Patent Publication Number: US-10781994-B2

Title: Ventilation member and lamp

Description:
TECHNICAL FIELD 
     The present invention relates to a ventilation member and a lamp. 
     BACKGROUND ART 
     Ventilation property has conventionally been required of an apparatus such as a vehicle lamp e.g., head lamp, rear lamp, fog lamp and turn lamp, an inverter, a converter, an electronic control unit (ECU) and a battery box to allow for elimination of a differential pressure generated inside the housing due to temperature change. These apparatuses have also been required of dust-proof property to prevent a foreign material from entering the housing, water-proof property to prevent water from infiltrating the housing, oil-repellant property to prevent oil from infiltrating the housing, and CCT-proof property to prevent salt from entering the housing. For this reason, these apparatuses are provided with a ventilation member having these functions of ventilation property, dust-proofness, water-proofness, oil-repellency and CCT-proofness. 
     For example, Patent Document 1 discloses an air-permeable cap (a ventilation member) wherein a substantially cylindrical body of a substantially cylindrical shape is fitted in a closed-end cylindrical cover member, an air passage is formed between an inner wall of the cover member and an outer wall of the substantially cylindrical body and between a bottom surface of the cover member and a lower end of the substantially cylindrical body, and a top opening portion of the substantially cylindrical body is formed at a mounting portion to be mounted on a mounting opening of an apparatus housing. Further, a bottom opening of the substantially cylindrical body is covered with an air-permeable filter. 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2001-143524 
     SUMMARY OF INVENTION 
     Technical Problem 
     With the configuration where a rib is formed on a cover member to secure a ventilation passage between the cover member and a ventilation body (a filter member) having ventilation property, the rib of the cover member may contact the ventilation body, which may result in buckling of the ventilation body. Further, due to the rib being located in the vicinity of the ventilation body, a liquid having infiltrated into the ventilation passage may adhere to the rib by surface tension and accumulate on the ventilation body. This buckling of the ventilation body and accumulation of a liquid on the ventilation body may impair the functions of ventilation property, dust-proofness, water-proofness, oil-repellency and CCT-proofness. 
     An object of the present invention is to provide a ventilation member and a lamp that are capable of preventing buckling of the ventilation member and accumulation of a liquid on the ventilation member. 
     Solution to Problem 
     With this object in view, the present invention is a ventilation member ( 1 ) including: a cylindrical member ( 20 ) of a cylindrical shape, the cylindrical member ( 20 ) including an outer projection portion ( 22 ) projecting outward from an outer circumferential surface of the cylindrical member ( 20 ); a ventilation body ( 10 ) mounted so as to cover one end of the cylindrical member ( 20 ) in a centerline direction, the ventilation body ( 10 ) preventing a liquid and a solid from entering an inside of the cylindrical member ( 20 ) from an outside of the cylindrical member ( 20 ), the ventilation body ( 10 ) permitting a flow of gas between the inside and the outside; and a cover member ( 30 ) provided around the ventilation body ( 10 ), the cover member ( 30 ) including a cylindrical portion ( 31 ), a lid portion ( 33 ), and an inner projection portion ( 32 ), the lid portion ( 33 ) closing one end of the cylindrical portion ( 31 ) in the centerline direction, the inner projection portion ( 32 ) projecting inward from an inner circumferential surface of the cylindrical portion ( 31 ) and contacting the outer projection portion ( 22 ) of the cylindrical member ( 20 ) so as to form a ventilation passage (R) between the ventilation body ( 10 ) and the lid portion ( 33 ), the ventilation passage (R) allowing gas to flow therethrough. 
     Here, the ventilation passage (R) may be formed by contact between one end face ( 22   a ) of the outer projection portion ( 22 ) of the cylindrical member ( 20 ) in the centerline direction and the other end face ( 32   aa ) of the inner projection portion ( 32 ) of the cover member ( 30 ) in the centerline direction. 
     Further, the cover member ( 30 ) may be prevented from moving to one side in the centerline direction by contact between an outer circumferential surface of the outer projection portion ( 22 ) of the cylindrical member ( 20 ) and an inner surface ( 32   ba ) of the inner projection portion ( 32 ) of the cover member ( 30 ). 
     Here, the outer circumferential surface of the outer projection portion ( 22 ) of the cylindrical member ( 20 ) may be parallel to the centerline direction, and the inner surface ( 32   ba ) of the inner projection portion ( 32 ) of the cover member ( 30 ) may gradually go inward as the inner surface ( 32   ba ) goes from one side toward the other side in the centerline direction. 
     In another aspect, the present invention is a ventilation member ( 3 ) including: a cylindrical member ( 320 ) of a cylindrical shape, the cylindrical member ( 320 ) including an outer projection portion ( 322 ) projecting outward from an outer circumferential surface of the cylindrical member ( 320 ); a ventilation body ( 10 ) mounted so as to cover one end of the cylindrical member ( 320 ) in a centerline direction, the ventilation body ( 10 ) preventing a liquid and a solid from entering an inside of the cylindrical member ( 320 ) from an outside of the cylindrical member ( 320 ), the ventilation body ( 10 ) permitting a flow of gas between the inside and the outside; and a cover member ( 330 ) provided around the ventilation body ( 10 ), the cover member ( 330 ) including a cylindrical portion ( 331 ) and a lid portion ( 333 ), the lid portion ( 333 ) closing one end of the cylindrical portion ( 331 ) in the centerline direction, the cylindrical portion ( 331 ) contacting the outer projection portion ( 322 ) of the cylindrical member ( 320 ) so as to form a ventilation passage (R) between the ventilation body ( 10 ) and the lid portion ( 333 ), the ventilation passage (R) allowing gas to flow therethrough. 
     Here, the cylindrical portion ( 331 ) of the cover member ( 330 ) may be press-fitted to the outer projection portion ( 322 ) of the cylindrical member ( 320 ), and an interference of a press-fitting portion may be larger on the other side than on one side in the centerline direction. 
     In still another aspect, the present invention is a ventilation member ( 1 ) including: a ventilation body ( 10 ) mounted so as to cover one end of a cylindrical portion ( 21 ) in a centerline direction, the ventilation body ( 10 ) preventing a liquid and a solid from entering an inside of the cylindrical portion ( 21 ) from an outside of the cylindrical portion ( 21 ), the ventilation body ( 10 ) permitting a flow of gas between the inside and the outside; a surrounding portion ( 31 ,  33 ) provided around the ventilation body ( 10 ); and a preventing portion ( 22 ,  32 ) at a position where the ventilation body ( 10 ) is not mounted, the preventing portion ( 22 ,  32 ) preventing the ventilation body ( 10 ) and the surrounding portion ( 31 ,  33 ) from coming close to each other in the centerline direction. 
     Here, the preventing portion ( 22 ,  32 ) may include an outer projection portion ( 22 ) projecting outward from the cylindrical portion ( 21 ), and an inner projection portion ( 32 ) projecting inward from a portion of the surrounding portion ( 31 ,  33 ) provided around the cylindrical portion ( 21 ), the inner projection portion ( 32 ) contacting the outer projection portion ( 22 ) in the centerline direction. 
     In still another aspect, the present invention is a lamp including: a housing ( 100 ) storing a light source; and a ventilation member ( 1 ) mounted on the housing ( 100 ), the ventilation member ( 1 ) preventing a liquid and a solid from entering an inside of the housing ( 100 ), the ventilation member ( 1 ) permitting a flow of gas between the inside and an outside of the housing ( 100 ), wherein the ventilation member ( 1 ) includes: a cylindrical member ( 20 ) of a cylindrical shape, the cylindrical member ( 20 ) including an outer projection portion ( 22 ) projecting outward from an outer circumferential surface of the cylindrical member ( 20 ); a ventilation body ( 10 ) mounted so as to cover one end of the cylindrical member ( 20 ) in a centerline direction, the ventilation body ( 10 ) preventing a liquid and a solid from entering an inside of the cylindrical member ( 20 ) from an outside of the cylindrical member ( 20 ), the ventilation body ( 10 ) permitting a flow of gas between the inside and the outside; and a cover member ( 30 ) provided around the ventilation body ( 10 ), the cover member ( 30 ) including a cylindrical portion ( 31 ), a lid portion ( 33 ), and an inner projection portion ( 32 ), the lid portion ( 33 ) closing one end of the cylindrical portion ( 31 ) in the centerline direction, the inner projection portion ( 32 ) projecting inward from an inner circumferential surface of the cylindrical portion ( 31 ) and contacting the outer projection portion ( 22 ) of the cylindrical member ( 20 ) so as to form a ventilation passage (R) between the ventilation body ( 10 ) and the lid portion ( 33 ), the ventilation passage (R) allowing gas to flow therethrough. 
     Note that the above reference signs in this section are added as examples for explaining the present invention and the present invention is not limited by these reference signs. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to prevent buckling of the ventilation body and accumulation of a liquid on the ventilation body. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a schematic configuration of a ventilation member according to the first exemplary embodiment; 
         FIG. 2  is a cross-sectional view of the ventilation member according to the first exemplary embodiment taken along the line II-II in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along the line III-III in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view taken along the line IV-IV in  FIG. 2 ; 
         FIG. 5  is a diagram illustrating a schematic configuration of a ventilation member according to the second exemplary embodiment; 
         FIG. 6  is a cross-sectional view of the ventilation member according to the second exemplary embodiment taken along the line VI-VI in  FIG. 5 ; 
         FIG. 7  is a diagram illustrating a schematic configuration of a ventilation member according to the third exemplary embodiment; 
         FIG. 8  is a cross-sectional view of the ventilation member according to the third exemplary embodiment taken along the line VIII-VIII in  FIG. 7 ; 
         FIG. 9  is a diagram illustrating a modified example of the cover member according to the third exemplary embodiment; 
         FIG. 10  is a diagram illustrating a schematic configuration of a ventilation member according to the fourth exemplary embodiment; and 
         FIG. 11  is a cross-sectional view of the ventilation member according to the fourth exemplary embodiment taken along the line XI-XI in  FIG. 10 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings. 
     First Exemplary Embodiment 
       FIG. 1  is a diagram illustrating a schematic configuration of a ventilation member  1  according to the first exemplary embodiment. 
       FIG. 2  is a cross-sectional view of the ventilation member  1  according to the first exemplary embodiment taken along the line II-II in  FIG. 1 . 
       FIG. 3  is a cross-sectional view taken along the line III-III in  FIG. 2 . 
       FIG. 4  is a cross-sectional view taken along the line IV-IV in  FIG. 2 . 
     The ventilation member  1  is mounted on an apparatus housing  100  of an apparatus such as a vehicle lamp e.g., head lamp, rear lamp, fog lamp and turn lamp, an inverter, a converter, an electronic control unit (ECU) and a battery box.  FIG. 2  shows, by a dashed-two dotted line, a mounted portion  110  that is formed in the apparatus housing  100  as a portion for mounting the ventilation member  1  and having an open end. 
     The ventilation member  1  includes a ventilation film  10  as an example of the ventilation body that prevents a liquid and a solid from entering the inside of the apparatus housing  100  from the outside of the apparatus housing  100  and has holes for permitting a flow of gas between the inside and the outside of the apparatus housing  100 . 
     The ventilation member  1  further includes a holding member  20  as an example of the cylindrical member that holds the ventilation film  10 , and a cover member  30  that covers a periphery of the ventilation film  10 . 
     [Ventilation Film  10 ] 
     The ventilation film  10  is a disk-shaped film. The outer diameter of the ventilation film  10  is larger than the diameter of a circle C 1  (described later) and smaller than the diameter of an inner circumferential surface  31   a  of a side wall portion  31  (described later) of the cover member  30 . 
     The structure and material of the ventilation film  10  is not particularly limited as long as the ventilation film  10  permits penetration of gas and prevents penetration of liquids. Examples of the ventilation film  10  include cloth, resin and metal that are mesh-shaped or fibrous. For example, the ventilation film  10  may be woven fabric, nonwoven fabric, resin mesh, net, sponge, metal porous body or metal mesh. 
     The ventilation film  10  according to the first exemplary embodiment is a film consisting of a porous resin film and a reinforcing layer laminated on the porous resin film to reinforce the ventilation film  10 . 
     Examples of the material of the porous resin film include a fluororesin porous body and a polyolefin porous body that can be manufactured by a known stretching method or extraction method. Example of fluororesin include PTFE (polytetrafluoroethylene), polychlorotrifluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer. Examples of the monomer constituting polyolefin include ethylene, propylene, 4-methylpentene-1 and 1-butene, and polyolefin obtained by polymerizing one of these monomers or copolymerizing these monomers may be used. Also, the material of the porous resin film may be in the form of a blend or a layered structure of two or more kinds of the above polyolefin. 
     Also, examples of the material of the porous resin film further include a nanofiber film porous body using polyacrylonitrile, nylon or polylactate. 
     The ventilation film  10  according to the first exemplary embodiment uses an PTFE porous film because the PTFE porous film can ensure a sufficient amount of ventilation even with a small area and is highly capable of preventing water and dust from entering the inside of the apparatus housing  100 . 
     An average hole diameter of the holes formed in the ventilation film  10  is in the range of not less than 0.01 μm and not more than 100 μm for example. In this range, the average hole diameter is preferably in the range of not less than 0.1 μm and not more than 50 μm, and more preferably in the range of not less than 0.5 μm and not more than 10 μm. 
     If the average hole diameter of the holes formed in the ventilation film  10  is less than 0.01 μm, it is difficult for air to pass through the ventilation film  10 . On the other hand, if the average hole diameter of the ventilation film  10  is more than 100 μm, liquids and solids may easily enter the inside of the apparatus housing  100  through the ventilation film  10 . 
     Although the thickness of the ventilation film  10  is not particularly limited, the thickness may be in the range of not less than 10 μm and not more than 1000 μm for example. 
     If the ventilation film  10  is extremely thin, the strength of the ventilation film  10  is likely to weaken. On the other hand, if the ventilation film  10  is extremely thick, the size of the ventilation member  1  is likely to increase. 
     The surface (of an outer side in particular) of the ventilation film  10  may be applied with a liquid-repellent treatment such as a water-repellent treatment and an oil-repellent treatment. Applying a liquid-repellent treatment to the ventilation film  10  prevents dirt and the like from adhering to the ventilation film  10 . As a result, this prevents clogging of the ventilation film  10 . 
     For example, a liquid-repellent treatment to the ventilation film  10  may be performed by applying, to the surface of the ventilation film  10 , a liquid-repellent agent composed of a compound having a hydrocarbon group (perfluoroalkyl group) saturated with fluorine in a side chain and having a main chain of acrylic, methacrylic, silicone or other nature. The method for applying a liquid-repellent agent to the surface of the ventilation film  10  is not particularly limited; for example, gravure coating, spray coating, kiss coating or dipping may be used. 
     The method of an oil-repellent treatment is not particularly limited as long as an oil-repellent film containing a polymer having a perfluoroalkyl group can be formed. Examples of the forming method include coating of a solution or a dispersion of a polymer having a perfluoroalkyl group by an air spray method, an electrostatic spray method, a dip coating method, a spin coating method, a roll coating method, a curtain flow coating method or an impregnation method, and film formation by electrodeposition coating or plasma polymerization. 
     [Holding Member  20 ] 
     The holding member  20  includes a cylindrical portion  21  of a cylindrical shape, and an outer projection portion  22  projecting outward from the cylindrical portion  21 . 
     The holding member  20  holds the ventilation film  10  at one end  21   a  of the cylindrical portion  21  in a direction of the centerline CL (hereinafter may be referred to as the “centerline direction”). The ventilation film  10  covers an opening at one end of the cylindrical portion  21  in the centerline direction. The method for fixing the ventilation film  10  to the cylindrical portion  21  will be described in detail later. Further, the holding member  20  is mounted on the apparatus housing  100  with the other end  21   b  of the cylindrical portion  21  in the centerline direction being press-fitted to the mounted portion  110  of the apparatus housing  100 . In other words, a contact pressure generated between an inner circumferential surface  21   c  on the other end  21   b  side of the cylindrical portion  21  and the apparatus housing  100  prevents the holding member  20  from falling off the mounted portion  110  of the apparatus housing  100 . A chamfer  21   d  is formed at an inner portion of the other end  21   b  side of the cylindrical portion  21 . 
     The outer projection portion  22  is a cylindrical portion projecting outward from an outer circumferential surface  21   e  of the cylindrical portion  21 . One end face  22   a , which is an end face on the one side of the outer projection portion  22  in the centerline direction, is a surface substantially perpendicular to the centerline direction. An outer circumferential surface  22   b  of the outer projection portion  22  is a surface substantially parallel to the centerline direction. 
     Examples of the material of the holding member  20  include thermoplastic resin, which is easy to mold. Examples of the thermoplastic resin include polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polysulfone (PS), polypropylene (PP), polyethylene (PE), ABS resin, thermoplastic elastomer and a composite material of these materials. Other than the above thermoplastic resin, the material of the holding member  20  may be a composite material produced by compositing thermoplastic resin with a reinforcing material such as glass fiber and carbon fiber, or metal for improved heat resistance, dimension stability and rigidity. Further, the material of the holding member  20  may be a metal or a synthetic rubber including NBR (nitrile rubber), EPDM (ethylene-propylene rubber), silicone rubber, fluoro-rubber, acrylic rubber and hydrogenated nitrile rubber. 
     The method for forming the holding member  20  is not particularly limited, and examples include injection molding and cutting. 
     The surface (of an outer side in particular) of the holding member  20  may be applied with a liquid-repellent treatment such as a water-repellent treatment and an oil-repellent treatment. Applying a liquid-repellent treatment to the holding member  20  prevents dirt and the like from adhering to the holding member  20 . As a result, this prevents clogging of the ventilation film  10 . For example, the water-repellent treatment and the oil-repellent treatment to the holding member  20  may be the same as those to the ventilation film  10  as described above. 
     The method for fixing the ventilation film  10  to the holding member  20  may be thermal welding such as iron welding, ultrasonic welding and laser welding in the case where the holding member  20  is thermoplastic resin. Alternatively, the ventilation film  10  may be fixed to the holding member  20  by insert molding, which injects resin into a die in which the ventilation film  10  is set. 
     [Cover Member  30 ] 
     The cover member  30  includes: a side wall portion  31  having a basically cylindrical shape and as an example of the cylindrical portion; an inner projection portion  32  projecting inward from an inner circumferential surface  31   a  of the side wall portion  31 ; and a disk-shaped top portion  33  covering an opening at one end of the side wall portion  31  and the inner projection portion  32  in the centerline direction and as an example of the lid portion. In  FIG. 2 , a cross-sectional shape of the side wall portion  31  and the top portion  33  is shown on the right side of the centerline CL, and a cross-sectional shape of the inner projection portion  32  and the top portion  33  is shown on the left side of the centerline CL. 
     The side wall portion  31  is formed such that a gap S 1  is formed between the inner circumferential surface  31   a  of the side wall portion  31  and the outer circumferential surface  22   b  of the outer projection portion  22  of the holding member  20 . 
     As shown in  FIG. 1 , plural (four in the first exemplary embodiment) inner projection portions  32  are formed in a circumferential direction at equal intervals and formed in the circumferential direction over a predetermined angle. As shown in  FIG. 2 , each inner projection portion  32  includes portions projecting inward in two stages from the inner circumferential surface  31   a  of the side wall portion  31 , namely a first projection portion  32   a  on one side in the centerline direction, and a second projection portion  32   b  on the other side in the centerline direction. In other words, each inner projection portion  32  includes the second projection portion  32   b  projecting inward from the inner circumferential surface  31   a  of the side wall portion  31 , and the first projection portion  32   a  projecting inward further from the second projection portion  32   b.    
     The other end face  32   aa , which is an end face on the other side of the first projection portion  32   a  in the centerline direction, is a surface substantially perpendicular to the centerline direction. Each of the other end faces  32   aa  of the plural (four in the first exemplary embodiment) first projection portions  32   a  is formed on the substantially same plane. 
     When the first projection portions  32   a  are cut in a plane perpendicular to the centerline CL, inner surfaces of the plural first projection portions  32   a  are formed substantially on the same circle C 1 , as shown in  FIG. 3 . The plural first projection portions  32   a  are formed such that the diameter of the circle C 1  is larger than the outer diameter of the outer circumferential surface  21   e  of the cylindrical portion  21 . 
     When the second projection portions  32   b  are cut in a plane perpendicular to the centerline CL, inner surfaces  32   ba  of the plural (four in the first exemplary embodiment) second projection portions  32   b  are formed substantially on the same circle C 2 , as shown in  FIG. 4 . Further, the inner surface  32   ba  of each second projection portion  32   b  gradually goes inward (to the centerline CL side) as it goes from the one side toward the other side in the centerline direction. More specifically, as shown in  FIG. 2 , when the second projection portions  32   b  are cut in a plane including the centerline CL, a straight line L 1  depicting the inner surface  32   ba  of the second projection portion  32   b  is inclined with respect to the centerline CL, and the distance between the straight line L 1  and the centerline CL is gradually smaller from the one side toward the other side in the centerline direction. In other words, the diameter D 2  of the above circle C 2  is gradually smaller from the one side toward the other side in the centerline direction. 
     The diameter D 2  of the circle C 2  at the one end of the plural second projection portions  32   b  in the centerline direction is substantially the same as the outer diameter of the outer circumferential surface  22   b  of the outer projection portion  22  of the holding member  20 . The diameter D 2  of the circle C 2  is gradually smaller than the diameter of the outer circumferential surface  22   b  of the outer projection portion  22  of the holding member  20  from the one side toward the other side in the centerline direction. 
     Further, a chamfer  32   bb  is formed at an inner portion of the other end of the second projection portion  32   b  in the centerline direction. 
     As shown in  FIG. 2 , the top portion  33  is provided such that a gap S 2  is formed between the top portion  33  and the ventilation film  10  in a state where the other end face  32   aa  of the cover member  30  and the one end face  22   a  of the holding member  20  contact each other. 
     In the ventilation member  1  with the above described configuration, the cover member  30  is assembled such that the other end face  32   aa  of the first projection portion  32   a  of the inner projection portion  32  of the cover member  30  contacts the one end face  22   a  of the outer projection portion  22  of the holding member  20 , as shown in  FIG. 2 . In other words, the cover member  30  is pushed against the holding member  20  until the other end face  32   aa  of the cover member  30  abuts on the one end face  22   a  of the holding member  20 . Thus, the inner projection portion  32  of the cover member  30  and the outer projection portion  22  of the holding member  20  are an example of the preventing portion that prevents, at a position where the ventilation film  10  is not mounted, the ventilation film  10  and the top portion  33 , which is an example of the surrounding portion, of the cover member  30  from coming close to each other in the centerline direction. 
     Since the outer diameter of the ventilation film  10  is larger than the diameter of the circle C 1  formed by the inner surfaces of the plural first projection portions  32   a  of the cover member  30 , the outermost diameter portion of the ventilation film  10  contacts the inner surfaces of the first projection portions  32   a  of the cover member  30  in a state where the cover member  30  is assembled to the holding member  20 . 
     As shown in  FIGS. 2 and 4 , in a state where the other end face  32   aa  of the cover member  30  and the one end face  22   a  of the holding member  20  contact each other, the gap S 1 , which is formed between the inner circumferential surface  31   a  of the side wall portion  31  of the cover member  30  and the outer circumferential surface  22   b  of the outer projection portion  22  of the holding member  20 , and the gap S 2 , which is formed between the top portion  33  of the cover member  30  and the ventilation film  10 , function as a ventilation passage R through which gas flows inside and outside the apparatus housing  100 . 
     Further, a gap S 3  formed between the first projection portion  32   a  of the cover member  30  and the outer circumferential surface  21   e  of the cylindrical portion  21  of the holding member  20  also functions as the ventilation passage R. However, since the inner surface of the first projection portion  32   a  of the cover member  30  is in contact with the ventilation film  10  as described above, liquids and solids are prevented from passing through the gap S 3  to enter the gap S 2  formed between the top portion  33  of the cover member  30  and the ventilation film  10 . 
     In the ventilation member  1  with the above described configuration, the ventilation film  10  held by the holding member  20  is not sandwiched by the cover member  30  and the holding member  20  in a state where the other end face  32   aa  of the cover member  30  and the one end face  22   a  of the holding member  20  contact each other (in a state where the cover member  30  is assembled to the holding member  20 ). Thus the ventilation film  10  is free from buckling because the ventilation film  10  does not receive force from the cover member  30  when fixed to the holding member  20 . 
     Further, since the cover member  30  is not present on the ventilation film  10  in a contacting manner, a liquid adhered to the cover member  30  by surface tension does not accumulate on the ventilation film  10 . 
     Therefore, with the ventilation member  1  of the first exemplary embodiment, functions such as ventilation property, dust-proofness, water-proofness, oil-repellency and CCT-proofness are prevented from being impaired by buckling of the ventilation film  10  and accumulation of a liquid on the ventilation film  10 . 
     Further, the inner surfaces  32   ba  of the plural second projection portions  32   b  of the cover member  30  gradually go inward (to the centerline CL side) as they go from the one side toward the other side in the centerline direction. In other words, when the inner surfaces  32   ba  of the plural second projection portions  32   b  of the cover member  30  are cut in a plane perpendicular to the centerline CL, the diameter D 2  of the circle C 2 , which is formed by cross-sectional lines of the inner surfaces  32   ba  of the plural second projection portions  32   b , is gradually smaller from the one side toward the other side in the centerline direction. On the other hand, the outer circumferential surface  22   b  of the outer projection portion  22  of the holding member  20  is a surface substantially parallel to the centerline direction. For this reason, when the cover member  30  is pushed against the holding member  20  until the other end face  32   aa  of the cover member  30  abuts on the one end face  22   a  of the holding member  20 , the plural second projection portions  32   b  of the cover member  30  are press-fitted to the outer projection portion  22  of the holding member  20 . Further, an interference between the plural second projection portions  32   b  of the cover member  30  and the outer projection portion  22  of the holding member  20  is gradually larger from the one side toward the other side in the centerline direction. As a result, even if a compression set occurs in the fitting portion (press-fitting portion) between the cover member  30  and the holding member  20 , the cover member  30  hardly moves toward the one side with respect to the holding member  20  in the centerline direction, as compared with a case where the interference of the fitting portion (press-fitting portion) is constant. Thus the cover member  30  hardly falls off the holding member  20 . 
     The outer circumferential surface  22   b  of the outer projection portion  22  of the holding member  20  may gradually go inward (to the centerline CL side) as it goes from the one side toward the other side in the centerline direction, similarly to the inner surface  32   ba  of the second projection portion  32   b  of the cover member  30 . With the outer circumferential surface  22   b  of the outer projection portion  22  of the holding member  20  having this shape, the cover member  30  hardly falls off the holding member  20  too and the inner circumferential surface  21   c  of the holding member  20  is prevented from deforming while the cover member  30  is mounted to the holding member  20 . 
     Consideration is now given to a vehicle lamp, such as head lamp, rear lamp, fog lamp and turn lamp, having the ventilation member  1  configured as above and the closed apparatus housing  100  storing an LED (light emitting diode) as an example of the light source emitting light. 
     When turned on, the LED stored in the apparatus housing  100  of the lamp generates heat to have high temperature. Accordingly, when the LED is turned on, an air in the internal space of the apparatus housing  100  of the lamp is heated to expand. On the other hand, when the LED is turned off, the LED stops generating heat and the heated air in the internal space of the apparatus housing  100  is cooled to shrink. In this way, when the pressure in the internal space of the apparatus housing  100  increases due to expansion of the air in the internal space and when the pressure in the internal space decreases due to shrinkage of the air in the internal space, gas flows through the ventilation passage R in the ventilation member  1  toward the outside of the lamp from the internal space of the apparatus housing  100 , or toward the internal space of the apparatus housing  100  from the outside of the lamp. This prevents breakage of the apparatus housing  100  and the like due to sudden increase in the pressure in the internal space of the apparatus housing  100  and sudden decrease in the pressure in the internal space. 
     Second Exemplary Embodiment 
       FIG. 5  is a diagram illustrating a schematic configuration of a ventilation member  2  according to the second exemplary embodiment. 
       FIG. 6  is a cross-sectional view of the ventilation member  2  according to the second exemplary embodiment taken along the line VI-VI in  FIG. 5 . 
     The ventilation member  2  of the second exemplary embodiment is different from the ventilation member  1  of the first exemplary embodiment in the holding member  20  and the cover member  30 . That is, the ventilation member  2  of the second exemplary embodiment includes the above-described ventilation film  10 , a holding member  220  described later, and a cover member  230  described later. Hereinafter, explanation will be given of the difference of the holding member  220  of the second exemplary embodiment from the holding member  20  of the first exemplary embodiment and the difference of the cover member  230  of the second exemplary embodiment from the cover member  30  of the first exemplary embodiment. Note that a major difference lies in their shapes, and explanation of the material, method, liquid-repellent treatment, etc. will be omitted because they are the same between the embodiments. 
     [Holding Member  220 ] 
     The holding member  220  includes a cylindrical portion  221  of a cylindrical shape, and an outer projection portion  222  projecting outward from the cylindrical portion  221 . 
     The holding member  220  holds the ventilation film  10  at one end of the cylindrical portion  221  in the centerline direction. The ventilation film  10  covers an opening at one end of the cylindrical portion  221  in the centerline direction. Further, the holding member  220  is mounted on the apparatus housing  100  (see  FIG. 2 ) with the other end of the cylindrical portion  221  in the centerline direction being press-fitted to the mounted portion  110  of the apparatus housing  100  (see  FIG. 2 ). 
     The outer projection portion  222  is a basically cylindrical portion projecting outward from an outer circumferential surface of the cylindrical portion  221 . However, an outer circumferential surface  222   b  of the outer projection portion  222  includes plural (four in the second exemplary embodiment) rectangular flat surfaces in a circumferential direction at equal intervals, and arc-shaped surfaces  222   ba  and the rectangular surfaces  222   bb  of a rectangular shape are alternately arranged. 
     One end face  222   a , which is an end face on one side of the outer projection portion  222  in the centerline direction, is a surface substantially perpendicular to the centerline direction. The outer circumferential surface  222   b  (the arc-shaped surfaces  222   ba  and the rectangular surfaces  222   bb ) of the outer projection portion  222  is a surface substantially parallel to the centerline direction. 
     &lt;Cover Member  230 &gt; 
     The cover member  230  includes: a side wall portion  231  having a basically cylindrical shape; an inner projection portion  232  projecting inward from an inner circumferential surface  231   a  of the side wall portion  231 ; and a disk-shaped top portion  233  provided at one end of the side wall portion  231  and the inner projection portion  232  in the centerline direction. In  FIG. 6 , a cross-sectional shape of the side wall portion  231  and the top portion  233  is shown on the right side of the centerline CL, and a cross-sectional shape of the side wall portion  231 , the inner projection portion  232  and the top portion  233  is shown on the left side of the centerline CL. 
     Plural (four in the second exemplary embodiment) inner projection portions  232  are formed in a circumferential direction at equal intervals and formed in the circumferential direction over a predetermined angle. The other end face  232   a , which is an end face on the other side of the inner projection portion  232  in the centerline direction, is a surface substantially perpendicular to the centerline direction. Each of the other end faces  232   a  of the plural inner projection portions  232  is formed on the substantially same plane. 
     When the inner projection portions  232  are cut in a plane perpendicular to the centerline CL, inner surfaces of the plural inner projection portions  232  are formed substantially on the same circle, and the diameter of the circle is formed such that the diameter is larger than the outer diameter of the outer circumferential surface of the cylindrical portion  221  of the holding member  220 . 
     A communication hole  231   b  communicating the inside and the outside is formed at a portion between two adjacent inner projection portions  232  of the side wall portion  231 . That is, plural (four in the second exemplary embodiment) communication holes  231   b  are formed in the circumferential direction at predetermined intervals. 
     A portion of the side wall portion  231  on the other side in the centerline direction relative to the portion where the inner projection portions  232  are formed has a substantially cylindrical shape, but the inner circumferential surface  231   a  gradually goes inward (to the centerline CL side) as it goes from the one side toward the other side in the centerline direction. More specifically, as shown in  FIG. 6 , when the side wall portion  231  is cut in a plane including the centerline CL, a straight line L 2  depicting the inner circumferential surface  231   a  is inclined with respect to the centerline CL, and the distance between the straight line L 2  and the centerline CL is gradually smaller from the one side toward the other side in the centerline direction. In other words, the diameter D 22  of the circle formed by cutting the inner circumferential surface  231   a  in a plane substantially perpendicular to the centerline direction is gradually smaller from the one side toward the other side in the centerline direction. 
     The diameter D 22  of the inner circumferential surface  231   a  at its portion somewhat closer to the other side than the communication hole  231   b  in the centerline direction is substantially the same as the outer diameter of the outer circumferential surface  222   b  of the outer projection portion  222  of the holding member  220 . The diameter D 22  of the inner circumferential surface  231   a  is gradually smaller than the diameter of the outer circumferential surface  222   b  of the outer projection portion  222  of the holding member  220  from the one side toward the other side in the centerline direction. 
     Further, a chamfer  231   c  is formed at an inner portion of the other end side of the side wall portion  231  in the centerline direction. 
     As shown in  FIG. 6 , the top portion  233  is provided such that a gap S 22  is formed between the top portion  233  and the ventilation film  10  in a state where the other end face  232   a  of the cover member  230  and the one end face  222   a  of the holding member  220  contact each other. 
     In the ventilation member  2  with the above described configuration, the cover member  230  is assembled such that the other end face  232   a  of the cover member  230  contacts the one end face  222   a  of the outer projection portion  222  of the holding member  220 , as shown in  FIG. 6 . In other words, the cover member  230  is pushed against the holding member  220  until the other end face  232   a  of the cover member  230  abuts on the one end face  222   a  of the holding member  220 . 
     As shown in  FIG. 6 , in a state where the other end face  232   a  of the cover member  230  is in contact with the one end face  222   a  of the holding member  220 , the communication hole  231   b  formed in the side wall portion  231  of the cover member  230  and the gap S 22  formed between the top portion  233  of the cover member  230  and the ventilation film  10  function as a ventilation passage R through which gas flows inside and outside the apparatus housing  100 . 
     In the ventilation member  2  of the second exemplary embodiment configured as above, the ventilation film  10  held by the holding member  220  is not sandwiched by the cover member  230  and the holding member  220  in a state where the other end face  232   a  of the cover member  230  and the one end face  222   a  of the holding member  220  contact each other (in a state where the cover member  230  is assembled to the holding member  220 ). Thus the ventilation film  10  is free from buckling because the ventilation film  10  does not receive force from the cover member  230  when fixed to the holding member  220 . 
     Further, since the cover member  230  is not present on the ventilation film  10  in a contacting manner, a liquid adhered to the cover member  230  by surface tension does not accumulate on the ventilation film  10 . 
     Therefore, with the ventilation member  2  of the second exemplary embodiment, functions such as ventilation property, dust-proofness, water-proofness, oil-repellency and CCT-proofness are prevented from being impaired by buckling of the ventilation film  10  and accumulation of a liquid on the ventilation film  10 . 
     Further, the inner circumferential surface  231   a  of the side wall portion  231  at a portion on the other side in the centerline direction relative to the portion where the inner projection portion  232  is provided gradually goes inward (to the centerline CL side) as it goes from the one side toward the other side in the centerline direction. In other words, the diameter D 22  of the circle formed by cutting the inner circumferential surface  231   a  in a plane substantially perpendicular to the centerline direction is gradually smaller from the one side toward the other side in the centerline direction. On the other hand, the outer circumferential surface  222   b  of the outer projection portion  222  of the holding member  220  is a surface substantially parallel to the centerline direction. For this reason, when the cover member  230  is pushed against the holding member  220  until the other end face  232   a  of the cover member  230  abuts on the one end face  222   a  of the holding member  220 , the side wall portion  231  of the cover member  230  is press-fitted to the outer projection portion  222  of the holding member  220 . Further, an interference between the side wall portion  231  of the cover member  230  and the outer projection portion  222  of the holding member  220  is gradually larger from the one side toward the other side in the centerline direction. As a result, even if a compression set occurs in the fitting portion (press-fitting portion) between the cover member  230  and the holding member  220 , the cover member  230  hardly moves toward the one side with respect to the holding member  220  in the centerline direction, as compared with a case where the interference of the fitting portion (press-fitting portion) is constant. Thus the cover member  230  hardly falls off the holding member  220 . 
     The outer circumferential surface  222   b  of the outer projection portion  222  of the holding member  220  may gradually go inward (to the centerline CL side) as it goes from the one side toward the other side in the centerline direction, similarly to the inner circumferential surface  231   a  of the cover member  230 . With the outer circumferential surface  222   b  of the outer projection portion  222  of the holding member  220  having this shape, the cover member  230  hardly falls off the holding member  220  too and the inner circumferential surface of the holding member  220  is prevented from deforming while the cover member  230  is mounted to the holding member  220 . 
     Third Exemplary Embodiment 
       FIG. 7  is a diagram illustrating a schematic configuration of a ventilation member  3  according to the third exemplary embodiment. 
       FIG. 8  is a cross-sectional view of the ventilation member  3  according to the third exemplary embodiment taken along the line VIII-VIII in  FIG. 7 . 
     The ventilation member  3  of the third exemplary embodiment is different from the ventilation member  1  of the first exemplary embodiment in the holding member  20  and the cover member  30 . That is, the ventilation member  3  of the third exemplary embodiment includes the above-described ventilation film  10 , a holding member  320  described later, and a cover member  330  described later. Hereinafter, explanation will be given of the difference of the holding member  320  of the third exemplary embodiment from the holding member  20  of the first exemplary embodiment and the difference of the cover member  330  of the third exemplary embodiment from the cover member  30  of the first exemplary embodiment. Note that a major difference lies in their shapes, and explanation of the material, method, liquid-repellent treatment, etc. will be omitted because they are the same between the embodiments. 
     [Holding Member  320 ] 
     The holding member  320  includes a cylindrical portion  321  of a cylindrical shape, and an outer projection portion  322  projecting outward from the cylindrical portion  321 . 
     The holding member  320  holds the ventilation film  10  at one end of the cylindrical portion  321  in the centerline direction. The ventilation film  10  covers an opening at one end of the cylindrical portion  321  in the centerline direction. Further, the holding member  320  is mounted on the apparatus housing  100  (see  FIG. 2 ) with the other end of the cylindrical portion  321  in the centerline direction being press-fitted to the mounted portion  110  of the apparatus housing  100  (see  FIG. 2 ). 
     As shown in  FIGS. 7 and 8 , the outer projection portion  322  includes portions projecting outward in two stages from the outer circumferential surface of the cylindrical portion  321 , namely a first outer projection portion  323  on one side in the centerline direction, and a second outer projection portion  324  on the other side in the centerline direction. The first outer projection portion  323  projects in a cylindrical shape from the outer circumferential surface of the cylindrical portion  321 . The second outer projection portion  324  projects in a doughnut-shape from the outer circumferential surface of the cylindrical portion  321 . In other words, the size of the first outer projection portion  323  in the centerline direction is larger than the size of the second outer projection portion  324  in the centerline direction. The projection amount of the second outer projection portion  324  from the outer circumferential surface of the cylindrical portion  321  is larger than the projection amount of the first outer projection portion  323  from the outer circumferential surface of the cylindrical portion  321 . 
     An outer circumferential surface  323   a  of the first outer projection portion  323  is a surface substantially parallel to the centerline direction. 
     One end face  324   a , which is an end face on one side of the second outer projection portion  324  in the centerline direction, is a surface substantially perpendicular to the centerline direction. 
     [Cover Member  330 ] 
     The cover member  330  includes: a side wall portion  331  having a cylindrical shape and as an example of the cylindrical portion; and a disk-shaped top portion  333  provided at one end of the side wall portion  331  in the centerline direction and as an example of the lid portion. 
     The cover member  330  is assembled such that the other end face  331   a  (described later) of the side wall portion  331  contacts one end face  324   a  of the second outer projection portion  324  of the holding member  320 . In other words, the cover member  330  is pushed against the holding member  320  until the other end face  331   a  of the cover member  330  abuts on the one end face  324   a  of the holding member  320 . 
     In the side wall portion  331 , plural (four in the third exemplary embodiment) communication holes  331   b  communicating the inside and the outside are formed in the circumferential direction at predetermined intervals. 
     The plural communication holes  331   b  are formed to be positioned on one side in the centerline direction relative to the first outer projection portion  323  of the holding member  320  in a state where the other end face  331   a , which is the other end face of the side wall portion  331  in the centerline direction, contacts the one end face  324   a  of the second outer projection portion  324  of the holding member  320  (the state shown in  FIG. 8 ). 
     In the state where the other end face  331   a  of the side wall portion  331  contacts the one end face  324   a  of the second outer projection portion  324  of the holding member  320  (the state shown in  FIG. 8 ), an inner circumferential surface  331   c  of the side wall portion  331  gradually goes inward (to the centerline CL side) as it goes from a position facing one end  323   b  in the centerline direction of the first outer projection portion  323  of the holding member  320  toward the other side in the centerline direction. More specifically, as shown in  FIG. 8 , when the side wall portion  331  is cut in a plane including the centerline CL, a straight line L 3  depicting the inner circumferential surface  331   c  is inclined with respect to the centerline CL, and the distance between the straight line L 3  and the centerline CL is gradually smaller from the one side toward the other side in the centerline direction. In other words, the diameter D 32  of the circle formed by cutting the inner circumferential surface  331   c  in a plane substantially perpendicular to the centerline direction is gradually smaller from the one side toward the other side in the centerline direction. 
     In the ventilation member  3  with the above described configuration, the cover member  330  (see  FIG. 7 ) is assembled such that the other end face  331   a  of the side wall portion  331  of the cover member  330  contacts the one end face  324   a  of the second outer projection portion  324  of the holding member  320 , as shown in  FIG. 8 . Further, as shown in  FIG. 8 , in a state where the other end face  331   a  of the cover member  330  is in contact with the one end face  324   a  of the holding member  320 , the communication hole  331   b  formed in the side wall portion  331  of the cover member  330  and a gap S 32  formed between the top portion  333  of the cover member  330  and the ventilation film  10  function as a ventilation passage R through which gas flows inside and outside the apparatus housing  100 . 
     In the ventilation member  3  of the third exemplary embodiment configured as above, the ventilation film  10  held by the holding member  320  is not sandwiched by the cover member  330  and the holding member  320  in a state where the other end face  331   a  of the cover member  330  and the one end face  324   a  of the holding member  320  contact each other (in a state where the cover member  330  is assembled to the holding member  320 ). Thus the ventilation film  10  is free from buckling because the ventilation film  10  does not receive force from the cover member  330  when fixed to the holding member  320 . 
     Further, since the cover member  330  is not present on the ventilation film  10  in a contacting manner, a liquid adhered to the cover member  330  by surface tension does not accumulate on the ventilation film  10 . 
     Therefore, with the ventilation member  3  of the third exemplary embodiment, functions such as ventilation property, dust-proofness, water-proofness, oil-repellency and CCT-proofness are prevented from being impaired by buckling of the ventilation film  10  and accumulation of a liquid on the ventilation film  10 . 
     In the state where the other end face  331   a  of the side wall portion  331  is in contact with the one end face  324   a  of the second outer projection portion  324  of the holding member  320  (the state shown in  FIG. 8 ), the inner circumferential surface  331   c  of the side wall portion  331  gradually goes inward as it goes from a position facing the one end  323   b  in the centerline direction of the first outer projection portion  323  of the holding member  320  toward the other side in the centerline direction. In other words, the diameter D 32  of the circle formed by cutting the inner circumferential surface  331   c  in a plane substantially perpendicular to the centerline direction is gradually smaller from the one side toward the other side in the centerline direction. On the other hand, the outer circumferential surface  323   a  of the first outer projection portion  323  of the holding member  320  is a surface substantially parallel to the centerline direction. For this reason, when the cover member  330  is pushed against the holding member  320  until the other end face  331   a  of the cover member  330  abuts on the one end face  324   a  of the holding member  320 , the side wall portion  331  of the cover member  330  is press-fitted to the first outer projection portion  323  of the holding member  320 . Further, an interference between the side wall portion  331  of the cover member  330  and the first outer projection portion  323  of the holding member  320  is gradually larger from the one side toward the other side in the centerline direction. As a result, even if a compression set occurs in the fitting portion (press-fitting portion) between the cover member  330  and the holding member  320 , the cover member  330  hardly moves toward the one side with respect to the holding member  320  in the centerline direction, as compared with a case where the interference of the fitting portion (press-fitting portion) is constant. Thus the cover member  330  hardly falls off the holding member  320 . 
     The outer circumferential surface  323   a  of the first outer projection portion  323  of the holding member  320  may gradually go inward (to the centerline CL side) as it goes from the one side toward the other side in the centerline direction, similarly to the inner circumferential surface  331   c  of the cover member  330 . With the outer circumferential surface  323   a  of the first outer projection portion  323  of the holding member  320  having this shape, the cover member  330  hardly falls off the holding member  320  too and the inner circumferential surface of the holding member  320  is prevented from deforming while the cover member  330  is mounted to the holding member  320 . 
     A chamfer may be formed at one end, in the centerline direction, of the first outer projection portion  323  of the outer projection portion  322  of the holding member  320  such that the diameter of the outer circumferential surface  323   a  is gradually larger from the one side toward the other side in the centerline direction. 
     Modified Example of the Cover Member  330  According to the Third Exemplary Embodiment 
       FIG. 9  is a diagram illustrating a modified example of the cover member  330  according to the third exemplary embodiment. 
     In the cover member  330  of the third exemplary embodiment as described above, a cutout  331   d  may be formed instead of the communication hole  331   b , as shown in  FIG. 9 . The cutout  331   d  extends the other end of the communication hole  331   b  in the centerline direction to the other end face  331   a  of the side wall portion  331 . In the cover member  330  of the third exemplary embodiment, forming the cutout  331   d  instead of the communication hole  331   b  can provide the same effects as those described above. 
     Fourth Exemplary Embodiment 
       FIG. 10  is a diagram illustrating a schematic configuration of a ventilation member  4  according to the fourth exemplary embodiment. 
       FIG. 11  is a cross-sectional view of the ventilation member  4  according to the fourth exemplary embodiment taken along the line XI-XI in  FIG. 10 . 
     The ventilation member  4  of the fourth exemplary embodiment is different from the ventilation member  1  of the first exemplary embodiment in the holding member  20  and the cover member  30 . That is, the ventilation member  4  of the fourth exemplary embodiment includes the above-described ventilation film  10 , a holding member  420  described later, and a cover member  430  described later. Hereinafter, explanation will be given of the difference of the holding member  420  of the fourth exemplary embodiment from the holding member  20  of the first exemplary embodiment and the difference of the cover member  430  of the fourth exemplary embodiment from the cover member  30  of the first exemplary embodiment. Note that a major difference lies in their shapes, and explanation of the material, method, liquid-repellent treatment, etc. will be omitted because they are the same between the embodiments. 
     [Holding Member  420 ] 
     The holding member  420  includes a cylindrical portion  421  of a cylindrical shape, and an outer projection portion  422  projecting outward from the cylindrical portion  421 . 
     The holding member  420  holds the ventilation film  10  at one end of the cylindrical portion  421  in the centerline direction. The ventilation film  10  covers an opening at one end of the cylindrical portion  421  in the centerline direction. Further, the holding member  420  is mounted on the apparatus housing  100  (see  FIG. 2 ) with the other end of the cylindrical portion  421  in the centerline direction being press-fitted to the mounted portion  110  of the apparatus housing  100  (see  FIG. 2 ). 
     Plural (four in the fourth exemplary embodiment) outer projection portions  422  are formed in a circumferential direction at equal intervals. As shown in  FIGS. 10 and 11 , each outer projection portion  422  includes portions projecting outward in two stages from an outer circumferential surface of the cylindrical portion  421 , namely a first outer projection portion  423  on one side in the centerline direction, and a second outer projection portion  424  on the other side in the centerline direction. The size of the first outer projection portion  423  in the centerline direction is larger than the size of the second outer projection portion  424  in the centerline direction. The projection amount of the second outer projection portion  424  from the outer circumferential surface of the cylindrical portion  421  is larger than the projection amount of the first outer projection portion  423  from the outer circumferential surface of the cylindrical portion  421 . 
     When plural (four in the fourth exemplary embodiment) first outer projection portions  423  are cut in a plane perpendicular to the centerline CL, outer circumferential surfaces  423   a  of the plural first outer projection portions  423  are formed substantially on the same circle C 423 . The outer circumferential surface  423   a  of the first outer projection portion  423  is a surface substantially parallel to the centerline direction, and the size of the circle C 423  is constant from the one side toward the other side in the centerline direction. However, as shown in  FIGS. 10 and 11 , a chamfer  423   b  may be formed on one end of the first outer projection portion  423  in the centerline direction, such that the diameter of the circle C 423  gradually increases from the one side toward the other side in the centerline direction. 
     One end face  424   a , which is an end face on one side of the second outer projection portion  424  in the centerline direction, is a surface substantially perpendicular to the centerline direction. 
     [Cover Member  430 ] 
     The cover member  430  includes: a side wall portion  431  having a cylindrical shape; and a disk-shaped top portion  433  provided at one end of the side wall portion  431  in the centerline direction. 
     The radial size of the other end face  431   a , which is the other end face of the side wall portion  431  in the centerline direction, is substantially same as the radial size of the one end face  424   a  of the second outer projection portion  424  of the outer projection portion  422  of the holding member  420 . 
     The cover member  430  is assembled such that the other end face  431   a  of the side wall portion  431  contacts the one end face  424   a  of the outer projection portion  422  of the holding member  420 . In other words, the cover member  430  is pushed against the holding member  420  until the other end face  431   a  of the cover member  430  abuts on the one end face  424   a  of the holding member  420 . 
     In the state where the other end face  431   a  of the side wall portion  431  contacts the one end face  424   a  of the second outer projection portion  424  of the holding member  420  (the state shown in  FIG. 11 ), an inner circumferential surface  431   c  of the side wall portion  431  gradually goes inward (to the centerline CL side) as it goes from a position facing one end in the centerline direction of the first outer projection portion  423  of the holding member  420  toward the other side in the centerline direction. More specifically, as shown in  FIG. 11 , when the side wall portion  431  is cut in a plane including the centerline CL, a straight line L 4  depicting the inner circumferential surface  431   c  is inclined with respect to the centerline CL, and the distance between the straight line L 4  and the centerline CL is gradually smaller from the one side toward the other side in the centerline direction. In other words, the diameter D 42  of the circle formed by cutting the inner circumferential surface  431   c  in a plane substantially perpendicular to the centerline direction is gradually smaller from the one side toward the other side in the centerline direction. 
     In the ventilation member  4  with the above described configuration, as shown in  FIG. 11 , in a state where the other end face  431   a  of the side wall portion  431  of the cover member  430  is in contact with the one end face  424   a  of the outer projection portion  422  of the holding member  420 , a gap S 41  formed between the side wall portion  431  of the cover member  430  and the outer circumferential surface of the cylindrical portion  421  of the holding member  420 , and a gap S 42  formed between the top portion  433  of the cover member  430  and the ventilation film  10  function as a ventilation passage R through which gas flows inside and outside of the apparatus housing  100  (see  FIG. 2 ). 
     In the ventilation member  4  of the fourth exemplary embodiment configured as above, the ventilation film  10  held by the holding member  420  is not sandwiched by the cover member  430  and the holding member  420  in a state where the other end face  431   a  of the cover member  430  and the one end face  424   a  of the holding member  420  contact each other (in a state where the cover member  430  is assembled to the holding member  420 ). Thus the ventilation film  10  is free from buckling because the ventilation film  10  does not receive force from the cover member  430  when fixed to the holding member  420 . 
     Further, since the cover member  430  is not present on the ventilation film  10  in a contacting manner, a liquid adhered to the cover member  430  by surface tension does not accumulate on the ventilation film  10 . 
     Therefore, with the ventilation member  4  of the fourth exemplary embodiment, functions such as ventilation property, dust-proofness, water-proofness, oil-repellency and CCT-proofness are prevented from being impaired by buckling of the ventilation film  10  and accumulation of a liquid on the ventilation film  10 . 
     In the state where the other end face  431   a  of the side wall portion  431  is in contact with the one end face  424   a  of the second outer projection portion  424  of the holding member  420  (the state shown in  FIG. 11 ), the inner circumferential surface  431   c  of the side wall portion  431  gradually goes inward as it goes from a position facing the one end in the centerline direction of the first outer projection portion  423  of the holding member  420  toward the other side in the centerline direction. In other words, the diameter D 42  of the circle formed by cutting the inner circumferential surface  431   c  in a plane substantially perpendicular to the centerline direction is gradually smaller from the one side toward the other side in the centerline direction. On the other hand, the outer circumferential surface  423   a  of the first outer projection portion  423  of the holding member  420  is a surface substantially parallel to the centerline direction. For this reason, when the cover member  430  is pushed against the holding member  420  until the other end face  431   a  of the cover member  430  abuts on the one end face  424   a  of the holding member  420 , the side wall portion  431  of the cover member  430  is press-fitted to the first outer projection portion  423  of the holding member  420 . Further, an interference between the side wall portion  431  of the cover member  430  and the first outer projection portion  423  of the holding member  420  is gradually larger from the one side toward the other side in the centerline direction. As a result, even if a compression set occurs in the fitting portion (press-fitting portion) between the cover member  430  and the holding member  420 , the cover member  430  hardly moves toward the one side with respect to the holding member  420  in the centerline direction, as compared with a case where the interference of the fitting portion (press-fitting portion) is constant. Thus the cover member  430  hardly falls off the holding member  420 . 
     The outer circumferential surface  423   a  of the first outer projection portion  423  of the holding member  420  may gradually go inward (to the centerline CL side) as it goes from the one side toward the other side in the centerline direction, similarly to the inner circumferential surface  431   c  of the cover member  430 . With the outer circumferential surface  423   a  of the first outer projection portion  423  of the holding member  420  having this shape, the cover member  430  hardly falls off the holding member  420  too and the inner circumferential surface of the holding member  420  is prevented from deforming while the cover member  430  is mounted to the holding member  420 . 
     REFERENCE SIGNS LIST 
     
         
           1  Ventilation member 
           10  Ventilation film 
           20  Holding member 
           21  Cylindrical portion 
           22  Outer projection portion 
           30  Cover member 
           31  Side wall portion 
           32  Inner projection portion 
           33  Top portion 
           100  Apparatus housing 
           110  Mounted portion