US2368791A

US2368791A - Servomotor

Info

Publication number: US2368791A
Application number: US413771A
Authority: US
Inventors: George A Waldie
Original assignee: Hydraulic Development Corp Inc
Current assignee: Hydraulic Development Corp Inc
Priority date: 1941-10-06
Filing date: 1941-10-06
Publication date: 1945-02-06
Anticipated expiration: 1962-02-06

Description

Feb. 6, 1945. G A. wALDlE 2,368,791

SERVOMOTOR Filed Oct. 6, 1941 Z5 Sheets-Sheet 1 G. A. WALDIE Feb'. 6, 1945.

SERVOMOTOR 3 Sheets-Sheet 2 Filedl oct. 6, 1941 mNENToR moQNEvs G. A. WALDIE Feb. 6, 1945.

S ERVOMO TOR Filed-oct. 6,-1941 A s sheets-sheet s Patented Feb. 6, 1945 UNITED SIA-Tas PATENTS l `asssaal v 5 y A s,EmvfoMo'ron e George A. =Waldie, Miamisburg,Ohio,assignorto"` l "The HydraulicDevelopmentCorp.,^:Inc;yaWil-f z gmington; Del., aogrporation of Delaware f Apniiafionocwher-6, 19a; Serials-of. 413;!711 12 claims; (C1.\.11d271+41) i A l y invention relates to f o'ontrol means and, f

particular,` toiluid operabley servomotor means for.. controlling as reciprocable element.

Itis an `abject of the invention to provide av l simplified fluid pressurecontrol inech'anismjor controlling the position ofafreciprocable` member. It is another object of the inventionto ,pro-

vide a control mechanism which, responsiveto different fluid.- pressures, isadaptdltohloli areciprocable element in a predetermined position ortomoveitawayjrom thesaid position.' y l 4A further object of the invention consistsfin the provision of ariiuid operable siervomotoruwhich may be Vused in connection with variable1 ,delivery pumps for controlling the same.

It is stillanother objectto provide auid ropl erable servomotor for `variable 'delivery fpumps which heretoforelrefquired rthe use cfa plurality of servomotors.

,A still further object ofthe inventioricpnsisns in the provisionof a liuid operable servornotor for V variable deliveryY pulnpspwllich is` universali in use inasmuch asit'is f adapten not only to Yput suchpumpson stroke but also to Vary the vdelivery thereoilin response to predetermined pressures. These and Other, Qblectsandadvantageshofj'tlie invention Willappear more clearly from, the; following specificationinwconnection Withtlce accompanying'drawin'gs;inwhich: y

Figure 1 diagrammatically illustrates a j hydraulicopen press circuit` comprising a' Vane Apump with a servomotor accordingto the invention.

`Figure 2l 'is alongitudinal section through the servomotor shown in'Figurel.

" Figures f 3 and l4: `illustrate the servmnotcirof Fguref2 in working position, andj pressure-holding position respectively.

' Figureft'A illustrates a hydraulic open presscirf cuit comprising `a radial piston pump with` a servomotor according to theinvention.V

Figure .6 is a diagrammaticillustrationoflfa closed hydraulic, presscircuit 'comprisinga vane pump which isr associated witha servomot'orac-` cording to the invention. l y

"Figure 7 shows, i n section,`a portion ofthe vane Dump as mayrbeiused in ,the circuitsshown inthe drawings.` u Y v. l

v l'Figure l 8 is@ diagrammatic illustration of ...a radial piston pump as may; be tion Witnthe circuit of Figure 5.

r Figurey 9 is. adiagrammaticy illustration o-f.= a closed vpress circuit comprising a yanepumpwith' twoy lservomotors according #to the invention.l for varying the-delivery1as -Wellas the-direction 'of thevanepump. Y* l t.'

4fio.

Genezrl construction stentiallrf esathrustfrodwithirek nd discharge por ,wliilrliasl ciprocably'mounted rod varies its vposltlon to 'allow Variation of tlie spring interposed between-the servofialvef'spool and the `thrust rod n iovesthvalve spool rintro, its initial-positi'onz' -`,tl;,-rebyA Aenabling -pressur fluid passingthrough the inlet port/t shift tlet'lzrust :.-Refen'ing now:totheudrawingsin detailgthe y to be moved into a position eccentric-tothe rotor 3 `Whicluhas a pluralitypf vanesMreciprocabl'-.in cylinders 5,-- and having'theirends infengagemet with.the. cylinder;walleli; i The lcylinder blockl nasa-fluid inlet'l andaffluid outletl 8. l fluid conduit 91-Figure l). which .leadstoafour-way y v valve lvoianyldesiredtype which lindts'turnis upper. and lowercportionoi ai l the groove 29.is adapted I8 leading to the inlet port I9 of the servomotor,

generally designated 20, and connected'in any desired manner,v forinstance by 'screws 2l, with the casing'ofthe pump I;

The servomotor comprises a cylinder 22 thereto.` The knob 51v engages athrust washer 58 threadedly engaging the left end portion of the thrust rod 26 which also threadedly engages a with a cylinder bore 23 having a shoulder 24.. j

Reciprocably mounted in the cylinder bore 23 is a cylindrical portion 25 of the thrust rod .n through conduit 9, four-way valve vtank l)6,"and from there through conduit Il back The thrust rod `26 has an extension 21 passing through the pump casing and/adapted to-engage the cylinder block 2.

klnterposed `between i cylinder block 2 is a weak spring 28 which is just the pumpcasing and the strong enough to shift the cylinder block 2 into` position eccentric to the rotor 3. It should, how'- n ever,A be noted that when the vanepump I is delivering pressure fluid Vso,thatthe well known re-r action, inherent to' /ane'pumps occurs,the spring 28 is not strong enough to oppose'said reaction, thereby allowing -the cylinder y block 2 Vto move against the thrust ofthe spring 28. H

The thrust rod o annular grooves 29v andurespectively, of which 'to communicate with the inlet port I9 and, furthermore, is in continu'- f ous.' hydraulic connection with ther passageway 3l.' ,'I'he passageway. 13| communicates through ducts 32.l and 33 with Vthe end of alsmall cylinder 34` provided in the extension 21 and having slidablymounted therein a piston 35 yconnected toa servoeval e spool, generally ydesignated 36. The servo-valve spool A* adapted vto effect .hydraulic communicationV bel- ,tween thek passageway 3'I andfa .passageway 38 lleading tothe leftfend portion of fthe cylinder bore 23. vThe thrust' rod 26 is provided withan annular groove 39 communicating through apassageway with the cylinder rbore 4I in the thrust rod 26.` The servo-valve spool 36 is slid-v ably mounted in the bore `4I and is alsoadapted, by means ofthe annular groove-V31, to effect hy-v drauli'c communication. between the passageway 38 andthe passageway. 40 which in its turn is adapted, throughgroove' 39', to communicate with the discharge port 42 in thefservomotor 20. The

, length of the annulargroove 31 is'preferably','al-

though not' necessarily, so dimensioned that` it equals the shortest distance between the passageways 3| and 40.

As will 'be seen from'Figure 2, the thrust rbd extension` 21 isprovidedat its ,left end with Aa' shoulder 43 for abutmentwith the lvalve spool 36 so` thatwhenthe valve spoolr 36 and ,theext en sion 21 engage each other an annular cylindrical space 44 remains. The space 44 communicates with a duct 45 leading to the annular groovel3|l which is adapted to communicate through duct 46 with a port 41. The port j4I .may be'connected `to a iiuid source but in thezexample of Figure 2 is closed byaplug 48.`

' Mounted withinthe'valve spool 36 is a spring 49,'oneend of which engages the valve spool 36, whereas the other end offspring 49 abuts a thrust nut50. The thrust nut 5I)v is providedwith wings 5I -passing through slots 52 in the thrust rod 26 and vslidably lmounted in longitudinal' grooves 53 provided in .the servomotor casing 54. `,The thrust nut is provided with an inner thread engaging a threaded portion 55 of a control stem 56 which is rotatable bythe knob 51 connected 'tion 725 is' provided with two 36 hasman vannular groove'31 duit II into the vupper portion of the cylinder tothe pump I.

in Figures l and 2 op- During this time the spring 28 maintains the cylinder block 2 of pump I in its eccentricposition relative to the pump rotor 3 and the elements of the servomotor 20 occupy the position shown in Figure v3.

If, now, the four-way valve I0 is shiftedto its working positionv for forward movement. of the piston I4, fluid delivered through conduit 9, four-way valve I0 and con` I3, while fluid expelled from cylinder,Av I3 'will'pass' through conduit I2, four-way'valve VIl] and., conduit I5 into tankl. ,d

As soon as'the piston I4 encounters resistance exerted'by a work piece, pressure begins to build up in veyed through conduit I8, port 'I9 and passageway 3l through the 'annular groove 31 'andpassageway 36 to the cylinder bore 23 adjacent the shoulder 24.` Here it actsfupon the pistonV area 62 of the thrust rod 26 soas to cause th'elatter positivelyto engage the cylinder block 2 and to support the action of the spring 28. against the reaction now occurringin the vane pump land tending to move the cylinder vblock 2 .into posi- As soon as a predetermined pressure has been builtiup in the upper portion ofthecylinder I3 and, thereby; also in conduitsr Ifl, 9' and I8, this pressure willovercome the thrust of spring49 and, acting upon the piston 35, will move the valve spool 36 toward the left, closing the passageway 3| and establishing hydraulic communication be-l tween the passageways' 38 and 46and the discharge port 42. The Apressure fluid acting upon the piston area 62 is, therefore, discharged and further .pressure acting upon piston 35 moves the valvefspool 36 together with the thrust rod 26 toward the left with regard to Figure '2. The

cylinder block 2 immediately follows up the leftward movement ofthe'thrust 'rod v26 rdue tothe reaction occuring in the vane pump I. The elements of the 'servomotorjZ' .then .cometo' a halt when 'equilibriumV is again estab-lished and occupy the pressure-holding position shown in Figure 4. If, for some reason, the Apressure Yacting upon piston I4 and prevailing in conduits II', .9 and I8 should drop, a corresponding drop in pressure will also occurin cylinder 34 so that the valve spool 36 is 'moved toward 4the right by spring 49. This movement causes hydraulic. communication again between passageway 3lv and passageway 38 so that pressure fluid is conveyed from conduity I8 te the piston area 62, thereby causing rightward movement of the thrust rod 26,555: j v 1 by the pump I will pass,

conduits I I and 9, andthis'pressure is conjIf it is-desired to retract the'pston I4, 'fthe four-way valve IIJ is s'hi-ftediinto retraction stroke position so that :pressure -fluid 4delivered by 4the pump -I passesthrough -.condu.it'9, foureway valve :lfllandlconduit I2to thelower -part of the cylinder I3, 4while `Huid expelled `.from ,the upper part -of cylinder I3 vpasses `through .conduit II, four-way valve `1I 0, .and conduit VIl5 .into the tankI 6. Otherwise, lthe operation of the :servomotor'ZU w'illbe the same as described 1in connection Vwith the forwardstrokezof piston I4. y

The possibility of .using a servomotor according to the vinvention in an `open hydraulic system powered byradialpump or anyshiftable pump in l'which `no .internal .reactive force', Aas'occurs ina vane pump, can be utilizedis: illustrated in Figure y'5. .The circuit shown in. this gure is the same open `circuit shown .in .Figure l.. The only .difference between the two is the additionl of a uidpressu-re responsive piston-63 reciprocable in a'cylinder 64 .associated withthe radial pump 65. .Thefpiston 63, when .acted .upon byuidipressure, -urgesfthefiow-control member or .shift ring (not shown) of the vradial pump '.65 into V.position .concentric .to the` rotor of the pump 165. `'Similar .parts in the :circuit yof .Figure '15 are, therefore, Adesignated with .the same reference numerals as 'the l,crrrrresponding vparts of. Figure l.

As will .be seen from Figure l5, the cylinder '64 is rconnected through conduit 6.6 with thevpres- `-sure line 9. In this way Apressure prevailing in cond-uit `SJ will V:be conveyed through conduit 66 into cylinder .64 where itacts upon piston 63 yso las to-move the flow-control member or shift ring -of pump towardztheleft with regard toFigure .6.; .1in other wordsy Lth'e fluid pressure acting upon piston 63 tends to move the ilowoontrol member .of pump 65'into concentric .position'withf-regard yto the .pump rotor. It will, therefore, beclear'that Athe reactive force .occurring in the 'vane Apump I' is replacedin the .circuit lof 'Figure 5 by the pressure :conveyed through .conduits `9 and 6.6'and acting upon :thepiston f6.3. Otherwise, the `operation 'of 'the .circuit'in Figure 5 is the- `sametas that Jde- :scribed in .connection .with thecircuit ashown in 'Figure 1. f

Two .possibilities for closed hydraulic circuits vare-illustrated in Eigures 6 and 9. i l

Referring first to IFigure. 6, the circuit-shown therein A.comprises a vane .pump 61, which may be of .any :desiredttypa for instance,v correspond to :thevanezpump l inJFigurel, orlmay be replaced .by aradial piston'pumpcomprising a spring -withinfrthe'pressure .cylinder lat 'therright side' of the pump. The Vane pump 6I`is of the reversible type and has connected .on .one side thereof the -servomotor '20 .asdescribed in detail in connection with Figure .2. .On the Vopposite side of the Avane. pumpi'lfis arranged a cylinder: 68 having re- Aciproca'bly mounted .therein ,a :fluid `pressure 'ree spons-.ive piston 69.vvhich is adapted to `engage Lthe cylinder block 2 and -to .move the latter toward-the left with regardto Figure 6.

The cylinder 68fis connected'torak conduit 'I0 lleading .to thefour-way valve I Whichin its .turn is :connected ytoa conduitII comprising a checkl `va1veI2 and leadingto a conduit 1:3. The conduit-13 which comprises a .choker rcheck valve 14 has `one end'connected. to the inletport t9 of the yser-vomotor.211,While the other end of the conduit ``I3.leads to .a'conduit 'I-5. The choker `checkvalve I4 isfpreferably of the type -shownin Figure 11, withla-byepass'.channel14a and e, choke 14h. One

.end-.of--theconduit15-isconnected Vto vthe vanev pumpk'l, whereasfthe otherendleads to .the up- -per portion or the cylinderI-3 A'having recipropably mounted Vtherein --the pis'ton ili4. lllh'e vpiston 2I4 4is connectedto Aalpiston rodi'IB whichcarries an ,mounted-on a-control roden. 'Theupperend of .the `controlrrod :19 :carries :an adjustable `.arm :SLI

yof .a .bell crank .leverl .the other 4arm y83 -of lwhich p .sadapted to V.engage .the knob =51so as tomove 4through the .latter .the thrust :washer and 'the thrustrod 2.6 .threadedly connected thereto., .f

The Vlower. portion of .cylinder 13 .in .Figure t6 .communicates with va :conduit ,84`Whichileadsito l 4the vane pump .61' and VcommunicatesY .through .conduit "with :a make-.up yfir-shuttle .valve 196` lor a well known type. The :valve :Shassaconduit A.8:1communicating.with the conduit 'I5andhasua further conduit 88 leading to the Iiuid tank .I.6.

Also communicating'wth theluidtank I6 'isa conduit .89 leading to-the four-way valve |11.'` VBranching 01T from .the-conduit 89 is a'conduit .9.0r

leading to the suction side of .a constant delivery pilot pump 9I, the pressure side of which is Yconnected to conduit 92 leading to the four-way valve I0. Branching off from the conduit 92 is a conduit 93which comprises a relief valve .94 `and leads to theconduit 89.` f

The operationofthe system shown in .6 o

is as follows: Y l i v supposing that the pumps SI land 61 .are running but that pumpVGI is in neutral orno delivery I I position, and that it is now desired to eiTectaiorvalve spool 36 by the spring 49 so that the valve spool 36 immediately follows uppthe movement .of the thrust rod 26. .The pump GI'then begins .to deliver pressure iiuid through conduit 'I5 into .the upper portionof the cylinderI 3, o

It should be noted that thepump 9| kis'adapted merely to create suiicient pressure to move the thrust -rod v26 for causing the latter to put'the pump on stroke, but is not adapted to create such .a pressure .as to causethevalve spool 36 to .move

'against the thrust of spring49.

' If the pump 9| has reached the pressure'required vfor the above referred to shifting "move,-

ment of the thrust rod 26, any excessive pressure delivered by the pump 9|v isr released through v,relief valve 94 into the tank I6. As'soon as pressure lbuilds up in the upper portion of the cylindery I3, this pressure is conveyed through `conduit I3 to port I9, and from there to the piston area 62 sojas' to positively maintain the thrust rod 26 in engagement with the cylinder block 2 as long as the pressure in the upper portion of cylinder 'I3does not exceed a predetermined value. At this time the check valve 'I2 closes, whereas the choker checkl valve 'I4 is open. l When a predetermined pressure has -been built up'in'the upper portion of cylinder "I3, forin-r stance at the end of the'stroke of piston I4, this pressure is, vconveyed .through conduits "I5 and 1.3, port I9 `and ductsf32 and '33 to cylinder r34 where-it acts upon the piston 35 as described-in connection with Figure 2so as to movethe Valve f spociss tcwarditne left. .As a result, the .thrust rod 26 likewise moves toward the left, asapre-v yiouslydescribed, and `thereaction inthevane the thrust rod 26 to `put the pump A,

.back pressure.

. in providing pressure control. d

between the arrangement of Figures 9 and l0' the piston I4, the four-way valve I is shifted so v as to establish hydraulic communication betweenV the conduits 92 and 10. Pressure uid delivered by the pilot pump 9| then acts upon .the piston 69 which shifts the cylinder block 2 to the left across the center and holds it there against the pump reaction which isrelatively low under pull- Fluid trapped by the piston 35 bleeds off during the reverse stroke of piston I4 by passing out through the channel 14a of the choker kcheck valve 14 in conduit 13.\ Finally, when the piston I4 has reached the end of its retraction stroke, the arm 11 engages the collar.

18, thereby lifting the control rod 19, whichlatter, through arm 80, acts upon the bell crank lever 82 which in its turn forces the thrust rod 26 through knob 51 and thrust'washer 58 to neutral position against the pilot pressure.l As mentioned above, the vane pump ure 6 may, if desired, be replaced by a reversible radial piston pump. In this instance the only alteration necessary consists in the addition of a light spring behind the piston 68 which is adapted to exert a for-ce just sucient to cause follow-up of the flow-control member or shift ring of the radial ypiston pump inthe pressureholding period to move the pump to neutral position'when the thrust rod 26 moves toward the left with regard to Figure 2.

' circuit of mitted into the space 44a which causesthe valve si of Fig? Y spool 36a to move towardthe right and to establish hydraulic connection between the piston area 62a andthe discharge port'I 42a4 which is connected with the tank I6. The exhaust of fluid from the piston area 62a allows the cylinder block 2 to move: the thrust rod 26a toward the right. The relative positions of the servomotors and 26a are then as illustrated in Figure 10.

lAs soon' as the pump 96 starts to build up pressure in the cylinder I3, the pressure fluid in the pressure line 15 supersedes the pilot pressure in line 91 in the same manner as previously described in connection withL Figure 6, rwhile the check valve 12 closes and the delivery of the pilot pump 95 is by-passed to the tank I6 through conduit 93 and relief valve 94. When a predetermined pressure has been established in the upper portion of cylinder I3, for instance at the end Referring now to Figure 9, this figure illustrates a further possibility for closed hydraulic systems, namely, pressure control for either forward or reverse delivery of a reversible pump by the use of two of the control units shown in Figure 2, of which one is to be arranged on each side of the pump. The primary object of such an arrangement is to provide pressure control on both strokes of the press, for example, in connection with reciprocating machine drives, or in connection with injection presses where knockout pressures are not controllable at present.

Another object of the arrangement shown in Figure 9 is to provide for'movin-g the pump to idling position under low pressure at the end of a cycle. As will be seen from the drawings, the hydraulic circuit of Figure 9 resembles that of Figure 6, a pilot pump 95 being employed to move the main pump 96 off center in either direction through the setting of the four-way valve I0, and the main pump pressure being adapted, through a choker check valve hook-up 14, to supersede pilot pressure in holding the pump on stroke and The difference on one hand and the circuit of Figure 6 lies in theuse of the annular cylindrical space 44 for nullifying the elTect of the Icontrol unit.I

As will be noted from Figure 9, the pilot line 91 leading to the port I9 of the servomotor 20 communicates through conduit 98 with the po-rt 41a of the servo-motor 20a, which in its construction completely -corresponds to the servomotor 20 so that corresponding elements are designated with the same reference numerals, however, with thev additional letter a. Similarly, the pilot line 99 leading to the port I9a of servomotor 20a communicates through conduit IDI] with the port 41 of the servomotor 2U. Otherwise, the circuit of Figure 9 substantially corresponds to that of Figure 6.

' v'Io elect a working )cycle of piston I4 in the of the forward stroke of piston I4, this pressure is conveyed through

conduits

15 and 13 to port I9 and from there, in the manner previously described, through cylinder 34 where it acts upon the piston S5 and moves the thrust rod 26 toward the left, so that the reactive force in pump 96 may bring about' movement of the cylinder block 2 to neutral position. .A

If, now, a retractionY stroke of the piston I4 is desired, the .four-way valve I0 is shifted so as to establish hydraulic connection between the conduits 92, I90 and 99, as previously described in connection with the servomotor 29 of Figure l0. This will result in aleftward movement of the thrust rod 26a so as to put the pump 96 on ff is then conveyed to the lower part of cylinder I3. When the piston I4 has reached the end o! its retraction stroke, or if for any other reason a predetermined vpressure has been Vestablished in the lower part of cylinder I3 according to the setting of spring 49a, this pressure is conveyed through port I9a intofcylinder 34a and causes the valvespool 36a to move toward the right, thereby enabling the reactive force in the vane pumpn96 to .move the latter to neutral or substantially no delivery position.

It should-be noted that while the four-way valve Ill'is shifted from forward stroke to reverse stroke position, pilot pressure enters the space 44, maintaining the control Vspring 49v in compressed condition, while pilot pressure is exhausted from the space 44a. Pressure does not area 62a, a slight lapse of time occurring while yfiuid'is `leaving the space 44a and spring 49a is pushing the valve spool 36a toward the left.

After that, another slight lapse occurs, while the thrust rod 26a is vmoved to absorb the space previously prevailing between the thrust-rod and the cylinder block 2. When contact is made between the cylinder block 2 and the thrust rod 26a, the sluiting of the pump from neutral to reverse is effected. In this way, a smooth shifting movement from forward to reverse stroke is effected. On' the other hand, during the lost Figure 9,'the pumps 95 and 96 are Pressure fluid from pump 96 motion movements ofthe servomotor 20a, nothing can` happen Within the servomotor `2l)y which would move the tion. l

If, instead of.' the vane pump 96, a radial `piston pump is used,` the reactive force in the vane pump 96 will be replaced by centering springs in the radial piston. pump, which centering springs actV upon. the .now-control member` or shift ring ofthe pump and tend to hold,l said pump to. .forward `stroke posi-l flow-control member or shiftring in neutral posi- 1.-In combination in a controlv mechanism,

a'casinvg having aninlet port and an outlet port, a uid operable `element reciprocably'mounted in said casing, fluid operable control means for controlling the admittance of.- pressure iluid'toan effective area of said reciprocablefelement,*yielding means Icontinuously urging saidA control means into position for establishing, iluid connection between said inlet port.v and said -eiective area to cause movement of said fluidi operable element into a first predetermined position in response to a first pressure atlrsaid inlethport, restricted conduit means connecting said inlet port with aneiective area of .said control means, means responsive to. a second uid pressure acting upon said ellective area of said control. means and higher thanr said first pressure iorl spacing said control meansfrom an adjacent portion of said reciprocable element, and. means responsive to said'last mentioned spacing movement of said control means for moving, said. reciprocable elementinto a second predetermined position.

2..In combinationin a servomotor, a casing having a iluid inlet port and afluid outlet port, a. control rod reciprocable in said 'casing and being provided with pa'ssageways adapted to communicate with said inlet and. outlet ports, said control rod also being pro-vided with. a uid operable piston portion adapted, response to a rst pressure at said inlet pOrt,A -to effect move# ment of said control rod -into a predetermined position,V a valve member for controlling hydrauand said ports 'through said passagewaysyielding means interposed between said vcontrol rod and said valve memberfor urging'said valve member and said control rod into ajpredetermined relative position, and means associated adapted to communicate with said ports, said piston comprising a larger cylinder and also comprising a smaller cylinder, conduit means continuously maintaining hydraulic communication between said smaller icyli'ndervand' said inlet port', l ar control "member reciprocably mounted ,inf said i larger cylinder and having an extension reciprocable in said smaller cylinder', said control member being" operable to selectively effect communication between said` inlet or outlet port and said piston, and yielding means for continuously urging 'said piston and said controlmember into a predetermined' relative position'.

4. In combination, a reciprocable element, a casing, a control member reciprocably mounted, in

said casing for operating said reciprocable ele i ment, said control member having a uidlnlet and a nuid outlet port andalso being provided with a piston area,` a valve member for controlling hydraulic communication between said pis-A ton areavand said ports, yielding -meanscontix'r- `uously urgingV said valve `member into abutment with said. controllmember, alfluidf operable cylinder-pistonassembly'associated with said'valve member andrsaidcontroimemberand adaptedto besupplied with pressure fluid fromA said inlet port to effect movement of saidi valve-'member relative to saidcon'tr'ol member against the influence ofsaid'yilding means," and means for urging said reciprocable element away'from said 'casing'. 1 l' 5'. 'In combination in a control `mechanism for controlling the*reciprocativermovement of a 're'- ciprocable member, a casing, a reciprocable `elementreciprocable infsaid casing, said recipro cable element having,associatedtherewith a` cyl` l inder and a'smaller cylinder and being provided with a piston area responsive toa rst iluid prese sure acting thereon for shifting said reciprocable element into a inst-"predetermined position, a control valve comprising av piston reciprocable `in said cylinder and means forming with an adjacent portion of saidreciprocable element a-fluid operable cylinder-piston-assemblyg vand meanslfor actuating said -cylinder-pivstcJn-assembly 1 in 1respouse toa second-'pressure' acting 'therein Vand being-'higher than' sai'dflrstpressure 'for' initiating movement of said reciprocable element'intofa second predetermined position;

6. In combinationin a servomotor, `a casing` having a fluid inlet and a fluid outlet, areciproe cable element movable in said casing and being provided with ailui'd' operable'pisto'n'area, saidv reciprocable. element-having a larger cylinder' and a smaller cylinderportion, a valve member; have ing- `associatedtherewith conduit means and cyL vlindricaln portions reciprocably mounted vin said larger and said smaller cylinder'portions respeci tively, lfor controlling fluid 4connection between' said inlet and outlet ports andl said piston area, said reciprocable element-being movable into 'a first predetermined position'in responsetoI pressure on said piston area and `beingmovable into a second predetermined vposition in response `to a predetermined pressure on the smaller cylindrical portion of said valve member, andy-ielding'means forl continuously urging said valve `member into v abutment with said reciprocable element.

'7l-In combination in' a servomotor, a casing vhaving a iluid inlet port and a fluid outlet port, .an

actuating member reciprocably mounted in said casing and having a larger cylinder with a piston area on the outside thereof and also having a smaller cylinder, said' actuating member also being provided with passageways adapted respectively to communicate with said ports and said piston area, conduit means continuously e'ecting f hydraulic communication between said inletport l.

and said smaller cylinder, acontrolmember vre ciprocable in said actuating member and having a piston reciprocable in said smaller cylinder and' a valve vmember reciprocable in said larger cylinderfor controlling hydraulic communication between said piston areaandvsaid ports, spring means arranged within said valve member :for continuously urging said smaller piston into the said smaller cylinder, means responsive to a rst 1 pressure at saidinlet port for moving said actuatingV member into; a first predetermined' position, means responsive to a second pressure,

higher than said first pressure, formoving said valve member againstl the thrust of said spring means away' from said smaller cylinder and means responsive to the last mentioned movement of said valve member for moving saidy actuating member together with said valve member to a second predetermined position.

8. In combination, a casing havingv a iiuid inletV port and a fluid outlet port, an actuating member reciprocable in said casing and having passageways therein for communication ,with said ports,- said actuating member having a fluid'operable piston area and a rst element of a cylinder pissaid inlet port, a valve member associated with said actuating member'and having connected t thereto a second elementl cooperating and forming with said rst element said cylinder-pistonways therein for communication with said ports,`

said actuating member having'a uid operable piston' area and a first element forming a part of a cylinder'-piston-assembly, conduit means continuously maintaining fluid connection between said `cylinderpistonassembly and said inlet port, a valve member associated with said actuating member and having connected thereto a second v ton-assembly continuously communicating with element cooperating and forming with said first n element said cylinder-piston-assembly, said valve member being operable to control hydraulic communication between said piston area and said ports, spring means'within said valve member for continuously urging the latter into abutment with said actuating member, and adjusting means operable'from thev outside of said casing for adl'usting'the thrust of said springl means.

10. In combination in a servomotor, a casing having a fluid inlet port and a fluid outlet port, a control rod reciprocable in said casing and having a fluid operable piston portion, a recipro-` cable member adapted to be held by said control rod in a rst predetermined position, saidcon= trol rod being provided with -passageways adapted to communicate withsaid inlet and outlet ports, a valve member for controlling hydraulic'` communication between said piston portion and said ports, the piston'area of said control rod being adapted in response to .a rst pressure at said inletport to actuate said control rod for `holding said reciprocable member in said first predetermined' position, lfluid operable means responsive to a secondpressure at said inlet port higher than said rst pressure for axiallyspacingsaid valve'member from said control rod,

and means 'responsive to said last mentioned spacing movement of said valve member for moving said reciprocable-member into a second predetermined position'. Y f Y Y 11. In combination with a reciprocable element, a uid operable cylinder-piston-ass'embly adapted to actuate said reciprocable element, factuating means i-or moving said reciprocable element into'a iirst position, first fluid pressure responsive means adapted, in response to a rst fluid pressure acting thereupon, to'holdjsaid reciprocable element-in said vrst position independently of said actuating means, means associated with said reciprocable element for urging theilatterinto alsecond position, second fluid pressure responsive means responsive" to a second pressure acting thereupon and-being higher than said rst pressure for making saidrst uid pressure responsive means ineffective ,toy thereby allow said last mentioned means associated with said ,reciprocable element to move said reciprocable element into said second'position, means for making said cylinder-piston-assembly eiective to move said reciprocable element `into a thirdV position, and means :operable to mechanically move said reciprocable element into said second'position.

12. In combination with a reciprocable element, a uid operable cylinder-piston-assembly adapted to actuate said reciprocable element, actuating means for movingsa'id reciprocable element into a rst predetermined position, first fluid pressure responsive means adapted, in response to a first fluid pressure acting thereupon.,

tohold said' reciprocable element in said first predetermined position independently of said actuating means, means associated with said reciprocable element for urging the latter into a second predeterminedv pressure, second uid pressure responsive means adapted automatically in response to a second uid pressure acting thereupon and higher than said rst fluid pressure lto make 'said first fluid pressure responsive means ineffective, thereby allowing said last mentioned means to move said reciprocable element into said second predetermined position, and means for making said cylinder-piston-assembly eiective to move said reciprocable element into a third predetermined position.

GEORGE'A. WALDIE.