Gas bearing and method for producing same

The invention relates to a gas bearing for contactlessly bearing a rotatable element (50). The gas bearing comprises: a housing (100) having an opening for receiving the rotatable element; and at least two sliding films (200), which are arranged on an interior (110) of the opening without overlap and which each have a first end portion (210) and a second end portion (220) for support on the housing (100). The sliding films (200) are designed to radially support the rotatable element relative to the housing (100) only by means of the first and second end portions (210, 220), the second end portion (220) providing frictional contact with the interior (110) and the first end portion (210) being fastened to the housing.

The present invention relates to a gas bearing (in particular an air bearing) and a method for manufacturing the gas bearing and, in particular, to an aerodynamic rotor bearing arrangement by means of (prestressed) sliding foils.

BACKGROUND

Air bearings, or gas bearings in general, are used for high-speed rotors (up to 180,000 revolutions per minute) to minimize friction. A bearing arrangement for such high speeds is only possible via air bearings, wherein the co-turning air forms a cushion on which the rotors are held.

FIGS.5A and5Bshow conventional air bearings comprising a housing510, a rotor520, at least one so-called top foil530and at least one bump foil540. For example, the top foil530may be formed as a single element as shown inFIG.5A. It is also possible for the top foil530to comprise multiple top foils, such as those shown inFIG.5B, which are then arranged adjacent to each other (along the angular movement of the rotor520). For example, the top foil(s)530may be attached to the housing510via fastening elements532, and the opposite section is free-floating between the rotor510and the bump foil540. The bump foils540serve to cushion the rotor520for radial impacts. Thus, they are used as shock absorbers or bumpers to keep the rotor520as centered as possible in the opening of the housing510.

When the rotor520rotates at very high speeds (several 10,000 rpm), the entrained air causes an air gap or air cushion to form between the rotor520and the top foil530, so that the rotor520is held floating in a centered position. Rotation of the rotor520thus causes the rotor520to lift off the top foil530, thereby significantly reducing frictional resistance, after which only air friction is present. The top foil(s)520and the bump foil(s)540serve as a support for a non-rotating rotor520or, as mentioned, as a damper when unexpected radial impacts occur.

A disadvantage of these conventional air bearing arrangements is that they are complex to manufacture and assemble and therefore require additional costs. In addition, these air bearing arrangements exhibit poor predictability due to the presence of many contact pairs for the components that are not precisely defined or are difficult to define.

Thus, there is a need for other solutions that are simpler and less expensive to manufacture, but still provide support comparable to that provided by conventional air bearings.

SUMMARY OF THE INVENTION

At least a part of these problems is solved by an air bearing according to claim1and a method of manufacture according to claim10. The dependent claims relate to advantageous further embodiments of the objects of the independent claims.

Embodiments relate to a gas bearing for supporting a rotatable element in a contact-free manner. The gas bearing comprises a housing with an opening for receiving the rotatable element and at least two sliding foils. The sliding foils are arranged without overlap on an inner side of the opening and each have a first end portion and a second end portion for support on the housing. The sliding foils are configured to radially support the rotatable element relative to the housing only through the first and second end portions, wherein the second end portion provides frictional contact with the inner side and the first end portion is secured to the housing.

In the context of the present invention, the term “rotatable element” is intended to be broadly construed to comprise, in particular, a rotor, a shaft, a journal, or any other rotating element. Radial impacts of the rotatable element are defined in such a way that an externally acting force or vibrations cause a force to act perpendicular to the axis of rotation the rotatable element (i.e. perpendicular to the axial axis of the rotatable element). The rotatable element can be at least partially supported against such radial impacts by each sliding foil. A gas bearing is in particular intended to mean an air bearing, even though the invention is not intended to be limited to air and may include other gaseous media.

The directions are defined as follows: The axial direction is parallel to the axis of rotation of the rotatable element, and the radial direction points radially away from the axis of rotation in the cross-sectional view perpendicular to the axis of rotation. The tangential direction is perpendicular to the axial direction and the radial direction.

The sliding foils are arranged one after another along the tangential direction between the rotatable element and the housing, wherein they can abut against each other. The end portions thus represent the regions at the two edges in the tangential direction, the second end portion being movable relative to the housing when the frictional force is overcome.

Although the operating principle of the air bearing is already possible with two sliding foils, it is particularly advantageous to have more than two sliding foils. For example, centering of the rotatable element is achieved by three or four sliding foils. However, the number of sliding foils should not be limited. For example, the rotatable element may be held by the sliding foils in an area between the end portions.

Optionally, at least one of the sliding foils is formed multilayered, wherein the individual layers are attached to the housing on the same side or on opposite sides. The individual layers can thus bend together or hold each other during radial impacts of the rotatable element.

Embodiments also relate to an air bearing for supporting a rotatable element in a contact-free manner, having a housing with an opening for receiving the rotatable element and a plurality of multilayered sliding foils. In this embodiment, each multilayered sliding foil is arranged without overlap with an adjacent multilayered sliding foil on an inner side of the opening, wherein the individual layers of the multilayered sliding foils are all attached to the housing by a first end portion and the opposite second end portion makes frictional contact with another layer of the multilayered sliding foil or with the housing. In addition, along a surface facing the rotatable element, each layer of the multilayered sliding foils forms a segment of a circle or a circular segment or an arc in a radial section.

In particular, the plurality of multilayered sliding foils can be arranged one on top of the other, wherein a maximum support force relative to the housing is to be applied by the first and second end portions (since no further supports are provided centrally).

To achieve the most effective support, a friction coefficient (coefficient of friction) of the frictional contact can be increased by at least one of the following features:Coating the second end portion and/or the inner side of the opening with a material that increases the coefficient of friction;the second end portion and/or the inner side of the opening has an increased roughness;the second end portion has a contour to increase friction to the inner side of the opening;the second end portion is angled in a radial cross-sectional view (along the tangential direction) to form an increased contact angle for frictional contact relative to the inner side of the opening.

The specific contours at the end of the sliding foils may comprise, for example, curves, slits, corners, teeth, tips, etc.

It is also possible that the opening in the housing deviates from a circular shape in order to increase the contact angle to the inner side compared to the circular shape.

An increased contact angle has the effect that the vertical component of the force (acting perpendicularly on the housing or the inner side) also increases, which in turn leads to a higher frictional force and friction work.

Optionally, to increase the stiffness of at least one sliding foil, a thickness of the at least one sliding foil (or layer) may vary between the first end portion and the second end portion. This increases the supporting effect for radially acting forces.

Optionally, the attachment of the first end portion to the housing comprises at least one of the following connections: a soldered connection, a welded connection, an adhesive connection, an at least partial insertion of the first end portion into a recess of the housing.

Embodiments also relate to a rotor suspension having an air bearing as previously described and a rotatable element insertable into the opening of the housing, such that the sliding foils are disposed between the rotatable element and the housing to support forces acting radially on the rotatable element relative to the housing and to form an air cushion with increasing rotational speeds.

Optionally, the at least two sliding foils are exchangeable to select the at least two sliding foils with respect to their stiffness and depending on the rotatable element and the expected radial impacts. This selection is intended to ensure that the rotatable element is reliably held centrally in the opening of the housing and, at the same time, that an air gap is created between the at least two sliding foils and the rotatable element during the rotational movement (at a desired speed). The exchangeable sliding foils can be inserted in grooves or recesses in the housing, for example.

Embodiments also relate to a method of manufacturing an air bearing for supporting a rotatable element in a contact-free manner. The method comprises:providing a housing having an opening for receiving a rotatable element;arranging at least two sliding foils extending in an arc-shaped manner single- or multilayered between a first end portion and a second end portion on an inner side of the opening without overlapping adjacent sliding foils, wherein relative to the housing the first end portion is tangentially immovable and the second end portion provides a frictional contact with the housing or other layer of a multi-layered sliding foil; andinserting the rotatable element into the opening so that the at least two sliding foils are disposed between the rotatable element and the housing.

In turn, the rotatable element only needs to be radially supported relative to the housing via the first end portion and the second end portion.

The bending of the sliding foils and the optimized geometry of the housing mean that the angle of impact of the sliding foils on the inner side is increased and thus the force acting perpendicularly on the inner side is intensified. This can increase the frictional force and thus the supporting force. It can also be used to adjust the friction path.

Optionally, arranging the sliding foils includes fixedly attaching the sliding foils to the housing or forming a releasable connection to the housing.

According to further embodiments, the sliding foils are arranged under a prestress between the rotatable element and the housing. It is also possible to adjust the support force of the air bearing via the selected prestress.

It is also possible that the stiffness or prestress of the individual sliding foils is not selected homogeneously to be the same for all sliding foils, but that, for example, a higher stiffness is provided in a foil (or certain layers of multilayered sliding foils) located vertically at the bottom. This can be useful, for example, if certain radial impacts or radial forces are to be expected in a particular direction, so that the sliding foils have a particularly high stiffness in this direction. Optionally, however, it is also possible for all the sliding foils to be of identical design and only to be arranged at different angular regions within the opening.

DETAILED DESCRIPTION

FIG.1shows an air bearing for supporting a rotatable element (in particular a high-speed rotor) in a contact-free manner according to an embodiment of the present invention. The air bearing comprises a housing100having an opening for receiving the rotatable element50and at least two sliding foils200(preferably three or four) arranged without overlap in a tangential direction on an inner side110of the opening. The sliding foils200are arc-shaped (not wave-shaped) and each comprise a first end portion210and a second end portion220for support on the housing100. The sliding foils200are configured to radially support the rotatable element50relative to the housing100only through the first end portion210and the second end portion220, wherein the rotatable element50contacts the sliding foil200, for example, between the first end portion210and the second end portion220.

The second end portion220provides frictional contact with the inner surface110of the opening and is thus movable relative to the housing. The first end portion210may be fixedly attached to the housing100, or in positive contact with the housing100(e.g., engaging a groove or recess in the housing, seeFIGS.4A and4Bbelow; more complex attachments, e.g., L-shaped or T-shaped, are also conceivable, seeFIGS.4C and4Dbelow), such that relative movement along the inner surface110is not possible.

It will be appreciated that as long as the rotatable element50is not yet rotating relative to the housing100, the rotatable element50is in contact with at least one (or all) of the sliding foils200. However, as the rotational speed50increases, air is entrained between the sliding foils200and the rotatable element50, forcing the sliding foils200away from the rotatable element50and creating an air cushion between the sliding foils200and the rotatable element50. The adhesion of the air to the rotatable element50thus creates an air film or air cushion at very high speeds so that the rotatable element50lifts off the sliding foils200. Typically, this effect only occurs at several 10,000 rpm or more than 100,000 rpm. These air bearings can be used, for example, for rotations of up to 200,000 rpm.

In order to provide reliable damping protection for impacts or radial movements of the rotatable element, the properties of the sliding foils200, such as a prestress or geometries or the coupling to the housing100, are important and must be set according to the application.

In the following, various measures are described that can be implemented in embodiments to achieve the desired damping protection.

FIGS.2A to2Dshow embodiments of the present invention that achieve a desired stability against radial impacts of the rotatable element50relative to the housing100by adjusting the frictional contact. For example, a high coefficient of friction between the sliding foil200and the housing100means that the sliding foils200are better able to dampen radial impacts, as higher friction makes it difficult for the sliding foils200to move relative to the housing100.

InFIG.2A, an embodiment is shown in which the second end portion220has, for example, a coating221that has the effect of increasing the coefficient of friction with respect to the housing100. Similarly, it is possible for the inner side110of the housing to have a coating111that increases the coefficient of friction between the sliding foil200and the housing100. The two coatings221,111may also be matched to each other so as to achieve the highest possible friction or matched. The same effect can be achieved if an increased roughness of the surface is formed in the area of the coatings111,221.

FIG.2Bshows an embodiment of the sliding foils200in which the second end portions220have a surface structure/contour222adapted to increase friction between the sliding foil200and the inner side110. For example, the surface structure222may include wave-shaped sections, indentations, tooth-like protrusions, or other structures that result in an increase in friction. It is also possible for the sliding foil200to be suitably thin, so that a sharp edge is formed at the end, resulting in high contact pressure and thus high friction.

FIG.2Cshows an embodiment of the present invention in which the second end portion220is angled relative to the remaining portion of the sliding foil200. This results in the end of the sliding foil200forming a larger contact angle α with the inner side110. The greater the contact angle α, the greater the force component acting perpendicularly on the inner side110during a radial impact. The contact angle can also be used to set the friction path. The vertical force component is relevant for the frictional force, so that the frictional force can be adjusted via an adapted chamfer of the second end portion220.

FIG.2Dshows another embodiment of the air bearing in which the opening in the housing100is not circular—even though the rotatable element50still has a circular cross-section. According to this embodiment, the opening in the housing100is changed such that the intersection angle α between the second end portion220and the inner side110becomes larger or is adjusted to a desired value in order to change, in particular increase, the frictional force (or the force component essential thereto) or the frictional path compared to a circular opening.

Thus, the embodiments ofFIGS.2A to2Dcan be used to adjust (especially increase) the coefficient of friction.

FIGS.3A to3Cshow further exemplary embodiments of the sliding foils200,300used, which can also be used to better cushion radial impacts.

For this purpose, the exemplary embodiment ofFIG.3Auses sliding foils300having a plurality of layers, wherein all layers of the sliding foil300are arranged on top of each other and are fixed to the housing100on the same side, as an example, i.e., the first end portions310of the layers are all located on the same side along the tangential direction.

InFIG.3B, an exemplary embodiment is shown in which at least one of the sliding foils300has multiple layers, wherein the individual layers are fixedly connected here to the housing100on opposite sides. Two layers are shown as an example. However, there can also be more than two layers, which are attached to the housing arbitrarily (e.g. alternately) on one side or the other (with respect to the tangential direction). The friction between the layers can in turn be adjusted via coating and/or a surface roughness.

FIG.3Cshows an exemplary embodiment of the present invention in which at least one sliding foil200,300(singlelayered or multilayered) has a variable thickness so as to better cushion the radial impacts of the rotatable element50without the sliding foil200,300coming into contact with the inner side110in a region between the end portions.

Only one sliding foil200,300was shown here at a time. The other sliding foils were omitted for simplicity. They can be formed in a similar way. Combinations of the different sliding foils200,300are also possible.

Furthermore, in these exemplary embodiments, the first end portions210,310may be connected to the housing100by, for example, a welded contact, an adhesive contact, a soldered contact. It is also possible to slide the first end portions210,310into corresponding grooves in the housing or to use rivet or screw connections as fasteners.

FIGS.4A to4Dshow embodiments for attaching the first end portion210,310of the single- or multilayered sliding foils200,300to the housing100. In the exemplary embodiments shown, the first end portions210,310of the sliding foils200,300engage corresponding recesses, grooves, or indentations of the housing100to provide a firm hold of the sliding foils200,300(or layers thereof) to the housing.

Here, there are various ways to form the recess in the housing100. For example, it is possible for a circular recess to be formed as shown inFIG.4A. Optionally, a square or quadrangular shape can also be selected, as shown inFIG.4B.FIG.4Cshows an embodiment with an L-shaped engagement, andFIG.4Dshows an example of a T-shaped engagement with the housing100. For both exemplary embodiments, the sliding foil200,300can be inserted into the recess in the axial direction. After insertion, the sliding foil200,300can be fixed accordingly (e.g. via a locking device). These recesses offer the advantage that the sliding foils200,300can be easily exchanged, so that the sliding foils200,300can be specifically selected according to the requirements.

Advantages of exemplary embodiments of the present invention can be summarized as follows:Bump foils, as used in conventional air bearings, can be omitted. Instead, single- or multilayered films200,300are used. This makes production easier and saves costs.The bearing function is provided solely by a modified sliding foil200,300, wherein the modification is achieved by effectively increasing the rigidity of the foils.Similarly, the foils200,300may be prestressed and thus pressed into the corresponding opening of the housing. This allows larger radial impacts to be absorbed.Damping of radial movements can be achieved by adjusting the friction between the foil200,300and the housing100.A defined interaction of the individual components results in better predictability.

The features of the invention disclosed in the description, the claims and the figures may be essential for implementing the invention both individually and also in any combination.

LIST OF REFERENCE NUMERALS

50,520rotatable element/rotor100housing with opening110inner side of the opening111,221coatings200,300sliding foils (singlelayered or multilayered)210,310first end portion of the sliding foils or of their layers220,320second end portion of the sliding foils or of their layers222edge contours of the end portions510conventional housing530conventional top foils540conventional bump foils532foil attachmentα angle of impact of the second end portion on the housing