DK152152B

DK152152B - PROCEDURE FOR MANAGING A DIFFERENCE PRESSED ACTIVATED VALVE VALVE AND CONTROL SYSTEM FOR EXERCISING THE PROCEDURE

Info

Publication number: DK152152B
Application number: DK687973A
Authority: DK
Inventors: Erik Nielsen
Original assignee: Hoeyer As O G
Priority date: 1973-12-18
Filing date: 1973-12-18
Publication date: 1988-02-01
Also published as: DK687973A; DK152152C

Description

DK 152152 BDK 152152 B

Opfindelsen angår en fremgangsmåde til styring af en differenstrykaktive-ret servoventil med et aktiveringsstempel, som på sine to sider er påvirket af henholdsvis et referencetryk og et af det styrede tryk afhængigt tryk.The invention relates to a method for controlling a differential pressure actuated servo valve with an actuating piston which is influenced on its two sides by a reference pressure and a pressure dependent on the controlled pressure, respectively.

På grund af friktionen mellem stempel og cylindervæg har en sådan servoventil en vis dødzone, i hvilken den ikke reagerer på ændringer i det styrede tryk, hvilket bl.a. kan være en alvorlig ulempe ved ventiler, der benyttes til styring af trykket i et køleanlægs fordamper og dermed fordampningstemperaturen. Ulempen gør sig ganske særlig bemærket ved kontinuerlige iscremefrysere, hvor selv små ændringer i cremens temperatur, forårsaget af temperaturvariationer i det benyttede kølemedium, kan føre til betydelige ændringer af cremens viskositet. En formindskelse af dødzonens bredde kan opnås ved anvendelse af en membranventil, men sådanne ventiler er betydelig mere pladskrævende end stempelaktiveDue to the friction between piston and cylinder wall, such a servo valve has a certain dead zone in which it does not respond to changes in the controlled pressure. can be a serious disadvantage of valves used to control the pressure of a refrigerator evaporator and thus the evaporation temperature. The disadvantage is particularly noticeable in continuous ice cream freezers, where even small changes in the temperature of the cream, caused by temperature variations in the refrigerant used, can lead to significant changes in the viscosity of the cream. A reduction in the width of the dead zone can be achieved by using a diaphragm valve, but such valves are considerably more space consuming than piston active

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rede ventiler, og membranerne har ofte begrænset holdbarhed over for aggresive medier, såsom kølemedier samt ved høje tryk og særlig høje eller lave temperaturer.prepared valves, and the membranes often have limited durability to aggressive media such as refrigerants as well as at high pressures and particularly high or low temperatures.

Den ovenfor påpegede ulempe ved de stempelaktiverede ventiler afhjælpes ifølge opfindelsen ved, at trykket på stemplets ene side med mellemrum forøges eller formindskes med en størrelse, som er tilstrækkelig til at overvinde de på stemplet virkende friktionskræfter.The above-mentioned disadvantage of the piston-activated valves is alleviated according to the invention by increasing or decreasing the pressure on one side of the piston by a size sufficient to overcome the frictional forces acting on the piston.

Det vil indses, at man ved deiforeskrevne intermitterende ændring af det på stemplet virkende differenstryk er i stand til at påvirke stemplet med kraftimpulser, som ved at overvinde friktionen bevæger stemplet et stykke ud fra dets øjeblikkeligestilling og derved forbigående også ændrer trykfaldet over ventilen. Når kraftimpulsen igen ophører, vil der være etableret en tilsvarende ændret trykdifferens på stenrølet, som er i stand til at føre stemplet tilbage til den korrekte stilling svarende til ønskeværdien af det styrede tryk og dermed genoprette denne værdi. Det vil forstås, at varigheden af de perioder, i hvilke den ensidige trykændring opretholdes, er afhængig af dødzonens bredde og størrelsen af trykændringen, og at varigheden af de mellemliggende intervaller primært afhænger af den ønskede styringsnøjagtighed, idet denne vokser med aftagende intervallængde.It will be appreciated that by de-prescribed intermittent alteration of the differential pressure acting on the piston, it is able to influence the piston with force pulses which, by overcoming the friction, move the piston a distance from its instantaneous position and thereby transiently also change the pressure drop across the valve. When the force pulse again ceases, a correspondingly altered pressure differential will be established on the rock roll which is able to return the piston to the correct position corresponding to the desired value of the controlled pressure and thus restore this value. It will be appreciated that the duration of the periods during which the unilateral pressure change is maintained depends on the width of the dead zone and the magnitude of the pressure change, and that the duration of the intermediate intervals depends primarily on the desired control accuracy as it increases with decreasing interval length.

Opfindelsen angår også et styreanlæg til udøvelse af fremgangsmåden og af den kendte art, som omfatter dels en servoventil med et fjederbelastet ventillegeme, der er fast forbundet med et servostempel, som er forskydeligt i en cylinder med to på hver sin side af stemplet beliggende kamre, som er forbundet indbyrdes gennem en snæver passage, og af hvilke kamre det ene gennem en styreledning er sluttet til et område, hvis tryk afhænger af det styrede tryk, medens det andet kammer står under et andet tryk, dels en afspærringsventil i styreledningen. Fra beskrivelsen til USA-patent 3 303 664 kendes et styreanlæg af denne udformning, hvor afspærringsventilen fungerer som hovedstopventil for anlægget.The invention also relates to a control system for carrying out the method and of the prior art, which comprises partly a servo valve with a spring-loaded valve body fixedly connected to a servo piston which is displaceable in a cylinder with two chambers located on each side of the piston. which are connected to one another through a narrow passage and from which chambers one is connected through a control line to an area whose pressure depends on the controlled pressure, while the other chamber is under a different pressure and partly a shut-off valve in the control line. From the disclosure of U.S. Patent 3,303,664, a control system of this design is known, in which the shut-off valve acts as the main stop valve for the system.

Styreanlægget ifølge opfindelsen er ejendommeligt ved, at det har et programværk til intermitterende åbning og lukning af afspærringsventilen. Herved opnås den foreskrevne forbigående ændring af differenstrykket over stemplet på enkel måde, idet der efter lukning af afspærringsventilen sker en udligning af trykkene på stemplets to sider gennem den snævre passage mellem de to cylinderkamre, således at fjederbelastningen midlertidig overvinder friktionskræfterne og derved forskyder ventillegemet, hvorved trykfaldet over ventillegemet ved den følgende genåbning af afspærringsventilen er ændret som ovenfor beskrevet.The control system according to the invention is peculiar in that it has a program network for intermittent opening and closing of the shut-off valve. Hereby, the prescribed transient change of differential pressure across the piston is achieved in a simple manner, after closing the shut-off valve, the pressure on the two sides of the piston is equalized through the narrow passage between the two cylinder chambers, so that the spring load temporarily overcomes the frictional forces, thereby displacing the valve body. the pressure drop across the valve body upon the subsequent reopening of the shut-off valve has changed as described above.

Opfindelsen forklares i det følgende nærmere under henvisning til den skematiske tegning, på Inalken fig. 1 er et skematisk billede af en udførelsesform for et styreanlag ifølge opfindelsen, ogThe invention is explained in more detail below with reference to the schematic drawing, in Inalken fig. 1 is a schematic view of an embodiment of a control system according to the invention; and

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fig. 2 et diagram over et muligt tidsforløb af trykket i et køleanlægs fordamper, som styres ved hjælp af anlægget ifølge fig. 1.FIG. 2 is a diagram of a possible time course of pressure in the evaporator of a refrigeration system which is controlled by means of the system according to FIG. First

Det i fig. 1 viste styreanlæg indeholder en servoventil med et cylindrisk hus 1 og et i huset aksialt forskydeligt stempel 2, som afgrænser to cylinderkamre 3 og 4. Stemplet 2 er gennem en stempelstang 5 fabundet med et ventillegeme 6, som er bdiggende i et til cylinderen 1 sluttet hus 7, og overgangen mellem husene 1 og 7 er udformet som et sæde for ventillegemet 6. En trykfjeder 8 i huset 7 belaster ventillegemet 6 i retning mod lukket stilling.The FIG. 1, a servo valve with a cylindrical housing 1 and an axially displaceable piston 2 defining two cylinder chambers 3 and 4. The piston 2 is formed through a piston rod 5 with a valve body 6, which binds in a connection to the cylinder 1. housing 7, and the transition between the housings 1 and 7 is designed as a seat for the valve body 6. A compression spring 8 in the housing 7 presses the valve body 6 in the direction towards the closed position.

Gennem en ledning 9 er huset 7 tilsluttet et ikke vist område, hvori der ved hjælp af ventilen skal opretholdes konstant tryk, specielt fordamperen i et køleanlæg. Til huset l's kammer 4 er sluttet en ledning 10, som fører til et område, hvor der hersker et lavere tryk, i det nævnte tilfælde sugesiden af køleanlæggets kompressor. De to kamre 3 og 4 i huset 1 er indbyrdes forbundet gennem en snæver kalibreret passage 11 i stemplet 2.Through a conduit 9, the housing 7 is connected to an area not shown, in which constant pressure must be maintained by means of the valve, especially the evaporator in a cooling system. To the chamber 4 of the housing 1 is connected a conduit 10 which leads to a region where a lower pressure prevails, in the said case the suction side of the compressor of the refrigeration system. The two chambers 3 and 4 of the housing 1 are interconnected through a narrowly calibrated passage 11 in the piston 2.

En grenledning 12 fra ledningen 9 udmunder i et hus 13, der indeholder en magnetventil omfattende en solenoide 14 og et ventillegeme 15. Ventillegemet 15 styrer forbindelsen mellem grenledningen 12 og en afgangsledning 16 fra huset 13, og ventilen indeholder ikke viste organer, f.eks. en fjeder, der søger at holde den nævnte forbindelse lukket. Når solenoiden får spænding, åbnes ventilen. Solenoidens to tilslutningsklemmer 17 er forbundet med et ikke vist programværk, som omtales nærmere nedenfor.A branch line 12 from line 9 opens into a housing 13 containing a solenoid valve comprising a solenoid 14 and a valve body 15. The valve body 15 controls the connection between the branch line 12 and a discharge line 16 from the housing 13, and the valve contains no means shown, e.g. . a spring which seeks to keep said connection closed. When the solenoid gets voltage, the valve opens. The two solenoid terminals 17 of the solenoid are connected to a program (not shown), which is discussed in more detail below.

Ledningen 16 udmunder i en pilotventils hus 18, fra hvilket en ledning 19 fører til kammeret 3 i servoventilens hus 1. Pilotventilen indeholder en mellem huset 18’s to dele fastspændt membran 20, som ved hjælp af en fjeder 21 belastes til lukning af ledningen 19’s munding. Den af fjederen 21 på membranen 20 udøvede kraft kan justeres ved hjælp af en stilleskrue 22. Kammeret i huset 18 over membranen 20 er gennem en åbning 23 tilsluttet atmosfæretrykket.The conduit 16 opens into the housing 18 of a pilot valve, from which a conduit 19 leads to the chamber 3 of the servo valve housing 1. The pilot valve contains a diaphragm 20 which is secured between the two parts of the housing 18, which is loaded by a spring 21 to close the conduit 19's mouth. The force exerted by the spring 21 on the diaphragm 20 can be adjusted by means of a set screw 22. The chamber in the housing 18 over the diaphragm 20 is connected to the atmospheric pressure through an opening 23.

Det ovenfor omtalte programværk indeholder to hensigtsmæssigt indstillelige tidsrelæer, af hvilke det ene fastlægger varigheden af de relativt lange intervaller, i hvilke solenoiden 14 står under spænding,og hvor ventilen 14, 15 derfor er åben. Det andet tidsrelæ fastlægger varigheden af de relativt korte mellemliggende perioder, i hvilke strømmen forbigående er afbrudt og ventilen dermed lukket. Når den viste ventil anvendes til konstantholdelse af trykket og dermed fordampningstempératuren i et køleanlægs fordamper, sker der følgende.The above-mentioned program includes two suitably adjustable time relays, one of which determines the duration of the relatively long intervals at which the solenoid 14 is under voltage and the valve 14, 15 is therefore open. The second time relay determines the duration of the relatively short intermediate periods in which the current is temporarily interrupted and the valve thereby closed. When the valve shown is used to maintain the pressure and thus the evaporating temperature in a refrigerator evaporator, the following occurs.

Så længe ventilen 14, 15 er åben, virker fordampningstrykket gennem ledningen 9, grenledningen 12, huset 13, ledningen 16, huset 18 og ledningen 19 i kammeret 3, medens det noget lavere kompressortryk, der hersker i ledningen 10, virker på stemplet 2’s underside i kammeret 4. TrykdifferenAs long as the valve 14, 15 is open, the evaporation pressure through the conduit 9, the branch conduit 12, the housing 13, the conduit 16, the housing 18 and the conduit 19 in the chamber 3, while the somewhat lower compressor pressure prevailing in the conduit 10 acts on the underside of the piston 2 in chamber 4. Pressure difference

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sen på stemplet opvejes af fjederen 8*s kraft, som derved holder ventillegemet i en sådan stilling, at trykfaldet over ventilen, dvs. fra ledningen 9 til ledningen 10, antager den ønskede værdi, i hvilken kræfterne på stemplet 2 og ventillegemet 6 er i balance. I fig. 2, hvor abscissen angiver tiden og ordinten trykket, er den ønskede værdi af fordampningstrykket angivet med p^.the tendon of the piston is offset by the force of the spring 8 *, thereby holding the valve body in such a position that the pressure drop across the valve, i.e. from line 9 to line 10 assumes the desired value in which the forces on piston 2 and valve body 6 are in balance. In FIG. 2, where the abscissa indicates the time and the order of pressure, the desired value of the evaporation pressure is indicated by p ^.

Friktionen mellem stemplet 2 og væggen af det cylindriske hus 1 medfører, at stemplet 2 først begynder at bevæge sig i cylinderen, når den tilstræbte ligevægtstilstand er forstyrret så meget, at differenskraften har antaget en vis værdi. Dette betyder i praksis, at fordampningstrykket kan variere inden for den såkaldte dødzone, der i fig. 2 er markeret ved sin overgrænse p^ og sin undergrænse p^, før der sker nogen ændring af ventillegemet 6's stilling og deemed af trykfaldet over ventilen. Uden de ovenfor beskrevne foranstaltninger ved servoventilen ville fordampningstrykket således kunne variere f.eks. efter den jævnt stigende, punkteret viste linie 24 i fig. 2, uden at ventilen reagerer. Denne ulempe afhjælpes ved de nævnte foranstaltninger, som medfører periodiske kortvarige lukninger af ventillegemet 15 styret af programværkets tidsrelæer.The friction between the piston 2 and the wall of the cylindrical housing 1 causes the piston 2 to start moving in the cylinder only when the desired equilibrium state is disturbed so much that the differential force has assumed a certain value. In practice, this means that the evaporation pressure can vary within the so-called dead zone, which in fig. 2 is marked at its upper limit p ^ and its lower limit p ^ before any change of the position of the valve body 6 and deemed by the pressure drop across the valve occurs. Thus, without the measures described above at the servo valve, the evaporation pressure could vary e.g. following the steadily increasing, dotted line 24 in FIG. 2 without the valve reacting. This disadvantage is remedied by the said measures, which cause periodic short-term closures of the valve body 15 controlled by the program relay's time relays.

Når ventillegemet 15 af spærrer forbindelsen mel lem. ledningerne 12 og 16, vil trykket i kammeret 3 falde på grund af trykdifferensen over stemplet 2, som fremkalder en strømning fra kammeret 3 gennem passagen 11 til kammeret 4, hvor der som før nævnt hersker et lavere tryk end i ledningen 9. Herved falder den på stemplet 2 virkende differenskraft så meget, at kraften fra fjederen 8 på et vist tidspunkt er i stand til at bevæge stemplet og det dermed forbundne ventillegeme 6 i retning mod lukkestillingen, hvilket umiddelbart fører til en trykstigning i ledningen 9. Denne trykstigning er i fig. 2 antydet ved en opadgående linie 25, hvis spids 26 ligger over dødzonens overgrænse p^·When the valve body 15 is off the connection between limb. lines 12 and 16, the pressure in the chamber 3 will decrease due to the pressure difference across the piston 2, which produces a flow from the chamber 3 through the passage 11 to the chamber 4, where as previously mentioned there is a lower pressure than in the line 9. differential force acting on the piston 2 so much that the force of the spring 8 is able at some point to move the piston and the associated valve body 6 towards the closing position, which immediately leads to a pressure rise in the line 9. This pressure rise is shown in FIG. . 2, indicated by an upward line 25, the tip 26 of which is above the upper limit of the dead zone p

Efter at stemplet 2 og dermed ventillegemet 6 har bevæget sig et stykke i retning mod lukkestillingen, slutter programværkets tidsrelæ strømmen til solenoiden 14, hvorved ventillegemet 15 igen åbner. Det forøgede tryk i ledningen 9 har nu gennem ledningen 16 adgang til membranen 20*s underside, og dersom denne i mellemtiden har lukket ledningen 19, løftes den igen af det forøgede tryk, som derved ledes videre til kammeret 3 på stemplet 2*s overside. Stemplet er herved igen påvirket af en resulterende nedadgående kraft fra trykdifferensen, og denne kraft bevæger stemplet og derned ventillegemet 6 tilbage igen mod åben stilling, hvorved fordampningstrykket falder efter det i fig. 2 viste kurveafsnit 27.Ventillegemet 15 forbliver herefter åbent i et interval, hvis længde i fig. 2 er angivet med tQ, hvorefter det ovenfor beskrevne hændelsesforløb gentager sig. Det fremgår af fig. 2, at man på denne måde er i stand til at holde det styrede tryk konstant med en afvigelse fra' den ønskede værdi pQ, som er væsentlig mindre end bredden, af dødzonen.After the piston 2 and thus the valve body 6 has moved a bit in the direction of the closing position, the program relay time switches the current to the solenoid 14, whereby the valve body 15 opens again. The increased pressure in the conduit 9 now has access to the underside of the diaphragm 20 * through conduit 16, and if it has in the meantime closed the conduit 19, it is again lifted by the increased pressure, which is then passed to the chamber 3 on the upper side of the piston 2 . The piston is hereby again affected by a resultant downward force from the pressure difference, and this force moves the piston and then the valve body 6 back again to the open position, whereby the evaporation pressure falls according to that of FIG. 2 of the curve section 27. The valve body 15 then remains open at an interval whose length in FIG. 2 is indicated by tQ, after which the sequence of events described above repeats. It can be seen from FIG. 2, in this way one is able to keep the controlled pressure constant with a deviation from the desired value pQ, which is substantially smaller than the width, of the dead zone.

Claims

1. A method for controlling a differential pressure actuated head with an actuating spring piston, which on its two sides is respectively influenced by a reference pressure and a pressure dependent on the controlled pressure, is known by the pressure on one side of the piston. at intervals one size increases or decreases sufficient to overcome the frictional forces acting on the piston.

A control system for carrying out the method according to claim 1 and comprising, in part, a servo valve with a spring-loaded valve body (6) fixedly connected to a servo piston (2) * which is slidable in a cylinder (1) with two on each side of piston located chambers (3, 4) which are interconnected through a narrow passage (11) and of which chambers one (3) is connected through a control line (12, 16 19) to an area whose pressure depends on it controlled pressure while the second chamber (4) is under a different pressure and partly a shut-off valve (14, 15) in the control line (12, 16, 19), characterized in that the system has a program for intermittent opening and closing of the shut-off valve ( 14, 15).

Control system according to claim 2, characterized in that the duration of the shut-off valve closing period and of the interval between successive closures of the valve (14, 15) is adjustable by means of two adjustable time relays in the program network.