US3437101A

US3437101A - Servovalve construction

Info

Publication number: US3437101A
Application number: US530916A
Authority: US
Inventors: James L Coakley; Charles A Kubilos
Original assignee: Abex Corp
Current assignee: PepsiAmericas Inc
Priority date: 1966-03-01
Filing date: 1966-03-01
Publication date: 1969-04-08
Anticipated expiration: 1986-04-08
Also published as: GB1180945A; SE354507B; DE1589430A1; FR1511251A; DE1589430B2; CH462573A; GB1180946A; SE334098B

Description

April 8, 1969 J. L.. coAKLx-:Y ET Al.

SERVOVALVE CONSTRUCTION Filed March 1. 196e MIL April s, 1969 J. L. COAKLEY ET AL 3,437,101

sERvovALvE CONSTRUCTION Filed March 1, 1966 INV TORJ United States Patent O 3,437,101 SERVOVALVE CNSTRUCTIN James L. Coakley and Charles A. Kubilos, Gxnard, Calif., assgnors to Abex Corporation, a corporation of Delaware Filed Mar. 1, 1966, Ser. No. 530,916 Int. Cl. F151) 9/03, 9/07, 9/12 U.S. Cl. 137-83 17 Claims ABSTRACT F THE DISCLOSURE This invention relates to servomechanisms and more particularly to force feedback operated Servovalves.

Servovalves of the general type to which this invention relates are operated by a torque motor and include two force amplification stages. Application of an electrical input control signal to an electromagnet coil in the torque motor causes an unbalanced flux distribution in the air gaps around the motor armature, causing a torque to act on the armature. The armature rotates in response to this torque, against spring means which bias the armature to its centered or null position. Movement of the armature shifts a jet of fluid issuing from a jet tube from a null position in which it is centered between two receiver ports, to a new position in which the jet impinges unequally on the two ports. This deflection of the jet establishes a differential pressure between the receiver ports which is proportional to the input current. The fluid employed in conjunction with the jet tube may, of course, be either hydraulic or pneumatic iiuid. In the description to follow, it is assumed that hydraulic fluid is utilized.

The pressure in the receiver ports are fed to the second stage of the servovalve, which is a spool valve hydraulic force amplifier. The differential pressure input from the first stage is reflected on opposed surfaces of a main spool or piston in the second stage, shifting the spool and establishing communication between various ports. Flow through these ports in the second stage varies with spool position. Spool movement in response to the differential pressure continues until a feedback spring member, through which the spool and jet tube are coupled, becomes suciently stressed that it returns the jet to the null position, thereby removing the pressure differential on the spool. When this has occurred the spool thereafter remains in that position, controlling flow through the second stage `at a rate and direction corresponding to the magnitude and polarity of the electrical input signal to the torque motor.

From an economic standpoint as well as from a performance standpoint, the Servovalves of the prior art have not been entirely satisfactory. The dissatisfaction can be traced to a number of structural features which, because of theirdesign, have introduced complexities into the manufacture and assembly of the various component parts constituting the valve. These complexities, in addition to increasing the costs of manufacture and assembly, have inherently limited the performance of the earlier valves.

For example, in one type of prior art servovalve the ICC spring means used to bias the torque motor armature and jet tube to their balanced, central or null positions has included a tubular element which surrounds the jet tube and which functions in bending as a spring when the armature and jet tube are moved from their null positions.

In such valves, the spring means bends as the armature rotates in response to a signal. The extent to which the spring means bends is proportional to the total spring constant, which in turn is a function of spring shape and thickness. Since predictable and reliable operation requires close control of the spring constant, it has been found necessary in practice to machine these items with precision in order to accurately regulate their characteristic, and, hence, their spring rates. This need for precision machining has obviously added to the cost of such servovalves.

It has been an objective of this invention to provide an improved servovalve torque motor having an armature supporting and biasing spring which is more eihcient of less critical manufacture, and which also is more economical than those which previous torque motors have used.

A lfurther disadvantage of previous valves of the general type described is they have not readily lent themselves to room temperature assembly procedures such as swaging, crimping, etc. Soldering or brazing has usually been required to make the critical connections, which invariably requires more skill, is costlier, and tends to produce warpage which may adversely affect valve operation unless compensated.

It has been a further object of this invention to provide a servovalve construction which eliminates the need for soldered or brazed connection at critical points, thereby eliminating warpage and misalignnient which might otherwise be caused by heating of component parts during assembly.

Moreover, the prior art Servovalves have often been diflicult to assemble and align or adjust for maximum operating efficiency `and performance. One assembled, they have been difficult to disassemble for cleaning, repair, and inspection purposes.

It has been an additional object of this invention to provide a servovalve which can be assembled and disassembled relatively easily, and in which the first and second stages are separate subassemblies.

It has been another object of this invention to provide interlocking pole piece mounting means for a servovalve which permit accurate air gap dimensioning during assembly and protect against pole piece positional shifts while in use.

In a preferred embodiment of the invention, the torque motor armature has a pair of arms or wings on either side of a transversely extending hollow central body. An elongated armature restoring element in the form of a thin walled tube extends through the interior lof the hollow central body of the armature. This tube is connected to and supports the armature only at a point forward of the wings, and is connected to a supporting base only at a point on the rear side of the wings. A shaft or driver also extends through the armature, internally of the armature restoring tube, and is connected to the armature and tube only at the front end thereof. Electromagnet coils are disposed on opposite sides of the armature and when energized are operative to turn the armature about the common axis of the shaft and tube, thereby rotating the shaft. The shaft or driver moves an elongated liexible jet tube which passes perpendicularly through an enlarged aperture in the rear portion of the driver. The jet tube is secured at its fluid inlet end to the body above the -driver and is connected to the driver through an elongated tube which vsurrounds the jet tube and which is clamped to the jet tube adjacent the fluid outlet end or nozzle thereof.

Use of the thin-walled tube described in this co-nstruction provides a number of advantages: a single length of precision tubing serves jointly as the support means for the armature, as a torsion spring biasing the armature to null position, and as an isolation element for preventing operating fluid within the hydraulic portion of the valve from reaching the inside of the electrical portion of the torque motor. In addition, the configuration of the hollow tube herein provided permits it to be connected toI the armature and supporting base by swaging techniques, thus avoiding the usual disadvantages of machining and warping due to soldering or brazing during assembly.

In the torque motor, a pair of opposed, nonmagnetic members mechanically engage reference surfaces on the pole pieces of the electromagnetic coils and provide spacing means for establishing the proper air gap dimensions during assembly.

These anld other objects and advantages of the present invention will be more readily apparent from a consideration of the following detailed 'description of the drawings illustrating a preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a vertical section of a preferred embodiment of the servovalve of this invention, and is taken along the axis of the torque motor.

FIGURE 2 is a longitudinal section taken along line 2-2 of FIGURE 1, and also illustrates a typical hydraulic system including the servovalve.

FIGURE 3 is an enlarged vertical axial `section of the iirst stage of the valve, showing the details of the torque tube, armature, hyldraulic jet tube and receiver, and the force feedback spring assembly.

FIGURE 4 is a section taken along line 4-4 of FIG- URE 3.

FIGURE 5 is a partially exploded perspective View of the torque motor assembly.

FIGURE 6 is an enlarged View in perspective of the armature.

FIGURE 7 is a side elevation of the assembled torque motor.

FIGURE S is an enlarged view in section of a portion of the jet tube and receiver.

The servovalve of this invention includes three principal sections, namely, a torque motor 1, a first force amplifying stage 2, and a second force amplifying stage 3. As best shown in FIGURES 1 and 2, in a preferred embodiment, the torque motor 1 and first amplifying stage 2 are supported by la common base or frame member 4. Base 4 is nonmagnetic, and is mounted on a boldy 5, the body 5 also serving as a casing for the second section 3 of the servovalve. A housing 6 mounted on a horizontally extending fiange 7 of the body 5 encloses motor 1 and ampliier 2.

The torque motor 1, as shown more particularly in FIGURES 5-7, includes a permanent magnet 8 having an upper north pole 9 and a lower south pole 10. Magnet S may be an alnico permanent magnet. Sandwiched between magnet 8 and' base 4 are opposed ferromagnetic upper and lower C-

shaped pole pieces

11 and 12, respectively. The opposed

planar end surfaces

13, 14 and 15, 116 of

pole pieces

11 and 12, respectively, are spaced, forming

air gaps

17 and 18, respectively (see FIGURE 2). The permanent magnet 8 functions to establish a urn'- directional magnetic flux in each of the

air gaps

17, 18.

Also sandwiched between magnet 8 and base 4 are a pair lof

nonmagnetic spacer members

19 and 20. Since

members

19 and 20 are similar, only the left member 19 will be described. Member 19 is C-shaped, as viewed from above, and includes opposed internal pole

piece engaging surfaces

21, 22 separated by pole piece end-engaging surface 23. Surface 22 is generally planar for engaging the back surfaces (adjacent base 4) of the .

pole pieces

11 and 12 to align them in its plane. Po-le piece-end-engaging surface 23 is provided with a horizontal slot 25, and from this slot horizontal grooves 24 extend across the inner 4 side faces of the spacer to permit the assembly to be placed over the armature. The surface 23 abuts the ends of

pole pieces

11 and 12, establishing alignment in its plane. The angulated internal surfaces 21, 21 (See FIG- URE 5) engage the opposed beveled corner surfaces 26, 26 of the

pole pieces

11, 12 and jointly function to locate and accurately space pole piece end `surfaces 13, 14, thereby dimensioning air gap 17. Thus, when spacer 19 is snugly .fitted over the left ends of

pole pieces

11 and 12, pole piece surfaces 13 and 14 are horizontally and vertically aligned by

surfaces

22 and 23, as well vas spaced apart to form an air gap 17 by angulated

surfaces

21, 21. Those skilled in the art will recognize the criticality of accurate air gap dimensioning.

A `forwardly extending, vertical ange 27 is formed on the rounded external surface 28 of each spacing member. Flange 27 is provided with a at shoulder surface 29, best shown on the spacing member 20 in FIGURE 5, and engages and seats in the internal end surface 30 of the magnet 8, thereby preventing movement of the spacing member relative to

pole pieces

11, 12 when the motor 1 is assembled.

The motor 1 also includes a pair of

coils

31, 32 through the open centers of which extend the

flat Wings

33, 34, respectively, of an armature 35 desecribed in detail hereinafter. In the assembled torque motor 1, the

coils

31, 32 are mounted by and between the opposed concave magnet surface 30 and concave base surface 30a,

pole pieces

11, 12, and

spacing members

19, 20. The coil leads 36 pass through slots 37 in the spacing `

members

19, 20 for connection to a suitable electrical signal input means (not shown) which may be conventional.

The various parts of the torque motor assembly are held in operative relation by two screws 38 and a plate 39. The screws 38 pass successively through plate apertures 40, magnet aperture 41, grooves 42 in

pole pieces

11, 12, and thence into tapped holes 43 in base 4. As screws 38 are tightened, magnet 8 and base 4 are drawn together, gripping the

pole pieces

11, 12 and holding the

spacing members

19, 20 between them. The spaces between

members

19, 20 and faces 30, 30a are lled with an epoxy which provides a positive interlock in the torque motor.

The operation of the torque motor 1 follows principles which are well known and need not be discussed in detail. It is sufficient for the purposes of understanding the various features of this invention to appreciate merely that a differential current applied to coils 31, 32 will result in a magnetic torque being applied to ferromagnetic armature 35, rotating it about its axis 44. Armature 35 rotates under the force of the applied torque to an angular position within

air gaps

17, 18 Where the applied torque equals the armature restoring torque produced by means to be described. The direction and magnitude of the applied torque is dependent upon the level and polarity of the differential current owing in the

coils

31, 32. For a detailed discussion of the operation of torque motors, reference may be had to U.S. Patent 2,891,181, to Raymond D. Atchley, issued June 16, 1959, and entitled Torque Motor.

The armature 35 of motor 1 is generally T-shaped as viewed in plan, and includes a central tubular portion 5t) provided with oppoistely extending

flat wings

33, 34 of equal length (see FIGURE 6). The dimensioning of

wings

33, 34 is such that they extend into

air gaps

17, 18 respectively. Clearance is provided between the

wings

33, 34 and the pole piece end surfaces 13, 14 and 15, 16 respectively, permitting the armature 35 to rotate about its axis 44 in response to the application of an electrical signal to the

windings

31, 32. The extent of armature rotation is selectively limited by adjusting

screws

51, 51 threaded into tapped holes in upper pole piece 11 (see FIGURE 2).

The forward extremity of central tubular portion 5t) of armature 35 has a reduced internal diameter resulting in a stepped-diameter bore having a small diameter bore section 52 and a large diameter bore section 53 separated by an internal shoulder. Positioned within the

bore sections

52, 53 is a non-magnetic stepped-diameter armature-'supporting torque and isolation tube 54. The torque tube 54 is secured at its reduced diameter front end portion 55 to the end 57 of the armature tubular portion 50, and at its other end 56 to the base 4. The portion of tube 54 intermediate ends 55 and 56 is coextensive lengthwise with bore section 53 of central armature portion 50, but is of reduced diameter and does not contact the armature.

The end 55 of torque tube 54 fits snugly within bore section 52 of the central armature portion 50 and is secured in place by an internally tapered swaging ferrule `60 which is pressed ove-r the externally tapered armature end 57. The complementary tapers of armature end 57 and ferrule 60 securely lock the armature 35 and torque tube 54 to the end of a coaxial driver 65, providing a solderless connection therebetween.

The tube 54 at its inner end 56 is flared and fits snugly into a tapered bore 61 in base 4. An externally tapered swaging ferrule 62 pressed within flared end 56 of torque tube 54 secures the torque tube to base 4. The complementary tapers of swaging ferrule 62 and base bore 61 lock the flared end 56 of torque tube 54, thereby providing a solderless connection between the base 4 and the torque tube 54.

Thus, armature is supported within motor 1, with its

wings

33, 34 centrally poistioned within

air gaps

17, 18 and biased against rotation about its axis 44 by torque tube 54, the latter being connected at its outer end to the front end of the armature and at its inner end, beyond the opposite end of the armature, to base 4 via ferrules and 62, respectively.

The relation of the torque tube 54 and armature 35, as herein described, wherein the tube passes axially through the armature and is connected at its outer end to the armature enables a relatively long torque tube 54 to be employed as the spring element in the torque motor 1. With a long torque tube 54 in contrast to a short one, there is less angular rotation of the tube per unit length for a given armature rotation.

To transmit the torque output of motor 1 to the first amplifying stage 2, a deflection or coupling means is provided. The coupling means includes a non-magnetic driver 65 which passes axially through torque tube 54. As previously mentioned, the outer end of driver 65 is secured to the armature 35 and torque tube 54 by swaging ferrule 60. At its other or inner end driver 65 is secured through an element 66 having an opening extending therethrough at right angles to the driver, to an arm or yoke 67 for movement therewith. Arm 67 has a right angle bend intermediate its ends, thereby forming an L-shape, and its lower portion thus projects forwardly beneath element 66 and parallel to driver 65. The connection between the vertical leg 73 of arm 67 and element 66 is by a screw 68 which passes through an oversized hole 69 in leg 73 and which is threaded into a tapped hole 70 in element 66. Radial teeth 71 formed on the element face (see FIG- URE 4) engage the forward surface 72 of vertical leg 73 to prevent relaitve angular movement between collar 66 and arm 67 when screw 68 is tightened.

The lower or forwardly extending leg 74 of arm 67 is provided with two holes 75 and 76. A tube 77 is secured in hole 76 by suitable means. Soldering or brazing may be employed here since warpage is not critical at this point. The lower end of tube 77, including the reduceddiameter lower end portion thereof, has circumferentiallyspaced longitudinal slots 78 therein. The slots 78 enable the reduced-diameter portion of tube 77 to secu-rely embrace the periphery of a vertically disposed flexible jet tube 85. This tube extends through and is gripped by the lower end portion of tube 77 under the action of a press fitted ring 80 which clamps the slotted, reduced-diameter end portion of tube 77 to jet tube 85.

In the first amplifying stage 2, jet tube extends through tube 77, hole 76, and element 66 and is secured at its upper end only to base 4 by a conical-ended retainer plug `86 and screw 84. Plug 86 and screw 84 cooperate with the sloping walls 87 of a threaded hole 88 to securely lock the flared end 89 of jet tube 85 relative to base 4 when screw 84 is tightened. At its lower end, jet tube 85 is fitted internally with a projector jet 90 having an outlet nozzle and which is secured in place by a crimp 91.

The first amplifying stage 2 also includes a receiver 92. Receiver 92 is a plug having a pair of fluid passages 93, 94 (see FIGURE 8) which meet over a central knife edge 95. Passages 93, 94 communicate

ywith passages

96, 97, respectively, formed in a receiver supporting member 98. The

passages

96, 97 in turn communicate with passages 99, 100 (see FIGURE 2) which constitute the inputs to the second amplifying stage 3.

The receiver supporting mem-ber 98 is connected to base 4 by means not shown and, when the servovalve is assembled, is positioned within a cavity 101 in body 5, seating and sealing on surface 102 thereof. A passage 103 is formed in member 98 which connects the upper end of jet tube 85 to a source of pressure fluid via passage 104 in plug l86, passage 105 in base 4, passage 106 in body 5, filter 107, and inlet port 108 in body 5.

In operation, when an electrical signal is applied to the torque motor 1, armature 35 initially rotates from a centered position to a point where the restoring force on the armature 35 equals the magnetic torque produced by the electrical input. These restoring forces arise from deflection of the torque tube 54, jet tube 85 and a feedback spring to be described. The armature rotation is transmitted to the jet tube `85 via driver 65, element 66, arm 67, and tube 77, bending or deflecting jet tube 85 from a centered position directly over knife edge 95 of the receiver. As the jet tube 85 is deflected from the centered, null position shown in FIGURE 8, it directs a greater proportion of the fluid issuing from its nozzle 90 to one or the other of the receiver passages 93, 94. The pressure in that receiver passage toward which the nozzle 90 is deflected will increase while the pressure in the other passage will decrease. Excess pilot llo-w from jet tube 85 which is not accepted by either receiver passage flows to a fluid reservoir. Thus a differential between the pressures in passages 93 and 94 is developed. This differential constitutes the input to the second amplifying stage. A slight rotation of armature 35 produces a relatively large displacement of jet tube 85 and a relatively large pressure differential develops between passages 93 and 94. This pressure differential is capable of developing much larger forces than could be developed by the armature alone. Hence, force multiplication is produced by the `first amplifying stage.

The second amplifying stage -3 includes a main spool valve having a spool or piston 110 slidable in a bore 111 of a sleeve 112 (see FIGURE 2). Spool 110 has a series of axially spaced peripheral grooves G1, G2, and G3. Sleeve 112 is fitted into a bore 113 in the body 5 and it is provided with a plurality of port means P1, P2, P3, P4 and P5 which communicate with bore 111 at axially spaced positions, and which cooperate with spool grooves G1-G3 to direct the flow of fluid through the main valve. Ports P1-P5 can be interconnected in various ways by the selective positioning of spool 110 relative to sleeve 112. For example, if the spool valve is to control or meter the flow of fluid a variable speed reversible motor M, motor ports M1 and M2 may be connected to ports P2 and P4, respectively. The pump outlet port is connected to both ports P1 and P5, and port P3 is connected to a tank T. In such a system, when spool 110 is moved to the right in sleeve 112, the motor M is driven in one direction by fluid from pump P lwhich takes the following path: port P1, lgroove G1, port P2, motor port M1, motor M, motor port M2, port P4, groove G2, port P3, to tank T. If spool 110 is moved to the left, motor M is driven in the opposite direction by iluid from pump P taking the path through port P5, groove G3, port P4, motor port Mz, motor M, motor port M1, port P2, groove G2, port P3, to tank T. The speed at which motor M is driven depends, of course, on the ow rate through motor M, which in turn depends on the extent to which spool 110 is displaced from the centered position wherein no flow occurs.

The port P3 in sleeve 112 also communicates with the region surrounding projector jet 90, thereby providing a path to tank T for excess jet stream fluid not entering either of the two receiver ports 93, 94.

The means for selectively moving spool 110 includes pressure chambers 115 and 116 in bore 111, pressure in which acts upon the opposite end surfaces of spool 110. Chambers 115 and 116 communicate with

passages

99, 96, 93 and 100, 97, 94 respectively, and reect the differential established by the lirst stage. Adjustable stops 117 and 118 are sealed to bore 111 and can be positioned axially therein to limit the movement of spool 110 by

plugs

119 and 120` respectively which are threaded into body 5.

In operation, the input to the second amplifier stage 3, that is, the pressure differential between passages 93, 94, produces a differential or net axial force on spool 110. The direction which this diiferential force moves spool 110 depends upon the polarity ofthe electrical signal input to the motor 1. Thus, fluid ows to motor M, in the selected direction.

Since the electrical signal is supplied for as long as it is desired to drive motor M, which usually will be much longer than it takes spool 1111 to shift an amount corresponding to the ow rate and motor speed desired, force feedback means are provided. This force feedback means includes a feedback spring 125 which is connected at its upper end 126 to horizontal leg 74 of arm 67. The connection is effected by securing end 126 in hole 75. The other end 127 of spring 125 has a ball 12S attached thereto. Ball 128 fits accurately and without play in a cross bore 129 in spool 110 forming a cam connection between the spool and the feedback spring.

Spool 110 will move in sleeve 112 as long as there is a pressure differential between chambers 115 and 116. Since this pressure differential is caused by the unequal impingement of iluid on receivers 93, 94 due to the deection of jet tube 85, the force on spool 110 will remain as long as the jet pipe 85 is deflected. However, spring 125 is responsive to the position of spool 110, and supplies a feedback force to driver 65 which returns jet tube 85 to null position and thereby removes any net force on the spool 110 when the spool has been shifted an amount corresponding to the magnitude of the input signal.

By way of example, referring to FIGURE 2, a counterclockwise jet tube rotation will produce an unbalanced force in chamber 116 which shifts spool 110 to the left. As spool 110 moves to the left, it rotates the feedback spring 125 clockwise. This clockwise motion is transmitted to arm 67, which in turn transmits it to the armature and tends to turn the jet tube clockwise to the null position. The spool position at which feedback spring 125 returns jet tube 85 to the null position corresponds to a unique and discrete input current level. Hence the servovalve will regulate the speed of motor M in accordance with the input signal. The spool 110 will remain in this position until the electrical signal is again varied.

It will be apparent from the symmetry of the valve that oppositely poled electrical input signals rotate the armature 35 and torque tube in the opposite direction, causing the spool to move toward the other side of its center or neutral position.

From the foregoing it will be apparent that the interrelation of the armature, torque tube, driver, arm, jet tube, and force feedback spring provides an assembly which is exceedingly compact in relation to the high gain which can be attained. The torsion spring length is relatively large in proportion tothe small size of the assembly, as shown in FIGURE 3. Moreover, the arrangement of the rst stage elements wherein the jet pipe projects through the driver and is engaged by the outer tube 77 only adjacent its lower end, provides a relatively long lever arm in compact form. Assembly of the valve is facilitated since the entire rst stage subassembly forms an integral unit with torque motor 1 which can be tted as a unit to the second stage 3.

While we have described a preferred form of this invention, it will be understood that it is susceptible of various modications and adaptations.

We claim:

1. Apparatus comprising:

a base;

a torque motor mounted by said base; said motor including an armature having an axis of rotation and an axially disposed central tubular portion;

torsion spring means mounting said armature to said base for torsionally constrained rotational motion about said axis of rotation, said torsion spring means comprising a torque tube which is connected at one end to said armature, said torque tube extending through said tubular portion of said armature and being connected at its other end to said base;

a flexible jet tube having a fluid inlet end and a uid outlet end, said fluid inlet end being secured to said base, said jet tube extending angularly with respect to said axis;

motion transmitting means connecting said armature and said jet tube for deflecting said jet tube in accordance with the rotation of said armature, said motion transmitting means extending angularly from said axis and comprising,

a driver extending axially through said torque tube and connected to said armature for rotational movement therewith, and coupling means extending at an angle to said axis of rotation and connecting said driver and said jet tube for angularly deliecting the uid outlet end of said jet tube in accordance with the rotation of said armature,

said jet tube being secured to said base above said driver and extending freely through an aperture provided in said driver,

and further wherein said coupling means is connected to said jet tube below said driver.

2. Apparatus comprising:

a base;

a flexible jet tube having a iluid inlet end and a fluid outlet end, said fluid inlet end being secured to said base, said jet tube extending angularly with respect to said axis;

motion transmitting means connecting said armature and said jet tube for deiiecting said jet tube in accordance with the rotation of said armature, said motion transmitting means extending angularly from said axis and comprising,

a driver extending axially through said torque tube and connected to said armature for rotational movement therewith, and coupling means extending at an angle to said axis of rotation and connecting said driver and said jet tube for angularly detiecting the fluid outlet end of said jet tube in accordance with the rotation of said armature,

said coupling means including a tubular clamp member through which at least a portion of said jet tube extends, said tubular clamp member at one end being connected to said driver, the internal wall of said clamp member being spaced over most of its length from said jet tube, said tubular clamp member at the other end thereof being connected to said jet tube adjacent said iiuid outlet end thereof.

3. The apparatus of claim 2 wherein said driver is connected to said armature through said torque tube at said one end thereof, and further wherein said coupling means also includes a generally L-shaped arm connected at one en-d to said driver and having a leg extending parallel to said driver, said jet tube passing freely through an aperture in said leg, said clamp member being secured to said leg.

4. The apparatus of claim 3 which further includes an elongated force feedback spring extending downwardly from said leg.

5. The apparatus of claim 2 wherein said jet tube is clamped to said base and said tubular clamp member is clamped to said jet tube, without the necessity of brazing.

6. Apparatus comprising:

a shaft rotatable about an axis in response to a signal;

a base;

a flexible jet tube angularly disposed relative to said shaft and which intersects the axis of said shaft, said jet tube having a liuid inlet end xed relative to said base, said jet tube also having a iluid outlet end; and

motion transmitting means angularly disposed relative to said shaft, said motion transmitting means being connected between said jet tube at a point intermediate said ends and said shaft for arcuately moving said lluid outlet end in a plane intersecting the axis of said shaft at an angle thereto.

7. Apparatus comprising:

a base;

a torque motor for angularly positioning rotatable means in response to an electrical input;

a exible jet tube having a fluid inlet end mounted to said base, said jet tube also having a iiuid outlet end, said tube between said inlet and outlet ends extending through an enlarged opening provided in said rotatable means, said jet tube being spaced from said rotatable means in said opening; and

a tubular clamp member through which at least a portion of said jet tube `freely extends, said tubular clamp member at one end being connected to said rotatable means for rotation therewith, said tubular clamp member at the other end thereof being connected to said jet tube adjacent said iiuid outlet end thereof.

8. The apparatus of claim 7 wherein said rotatable means comprises a generally cylindrical driver and an L- shaped portion projecting generally perpendicularly to said driver, said L-shaped portion having a leg extending substantially parallel to said driver, said driver and leg both having apertures therein through which said jet tube freely extends, said clamp member being secured at said one end thereof within said aperture of said leg and projecting away from said driver.

9. Apparatus for amplifying an input signal applied as a torque acting on a shaft, said apparatus comprising:

a frame member;

a flexible jet tube having a fluid inlet end cantilevered to said frame member and having a jet outlet at the other end thereof;

a receiver having two adjacent receiver ports, said receiver being mounted to said frame member, said jet outlet being positioned to direct uid issuing therefrom to impinge on said receiver ports;

a substantially tubular clamp member within which at least a portion of said jet tube is positioned, said tubular clamp member at one end loosely encircling an intermediate portion of said jet tube between the ends of said jet tube, said clamp member at said one end being connected to said shaft, said tubular clamp member at the other end thereof being connected to said jet tube between said jet outlet and said intermediate portion, dellection of said jet tube by said clamp member in response to rotation of said shaft in operation developing a pressure differential between said receiver ports;

a body;

a spool valve including a bore in said body and a spool slidable within said bore for varying the iiow of fluid through said valve;

two passages formed in said body and communicating, respectively, with each of said receiver ports; and

force feedback means operatively connected between said spool and said jet tube for centering said jet outlet between said receiver ports when said spool advances to a position correlated with the input signal.

10. The apparatus of claim 9 wherein said force feedback means includes a spring element having lirst and second ends, said tirst end being connected to said jet tube through said clamp member, and said second end including a cam follower in sliding contact with a cam surface formed by said spool for imparting pivotal motion to said spring element in response to sliding movement of said spool.

11. The apparatus of claim 9 wherein said shaft is operated by a torque motor.

12. The apparatus of claim 9 further comprising:

a torque motor mounted on said frame member; said motor including an armature having an axis of rotation and having an axially disposed tubular portion; torsion spring means mounting said armature to said Iframe member for torsionally constrained rotational motion about said axis, said torsion spring means comprising a torque tube positioned within said tubular portion of said armature and connected at axially spaced points to said torque tube and said frame member, and further wherein said shaft comprises a member concentric with said torque tube and connected to said armature for rotational movement therewith.

13. The apparatus of claim 9 further comprising:

a torque motor including magnetic circuit means mounted on said frame member, said magnetic circuit means having spaced poles defining an air gap, said spaced poles having reference surfaces thereon; a spacing member enclosing at least a portion of said pole pieces, said spacing member having geometrically spaced means for engaging said reference surfaces for establishing and maintaining a predesigned air gap; an armature having an axially disposed tubular portion; a torque tube positioned within said tubular portion and connecting said armature and said frame member for torsionally constraining rotational motion of said armature; and wherein said shaft comprises a driver concentric with said torque tube and connected to said armature for rotational movement therewith.

14. Apparatus comprising:

a base;

a tiexible jet tube having a uid inlet end and a fluid outlet end, said uid inlet end being secured t-o said base, said jet tube extending angularly with respect to said axis;

motion transmitting means connecting said armature and said jet tube for deecting said jet tube in accordance with the rotation of said armature, said motion transmitting means extending angularly from said axis and comprising,

a driver extending axially through said torque tube and connected to said armature for rotational movement therewith, and coupling means extending at an angle to said axis of rotation and connecting said driver and said jet tube for angularly deecting the uid outlet end of said jet tube in accordance with the rotation of said armature,

said armature, torque tube, and driver being secured together by a swaging ferrule around a tapered surface provided on said armature.

15. Jet tube servovalve apparatus comprising:

a frame;

a torque tube rigidly mounted to said frame;

an armature;

means rigidly connecting said armature to said tube at a position on said tube spaced from the rigid mounting of said tube to said frame;

magnetic means tending to rotate said armature about the axis of said tube;

a flexible jet pipe having a fluid outlet end;

means fixedly securing said jet pipe to said frame at a position spaced from said outlet end;

conduit means for supplying pressure fluid into said jet pipe;

t-ube means surrounding and connected at one end to the jet pipe, said tube means having a free end sur- 30 rounding said jet pipe; means responsive to rotational movement of said armature about said axis and connected to the free end of said tube means, to deflect the outlet end of said jet pipe relative to the position at which the jet pipe is xedly secured to the frame,

a feedback spring connected to said free end of said tube means,

and receiver port means for said jet pipe, said receiver port means being xedly positioned with respect to said frame.

16. The apparatus of claim 15 wherein a shaft extends through said torque tube and is connected for rotational movement with said armature; and

coupling means are connected between said shaft and said `jet pipe, said coupling means extending at an angle to said axis and angularly defiecting the fluid outlet end of said jet pipe in accordance with the rotation of said armature.

17. The apparatus of claim 16 in which said jet pipe is a normally straight tube having a uid inlet at one end thereof remote from said outlet end, said inlet being xedly connected to said frame,

ALAN COI-IAN, Pri-mary Examiner.

U.S. Cl. XR.