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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to hydrostatic transaxles and, more
particularly, is concerned with a control arrangement for the pump track
ring.
2. Description of the Prior Art
Hydrostatic transmissions transmit rotary mechanical motion, typically from
an internal combustion engine, to fluid motion, then back to rotary
mechanical motion to rotate a drive axle in order to drive a vehicle such
as a lawn and garden tractor or riding mower. The hydrostatic transmission
regulates or controls the output rotary mechanical motion such that
varying output speeds in the forward and reverse directions are possible
with a single speed input rotary mechanical motion. Within a hydrostatic
transmission of the radial piston type, a pump and motor each having a
cylinder unit that rotates on a fixed pintle with pistons positioned
within the cylinders and attached to slippers mounted in an expander band
so that as the cylinder unit rotates, the slippers engage the surrounding
eccentric annular track ring of the pump and motor. The pistons of the
pump create a pressurized fluid flow that drives the motor pistons which
rotate an output shaft. The transmission ratio is therefore directly
proportional to the eccentricity of the track ring of the pump relative to
the fixed pintle.
The eccentricity of the pump track ring must therefore be variable and this
is accomplished by pivoting the track ring around an axis located at one
end of the track ring, the axis generally being a pivot pin. In addition,
a control mechanism adapted to swing or pivot the track ring around the
pivot axis must also be provided so that an operator can change the
eccentricity of the track ring.
Generally the track ring pivots around a pin or rod extending at least
through the track ring on the inboard side, or proximal side relative to
the gearing, of the transaxle casing and is held by the clamping force
exerted by the two transmission casing halves that are bolted together. It
is necessary, however, for the pivot pin to be mounted as securely as
possible since the pivot pin bears a large amount of load. This is because
of the pressure exerted on the pump track ring by the hydrostatic pressure
within the pump and the torsional forces created by the pivotal movement
of the track ring. This type of hydrostatic transmission is shown in U.S.
Pat. No. 4,979,583, entitled VARIABLE SPEED TRANSAXLE, issued Dec. 25,
1990, and pending application Ser. No. 07/535,462, entitled VARIABLE SPEED
TRANSAXLE, filed Jun. 8, 1990, both of which are specifically incorporated
herein by reference.
The control rod mechanism for the pump track ring has heretofore been
located on the outboard side, or distal side relative to the gearing, of
the transaxle casing. This is disadvantageous in that the transmission
casing must be extended in the forward direction as it is necessary to
accommodate the control rod mechanism, which can cause interference with
or the restriction of the area in which the mower blade deck is located on
a conventional riding mower, in which the transmission is installed. It is
thus desirable to maintain the front dimension of the transmission casing
as small as possible so as to allow sufficient room for the mower deck to
be raised.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a control mechanism
for the pump output adjustment mechanism, such as the pump track ring of a
hydrostatic transmission, is located on the inboard or proximal side of
the hydrostatic transaxle. In a radial piston type unit, the control unit
varies the eccentricity of the pump track ring relative to the fixed
pintle.
The pump track ring control mechanism, according to the present invention,
solves the aforementioned problems by locating the control mechanism on
the inboard side of the unit, thus decreasing the size of the transmission
casing on the outboard side. A rotatable control rod extending into the
transmission casing has a radially extending control rod pin located
adjacent the pump track ring and adapted to pivot around the control rod
in the same direction of rotation as the control rod thus causing the pump
track ring to likewise pivot around its pivot pin.
In accordance with a further aspect of the present invention, the pivot pin
for the pump track ring is located on the outboard or distal side of the
hydrostatic transaxle allowing pivotally eccentric movement of the track
ring about the pintle.
On the outboard side of the transmission casing the pump track ring is
pivotally mounted on the pivot pin which is disposed between the two
halves of the transmission casing, the mounting bolts for the halves are
directly above the pivot pin and extend through bores located at each end
of the pivot pin. The full clamping force on the housing occurs directly
over the pin, which maintains it immobile, thereby providing a good
bearing point for the track ring and eliminating noise and vibration.
A similar arrangement could be provided in a swash plate type hydrostatic
transmission.
An advantage of the present invention is the compact design achievable over
prior art systems.
Another advantage of the present invention is the high torque loads the
pump track ring can withstand and the stability of the pivot pin within
the transmission casing.
The invention, in one form thereof, provides in a hydrostatic transaxle a
housing having a hydrostatic transmission and gear means driving an axle,
the transmission having a pump and motor each including displaceable,
rotatable pistons, the pump and motor being in fluid communication with
each other through a conduit, and control means disposed proximal to said
axle for varying the displacement of the pistons. The control means
includes a surface engaged by the rotating pistons and means for rotating
the surface to adjust the displacement of the pistons.
The invention in another form thereof provides in a hydrostatic transaxle a
housing having a first part and a second part including a plurality of
bolts for clampingly holding together the first part and the second part,
and a hydrostatic transmission disposed within the housing. The
transmission includes a pump fluidly connected to a motor, the pump having
a plurality of displaceable, radially extending pistons, gearing operably
connected to the motor, an axle assembly including differential means for
operably connecting the gearing to the axle assembly, a pivot pin clamped
between the housing parts, a track ring pivotally disposed on the pivot
pin and radially surrounding the pistons for varying the displacement of
the pistons as the track ring pivots, the pivot pin defining a pivot axis
for the track ring, wherein the pin has at least one opening through which
at least one of the plurality of bolts extends, the clamping force exerted
by the bolt to clampingly hold together the housing secures the pivot pin.
It is therefore an object of the present invention to provide a more
compact and smaller transmission casing.
BRIEF DESCRIPTION OF THE DRAWINGS
The above mentioned and other features and objects of this invention, and
the manner of attaining them, will become more apparent and the invention
itself will be better understood by reference to the following description
of embodiments of the invention taken in conjunction with the accompanying
drawings, wherein:
FIG. 1 is a horizontal sectional view showing a variable transaxle in
accordance with the a preferred embodiment of the present invention;
FIG. 2 is a partially cut away end view of the variable speed transaxle;
FIG. 3 is a sectional view of the track ring capturing arrangement in
accordance with a preferred embodiment of the present invention;
FIG. 4 is an enlarged fragmentary view of the pivot pin bolt taken along
line 4--4 of FIG. 15;
FIG. 5 is an enlarged fragmentary sectional view of the control guide
assembly;
FIG. 6 is an end view of the control guide;
FIG. 6A is an elevational view of the control guide;
FIG. 7 is a plan view of the ring guide;
FIG. 8 is an enlarged sectional view of the dump valve assembly taken along
line 8--8 of FIG. 1;
FIG. 9 is a plan view of the pulley;
FIG. 10 is a plan view of the input drive coupling;
FIG. 11 is a bottom view of the fan;
FIG. 12 is a top view of the fan;
FIG. 13 is a fragmentary plan view of the upper transaxle housing over the
input drive portion depicting the cast-in cooling vanes;
FIG. 14 is an elevational view of the pump track ring pivot pin;
FIG. 15 is an enlarged fragmentary view of the dashed circular portion of
FIG. 1 showing the connection of the pivot pin; and
FIG. 16 is an enlarged fragmentary view of the oil seal.
Corresponding reference characters indicate corresponding parts throughout
the several views. The exemplifications set out herein illustrate a
preferred embodiment of the invention, in one form thereof, and such
exemplifications are not to be construed as limiting the scope of the
invention in any manner.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, and particularly to FIG. 1, there is shown a
variable speed hydrostatic transaxle (HST) 20 in accordance with the
principles of the present invention. HST 20 includes a hydraulic or
hydrostatic unit 21 housed in a lower transaxle casing 22 having bolt
holes 23, the hydrostatic unit 21 including a pump 24 and motor 26, being
described in detail hereinbelow, for transferring rotary motion from an
energy source such as an internal combustion engine (not shown) to the
drive wheels of a vehicle (not shown) in which the HST 20 is installed.
The drive wheels (not shown) are drivingly connected to the hydrostatic
unit 21 through a succession of gearing beginning with an output member 28
axially connected to motor 26 so as to rotate therewith. Output member 28
is drivingly connected to an output shaft 30 seated in the transaxle
casing of which only lower transaxle casing 22 is shown in FIG. 1, while
pinion gear 36 is disposed on output shaft 30 which meshes with an output
gear 37 disposed on a transfer shaft 38 supported by bearings 40 and 41.
Disposed on transfer shaft 38 is a transfer gear 42 imparting its
rotational energy to differential 44 for driving right and left axle
shafts 46 and 47 each respectively supported in lower transaxle casing 22
by right and left axle bearings 48 and 49. Differential 44 includes a ring
gear 50 meshed with transfer gear 42, a transverse shaft 51 and bevel
gears 52, 53, 54, and 55, which are drivingly connected to right axle
shaft 46 and left axle shaft 47. Surrounding differential 44 and the
gearing is an oil chamber 56, which is separated from the chamber for the
hydrostatic unit 21, and serves as a reservoir of oil to lubricate the
differential 44. Thus as the motor 26 rotates, the motion is transferred
to the axle shafts 46 and 47 to turn the wheels (not shown) attached
thereto in order to drive the vehicle. Since the oil chamber 56 is
separate from the hydrostatic unit 21, it is necessary to ensure that the
oil from oil chamber 56 does not mix with the oil in the hydrostatic unit
21 to avoid contamination of this hydrostatic oil. Thus, there is radially
provided on output shaft 30 a double-lipped oil seal 31 located adjacent
output member 28. Referring to FIG. 16, the double-lipped oil seal 31 is
essentially W-shaped having two lips 34 and 35 which are urged into
contact with the surface of output shaft 30 by annular spring clip 32 and
annular retainers 33. The retainers 33 hold lips 34 and 35 against shaft
30 while spring clip 32 urges the bowed center portion 39 inwardly. The
double-lipped construction of oil seal 31 thus prevents the flow of oil
from the differential side of the transaxle to the hydrostatic unit side,
and vice versa.
The hydrostatic unit 21, as mentioned above, is driven by an external
energy source such as an internal combustion engine (not shown) and,
referring to FIG. 2, is generally connected to the hydrostatic
transmission 20 via a belt (not shown) from an output shaft of the
internal combustion engine to a pulley 58. The pulley 58, depicted in FIG.
9, has an input drive shaft bore 74 that allows input drive shaft 60 to
extend therethrough and is drivingly connected thereto by a nut 59
threaded onto the input drive shaft 60 which also extends through a bore
62 in the upper transaxle casing 64 (see FIG. 13) and terminates with a
bevel gear 66 that meshes with a pump input bevel gear 68 mounted to a
cylinder 70 being rotatably mounted on pintle 72 being fixed within the
hydrostatic unit 21 by pin 73 and saddle clamp 75 (see FIG. 2). Thus, the
rotation of input drive shaft 60 is imparted to the pump 24 to cause
rotation thereof in order to drive motor 26 and the axles 46 and 47 as
described above.
Referring to FIGS. 2 and 9-13, pulley 58 (FIG. 9) forms part of an external
transaxle cooling system which, in cooperation with a fan 76 (FIGS. 11 and
12), a drive coupling 78 (FIG. 10), and external helical fins 80 (see FIG.
13) on the upper transaxle casing 64, all of which are described in detail
hereinbelow, provides a continuous, helical air flow pattern that smoothly
and unimpededly flows over the hydrostatic transmission 20 effecting
cooling thereof with minimal air turbulence, since the fins 80 being
curved in the same direction as the air flow pattern produced by the fan
76 act in mutual cooperation.
As best seen in FIG. 2, axially downwardly of pulley 58 is the drive
coupling 78 likewise disposed or splined on input drive shaft 60 extending
through an input drive shaft bore 82 of the drive coupling 78, and axially
downwardly of drive coupling 78 is the fan 76 also disposed on input drive
shaft 60 extending through an input drive shaft bore 84 of the fan 76.
Thus, the drive coupling 78 is connected with input drive shaft 60 so as
to rotatable therewith. Pulley 58, FIG. 9, drive coupling 78, FIG. 10, and
fan 76, FIGS. 11 and 12, each respectively include bolt apertures 86, 88,
and 90 in which are received coupling bolts 92 (of which only one is shown
in FIG. 2) that hold pulley 58, drive coupling 78 and fan 76 together
while disposed on the input drive shaft 60. Bolt apertures 88 are located
at the apexes of the equilateral triangular shaped drive coupling 78 while
bolt apertures 86, and 90 each form the apexes of an equilateral triangle
that correspond with the shape of drive coupling 78. The drive coupling 78
is triangular shaped to correspond with a triangular shaped hub portion 94
in the center of fan 76 forming a semi-locking driving fit between the
drive coupling 78 and fan 76. In addition, the triangular shape of drive
coupling 78 allows for the communication of air apertures 96 and 98
respectively located in pulley 58 and fan 76 on the sides of the triangle
formed by respective bolt apertures 86 and 90. Thus, when the pulley 58,
drive coupling 78, and fan 76 are bolted together the air apertures 96 of
the pulley 58 and air apertures 98 of the fan 76 are axially aligned (FIG.
2).
The fan 76, referring to FIGS. 11 and 12, has three different shapes of
outer fan blades X, Y, and Z, which axially extend from the top to the
bottom of the fan 76 such that rotation of the fan 76 on input drive shaft
60 causes air to be drawn downwardly towards the hydrostatic transaxle 20,
then outwardly. Blades X, Y, and Z also radially extend from the outer
periphery 100 to an inner radius 102 for an extension distance that is
approximately 1/3 of the total radius of the fan 76. Extending from the
inner radius 102 to the triangular shaped hub portion 94 are fan ribs 104
that also axially extend from the top to the bottom of the fan 76 and act
to direct the inflowing air downwardly toward external fins 80.
In operation, three elements, namely the air apertures 96 and 98, the
blades X, Y, and Z, and the fan ribs 104 cooperatively serve to draw air
into the fan 76 and create a helical air flow pattern which spreads
downwardly and outwardly over the external fins 80 formed in the transaxle
upper casing 64, while the radial shape of the external fins 80 correspond
to the rotational direction of the helical air flow pattern to permit
smooth and efficient cooling of the hydrostatic transaxle 20 by allowing
the air to flow without impediment or created air turbulence that would
retard or hinder the constant flow pattern created by the fan 76.
Now, referring again to FIG. 1, the hydraulic unit 21 of the hydrostatic
transaxle 20, includes a pump 24, driven by the input system described
above, which in turn drives the motor 26, both the pump and motor 26 being
mounted on a fixed conduit in the form of pintle 72. The pintle 72
comprises two passageways or conduits 106 and 107 each having a spring 108
and 109 disposed therein which retain ball valves 110 and 111 adjacent
seats 119 and 121 of plugs 112 and 113 threaded into one end of the
pintle, each defining discharge ports 115 and 117. Thus, ball valves 110
and 111 normally close discharge ports 115 and 117 during operating
condition due to the pressure exerted within pintle 72, except when
make-up oil is needed, and this maintains a closed pressure system between
the pump 24, the motor 26, and pintle 72. Radially outwardly surrounding
pintle 72 is pump 24 (in FIG. 1 being on the left side) and motor 26 (in
FIG. 1 being on the right side). The specific principles of operation of a
hydrostatic unit 21 of the type as described hereinabove and below, will
not be explained as the principles are known in the art and do not form a
part of this invention. In general, however, a cylinder such as pump
cylinder 70, being applicable to both the pump 24 and motor 26 of the
hydrostatic unit 21, is rotatable on pintle 72 and has a plurality of
bores (not shown) in which are disposed a plurality of pistons (e.g. pump
piston 134 and motor piston 116) that axially reciprocate within the bores
and radially rotate with respect to the pintle 72. The cylinders thus
rotate around pintle 72 and within their respective track ring, described
hereinbelow, while the respective pistons pump fluid through rotating
action of the cylinder as in the case of pump 24, or are pumped by fluid
pressure flowing through pintle passageways 106 and 107 of pintle 72 as in
the case of motor 26. The pump 24 and motor 26 form a closed fluid path
being in communication with each other via the pintle 72 and its pintle
passageways 106 and 107, the fluid flowing from the action of the rotating
pistons 134 of the pump 24 into the pistons 116 of the motor 26 causing
the motor to rotate output member 28 being attached to the motor cylinder
71.
Motor 26 comprises a motor track ring 114 radially surrounding a plurality
of pistons 116 having corresponding slippers 118, of which only one of
each is shown, the slippers 118 radially adjacent to the inner radius 120
of motor track ring 114. The pistons 116 with their slippers 118 are
rotatable around pintle 72 within the motor track ring 114 and are in
fluid communication with the pintle tubes 106 and 107 via motor pintle
ports 122 and 123. The motor track ring 114, however, is fixed
eccentrically relative to the pintle 72 so that the pistons 116
reciprocate radially and rotate.
Referring to FIG. 3, the motor track ring 114 includes radially extending
lug portions 124 and 125 which fit into recesses 126 and 127 cast into the
lower transaxle Casing 22. The upper transaxle casing 62 being attached to
the lower transaxle casing 22, includes, radially adjacent the lug
portions 124 and 125, bolt apertures 128 and 129 through which bolts 128
and 129 extend to thereby clampingly fix the motor track ring 114 between
the upper and lower transaxle housings 64 and 22. The elimination of a pin
or rod extending through the transaxle 20 to retain or fix the motor track
ring 114 shortens the overall axial length of the transaxle and permits
drive train gearing to be closer to the motor 26.
Alternatively, recesses could be formed in both housing halves 22 and 64,
or in only the upper half 64. Other techniques could be used to clamp
track ring 114 other than lugs 124 and 125.
As stated above, pump 24 radially surrounds pintle 72 and comprises a pump
output adjustment means in the form of track ring 132 surrounding a
plurality of pistons 134 having corresponding slippers 135, of which only
one of each is shown, the slippers 135 radially adjacent to the inner
radius 138 of pump track ring 132. The pistons 134 with their slippers 136
are rotatable around pintle 72 within the guide surface of the pump track
ring 132 and are in fluid communication with the pintle tubes 106 and 107
via pump pintle ports 140 and 141. Pump track ring 132, however, is not
fixed relative to pintle 72 as is motor track ring 114 although pump 24 is
eccentric relative to pintle 72 as is motor 26. In order to create a
variable output in both the forward and reverse directions from motor 26
and thus the axles 46 and 47, the pump track ring 132 eccentrically pivots
around the pintle 72 which causes more or less fluid to be pumped from
pistons 134 into pintle ports 140 and 142 through pintle tubes 106 and 107
out through motor pintle ports 122 and 123 driving motor pistons 116
depending on the degree and relative direction of eccentricity of the pump
track ring 132 to the pintle 72.
Referring to FIGS. 1, 4, and 14-15, the hydrostatic transaxle in accordance
with the present invention comprises a pivot pin 142 having radial
clearance bores 144 and 145 on both ends thereof is located on the
outboard side 146 of the hydrostatic transaxle 20 relative to axle 46 and
47 and extends through the pump track ring 132 so that the pump track ring
132 may pivot about pivot pin 142. Since pivot pin 142 is subjected to a
large amount of stress due to large hydrostatic pressures within pump 24,
pivot pin 142 must be rigidly held in place. Two hydrostatic casing bolts
148 extend through the casing and through bores 144 and 145. Thus, as
shown in FIGS. 15 and 4, pivot pin 142 is secured between the upper and
lower casing halves 64 and 22 not only by the normal clamping force
existing between the casing halves but also by the casing bolts extending
through the pivot pin 142 itself exerting high localized clamping force.
In order to promote smooth pivoting of the pump track ring 132, pivot pin
guides 150 and 151 having pivot pin guide bores 152 (see FIG. 7) are
disposed on pivot pin 142 on both sides of pump track ring 132 adjacent
pump track ring 132 and the upper and lower casings 64 and 22. The pivot
pin guides are preferably made of a resilient plastic material such as
Hytrel.RTM. or nylon since this would prevent rattling and promote smooth
pivoting.
Referring now to FIGS. 1, 2, and 5, pump track ring 132, being pivotable
around pivot pin 142 so as to be eccentrically pivotable about pintle 72,
and controlled by an operator through a control mechanism 156 is located
on the inboard side 154 of the hydrostatic unit 21 in accordance with
another aspect of the present invention. The control mechanism 156
consists of a control rod 158 extending into the transaxle and which
rotates therein through action of a control lever 162 attached to the
control rod 158 via nut 164 threaded on the end of control rod 158
projecting beyond the transaxle. The control rod 158 has a radial bore 166
in which is disposed a control pin 168 that pivots in the direction of
rotation of control rod 158, being attached thereto. The control pin 168
radially extends beyond the control rod 158 in one direction into a recess
170 formed in the upper and lower casings 64 and 22 in which is disposed a
control guide 172. The control guide 172, FIGS. 6 and 6A, is a
longitudinally elongated U-shaped member, preferably made of a plastic
material such as Hytrel.RTM. or nylon, and serves to eliminate noise and
rattling as the control pin 168 pivots within the recess 170 when the
control unit 156 is actuated. The control pin 168 also radially extends in
the other direction and is captured in a recess of rod 174 disposed
between pump track ring ears 176 and 177 so as to pivot pump track ring
132 around pivot pin 142 and eccentrically around pintle 72. Thus as
control lever 162 is moved by the operator, the stationary control rod 158
is rotated within the transaxle (FIG. 5), the dotted lines showing the
movement of the control unit 158 and pump track ring 132. This pivots pump
track ring 132 around pintle 72, and depending on the direction and
relative degree of movement of the pump track ring 132, drives the motor
26 faster or slower in a forward or reverse direction according to the
general principles of hydrostatic transmissions.
As pump track ring 132 is rotated, stops 178 and 179 radially disposed
180.degree. from each other and 90.degree. in both radial directions from
the control unit 156, respectively cast in the upper and lower casings 64
and 22 (FIG. 2) provide a positive stop to prevent overtravel of the pump
track ring 132. As pump track ring 132 upwardly pivots towards upper inner
surface 189, the pump track ring contacts projection 178, and as pump
track ring downwardly pivots towards lower inner surface 191, the pump
track ring contacts projection 179. Thus on upward or downward travel,
pump track ring 13 contacts the respective projection.
Referring to FIGS. 1 and 8, there is shown a flat one-piece dump valve
plate 180 fabricated from stamped metal or alternatively made of a plastic
material, having a bore 185 and plate fingers 182 and 183. Dump valve
plate 180 with fingers 182 and 183 is disposed at the end of pintle tubes
106 and 107 where ball valves 110 and 111 are located within clearance
slot 181 formed between the upper and lower casings 64 and 22. The plate
fingers 182 and 183 respectively extend through discharge ports 115 and
117 to urge respective ball valves 110 and 111 off their seats 119 and 121
thereby causing communication of pintle passageways 106 and 107 with the
interior chamber of the hydrostatic transaxle 20. A cam rod 184 having
offset portion 186 extends through the plate 180 and is seated in cam rod
journal 187 in lower housing 22. The cam rod 184 also extends in the axial
direction through the upper housing 64 (see FIG. 13) and is connected to
an operator controlled actuating lever (not shown) which allows the
operator to rotate the cam rod 184 to cause disengagement of the
hydrostatic unit 21. Upon a 90.degree. rotation of cam rod 184, the cam
portion 186 engages the plate 180 so as to cause radial movement of the
plate 180 and fingers 115 and 117 towards pintle 72 to unseat the ball
valves 110 and 111. Counter-rotation of the cam rod 184 by 90.degree. thus
rotates the cam portion 186 to urge plate 180 and fingers 115 and 117 away
from ball valves 110 and 111 whereupon fluid pressure within pintle
passageways 106 and 107 force the ball valves 110 and 111 into a closed
position so that the hydrostatic unit 21 may again be operable.
In operation, when the operator of the vehicle in which the hydrostatic
transaxle 20 is installed wants to manually push the vehicle, the
hydrostatic unit 21 must be disengaged so that motion transmitted through
the axles 46 and 47 does not cause the motor 26 to pump fluid to the pump
24 thereby transferring motion back to the input drive shaft 60 and the
external energy source such as an internal combustion engine (not shown),
as it would be difficult to act against the resistance of the hydrostatic
unit 21 and the input shaft 60. Releasing the oil within the pintle
passageways 106 and 107 of the pintle 72 fluidly disconnects the motor 26
from the pump 24 as the oil pumped from the motor 26 thereby exits from
the discharge ports 115 and 117, into the hydrochamber, rather than into
pump 24. The release of oil pressure within pintle 72 is accomplished by
unseating the ball valves 110 and 111, being urged closed against threaded
plug 112 and 113 defining discharge ports 115 and 117, through rotation of
cam rod 184. Upon reseating of ball valves 110 and 111 when fingers 182
and 183 retract, the pump 24 and motor 26 are once again in fluid
communication.
Referring to FIG. 2, particulates in the hydrostatic fluid circulating
through the hydro unit are captured by cast-in protrusions or baffles 188
located in the lower transaxle housing 22 which serve as particulate
traps, the impinging particulates settling to the bottom of the troughs
190 defined by the protrusions 188. Thus, any particulates that might be
suspended in the oil are settled out upon circulation. This keeps the oil
within the transaxle 20 relatively free from particulates that would
otherwise degrade the performance and damage the various sensitive moving
parts of the transaxle 20, and eliminates the need for a filter. In
addition, a magnet 192 can be attached to the interior of lower housing 22
to attract and capture large ferrous materials that would not otherwise be
captured by protrusions 188.
While this invention has been described as having a preferred design, the
present invention can be further modified within the spirit and scope of
this disclosure. This application is therefore intended to cover any
variations, uses, or adaptations of the invention using its general
principles. Further, this application is intended to cover such departures
from the present disclosure as come within known or customary practice in
the art to which this invention pertains and which fall within the limits
of the appended claims.
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