US3058450A

US3058450A - Hydraulic positioning servo system

Info

Publication number: US3058450A
Application number: US822774A
Authority: US
Inventors: Lissau Frederic
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-06-25
Filing date: 1959-06-25
Publication date: 1962-10-16
Anticipated expiration: 1979-10-16

Description

Oct. 16, 1962 HYDRAULIC POSITIONING Filed June 25, 1959 .-.llrEll- F. LISSAU SERVO SYSTEM 4 Sheets-Sheet 2 Oct. 16, 1962 Filed June 25, 1959 F. LISSAU HYDRAULIC POSITIONING SERVO SYSTEM 4 Shee'cs-SheecI 3 f 92 ,e7/H 93" INVENTOR.

FR EDEN/c L 55A z/ ley/My Q1 M Oct. 16, 1962 F, USSAU 3,058,450

HYDRAULIC POSITIONING SERVO SYSTEM Filed June 25, 1959 4 Sheets-Sheet 4 INVENTOR.

FREDERIC L /55/1 L/ BEM/f Unite @rates This invention relates to a hydraulic `system for controlling apparatus, and more particularly to a hydraulic positioning servo system. i

The prior art for this invention is to be found in the text Oil Hydraulic Power and Its Industrial Applications lby Ernst, on page 309, where FIG. 242 shows a flow divider valve. The flow divider valve, or flow control, may be compared to an electrical component, such -as a Wheatstone bridge. Referring to this ligure, which for the sake of discussion is illustrated in the drawings of this application, the illustration has been identiiied according to the text, and it P2 exceeds P1 the valve will move to the left, decreasing resistance R4 and increasing resistance R3. This will cause Pl. to approach and finally equal P2. The iluid flow through each leg of the bridge as illustrated is determined by the equation Since P1 must equal P2 at [all times, the right sides can be equated, thereore The ilows Q1 and Q2 are independent of the pressures in the system. If resistances R1 and R2 are made exactly equal, the ows in each leg of the bridge -will be equal, regardless of loads L1 and L2, either of which may be zero.

The text labove identified, according to this ligure, shows a flow from Q to either side of the flow `divider and out legs L1 and L2, whereas applicants -device is a reverse flow, that is applicant provides a flow to the center of the :Elow divider, land in turn to either end of the ilow divider out of two legs similar to L1 and L2.

Prior art includes the servo valve manufactured by Cadillac Gauge Co., and identitied as their Series FCZOO. In this particular valve, shown as FIG. l in their catalog, they use a apper valve that is electrically operated and controlled. This ilapper valve is used for a displacement of the ratio ilow divider. The operation of the apper valve controls the displacement of the rspool valve illustrated, and the spool is displaced proportionally. In o this valve with an axial load the pressure deteriorates. This is because the iiow will he throttled by the motion of the spool valve in such a way as to drop the pressure on the side opposing the load. In the Cadillac valve the pressure is fed to both ends of the spool and there is thus provided an orifice at each end where the fluid passes through to the apper valve. The movement of the spool valve is not similar in any sense to the repositioning of the piston as in applicants device. In the Cadillac valve the spool movement is limited to a Small displacement. In this valve, the spool cannot resist any load, further the spool is not connected to any other member, it moves perfectly free, and in this valve, for proper functioning of the apper valve, it is necessary that the flow be directed against the dapper.

The prior art illustrates Various positioning servo systems, but in each instance the servo system is either electrically operated or a combination of hydraulic and electric or a hydraulic system with a mechanical feedback, whereas it is an object 4of the present invention to provide a remote controlled positioning servo system comprised entirely of hydraulic components.

MESAS@ Patented Oct. 16, 1962 ry ic@ All prior art discloses the position of a valve (in the form of a spool) which acts as a governing element, whereas it is an object of this invention to provide a cylinder primarily designed to perform a force displacement relationship.

It is 'a further object of this invention to provide a. hydraulic servo system in which there is provided a hydraulic cylinder with a linear position seeking piston therein, :and in which a fluid pump is connected through a ratio flow divider to opposite ends of said Ihydraulic cylinder.

A still further object of this invention is to provide a hydraulic servo system in which there is provided a hydraulic cylinder with a linear position seeking or nonposition seeking piston therein, and in which a lluid pump is connected through a ratio flow divider, and the ratio flow divider in turn to a sensing null unit Iand in turn to opposite ends of said hydraulic cylinder, and in which said position seeking piston is in turn connected to a piston in `a power cylinder that is either in alignment or in parallel with said iirst cylinder, and a second fluid pump may be connected through an amplifier valve to opposite ends 4of said power cylinder, and said ampliiier valve is controlled in its movement by the sensing element of the null unit.

It is 'a still further object of this invention to provide a hydraulic servo system, in which there is provided a circular hydraulic cylinder with a position seeking rotor therein, and in which a fluid pump is connected through a ratio dow divider to opposite sides of said rotor in said hydraulic cylinder.

A still further object of this invention is to provide a plurality of hydraulic cylinders, in which each cylinder is provided with a linear position seeking piston therein, Iand in which a fluid pump is connected through ya ratio ow divider to opposite ends of each hydraulic cylinder.

A still further object of this invention is to provide a plurality of hydraulic cylinders in which each cylinder is provided with a linear position seeking piston therein and in which a iluid pump is connected to a plurality of ratio flow dividers, and in which all of the ratio flow dividers may be synchronized hy la single element, and in which each ratio ilow divider is utilized with one of said hydraulic cylinders by connecting said ratio flow divider to opposite ends of said cylinder.

A still further object of this invention is to provide a plurality of hydraulic cylinders in which each cylinder is provided with a linear position seeking piston therein, and in which there is provided a ratio flow divider connected to each cylinder at opposite ends thereof, and in which there is provided a pump that is connected to the hrst ratio iiow divider to eiect the operation of the position seeking piston in the iirst cylinder, and in which the iluid ow out of said first cylinder is in turn connected to the ratio flow divider of the next cylinder, and in which each subsequent ratio ilow divider and cylinder are similarly connected and in which said linear position seeking pistons will be operated in series.

A still further object of this invention is to provide `a plurality of hydraulic cylinders in which each cylinder is provided with a linear position seeking piston therein, and in which there is provided a ratio flow divider connected to each cylinder, and in which there is provided a pump that is connected to each ratio flow divider and in which said linear position seeking pistons will be operated in parallel relationship.

A still further object of this invention is to provide a hydraulic servo system in which there is provided a hydraulic cylinder with a linear non-position Seeking piston therein, and in which a fluid pump is connected through a ratio tiow divider to opposite ends of said hydraulic cylinder.

A stili further object of this invention is to provide a hydraulic servo system, in which there is provided a circular hydraulic cylinder with a non-position seeking rotor' therein, and in which a fluid pump is connected through a ratio ilow divider to opposite sides of said rotor in said hydraulic cylinder.

It is a further object of this invention to provide a hydraulic fluid servo system in which there is provided a fluid ilow divider, and in which a hydraulic cylinder with .a linearly positioned piston therein is connected from .either end of said cylinder to either end of said ow divider, and in which a iluid pump is connected to a central inlet on said hydraulic cylinder to produce a capillary flow over said piston to either side of said cylinder -and in turn to either side of said iiow divider and to be discharged Ifrom the single outlet of said ow divider.

Other objects of this invention shall be apparent by reference to the accompanying detailed description and the drawings in which:

' FIG; 1 is a schematic, partially in cross-section, of a linear position seeking hydristor system;

CFIG. 2 is a schematic, partially in cross-section, of a non-position seeking hydristor system;

FIG. 3 is a schematic, partially in cross-section, of a rotary position seeking hydristor system;

FIG. 4 is a schematic, partially in cross-section, of an lunbalanced linear position seeking hydristor system;

'-FIG. 5 is a schematic, partially in cross-section, ratio ow divider;

FIG. 6 is a schematic, partially in cross-section, further embodiment of FIG. `1;

FIG. 7 is a schematic, partially in cross-section, still further embodiment of FIG. l;

FIG. 8 is 'a schematic of a`still lfurther embodiment of FIG. l;

FIG. 9 is'a schematic of a still further embodiment of FIG. l;

FIG. 10 is a schematic, partially in cross-section, of a further embodiment of FIG. l;

FIG. 11 is a schematic, partially in cross-section, of a still further embodiment of FIG. l;

FIG. 12 is a cross-sectional view of a further embodiment of FIG. 3;

FIG. 12A is a cross-sectional View taken on line 12A-12A of FIG. 12;

FIG. 13 is a cross-sectional view of 'a further embodiment of FIG. 2; FIG. 14 is a cross-sectional View of a still -urther embodiment of FIG. 2;

FIG. 15 is a schematic of a further embodiment of a non-position seeking hydristor;

FIG. 16 is a cross-sectional view of a further embodiment of FIG. 3; Y

FIG. 17 is a cross-sectional View of a further embodiment of a non-position seeking hydristor;v

FIG. 18 is a schematic, partially in cross-section, of a servo system with position seeking hydristor;

FIG. 19 is 'a schematic of a load compensated power system;

FIG. 20 is a schematic Vshowing a sub-system which may be addedto FIG. 18; FIG. 2l is a schematic showing a prior art reference; and

FIG. 22 is a schematic showing a further embodiment of this' invention. Referring to the drawings and particularly FIG. 1, there is illustrated a hydraulic cylinder lil, which there is mounted a piston 11. The piston is provided with a piston rod 12 that extends either side of said piston and passes through a rod bearing or aperture 1li at either end thereof. 'Ihe cylinder 10 is provided with three ports, a central outlet port 1S and a pair of

inlet ports

16 and 17,

ports

16 and 17 being positioned adjacent the opposite ends of said cylinder 10. It is to be noted that the outlet ofa ofa

ofa

port 15 is in fact a circular groove or opening surrounding the center of said cylinder.

It is to be noted that piston 11 may be provided with very slight clearance or with fairly large clearance lfrom the walls of the cylinder 10, and due to the piston rod 12, piston 11 -will be maintained in a concentric position at all times. The clearance between the piston 11 and the inner wall of cylinder 1t) is to permit the flow of the hydraulic fluid from either side of the cylinder over the surface of the piston and out through the outlet port 15. This device as described shall be referred to hereinafter as the hydristor. Hydristor, being a coined word, may be defined as amechanical assembly such as a hydraulic cylinder with a piston mounted therein, a Ifluid inlet pressure port at each end and a luid return port at the center of said cylinder. The piston is iitted within the cylinder with enough clearance to allow a capillary flow or leakage past the piston. The piston member is displaced as a function of output position, there are two complementary resistances created, R1 and R2; their ratio R1/R2 is therefore a function of output position. Each of the resistances is connected in series, that is through the legs or pipes to opposite ends of the ratio ilow divider 30 with similar resistances r1 and r2, which are created in reverse'order in the ratio flow divider as a yfunction of input position, so that the pressure pl and p2 in the legs or pipe connections equal each other if Rl r1 Thus, it is the purpose of the hydristor to utilize the pressure diterential p1 and p2 as a remote input signal or error signal. Since the pressures p1 and p2 are created by the input setting of rl/rZ, it would be equally correct to state that the ratio rl/rZ is used as the input signal, and the pressure differential P1 and P2 as the error signal. There are two types of hydristors; I is a position seeking type, and II is a non-position seeking type. With the position seeking hydristor, both ends of the cylinder are closed to allow the iluid to act on the area at the end of the piston. When the pressure on each side of the piston is equal, the piston will be in equilibrium. It is apparent that as the pressure on either side changes, the piston will seek a new position.

VReferring to FIG. 2, there is illustrated a non-position seeking type of hydristor that is comprised of a cylinder 20 with :both ends open. Mounted within the cylinder is a double piston 21. The double piston is formed with two equal piston exterior surface areas 22. and 23, spaced from each other but connected by a rod 24. Piston 21 is provided with a seal 25 at either end thereof, cylinder 20 is provided with three ports, an outlet port 26 and two

inlet ports

27 and 28. The inlet ports are provided 'as a circular groove or opening surrounding the piston, and should be positioned about the center of the normal linear movement of the piston, whereas the outlet port is positioned at the center of cylinder Ztlu adjacent the open area surrounding rod 24. U

It is to ybe noted that with the nonposition seeking type, both ends of the cylinder are open and the piston is in reality two spaced equal displacement pistons that are joined -by a piston rod, leaving an open area in the center of the cylinder adjacent the outlet port. Both pistons may be provided with a seal over their outer ends, and vthe inlet ports must lbe positioned about the lineal center of each piston. The uid that is normally -fed in through the inlet ports 27 and 28will leak or seep or flow from veach inlet port toward the outlet port (center) providing a complementary hydraulic resistance whose ratio is a function of the displacement of the moving member (two pistons). The non-position seeking hydristor does not provide any effective pressure areas.

Y The hydristor lends itself to many variations in design and structure and also to many application in use, and of course, the hydristor whether of type I, position seeking, or II, non-position seeking, is not usable or operative as a single element, but must be considered as a part of a system or combination of component parts, depending upon the particular problem.

The simplest combination for the position seeking hydristor is with a ratio flow divider 30, YFIG. 1. The ratio flow divider may take the form of a three ported body 31, the inlet port 32 at the center, and both

outlet ports

33 and 34 equally spaced `from center (laterally); `a central bore 35 is iitted with a slidable piston 36, the piston is provided with an enlarged central portion 137 to divide the ow, and is also connected to rod 38 extending in a linear direction through either end of the body to allow physical movement of the flow dividing body 37. A pump 40 is connected to a rlluid supply 41 and thus the fluid pressure outlet of said pump is in turn connected to the inlet port 32 of the ratio ow divider 30. With the flow dividing body 37 centrally positioned there is an equal flow to both

outlet ports

33 and 34 and the hydristor will receive an equal flow to each

inlet port

16 and 17 and remain in equilibrium; however, if the rod control 38 is moved laterally right or left the flow is divided in an unequal proportion, depending upon the degree of movement and in turn the iluid flow to the hydristor is effected, one inlet receiving a greater flow than the opposite inlet and effecting an unbalance or movement of the piston until a static position is reached.

Referring to the ratio ilow divider 30, the position of the central portion 37, which is generally spool shaped with an angular land 42. on one side and `43 on the other, provides an everchanging opening between the land 42 or 43 and the associated edge 44 of the body 31. Thus, there are provided two complementary openings, one on either side of the central body 37, which We may refer to as L1 and L2. The magnitude of each opening divided by a constant C forms the hydraulic resistances r1 and r2. Thus,

rl :Z-1 and r2=% It is to be noted that the hydraulic constant C may be affected by the viscosity of the uid, temperature of the fluid, diameter -of the spool or central body, etc. It is obvious that the ratio of the two complementary resistances 1'1/12 is independent of this constant, since L1 rl O Ll 72!2-122 C' Therefore, the ratio of the resistances r1 and r2 equals the ratio of the displacement L1 and L2, and is independent of all other variables.

It it to be noted, referring to FIG. 1, that the hydristor creates two complementary resistances opposing the ow of the two pressure legs r1 and r2, whose ratio is a `function of the displacement of the hydristor piston 11 so that R-z-Lz' Referring to FIG. 1, and particularly the piston 11, it may be desirable to increase the flow or leakage over the piston to the outlet 15. It may not be desirable to increase the clearance of the piston. The leakage or oW may be readily increased -by inserting one or more lateral slots -13 along the surface of piston 11. Thus the piston 11 may be maintained in its lateral position with only the desired clearance for movement within the cylinder and the lateral slots `13 may provide the desired flow.

The same combination of hydraulic components used in FIG. 1, with the position seeking hydristor, may also be used in FIG. 2, with the non-position seeking hydristor, that is the

inlet ports

27 and 28 may be connected to the ratio ilow divider 30 by

ports

33 and 34, and the ratio flow divider, in turn, may be connected to S the pump `40 through port 3-2. With the device so connected, the non-position seeking hydristor can be used as a `feedback element to attain position control.

Referring to FIG. 3, there is illustrated a rotary position seeking hydristor 5th This is similar to the linear hydristor shown in FIG. 1, except that the hydraulic cylinder in this example takes the form of a circular housing 51 closed at either end thereof, with a circular aperture 52 at either end thereof. A stationary partition 53 is provided that is aiixed to body 51 and bears against the edge of a rotor `54. Rotor 54 is pivotally mounted in the circular apertures 52 at either end of body -51 and extends through these apertures to provide a rotary piston rod or drive shaft on eit-her side of the body 51. Rotor 54 is also provided with a semicircular body 55 of a diameter slightly less than the internal diameter of body 5-1. The clearance between the outer periphery of this body and the inner periphery of body 51 provides the necessary clearance or space `for the flow of fluid from the area 0n either side of the partition 53 to an outlet port 56. A pair of inlet ports 57 and 5S are provided adjacent either side of partition 53. The rotary position seeking hydristor 50 is combined with the other hydraulic components namely the ratio flow divider `and, fluid pump, in the same order as described in FIG. 1, so that with a fluid flow from the pump through the ratio dow divider, vlluid will ow into the chambers on either side of the partition 53, and with equal pressure on either side thereof, the rotor body 55 will maintain the position as illustrated in FIG. 3, with the uid leaking, seeping or passing over the surface of the rotor body 55 to the outlet port 56 `and thus being expelled. It is apparent as in FIG. 1, when rod 3S is moved to the right or left that the fluid pressure on either side of partition 53 -will be changed and there will no longer be an equilibrium. Thus, with an increase in pressure on one side and decrease on the opposite side, rotor body 55 will be rotated to a new position until a static balance is obtained. This degree of rotation is utilized by apparatus not shown in the same manner in which degree of linear movement of piston 111 may be utilized as shown in FIG. 1. With the rotary position seeking hydristor two effective areas, A1 and A2, may be effected by pressures in leg 1 (inlet 57) and leg 2 (inlet 58) creating the motive forces for the hydristor piston and piston rod. The areas A1 and A2 do not have to be of the same magnitude, as the hydristor can also be operable with the piston rod protruding from one side only.

Referring to FIG. 4, there is shown what may be termed :an unbalanced hydristor. In for-1n, it is quite lsimilar to that shown in FIG. 1, except that piston 11 is provided with a single piston rod 14, which protrudes through one end of cylinder 10. The unbalanced hydristor is designed specifically for one 'type' of installation `and that is Where response in one direction should be faster land/or with more power than in the opposite direction. In this example, the piston 11, under the influence of a dierential pressure, will move in the direction of the lower pressure until equilibrium is` obtained. The equilibrium position of the hydristor piston with no load -applied depends on the ratio r1/r2. Due to the unequal areas a diierential pressure must exist for equilibrium. The equilibrium position of the piston is modiiied proportionally tand in the direction of the load. The hydristor piston rod will give under a load and the contact pressure of .the hydristor piston rod can be varied by ychanging the ratio rl/ r2. The effective Area A (FIG. 4) used for motive power can be combined with the hydristor 10 to form a position seeking hydristor. The pressure differential p1-p2 thus will act on the eiective area of the hydristor piston 11 and seek -to move the piston 11 into the desired position. Under a load Ithe piston 11 will 4reposition itself tto la new position which will be proportional to the load. The hydristor 111 (FIG. 4) can valso be used as a feedback element in Ia 'servo system'.

'ansa-.tao

Referring to FIG. 5, there is illustrated an enlarged det-ail of the ratio dow divider 30v of FIG. 1.V The ratio ow divider may be of an unbalanced design so that the operator may actually feel Iany transfer of position. The unbalance. is due to the design Without the balancing pistons. Even with this design, the move-ment of rod 38 can create a hydraulic balance, a point at which no load is felt. However, if a load is applied on the hydraulic piston immediately the balance will be changed and the operator may lfeel the load on the lsignal input rod 38.

Referring to FIG. 6, there is illustrated a plurality of hydraulic cylinders 10, similar to those illustrated in FIG. l, and a ratio How divider 30 `and a pump 40. In this embodiment, the

ports

33 and 34 of the ratio iloW divider are connected in parallel, that is port 33 is connected to each of the ports I6 of the hydristor 10 while port 34 is connected -to each of the ports 17 of the hydristor 10. Thus, With this arrangement, When the ratio flow divider 3i) is in equilibrium, the fluid ow Will be equal to each of the hydristors `and as in the previous embodiment any movement of the control rod 38 will change the proportionate iiow increasing or decreasing the ilow to the opposite sides of the various hydristors. Of `cou-rse it is apparent that any change will produce Ian equal response on each hydristor.

Referring -to FIG. 6, it is obvious that if a load is applied to the piston rod of one of the hydristors, its Rl/RZ ratio -Will change. With this change, the pressures P1 iand P2 Will also change. Thus, a new flow pattern will be superimposed on the pattern set up by RI/RZ for the remaining hydristors. For example, if a load i-s applied on the piston 14' of hydristor #2, then the piston rods of hydristors #l Iand #3 will reposition themselves since the fluid will take the path of least Iesistance with the motors connected in parallel, moving upward by :a distance proportional to thel load applied on piston rod 14' of hydiistor #2. This general arrangement or application `of the device may be, 1for example, a remote reading pressure transducing device Where one piston 14 is the pressure transducer and the other piston may be connected to gauges measuring the force or pressure.

Referring toYFIG. 7, there is illustrated a cross-sec- 'tional view of `a ratio dow divider 30'. In this embodiment, the design of the original flow divider 30 shown in FIGS. 1 and 6 is simply multiplied. There arel lthree central bores 35 and there are three slidable pistons 36, one in each bore, and there are three connecting rods 38, each one connected to the slidable piston 36, and the three connecting -rods 38 faire in turn joined eto 'a single control rod 38'. Each bore 35 is provided with the same configuration as in FIGS. 1 'and 6 and with the same porting. However, it lis to be noted that in the enlarged body 31', the inlet port 32 from the pump must he ported from the one bore 3S to Vthe next bore 35 and Vagain ported 'to the third bore 35', so that the iiuid flow Will be to the center of each bore 35, as shown in FIG. 7. The ratio flow divider 30 .thus provides (in this instance) three controls or ratio flow dividers which may be of the unbalanced design, each one being connected fto a separate hydristor. The importance of this embodiment is in the use of a multiplicity of position seeking hydristors Where there iare. diierent individual loads. In this embodiment, the interaction as in the yabove embodi- 'ment is eliminated, `the ratio flow dividers may be actuated in unison and they will have equal effect if the ratio ow dividers are identical or if the ratio flow dividers are varied, having diierent sizes land creating different displacement, the yactuation of the ratio dow dividers in unison can produce a sequence of different displacement patterns in the hydristors to which they are connected. This embodiment provides a predetermined positive displacement in each hydristor. This illustrates tlait is not load compensated.

Referring to FIG. 8, in which there is a duplication of ,the general arrangement of pump, ratio iiow divider and position seeking hydristor shown in FIG. l, this duplication is provided for a purpose, that is where it is desirable to produce a series of similar controls. The sen'es of components Will be controlled by a three independent single input 4signal or movement of the control rods 38", which is physically connected to `affect in equal degree each ratio flow divider. The effect of this signal produces a change in hydristor #1. Similarly each signal produces a change in hydristors #2 and #3. If there is a small tlow with high pressure We would use a series circuit, but if there is a large iioW of low pressure We Would use them in parallel.

A still further embodiment, is illustrated in FIG. 9, in which the same components are utilized, that is a pump, a plurality of ratio iiow dividers 30 and a plurality of position seeking hydristors. In this instance, the pump is connected by a single line to the inlet port of each ratio flow divider 30 to provide an equal flow and to provide that flow iat the same time. The ratio oW dividers 30 4are connected in the same fashion as illustrated in all of the previous embodiments to the hydristors. Thus, in this embodiment, the input signal produced by the movement of rod 38 for each ratio low divider may be considered individually.

Although we have described FIGS. 6, 7, 8 and 9 With relation t-o a linear position seeking hydristor, it is understood that this includes Aany form of hydristor that shall be included herein.V

In addition to the various combinations of hydristors, ratio ilow dividers and pump, there are a number of variations in the design of the position seeking hydristr, the non-position seeking hydristor and the ratio ilow divider.

Referring to FIG. 10, in which there is illustrated a linear position seeking hydristor 16', which is a further embodiment of FIG. l, in this embodiment all of the components are similar but piston l1 is, in this embodiment, provided with a central bore 19 larger than the piston and a bore 18 of equal diameter at either side thereof, slightly smaller than the diameter of the piston, and as in FIG. l the connecting

rods

12 and 14 are similarly passed through the cylinder and piston extending to a position where the movement of piston 11 may be utilized to control an auxiliary device. In this embodiment, the piston 11 is provided as a tapered piston, that is, tapered toward either end; the taper being designed to provide a flow from minimum to maximum. This design permits a greater proportional ow than that illustrated in FIG. l. y

Referring to FIG. l1, there is illustrated a still further embodiment ofthe position seeking hydristor as illustrated in FIG. l. The cylinder l0 in this embodiment is provided lwith an inner cylinder 9 that is in fact a porous material. The piston 11 is mounted within cylinder 9, and to permit the installation of cylinder 9 Within cylinder It), the ports I6 and 17 may be moved to enter the opposite ends of cylinder 9. The porous cylinder 9 may be designed to provide a very small or fairly large seepage or llow therethrough.

Referring to FIG. l2, there is illustrated a further .modification of FIG. 3. In this iigure, there is provided a rotary type hydristor and since the degree of movement of the rotor in FIG. 3 is limited to slightly less than 180, FIG. 12 provides a rotor that will permit the movement of slightly less than 360. The hydristor 50 is of a circular housing or body 51 with a circular aperture 52 at either end thereof, a stationary partition 53, that is aiiixed to the body 51 and extends laterally the length of the body and bears against the edge of a rotor 54. Rotor 54 is pivotally mounted in circular apertures 52 at either end of body 51', and extends through these apertures to provide a rotary piston rod or drive shaft on either side of the body 51. Rotor 54 is also provided with a blade 55. The blade 55 does not extend to the internal surface of housing or body 51. instead there is provided a circular partition 59, which extends from either end of said body 51 and is provided with a slot 59 at the lineal center of said body. lt is also to be noted that the

ports

57 and 58 must extend through housing 5l and through the circular partition 59 on either side of the stationary partition 53. rihus, in operation, with an equal ow on either side of partition 53, the rotor 54 will be moved so that blade 55 is in an upright position (as shown in dotted lines, FIG. 12), and of course the fluid flow will be through the slot 59 and out the outlet 56. A change in the proportionate flow may move the rotor to a position as illustrated and of course the control of the rotor will be to a degree of slightly less than 360.

FIG. 13 illustrates a further embodiment of the nonposition seeking hydristor illustrated in FIG. 2. In this embodiment, the piston 31 has been modified with a central body 2l. of smaller diameter than the internal surface of the cylinder and the piston 21 is provided with three enlarged portions 22' and Z3 at either end thereof and 24 at the center of said piston. The port 26 is also connected to a lateral slot 29 in juxtaposition with the surface of enlarged portion 24', and approximately equally spaced either side of center. Thus, with this design, the fluid ow in ports 27 and 2S will not be interrupted by the movement of piston 21 but the position of the enlarged portion 24 will be in proportion to the flow from inlet ports 27 and 2.8.

FIG. 14 illustrates a still further embodiment of the non-position seeking hydristor illustrated in FIG. 2. In this embodiment, the cylinder 20' becomes a movable reciprocating sleeve while the piston 21" ecomes a stationary supporting element. The porting to this further embodiment is also changed, that is the

inlets

27 and 28 are positioned at either end of the stationary piston 21 and the outlet port 26 is eliminated, as the fluid will escape through either end of the cylinder or sleeve 2d' and drop by gravity into the sump positioned below the cylinder. The piston 21 is provided with two bores, one bore 27 leading from port 27 to a cross bore 27" while a bore 2S leads from the port 28 to a cross bore 28". The cross bores 27 and 2S are positioned either side of a central seal 25', seal 25 being positioned at the center of piston 2l" and surrounding the periphery of the piston to prevent duid flow past the central portion of the piston. The cross bores 27 and 28" may be recessed at the periphery of the piston or a circular groove may be provided in the periphery of the piston. It is apparent that in any operation with

ports

27 and 28 connected to a radio flow divider, as in the previous embodiments, that liuid flow through

ports

27 and 23 will pass through the bores 27 and 28', through the cross bores 27 and 28, and due to the seal 25', the fluid will seep or leak between the piston exterior surface and the internal surface of the cylinder or sleeve 20".

FIG. l illustrates a still further embodiment of the non-position seeking hydristor illustrated in FIG. 2. In this embodiment, the components are slightly diierent although the method of operating is similar to that of the device illustrated in FIG. 2. The cylinder is replaced by a pair of identical complementary valves 90' and 91. These valves are fairly simple in structure, that is, a simple cylinder 92. with a reciprocal piston 93 mounted therein. The piston 93 is provided with an upper reciprocal guide 93 and a lower poppet valve portion 93". The piston is retained open or in contact with earn 96 by a spring 97. Cylinder 92 is provided with a bore for the upper portion 93 of piston 93 and an enlarged chamber 92 with a valve seat at the bottom of this chamber to receive the poppet valve portion 93". It is to be noted that the inlet is below the poppet seat, while the outlet is above the poppet seat. Piston 93 is provided with a connecting rod 94, there is an inlet port at one end and an outlet port at the other end. The inlet port of valve l@ may be connected to the same inlet 27 as in the previous embodiment, and the inlet port of valve 91 may be connected to the inlet port 2S as in the previous embodiment. The outlet port of each valve may be interconnected to a common outlet port 26 as in the previous embodiments. The connecting rod 94 may be provided with a roller or ball 95. A cam 96 is positioned to abut with both of the rollers or balls 95. Cam 96 is supported by rod 97 and rod 97 in turn may be supported in a pair of bearings 93 at either side of said cam 96. It is to be noted that cam 96 is comprised of two cone shaped surfaces with the bases abutting at the center so that the rollers may roll against the surface of the cam on either side thereof. Rod 97 may be connected to an auxiliary device such as a power cylinder. The operation of the device is somewhat similar to the embodiments already described, in that the iiuid flow from a ratio flow divider will provide the flow through

inlet ports

27 and 28. This is a non-position seeking hydristor, and the cam 96 is necessarily a linear cam that is moved horizontally by a power cyiinder (not shown). The valves 90 and 91 are balanced valves. The position of the linear carn 96 will depend upon the fluid ow `from the ratio ow divider and of course this flow, in addition to being connected to the balanced valves 9@ and 91, will also be connected to the power cylinder (not shown), thus any movement of the linear cam 96 by the power cylinder will be similarly reflected in the position taken by the balanced valves. That is, in the event the greater iiow is through inlet 27 and the lesser ilow through inlet 28, the power cylinder should move cam 96 to the right, and 'the roller or ball 95 of valve 96 will rise, while the ball or roller 95 of valve 91 will be forced downward to further restrict the ow.

Referring to FIG. 16, there is illustrated a still further embodiment of a non-position seeking rotary hydristor, which is related to the rotary hydristor of FIG. 3, but dilers in its construction in that the body 51A is provided with a single outlet port 56 at the bottom of the body, and the internal rotating body 55A is eccentrically mounted with respect to body 51A on shaft 52A. That is internal body 55A will rotate concentrically about its axis. The internal body 55A is provided with two inlet bores 57 and 58. The inlet bores are in turn connected to a pair of radial bores 57" and 58, the radial bores extending to the periphery of the internal body 55A. The inlet bores 57 and 5S are connected to a ratio ow divider (not shown). Thus, in operation, if there is an equal iow to each inlet port the internal body 55A will assume a balanced position with the radial bores 57 and 53" in a horizontal position, showing equal clearance between the internal body and external body on `either side. However, in the event the ow through inlet port 57 is more than the ow through the inlet port 58', the internal rotor 55A will assume a position as illustrated in FIG. 16, and thus produce a rotary motion indicating the unbalance. lIt is this rotary movement that is utilized to indicate the change in flow produced by the ratio ow divider.

Referring to FIG. 17, there is illustrated a `still further embodiment of a non-position seeking hydristor. This is similar to FIG. l, except that the piston 11 is provided with a threaded external periphery and the internal surface of the cylinder 10 is similarly threaded to permit a rotary movement of piston lll'. Thus even though this construction provides eiective areas for the fluid pressure that will be produced on either side of the piston, the loads or pressures would be absorbed by the threads, and although this embodiment illustrates a threaded element, it is to be understood that there will be suicient clearance at the crests and roots of the threads to permit a iluid iiow therethrough. Thus, with inlet ports i6 and 17 similar to FIG. l, the uid ilow to either side of piston lll will permit a seepage or leakage past the threads to the outlet port `15. The piston 11 will react to equal pressures or variance of pressures in the same manner 11 as the piston 11 of FIG. l. In FIG. 17, if the helix of the external Vthread of the piston is made big enough, the unit will become a position seeking hydristor. The rotary portion of the motion provides feed-back for more than 360.

It is obvious that the design and construction of the hydristor may be varied and many different forms may be utilized. However, in all of the forms described, there are two complementary resistances that are a function of displacement of a member to be regulated by these resistauces and in all instances have two pressure ports and one return port, with the exception of the FIG. 14 modification which has two return ports.

Referring to FIG. "1S, there is illustrated a schematic Yof a po-wer system using either a non-position seeking or a position seeking hydristor. For example, using the position seeking hydristor 10, not load compensated, of FIG. 1, the ratio flow divider 36 and the pump 40 in the same sequence, we may add a power cylinder 70 with a piston 71 mounted therein, in which the piston 71 is provided with a connecting rod 14 and in which rod 114 extends through sealed Ibearings at either end of the cylinder 70 and in which rod 14 is either connected to or is the same rod 14 extending from hydristor `1li). Cylinder 70 is provided with two

ports

72 and 73 at either end thereof.

Ports

72 and 73 are in turn connected to the same lines extending from the ratio iiow divider 30, that is port 72 of the cylinder 70 may be connected to the same port 33 of the ratio ow divider as is the line to the hydristor, while port 73 of the power cylinder may be connected to port 34 of the ratio flow divider, the same port that is connected to the opposite end of the hydristor. Thus with the operation of pump 40, when the ratio flow divider is in a central position to divide the flow equally, the uid ow to the hydristor and similarly to the power cylinder 70 will produce a movement of piston 11 of the hydristor to a central position and at the same time movement of piston 71 of the power cylinder to a central position. V-It is obvious that any input signal on the ratio flow divider that shall change the ratio ow produces the same change of dow to both the hydristor and the power cylinder so that they will work simultaneously to correct their position. It is obvious that the effective areas of the hydristor, if position seeking, will simply be added to the eifective area of the actuator (piston) of the power cylinder. In this system, the position error is sensed because P1-P2 exists lbut is not compensated.

AIt is also to be noted in FIG. 18 that a position seeking hydristor system, not load compensated system, can be created with a non-position seeking hydristor. This particular system demonstrates the interrelation lbetween the two hydristor types (position seeking and non-position seeking) because there is added an effective area to the non-position seeking hydristor. Such a system will find application where large, not load compensated, forces have to be created. This system has a much higher volumetric eiciency than the single position seeking hydristor; this is due to the fact that the etfective area of a connected actuator can be increased at will.

It is also of interest to note that by reversing the hydristor, that is reversing the fluid flow, using the outlet port as a single pressure port and the two inlet ports as two outlet ports, the hydristor becomes a ratio iiow divider and it is also to be noted that with this form of ratio ow divider utilizing the position seeking type of hydristor, the operator who shall actuate the input signal is provided with a resistance or feel on the operating rod.

The hydristors as above described may also be used as a feed back element in a hydraulic servo system.

`Referring to FIG. 19, there is illustrated a schematic of a servo system utilizing the position seeking type hydristor as a feed back element. This is comprised of the same cylinder of FIG. 1, with the piston 11 and piston rods 12 and 1.4, with the cylinder 10 connected by its

inlet ports

16 and 17 to ratio ilow divider 30,

and the ratio flow divider, in turn, being connected to a pump 40. However, in this instance, the two fluid lines connecting

inlet ports

16 and 17 to the flow divider 30 are provided with a null unit 60, which is in the lform of a single enclosed cylinder with spring centered diaphragm, the lines being intercepted to pass into and out of either end of the cylinder 6i). A single piston 64 is mounted in the center of cylinder 62) to divide this uid how on either side of the cylinder. Piston 64 is also provided with a pair of piston rods 62 and 63, which extend through and out of either end of cylinder 64). It is apparent that piston 64 becomes a sensing element that is moved in either direction depending upon the pressures on either side of said piston, and such movement is reproduced by the piston rods 62 and 63.

In FIG. 19 it is to be noted that one end of cylinder 10 is joined to an enlarged power cylinder 70, the power cylinder 70 being provided with a piston 71 and two

ports

72 and 73 at either end of said cylinder. It is also to be noted that the piston rod 12 of cylinder 10 extends through the power cylinder and is aixed to the piston 71 and is moved with the movement of piston 71 of the power cylinder and piston 11 of the hydristor. The power cylinder 761 is also connected by means of its

ports

72 and 73 to a power hydraulic pump 7S, that is hydraulic fluid under high pressure and proper volume is supplied by this pump 7S through an amplifier valve '76. Valve 76 is a five ported valve with a closed cylindrical core 77, and a double piston 7S mounted therein. Piston 78 is actually two pistons, 79 and 80, fitted to the cylindrical core but connected by a central core of lesser diameter. The fluid from said pump 7S passes through an inlet 81 at the center of said valve to surround the lesser diameter of the piston. With the piston 78 in its central position, the outlet ports -82 and 83 are closed. Piston 78 is also connected by the rod 63 extending through the -body and attached to rod 63 of the null unit 60. Thus, with movement of piston 64 of the null unit 60, the double piston 78 of valve 76 may be effected to move piston 78 in either direction, and the slightest degree of movement in one direction, for example to the left, will open port 82 to permit a iiow of fluid from pump 'through valve 76, through port 82, to inlet port 73 of the power cylinder. The opposite side of the power cylinder will expell iluid through por-t 72, through the opposite line to the opposite port 83 of valve 76, which is in turn connected to return port S4. Similarly, if piston 7S had been moved in the opposite direction, fluid would be expelled through the opposite return port 85.

Referring to FIG. 20, there is illustrated a schematic partially in cross-section of a servo system somewhat similar to FIG. 19; however, in this embodiment there is added a subsystem 100, Which is, in fact, the hydristor system illustrated in FIG. 1. However, pump 4d must be connected to both the ratio flow divider 30' of the servo system and to the combined null unit and arnplii'ier valve 101 and to the ratio flow divider of the subsystem 100, and in this instance connecting rod 14 of the hydristor 10 is connected to the actuator Signal input rod 38' of the ratio flow divider 30' of the servo system. Thus, the signal input or control yrod 38 of the subsystem y becomes the controlling element for the complete system. A non-position seeking hydristor 20A is shown, this can be used as a feed back device. When a position seeking hydristor is used a resisting force will be acting against loads before power correction takes place. In FIG. 20, the hydristor 20A is somewhat similar to the hydristor shown in FIG. 2 except for the fact that piston 21A has only one piston area 22A and the piston has `a hollow center connecting both end chambers. There is no effective pressure area acting on this piston. It is a non-position seeking hydristor. 'Ihe combined null unit and amplifier Valve 101 is a single cylinder closed Iat both ends and provided with a piston 78 as well as two opposed control inlet ports I and I and one main inlet port I", also two pressure ports P and P that are connected by fluid lines to either side of the power cylinder 70. There are also two exhaust ports O and O. The piston 78 is divided into four cylinder engaging areas or lands, C1, C2-C3 and C4, with trapped chambers T1, T2 and T3. Main inlet port I" is situated centrally within chamber T2. Pressure ports P1 and P2' are aligned with areas or lands C2 and C3 when the piston is centrally positioned. Exhaust ports O and Ol are connected to the trapped chambers T1 and T3.

The operation of this unit may be followed starting with actuation of the signal input rod 38 of unit 10i). Movement of the input rod 38 will change the fluid flow to cylinder 10, that is movement of -rod 38 to the right or left unbalances the balanced flow. Assuming that rod 38 is moved in to the right, the greater ow will be to the lefthand side of cylinder `and the lesser ow to the righthand side; thus, rod 14 will be moved to the right and thus affect the ratio flow divider 30 of the servo system. The effect will be similar, causing a greater flow through the lefthand side of the ratio iiow divider and a lesser flow through -the righthand side, thus the fluid ow to the lefthand yside of the hydristor A will be greater while there will be a lesser flow of fluid to the righthand side of hydristor 20A. Likewise, there will be a greater ow through inlet I to the amplifier valve 101 and a lesser ow through inlet I', thus, the piston 78' will move to the right and the iluid flow from pump 40 through inlet I will iiow through pressure port P -to the lefthand side of power cylinder 70, creating a power stroke of the piston toward the right, and of course moving piston 21A in a similar fashion. The pistons of

cylinder

70 and 20A will move a predetermined degree, at which time a balance will again exist; that is, with a movement of the piston in power cylinder 70, there will be a return flow out of the opposite side of the cylinder and the amplifier valve piston 78 will also assume a position at which the pressures will again balance. It is apparent that actual control of the power cylinder and the hydristor 20A may be maintained with the input rod 38 of the sub-system 100.

Although applicant is primarily interested in a hydraulic servo system similar to that illustrated in FIGS. 19 or 20, it is to be understood that various changes or modifications may be made in the components of the system, without `departing from the spirit of this invention. In every instance there must be a hydristor used. In FIG. 19 there is shown a position seeking linear type hydristor, in FIG. 20 there is shown a non-position seeking linear type hydristor. A rotary hydristor, such as that illustrated in FIGS. 3, 12 or 16 may be similarly used, or a modification of the non-position seeking hydristor, FIG. 2, may also be used, or a porous type linear position seeking hydristor, FIG. l1, may be used, or a nonposition seeking linear type of a different design, shown in FIG. 14, may also -be used. In every instance, a pump and ratio flow divider shall also be necessary; in fact, the components shown in FIG. l lare the necessary elements for every system.

It is apparent, referring to FIG. 1, that the signal input rod 38 creates two complementary resistances as a function of position, R1 and R2; it also creates two flows, Q1 and QZ. This flow also creates two internal pressures on effective areas of null unit to sense the pressure differential P1 and PZ. Thus, this invention takes advantage of the pressure differential Pl-PZ in conjunction with the hydraulic element which we call hydristors, as the feed back criterion for control of the position and load of an actuator.

In FIG. 20 we utilize an amplifier valve to convert the feed back and control signals into power motion. It is apparent that by variations and combinations of these elements that novel systems may be created, but in each instance, a hydristor, null unit and pump is used. Whether we used a position seeking hydristor or nonposition seeking hydristor, the same results may be obtained, and with a position seeking hydristor, Whether we used a linear or rotary type, the same results may be obtained; and, similarly, with a non-position seeking hydristor, we may use a linear or rotary type. When using a linear or rotary type hydristor, the same principle of leakage over piston clearance may be the controlling factor, or it may be leakage through slots and piston, or it may be leakage through slots in the housing, or it may be leakage through -a porous medium, or it may be leakage over tapered or eccentric lands to control the iiuid ow. With a linear type hydristor,the direction of leakage is axial, While with a rotary type, the direction of leakage is circumferential (plus leakage through side plate clearance).

Although we .have shown the ratio flow divider as the signal input unit for positioning the position seeking hydristor (because the displacement of the ratio iiow divider is usually very small), in FIG. 22 we may reverse their relationships, that is the pump P will be connected directly to the port l5 of cylinder 10i, and the iiuid iiow becomes a reversal of that shown in FIG. l, and in similar fashion every modification disclosed herein permits this reversal of relationship between the two units.

What is claimed is:

l. A hydraulically positioned servo system which includes a hydristor, said hydristor comprising a cylinder with a reciprocable piston mounted in a central position therein, said cylinder provided with inlet ports and an outlet port, said piston provided with an exterior surface and being loosely fitted within said cylinder to allow two complementary flows over said piston surface from either of the inlet ports to said outlet, s-aid servo-system divided into a power stage and a feed back control stage, said power stage comprising a power cylinder and piston, a main pressure source and a four way valve, said feed back control stage comprising an auxiliary power source, a controlling ratio-flow divider, a differential pressure sensing means, which is mechanically connected to said four way valve, and said hydristor, said hydristor having its piston mechanically connected to the moving piston of said power cylinder as a feed back element, said ratioilow divider comprising a closed cylinder with an inlet port at its center and two -outlet ports, one at each end of said cylinder, a piston and rod mounted loosely and centrally within said cylinder, said rod providing the means for a mechanically produced input signal, said piston rod extending through said cylinder, said piston provided with cone shape faces on either side to reduce its effective area exposed to the iiuid pressure flow, said differential pressure sensing device comprising a closed cylinder with two inlet ports and two outlet ports, one inlet and one outlet port connected to each end of said cylinder, a dividing piston with its piston rod extending through said cylinder, and a resilient element positioned on either side of said piston to normally retain said piston balanced.

2. A hydraulically positioned servo system according to claim l, in which the control ow is divided by the controlling ratio flow-divider into two complementary flows which are connected to either end of said hydristor, said differential pressure sensing means positioning said four way Valve to regulate the flow of liuid from the main pressure source to the power cylinder proportional to the pressure differential effect of the complementary ilows.

3. A hydraulically positioned servo-system according to claim 2 in which the two complementary ows created by the ratio-flow divider are connected to either side of said differential pressure sensing means and in turn to opposite ends of said hydristor so that the flows are exhausted over two complementary piston surfaces, whose ratio is determined by the position of the moving piston of the hydristor which is mechanically connected to the piston of the power cylinder.

4. A hydraulically positioned servo system according to claim 3 in which the mechanically produced input signal determines the ratio of said complementary How (in said hydraulic resistor) and the ratio of the two complementary resistances created by the complementary flows represents the hydraulic feedback signal and said dif-V ferenta-l pressure sensing device and said four -way valve represents the regulating means, said regulating means equalizing the ratio of the complementary flow-through of the hydristor with the ratio of the complementary flow of said ratio-110W divider by admitting the proper amount of uid from the main pressure source to the power cylinder to in turn move the piston of the power cylinder into the desired position.

5. A hydraulically positioned servo-system according to claim 4 in which the pressure sensing device and the four Way valve are two separate units Whose sensing and valving members are mechanically connected.

6. A hydraulically positioned servo-system according to claim 4 in which the pressure sensing device and the four way valve are combined into one unit.

7. A hydraulically positionedV servo-system according to claim 1 using as an input signal a displacement elcment motivated mechanically.

8. A hydraulically positioned servo-system according to claim l using as an input signal a displacement element motivated electrically.

9. A hydraulically positioned servo-system according to claim l using as an input signal a displacement element motivated by an auxiliary hydraulic system.

References Cited in the le of this patent UNITED STATES PATENTS 1,943,061 Douglas Jan. 9, 1934 2,396,951 Horstmann Mar. 19, 1946 2,520,944 Lynn et a-l Sept. 5, 1950 2,709,421 Avery May 3l, 1955 2,907,304 Macks Oct. 6, 1959 2,942,581 Gaincy June 28, 1960