U.S. patent application number 10/256782 was filed with the patent office on 2003-02-06 for axle driving apparatus.
This patent application is currently assigned to SAUER-DANFOSS INC.. Invention is credited to Johnson, Alan W..
Application Number | 20030027676 10/256782 |
Document ID | / |
Family ID | 27582679 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030027676 |
Kind Code |
A1 |
Johnson, Alan W. |
February 6, 2003 |
Axle driving apparatus
Abstract
An axle assembly has a housing. A hydrostatic transmission
separate from the housing is mounted therein. Horizontal axle
shafts are rotatably supported in the housing. The hydrostatic
transmission includes a center section separate from the housing
with fluid conduits connected to hydrostatic rotatable cylinder
blocks. A drive shaft extends from one of the blocks and is
operatively connected to the axle shafts. Check valves are
associated with the conduits to affect fluid flow and are
positioned to move in a vertical path at right angles to the axle
shafts.
Inventors: |
Johnson, Alan W.; (Ames,
IA) |
Correspondence
Address: |
ZARLEY LAW FIRM, P.L.C.
CAPITAL SQUARE
400 LOCUST, SUITE 200
DES MOINES
IA
50309-2350
US
|
Assignee: |
SAUER-DANFOSS INC.
Ames
IA
|
Family ID: |
27582679 |
Appl. No.: |
10/256782 |
Filed: |
September 27, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10256782 |
Sep 27, 2002 |
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09412448 |
Oct 4, 1999 |
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09412448 |
Oct 4, 1999 |
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09298676 |
Apr 22, 1999 |
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5979271 |
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09298676 |
Apr 22, 1999 |
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09141550 |
Aug 28, 1998 |
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5921151 |
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09141550 |
Aug 28, 1998 |
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08658618 |
Jun 5, 1996 |
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5634526 |
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08658618 |
Jun 5, 1996 |
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Jun 5, 1996 |
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5593000 |
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08658747 |
Jun 5, 1996 |
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Jun 5, 1996 |
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5626204 |
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08658535 |
Jun 5, 1996 |
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08595276 |
Feb 1, 1996 |
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5802931 |
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08595276 |
Feb 1, 1996 |
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08354525 |
Dec 13, 1994 |
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5542494 |
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08354525 |
Dec 13, 1994 |
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08181983 |
Jan 14, 1994 |
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5513717 |
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08181983 |
Jan 14, 1994 |
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08182769 |
Jan 14, 1994 |
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5577572 |
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08182769 |
Jan 14, 1994 |
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07706279 |
May 28, 1991 |
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5505279 |
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Current U.S.
Class: |
475/83 |
Current CPC
Class: |
Y10T 74/2186 20150115;
Y10T 74/19149 20150115; B60K 17/105 20130101; B60K 17/10 20130101;
B60Y 2200/223 20130101 |
Class at
Publication: |
475/83 |
International
Class: |
F16H 047/04 |
Claims
I claim:
1. An axle assembly, comprising a housing for an internally
disposed hydrostatic transmission, a hydrostatic transmission
separate from the housing and mounted within the housing, axle
shafts rotatably supported in the housing and having horizontal
axes, the hydrostatic transmission including a center section
separate from the housing and having fluid conducting conduits
interconnecting hydrostatic rotatable cylinder blocks, a drive
shaft extending from one of the cylinder blocks and being
operatively connected to the axle shafts, check valves associated
with the fluid conducting conduits and including check valve balls
to affect fluid flow through the conduits and being positioned to
move in a vertical path in a direction at right angles to the axes
of the axle shafts.
2. An axle assembly, comprising a housing for an internally
disposed hydrostatic transmission, a hydrostatic transmission
separate from the housing and mounted within the housing, axle
shafts rotatably supported in the housing and having horizontal
axes, the hydrostatic transmission including a center section
separate from the housing and having fluid conducting conduits
interconnecting hydrostatic rotatable cylinder blocks, the center
section having a horizontal base portion, and a vertical portion
extending upwardly therefrom to create an L-shape, a drive shaft
extending from one of the cylinder blocks and being operatively
connected to the axle shafts, check valves associated with the
fluid conducting conduits and including check valve balls to affect
fluid flow through the conduits, the check valves being located in
the horizontal base portion of the center section.
3. The axle assembly of claim 1 wherein the check valve balls are
positioned to move in a vertical path in a direction at right
angles to the axes of the axle shafts.
4. The axle assembly of claim 1 wherein movement of the balls in a
vertical direction will short circuit the flow of fluid between the
cylinder blocks to create a bypass mode whereupon the hydrostatic
transmission is inoperative to drive the axle shafts and the axle
shafts are free to rotate without hydraulic resistance from the
rotatable cylinder blocks.
5. The axle assembly of claim 4 wherein rotatable means is
operative with the check valves to selectively raise the balls in a
vertical direction.
6. The axle assembly of claim 4 wherein the rotatable means
includes a bypass actuation rod which is vertically positioned in
the housing for vertical movement in a direction at right angles to
the axes of the axle shafts.
7. The axle assembly of claim 1 further comprising a differential
mounted in said housing and being operatively connected to said
drive shaft and said axle shafts.
8. The axle assembly of claim 7 further comprising a gear train
mounted in said housing, said gear train driven by said drive shaft
and connected to said differential.
9. An axle assembly, comprising a housing forming an oil sump; a
hydrostatic transmission mounted within said housing and comprising
a hydraulic circuit interconnecting first and second hydrostatic
rotatable cylinder blocks; said hydraulic circuit having a closed
state wherein hydraulic fluid is transferred between said first and
second rotatable cylinder blocks and an open state where the
circuit is open to the sump; an input shaft drivingly connected to
said first rotatable cylinder block; an output shaft drivingly
connected to said second rotatable cylinder block, wherein said
output shaft is mounted perpendicular to said input shaft; a
rotatable bypass arm mounted in said housing parallel to said input
shaft and rotatable to move said hydraulic circuit from its closed
position to its open position.
10. The axle assembly of claim 9 further comprising a cam mechanism
associated with said rotatable bypass arm.
11. The axle assembly of claim 9 further comprising a plurality of
check valves mounted in said center section, wherein said check
valves are closed when the circuit is in its closed position and
the check valves are open when the circuit is in its open
position.
12. The axle assembly of claim 9 further comprising a plurality of
check valves mounted in said center section and connected between
said hydraulic circuit and said sump, wherein the check valves are
operatively connected to the rotatable bypass arm so that rotation
of the arm opens the check valves to place the hydraulic circuit in
its open position.
13. An axle assembly comprising: a housing forming a fluid sump; a
hydrostatic transmission mounted in said housing and comprising a
center section, a hydrostatic pump mounted on the center section
and a hydrostatic motor mounted on the center section; an input
shaft operatively connected to the hydraulic pump and having a
generally vertical axis; an output shaft operatively connected to
the hydraulic motor and having a generally horizontal axis; a pair
of axles mounted in the housing parallel to said shaft, said axles
being drivingly connected to the output shaft; hydraulic porting
formed in the center section to hydraulically connect the pump and
motor, said porting comprising at least two vertically disposed
check passages formed generally parallel to said input shaft to
permit oil to flow between the hydraulic porting and the fluid
sump.
14. The axle assembly of claim 13, wherein said center section
comprises a horizontal base portion on which said hydrostatic pump
is mounted and a vertical portion extending therefrom on which said
hydrostatic motor is mounted, and said check passages are formed in
said horizontal base portion.
15. The axle assembly of claim 13, further comprising check valves
mounted in both said check passages.
Description
TECHNICAL FIELD
[0001] This invention pertains to a center section for a
hydrostatic transmission, with the hydrostatic transmission having
particular utility as a component of an integrated hydrostatic
transaxlee A transaxle of a type used in equipment, such as a lawn
tractor, has gear reduction and axle components mounted in a
housing providing a sump for lubricating oil. The disclosed center
section is directed toward an economical integration of the
hydrostatic transmission with the transaxle components in a common
housing providing a common sump.
BACKGROUND ART
[0002] Hydraulically driven equipment, such as a lawn tractor, have
had transaxle structure mounted in a housing including a drive
input connection, a gear reduction drive, and oppositely-extending
differentially-connected axles, and a hydrostatic transmission is
connected to the exterior of the housing whereby a drive output
from the hydrostatic transmission connects to the drive input to
the transaxle structure.
[0003] The known prior art structures have not integrated the
hydrostatic transmission with the transaxle components in a common
housing to provide a common sump and with the use of a unique
center section between the hydraulic components of the hydrostatic
transmission as disclosed herein.
[0004] A hydrostatic transmission has a pair of hydraulic
displacement units with fluid connections therebetween. In a
typical hydrostatic transmission, the hydraulic displacement units
each have a rotatable cylinder block mounting a plurality of
reciprocal pistons and with the piston-receiving chambers in the
cylinder block communicating with ports for fluid flow to and from
the piston-receiving chambers. Many different types of structure
are known for achieving fluid communication between the arcuate
ports associated with the pair of rotatable cylinder blocks. Such
structure can be by means of tubing or by means of a structural
section with fluid passages and positioned adjacent both rotatable
cylinder blocks. This structural section can be either integral
with a housing for the hydrostatic transmission or a separate
component mountable between the hydraulic displacement units and
separable from the housing.
[0005] A prior art hydrostatic transmission has a pair of hydraulic
displacement units generally in side-by-side relation and with a
rotatable cylinder block of each of the hydraulic displacement
units being associated with a structural section having arcuate
ports for association with both of the hydraulic displacement
units. A pair of generally parallel straight passages, formed in
the structural section intersect and communicate with the arcuate
ports in pairs whereby there is fluid communication between a pair
of arcuate ports associated one with each of the hydraulic
displacement units.
[0006] The prior art also includes hydrostatic transmissions
wherein the hydraulic displacement units are disposed at a selected
fixed angle relative to each other whereby the axes of rotation of
the rotatable cylinder blocks thereof are at an angle to each other
and a structural section disposed therebetween has had a pair of
faces at the selected angle whereby arcuate ports associated
therewith may coact with the angularly-related cylinder blocks of
the hydraulic displacement units.
DISCLOSURE OF THE INVENTION
[0007] The integrated hydrostatic transaxle disclosed herein has
resulted from efforts to reduce the cost, size and weight of a
transaxle package which has had a non-integrated relation between
the housings for a hydrostatic transmission and the gear reduction,
differential and axle components. Elimination of as much machining
as possible contributes substantially to cost reduction.
[0008] A primary feature of the invention is to provide a
one-piece, generally L-shaped center section for a hydrostatic
transmission which is positionable in a housing and has first and
second faces for coaction with rotatable cylinder blocks of a pair
of hydraulic displacement units of the hydrostatic transmission and
with the center section designed to require a minimal amount of
machining to the body thereof with resultant maximum cost
savings.
[0009] The lowest possible machining cost for the center section
can be achieved by going to a casting process, such as die casting
or the lost foam process. A casting process results in a more
porous center section and, with passages therein having fluid at
high pressure, it is important to assure that leakage from the
center section shall not be a problem.
[0010] The one-piece generally L-shaped center section being
separable from the housing for the hydrostatic transmission and
mountable therein permits casting of the center section since
leakage from a porous cast center section will leak into a sump
defined by the housing for the hydrostatic transmission, rather
than through a wall of the housing.
[0011] An object of the invention is to provide, in combination, a
hydrostatic transmission comprising a pair of hydraulic
displacement units each having a rotatable cylinder block with
reciprocal pistons and a housing for the displacement units
providing a fluid sump along with a unique, one-piece, generally
L-shaped center section positionable in the housing to facilitate
utilization of such a structure with drive components for a
hydraulically-driven device all in a common housing having a common
sump.
[0012] Additionally, the center section of the hydrostatic
transmission is uniquely designed with passages in addition to
first and second generally straight passages interconnecting the
hydraulic displacement units to provide for mounting of bypass
valves as well as delivery of make-up oil to the hydraulic circuit
and provide for bleed of air from the hydraulic circuit during
operation of the bypass valves.
[0013] A further object of the invention is to provide, in
combination, a hydrostatic transmission comprising a pair of
hydraulic displacement units each having a rotatable cylinder block
with reciprocal pistons, and a housing for said displacement units
providing a fluid sump, said rotatable cylinder blocks having their
axes of rotation generally normal to each other, a one-piece
generally L-shaped center section positionable in said housing and
having first and second faces generally at right angles to each
other, said center section being positioned to have said first face
engage an end of one rotatable cylinder block and the second face
engage an end of the other rotatable cylinder block, arcuate fluid
ports at the face of each of said center section faces for coaction
with a rotatable cylinder block, a first straight fluid passage in
said center section connecting one of the ports at each face to
define a pair of fluid communicating ports and terminating at one
of said pair of ports, and a second straight fluid passage in said
center section connecting another of the ports on each face to
define a second pair of fluid communicating ports and terminating
at one of the ports of said second pair.
[0014] Another feature of the invention is to provide an integrated
hydrostatic transaxle having a common housing for a hydrostatic
transmission and a pair of oppositely-extending,
drivingly-connected axles to provide a common sump, with the
hydrostatic transmission having the center section as described in
the preceding paragraphs. Cost effectiveness is achieved by use of
the common housing, common sump and one-piece center section
whereby leakage from the hydrostatic transmission including from a
fluid passage in the center section containing fluid pressure may
reach the common sump at atmospheric pressure. This makes it
possible to cast the center section and minimize costly machining
even though the center section may be more porous.
[0015] An object of the invention is to provide an integrated
hydrostatic transaxle having the structure referred to in the
preceding paragraph.
[0016] Still another object of the invention is to have, in
combination, a hydrostatic transmission comprising a pair of
hydraulic displacement units each having a rotatable cylinder block
with reciprocal pistons, and a housing for said displacement units
providing a fluid sump, said rotatable cylinder blocks having their
axes of rotation normal to each other, a one-piece L-shaped center
section separate from said housing and having first and second
faces at right angles to each other, said center section being
positioned to have said first face engage an end of one rotatable
cylinder block and the second face engage an end of the other
rotatable cylinder block, each of said center section faces having
arcuate fluid ports for coaction with a rotatable cylinder block, a
first straight fluid passage in said center section connecting one
of the ports on each face and terminating at one of said ports, a
second straight fluid passage in said center section connecting
another of the ports on each face and terminating at one of said
ports, said center section being of material which may be
sufficiently porous to permit leakage of high pressure fluid from
whichever one of said straight fluid passages contains high
pressure fluid with said leakage flowing to said fluid sump, and
said center section having third and fourth straight fluid passages
intersecting said first and second fluid passages, respectively,
and opening to a surface of said center section opposite to one of
the faces thereof for mounting of check valves.
[0017] Still another object of the invention is to have the
combination as set forth in the preceding paragraph wherein said
first and second fluid passages are generally parallel, said center
section has a through bore extending perpendicular to and
positioned between said first and second fluid passages, a fifth
fluid passage extending generally parallel to and positioned
between said first and second fluid passages and opening to said
bore for delivery of make-up fluid to said bore, and a sixth fluid
passage extending between the fifth fluid passage and a recess set
back from the surface to which the third and fourth fluid passages
open for communication with a source of filtered make-up fluid.
DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a side elevation view of the integrated
hydrostatic transaxle, taken looking toward the left in FIG. 2;
[0019] FIG. 2 is a plan view of the integrated hydrostatic
transaxle, with parts broken away;
[0020] FIG. 3 is a vertical section, taken generally along the line
3-3 in FIG. 2, and on an enlarged scale;
[0021] FIG. 4 is a fragmentary section of the bottom part of the
housing and structure related thereto, as shown generally along
section 4-4 in FIG. 3;
[0022] FIG. 5 is a fragmentary plan view of structure shown in FIG.
2:
[0023] FIG. 6 is a fragmentary section, taken generally along the
line 6-6 in FIG. 5;
[0024] FIG. 7 is a vertical section of the center section, taken
generally along the line 7-7 in FIG. 8 and with check valve and
bypass structure shown in association therewith;
[0025] FIG. 8 is a top view of the center section for the
hydrostatic transmission;
[0026] FIG. 9 is a bottom view of the center section of the
hydrostatic transmission;
[0027] FIG. 10 is a side elevation of the center section, looking
toward the right side thereof, as shown in FIG. 8; and
[0028] FIG. 11 is a vertical section of the center section, taken
generally along the line 11-11 in FIG. 8 and with the structure
associated with the center section being omitted.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] The integrated hydrostatic transaxle is shown generally in
FIGS. 1 to 3.
[0030] The integrated hydrostatic transaxle has a common housing 10
for the components thereof. The common housing 10 is of two parts,
with a top part 12 and a bottom part 14 which are joined together
along a split line 16 which is disposed generally horizontal when
the integrated hydrostatic transaxle is installed in operative
position. The housing parts 12 and 14 are held in assembled
relation by a series of bolts 18 extending through peripheral
flanges of the top and bottom housing parts which abut at the split
line 16.
[0031] The shape of the housing parts in plan is shown in FIG. 2
wherein a portion of the top housing part 12 is seen in the lower
left part of the Figure and with the remainder thereof broken away
to show the bottom housing part 14.
[0032] The common housing 10 encloses a hydrostatic transmission
having a pair of hydraulic displacement units, indicated generally
at 20 and 22, respectively, and also houses transaxle components,
seen particularly in FIG. 2. The transaxle components include a
pair of oppositely-extending axles 23 and 24 having ends extended
beyond the bottom housing part for mounting of drive wheels (not
shown) and their centerlines are coincident with the housing split
line 16. The bottom housing part 14 has bearings 25 and 26 at the
outboard ends and thrust bearings 27 and 27a at the inboard ends of
the axles for rotatable support thereof and with the axles being
geared together through a differential, indicated generally at 28.
This differential includes bevel gears 29 and 30 at the inner end
of the respective axles 23 and 24 with drive input gears thereto
including a gear 31 which meshes with an output gear 32 of a gear
reduction drive. The gear reduction drive has a drive input
connection from the hydraulic displacement unit 22, with the output
shaft 35 (FIG. 3) of the latter having a gear 36 which meshes with
a gear 37. The latter gear is rotatably fixed to a gear 38 which
meshes with the previously-mentioned gear 32.
[0033] A brake for the drive is mounted externally of the common
housing 10 and associated with an end of the drive output shaft 35,
with this brake structure, including a brake 40, a brake drum 41
and a brake cover 42.
[0034] Each of the hydraulic displacement units 20 and 22 is shown
in detail in FIG. 3 and is of generally the same construction. The
hydraulic displacement unit 20 has a rotatable cylinder block 45
connected by a splined connection 46 to a drive input shaft 47
having an internal end rotatable in a journal 47a positioned in a
center section, indicated generally at 48, of the hydrostatic
transmission. The outboard end of the drive input shaft 47 is
rotatably supported by the top housing part 12 by means of a
bearing 49. A lip seal 50 seals the shaft opening in the top
housing part 12.
[0035] The rotatable cylinder block 45 has a series of
piston-receiving chambers, each of which movably mount a piston 51
of a relatively large diameter and with each of the pistons 51
being urged by an associated spring 52 into following engagement
with a swashplate structure. The hydraulic displacement unit 20 has
overcenter variable displacement, with this operation being
achieved by angular adjustment of a swashplate 54 which, as well
known in the art, can have its angle varied from the clockwise
position shown. in FIG. 3 to an opposite extreme position in a
known manner and by manually operable structures not shown. The
swashplate can pivot about a pivot axis in a counterclockwise
direction and past a horizontal center position, as viewed in FIG.
3. The swashplate 54, as known in the art, mounts a thrust plate 55
against which the pistons abut and a bearing and bearing guide
structure rotatably support the thrust plate 55 relative to the
body of the swashplate.
[0036] Each of the piston-receiving chambers has a passage 57
opening to a face of the rotatable cylinder block 45 for coaction
with arcuate ports of the center section 48 which will be described
subsequently.
[0037] The hydraulic displacement unit 22 is a fixed displacement
unit and has a rotatable cylinder block 58 with a plurality of
piston-receiving chambers each movably mounting a piston 59 which
is spring-urged by a spring 60 toward a swashplate 61. The
swashplate 61 has a thrust plate 62 against which an end of the
pistons engages and a ball thrust bearing 63 interposed between the
thrust plate and the swashplate to rotatably mount the thrust
plate.
[0038] The rotatable cylinder block 58 drives the drive output
shaft 35 through a splined connection 64 therebetween.
[0039] An inner end of the drive output shaft 35 rotates within an
opening 65 in the center section 48 which may optionally receive a
journal 66 and, if the journal is not used, the opening 65 is
cylindrical as shown in FIG. 11. The outboard end of the drive
output shaft 35 is sealed by a lip seal 67 and with bearing
structure disposed interiorly thereof including a ball bearing
68.
[0040] Each of the piston-receiving chambers of the rotatable
cylinder block 58 has a passage 69 opening to a face thereof which
coact with arcuate ports associated with a face of the center
section 48 to be subsequently described.
[0041] Since the hydraulic displacement unit 22 is of a fixed
displacement, the swashplate 61 need not be adjustably mounted and,
therefore, can be supported by the common housing 10 against
hydraulic forces exerted through the pistons 59. As seen in FIG. 3,
the centerline of the drive output shaft 35 is located on the split
line 16 of the housing parts 12 and 14 and extends through a
central opening 69 in the swashplate 61. The swashplate 61 spans
the split line and support thereof against fluid forces is provided
by the common housing at both sides of the split line.
[0042] The foregoing description generally describes the integrated
hydrostatic transaxle wherein the bottom housing part 14 provides a
common sump for the transaxle components as is evident in FIGS. 1
and 2 and also for the hydrostatic transmission as is evident from
FIGS. 1 to 3.
[0043] The hydraulic displacement units 20 and 22 have their
respective rotatable cylinder blocks arranged with .their axes of
rotation generally at right angles to each other. It is the primary
function of the center section 48 to provide communication between
selected piston-receiving chambers of the respective cylinder
blocks 45 and 58. In achieving this primary function, center
section 48 has been uniquely designed to minmize costly machining
operations and enable formation of the body of the center section
by casting. Examples of such casting, without limitation, are lost
foam casting and die casting. The resulting material of the cast
body of the center section has a relatively high degree of porosity
as compared to a conventional machined center section for a
hydrostatic transmission and in order to assure any leakage problem
of high pressure fluid contained within a passage in the center
section, because of porosity, is confined within the common
housing, the center section 48 has been constructed as a separate
one-piece center section which is positionable within the bottom
housing part 14 as seen in FIG. 3. The one-piece center section 48
is generally L-shaped to have a pair of faces generally at right
angles to each other with one planar face 72 coacting with a face
of the rotatable cylinder block 45 of the variable displacement
unit 20 and a second planar face 73 coacting with a face of the
rotatable cylinder block 58 of the hydraulic displacement unit 22.
The center section body has two integral parts 74 and 75 oriented
to have the two parts define the legs of the L shape of the center
section, with the part 74 having the planar face 72 and the part 75
having the planar face 73.
[0044] The planar face 72 has a pair of arcuate ports 76 and 77 and
the planar face 73 has a pair of arcuate ports 78 and 79, as seen
in FIGS. 8 and 10, respectively.
[0045] First and second straight, generally parallel passages 80
and 81 are cast into the center section body and function to
intersect the arcuate ports and place the arcuate ports in paired
relation for fluid communication. The first passage 80 intersects
with arcuate port 76 and arcuate port 78 to provide a first pair of
ports in fluid communication. The second passage 81 intersects
arcuate ports 77 and 79 and places them in paired fluid
communication.
[0046] In operation of the integrated hydrostatic transaxle, one or
the other of the first and second fluid passages functions to
deliver fluid under pressure from the variable displacement unit 20
functioning as a pump to the fixed displacement unit 22,
functioning as a motor, and with the other fluid passage providing
for return of fluid from the motor to the pump. The first and
second fluid passages 80 and 81 terminate at one end at their
intersection with the arcuate ports 78 and 79 and are closed at
their other end as formed in the casting process.
[0047] The center section 48 has a third passage 84 intersecting
said first passage 80 and a fourth passage 85 intersecting the
second passage 81, with the passages 84 and 85 opening to a surface
86 of the center section opposite to the planar face 72.
[0048] A through bore 87 extends perpendicular to and is positioned
between the first and second fluid passages 80 and 81 and a fifth
fluid passage 88, sealed intermediate its ends by journal 47a,
extends generally parallel to the through bore 87 and is positioned
between the first and second fluid passages 80 and 81. A sixth
fluid passage 90 extends between and normal to the fifth fluid
passage 88 and a recess 91 in the center section set back from the
surface 86 of the center section.
[0049] The utility of the through bore and third through sixth
passages will be readily understood by reference to FIGS. 3 to 7
and the following description.
[0050] The third and fourth fluid passages 84 and 85 mount a pair
of check valves which each having a tubular seat member 93 and 94,
respectively, fitted therein and which form seats for a pair of
check valve balls 95 and 96 spring-urged downwardly against the
seats. The check valves function, when closed, to block fluid flow
from either of the first and second passages 80 and 81 to a recess
or well 100 (FIG. 3) formed by a cavity in the bottom housing port
14. This recess is generally oval and is defined by a continuous
upstanding wall on the bottom housing part with wall sections shown
at 101 and 102. The lower ends of the third and fourth passages 84
and 85 open into this generally oval recess. The oval recess 100 is
sealed off, at its top, by a generally oval-shaped wall 103 on the
underside of the center section 48 and which has a sealing O-ring
104 therebetween. This is a sealed recess or well so that filtered
fluid in the recess may be a source of make-up fluid to the
hydrostatic transmission. Structure associated with the check
valves also provides for a bypass function wherein, even though the
pump is set at a displacement and is operable, there is no drive of
the motor since the first and second passages 80 and 81 are
cross-connected through opening of the check valves and the
generally oval recess 100.
[0051] The make-up fluid is delivered to the generally oval recess
100 from the common sump within the bottom housing part 14 by flow
through an open space beneath the center section 48 (FIG. 3) and
through a cylindrical filter 110 having O-ring seals at its top and
bottom. The interior of the filter 110 communicates with the sixth
fluid passage 90 in the center section. As previously described,
the sixth fluid passage 90 communicates with the fifth fluid
passage 88 and the fifth fluid passage 88 communicates with the
through bore 87 so that fluid reaches the recess 100.
[0052] The center section has a series of through mounting holes at
115, 116, and 117 whereby, as seen in FIG. 3, in assembly, the
center section 48 can be secured to the upper housing part 12, as
by self-tapping screws 118 and the final assembly achieved by
bringing the bottom housing part 14 into association with the top
housing part 12 along the split line 16.
[0053] All of the first through sixth fluid passages of the center
section as well as the through bore 87, recess 65, recess 91 and
through mounting holes 115-117 can be formed in the center section
in a casting process. There is only a limited amount of machining
required to finish the center section. As previously stated, a cast
center section has a higher porosity than a conventional machined
center section, which could create the possibility of leakage from
whichever of the first and second passages 80 and 81 may have
pressure fluid therein; however, the one-piece, integral center
section which is independent of the housings avoids any problem
from such leakage since such leakage would merely be into the
common sump of the integrated hydrostatic transaxle and which is
open to atmosphere through a bleed tube 140.
[0054] The bypass operation previously referred to is effected by
opening the check valves by raising the check valve balls 95 and 96
off their seats. The structure for this includes a bypass actuator
structure including a bypass actuator plate 120 and a bypass rod
121. The bypass actuator plate 120, as seen in FIGS. 4 and 7, is
positioned in the generally oval recess 100 in the bottom housing
part 14 and, at its middle, is connected to the lower end of the
bypass rod 121 and has a pair of upturned ends (FIG. 7) positioned
beneath the check valve balls 95 and 96. Lifting of the bypass rod
121 causes the bypass actuator plate to lift the check valve balls
and place the center section first and second passages 80 and 81 in
fluid communication. Lifting of the bypass rod 121 is achieved by
rotation of a handle 125 positioned above top housing part 12 and,
as seen particularly in FIGS. 2, 3 and 5. The bypass rod 121 is
longitudinally movable in an opening 126 in the top housing part 12
as well as having its lower part extending downwardly through the
through bore 87 of the center section and is normally urged
downwardly by a spring 127. As seen in FIG. 6, the handle 125 has
cam shapes 130 formed thereon which coact with ends of a through
pin 131 fitted into an end of the bypass rod 121. Rotation of the
handle 125 from the position shown in the drawings to bring the
cams 130 under the through pin 131 raises the through pin and the
bypass rod 121 to establish the bypass operation.
[0055] The bypass rod 121 and center section 48 are uniquely
associated with the housing structure whereby a bypass operation
also results in bleeding air from the system fluid. When the bypass
rod 121 is in its lower position and the check valves are closed,
the upper end of the through bore 87 of the center section 48 is
closed by a seal washer 135 backed up by peripheral flange on the
bypass rod, so that there is no fluid communication between the
through bore 87 and the interior of the common housing 10. When the
bypass rod 121 is raised to effect a bypass operation, the seal
washer 135 is moved upwardly from its seat whereby the upper end of
the through bore 87 is open to the interior of the common housing
and air can bleed off to the housing interior. Air that accumulates
in the common sump can bleed off to atmosphere through the bleed
tube 140 (FIG. 1).
[0056] It is believed that the operation of the integrated
hydrostatic transaxle is clearly apparent from the foregoing
description. However, it may be briefly summarized as follows. An
engine drives the drive input shaft 47 for the variable
displacement unit 20 (functioning as a pump) to cause operation of
the displacement limit 22 (functioning as a motor) and the drive
output shaft 35 drives the transaxle components shown in FIG. 2 for
rotation of the wheel axles 23 and 24. The direction of rotation of
the wheel axles can be shifted from forward to reverse by shifting
the swashplate 54 of the variable displacement unit 20 to a
position opposite side of center from that shown in FIG. 3 and with
resulting reversal of pressure fluid flow through the center
section 48 from the pump to the motor. In the event there is to be
no rotation of the wheel axles 23 and 24 while the pump is still
operating and set for displacement, a bypass operation is achieved
by rotation of the handle 125 to raise the bypass rod 121 and open
the check valve balls 95 and 96. As previously mentioned, any air
in the passages in the center section can bleed to the sump of the
common housing. Either one of the check valves can automatically
open to provide make-up fluid to the transmission circuit from the
generally oval recess 100 when the pressure existing in one or the
other of the first and second straight passages 80 and 81 in the
center section is sufficiently less than that of the fluid in the
oval recess to overcome the spring closing force on a check valve
ball.
* * * * *