Patent Application
20080073609
The same physical elements are each denoted by the same reference numbers in the drawing.
The air flow 10 passes through the air inlet 3 in the side face 6 of the housing 2 into the compressed-air needle valve 1. The air outlet 4 is located in the area of the front face 7 of the housing 2. The control rod 5 is held, such that it can be moved longitudinally, in a (linear) bearing 9 which is arranged in the rear face 8 of the housing 2. The compressed-air needle valve 1 is controlled by moving the control rod 5 in the longitudinal direction, in the direction of the double-headed arrow 11.
A Venturi insert 12 is arranged in the area upstream of the air outlet 4. The Venturi insert 12 has a circular cross section which varies over its longitudinal extent. The cross section of the Venturi insert 12 tapers in an inlet section 13, while the cross section increases continuously in an outlet section 14.
A needle 16 is also attached to a first end 15 of the control rod 5. The geometric shape of the needle 16 represents, approximately, a parabolic rotational solid. There is an annular gap 17 between the needle 16 and the Venturi insert 12. The size of the annular gap 17 can be increased or decreased continuously by moving the control rod 5 in the direction of the double-headed arrow 11. This allows the air flow passing through the compressed-air needle valve 1 to be set with very high precision between 0 kg/s and 5 kg/s. In this case, the air flow 10 enters the air inlet 3 at a pressure of up to 100 bar. By way of example, the needle 16 can be mounted on the first end 15 of the control rod 5 by means of a screw thread. The control rod 5 is moved parallel to the double-headed arrow 11 in the longitudinal direction of the compressed-air needle valve 1 by means of a precision linear actuating member, which is not illustrated in
A Teflon ring 20, a nylon ring, a polyethylene ring or the like in the form of a disc is arranged between the needle 16 and the first end 15 of the control rod 5. In order to block the compressed-air needle valve 1 completely, the needle 16 is moved into the Venturi insert 12 until the Teflon ring 20 has reached a centre section 21 of the Venturi insert 12, which has the minimum cross-sectional area in comparison to the inlet and outlet cross section 13, 14. In order to achieve a slight interference fit between the Teflon ring 20 and the centre section 21, and to increase the sealing effect, the Teflon ring 20 is slightly oversized, by up to 0.05 mm, with respect to the internal diameter of the centre section 21. The Teflon ring 20 allows the compressed-air needle valve 1 to be sealed completely, at the same time reducing wear phenomena and friction processes between the needle 16 and the Venturi insert 12. Furthermore, the control rod 5 has a conical surface 22 in the area of the first end 15, in order to prevent the control rod 5 from jamming with the Venturi insert 12. The needle 16 is preferably formed using stainless steel, while the Venturi insert 12 is composed of bronze, in order to achieve good dimensional constancy with acceptable manufacturing effort.
Furthermore, the needle 16 is coaxially surrounded by an insert 23 which, in the illustrated exemplary embodiment, is a thin-walled hollow cylinder 24. A multiplicity of holes—which are not provided with a reference number in the illustration shown in FIG. 2—are incorporated in the insert 23. The holes are arranged in the form of a matrix or a uniform grid. The holes are also recessed from an inner surface and an outer surface of the insert 23 in order to prevent the formation of vortices in the air flow 10. The insert 23 is used to smooth the air flow 10 within the compressed-air needle valve 1. Furthermore, the insert 23 is intended to ensure a uniform incident flow, which is as laminar as possible, onto all sides of the needle 16, while at the same time damping oscillation phenomena of the needle 16 resulting from the high input pressure of up to 100 bar.
The contour of the needle 16 and of the Venturi insert 12 must be calculated individually for each engine simulator to be controlled by means of the compressed-air needle valve 1. A corresponding situation applies to the design of the insert 23. By way of example, the diameter of the holes in the (smoothing) insert 23 and/or their grid separations can be varied in order to match the insert 23 to different types of engine simulators. It is also possible to vary the depth of the depressions and/or the respective countersinking angle of the holes. The wall thickness of the thin-walled hollow cylinder 24 and of the insert 23 is between 1 mm and 5 mm.
The Venturi insert 12 and the needle 16 can easily be interchanged, using standardized Venturi inserts and needles for matching to different types of engine simulators, in a simple manner. All that need be done for this purpose is to release the air inlet 3, which is flange-connected in the area of the front face 7 of the housing 2, and to remove the bearing 9, which is flange-connected to the rear face 8 of the housing 2. The needle 16 can then be unscrewed from the control rod 5 and can be replaced by a needle with a different geometric form. The Venturi insert 12 can likewise easily be removed from the housing once the air outlet 4 has been released, and can be replaced by a different one, with a different flow geometry.
The insert 23 is once again surrounded by an annular chamber 25 whose external surface is formed by the housing 2 and whose internal area, apart from the air inlet 3, corresponds essentially to the geometric shape of a hollow cylinder. The object of the annular chamber 25 is to form an air reservoir or a buffer reservoir with a relatively small volume for the air flow 10, thus contributing to further smoothing of the air flow 10 passing through the compressed-air needle valve 1.
The above-described compressed-air needle valve 1 allows accurate control of an air mass flow 10 between 0 kg/s and 5 kg/s in order to drive compressed-air-operated engine simulators. The compressed-air needle valve 1 can be used to set the rotation speed of engine simulators with an accuracy of up to ±50 rpm with an inlet air pressure of up to 100 bar. The compact design allows direct integration in aircraft models which are used for wind tunnel measurements. The insert 23 which coaxially surrounds the needle 16 and has a multiplicity of holes which are arranged in the form of a grid and pass all the way through smoothes the incident air flow onto the needle 16 and damps any oscillation phenomena in the area of the needle 16.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 044 996.7 | Sep 2006 | DE | national |
