Spin test bench with an oil damper

Abstract

Centrifuge test stand (15) with an oil damper (1) with an oil-filled inner oil chamber (2) designed as a hollow chamber, an outer oil chamber (5) connected to the inner oil chamber (2) via at least one passage (3) and also containing oil, with a piston rod (7) projecting through the passage (3) and the inner oil chamber (2), movable in its longitudinal direction and connectable to a centrifuge shaft (16) of the centrifuge test stand (15), and with a piston (11) fixed to the piston rod (7), which divides the inner oil chamber (2) into two inner oil chamber parts (12), wherein a passage (3) is arranged in at least one of the inner oil chamber parts (12), wherein the inner oil chamber parts (12) are fluidically connected to one another via at least one oil passage means (13), and with at least one shaft guide element (14) arranged in the passage (3) and not sealed with respect to the inner oil chamber (2), so that oil from the inner oil chamber (2) can flow into the outer oil chamber (5),wherein the outer oil chamber (5) has a sealed shaft passage for the passage of the piston rod (7) in the form of a flexible sealing element, and wherein the inner oil chamber (2) and the outer oil chamber (5) are connected via a check valve (18) so that oil can flow from the outer oil chamber (5) into the inner oil chamber (2).

Description

The invention relates to a damping unit designed as an oil damper, which damping unit comprises an inner oil chamber and an outer oil chamber which is fluidically connected thereto, wherein the inner oil chamber is divided into two inner oil chamber parts by a piston rod connected to a piston. The invention further relates to a spin test stand with such an oil damper.For example, to measure loads acting on a rotating body, spin test stands may be used in which the body, such as a rotor, is operated in its operating speed range and also above it. In addition, the rotor can be exposed to, for example, cyclic changes in speed or temperature fluctuations. The rotor can be fastened and accelerated in a suspended manner, for example via its shaft journal, on a thin, elastic shaft. The rotor then rotates about its mass axis of inertia instead of about its geometric axis, so that the rotor moves quasi-free from unbalance forces. Since the elastic natural frequencies of the shaft are generally passed through and large deflections can occur in the process, dampers are often used to restrict the shaft deflection, so that the stability of the centrifugal shaft can be maintained.Known damping units are oil dampers. These consist of an oil-filled cylinder tube which is closed at both ends by end pieces. A piston rod passes through one of the end pieces and is connected inside the cylinder tube to a piston which slides sealingly on the inner wall of the cylinder tube. A passage can pass through the piston and acts as a throttle to brake the speed at which the piston is adjusted.Oil dampers are known, for example, from DE 37 26 031 C2. Here, the damper has a housing with a cylindrical cavity open at one end and housing a cylindrical intermediate rotor. In the cylindrical intermediate rotor, a further cylindrical rotor is again arranged, which is led out from the open side of the housing. Between the rotors there is an annular space which is closed off at the closed end of the housing, wherein the hollow cylindrical rotor projects into the annular space and a shear gap and a directional locking mechanism are formed both on the inner side and on the outer side in an annular gap between the intermediate rotor and the housing.EP 2 562 440 B1 discloses a damper system with a magnetic coupling. The magnetic coupling includes two magnets to apply radial counter forces at radially opposite points around the rotor such that no resultant force is applied to the rotor when the rotor is centered in the damper system.DE 10 2005 055 558 A1 describes an adjustable oil damper which has two tubes which are inserted coaxially into one another and are both closed at the end by two closure members. The piston rod passes through one of the closure members, while the other closure member contains a throttle device by means of which the flow resistance which the damper oil must overcome during displacement of the piston can be regulated.DE 10 2004 014 458 A1 discloses a front fork having an outer tube and an inner tube, wherein the inner tube is inserted into the outer tube in such a way that it can be extended and retracted. Further, the front fork includes a double-rod shock absorber disposed inside the outer tube and the inner tube, the double-rod shock absorber including an upper chamber and a lower chamber defined therein in which oil is contained, and an internal-fork oil chamber defined by the outer tube, the inner tube, and the double-rod shock absorber and in which oil and air are contained.US 2019 / 0 195 306 A1 describes an underwater damper unit comprising a cylinder body provided with an internal damper chamber filled with damper oil, wherein the damper chamber contains a continuous piston rod with a piston dividing the damper chamber into two chamber parts. The piston is equipped with one or more valves that allow fluid communication between the chamber parts.DE 10 2011 087 909 B3 relates to an arrangement for a component test stand. The arrangement comprises a shaft for transmitting a rotational force from a rotational drive to a component to be examined, wherein the shaft is rotatably mounted on the component side and on the drive side in at least one bearing each. The component-side bearing is connected to a damping system which has a plurality of damping units arranged in a hexapod arrangement with respect to the bearing.The problem with the known oil dampers is that the oil chambers must be sealed against leakage due to the strong alternating pressure which arises as a result of the movement of the piston. However, adequate tightness can only be achieved with a flexible sealing element which is connected both to the piston rod and to the housing of the oil damper. In order to avoid bulging of the sealing element due to the high pressure, the sealing element would in turn have to be designed to be sufficiently stiff. However, this leads to a high spring stiffness, which is not desirable in many oil dampers.The object of the invention is to provide a spin test stand with an oil damper which, despite sealing, entails a low spring stiffness.The object is achieved by the features of claim 1.The object is achieved according to the invention in that a spin test stand is provided with an oil damper, having an oil-filled inner oil chamber designed as a hollow chamber, an outer oil chamber which is connected to the inner oil chamber via at least one passage and likewise comprises oil, having a piston rod which protrudes through the passage and the inner oil chamber and is movable in its longitudinal direction and can be connected to a spin shaft of the spin test stand, and having a piston which is fixed to the piston rod and divides the inner oil chamber into two inner oil chamber parts, wherein a passage is arranged in at least one of the inner oil chamber parts, wherein the inner oil chamber parts are fluidically connected to one another via at least one oil passage means, and having at least one shaft guide element which is arranged in the passage and is not sealed with respect to the inner oil chamber, such that oil can flow from the inner oil chamber into the outer oil chamber, wherein the outer oil chamber has a sealed shaft passage for passing through the piston rod in the form of a flexible sealing element, and wherein the inner oil chamber and the outer oil chamber are connected via a check valve, such that oil can flow from the outer oil chamber into the inner oil chamber.In a preferred embodiment, an oil damper is provided, having an oil-filled inner oil chamber designed as a hollow chamber, an outer oil chamber which is connected to the inner oil chamber via two passages and likewise comprises oil, having a piston rod which projects through the passages and the inner oil chamber and is movable in its longitudinal direction and can be connected to an object to be damped, and having a piston which is fixed to the piston rod and divides the inner oil chamber into two inner oil chamber parts each having a passage arranged therein, wherein the inner oil chamber parts are fluidically connected to one another via at least one oil passage means, and having shaft guide elements which are arranged in the passages and are not sealed with respect to the inner oil chamber, with the result that oil can flow from the inner oil chamber into the outer oil chamber.The advantages and embodiments of the oil damper are applicable analogously to the spin test stand. The oil damper may be fixedly installed in the spin test stand and may be connectable to the spin shaft of the spin test stand. With the aid of the oil damper according to the invention, efficient damping of an excitation movement of the centrifugal wave can be damped and the stability of the centrifugal wave can thus be ensured.Due to the design according to the invention, a leakage of the shaft guide element is tolerated, that is to say the desired damping effect is achieved despite leakage and complicated and expensive seals can be dispensed with. Especially since this allows smooth displacement of the piston. The oil emerging from the inner oil chamber flows via at least one wave guide element, preferably via both wave guide elements, into the outer oil chamber. Since the outer oil chamber is fluidically connected to at least one passage, pressure equalization preferably takes place therein. Consequently, a nearly constant oil pressure is established in the outer oil chamber, which approximately corresponds to atmospheric pressure.In one embodiment, the inner oil chamber has a cylindrical shape and is made of metal. The piston can preferably likewise have a cylindrical shape and in particular be designed as a disk.The oil passage means, which fluidically connects the two inner oil chamber parts to one another, can advantageously be designed as a gap between piston, in particular its circumferential surface and inner wall of the inner oil chamber, in particular the inner surface of the hollow chamber wall. Depending on the design of the piston and its position in the inner oil chamber, the gap can extend only in regions over the circumference of the piston or surround the latter over its full circumference.In a further embodiment, the oil passage means can be designed as a throttle or throttle valve, which is preferably integrated in the piston or between the piston and the inner surface of the hollow chamber wall. The throttle could also be arranged outside the cylinder, wherein two connections are provided in the inner oil chamber chambers and the throttle is integrated in the connection of these two connections. In this regard, a plurality of throttles may also be provided, through which the oil can move back and forth between the inner oil chambers. Furthermore, it can be provided that the oil passage means is designed as an aperture or a plurality of apertures in the piston, by means of which or by means of which a pressure equalization between the inner oil chamber parts is possible.The described wave guide elements or the described wave guide element are used in an analogous manner below to explain configurations and functions, so that singular and plural are interchangeable and can be used for both configurations. The shaft guide element is configured to be leak-proof and allows oil to escape from the inner oil chamber into the outer oil chamber. The shaft guide elements serve for guiding the shaft, i.e. in particular the piston rod, and are arranged in particular in the passages between the inner oil chamber and the outer oil chamber. In one embodiment, however, it can also be preferred that only one shaft guide element is provided in one passage, provided that a single-acting piston or piston rod is preferred. An advantage of the leaky shaft guide elements is that sealing elements can be dispensed with and spring restoring forces can thus be avoided. Oil can emerge between the piston rod and the guide elements, in particular on both sides, and flow into the surrounding outer oil chamber, which is advantageously likewise filled with oil.The wave guide members are preferably designed such that the flow resistance caused by them is higher than the flow resistance between the inner oil chamber parts in dynamic operation. As a result, a pressure necessary for efficient damping can build up in the inner oil chamber.The leaky wave guide elements can be designed in particular as linear bearings. Linear ball bearings or slide bearings are particularly preferred here, which allow sufficient axial movability of the piston rod, wherein leakage is tolerated.The inner oil chamber is preferably perforated along its central axis by the two passages, which are designed, for example, as bores and which advantageously each open into a chamber of the outer oil chamber. In this regard, it is preferred that the two chambers are arranged diametrically and are connected to one another fluidically via a line, for example a pipe connection.The piston rod can be connectable to a shaft, for example. The piston rod protrudes with one end out of the end of the oil damper and can be connected to a shaft. In order to prevent oil from escaping from the outer oil chamber, the outer oil chamber has a sealed shaft passage for passing through the piston rod. This can be achieved, for example, by a flexible sealing element, such as a sealing bellows.In order to return oil from the outer oil chamber to the inner oil chamber, the outer oil chamber and the inner oil chamber may be connected to each other via a check valve so that oil may flow from the outer oil chamber to the inner oil chamber. As a result of the movement of the piston, a negative pressure can be generated in the inner oil chamber, in particular in one of the two inner oil chamber parts, by means of which negative pressure oil is sucked back into the inner oil chamber via the check valve.The invention is explained in more detail below with reference to an exemplary embodiment of the invention, which is illustrated in the drawing. They show FIG. 1 shows a schematic illustration of an embodiment of an oil damper, and FIG. 2 shows a schematic illustration of a spin test stand with a damping unit.FIG. 1 schematically shows an embodiment of an oil damper, whereas FIG. 2 schematically indicates a spin test stand with a damping unit. The oil damper 1 comprises an inner oil chamber 2, which can be formed, for example, by a cylindrical hollow chamber. The hollow chamber can be designed in multiple parts, for example, wherein the parts can be screwed together and are correspondingly sealed. The inner oil chamber 2 has two diametrically arranged passages 3, which can be formed, for example, as bores in the wall of the inner oil chamber 2 and are preferably arranged along the central axis of the inner oil chamber 2. The passages 3 each open into a chamber 4 or a space of an outer oil chamber 5, which are connected upstream or downstream of the inner oil chamber 2. The two chambers 4 of the outer oil chamber 5 are fluidically connected to one another via a line 6 or through a hollow bore through the hollow chamber wall.The passages 3 and the inner oil chamber 2 are traversed by a piston rod 7. The piston rod 7 has a first end 8 extending into the oil damper 1 and a second end 9 protruding therefrom. The first end 8 of the piston rod 7 is arranged at a distance from the inner wall of the outer oil chamber 5, and the second end 9 of the piston rod 7 can be connected to a centrifugal shaft of a centrifugal test stand, for example. The outer wall 10 of the outer oil chamber 5, through which the second end 9 of the piston rod 7 protrudes, can be designed as a sealing element. However, it can also be advantageous for only a part of the wall 10 to be configured as a sealing element or for a bore to be provided in the wall 10 with a wave guide which is sealed with respect to the outer oil chamber.The piston rod 7 is connected to a piston 11 which extends radially from the piston rod 7 into the inner oil chamber 2, wherein the piston rod 7 is configured to act on both sides, i.e. to act double. The piston 11 can be constructed in one part or in several parts and can be fastened to the piston rod 7 for example by means of fastening means. The piston 11 can have a cylindrical shape or be designed as a disk piston or plunger, wherein in this configuration the piston rod 7 is shorter and preferably does not open into a chamber 4 of the outer oil chamber 5.The piston 11 divides the inner oil chamber 2 into two inner oil chamber parts 12 each with a passage 3 arranged therein, wherein the inner oil chamber parts 12 are fluidically connected to one another via at least one oil passage means 13. The size of the inner oil chamber portions 12 varies depending on the position of the piston 11 in the inner oil chamber 2, and the oil passage means 13 may be provided, for example, as a gap between the circumferential surface of the piston 11 and the inner surface of the inner oil chamber 2 radially spaced therefrom. However, it can also be provided that the oil passage means 13 is designed as a throttle, not shown, via which a fluidic exchange between the inner oil chamber parts 12 can take place. Furthermore, holes or apertures can be present in the piston 11, which holes or apertures likewise permit fluidic exchange between the inner oil chamber parts 12, but are not illustrated in the figures. In this embodiment, an O-ring could preferably be present as sealing means in a groove on the circumferential surface of the piston 11.In the passages 3 between the inner oil chamber 2 and the outer oil chamber 5, shaft guide elements 14 are present. Depending on the configuration of the piston rod 7, one or two shaft guide elements 14 are provided in the passages 3. Depending on the design of the piston 11, only one passage 3 can also be provided between the inner oil chamber 2 and the outer oil chamber 5, and thus only one shaft guide element 14. The shaft guide elements 14 can be designed as linear guides, in particular as linear bearings. The wave guide elements 14 or wave guides allow a linear movement of the piston rod 7 along its longitudinal axis, which in turn causes a movement of the piston 11 in the inner oil chamber 2, which results in an increase or decrease in the volume of the inner oil chamber parts 12. The shaft guide elements 14 are in particular configured leak-proof, that is to say sealing elements are deliberately dispensed with and leakage is tolerated, with the result that oil can move from the inner oil chamber 2 into the outer oil chamber 5.As can be seen well in FIG. 2, the oil damper 1 can be provided as a component of a centrifugal test stand 15 and can be fixedly installed therein. However, the oil damper 1 can also be used in any desired application if linear movements with a high frequency are to be damped. The oil damper 1, more precisely the piston rod 7, can be connected to a flexible centrifugal shaft 16 of the centrifugal test stand 15 which in turn carries a rotor 17 to be tested. The rotor 17 is accelerated beyond its operating speed. By rotating the rotor 17, an excitation movement to be damped is exerted on the centrifugal shaft 16. The excitation movement is introduced into the damper 1 via the piston rod 7, which is schematically illustrated in FIG. 2. However, it can also be advantageous if two oil dampers which are orthogonal to one another are used. By the movement of the piston rod 7, the piston 11 connected to it moves and pumps the oil present in the inner oil chamber 2 back and forth, for example, through the gap, designed as an oil passage means 13, between the two inner oil chamber parts 12. Due to the energy dissipated in the gap, a pressure difference is formed between the inner oil chamber parts 12 which acts on the piston 11 as a desired damping force and dampens the induced excitation movement.In order to achieve low spring rigidity despite high damping force, the inner oil chamber 2 is connected to the outer oil chamber 5 via the leaky wave guide members 14. As a result, oil can pass via the shaft guide elements 14 into the outer oil chamber 5, which is likewise filled with oil. Since the outer oil chamber 5 is connected to both passages 3 via the shaft guide members 14, pressure equalization takes place in the outer oil chamber 5 between both exit points, i.e., the passages 3. As a result, a nearly constant oil pressure is established in the outer oil chamber 5, which approximately corresponds to atmospheric pressure. It is provided in particular that the flow resistance arising through the shaft guide elements 14 is significantly higher than the flow resistance caused by the oil passage means, in particular the gap, so that a pressure can build up in the inner oil chamber 2 and the desired damping behavior of the oil damper is not hindered.In order to return oil from the outer oil chamber 5 into the inner oil chamber 2, a valve, in particular a check valve 18, can be provided between the outer oil chamber 5 and the inner oil chamber 2. The check valve 18 can be designed, for example, to be spring-biased or non-spring-biased. When negative pressure is generated in the inner oil chamber part 12 connected to the outer oil chamber 5 via the check valve 18 by the movement of the piston 11, oil is moved from the outer oil chamber 5 into the inner oil chamber 2.The preferred embodiments make it possible to provide an oil damper which is suitable for high-frequency continuous oscillations >200 Hz and for oscillation amplitudes >2 mm, which has a spring stiffness of <0.1 N / mm and damping values of >100 Ns / m and is additionally oil-tight.

Claims

Spin test stand (15) having an oil damper (1) with an oil-filled inner oil chamber (2) designed as a hollow chamber, an outer oil chamber (5) which is connected to the inner oil chamber (2) via at least one passage (3) and likewise comprises oil, having a piston rod (7) which projects through the passage (3) and the inner oil chamber (2) and is movable in its longitudinal direction and can be connected to a spin shaft (16) of the spin test stand (15), and having a piston (11) which is fixed to the piston rod (7) and divides the inner oil chamber (2) into two inner oil chamber parts (12), wherein a passage (3) is arranged at least in one of the inner oil chamber parts (12), wherein the inner oil chamber parts (12) are fluidically connected to one another via at least one oil passage means (13), and having at least one shaft guide element (14) which is arranged in the passage (3) and is not sealed with respect to the inner oil chamber (2) such that oil can flow from the inner oil chamber (2) into the outer oil chamber (5), wherein the outer oil chamber (5) has a sealed shaft passage for passing through the piston rod (7) in the form of a flexible sealing element, and wherein the inner oil chamber (2) and the outer oil chamber (5) are connected via a nonreturn valve (18) such that oil can flow from the outer oil chamber (5) into the inner oil chamber (2).Spin test stand (15) with an oil damper (1) according to Claim 1, characterized in that the inner oil chamber (2) is connected to the outer oil chamber (5) via two diametrically arranged passages (3), and the piston (11) divides the inner oil chamber (2) into two inner oil chamber parts (12) each having a passage (3) arranged therein.Spin test stand (15) with an oil damper (1) according to Claim 1 or 2, characterized in that the oil passage means (13) is designed as a gap between the piston (11) and the inner wall of the inner oil chamber (2).Spin test stand (15) with an oil damper (1) according to Claim 1 or 2, characterized in that the oil passage means (13) is designed as a throttle.Spin test stand (15) with an oil damper (1) according to Claim 1 or 2, characterized in that the piston (11) comprises oil passage means (13) designed as apertures.Spin test stand (15) with an oil damper (1) according to one of the preceding claims, characterized in that the wave guide element (14) or the wave guide elements (14) are designed such that the flow resistance caused by them is higher than that caused by the oil passage means (13).Spin test stand (15) with an oil damper (1) according to one of the preceding claims 5 or 6, characterized in that the shaft guide element (14) or the shaft guide elements (14) are linear bearings.Spin test stand (15) with an oil damper (1) according to Claim 2, characterized in that the outer oil chamber (5) comprises two fluidically connected and diametrically arranged chambers (4), into each of which one of the passages (3) opens.

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