U.S. patent application number 11/449859 was filed with the patent office on 2006-12-14 for hydraulically driven vehicle.
Invention is credited to Norihiro Ishii, Fumitoshi Ishino, Koji Iwaki.
Application Number | 20060278459 11/449859 |
Document ID | / |
Family ID | 35345388 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060278459 |
Kind Code |
A1 |
Iwaki; Koji ; et
al. |
December 14, 2006 |
Hydraulically driven vehicle
Abstract
A hydrostatic transaxle, comprises: a transaxle casing; a pair
of left and right axles disposed in the transaxle casing; a pair of
hydraulic motors for driving the respective axles; and a pair of
left and right steerable drive wheels disposed on left and right
outsides of the transaxle casing so as to be drivingly connected to
the respective axles. The hydraulic motors are disposed in the
housing so as to be fluidly connected to a common hydraulic
pressure source in parallel to each other. One of the hydraulic
motors is a fixed displacement hydraulic motor, and the other is a
variable displacement hydraulic motor. Displacement of the variable
displacement hydraulic motor is changed according to change of
steered angles of the drive wheels.
Inventors: |
Iwaki; Koji; (Amagasaki-shi,
JP) ; Ishii; Norihiro; (Amagasaki-shi, JP) ;
Ishino; Fumitoshi; (Amagasaki-shi, JP) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX PLLC
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Family ID: |
35345388 |
Appl. No.: |
11/449859 |
Filed: |
June 9, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11214056 |
Aug 30, 2005 |
|
|
|
11449859 |
Jun 9, 2006 |
|
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Current U.S.
Class: |
180/242 |
Current CPC
Class: |
F16H 61/40 20130101;
F16H 61/427 20130101; B60W 2540/18 20130101; B60W 2300/156
20130101; F16H 61/456 20130101; B60W 2510/20 20130101; B60K 17/356
20130101; B60Y 2200/223 20130101 |
Class at
Publication: |
180/242 |
International
Class: |
B60K 17/356 20060101
B60K017/356 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 2, 2004 |
JP |
2004-256186 |
Jan 31, 2005 |
JP |
2005-23438 |
Claims
1. A hydraulically driven vehicle, comprising: a first transaxle,
including a first transaxle casing, a pair of left and right first
axles disposed in the first transaxle casing, a first hydraulic
motor disposed in the first transaxle so as to drive the first
axles, and a pair of left and right first drive wheels steerably
disposed on left and right distal ends of the first transaxle
casing and drivingly connected to the respective first axles; a
second transaxle, including a second transaxle casing, a pair of
left and right second axles disposed in the transaxle casing, a
second fixed displacement hydraulic motor disposed in the second
transaxle casing so as to drive one of the second axles, a third
variable displacement hydraulic motor disposed in the second
transaxle casing so as to drive the other second axle, and a pair
of left and right second drive wheels steerably disposed on left
and right distal sides of the second transaxle casing and drivingly
connected to the respective second axles, wherein a displacement of
the third hydraulic motor is changed according to change of steered
angles of the second drive wheels; and a common hydraulic pressure
source for the first, second and third hydraulic motors, wherein
the first hydraulic motor and the pair of second and third
hydraulic motors are fluidly connected in series to the hydraulic
pressure source, and wherein the second hydraulic motor and the
third hydraulic motor are fluidly connected in parallel to the
hydraulic pressure source.
2. The hydraulically driven vehicle according to claim 1, wherein
the first transaxle casing is pivoted onto a vehicle frame so as to
be horizontally rotatable, and wherein the left and right first
drive wheels are unsteerably connected to the respective first
axles.
3. The hydraulically driven vehicle according to claim 1, further
comprising: a pair of left and right steerable casings relatively
horizontally rotatably attached onto respective left and right ends
of the first transaxle casing so as to support the respective first
drive wheels, thereby making the first drive wheels steerable; a
rotary member pivoted on the first transaxle casing so as to be
connected to a steering actuator; and a pair of link members each
of which is pivotally interposed between the rotary member and each
of the steerable casings.
4. The hydraulically driven vehicle according to claim 1, further
comprising: a pair of left and right steerable casings relatively
horizontally rotatably attached onto respective left and right ends
of the second transaxle casing so as to support the respective
second drive wheels, thereby making the second drive wheels
steerable; and a displacement control section for controlling
displacement of the third hydraulic motor, wherein the displacement
control section is connected to a link member extended from one of
the steerable casings so as to enable the change of displacement of
the third hydraulic motor according to change of steered angles of
the second drive wheels.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 11/214,056, filed Aug. 30, 2005, the entire
disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a hydraulically driven
vehicle.
[0004] 2. Related Art
[0005] Conventionally, as disclosed in International Publication WO
2004/062956, there is a well-known hydraulically driven vehicle
having a main transaxle and an auxiliary transaxle. The main
transaxle supports main drive wheels, and comprises a hydraulic
motor for driving the main drive wheels. The auxiliary transaxle
supports a pair of auxiliary drive wheels, and comprises a pair of
hydraulic motors for driving the respective auxiliary drive wheels.
The vehicle has a hydraulic circuit fluidly connecting the
hydraulic motors of the main and auxiliary transaxles to a
hydraulic pump. In the hydraulic circuit, the hydraulic motor of
the main transaxle and the pair of hydraulic motors of the
auxiliary transaxle are connected in series to the hydraulic pump,
and the hydraulic motors of the auxiliary transaxle are connected
to the hydraulic pump in parallel to each other.
[0006] The left and right auxiliary drive wheels are steerable
wheels. Both of the hydraulic motors of the auxiliary transaxle are
variable in displacement so as to prevent drag of the steerable
wheels or the main drive wheels. The hydraulic motors of the
auxiliary transaxle are provided with respective movable swash
plates moved according to steering operation of the vehicle, or
according to change of left or right turning angle of the steerable
wheels, so as to change rotary speed of the steerable wheels, i.e.,
generate difference between the main drive wheels and the auxiliary
drive wheels, according to change of the left or right turning
angle of the vehicle. However, the link mechanism for moving the
two movable swash plates according to the turning of the steerable
wheels is complicated, and expanded so as to reduce spaces for
other parts. Further, the link mechanism requires a large operation
force because of its small operational efficiency.
[0007] Further, the conventional main drive wheels are unsteerable
wheels, which restrict reduction of the turning radius of the
vehicle relative to the steering operation degree (i.e.,
improvement of replication of reduction of the turning radius of
the vehicle to the steering operation).
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a
hydraulically driven vehicle, in which a hydrostatic transaxle,
supporting a pair of left and right steerable drive wheels and
comprising a pair of hydraulic motors for driving the respective
drive wheels, is provided with a simple and compact link mechanism
for controlling displacement of the hydraulic motors during turning
of a vehicle, and the turning radius of the vehicle relative to the
steering operation can be further reduced.
[0009] To achieve the object, a hydraulically driven vehicle
according to the present comprises a first transaxle, a second
transaxle and a common hydraulic pressure source. The first
transaxle includes a first transaxle casing, a pair of left and
right first axles disposed in the first transaxle casing, a first
hydraulic motor disposed in the first transaxle so as to drive the
first axles, and a pair of left and right first drive wheels
steerably disposed on left and right distal ends of the first
transaxle casing and drivingly connected to the respective first
axles. The second transaxle includes a second transaxle casing, a
pair of left and right second axles disposed in the transaxle
casing, a second fixed displacement hydraulic motor disposed in the
second transaxle casing so as to drive one of the second axles, a
third variable displacement hydraulic motor disposed in the second
transaxle casing so as to drive the other second axle, and a pair
of left and right second drive wheels steerably disposed on left
and right distal sides of the second transaxle casing and drivingly
connected to the respective second axles. A displacement of the
third hydraulic motor is changed according to change of steered
angles of the second drive wheels. The common hydraulic pressure
source is provided for the first, second and third hydraulic
motors. The first hydraulic motor and the pair of second and third
hydraulic motors are fluidly connected in series to the hydraulic
pressure source. The second hydraulic motor and the third hydraulic
motor are fluidly connected in parallel to the hydraulic pressure
source.
[0010] Therefore, the change of steered angles of the second drive
wheels does not have to be transmitted to a fixed swash plate or
another fixed displacement-setting member of the fixed displacement
second hydraulic motor. Therefore, a link mechanism for moving a
movable swash plate or another variable displacement-setting member
of the variable displacement third hydraulic motor according to
change of turning angle of the vehicle can be simple and compact in
comparison with the conventional type transaxle having a pair of
variable displacement hydraulic motors, thereby expanding a space
around the hydrostatic transaxle for arrangement of other members,
and increasing variation of layout in the vehicle. Further, when
the displacement of the third hydraulic motor is reduced during
turning of the vehicle so as to increase peripheral speed of the
second drive wheel driven by the variable displacement third
hydraulic motor, peripheral speed of the drive wheel driven by the
fixed displacement second hydraulic motor is also increased
according to the increase of peripheral speed of the second drive
wheel driven by the third hydraulic motor so as to ensure smooth
turning of the vehicle without drag of the drive wheels while
keeping proper driving force. Further, in the first transaxle, the
first drive wheels are also steerably disposed on left and right
distal ends of first transaxle casing, thereby further reducing the
turning radius of the vehicle relative to the steering operation
degree, i.e., improving replication of reduction of the turning
radius of the vehicle to the steering operation.
[0011] Preferably, the first transaxle casing is pivoted onto a
vehicle frame so as to be horizontally rotatable, and wherein the
left and right first drive wheels are unsteerably connected to the
respective first axles.
[0012] Therefore, the left and right first drive wheels are
assembled into the first transaxle without a complicated mechanism
for making the first drive wheels steerable, thereby facilitating
assembly.
[0013] Preferably, a pair of left and right steerable casings are
relatively horizontally rotatably attached onto respective left and
right ends of the first transaxle casing so as to support the
respective first drive wheels, thereby making the first drive
wheels steerable. A rotary member is pivoted on the first transaxle
casing so as to be connected to a steering actuator. Each of a pair
of link members is pivotally interposed between the rotary member
and each of the steerable casings.
[0014] Therefore, in comparison with a space adjacent to the
conventional transaxle supporting steerable wheels occupied by a
tie rod connecting the left and right steerable casings, the major
of a space adjacent to the present first transaxle with the above
steering mechanism can be freely opened for transmission means such
as hydraulic piping or a transmission shaft, or for another device
or member, thereby expanding variation of layout and improving
facility of assembly and maintenance.
[0015] Preferably, a pair of left and right steerable casings are
relatively horizontally rotatably attached onto respective left and
right ends of the second transaxle casing so as to support the
respective second drive wheels, thereby making the second drive
wheels steerable. The third hydraulic motor is provided with a
displacement control section for controlling displacement of the
third hydraulic motor. The displacement control section is
connected to a link member extended from one of the steerable
casings so as to enable the change of displacement of the third
hydraulic motor according to change of steered angles of the second
drive wheels.
[0016] Since the displacement control section changes the
displacement of the third hydraulic motor correspondingly to the
change of steered angles of the second drive wheels, the link
member does not have to be extended adjacent to the steerable
casing supporting the second drive wheel driven by the second
hydraulic motor, thereby ensuring a large space for arrangement of
another member (such as a steering actuator connected to this
steerable casing or suction-and-delivery ports for fluidly
connecting the second and third hydraulic motors to the hydraulic
pressure source).
[0017] These, further and other objects, features and advantages
will appear more fully from the following description with
reference to accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a side view of a four-wheel drive lawn tractor
serving as a hydraulically driven vehicle according to a first
embodiment.
[0019] FIG. 2 is a skeleton diagram showing a hydraulic circuit and
a structure for driving front and rear transaxles equipped on the
vehicle of FIG. 1, wherein the front transaxle incorporates a
combination of a variable displacement hydraulic motor and a fixed
displacement hydraulic motor.
[0020] FIG. 3 is a skeleton diagram showing a hydraulic circuit and
a structure for driving front and rear transaxles equipped on the
vehicle of FIG. 1, wherein the front transaxle incorporates a pair
of fixed displacement hydraulic motors.
[0021] FIG. 4 is a side view of a four-wheel drive lawn tractor
serving as a hydraulically driven vehicle according to a second
embodiment.
[0022] FIG. 5 is a plan view of the vehicle of FIG. 4.
[0023] FIG. 6 is a skeleton diagram showing a hydraulic circuit and
a structure for driving front and rear transaxles of the vehicle of
FIGS. 4 and 5.
[0024] FIG. 7 is a side view of a four-wheel drive lawn tractor
serving as a hydraulically driven vehicle according to a third
embodiment.
[0025] FIG. 8 is a plan view of the vehicle of FIG. 7.
[0026] FIG. 9 is a sectional rear view of the vehicle of FIGS. 7
and 8.
[0027] FIG. 10 is a front view of the front transaxle for the
vehicles according to the first to third embodiments, wherein the
front transaxle incorporates the combination of the variable
displacement hydraulic motor and the fixed displacement hydraulic
motor.
[0028] FIG. 11 is a plan view of the front transaxle.
[0029] FIG. 12 is an enlarged sectional front view of a portion of
the front transaxle incorporating a motor assembly and axles.
[0030] FIG. 13 is an enlarged sectional front view of the front
transaxle, showing a steerable casing thereof.
[0031] FIG. 14 is a sectional front view of a motor casing fitted
into the front transaxle.
[0032] FIG. 15 is a sectional plan view of the motor casing.
[0033] FIG. 16 is a rear view of a portion of the front transaxle,
showing the motor casing.
[0034] FIG. 17 is a rearwardly perspective view of the motor
assembly to be disposed in the motor casing.
[0035] FIG. 18 is a front view partly in section of an inside
portion of a motor cover covering a rear opening of the motor
casing.
[0036] FIG. 19 is a fragmentary sectional side view of the motor
casing and the motor cover supporting shafts for controlling
displacement of the hydraulic motor.
[0037] FIG. 20 is a sectional side view of the motor casing, the
motor cover and a pipe connector block, showing hydraulic passages
for driving the hydraulic motor therein.
[0038] FIG. 21 is plan view of the four-wheel lawn tractor
according to the second embodiment of the present invention,
employing a system for steering rear wheels.
[0039] FIG. 22 is a rear view of the rear wheel steering system of
FIG. 21.
[0040] FIG. 23 is a rear view of another rear wheel steering
system.
[0041] FIG. 24 is a rear view of the rear wheel steering system of
FIG. 23 modified about the structure for connection to a steering
actuator.
[0042] FIG. 25 is a plan view of front and rear transaxles and
steerable casings supported on the respective transaxles in a
four-wheel steering and hydraulically four-wheel driven vehicle
employing the rear wheel steering system of FIG. 24, with a
hydraulic circuit diagram for controlling hydraulic actuators for
steering the steerable casings.
DETAILED DESCRIPTION OF THE INVENTION
[0043] Referring to FIGS. 1 and 2, description will be given of a
lawn tractor employing an Ackerman type front wheel steering
system, serving as a hydraulically driven four-wheel drive vehicle
according to a first embodiment of the present invention. The lawn
tractor has a vehicle frame 3, which supports a rear transaxle 1
below a front portion thereof. A bracket 4 is fixed onto a front
bottom portion of vehicle frame 3. A front transaxle 2 is suspended
from bracket 4 via a fore-and-aft horizontal center pin 5 so that
left and right ends of front transaxle 2 are vertically swingable.
Rear transaxle 1 journals left and right opposite axles 6, which
project laterally outward from rear transaxle 1 so as to be fixed
at outer ends thereof to respective center portions of rear wheels
7. Front transaxle 2 journals left and right opposite axles 8,
which project laterally outward from front transaxle 2 so as to be
steerably and drivingly connected at outer ends thereof to
respective center portions of front wheels 9.
[0044] An engine 10 is vibro-isolatingly supported on a front upper
portion of vehicle frame 3 via vibro-isolating rubbers or the like,
and covered with a bonnet 11. A steering wheel 12 is extended
upwardly rearward at a rear end of bonnet 11, and a speed change
pedal 13 is disposed at the bottom portion of the rear end of
bonnet 11. Speed change pedal 13 is shaped like a seesaw such as to
have a front portion depressed for setting forward traveling speed
and a rear portion depressed for setting backward traveling speed.
Speed change pedal 13 is linked to a speed change lever 14 pivoted
on a casing of rear transaxle 1. A rear cover 15 is mounted on a
rear upper portion of vehicle frame 3. A reservoir tank 28 is
disposed in rear cover 15. A driver's seat 16 is mounted on rear
cover 15.
[0045] Engine 10 has a downwardly vertical output shaft 10a on
which pulleys 10b and 10c are fixed. An input shaft 17 (serving as
a pump shaft of a later-discussed hydraulic pump P) projects upward
from the casing of rear transaxle 1. A belt 18 is interposed
between a pulley 17a fixed on input shaft 17 and pulley 10b on
engine output shaft 10a, so as to drivingly connect hydraulic pump
P in rear transaxle 1 to engine 10. Further, a cooling fan 17b is
fixed on input shaft 17 so as to blow cooling air to the casing of
rear transaxle 1.
[0046] A mower 20 is vertically movably suspended below vehicle
frame 3 between front wheels 7 and rear wheels 9. An input pulley
20b is disposed on a top of mower 20. A belt 19 is interposed
between pulley 10c on engine output shaft 10a and input pulley 20b
so as to drivingly connect a rotary blade 20a in mower 20 to engine
10.
[0047] Hydraulic pump P, and hydraulic motor M1 for driving rear
wheels 7 (axles 6) are disposed in the casing of rear transaxle 1.
On the other hand, a pair of hydraulic motors M2 and M3 for driving
respective left and right front wheels 9 (axles 8) are disposed in
a casing of front transaxle 2. HST fluid pipes 23 and 26 including
respective intermediate flexible hydraulic fluid hoses 23a and 26a
are interposed between the casings of front and rear transaxles 1
and 2 so as to constitute an HST circuit HC1 including hydraulic
pump P and hydraulic motors M1, M2 and M3.
[0048] HST circuit HC1 will be described with reference to FIG. 2.
The casing of rear transaxle 1 has outwardly opened HST fluid ports
1a and 1b, and the casing of front transaxle 2 has outwardly opened
HST fluid ports 2a and 2b. Pipe 23 including hose 23a is interposed
between ports 1a and 2a, and pipe 26 including hose 26a is
interposed between ports 1b and 2b.
[0049] In the casing of rear transaxle 1, a fluid passage 21 is
interposed between hydraulic pump P and hydraulic motor M1, a fluid
passage 27 is interposed between hydraulic pump P and port 1b, and
a fluid passage 22 is interposed between hydraulic motor M1 and
port 1a.
[0050] In the casing of front transaxle 2, hydraulic motor M2 is
fixed in displacement, and hydraulic motor M3 is variable in
displacement. In the casing of front transaxle 2, a fluid passage
24 is extended from port 2a toward hydraulic motors M2 and M3, and
a fluid passage 25 is extended from port 2b toward hydraulic motors
M2 and M3. Fluid passage 24 bifurcates into a fluid passage 24a
connected to hydraulic motor M2 and a fluid passage 24b connected
to hydraulic motor M3. Fluid passage 25 bifurcates into a fluid
passage 25a connected to hydraulic motor M2 and a fluid passage 25b
connected to hydraulic motor M3.
[0051] In HST circuit HC1, hydraulic motor M1 of rear transaxle 1
and the pair of hydraulic motors M2 and M3 of front transaxle 2 are
connected in series to hydraulic pump P. Hydraulic motors M2 and M3
in front transaxle 2 are fluidly connected to hydraulic pump P in
parallel to each other so as to be rotatable relative to each other
according to conditions of load or the like.
[0052] In HST circuit HC1, during forward traveling of the vehicle,
fluid delivered from hydraulic pump P flows through fluid passage
21, hydraulic motor M1, hydraulic passage 22, port 1a, pipe 23,
port 2a, fluid passage 24, the pair of hydraulic motors M2 and M3,
fluid passage 25, port 2b, pipe 26, port 1b, and fluid passage 27,
so as to return to hydraulic pump P. In other words, during forward
traveling of the vehicle, pressurized fluid from hydraulic pump P
is supplied to hydraulic motor M1 of rear transaxle 1 before the
pair of hydraulic motors M2 and M3 of front transaxle 2. During
backward traveling of the vehicle, the fluid circulation route in
HST circuit HC1 is reversed, that is, pressurized fluid from
hydraulic pump P is supplied to the pair of hydraulic motors M2 and
M3 of front transaxle 2 before hydraulic motor M1 of rear transaxle
1.
[0053] Of course, forward traveling is more frequent than backward
traveling. It is now assumed that the circulation route in HST
circuit HC1 during each of forward and backward travels is opposite
to the above-mentioned route. On the assumption, when the vehicle
climbing over a step is caught on the step and front wheels 9 are
stuck, hydraulic motor M1 of rear transaxle 1 cannot be supplied
with fluid through hydraulic motors M2 and M3 of front transaxle 2,
whereby rear wheels 7 also stop. For this reason, the vehicle may
stop every time it climbs over a step. Considering this problem,
actual HST circuit HC 1 is constructed as mentioned above so that
fluid from hydraulic pump P is supplied to hydraulic motor M1
before hydraulic motors M2 and M3. Therefore, even if front wheels
are stuck, hydraulic motor M1 is supplied with fluid from hydraulic
pump P so as to drive rear wheels 7, thereby canceling the stuck
condition of front wheels 9.
[0054] Additionally, a drive-mode setting valve may be interposed
across pipes 23 and 26 between transaxles 1 and 2. The drive-mode
setting valve is opened so as to complete connection between ports
1a and 2a and between ports 1b and 2b, thereby putting the vehicle
into a four-wheel drive mode where fluid from hydraulic pump P
circulates through hydraulic motors M1, M2 and M3. The drive-mode
setting valve is closed so as to shut off ports 2a and 2b from
ports 1a and 1b, and make a closed fluid circuit between hydraulic
pump P and hydraulic motor M1 isolated from hydraulic motors M2 and
M3, thereby putting the vehicle into a two-wheel drive mode where
only hydraulic motor M1 is driven by fluid supplied from hydraulic
pump P.
[0055] The casings of transaxles 1 and 2 are filled with fluid so
as to form respective fluid sumps therein. The casing of rear
transaxle 1 is provided with a drain port 1c from which a drainpipe
29 is connected to reservoir tank 28. The casing of front transaxle
2 is provided with a drain port 2c from which a drainpipe 30 is
connected to reservoir tank 28. Therefore, reservoir tank 28
absorbs excessively expanded fluid in the respective fluid sumps of
transaxles 1 and 2.
[0056] Rear transaxle 1 incorporates a charge pump 33 for supplying
fluid to HST circuit HC1. As shown in FIG. 2, charge pump 33 is
preferably driven together with hydraulic pump P by input shaft 17
serving as the pump shaft of hydraulic pump P. Charge pump 33 sucks
fluid from the fluid sump in the casing of rear transaxle 1 through
a suction line 31 (having an oil filter 32 at its start end).
Alternatively, fluid to charge pump 33 may be introduced from
reservoir tank 28 out of rear transaxle 1.
[0057] In the casing of rear transaxle 1, a charge fluid passage 34
is interposed between fluid passages 21 and 27 with hydraulic pump
P therebetween, so as to charge fluid from charge pump 33 to
hydraulically depressed one of fluid passages 21 and 27 via
corresponding one of check valves 35. Charge fluid passage 34 is
connected at a portion thereof between check valves 35 and 35 to a
hydraulic pressure control valve 36, so as to drain excessive
pressurized fluid via hydraulic pressure control valve 36 into the
fluid sump in the casing of rear transaxle 1. Charge fluid passage
34 is also connected at the portion thereof between check valves 35
to suction line 31 via a check valve 39, in parallel to charge pump
33. Check valve 39 is opened when either fluid passage 21 or 27 is
hydraulically depressed to open corresponding check valve 35 so as
to absorb the suction port of charge pump 33 (suction line 31),
thereby preventing cavitation in HST circuit HC1 during straight
travel of the vehicle.
[0058] In the casing of rear transaxle 1, a differential gear unit
38 is disposed so as to differentially connect axles 6 to each
other. Distal ends of axles 6 project oppositely laterally outward
from the casing of rear transaxle 1 so as to be fixed to respective
rear wheels 7 (alternatively, rear wheels 7 may be steerably
connected to the distal ends of axles 6, as discussed later with
reference to FIG. 23). In the casing of rear transaxle 1, a
deceleration gear train 37 is interposed between a motor shaft M1a
of hydraulic motor M1 and differential gear unit 38. In this way,
rear transaxle 1 drives hydraulic motor M1 for driving both rear
drive wheels 7 by pressurized fluid supplied from hydraulic pump P.
Hydraulic pump P is provided with a movable swash plate Pa (see
FIG. 2) linked with a speed change lever 14 (see FIG. 1) pivoted on
the casing of rear transaxle 1. By depression of speed change pedal
13, movable swash plate Pa is set in direction and angle so as to
set the fluid delivery direction and amount of hydraulic pump P,
thereby setting the rotary direction and speed of rear wheels
7.
[0059] Description will now be given on peripheral speed setting of
rear wheels 7 and front wheels 9 depending on the output rotary
speed setting of hydraulic motor M1 and the pair of hydraulic
motors M2 and M3, and design of HST circuit HC1 in correspondence
to the peripheral speed setting of wheels 7 and 9. In a general
manner, hydraulic motor M1 and hydraulic motors M2 and M3 would be
set in output rotary speed so as to equalize peripheral speeds of
rear wheels 7 to those of front wheels 9 during straight travel of
the vehicle. However, if the setting is excessively strict,
peripheral speed difference between rear wheels 7 and front wheels
9 due to road conditions causes stiff travel of the vehicle. That
is, on one occasion, the peripheral speeds of rear wheels 7 exceed
those of front wheels 9 (i.e., the peripheral speeds of front
wheels 9 become lower than those corresponding to the set output of
hydraulic motors M2 and M3), so as to cause a condition where front
wheels 9 rotate following rotation of rear wheels 7. On another
occasion, the peripheral speeds of front wheels 9 exceed those of
rear wheels 7 (i.e., the peripheral speeds of rear wheels 7 become
lower than those corresponding to the set output of hydraulic motor
M1), so as to cause a condition where rear wheels 7 rotate
following rotation of front wheels 9.
[0060] Therefore, the output rotary speeds of hydraulic motors M1,
M2 and M3 are actually set so that, during straight travel of the
vehicle, peripheral speeds of rear wheels 7 strictly exceed those
of front wheels 9. Due to this setting, front wheels 9 almost
constantly rotate following rotation of rear wheels 7. Even if the
slowing-down degree of rear wheels 7 is considerably large (the
peripheral speeds of rear wheels 7 is considerably reduced to be
lower than those corresponding to the set output of hydraulic motor
M1), peripheral speeds of rear wheels 7 is still larger than
peripheral speeds of front wheels 9, or equal to peripheral speeds
of front wheels 9. Even if the reduced peripheral speeds of rear
wheels 7 become lower than the peripheral speeds of front wheels 9,
the major case is that the peripheral speed difference between rear
wheels 7 and front wheels 9 is still small so that rear wheels 7
are rotated with a little assistance of front wheels 9, and the
difference of reduced peripheral speeds of rear wheels 7 from
peripheral speeds of front wheels 9 hardly becomes sincerely large.
Consequently, the vehicle is substantially prevented from stiffly
traveling.
[0061] However, due to the output speed setting of hydraulic motors
M1, M2 and M3 for making peripheral speeds of rear wheels 7 exceed
peripheral speeds of front wheels 9, i.e., for rotating front
wheels 9 following rotation of rear wheels 7, hydraulic motors M2
and M3 receive opposite torque from respective axles 8 so as to act
as pumps. Consequently, primary (suction) ports of hydraulic motors
M2 and M3 are hydraulically depressed. This phenomenon remarkably
happens during turning of the vehicle, especially during sharp
turning of the vehicle, thereby causing cavitation in the HST
circuit, and causing hunting of the vehicle. Therefore, HST circuit
HC1 includes a check valve disposed on the suction side fluid
passage of the pair of hydraulic motors M2 and M3 so as to
introduce fluid from the outside of HST circuit HC1 into HST
circuit HC1. During forward travel of the vehicle, the suction side
fluid passage comprises fluid passages 22 to 24a and 24b between
hydraulic motor M1 and the pair of hydraulic motors M2 and M3.
During backward travel of the vehicle, the suction side fluid
passage comprises fluid passages 21 to 25a and 25b between
hydraulic motor M1 and the pair of hydraulic motors M2 and M3
through hydraulic pump P. In the embodiment of FIG. 2, in front
transaxle 2, a check valve 40 is connected to fluid passage 24a so
as to introduce fluid from the fluid sump in the casing of front
transaxle 2 to the suction side fluid passage of the pair of
hydraulic motors M2 and M3 during forward travel of the vehicle. An
oil filter 40a is interposed between check valve 40 and fluid
passage 24a. On the other hand, in rear transaxle 1, the
above-mentioned check valve 39 is provided for introducing fluid
from the fluid sump in the casing of rear transaxle 1 to the
suction side fluid passage of the pair of hydraulic motors M2 and
M3 during backward travel of the vehicle.
[0062] Alternatively, check valve 40 to be opened during forward
travel of the vehicle may be connected to fluid passage 24 or 24b
in front transaxle 2. Alternatively, a check valve for absorbing
fluid from the fluid sump in the casing of rear transaxle 1 may be
connected to fluid passage 22 in rear transaxle 1 so as to have the
same effect as check valve 40. On the other hand, in stead of check
valve 39 in rear transaxle 1, a check valve may be connected to
fluid passage 25, 25a or 25b in front transaxle 2 so as to
introduce fluid from the fluid sump in the casing of front
transaxle 2 to the suction side fluid passage of the pair of
hydraulic motors M2 and M3 during backward travel of the
vehicle.
[0063] In association with the peripheral speed setting such that
peripheral speeds of rear wheels 7 exceed peripheral speeds of
front wheels 9 during straight travel of the vehicle, fluid
circulates in HST circuit HC1 during forward travel of the vehicle
so as to flow from hydraulic pump P to the pair of hydraulic motors
M2 and M3 through hydraulic motor M1. Therefore, during forward
climbing a slope, rear wheels 9 can be effectively rotated for
smooth climbing of the vehicle over a slope, because hydraulic
motor M1 for driving rear wheels 7 weighed more than front wheels 9
is effectively supplied with fluid from hydraulic pump P before the
pair of hydraulic motors M2 and M3 is supplied.
[0064] However, during forward descending a slope, front wheels 9
weighed more than rear wheels 7 require larger driving force than
that for rear wheels 7. If the forward descending on a slope is
more important than the forward ascending on a slope, the
circulation route in HST circuit HC1 may be reversed so that,
during forward travel of the vehicle, fluid from hydraulic pump P
is supplied to hydraulic motor M1 through the pair of hydraulic
motors M2 and M3.
[0065] Due to the above output setting of hydraulic motors M1, M2
and M3 and construction of HST circuit HC1, front wheels 9 receive
driving forces from hydraulic motors M2 and M3 with the assistance
of rotation of rear wheels 7. Therefore, the vehicle can travel
straight without stiff movement, and the operation force required
for steering front wheels 9 can be lightened so as to enable the
vehicle to turn smoothly with the feeling of almost two-wheel drive
mode travel. It may be said that acceleration of the forward wheels
during turning of the vehicle is unnecessary. Due to this theory,
as shown in FIG. 3, both of the hydraulic motors in front transaxle
2 for driving respective axles 8 may be fixed displacement
hydraulic motors M2. In this case, fixed displacement hydraulic
motors M2 of front transaxle 2 are fluidly connected to common
hydraulic pump P in parallel to each other, and in series with
hydraulic motor M1, so as to make peripheral speeds of rear wheels
7 slightly exceed or equal to peripheral speeds of front wheels 9
during straight travel of the vehicle. Check valve 40 is provided
for introducing fluid from the fluid sump in front transaxle 2 to
the suction side passage (in FIG. 3, fluid passage 24a) of the pair
of hydraulic motors M2 in HST circuit HC1. Due to this
construction, a later-discussed link mechanism for changing the
displacement of the hydraulic motor is unnecessary.
[0066] Referring to FIGS. 4, 5 and 6, an Ackerman-type steering
lawn tractor serving as a four-wheel drive vehicle equipped with a
hydraulic transaxle according to a second embodiment of the present
invention will be described. The lawn tractor has vehicle frame 3
supporting a rear transaxle 101 at a rear portion thereof, and
front transaxle 2 at a front portion thereof. A pump unit 50 and
reservoir tank 28 are laterally juxtaposed and supported by vehicle
frame 3 just in front of rear transaxle 101. Preferably, similar to
the vehicle of FIG. 1, the present vehicle includes bracket 4 fixed
on a front end portion of vehicle frame 3, and fore-and-aft
horizontal center pin 5 pivoted on bracket 4 for rotatably
suspending front transaxle 2 therefrom. Rear transaxle 101 supports
left and right axles 6 whose outer ends are fixed to the center
portions of respective rear wheels 7 (alternatively, steerably
connected to respective rear wheels 7, as discussed later). Front
transaxle 2 supports left and right axles 8 to which respective
front wheels 9 (serving as steerable second drive wheels) are
vertically swingably and drivingly connected.
[0067] Engine 10 is vibro-isolatingly supported on vehicle frame 3
via vibro-isolating rubbers or the like. Pulley 10b is fixed on
output shaft 10a of engine 10. Input shaft 17 serves as the pump
shaft of hydraulic pump P in the casing of pump unit 50. Input
shaft 17 projects upward from a casing of pump unit 50 so as to be
fixedly provided thereon with pulley 17a. Belt 18 is interposed
between pulleys 10b and 17a so as to drivingly connect hydraulic
pump P to engine 10. Cooling fan 17b is fixed on input shaft 17
above the casing of pump unit 50 so as to blow cooling air to the
casing of pump unit 50 and reservoir tank 28 adjacent to the casing
of pump unit 50. Pipes 51, 123 and 126, constituting a
later-discussed HST circuit HC2, and drainpipes 52, 129 and 30
connected to reservoir tank 28 are partly disposed in an area blown
by cooling wind generated from cooling fan 17b so as to enhance the
effect of cooling fluid therein.
[0068] Pump unit 50 also obtains the vibro-isolating effect of
engine 10 against vehicle frame 3. More specifically, pump unit 50
is vibro-isolatingly supported together with engine 10 onto vehicle
frame 3. To get such vibro-isolating effect, engine output shaft
10a may be coaxially and integrally rotatably connected to input
shaft 17, or single engine output shaft 10a may be extended so as
to serve as input shaft 17 of pump unit 50.
[0069] Variable displacement hydraulic pump P in pump unit 50 is
provided with movable swash plate Pa linked to speed change lever
14 pivoted on the casing of pump unit 50, and speed change lever 14
is linked to speed change pedal 13. By depression of speed change
pedal 13, movable swash plate Pa is set in direction and angle so
as to set the fluid delivery direction and amount of hydraulic pump
P.
[0070] Mower 20 is disposed below vehicle frame 3 between front
wheels 9 and rear wheels 7. Rotary blade 20a in mower 20 is
drivingly connected to engine 10 via power transmission means,
e.g., a belt transmission, such as the belt transmission of the
vehicle shown in FIG. 1 including pulleys 10c and 20b and belt
19.
[0071] A duct 92 is extended rearward from mower 20 so as to send
grass mowed by rotary blade 20a. Rear transaxle 101 having no
hydraulic pump is vertically and laterally slimed. Such rear
transaxle 101 is laterally eccentrically disposed toward one of
left and right sides of the vehicle (in this embodiment, leftward)
so as to ensure a large space for duct 92 on the other right or
left side of the vehicle (in this embodiment, right side).
Therefore, duct 92 can have such a large capacity as to prevent wet
grass from clogging therein.
[0072] Further, as shown in FIG. 5, pump unit 50 and reservoir tank
28 are aligned in the fore-and-aft direction on one of left and
right sides of the vehicle along one side surface of duct 92, so as
to increase the capacity of duct 92, and to compactly collect fluid
pipes including pipe 126.
[0073] Cooling fan 17b fixed on a bottom end of input shaft 17 of
pump unit 50 blows upward cooling wind to adjoining pump unit 50
and reservoir tank 28 and fluid pipes so as to cool fluid therein.
Additionally, as drawn in phantom lines, input shaft 17 may be
extended upward from pump unit 50 so as to be provided thereon with
another cooling fan 17b for blowing downward cooling wind. In this
case, vehicle frame 3 is opened to lead the downward cooling wind
to pipes.
[0074] Hydraulic motor M1 for driving rear wheels 7 (axles 6) are
disposed in the casing of rear transaxle 101. On the other hand, a
pair of hydraulic motors M2 and M3 for driving respective left and
right front wheels 9 (axles 8) are disposed in the casing of front
transaxle 2. An HST fluid pipe 51 is interposed between pump unit
50 and rear transaxle 101, an HST fluid pipe 123 between rear
transaxle 101 and front transaxle 2, and an HST fluid pipe 126
between front transaxle 2 and pump unit 50, thereby constituting
HST circuit HC2. Pipes 123 and 126 may be provided at intermediate
portions thereof with flexible hoses, respectively, similar to
fluid pipes 23 and 26 including flexible hoses 23a and 26a in the
vehicle according to the first embodiment as shown in FIG. 1.
[0075] HST circuit HC2 will be described with reference to FIG. 6.
The casing of pump unit 50 has outwardly opened HST fluid ports 50a
and 50b, the casing of rear transaxle 101 has outwardly opened HST
fluid ports 101a and 101b, and the casing of front transaxle 2 has
outwardly opened HST fluid ports 2a and 2b. Pipe 51 is interposed
between ports 50a and 101a, pipe 123 is interposed between ports
101b and 2a, and pipe 126 is interposed between ports 2b and
50b.
[0076] In the casing of pump unit 50 incorporates common hydraulic
pump P for supplying fluid to hydraulic motors M1, M2 and M3. In
the casing of pump unit 50, a fluid passage 121a is extended from
hydraulic pump P to port 50a, and a fluid passage 127 from
hydraulic pump P to port 50b. In the casing of rear transaxle 101,
a fluid passage 121b is extended from hydraulic motor M1 to port
101a, and a fluid passage 122 from hydraulic motor M1 to port 101b.
Fluid passages 121a and 121b and pipe 51 constitute a fluid passage
121 between hydraulic pump P and hydraulic motor M1.
[0077] Similar to front transaxle 2 of the vehicle shown in FIG. 1,
in the casing of the present front transaxle 2, fixed displacement
hydraulic motor M2 for driving one front wheel 9 and variable
displacement hydraulic motor M3 for driving the other front wheel 9
are disposed, fluid passages 24, 24a and 24b are interposed between
port 2a and the pair of hydraulic motors M2 and M3, and fluid
passages 25, 25a and 25b between port 2b and the pair of hydraulic
motors M2 and M3.
[0078] In HST circuit HC2, hydraulic motor M1 of rear transaxle 101
and the pair of hydraulic motors M2 and M3 of front transaxle 2 are
connected in series to hydraulic pump P. Hydraulic motors M2 and M3
in front transaxle 2 are fluidly connected to hydraulic pump P in
parallel to each other.
[0079] In HST circuit HC1, during forward traveling of the vehicle,
fluid delivered from hydraulic pump P flows through fluid passage
121 (i.e., fluid passage 121a, pipe 51 and fluid passage 121b),
hydraulic motor M1, hydraulic passage 122, outwardly opened port
101b, pipe 123, outwardly opened port 2a, fluid passage 24, the
pair of hydraulic motors M2 and M3, fluid passage 25, outwardly
opened port 2b, pipe 126, outwardly opened port 50b, and fluid
passage 127, so as to return to hydraulic pump P. In other words,
during forward travel of the vehicle, pressurized fluid from
hydraulic pump P is supplied to hydraulic motor M1 of rear
transaxle 1 before the pair of hydraulic motors M2 and M3 of front
transaxle 2. During backward travel of the vehicle, the fluid
circulation route in HST circuit HC2 is reversed, that is,
pressurized fluid from hydraulic pump P is supplied to the pair of
hydraulic motors M2 and M3 of front transaxle 2 before hydraulic
motor M1 of rear transaxle 1.
[0080] Such circulation route of HST circuit HC2 is set for the
same reason as the circulation route setting of HST circuit HC1 of
the vehicle shown in FIGS. 1 and 2 (and FIG. 3).
[0081] Additionally, a drive-mode setting valve for switching drive
mode of the vehicle between four-wheel drive mode and two-wheel
drive mode may be interposed between hydraulic motor M1 and the
pair of hydraulic motors M2 and M3 in HST circuit HC2.
[0082] The casings of pump unit 50 and transaxles 1 and 2 are
filled with fluid so as to form respective fluid sumps therein. As
shown in FIG. 6, the casing of pump unit 50 is provided with a
drain port 50c from which a drainpipe 52 is connected to reservoir
tank 28. The casing of rear transaxle 101 is provided with a drain
port 101c from which a drainpipe 129 is connected to reservoir tank
28. The casing of front transaxle 2 is provided with drain port 2c
from which drainpipe 30 is connected to reservoir tank 28.
Therefore, reservoir tank 28 absorbs excessively expanded fluid in
the respective fluid sumps of pump unit 50 and transaxles 101 and
2.
[0083] Pump unit 50 incorporates charge pump 33 for supplying fluid
to HST circuit HC2. As shown in FIG. 6, charge pump 33 is
preferably driven together with hydraulic pump P by input shaft 17
serving as the pump shaft of hydraulic pump P. Pump unit 50 is
provided with a charge pump port 50d. A charge pipe 131 including
an intermediate oil filter 132 is interposed between reservoir tank
28 and charge pump port 50d, so as to introduce fluid from
reservoir tank 28 to charge pump 33.
[0084] In the casing of pump unit 50, charge fluid passage 34 is
interposed between fluid passages 121a and 127 with hydraulic pump
P therebetween, so as to charge fluid from charge pump 33 to
hydraulically depressed one of fluid passages 121 and 127 via
corresponding one of check valves 35. Charge fluid passage 34 is
connected at a portion thereof between check valves 35 and 35 to
hydraulic pressure control valve 36, so as to drain excessive
pressurized fluid via hydraulic pressure control valve 36 into the
fluid sump in the casing of pump unit 50. Check valve 39 for
preventing cavitation is interposed between charge fluid passage 34
and hydraulic pressure control valve 36 so as to bypass one of
check valves 35.
[0085] Similar to rear transaxle 1 of the vehicle shown in FIGS. 1
and 2, rear transaxle 101 incorporates differential gear unit 38
for mutually differentially connecting axles 6, and deceleration
gear train 37 interposed between motor shaft M1a of hydraulic motor
M1 and differential gear unit 38.
[0086] As the vehicle shown in FIGS. 1 and 2, the present vehicle
shown in FIGS. 4, 5 and 6 has the same relative peripheral speed
setting of rear wheels 7 and front wheels 9, and the same output
rotary speed of hydraulic motor M1, M2 and M3 for ensuring the
relative peripheral speed setting of rear wheels 7 and front wheels
9. Further, similar to HST circuit HC1, HST circuit HC2 is provided
with check valves for compensation of fluid reduced by the output
rotary speed setting of hydraulic motors M1, M2 and M3. More
specifically, peripheral speeds of rear wheels 7 exceed or are
equal to peripheral speeds of front wheels 9 during straight travel
of the vehicle. A check valve for introducing fluid into HST
circuit HC2, e.g., check valve 40 in front transaxle 2 as shown in
FIG. 6, is connected to the suction side fluid passage of the pair
of hydraulic motors M2 and M3. Alternatively, the vehicle of FIGS.
4, 5 and 6 with HST circuit HC2 may be provided with fixed
displacement hydraulic motors M2 serving as the pair of hydraulic
motors in front transaxle 2, similar to that shown in FIG. 3.
[0087] Referring to FIGS. 7, 8 and 9, an Ackerman-type steering
lawn tractor serving as a four-wheel drive vehicle equipped with a
hydraulic transaxle according to a third embodiment of the present
invention will be described. In the present lawn tractor, pump unit
50 incorporating hydraulic pump P is separated from rear transaxle
101 incorporating hydraulic motor M1, similar to those in the lawn
tractor of the second embodiment. The different point of the
present vehicle from the vehicle of the second embodiment is that a
duct 192 is extended rearward from mower 20 at the lateral center
of the vehicle.
[0088] Separated pump unit 50 and rear transaxle 101 are so compact
as to be distributed on vehicle frame 3 while ensuring sufficient
capacity in duct 192. In the present embodiment, pump unit 50 and
reservoir tank 28 are laterally juxtaposed on vehicle frame 3 just
in front of duct 192, and rear transaxle 101 is supported on
vehicle frame 3 just above a fore-and-aft intermediate portion of
duct 192. Cooling fan 17b fixed on a bottom end of input shaft 17
of pump unit 50 blows upward cooling wind to adjoining pump unit 50
and reservoir tank 28 and fluid pipes so as to cool fluid therein.
Additionally, as drawn in phantom lines, input shaft 17 may be
extended upward from pump unit 50 so as to be provided thereon with
another cooling fan 17b for blowing downward cooling wind. In this
case, vehicle frame 3 is opened to lead the downward cooling wind
to pipes. Rear transaxle 101 may be disposed on vehicle frame 3 in
front or rear of pump unit 50. Especially, as shown in FIG. 7, rear
transaxle 101 may be disposed so as to have a bottom surface
thereof sloped along a sloped upper surface of duct 192, thereby
approaching pump unit 50 and reducing a dead space. This is
appropriate for a small size vehicle. Another effect of rear
transaxle 101 disposed at such a high position on vehicle frame 3
is that a space in rear cover 15 can be used for locating a portion
of rear transaxle 101 projecting upward from vehicle frame 3.
[0089] Rear transaxle 101 has left and right rear-wheel-driving
output shafts 106 which are differentially connected to each other
by differential gear unit 38 and extended oppositely outward from
the casing of rear transaxle 1. As shown in FIGS. 8 and 9, left and
right chain casings 108 are disposed at left and right outsides of
duct 192. Outer ends of output shafts 106 are inserted into upper
portions of respective chain casings 108, and sprockets 106a are
fixed on the outer ends of respective output shafts 106 in
respective chain casings 108. When viewed in front or rear, left
and right output shafts 106 and chain casings 108 look like a
gate.
[0090] Left and right rear wheels 7 has respective axles 107
extended laterally proximally of the vehicle. Axles 107 are
inserted into lower portions of respective chain casings 108, and
sprockets 107a are fixed on the proximal ends of respective axles
107 in respective chain casings 108. In each of chain casings 108,
a chain 109 is interposed between sprockets 106a and 107a so as to
transmit the driving force of output shaft 106 to axle 107, thereby
driving left and right rear wheels 7.
[0091] A drive system of the present vehicle is represented by the
description of drive system of the vehicle according to the second
embodiment with reference to FIG. 6, except that the chain
transmissions are interposed between differential gear unit 38 and
respective rear wheels 7. Alternatively, both the hydraulic motors
in front transaxle 2 may be fixed displacement hydraulic motors
M2.
[0092] Front transaxle 2 incorporating fixed displacement hydraulic
motor M2 and variable displacement hydraulic motor M3 will be
described with reference to FIGS. 1, 2 and 4 to 20.
[0093] Referring to a casing structure of front transaxle 2, as
shown in FIGS. 10 to 12, a motor casing 201 is disposed between
left and right axle casings 203, and detachably attached to each
axle casing 203. Axle casings 203 incorporate respective axles 8. A
spacer may be interposed between motor casing 201 and any of axle
casings 203, if a tread between front wheels 9 has to be
lengthened. Kingpin casings 204 are fixed on distal ends of
respective axle casings 203, extended laterally outwardly downward
at kingpin angles, and inserted into respective steerable casings
205. Steerable casings 205 are rotatable centered on the axes of
respective kingpin casings 204.
[0094] As shown in FIGS. 11 and 15, motor casing 201 is opened at a
rear end thereof. A motor cover 202, onto which a assembly of
hydraulic motors M2 and M3 (motor assembly) are attached as shown
in FIG. 17, is fitted to the rear end of motor casing 201 so as to
cover the rear opening of motor casing 201, thereby setting
hydraulic motors M2 and M3 in motor casing 201. Motor casing 201
can be removed from motor casing 202 so as to easily take out the
assembly of hydraulic motors M2 and M3 from motor casing 201,
thereby facilitating maintenance of hydraulic motors M2 and M3.
[0095] The motor assembly will be described with reference to FIGS.
14, 15, 17 and others. Each of hydraulic motors M2 and M3
comprises: a horizontal motor shaft 61 to be drivingly connected to
corresponding axle 8; a cylinder block 62 which is rotatable
together with motor shaft 61 centered on the axis of motor shaft
61; and horizontal pistons 63 reciprocally slidably fitted in
respective cylinder holes of cylinder block 62 around motor shaft
61. Cylinder blocks 62 of hydraulic motors M2 and M3 are slidably
rotatably fitted onto a center section 60 disposed between cylinder
blocks 62.
[0096] As best shown in FIGS. 12, 17 and 20, a pair of parallel
fluid passages 60a and 60b are bored in center section 60 so as to
be extended in the fore-and-aft direction and opened rearward.
Fluid passages 60a and 60b serve as respective fluid passages 24
and 25 in each of HST circuit HC1 shown in FIG. 2 and HST circuit
HC2 shown in FIG. 6. As best shown in FIGS. 15 and 20, a pair of
kidney ports 60c and 60d laterally penetrate center section 60 so
as to be opened at left and right ends thereof to the cylinder
holes of respective cylinder blocks 62. Fluid passage 60a is
connected to kidney port 60c, and fluid passage 60b to kidney port
60d. Therefore, kidney port 60c serves as bifurcating fluid
passages 24a and 24b, and kidney port 60d serves as bifurcating
fluid passages 25a and 25b. Center section 60 is penetrated between
kidney ports 60c and 60d by a laterally horizontal shaft hole 60e,
into which proximal end portions of motor shafts 61 are slidably
rotatably fitted. Further, a fluid drain passage 60f is bored in
center section 60. Fluid drain passage 60f is opened at one end
thereof to a portion of shaft hole 60e between the proximal ends of
motor shafts 61, and be opened at the other end thereof outward
from center section 60 to the fluid sump in motor casing 201,
thereby fluidly connecting shaft hole 60e to the fluid sump in
motor casing 201. As shown in FIG. 14, in shaft hole 60e, a bush
61a (or a needle bearing) is interposed between center section 60
and motor shafts 61 so as to reduce frictional resistance to motor
shafts 61, thereby improving mechanical efficiency of rotation of
motor shafts 61.
[0097] As shown in FIGS. 12, 14, 15 and 17, each of hydraulic
motors M2 and M3 has a thrust bearing 64 pressed against heads of
pistons 63. Thrust bearing 64 of fixed displacement hydraulic motor
M2 is positionally fixed in a fixed swash plate support 65, thereby
serving as a fixed swash plate (hereinafter referred to as "fixed
swash plate 64"). Some fixed swash plate supports 65 having
different slant angles may be prepared for optional setting of
slant angle fixed swash plate 64 of hydraulic motor M2. Variable
displacement hydraulic motor M3 has a movable swash plate 67, which
is rotatably supported by a movable swash plate support 66 so that
its tilt angle relative to movable swash plate support 66 can be
changed. Thrust bearing 64 of hydraulic motor M3 is integrally
assembled in movable swash plate 67.
[0098] To fix the motor assembly to an inside (front) surface of
motor cover 202, as best shown in FIG. 17, bolts 68 project
rearward from rear end surfaces of respective swash plate supports
65 and 66. A bolt hole 60g is bored in center section 60 and opened
at the rear end surface of center section 60. Swash plate supports
65 and 66 are fastened to motor cover 202 by bolts 68, and center
section 60 is fastened to motor cover 202 by a bolt 96 (see FIG.
18) screwed into bolt hole 60g. Additionally, a knock pin 69 for
locating motor cover 202 projects rearward from the rear end
surface of center section 60.
[0099] As best shown in FIG. 15, rearwardly opened front joggle
holes are bored in a front wall of motor casing 201. Forwardly
opened rear joggle holes are bored in center section 60 and swash
plate supports 65 and 66, respectively. When the motor assembly is
inserted into motor casing 201, the rear joggle holes of center
section 60 and swash plate supports 65 and 66 coincide to the
respective front joggle holes of motor casing 201 with respective
joggles 93 fitted between the coinciding front and rear joggle
holes, thereby retaining center section 60 and swash plate supports
65 and 66 to motor casing 201 onto the front wall of motor casing
201. In this state, motor cover 202 is fitted to motor casing 201
so as to cover the rear opening of motor casing 201. Then, bolts 95
are screwed forward together with motor cover 202 into motor casing
201, thereby completing setting of the motor assembly.
[0100] Motor cover 202 with the motor assembly in motor casing 201
is fixedly provided with a pipe coupling block 70 on the rear
surface thereof just in rear of center section 60. Pipe coupling
block 70 is bored by fluid passages 70c and 70d, which are opened
to respective fluid passages 60a and 60b via respective fluid
passages 202a and 202b penetrating motor cover 202. Pipe couplings
70a and 70b are disposed at outer ends of respective fluid passages
70c and 70d, and project outward from pipe coupling block 70. Pipe
couplings 70a and 70b serve as fluid ports 2a and 2b of each of HST
circuits HC1 and HC2 shown in FIGS. 2 and 6. The series of fluid
passages 70c, 202a and 60a serves as fluid passage 24. The series
of fluid passages 70d, 202b and 60b serves as fluid passage 25.
[0101] In comparison with the case where pipe couplings 70a and 70b
are directly attached to motor cover 202, pipe coupling block 70
with pipe couplings 70a and 70b is advantageous in increasing angle
variation of pipe couplings 70a and 70b relative to fluid passages
60a and 60b and the like serving as fluid passages 24 and 25.
Therefore, pipe coupling block 70 with pipe couplings 70a and 70b
can be designed so that angles of pipes 23 (or 123) and 26 (or 126)
coupled to respective pipe couplings 70a and 70b are optimized in
relation to a later-discussed linkage for controlling the swash
plate of hydraulic motor M3.
[0102] Alternatively, pipe coupling block 70 may be separated from
motor cover 202 and supported on vehicle frame 3 or the like, so as
to have pipes between pipe coupling block 70 and motor cover
202.
[0103] As shown in FIGS. 11, 15 and 16, a pipe coupling 71, serving
as drain port 2c of each of HST circuits HC1 and HC2 shown in FIGS.
2 and 6, projects from the rear end surface of motor cover 202
adjacent to pipe coupling block 70 so as to be connected to
reservoir tank 28 via drainpipe 30. As shown in FIG. 18, a drain
hole 202c is bored through motor cover 202 between pipe coupling 71
and the fluid sump in motor casing 201. Therefore, excessively
expanded fluid in the fluid sump in motor casing 201 can be drained
to reservoir tank 28. Pipe coupling 71 is disposed in a space
behind fixed displacement hydraulic motor M2, where the linkage for
controlling the displacement of hydraulic motor M3 is not
disposed.
[0104] As shown in FIG. 20, above-mentioned check valve 40 is
disposed in center section 60 so as to be connected to kidney port
60c serving as a part of fluid passage 24 (and fluid passages 24a
and 24b) which is hydraulically higher-pressurized in each of HST
circuits HC1 and HC2 during forward travel of the vehicle. If
kidney port 60c, i.e., fluid passage 24 is hydraulically depressed,
check valve 40 is opened to introduce fluid from the fluid sump in
motor casing 201 into fluid passage 24. Check valve 40 is provided
with an oil filter 40a interposed between check valve 40 and kidney
port 60c.
[0105] The linkage for controlling the displacement of hydraulic
motor M3 will be described. As shown in FIGS. 15, 16 and 17, a
fore-and-aft horizontal swash plate pivot shaft 73 is pivoted onto
motor cover 202 in rear of hydraulic motor M3. In motor casing 201,
an inner arm 74 is fixed on an inner (front) end of swash plate
pivot shaft 73 and engages with movable swash plate 67 of hydraulic
motor M3. In motor casing 201, a spring 75 is wound around swash
plate pivot shaft 73 so as to return swash plate pivot shaft 73 and
inner arm 74 to their initial position (that is, the swash plate
angle setting position during straight travel of the vehicle).
[0106] As shown in FIGS. 18 and 19, inner arm 74 has a projection
74a fitted to swash plate 67. A pushpin 74b projects from inner arm
74. One end of spring 75 is constantly pressed against an inner
surface of a wall of motor casing 202 so as to be retained. During
turning of the vehicle, inner arm 74 is rotated for changing the
displacement of hydraulic motor M3 so that pushpin 74b pushes the
other end of spring 75 away from the retained end of spring 75,
whereby spring 75 generates biasing force for returning inner arm
74 to the initial position. A stopper pin 76 is planted into a wall
of motor casing 202 so as to abut against inner arm 74 disposed at
the initial position. Stopper pin 76 is an eccentric pin, which is
usually fastened to motor casing 202 by a nut 76b. By loosening nut
76b and revolving stopper pin 76 around its center axis portion
76a, the relative position of stopper pin 76 to inner arm 74 can be
adjusted so as to adjust the initial position of inner arm 74 and
swash plate pivot shaft 73, thereby canceling positional error of
inner arm 74 and swash plate pivot shaft 73 relative to the initial
slant angle position of swash plate 67.
[0107] As shown in FIGS. 11, 15, 16 and 18, a camshaft 80 is
disposed in parallel to swash plate pivot shaft 73, and pivoted
onto motor cover 202 on one of left and right sides of swash plate
pivot shaft 73 (preferably, leftwardly or rightwardly outward from
hydraulic motor M3) adjacent to swash plate pivot shaft 73. A cam
plate 81 is fixed on an outer (rear) end of camshaft 80 on the
outside of (in rear of) motor cover 202. Cam plate 81 has a pair of
cam profiles 81a above camshaft 80. An upper edge of cam plate 81
between cam profiles 81a is disposed horizontally when cam plate 81
is disposed at the initial position. On the outside (in rear) of
motor cover 202, an outer arm 77 is fixed on an outer (rear) end of
swash plate pivot shaft 73. A pressure plate 78 is fixed on outer
arm 77 so as to be pressed at a bottom edge thereof against the
upper edge of cam plate 81.
[0108] Pressure plate 78 is fastened to outer arm 77 so as to be
shiftable relative to outer arm 77, so that, when cam plate 81 is
disposed at the initial position, the bottom edge of pressure plate
78 is disposed horizontally to abut against the upper edge of cam
plate 81 regardless of the initial position of swash plate pivot
shaft 73 with inner and outer arms 74 and 77 adjusted by stopper
pin 76. In this regard, outer arm 77 is bored by a pair of bolt
holes. One of the bolt holes is disposed toward a tip of outer arm
77, and the other toward a basal end of outer arm 77. As shown in
FIG. 16, a pair of bolts 79 screwed into the respective bolt holes
of outer arm 77 are passed through respective slots 78a and 78b
bored in pressure plate 78. Nuts are screwed on respective bolts 79
so as to fasten outer arm 77 and pressure plate 78 together. By
loosening the nuts and adjusting positions of bolts 79 in slots 78a
and 78b, the position of pressure plate 78 relative to outer arm 77
can be adjusted. Due to this construction, the present linkage for
controlling the displacement of hydraulic motor M3 can be adapted
to various vehicles having different steering angle settings.
[0109] Cam plate 81 is extended downward from camshaft 80. An
acceleration rod 82 is pivotally connected at one end thereof to a
bottom end of downwardly extended cam plate 81. Acceleration rod 82
is pivoted at the other end thereof onto one of left and right
steerable casings 205. Preferably, the other end of acceleration
rod 82 is pivoted onto a pivot pin 83 (as best shown in FIGS. 10
and 11), which is planted into a wall of steerable casing 205
supporting front wheel 9 drivingly connected to variable
displacement hydraulic motor M3. In this way, steered steerable
casings 205 are rotated leftward or rightward centered on
respective kingpin casings 203 so as to push or pull acceleration
rod 82, thereby swinging the bottom end of cam plate 81 leftward or
rightward. Accordingly, the upper edge of cam plate 81 is slanted
so that one of cam profiles 81a rises to push up pressure plate 78.
Consequently, outer arm 77 are rotated upward so as to integrally
rotate swash plate pivot shaft 73 and inner arm 74, thereby
reducing the tilt angle of swash plate 67 of hydraulic motor
M3.
[0110] As shown in FIGS. 10 and 11, acceleration rod 82 has an
intermediate spline collar 82a so as to be telescoped in
correspondence to the above-mentioned tread adjustment by
interposition of a spacer between motor casing 201 and any of axle
casings 203.
[0111] In this way, the cam system including cam plate 81 and
pressure plate 78 abutting against each other, and arms 77 and 74
connected to pressure plate 78 so as to rotate integrally with
movable swash plate 67 constitute the linkage for moving swash
plate 67 of hydraulic motor M3 according to lateral rotation of
steerable casings 205 during turning of the vehicle. The linkage is
disposed on the outer surface of motor cover 202 in rear of
variable displacement hydraulic motor M3. Pipe coupling block 70 is
disposed on the outer surface of motor cover 202 in rear of the
portion between hydraulic motors M2 and M3 adjacent to the
linkage.
[0112] It is now assumed that both the hydraulic motors in front
transaxle 2 are variable displacement hydraulic motors M3. The
linkage must have a cam system for converting the push-and-pull
movement of a rod for the lateral rotation of steerable casings 205
into rotation of movable swash plates 67 of both hydraulic motors
M3. Therefore, the linkage must be complicated and large so as to
substantially entirely cover the outer surface of motor cover 202
(the rear surface of front transaxle 2) in the left-and-right
direction. Accordingly, a port member having ports for fluidly
connecting both hydraulic motors M3 to hydraulic pump P and motor
M1 (such as pipe coupling block 70) has to be disposed on a surface
of rear transaxle 2, which is different from the outer surface of
motor cover 202. For instance, the port member has to be attached
to the front surface of front transaxle 2 opposite to the outer
surface of motor cover 202. Pipes to be connected to the port
member have to be extended along or beyond motor casing 201.
[0113] However, in front transaxle 2 of the present embodiment, one
of the pair of hydraulic motors therein is fixed displacement
hydraulic motor M2. The linkage for angle controlling of movable
swash plate 67 does not have to be disposed on the outer (rear)
surface of motor cover 202 in rear of hydraulic motor M2 or in rear
of the portion between hydraulic motors M2 and M3, thereby ensuring
a space in rear of the rear surface of front transaxle 2 for
attaching pipe coupling block 70 and drain pipe coupling 71. Due to
pipe coupling block 70 disposed at this position, pipes connected
to front transaxle 2 from rear transaxle 1 (or from pump unit 50
and front transaxle 101) are streamlined so as to increase fluid
circulation efficiency, and to reduce interference thereof with
other parts or members.
[0114] A drive train from each motor shaft 61 to corresponding
front wheel 9 will be described. As shown in FIG. 12, motor shaft
61 of each of hydraulic motors M2 and M3 freely rotatably passes
through thrust bearing 62 and swash plate support 65 or 66 so as to
be connected to coaxial axle 8 supported in axle casing 203. Facing
ends of motor shaft 61 and axle 8 are spline-fitted into a bush 85
disposed in a proximal end portion of axle casing 203 from opposite
openings of bush 85, whereby coaxial motor shaft 61 and axle 8 are
integrally rotatably connected to each other. Alternatively, single
motor shaft 61 may be extended into axle casing 203 so as to serve
as axle 8.
[0115] As best shown in FIG. 13, a bevel gear shaft 86 is
journalled by a distal end portion of axle casing 203. A distal end
of axle 8 and a proximal end of bevel gear shaft 86 are
spline-fitted into bush 85 disposed in the distal end portion of
axle casing 203 from opposite openings of bush 85, wherein coaxial
axle 8 and bevel gear shaft 86 are integrally rotatably connected
to each other. The distal end portion of axle casing 203 projects
into kingpin casing 204, so that a distal end of bevel gear shaft
86, formed thereon with a bevel gear 86a, projects from axle casing
203 into an upper portion of kingpin casing 204. A kingpin center
shaft 87 is rotatably passed through the downwardly extended
portion of kingpin casing 204. A bevel gear 87a is fixed on a top
of kingpin center shaft 87 in the upper portion of kingpin casing
204, so as to mesh with bevel gear 86a.
[0116] A top opening of kingpin casing 204 facing the inner space
of kingpin casing 204, in which meshing bevel gears 86a and 87a are
disposed, is wide so as to be adapted for economically forming
kingpin casing 204 by die casting. Further, the wide opening
facilitates easy and accurate forming of bearing grooves in the
inner wall surface of kingpin casing 204. The opening is closed by
a grommet after the bevel gears and others are completely disposed
in kingpin casing 204.
[0117] The downwardly extended portion of kingpin casing 204 is
inserted into steerable casing 205. Steerable casing 205 relatively
rotatably supports the downwardly extended portion of kingpin
casing 204 therein with bearings. In other words, steerable casing
205 is laterally rotatable around kingpin casing 204. Kingpin
center shaft 87 is extended downward from a bottom end of kingpin
casing 204, and fixedly provided on a bottom end thereof with a
bevel gear 87b in steerable casing 205 below kingpin casing 204.
Bevel gear 87b is journalled by a bottom portion of steerable
casing 205.
[0118] A bearing cover support portion 205a is formed on a lateral
distal end of steerable casing 205 so as to journal a proximal end
of a center axis shaft 9a of front wheel 9 in a center hole
thereof. A diametrically large bevel gear 89 is fixed on center
axis shaft 9a and meshes with bevel gear 87b. A bearing cover 206
is fastened to bearing cover support portion 205a so as to cover
bevel gear 89. Center axis shaft 9a is extended distally outward
from bevel gear 89 so as to be pivoted onto bearing cover 206 via
bearings, and further extended distally outward from bearing cover
206 so as to be connected at a distal end thereof to front wheel
9.
[0119] In this way, front wheels 8 can be steered by rotating
steerable casing 205 around kingpin casing 204 while receiving the
output force of respective hydraulic motors M2 and M3 through
respective motor shafts 61, axles 8 and kingpin center shafts
87.
[0120] As mentioned above, the entire casing of front transaxle 2
is formed by joining motor casing 201 (with motor cover 202), left
and right axle casings 203, kingpin casings 204, steerable casings
205 and bearing covers 206 to one another. A bearing for
journalling a shaft is disposed at a junction between any adjoining
casings of rear transaxle 2. The bearing is provided with no oil
seal. In this regard, lube (also used as operation fluid for the
HST) filled in motor casing 201, axle casings 203, kingpin casings
204, steerable casings 205 and bearing covers 206 can freely pass
among these casings and covers. The costs for oil seals are saved.
Oiling ports to fill entire front transaxle 2 with fluid (lube) can
be reduced, and even only a single oiling port can be provided.
Further, the total amount of fluid and the total surface area of
hydraulic devices are increased so as to suppress heating of the
hydraulic devices, thereby improving the hydraulic devices in
endurance and mechanical efficiency.
[0121] The linkage from steering wheel 12 to steerable casing 205
will be described with reference to FIGS. 2 and 21. A steering link
bracket 207 is fixed on one of steerable casings 205 so as to cover
the top surface of this steerable casing 205. Preferably, steerable
casing 205 having no acceleration rod 82 connected thereto is
provided with steering link bracket 207, so as to prevent steering
link bracket 207 from interfering with acceleration rod 82 and the
like. A drag rod 90 is extended in parallel to an outer side
surface of vehicle frame 3, and pivotally connected at a front end
thereof to steering link bracket 207. A gearbox 12b is provided on
a bottom end of a stem 12a (see FIG. 2) of steering wheel 12, and
an arm 12c is fore-and-aft rotatably attached onto an output end of
gearbox 12b. Drag rod 90 is pivotally connected at a rear end
thereof to a free tip of arm 12c. Drag rod 90 may be replaced with
a hydraulic power steering cylinder. Preferably, drag rod 90 or the
hydraulic power steering cylinder is disposed substantially in
parallel to vehicle frame 3.
[0122] As best shown in FIGS. 10 and 11, steering casing 205 on
variable displacement hydraulic motor M3 side and steering casing
205 on fixed displacement hydraulic motor M2 are connected to each
other via tie rod 84 so as to be laterally rotatable substantially
integrally with each other. An end of tie rod 84 toward steering
casing 205 on variable displacement hydraulic motor M3 side is
pivoted onto pivot pin 83. Preferably, pivot pin 83 is stepped so
that upper and lower portions of pivot pin 83, onto which
accelerator rod 82 and tie rod 84 are pivotally connected
respectively, have different diameters. In this way, ends of
accelerator rod 82 and tie rod 84 are pivoted on common pivot pin
82, so as to save the parts count, and to prevent rods 82 and 84
from intercrossing each other hindering their own movement and
movement of steerable casing 205.
[0123] Referring to FIGS. 1, 16, 20 and others, a structure for
supporting front transaxle 2 onto vehicle frame 3 will be
described. Upright stays 201a are disposed at optimal positions
(e.g., four stays 201a are disposed at the front, rear, right and
left) on a top surface of motor casing 201, and a center pin boss
member 200 is mounted over all stays 201a. Center pin boss member
200 includes a horizontal plate portion 200a, which is integrally
formed at the lateral center portion thereof with a fore-and-aft
axial boss portion 200b. Four corners of plate portion 200a are
screwed onto respective stays 201a. Center pin 5 is freely
rotatably passed through a boss hole of boss portion 200b.
[0124] Some different designed center pin brackets 200 are
prepared, and one corresponding to relative pivot positions of
front transaxle 2 in a vehicle is selected to be fastened to stays
201a of motor casing 201. Therefore, front transaxle 2 can be
standardized for various designed vehicles.
[0125] Center pin 5 is journalled at front and rear ends thereof by
front axle bracket 4 fixed on the front end of vehicle frame 3.
Front axle bracket 4 comprises a pair of left and right vertical
side plates 4a, a vertical rear plate 4b connecting side plates 4a
to each other, a front plate 4c, and a horizontal plate 4d
connected between rear and front plates 4b and 4c.
[0126] Each of left and right side plates 4a has bolt holes 4h
bored in a rear end portion thereof. Bolts are passed through bolt
holes 4h of left and right side plates 4a so as to fasten left and
right side plates 4a onto front end portions of respective left and
right side plate portions of vehicle frame 3, thereby fixing front
axle bracket 4 onto the front end portion of vehicle frame 3.
Center pin 5 passed through center pin bracket 5 is journalled at
the rear end portion by rear plate 4b, and at the front end portion
by front plate 4c. Therefore, front transaxle 2 is swingably
supported. Flexibility of hydraulic fluid hoses 23a and 26a permits
the swing of front transaxle 2.
[0127] In this state, horizontal plate 4d covers the top of motor
casing 201 disposed in front of the front end of vehicle frame 3. A
pair of left and right stoppers 4e are hung down from the bottom
surface of horizontal plate 4d. The position where one of stoppers
4e abuts against the top of plate portion 200a of center pin
bracket 200 fixed on front transaxle 2 is defined as the limit
swing position of front transaxle 2 centered on center pin 5.
Stoppers 4e also serve as ribs for reinforcing horizontal plate
4d.
[0128] Further, horizontal plate 4d is at a lower degree than the
top of the front end of vehicle frame 3. An engine muffler 10d is
mounted on horizontal plate 4d, so as to be covered at a rear
portion thereof with rear plate 4b, and at left and right end
portions thereof with left and right side plates 4a. In this way, a
suitable space for efficient radiation of engine muffler 10d is
ensured in front axle bracket 4. Further, horizontal plate 4d
protects front transaxle 2 from the heat radiated from engine
muffler 10d.
[0129] As shown in FIG. 20, front ends of left and right side
plates 4a are extended upwardly forward so as to serve as bonnet
brackets 4f for supporting a pivot shaft for opening and closing
bonnet 11. The pivot shaft is passed through holes 4g formed in
bonnet brackets 4f. A rear end of bonnet 11 can be rotated upward
centered on the pivot shaft so as to open engine 10 mounted on
vehicle frame 3. Front axle bracket 4 can be fastened by bolts, or
joined by welding, to a front end of a vehicle frame for a
two-wheel drive vehicle, thereby platforming the vehicle frame for
both two-wheel drive vehicles and four-wheel drive vehicles.
[0130] A part of each side plate 4a adjacent to corresponding
bonnet bracket 4f is cut off and bent laterally inward of the
vehicle so as to form a spring stay 4j, onto which an end of a
spring for biasing bonnet 11 to its initial closed position is
connected.
[0131] As shown in FIGS. 1, 4 and 7, mower lifting cradles 91 are
extended downward from front ends of respective side plates 4a so
as to guide the vertical movement of mower 20. Link rods 91a are
extended rearward from respective cradles 91 and connected to mower
20. Plurality of bolt holes are bored in each of cradles 91. On the
other hand, as shown in FIG. 20, a bolt hole 4k is bored in each
side plate 4 below spring stay 4j. Each cradle 91 is disposed so as
to selectively coincide one of the bolt holes thereof to bolt hole
4k, and fastened to each side plate 4a by a bolt through the
selected bolt hole thereof and bolt hole 4k. In this way, the
vertical position of mower 20 relative to front axle bracket 4 can
be adjusted by selecting one of the bolt holes in each cradle
91.
[0132] Front axle bracket 4 may be replaced with a simple vertical
plate covering the front end of vehicle frame 3, if the vehicle is
a two-wheel drive vehicle having no front transaxle 2 incorporating
the pair of hydraulic motors.
[0133] Referring to FIGS. 21 to 23, two type rear-wheel steering
systems will be described. These steering systems are applicable to
the respective four-wheel drive lawn tractors according to the
first embodiment shown in FIGS. 1 and 2, the second embodiment
shown in FIGS. 4 and 5, and the third embodiment shown in FIGS. 7
and 8. The rear-wheel steering system shown in FIGS. 21 and 22 is
applied to the lawn tractor as shown in FIGS. 4 and 5, having
separate pump unit 50 and rear transaxle 101. However, as shown in
FIGS. 1 and 2, rear transaxle 1 can be applied to a lawn tractor
having rear transaxle 1 incorporating hydraulic pump P, such as the
lawn tractor shown in FIGS. 1 and 2.
[0134] Referring to the rear-wheel steering system of FIGS. 21 and
22, a connection portion 3b is connected between left and right
side plates 3a of vehicle frame 3. Connection portion 3b is
provided at the lateral center portion thereof with a bearing
portion 3c. A vertical pivot shaft 221 is journalled by bearing
portion 3c. A rear axle support frame 222 has a laterally central
boss 222a, into which pivot shaft 221 extended downward from
bearing portion 3c is inserted and fixed. A horizontal arm 222b is
extended from boss 222a so as to be interlockingly connected to
steering wheel 12. Rear axle support frame 222 has laterally
opposite first and second end portions 222c and 222d. First end
portion (in this embodiment, the left end portion) 222c of rear
wheel support frame 222 is extended downward, and fastened at the
bottom end portion thereof to one of left and right end portions
(in this embodiment, the left end portion) of the casing of rear
transaxle 101. Second end portion (in this embodiment, the right
end portion) 222d of rear wheel support frame 222 is extended
downward, and provided at the bottom thereof with a bearing 222e
for longer axle 6 (in this embodiment, right axle 6) extended
outward from rear transaxle 101. A space for duct 92 extended from
mower 20 is ensured below axle 6 between bearing 222e and the other
right or left end portion (in this embodiment, the right end
portion) of rear transaxle 101.
[0135] Rear transaxle 101 has longer and shorter axles 6. Shorter
axle 6 is extended laterally outward from the end portion of the
casing of rear transaxle 101 fastened to the bottom of first end
portion 222c of rear wheel support frame 222, and fixed at the
distal end thereof to one rear wheel 7. Longer axle 6 is further
extended laterally outward from bearing 222e, and fixed at the
distal end thereof to the other rear wheel 7.
[0136] Therefore, by rotating steering wheel 12, rear wheel support
frame 222 rotates integrally with rear transaxle 101, left and
right axles 6 and rear wheels 7 relative to vehicle frame 3
centered on pivot shaft 221, thereby steering rear wheels 7.
[0137] A structure of rear wheel support frame 222, and a structure
of the casing of rear transaxle 101 with axles 6 to be supported by
rear wheel support frame 222 may be different from those shown in
FIGS. 21 and 22. The only important thing for this embodiment is to
make the casing of rear transaxle 101 with axles 6 horizontally
rotatable relative to vehicle frame 3 according to operation of
steering wheel 12 while ensuring the driving of axles 6.
[0138] Referring to the rear wheel steering system of FIG. 23, rear
wheel support frames 223 are fixed onto respective left and right
side plates 3a of vehicle frame 3. Each rear wheel support frame
223 has a portion extended downward from the bottom end of
corresponding side plate 3a. The downwardly extended portion of
rear wheel support frame 223 may be fastened to an end portion of
the casing of rear transaxle 101 while avoiding interference
thereof with corresponding axle 6 (axle 6 may be freely rotatably
passed through the downwardly extended portion of rear wheel
support frame 223), as the downwardly extended portion of left rear
wheel support frame 223 in FIG. 23 is so. Otherwise, the downwardly
extended portion of rear wheel support frame 223 may be provided
with a bearing portion 223a for journaling corresponding axle 6, as
the downwardly extended portion of right rear wheel support frame
223 in FIG. 23 is so provided. Both left and right rear wheel
support frames 223 may be fastened to the casing of rear transaxle
101. Alternatively, both left and right rear wheel support frames
223 may be provided with respective bearing portions 223a for
respective axles 6. The important distinction of this steering
system of FIG. 23 from the above steering system of FIGS. 21 and 22
is that the casing of rear transaxle 101 is fixed to vehicle frame
3 regardless of steering of rear wheels 7.
[0139] An upper kingpin support portion 223b and a lower kingpin
support portion 223c are extended laterally outward from each rear
wheel support frame 223. The distal end of each axle 6 extended
outward from the casing of rear transaxle 101 is disposed between
upper and lower kingpin support portions 223b and 223c. The distal
end of axle 6 is connected to center axis shaft 7a of rear wheel 7
via a universal joint 6a, so that rear wheel 7 with center axis
shaft 7a can be substantially horizontal relative to axle 6.
[0140] Center axis shaft 7a is journalled in a bearing block 224.
An upper arm 224a is extended from an upper portion of bearing
block 224 so as to be pivotally connected to upper kingpin support
portion 223b via a kingpin 225. A lower arm 224b is extended from a
lower portion of bearing block 224 so as to be pivotally connected
to lower kingpin support portion 223c via a kingpin 226. Upper and
lower kingpins 225 and 226 are disposed coaxially, and the pivot of
universal joint 6a is coaxially disposed between upper and lower
kingpins 225 and 226.
[0141] A tie rod (not shown) is interposed between tie rod stays
224c extended from respective upper portions of bearing blocks 224,
and connected to steering wheel 12. By rotating steering wheel 12,
left and right bearing blocks 224 are substantially horizontally
rotated around respective kingpins 225 and 226 so as to steer left
and right rear wheels 7.
[0142] The rear wheel steering system shown in FIGS. 24 and 25 is
equal to the steering system of FIG. 23 in which a structure for
connecting left and right bearing blocks 224 to a steering actuator
(power steering cylinder). Instead of tie rod stays 224c integrally
formed on respective bearing blocks 224, each of a pair of arms 232
is pivoted at one end thereof onto lower king pin 226 just below
each bearing block 224 (lower arm 224b). As shown in FIG. 25, when
viewed in plan, each arm 232 is extended rearwardly and laterally
proximately from the end thereof pivoted onto king pin 226, when
both rear wheels 7 are oriented in the straight traveling state.
Incidentally, vehicle frame 3 shown in FIG. 3 includes left and
right side plates 3a as shown in FIG. 24, so that, similar to those
in the embodiment of FIG. 23, bearing block 224 and rear wheels 7
are laterally horizontally rotatably (steerably) attached to rear
wheel support frame 223 fixed on each side plate 3a through king
pins 225 and 226.
[0143] A rotary plate 230 is pivoted through a vertical pivotal
shaft 230a onto a bottom portion of the casing of rear transaxle
101 at the lateral middle position between left and right drive
wheels 7. As shown in FIG. 25, when viewed in plan, rotary plate
230 is a isosceles triangular plate whose equal edges are extended
forward from the corner including pivotal shaft 230a. Each of the
equally angled left and right front corners of rotary plate 230 is
pivotally connected to an end of each arm 232 opposite to the end
pivoted onto kingpin 226 through each of a pair of link rods 231
having equal lengths.
[0144] Rotary plate 230, left and right link rods 231 and left and
right arms 232 connected in the above mentioned way are disposed in
principle so that, in the initial state (in the straight traveling
state of rear wheels 7), when viewed in plan, as shown in FIG. 25,
the front edge of rotary plate 230 is disposed laterally
horizontally, and the angle between left link rod 231 and left arm
232 is equal to the angle between right link rod 231 and right arm
232. Alternatively, the front edge of rotary plate 230 may be
slanted in the lateral direction, and the angle between left link
rod 231 and left arm 232 may be different from the angle between
right link rod 231 and right arm 232, if such an arrangement is
necessary. Incidentally, one or both of link rods 231 may be
adjustable in length.
[0145] An arm 230b is pivoted at one end thereof onto pivotal shaft
230a so as to be rotatable integrally with rotary plate 230. Arm
230b is extended leftward or rightward from the end thereof pivoted
onto pivotal shaft 230a, and pivotally connected at a tip thereof
to a tip of a piston rod 233a of a rear wheel power steering
cylinder 233. Piston rod 233a of rear wheel power steering cylinder
233 is selectively extended or contracted depending on whether
steering wheel 12 is rotated rightward or leftward. Due to the
telescopic movement of piston rod 233a, rotary plate 230 is rotated
so that the angle between link rod 231 and arm 232 on one of left
and right sides is expanded so as to turn the front end of
corresponding rear wheel 7 laterally outward (in FIG. 25, right
rear wheel 7 drawn in a phantom line), and the angle between link
rod 231 and arm 232 on the other right or left side is narrowed so
as to turn the front end of corresponding rear wheel 7 laterally
inward (in FIG. 25, left rear wheel 7 drawn in a phantom line). In
association with the later-discussed lateral turning direction of
left and right front wheels 9, rear wheel 7 whose front end is
turned laterally outward (in FIG. 25, right rear wheel 7 in the
phantom line) is disposed on the outside of the turning vehicle,
and rear wheel 7 whose front end is turned laterally inward (in
FIG. 25, left rear wheel 7 in the phantom line) is disposed on the
inside of the turning vehicle.
[0146] In the vehicle shown in FIG. 25, a piston rod 234a of a
front wheel power steering cylinder 234, serving as the
above-mentioned alternative means replacing drag rod 90, is
pivotally connected to steering link bracket 207 fixed on one of
left and right steerable casings 205 supported on front transaxle
2. According to the leftward or rightward rotation of steering
wheel 12, piston rod 234a of front wheel power steering cylinder
234 is telescopically moved synchronously to the telescopic
movement of piston rod 233a of rear wheel power steering cylinder
233, so that one front wheel 9 whose front end is turned laterally
outward (in FIG. 25, left front wheel 9 drawn in a phantom line) is
disposed on the inside of the turning vehicle, and the other front
wheel 9 whose front end is turned laterally inward (in FIG. 25,
right front wheel 9 drawn in a phantom line) is disposed on the
outside of the turning vehicle. In this way, in FIG. 25, the
vehicle, having rear wheels 7 and front wheels 9 turned as drawn in
the phantom lines, turns left. This lateral turning of left and
right front wheels 9 according to the telescopic movement of piston
rod 234a of front wheel power steering cylinder 234 coacts with the
lateral turning of left and right rear wheels 7 according to the
telescopic movement of piston rod 233a of rear wheel power steering
cylinder 233 so as to improvement replication of reduction of the
turning radius of the vehicle to the operation of steering wheel
12.
[0147] Other structures, including rear transaxle 101, pump unit 50
and front transaxle 2, are the same as those in each of the
above-mentioned embodiments. In this regard, the casing of rear
transaxle 101 incorporates hydraulic motor M1 for driving left and
right axles 6. Motor casing 201 of front transaxle 2 incorporates
fixed displacement hydraulic motor M2 and variable displacement
hydraulic motor M3 for driving respective left and right axles 8.
Hydraulic motor M1 and the pair of hydraulic motors M2 and M3 are
fluidly connected in series to hydraulic pump P in pump unit 50,
and hydraulic motors M2 and M3 are fluidly connected in parallel to
hydraulic pump P. Alternatively, pump unit 50 and rear transaxle
101 may be replaced with rear transaxle 1 incorporating hydraulic
pump P together with hydraulic motor M1, and the steering system as
shown in FIGS. 24 and 25 may be disposed on left and right sides of
rear transaxle 1 so as to steerably support rear wheels 7.
[0148] Incidentally, the above-mentioned casing 12b serves as a
hydraulic steering device casing, in which a directive control
valve 235 for supplying fluid to power steering cylinders 233 and
234, and a hydraulic motor 236 for shifting directive control valve
235 are disposed. Hydraulic motor 235 is rotated in one of opposite
directions selected depending on whether steering wheel 12 is
rotated leftward or rightward, so as to telescopically move piston
rods 233a and 234a of respective power steering cylinders 233 and
234. Further, ports 237 and 238 are provided on casing 12b so as to
supply fluid to directive control valve 235 and hydraulic motor
236, and connected to a hydraulic pressure source outside casing
12b through pipes or the like. Preferably, the hydraulic pressure
source is charge pump 33 in pump unit 50.
[0149] The hydrostatic transaxle and the hydraulically driven
vehicle of the present invention are applicable to various vehicles
such as working vehicles including disclosed lawn tractors. The
illustrated vehicles have Ackerman-type steering systems. However,
the peripheral speed setting of front and rear wheels, the
structure of the hydraulic pump unit separated from the front and
rear transaxles, and the like are applicable to vehicles having
different steering systems, such as an articulated vehicle.
[0150] It is further understood by those skilled in the art that
the foregoing description is a preferred embodiment of the
disclosed apparatus and that various changes and modifications may
be made in the invention without departing from the spirit and
scope thereof.
* * * * *