Patent Application
20080110513
The present invention is directed toward a torque motor having a hermetic seal between a jet tube and a jet tube housing, and, more specifically, toward a torque motor having a flexible, hermetic sealing element connected between the jet tube and the jet tube housing.
Torque motors may be used to form the first stage of a two-stage electrohydraulic servo-valve (EHSV).
The jet tube 202 itself is contained within a jet tube housing 208 which is in fluid communication with a chamber 216, and the openings of the control passages 204, 206 are located in the chamber 216, spaced from the end of the jet tube 202. While some of the fluid leaving the jet 214 enters one or the other of the control passages 204, 206, much enters the chamber 216 and flows into the space around the jet tube 202 inside the jet tube housing 208 before passing out of the EHSV through an output line (not shown).
The jet tube 202 must be free to pivot to a limited degree within the jet tube housing 208, and at the same time a seal must be provided in the jet tube housing 208 to prevent fluid from leaking out of the jet tube housing 208. This has previously been done by providing an elastomeric packing such as an O-ring seal 218 between the jet tube 202 and the jet tube housing 208 and using an aluminum plug 220 to limit movement of the O-ring. However, such seals tend to fail or exhibit degraded performance at low temperatures. High magnitude performance shifts over temperature or pressure extremes are common. It would therefore be desirable to provide an improved seal that offers improved performance over a wider range of operating temperatures and/or pressures.
These problems and others are addressed by the present invention, a first aspect of which comprises a torque motor that includes a support, a jet tube passage in the support having a first end opening and a second end opening, and a jet tube extending into the jet tube passage through the first end opening for directing a flow of fluid into a chamber in fluid communication with the jet tube passage second end opening. A flexible, convoluted, seal is hermetically connected to the jet tube passage and the jet tube and seals the jet tube passage first end while permitting at least a portion of the jet tube to move relative to the jet tube passage.
Another aspect of the invention comprises a torque motor that includes a support, a jet tube passage in the support having a first end opening and a second end opening, and a jet tube extending into the jet tube passage through the first end opening for directing a flow of fluid into a chamber in fluid communication with the jet tube passage second end opening. A flexible metallic seal is brazed or electrojoined to the jet tube passage and to the jet tube to seal the jet tube passage first end while permitting the jet tube to pivot in the jet tube passage.
These aspects and features of embodiments of the present invention will be better understood after a review of the following detailed description together with the attached drawings wherein:
Referring now to the drawings, wherein the showings are for purposes of illustrating presently preferred embodiments of the invention only and not for the purpose of limiting same,
The first stage 10 also includes a fluid supply tube 28 connected to a jet tube 30 which extends through an opening 32 in a central portion of armature 22 and which includes a nozzle 34 at distal end 36. The armature is connected to the jet tube 30 so that rotation of the armature 22 causes jet tube 30 to pivot and the distal end 36 to move. The position of nozzle 34 can therefore be controlled by controlling the current applied to windings 24.
Armature support 20 is mounted on the housing 38 of second stage 16 over a chamber 40 such that jet tube 30 extends past a bottom surface of the armature support 20 and into chamber 40. A tubular jet tube housing 42 having a first end opening 43 and a second end opening 45 extends from the bottom of armature support 20 toward armature 22 and forms a jet tube passage 44 surrounding jet tube 30 at a spacing such that jet tube 30 can pivot within jet tube passage 44 without contacting the wall of the jet tube housing 42. A seal 46, described hereafter, connects jet tube 30 and jet tube housing 42 and prevents fluid from leaking from first end 43 of jet tube housing 42.
First and second passages 48, 50 leading to chambers at first and second ends 52, 54 of spool valve 18 terminate in chamber 40. Armature 22 has a neutral position such that jet 34 is directed generally between the first and second passages 48, 50. The rotation of armature 22 controls the position of jet 34 and thus controls the amount of fluid flow directed toward each of the first and second passages 48, 50. When jet 34 directs more fluid toward first passage 48, the pressure on first end 52 of spool valve 18 becomes greater than the pressure on second end 54 of spool valve 18 and shifts spool valve 18 in the direction of second end 54—toward the right as viewed in
As best seen in
Seal 46 may be formed in any conventional manner, such as by stamping or hydroforming; however, electroforming the seal from a high-strength nickel-cobalt alloy is presently preferred. A presently preferred nickel-cobalt alloy is available from the Nicoform, Inc. of Rochester, N.Y., under the trade name NiColoy. In such an electroforming process, a nickel-cobalt alloy is deposited by plating one molecule at a time onto an aluminum mandrel that has the shape of the convoluted diaphragm on its face. When a desired thickness is obtained in a plating bath, the mandrel and plated diaphragm are removed from the plating tank. The mandrel is then released from the diaphragm by dissolving it in a chemical solution. This electroforming process is followed by a stress-relieving heat treatment process, about one hour at 300 degrees C., for example, to provide a homogeneous, relatively stress-free seal element. When formed in this manner, seal 46 beneficially has high strength, good flexibility, and resistance to high-cycle fatigue. Nickel-cobalt alloys with coefficients of thermal expansion similar to that of the stainless steels to which they are joined also reduces the stresses at the boundaries between the seals and the structures to which they are connected.
To attach seal 46 to jet tube 30 and jet tube housing 42, seal 46 is slid over jet tube 30 so that inner projecting sleeve 64 overlies a portion of the outside of jet tube 30. Outer projecting sleeve 70 is placed over the sidewall of jet tube housing 42 over opening 43, and seal 46 is hermetically sealed to the jet tube 30 and jet tube housing 42. In an embodiment of the present invention, a first metallic band 68, which may comprise a high strength nickel-cobalt alloy, overlies a portion of jet tube 30 and the outer surface 62 of inner projecting sleeve 64. Band 68 may be created by plating the nickel-cobalt alloy over the junction between the jet tube 30 and inner projecting sleeve 64 using an electrojoining process. A second metallic band 88, which may also be a high strength nickel-cobalt alloy, surrounds an outer portion of jet tube housing 42 and overlies the lower end 74 of outer projecting sleeve 70. Second band 88 may also be created by an electrojoining process to connect the seal 46 to the jet tube housing 42. The jet tube housing 42 may be formed from a non-magnetic stainless steel.
In the present embodiment, seal 46 has a thickness between inner surface 60 and outer surface 62 of about 0.005 inches and the diameter of projecting outer sleeve portion 68 is about 0.285 inch. The vertical distance from a crest 82 to a trough 84 of the convoluted wall 76 is about 0.02 inches. The connection between jet tube housing 42 and armature support 20 may be joined using a silver braze alloy that is heated with a micro torch or by electric induction. Seal 46 and jet tube 30 and jet tube housing 42 may alternately be brazed by electric induction heating with a gold nickel palladium alloy in an inert atmosphere.
In use, torque motor 14 is turned to move armature 22 and thus jet 34 relative to first and second passageways 48 and 50. The convolutions 80 in seal 46 allow convoluted wall 76 to elastically bend and/or deform and this allows the jet tube 30 to pivot while maintaining hermetic seals between the seal 46 and the jet tube 30 and the jet tube passage 42. The effective centerline of seal 46 is placed at the center of the axis of rotation of the torque motor 14 to help minimize stress at the brazed seams. The convolutions provide good compliance at normal operating temperatures and maintain integrity when exposed to high internal fluid pressure. System spring rate, the rate at which jet tube 30 and armature 22 return jet 36 to a neutral position is largely unaffected by this new seal 46. In addition, armature 22 controls the distance between jet tube 30 and control passages 48, 50 so that seal 46 is not subjected to significant stresses in the direction parallel to the centerline of jet tube 30.
A second embodiment of the invention is illustrated in
A third embodiment of the invention is illustrated in
The present invention has been described herein in terms of several preferred embodiments. However, obvious modifications and additions to these embodiments will become apparent to those of ordinary skill in the art upon a reading of the foregoing description. It is intended that all such obvious modifications and additions form a part of the present invention to the extent they fall within the scope of the several claims appended hereto.
