US2408362A - Oscillating fluid-displacing machines operating in parallel - Google Patents

Description

E. s.l L. BEALE Oct. l, 1946.

OSCILLATING FLUID-DISPLACING MACHINES ,OPERATING IN PARALLEL f1 Sheets-Sheet l Filed NOV. 17, 1943 r I Il n 11111111/ ,66' 607 ff A 3412 352 3e;2

a o T N E V N Oct. 1, 1946.

OSCILLATING FLUID-DISPLACING MACHINES OPERATING IN PARALLEL Filed NOV` 17, 1943 4 Sheets-Sheet 2 Pfg. 2.-

Evelqn Shwar* lomsdomhe. (Segu,

E. s. L. BEALE A 2,408,362

Oct. 1, 1946. E. s. g.. BEALE i v i 2,408,362

OSCILLATING' FLUID-DISPLACING MACHINES OPERATIlNG' IN PARALLEL Filed Nov. 17, 1945 4 Sheets-Sheet 3 (Smm/ML 1., www

Oct.' l, 1946.

E. s.. l.. BEALE 2,408,362 A OSCILLAT'INGFLUID-DISPLACING-MACHINES OPERATING IN PARALLEL Filed NOV. 17. 1943 y 4 Sheets-Sheet 4 NVENTOR 2.2. AT'roRNEY.

` ating machines. c

Patented Oct. l, 1946 OSCILLATING FLUID-DISPLACING MA- CHINES OPERATING IN PARALLEL Evelyn Stewart Lansdowne Beale, Staines, England, assignor to Alan Muntz & Company Limited, Hounslow, England, a companyY of Great Britain Application' November 17, 1943, Serial No. 510,638 In Great Britain November 25, 1942 15 claims. (ci. iso- 97) This invention relates to oscillating fluid-displacing machines arranged to operate in parallel on a common mamas either pumps or motors, ,and liable to variation in the phase-relationship of their respective oscillating duid-displacing elements.

The invention is concerned especially, but not exclusively, with Vinternal-combustion-operated air-compressors and .motive gas generators of the free-piston type, in which the oscillating element rincludesa power piston and a compressor piston arranged to reciprocate in unisony and unconstrained `by any continuously-rotatable crankshaft, so that the period of reciprocation depends on vthe inertia of the free-piston assembly, the

gas pressures acting on it, and the restraint due to friction and the driving of accessories.

When oscillating fluid-displacing machines are .delivering uid to-or drawing fluid from a common main iny parallel, the magnitude of the fluid pulsations in the main depends upon the phaserelationship of the4 several machines, and it is y usuallyrdesirable to maintain such a phase-relationship that the duid-pulsations inthe main are minimised.. An object of this invention is to provide means for automatically controlling both the magnitude and the'sign of the relative phase displacement of two such parallel-operating machine'sf A further object isto provide improved means for automatically controlling the phaserelationship of three or more'such parallel-oper- According to this invention a combination of at least two oscillating fluid-displacingV machines arranged tooperatein parallel on a. common main is provided with means for maintaining automatically a` predetermined phase relationship ybetween them',-said means includinga source of fluid under pressurea device actuated by one of said machines which servesas a master for interrupting the flow of said pressure fluid synchronously Aonly -once per cycle of saidimaster machine, a deviceV4 actuated by the other of said two machines which 3 acts as a slave, saidslave device being connected to receive the interruptedflow of pressure fluid said intendedphase relationship. Synchronously herein means during like portions of successive cycles of the oscillating machine concerned.

According to this invention in a. further aspect,

4a combination of at least three oscillating iluiddisplacing machines arranged to operate in parallel on a common main is provided with means fory maintaining automatically a predetermined phase-relationship between them, said means including a source of fluid under pressure, a device actuated by one of said machines which serves as a master for interrupting the flow of said pressurefluid synchronously only once per cycle of,

said master machine, two devices actuated respectively by the other two of said machines which serve as slaves, said two slave devices being connected to receive in parallel the interrupted flow of pressure fluid passed by said master device for interrupting the flow of pressure uid synchronously only orrce per cycle of the respective slave machines, the arrangement being such that there is normally an overlap of the non-interrupting period ofl said master device with the non-interrupting period ofeach of said slave devices, and two controllers for varying the periods 'of oscillation of therespective slave machines,

said controllers vbeing responsive to the mean rate passed by said master device and serving for inlterrupting the ,flowfof pressure vfluid synchronously `only once per cycle ofsaid slave machine, thearrangement being such that there is normally an overlap of the non-interrupting periods rofsaid .two devices, and a, Vcontroller for` varying `the'p'eriod of oscillation of said kslave machine, in

response to variation in the mean rate of flowof 'i pressrefilid'passedlby said two devices in series, sich.. a ense as @mais departure' from of flow of pressure fluidy passed by said slave devices respectively and being so set that one of them increases, while the other decreases, the period of oscillation of its associated slave Ina- 'chine in response to an increase in the flow of `pressure fluid passed by its associated slave device.

.'I'hus, where three oscillating machines are combined to operate in parallel, each of said three devices maybe so arranged that its non-interrupting period occurs over one .of the dead points 'of the oscillating elements. Y

Where it is desired that any of said devices shall .be oscillatory and that the non-interrupting period of said oscillatory device shall occur in vcourse of the displacement of the oscillating ele-V ment between its, dead points, the saidrdevice maybe provided .with a disabling element adapted to maintain it in interrupting condition during alternate strokes, e. either the instrokes or the outstrokes.

Tli'e 'word iluidg herein referred to as being v fluid underpreSSure or pressure fluid, means a liquid, electricity or a gas. A rv"Where" the pressure uidis a liquid', forexample oil, the interruptingdevices are hydraulic.

, The master valve inay have a plurality of sepa- ,rate prts arrangedto'feed'different 'slave valvesy i respectively v;, alternativelypthe.master valve may be arranged to feed a plurality of slave valves through a common valve port, the ducts connecting this common port to the respective slave valves containing nonreturn valves.

llhercthel oscillating machines are` of the :treepiston ityp'e, 'the floweinterrupting *devices vare conveniently arranged to oscillate with amplitudes dependent on the stroke of the associated free--y piston machines, so that these amplitudes var-y in dependence on the operatingjconditionsfofithe 5 machines; and in this case compensating means may be provided for reducingoreli'minating:the

in the receiver I8. The air content of the cushrupting period to the period'of os'illation'consequent on variation in the operating conditions.

Each of the controllersforveryiigithejperio. of oscillation of the slave machines i'niayiin'clude a differential fluid pressure-responsive deviceboth sides of which are connected to saidsurce of fluid pressure.

' JEmloodim'errts 'of Athe invention `as applied to a 'grou'pof 'free-piston"gasgenerat'ors 'will Qhe describe'd -loy 'way 'of erzarnple'with lreference lvto the "accompanying -diagrammatic drawings, uin which only those parts "of Lthe 'control 'mechanism with which'this'invention'isconcernied =are shown. In "the drawings:

lFig. :'l shows in sectiona "groupo'f `three ga's -geri'eratorsarranged to loperate inp'ara'llel,

Fig. 2 isa di'agramillustratingtheoperation of Ythisigrrmp,

lFig. '3 shows in section a 'group of '-ve 1gasfgen'erators,

Fig. 4 vis a diagram "illustrating the 'operation 'offtlie'group'shown in Fig.3 Fig's'B anu v6show'nio'clificationsof parts o'f FigL Fig.showspart'ovan' arrangement' equivalent tot that shownk in Fig." 3, and ir'igja isaisectron of adetaiiofrig. '1. `In kkth'e "examples herein V`'to 'be described with referencek to'Figs. 1"t`o"6v thepha'se control system fis hy'dr'auliothe pr'es'sureuid employedloeing 'il. Figs. and "B 'show analogous electrica-l '."sy'fstem 'wherein' switches; rsistances 'and vv.electromagnetic devices talie fthe plac'es respectively Y of jf the :piston valves, "restricted princes and fluidpre'ssur-eresponsiv'e adevices of V"the v"hydraulic ,-yst'ems.

In Ting. '1" 'the 'master 'gas-generators denoted *store energy"during'theptstrokes of'thepisto'ns'' ions canlbevar-iedby a control valve 2I, adapted -fwhenrinitherneutral position shown to seal a balance pipe 22 connecting the two cushions. The Valve 2'I, when -move'd to the left of the neutral position, lputs lthe cushions into communication withthe'scavengezair receiver I5 through a nonreturn valve 23 which allows air to pass only from ithecushi'onsitofthexreceiver, which will occur dur- 5mg 'that part or" each cycle when the cushion pressure. exceeds the receiver pressure. When the "valve'i is moved to the right from its neutral position, it connects the cushions to the receiver i5 "throughea non-return valve-'21H lvv'l'iich allows 'airJ topass` only from the 'receiver l'tolthe'cushions Ywhich Willpccur during that partei -e'achcycl'e when fthe *cushion pressure Ais Alower than the re- .f lceiver vpressure. In Y`such a gas-generator the periodic time of a cycle can be reduced Lby in- Icreasing the "quantity V'oi --air contained 'in the cushions. Consequently movement of the'valve '2l to the 3'left l*and "right lrespe'ctively will 'gradually-reduce and vincrease'respectively Vthe cyclical speed of the gas-generator. IThe 7free-'piston -assemoliesp the master 'gas-'generator M operate synchronously "a 'hydra'iiiic Uvalve 'shown diagrammatically als'a piston -v'alve the piston f f 4whic'nis V'fonneiion atailrod 225 :offene of th'e free-'piston assemblies. This vvalvehas two'similar sets'o'i'portsl and262 operating'in'parallel and *arranged ito remainlopen ltiming v'a part of Aeach Y'cycle when the free-pistons are approaching, A'passing through and Vreceding from their 'innen dead "pintandtoJrem'ain-closed 1during the rest of 'thercycieincluding:the outer dead point. 'Theslavegas-:generatorsfs I -and'SZ are' provided `withhydraulic LvalvesVVI and V2 similar to the vai-ve VM, V'except :that each i has only lone set of ports. ZThettwosetsjoirports 261 vand V262 of the "master valvelV-Mcontrol lrespectivelythe now of cillin two "pipes :2211 *and 212 l*which branch irom'fa "source "Aof oil `at constant pressure. The vtwo branches "2?'1 "and 212' are 'also controlled respec- "tively by't'he twoslavevalves VI 'and'VL Each branch includes a metering orifice 313.

'The Lbranch 271 terminates .in a 'cylinder /3I1 j'cont'aining a piston .321v loaded 'by a :spring 331. The piston/B21 "is "connected l"t'o "the cushion "air it "causes'th'e speed ftlie gas-'generator SI to increase, 'while the foil 'pressure iin the cylinder f3! 1 u'r'gestlie valvef I'1 in "the 'opposite direction. "The 'cylinder 3(1' crnmlmi'cateswi'th an air-colanni chamiermll ."and'with' 'a' leakage V'orifice 351. "The 'liranl'i[71?12"te'rrni'n'eites 'in a 'cylinder 312 "containing a piston322 connected "'to' the 'cushion 'air control valve2"I 2 'of the 'slave 'gas-'generator 'The pistonvizfis,j loaded b'y'a spring3'321which 'fbiasesth'e 'valveiz f2towa'rds 'the position in which v it .causes'thesp'eed 'of the gasfgenera'tor "S2 'to "decrease, while'theilpressure'in the cylinder 552 urges the 'v-alve'ZI"2 inthe l'opposite direction. 'The'.cylinde'r 3 f 2 communicates with an air-col- `1rnn "chaniiloe'r L$3112"en'dfwith aleaka'ge 'ori'ce 352. "Theirequencyereglating' means 'of the slave gasgenerator 'SZ 'arethus arranged to operate' in the ment of one-third of a cycle as shown, which condition vmay beinitially established by manual control, the period during 'which theY master valve VM is open overlaps by the equal intervals t1 and tz the periods during vwhich the slave valves VI and V2 are open respectively.l The flow capacities of the orifices130, 351 and 352 are so selected, in relation to the pressures exerted by the'springs 331.and 332 and to the ratio of the intervals trand tz to the periodic time of. the cycle, that the quantity of oil that flows into each of the cylinders 3I1`and 3I2 during onersuch interval is I.suficient to-replace the quantityrthat escapes' through the leakage orifices 351. and Y'352 during onecomplete cycle. The air columns 341 and 342 compensate for the 'pulsating admission of oil so that thepistons V321l and 322 remain substantially stationary, their' mean positions being asshown. Y e A vvNow fif the 'slave gas-generator S2, which' is leadingthe mastergas-generator M by one-third Vofa cycle -in phase, tends to Vrun-forl example slow,`v` the interval of overlap .t2 between the nolL interrupting periods of its valveV V2 and the master valve VM increases, yand the 'resulting infcreased admission of pressure oil to the cylinder 3I2 causes the valve 2|2 to befmoved to the right so that the gas-generator S2 .is speeded up. yIf theV slave gas-generator Sl, which is lagging the masterY gas-generator'by onethi-rd 'of a y 'Cycle inv phase, 'tendstorun' for example slow, the valve 'overlap interval: t1 decreases, and. Vthe 'resulting decreasedadmission 1 of pressure oil to to thel right sothat the gas-'generator Si is speed- ''Asregulationof the'power output or delivery pressure of any of the gas-generators may cause -a'variation of the outer and inner dead points of its free pistonsfif ythe oil pressure line control vvalve is operated, as in the example shown in fFigpl, bya'member moving' proportionally to the'fdisplacement of the free pistons, the `ratio-iol? 'the valve overlap interval tothe duration of a cycle -Will -vary with variation of lload on'they gas'- generator. Insome circumstances, and with a careful choice of xedopening positions of the 'valve ports, the irregularity yin phase relationship, fdue'tc regulation of thepoweroutput yor delivery` pressure" of the'` gas-generator, can beV kept fwithin tolerable limits. Neverthelessin other circumstances, it may be necessary to provide .the phase-controlling mechanism with means adaptved to` compensate forv variation in .load on the ga's-generaton In Fig. V1 is shown one possible compensating arrangement 'which serves to vary theratio of the-eiectiveareas of themetering -orice 30 and the'leakage'nrice 351 or 352. i, The 'areas `Aof vthe leakage orifices/are icontrolled by needles 361 and 362 rigid with pistonsy 311Y `and Y1312 whichwork in cylinders 381Land382 and are 4l` ia .sed'bry"springs 391 and 392 insuch adirectin as to increase the leakage; area.` I,Pipes v461 `of five gas-generators M, Sl, S2, S3 and S4 sinirthe`cylinder 3l'1 causes the valve 2|.1.to bemoved s and 402 branch from a pipe 40 connected Vto the source '26A ofl oil under constant'pre'ssure and lead to the cylinders 381 and 382 so as to admit oil Vwhich urges ythe pistons 311 and 312 in such a direction as to' decrease ythe area of the leakage orifices 351 and 352. .The tail rods 251 and 252 are provided with piston valve chambers 60-1 and 602 which, while the free pistons of the as# sociated gas-generator are passing through their outer dead point, open `valves ports 6l1 and 6|2 controlling the pipes 401 and v402, the opening period increasing as the outer dead point increases (i. e. recedes from the middle of the gasgenerator). Meteringorices 621 and 622 arearranged in series with the valve ports 6|1 and6|2 respectively. Pipes 631 and 632 branch from the pipes 401 and 402 downstream of the valveports and metering orifices just described and lead directly torestricted leakage orices 641 and 642 andalso through metering orices 651 and 652 to valve ports i 661 andV 662 forming. additional leakage paths and controlled by the pistonvalve chambers 601 and 602 in such a manner vthatfthe additional leakage paths are open while the free pistons of the associated gas-generators. are passing through their inner dead point, the opening perioddecreasing as the inner dead point increases` (i. e. recedes from the middle of the gasgenerator). y fi The effect on.A the opening period of the slave valve Vl or V2 of achange in inner dead point is not the same as that of the same.l change in outer deadv point, and furthermore the effect of a change in inner dead point is different according to the nature of the change in the operating conditions of the gas-generator. The leakage orices 641 and 642 are of such a capacity as to provide the best compromise for `the inner'dead point.- f K .1

Fig. 3` shows phase-controlling gear Vfor a group ilar tothe gas-generators shown in Fig. 1. Like `parts in thes two iigures are denoted by the same reference numerals, the two plants being gener.- allyvsimilar in arrangement, except for the following differences.

f The master valve VM.r has only one set of ports common to all the branches to the slave valves,

and each of these branches is provided with a y non-return valve 29 permitting oiltov flow only in the direction from the master valve towards .the slave valve and serving to prevent any ilow ,rofioil between the cylinders 3|1, 3l2 etc. during ,intervals-.of overlap of the non-interrupting pe.-

valve pistonand-the valvebody and which lmask theports during alternate strokes. These sleeves are drivenby collars 43 and 44 on the valve pistons .arranged to provide the appropriate degree ,of backlash.

In the present example the durationof the Youtstrokeof rthe freeV pistons is about three# guarters vo f that of their irl-stroke, and the four slavegasgenerators are karranged to lead the `and slave piston 'Y master gas-generator respectively by phase displacements which increase by equal increments from gas-generator S4 `to gas-generator SI, as shown in the upper part of Fig 4 .whichfshows on a base of time, the displacements ofthe free pistons. The valves VM', Vl' and V4' are arranged to be masked on the out-strokes, while the valves V2 and V3 are masked on the instrokes, The lower part ofV Fig. 4 shows' by the shaded rectangles the times during which the valves are closed, the dotted horizontal lines denoting the times during which the valve ports are masked by the disabling sleeves. The noninterrupting periods of the individual valves are shown in the upper part of Fig. 4 where OM denotesthis period for each of the valves VM', VI' andy V4', O2 the period for the valve V2', and O3 that for the valve V3.

- When the gas-generators are running fat a constant speed with their intended phase relationship, the periods of overlap of opening of the master valve VM' and of the slave valves Vl', V2', V3' and Vd' are those .denoted by t1, t2, ta and t4 in Fig. 4. Lagging of the slave gas-generators Sl and S3 will cause the periods t1 and t3 to decrease and consequently the cylinders 3l1 and 3 I3 are so arranged that a reduction in the quantity of oil supplied to them through the piston valves causes the pistons 32l and 323 to operate the cushion control valves 2l1 and 213' in such a sensexas to speedup the gas-generators SI and S3. If, however, the. gas-generators S2 and S4 lag, the periods t2 and .te increase, and the cylinders 3JI2`and 314 are setto operate oppositely to the cylinders 3l1 and 3l3, so that an increase in the. quantity of o-il supplied to the cylinders 312 and' 3|4 causes the gas-generators S2l and S4 to be speeded up.

It will thus be apparent that such a combination of ve gas-generators is constituted by two groups of three gas-generators each of which groups is arranged similarly to that shown "in Fig. 1, and which have however a common master gas-generator, the non-interrupting periods of the slave devices of one group diiering from the non-interrupting periods of the yslave devices of the other group in such a manner that the phase `differences of the ve machines are substantially uniform.

When it is desired to maintain a substantially constant phase displacement when the power output or the working pressure of a group of units is varied, the opening period of the phasing valve may be varied in laccordance with variation in the inner dead point or the outer dead point or both of these points `of the free-piston assembly. This result may be attained by providing piston.- type phasing "valves with `ported sleeves controlled by spring-loaded pistons working in cylinders supplied with pressure fluid in the same way Vas the cylinders 381 and 382 in Fig. 1. Alternatively lthe ported sleeves of the phasing valves'may be controlled by dead-point followers, and these sleeves may beY actuated by a linkage so .arranged that the opening or closing of the phasing ports occurs at a constant percentage of the free-piston stroke. With phasing ports arranged .to vbe open over a dead point, the valve opening or cut-ofi point maybe displaced through thel agency for a floating lever in accordance with v'the weighted mean of the inner and the outer dead points. With phasing ports having an opening period lying between the inner and the `outer dead points, vthe opening or the cut-oir points may be similarly displaced lin accordance with Isuitably weighted means; a simple but approximate compensation for such ports is todisplace each cut-off point independently by inner andk outer deadfpoint followers respectively, so as to maintain them at fixed distances from the dead points.

Fig. 5 shows a compensating mechanism applicable to each of the valves of the plant shown in Fig. 1. The phasing valve, here denoted by V, is provided with a ported sleeve 15, the position of which determines the beginning of the non-interrupting period. An inner dead point follower 4.6, of the kind described in application Serial No. 492,865, led June 30, 1943, has a connecting member 41 the position of which corresponds to the inner dead point of the free pistons. A similar outer dead point follower 48v has a connecting member 49 the position of which corresponds to the outer'deadv point of the freepistons. One end of a floating lever 55 is pivotally connected to the connecting member 49 and its other end is coupled by a link 52 to the connecting member 4l. An intermediate point on thev floating lever is coupled by a link 5l to the valve sleeve 45. The ratio of the .arms of the lever 50 above and below the link 5l is so selected that the opening point of the valve is displaced in accordance with the weighted mean of the inner and outer deadv points.

The uuid-pressure-responsive devices that -operate the cushion air control valves may be of the differential type arranged to balance two hydraulic pressures, instead of beingv spring controlled as in the examples hereinbefore described. Fig. 6 shows a part of a plant similar to that shown in Fig. l, except that such a balanced system is used, the means for .compensating for variation in load on the gas-generators are omitted, and a master valve VM having lone set of ports common to both branches 211V and l212 is used, these branches having non-return Valves 28. Corresponding parts. in Figs. 1 and -6 have the same referencenu-merals.

In Fig. `6 the iiuid-pressure-respensive device that operates the cushion air control valve 21,1 `of the slave gas-.generator Sl vis a cylinder |311 containing the piston 321, which lis springl bia-sed to its central positicm.l The vright-hand end :of this cylinder is supplied with oil in exactly the same way as the right-hand endv of thecylinder 311 in- Fig. yl, through the valves VM and VI.

'The left-hand end of the cylinder!! 3.11 is provided with a restricted leakage orifice 55 and is connected by a branch pipe 53, which ycontains a metering orifice :511, to a pipe l 2.6 communicating vwith the source of oil under pressure that snpplies the lmaster phasing valve- VM. When the master and slave machines :are .in the correct phase relationship, the force tending vto move the piston 321 to the right -due to the oil pressure inthe left-hand end of the cylinder i3 I'1 balances the mean force act-ingl on the right hand face of this piston due to the pressure of .the oil passed by the phasing valves VM and Vl.

This balanced system ,has the advantage that it is unaffected by .accidental variations in the pressure of the .oil supplied to the pipe 26.

In ,order to avoid irregularity operation of such hydraulic phase-control mechanisms -due to variation in viscosity' of the Pressure liquid. Awhich is conveniently lubricating oil, the Vsaid metering orices and leakage ori-ces should -be so designed that the resistance which they im- --pose'ito the flow of liquid is substantially pro.-

portional tothe viscosity of the liquid,fthat to say, they should provide a streamline ow with only small kinetic energy eiects. rrrI'hus the metering orices and the leakageVv oriiices will besimilarly affected by changes in viscosity. A large battery of gas-generators may be conveniently and simply phasedv in two or more groups of two or fourslave gas-generators. all the groups having a common master gas-generator. In special cases, it -is'possible to control, in accordance ywith this invention. the phaserelatio'nships of the master generators of two or more separate phase-controlled batteries.

' As -hereinbefore mentioned, an electrical systeml may be used inplace of a hydraulic vsystem,v4 and the analogy between the. two will" be illustrated by reference to Figs. '1 and 8which are comparable-with Fig: 3. The pipe 26- of Fig. 3 isreplaced by a lead226 to one terminalV of a current source, 226A, the other terminal of which is grounded. The hydraulic -valves VM' and VI- to V4' are replaced respectivelyby electrical switches SwM, Swl, etc. operatively connected with vthe free vpistons of the gas'- generators. Where the gas-generators are, as shown, ofthe usualv opposed-piston type, each switch is conveniently formed by a ring 80 of insulating material fast on the oscillatory shaft 8| of the vpiston 'synchronising mechanism, each ring havingv a conducting segment 82 co-operating witha pair of brushes 83. The synchronising mechanism shown in Fig. '1 is of the known rack-and-pinion'type, so arranged that the maximum amplitude of oscillation of the shaft 8| is substantially less than 360-. I

*The* sleeves 42 vand 421 to 424 of Fig.'3 are replaced by switches 242, 2.421 etc., which are generally similar to the rotary switches SwM, etc., but in which the ring 88A is drivably connected to the shaft 8| -by friction disks 84 (Fig. 8) loaded by acompressionv spring 85, and have a range of displacement, which is limited by an arm 86 co-operating with stops 8.1, between the on and o positions of the segment 88. The branch pipes .211 to 214 of Fig. 3Vare relplaced by branch leads 2211` and 2214 respectively, each including a rectifier 229 and a resistor 123i), replacing the non-return valves 29 and the orices 30 of Fig, ,3; The cylinder and piston devices ofy Fig. 3 actuating the air-transfer valves 211 to 2|4 are replaced by spring-biased electromagnetic devices energized from the appropriate branch lead 2211, 2212, etc., throughzthe appropriate pair of switches 2421 and Swl, etc.. vSuch a'device in its simplest form would be a solenoid having a spring-loadedv armature adapted to take up a position dependentV on the mean .valueofl the unidirectional current passing through its exciting winding. `In practice it isy morecon'venient to use torque motors, one ofwhich appears in Fig. '7. The motor is of the direct-current type and its armature 2321 isy connected between ground and the respective branch 1ead2111. Its :deld winding 89 is separately energised through a conductor 90 leading directly to the ungrounded sideof the current vsource 225A. A resistor n9i may be shunted across the armature in order to reduce sparking at thev contacts of the rotary switches. The armature 2321 is coupled by a suitable transmission, indicated diagrammatically at 92, to the transfer valve 2I1'and the biasing spring 2331.` In practice the Y'efiiciency of the' electromagnetic devices will usually be so l'ow that, when they operateas generators, their output will be negligible; thus the rectifiers`229 can be omitted. A

Iclaim: i i ,Y

1. 4A icombination of at least Atwo oscillatory fluid-displacing. machines arranged to operate in parallel on a common main and provided with 51 means fori maintaining automatically a predetermined phase relationship between 'them, said meansincluding a source of iiuid under pressure, a device actuated byone of said machines which serves as aV master for interrupting the iiow of said pressure iiuid synchronously only once per cycle of said master machine, a device actuated by the other of said two machines which acts as a slave, said slave device being connected to receive the interrupted flow of pressure fluid` passed by said master ,device and serving for interrupting the: flow of'pressure fluid synchronously only once per cycle of said slave machine-1 the 'arrangement being such that, when said predetermined phase relationship exists, -there is an overlap between the non-interrupting periods of said two devices, and a controller for varyingthe period' of` oscillation of said ,sla-ve machine, in responsetof variation in the meanrate of flow of pressureuidpassed by Isaid two vdevices in series,.in such a sense as toeliminate departure from-said predetermined phase relationship; e

2. A- combination of at least three oscillatory uid-displacing-machines arranged to operate parallel on a common jmain Iand providedwith means .for'maintaining automatically a predeter-` mined phase` relationship between them, said means rincluding: av source ci uid under pres-A sure, al device actuatedgby oneof said machines which serves as amaster for interruptingthe ow of saidpressure fluidsynchronously only once per` cycle ofsaid master ,mahineftwo devices, actuatedfrespectivelybythe other two of said machines which act asfslaves, saidftwo slave devices being connected tore ceive in vparallel the interrupted ow ofpressure fluid passed by said master, devicev for interrupting. the flowr of pressure fluid synchronously Ionly-,once yper cycle of the respective slave machines, the arrangement beingv such that, when said predetermined phase rela- 45'tionship exists, there isan overlap ofthe noninterrupting periods of-said vvmasterfdevice Ywith the non-interrupting periods of each of said slave devices, and two controllers for varying vtheperiods of oscillationof the respective slave ma'- chines, said controllers being responsive to variation in the mean rate ofjfl'iow'of pressure fluid passed `by said slave-devices respectively and beine.rv so set-that onefof thernjincreaseswhile. the Yother decreases, fthe period of oscillatiogof its associated slavev machines-Kin`- response .to an. rincrease inthe-flow v,of pressure fluid passed-,by itsassoci'ated slavedevice.;r f

i3. A combination of:l at lleast ,two oscillatoryiiuid-displacingmachines arranged toV operatein parallel on av common-m'ain'and providedwith meansfor maintaining automatically .a predetermined phase relationship {between them, said means including a source of iluid under pressure, a devicefactuated .byeone of said machines which servesA as. a *master for interrupting the iiow of s aid pressure fluid synch ronouslyV with the operationof said master machine, [a device actuated by the other of said two'machines which acts as a slave, said slave device being Vconnected to re- O ceive the'inter'rupted flow of pressure uid passed by Vsaid masterdevice' and serving for interrupt:

ing the iiow of pressure'fiuid synchronously with ther operation 'of said slave machine,v the noninterruptingiperiod of. each-of -said vdevices occur- 75 ringl 'over onlyoneof the deadpointsl of the associated oscillatory machine, and the arrangement heingfrsuch that, Whensaidipredetermineii phase relationship exists; therel isa: overi'apz liettizeenil tl-'ienon sinterruptirrgf. periods oi?A said-itwo' devices; and? au controller: for: t'liebperioch of csail-.+- lati'on .ofi saidslave: machine;v in@.respmiseL-toivar-1 ation. irr-.the' mean rateofiiiow. ofpressureffluid; passed;l by said two devices; in': serie-ss. irr. such'i a'. sensei as' tofV eliminate departure: from: said: preedeterminedrphasezrelationslp:.

4i A= combinationzofa aztleast threesoscillators? uiddisplacinga machines `:a1-ranged'. toi operatim paralleli orma common: main and provided; witin meansi forl maintaining' automatically a.: prede@ termined phase relationship f: between. them; said meanssincludingoa' sourceeof Huid-funden. pressure; ae device actuated-hy. onesof said'v machines, Wlrlielr` serves as a1 master:- frfinterrupting tires now" off said?" pressure fluid synchronouslyfwitlr. then-openl ation` off'said master`^ machine; .tivo-devices; actua ated respectively'-v b'y tliel otherttvo-A oi:q said mai-1, chinesswhi'ch act`` as slaves;V saidtwo'flslaveidvices being connectedtoreceive' ina paraileltlrenters ruptedi-fiw 1or"pressureeililiiipassed?bwsaiiirxrasa ter" device fr'- iriterruptingv-tlrei flow: off pressure fluidesynelironeusiywith the operation of-thei-resspective-'e slave maeliihes;l theU none-interrupting period'-ofi'eanniofisaiddevieessocourrirrgfoveronly: OnemEStiie dead pcintsf-of the= associated oscilla toryr machine',- and' the.a arrangement? beings such. that; when\said#predeterminedpliaserrelationship exists, there#issanoverlapiofl'the noir-interruptingiV peribdssofisaid master devioewitirethe'rrondnters rupt-iiigfperiod's' 'offeaoii* voffsaidY slavev devices; andL tivo. controllers;forx varying? tiie-period of? asciiT lation off'tiieerespectlveeslavermachines.saidconetrollersflieing responsive t'ofvvariatiorrdname-mean rateof" pressurefffiidl passed kyfsaidsi'avee devices"resp'eetivelfv andi being1 so .-se't tliaeone-f of? tliem increases? wliil'ei the-f other decreases;` the?. period" of oscillationj ofi its4 associate'dl sla-vermaachii1ein response t"o ane increase@ theY iiow.1 off pressureiiiid passedbyj its-f associated save: device:

5 A; combinati'orr--v off at? least; two oscillatoryf iiiii'd displaciiigsmachiires' arrangedtovoperateeim parallif orr a'l commonm maine andi provided with means4` forv maintaining automatiizallyfa prede@ termiiied" phase` relationship Betweem tI'iem'-, said a* device actuated ldyfone or`saii-maciiines@whichV servess as a'J masten for"V interrupting`r`v the@ domi said? pressure fluid syncl'ironousii'I only once?Y per` cyclF4 or* saidA master lm'aoliine'; a:i device actuated* two-devioesfirr-seriesgsucia asensetas. toselmi lik' 1a nate departure; trom:v said predetermined phase relationships. y

6.=.A. combination; of: at least; live. oscillatom uid-displaeing. machines arranged YIto: operaterin! parallelf onf a. common mainz and'. provided; with mea-ns ior maintaining automatically'a predeten-A minedv phase. relationshipf, between; thenne said; meanssincluding-i a.- sourceof. iluid.u-nderl pressure;l as deviee actuatedby onefof. said. machines' which: serves.- ass. a1- mastern for interrupting@ thef.- ilovev on pressure fluidi synchronously with'. thas operation of said master machines. foiir-h devices-actuated respectively by the otlfiex. four oi-.saiclimachines whichL aot-as-sslavesi ,said ,ioun deyioesibeing; cone nected.- to.: receive.; dansz of; pressere.:v uidi inte-ry rnpted by f said: masten devine;l and. servings to; interrupt said: flows f of: pressures fluidi ssnnehrofh nonslyl withethei operation ofi. therespeotiveifslave: machinessadi fives devices: beingi oscillators/5- with; their nonf-interriuptingsperiods occurring in course.- ofi thef4 motion; of theA associ-ated oscillatory man chine-C- betweents dead' points, iives disabling.:v cles. ments. associatedewith said rive devicesi respeotively; for; eliminating?. noneinterrupting. periods; one alternate .strokes-thefarrangement: beingesuchf that?, when.saidpredeterminephase:relationship exists, thererisnn overlap cinnamon-interrupting; periodssoi .saidmasten deviceiw-ith lth amour-inten rnpti-ng periodss of each of.r saidrslavedevioes; and, foun'eontrollersfior varying?l the periodse oie: csail-.f-A lation ofA` the; respective;4 slave; machinesl im re.`v` spense to a variation-r the, mean ratei ori. flora ofq pressurer fluid passedlbistheJ respective..- slaveedef. vices, a iirst pair of saichoontrollers beingrsofsete f that theyw increase therperfiods of' oscillatiomof the. associatedv rstepair.r of' said slave, machines. inrresponseto. increase inlthe flowsmf pressure; fluid. passedrbyA` ther associated first-pair ofi. saisi slave. devices-,..the;second, pair of.. said contm'llersJ being soset; that., they. decrease the.. periodsf on oscillation of; the associated-.seconds pair oi, said. slave machines,x inl response. toi increase in the; flows` ofi pressure. fluid. passed-by theassociatedi secondpair. ofisaidislave devic.es,.and;.the overlap of.. the. norr-inter-ruptine` per-lodi of.' one: dei/ice. of.. each .oi'sai'dpairswithithatxoi saidlmasterdevioe. occurring during. lkestrokes, oi. the` master. and slave,.whi1e the overlapof. the non-interrupting period of; the. other deviceof each oi! said pairsJ with. thatl of.' said'. master; device.. occurs` di1rin. ;-.l oppositestrolies oil the master.; andlslave...

7.1.5, combinationi of.V at least three oscillatory IluddisplacingD-machines arranged.' to operaterin, parallel; on a common, main and; provided; with means .fnrn maintaining. automatically. appredeten minedphase. relationship, hetweenthem, said; means includingasource ,olitiilid'unden pressure,-. a hydraulic. valve actuated'. liy.- one of; said; ma.- chineswhichfserves as ama'ster. andlliavi'ng; two.- port's. fori` deliveringf, two separate flows. of." saidl liquid; each4 interrupted-i synchronouslyI once perl cycle of. said master machine, two.- hydraul'i"k valvesactuatedirespectivelr, by the other. twofoi.' saidmacliir1eswhichlactslslaafes, sailtwoslave valveslbeing conneotedltoleceiyethe interrupted; ilowssof.' liquid. deliyeredlliy said. two respe.o.. tively, ofthe mastenvalve and servinggtointerruptl the. flow., of. liquid; synchronously; onlyy once; per. cycle of; the. respective, slave machined. the are. rangement; being solch*I that,L whent said; prede-terimiriedlplfiase;reiationshipexistsi therefissan over lapzofimanon-interrupting@eriodsoiisaid.masten valve with thee. nonfinterruptina, periods: o each; oiisaid slava-valves, l.and twol controllerseforrvarszr,

. ing the periods of oscillation of the slave machines, said controllers being responsive fluid-displacing machines arranged to oprei'aftehin4` parallel on a commonmainaandiprovidedywith means v fmgmairitairiligautomatically a vpredeter- 1 x'nireiif'ph'ase "relationship between them, said 'means including a source of liquid under pressure,

a hydraulic valve actuated by one of said machines which serves as amaster and having a port for delivering a ilow of said liquid interrupted synchronously once per cycle of said master machine, two hydraulic valves actuatedrespectively by the other two of said machines, which act as slaves, said two valves being connected to receive in parallel the flow of liquid delivered from said port and serving to interrupt the ow of liquid synchronously only once per cycle of the respective slave machines, the arrangement being such that, when said predetermined phase relationship exists, there is an overlap of the non-interrupting periods of said master valve with the non-interrupting periods of each of said slave valves, and two controllers for varying the periods of oscillation of the respective slave machines, said controllers being responsive to lvariation in the mean rate of flow ofv pressure liquid passed by said slave valves respectively, in such a sense as to eliminate departure from said predetermined phase relationship.

9. A combination of atleast two free-piston fluid-displacing machines arranged to operate on a common main and provided with means for maintaining automatically a predetermined phase relationship between them, said means including a source of uid under pressure, a uid path connected with said source and including two devices arranged in series in said path and actuated respectively by said machines for interrupting the ilow of pressure uid in said path synchronously with the operation of said machines respectively, the arrangement being such that, when said predetermined phase relationship exists, there is an overlap between the non-interrupting periods of said two devices, a controller for varying the period of oscillation of one of said machines, in response to variation in the mean rate of iiow of pressure uid along said path, in such a sense as to eliminate departure from said predetermined phase relationship, said devices having oscillatory elements arranged to oscillate with amplitudes varying with variation in the length of the free-piston strokes of said machines, and meansv for at least reducing automatically the eil'ect of variation of the ratio of the noninterrupting period of each of said devices to its period of oscillation consequent on variation in the free-piston stroke of the associated machine.

10. A combination of at least two free-piston fluid-displacing machines arranged to operate on a common main andprovided with means for maintaining automatically a predetermined phase relationship between them, said means including a source of liquid under pressure, a duct connected with said source and including two hydraulie valves arranged in series in said duct and actuated respectively by said machines for interrupting the flow of liquid in said duct synchronously with the operation of said machines respectively, the arrangement being such that, when said predetermined phase relationship exists, there is an overlap between the non-interrupting 14 periods of said two valves, a controller for varying 'the period/of oscillation of one of said ma` chines which acts as a slave, said controller including a hydraulic fluid-pressure-responsive device connected to be supplied with liquid by said duct and through a metering port and to discharge liquidlthrough` a leakage port, said con- "-troller" acting to eliminateY departure from said predetermined phase relationship, and said valve actuated by said slave machine having an oscillatory'element arranged to-oscillate with an amplitude varying with variation in the length of the free-piston strokes of said slave machine, and means responsive to variation of the ratio of the non-interrupting period of the said valve actuated by said slave machine to its period of oscillation for varyingthe ratio of the ow capacities of said ports so as to compensate at least in-par't for variation in said free-piston stroke. 'i

11. A free-piston fluid-displacing machine in-= tended for operation in predetermined phase relationship in parallel with other like machines on a common main and having a controller for varying the period oi oscillation of its freepistons, means for conducting a variable supply of fluid under pressure for actuatingV said controller, and a device having an oscillatory member connected for movement in synchro-nism with said free pistons and serving to interrupt synchronously the flow of pressure fluid through said conducting means, and means for adjusting the non-interrupting period of said device automatically in response to variation in at least one of the dead points of said free pistons so as at least to reduce rthe effect of variation of the length of the freepiston stroke on the ratio of said non-interrupting period to the period of oscillation of said free pistons.

12. A free-piston fluid-displacing machine intended for operation in predetermined phase relationship in parallel with other like machines on a common main and having a controller for varying the period of oscillation of its free pistons, said controller including a hydraulic actuating device responsive to variation in mean rate of flow of liquid thereto, a duct for admitting liquid to said actuating device and including a valve having an oscillatory member connected for movement in synchronism with said free pistons, and means for adjusting the non-interrupting period of said valve automatically in response to variation in at least one of the dead points of said free pistons so as at least to reduce the effect of variation of the length of the free-piston stroke on the ratio of said non-interrupting period to the period of oscillation of said free pistons.

13. A combination of at least two oscillatory fluid-displacing machines arranged to operate in parallel on a common main and provided with means for maintaining automatically a predetermined phase relationship between them, said means including a source of fluid under pressure, a device actuated by one of said machines which serves as a master for interrupting the ow of said pressure fluid synchronously only once per cycle of said master machine, a device actuated by the other of said two machines which acts as a slave, said slave device being connected to receive the interrupted flow of pressure fluid passed by said master device and serving for interrupting the flow of pressure fluid synchronously only once per cycle of said slave machine, the arrangement being such that, when said predetermined phase relationship exists, there is an overlap between the non-interrupting periods of said two devices,

andacontroiler-fer varyingy thefper-icd ci. oscilla.m tiem cf'; saidzslave machine;X inrespnnse tofva-riaf tion ine ti'iegmeanA rate. of .flow oi pressure iiuid. passedf; by said. two: devices: in. series; in such a. sensefas zt'o: eliminate. departure from .said-prede termined phaseJ relationship;. Said.; controller infcludingg. a, differential fluidepressureeresponsive. actuating* device. both sidess. of Whichf. are.` cnnnected'fto.saidsourceiiuid pressure;

14..- ,A1, combination of. at;` least 1 two -free-piston fluid-displacing, machines arranged to:` oper-ate: on arcommonmainand provided withmeanssfor, maintaining'. autnmaticallyM apredetermined phasereiationship betweenthemg. saidfmeans i in.u cluding. a g source; of liquid 1 under. pressure,- a duct. cennectediwithisaidesource andincludingtwohydrauliczvalyes arranged in serie-sv in-sadzdlletzand. actuated. respectivelyf by saidA machines; for inim terrupting the flow-f of, liquid. in said: ductesyfnl chronously-.- with`v the operationl of said. machines respectively,Yc the. arraiigaement.:beingsuclr. that,` when. said: predetermined phase. relationshipfeie ists. there. is: anf overlap: between. the non-interrupting; periods? of said@ two Valves,- a. controller forY varyings the.A period of oscillation of-l one; of.Y said machines whichi acts: as a: slavesaidncnn trnller. including. a.. differential. hydraulic. prese sure-responsive :device .onef side cf- Whichisl con nectedmeAbeesupplied-WithiliquidJoy; said duct and a. meteringgpcrtJ and.- tofdischarge.- liquid 1:6 thmugin a leakage;- port; .Y while; the.: other-` side.; oi. saidzdeviceis connected tabel-suppliedfwithiliquid from; said, sourcef through a meteringA port inde'- pendently of said.I ductl andfto: discharge liquid. through a leakagepcrt,.said controller being; set to.. eliminate departure from said; predetermined phase -relationship.;,

15. AtV least. two:internal?ccmbustion-foperated; gasegenerators; of.` the free-piston type; connected.- to fdeliver gas tofa-y common-main', in"Y combination With means for.A maintaining; them. in. predeterf mined.- phase relationship` eachnof; said tw0- gas-v generators: havingv af speedfcontrollen; ai. pressure. fluid; circuit for. actuating'v said.: controller: and` ade viceeion interruptingsaid circuit'.syncl'ironnuslyfy oncez per; cycle 0L the-associated: gassgeneratcr; andga'master devicefcapableof interruptinggeach: of. said circuits; synchron311513Zata:predetermined.v frequency, .the arrangement beingsuchithaa'whem said: gasfgener-ators; arei maintained in saidipre`` determined pliasefrelationship, there are overlaps? between the? noneinterruptingperiods: of saich master. device andi. of each. of sa-idslave'.4 devices; variation oil said overlaps: due to;- departure: oi

f. said\ gas--generators. from: said: predeterminismA phase*relationshipcausing: Vania-tion of. thefznea'ny rates: of. nwfo. fiuidfinf said circuits andspeedk correcting actuation' df; said: contrcll'erss

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