without departing from the spirit and the
scope of the invention as hereinafter claimed.
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