News Column

Patent Issued for Servo Valve

August 6, 2014



By a News Reporter-Staff News Editor at Defense & Aerospace Week -- Liebherr-Aerospace Lindenberg GmbH (Lindenberg, DE) has been issued patent number 8783291, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Weixler, Franz (Kempten, DE); Lau, Florian (Grunenbach, DE).

This patent was filed on September 30, 2010 and was published online on July 22, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "The present invention relates to a two-stage electrohydraulic servo valve with a first stage, which operates as pilot stage and includes a movable nozzle tube, and a second stage which operates as power stage.

"In modern hydrosystems engineering, particularly high demands often are placed on the operating behavior of the installed hydraulic components within such hydrosystem. In particular, the installed hydraulic components are meant to regulate certain hydraulic volume flows and pressures with high precision corresponding to given control signals. Valves suitable for this purpose, in particular continuous valves, allow to permit a continuous transition of the switching positions of the valve. In said continuous valves, an electrical input signal correspondingly is converted into a hydraulic output signal for actuating the continuous valve. One category of the continuous valves includes the well-known servo valves, which allow a highly precise and above all continuous adjustment of the valve switching position, which in particular in modern aircraft technology is regarded as a basic prerequisite.

"From the prior art, so-called two-stage servo valves are known, whose power stage includes a control piston which in its starting position normally prevents the volume flow between a pressure input and a pressure output channel. Inside the power stage, the control piston is in a pressure equilibrium. For actuating the power stage, i.e. for the controlled deflection of the control piston, which permits a volume flow between an input channel and an output channel, an electrically actuatable pilot stage is used, which effects the required deflection of the control piston.

"One embodiment of the pilot stage operates according to the known nozzle tube principle. For this purpose, a nozzle tube supplied with hydraulic fluid is movably articulated in a pivot point of the pilot stage. The pressure equilibrium of the control piston of the power stage in the zero-point position can be influenced by corresponding control lines connected to the nozzle tube. By means of the electrical control signals output to the pilot stage, the nozzle tube can be swivelled to and fro between the two control lines, whereby the pressure can be increased selectively to certain points of the control piston of the power stage. The change in pressure enforces a movement of the control piston out of the zero-point position, which corresponds to a continuous switching transition of the valve.

"In the pilot stages known so far, the pressure supply of the nozzle tube is achieved by an external tube conduit, whose connection point is susceptible to the vibrations, pressure fluctuations and zero-point shifts occurring in the valve during the operation."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "It is the object of the present invention to provide the skilled person with a two-stage servo valve which offers a more robust behavior in the case of vibrations and pressure fluctuations as well as a better behavior in the case of a zero-point shift.

"The present invention is solved by the combination of features herein. Accordingly, in a two-stage electrohydraulic servo valve with a first stage, which operates as pilot stage and includes a movable nozzle tube, and a second stage which operates as power stage, the nozzle tube of the pilot stage is guided by means of a torsion element, wherein the oil supply of the movable nozzle tube is integrated in the torsion element. Accordingly, the pilot stage operates according to the known nozzle tube principle for actuating the power stage.

"In accordance with the invention, it hence is omitted to solder an external tube to the nozzle tube for supplying the same with pressure, but the feed conduit for the pressure supply of the nozzle tube is integrated within the torsion element. Via the torsion element the nozzle tube is rotatably arranged about the torsion axis which extends in direction of the longitudinal axis of the torsion element. Due to this inventive arrangement of nozzle tube, torsion element and supply conduit, less parts must be moved in actual operation of the two-stage electrohydraulic servo valve. Consequently, advantages can be achieved thereby in terms of the dynamics of the electrohydraulic servo valve and the robustness with respect to vibration influences. The maximum angle of rotation of the nozzle tube is dependent on the elasticity and the length of the torsion element. The torsion of the torsion element also serves for resetting the nozzle tube. The oil supply is effected through the interior or cavity present in the torsion element. It is also conceivable, however, that for this purpose an extra conduit is provided in the interior of the torsion element.

"Advantageously, the oil supply of the nozzle tube is arranged in the neutral fiber of the torsion element. The neutral fiber of the torsion element designates the region in which no bending stress occurs during a bending operation or a torsion. As a result, the loads acting on the oil supply inside the torsion element due to the occurring forces on the torsion element are reduced significantly, whereby a sufficient and satisfactory oil supply of the nozzle tube is ensured at any time. Consequently, the robustness with respect to vibrations and the valve dynamics as well as the switching precision of the valve are optimized.

"The torsion element used preferably is a torsion bar spring in whose middle region the nozzle tube is arranged on the longitudinal axis. To obtain a symmetric rigidity in both branches of the torsion element, which extend laterally from the mounting point of the nozzle tube in both directions, it can be provided that in addition to the oil supply bore on one branch side of the torsion element a further bore is arranged on the opposite branch. The oil supply bore serves to supply fluid to the oil supply integrated in the torsion element. Particularly preferably, both of said bores are arranged symmetrically with respect to the connection point of the nozzle tube. As a result, there is not only achieved a symmetric rigidity in both branches of the torsion element, but the entire torsional rigidity of the torsion element also is reduced.

"It is conceivable that the torsion element is made of copper-beryllium and/or of titanium and/or of steel. All three material variants represent a particularly stable and vibration-resistant design possibility of the torsion element.

"To seal the connection of torsion element and nozzle tube and thus prevent a loss of hydraulic fluid, a seal can be provided at the connection of torsion element and nozzle tube in the pivot point. A radial O-ring seal is particularly preferred, which allows a complete sealing of the nozzle tube in the connection point to the torsion element and does not substantially influence the precision of the rotary movement of the nozzle tube for actuating the power stage.

"Advantageously, the nozzle tube is connected with the torsion element by press fit, whereby a particularly stable and robust connection of the two elements is achieved.

"It is conceivable that the bores inside the torsion element are closable or closed by means of ball bearing balls. It is also conceivable that the bores of the torsion element are closable or closed by means of cylindrical plugs instead of ball bearing balls, or a combination of the two closing techniques is employed.

"Advantageously, the pilot stage includes a base plate. The same adjoins the region or the block of the power stage. The base plate serves to accommodate the torsion element, wherein the longitudinal axis of the nozzle tube takes a vertical position and is guided through the base plate in direction of the power stage or into the same. In particular, the sealing of the nozzle tube in the region of the pivot point of the torsion element is integrated in the base plate. This corresponds to a particularly stable and robust arrangement with respect to vibration influences which can act on the two-stage electrohydraulic servo valve.

"It can be provided that the base plate is sealed with respect to the power stage or with respect to the block of the power stage by means of an axial seal. In particular, the axial seal is located in the region of the vertical extension of the nozzle tube between the base plate and the block of the power stage.

"Since the oil supply of the nozzle tube extends out of the oil supply of the power stage. it is particularly advantageous that an oil supply conduit is guided through the base plate up to the torsion element. The further extension of the oil supply then is integrated within the torsion element up to the nozzle tube in accordance with the invention. Consequently, in the inventive arrangement of the two-stage electrohydraulic servo valve an external pressure supply of the nozzle tube is completely omitted. Soldering an external tube for pressure supply can be prevented, whereby a better and more robust behavior of the servo valve is obtained in the case of vibrations, pressure fluctuations and a zero-point shift.

"For preservation and further sealing of the oil supply conduit it is advantageous to seal the same by means of an axial seal in the region between torsion element and base plate. What is conceivable here is the use of several sealing means, in particular in the region of the transition between the valve block of the power stage and the base plate as well as in the region between torsion element and base plate."

For the URL and additional information on this patent, see: Weixler, Franz; Lau, Florian. Servo Valve. U.S. Patent Number 8783291, filed September 30, 2010, and published online on July 22, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8783291.PN.&OS=PN/8783291RS=PN/8783291

Keywords for this news article include: Liebherr-Aerospace Lindenberg GmbH.

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Source: Defense & Aerospace Week


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