US2739571A - Cylinder assembly for hydraulic actuator - Google Patents

Description

March 27, 1956 s, A, HALL 2,739,571

CYLINDER ASSEMBLY FOR HYDRAULIC ACTUATOR Filed D60. 29, 1952 2 Sheets-Sheet l March 27, 1956 AI HALL CYLINDER ASSEMBLY FOR HYDRAULIC ACTUATOR 2 Sheets-Sheet 2 Filed Dec. 29. 1952 @GMW CYLINDER ASSEMBLY FOR HYDRAULIC ACTUATOR Stanley A. Hall, Gardena, Calif., assignor to Northrop Aircraft, Inc., Hawthorne, Calif., a corporation of California Application December 29, 1952, Serial No. 328,328 2 Claims. (Cl. 121 38) This invention relates to hydraulic actuators and more particularly to working cylinders for actuators in which it is necessary to maintain minimum dimensions for the cylinder and at the same time deliver a maximum power output.

Available space quite frequently limits the size of a hydraulic actuator cylinder which can be utilized in a given installation; This is particularly true in airplanes and guided missiles in which their control surfaces are operated by hydraulic actuators. It has been determined that a force of approximately 8000 pounds is required, under extreme operating conditions, to move the aileron control surfaces of certain large planes traveling at high speeds. To accommodate a hydraulic cylinder, in the space available in a wing section, large enough to deliver suilicient force to properly actuate the control surfaces presents quite a design problem.

It is, therefore, an object of the present invention to provide an eicient and economical hydraulic actuator, having a working cylinder of minimum dimensions which may be utilized in installations where space is critical, and at the same time be capable of delivering7 a force equal to that of a conventional actuator, having a working cylinder of greater diameter, when operating under the same conditions.

A further object is to provide a hydraulic actuator in which the walls of the hydraulic cylinder may be made relatively thin without danger of failure, due to the fluid pressure therein, and yet deliver a force equal to a conventional cylinder having thicker walls and consequently greater overall dimensions.

Other objects and advantages of this invention will be apparent from the following description forming a part of this specification, but the invention is not limited to the embodiment herein described, as various forms may be adopted within the scope of the appended claims.

The invention may be more fully understood by reference to the accompanying drawings, wherein:

Figure l is a diagrammatic perspective View of an airplane showing one embodiment of the present invention in connection with its aileron cable control system.

Figure 2 is an enlarged perspective view of the hydraulic actuator in its installed position as shown .in Figure l.

Figure 3 is a sectional view of the hydraulic actuator shown in Figure 2 taken on the line 3 3 thereof.

Figure 4 is a cross sectional view of the hydraulic actu* ator shown in Figure 3 taken on the line 4 4 thereof.

Figure 5 is a cross sectional view of the hydraulic actuator shown in Figure 3 taken on the line 5 5 thereof.

Referring first to Figure l, for a detailed description of the present invention, an airplane 1 is shown having ailerons 2. Each aileron is pivotally moved about its hinge line by two cable controlled hydraulic actuators 3, of the type herein disclosed, located near the end portions of the ailerons. Each actuator is controlled through suitable linkage by control cables 4 which connect with an aileron control quadrant 5. Movements of the control nited States Patent cylinder assembly through 2,739,571 Patented Mar. 27, 1956 by means of a control element 6 connected with the quadrant through conventional linkage. Also located in the trailing edge of each wing, midway between the aileron actuators 3, is a centering spring 7 which is connected with the control cables through suitable linkage. The centering spring provides synthetic feel which is fed back to the pilots controls, thereby simulating conventional control pressures.

One embodiment of the present invention, shown in its installed position (Figure 2) to operate ailerons 2, comprises a valve assembly 8 and a cylinder assembly 9. The cylinder assembly at its closed end is attached to aileron hinge bracket 10 by means of a connector element 11 and hinge pin 12, aileron hinge bracket 10 being rigidly attached to a forward aileron spar 13. A lower hinge pin 14 pivotally secures aileron hinge bracket 10 to a wing bracket 15 attached to a lower ange of a rear wing spar 16. The other end of the cylinder assembly'is attached to a thrust bracket 17 by means of its piston rod assembly and pin 19, the thrust bracket being rigidly secured to a stationary structural element of the plane.

Valve assembly 8, as best seen in Figure 3, comprises a spool housing 20, a spool casing 21, adapted to be secured in cylindrical bore 22 of the housing, and a Valve spool 23. Spool 23 is provided with an integral end p0rtion 24, provided with an eye, bymeans of which the spool is connected to element 25, which in turn is connected by cables 4 to the pilots control element 6. Movement of spool 23 results in fluid being admitted to cylinder assembly 9 to move ailerons 2, the moment arm being between the axis of pin 12 and 14.

Spool housing is provided with fluid inlet and return ports 26 and 27, respectively. The spool casing constitutes a hollow cylindrical sleeve xedly secured in housing 20 by means of dowel pin 28 and set screw 29 in a well known manner. The spool casing is provided with four circumferential lluid grooves longitudinally spaced on its outer surface. The grooves communicating with inlet and return ports 26 and 27 are generally referred to a pressure groove 30 and a return groove 31, respectively, while the other two grooves 32 and 33 are referred to as cylinder grooves as they communicate directly with the various chambers of cylinder assembly 9. As viewed in Figure 3, groove 32 is positioned to the right of pressure groove 30 and supplies uid to chambers C1 and C2 of the passageway 34. Groove 33, positioned between the pressure and return grooves, supplies fluid to chambers C3 and C4 through passageways 35, 36 and 37, all of these passageways are plugged at their free ends to provide a closed lluid tight path. Separating each of the above iluid grooves are sealing ring grooves containing sealing rings 38. Sealing ring grooves 39 and 40 are also provided at each end of the casing and around the inner cylindrical surface of the casing, respectively, the grooves 40 being ad'acent end portions of the casing. Packing, one preferred form being of the 0 ring type, is positioned in the above sealing ring grooves to effectively confine lluid to the various tluid pressure grooves and prevent its escape from the end portions of the housing 20 and casing 21.

Spool 23 constitutes a rod of circular cross-section which is lapped to provide a near uid tight longitudinal sliding t in bore 41 of casing 21. The longitudinal travel of spool 23 is limited by pin 42 which is secured in the walls of casing 21 and spans the bore 41, passing through a diametrical slot 43 in the spool 23. A longitudinal bore 44 extends from its short of slot 43 in spool 23, open end by a plug 45.

The outer surface of valve spool 23 is also provided with four longitudinally spaced circumferential fluid grooves 46, 50, 52 and 53. Groove 46, generally referred quadrant are pilot initiated the bore being closed at its non-attaching end and terminates" 'to as the spool pressure groove, is positioned to communicate with pressure groove at all operational positions of the spool, radial passageways 47 provide means for the .HOW @f ,fluid between .these tvv@ grooves, 1n the spools neutral position, Yas Ashown in Figure .3, groove 46 extends an equal distance on eaeh side of passageway 47 so `that its side walls bisect the innermost aperture of two groups of rflow holes 48 and 49 ina manner to be described later. Groove 50, generally kreferred to as the spool return groove, is positioned to communicate withreturn groove 31 at all operational positions ,of the spool, radial passageways 5 1 provide means for the ow of liuid between these two grooves. Groove 52, positioned to the right o f spool pressure groove 46 communicates with cylinder groove 32 through ow holes 48 during predetermined positions of the spool. Groove 53, positioned between the spool pressure and return grooves, communicates with cylinder groove 33 also during predetermined positions of the spool. Spool grooves 50, 52, and 53 communicate with the bore 44 of the spool, radial passageways 54 provide means for the flow of iiuid between these respective grooves and the bore. The spool grooves 46, 50, 52, and 53 are separated by lands 55, 56, and 57.

The valve assembly construction is completed by the two groups of ow holes 48 and 49 referred to above. The deiinite pattern and function of the flow holes have been disclosed and claimed in U. S. application No. 17,624, dated March 29, 1948, now U. S. Patent No. 2,631,571, issued March 17, 195.3, and constitutes no part of the present invention therefore they will not be described in detail in the present disclosure. The above ow holes are normal to the peripheral surface of spool casing 21 and spool 23, all liquid flowing to the cylinder assembly passing therethrough. It should be noted that all fluid flowing to cylinder chambers C1, and C2 must pass through flow holes 48, all return fluid from these chambers (C1 and C2) also ows through these same holes, the same is true of flow holes 49 and chambers C3 and C4.

In a valve as disclosed above, return iluid from any of the cylinder chambers (C1, Cz, C3, or C4) Hows to the boreY 44 located interiorly of spool 23. Fluid under pressure does not contact either end portion of the spool, it is, therefore, not subject to any exterior or unequal fluid pressures which will inherently tend to move the spool from a given operational position and require additional parts to balance the spool, as in the case in the valve disclosed in U S. Patent No. 2,612,872, issued October 7, 1952. Since ther proposed spool isI not contacted externally by any iiuid it is not subject to movement by hydraulic pressures and is, therefore, inherently balanced as pertains to non-flow conditions.

Further the balanced condition of the` valve spool permits a material reduction in the number of parts and consequent machine Work. The valve of the present invention consists of only four major parts while a valve as disclosed in the above referred to application consists of twelve major parts.

The cylinder assembly of theA present invention consists of a cylinder casing 58, having a longitudinal cylindrical bore 59, and a piston rod assembly 60. The piston rod assembly includes a cylindrical sleeve member 61 coaxially positionedl with respect to the bore 59,. A rod. connector element 62 is threadably secured tov sleeve member 61, an eye 63v in its outer end providing means for securing the actuator toy bracket 1,7 in a manner previouslyexplained. At the other end of cylinder 5,8 an inwardly extending annular shoulder 64 provides a bearing surface for one end of sleeve member 61, the other end being supported by a removable bearing 65. Positioned between shoulder 64 and bearing 65 is another removable bearing 66, dividing` the bore 594 into two chambers. 0f` equal PIO' portions. Bearings 65 and 66 are retained in fixed relationship with casing 53 by means of pins 67 in a Well known manner. The centralbores of bushings 65 and 66 and shoulder 64 provide a slidingY t for: Sleeve member 61, bearings 65 and 66 are provided with conventional sealing grooves 68 and sealing rings 69 rendering the cylinder casing uid tight and precluding the flow of fluid from one side of bushing 66 to the other.

Pistons 70 and 71 are secured to sleeve member 61 in tixed relationship to move therewith, the pistons being relatively positioned on each side of bushing 66 so that they form chambers C1, Cz, Cs, and C4 of equal proportions when the piston rod assembly is in its neutral position. The outer peripheral surface of each of the pistons 70 and 71 are provided with a pair of conventional sealing ring grooves and sealing rings. The peripheral portion of the pistons between their seals are vented to the atmosphere. Venting of the pistons assures instantaneous movement of the rod assembly in response to changes of uid pressure in chambers C1 and C2 or Ca and C4, respectively.

To vent the pistons, as outlined above, a circular rod member 72 is coaxially positioned insleeve member 61 in fluid tight relation therewith throughout a major portion of its length, a central bore 73 extending from piston 71 to its end adjacent shoulder 64. Radial passageways 81 provide communication between that peripheral portion of the pistons between their sealing rings and bore 73. The non-connecting end portion of sleeve element 61 is protected by connector element 11 which is threadably secured to the adjacent end portion of cylinder casing 58. Connector element 11 is provided with an eye by means of which it is attached to the aileron hinge bracket as previously explained. An aperture 74, provided in the wall of element 11, completes the venting system and subjects that peripheral portion of each piston, as mentioned above, to atmosphere pressure or a pressure lower than that of the iiuid in chambers C1-C4, inclusive.

The cylinder assembly is completed by longitudinal extending grooves 75 and 76 provided in the outer peripheral surface of rod 72. Groove 75 extends between apertures 77 and 78 in the wall of sleeve 61 thereby providing a passageway for uid between chambers C3-C4. Groove 76 extends between apertures 79 and 80 providing a passageway for iluid between chambers C1 and C2.

With the valve spool in its neutral position, as shown in Figure 3, there. is a relatively small. quantity of uid constantly owing or leaking through the valve assembly. In one preferred embodiment fluid under a pressure of approximately 3000 p. s. i, enters the valve as sembly through port 26. This fluid,during its passage through the valve assembly, Hows through the innermost hole of each iiow hole group as the vertical side walls of groove 46 bisect the innermost hole of each iiow hole group. As the individual holes of each flow hole group are small, and further being bisected by the side walls of groove 46, a pressure drop of approximately 1500 p. s. i. occurs as liuid ilows therethrough. This pressure is conveyed vto both sides of each piston 70 and 71, creating a preload of approximately l500p. s. i, in cylinder chamber C1, Cs,y C3, and C1, thus preventing motion of any control surfaces under shock conditions, which may be connected to the actuator. Return ilcw occurs through the outermost hole of each how hole group returning to central bore 44 ot the valve spool as is apparent from its position. With. spool 44, in its neutral position, all holes except the innermost and outermost ones of each ow hole group are closed by spool lands 56 and 57, respectively.

lf spool 23 is moved to the right of its neutral position more flow holes of group 48 are. opened tothe low of pressure iluid by land 57 and all ow holes of the group are closed to return iluid bythe. same land. Accordingly pressurefluid ows to chamber C1 via groove 32 and passageway 3,4. As. cylinder chambers C1 andr C2` are connected by longitudinaly passageway 76 and apertures 79 and 80.: Huid flowing into-chamber C1 will also low to chamber C2 causing the, actuator cylinder to move tothe right as the pistonsrodfassembly 60|is immovable, the

same being iixedly secured to a structural element of the airplane. The above movement of the spool also closes all ilow holes of group 49 @i pressure iiuid but allows luid from chambers C3 and C4 to flow to bore 44 and pass from the valve assembly. Under the above conditions, actuator cylinder Sit will continue to move to the right until it reaches a position where the iiuid pressure cting on each side of pistons 7d and 71 is equal, this pon sition will not be the neutral position of the valve spool as a portion of the pressure on fluid contained in chambers C3 and C4 will now be supplied by external forces acting on the ailerons 2.

From the above, it is seen a fluid pressure cylinder for a hydraulic actuator is provided in which a pair of pistons are mounted in tandem on a common piston rod. The combined iluid pressure area of the two pistons, being equal to a single larger piston, permits a reduction in net cross sectional area of the Working cylinder while maintaining its power output. Also, as the stress at which the walls of a hydraulic cylinder rupture or burst varies in an inverse ratio to its diameter, a reduction in wall thickness is possible. Cylinder walls of less thickness permit a further reduction in the net cross sectional area of the cylinder, accompanied by a saving or reduction in material, weight and space required to mount the subject cylinder,

A comparison of the hydraulic cylinder of the present invention and a cylinder of the type disclosed in U. S. application No. 137,622, now Patent No. 2,619,304, issued November 25, 1952, follows, both operating at a iiuid pressure of 3000 pounds per square inch.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the speciiic features shown, but that the means and construction herein disclosed comprises a preferred form of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

What is claimed is:

l. In a hydraulic actuator, a casing having a cylindrical bore therein, annular elements positioned in said bore adjacent to the ends thereof, a piston rod arranged coaxially in said bore and extending through said annular elements in uid tight relationship, annular means surrounding said piston rod and dividing said bore into two equal fluid tight portions, a rst piston ixedly secured on said piston rod so that one of said portions is divided into a first chamber adjaceitt one end of said bore and a second chamber adjacent said annular means, a second piston lixedly secured on said piston rod so that the other of said portions is divided into a third chamber adjacent said annular means and a fourth chamber adjacent the other end of said bore, Wall portions of said casing defining rst and second passages whereby uid from an external source may communicate with said first and second chambers, portions of said piston rod defining a third passage adapted to provide iiuid communication between said irst and third chambers, and other portions of said piston rod defining a fourth passage adapted to provide fluid communication between said second and third chambers.

2. In a hydraulic actuator, a casing having a cylindrical bore therein, annular elements positioned in said bore adjacent the ends thereof, a piston rod comprising a cylindrical sleeve arranged coaxially of said bore and extending through said annular elements in iiuid tight relationship, annular means surrounding said piston rod and dividing said bore into two equal fluid tight portions, a irst piston iixedly secured to said piston rod so that one of said portionsis divided into a iirst chamber adjacent one end of said bore and a second chamber adjacent said annular means, a second piston xedly secured to said piston rod so that the other of said portions is divided into a third chamber adjacent said annular means and a fourth chamber adjacent the other end of said bore, wall portions of said casing defining first and second passages whereby iiuid from an external source may communicate with said first and second chambers, wall portion of said piston rod detining a plurality of passages whereby each of said chambers may communicate with the interior of said piston rod, a filler rod positioned within said piston rod in Huid tight relationship and extending substantially throughout the length of said piston rod, outer portions of said filler rod defining a irst groove extending between said radial passages communieating with said rst and third chambers and a second groove extending between said radial passages communieating with said second and fourth chambers.

References Cited in the le of this patent UNITED STATES PATENTS 1,289,795 Johnson Dec. 31, 1918 1,339,939 Alter May 11, 1920 1,978,667 Breese Oct. 30, 1934 2,085,105 Lex lune 29, 1937 2,361,130 Simpson Oct. 24, 1944 2,383,082 Rossmann Aug. 21, 1945 2,501,720 Godden Mar. 28, 1950 2,513,546 Atteslander July 4, 1950

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