CA1051750A

CA1051750A - Hydraulic controller

Info

Publication number: CA1051750A
Application number: CA273,459A
Authority: CA
Inventors: Kenneth K. Knapp
Original assignee: Eaton Corp
Current assignee: Eaton Corp
Priority date: 1976-07-02
Filing date: 1977-03-08
Publication date: 1979-04-03
Also published as: DE2719029C2; BR7702172A; AR215008A1; FR2360773B1; GB1582453A; FR2360773A1; IT1084662B; DE2719029A1; JPS5728821B2; JPS535365A

Abstract

APPLICATION OF: Kenneth K. Knapp FOR: HYDRAULIC CONTROLLER

A B S T R A C T

An electro-hydraulic control for a hydrostatic trans-mission to control a number of functions of the transmission or the pump or motor of the transmission. The transmission includes a variable displacement pump driving a fixed displacement motor along with the appropriate standard valving for control of the displacement of the pump and the high and low pressure conduits communicating hydraulic fluid between the pump and the motor. An electro-hydraulic control valve is supplied to port a varying pressure of fluid to the standard controller used to vary the displacement of the pump. The control valve includes a spool biased in one direction in a housing to port fluid from the charge pump of the transmission to the standard controller. A fluid chamber is in communication with the other end of the spool and with the fluid from the charge pump. A variable orifice communi-cates the fluid chamber with a drain. The size of the orifice is controlled by an electrical force positioning valve which receives a signal representative of the location of the swashplate of the pump. Depending upon the pressure of the fluid in the fluid chamber the control valve will directly vary the pressure ported from the charge pump to the standard controller. A needle roller has one end in contact with the end of the spool communicating with the fluid chamber. A high pressure signal is provided via a shuttle value across the high and low pressure conduits of the transmission to the other end of the needle roller. Accordingly, the control valve is responsive to both the pump displacement and the highest pressure within the transmission thereby making it a torque limiting controller. Various modifications can be made within the spirit of the invention to control the fluid pressure within the fluid chamber and against the one end of the needle roller to change the function of the control valve.

Description

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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 .
~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 1, 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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-~5175ql 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.
Il 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.
,, 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 ' ~ -6-1, ~51'~
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 , ' , . . - ; i; . . ~ - . ,, ~ ,:

~i~5~75~:) 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 ~ j!

g ~D5~750 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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A control for use with a variable hydraulic pump unit 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 said unit, a source of fluid at a relatively constant pressure irrespective of the displacement of said unit, and a drain, said control comprising:
a housing defining an axially extending bore;
a first port in said housing communicating with said bore and adapted for fluid communication with said fluid operable means;
a second port in said housing communicating with said bore and adapted for fluid communication with said source of fluid;
a third port in said housing communicating with said bore and adapted for fluid communication with said drain;
valve means in said bore for selectively communi-eating said first port with either said second port or said third port, said valve means having a first axial position communicating said first port with one of said second and third ports and a second axial position communi-eating said first port with the other of said second and third ports;
spring biasing means to bias said valve means axially toward said first position;
second biasing means to bias said valve means against said spring biasing means axially toward said second position, said second biasing means including:
a fluid chamber, inlet conduit means adapted to communicate said source of fluid under pressure with said fluid chamber, inlet fluid flow restriction means within said inlet conduit means to restrict fluid flow from said source of fluid to said fluid chamber, means responsive to the pressure of fluid within said fluid chamber to bias said valve means to-ward said second position, and means responsive to a signal to vary the pressure of the fluid within said fluid chamber.

2. A control according to claim 1 wherein said signal is electrical.

3. A control according to claim 1 or 2 further comprising:
another fluid chamber;
means responsive to pressure of fluid within said other fluid chamber to bias said valve means against said spring biasing means axially toward said second position;
and conduit means adapted to communicate said relatively high pressure fluid conduit with said other fluid chamber.

4. A control according to claim 1 further comprising:
outlet conduit means in fluid communication with said fluid chamber and adapted for fluid communication with said drain;
outlet fluid flow restriction means within said outlet conduit means to restrict fluid flow from said fluid chamber to said drain; and wherein said means responsive to a signal varies the amount of restriction of one of said flow restriction means in one of said conduit means to vary said pressure within said fluid chamber.

5. A control according to claim 4 wherein:
one of said fluid flow restriction means is an electrically responsive on/off valve; and said means responsive to a signal either fully opens or fully closes said on/off valve to vary said pressure within said fluid chamber.

6. A control according to claim 4 wherein:
one of said fluid flow restriction means is an electrically responsive variable force valve defining a variable orifice; and said means responsive to a signal varies the force exerted by said variable force valve to vary said pressure within said fluid chamber.

7. A control according to claim 4 wherein the signal is directly related to the displacement of said unit.