Note: Descriptions are shown in the official language in which they were submitted.
CA 02225564 1997-12-22
Frederick P. Eberle
TRANSAXLE WITH HYDROSTATIC TRANSMISSION
FIELD OF THE INVENTION
The present invention relates to transaxles of the type having an input shaft
for receiving rotary power from an energy source, e.g., an internal combustion
engine, and an output shaft for transferring rotary mechanical motion to
objects,
e.g., wheels, to be rotatably driven. More particularly, the present invention
relates
to variable speed transaxles including a hydromechanical transmission for
operationally coupling the input shaft to the output shaft.
BACKGROUND OF THE INVENTION
Small vehicles, such as lawn mowers, lawn and garden tractors, snow
throwers, and the like, include an energy source, such as an internal
combustion
engine, which is used to provide power for rotatably driving an axle which is
coupled to wheels which are to be rotatably driven. Most typically, the energy
source operates at a single, rotary mechanical speed. Yet, for practical
reasons, the
axle needs to be able to be rotatably driven at a variety of forward, reverse,
and/or
neutral speeds. Accordingly, such vehicles may incorporate a transaxle which
is
used to convert the single speed, rotary mechanical motion of the energy
source into
a variety of output speeds.
Generally, a transaxle comprises a transaxle input shaft which is
operationally coupled to the energy source, a transaxle output shaft, e.g., an
axle,
which is operationally coupled to the items, e.g., wheels, which are to be
rotatably
driven, and transaxle componentry which operationally couples the transaxle
input
shaft to the transaxle output shaft. It is the transaxle componentry which
converts
the single speed, rotary mechanical motion received from the energy source
into a
variety of output speeds for rotatably driving the output shaft.
Variable speed transaxles have been developed which control output speed
through a single lever. In a typical mode of operation, the lever is moved
forward
to move the vehicle in the forward direction or pulled backward to move the
vehicle
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in the reverse direction. The farther forward or backward the lever is
displaced, the
faster the vehicle travels in the corresponding direction.
One form of variable speed transaxle now in use includes a hydrostatic
transmission of the type including a hydrostatic pump fluidly coupled to a
hydrostatic motor. The hydrostatic pump converts rotary mechanical motion of
an
input shaft into controllably variable fluid motion. The motor converts such
fluid
motion back into variable rotary mechanical motion. The rotary mechanical
output
of the motor is then transferred to the axle by componentry such as a
mechanical
gear train. The rotational speed outputted by the motor and transmitted to the
axle
depends, in substantial part, upon the flow rate of the fluid being pumped.
Radial piston pumps and radial piston motors have both been widely used in
hydrostatic transmissions of previously known transaxles. A radial piston pump
and
motor each generally include a rotary cylinder block including radially
disposed
cylinder bores. The bores house pistons which are capable of reciprocating
motion
within the bores. The rotary cylinder block is rotatably mounted inside a
track ring.
The heads of the pistons are coupled to the track ring by slippers which
travel
around the inside of the track ring as the rotary cylinder block rotates. The
track
ring is disposed eccentrically around the rotary cylinder block so that the
pistons are
pulled out of the bores on one side of the rotation cycle (i.e., the suction
part of the
cycle) and are driven into the bores on the other side of the rotation cycle
(i.e., the
discharge part of the cycle).
In operation, the rotary cylinder block of the pump is rotatably driven by an
input shaft, thus causing the pump pistons to reciprocate in the pump cylinder
bores.
Such reciprocation creates a pumping action for transporting hydrostatic fluid
to and
from the motor which is fluidly coupled to the pump. The transport of the
fluid
creates a pressurized fluid flow that drives the motor pistons. This, in turn,
causes
the motor rotary cylinder block to rotate within the motor track ring.
Rotation of
the motor rotary cylinder block rotatably drives a motor output shaft. The
track
ring of the pump is pivotable, which allows the operator to vary the
eccentricity of
the track ring relative to the pump rotary cylinder block. Generally,
increased
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eccentricity increases the length of the pump piston stroke, and a longer
piston
stroke corresponds to higher output speeds. Thus, by pivoting the track ring,
the
operator controls output speed. The pump track ring can also be pivoted in two
directions away from a neutral setting. One direction corresponds to a forward
mode of operation, and the other corresponds to a reverse mode of operation.
Whereas the pump track ring is pivotable, allowing the operator to control
output
speed and direction, the motor track ring is most typically eccentrically
fixed
relative to the motor rotor cylinder block. U.S. Patent No. 5,182,966 (von
Kaler),
as one example, describes a particularly effective and reliable hydrostatic
transmission for a transaxle in which the transmission includes a radial
piston pump
fluidly coupled to a radial piston motor.
A radial piston pump is one of the most efficient and effective ways for
converting rotary mechanical motion into fluid motion. However, a radial
piston
motor is somewhat less efficient at converting fluid motion back into rotary
mechanical motion. Accordingly, it would be desirable to improve the
efficiency of
the motor component of a hydrostatic transmission of the type including a
radial
piston pump so that the overall efficiency of the transmission could be
improved.
In previously known radial piston pump and motor assemblies, the piston
heads are typically coupled to the slippers by a direct mechanical linkage
such as
rivets, pins, and the like. Although reliable as far as the operator is
concerned, such
linkage tends to increase the complexity, parts count, expense, and/or time
required
for transmission assembly. It would be desirable, therefore, to simplify the
manner
in which the piston heads are coupled to the slippers.
Radial piston pump and motor assemblies tend to be subject to vibration
forces which arise due to the substantial pressure differences between the
suction
and discharge sides of the rotary cylinder block. For example, the discharge
side of
a rotary cylinder block of a radial piston pump may be typically characterized
by a
discharge pressure on the order of 1500 psi, whereas the suction side of the
rotary
cylinder block may be characterized by a suction pressure on the order of -5
psi.
When the rotary cylinder block rotates at ordinary rotational speeds, e.g.,
1500 to
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4000 rpm, such pressure differences tends to set up vibrations that are not
only noisy,
but may also be sever enough such that the vibrations could even damage the
transmission if not controlled properly. Previously, transaxles have employed
mechanical means, e.g., clamps, to help hold a radial piston assembly in
proper
position and thereby attempt to overcome vibrations by physical clamping
force.
Such techniques, however, do not eliminate the magnitude of the vibration
forces,
thus requiring the mechanical means to absorb and control the full magnitude
of such
forces. Accordingly, there is a need to provide such transmissions with a way
to
reduce the magnitude of the vibration forces in order to reduce, and even
eliminate,
the demands placed upon the mechanical means used to absorb and control such
forces.
SUMMARY OF THE INVENTION
According to one aspect, the present invention provides a hydrostatic
1 S transmission, comprising:
a reciprocating piston pump including a rotatable cylinder having a plurality
of
pistons therein, said cylinder rotatable about an axis of rotation;
a gear motor having first and second rotatable spur gears in intermeshing
engagement, wherein at least one of said gears is rotatable about an axis of
rotation
that is oriented 900 relative to the pump axis of rotation;
a fluid pathway extending between said motor and pump such that said motor
is fluidly coupled to said pump, said fluid pathway extending between said
gears such
that said gears are rotated by the fluid; and
a motor output shaft fixedly coupled to one of said gears such that the motor
output shaft has an axis of rotation that coincides with the axis of rotation
of said one
gear, whereby rotation of said one gear causes said motor output shaft to
rotate.
According to a further aspect, the present invention provides a variable speed
transaxle, comprising:
a rotatable input shaft for receiving rotary power from an engine;
a hydrostatic transmission comprising:
a reciprocating piston pump including a rotatable cylinder having a plurality
of
pistons therein, said cylinder rotatable about an axis of rotation;
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a gear motor having first and second rotatable spur gears in intermeshing
engagement, wherein said gears are rotatable about parallel axes of rotation
that are
oriented 90° relative to the pump axis of rotation;
a fluid pathway extending between said motor and pump such that said motor
5 is fluidly coupled to said pump, said fluid pathway extending between said
gears such
that said gears are rotated by the fluid;
a motor output shaft fixed to one of said gears such that the motor output
shaft
has an axis of rotation that coincides with the axis of rotation of said one
gear,
whereby rotation of said one gear causes said motor output shaft to rotate;
and
a differential mechanically coupled to said motor output shaft.
According to another aspect, the present invention a hydrostatically dampened
transmission assembly, comprising:
(a) a radial piston pump including a rotary cylinder block comprising a
plurality
of radially disposed cylinder bores, wherein the rotary cylinder block is
capable of
rotation about an axis, wherein the rotary cylinder block is provided with
first and
second axial faces, wherein a plurality of said cylinder bores includes first
and second
fluid ports, and wherein each of the first fluid ports of said plurality of
cylinder bores
is in fluid communication with the first axial face of the rotary cylinder
block and
each of the second fluid ports of said plurality of cylinder bores is in fluid
communication with the second axial face of the rotary cylinder block;
(b) a first valve plate disposed against the first axial face of the rotary
cylinder
block, wherein said valve plate comprises intake and discharge ports, said
first fluid
ports of said plurality of cylinder bores successively communicating with the
suction
and discharge ports during rotation of the rotary cylinder block;
(c) a second valve plate disposed against the second axial face of the rotary
cylinder block, wherein said valve plate comprises at least one port, said
second fluid
ports of said plurality of cylinder bores successively communicating with said
at least
one port during rotation of the rotary cylinder block;
(d) a motor for converting fluid motion into rotary mechanical motion, said
motor
operationally engaging an output shaft;
(e) a hydrostatic fluid pathway extending between the radial piston pump and
the
motor for fluidly coupling the radial piston pump to the motor; and
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(f) a hydrostatic shock absorber in fluid communication with said at least one
port
of the second valve plate, said shock absorber adapted to absorb fluid
pressure pulses
transmitted through the second fluid ports of the cylinder bores and the port
of the
second valve plate by the radial piston pump as the rotary cylinder block of
the radial
piston pump rotates.
According to still yet a further aspect of the present invention there is
provided
a hydrostatically dampened assembly, comprising:
(a) a radial piston pump comprising a rotary cylinder block provided with
first
and second axial faces, wherein the rotary cylinder block comprises a
plurality of
radially disposed cylinder bores including first and second fluid ports,
wherein the
first ports of the cylinder bores are in fluid communication with the first
axial face of
the rotary cylinder block and the second ports of the cylinder bores are in
fluid
communication with the second axial face of the rotary cylinder block, and
(b) a hydrostatic shock absorber comprising at least one hydraulically
displaceable surface disposed in fluid communication with said second fluid
ports
wherein said hydraulically displaceable surface is biased in a direction
opposing said
hydraulic displacement.
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7
BRIEF DESCRIPTION OF THE DRAWINGS:
The above-mentioned and other features and advantages of this invention, and
the manner of attaining them, will become more apparent and the invention will
be
better understood by reference to the following description of an embodiment
of the
invention taken in conjunction with the accompanying drawings, wherein:
Fig. 1 is a front sectional view of a transaxle embodiment configures in
accordance with the principles of the present invention;
Fig. 2 is a side view of the transaxle of Fig. 1 with some parts shown in
section;
Fig. 3 is a plan view of the radial piston pump assembly used in the transaxle
embodiment of Fig. 1;
Fig. 4 is a sectional view of the radial piston pump assembly of Fig. 3;
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g
Fig. 5 is a side view of the radial piston pump assembly of Fig. 3 with some
parts shown in section;
Fig. 6 is a plan view of a valve plate which is disposed between the radial
piston pump assembly and motor housing of the transaxle shown in Fig. 1;
Fig. 7 is a side view of a piston used in the radial piston pump assembly of
Fig. 3;
Fig. 8 is a sectional view of a slipper used in the radial piston pump
assembly of Fig. 3;
Fig. 9 is a side sectional view of the slipper used in the radial piston pump
assembly of Fig. 3;
Fig. 10 is a side view showing a piston of Fig. 7 seated against the slipper
of
Figs. 8 and 9, wherein the slipper is shown in cross section;
Fig. 11 is a plan sectional view of the gear motor and corresponding motor
housing used in the transaxle embodiment of Fig. 1;
Fig. 12 is a side view of the gear motor and housing of Fig. 11;
Fig. 13 is a side sectional view of the gear motor and motor housing of
Fig. 11;
Fig. 14 is an end view showing the valve plate of Fig. 6 fastened to the
motor housing of Fig. 11;
Fig. 15 is an end view partially in section of the motor housing of Fig. 11
showing check valves used to provide makeup oil to the hydrostatic fluid
pathways
provided in the motor housing;
Fig. 16 is a plan view showing the valve plate disposed between the radial
piston pump assembly and shock absorber of the transaxle embodiment of Fig. 1;
Fig. 17 is a side sectional view of the shock absorber incorporated into the
transaxle embodiment of Fig. 1;
Fig. 18 is an alternative embodiment of the present invention in which a gear
motor is fluidly coupled to a radial piston pump assembly such that the axis
of
rotation of the radial piston pump assembly and the gear motor are
substantially
parallel;
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Fig. 19 is a side sectional view showing spur gears of the gear motor of
Fig. 18; and
Fig. 20 is a side sectional view of the gear motor of Fig. 19 showing check
valves which are used to provide makeup oil to the system.
Corresponding reference characters indicate corresponding parts throughout
the several views. The exempliflcations set out herein illustrate preferred
embodiments of the invention and such exemplifications are not to be construed
as
limiting the scope of the invention in any manner.
DETAIL D DESCRIPTION OF THE INVENTION
The various aspects of the present invention will now be described with
reference to the particular variable speed transaxle embodiments shown in
Figs.
1-20. However, the embodiments disclosed below are not intended to be
exhaustive
or to limit the invention to the precise forms disclosed in the following
detailed
description.
Referring to Figs.l-17, there is shown one embodiment of a variable speed
transaxle, generally designated 10, configured in accordance with the
principles of
the present invention. Transaxle 10 is particularly well suited 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 transaxle 10 is installed.
With particular reference to Figs. 1 and 2, the components of transaxle 10
are encased within a single housing 12 filled with oil. Advantageously, the
same oil
that is used for lubricating the moving components of transaxle 10 is also
used for
hydrostatic operation. Housing 12 includes input shaft housing portion 14,
motor
housing portion 16, drive train housing portion 18, and track ring control
housing
portion 20. Although housing 12 functionally includes these four housing
portions,
housing 12 need not be manufactured from four different pieces corresponding
to
these four portions, but rather may be formed from more or less parts which
may or
may not correspond to these four housing portions, as desired, in accordance
with
conventional practices in the art. For example, motor housing portion 16 can
be
fabricated from pieces 22, 24, and 26 in order to facilitate assembly of the
motor
CA 02225564 1997-12-22
componentry, whereas input shaft housing portion 14, drive train housing
portion
18, and track ring control housing portion 20 may be collectively formed from
two
pieces which are joined along a planar or nonplanar parting line which may be
oriented either horizontally or vertically, as desired. Transaxle 10 includes
5 rotatable input shaft 28 for receiving rotational power from the energy
source,
which in most typical applications is an internal combustion engine. Input
shaft 28
has a top end 30 which is rotatably journalled upon needle bearings 32
provided in
input shaft housing portion 14. Input shaft 28 also includes a bottom end 34
which
is rotatably journalled upon needle bearings 36 provided in motor housing
portion
10 16. Oil seals 38 provide a fluid tight seal between input shaft 28 and the
portion of
input shaft housing portion 14 at which input shaft 28 extends from housing
12.
Rotational power from the energy source is transmitted to input shaft 28 using
a
drive belt (not shown) connected to pulley 40 which is secured to the top end
30 of
input shaft 28. Top end 30 of input shaft 28 is threaded to receive threaded
fasteners 44 for holding pulley 40 and fan assembly 42 on input shaft 28.
Pulley 40
and fan assembly 42 cooperate to provide an external cooling system for
transaxle
10. Fan assembly 42 and pulley 40 are fixedly mounted to input shaft such that
rotational power transmitted to input shaft 28 by pulley 40 causes input shaft
28 to
rotate about axis of rotation 46.
Referring now to Figs. 1-10, radial piston pump assembly 48 is fixedly
splined to the lower portion of input shaft 28 so that rotation of input shaft
28 is
imparted to radial piston pump assembly 48. Thus rotation of input shaft 28
causes
radial piston pump assembly 48 to rotate about axis of rotation 46.
Radial piston pump assembly 48 includes rotary cylinder block 50 which
includes a plurality of radially disposed cylinder bores 52. As seen best in
Fig. 3,
rotary cylinder block 50 includes six cylinder bores 52. However, a rotary
cylinder
block including more or less cylinder bores also could be used, as desired. In
the
practice of the present invention, cylinder bores 52 are advantageously
provided
with dual ports. One set of the ports allows radial piston pump assembly 48 to
be
hydrostatically coupled to a motor as will be described in more detail below.
The
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other set of ports advantageously allows radial piston pump assembly 48 to be
advantageously coupled to a hydrostatic damping means which is used to
significantly reduce the vibration and noise which has characterized some
radial
piston pump assemblies of the prior art. Thus, as seen best in Fig. 4,
cylinder bores
S 52 are provided with first ports 54 which are in fluid communication with
first axial
face 56 of rotary cylinder block 50. Cylinder bores 52 are also provided with
second ports 58 which are in fluid communication with second axial face 60 of
rotary cylinder block 50. Fig. 4 also illustrates how rotary cylinder block 50
includes splined central aperture 62 for receiving input shaft 28.
As seen best in Figs. 3, 4, 7, and 10, a plurality of pistons 64 are disposed
in
cylinder bores 52. Each of pistons 64 is capable of reciprocating movement in
a
corresponding bore 52. Pistons 64 each include a base end 66 interconnected to
head 68 by neck 70. Neck 70 has a reduced diameter relative to head 68 such
that
head 68 is provided with an underside surface 72. Piston heads 68 also include
a
top convex surface 74. As will be described below, the convex characteristics
of
top surfaces 74 advantageously facilitates the unique manner in which pistons
64 of
the present invention are coupled to corresponding slipper 86 in particularly
preferred embodiments of the invention.
Referring now primarily to Figs. 1-5, radial piston pump assembly 48
includes eccentrically pivotable track ring surrounding and spaced apart from
rotary
cylinder block 50. Track ring 76 includes an inner face 78 disposed towards
the
rotary cylinder block 50, outer face 80 disposed away from rotary cylinder
block
50, a first axial face 82 and a second axial face 84. Track ring 76 is
eccentrically
pivotable relative to rotary cylinder block 50 by means of structure including
pivoting extension member 88 which extends from one side of track ring 76 to
be
received by a correspondingly shaped aperture 90 provided in housing portion
92.
The outer surface of pivoting extension member 88 is convexly shaped and
aperture
90 is concavely shaped such that pivoting extension member 88 and aperture 90,
in
effect, form a ball and socket joint to thereby provide an axis 94 about which
track
ring 76 is pivotable.
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The pivotable connection between track ring 76 and housing portion 92
allows track ring 76 to eccentrically pivot and thereby vary the piston stroke
of
pistons 64. Variation of the piston stroke, in turn, changes the volumetric
displacement of the radial piston pump assembly 48. Generally, a greater
piston
stroke, which corresponds to greater volumetric displacement, provides a
higher
output speed. Thus, track ring 76 can be pivoted in one direction to provide
variable output speeds in a forward direction and can be pivoted in the other
direction to provide variable speeds in the reverse direction. Track ring 76
can also
be pivoted into a position in which track ring 76 is substantially concentric
about
rotary cylinder block 50. When track ring 76 and rotary cylinder block 50 are
substantially concentric, there is substantially no piston stroke as rotary
cylinder
block 50 rotates. In such a setting, transaxle 10 is in neutral. Pivoting
track ring 76
in the direction indicated by arrows 96 and 98 corresponds to variable output
speeds
in the forward and reverse directions.
In order to allow an operator to pivot track ring 76 and thereby control the
output speed and direction, is provided with a bifurcated extension 100 which
includes stem 104 and arms 106 which engage control mechanism 102. In the
embodiment shown in the figures, stem 104 is press fit into track ring 76.
Stem
104, for example, can be joined to track ring 76 in any convenient manner and
could even be formed integrally as desired.
Control mechanism 102 includes a U-shaped body 108 having arms 110 at
one end and a control rod 112 at the other end. Arms 110 of control mechanism
102 are oriented transversely to arms 106 of bifurcated extension 100. Pin 114
extends between arms 110 and is rotatably received in aperture 116 of lug
element
118. Top end 120 of control rod 112 extends outside housing 12 as seen best in
Fig. 2. Top end 120 of control rod 112 includes an aperture 122 for receiving
a
lever (not shown) by which the operator can rotate control rod 112 about axis
124
and thereby cause track ring 76 to pivot about axis 94.
Referring now primarily to Figs. 1-4 and 7-10, each piston 64 is provided
with a corresponding slipper 126. Slippers 126 are coupled to the inner face
78 of
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track ring 76 for travel around a circumferential path corresponding to the
inner face
78 of track ring 76. In the embodiment shown in the Figures, slippers 126 are
coupled directly to inner face 78, but could be coupled to inner face 78
indirectly by
intervening coupling parts, if desired. Use of an indirect coupling is less
desirable,
however, because indirect coupling would involve more parts which would tend
to
increase the complexity, expense, andlor time for assembly of transaxle 10.
Each
slipper 126 includes an inner surface 128 disposed toward rotary cylinder
block 50.
The inner surface 128 of each slipper 126 is configured to receive the head 68
of the
corresponding piston 64. In particularly preferred embodiments of the present
invention in which each piston head 68 includes a top convex surface 74 as
depicted
in the drawings, inner surface 128 of slippers 126 includes a surface portion
130
which is concave to receive the corresponding convex head 68 of the
corresponding
piston 64. Each slipper 126 is also provided with a through aperture 132 which
facilitates lubrication of the interface between concave surface portion 130
and the
corresponding convex piston head 68.
In preferred embodiments of the present invention, pistons 64 are not
directly connected to slippers 126 by conventional mechanical means such as
rivets,
pins, or the like. Instead, in the practice of the present invention, convex
heads 68
of pistons 64 are retained against slippers 126 by novel piston guide
generally
designated as 134. Thus, in preferred embodiments of the invention, there is
no
direct mechanical linkage between piston heads 68 and slippers 126.
As shown best in Figs. 3 and 4, preferred embodiments of the piston guide
of the present invention include a first annular shaped ring 136 and a second
annular
shaped ring 137. First annular shaped ring 136 includes base 139. A portion of
base 139 engages first axial face 56 of rotary cylinder block 50 and the
second
portion of base 139 extends radially inward from track ring 76 in a direction
substantially toward rotary cylinder block 50. A flange 142 extends axially
inward
from base 139 such that flange 142 is spaced apart from track 76 and such that
flange 142 engages the underside surfaces 72 of piston heads 68 to retain
pistons 64
loosely against or in close proximity to slippers 126. Centrifugal force
presses the
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pistons radially outwardly into engagement with the slippers. Annular shaped
ring
136 further includes a second flange 145 which extends axially inward from
base
139 such that the second flange 145 is disposed proximal to the outer face 80
of
track ring 76. The second annular shaped ring 137 includes a corresponding
base
140 and flanges 143 and 146. Annular shaped rings 136 and 137 can be adapted
for
a snap-fit or press-fit engagement with track ring 76, or could be attached to
track
ring 76 by other suitable fastening techniques such as screws, rivets, welds,
combinations thereof, or the like, as desired.
The combination of convex piston heads 68 and concave slipper surfaces 130
is uniquely well adapted to work in cooperation with piston guide 134.
Advantageously, when rotary cylinder block 50 rotates, centrifugal force
acting
upon convex piston heads 68 tends to keep piston heads 68 centered and in
proper
position against the concave surface portions 130 of slippers 126 even without
any
direct mechanical connection linking piston heads 68 to slippers 126. In
contrast, if
piston heads 68 were to be concave and slippers 126 were to be convex,
centrifugal
forces acting upon piston heads 68 would tend to throw piston heads 68 off of
slippers 126 during rotation in the absence of mechanical linkage between
piston
heads 68 and slippers 126. As an additional advantage, the convex/concave
configuration of piston heads 68 and slippers 126 acts as a ball and socket
joint
allowing heads 68 and slippers 126 to pivot relative to each other during
rotation of
rotary cylinder block 50.
Referring now to Figs. 1, 2, 5, 6, and 14, valve plate 148 is disposed
between motor housing portion 16 and first axial face 56 of rotary cylinder
block
50. In the particular setting of track ring 76 in which track ring 76 has been
pivoted
in the direction of arrow 96 (i.e., transaxle 10 is in a forward mode of
operation),
valve plate 148 includes arcuate shaped suction port 152 and arcuate shaped
discharge port 154. Of course, when transaxle 10 is reversed by pivoting track
ring
76 in the direction of arrow 98, suction port 152 becomes the discharge port
and
discharge port 154 would become the suction port. First ports 54 of rotary
cylinder
block 50 successively communicate with suction and discharge port 152 and 154
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during rotation of rotary cylinder block 50. Thus, during rotation of rotary
cylinder
block 50, hydrostatic fluid is discharged through first ports 54 and through
discharge port 154 of valve plate 148, and hydrostatic fluid is drawn into
first ports
54 of rotary cylinder block 50 through suction port 152 of valve plate 148. As
seen
5 best in Fig. 14, valve plate 148 is secured to motor housing portion 16 by
fasteners
156.
Referring now to Figs. 1, 2, and 11-15, motor housing portion 16 houses
gear motor 158 which is hydrostatically coupled to radial piston pump assembly
48.
Gear motor 158 includes spur gear 160 which is coupled to spur gear shaft 162.
10 Spur gear shaft 162 is rotatably journalled in motor housing portion 16
upon
bearings 164. As seen best in Fig. 11, spur gear 160 and spur gear shaft 162
essentially function as an idler mechanism. Optionally, however, spur gear
shaft
162 can be extended through motor housing portion 16 to act as an additional
power
take off. Gear motor 158 also includes spur gear 166 which is fixedly coupled
to
15 spur gear shaft 168. Spur gear shaft 168 is rotatably journalled in motor
housing
portion 16 upon bearings 170. Spur gear shaft 168 extends outside motor
housing
portion 16 through side face 172 for rotational power take off. Thus, spur
gear
shaft 168 functions as a motor output shaft for power take off from gear motor
158.
Spur gear shaft 168 has an axis of rotation 174 which is substantially
perpendicular
to the axis of rotation 46 of input shaft 28 and rotary cylinder block 50.
Advantageously, this perpendicular orientation allows input shaft 28 to be
oriented
vertically for receiving power from the energy source in the most convenient
manner, while spur gear shaft 168 is oriented horizontally for power transfer
to
objects, such as wheels, which are to be rotatably driven by transaxle 10. As
Figs. 1 and 11 illustrate, either spur gear shaft 162 or 168 of the gear motor
can be
used as the power output shaft and a variety of drive connections are
possible.
Advantageously, gear motor 158 is highly efficient at converting hydrostatic
fluid motion into rotary mechanical motion. Thus, in preferred embodiments of
the
present invention comprising a radial piston pump and a gear motor such as
gear
motor 158, the resultant transaxle includes a combination of a highly
efficient pump
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with a highly efficient motor, thus providing a pump and motor combination
which
has overall enhanced efficiency relative to pump and motor combinations which
have been previously known.
Referring now to Figs. 1, 6, and 11-15, transaxle 10 includes a hydrostatic
fluid pathway 180 coupling radial piston pump assembly 48 to gear motor 158,
which allows gear motor 158 to be rotatably driven as hydrostatic fluid is
transported along hydrostatic fluid pathway 180 by pump 48. Hydrostatic fluid
pathway 180 includes discharge port 182 providing fluid communication between
arcuate shaped discharge port 154 of valve plate 148 and discharge fluid
passageway
184. Discharge fluid passageway 184 extends from discharge port 182 to
discharge
region 186 disposed above intermeshing spur gears 160 and 166. Discharge fluid
passageway 184 further includes check valve 188 through which make up
hydrostatic fluid is provided to the system in a conventional manner.
Similarly,
hydrostatic fluid pathway 180 further includes suction port 190 providing
fluid
communication between arcuate shaped suction port 152 of valve plate 148 and
suction fluid passageway 192. Suction fluid passageway 192 extends from
suction
port 190 to intake region 196 disposed below intermeshing spur gears 160 and
166.
Suction fluid passageway 192 also includes check valve 198 for providing make
up
hydrostatic fluid to the system.
In embodiments of the present invention in which rotary mechanical output
motion of transaxle 10 is not intended to be parallel to the axis of rotation
of input
shaft, it is preferred that the hydrostatic fluid passageways 184 and 192 are
sufficiently non-linear such that a hydrostatic fluid transported along such
passageways is capable of rotatably driving spur gears 160 and 166 on an axis
of
rotation which is substantially non-parallel to axis of rotation 46 of rotary
cylinder
block 50. For example, as shown in the Figures, suction fluid passageway 192
includes a first portion 200, a second portion 202, as well as intake region
196.
First portion 200 of fluid passageway 192 extends away from valve plate 148 in
a
direction substantially parallel to axis of rotation 46 of radial piston pump
48.
Second portion 202 of fluid passageway 192 extends away from first portion 200
CA 02225564 1997-12-22
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and is oriented at 90° to first portion 200, and thus accomplishes a
90° turn of the
hydrostatic fluid. Intake region 196, in turn, extends 90° away from
second portion
202 in a direction which is substantially perpendicular to the plane defined
by first
portion 200 and second portion 202. Such non-linearity of suction fluid
passageway
192 allows hydrostatic fluid to be delivered to intermeshing gears 160 and 166
in a
manner such that gears 160 and 166 are rotatably driven on an axis which is
substantially perpendicular to that of input shaft 28. Although not depicted
in the
drawings, discharge fluid passageway 184 includes a corresponding first
portion,
second portion, and discharge regions to accomplish the same kind of change of
direction as the hydrostatic fluid is transported through discharge fluid
passageway
184. As also seen in Figs. 1 and 11, motor housing portion 16 further includes
lubrication passages 204 for transporting lubricating fluid to the various
moving
components of gear motor 158.
Spur gear shaft 168, which functions as a motor output shaft, may be
drivingly connected to output shaft 206 by a suitable driving mechanism in
accordance with conventional practices. A representative example of a
preferred
mechanism is shown in Fig. 1. There, a driving mechanism, generally designated
as 208, includes a first countershaft 210, a second countershaft 212,
differential
214, a first reduction gearing set 216, and a second reduction gearing set
218. First
countershaft 210 has first end 220 operatively coupled to spur gear shaft 168
by
linkage 222, 224, 226, 228, and 230. Second end 232 of first countershaft 210
extends from housing 12 and is rotatably supported upon needle bearings 234.
Oil
seal 236 provides a fluid tight seal between first countershaft 210 and
housing 12.
Second end 232 of first countershaft 210 is splined to facilitate connection
to a
device such as a braking assembly (not shown) or other items to be rotatably
driven
by first countershaft 210. First countershaft 210 has an axis of rotation 238
which
is substantially perpendicular to axis of rotation 46.
First reduction gearing set 216 is provided to drivingly connect first
countershaft 210 to second countershaft 212. First reduction gear set 216
includes
pinion gear 260 fixedly splined to first countershaft 210. Pinion gear 246
meshingly
CA 02225564 1997-12-22
1g
engages large diameter portion 248 of transfer gear 250, which is mounted for
free
wheeling rotation upon second countershaft 212. Small diameter portion 252 of
transfer gear 250 meshingly engages large diameter portion 254 of transfer
gear 256
which is mounted for free wheeling rotation upon first countershaft 210. Small
diameter portion 258 of transfer gear 256 rotatably engages pinion gear 260,
which
is fixedly splined to second counter shaft 212. Thus, rotary motion of first
countershaft 210 is transferred to second countershaft 212 through first
reduction
gearing set 216.
Rotary motion of second countershaft 212 is transferred to differential 214
through second reduction gearing set 218. In the embodiment shown in the
drawings, second reduction gearing set 218 is in the form of a pinion gear
which
meshingly engages differential 214. Differential 214 includes ring gear 264,
transverse shaft 266, and bevel gears 268, 270, 272, and 274. Differential 214
transfers rotary mechanical motion from pinion gear 218 to output shaft 206,
which
includes right axle shaft 276 and left axle shaft 278.
Preferred embodiments of the present invention are provided with a
hydrostatic shock absorber which is adapted to absorb fluid pressure pulses
generated by the radial piston pump 48 as rotary cylinder block 50 of radial
piston
pump 48 rotates. Referring to Figs. 2, 16, and 17, a preferred embodiment of
the
shock absorber, generally designated as 280, is disposed in input shaft
housing
portion 14 and includes cylinder bores 282. Cylinder bores 282 each have an
opening on face 284 of input shaft housing portion 14 such that cylinder bores
282
are in fluid communication with second ports 48 disposed between cylinder
bores 53
and second axial face 60 of rotary cylinder block 50. Each cylinder bore 282
is
provided with a piston 286 which is capable of reciprocating movement in a
corresponding cylinder bore 282 in an outward direction toward the opening of
cylinder bore 282 and in an inward direction away from the opening of cylinder
bore 282. Each of pistons 286 is biased toward the opening of the cylinder
bores
282 by a spring 288. To facilitate fluid communication between cylinder bores
282
and second ports 58, second valve plate 290 is disposed between second axial
face
CA 02225564 1997-12-22
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60 of rotary cylinder block 50 and shock absorber 280. Second valve plate 290
includes a pair of arcuate shaped ports 292 and 294. Ports 292 and 294 are in
successive fluid communication with second ports 58 of rotary cylinder block
50
during rotation of rotary cylinder block 50. As seen best in Fig. 16, each
port 292
and 294 is also in constant fluid communication with respective pairs of
cylinder
bores 282. Thus, an increase in pressure transmitted to the ports 292 and 294
of
second valve plate 290 may be absorbed by one or more of pistons 286 as such
pressure increase causes one or more of pistons 286 to move inward into its
corresponding cylinder bore 282 in response to the pressure increase. In
effect,
each piston 286 provides a hydraulically displaceable surface disposed in
fluid
communication with second ports 58 for absorbing pressure pulses generated by
the
rotating cylinder block 50.
An alternative embodiment of the present invention is shown in Figs. 18-20.
This embodiment is substantially identical to the embodiment of Figs. 1-17
except
that in the embodiment of Figs. 18-20, motor 158 is aligned such that the axis
of
rotation of intermeshing spur gears 160 and 166 is substantially parallel to
the axis
of rotation of the radial piston pump assembly 48. To accommodate such a
difference, discharge fluid passageway 184 and suction fluid passageway 192
extend
substantially linearly away from radial piston pump assembly to corresponding
discharge and intake regions disposed above and below gears 160 and 166. Other
than this difference, the transaxle embodiment of Figs. 18-20 is substantially
the
same as transaxle embodiment 10 of Figs. 1-17. Corresponding parts of the
transaxle embodiment of Figs. 18-20 have therefore been identified by an
identical
numbering scheme.
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
CA 02225564 1997-12-22
20
or customary practice in the art to which this invention pertains and which
fall
within the limits of the appended claims.
