Flexible foil radial bearing

Abstract

A flexible foil radial bearing (100) comprising: a bushing (110) including a bore defined thereby; spring foils (120, 130) arranged to conform to the radially inner surface of the bushing; and fluid foils (140, 150) arranged to conform to the radially inner surface of the spring foil for rotatably receiving a rotor, the radially inner surface of the bore including a plurality of axially oriented pads arranged around its circumference.

Description

Technical Field

[0001] The subject matter disclosed herein generally relates to flexible foil radial bearings.

Background Art

[0002] Microturbines can be used as distributed energy resources and can convert fuel into a local power source using a compressor, combustor, turbine, and generator. Due to their small footprint, high rotational speed, and high operating temperature, conventional bearings such as oil-based hydrostatic bearings are not practical.

[0003] A flexible fluid foil radial bearing utilizes a bushing, a flexible spring foil that conforms to the inner surface of the bushing, and a fluid top foil that conforms to the inner surfaces of the inner surface of the flexible spring foil and the fluid top foil for receiving the rotor.

[0004] Before spin-up, the gravitational force acting on the rotor compresses the fluid foil and spring foil between the rotor and the inner surface of the bushing. Following spin-up, when a thin film of fluid is created between the non-rotating fluid foil and the rotating rotor, the rotor lifts off, so to speak, from the fluid foil, resulting in a low-friction hydrodynamic bearing, and further, the movement of the fluid promotes heat transfer.

[0005] Thus, a flexible fluid foil radial bearing can be used in a microturbine to counter the impracticalities associated with other conventional forms of radial bearings, given high rotational speeds and operating temperatures.

[0006] In existing fluid foil bearing designs, generally, a wavy spring foil and a fixing mechanism are adopted between the spring foil and the bushing, which makes the manufacturing overly complex. Furthermore, the effectiveness of such existing designs at low rotational speeds per minute is quite low, and excessive bearing wear is introduced even during spin-up and normal operation after spin-up. The performance of such existing designs overly depends on the manufacturing details related to the spring foil. Finally, the scope for optimizing the friction characteristics of these existing designs is limited.

[0007] Therefore, it is desirable to provide a fluid foil bearing that solves one or more of the above-mentioned defects in existing designs.

Brief Description of the Drawings

[0008] The disclosed arrangement will be further described below with reference to the accompanying drawings by way of example.

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Best Mode for Carrying Out the Invention

[0009] FIG. 1 shows a flexible foil radial bearing 100 including a bushing (bearing cylinder) 110 including a bore (hole) passing through the bushing, spring foils 120, 130 disposed to conform to the radially inner surface of the bushing, and fluid foils 140, 150 disposed to conform to the radially inner surface of the spring foils for rotatably receiving a rotor. The surface of the bore includes a plurality of axially oriented pads 115 or ridges disposed around its circumference, by way of example.

[0010] The pads 115 can define axially oriented ridges extending in a radially inward direction. The radially inner surface of the bushing can define an alternating series of axially oriented grooves and ridges disposed around its circumference.

[0011] The pads can be formed by forming axially oriented grooves formed in the radially inner surface of the bore. Thus, the pads can be integral with the bushing. Alternatively, the pads can be formed separately from the bushing.

[0012] In the example of FIG. 1, the spring foil includes a first spring foil segment 120 and a second spring foil segment 130. Similarly, the fluid foil includes a first fluid foil segment 140 and a second fluid foil segment 150. This arrangement corresponds to a two-lobe radial bearing, but the disclosure herein is equally applicable to one, three or other lobe bearings where the spring foil and fluid foil include one, three or another number of segments.

[0013] FIG. 2 shows the bushing 110 and axially oriented pads 115 extending in a direction parallel to the axis of the bushing. The pads 115 can be coaxial with the bushing.

[0014] The pad 115 can be integrally formed with the bushing 110, simplifying manufacturing. For example, the pad can be formed by forming axially oriented grooves 118 on the inner surface of the bushing. The cross-sectional profile (shape) of the axially oriented grooves 118 can substantially define at least a part of a rectangular profile, a trapezoidal profile, or a circular profile.

[0015] Alternatively, the pad 115 can be formed separately from the bushing 110. The pad can be fixed to the bushing. The pad and the bushing can be arranged to fit with each other. For example, the pad may be provided with a retaining plug to fit into a retaining socket provided in the bushing, or vice versa. Forming the pad separately from the bushing facilitates the possibility of replacing the pad for repair purposes or for different applications, load conditions, etc.

[0016] The pads 115 can be uniformly distributed around the circumference of the bore. Alternatively, the pads 115 may be non-uniformly distributed around the circumference of the bore.

[0017] FIG. 3 shows a spring foil 120. The spring foil (thin metal sheet, metal film) 120 can be formed from sheet metal.

[0018] The spring foil 120 can be arranged to extend into the grooves between adjacent pads and provide one or more axially oriented strips or contact regions for elastically contacting the fluid foil 140.

[0019] The spring foil 120 can include one or more axially oriented strips or contact regions for contacting the fluid foil 140. Each strip for contacting the fluid foil 140 can extend into and be fixed to the groove between the pads 115 and be supported on one or both sides by an axially oriented portion of the spring foil. In this way, the contact region can provide elastic support for the fluid foil in the form of a cantilever or beam between axially oriented support regions. For example, a plurality of axially oriented strips for contacting the fluid foil 140 around the bushing can be provided. FIG. 3 shows a plurality of axially oriented strips extending into the connected grooves and axially oriented support regions, but the strips and one or both axially oriented support regions can be separated from each other.

[0020] Accordingly, the spring foil 120 can include a plurality of axially oriented strips for contacting the fluid foil, and each strip extends radially into and can be fixed to the groove between the pads 115 and is supported at one or both of its circumferential ends by an axially oriented support section.

[0021] Each pad can include a radially inner surface arranged to contact the spring foil in an axially oriented contact region spaced circumferentially. For example, the radially inner surface of each pad can be arranged such that the contact between the pad and the spring foil defines a gap therebetween. Such a gap provides space for elastic deformation of the spring foil relative to the pad.

[0022] Each pad can include a radially inner surface that includes a circumferential concave surface. In this way, the spring foil can contact each pad such that a gap exists between the radially inner surface of each pad and the spring foil. The gap can be located between axially oriented contact regions between each pad and the spring foil.

[0023] As shown in FIG. 3, the spring foil may have a twist or loop 125 formed therein. The loop 125 can be formed by bending the sheet metal, thereby forming a twist or loop in the cross-section. The loop 125 can extend in a parallel direction from one end of the sheet metal to the other end. When the spring foil is inserted into the bushing, this parallel direction can be the axial direction. The spacing between the loops 125 can correspond to the circumferential spacing between the grooves formed within the bushing 110 between the pads 115. In this way, the loop 125 can be inserted into the groove 118.

[0024] The spring foil 120 shown in FIG. 3 is considered to be significantly less burdensome to manufacture compared to the implementation of a corrugated spring foil that requires a complex manufacturing process.

[0025] The spring foil 125 can be provided with a retaining portion 128 at one or both ends thereof that is arranged to wrap around the retaining members 170, 180. This example is apparent by considering FIG. 5. The spring foil 125 includes two circumferential end regions between the end loop and the circumferential ends, and one circumferential end region can be considered to include a longer circumferential length than the other to provide the retaining portion 128.

[0026] Referring to FIG. 2, one or more grooves 118 may include a radially outer retaining socket region 175 for retaining one or more retaining members 170, 180. As shown in FIG. 5, the radially outer retaining region 175 can take the form of a bulbous socket portion within the groove 118. According to one configuration, each of the grooves 118 may include such a retaining region. This facilitates enhanced configurability since the retaining members 170, 180 can be inserted at different positions around the circumference of the bushing 110 depending on different applications, usage conditions, etc.

[0027] As shown in FIG. 4, a clearance 119 can be provided between the radially outer end of the spring foil 120 and the radially outer end of the groove 118.

[0028] Figure 4 shows a groove 118 that includes a uniform circumferential cross-sectional width. This simplifies manufacturing. However, the groove 118 can include a non-uniform circumferential cross-sectional width. The groove 118 can include a circumferential cross-sectional width that decreases in the radially inward direction. The latter facilitates holding the loop 125 within the groove 118.

[0029] The loop 125 can include a radially outer circumferential width that is larger than the radially inner circumferential width of the groove 118. This facilitates securely holding the spring foil 120 within the bushing 110.

[0030] Accordingly, the spring foil can be inserted into the bushing by sliding the loop 125 into the groove 118, and then the loop 125 is held within the groove 118.

[0031] Each pad 115 may include a radially inner surface 116 that is arranged to support the spring foil 120 between circumferentially spaced axially oriented contact regions 114 formed by contact between the radially inner surface 116 and the spring foil 120. In this way, the fluid foil 140 can be supported by axially oriented elastic strips arranged between the loops 125 of the spring foil 120.

[0032] The above-described contact configuration between the spring foil 120 and the pads 115 facilitates the establishment of a pin-pin beam provided by the spring foil 120, and the beam is supported between two axially oriented contact regions 114 that are circumferentially spaced at each pad. In this way, elasticity is provided to the portions of the spring foil adjacent to each pad, for example at the midpoint 126 of the circumferentially spaced elastic strips, to provide circumferentially spaced elastic strips that support the fluid foil.

[0033] This arrangement serves to provide a mechanism for supporting the fluid foil 120 with support regions 126 that are axially oriented and spaced circumferentially, such a support mechanism being identified as providing improved radial bearing performance characteristics.

[0034] The stiffness of the spring foil 120 can be adjusted by changing the circumferential profile (shape, outer contour) of each pad. For example, wider pads can be used to lengthen the pin - pin beam between the circumferentially spaced contact regions 114. The circumferential width of the pads and / or the spacing between the pads may be uniform or non - uniform.

[0035] The clearance 119 provided between the radially outer distal end of the loop 125 and the radially outer distal end of the groove 118 synergistically promotes the improved pin - pin beam operation as described above. In particular, the lack of contact between the distal end of the loop 125 and the distal end of the groove 118 prevents force transmission between them, which can interfere with the operation of the pin - pin beam.

[0036] Furthermore, the play between the loop 125 and the groove end helps to establish the independence between adjacent pin - pin beams. This effect can be increased by providing the loop 125 with a region that includes a circumferential width that increases in the radially outward direction.

[0037] FIG. 6 shows a further example of a flexible foil radial bearing 600. According to this example, the spring foil 630 includes a plurality of axially oriented segments 635.

[0038] Each spring foil segment 635 can at least partially cover the pad.

[0039] Each spring foil segment 635 can be arranged to extend on the surface facing radially inward of each pad in order to elastically support the fluid foil 650.

[0040] The spring foil segment 635 fits onto the pad, thereby providing an axially oriented strip that is elastic and can support the top foil. The strip can be supported at one or both ends by the pad. Thus, the strip may present a cantilever or may present a beam for supporting the top foil.

[0041] Each spring foil segment 635 can be arranged to cover the pad 615 so as to provide a gap 638 between the spring foil segment and the pad. This gap 638 facilitates the elastic radial deformation of the spring foil segment.

[0042] One or more axially oriented spring foil segments 635 can be arranged to fit around one or more of the axially oriented pads 615 of the bushing 610. The spring foil segment 635 can be substantially U-shaped as shown in FIG. 6.

[0043] Each spring foil segment 635 can include a base portion 636 for contacting the inner radial surface of the pad and one or two leg portions 637 on either side of the base portion for extending between adjacent pads. The base portion can be circumferentially aligned and / or the leg portions can be radially aligned with respect to the bore.

[0044] The spring foil segment 635 can be fixed to the pad 615. For example, the spring foil segment 635 can be fixed to the pad 615 by a friction fit or other retaining means. Each pad 615 and each spring foil segment can include side surfaces that narrow in the radially outward direction. Such an arrangement can facilitate fixing the spring foil segment 636 to the pad 615.

[0045] As shown in FIG. 7, a plurality of retaining members in the form of spring foil segment retaining pins 618 can be provided. The spring foil segment retaining pins 618 can be arranged to fit between adjacent pads, thereby fixing the spring foil segment 635 to the pads 615. For example, the spring foil segment retaining pins 618 can be arranged to fit into a retaining socket in a groove between the pads, such as a bulbous portion. The spring foil retaining pins 618 can wedge the legs of the spring foil segment 635 against the side surfaces of the pads. In this way, the spring foil can include a plurality of axially oriented radially extending legs that extend into the grooves between the pads 615 and are fixed with respect to the grooves between the pads 615, and support the fluid foil at one or both circumferential ends thereof to contact the fluid foil.

[0046] Providing a plurality of separate spring foil segments 635 that cover the pads facilitates improved independence between circumferentially adjacent portions of the spring foil that cover adjacent pads, thereby facilitating improved elastic properties.

[0047] As shown in FIGS. 6 and 7, the fluid foil 650 is provided in the form of two fluid foil segments, and the spring foil 630 is provided in the form of a plurality of spring foil segments 635. In this way, more spring foil segments 635 can be provided than fluid foil segments 650.

[0048] The fluid foil 650 can be supported by a plurality of spring foil segments 635 that are uniformly or non-uniformly distributed around the circumference of the bore.

[0049] Each spring foil segment 635 can be arranged to contact each axially oriented side surface of the pad covered by the spring foil segment 635.

[0050] The fluid foil 650 can be held by retaining pins 619 arranged to fit between adjacent pads that wedge the fluid foil against a first side of the fluid foil retaining pads of the plurality of pads 615. A spring foil segment 635 arranged to cover the fluid foil retaining pads can be arranged to contact only a second side of the fluid foil retaining pads. Thus, the fluid foil retaining pads can be circumferentially sandwiched between an axially oriented spring foil segment 635 that contacts one side of the fluid foil retaining pads and an axially oriented portion of the top foil that contacts the opposite side of the fluid foil retaining pads.

[0051] A substantially U-shaped spring foil segment 635 arranged to contact both side surfaces of the pad and / or a substantially right-angled spring foil segment 635 arranged to contact one surface of the pad can be provided.

[0052] As shown in FIGS. 6 and 7, the fluid foil retaining pads may be wider than the remaining pads.

[0053] As shown in FIGS. 6 and 7, one or more pads 615 adjacent to one or more retaining pins 619 may have an increased width compared to the width of the remaining pads.

[0054] Next, a method 800 for manufacturing a flexible foil radial bearing will be described in connection with FIG. 8.

[0055] The method 800 can include one or more of: forming 810 a bushing having an axially oriented groove running through its radially inner surface; forming 830 a spring foil from a sheet metal having parallel arranged loops running therethrough; and inserting 850 the spring foil and optionally a fluid foil into the bushing.

[0056] After providing the bushing 110, in step 801, axially oriented grooves 118 can be formed in the radially inner surface of the bushing 110. The grooves 118 can be formed in the bushing 110 by using electrical discharge machining (EDMing), for example, wire electrical discharge machining (WEDMing). This process simplifies manufacturing, improves consistency, and allows for finer control of the groove shape. The grooves may have a cross-sectional profile that at least partially defines a rectangular, trapezoidal, or circular cross-section.

[0057] Although not shown, a retaining region 175 for retaining retaining members 170, 180, which can be pins, can be formed in one or more, or each, of the grooves 118.

[0058] In step 831, the sheet metal can be deformed to provide raised regions that are arranged in parallel, which can define a loop in cross-section. The spring foil 120 can be formed by forming loops 125 having a separation therebetween that corresponds to the circumferential spacing between the grooves 118 formed in the bushing 110. The spacing between the grooves and the loops may be uniform or non-uniform. Uniform spacing facilitates simplified manufacturing, while non-uniform spacing improves adaptation to the gravity acting on the rotor during operation. For example, the spacing in the region of the spring foil and the bushing under the rotor can be decreased to provide a greater contact density at the base of the rotor.

[0059] In steps 851 and 852, the spring foil 120 and the fluid foil 140 can be inserted into the bushing. In the case of step 851, the loops 125 formed in the spring foil 120 can be slid into the grooves 118, which can be formed with a circumferential width at a radially inner proximal end that is smaller than the circumferential width of the loops 125.

[0060] FIG. 9 shows a further method 900 for manufacturing a flexible foil radial bearing.

[0061] Method 900 may include one or more of forming 901 a bushing having axially oriented grooves running through its radially inner surface, forming 931 a strip from a sheet metal having one or two sides arranged to extend within the grooves, where each strip may be formed to include a region arranged to extend within the grooves and a region arranged to extend over one or more pads formed between the grooves, inserting 951 a spring foil segment into the bushing, and inserting 952 a fluid foil into the bushing.

[0062] According to step 930, the strip may be formed from a sheet metal, thereby providing a spring foil segment 635 arranged to at least partially cover the pads 615 of the bushing formed between the grooves. The strip may include one or more bends for axially orienting. The bends may be aligned with axially oriented bends of the pads formed at the radially inner portion of the grooves. The bends of the pads may be regions of the pads that cross in cross-section the grooves having the radially inner surface of the pads. The spring foil segment may cover one or both of the axially oriented bends of the pads.

[0063] Each of the examples disclosed herein, including the claimed examples, may be provided in a gas turbine system, such as a microturbine system, including a fluid foil radial bearing according to any one example. Employing such a fluid foil radial bearing in a gas turbine system provides a gas turbine system with improved friction loss and heat management.

[0064] It will be recognized that the examples disclosed herein are not limiting and that numerous changes and substitutions are possible.

Claims

Claim 1 A bushing, comprising a bushing including a bore therethrough, a spring foil disposed to conform to the radially inner surface of the bore, the spring foil including first and second spring foil segments spaced circumferentially apart, a fluid foil disposed to conform to the radially inner surface of the spring foil for rotatably receiving a rotor, one or more axially oriented fluid foil retaining pins, wherein the radially inner surface of the bore includes a plurality of axially oriented pads disposed about its circumference, each fluid foil retaining pin being disposed to fit between adjacent pads to secure the fluid foil to the bushing, the spring foil including a plurality of axially oriented loops disposed to fit within axially extending grooves formed between adjacent pads, a flexible foil radial bearing, wherein each of the plurality of axially oriented loops is received within one of the axially extending grooves such that the spacing between adjacent axially oriented loops matches the circumferential spacing between adjacent axially extending grooves. Claim 2 The flexible foil radial bearing according to claim 1, wherein the loops and the grooves are arranged to define a clearance between the radially outer portion of the loops and the radially outer portion of the grooves. Claim 3 The flexible foil radial bearing according to claim 1 or 2, wherein the circumferential width of each groove decreases radially inwardly. Claim 4 The flexible foil radial bearing according to any one of claims 1 to 3, wherein each pad includes a radially inner surface disposed between axially oriented contact regions spaced circumferentially apart formed by contact with the spring foil. Claim 5 Comprising one or more axially oriented fluid foil retaining pins, The flexible foil radial bearing according to claim 1, wherein each fluid foil retaining pin is disposed to fit between adjacent pads to secure the fluid foil to the bushing. Claim 6 The flexible foil radial bearing according to claim 1, wherein the one or more fluid foil retaining pins are disposed to fit within a radially outer retaining region of an axially oriented groove formed between adjacent pads.

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