US2346418A - Fluid operated means for controlling apparatus at a distance - Google Patents

Description

April 11, 1944. N o so 2,346,418

FLUID OPERATED MEANS FOR CONTROLLING APPARATUS AT A DISTANCE Filed Feb. 18, 1942 3 Sheets-Sheet 1 April 11, 1944. E. DODSON 2,346,418

' FLUID OPERATED MEANS FOR CONTROLLING. APPARATUS AT A DISTANCE Filed Feb. 18, 1942 5 Sheets-Sheet 2 April 11, 1944. E. DODSON FLUID OPERATED MEANS FOR CONTROLLING APPARATUS AT A DISTANCE-1 I 3 Sheets-Sheet 3 Filed Feb. 18, 1942 Patented Apr. 11, 1944 UNITED STATES FLUID OPERATED MEANS FOR @ONTROL- LING APPARATUS AT A DISTANCE Edward Dodson, Puriton, near Bridgwater,

England Application February 18, 1942, Serial No. 431,345 In Great Britain. October 1, 1941 Claims.

This invention relates to fluid-pressure-operated remote control systems of the kind, described for example in British specification No. 483,049,

comprising a sender unit at one station, a receiver unit at a distant station, a pipe line connecting the twounits, a control device at the first station, coupled to the sender unit, and an apparatus at the distant station coupled to the receiver unit and arranged to be operated, in accordance with the setting of the control device, by fluid pressure transmitted through the pipe line to the receiver unit underthe control of the sender unit. g

In Britishspecification No. 483,049 and United States applicatiomserial No. 358,415, I have described receiver units for remote control systems of the above kind, comprising a bellows or diaphragm sensitive to the pressure in the pipe line, a hydraulic servo-motor, a piston valvefixed to the sensitive bellows or diaphragm for controlling connections from pressure and exhaust to the cylinder of the servp-motor so as toproduce a movement of the power piston oi the servo-motor in the opposite direction to that of its own movement, and a follow-up gear constituted by a link, pivoted at one end to a fixed point, pivoted at its other end to the'power piston, and pivoted centrally to a member linked to the piston valve.

- the piston valve is in its neutral position, irrespective of the pressure in the pipe line, the pressure on the sensitive member exerted by the fluid difierent positions as the pressure in the pipe line is altered,,and the point of connection of the end of the swinging link to the-sensitive element becomes, in effect, a fixed fulcrum until the pipe line pressure is changed. In order that this point may be as nearly as possible a fixed fulcrum, thepoint of connection of the piston or equivalent valve to the link should be located nearer to the point of connection 01 the power piston than to that of the sensitive element, so as to obtain a mechanical advantage enabling the sensitive element to remain stationary while the valve is beingreturned to the neutral position on movement of the power piston.

Where the receiver unit is to be'used for pneumatic transmission, the sensitive element may be constituted by a diaphragm, but for high pressure hydraulic transmission it is necessary to use a piston or bellows. V

A further object of the invention is to enable a long power stroke to be obtained, which is often desirable to avoid mechanical complication to achieve multiplication ofthe movement. It is not feasible to obtain this with a direct connection between the power piston and the swinging link of the follow-up gear, as the link would have to be made impossibly long and the valve I would have to be placed at too large adistance in the pipe line being balanced by the pressure of a spring (which may be constituted by the bellows itself where a bellows is employed as the sensitive element) the compression of which is varied by the movement of the power piston.

It is an objectof the invention to provide a I modified form of receiver unit which will enable a movement of the power piston to be obtained,

which conforms more vexactly withvariations in the pressure in the pipe line.

In the receiver unit according to the invention the power piston, the piston or equivalent valve for controlling the same and the sensitive element are disposed in separate chambers, the sensitive element is balanced by a spring the load on which is determined only by the pressure in the pipe line and not by the movement of the power from the power piston.

According to the invention, this object is achieved by means of an indirect connection between the power piston and the swinging link, such that a large movement of the power piston only communicates a smalloscillating movement to the link. Thus an inclined plane, running on a roller external to the cylinder, may be attached to the power piston, this plane cooperating with a roller mounted on one end of a bell-crank lever pivoted at its other end to the swinging lever, and a spring being provided for maintaining the roller in contact with the inclined plane.

Some alternative forms of receiver unit con structed in accordance with the invention will now be described in detail, byway of example,

with reference to the accompanying drawings in which-- fig. 1 is a diagram showing a hydraulic remote control system embodying a receiver unit according to the invention,

Fig. 2 is a vertical section, on an enlarged scale, through thereceiver unit shown in Fig. i,

Fig. 3 is a similar section through a portion of an alternative form of receiver unit, and

Fig. 4 is a vertical section showing an alterna- 150'1eadihg respectively to the top and bottom of the cylinder of the servo-motor.

tive form of biasing device to that shown in Fig. 3.

The system shown in Fig. 1 comprises a reser. voir III to contain oil, a pump II, serving to pump the oil via a pipe I2 to a sender unit I3, the details of which are fully described in my United States application Serial No. 431,344 and a receiver unit I4, relay valve I5, servo-motor I6 and follow-up gear I1 the details of whichare fully described below.

The sender unit I3 is connected to the receiver unit I4 by a pipe line consisting of two duplicated sections I8, I8. At each end of each duplicated section of the pipe line is located a cut-out valve 26 constructed as described in my United States application Serial No. 419,719, these cut-out valves serving to cut off the supply of pressure fluid from a broken or damaged pipe in either section of the duplicated line. Between the two duplicated sections of the line is disposed a relay valve 2I, the construction of which is fully de scribed in my United States application Serial No. 431,343. This relay valve 2| serves, when required, to boost up the pressure in the portion I9 of the pipe line connected to the receiver unit I4 by pressure tapped direct from the pressure Q line I2 througha branch pipe 22, and at the same time preserves an equal pressure in the two portions I8, I9 of the pipe line.

The sensitive piston 30 of. the receiver unit I4 takes up a position determined by the position of the actuating member 23 of the sender unit, and causes the piston 24 of the servo motor I6 to take up a corresponding position. The apparatus to be remotely controlled is connected to the piston rod- 25, and its setting is therefore determined by the setting of the actuating member 23 of the .sender unit I'he--pressur transmitter son the nous-operating ends'of the d receiving elements in the sender and receiver-units are balanced by connecting them to exhaust by pipes 26, 2'! respectively. The two ends of the relay valve I controlling the servo motor are likewise exposed to the same balancing: pressure by means of the conduits 21, 28.

A relief valve 23 connects the pipes I2 and 26.

As shown in-Fig. 2, the sensitive piston 30 of .1 the receiver unit is exposed at its upper end to the pressure inthe signal line from the sender unit acting through the pipe 66 and is balanced by a spring 3|, and the follow-up gear I! is constituted by a swinging link 32, pivoted at one end: 33 to the sensitive piston and at the other end 34 to onearm of a bell-crank lever 35 operatively connected to the power piston 24 of the servomotor I6. Intermediately of its length at 36, the link 32 is connected to the piston valve I5. The bell-crank lever 35, which is mounted on a fixed pivot 31, carries on its other arm a roller 38. The spindle 39 on which this roller is mounted, rests in'the forked end of a member 40 which is urged by a spring H to press the roller 38 This will cause the link Normally the piston valve I5 occupies the central position shown in Fig. 2, in which it masks ports ll, 82 communicating respectively with the passages 49, 60. If, however. the pressure in the signal line should increase, the sensitive piston 30 will move down, compressing the spring 2|. 32 to swing clockwise about the fulcrum 34, thereby moving the piston valve I5 down. This admits pressure from the pipe 48, through the groove 46, port 52 and passage to the bottom of the servo-motor cylinder, and connects the top of the cylinder to exhaust through the passage 49, port 5| and groove 44. The power piston 24 will accordingly rise, thereby, through the agency of the inclined plane, rocking the bell-crank lever 35 counterclockwise, and causing the link 32 to swing clockwise about the fulcrum 33, until it has lifted the piston valve I5 back into its central position. The upward movement of the power piston 24 will then cease, the power piston having moved a distance determined by the increase in pressure in the signal line and having set the apparatus coupled to the piston rod 25 accordingly.

Similarly, if the pressure in the signal line should fall, the spring 3I will cause the sensitive piston 3|] to rise, thereby lifting the piston valve from the central position. This will admit pressure from the pipe 48 and through the groove 46, port 5I and passage 43 to the top of the servomotor cylinder, and connect the bottom of the cylinder to exhaust through the passage 50, port 52 and groove '45. The power piston 24 will accordingly descend, thereby, owing to the withdrawal of the inclined plane 42, enabling the spring M to rock the bell-crank lever 35 clockwise and pull the piston valve I5 down into its central position again.

With this arrangmenet, each time the pressure in the signal line changes, the sensitive piston 30 will take up a corresponding position against aninclined plane 42 fixed to the piston g rod- 25 of the servo-motor and running on a roller 43 external to the cylinder of the servo-motor.

The piston valve I5 is formed with two end annular grooves 44, 45 and with a central annular groove 46. The end grooves 44,45 are permanently in communication with the limbs of a bifurcated pipe 41 connected to exhaust, and-the central groove 46 is in permanent communication with a pipe 48 leading from the pressure line The piston valve controls two passages 49,

- of the power such that the pressure in the signal line is balanced by the spring 3|, and, during the consequentmoveme'nt of the servo-motor piston, the point 33 will remain a fixed fulcrum. It will be observed that the point of connection 36 of the piston valve to the swinging link 32 is located nearer to the point of connection 34 n piston than to that 33 of the sensitive element, thus obtaining a mechanical advantage which will enable the sensitive element to remainstationary while the valve is being returned to the central position on movement of the power piston.

The purpose of the indirect connection between the power piston 25 and the swinging link 32, constituted by the inclined plane 42 and the bell-crank lever 35, is to enable a very long power stroke to be obtained. If a direct connection were used, the link 32 would have to be made impossibly long and the valve I5 would have to be placed at too large a distance from the power piston. The slope of the inclined plane 42 will determine the amount of movement given to the power piston for a given alteration in the signal line pressure. Also the connection between the bell-crank lever 35 and the swinging link is, due to the fact that the bell-crank lever is formed with a slot 53 embracing the pivot pin 34, an adjustable one. This enables a. number of apparatus according to the invention to be synchronized with one another despite minor differences in spring strength and slight machining inaccuracies.

It is in some cases desirable if the signal lines evacuating the leakage. .a piston 61 workingin .a cylinder 62 and connected by a link, 63;to :an extension E l -of the of the signal line pressure.

are shot away, or otherwise caused to be inoperative, and the pressure line for supplying the power piston remains intact, for the power piston totake some predetermined position in the cylinder as, for instance, to centralise an aircraft control. To this end an arrangement similar to that which isthe subject of my. copendlng United States application'Serial No. 419,720 maybe used.

An arrangement of this character is shown in Fig. 3. The receiver unit shown in this figure is identical with that shown in ,Fig. 2, apart from theinclusion of this added feature, and also means, which will be later described vfor evacuating leakage fluid from. the chamber containing the spring 31. i

In the arrangement shown. in Fig. 3,"there is disposed above the sensitive piston, aspring 54 held'in compression between a plate 55 and a piston .56.

The plate 55 bears against an adjusting screw 51 and .the piston 55 carries on its undersurface-a tappet 58. Normallythe pressure inv the-signal :line, admitted through the pipe 60, is sufilcientto hold the spring '54 compressed, with the result that the tappet 58 is held away from and does not impede the move- Should howments of the sensitive piston 30. ever the pressure in the signal line, fail or fall below a predetermined minimum-the spring 156 will cause the tappet 58 "to descend and-overi conditions.

Glanding :or the sensitive piston an is .inadvi-s- I able, so that pressure-liquid may leak from the signal line past the ,pistoninto the spring-chamber. :In tthe caserofthe apparatus shown in Fig. .2 this leakage'is evacuated to exhaust throughthe pipe 21.- In :the case of zth arrangement shown in :Fig. .3. a-pumpis provided for This is constituted by bell-cranklever-ifi; The cylinder 62 communicates with the spring chamber 59 by a passage 65, controlled by a platevalve 66, and with exhaust by a pipe 121 controlled by a ball valve 61. As will be readilyunderstood this pump is operated *by the movements of the power piston 24. The spring chamber 59 is provided with a vent to atmosphere, constituted by a tube 68 closed at its lower end-.by a deflector plate 69 and provided withvent holes iii. .If the apparatus should be turned upside down, which is 01' course likely when it :isinstalled in an aircraft, the leakage ffluid will-beflung againstthe top of the spring chamber 59 and the deflector. 89 will prevent it from escaping through. the air vent.

Fig. 4 shows .an alternative form of biassing device for moving the sensitive piston 30 to a predetermined position .in the event of failure This v:is constituted by a piston 556, carrying sa-tappet i58, which is normally held up against the action of a spring 54 bythe signal line pressure admitted through the pipe 60. so that the tappet dcesnot interfere with the movements of thesensitive piston. When thesignal line pressure failshowever, the

piston I56 will be moved downby the spring :54.

exposinga port ll through which the full pump pressure will be admitted from a pipelz to the piston 30 to the predetermined position.

space 18 above 'the piston Hi8, thus causing the tappet 158 to move down and set the sensitive The space 13 is normally open to exhaushvia a passage '14, port 18, groove 15 in the piston I66, space 16 and pipe 11. Immediately, howeventhe piston 156 begins to move down it masks the port 18 and so cuts oil the space 13' from exhaust.

'The high pressure from the pump (e. g, 1000 lbs/sq. in.) acting on the small area' at the top of the piston I56 is sufiicient completely to overpower the balancing spring 3| oi the sensitive piston. When however the pressurein the signal line is restored, this pressure, although only of the order of from 65 to 260 lbs/sq. in. actin .on thelarge area at the bottom of the piston 556 is sufficient to overcome the pump pressure in the space l3,-and so will move the piston 556 up again, closing the port 1| and reopening the port 18. This arrangement, although more complicated than the spring-biassing mechanism shown in Fig. 3, has the advantage of giving a lone stroke on the piston withoutthe necessity of placed in such a position as to give it a real mechanical advantage over the valve, and when the powerpiston .moves the piston valve, the sensitive piston is likely to remain as a fixed fulcrum, and as its total travel is very large inrelation to the-necessary travel of the piston valve, small errors caused by friction will thereforehave only a minor effect on the piston valve.

Secondly, the sensitive piston will always take up a definite position in relation to the signal pressure fluid and the opposing spring strength; whereas where-the diaphragm is placed directly ontop of the piston valve, as in United States application Serial No. 358,415, on increase of the-signal line pressure the diaphragm-will move in. a downward direction and cause the piston valve to open a pressure port leading to one sideof the power piston, and an exhaust port leading to the other side of it. Thenthe movement of the powerpiston which follows increases the compression on a spring under the piston valve until this is sufficient to move the diaphragm back to its original central position and thus return the piston valve to the central position. and this action entails an increase in the signal line pressure sufiicient to cause the sender diaphragm to move against its spring and open the sender unit exhaust valve until the pressure in. the signal line again balances the sender .spring. The exhaust valve in the sender unit is of course loaded and some efiort is required by the diaphragm to open it.

This reverse flow in the signal line is liable to cause an increase in the hysteresis factor, and a slight hunting movement of the power piston, until conditions in the signal line are again stabilised. When pressure in the'signal line decreases, the return movement of the receiver diaphragm to its .centralposition will cause a reduction in the signal line pressure'which will cause the sender diaphragm to open the pressure valve in the senderunit and re-establish the signal line pressure.

What I claim as my invention and desire to secure by Letters Patent is:

i. A receiver unit for attachment to the pipe line of a fluid-pressure-operated remote control system of the kind specified, comprising a cylinder to communicate with the pipe line,.a sensitive piston in the cylinder exposed at one end to the fluid pressure in the pipeline, a bath ancing spring operating on the other end of the sensitive piston, a chamber containing said spring, an air vent pipe extending into the interior of said chamber from the top thereof, a deflector arranged to prevent escape of leakage fluid from the chamber through the air vent pipe in the event of the apparatus being turned upside down, a hydraulic servo-motor, a relay valve for controlling the same, and a swinging link operatively connected at its ends to the sensitive piston and to the power piston and at an intermediate, point to the relay valve.

2. A receiver unit for attachment to the pipe line of a fluid-pressure-operated remote control system of the kind specified, comprising a cylinder to communicate with thepipe line, a sensitivej piston in the cylinder exposed at one end to the fluid pressure in the pipe line, a balancing spring operating on. the other end of the sensitive piston, a chamber containing said spring,

a hydraulic servo-motor including a power piston, a relay valve for controlling the servo-motor, fa" swinging link operatively connected at its ends to the sensitive piston and to the powerpiston and at an intermediate point to therelay valve,

a pump comprising a. cylinder. oommunicating by' valvecontro1led passages with the chamber and to' exhaust, and a piston mounted for re- "ciprocation in said chamber, and actuating means for operating thepump to expel leakage fluid from said chamber, said actuating means comprising a pivoted bell-crank, a cam member conneoted to the power piston, a follower on the bell-crank cooperating with the cam member,

; aspring for holding the follower in engagement with the cam member, and a link connecting the bell-crank and the pump 'piston'for' displacing; the latter in its cylinder on movement of the power piston.

3. A receiver unit for attachment to the pipe line of a fluid-pressure-operated remote control system of the kind specified, comprising a cylinder to communicate with'the pipeline, a sensitive piston in the cylinder exposed at one end to the fluid pressure in the pipe line, a balancing spring operating on the other end of the sensitive piston,

a hydraulic servo-motor including a power piston, a relayvalve for-controlling the servo-motor, a swinging link operatively connected at its ends to the sensitive piston and to the power piston and, at an intermediate point to the relay valve, a blessing piston mounted in alignment with the sensitive piston, a spring, normally overridden by the. fluid pressure-in the pipeline, but tending to move the biassing piston towards the sensitive piston, and a pressu're inlet to the side of the biassing piston remote from the sensitive piston,

. said-inlet being'normall-y closedby the biassing piston but operating to admit pressure to the remote side'of the blessing piston on failure of the pipe line pressure and consequent displacement of the biassing piston by the spring.

. 4. A receiverunit fora fluid-pressure-operated remote control system of the kind specified, comprising an element sensitive to the pressure in the pipe line, a spring for balancing the same, the load on which is determined only by the pressure in the pipeline, a hydraulic servo-motor and a valve for controlling the same, and a swinginglink-operatively connected at its ends to the sensitive element and to the power piston of the servo-motor, and operatively connected to the valve at a point nearer to the point of'connection of the power piston than to that of the sensitive element, the receiver unit having an air vent pipe extending into the interior of the chamber containing the balancing spring of the sensitive eleevent ofthe apparatus remote control system -ment, and a deflector arranged to'prevent escape of leakage fluid through-the air vent pipe in the beingturned upside down. '5. A receiver unit tor a'fluid-pressure-operated of the kind specified, comprising an element sensitive to the pressure in the pipe line, a spring for balancing the same, the loaduon which is determined only by the pressure in the pipeline, a hydraulic servo-motor and a valve for controlling'the same, and aI'swinging link operatively connected at its ends 'to the sensitive element and to the power piston of the from the sensitive servoemotor, and 'operatively connected to the valveat a pointnearer 'to the point of connection of the'power'plston than to that of the sensitive element, the receiver unit having a biassing piston, which is normally maintained clear of the sensitive element by the pipe line pressure, said biassing piston being arranged to move when the pipe line pressure falls below a given minimum, and thereby unmask a port for admittin Dump pressure to the side" of the biasslng piston remote element;

EDWARD DODSON.

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