Patent Publication Number: US-2022218060-A1

Title: Ventilation apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Japanese patent application No. 2021-002795 filed on Jan. 12, 2021, the contents of the which are hereby fully incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a ventilation apparatus that is removably attachable to (mountable on) a garment. 
     BACKGROUND 
     Some known ventilation apparatuses can be removably attached to (mounted on) a garment, which is worn by a worker in hot work environment, and deliver air and ventilate inside the garment. For example, Japanese Patent No. 6200606 discloses a fan for use with a garment that includes a body and a separate retainer ring that is mountable around the body. The body includes a fan and a housing that accommodates the fan. The housing and the retainer ring each has a corresponding flange part. Engagement between internal threads on the retainer ring and external threads on a peripheral wall part of the housing allows a fabric to be held between the flange part of the housing and the flange part of the retainer ring. 
     SUMMARY 
     In order to attach and remove the above-mentioned fan to and from the garment, the user needs to rotate the retainer ring relative to the housing by a considerable angle in one direction. Therefore, this known fan still has room for improvement in the procedure for attachment and removal. 
     It is one, non-limiting object of the present disclosure to improve operability of a ventilation apparatus that is removably attachable to a garment. 
     One aspect of the present disclosure herein provides a ventilation apparatus that is removably attachable to a garment is provided. The ventilation apparatus includes a motor, a fan, a housing, and a ring. 
     The fan is configured to be rotationally driven by the motor around a first axis that defines a front-rear direction of the ventilation apparatus. The housing accommodates the motor and the fan. The housing includes a peripheral wall part and a first clamping part. The peripheral wall part has a hollow cylindrical shape and is disposed around the fan. The first clamping part protrudes radially outward from a rear end portion of the peripheral wall part. The ring has a hollow cylindrical shape and is removably mounted around the peripheral wall part of the housing. The ring has a second clamping part that is disposed in front of the first clamping part of the housing and configured to clamp a fabric of the garment in conjunction with the first clamping part. 
     At least one projection is provided on a first surface, which is one of an outer peripheral surface of the peripheral wall part and an inner peripheral surface of the ring. The at least one projection protrudes from the first surface in a radial direction of the peripheral wall part. At least one engagement wall and at least one guide wall are provided on a second surface, which is the other one of the outer peripheral surface of the peripheral wall part and the inner peripheral surface of the ring. The at least one engagement wall and the at least one guide wall respectively protrude from the second surface in the radial direction. The at least one engagement wall is located adjacent to one end of the at least one guide wall in a circumferential direction. Note that “the at least one engagement wall is located adjacent to one end of the at least one guide wall in a circumferential direction” may include (i) a first case in which “one end of the at least one engagement wall is located at a substantially same position as one end of the at least one guide wall in a circumferential direction”, (ii) a second case in which “one end of the at least one engagement wall and one end of the at least one guide wall are spaced apart from each other with a slight gap therebetween in a circumferential direction”, and (iii) a third case in which “one end of the at least one engagement wall and one end of the at least one guide wall are located to have a slight overlap with each other in a circumferential direction”. The at least one engagement wall has at least one engagement surface. The at least one engagement surface is configured to block (prevent) the ring and the housing from moving away from each other in the front-rear direction. 
     The at least one guide wall has a guide surface that is configured to guide the ring rearward relative to the housing and to guide the at least one projection to at least one engagement position at which the projection is abuttable on the at least one engagement surface. In a direction in which the projection moves away from the guide surface in the front-rear direction, an open space extends from the guide surface to an area that corresponds to an end of the second surface. 
     The ventilation apparatus of this aspect can be attached to (mounted on) the garment by having the fabric of the garment clamped in the front-rear direction between the first clamping part of the housing and the second clamping part of the ring mounted around the peripheral wall part of the housing. When the ring is attached to the housing, the at least one projection provided on one of the housing and the ring abuts on and engages the engagement surface of the engagement wall provided on the other one of the housing and the ring. This configuration can thus prevent the ring from disengaging from (coming off) the housing. 
     Furthermore, in the process of attaching the ring to the housing, the guide surface of the guide wall guides the ring rearward relative to the housing and also guides the at least one projection to the at least one engagement position. In the direction in which the projection moves away from the guide surface in the front-rear direction, the open space extends from the guide surface to the area that corresponds to the end of the second surface. Specifically, in an embodiment in which the at least one projection abuts on the guide surface from the front (that is, the at least one guide wall is provided on the outer peripheral surface of the peripheral wall part of the housing), the open space extends in front of the guide surface. On the other hand, in another embodiment in which the at least one projection abuts on the guide surface from the rear (that is, the at least one guide wall is provided on the inner peripheral surface of the ring), the open space extends behind (to the rear of) the guide surface. In other words, the second surface has no protrusion in front of or behind the guide surface that may block the at least one projection from moving in the front-rear direction. 
     The configuration according to this aspect can eliminate the need for a user to position the ring relative to the housing precisely at a specific position in the circumferential direction. Instead, the user only needs to move the ring rearward until the at least one projection abuts on the guide surface of the at least one guide wall, followed by rotating the ring in the circumferential direction so that the at least one projection slides on (along) the guide surface. This simple manipulation can swiftly place the at least one projection at the at least one engagement position where the projection abuts on the engagement surface. According to this aspect, the ventilation apparatus can thus have an improved operability in attaching the ring to the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a rear view of a jacket. 
         FIG. 2  is an illustration that shows a fan attachment portion of the jacket, a battery holder, and a connecting cable. 
         FIG. 3  is a perspective view of a fan unit  1 , with a ring removed from a body. 
         FIG. 4  is a side view of the fan unit. 
         FIG. 5  is a rear view of the fan unit. 
         FIG. 6  is a cross-sectional view taken along line VI-VI of  FIG. 5 . 
         FIG. 7  is a cross-sectional view taken along line VII-VII of  FIG. 4 . 
         FIG. 8  is a perspective view of a front member, a rear member, and the ring each separated from one another. 
         FIG. 9  is a partial, enlarged view of  FIG. 6 . 
         FIG. 10  is a cross-sectional view taken along line X-X of  FIG. 5 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In one or more embodiments of the present disclosure, at least one first rotation-restriction part may be provided on one of the housing and the ring. At least one second rotation-restriction part may be provided on the other one of the housing and the ring. The at least second rotation-restriction part may be configured to engage with the first rotation-restriction part to restrict rotation of the ring relative to the housing around the first axis. 
     According to the this embodiment, engagement between the first rotation-restriction part and the second rotation-restriction part restricts rotation of the ring relative to the housing. This reduces the possibility that the at least one projection moves in the circumferential direction from the at least one engagement position and away from the engagement wall, which may cause the ring to come off the housing. Note that the term “restrict” used herein not only refers to completely preventing (prohibiting) rotation but also to allowing some rotation under a certain condition (when subjected to an external force, for example); therefore, the term can also be rephrased as “selectively (conditionally) prevent”. 
     In one or more embodiments of the present disclosure, the at least one first rotation-restriction part may include the at least one projection provided on the first surface. The at least one second rotation-restriction part may include at least one restriction wall protruding from the second surface. The at least one restriction wall may be located on a side of the at least one engagement position toward the at least one guide wall in the circumferential direction. 
     In the ventilation apparatus of this aspect, the at least one projection can fulfill two functions of: (i) preventing the ring from moving away from the housing in the front-rear direction; and (ii) restricting the ring from rotating in a direction that causes the at least one projection to disengage from the engagement wall in the circumferential direction. This simple structure can thus reduce more effectively the possibility of the ring coming off the housing. 
     In one or more embodiments of the present disclosure, in a case where the at least one guide wall is provided on the outer peripheral surface of the peripheral wall part, the guide surface may be a front surface of the at least one guide wall and may at least partially be inclined rearward as it extends toward the above-mentioned one end in the circumferential direction. In a case where the at least one guide wall is provided on the inner peripheral surface of the ring, the guide surface may be a rear surface of the at least one guide wall and may at least partially be inclined frontward as it extends toward the above-mentioned one end in the circumferential direction. According to this aspect, the user can attach the ring to the housing through ergonomically natural operations of rotating the ring circumferentially relative to the housing while moving the ring rearward. 
     In one or more embodiments of the present disclosure, the at least one engagement surface may include a plurality of engagement surfaces that are located differently from each other in both the front-rear direction and the circumferential direction. According to this aspect, the user can select one of the engagement positions for the projection according to the thickness of the fabric of the garment to which the ventilation apparatus is attached, so that the fabric can be clamped appropriately between the first clamping part and the second clamping part. Furthermore, according to this aspect, the plurality of engagement surfaces are formed on the same engagement wall. This allows the user to stop the ring such that the projection engages one suitable engagement surface, among the plurality of engagement surfaces, according to the thickness of the fabric while rotating the ring circumferentially relative to the housing. This configuration can eliminate the need for the user to remove the ring from the housing and then attach it again, and thus allows for a simplified procedure. 
     In one or more embodiments of the present disclosure, the at least one projection may include a plurality of projections that are disposed at equal intervals in the circumferential direction. The at least one guide wall may include a plurality of guide walls that are disposed at equal intervals in the circumferential direction. The at least one engagement wall may include a plurality of engagement walls that are disposed at equal intervals in the circumferential direction. Each of the plurality of guide walls may extend in the circumferential direction between two neighboring engagement walls among the plurality of engagement walls. According to this aspect, the plurality of projections can respectively engage with the plurality of engagement walls. This configuration can reduce more reliably the possibility of the ring coming off the housing. Furthermore, the guide surfaces of the plurality of guide walls, which respectively correspond to the plurality of the engagement walls, can guide the plurality of projections respectively to their suitable engagement positions. 
     In one or more embodiments of the present disclosure, the at least one projection may protrude from the inner peripheral surface of the ring. The at least one guide wall and the at least one engagement wall may each protrude from the outer peripheral surface of the peripheral wall part of the housing. The housing has a length of a certain level in the front-rear direction such that the motor and the fan can be accommodated in the housing. According to this aspect, the at least one guide wall and the at least one engagement wall are provided on the housing, and thus the ring, on which the projection is provided, is allowed to have a minimum length in the front-rear direction. 
     In one or more embodiments of the present disclosure, the housing may be formed by a first member and a second member that are separably connected to each other in the front-end direction. The first member may at least include the first clamping part and an inlet-side cover. The inlet-side cover may have a plurality of inlet openings and cover an opening at a rear end of the peripheral wall part. The second member may at least include a portion of the peripheral wall part and a discharge-side cover. The discharge-side cover may have a plurality of discharge openings and cover an opening at a front end of the peripheral wall part. The first member may include the at least one engagement wall. Prolonged use of the ventilation apparatus may cause dustiness inside the housing and on the fan. According to this aspect, the user can separate the first member and the second member to clean the fan and inside the housing. Furthermore, since the at least one engagement wall is provided on the first member, the ring cannot be attached to the housing unless the first member is connected to the second member. This configuration can prevent the ventilation apparatus from being attached to and used with the garment when the housing is incomplete. 
     In one or more embodiments of the present disclosure, the motor and the fan may be accommodated in the second member. Therefore, according to this aspect, the ventilation apparatus can be prevented from being used without the inlet-side cover (that is, the cover for the fan) in place. 
     In one or more embodiments of the present disclosure, the second member may include the at least one guide wall. On the inner peripheral surface of the ring, at least one additional projection may be provided more frontward than the at least one projection and may protrude radially inward from the inner peripheral surface. According to this aspect, in the event that the first member and the second member are disconnected while the at least one projection of the ring is engaged with the at least one engagement wall of the first member, the at least one additional projection of the ring can abut on the at least one guide wall to thereby prevent the second member from coming off through the ring. 
     In one or more embodiments of the present disclosure, the first member may include a first peripheral wall part that is a portion of the peripheral wall part. The second member may include a second peripheral wall part that is another portion of the peripheral wall part and that is partially fitted around the first peripheral wall part. An outer peripheral surface of the second peripheral wall part may form the above-mentioned outer peripheral surface of the peripheral wall part. The at least one engagement wall may be provided on the first peripheral wall part of the first member, and may protrude radially outward from the outer peripheral surface through at least one recess formed in the second peripheral wall part. This allows the at least one engagement wall to be provided on the first member in a reasonable configuration. 
     In one or more embodiments of the present disclosure, the second member may include at least one engagement piece. The at least one engagement piece may each have a hook on its tip end portion and may be elastically deformable in the radial direction. The hook may be engaged with the at least one engagement wall such that the hook is disengageable in response to elastic deformation of the at least one engagement piece. This achieves a reasonable structure for separably connecting the first and the second members utilizing the at least one engagement wall. 
     In one or more embodiments of the present disclosure, the at least one projection may include a plurality of projections that are disposed at equal intervals in the circumferential direction. The at least one guide wall may include a plurality of guide walls that are disposed at equal intervals in the circumferential direction. The at least one engagement wall may include a plurality of engagement walls that are disposed at equal intervals in the circumferential direction. Each of the plurality of guide walls may extend in the circumferential direction between two neighboring engagement walls among the plurality of engagement walls. Each of the plurality of guide walls may have a first end and a second end in the circumferential direction. The guide surface may be a front surface of each of the plurality of guide walls, and may be configured to guide the projection in a first direction, which is a direction from the first end toward the second end. Each of the plurality of guide walls may be disposed such that the guide surface extends in the first direction substantially continuously from a front surface of one of the plurality of engagement walls that is located on a second direction side of the guide wall. The second direction is opposite to the first direction (i.e., a direction from the second end toward the first end). According to this aspect, the front surface of one guide wall and the front surface of one engagement wall that is located on the second direction side of the guide wall can, as a whole, function as a continuous guide surface for a next engagement wall that is located on a first direction side (i.e., on the opposite side) of the guide wall. Furthermore, engagements between the plurality of projections and the plurality of engagement walls at respective multiple positions in the circumferential direction can reduce more reliably the possibility of the ring coming off the housing. 
     In one or more embodiments of the present disclosure, the at least one guide wall has an approximately right triangular shape when the peripheral wall part is viewed from a position radially outward of the peripheral wall part. The first end may substantially connect to an end of the one engagement wall, among the plurality of engagement walls, that is located on the second direction side of the guide wall. A rear end of the at least one guide wall may substantially connect to a front surface of the first clamping part. The guide surface may be inclined rearward at a substantially constant angle as it extends from the first end to the second end. According to this aspect, the user can attach the ring to the housing through ergonomically natural operations of rotating the ring relative to the housing in the first direction while moving the ring rearward. 
     A fan unit  1  is described below as a representative, non-limiting example of a ventilation apparatus according to the present disclosure, with reference to the drawings. Also, a jacket  9  is described below as a representative, non-limiting example of a garment, to (on) which the ventilation apparatus can be removably attachable (mountable). 
     Firstly, an aspect of use of the fan unit  1  of this embodiment is briefly described. 
     As shown in  FIG. 1  and  FIG. 2 , the fan unit  1  of this embodiment is used in a state of being attached to (mounted on), for example, a jacket  9 . The jacket  9  is a long-sleeved, open-front upper-body garment that is mainly made of a fabric  90  covering the upper half of a wearer. The fabric  90  has two attachment holes (mounting holes)  91  for attachment (mounting) of the fan unit  1 . The attachment holes  91  are arranged at two positions in the lower section of a back-body portion of the fabric  90 . Thus, two fan units  1  can be attached to the jacket  9 . Each attachment hole  91  is an opening into which a housing  4  (specifically, a tubular part  41 ) of the fan unit  1  (see  FIG. 3 ) can be inserted. Note that in the following description, the peripheral portion of each attachment hole  91  is also referred to as a fan attachment portion  93 . An inner surface of the jacket  9  (of a front-body portion, for example) has a pocket  94  that can house a battery holder  95 . The battery holder  95  has a rechargeable battery  96  mounted therein. A branched-end connecting cable  97  electrically connects the battery holder  95  and the two fan units  1 . 
     When attached, the fan unit  1  is partially inserted inside the jacket  9  (to the side that faces the wearer&#39;s body) through the attachment hole  91 , while inlet openings  471  are left exposed outside the jacket  9 . The fan unit  1  sucks air outside the jacket  9  through the inlet openings  471  and discharges the air inside the jacket  9  through discharge openings  481  placed inside the jacket  9  (see  FIG. 3 ). The air discharged inside the jacket  9  cools down the wearer&#39;s body as it circulates inside the jacket  9 , and then flows out of the jacket  9  through cuffs and a collar. As such, the fan unit  1  attached to the jacket  9  can ventilate inside the jacket  9  and provide the user a comfortable environment for working. 
     Next, the general structure of the fan unit  1  is described. 
     As shown in  FIGS. 3 to 6 , the fan unit  1  includes a body  3  and a ring  5 . The body  3  is mainly formed by a motor  33 , a fan  36  that is rotationally driven by the motor  33 , and the housing  4  that accommodates the motor  33  and the fan  36 . The housing  4  is configured as a casing of an approximately circular shape as viewed in an extension direction of a rotational axis A 1  of the fan  36  (hereinafter also simply referred to as a rotational-axis-A 1  direction). At an end of the housing  4  in the rotational-axis-A 1  direction, a flange  46  protrudes radially outward. The ring  5 , as a whole, forms a short, hollow cylindrical body with a central axis A 2 . The ring  5  is removably attachable to (mountable around) the outer peripheral portion of the housing  4 . At an end of the ring  5  in an extension direction of the central axis A 2  (hereinafter also simply referred to as a central-axis-A 2  direction), a flange  55  protrudes radially outward. 
     In this embodiment, the flange  46  of the body  3  is disposed outside the jacket  9  while the remaining parts of the body  3  other than the flange  46  are inserted inside the jacket  9  (that is, the side that faces the wearer&#39;s back) through the attachment hole  91 . Then, from inside the jacket  9 , the ring  5  is coaxially fitted (mounted) around the outer peripheral portion of the body  3  (the housing  4 ). This allows the flange  46  of the housing  4  and the flange  55  of the ring  5  to clamp the fabric  90  around the fan attachment hole  91  (at the fan attachment portion  93 ), and thereby results in the attachment of the fan unit  1  to the jacket  9 . 
     Note that in the following description, for the sake of convenience, directions related to the fan unit  1  are defined based on the direction that the user faces when the user has put on the jacket  9  with the fan unit  1  attached thereto. Specifically, the direction along the rotational axis A 1  of the fan  36  and of the central axis A 2  of the ring  5  is defined as a front-rear direction. In the front-rear direction, a side on which the inlet openings  471  are located is defined as a rear side and the other side on which the discharge openings  481  are located is defined as a front side. According to the definitions of the directions, the flange  46  of the housing  4  may sometimes be referred to as the rear flange  46 , whereas the flange  55  of the ring  5  may sometimes be referred to as the front flange  55 . As for directions circumferentially around the rotational axis A 1  and the central axis A 2 , the clockwise direction when the fan unit  1  is viewed from the front is defined as a first direction D 1 , and the counterclockwise direction is defined as a second direction D 2 . 
     The structures of the body  3  and the ring  5  of the fan unit  1  are described below in detail in this order. 
     Firstly, the ring  5  is described. As shown in  FIGS. 3,4,6, and 7 , the ring  5  includes a tubular part  51 , the above-described front flange  55 , and tabs  58 . Note that in this embodiment, the tubular part  51 , the front flange  55 , and the tabs  58  are integrally formed of synthetic resin (polymeric material). The ring  5  is at least partially elastically deformable (deflectable, flexible) by a slight amount, at least in its radial direction. 
     The tubular part  51  is a short, hollow cylindrical body. The tubular part  51  is configured to be fitted (mounted) around the tubular part  41  of the housing  4 . Three projections  52  are formed on the inner periphery of a rear end portion of the tubular part  51 . Each projection  52  protrudes radially inward of the tubular part  51  from an inner peripheral surface  510  thereof. Each projection  52  is configured to be engaged with and held by an engagement wall  42  and a rotation-restriction part  43  of the tubular part  41  of the body  3 , as will be described later. In this embodiment, each projection  52  has a generally rectangular (parallelepiped) shape, and has a front surface  520  that is approximately orthogonal to the central axis A 2  of the ring  5 . Furthermore, the three projections  52  are disposed at approximately equal intervals in a circumferential direction of the ring  5 . In this embodiment, a length of protrusion of each projection  52  is set such that when the ring  5  is attached to the housing  4 , a tip end (protruded end) of the projection  52  has no substantial contact with an outer peripheral surface  410  of the tubular part  41  of the housing  4 . However, in a case where the rotation-restriction parts  43  (described below) are not provided, the projections  42  may be allowed to contact the outer peripheral surface  410  of the tubular part  41 . 
     Three ridges  53  are formed on the inner periphery of a front end portion of the tubular part  51 . Each ridge  53  extends in the circumferential direction, corresponding to a region between two neighboring projections  52 . In other words, the ridges  53  are formed at positions different from those of the projections  52  (formed in regions with no projections  52 ). Note that a length of protrusion of each ridge  53  is set such that when the ring  5  is attached to the housing  4 , a tip end (protruded end) of the ridge  53  substantially contacts the outer peripheral surface  410  of the tubular part  41  of the housing  4  (see  FIG. 10 ). 
     The front flange  55  is a portion that functions to clamp the fan attachment portion  93  of the jacket  9  in conjunction with the rear flange  46  of the body  3 . The front flange  55  protrudes radially outward from an end portion of the tubular part  51  in the central-axis-A 2  direction (specifically, from the rear end portion). In this embodiment, the front flange  55  is formed into a circular ring. The front flange  55  has a rear surface  550  that extends in a direction approximately orthogonal to the central axis A 2 . Note that in this embodiment, the rear surface  550  of the front flange  55  is located at an approximately same position as rear ends of the projections  52  in the front-rear direction. 
     Each of the tabs  58  is a protruding piece of an approximately trapezoidal shape when viewed from the front. The tab  58  protrudes radially outward from an end portion of the tubular part  51  that is opposite to the end portion where the front flange  55  is provided (that is, from the front end portion). In this embodiment, six tabs  58  are provided on the tubular part  51  at approximately equal intervals in the circumferential direction. The user can have his/her fingers on the tabs  58  when rotating the ring  5  relative to the housing  4 . This allows for easy rotation of the ring  5  relative to the body  3 . Note that three of the tabs  58  are respectively arranged at the same positions as the three projections  52 , circumferentially around the ring  5 . A front surface of each of these three tabs  58  has an indication that shows where the corresponding projection  52  is. 
     The body  3  is described below. As described above, the body  3  is mainly formed by the motor  33 , the fan  36 , and the housing  4 . 
     As shown in  FIG. 6 , the motor  33  and the fan  36  are disposed coaxially in the housing  4 . A brushless DC motor is employed as the motor  33  in this embodiment; however, a brushed motor may alternatively be employed. An axial fan is employed as the fan  36 . More specifically, the fan  36  includes a cup-shaped base part  361  and a plurality of blades  363  protruding from the base part  361 . The base part  361  is disposed to cover the motor  33  from the rear and is coaxially fixed to an output shaft  331  of the motor  33 . The fan  36  is rotated around the rotational axis A 1  integrally with the output shaft  331 , while the motor  33  is driven. Note that the structures of the fan  36  (such as the shape of the base part  361 , the number of the blades  363 , the arrangement of the fan  36  relative to the motor  33 ) may be changed as needed. 
     As shown in  FIGS. 3 to 5 , the housing  4 , when viewed as a whole, includes the tubular part  41 , the rear flange  46 , an inlet-side cover  47 , and a discharge-side cover  48 . Furthermore, as shown in  FIG. 6  and  FIG. 8 , the housing  4  is formed by a front member  401  and a rear member  402  in this embodiment. Each of the front member  401  and the rear member  402  is a single, integrally molded member formed of synthetic resin. The front member  401  includes an outer tubular part  411  of a hollow cylindrical shape, and the discharge-side cover  48  described above. The rear member  402  includes an inner tubular part  416  of a hollow cylindrical shape, and the rear flange  46  and the inlet-side cover  47  described above. The front member  401  and the rear member  402  are connected to each other by having the outer tubular part  411  of the front member  401  mounted (fitted) around the outer periphery of the inner tubular part  416  of the rear member  402 . The inner tubular part  416  and the outer tubular part  411  together form the tubular part  41 . Note that in this embodiment, the front member  401  and the rear member  402  are connected to each other in a separable manner, as will be described in detail later. 
     The tubular part  41  is a wall part of a hollow cylindrical shape (i.e. a peripheral wall part). As described above, since the tubular part  41  is formed by the inner tubular part  416  and the outer tubular part  411 , a large part of the tubular part  41  has a double-walled structure. The outer peripheral surface  410  of the tubular part  41  is formed by the outer peripheral surface of the outer tubular part  411 . The tubular part  41  is disposed at least partially around the fan  36  (surrounding the fan  36 ), coaxially with the rotational axis A 1  of the fan  36 . The outer diameter of the tubular part  41  is set smaller than the inner diameter of the tubular part  51  of the ring  5 . That is, a distance between the rotational axis A 1  of the fan  36  (the central axis of the tubular part  41 ) and the outer peripheral surface  410  of the tubular part  41  (specifically, of the outer tubular part  411 ) is smaller than a distance between the central axis A 2  and the inner peripheral surface  510  of the tubular part  51  of the ring  5 . Therefore, when the ring  5  is mounted (fitted) around the housing  4 , the outer peripheral surface  410  of the tubular part  41  is spaced apart from the inner peripheral surface  510  of the ring  5  (see  FIG. 7 ). 
     As shown in  FIG. 3 , the engagement walls  42 , the rotation-restriction parts  43 , and guide walls  44  are provided on the outer peripheral portion of the tubular part  41 . Details of the engagement walls  42 , the rotation-restriction parts  43 , and the guide walls  44  will be described later. 
     As shown in  FIG. 3  and  FIG. 6 , the rear flange  46  is a portion that is opposed to the front flange  55  of the ring  5  in the front-rear direction, and functions to clamp the fan attachment portion  93  (fabric  90 ) in conjunction with the front flange  55 . The rear flange  46  protrudes radially outward of the tubular part  41  from an end portion thereof in the rotational-axis-A 1  direction (the front-rear direction) on a suction side of the fan  36  (that is, a rear end portion of the tubular part  41 ). In this embodiment, the rear flange  46  is formed into a circular ring. Note that in this embodiment, the outer diameter of the rear flange  46  is set slightly larger than that of the front flange  55  of the ring  5 . The rear flange  46  has a front surface  460  that extends in the direction approximately orthogonal to the rotational axis A 1 . 
     As shown in  FIG. 5  and  FIG. 6 , the inlet-side cover  47  is configured as a circular cover that covers an opening at the rear end of the tubular part  41  (that is, an opening on the suction side of the fan  36 ). Multiple inlet openings  471  are formed in the inlet-side cover  47 . As the fan  36  is rotated, air is sucked through the inlet openings  471  into the housing  4 . 
     As shown in  FIG. 3  and  FIG. 6 , the discharge-side cover  48  is disposed to cover an opening at a front end of the tubular part  41  (that is, an opening on a discharge side of the fan  46 ). In this embodiment, the discharge-side cover  48 , as a whole, has a circular dome shape that protrudes frontward from the front end of the tubular part  41 . Multiple discharge openings  481  are formed in the discharge-side cover  48 . As the fan  36  is rotated, the air sucked through the inlet openings  471  into the housing  4  is discharged from the fan  46  through the discharge openings  481 . A recess  489  is formed across a segment of the discharge-side cover  48  in the circumferential direction. A connector  37  is disposed between the recess  489  and the rotational axis A 1 . The connector  37  is electrically connected to the motor  33 . A connector  973  (see  FIG. 2 ) of the connecting cable  97 , which is connected to the battery holder  95 , can be placed in the recess  489  and connected to the connector  37 . This makes electrical connection between the battery holder  95  and the fan unit  1 . 
     The engagement walls  42 , the rotation-restriction parts  43 , and the guide walls  44 , all of which are provided on the outer peripheral portion of the tubular part  41 , are now described in this order. 
     First, the engagement walls  42  are described. As shown in  FIGS. 3, 6, 7, 9, and 10 , each of the engagement walls  42  is a wall part (protruding part) that protrudes radially outward of the outer peripheral surface of the tubular part  41  (or more specifically, of the outer tubular part  411 ). Thus, the engagement wall  42  is a wall part that has a thickness in the radial direction of the tubular part  41 . The engagement wall  42  is spaced apart from the rear flange  46  in the rotational-axis-A 1  direction (i.e., in the front-rear direction) of the tubular part  41  and extends in the circumferential direction of the tubular part  41 . When viewed from the side of (or from a position radially outward of) the tubular part  41 , the engagement wall  42  is narrow in the front-rear direction and elongate in the circumferential direction. A front end of the engagement wall  42  is located around midway through the tubular part  41  in the front-rear direction. In this embodiment, three such engagement walls  42  are disposed on the tubular part  41  at approximately equal intervals in the circumferential direction. 
     A distance between the rotational axis A 1  of the fan  36  (the central axis of the tubular part  41 ) and an outer peripheral surface of the engagement wall  42  is approximately equal to or slightly smaller than the distance between the central axis A 2  of the tubular part  51  and the inner peripheral surface  510  of the ring  5 . Therefore, when the ring  5  is mounted (fitted) around the body  3 , the outer peripheral surface of the engagement wall  42  at least partially makes substantial contact with the inner peripheral surface  510  of the ring  5 . 
     Moreover, in front of a front surface  420  of each engagement wall  42 , an open space  425  extends from the front surface  420  to the front end of the tubular part  41 . The open space  425  has a shape that conforms to a segment (portion) of a hollow cylinder in its circumferential direction. More specifically, a radially outward end of the open space  425  is defined by a virtual curved surface containing the outer peripheral surface of the engagement wall  42 , and a radially inward end of the open space  425  is defined by the outer peripheral surface  410  of the tubular part  41 . Further, the open space  425  extends circumferentially from one end to the other end of the engagement wall  42  in the circumferential direction. Thus, in this embodiment, there is nothing particular protruding from the outer peripheral surface  410  of the tubular part  41  in front of the engagement wall  42 . In other words, in an area that extends in front of the engagement wall  42  and that corresponds to the engagement wall  42  in the circumferential direction (ranges from one end to the other end of the engagement wall  42  in the circumferential direction), the outer peripheral surface  410  of the tubular part  41  forms a smooth surface (curved surface) with no projections. 
     In this embodiment, the engagement wall  42  includes a ring engagement part  421  and a hook engagement part  427 . The hook engagement part  427  is an end portion of the engagement wall  42  that faces the first direction D 1  (i.e. an end portion of the engagement wall  42  that is located on the first direction D 1  side). The ring engagement part  421  is the remaining portion of the engagement wall  42  other than the hook engagement part  427 , and occupies generally two thirds of the engagement wall  42  from an end that faces the second direction D 2  (i.e. an end of the engagement wall  42  that is located on the second direction D 2  side). 
     The ring engagement part  421  is configured to abut on the projection  52  of the ring  5  and thereby block (prevent) the ring  5  from moving away from the body  3  (the housing  4 ) in the rotational-axis-A 1  direction (in other words, in a direction that the front flange  55  and the rear flange  46  move away from each other). Thus, the ring engagement part  421  is configured to block the ring  5  from moving frontward relative to the housing  4 . 
     More specifically, a rear surface of the ring engagement part  421  (that is, a surface that is opposed to the rear flange  46 ) includes two engagement surfaces  423 ,  424 . The engagement surfaces  423 ,  424  are located differently from each other in both the front-rear direction and the circumferential direction. Hereinafter, among the two engagement surfaces  423 ,  424 , the engagement surface that is located more frontward (that is, farther from the rear flange  46 ) is referred to as the front engagement surface  423 ; whereas the engagement surface that is located more rearward (that is, closer to the rear flange  46 ) is referred to as the rear engagement surface  424 . The rear engagement surface  424  is located on a side of the front engagement surface  423  that faces the first direction D 1  (i.e. located on the first direction D 1  side of the front engagement surface  423 ). 
     Each of the front engagement surface  423  and the rear engagement surface  424  is a flat surface that extends in a direction approximately orthogonal to the rotational axis A 1 . Each of the front engagement surface  423  and the rear engagement surface  424  is configured to make plane contact (or to make contact via multiple points or lines) with the front surface  520  (flat surface) of the projection  52  with stability. In this embodiment, the front engagement surface  423  and the rear engagement surface  424  are connected in the circumferential direction by an inclined (oblique) surface that is inclined (slopes) gradually as it extends circumferentially. Note that, however, the front engagement surface  423  and the rear engagement surface  424  may alternatively be connected by a surface that is approximately orthogonal to the front engagement surface  423  and the rear engagement surface  424 . 
     Owing to the above-described configuration, a distance d 1  between the front engagement surface  423  and the front surface  460  of the rear flange  46  in the front-rear direction is larger than a distance d 2  between the rear engagement surface  424  and the front surface  460  of the rear flange  46  in the front-rear direction (see  FIG. 3 ). Also, both the distance d 1  and the distance d 2  are set larger than a distance d 3  between the front surface  520  of the projection  52  and the rear surface  550  of the front flange  55  of the ring  5  in the front-rear direction (see  FIG. 9 ). Therefore, when the front surface  520  of the projection  52  is in contact with the front engagement surface  423  and also when the front surface  520  of the projection  52  is in contact with the rear engagement surface  424 , the projection  52  is spaced apart frontward from the rear flange  46 . In other words, a gap is formed (defined) between the rear surface  550  of the front flange  55  of the ring  5  and the front surface  460  of the rear flange  46  of the housing  4 . The fabric  90  is placed in this gap and clamped between the front flange  55  and the rear flange  46 . 
     The hook engagement part  427  is a portion of a mechanism for connecting the front member  401  and the rear member  402 . The hook engagement part  427  is configured to engage with a hook (claw, projection, catch)  414  of an engagement piece (cantilever)  413  which will be described later. A rear surface of the hook engagement part  427  is a flat surface that extends in a direction approximately orthogonal to the rotational axis A 1 . An insertion hole  428  penetrates through the hook engagement part  427  in the front-rear direction. The insertion hole  428  is configured to receive the engagement piece  413  inserted therethrough. 
     Two partition walls  429  are provided rearward of the hook engagement part  427 . Each partition wall  429  is configured as a wall part (protruded piece) that protrudes radially outward of the outer peripheral surface  410  of the tubular part  41  (more specifically, of the outer tubular part  411 ). The two partition walls  429  are located on both sides of the insertion hole  428  of the hook engagement part  427  in the circumferential direction of the tubular part  41 , and extend in the front-rear direction so as to connect a rear surface of the engagement wall  42  and the front surface  460  of the rear flange  46 . Note that a distance between the rotational axis A 1  of the fan  36  (the central axis of the tubular part  41 ) and a tip end (protruded end) of each partition wall  429  is generally equal to or slightly smaller than the distance between the central axis A 2  of the tubular part  51  and the inner peripheral surface  510  of the ring  5 . Therefore, when the ring  5  is mounted around the body  3 , the tip end of each partition wall  429  at least partially makes substantial contact with the inner peripheral surface  510  of the ring  5 . 
     Next, the rotation-restriction parts  43  are described. each of the rotation-restriction part  43  is configured to abut on the projection  52  of the ring  5  and thereby restrict the ring  5  from moving (rotating) relative to the housing  4  in the circumferential direction around the rotational axis A 1 . More specifically, the rotation-restriction part  43  is configured to restrict the projection  52  placed at a position corresponding to the front engagement surface  423  (hereinafter referred to as a first engagement position) or at a position corresponding to the rear engagement surface  424  (hereinafter referred to as a second engagement position) from moving in a direction that causes the projection  52  to disengage from the engagement wall  42  (specifically, in the second direction D 2 ). 
     As shown in  FIG. 3  and  FIG. 7 , the rotation-restriction part  43  includes two restriction walls  431 ,  432 . Each of the restriction walls  431 ,  432  is configured as a wall part (protruded piece) that protrudes radially outward of the outer peripheral surface  410  of the tubular part  41  (more specifically, of the outer tubular part  411 ). Each of the restriction walls  431 ,  432  extends in the front-rear direction so as to connect the rear surface of the engagement wall  42  and the front surface  460  of the rear flange  46 . The restriction wall  431  is located on a side of the front engagement surface  423  that faces the second direction D 2  (i.e. located on the second direction D 2  side of the front engagement surface  423 ). The restriction wall  432  is located on a side of the rear engagement surface  424  that faces the second direction D 2  (i.e. located on the second direction D 2  side of the rear engagement surface  424 ). Hereinafter, the restriction wall  431  that corresponds to the front engagement surface  423  is also referred to as the first restriction wall  431 ; whereas the restriction wall  432  that corresponds to the rear engagement surface  424  is also referred to as the second restriction wall  432 . Also, in this embodiment, three rotation-restriction parts  43  (i.e., the three pairs of restriction walls  431 ,  432 ) are provided, respectively corresponding to the three engagement walls  42 . 
     For each tip end portion (each radially outward end portion) of the restriction walls  431 ,  432 , a surface that faces the second direction D 2  (a second direction D 2  side surface) is inclined (slopes) toward the first direction D 1  as it extends radially outward. On the other hand, for each tip end portion of the restriction walls  431 ,  432 , a surface that faces the first direction D 1  (a first direction D 1  side surface) is inclined (slopes) toward the second direction D 2  as it extends radially outward. Assuming a circle of a radius extending from the rotational axis A 1  to the tip end of the restriction wall  431  in a cross-section orthogonal to the rotational axis A 1 , an angle between a tangent line at the tip end of the restriction wall  431  and the first direction D 1  side surface of the wall is larger than an angle between the same tangent line and the second direction D 2  side surface of the wall. The same is true for the two surfaces of the restriction wall  432 . The angles make it more difficult for the projection  52  to ride over the restriction walls  431 ,  432  when the ring  5  is rotated relative to the housing  4  in the second direction D 2 , than when the ring  5  is rotated relative to the housing  4  in the first direction D 1 . 
     Further, a distance between the rotational axis A 1  of the fan  36  (the central axis of the tubular part  41 ) and the tip end (protruded end) of each restriction walls  431 ,  432  is smaller than the distance between the central axis A 2  of the tubular part  51  and the inner peripheral surface  510  of the ring  5 . Therefore, when the ring  5  is mounted around the body  3 , the tip end of each restriction walls  431 ,  432  is located radially inward and spaced apart from the inner peripheral surface  510  of the tubular part  51  of the ring  5 . Thus, neither tip of the restriction walls  431 ,  432  contacts the inner peripheral surface  510  of the ring  5 . A distance between the tip end of each of the restriction walls  431 ,  432  and the inner peripheral surface  510  in the radial direction at this time is set slightly smaller than the length that the projection  52  protrudes from the inner peripheral surface  510  of the ring  5 . 
     The guide walls  44  are described below. Each of the guide walls  44  is configured such that the guide wall  44  abuts on the projection  52  and thereby guide the projection  52  to a position where the projection  52  can engage the engagement wall  42  (the first engagement position) in the process of mounting the ring  5  on (around) the body  3 . 
     Specifically, as shown in  FIGS. 3, 6, and 7 , each of the guide walls  44  is configured as a wall part (protruding or stepped part) that protrudes radially outward of the outer peripheral surface  410  of the tubular part  41  (more specifically, of the outer tubular part  411 ). That is, the guide wall  44  has a thickness in the radial direction of the tubular part  41 . The guide wall  44  extends in the circumferential direction between two neighboring engagement walls  42 . In this embodiment, three guide walls  44  are located at approximately equal intervals in the circumferential direction. An end of each guide wall  44  that faces the second direction D 2  (a second direction D 2  side end of the guide wall  44 ) is located at a substantially same position in the circumferential direction as an end of one engagement wall  42  that faces the first direction D 1  (a first direction D 1  side end of the engagement wall  42 ). This end of the guide wall  44  is hereinafter referred to as a first end  441 . Another end of each guide wall  44  that faces the first direction D 1  (a first direction D 1  side end of the guide wall  44 ) is located at a substantially same position in the circumferential direction as an end of another engagement wall  42  that faces the second direction D 2  (a second direction D 2  side end of the engagement wall  42 ). This end of the guide wall  44  is hereinafter referred to as a second end  442 . In this manner, in this embodiment, three engagement walls  42  and three guide walls  44  are arranged alternatingly in the circumferential direction, substantially with no gap therebetween. 
     In this embodiment, the guide wall  44  has an approximately right triangular shape as viewed from the side of the tubular part  41 . More specifically, the first end  441  of the guide wall  44  extends linearly in the front-rear direction, and substantially contacts the first direction D 1  side end of the engagement wall  42 . A rear end of the guide wall  44  connects to the front surface  460  of the rear flange  46 . A front surface  440  of the guide wall  44  is gradually inclined (slopes) rearward (in a direction toward the rear flange  46 ) at a substantially constant angle as it extends from the first end  441  to the second end  442  of the guide wall  44  (as it extends in the first direction D 1 ). The front surface  440  of the guide wall  44  functions as a guide surface that abuts on the projection  52  and guides the projection  52 . 
     At the first end  441 , the front surface  440  of the guide wall  44  is at an approximately same position as the front surface  420  of the engagement wall  42  in the front-rear direction. That is, the front surface  440  substantially connects to (is substantially continuous with) the front surface  420  of the engagement wall  42 . Also, at the second end  442  of the guide wall  44 , the front surface  440  is at a position that is slightly spaced apart frontward from the front surface  460  of the rear flange  46  in the front-rear direction. More specifically, a distance in the front-rear direction between the front surface  440  of the guide wall  44  and the front surface  460  of the rear flange  46  at the second end  442  is approximately equal to a distance in the front-rear direction between the rear surface  550  of the front flange  55  and front surface  460  of the rear flange  46  when the projection  52  is engaged with (abuts on) the front engagement surface  423  (when the front surface  520  is in contact with the front engagement surface  423 ) (that is, the thickness of the fabric  90  to be clamped). Thus, the position of the front surface  440  at the second end  442  in the front-rear direction is set according to the thickness of the fabric  90  to be clamped by the front flange  55  and the rear flange  46 . 
     A length that the guide wall  44  protrudes from the outer peripheral surface  410  of the tubular part  41  is approximately equal to a length that the engagement wall  42  protrudes from the outer peripheral surface  410 . That is, a distance between the rotational axis A 1  of the fan  36  (the central axis of the tubular part  41 ) and the outer peripheral surface of the guide wall  44  is generally equal to or slightly smaller than the distance between the central axis A 2  of the tubular part  51  and the inner peripheral surface  510  of the ring  5 . Therefore, when the ring  5  is mounted on the body  3 , the outer peripheral surface of the guide wall  44  at least partially makes substantial contact with the inner peripheral surface  510  of the ring  5 . 
     Furthermore, in front of each front surface  440  of the guide wall  44 , an open space  445  extends from the front surface  440  to the front end of the tubular part  41 . The open space  445  has a shape that generally conforms to a segment (portion) of a hollow cylinder. More specifically, a radially outward end of the open space  445  is defined by a virtual curved surface containing the outer peripheral surface of the guide wall  44  and a radially inward end of the open space  445  is defined by the outer peripheral surface  410  of the tubular part  41 . Further, the open space  445  extends circumferentially from the first end  441  to the second end  442  of the guide wall  44 . Thus, in this embodiment, there is nothing particular protruding from the outer peripheral surface  410  of the tubular part  41  in front of the guide wall  44 . In other words, in an area that extends in front of the guide wall  44  and that corresponds to the guide wall  44  in the circumferential direction (ranges from the first end  441  to the second end  442  in the circumferential direction), the outer peripheral surface  410  of the tubular part  41  forms a smooth surface (curved surface) with no projections. 
     The following describes the action of the fan unit  1  in the process of being attached and removed to and from a garment (the jacket  9 , for example). 
     When attaching (mounting) the fan unit  1  to (on) the jacket  9 , the user first inserts a portion of the body  3 , with no ring  5  attached thereto, into the attachment hole  91  of the jacket  9  (see  FIG. 2 ). Specifically, the tubular part  41  and the discharge-side cover  48  are inserted inside the jacket  9  through the attachment hole  91  while the rear flange  46  is held outside the back-body portion (the fan attachment portion  93 ). This results in the fan attachment portion  93  (the fabric  90 ) being located in front of the rear flange  46 . 
     Thereafter, the user places the tubular part  51  of the ring  5  around the tubular part  41  of the housing  4  from inside the jacket  9 . As described above, the open space  425  and the open space  445  respectively exist in front of each of the engagement wall  42  and each of the guide wall  44 , and either space has nothing particular protruding from the outer peripheral surface  410  of the tubular part  41 . Therefore, in the early phase of mounting the tubular part  51  around the tubular part  41 , the projections  52  of the ring  5  are slightly spaced apart from the outer peripheral surface  410  of the tubular part  41  and thus free to move with no interference. 
     Once the user has moved the ring  5  rearward relative to the housing  5  to some extent, the rear end portion of each of the projections  52  abuts on the front surface  420  of one of the engagement walls  42  or on the front surface  440  of one of the guide walls  44 . Based on the recognition that the projections  52  have abutted on something, the user rotates the ring  5  in the first direction D 1  while pushing the ring  5  rearward relative to the housing  4 . In a case where the projection  52  has abutted on the engagement wall  42 , then the rear end portion of the projection  52  slides in the first direction D 1  along the front surface  420  of the corresponding engagement wall  42  and the front surface  440  of the corresponding guide wall  44  until the projection  52  reaches the second end  442  of the corresponding guide wall  44 . In a case where the projection  52  has abutted on one of the guide walls  44 , then the rear end portion of the projection  52  slides in the first direction D 1  along the front surface  440  of the corresponding guide wall  44  until the projection  52  reaches the second end  442  of the corresponding guide wall  44 . 
     As the user rotates the ring  5  further in the first direction D 1 , each of the projections  52  rides over the first restriction wall  431  into a region behind one of the engagement walls  42  and reaches the first engagement position. Note that a slight elastic deformation of the tubular part  51  in the radial direction is sufficient to enable the projection  52  to ride over the first restriction wall  431 , since the second direction D 2  side surface of the first restriction wall  431  is inclined and the lengths of protrusion of the projection  52  and the first restriction wall  431  are respectively set as discussed above. In a case where the jacket  9  is made of a relatively thick fabric  90 , the fan attachment portion  93  is clamped between the front flange  55  and the rear flange  46  once the projections  52  reach their respective first engagement positions. This completes the attachment of the ring  5  to the body  3  (housing  4 ) and in turn the attachment of the fan unit  1  to the jacket  9 . 
     At the first engagement position, the projection  52  is engaged with the engagement wall  42  and held (retained) in the position in the rotational-axis-A 1  direction (the front-rear direction) by the engagement wall  42 . More specifically, when the projection  52  is at the first engagement position, the front surface  520  of the projection  52  abuts on the front engagement surface  423  of the engagement wall  42 , and this blocks (prevents) the ring  5  from moving frontward relative to the housing  4  (that is, in a direction that the ring  5  moves away from (or comes off) the body  3  in the front-rear direction). As described above, the engagement wall  42  protrudes radially outward such that the engagement wall  42  substantially contacts the inner peripheral surface  510  of the tubular part  51  of the ring  5 . Therefore, even if the ring  5  undergoes a slight elastic deformation in the radial direction, the projection  52  may not ride over and disengage from the engagement wall  42  frontward. 
     In a case where the fan attachment portion  93  has a sufficient thickness relative to the distance between the front flange  55  and the rear flange  46 , then the front surface  520  of each of the projections  52  is pressed against the front engagement surface  423  by an elastic force from the fan attachment portion  93  (the fabric  90 ) clamped between the front flange  55  and the rear flange  46 . This allows the ring  5  to be stably attached to the housing  4 . 
     At the first engagement position, the projection  52  is also held (retained) in the position in the circumferential direction by the first restriction wall  431  and the second restriction wall  432 . More specifically, when the ring  5  is rotated relative to the housing  4  in the second direction D 2  (that is, in a direction that causes the projection  52  to come off the engagement wall  42  in the circumferential direction), the tip end portion of the first restriction wall  431  abuts on the tip end portion of the projection  52  and thereby restricts rotation of the ring  5 . This reduces the possibility of the ring  5  coming off the housing  4 . Furthermore, when the ring  5  is rotated relative to the housing  4  in the first direction D 1 , the tip end portion of the second restriction wall  432  abuts on the tip end portion of the projection  52  and thereby restricts the ring  5  from rotating. Note that the term “restrict” used herein means that some rotation would be allowed if the ring  5  undergoes an elastic deformation in the radial direction in response to an external force, rather than that the ring  5  would be completely prohibited from rotating relative to the body  3 . As described above, the angle of inclination of the first direction D 1  side surface of the first restriction wall  431  is set such that the first restriction wall  431  would be difficult for the projection  52  to ride over in the second direction D 2 . 
     On the other hand, in a case where the jacket  9  is made of a relatively thin fabric  90 , the user rotates the ring  5  further in the first direction D 1 . Each of the projections  52  then rides over the second restriction part  432 , moving from the first engagement position to the second engagement position. Note that similarly to when riding over the first restriction wall  431 , a slight elastic deformation of the tubular part  51  in the radial direction enables the projection  52  to ride over the second restriction wall  432 . Once the projections  52  have reached their respective second engagement positions, the fan attachment portion  93  is clamped between the front flange  55  and the rear flange  46 . This completes the attachment of the ring  5  to the body  3 , that is, the attachment of the fan unit  1  to the jacket  9 . 
     When the projection  52  is at the second engagement position, the front surface  520  of the projection  52  abuts on the rear engagement surface  424  of the engagement wall  42 . This blocks (prevents) the ring  5  from moving frontward relative to the housing  4 . 
     At the second engagement position, the projection  52  is also held (retained) in the position in the circumferential direction by the second restriction wall  432  and the partition wall  429 . More specifically, when the ring  5  is rotated relative to the housing  4  in the second direction D 2  (that is, in a direction that causes the projection  52  to come off the engagement wall  42  in the circumferential direction), the tip end portion of the second restriction wall  432  abuts on the tip end portion of the projection  52  and thereby restricts rotation of the ring  5 . When the ring  5  is rotated relative to the housing  4  in the first direction D 1 , the tip end portion of the partition wall  429  abuts on the tip end portion of the projection  52  and thereby blocks (prevents) the ring  5  from rotating. As described above, the partition wall  429  protrudes radially outward such that the partition wall  429  substantially contacts the inner peripheral surface  510  of the tubular part  51  of the ring  5 . Therefore, even if the ring  5  undergoes a slight elastic deformation in the radial direction, the projection  52  does not move in the first direction D 1  over the partition wall  429 . 
     In order to remove the fan unit  1  from the jacket  9 , the user rotates the ring  5  relative to the housing  4  in the second direction D 2 . Each of the projections  52  positioned at the first engagement position (or at the second engagement position) rides over the first restriction wall  431  (or the second restriction wall  432  and the first restriction wall  431 ) as the ring  5  undergoes a slight elastic deformation, and leaves (disengages from) the engagement wall  42  at its second direction D 2  side end. Thereafter, the user  5  moves the ring  5  frontward relative to the housing  4  and removes (separates) the ring  5  from the body  3 . As described above, the open space  425  or the open space  445  extends in front of each of the projections  52  at this time, and either space has no protrusion that could interfere with the projection  52 . Therefore, no matter where the projections  52  are located in the circumferential direction, the user can easily remove the ring  5  from the body  3  by moving the ring  5  frontward. 
     If the ring  5  and the housing  4  are engaged through an engagement between external threads and internal threads, as in a known example, the ring  5  needs to be rotated in one direction all the way until the projection  52  reaches a predefined position in the front-rear direction. If the ring  5  and the housing  4  are engaged through an engagement between a projection and a groove that has a specific opening for receiving the projection, as in another known example, the attachment of the ring  5  to the housing  4  requires positioning of the ring  5  and the housing  4  in a predefined direction in the circumferential direction. 
     On the other hand, for the fan unit  1  of this embodiment, the process of attaching the ring  5  to the housing  4  proceeds differently. Specifically, the front surface  440  (guide surface) of one of the guide walls  44  abuts on the projection  52  from the rear so as to guide the ring  5  rearward relative to the housing  4  and also to guide the projection  52  to the engagement position. Furthermore, the open space  445  extends from the front surface  440  in the direction toward which the projection  52  moves away from the front surface  440  in the front-rear direction (in a direction toward which the ring  5  moves away from the housing  5  or on a side of the front surface  40  where the ring  5  is received). Specifically, in front of the front surface  440 , the open space  445  extends from the front surface  440  to the front end of the tubular part  41 . This eliminates the need for the user to position the ring  5  relative to the housing  4  precisely at a specific position in the circumferential direction. 
     Instead, the user only needs to move the ring  5  rearward until the projections  53  respectively abut on the front surface  440  of the guide walls  44 , followed by rotating the ring  5  in the first direction D 1  such that the projections  52  slide on the front surfaces  440  of the guide walls  44 , respectively. This swiftly brings the ring  5  to the engagement position. 
     In particular, in this embodiment, three engagement walls  42  and three guide walls  44  are arranged alternatingly at equal intervals in the circumferential direction. The front surface  440  of each guide wall  44  extends in the first direction D 1  substantially continuously (continuatively) from the front surface  420  of one engagement wall  42 , among the three engagement walls  42 , that is located on the second direction D 2  side of the guide wall  44  (that is, one of the engagement walls  42  located adjacent to the first end  441  of the guide wall  44 ). Therefore, the front surface  420  and the front surface  440  that are substantially continuous in the first direction D 1  can function as, as a whole, one continuous guide surface for a next engagement wall  42  that is located on the first direction D 1  side of the guide wall  44 . Such three continuous guide surfaces (that is, three pairs of the front surface  420  and the front surface  440 , each in continuation) can reliably guide the three projections  52  to their respective engagement positions. Furthermore, the three guide surfaces are arranged with no substantial gaps therebetween in the circumferential direction. This arrangement can completely eliminate the need for positioning the ring  5  in the circumferential direction, and therefore facilitate attaching procedure. 
     Also, in this embodiment, the front surface  440  (guide surface) of the guide wall  44  is inclined rearward as it extends in the first direction D 1 . This allows the user to achieve the attachment through ergonomically natural operations of rotating the ring  5  relative to the housing  4  in the first direction D 1  while moving the ring  5  rearward. 
     Also, in this embodiment, the two engagement surfaces  423 ,  424  are provided on the same engagement wall  42 , as described above. This allows the user to engage the ring  5  (projection  52 ) with one of the engagement surfaces  423 ,  424  as suitable according to the thickness of the fabric  90  while rotating the ring  5  relative to the housing  4  in the first direction D 1 . Thus, this configuration can eliminate the need for the user to remove the ring  5  from the housing  4  and then attach it again, and therefore facilitate attaching procedure. 
     Further, in this embodiment, once the three projections  52  are brought to their respective engagement positions, the three projections  52  respectively abut on the engagement walls  42  at three positions in the circumferential direction. This configuration can reduce the possibility of the ring  5  disengaging from (coming off) the housing  4 , more reliably than in a case where only one projection  52  is provided. 
     Further, in this embodiment, each of the projections  52  abuts on the restriction walls  431 ,  432  each provided on the second direction D 2  side of the corresponding engagement position, and this restricts the ring  5  from rotating relative to the housing  4  in the second direction D 2 . Thus, in this embodiment, each of the projections  52  fulfills two functions of: (i) blocking (preventing) the ring  5  from moving in a direction away from the housing  4  in the front-rear direction; and (ii) restricting the ring  5  from rotating in a direction that causes the projection  52  to disengage from (come off) the corresponding engagement wall  42  in the circumferential direction. In this manner, the possibility of the ring  5  disengaging from the housing  4  can be reduced by a simpler structure compared with a case in which an additional structure is required for restricting rotation of the ring  5 . 
     The structures for connecting the front member  401  and the rear member  402  are now described. 
     As shown in  FIG. 6 , the motor  33 , the fan  36 , and the connector  37  are all disposed inside the front member  401 . When the front member  401  is not connected to the rear member  402 , an opening at a rear end of the outer tubular part  411  is not closed. Thus, the fan  36  is visible through this opening. On the other hand, no parts (components) are disposed inside the rear member  402 . In this embodiment, the rear member  402  also functions as a cover member that closes the opening on the rear end of the front member  401  after the parts such as the motor  33  and the fan  36  have been mounted therein. 
     In this embodiment, the outer tubular part  411  of the front member  401  is connected to the inner tubular part  416  of the rear member  402  such that the outer tubular part  411  partially covers the periphery of the inner tubular part  416 . Therefore, as shown in  FIGS. 6 to 8 , the outer tubular part  411  and the inner tubular part  416  are provided with connecting structures described below. 
     In addition to the three engagement walls  42 , the three rotation-restriction parts  43 , and the three pairs of partition walls  429  described above, three pairs of (six) hook insertion guides  417  and two guide projections  418  are provided on the inner tubular part  416  of the rear member  402 . 
     Each pair of (two) hook insertion guides  417  is provided for each hook engagement part  427  of each engagement wall  42 . The two hook insertion guides  417  are located in front of the corresponding hook engagement part  427 . Each of the two hook insertion guides  417  is an elongate projection provided on the outer peripheral surface of the inner tubular part  416 , and extends, in pair, from each side of the insertion hole  428  of the hook engagement part  427  to a front end of the inner tubular part  416 . 
     Each guide projection  418  is an elongate projection that is provided on the outer peripheral surface of the inner tubular part  416  and extends from the front surface of the rear flange  46  to a front end portion of the inner tubular part  416 . The two guide projections  418  are spaced apart from each other in the circumferential direction. 
     Correspondingly, in addition to the three guide walls  44  described above, three recesses  412 , three engagement pieces  413 , and two guide grooves  415  are provided on the outer tubular part  411  of the front member  401 . 
     Each recess  412  is recessed frontward from the rear end of the outer tubular part  411 . The recesses  412  allow the engagement walls  42 , the rotation-restriction parts  43 , and the partition walls  429  provided on the inner tubular part  416  to project radially outward of the outer tubular part  411 . Therefore, each recess  412  has an approximately rectangular shape when viewed from the side of (or from a position radially outward of) the outer tubular part  411  such that the recess  412  corresponds to an area where the engagement wall  42 , the rotation-restriction part  43 , and the pair of partition walls  429  are provided. Each recess  412  is formed in a range from the first end  441  of one guide wall  44  to the second end  442  of another neighboring guide wall  44  in the circumferential direction. A front end of each recess  412  is situated at where the front end of each engagement wall  42  is. Furthermore, a length of each recess  412  in the circumferential direction is generally equal to a length of each engagement wall  42  in the circumferential direction. 
     Each engagement piece (cantilever)  413  is formed into a strip (sheet) and extends rearward from the front end of each recess  412 . The engagement piece  413  protrudes in an end portion of the recess  412  that faces the first direction D 1  (an end portion of the recess  412  that is located on the first direction D 1  side). The hook (claw, projection, catch)  414  is provided on a tip end portion (protruding end portion) of the engagement piece  413 , and protrudes radially outward of the outer tubular part  411 . The hook  414  has a front surface and a rear surface. The front surface extends in a direction approximately orthogonal to the rotational axis A 1 . The rear surface is inclined (slopes) radially inward of the outer tubular part  411  as it extends towards the tip end (rear end) of the engagement piece  413 . The engagement piece  413  is elastically deformable (deflectable, flexible) at least in the radial direction of the outer tubular part  411 . 
     Each guide groove  415  is an elongate groove formed on the inner peripheral surface of the outer tubular part  411 . The guide groove  415  is engageable with the guide projection  418  on the inner tubular part  416 . Two guide grooves  415  are formed at positions that respectively correspond to the two guide projections  418  on the inner tubular part  416  in the circumferential direction. Each projection  418  extends frontward from the rear end of the outer tubular part  411 . 
     In order to connect the front member  401  to the rear member  402 , an assembly worker or a user positions the front member  401  relative to the rear member  402  in the circumferential direction such that the three engagement pieces  413  are respectively situated in front of the three pairs of hook insertion guides  417 . The worker/user then moves the hooks  414  rearward along the hook insertion guides  417 . The guide projections  418  on the inner tubular part  416  proceed into the respective guide grooves  415  and thereby stably guide the movement of the front member  401  relative to the rear member  402  in the front-rear direction. Once the rear surface (inclined surface) of each hook  414  abuts on an upper end of the corresponding hook engagement part  427 , the engagement piece  413  deflects radially inward and the hook  414  proceeds into the insertion hole  428 . The engagement wall  42 , the rotation-restriction part  43 , and the pair of partition walls  429  then proceed into the recess  412 . Once the hook  414  has passed through the insertion hole  428 , the engagement piece  413  recovers its original position due to its resiliency. This allows the engagement piece  413  to be engaged with the hook engagement part  427  while the front surface of the hook  414  abuts on the rear surface of the hook engagement part  427 . The rear end surface of the outer tubular part  411  is located at a generally same position as the front surface of the rear flange  46 . The procedure described hereinabove achieves connection of the front member  401  and the rear member  402 . 
     In order to separate the front member  401  from the rear member  402 , the user may push the hook  414  radially inward from outside the tubular part  41  by using a tool with an elongate end (a screwdriver, for example). The user can thus deflect the engagement piece  413  and releases (disengages) the hook  414  from the hook engagement part  427 . With all the hooks  414  released from engagement, the user can move the front member  401  frontward and away from the rear member  402 . Prolonged use of the fan unit  1  may cause dustiness inside the housing  4  and on the fan  36 . In such cases, the user can separate the front member  401  and the rear member  402  following the above-described procedure to clean the fan  36  and inside the housing  4 . 
     Also, in this embodiment, since the engagement walls  42  are provided on the rear member  402  (specifically, on the inner tubular part  416 ) as described above, the ring  5  cannot be attached to the housing  4  unless the rear member  402  is connected to the front member  401 . This configuration can prevent the fan unit  1  to be attached to and used with the jacket  9  before the complete assembling of the housing  4 . In particular, since the motor  33  and the fan  36  are accommodated in the front member  401  in this embodiment, the fan  36  is accessible via the opening on the rear end of the front member  401  when the rear member  402  including the inlet-side cover  47  (that is, the fan guard) is not yet connected to the front member  401 . Therefore, in this embodiment, the fan unit  1  can be prevented from being used without the inlet-side cover  47  in place. 
     Also, as described above, the ridges  53  are formed on the inner peripheral surface  510  of the ring  5  more frontward than the projections  52 . Therefore, in the event that the front member  401  and the rear member  402  are disconnected due to some reasons while the projections  52  of the ring  5  are respectively engaged with the engagement walls  42  of the rear member  402 , the ridges  53  of the ring  5  will abut on the guide walls  44  from the front to prevent the front member  401  from falling off through the ring  5 . 
     Correspondences between the features of the above-described embodiment and the features of the present disclosure or invention are as follows. The features of the above-described embodiment are, however, merely exemplary and thus do not limit the features of the present disclosure. 
     The fan unit  1  is an example of the “ventilation apparatus”. The motor  33  is an example of the “motor”. The fan  36  is an example of the “fan”. The rotational axis A 1  is an example of the “first axis”. The housing  4 , the tubular part  41 , and the rear flange  46  are examples of the “housing”, the “peripheral wall part”, and the “first clamping part”, respectively. The ring  5  and the front flange  55  are examples of the “ring” and the “second clamping part”, respectively. The projection  52  is an example of the “projection”. The inner peripheral surface  510  of the ring  5  is an example of the “first surface”. The outer peripheral surface  410  of the tubular part  41  is an example of the “second surface”. The engagement wall  42  is an example of the “engagement wall”. Each of the engagement surfaces  423 ,  424  is an example of the “engagement surface”, respectively. The guide wall  44  is an example of the “guide wall”. The front surface  440  is an example of the “guide surface”. The open space  445  is an example of the “open space”. 
     The projection  52  is an example of the “first rotation-restriction part”. Each of the restriction walls  431 ,  432  is an example of the “second rotation-restriction part” and is also an example of the “restriction wall”. The rear member  402  and the front member  401  are examples of the “first member” and the “second member”, respectively. The inlet-side cover  47  and the inlet opening  471  are examples of the “inlet-side cover” and the “inlet opening”, respectively. The discharge-side cover  48  and the discharge opening  481  are examples of the “discharge-side cover” and the “discharge opening”, respectively. The ridge  53  is an example of the “additional projection”. The inner tubular part  416  and the outer tubular part  411  are examples of the “first peripheral wall part” and the “second peripheral wall part”, respectively. The recess  412  is an example of the “recess”. The engagement piece  413  and the hook  414  are examples of the “engagement piece” and the “hook”, respectively. The first end  441  and the second end  442  of the guide wall  44  are examples of the “first end” and the “second end”, respectively. The first direction D 1  is an example of “the first direction”. The second direction D 2  is an example of “the second direction”. 
     Note that the above-described embodiment is merely an exemplary embodiment of the present disclosure, and ventilation apparatuses according to the present disclosure are not limited to the fan unit  1  of the above-described embodiment. For example, following modifications may be made. Note that one or more of these modifications may be employed in combination with the fan unit  1  of the above-described embodiment or any one of the claimed features. 
     For example, as long as the ring  5  is removably attachable to the housing  4 , the structures (such as shapes, sizes, and components) of the housing  4  and the ring  5  may be changed appropriately. 
     For example, the structures of the inlet-side cover  47  and the discharge-side cover  48  of the housing  4  (such as the numbers and the arrangements of the inlet openings  471  and the discharge openings  481 ) may be changed. Furthermore, the structures for clamping the fan attachment portion  93  (fabric  90 ) are not limited to the rear flange  46  and the front flange  55  described above. For example, the rear flange  46  and the front flange  55  may each have a polygonal outer periphery rather than the circular outer periphery. Furthermore, at least one of the rear flange  46  and the front flange  55  may be notched at least partially on its circumference, or may have openings. Furthermore, instead of the front flange  55 , a plurality of projections may be provided at a plurality of circumferential positions and protrude radially outward from the tubular part  51 . Alternatively, in a case where the wall that forms the tubular part  51  has a radial thickness of a certain level, the fan attachment portion  93  (fabric  90 ) may be clamped between the rear flange  46  and the rear end of the tubular part  51 . Similar modifications may be made as appropriate for the rear flange  46 . Furthermore, the shape of the tabs  58  of the ring  5  may be changed appropriately or the tabs  58  may be omitted. 
     In the above-described embodiment, each of the guide walls  44  is configured to guide the ring  5  rearward in response to the ring  5  being rotated relative to the housing  4  in a clockwise direction as viewed from the front. However, the guide wall  44  may be configured the other way around. Specifically, the guide wall  44  may alternatively be configured to guide the ring  5  rearward in response to the ring  5  being rotated relative to the housing  4  in a counterclockwise direction as viewed from the front. Furthermore, inversely to the structures of the above-described embodiment, a projection/projections may be provided on the outer peripheral surface  410  of the tubular part  41  of the housing  4 ; whereas an engagement wall/engagement walls and a guide wall/guide walls may be correspondingly provided on the inner peripheral surface  510  of the ring  5 . In this case, the guide wall of the ring  5  may have a rear surface (guide surface) that is inclined (slopes) frontward as it extends in a predetermined direction around the rotational axis A 1  (central axis A 2 ) and can abut on the projection of the housing  4  from the front. The engagement wall of the ring  5  may be provided adjacent to an end of the guide wall that faces a predetermined direction (located on the predetermined direction side) and may have an engagement surface that can abut on the projection of the housing  4  from the rear. 
     In the above-described embodiment, the second direction D 2  side end of the engagement wall  42  is at an approximately same position as the first direction D 1  side end (the second end  442 ) of the guide wall  44 . However, as long as the projection  52  has a sufficient length in the circumferential direction and the front surface  440  of the guide wall  44  (the guide surface) is capable of guiding the projection  52  to the first engagement position, the second direction D 2  side end of the engagement wall  42  may be slightly spaced apart from the second end  442  of the guide wall  44 . Also, the second direction D 2  side end of the engagement wall  42  may extend further in the second direction D 2 , past the second end  442  of the guide wall  44 . In other words, the second direction D 2  side end portion of the engagement wall  42  and the first direction D 1  side end portion of the guide wall  44  may have a slight overlap in the circumferential direction. Specifically, the second direction D 2  side end of the engagement wall  42  may be located more frontward than the first direction D 1  side end of the guide wall  44 , and the engagement surface  423  (and the engagement surface  424 ) may be opposed to the front surface  440  of the guide wall  44 . 
     The shape and the number of the projections  52 , and positions of the projections  52  on the ring  5  may be changed appropriately, as long as the projection(s)  52  can be engaged with (retained/held by) the engagement surfaces  423 ,  424 . For example, the projection  52  may not necessarily be approximately rectangular-shaped. Note that, however, in order for the projection  52  to be stably held in place with respect to the engagement surfaces  423 ,  424 , the contact of the projection  52  with the engagement surfaces  423 ,  424  may preferably be on multiple points or lines, or on a surface, rather than just on one point. Also, even though only one projection  52  is acceptable, it may be preferable that two or more projections  52  are provided in order to keep the ring  5  stably attached to the housing  4 . Note that the numbers of the engagement walls  42  and the guide walls  44  may also be changed according to the number of the projections  52 . The projection(s)  52  may not necessarily be located on the rear end portion of the ring  5  (tubular part  51 ), but may alternatively be located around midway in the front-end direction or on the front end portion. The distance between the engagement surfaces  423 ,  424  and the front surface  460  of the rear flange  46  on the housing  4  may be changed appropriately according to the distance between the front end of the projection  52  and the rear surface  550  of the front flange  55 . 
     The number of the engagement surface, which engages with the projection  52 , on the engagement wall  42  may be one. That is, the fan unit  1  may not necessarily be adaptable to fabrics  90  of different thicknesses. Alternatively, the number of the engagement surfaces may be three or more. If the number of the engagement surfaces (engagement positions) is changed, then the numbers of the restriction walls  431 ,  432  may also be changed accordingly. 
     Furthermore, in the above-described embodiment, the projection  52  has two functions of: (i) preventing the ring  5  from moving in a direction away from the housing  4 ; and (ii) restricting the ring  5  from rotating in a direction that causes the projection  52  to disengage from (come off) the engagement wall  42  in the circumferential direction. However, separately from the projection  52 , an additional structure may be provided to restrict rotation of the ring  5  relative to the housing  4 . For example, a recess may be provided on the outer peripheral surface  410  of the tubular part  41 , and correspondingly, the ring  5  may have an elastically deformable engagement piece that has a hook engageable with the recess. Also, the rotation-restriction part  43  (the restriction walls  431 ,  432 ) may be omitted. The omission is possible because rotation of the ring  5  relative to the housing  4  can be restricted to some extent by the front surface  520  of the projection  52  being pressed against the engagement surface  423 ,  424  by the elastic force of the fabric  90 . 
     In the above-described embodiment, the front surface  440  (guide surface) of the guide wall  44  is, as a whole, inclined at a substantially constant angle as it extends from the first end  441  to the second end  442 . However, the structure of the front surface  440  may be changed appropriately, as long as it allows the ring  5  to move rearward relative to the housing  4  in response to the projection  52  moving in the first direction D 1  while being abutted on the front surface  440 . For example, the angle of inclination of the front surface  440  may vary between the first end  441  and the second end  442 . As another example, the front surface  440  may partially be curved in the front-end direction. As a further example, the front surface  440  may be configured such that its position in the front-rear direction varies in a stepwise manner between the front end  441  and the second end  442 . In other words, the front surface  440  may be formed into a step-like surface. Specifically, the front surface  440  may be formed by multiple flat surfaces that are approximately orthogonal to the rotational axis A 1  (or multiple inclined surfaces inclined in the circumferential direction); and at least one connecting surface that connects two neighboring flat surfaces (or inclined surfaces). In this case, the closer the flat surface (or inclined surface) is to the second end  442 , the more rearward it may be located compared to the flat surface (or inclined surface) closer to the first end  441 . 
     Similar to the front surface  440  of the guide wall  44 , the front surface  420  of the engagement wall  42  may also be inclined rearward as it extends in the first direction D 1 . In this case, the front surface  420  of the engagement wall  42 , together with the front surface  440  of the guide wall  44  that substantially connects thereto on the first direction D 1  side of the guide wall  44 , form a continuous guide surface that is inclined rearward as it extends in the first direction D 1 . Note that even if the first end  441  of the guide wall  44  is slightly spaced apart from the engagement wall  42  that is located on the second direction D 2  side of the guide wall  44 , the front surface  420  of the engagement wall  42  and the front surface  440  of the guide wall  44  can form, as a whole, a substantially continuous guide surface, in a case where the projection  52  has a length in the circumferential direction that is sufficiently longer than the length of a gap between the engagement wall  42  and the guide wall  44  in the circumferential direction. 
     In the above-described embodiment, the front member  401  and the rear member  402  are separably connected to each other through an elastic engagement (snap-fit engagement) between the engagement piece  413  of the front member  401  and the engagement wall  42  of the rear member  402 . However, separately from the engagement wall  42 , an engagement part that is engageable with the engagement piece  413  may be provided on the rear member  402 . Alternatively, the front member  401  and the rear member  402  may be separably connected to each other through a different mechanism. Further alternatively, the front member  401  and the rear member  402  may be connected to each other in a substantially inseparable manner. 
     The garment to which the fan unit  1  is removably attachable may not necessarily be an upper-body garment such as the jacket  9 , but may also be, for example, a lower-body garment such as pants (trousers). Furthermore, in a case where the garment has a double-layered structure including an outer fabric and an inner fabric, the fan attachment portion  93  may be provided on the outer fabric and the discharge-side cover  48  may be disposed within an internal space formed (defined) between the outer fabric and the inner fabric when the fan unit  1  is attached. In this case, the outer fabric and the inner fabric may be left unsawn to define openings, as needed, in some areas such as cuffs and collar, so that air sent into the internal space can be discharged outside through the openings. Also, the position and the number of the fan attachment portion  93  on the garment may be changed appropriately. 
     Furthermore, in view of the nature of the present invention, the above-described embodiment and the modifications thereto, the following aspects are provided. At least one of the following aspects can be employed in combination with at least one of the above-described embodiment and modifications thereto, and the claimed features. 
     [Aspect 1] 
     Of the outer peripheral surface of the peripheral wall part of the housing, at least an area in front of the guide wall has no projection protruding radially outward from the outer peripheral surface. 
     [Aspect 2] 
     The distance from the first axis to the outer peripheral surface of the at least one engagement wall is approximately equal to the distance from the first axis to the outer peripheral surface of the at least one guide wall. 
     [Aspect 3] 
     The inner peripheral surface of the ring is at least partially substantially slidable with respect to the outer peripheral surface of the at least one engagement wall and the at least one guide wall. 
     [Aspect 4] 
     The distance from the first axis to the outer peripheral surface of the at least one restriction wall is smaller than the distance from the first axis to the outer peripheral surface of the at least one engagement wall. 
     [Aspect 5] 
     The plurality of engagement walls and the plurality of guide walls are arranged alternatingly in the circumferential direction, substantially with no gap therebetween. 
     [Aspect 6] 
     The at least one engagement wall is spaced apart frontward from the front surface of the first clamping part, and in the front-rear direction, the at least one engagement wall is located more rearward than the first end of the guide surface and more frontward than the second end of the guide surface. 
     [Aspect 7] 
     The plurality of engagement surfaces include a first engagement surface and a second engagement surface that is further in the first direction than the first engagement surface in the circumferential direction, and in the front-rear direction, the second engagement surface is located more rearward than the first engagement surface. 
     [Aspect 8] 
     The at least one engagement surface is configured to abut on the at least one projection from the rear or from the front to block the ring and the housing from moving away from each other in the front-rear direction. 
     [Aspect 9] 
     The at least one guide wall has a first end and a second end in the circumferential direction, 
     the at least one engagement wall is located adjacent to the second end of the at least one guide wall in the circumferential direction, and 
     the guide surface is configured such that its position in the front-rear direction varies as it extends from the first end to the second end. 
     [Aspect 10] 
     the guide surface is configured to guide the ring rearward relative to the housing, in the process of attaching the ring to the housing, by abutting on the at least one projection from a direction in the front-rear direction opposite to the at least one engagement surface and guiding the at least one projection in a first direction which is from the first end toward the second end, and also to guide the at least one projection to at least one engagement position at which the projection can abut on the at least one engagement surface. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
       1 : fan unit,  3 : body,  33 : motor,  331 : output shaft,  36 : fan,  361 : base part,  363 : blade,  37 : connector,  4 : housing,  401 : front member,  402 : rear member,  41 : tubular part,  410 : outer peripheral surface,  411 : outer tubular part,  412 : recess,  413 : engagement piece,  414 : hook,  415 : guide groove,  416 : inner tubular part,  417 : hook insertion guide,  418 : guide projection,  42 : engagement wall,  420 : front surface,  421 : ring engagement part,  423 : engagement surface (front engagement surface),  424 : engagement surface (rear engagement surface),  425 : open space,  427 : hook engagement part,  428 : insertion hole,  429 : partition wall,  43 : rotation-restriction part,  431 : restriction wall (first restriction wall),  432 : restriction wall (second restriction wall),  44 : guide wall,  440 : front surface,  441 : first end,  442 : second end,  445 : open space,  46 : flange (rear flange),  460 : front surface,  47 : inlet-side cover,  471 : inlet opening,  48 : discharge-side cover,  481 : discharge opening,  489 : recess,  5 : ring,  51 : tubular part,  510 : inner peripheral surface,  52 : projection,  520 : front surface,  53 : ridge,  55 : flange (front flange),  550 : rear surface,  58 : tab,  9 : jacket,  90 : fabric,  91 : attachment hole,  93 : fan attachment portion,  94 : pocket,  95 : battery holder,  96 : battery,  97 : connecting cable,  973 : connector, A 1 : rotational axis, A 2 : central axis, D 1 : first direction, D 2 : second direction.