US3033232A - Control valves - Google Patents

Description

May 8, 1962 E- BAHNUK 3,033,232

CONTROL VALVES Filed Aug. 51, 1960 i@ z/Q/ had@ a@ ite States This invention relates generally to hydraulic control or power valves, and more particul-arly to improvements in such control valves las applied in electro hydraulic servomechanisms.

Valves of this type are normally used to control the supply and/or pressure of hydraulic fluid to a motor or other such hydraulically operated devices. In normal operation of the embodiment herein described, the spool is moved in a certain direction thereby causing one or more fluid ports to be progressively opened for the purpose of allowing iiuid from the supply source to reach the fluid motor and return.

Valves of this type are often employed in combination with an electrical device which receives an electrical signal which is interpreted in the form of a low level force. The electrical device transmits the signal to the control valve for the purpose of actuating said control valve in response to the electrical input. Ideally, the purpose of the combination herein referred to as an electro-hydraulic servo, is to increase or decrease iiuid pressure supplied to the hydraulic output member in response to demands communicated to the valve by the electric signal.

It is highly desirable that the response of the control valve be linear, Le., that the change in hydraulic pressure to the output member be linear with respect to the input signal sensed by the electrical mechanism. It is also very desirable that the amount of force required to move the spool of the control valve be as small as possible in order that the electrical input signal may be as small as possible.

However, there are certain forces which inherently occur in conventional valves of this type which act in derogation of these desirable characteristics. These forces have been the subject of extensive research, voluminous publications, and a number of patented valve mechanisms, none of which have served to satisfactorily solve the'numerous attendant problems.

The forces which create the most concern are those created byl iiuid iiow through the orifices created by the lands of the spool partially opening the valve ports. These forces may be grouped into general categories, the first category being referred to as steady state forces, and the second group being termed transient iiow forces.

One of the more recent learned works relating to these forces is found in the A.S.M.E. transactions of 1952, given by Dr. Lee and I. F. Blackburn of the Massachusetts Institute of Technology. In a series o-f two papers, .a mathematical derivation of steady state and transient flow forces was presented, and these derivations are generally accepted for the purpose of this invention. In these papers a number of possible solutions to the problems arising from the presence of these forces are set forth, among which is a new port configuration subsequently patented by Dr. Lee, Patent No. 2,747,612. It is to be noted that this configuration is particularly concerned with eliminationrof steadystate forces.

The forces with which the present invention is most concerned are those known as transient iiowforces. Basically, these transient flow forces are the summation of the reaction forces to theja'cceleration of the individual particles of fluid entering and leaving the valve and in conventional valve designs they are impressed on the movable valve element. This tends to cause valve instability, as well' as other undesirable characteristics.

atet

According to the papers of Lee and Blackburn, these forces are a function of the length of the iiow path and the angle of fluid flow entering and/or leaving the valve. The angle of the tiuid flow leaving or entering a metering port is -generally referred to as the jet flow angle. However, for the purposes of the present invention, jet fiow angle is interpreted to be the flow entering or leaving the valve from both metering and nonmetering ports.

On the basis of work by Von Mises, discussed in the papers before referred to, it has been generally accepted that the jet angle must remain constant, or `substantially so, at 69. Therefore, most attempts to dampen the forces acting on the spool have been in the area of varying the length of the flow path.

Basically, it is the intent and purpose of this invention to control transient flow forces in order to prevent valve instability and oscillation which is,r an eiiect of these forces, whereby a valve may be provided which will be linearly responsive, 'and stable in operation.

Accordingly, it is an object of the presentjinvention to provide a control valve having the above stated characteristics which may function in cooper-ation with a low input servo mechanism. j

It is a further general object to provide a valve which is not subject to the eiiects of adverse fluid forces which would otherwise contribute to instability and nonlinearity of operation.

It is a more particular object of the present invention to substantially control the effects of steady state and transient forces resulting from fluid flow to'or from the valve ports. f

It is a further object of the present invention'to provide a valve having the above advantages without increasing the expense thereof through use of exotic land and port configurations, but retaining the conventional squue edged land in order that no sacrifice to response be ma e.

It is a more particular object of the present invention to accomplish the above advantages and their desirable results by changing or altering the angle of 'fluid iiow entering and leaving the spool.

It is a speci-fic objective of the Ipresent invention to cause the angle of ingress and egress of the fluid inthe valve to ybe altered by modifying the relative diameter of the spool between certain lands in relation to the diameter of the valve bore.

The invention consists of the novel constructions, arrangements, and devices to be hereinafter described and claimed for carrying out the above stated objects and such other objects as will be apparent from the following description of the preferred form of the invention, illustrated with reference to the accompanying drawings, wherein:

FIG. l is a schematic view, partially in section, i1lustrating a preferred embodiment of a servo-:mechanism including a control valve.

FIG. 2 is an enlarged sectional view of the control valve of FIG. 1.

FIG. 3 is a scalar diagram of the fluid flow through a port of the control valve of FIG. 2. l

Referring now to the figures whereinlike Ynumerals'refer to like parts in the various views, an electro-hydraulic servo `mechanism is indicated generally at 10. The servo 10 comprises an electro-hydraulic preamplifier generally 3 struction lformed with a plurality of enlarged diameter portions, or lands 27, 28, 29 and 30. Lands 27 and 28 are separated by a valve body portion 31; lands 28 and 29 are separated by valve body portion 32 and lands 29 and 30 are separated by valve body portion 35. Each land is formed `with a pair of opposed faces substantially perpendicular to the axis of the spool 14. Land 27 has faces 271 and 27r; land 28 has faces 28! and 28m land 29 has faces 29Z and 291'; and land 30 has faces Stil and fr.

Valve body portion 32 is relatively greater in diameter than valve body portions 31 and 33, and is of a slightly smaller diameter than the lands 27, 28, 29 and 30.

Lands 27 and 28 define in conjunction with valve body portion 31, and bore 15, a uid chamber' 34. Lands 29 and 3ft, in a like manner, dene a substantially identical fluid chamber 35 in conjunction with valve body portion 33 and bore 15. A third fluid chamber 36 is dened by lands 28 and 29, valve tbody portion 32 and 'bore 15. Fluid chamber 36, due to the relatively large diameter of valve body portion 32 is of a substantially lesser volume than chambers 34 and 35.

Port 19 is connected tol conduit 37 which is connected to a tiuid motor M. Port 23 is connected to conduit 38 which is in communication with the opposite side of the motor M. The valve 12 is operable to select the direction of fluid flow by connecting port 19 or 23 with the uid pressure source.

Port 18 is in communication with a source of uid pressure provided by a pump P, as is port 25, and port 22 is an exhaust port and is in communication with the sump S.

Port 17 is connected to conduit 40 which is in communication with branch conduit 41. Branch conduit 41 is in communication with a fixed nozzle 42 at one end thereof, and a fixed orifice 43 at the other end thereof. Similarly, port 26 is in communication with conduit 44 which in turn communicates with branch conduit 45. Branch couduit 45 is connected to nozzle 46 at one end thereof, and orifice 47 at the other end. Nozzles 42 and 46 are situated in case 16 in a position diametrically opposed to one another in a central discharge chamber 48. The orifices 43 and 47 are connected to the pressure source through ports 49 and 50 respectively.

Port 2i) is in communication with a diaphragm 51 through a conduit 52. A diaphragm 50 is secured in any manner well known in the art in the casing 16, and divides an enlarged portion 53 of conduit 52 into chambers 53a and 53b. In a like manner, port 24 is in communication with diaphragm 54 by means of conduit 5S which has an enlarged portion 56. Diaphragm 54 is secured in the enlarged portion 56 of conduit 55 in any manner well known in the art and divides enlarged portion 56 into chambers 56a and 56b. Slots 57 and 5S are provided in casing 16 in order to allow communication of chambers 53b and 56b with discharge chamber 48. Rigid projections or pins 59 and 60 are secured respectively to diaphragms 51 and 54, perpendicular thereto and extend through slots 57 and 5S, and into chamber 48.

Port 21 is in communication with chamber 48 through conduit 61 which is in constant communication with port 22 and thence to sump S, thereby maintaining chamber 48 and chambers 53b and 56b at sump pressure at all times.

Referring now to the electro-hydraulic preamplifier 11, there is found an electrical input sensing device 65 comprising a permanent magnet 66 having a laterally extending north pole piece 67 and south pole piece 68, and a mechanical input amplifier 69.

'I'he amplifier 69 which is used here is generally known as a flapper valve. The dapper is of a generally T shape, having a cross bar 70` and stern portion 71. The dapper is mounted on a pair of fulcrums 72 secured to casing 16 in a channel 73 -which is in communication with charnber 48.

The cross bar 70 acts as an armature, having a plurality of winds of electrical conducting wire thereabout. The terminals of the cross bar extend between the pole pieces 67 and 68 of the permanent magnet, and are operable to assume any position between the pole pieces by pivoting about the pivots 72.

The stem 71 of the apper extends through channel 73 and into the chamber 4S. in so doing it passes between the diametrically opposed nozzles 42 and 46, which are continuously discharging fluid against the face of the stem. The discharge from both nozzles is substantially equivalent and opposite in direction thereby providing a balance of fluid forces on the stem. At the terminal of the stem 71 opposite that which joins with the cross bar 70, there is a transverse member 75 to which a pair of relatively exible members such as cantilever springs 76 and '77 (shown by way of example in FIG. l) are attached. The cantilever springs extend downward (as seen in FIG. l) into chamber 43 parallel to stem '71, so as to be in a position opposite the pins 59 and et), and in such relation so as to allow the pins 59 and 69 to effect a movement of its adjacent cantilever spring in a manner which will be described hereinafter.

In operation, an input signal in the form of an electric current is transmitted to the armature 79 of the l'lapper 69. The iiow of current in the windings about the armature creates a magnetic field having a certain polarity depending upon the direction of current flow. The terminal points of the armatures will accordingly assume the nature of a south or north pole. The pole thus created will then be attracted to its opposite on the permanent magnet 66 and the flapper will rotate accordingly to a position where the magnetic and fluid forces, which consist of the opposing discharge from nozzles 42 and 46, are again balanced. The amount of attraction is a function of the strength of the input signal or current.

In response to the input signal the apper 69 will be rotated about the fulcrum 72 in `amount proportional to the strength of the input signal. The resultant movement will bring the stem 71 relatively closer to one of the nozzles 42 or 46.

Simultaneously, assuming the valve 12 to be initially in a neutral position, fluid pressure is continuously provided to uid chambers 34 and 35 by means of pump P. In a like manner, fluid under pressure is supplied to ports 49 and 50. The fluid under pressure supplied to ports 49 `and 56 passes respectively through orifices 43 and 49 and into conduits 41 and 45 respectively at `a reduced pressure as determined by the orifice size and initial pressure of the fluid. The fluid flow in conduit 41 is then divided, a portion thereof being discharged through nozzle 42 Ias before mentioned While the other portion thereof is passed through conduit 40, through port 17 and into bore 15 Where it is impressed upon face 271 of spool 14. In a like manner, the fluid in conduit 45 is divided, a portion thereof being discharged through nozzle 46 while the remaining portion passes through conduit 44, through conduit 46 and into bore 15 at the opposite end thereof where it is impressed upon face 301l of spool 14.

The hydraulic circuit previously described is so constructed that when the val-ve spool 14 is in the steady state neutral position, the pressures on the spool 14 are everywhere in balance. That is to say, the forces of the uid on face 271 are equivalent to the forces of the uid on face 301, and in a like manner, the fluid forces in each chamber 34, 35 and 36 are balanced so that the valve spool 14 is static.

The uid being discharged through nozzles 42 and 46 passes into discharge chamber 48, and through conduit 61 and is exhausted to sump.

As previously indicated, the iiapper 69 is caused to rotate when an input signal is transmitted to the preamplifier 11. This rotation yabout the fulcrum 72 causes the stem 71 to move relatively closer to one of the nozzles 42 and 46. In so doing, the stem offers a restriction to Y the ow of uid from the nozzle to which the stem has moved. f

For example, assume thatl an input signal has been received which causes a clockwise rotation of the iiapper. The stem 71 is then moved relatively closer to nozzle 42. The result of this movement is a restriction of the uid ow from the nozzle 42 accompanied by a decrease in restriction of uid flow from nozzle 46. The fluid flowing in conduit 41, sensing a greater resistance to flow through the nozzle 42 will begin back up in conduit 41 building pressure in conduit 40 and subsequently the fluid force on face 271 will increase.

Simu-ltaneously, more fluid will flow through nozzle 46 which is now relatively less restricted by the stem 71. This change in flow is accompanied by a decrease in pressure in conduit 44- and an accompanying decrease in the fluid forces on face 301'.

This adjust-ment of the pressures acting on the spool results in a movement of the spool 14 tothe right as seen in FIG. 1.

As spool 14 moves to the right, land 28 will gradually uncover ports 19 and 20. The progressive uncovering of port V19 allows iiuid under pressure from the pump to pass from chamber 34 through port 19 and into conduit 37 with increasing lacceleration to the fluid motor M, which is here shown as of a diierential pressure type. As before noted, as port 19 is uncovered .port 20 is also uncovered, and in a like manner, uid under pressure from iluid chamber 34 will flow through port 20, conduit 52, and into chamber 53a where it is imposed upon the diaphragm 51.

As the spool moves to the right, port 23 is simultaneously opened by the land 29, thereby allowing iuid in conduit 38, which is attached to the other side of the diierential pressure `motor M, to pass through port 23 into chamber 36 and thence to sump through port 22. In this manner, the pressure in conduit 38 is reduced whereby a diiferential pressure is created on the motor M to'actuate the same. As land 28 opens ports 23 and 24 are also opened, thereby exposing chamber 56a to atmospheric pressure through chamber 36 land port 22 to sump.

The spool 14 will continue to move to the right as long as there is an unbalance of iiuid forces, in that direction, on it. In order that the spool response will be proportional to the inputsignal, it is necessary to provide a means -for stopping the spool progress when it has successfully opened port 19 the precise amount to provide the uid pressure differential to the motor which is called for by the input signal. To this end, -means is provided in the uid circuit for sensing the iiuid pressure delivered to the motor including means -for causing retardation of the valve spool and feeding the information back to the operating mechanism in order that the valve spool may be stopped in a position which will allow the delivery of the desired output pressure.

The before mentioned means includes opposed diaphragms 51 and 54 having transverse pins 59 and 60 respectively mounted thereto. The pins are so positioned as to contact the cantilever springs 76 and 77, when the desired output pressure is attained, for urging the springs, and subsequently the stem 71, away from the particular nozzle which is being restricted thereby in response to the input signal.

The actuation of this feedback 4mechanism is accomplished as follows:

It is seen from FIG. 1 that as the valve spool 14 moves to the right, thereby uncovering ports 19 and 23, that ports 20 and 24, being diametrically opposed (as shown in the drawings), in casing 16, to ports 19 and 23', will also be uncovered at the same time and by the precise amount as por- ts 19 and 23. Therefore, as the iiuid under input pressure which is in chamber 34, flows between land 28 and port 19, so too, fluid at the same pressure flows through port 20. Land 28 in conjunction with ports 19 and 20 form a sharp edged orifice which will cause a 6 reduction in fluid pressure proportional to the size of the orifice. Therefore, the pressure flowing to the motor M through conduit 37 will kbe at some pressure less than that input pressure which is in chamber 34. Since the size of the orifice at port 20 is identical to that at the por-t 19, the pressure in conduit 52, and that subsequently acting against diaphragm 51, will be the same pressure which is applied to the uid motor M.

Accordingly, and in the same manner, the pressure in chamber 56a acting on diaphragm 54 will be substantially equivalent to the pressure in conduit 38, which represents the pressure on the low pressure side of thermotor as a result of the rightward movement of the valve. As beforer mentioned, the -low side pressure is normally at sump pressure due to the direct connection through port 23, chamber 36 and port 22 to sump. .y

In this manner, the pressures acting on diaphragms 31 and 34 which is sensed by stem 71 through the action of pins 59and 60 on springs 76 and 77, represents the differential pressure on the uid motor M which is actuating the same. Accordingly, each diaphragm Vwill respond to the iiuid pressure acting thereon, which in the present r description will result in a rightward movement of diaphragm 51 and pin 59 against spring 76.

The rightward movement of the pin 59 exerts a force on the spring 76, in proportion to the pressure acting on diaphragmrSl, to urge spring 76, and accordingly ste-m 71,`towards the right. At the same time, spring 77 which is in contact with diaphragm 54 by means of pin 60 will be urged towards the right, the result being a tendency to urge the stem 71 in a counter clockwise direction in opposition to the force of the input signal.

The subsequent movement of the stem 71 back in the counter clockwise direction, will, of course, tend to relieve the restriction at the nozzle 42. As the restriction is relieved, the pressure in conduit I40, which is acting on face 271 to move it to the right, will decrease. This readjustyment will continue until the unbalance of the pressures on the diaphragms 51 and 54 are no longer effective to cause movement of the stem 71. `At this time, theoretically all the -forces acting on the spool 14 will be balanced and the spool will be stationary at some position which will provide the precise output pressure called for by the input signal.

In servo systems of the general type described hereinabove, there is sometimes a tendency towards instability which may result in oscillation of the valve and other attendant diiliculties. The unstable conditions in systems of this type may be `founded in a variety of adverse forces, among which are transient tiow forces, which in certain instances may be a determinate cause of instability. FIG. 3 is a scalar diagram of these `forces showing how they effect the valve 12. Transient yiiow forces include the reaction forces to the acceleration and deceleration of the iiuid entering and exhausing from the valve.

In the instant example, uid under pressure passes through the orifice formed between land 28 and ports 19 and 20 at a progressively increasing velocity as spool v14 uncovers the ports. This fluid passes through the orifice at an angle 01. Fluid from the motor M re-enters valve 12 through an orifice -formed between land 29 and port 23 at an angle 62.

Remembering that in the example, the valve spool 14 is -moving to the right, a particle of iiuid in chamber 34 will -be accelerated to the right as the spool moves. Accordingly, there is a reaction vforce to the acceleration of the iiuid particle which will be imposed upon the spool in opposition to its direction of motion. The magnitude of the force is a yfunction of jet angle and the amount of fluid in the chamber which is proportional to the len-gth of the chamber, and the rate of fluid acceleration.

In a like manner iiuid entering through the orifice be tween port 23 and land 29 will enter at an angle greater than the fluid entering having an acceleration to the left. The reaction -forces to this acceleration will be in the same direction as the movement of the spool and therefore will complement the movement of the spool and tend to further accelerate it. This is known as negative damping.

Assuming the fluid ow to enter and leave chambers 34 and 36 at the same angle, it is seen that if the number of particles in chamber 34 is greater than the number of particles in chamber 36 the sum of the reaction forces will be greater acting in opposition to the movement of the spool than the reaction forces acting to complement the movement of the spool, thus causing a very unstable situation in which the valve spool may tend to oscillate at a high frequency and otherwise show unstable tendencies.

It is the basic purpose of this invention to provide a method of controlling the transient ilow forces by means of modifying the jet flow angle of the fluid. It has been found that if the particles of fluid entering chamber 36 are allowed to enter and leave in such a manner that the greater portion of the reaction forces will not act upon the spool itself, but rather on the valve casing 16, that the negative damping forces will be reduced. To this end, valve body portion 32 has been greatly increased in diameter so as to cause a decrease in the volume of chamber 36. As seen therefore, in FIG. 3, uid entering and leaving chamber 36 must then do so at an angle approaching 180. This being the case, the greater portion of the negative damping forces of the uid are on the casing 16 and conduit 38.

In chamber 34, however, the valve body portion 31 is of a conventional size, and as shown in FIG. 4, the jet angle of the fluid entering and leaving chamber 34 approaches 90. Thus an opposite result is attained in that a great portion of the reaction forces to the acceleration of the uid particles in chamber 34 acts on the spool in opposition to its velocity to the right. This provides a desirable positive damping of the spool with little or no negative damping, and accordingly no valve oscillation or instability.

The total result of the improved structure is the damping of the spool accompanied by the increased stability of the hydraulic valve.

While this invention has been described in connection with certain specic embodiments thereof, it is to be understood that is by way of illustration and not by way of limitation and the scope of this invention is defined solely by the appended claims which should be construed as broadly as the prior art will permit.

What is claimed is:

l. In a uid system through which uid under pressure is owing, a control valve comprising a casing having a bore, a movable valve element slidably retained in said bore, said element being formed with a plurality of body portions and a plurality of lands, said body portions and said lands defining, in co-operation with said casing, a plurality of fluid chambers, each of said chambers having at least one port to allow the intake or exhaust of uid, said movable element being operable to allow Huid to exhaust or enter said chambers, said chambers having an axial area considerably greater than the area of said ports to provide a linear ow path in said chambers, said fluid when entering or exhausting from said chambers exerting certain flow forces on said movable element whereby said movable element is urged to move in an oscillatory manner, said movable element having relatively larger body portions between sorne of said lands and relatively smaller body portions between others of said lands, whereby tluid entering or exhausting from certain of said chambers will do so in a relatively axial direction `while fluid entering or exhausting from others of said chambers will do so in a relatively radial direction, whereby oscillation damping forces are created to act on said movable element whereby said movable element is stabilized.

2. In a fluid system, a control valve comprising a. casing having a bore, a movable valve element slidably retained in said bore, said element being formed with a plurality of body portions and a plurality of lands having a diameter substantially equivalent to that of the bore, said lands being in axial spaced relation between said body portions of said movable element, said body portions and said lands together defining, in cooperation with said casing, a plurality of fluid chambers, each chamber having a uid port to allow the intake or exhaust of uid, said movable element being operable to allow uid to exhaust from certain of said chambers and to enter others of said chambers, said fluid exerting certain ow forces on said movable element by virtue of its movement whereby said movable element is urged to oscillate, said movable element having an enlarged body portion between said lands defining, in co-operation with said Casing, said others of said chambers, into which Huid is flowing, and a relatively smaller body portion between said lands defining, in co-operation with said casing, said certain of said chambers from which fluid is exhausted, whereby uid llowing in said certain of said chambers exhausts in a relatively radial direction while the fluid owing in said others of said chambers is caused to enter in a relatively axial direction, whereby oscillation damping forces are created which stabilize said movable element,

References Cited in the file of this patent UNITED STATES PATENTS Hodgson Nov. 12, 1957

Images