Note: Descriptions are shown in the official language in which they were submitted.
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S P E C I F I C A T I 0 N
The present invention relates to a hydraulic
control for varying the contro:l pressure to a variable control
valve used to port fluid to the servos of a variable displacement
pump or motor.
It is common in designing controls fox hydrostatic trans-
missions to design a distinct control for each desired function.
For example, a pressure override (P.O.R.) control is designed to
monitor the high pressure of a transmission to protect the trans-
mission from extended excessive overloads. P.O.R. controls arewell known in the art and will be disclosed, in part, in the
present application. Further, an anti-stall control is used to
destroke the swashplate of a pump in response to loading of the
prime mover of the pump. Anti-stall controls generally make use
of governors (see U. 5. Letters Patent 2,516,662 and ?,~76,685)
to directly control movement of a valve spool and thereby control
fluid pressure. Another type of control is a phasing control
which is used to first increase the displacement of the swashplate
~of a pump in a hydrostatic transmission to its maximum and then
~ decrease the displacement o the swashplate motor to a minimum
;during an increase in speed of the transmission and to reverse
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~such prooess during a decrease in speed. Phasing controls gener-
F ally make use of cams (see U. S. Letters Patent 2,516,662). Yet
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F a further control is an input torque limiter (I.~.L.) control
~ ¦1 whioh~matches the torque of a hydrostatic transmission to that of
the prime mover. I.T.L. controls generally make use o cams to
reset the~compensating 0verride pressure for each swashplate
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position to maintaln a cons-tan-t value of system pressure
times pump displacement. Other known I.T.L. controls are
hydraulic wherein a pressure drop across a compensating
or override spool is maintainecl proportional to the pump
displacement. This is generally accomplished by a variable
orifice. Further, other known I.T.L. controls are elec-
rical. In the electrical I.T.L. controls the displacement
of the pump and the system pressure are each measured and
then multiplied to produce a signal which is then used to
control the displacement of the pump. All of the electrical
I.T.L. controls which applicant is aware of make use of a
pressure transducer.
Although each of the preceding referenced controls
perform their respective functions satisfactoxily, they
are relatively cumbersome, complicated, difficult to adjust, -~
and expensive. Further, a separate, distinct control exists
for each of the functions. Generally, the parts of each of
the controls cannot be interchanged with parts from another
control.
Accordingly, it is an object of the present invention
to provide a simple, inexpensive control which may be
re-adily adapted to perform a number of -functions in con-
trolling the operation of a variable displacement pump, a
variable displacement motor, or a hydrostatic transmission
including a pump and motor combination.
It is a further object of the present invention to
provide a basic component which may be simply and easily
adapted to control any one of a number of functions of
either a hydrostatic transmission or the pump or motor of
the transmission.
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According to the present inVention there is pro--
vided a control for use with a variable hydraulic pump unit
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or motor unit having a relatively high pressure fluid
conduit and a relatively low pressure fluid conduit and
fluid operable means for varying the displacement of the
unit, a source of fluid at a re:Latively constant pressure
irrespective of the displacement of the uni~, and a drain.
The control includes a housing defining an axially ex-
tending bore with a first port in the housing communicating
with the bore and adapted for ~luid communication with the
fluid operable means, a second port in the housing communi-
cating with the bore and adapted for fluid communication
with the source of fluid and a third port in the housing
communicating with the bore and adapted for fluid communi-
cation with the drain. Valve means is provided in the bore
for selectively communicating the first port with either of
the second or the third port, the valve means having a
first axial position communicating the first port with one
of the second and third ports and a second axial position
commuhicating the first port with the other of the second
and third ports. Spring biasing means bias the valve
means axially toward the first position, and second biasing
means bias the valve means ayainst the spring biasing means
axially toward the second position. The second biasing
means includes a fluid chamber, inlet conduit means adapted
to communicate the source of fluid under pressure with -the
fluid chamber, inlet fluid flow restriction means within
the inlet conduit means to restrict fluid flow from the
source of fluld to the fluid chamber, means responsive to
the pressure of fluid within the fluid chamber to bias the
valve means toward the second position, and means responsive
to a signal to vary the pressure of the fluid within the
fluid chamber.
FIG. 1 illustrates a hydrostatic transmission incor~
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porating an electro-hydraulic control according to a feature of
the invention.
FIG. 2 is a cross sectional view partly in schematic ofi
the electro-hydraulic control illustrated in FIG. 1.
The hydrostatic transmission of FIG. 1 includes a
variable displacement swashplate axial piston pump 10 hydraulically
coupled to a fixed displacement motor 12 via conduits 14 and 16.
Pump 10 is a well known type and includes an input shaft 18 which
is used to drive the rotating group of the pump and also drive a
charge pump 20 hydraulically coupled via check valves 22 and 24
respectively to conduits 14 and 16. Pump 10 further includes a
swashplate 26 which is movable cross center by a pair of known
piston-cylinder servos 28 and 30. Motor 12 includes an output
shaft 32. Hydraulically coupled in parallel with motor 12 is a
known control mechanism 34 which includes a shuttle valve, a high
pressure relief valve and a charge pressure relief valve. A
charge pump relief valve 36 is hydraulically coupled to the output
of charge pump 20. Pump 10, motor 12, and charge pump 20 are all
in hydraulic communication with a reservoir 38. A filter 40 is
provided in the drain conduit from pump 10 and motor 12 to reser-
~voir 38.
Se~rvos 28 and 30 are hydraulically coupled via conduits
42 and 44 to a manual servo control valve 46. Conduit 48 communi-
cates the spring chamber~of control valve 46 with the reservoir.
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- 25 l Another conduit 50 communicates the bore of con~rol valve 46 with~the charge~pump as is well known in the art. Control valve 46
includes a control lever 52 and linkage connecting the control
valve spool 54 with swashplate 26 to center spool 54 when the
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position of the swashplate matches the desired position set by
control lever 52.
All of the preceding elements are well known in the art
of hydrostatic transmission controls. Accordingly, a further
description of the operation of these elements does not appear to
be warranted. The remalning portion of the specification will
therefore be directed toward a description of the electro hydraulic
control 56 and its operation with the previously described portions
of the hydrostatic transmission.
Electro-hydraulic control 56 includes a housing defining
a first bore 58 and a second bore 60. A plurality of axially
spaced annular grooves 62, 64, and 66 are provided in first bore
58 and respectively are in fluid communication with charge pump 20,
servo control valve 46, and reservoir 38.
A spool 68 is located within bores 58 and 60 and includes
a pair of axially spaced lands 70 and 72 in bore 58 and another
land 74 in bore 60. An adjustable spring 76 resiliently biases
spool 68 to the right in FIG. 1 to t~e stop position illustrated
~ thereby opening communication between annular grooves 62 and 64.
A pair of chambers 80 and 82 are defined on opposite
sides of land 74 within bore 60. Chamber 80 is always in fluid
communication with reservoir 38 while chamber 82 is in fluid
communication with charge pump 20 via an orifice 84 and with
reservoir 38 via a conduit 86 and a variable force valve 88.
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25 ~ Valve 88 includes a spool 90 upon which a variable force
~l is exerted. Progressive movement of spool 90 to the left in FIG.
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1 results in the progressive closing of opening 92 thus creating
a variable orifice. Accordingly, progressive movement of spool 90
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to the right in FIG. 1 progressively opens opening 92. The left~
ward force exerted on spool 90 is directly related to the amount
of electrical current flowing from an electrical control 94.
Electrical control 94 is coupled to a power source 96
and in the illustrated embodiment to a swashplate position indi-
cator 98. The swashplate position indicator includes a rheostat
100 and a p~inter 102. Accordingly, an electrical signal indic-
ative of swashplate position is provided via swashplate position
indicator 98 to electrical control 94. As is well known, the
position of swashplate 26 of pump 10 is directly related ~o the
displacement of pump 10 and accordingly the volume of fluid flow-
ing from pump 10 to motor 12 at a given speed of input shaft 18.
Electro-hydraulic control 56 further includes a roller
needle 104 having one end in contact with land 74 and the other
lS end hydraulically coupled via a shuttle valve 106 to the high
pressure eonduit 14 or 16. Accordingly, the leftward force
exerted by roller needle 104 on spool 68 will be directly propor-
tional to the highest pressure within conduits 14 and 16. This
pressure in most instances will be the pressure of the fluid
flowing from pump 10 to motor 12 to drive output shaft 32.
The electro-hydraulie eontrol 56 is illustrated as being
eonnected as an input torque limiter for the hydrostatic trans-
mission. As will be hereinafter described it may be used in a
~ ~ number of other ways to control the operation of the hydrostatic
~ transmission simply by providing different electrical controls 94
having differellt inputs.
:~ As described electro-hydraulie eontrol 56 operates in
the following manner. It is well known in the hydraulic art that
system pressure times displaeement (volume of hydraulic fluid) is
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directly related to the torque of the hydraulic system. There-
fore by maintaining the multiple of system pressure times dis-
placement constant one can provide torque limiting means for the
system and thereby match the maximum torque of the hydraulic
system with the maximum torque provided by the prime mover used
to drive input shaft 18. As illustrated, the displacement of
pump lO is proyided via swashplate position indicator 98 to elec-
trical control 94. The system pressure is provided via shuttle
valve 106 to needle roller 104. As the system pressure acting
on the needle roller increases and overcomes the force of spring
76, the pressure of the fluid ported from charge pump 20 to servo
control valve 46 is reduced. This occurs by movement of land 72
to a position in which annular grooves 64 and 66 are placed in
communication with one another. As the pressure to servo control
valve 46 is reduced the centering moment of pump lO and the springs
within servos 28 and 30 act to decrease the displacement of the
pump to that required to maintain the said system pressure. As
the displacement is decreasing, however, an electrical signal is
~eing fed via swashplate position indica~or 98 to electrical
control 94. This results in a decrease in leftward force on spool
90 thereby reducing the pressure of the fluid in chamber 82 and
accordingly allowing spool 68 to move back to the right in FIG. l
and port fluid from charge pump 20 to servo control valve 46.
Similarly, as system pressure is decreased, spool
1 6a will move to the righ~ in FIG. l increasing the pressure of
the fluid from charge pump 20 to control valve 46 and accordingly
the displacement of pump lO. However, as this is occurring,
swashplate position indicator 98 will feed an electrical signal
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to electrical control 94 which ~ill result in an increase in
ieftward force on spool 90 moving the spool toward opening 92 and
thereby increasing the pressure in chamber 82. This increase in
pressure will result in spool 68 moving to the left in FIG. 1 and
returning to the desired position.
In operation, charge pump relief valve 36 is set to main-
tain a maximum charge pump pressure of about 20Q psi. Variable
force valve 88 is provided to maintain the pressure of the fluid
within chamber 82 linearly from 10 psi to 150 psi depending upon
the signal from electrical control 94. The high pressure relief
valve in control mechanism 34 will generally be set in the area of
3500 psi to 6000 psi. Appropriate modification to the area of
land 74 subject to fluid pressure in chamber 82 and the area of
roller needle 104 subject to system pressure can be made by those
skilled in the art. An operative design for the electronic circuit used in
electrical control 94 may be made by to those skilled in the
art of electrical controls.
Referring now to FIG. 2 which illustrates a specific
embodiment of a~ electro-hydraulic control according to the in-
vention, charge pump 20 ports fluid to control 56 via passages 108
and 110. Passage 111 is in fluid communication with servo control
valve 46 via conduit S0. A passage 112 fluidly communicates cham-
b~r 80 with reservoir 38.
' ~ Spool 68 is located in a multi-stepped bore 114, 116,
and 118 and includes lands 120, 122, 124, 126, 128, and 130. Land
120 prevents fluid from flowing from bore 114 to the cha~ber
housing adjustablle sprin~ 76. Land 122 or 124 contacts the wall . ~ :
of bore 114 de?ending upon the position of spool 68. Land 126 is
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spaced from the walls of bore 116 to allow fluid to flow from
passage 111 through bore 114, bore 116 in~o chamber 80 and then
through conduit 112 to the reservoir. Lands 128 and 130 are in
contact with the wall of bore 118~
Variable force valve 88 is illustrated as a standard
proportional pressure controller valve Model 80 provided by Fema
Corporation, Portage, Michigan. The variable orifice defined by
spool 90 and opening 92 in FIG. 1 is illustrated schematically in
valve 88 by variable orifice 132. Orifice 132 as well as orifice
84 are component parts of the Fema valve. Passages 134 and 136 in
control 56 are provided to direct fluid from passage 110 to ori-
fice 84 via bore 118 and from ~here either to passage 86 or 112
depending upon the degree that variable orifice 132 is opened.
Adjustable spring 76 includes an adjustable stop 138
which may be screwed into or out of control 56. The position of
adjustable~stop 138 will control the riyhtward force exerted by
spring 76 on spool 68.
~riefly, in operation, the pressure of the fluid in
chambers 82 and 140 of shuttle valve 106 will respectively be
exerted against the areas of land 130 and needle roller 104 to
bias spool 68 to the left in FIGo 2 against the force of spring
76~ As spool 68 is moved to the left, the fluid f~owing from
charge pump 20 thxough passage 108 around land 122 to passage 111
and from there to servo control valve 46 is slowly restricted
until a point is reached when land 122 makes ~ontact with the wall
' of bore 114 to terminate such flow. At this point, land 124
begins to move away from tha wall of bore 114 allowing fluid
` communication between passage 111 and bore 116 to drain fluid from
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passage 111 into the reservoir. It may therefore readily be seen
that the fluid pressure directed through passage 111 from charge
pump 20 is directly dependent upon the position of spool 68 in
control 56. The position of spool 68 is directly related to the
force exerted by spring 76 and the force exerted by the pressure
of fluid in chamber 82 against the area of land 130 and the force
exerted by the pressure of fluid in chamber 140 against the area
of needle roller 104.
Shuttle valve 106 may comprise a separate housing 142
which may be secured by bolts 144 to housing 145 of control 56.
If desired, shuttle valve 106 may be removed and a flat plate may
be bolted on housing 146 in its place. In this latter arrangement,
the pressure of the fluid in chamber 82 and the force of spring 76
would be the only two factors used to position spool 68 within
valve 56.
Various electrical controls can also be designed to oper-
ate variable force valve 88 and, accordingly, control the pressure
of the fluid within chamber 82. These controls can have inputs
from the position of the swashplates of a variable displacement
pump and/or a variable displacement motor. Further, the pressure
of the fluid in chamber 82 may be directly dependent upon system
pressure by sealing passage 110 and removing needle roller 104 in
the valve illustrated in FIG. 2. Electrical controls may also be
' operated by inputs from a prime mover rotating input shaft 18 of
pump 10 and the position of swashplate 26 to prevent the prime
mover from stalling during overload conditions. Other variations
in the electrical controls are also contemplated.
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' By the foregoing, applicant has developed a single
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hydraulic control whose basic components may be readily changed
to perform a number of control functions. It is to this hydraulic
control that the following claims are directed. It should be
appreciated that the orifice 132 may be varied in other ways, e.g.,
mechanically or hydraulically~ Further, the fluid chamber 82 may
be in communication with the spring end of spool 68 and be used
to exert a force against the force exerted by needle roller 104.
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