Patent Publication Number: US-2023160392-A1

Title: Airfoil jounal bearing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/KR2022/014782 designating the United States, filed on Sep. 30, 2022, in the Korean Intellectual Property Receiving Office and claiming priority to Korean Patent Application No. 10-2021-0162428, filed on Nov. 23, 2021, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     The disclosure relates to an airfoil journal bearing. 
     2. Description of Related Art 
     A bearing may fix a rotation shaft in a predetermined position and rotate the rotation shaft while supporting a load generated by rotation of the rotation shaft. There are various types of bearings, such as a ball bearing, a journal bearing, a foil bearing, and the like. An airfoil journal bearing may support a load in a radial direction perpendicular to an axis direction of the rotation shaft. 
     SUMMARY 
     According to an example embodiment of the present disclosure, an airfoil journal bearing may include a bearing housing having an inner surface forming a hollow through the bearing housing so that a rotation shaft is insertable in the hollow and so that, when the rotation shaft is inserted in the hollow, an axial direction of the airfoil journal bearing is the same as a longitudinal direction of the rotation shaft and the hollow longitudinally extends in the axial direction; an airfoil in the hollow and extending in a circumferential direction of the hollow so that, when the rotation shaft is inserted in the hollow, the airfoil encloses at least 180 to 360 degrees of a circumference of the rotation shaft, and a ring member that is annular and is connected to the bearing housing, and enclosing an outer surface of the bearing housing in a circumferential direction of the bearing housing. The bearing housing may include, based on a cross-section perpendicular to the axial direction, an insert slit formed through the bearing housing in a radial direction of the bearing housing from the inner surface of the bearing housing forming the hollow to the outer surface of the bearing housing. The airfoil may include, based on a cross-section perpendicular to the axial direction, an insert part bent from a circumferential direction of the airfoil to the radial direction of the bearing housing and extending, through the insert slit, to the outer surface of the bearing housing. The airfoil may be engaged with an outer surface of the ring member through the insert part. 
     According to an example embodiment of the present disclosure, the airfoil may including an engagement part formed at an edge of the insert part extending to the outer surface of the bearing housing and being concave so that at least some of the outer surface of the ring member is inserted into the engagement part. 
     According to an example embodiment of the present disclosure, a plurality of ring members may be connected to the outer surface of the bearing housing, and a plurality of the engagement parts may be at the edge of the insert part, wherein the plurality of engagement parts may be respectively connected to the plurality of ring members. 
     According to an example embodiments of the present disclosure, the insert slit may be in the axial direction, and the ring members may be spaced apart from one another in the axial direction. 
     According to an example embodiments of the present disclosure, the bearing housing may include a seating groove formed in the outer surface of the bearing housing in the circumferential direction of the bearing housing and where the ring member sits. 
     According to an example embodiments of the present disclosure, the airfoil may include a first foil extending along the inner surface of the bearing housing forming the hollow in the circumferential direction of the hollow, and a second foil extending along the inner surface of the bearing housing forming the hollow from the first foil in the circumferential direction of the hollow and including a plurality of elastic bumps having an uneven shape in the circumferential direction of the hollow. The first foil and the second foil may be formed integrally as one body, and, based on a cross-section perpendicular to the axial direction, the second foil may enclose at least some of the first foil, and the insert part may be connected to an edge of the second foil extending in the circumferential direction of the hollow. 
     According to an example embodiments of the present disclosure, based on a cross-section perpendicular to the axial direction, the first foil may enclose at least 360 degrees of the circumference of the rotation shaft when the rotation shaft is inserted in the hollow. 
     According to an example embodiments of the present disclosure, based on a cross-section perpendicular to the axial direction, the second foil may enclose at least 180 to 360 degrees of the circumference of the rotation shaft when the rotation shaft is inserted in the hollow. 
     According to an example embodiments of the present disclosure, based on a cross-section perpendicular to the axial direction, a second insert part bent in a radial direction of the bearing housing may be at an edge of the first foil, a first through hole and a second through hole may be respectively formed through the first foil and the second foil in a radial direction of the bearing housing, and the second insert part may be inserted, through the first through hole and the second through hole, into the insert slit. 
     According to an example embodiments of the present disclosure, the airfoil may include a first foil extending along the circumferential direction of the hollow and enclosing at least 180 to 360 degrees of the circumference of the rotation shaft when the rotation shaft is inserted in the hollow, and a pair of second foils respectively connected to opposite edges of the first foil parallel to the axial direction, extending in the circumferential direction of the hollow and enclosing at least 180 to 360 degrees of the circumference of the rotation shaft when the rotation shaft is inserted in the hollow, and including a plurality of elastic bumps having an uneven shape in the circumferential direction of the hollow. The first foil and the pair of second foils may be formed integrally as one body. 
     According to an example embodiments of the present disclosure, based on a cross-section perpendicular to the axial direction, the airfoil may enclose at least 360 degrees of the circumference of the rotation shaft when the rotation shaft is inserted in the hollow. 
     According to an example embodiments of the present disclosure, the plurality of elastic bumps may protrudes toward the inner surface of the bearing housing. 
     According to an example embodiments of the present disclosure, based on a cross-section perpendicular to the axial direction, the insert slit may include a first insert slit and a second insert slit through the bearing housing in different radial directions of the bearing housing, and the insert part may include a first insert part and a second insert part respectively at opposite edges of the airfoil in a circumferential direction of the airfoil. The first insert part may be engaged with a first part of the ring member through the first insert slit, and the second insert part may be engaged with a second part of the ring member through the second insert slit. 
     According to an example embodiments of the present disclosure, the airfoil may include a top foil in the hollow and that, when the rotation shaft is inserted in the hollow, encloses a range of at least 180 to 360 degrees of the circumference of the rotation shaft; a first bump foil in the hollow, enclosing a first part of the top foil in a circumferential direction of the hollow and including a plurality of elastic bumps having an uneven shape in the circumferential direction of the hollow; and a second bump foil in the hollow, enclosing, in the circumferential direction of the hollow, a second part of the top foil spaced, in the axial direction, apart from the first part of the top foil and including a plurality of elastic bumps having an uneven shape in the circumferential direction of the hollow. The insert part may be at each edge of the top foil, the first bump foil, and the second bump foil. 
     According to an example embodiments of the present disclosure, to an outer surface of the bearing housing, three ring members may be connected, wherein the ring members may be spaced, in the axial direction, apart from one another, and may be respectively engaged with the insert parts of the top foil, the first bump foil and the second bump foil. 
     According to an example embodiments of the present disclosure, an airfoil journal bearing may include a bearing housing having an inner surface forming a hollow through the bearing housing so that a rotation shaft is insertable in the hollow and so that, when the rotation shaft is inserted in the hollow, an axial direction of the airfoil journal bearing is the same as a longitudinal direction of the rotation shaft and the hollow longitudinally extends in the axial direction; an airfoil in the hollow and extending in a circumferential direction of the hollow so that, when the rotation shaft is inserted in the hollow, the airfoil encloses at least 180 to 360 degrees of a circumference of the rotation shaft and the airfoil receives pressure generated by rotation of the rotation shaft; and a ring member connected to the bearing housing and enclosing an outer surface of the bearing housing in a circumferential direction of the bearing housing, and configured to fix a position of the airfoil in the axial direction. The bearing housing, based on a cross-section perpendicular to the axial direction, may include an insert slit formed through the bearing housing from the inner surface of the bearing housing forming the hollow to the outer surface of the bearing housing. At least some of the airfoil may pass through the insert slit and is engaged with the ring member. 
     According to an example embodiments of the present disclosure, the airfoil may include, based on a cross-section perpendicular to the axial direction, an insert part, of which an edge toward the circumferential direction of the hollow is bent toward a radial direction of the bearing housing, extending through the insert slit to the outer surface of the bearing housing. The insert part may include an engagement part into which at least some of an outer surface of the ring member is inserted. 
     According to an example embodiments of the present disclosure, the insert slit may extend in the axial direction, ring members may be spaced apart from one another and connected to the outer surface of the bearing housing, and the insert part may include engagement parts respectively engaged with the ring members. 
     According to an example embodiments of the present disclosure, a seating groove may be concavely formed in a circumferential direction of the bearing housing in the outer surface of the bearing housing so that the ring member is seated in the seating groove. 
     According to an example embodiments of the present disclosure, a mechanical device may include a motor housing; a motor inside the motor housing and including a rotation shaft; an impeller connected to the rotation shaft, an airfoil journal bearing rotatably supporting the rotation shaft, and a bearing seating part connected to the motor housing and including a seating space in which the airfoil journal bearing is seated. The airfoil journal bearing may include a bearing housing having an inner surface forming a hollow through the bearing housing into which the rotation shaft is inserted, an airfoil in the hollow, extending in a circumferential direction of the rotation shaft, and enclosing at least 180 to 360 degrees of a circumference of the rotation shaft, and receiving pressure generated by rotation of the rotation shaft, and a ring member connected to the bearing housing and enclosing an outer surface of the bearing housing in a circumferential direction of the bearing housing. The bearing housing, based on a cross-section perpendicular to an axial direction of the rotation shaft, may include an insert slit formed in a radial direction of the bearing housing through the bearing housing from the inner surface of the bearing housing forming the hollow to the outer surface of the bearing housing. The airfoil may include an insert part bent from an edge of the airfoil in the circumferential direction of the rotation shaft and extending through the insert slit to the outer surface of the bearing housing. An outer surface of the ring member may be engaged with the insert part and configured to fix a position of the airfoil in an axial direction of the airfoil. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a perspective view illustrating a mechanical device according to an example embodiment; 
         FIG.  2 A  is a perspective view illustrating a motor assembly according to an example embodiment; 
         FIG.  2 B  is an exploded perspective view illustrating the motor assembly according to an example embodiment; 
         FIG.  2 C  is a cross-sectional view illustrating the motor assembly according to an example embodiment; 
         FIG.  3 A  is a perspective view illustrating an airfoil journal bearing according to an example embodiment; 
         FIG.  3 B  is an exploded perspective view illustrating the airfoil journal bearing according to an example embodiment; 
         FIG.  3 C  is a cross-sectional perspective view illustrating an airfoil journal bearing according to an example embodiment; 
         FIG.  3 D  is a cross-sectional view illustrating the airfoil journal bearing viewed in an axial direction, according to an example embodiment; 
         FIG.  3 E  is a cross-sectional view illustrating the airfoil journal bearing viewed in an axial direction, according to another example embodiment; 
         FIG.  4 A  is an exploded perspective view illustrating an airfoil journal bearing according to another example embodiment; 
         FIG.  4 B  is a diagram illustrating a ring member arrangement region of the airfoil journal bearing viewed in an axial direction, according to an example embodiment; 
         FIG.  4 C  is a diagram illustrating a ring member arrangement region of the airfoil journal bearing viewed in an axial direction, according to another example embodiment; 
         FIG.  5 A  is a perspective view illustrating an airfoil journal bearing according to another example embodiment; 
         FIG.  5 B  is an exploded perspective view illustrating the airfoil journal bearing according to another example embodiment; 
         FIG.  6 A  is a perspective view illustrating an airfoil journal bearing according to another example embodiment; 
         FIG.  6 B  is an exploded perspective view illustrating the airfoil journal bearing according to another example embodiment; 
         FIG.  7 A  is an exploded perspective view illustrating an airfoil journal bearing according to another example embodiment; and 
         FIG.  7 B  is a diagram illustrating a ring member arrangement region of the airfoil journal bearing viewed in an axial direction, according to another example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, example embodiments will be described in detail with reference to the accompanying drawings. When describing the example embodiments with reference to the accompanying drawings, like reference numerals refer to like elements and a repeated description related thereto will be omitted. 
     Various example embodiments of the present disclosure are provided as examples to assist better understanding of technological features described herein. It should be appreciated that various example embodiments of the present disclosure and the terms used therein are not intended to limit the technological features set forth herein to particular example embodiments and include various changes, equivalents, or replacements for a corresponding example embodiment. In connection with the description of the drawings, like reference numerals may be used for similar or related components. It is to be understood that a singular form of a noun corresponding to an item may include one or more of the things unless the relevant context clearly indicates otherwise. As used herein, “A or B”, “at least one of A and B”, “at least one of A or B”, “A, B or C”, “at least one of A, B and C”, and “A, B, or C,” each of which may include any one of the items listed together in the corresponding one of the phrases, or all possible combinations thereof. Terms such as “first”, “second”, or “first” or “second” may simply be used to distinguish the component from other components in question and may refer to components in other aspects (e.g., importance or order) is not limited. It is to be understood that if an element (e.g., a first element) is referred to, with or without the term “operatively” or “communicatively”, as “coupled with,” “coupled to,” “connected with,” or “connected to” another element (e.g., a second element), it means that the element may be coupled with the other element directly (e.g., wired), wirelessly, or via a third element. 
     As used in connection with various example embodiments of the disclosure, the term “module” may include a unit implemented in hardware, software, or firmware, and may interchangeably be used with other terms, for example, “logic,” “logic block,” “part,” or “circuitry”. A module may be a single integral component, or a minimum unit or part thereof, adapted to perform one or more functions. For example, according to an example embodiment, the module may be implemented in a form of an application-specific integrated circuit (ASIC). 
     Various example embodiments as set forth herein may be implemented as a machine. For example, the machine (e.g., a processor of a mechanical device) may invoke at least one of the one or more instructions stored in the storage medium and execute it. This allows the machine to be operated to perform at least one function according to the at least one instruction invoked. The one or more instructions may include code generated by a compiler or code executable by an interpreter. The machine-readable storage medium may be provided in the form of a non-transitory storage medium. Here, the term “non-transitory” simply means that the storage medium is a tangible device, and does not include a signal (e.g., an electromagnetic wave), but this term does not differentiate between where data is semi-permanently stored in the storage medium and where the data is temporarily stored in the storage medium. 
     According to various example embodiments, each component (e.g., a module or a program) of the above-described components may include a single entity or multiple entities, and some of the multiple entities may be separately disposed in different components. According to various example embodiments, one or more of the above-described components may be omitted, or one or more other components may be added. Alternatively or additionally, a plurality of components (e.g., modules or programs) may be integrated into a single component. In such a case, according to various example embodiments, the integrated component may still perform one or more functions of each of the plurality of components in the same or similar manner as they are performed by a corresponding one among the plurality of components before the integration. According to various example embodiments, operations performed by the module, the program, or another component may be carried out sequentially, in parallel, repeatedly, or heuristically, or one or more of the operations may be executed in a different order or omitted, or one or more other operations may be added. 
     A mechanical device, such as a vacuum cleaner and a compressor, may include a motor for rotating a rotor. According to an example embodiment, the mechanical device may include a bearing for supporting rotation of a rotation shaft while constantly maintaining a position of the rotation shaft during operation of the motor. An airfoil journal bearing may include an airfoil for forming a fluid layer on the outer surface of the rotation shaft, and the airfoil may support a load of the rotation shaft not in contact with the rotation shaft through pressure of the fluid layer. Recently, miniaturized mechanical devices have been in demand to satisfy the desires of consumers. The demand for miniaturized mechanical devices may require miniaturization of accessories, such as a motor and a bearing. Accordingly, technology for manufacturing components in a simplified structure has been developed to minimize manufacturing tolerance and resolve an issue of a narrow assembly space. 
     Example embodiments of the disclosure may provide a mechanical device including an airfoil bearing. 
     According to example embodiments, a position, in an axial direction, of an airfoil may be fixed by connecting a ring member connected to an outer surface of a bearing housing to the airfoil in a hollow. 
     According to example embodiments, in an airfoil, a first foil region receiving pressure may be parallel to a second foil region having an elastic effect in an axis direction of a rotation shaft. 
     According to example embodiments, an airfoil bearing may be miniaturized by minimizing the thickness of an airfoil, and assembly may be less difficult. 
     According to example embodiments, a position, in an axial direction, of an airfoil may be fixed by connecting a ring member connected to an outer surface of a bearing housing to the airfoil in a hollow.  FIG.  1    is a perspective view illustrating a mechanical device according to an example embodiment. 
     Referring to  FIG.  1   , a mechanical device may include a motor assembly  100  for generating air pressure through rotational force. Although a vacuum cleaner, to which the motor assembly  100  is applied, is illustrated as an example herein for ease of description, the foregoing example is merely an example and a mechanical device  1 , to which the motor assembly  100  is applied, is not limited to the vacuum cleaner. 
     The mechanical device  1  may be a vacuum cleaner for generating air pressure through an operation of the motor assembly  100 . The vacuum cleaner may include a main body  10 , a suction head  30 , a stick  20 , and a handle  40 . 
     The handle  40  may be coupled to the main body  10  and may be gripped by a user such that the user may operate the vacuum cleaner (e.g., the mechanical device  1 ). The handle  40  may include an operator receiving operation information such that the user may control the vacuum cleaner (e.g., the mechanical device  1 ). 
     The suction head  30  may be connected to the main body  10  and may suck dust or contaminants from a surface to be cleaned through sucking force generated from the motor assembly  100  to be described below. The suction head  30  may contact the surface to be cleaned. 
     The stick  20  may connect the main body  10  to the suction head  30  and include a duct inside the stick  20  such that foreign materials sucked through the suction head  30  may move to the main body  10 . 
     The main body  10  may include a dust collector  11  and a driver  12  inside the main body  10 . The dust collector  11  may collect dust by separating foreign materials, such as dust or contaminants, from air sucked in the suction head  30 . The driver  12  may generate power for a sucking motion of the vacuum cleaner (e.g., the mechanical device  1 ). The driver  12  may include the motor assembly  100  inside the driver  12 , and the motor assembly  100  may generate rotational force by using electric power. 
       FIG.  2 A  is a perspective view illustrating a motor assembly according to an example embodiment,  FIG.  2 B  is an exploded perspective view illustrating the motor assembly according to an example embodiment, and  FIG.  2 C  is a cross-sectional view illustrating the motor assembly according to an example embodiment. 
     Referring to  FIGS.  2 A to  2 C , the motor assembly  100  may generate air pressure through rotational force. The motor assembly  100  may include a motor  210 , a motor housing  260 , an impeller  240 , a diffuser  290 , a bearing  220 , a bearing seating part  280 , and a substrate  270 . 
     The motor  210  may include a stator  211 , a rotor  212 , and a rotation shaft  213  connected to the rotor  212 . The rotor  212  may rotate around an axis through electromagnetic force between the rotor  212  and the stator  211 . The stator  211  may annularly surround outside the rotor  212 . Although an example of the motor  210  as being a brushless direct-current (BLDC) motor and the stator  211  as being outside the rotor  212  is illustrated herein, examples of the motor assembly  100  may not exclude a structure of the stator  211  being inside the rotor  212 . The rotation shaft  213  may be connected to the rotor  212  and may rotate around an axis upon rotation of the rotor  212 . The rotation shaft  213  may include a longitudinal direction extending in an axial direction A from the rotor  212 . 
     The motor housing  260  may form the exterior of the motor assembly  100 . The motor  210  may be inside the motor housing  260 . The motor housing  260  may include a first motor housing  262  and a second motor housing  261  connected to each other in two directions with the motor  210  between the first and second motor housings  262  and  261 . In this case, the first motor housing  262  and the second motor housing  261  may be fixed and coupled to each other through a coupling member  263 . 
     The impeller  240  may be connected to the rotation shaft  213 . The impeller  240  may be rotated by the motor  210  and may generate air flow. The center of the impeller  240  may be connected to the rotation shaft  213 . The impeller  240  may include a body surface formed in a radial direction D from the center of the impeller  240  and a plurality of blades radially formed on the body surface of the impeller  240 . 
     The diffuser  290  may be connected to the motor housing  260  and may guide flow of air flowing through the impeller  240 . The diffuser  290  may include a plurality of vanes in a circumferential direction R and may guide a direction of air flowing through the diffuser  290  through the vanes. 
     The bearing  220  may rotatably support the rotation shaft  213 . The rotation shaft  213  may be inserted through inside the bearing  220 , and the bearing  220  may enclose the circumference of the rotation shaft  213  and may fix a position of the rotation shaft  213  in the radial direction D perpendicular to the axial direction A. A plurality of first and second bearings  220   a  and  220   b  may be connected to the rotation shaft  213 . For example, the bearing  220  may include the first and second bearings  220   a  and  220   b  respectively connected to different parts of the rotation shaft  213  with the rotor  212  between the first and second bearings  220   a  and  220   b . A pair of bearings  220  may each be fixed to the motor housing  260  through the bearing seating part  280  to be described below and may support rotation of the rotation shaft  213  while fixing a position of the rotation shaft  213  by enclosing and supporting the outer circumferential surface of the rotation shaft  213 . 
     The bearing  220  may be seated in the bearing seating part  280 . The bearing seating part  280  may be connected to the motor housing  260 , and a position of the bearing  220  to the motor housing  260  may be fixed by the bearing  220  seated in the bearing seating part  280 . When a plurality of bearings (e.g., the first and second bearings  220   a  and  220   b ) is connected to the rotation shaft  213 , a plurality of bearing seating parts (e.g., first and second bearing seating parts  280   a  and  280   b ) respectively supporting the plurality of bearings (e.g., the first and second bearings  220   a  and  220   b ) may each be connected to the motor housing  260 . For example, the first bearing  220   a  may be connected to the first bearing seating part  280   a  and the second bearing  220   b  may be connected to the second bearing seating part  280   b . In this case, the first bearing seating part  280   a  may be connected to the first motor housing  262  and the second bearing seating part  280   b  may be connected to the second motor housing  261 . 
     At least one of the pair of bearings  220  (e.g., the first and second bearings  220   a  and  220   b ) may be an airfoil journal bearing (e.g., an airfoil journal bearing  320  of  FIG.  3 A ). In this case, when one bearing  220 , for example, the first bearing  220   a , is an airfoil journal bearing, the other bearing  220 , for example, the second bearing  220   b  may be a ball bearing. However, the foregoing example is provided merely as an example, and there may be other examples that the second bearing  220   b  may be an airfoil bearing or both the first and second bearings  220   a  and  220   b  may be airfoil bearings. 
       FIG.  3 A  is a perspective view illustrating an airfoil journal bearing according to an example embodiment,  FIG.  3 B  is an exploded perspective view illustrating the airfoil journal bearing according to an example embodiment,  FIG.  3 C  is a cross-sectional perspective view illustrating an airfoil journal bearing according to an example embodiment,  FIG.  3 D  is a cross-sectional view illustrating the airfoil journal bearing viewed in an axial direction, according to an example embodiment, and  FIG.  3 E  is a cross-sectional view illustrating the airfoil journal bearing viewed in an axial direction, according to another example embodiment. 
     Referring to  FIGS.  3 A to  3 D , an airfoil journal bearing  320  may rotatably support a rotation shaft  363 . The airfoil journal bearing  320  may support some of the outer surface of the rotation shaft  363  and may fix the rotation shaft  363  in a predetermined position while supporting a load generated by rotation of the rotation shaft  363 . The airfoil journal bearing  320  may form an air layer between itself and the outer circumferential surface of the rotation shaft  363 , may decrease frictional force generated between itself and the outer circumferential surface of the rotation shaft  363  through the air layer, and may support a load, in a radial direction D, generated by rotation of the rotation shaft  363 . Hereinafter, for ease of description, a longitudinal direction of the rotation shaft  363  may be referred to as an axial direction A, and a circumferential direction of a virtual circle perpendicular to the axial direction A may be referred to as a circumferential direction R. In addition, based on a cross-section of the rotation shaft  363 , a straight line direction from the center of the virtual circle perpendicular to the axial direction A to a circumference of the virtual circle may be referred to as a radial direction D. Radial direction D may also be referred to as the radial direction of the bearing housing  321 . 
     The airfoil journal bearing  320  may include a bearing housing  321 , a ring member  323 , and an airfoil  322 . 
     The bearing housing  321  may include a hollow  3210  into which the rotation shaft  363  is inserted. The hollow  3210  may be formed through the bearing housing  321  in the axial direction A of the rotation shaft  363  such that the rotation shaft  363  may be inserted through the bearing housing  321 . The hollow  3210  may have a shape practically corresponding to a cross-sectional shape of the cross-section of the rotation shaft  363 , for example, a circular shape. In this case, based on a cross-section perpendicular to the axial direction A, the hollow  3210  may have a circular shape having a diameter that is greater than a diameter of the rotation shaft  363 . 
     The bearing housing  321 , based on a cross-section perpendicular to the axial direction A, may include an insert slit  3211  formed through the bearing housing  321  from the hollow  3210  to an outer surface  321 B. In this case, the insert slit  3211  may be formed through the bearing housing  321  in the radial direction D. The insert slit  3211  may be formed in the axial direction A. For example, as illustrated in  FIG.  3 A , the insert slit  3211  may face the outer surface  321 B of the bearing housing  321  and may be formed by cutting off the outer surface  321 B of the bearing housing  321  in the axial direction A. In this case, the insert slit  3211  may have the same length as the length of the bearing housing  321  in the axial direction A. As another example, the insert slit  3211  may have a length that is less than the length of the bearing housing  321  in the axial direction A. In this case, the insert slit  3211  may be formed by cutting off at least some of the outer surface  321 B of the bearing housing  321 . 
     The ring member  323  may be connected to the outer surface  321 B of the bearing housing  321 . The ring member  323 , when the airfoil journal bearing  320  is seated in another component, for example, a bearing seating part (e.g., the bearing seating part  280  of  FIG.  2 B ), may fill a tolerance space for assembly between the bearing housing  320  and the bearing seating part and may maintain a stable structure. The ring member  323  may be formed from an elastic material and may absorb an impact or vibration applied to the bearing housing  321 . The ring member  323  may enclose the outer surface  321 B of the bearing housing  321  in the circumferential direction R. The ring member  323 , based on a cross-section perpendicular to the axial direction A, may be formed in an annular loop. The bearing housing  321  may include a seating groove  3212  recessed in the outer surface  321 B in the circumferential direction R. In this case, the ring member  323  may be seated in the seating groove  3212  and may stably maintain a connecting position to the bearing housing  321 . 
     When the ring member  323  encloses the outer surface  321 B of the bearing housing  321 , the ring member  323  may overlap at least some of the insert slit  3211 . For example, when the insert slit  3211  is viewed from the outer surface  321 B of the bearing housing  321 , the ring member  323  may overlap the insert slit  3211 . Accordingly, an edge of the airfoil  322  to be described below may be connected, through the insert slit  3211 , to the ring member  323 . The ring member  323 , by being connected to the airfoil  322  to be described below, may fix a position, in the axial direction A, of the airfoil  322 . 
     The airfoil  322  may be in the hollow  3210 . The airfoil  322  may be between the outer surface  321 B of the rotation shaft  363  in the hollow  3210  and an inner surface  321 A of the hearing housing  321  forming the hollow  3210 . Based on a cross-section perpendicular to the axial direction A, the airfoil  322  may enclose the circumference of the outer surface  321 B of the rotation shaft  363  in the hollow  3210  and may extend along the circumference direction R of the hollow  3210 . For example, as illustrated in  FIG.  3 D , on a cross-section perpendicular to the axial direction A, the airfoil  322  may enclose the outer surface  321 B of the rotation shaft  363  in the circumferential direction R. The airfoil  322  may support the rotation shaft  363  while receiving pressure in the radial direction D during rotation of the rotation shaft  363 . For example, an air layer may be between the airfoil  322  and the rotation shaft  363 . In this case, during rotation of the rotation shaft  363 , when the rotation shaft  363  slightly moves in a certain radial direction (e.g., the radial direction D), the airfoil  322  may receive air pressure from compression of the air layer and may be pushed in the certain radial direction (e.g., the radial direction D). Accordingly, the airfoil  322  may support the rotation shaft  363  to smoothly rotate while minimizing contact with the outer surface  321 B of the rotation shaft  363  or maintaining a non-contact state with the outer surface  321 B of the rotation shaft  363 . 
     At least some of the airfoil  322  may pass through the insert slit  3211  and may be engaged with the ring member  323 . For example, the airfoil  322 , based on a cross-section perpendicular to the axial direction A, may include an insert part  3220  bent in the radial direction D from an end in the circumferential direction R. The insert part  3220  may extend to the outer surface  321 B of the bearing housing  321  through the insert slit  3211 , and the extended edge of the insert part  3220  may be engaged with the outer surface  321 B of the ring member  323  overlapping the insert slit  3211 . The edge of the insert part  3220  extending to the outer surface  321 B of the bearing housing  321  may include an engagement part  3221  concavely formed such that at least some of the outer surface  321 B of the ring member  323  may be inserted into the engagement part  3221 . For example, when the ring member  323  have a circular cross-sectional shape, based on a cross-section perpendicular to the axial direction A, the engagement part  3221  may have a semicircular concave shape and be at an edge of the insert part  3220 . In this case, the airfoil  322 , by being engaged with the ring member  323  through the insert part  3220 , may prevent itself from deviating in the axial direction A while supporting rotation of the rotation shaft  363 . 
     The airfoil  322 , based on a cross-section perpendicular to the axial direction A, as illustrated in  FIG.  3 D , may include a first foil  3223  and a second foil  3224 , in which the first foil  3223  encloses the outer surface  321 B of the rotation shaft  363  in the circumferential direction R and the second foil  3224  extends from the first foil  3223  in the circumferential direction R and has a plurality of elastic bumps on its surface. 
     The first foil  3223  may extend along the inner circumferential surface of the hollow  3210  in the circumferential direction R. The first foil  3223  may directly receive air pressure, in the radial direction D, generated by rotation of the rotation shaft  363 . In this case, the first foil  3223  may have a smooth curve surface to effectively receive air pressure. A coating layer may be on the surface, facing the outer surface  321 B of the rotation shaft  363 , of the first foil  3223  to minimize frictional force generated by contact between the first foil  3223  and the rotation shaft  363 . For example, the coating layer may be formed from a polytetrafluorethylene (PETE) material. The rotation shaft  363  may float, spaced apart from the first foil  3223 , by pressure of air flowing when the rotation shaft  363  rotates, and accordingly, may smoothly rotate. 
     The second foil  3224  may extend from the first foil  3223  along the inner surface  321 A of the bearing housing  321  forming the hollow  3210  in the circumferential direction R. In this case, the second foil  3224  may be between the first foil  3223  and the inner surface  321 A of the bearing housing  321  forming the hollow  3210 . A plurality of elastic bumps having an uneven shape may be on a surface of the second foil  3224  in the circumferential direction R. The plurality of elastic bumps, based on a cross-section perpendicular to the axial direction A, may have an uneven shape concave or convex in the radial direction D and may be spaced apart from one another in the circumferential direction R. The second foil  3224  may receive, through the first foil  3223 , external force generated by rotation of the rotation shaft  363 , in the radial direction D, and may maintain a non-contact state between the outer surface  321 B of the rotation shaft  363  and the first foil  3223  through an elastic effect of the elastic bumps. 
     The insert part  3220  may be at the edge, extending from the first foil  3223  in the circumferential direction R, of the second foil  3224 . The insert part  3220  may be bent in the radial direction D from the edge, in the circumferential direction R, of the second foil  3224  and may extend to the outer surface  321 B of the bearing housing  321  through the insert slit  3211 . 
     The first foil  3223  and the second foil  3224  may be formed integrally as one body. For example, the first foil  3223  and the second foil  3224  may be formed integrally as one body by rolling one plate in the circumferential direction R. For example, a plate region corresponding to the second foil  3224  may be pressed to form elastic bumps having an uneven shape, the second foil  3224  may be rolled to enclose the outside of the first foil  3223 , and accordingly, the airfoil  322  may have an integral form. The first foil  3223  and the second foil  3224  may not separately be formed and assembled, and the airfoil  322  is formed integrally as one body. Therefore, assembling the bearing housing  321  may be simplified. 
     The first foil  3223  and the second foil  3224  may each have a predetermined width, and their widths parallel to the axial direction A may be the same. In this case, the airfoil  322  may maintain a predetermined width in the circumferential direction R. 
     The second foil  3224 , based on a cross-section perpendicular to the axial direction A, may have a forming angle, enclosing the rotation shaft  363 , from 180 to 360 degrees. For example, as illustrated in  FIG.  3 D , when a position in which an insert part  3220  of the second foil  3224  is 0 degrees based on the circumferential direction R, the first foil  3223  may enclose the outer surface  321 B of the rotation shaft  363  in a half to a full circle in a counterclockwise direction from the insert part  3220 . In this case, a forming angle of the second foil  3224  may be determined based on a load applied by the rotation shaft  363 , friction, vibration, or design conditions, such that the second foil  3224  may enclose the rotation shaft  363  at various angles. 
     The first foil  3223 , based on a cross-section perpendicular to the axial direction A, may have a forming angle, enclosing the rotation shaft  363 , greater than or equal to 360 degrees. In this case, the first foil  3223  may enclose the exterior of rotation shaft  363 , and the rotation shaft  363  may be and rotate in the hollow  3210 , preventing a bump foil and the inner surface  321 A of the bearing housing  321  forming the hollow  3210  of the bearing housing  321  from directly facing the outer surface  321 B of the rotation shaft  363 . In this case, one surface, toward the rotation shaft  363 , of the second foil  3224  may face and overlap the outer surface  321 B, toward the inner surface  321 A of the bearing housing  321  forming the hollow  3210 , of the first foil  3223 , and accordingly, may enclose at least some of the first foil  3223 . 
     The airfoil  322  may be fixed to the bearing housing  321  through the second foil  3224 . For example, the insert part  3220  may be connected to an edge extending in the circumferential direction R of the second foil  3224 , and the second foil  3224  may be fixed to the bearing housing  321  through the insert part  3220 . An edge, in the circumferential direction R, of the first foil  3223  may be formed as a free edge as illustrated in  FIG.  3 D . 
     Both edges of the airfoil  322  may be fixed to the bearing housing  321 . For example, as illustrated in  FIG.  3 E , the second foil  3224  may be inserted and fixed into the insert slit  3211  through the insert part  3220  at the edge, extending in the circumferential direction R, of the second foil  3224 , and the first foil  3223  may be inserted and fixed into the insert slit  3211  through a second insert part  3222  at the edge, extending in the circumferential direction R of the first foil  3223 , and accordingly, both edges of the airfoil  322  may be fixed to the bearing housing  321 . The second insert part  3220  may be bent in the radial direction D from the edge, in the circumferential direction R, of the first foil  3223  and inserted into the insert slit  3211 . In this case, the second insert part  3220  may pass through the bearing housing  321  through the insert slit  3211  to be engaged with the ring member  323 . The airfoil  322 , based on a cross-section perpendicular to the axial direction A, may include a through hole in a region overlapping the insert slit  3211 . For example, a first through hole and a second through hole may be respectively formed through surfaces of the first foil  3223  and the second foil  3224 . In this case, the second insert part  3220  may pass through the first and second through holes and be inserted into the insert slit  3211 . 
       FIG.  4 A  is an exploded perspective view illustrating an airfoil journal bearing according to another example embodiment,  FIG.  4 B  is a diagram illustrating a ring member arrangement region of the airfoil journal bearing viewed in an axial direction, according to an example embodiment, and  FIG.  4 C  is a diagram illustrating a ring member arrangement region of an airfoil journal bearing viewed in an axial direction, according to another example embodiment. 
     Referring to  FIGS.  4 A and  4 B , an airfoil journal bearing  420  may rotatably support a rotation shaft  463 . The airfoil journal bearing  420  may include a bearing housing  421 , a ring member  423 , and an airfoil  422 . 
     The bearing housing  421  may include a hollow  4210  into which the rotation shaft  463  is inserted. The hollow  4210 , in the axial direction A, in which the rotation shaft  463  is inserted, may be formed through the interior of the bearing housing  421 . Based on a cross-section perpendicular to the axial direction A, an outer surface  421 B of the bearing housing  421  and an inner surface  421 A of the bearing housing  421  forming the hollow  4210  may each have a circular cross-sectional shape. The bearing housing  421 , based on a cross-section perpendicular to the axial direction A, may include an insert slit  4211  formed through the bearing housing  421 , in the radial direction D, from the hollow  4210  to the outer surface  421 B of the bearing housing  421 . The insert slit  4211  may be formed by cutting off, in the axial direction A, the outer surface  421 B of the bearing housing  421 . 
     The ring member  423  may be connected to the outer surface  421 B of the bearing housing  421 . The ring member  423  may be connected to enclose the outer surface  421 B of the bearing housing  421  in the circumferential direction R. In this case, a seating groove  4212  is recessed, in the circumferential direction R, in the outer surface  421 B of the bearing housing  421 , and the ring member  423  may be seated in the seating groove  4212  and stably connected to the outer surface  421 B of the bearing housing  421 . The ring member  423  may be formed from an elastic material, for example, rubber. 
     The airfoil  422  may be in the hollow  4210  and enclose the outer surface  421 B of the rotation shaft  463 . The airfoil  422 , based on a cross-section perpendicular to the axial direction A, may extend in the circumferential direction R along a circumference of the rotation shaft  463  as illustrated in  FIG.  4 B . The airfoil  422  may include an insert part  4220  of which the edge in the circumferential direction R is bent in the radial direction D. The insert part  4220 , through the insert slit  4211 , may extend from the hollow  4210  to the outer surface  421 B of the bearing housing  421 . In this case, the insert part  4220  may be engaged with the ring member  423  connected to the outer surface  421 B of the bearing housing  421 . For example, the edge of the insert part  4220 , extending to the outer surface  421 B of the bearing housing  421 , may include an engagement part concavely formed such that at least some of the outer surface  421 B of the ring member  423  may be inserted into the engagement part. The airfoil  422  may be engaged with the ring member  423  through the insert part  4220 , and accordingly, a position of the airfoil  422 , in the axial direction A, may be fixed. The airfoil  422 , while supporting the rotation shaft  463  to rotate, may prevent itself from deviating, in the axial direction A, outside the hollow  4210 . 
     The airfoil  422  may include a first foil  4223  and a pair of second foils  42241  and  42242  (collectively referred to as  4224 ) respectively at both edges of the first foil  4223 . For example, based on the axial direction A, the first foil  4223  may be between the pair of second foils  4224 . The first foil  4223  and the pair of second foils  4224  may extend, in the circumferential direction R, and enclose the circumference of the rotation shaft  463  and may enclose different outer surfaces  421 B of the rotation shaft  463  in the hollow  4210  in the axial direction A. In this case, the first foil  4223  and the pair of second foils  4224  may have practically the same length in the circumferential direction R. 
     The first foil  4223  may receive pressure generated by rotation of the rotation shaft  463 . The first foil  4223  may receive pressure of an air layer upon rotation of the rotation shaft  463  through the air layer between the first foil  4223  and the outer surface  421 B of the rotation shaft  463 . The first foil  4223  may have a smooth curve surface. In this case, a coating layer including a PETE material may be on the inner surface  421 A of the first foil  4223  facing the outer surface  421 B of the rotation shaft  463 . The coating layer, when the first foil  4223  and the rotation shaft  463  are in contact with each other during rotation of the rotation shaft  463 , may decrease friction from contact, maintain a floating state of the first foil  4223  from the outer surface  421 B of the rotation shaft  463 , and support the rotation shaft  463  to smoothly rotate. 
     The second foils  4224  may respectively be, in the axial direction A of the rotation shaft  463 , connected to both edges of the first foil  4223 . In this case, a plurality of elastic bumps  42240  having an uneven shape may be, in the circumferential direction R, in each of the second foils  42241  and  42242 . The plurality of elastic bumps  42240  may protrude from the outer surface  421 B of the rotation shaft  463  toward the inner surface  421 A of the bearing housing  421  forming the hollow  4210 . In this case, the elastic bumps  42240  may be formed by pressing at least some of the second foils  4224  such that the at least some of the second foils  4224  have a relatively great curvature than another region. The plurality of elastic bumps  42240  may be formed by other known methods, for example, embossing. The elastic bumps  42240  may be spaced apart from one another at regular distance, in the circumferential direction, in the second foils  4224 . However, the foregoing example is merely an example, and the distance between the elastic bumps  42240  may vary depending on design conditions of the airfoil  422 . For example, the airfoil  422 , to match a damping function performed by the plurality of elastic bumps  42240  with design conditions, may include a relatively long distance between the plurality of elastic bumps  42240 . In addition, although, in the examples illustrated in the drawings (e.g.,  FIG.  4 A ), each foil region includes one elastic bump  42240  in the axial direction A of the airfoil  422 , each of the second foils  4224  may include a plurality of elastic bumps  42240  in the axial direction A of the airfoil  422 . 
     The airfoil  422  may receive external force, in the radial direction D, generated by rotation of the rotation shaft  463  through the first foil  4223 , maintain a non-contact state with the outer surface  421 B of the rotation shaft  463  through an elastic effect in the radial direction D through the second foils  4224 , and support the rotation shaft  463  to rotate. 
     The first foil  4223  and the pair of second foils  4224  may be formed integrally as one body. For example, the airfoil  422  may have the elastic bumps  42240  formed in the second foils  4224 , and then, may be formed integrally as one body by rolling a processed plate-shaped single member in the circumferential direction R. Accordingly, the first foil  4223  and the second foils  4224  may be formed in a single member, in which the first foil  4223  receives external force in the radial direction D from the rotation shaft  463  and the second foils  4224  perform an elastic function in response to the external force in the radial direction D. Therefore, the first foil  4223  and the second foils  4224  may not need a separate assembly process for connection, and assembly and maintenance on the bearing housing  421  may be simplified. The first foil  4223  and the second foils  4224  may not be stacked and may be formed parallel to the axial direction A. Therefore, the thickness, in the radial direction D, of the airfoil  422  in the hollow  4210  may be minimized. The diameter of the hollow  4210 , into which the airfoil  422  is inserted, may decrease, and accordingly, the bearing housing  421  may be miniaturized. 
     The airfoil  422 , based on a cross-section perpendicular to the axial direction A, may have a forming angle, enclosing the rotation shaft  463 , from 180 to 360 degrees. For example, the airfoil  422 , as illustrated in  FIG.  4 B , may enclose the outer surface  421 B of the rotation shaft  463  in a half to a full circle in a counterclockwise direction from an edge of the airfoil  422  including the insert part  4220 . 
     Referring to  FIG.  4 C , an airfoil journal bearing  420 C may include the bearing housing  421 , the ring member  423 , and the airfoil  422 . 
     The bearing housing  421  may form an exterior of the airfoil journal bearing  420 . The bearing housing  421  may include the hollow  4210  formed through the bearing housing  421  in the axial direction A such that the rotation shaft  463  may be inserted. The bearing housing  421 , based on a cross-section perpendicular to the axial direction A, may include a plurality of first and second insert slits  4211  and  4215  formed through the bearing housing  421 , in the radial direction D, from the hollow  4210  to the outer surface  421 B of the bearing housing  421 . For example, the plurality of first and second insert slits  4211  and  4215 , based on a cross-section perpendicular to the axial direction A, may include the first insert slit  4211  and the second insert slit  4215  formed through the bearing housing  421  in different radial directions D. 
     The ring member  423  may be connected as one unit and enclose the outer surface of the bearing housing  421  in the circumferential direction R. In this case, the ring member  423 , viewed from outside the bearing housing  421 , may overlap each of the first insert slit  4211  and the second insert slit  4215 . For example, a first part of the ring member  423  may overlap the first insert slit  4211  and a second part of the ring member  423  may overlap the second insert slit  4215 . 
     The airfoil  422  may be in the hollow  4210  such that the airfoil  422  may enclose the outer surface of the rotation shaft  463  in the circumferential direction R. Both edges, in the circumferential direction R, of the airfoil  422  may be fixed to the bearing housing  421 . For example, the airfoil  422  may include the first insert part  4220  and the second insert part  4225  bent in the radial direction D respectively at both edges, in the circumferential direction R, of the airfoil  422 . The first insert part  4220  may be inserted into the first insert slit  4211 , and the second insert part  4225  may be inserted into the second insert slit  4215 . In this case, the first insert part  4220  may extend through the first insert slit  4211  outside the bearing housing  421  and an edge of the first insert part  4220  may be engaged with the first part of the ring member  423 . In addition, the second insert part  4225  may extend through the second insert slit  4215  outside the bearing housing  421  and an edge of the second insert part  4225  may be engaged with the second part of the ring member  423 . In this case, both edges, in the circumferential direction R, of the airfoil  422  may be engaged with the first and second parts of the ring member  423 , and accordingly, the airfoil  422  may be fixed to the bearing housing  421 . Therefore, during rotation of the rotation shaft  463 , a position, in the axial direction A, of the airfoil  422  may be fixed. 
       FIG.  5 A  is a perspective view illustrating an airfoil journal bearing according to another example embodiment, and  FIG.  5 B  is an exploded perspective view illustrating an airfoil journal bearing according to another example embodiment. 
     Referring to  FIGS.  5 A and  5 B , an airfoil journal bearing  520  may include a bearing housing  521 , a plurality of ring members  523 , and an airfoil  522 . 
     The bearing housing  521  may include a hollow  5210  formed through the bearing housing  521  in the axial direction A. The bearing housing  521  may include an insert slit  5211  penetrating the bearing housing  521  in the radial direction D from an inner surface  521 A of the bearing housing  521  forming the hollow  5210  to an outer surface  521 B of the bearing housing  521 . The insert slit  5211  may be formed in the axial direction A from the outer surface  521 B of the bearing housing  521 . 
     The plurality of ring members  523  may each be connected to the outer surface  521 B of the bearing housing  521 . The plurality of ring members  523  may enclose the bearing housing  521  in the circumferential direction R and may be spaced apart from one another in the axial direction A. For example, the plurality of ring members  523  may include a first ring member  523   a  and a second ring member  523   b . In this case, the outer surface  521 B of the bearing housing  521  may include a plurality of seating grooves (e.g., first and second seating grooves  5212   a  and  5212   b ) recessed in the circumferential direction R and respectively seating the plurality of ring members  523 . For example, the outer surface  521 B of the bearing housing  521  may include the first seating groove  5212   a  for seating the first ring member  523   a  and the second seating groove  5212   b  for seating the second ring member  523   b . The first and second ring members  523   a  and  523   b  may overlap the insert slit  5211 , facing the outer surface  521 B of the bearing housing  521 . 
     The airfoil  522  may be in the hollow  5210 . The airfoil  522  may enclose, in the circumferential direction R, the outer surface of a rotation shaft in the hollow  5210 . At least some of the airfoil  522  may be engaged with the ring member  523  through the insert slit  5211 . For example, the airfoil  522  may include an insert part  5220  of which the edge is bent in the radial direction D and inserted into the insert slit  5211  from the hollow  5210 . In this case, the insert part  5220  may extend outside the bearing housing  521  through the insert slit  5211 . The extended edge of the insert part  5220  may include one or more engagement parts  5221  for engaging with the ring members  523 . For example, as illustrated in  FIG.  5 B , a first engagement part  5221   a  for engaging with the first ring member  523   a  and a second engagement part  5221   b  for engaging with the second ring member  523   b  may each be at an edge of the insert part  5220 . In this structure, the airfoil  522  may be engaged with the plurality of ring members  523 , and accordingly, a position, in the axial direction A, of the airfoil  522  may be stably fixed. 
       FIG.  6 A  is a perspective view illustrating an airfoil journal bearing according to another example embodiment, and  FIG.  6 B  is an exploded perspective view illustrating the airfoil journal bearing according to another example embodiment. 
     Referring to  FIGS.  6 A and  6 B , an airfoil journal bearing  620  may include a bearing housing  621 , a plurality of ring members  623 , and an airfoil  622 . 
     The bearing housing  621  may include a hollow  6210  into which a rotation shaft is inserted. The hollow  6210  may be formed through, in the axial direction A, the bearing housing  621 . The bearing housing  621 , based on a cross-section perpendicular to the axial direction A, may include an insert slit  6211  formed through the bearing housing  621 , in the radial direction D, from the hollow  6210  to the outer surface of the bearing housing  621 . The insert slit  6211 , facing the outer surface of the bearing housing  621 , may be formed by cutting off the bearing housing  621  parallel to the rotation shaft. 
     The plurality of ring members  623  may be connected to the outer surface of the bearing housing  621 . In this case, each of the plurality of ring members  623  may enclose the bearing housing  621  in the circumferential direction R. The plurality of ring members  623  may be spaced apart from one another in the axial direction A and connected to the outer surface of the bearing housing  621 . For example, the plurality of ring members  623  may include a first ring member  623   a , a second ring member  623   b , and a third ring member  623   c . The outer surface of the bearing housing  621  may include a plurality of seating grooves (e.g., first, second, and third seating grooves  6212   a ,  6212   b , and  6212   c ) recessed in the circumferential direction R and respectively seating the plurality of ring members  623 . For example, the outer surface of the bearing housing  621  may include the first seating groove  6212   a , the second seating groove  6212   b , and the third seating groove  6212   c , spaced apart from one another in the axial direction A. In this case, the first, second, and third seating grooves  6212   a ,  6212   b , and  6212   c  may respectively seat the first, second, and third ring members  623   a ,  623   b , and  623   c.    
     The airfoil  622  may be in the hollow  6210  and support the rotation shaft to rotate. The airfoil  622  may include a top foil  6221 , a first bump foil  6222   a , and a second bump foil  6222   b.    
     The top foil  6221  may be in the hollow  6210  and may enclose the outer surface of the rotation shaft (e.g., the rotation shaft  363  of  FIG.  3 D ) in the circumferential direction R. The top foil  6221  may have a cylindrical shape. The top foil  6221  may receive a load, in the radial direction D, generated by rotation of the rotation shaft. For example, an air layer may be between the top foil  6221  and the rotation shaft, and the top foil  6221  may receive pressure, in the radial direction D, from pressure of the air layer upon rotation of the rotation shaft. The top foil  6221  may have a curved inner surface facing the outer surface of the rotation shaft. In this case, the inner surface of the top foil  6221  may include a coating layer for decreasing frictional force generated from contact with the rotation shaft. The coating layer may be formed from, for example, a PETE material. The length, in the axial direction A, of the top foil  6221  may practically be the same as the length, in the axial direction A, of the bearing housing  621 . 
     The first bump foil  6222   a  and the second bump foil  6222   b  may respectively be connected to first and second parts A1 and A2 of the top foil  6221 . The first bump foil  6222   a  may be in the hollow  6210  and enclose the first part A1 in the circumferential direction R, and the second bump foil  6222   b  may be in the hollow  6210  and enclose the second part A2 in the circumferential direction R. In other words, the first bump foil  6222   a  may be between the first part A1 of the top foil  6221  and the inner surface of the bearing housing  621  forming the hollow  6210 , and the second bump foil  6222   b  may be between the second part A2 of the top foil  6221  and the inner surface of the bearing housing  621  forming the hollow  6210 . In this case, the first and second parts A1 and A2 of the top foil  6221  may be spaced apart from each other in the axial direction A at a predetermined distance. The first and second bump foils  6222   a  and  6222   b  each may have a cylindrical shape and include a plurality of elastic bumps  6225  having an uneven surface. The plurality of elastic bumps  6225  on each surface of the first and second bump foils  6222   a  and  6222   b  may be in the circumferential direction R of the first and second bump foils  6222   a  and  6222   b . The first and second bump foils  6222   a  and  6222   b  may generate elastic force in response to external force applied, in the radial direction D, to the top foil  6221  during rotation of the rotation shaft. 
     Each of the top foil  6221 , the first bump foil  6222   a , and the second bump foil  6222   b  may be fixed, through the ring members  623 , to the bearing housing  621 . The top foil  6221 , the first bump foil  6222   a , the second bump foil  6222   b , which are inserted into the hollow  6210 , may respectively include insert parts  62210 ,  62220   a , and  62220   b  inserted into the insert slit  6211 . In this case, the insert part  62210  of the top foil  6211  may extend outside the bearing housing  621  through the insert slit  6211  and may be engaged with the third ring member  623   c . Similarly, the insert part  62220   a  of the first bump foil  6222   a  and the insert part  62220   b  of the second bump foil  6222   b  may extend outside the bearing housing  621  through the insert slit  6211  and may be respectively engaged with the first and second ring members  623   a  and  623   b . An edge of the insert part  62210  of the top foil  6221  may include a first engagement part  62211  for engaging with the third ring member  623   c , an edge of the insert part  62220   a  of the first bump foil  6222   a  may include a second engagement part  62221   a  for engaging with the first ring member  623   a , and an edge of the insert part  62220   b  of the second bump foil  6222   b  may include a third engagement part  62221   b  for engaging with the second ring member  623   b . In this structure, the top foil  6221 , the first bump foil  6222   a , and the second bump foil  6222   b  may respectively be connected to the plurality of ring members  623 , and their position in the axial direction A may be fixed. 
       FIG.  7 A  is an exploded perspective view illustrating an airfoil journal bearing according to another example embodiment, and  FIG.  7 B  is a diagram illustrating a ring member arrangement region of the airfoil journal bearing viewed in an axial direction, according to another example embodiment. 
     Referring to  FIGS.  7 A and  7 B , an airfoil journal bearing  720  may include a bearing housing  721 , a ring member  723 , and an airfoil  722 . 
     The bearing housing  721  may include a hollow  7210  into which a rotation shaft is inserted. The hollow  7210  may be formed through, in the axial direction A, the bearing housing  721 . The bearing housing  721 , based on a cross-section perpendicular to the axial direction A, may include an insert slit  7211  formed through the bearing housing  721 , in the radial direction D, from the hollow  7210  to the outer surface of the bearing housing  721 . The insert slit  7211 , facing the outer surface of the bearing housing  721 , may be formed by cutting off the bearing housing  721  parallel to the rotation shaft. 
     The ring member  723  may be connected to the outer surface of the bearing housing  721 . In this case, the ring member  723  may enclose the bearing housing  721  in the circumferential direction R. The ring member  723  may be seated in a seating groove  7212 , which is recessed in the outer surface of the bearing housing  721  in the circumferential direction R. 
     The airfoil  722  may be in the hollow  7210  and support the rotation shaft to rotate. The airfoil  722  may include a top foil  7221  and a bump foil  7222 . 
     The top foil  7221  may be in the hollow  7210  and may enclose the outer surface of the rotation shaft in the circumferential direction R. The top foil  7211  may receive a load, in the radial direction D, generated by rotation of the rotation shaft. An air layer may be between the top foil  7211  and the rotation shaft, and the top foil  7211  may receive pressure, in the radial direction D, in response to a pressure change of the air layer upon rotation of the rotation shaft. The top foil  7211  may include a coating layer on the inner surface of the top foil  7211  facing the rotation shaft. The coating layer may decrease frictional force generated from contact between the top foil  7211  and the rotation shaft. For example, the coating layer may include a PETE material. The length, in the axial direction A, of the top foil  7211  may practically be the same as the length, in the axial direction A, of the bearing housing  721 . The top foil  7221  may include an insert part  72210 , in which at least some of an edge of the top foil  7221  extending in the circumferential direction R is bent in the radial direction D. The insert part  72210 , while the top foil  7211  is in the hollow  7210 , may extend outside the bearing housing  721  through the insert slit  7211 . In this case, the insert part  72210  may be engaged with the ring member  723 . For example, the insert part  72210  may include an engagement part  72211  for engaging with the ring member  723 . 
     The bump foil  7222  may be in the hollow  7210  such that the bump foil  7222  may enclose the outer surface of the top foil  7221  in the circumferential direction R. The bump foil  7222  may be between the top foil  7221  and the inner surface of the bearing housing  721  forming the hollow  7210 . The bump foil  7222  may have a cylindrical shape and include a plurality of elastic bumps  7225  having an uneven surface. The plurality of elastic bumps  7225  may be in the circumferential direction R of the bump foil  7222 . The bump foil  7222  may generate elastic force in response to external force applied, in the radial direction D, to the top foil  7221  during rotation of the rotation shaft. The bump foil  7222  may include an opening  72221  through which the insert part  72210  of the top foil  7221  passes. In this case, while the bump foil  7222  is in the hollow  7210 , the opening  72221  may be in a region overlapping the insert slit  7211 . 
     Although the example illustrated in the drawings may be the insert part  72210  inserted into the opening  72221  of the bump foil  7222  and the bump foil  7222  and the top foil  7221  connected to each other, the foregoing example is merely an example. The bump foil  7222 , similar to the top foil  7221 , may include an insert part connected to the ring member  723  through the insert slit  7211  at an edge. 
     According to example embodiments, an airfoil journal bearing  320  is configured to rotatably support a rotation shaft  363  and includes a bearing housing  321  including a hollow  3210  formed through the bearing housing  321  in an axial direction A such that the rotation shaft  363  is inserted into the hollow  3210 ; an airfoil  322 , in the hollow  3210 , enclosing the circumference of the rotation shaft  363  and extending in a circumferential direction of the hollow  3210 ; and a ring member  323  that is annular and connected to the bearing housing  321  and enclosing an outer surface  321 B of the bearing housing  321  in a circumferential direction. The bearing housing  321  includes, based on a cross-section perpendicular to the axial direction, an insert slit  3211  formed through the bearing housing  321  in a radial direction D from the hollow  3210  to the outer surface  321 B of the bearing housing  321 , and the airfoil  322  includes, based on a cross-section perpendicular to the axial direction, an insert part  3220  bent from a circumferential direction R to the radial direction D and extending, through the insert slit  3211 , to the outer surface  321 B of the bearing housing  321 , in which the airfoil  322  is engaged with an outer surface  321 B of the ring member  323  through the insert part  3220 . 
     The airfoil  322  may include an engagement part  3221  formed at an edge of the insert part  3220  extending to the outer surface  321 B of the bearing housing  321  and being concave such that at least some of the outer surface  321 B of the ring member  323  is inserted into the engagement part  3221 . 
     A plurality of ring members  523  may be connected to the outer surface of the bearing housing  521 , and a plurality of engagement parts  5221  may be at the edge of the insert part  5220 , in which the engagement parts  5221  are respectively connected to first and second ring members  523   a  and  523   b.    
     The insert slit  5211  may be in the axial direction A, and the first and second ring members  523   a  and  523   b  may be spaced apart from one another in the axial direction A. 
     The bearing housing  321  may include a seating groove  3212  formed in the outer surface  321 B of the bearing housing  321  in a circumferential direction R of the bearing housing  321  and where the ring member  323  sits. 
     The airfoil  322  includes a first foil  3223  extending along the inner circumferential surface of the hollow  3210  in the circumferential direction of the hollow  3210 , and a second foil  3224  extending along the inner circumferential surface of the hollow  3210  from the first foil  3223  in the circumferential direction R of the hollow  3210  and including a plurality of elastic bumps having an uneven shape in the circumferential direction R of the hollow  3210 , in which the first foil  3223  and the second foil  3224  are formed integrally as one body, and based on a cross-section perpendicular to the axial direction, the second foil  3224  may enclose at least some of the first foil  3223 , and the insert part  3220  may be connected to an edge of the second foil  3224  extending in the circumferential direction R of the hollow  3210 . 
     Based on a cross-section perpendicular to the axial direction A, a forming angle, of the first foil  3223 , enclosing the rotation shaft  363  may be greater than or equal to 360 degrees. 
     Based on a cross-section perpendicular to the axial direction A, a forming angle, of the second foil  3224 , enclosing the rotation shaft  363  may be from 180 to 360 degrees. 
     Based on a cross-section perpendicular to the axial direction A, a second insert part  3222  bent in the radial direction D is at an edge of the first foil  3223 , a first through hole and a second through hole may be respectively formed through the first foil  3223  and the second foil  3224  in the radial direction D, and the second insert part  3222  is inserted, through the first through hole and the second through hole, into the insert slit  3211 . 
     The airfoil  422  may include a first foil  4223  and a pair of second foils  4224 , in which the first foil  4223  extends in the circumferential direction R and encloses the circumference of the rotation shaft  463 , and the second foils  4224  are respectively connected to both edges of the first foil  4223  parallel to the axial direction A, extend in a circumferential direction and enclose the circumference of the rotation shaft, and include a plurality of elastic bumps  42240  having an uneven shape in the circumferential direction R. The first foil  4223  and the pair of second foils  4224  may be formed integrally as one body. 
     Based on a cross-section perpendicular to the axial direction A, a forming angle, of the airfoil  422 , enclosing the rotation shaft  463  may be from 180 to 360 degrees. 
     The plurality of elastic bumps  42240  may protrude toward the inner circumferential surface of the hollow. 
     Based on a cross-section perpendicular to the axial direction A, the insert slit may include a first insert slit  4211  and a second insert slit  4215  through the bearing housing  421  in different radial directions D, and the insert part may include a first insert part  4220  and a second insert part  4225  respectively at both edges of the airfoil  422  in a circumferential direction R of the airfoil  422 . The first insert part  4220  may be engaged with a first part of the ring member  423  through the first insert slit  4211 , and the second insert part  4225  may be engaged with a second part of the ring member  423  through the second insert slit  4215 . 
     The airfoil  622  may include a top foil  6221 , a first bump foil  6222   a , and a second bump foil  6222   b , in which the top foil  6221  is in the hollow  6210  and encloses the rotation shaft in a circumferential direction R, the first bump foil  6222   a  is in the hollow  6210 , encloses a first part of the top foil  6221  in a circumferential direction R, and includes a plurality of elastic bumps having an uneven shape in the circumferential direction R, and the second bump foil  6222   b  is in the hollow  6210 , encloses, in the circumferential direction R, a second part of the top foil  6221  spaced, in the axial direction A, apart from the first part of the top foil  6221 , and includes a plurality of elastic bumps having an uneven shape in the circumferential direction R. The insert parts  62210 ,  62220   a , and  62220   b  may be respectively at edges of the top foil  6221 , the first bump foil  6222   a , and the second bump foil  6222   b.    
     Three of the ring members  623  may be connected to the outer surface of the bearing housing  621 , in which the ring members  623  are spaced, in the axial direction A, apart from one another, are respectively engaged with the insert portions of the top foil  6222 , the first bump foil  6222   a  and the second bump foil  6222   b.    
     According to example embodiments, an airfoil journal bearing  320  is configured to rotatably support a rotation shaft  363 . The airfoil journal bearing  320  includes a bearing housing  321 , an airfoil  322 , and a ring member  323 , in which the bearing housing  321  includes a hollow  3210  formed through the bearing housing  321  in an axial direction A such that the rotation shaft  363  is inserted into the hollow  3210 , the airfoil  322  is in the hollow  3210 , extends, in a circumferential direction R, and encloses the outer surface of the rotation shaft  363 , and receives pressure generated by rotation of the rotation shaft  363 , and the ring member  323  is connected to the bearing housing  321 , encloses the outer surface of the bearing housing  321  in a circumferential direction R, and fixes a position of the airfoil  322  in an axial direction A. The bearing housing  321 , based on a cross-section perpendicular to the axial direction A, includes an insert slit  3211  formed through the bearing housing  321  from the hollow  3210  to the outer surface of the bearing housing  321 , and at least some of the airfoil  322  passes through the insert slit  3211  and is engaged with the ring member  323 . 
     The airfoil  322  may include an insert part  3220 . Based on a cross-section perpendicular to the axial direction A, the insert part  3220 , of which the edge toward a circumferential direction R is bent toward a radial direction D, may extend through the insert slit  3211  to the outer surface of the bearing housing  321 . The insert part  3220  may include an engagement part  3221  into which at least some of the outer surface of the ring member  323  is inserted. 
     The insert slit  5211  may be in an axial direction A of the bearing housing  521 , a plurality of ring members  523  may be spaced apart from one another and connected to the outer surface of the bearing housing  521 , and the insert part  5220  may include first and second engagement parts  5221   a  and  5221   b  respectively engaged with the first and second ring members  523   a  and  523   b.    
     A seating groove  3212  may be concavely formed in a circumferential direction R in the outer surface of the bearing housing  321  such that the ring member  323  is seated in the seating groove  3212 . 
     According to example embodiments, a mechanical device includes a motor housing  260 , a motor  210  inside the motor housing  260  and including a rotation shaft  213  for performing a rotating function, an impeller  240  connected to the rotation shaft  213 , an airfoil journal bearing  320  for rotatably supporting the rotation shaft  213 , and a bearing seating part  280  connected to the motor housing  260  and including a seating space for seating the airfoil journal bearing  320 . The airfoil journal bearing  320  includes a bearing housing  321  including a hollow  3210  into which the rotation shaft  363  is inserted, an airfoil  322  in the hollow  3210 , extending, in a circumferential direction R, and enclosing the outer surface of the rotation shaft  363  and receiving pressure generated by rotation of the rotation shaft  363 , and a ring member  323  connected to the bearing housing  321  and enclosing an outer surface  321 B of the bearing housing  321  in the circumferential direction R. The bearing housing  321 , based on a cross-section perpendicular to an axial direction A of the rotation shaft  363 , includes an insert slit  3211  formed in a radial direction D through the bearing housing  321  from the hollow  3210  to the outer surface  321 B of the bearing housing  321 . The airfoil  322  includes an insert part  3220  bent from an edge of the airfoil  322  in the circumferential direction R and extending through the insert slit  3211  to the outer surface  321 B of the bearing housing  321 . The outer surface of the ring member  323  is engaged with the insert part  3220  and fixes a position of the airfoil  322  in an axial direction A of the airfoil  322 . 
     The technical goals to be achieved through example embodiments of the present disclosure are not limited to those described above, and other technical goals not mentioned above may be clearly understood by one of ordinary skill in the art from the disclosure herein. 
     Although example embodiments have been described herein in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the embodiments.