United States Patent c191
`Martin
`
`[11)
`
`[45]
`
`4,201,116
`May 6, 1980
`
`[54] ELECTRO-HYDRAULIC PROPORTIONAL
`CONTROL SERVO VALVE
`Robert J, Martin, Hutchinson, Kans.
`Inventor:
`(75]
`The Cessna Aircraft Company,
`[73] ~ssignee:
`Wichita, Kans.
`(21) Appl. No.: 814,764
`[22] Filed:
`Jul. 11, 1977
`Int. CJ.2 .............................................. F15B 13/16
`(51]
`[52] U.S. CI ......................................... 91/387; 91/365;
`137/625.64; 251/30; 335/266
`[58] Field of Search ......................... 91/365, 387, 367;
`137/625.64; 251/30; 335/256, 258, 266
`References Cited
`U.S. PATENT DOCUMENTS
`Jacobs .................................. 335/256
`8/1917
`Donaldson, Jr . ...................... 91/461
`2/1939
`Schwendner ...................... 91/387 X
`5/1950
`Schindler ........................ 323/43.5 R
`10/1956
`Hayner et al ...................... 91/387 X
`9/1959
`Williams ................................ 91/387
`1/1961
`Rouvalis ................................ 91/387
`10/1961
`Chatham et al. .................. 251/30 X
`7/1963
`
`1,236,177
`2,146,176
`2,507,353
`2,767,369
`2,896,588
`2,966,891
`3,003,475
`3,099,290
`
`(56]
`
`3,208,352
`3,390,613
`3,429,225
`3,788,194
`3,954,045
`
`9/1965 Lucien ............................... 91/387 X
`7/1968 Westbury et al ...................... 91/363
`2/1969 Keyworth .............. : ................... 91/3
`1/1974 Bums ..................................... 91/386
`5/1976 Barlow .............................. 91/387 X
`
`OTHER PUBLICATIONS
`SLI Industries Catalog (1976), p. 3.
`Primary Examiner-Irwin C. Cohen
`ABSTRACT
`(57]
`A conventional control valve hydraulically powered by
`a double acting cylinder and controlled electrically
`through a double acting solenoid supplied by a variable
`D.C. supply. The solenoid transmits varying forces to a
`four-way pilot valve which in tum controls the posi(cid:173)
`tioning of the double acting cylinder. The de-energized
`solenoid, control valve spool and pilot spool are neu(cid:173)
`trally balanced between two springs equally loaded
`with differing spring rates so that a small movement of
`the solenoid core will cause a proportionally larger
`movement of the main control valve spool propor(cid:173)
`tioned to the different spring rates.
`
`10 Claims, 3 Drawing Figures
`
`

`

`U.S. Patent May 6, 1980
`US. Patent
`
`May 6, 1980
`
`Sheet 1 of 2
`Sheet 1 of 2
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`4,201,116
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`U.S. Patent May 6, 1980
`U.S. Patent May 6, 1980
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`Sheet 2 of 2
`Sheet 2 of 2
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`4,201,116
`4,201,116
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`1
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`4,201,116
`
`ELECTRO-HYDRAULIC PROPORTIONAL
`CONTROL SERVO VALVE
`
`BACKGROUND OF THE INVENTION
`Solenoid operated directional control valves have
`long been available; however, they have been the on/(cid:173)
`off-type valves which when operated electrically shift
`to a fully open or fully closed position. In more recent 10
`times, electro-hydraulic servo valves have been devel(cid:173)
`oped which accurately control the velocity, accelera(cid:173)
`tion, and position of actuators by an electrical signal
`controlling a hydraulic output. These valves can be
`used to meter flow to and from hydraulic actuators or 15
`to control a variable displacement pump. Servo valves
`of this nature are either single-stage or double-stage
`with the latter being prevalent where the pressures and
`flow rates are significant. In a two-stage valve, the main
`control spool is actuated by a double acting actuator 20
`which is supplied by a pilot valve which is in tum con(cid:173)
`trolled by some form of electro-mechanical transducer
`such as a solenoid or torque motor. What the pilot stage
`does is take a low level mechanical signal, amplify it and
`with the amplified signal control the main control valve 25
`spool. A variety of different types of amplifiers in the
`pilot stage have been used such as spool-type valves;
`jet-pipe type, single-flapper type and double-flapper
`type. Also, these types of valves include a feedback
`function whereby the position of the main control spool 30
`provides a signal to the pilot stage so that any error in
`the main stage can be corrected. This feedback function
`provides
`the fine metering and accuracy factor
`achieved in current generation servo valves.
`
`SUMMARY OF THE INVENTION
`The electro-hydraulic servo valve of the present in(cid:173)
`vention utilizes a spool type pilot valve for its amplify(cid:173)
`ing stage which controls a double acting cylinder at(cid:173)
`tached to the main control valve spool with the feed- 40
`back signal provided by a compression spring posi(cid:173)
`tioned between the pilot spool and main control valve
`spool. The pilot spool is controlled by a small double
`acting solenoid having a pair of coils capable of actuat(cid:173)
`ing the solenoid core in opposite directions which pro- 45
`vide a very small actuation stroke to the pilot spool.
`The pilot spool with the solenoid de-energized is bal(cid:173)
`anced between the feedback spring and a second spring
`with a substantially higher spring rate than the feedback
`spring in the neutral spool position. The solenoid rate of 50
`force change with respect to position shall always be
`less than the combined spring rates of the two balancing
`springs.
`Therefore, the principal object of the present inven(cid:173)
`tion is to provide a new and improved electro-hydraulic 55
`servo valve with a very simplified design which can be
`powered by a solenoid of minimal size and displace(cid:173)
`ment.
`Another object of the present invention is to provide
`an electro-hydraulic servo valve which can be either 60
`single or two-stage which in its two-stage embodiment
`controls a main four-way or three-way valve.
`Another object of the present invention is to provide
`a pilot system with no wasted neutral flow.
`A further object of the present invention is to provide 65
`a system where the solenoid coils can be replaced in the
`field without distrubing the null adjustment of the pilot
`valve.
`
`2
`These and other important objects and advantages of
`the present invention are specifically set forth in or will
`become apparent from the following detailed descrip(cid:173)
`tion of preferred embodiments of the invention, when
`5 read in conjunction with the accompanying drawings,
`wherein:
`FIG. 1 is a longitudinal sectional view of the servo
`valve of the present invention with portions of the main
`control valve broken away;
`FIG. 2 is an enlarged sectional view of the pilot
`spool; and
`FIG. 3 is a longitudinal sectional view of a modified
`form of the invention.
`Turning now more particularly to FIG. 1, the elec(cid:173)
`tro-hydraulic proportional control servo valve of the
`present invention is generally described by reference
`numeral 10. The valve 10 is made up of solenoid unit 12
`attached to the hydraulic amplifier section 14 which is
`attached to the casting of the main directional control
`valve 16. Main control valve 16 operates a double act(cid:173)
`ing cylinder 18 which could be any type of linear or
`rotary motor. Control valve 16 which is only partially
`shown, is a conventional control valve having a valve
`spool 20 positioned in a bore 21 which in turn is formed
`in a casting 22. While control valve 16 is a four-way
`valve, only half of the valve is shown incll!ding pump
`pressure cavity 24, main motor port cavity 25 and drain
`cavity 26. On the opposite end of spool 20, not shown in
`the drawing, is a conventional centering spring mecha(cid:173)
`nism which returns valve spool 20 to its neutral position
`when all actuating forces are removed from the spool.
`Valve spool 20 is illustrated in its neutral flow blocking
`position with spool land 23 blocking pump pressure
`from the motor port 25 while land 11 blocks motor port
`35 passage 25 from drain passage 26. While valve 16 is a
`closed-center type control valve, the present invention
`would have equal application on open-center type
`valves.
`Low pressure pump 28 supplies pressure to pilot
`spool 27 via passage 29 into bore 30. Any other pressure
`source utilized for another function could also be used.
`Pilot spool 27, which is a closed-center type valve,
`includes a pair of lands 31 and 32 which in the neutral
`position block the cylinder port passages 33 and 34.
`Spool 27 has a longitudinal bore 35 intersected by a
`lateral hole 36 which connects the areas adjacent both
`ends of spool 27 with drain cavity 38. The groove area
`40 in spool 27 defined by the two lands 31 and 32 is
`always pressurized with low pressure fluid from pump
`28. Groove 41 on the opposite side of land 32 is con(cid:173)
`nected to drain via passages 36, 35 and 38, while the
`groove 42 on the opposite side of land 33 connects
`directly to drain passage 38.
`Referring to the main control valve 16, spool bore 21
`is axially aligned with an enlarged bore 44 which con(cid:173)
`tains a piston 45 slidably positioned therein and attached
`to spool 20. Piston 45 and bore 44 define a double acting
`cylinder 46 including two chambers 47 and 48. Cham(cid:173)
`ber 47 is connected with motor port 33 via passage 49,
`while chamber 48 is connected to motor port 34 via
`passage SO. Solenoid unit 12 contains a pair of coils 54
`and 55 surrounding a single core 56. Power is supplied
`to coils 54 and 55 through contacts 57, 58 and 59. Posi(cid:173)
`tioned on the left end of solenoid core 56 is an attach(cid:173)
`ment fitting 60 which has a threadable end 61 thereon
`for receipt into the amplifier section 14. While not
`shown in the drawings, shims can be placed between the
`flange of fitting 60 and the amplifier section 14 to bal-
`
`

`

`3
`ance the spool 27. Passing longitudinally through fitting
`60 is a bore 62 which receives an extension portion 63 of
`the solenoid col'e 56. A similar extension 64 extends
`from the opposite end of core 56 and is in contact with
`compression spring 65 located in cavity 66. Shims 67 5
`located on the end of spring 65 can be added or re(cid:173)
`moved to assist in balancing the pilot spool 27 and core
`56. Longitudinally passing through the complete length
`of core 56 and its respective extension portions 63 and
`64, is a passage 68 which connects spring cavity 66 with 10
`drain cavity 38 allowing oil to flow therethrough. A
`lateral opening 70 in core 56 allows unpressurized oil to
`move around the periphery of core 56 including the
`core displacement cavities 7ll. and 72. Core 56, as shown
`in the drawing, is neutrally positioned with its maxi- 15
`mum displacement in each direction indicated by di(cid:173)
`mensions A and B. The package of coils 54 and 55 can
`be removed from the core 56 by removal of nuts 80 and
`81, without affecting the neutral (or null) adjustment of
`the pilot spool 27. Bearing against the left end of pilot 20
`spool 27 is a compression spring 75 which provides the
`feedback function to the pilot valve. Bearing against the
`right end of spool 27 is the extension portion 63 of the
`solenoid core 56 urged by second spring 65. Pilot spool
`27 and solenoid core 56 are balanced between the two
`springs 65 and 75 in their neutral positions when the
`control valve spool 20 is neutrally positioned. Spring 65
`has a spring rate greater than that of feedback spring 75.
`As for example, spring 65 could have a spring rate 10 30
`times that of spring 75. In other words, for each incre(cid:173)
`ment of displacement of spring 75 causing a force
`change, the change in spring 65 would be 10 times that
`of spring 75. The rate of force change of solenoid core
`56 with respect to the change in core position, is always 35
`less than the combined spring rates of springs 75 and 65,
`so that when solenoid 12 is energized, it will not go to
`its maximum position.
`·
`
`25
`
`40
`
`OPERATION
`As shown in FIG. 1, the servo valve unit 10 is shown
`in its neutral de-energized position. Control valve spool
`20 is in its neutral flow blocking position, pilot spool 27
`and solenoid core 56 are balanced between springs 75
`and 6S in their respective neutr11,I positions. When one of 45
`the solenoid cores 54 or 55 is energized, the force bal(cid:173)
`ance on pilot spool 27 changes causing a slight move(cid:173)
`ment due to the added force from the solenoid added to
`one of the springs 75 or. 65. If coil 54 is energized, a
`force to the left is applied to the pilot spool 27 counter- 50
`acting the force of spring 75. This force imbalance will
`cause the pilot spool to move to the left compressing
`spring 75 until the forces are equalized. This leftward
`movement compresses spring 75 increasing its force,
`and extends spring 65 decreasing its force. This leftward 55
`movement stops at that point when the three forces are
`again balanced on the pilot spool 27. This slight move(cid:173)
`ment of spool 27 causes land 31 to slightly open motor
`port 33 to pressure from pump 28 and land 32 to open
`motor port 34 to drain, thereby causing piston 45 and 60
`control valve spool 20 to move to the right opening
`main motor port cavity 25 to drain 26. Control valve
`spool 20 will continue to move until pilot spool 27 is
`returned to its neutral position blocking flow to cylin(cid:173)
`der 46. As spool 20 moves to the right, spring 75 is 65
`compressed, increasing the force on pilot spool 27.
`When the increases match the added force created by
`the solenoid 12, pilot spool 27 will return to neutral and
`
`4,201,116
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`4
`control valve spool 20 will stop at a precise position
`determined by the electrical signal supplied to coil 54.
`The movement of the control valve spool 20 is pro(cid:173)
`portional to the rate of spring 75, assuming a constant
`solenoid force. The· movement of the control valve
`spool is also proportional to the force generated in the
`solenoid, assuming the spring rate of spring 75 remains
`constant. If, for example, spring 75 has a spring rate of
`20 pounds per inch, spool 20 will move 0.5 inches if a
`solenoid force of 10 pounds is placed on pilot spool 27.
`If the control valve spool 20 requires additional spool
`travel for added functions such as a float position or a
`regeneration position, the spring rate of the feedback
`spring 75 can be decreased. With a decreased spring
`rate on the feedback spring 75, the valve spool 20 must
`move a greater distance to build up the same force
`change. By changing the feedback spring rate, the same
`controller device which provides the electrical signal to
`the solenoid (not shown in the drawing) can be used on
`functions requiring different spool travel.
`The greater the electrical signal applied to the sole(cid:173)
`noid coil, the farther control valve spool 20 opens be(cid:173)
`fore it reaches its equilibrium point. With coil 55 ener(cid:173)
`gized, with a maximum signal or force, control valve
`spool 20 would be in its far left position with land 23
`providing a maximum opening of pump pressure into
`motor port 25. In this static condition, pilot spool 27 is
`neutrally positioned, as shown in the drawing. When
`coil 54 is de-energized, the force imbalance on pilot
`spool 27 and core 56 causes pilot spool 27 to shift to the
`left opening motor port 33 to pump pressure in groove
`40, while land 32 opens motor port 34 to drain via 41,
`36, 35 and 38. In this dynamic condition, pressure flows
`from pump 28 into cylinder chamber 47 causing control
`valve spool 20 to move to the right, thus closing down
`flow into motor port 25. As spool 20 moves to the right,
`the balancing force exerted by spring 75 is increasing,
`due to its compression. When its spring force reaches a
`certain level, control valve spool 20 will have reached
`its neutral position and pilot spool 27 will return to its
`neutral position stopping the movement of control
`valve spool 20. In this static condition, springs 75 and 65
`are· balanced with pilot spool 27 in its neutral flow
`blocking position.
`In FIG. 3, the main control valve 16a is a two-posi(cid:173)
`tion four-way valve, rather than a three-position valve
`as shown in FIG. 1. The cylinder 46a controlling the
`valve is single acting rather than double acting, with
`one chamber 47a and a spring 86 which opposes cham(cid:173)
`ber 47a and moves the spool 20a in the opposite direc(cid:173)
`tion when chamber 47a is drained. Pilot spool 27a is
`three-way, rather than four-way, having positions
`blocking flow to chamber 47a, applying pressure to
`chamber 47a or draining chamber 47a. Solenoid 12a has
`a single coil 54a and therefore moves core 56a in a
`leftward direction only. With coil 54a de-energized,
`pilot spool 27a will drain chamber 47a, via groove 42a,
`regardless of the position of control valve spool 20a.
`When coil 54a is energized with a certain electrical
`signal, a known force is applied by core 56a to the end
`df spool 27a in opposition to spring 75a. This solenoid
`force combined with the force of spring 65a is greater
`than the force of spring 75, thereby causing spool 27a to
`shift to the left sufficiently to open the pump pressure in
`groove 40a into chamber 47a. Control valve spool 20a
`will shift from its leftward position in the drawing to the
`right until the compression of spring 75a makes up the
`force difference caused by the solenoid 12a, at which
`
`

`

`20
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`25
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`4,201,116
`5
`point pilot spool 27a will shift to the right to a neutral
`position blocking flow to or from chamber 47a. · If the
`electrical signal is sufficiently strong, main control
`valve spool 20a wiU move to its far right position full)'.
`opening motor port 25a to drai~. port ~6a. Whenever s
`the solenoid 12a · is de-energized, i,pool lOa . will again
`shift to its full left position, opening motor port 2Sa to
`pump pressure cavity 24a. ..
`. .·
`.
`While the drawings illustrate a two-stage el.ectro(cid:173)
`hydraulic servo valve, the invention would have utility 10
`in a single-stage valve, without the main control valve
`20. Pilot spool 27 would be a niain control valve and
`double acting cylinder 46 would be the ultimate motor
`·
`which is controlled.
`Having described the invention with sufficient clarity IS
`to enable those familiar with the art to construct and use
`it, I claim:
`1. An electr~-hydraulic proportional . control servo
`valve including a valve spool of a conventional direc-
`tional control valve:
`a dC>uble acting cylinder connected to the directional
`control valve spool;
`an electro~inechanical transducer means capable of
`produc;ing varying l_ineal forces with a varied elec-
`trical input signal;
`·
`.
`. a pressure-source and drain;
`a four-way pilot valve including a valve spool con(cid:173)
`nected at one end to the transducer means which
`controls the position of the double acting cylinder,
`the pilot spool having a neutral position, a first 30
`operating position connecting the pressure source
`with a first chamber of the double acting cylinder
`while connecting the opposing second chamber of
`said cylinder to drain and a second operating posi(cid:173)
`tion connecting the pressure source with the sec- 3S
`ond chamber while draining the first chamber;
`a first spring means positioned between the pilot
`spool and the control valve spool providing a feed(cid:173)
`back function;
`a second spring means having a spring rate greater 40
`than the first spring means, acting in opposition to
`the first spring means, with the pilot spool balanced
`therebetween, the second spring means is so posi(cid:173)
`tioned that when the transducer is not energized,
`the control valve spool and the pilot spool will 45
`return to their neutral positions, and the combined
`spring rates of the first and second spring means
`being greater than the rate of force change of the
`solenoid with respect to solenoid travel.
`2. A proportional control servo valve as set forth in SO
`claim 1, wherein the double acting cylinder, pilot spool
`and transducer means are all axially positioned in align(cid:173)
`ment with the control valve spool.
`3. A proportional control servo valve as set forth in
`claim 1, wherein the transducer means is a double acting SS
`solenoid having a pair of coils with a single core capable
`of actuation in opposite directions, the directional con(cid:173)
`trol valve is of a four-way type having a centering
`spring which urges the control valve spool towards its
`neutral position.
`4. A proportional control servo valve as set forth in
`claim 1, wherein the transducer means is a double acting
`solenoid having a pair of coil means with a single core
`capable of actuation in opposite directions, the coil
`means being removable without disturbing the core.
`5. A proportional control servo valve as set forth in
`claim 1, wherein the transducer means is a double acting
`solenoid having a pair of coil means with a single core
`
`6
`capable of actuation in opposite directions, the maxi(cid:173)
`mum core movement in either direction being less than
`0.10 inches.
`6. A proportional control servo valve as set forth in
`claim 1, wherein the four-way pilot valve is a closed-
`center valve.
`·
`7. A single stage electro-hydraulic proportional con(cid:173)
`trol servo valve including a double acting cylinder
`having a piston separating first and second chambers;
`an electro-mechanical transducer means capable of
`producing varying lineal forces with a varied elec(cid:173)
`trical input signal;
`a pressure source and drain;
`a four-way pilot valve including a valve spool con(cid:173)
`nected at one end to the transducer means which
`controls the position of the double acting cylinder,
`the pilot spool having a neutral position, a first
`operating position connecting the pressure source
`with a first chamber of the double acting cylinder
`while connecting the opposing second chamber of
`said cylinder to drain and a second operating posi(cid:173)
`tion connecting the pressure source with the sec(cid:173)
`ond chamber while draining the first chamber;
`a first spring means positioned between the pilot
`spool and.the.piston of the double acting·cylinder
`providing a feedback function;
`a second spring means having a spring rate greater
`than the first spring means acting in opposition to
`the first spring means, with the pilot spool balanced
`therebetween, the second spring means is so posi(cid:173)
`tioned that when the solenoid is not energized, the
`piston of the double acting cylinder and the pilot
`spool will return to their neutral positions, and the
`combined spring rates of the first and second spring
`means being greater than the rate of force change
`of the solenoid with respect to solenoid travel.
`8. An electro-hydraulic proportional control servo
`valve including a conventional directional control
`valve and control valve spool;
`a double acting cylinder connected to the directional
`control valve spool having first and second cham(cid:173)
`bers;
`a double acting solenoid having a pair of coils capable
`of actuating the solenoid core in opposite direc(cid:173)
`tions;
`a pressure fluid source and drain;
`a four-way pilot valve including a valve spool con(cid:173)
`nected to one end of the solenoid core which con(cid:173)
`trols the position of said double acting cylinder, the
`pilot spool having a neutral flow blocking position;
`a first operating position connecting said pressure
`source with a first chamber of said double acting
`cylinder while connecting the opposing second
`chamber of said cylinder to drain, and a second
`operating position connecting the pressure source
`with the second chamber while draining the first
`chamber;
`a first spring means positioned between the pilot
`spool and the control valve spool providing a feed(cid:173)
`back function urging the pilot spool toward its first
`operating position;
`a second spring means having a spring rate greater
`than the first spring means connected to the sole(cid:173)
`noid core, acting in opposition to the first spring
`means urging the pilot spool toward its second
`operating position, the second spring means being
`so positioned that when the solenoid is not ener(cid:173)
`gized and the control valve spool is neutrally posi-
`
`60
`
`6S
`
`

`

`4,201,116
`
`7
`tioned, the pilot spool will be neutrally balanced
`between the two spring means, and the combined
`spring rates of the first and second spring means
`being greater than the rate of force change of the
`solenoid with respect to solenoid travel.
`9. A single stage electro-hydraulic proportional con(cid:173)
`trol servo valve comprising:
`a hydraulic cylinder having a piston and at least one
`chamber;
`an electro-mechanical transducer means capable of 10
`producing varying lineal forces with a varied elec(cid:173)
`trical input signal;
`a pressure source and drain;
`a pilot valve including a valve spool connected at one
`end to the transducer means which controls the 15
`position of the cylinder piston, the pilot spool hav(cid:173)
`ing a neutral position, a first operating position
`connecting the pressure source with a chamber of
`the cylinder, and a second operating position con-
`necting said cylinder chamber to drain;
`a first spring means positioned between the pilot
`spool and the piston of the cylinder providing a
`feedback function;
`a second spring means having a spring rate greater
`than the first spring means actmg in opposition to 25
`the first spring means, with the pilot spool balanced
`therebetween, the second spring· means is so posi(cid:173)
`tioned that when the solenoid is not energized, the
`piston of the cylinder and the pilot spool _ will re(cid:173)
`turn to their neutral positions, and the combined 30
`spring rates of the first and second spring means
`
`8
`being greater than the rate of force change of the
`solenoid with respect to solenoid travel.
`iO. An electro-hydraulic proportional control servo
`vaive including a conventional four-way, two position
`5 ditectional control valve and control valve spool;
`a single acting cylinder spring biased to the return
`position connection to the directional control valve
`spool;
`a solenoid having a coil and a core;
`a pressure fluid source and drain;
`a three-way pilot valve including a valve spool con(cid:173)
`nected to one end of the solenoid core which con(cid:173)
`trols the position of said cylinder, the pilot spool
`having a neutral flow blocking position; a first
`operating position connecting said pressure source
`with said cylinder, and a second operating position
`connecting said cylinder to drain;
`a first spring means position between the pilot spool
`and the control valve spool providing a feedback
`function;
`a second spring means having a spring rate greater
`than the first spring means connected to the sole(cid:173)
`noid core, acting in opposition to the first spring
`means, the second spring means being so positioned
`that when the solenoid is not ·energized the pilot
`spool will be in its second operating position be-
`tween the two spring means, and the combined
`spring rates. of the first and· second spring means
`being· greater than the rate of force change of the
`solenoid with· respect to solenoid travel.
`• • • • •
`
`20
`
`35
`
`40
`
`45
`
`so
`
`55
`
`(j()
`
`65
`
`