Abstract:
An air cleaner having a filter, causing air to pass through the filter and discharging the filtered air. The air cleaner includes: an air duct having an inlet via which air is received and an outlet facing a first part of a main surface of the filter and via which the received air is output towards the first part of the main surface; a fan causing air to be received by the air duct via the inlet, to be output from the air duct via the outlet, and to pass through the filter; and a flow distributer disposed between the outlet and the filter. The flow distributer changes a direction of flow of air output from the air duct from towards the first part of the main surface to towards a second part of the main surface of the filter that does not facing the outlet.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on application No. 2015-035337 filed in Japan, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     (1) Field of the Invention 
     The present disclosure is related to an air cleaner that takes in air discharged from a fixing device and the like included in an image forming device such as a printer, a copier, or a multifunctional peripheral (MHP), causes the air from the fixing device and the like to pass through a filter, and discharges the filtered air. 
     (2) Related Art 
     Conventionally, a fixing device, etc., included in an image forming device such as a printer or a copier may generate undesirable airborne substances such as volatile organic compounds (VOCs) and the like. Such undesirable airborne substances, when discharged to the outside of the image forming device, may negatively affect office environment. Thus, in order to achieve a comfortable office environment, a conventional image forming device is provided with a mechanism that takes in air from the image forming device, which contains the undesirable airborne substances discharged from the fixing device, etc., causes the air from the image forming device to pass through a filter, and discharges the filtered air. 
     Such a mechanism is commonly referred to as an air cleaner, and typically includes, in addition to a filter, a discharge fan and an air duct. 
     Recently, more interest is being directed to maintaining a clean office environment. This trend gives rise to the necessity of improving filter performance of air cleaners and thereby reducing the amount of undesirable airborne substances discharged to the outside of image forming devices to as small an amount as possible. Filter performance may be improved, for example, by increasing filter surface area and filter thickness. However, increasing filter thickness unfortunately brings about an increase in depth-direction length of image forming devices, which results in inefficient use of office space. As such, typically, filter surface is increased to improve filter performance. 
     For example, Japanese Patent Application Publication No. 2002-014583 (referred to in the following as Patent Literature 1) discloses one example of a technology for achieving such an improvement in filter performance without increasing the overall size of an image forming device. In specific, Patent Literature 1 discloses an air cleaner (a dust removing device) that has a pleated filter (i.e., a pleats part 6) that achieves both compact size and increased filter surface area. In addition, Patent Literature 1 discloses a structure where a cross-sectional area of an air flow path in the air cleaner, which guides air from the image forming device containing undesirable airborne substances to the filter, increases considerably upon reaching an inlet of a part where the filter (i.e., the pleats part 6) is accommodated, and where the inlet and the filter are located close to one another. 
     Accordingly, the air cleaner disclosed in Patent Literature 1 improves filter performance without increasing overall image forming device size. 
     Meanwhile, as described above, Patent Literature 1 discloses a structure where the air flow path in the air cleaner expands considerably upon reaching the inlet of the part where the filter is accommodated, and where the inlet and the filter are located close to one another. This structure causes air containing undesirable airborne substances, upon being taken in to the part where the filter is accommodated via the inlet, to be mainly guided towards an area of the filter that faces the inlet, before spreading over the entirety of the surface of the filter. This results in the filter capturing the undesirable airborne substances mainly at an area thereof facing the inlet, which then results in a decrease of filter performance (i.e., the ability of capturing undesirable airborne substances) occurring at a faster rate at the area facing the inlet than at other areas of the filter. As a result, filter clogging is accelerated at the area facing the inlet, which shortens filter lifetime. 
     In view of such technical problems, the present disclosure aims to provide an air cleaner that suppresses a local decrease in filter performance, and an image forming device including such an air cleaner. 
     SUMMARY 
     To achieve at least one of the abovementioned aims, an air cleaner reflecting one aspect of the present disclosure is an air cleaner having a filter, causing air from an image forming device to pass through the filter and discharging the filtered air, the air cleaner including: an air duct having an inlet via which air from the image forming device is received and an outlet facing a first part of a main surface of the filter and via which the received air is output in a direction towards the first part of the main surface; a fan causing air from the image forming device to be received by the air duct via the inlet, to be output from the air duct via the outlet, and to pass through the filter; and a flow distributer disposed between the outlet and the filter, the flow distributer changing a direction of flow of air output from the air duct from the direction towards the first part of the main surface to a direction towards a second part of the main surface of the filter, the second part being a part of the main surface that does not face the outlet. 
     In the air cleaner reflecting one aspect of the present disclosure, it is desirable that the air duct have a curve between the inlet and the outlet, and a path of air flow have greater cross-sectional area between the outlet and the main surface of the filter than at the outlet. 
     In the air cleaner reflecting one aspect of the present disclosure, it is desirable that the flow distributer have a mountain-shaped protrusion protruding towards the outlet. 
     The air cleaner reflecting one aspect of the present disclosure desirably further includes a plurality of ribs disposed about the outlet, and it is desirable that the flow distributer be supported by the ribs. 
     In the air cleaner reflecting one aspect of the present disclosure, it is desirable that the flow distributer have at least one through hole penetrating through a main surface thereof facing the outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings those illustrate a specific embodiment of the invention. 
       In the drawings: 
         FIG. 1  is a perspective view illustrating the exterior of an image forming device  1  pertaining to an embodiment; 
         FIG. 2  is a cross-sectional view illustrating the structure of the image forming device  1 ; 
         FIG. 3  is a perspective view illustrating the relationship between a fixing device  40 , a paper ejector  80 , and an air cleaner  90 ; 
         FIG. 4  illustrates a state where the air cleaner  90  has been detached from the paper ejector  80 ; 
         FIG. 5  is a magnified perspective view illustrating the detailed structure of a fan  901  and an air duct  902 ; 
         FIG. 6  is a perspective view illustrating ribs  9021  and an air flow distributer  903 , as seen from a position upstream than an outlet  902 B of the air duct  902  in a direction in which air flows in the air cleaner  90 ; 
         FIG. 7  is an exploded perspective view illustrating the ribs  9021  and the air flow distributer  903 , as seen from a position downstream than the outlet  902 B of the air duct  902  in the direction in which air flows in the air cleaner  90 ; 
         FIG. 8  is a schematic illustrating air flow from the air duct  902  to an electrostatic filter  904 , when the air flow distributer  903  is implemented by using a member whose portion facing the outlet  902 B has a flat, circular disc shape; 
         FIG. 9  is a schematic illustrating air flow from the air duct  902  to the electrostatic filter  904 , when the air flow distributer  903  is implemented by using a member whose portion facing the outlet  902 B has a symmetric conical shape; and 
         FIG. 10  is a schematic illustrating air flow from the air duct  902  to the electrostatic filter  904 , when the air flow distributer  903  is implemented by using a member whose portion facing the outlet  902 B has an asymmetric conical shape. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following describes an image forming device pertaining to one embodiment of the present disclosure, with reference to the accompanying drawings. 
     [1] Structure of Image Forming Device 
       FIG. 1  is a perspective view illustrating the exterior of the image forming device pertaining to the present embodiment (image forming device  1 ). The image forming device  1  is a multifunctional peripheral (MFP). The image forming device  1  includes an operation panel  60 , an air cleaner (not depicted in  FIG. 1 ), and an image reader  70 . The operation panel  60  is located at a front side of the image forming device  1 , which is indicated by arrow A in  FIG. 1 . The air cleaner is located at a rear side of the image forming device  1 , which is indicated by arrow B in  FIG. 1 . The image reader  70  is located above the housing of a main part of the image forming device  1 . 
       FIG. 2  is a cross-sectional view illustrating the structure of the image forming device  1 , which forms images by using the electro-photographic method. As illustrated in  FIG. 2 , the image forming device  1  includes, in addition to the operation panel  60  and the image reader  70 , an image processing unit  10 ; a paper feeder  30 ; a fixing device  40 ; and a control unit  50 . 
     The image forming device  1  is connected to a network, such as a LAN. When receiving a print instruction from an external terminal device (not depicted in any of the drawings) or from the operation panel  60 , the image forming device  1  performs printing onto a recording sheet in response to the print instruction by forming toner images of the respective colors yellow, magenta, cyan, and black, and transferring all of the toner images so as to be overlaid on one another on the recording sheet. In the following and in the drawings, the colors yellow, magenta, cyan, and black are respectively indicated by using the alphabets Y, M, C, and K. Further, in the following and in the drawings, constituent elements of the respective colors (e.g., image formers of the respective colors) are distinguished from one another by adding the alphabets Y, M, C, and K to reference numbers. 
     The image processing unit  10  includes: image formers  10 Y,  10 M,  10 C,  10 K; an intermediate image transfer belt  21 ; and a secondary image transfer roller  27 . The image formers  10 Y,  10 M,  10 C,  10 K have identical structures, and thus, are described in the following by focusing on the image former  10 Y as one example. 
     The image former  10 Y includes: a photosensitive drum  11 ; a charger  12 ; an exposure unit  13 ; a developer  14 ; and a cleaner  15 . The charger  12 , the exposure unit  13 , the developer  14 , and the cleaner  15  are disposed around the photosensitive drum  11 . The image former  10 Y forms a toner image of color Y on the photosensitive drum  11 . The charger  12  charges a circumferential surface of the rotating photosensitive drum  11 , and the cleaner  15  cleans the photosensitive drum  11 . 
     The exposure unit  13  includes light-emitting elements such as laser diodes. Upon receiving a drive signal from the control unit  50 , the exposure unit  13  emits a laser L for forming an image of the color Y, and exposes the charged circumferential surface of the photosensitive drum  11  to the laser L. Thus, an electrostatic latent image is formed on the photosensitive drum  11 . 
     The developer  14  faces the photosensitive drum  11 , and carries toner to the photosensitive drum  11 . The intermediate transfer belt  21  is an endless belt that is suspended in tension state across a drive roller  24  and a pair of driven rollers  25 ,  26 , and is driven to rotate in the direction indicated by arrow C in  FIG. 1 . An electrostatic latent image having been formed on each photosensitive drum (i.e., photosensitive drums of the image formers  10 Y,  10 M,  10 C,  10 K) is developed by the developer in the same image former, whereby an unfixed toner image of the corresponding color is formed on the photosensitive drum. 
     The toner images formed on the photosensitive drums undergo primary transfer by primary transfer rollers provided in one-to-one correspondence with the image formers, and thus are transferred onto the intermediate transfer belt  21 . Note that in  FIG. 1 , only the primary transfer roller corresponding to the image former  10 Y is explicitly indicated by being provided with the reference number  22 . Here, the primary transfer of the toner images formed on the respective photosensitive drums is performed such that the toner images are transferred at different timings onto the intermediate transfer belt  21  so as to be overlaid one on top of another on the same position of the intermediate transfer belt  21 . Subsequently, the electrostatic force applied by the secondary transfer roller  27  causes the toner images on the intermediate transfer belt  21  to undergo secondary transfer, such that the toner images are transferred all at once onto a recording sheet. 
     The paper feeder  30  includes: a paper supply cassette  31 ; a feed roller  32 ; a transport roller pair  33 ; and a timing roller pair  34 . The paper supply cassette  31  accommodates a plurality of recording sheets, one of which is indicated by reference sign S in  FIG. 1 . The feed roller  32  feeds the recording sheets S onto a sheet transport path, one at a time. The transport roller pair  33  transports the recording sheet S along the sheet transport path. 
     The timing roller pair  34  transports the recording sheet S to a position  28  where the secondary transfer takes place so that the recording sheet S and the toner images overlaid on the same position of the intermediate transfer belt  11  through primary transfer arrive at the position  28  at the same time. As already discussed above, at the position  28 , the secondary transfer roller  27  causes the toner images on the intermediate transfer belt  21  to undergo secondary transfer, such that the toner images are transferred all at once onto the recording sheet S. 
     The fixing unit  40  includes: a fixing roller  41 ; a heating roller  42 ; a fixing belt  43 ; and a pressing roller  44 . Here, as one example, the heating roller is heated by a halogen heater. The fixing belt  43  is suspended in tension state across the fixing roller  41  and the heating roller  42 . The pressing roller  44  forms a fixing nip by pressing on the fixing roller  41  with the fixing belt  43  in between. The fixing unit  40 , at the fixing nip, applies heat and pressure to the recording sheet S carrying the toner images having been transferred thereon through the secondary transfer, and thereby heat-fixes the toner images onto the recording sheet S. 
     The above-described components of the fixing unit  40  (i.e., the fixing roller  41 , the heating roller  42 , the fixing belt  43 , and the pressing roller  44 ) are housed inside a housing  45  of the fixing unit  40 . The housing  45  has undepicted slits (openings) formed therein, one at each side thereof in the direction along which the recording sheet S is transported thereto. The slits are for letting the recording sheet S in and out of the housing  45 . 
     The recording sheet S carrying the heat-fixed image is transported to an eject roller pair  81  via a paper ejector (the paper ejector is described in detail later in the present disclosure). Further, the recording sheet S is ejected onto an eject tray  82  by the eject roller pair  81 . 
     The control unit  50  is a so-called computer, and includes a central processing unit (CPU), a read-only memory (ROM), and a random access memory (RAM). The control unit  50  has overall control over the image forming device  1 . The operation panel  60  includes a liquid crystal display, a touch panel laminated on the liquid crystal display, and one or more operation buttons allowing input of various instructions. The operation panel  60  receives input of instructions from a user when the user operates the touch panel, the operation buttons, etc., provided to the operation panel  60 . The image reader  70  includes an image input device such as a scanner. The image reader  70  reads information from a recording sheet (e.g., a sheet of paper). The information is related to one or more images printed on the recording sheet. The images may be images of characters, shapes, and photographs appearing on the recording sheet. Further, by using the information read from a recording sheet, the image reader  70  generates image data. 
     [2] Structure of Air Cleaner 
       FIG. 3  is a perspective view illustrating the relationship between the fixing device  40 , a paper ejector  80 , and an air cleaner  90 . As illustrated in  FIG. 3 , the air cleaner  90  includes: a fan  901 ; an air duct  902 ; an air flow distributer  903 ; and an electrostatic-type filter  904  (referred to in the following as the “filter  904 ”). Note that the filter  904  is implemented by using an electrostatic-type filter having a pleated shape. Thus, the main surface of the filter  904  has greater surface area than a main surface of an electrostatic-type filter not having a pleated shape. Further, the air cleaner  90  can be attached to and detached from the paper ejector  80 , as illustrated in  FIG. 4 . Specifically, as illustrated in  FIG. 4 , the air cleaner  90  can be attached to the paper ejector  80  by causing an engagement portion  9010  provided to the fan  901  to engage with an outlet of a duct  801  of the paper ejector  80 , and thereby connecting the fan  901  to the outlet of the duct  801 . The engagement portion  9010  is provided with a rectangular opening that allows the engagement portion  9010  to engage with the outlet of the duct  801 . 
     Referring to  FIG. 3  once again, the fan  901  is provided at an entrance portion of the air cleaner  90 , and is connected to the outlet of the duct  801 . 
       FIG. 5  is a magnified perspective view illustrating the structure of the fan  901  and the air duct  902  in detail. As illustrated in  FIG. 5 , the fan  901  is a centrifugal fan (sirocco fan), and includes: a blower wheel  901 A having a plurality of blades; a casing  901 B; and a fan motor  901 C. The fan  901  causes air from a main body of the image forming device  1 , which includes the fixing device  40  and the surrounding of the fixing device  10 , to enter the duct  801  (illustrated in  FIG. 3 ) from an undepicted inlet provided to the duct  801 . Note that the air from the main body of the imaging forming device  1  contains atmospheric air and undesirable airborne substances generated at the fixing device  40  and the surrounding of the fixing device  40 . Further, the fan  901  takes in the air having entered the duct  801  towards a rotation axis thereof (in the direction illustrated by dotted arrow E in  FIGS. 3 and 5 ) and discharges the air in a direction along the main surface of the filter  904  (the direction illustrated by dotted arrow F in  FIGS. 3 and 5 ), due to centrifugal force caused by rotation so that the air arrives at the inlet of the air duct  902 . 
     As illustrated in  FIGS. 3 and 5 , the air duct  902  has a curve between the inlet and an outlet  902 B, and faces the main surface of the filter  904  at the outlet  902 B. The air duct  902  connects to the inside of a housing  905 , which houses the filter  904 . Further, as illustrated in  FIGS. 5, 6, and 7 , ribs  9021  are disposed spirally about the outlet  902 B. The ribs  9021  support the air flow distributer  903 . The air flow distributer  903  is described in detail later in the present disclosure. 
       FIG. 6  is a perspective view illustrating the ribs  9021  and the air flow distributer  903 , as seen from a position upstream than the outlet  902 B in a direction in which air flows in the air cleaner  90 .  FIG. 7  is an exploded perspective view illustrating the ribs  9021  and the air flow distributer  903 , as seen from a position downstream than the outlet  902 B in the direction in which air flows in the air cleaner  90 . 
     In specific,  FIG. 7  is an exploded perspective view illustrating how the ribs  9021  are formed about the outlet  902 B, which is formed in an outlet part member of the air duct  902 . Further,  FIG. 7  illustrates how the ribs  9021  support the air flow distributer  903 , and illustrates that a portion of the air flow distributer  903  facing the outlet  902 B has an asymmetric conical shape. 
     The ribs  9021  are formed spirally, to conform to a direction in which air discharged from the outlet  902 B whirls. Here, note that the air flow distributer  903  may either be adhered to the ribs  9021  or integrally formed with the ribs  9021 . 
     Meanwhile, it is also possible to fix the position of the air flow distributer  903  inside the housing  905  without providing the ribs  9021 . However, providing the ribs  9021  allows effectively guiding air discharged from the outlet  902 B to the air flow distributer  903  along the ribs  9021 . Thus, providing the ribs  9021  reduces pressure loss of air discharged from the outlet  902 B and improves discharge efficiency compared to not providing the ribs  9021 . 
     Returning to  FIG. 3  once again, the air taken-in to the air duct  902  leaves the air duct  902  via the outlet  902 B, and enters the housing  905  by flowing along the portion of the air flow distributer  903  facing the outlet  902 B. The air flow distributer  903  is disposed between the outlet  902 B and the filter  904 . As already described above, the housing  905  houses the filter  904 . Thus, the undesirable airborne substances contained in the air from the main body of the image forming device  1  are captured at the filter  904 , before being discharged to the outside. 
     Accordingly, the air from the main body of the image forming device  1  is prevented from directly reaching an area of the main surface of the filter  904  facing the outlet  902 B, from the outlet  902 B. That is, a direction in which the air discharged from the outlet  902 B flows is changed so that the air spreads over the entirety of the main surface of the filter  904  without intensively flowing towards the area of the main surface of the filter  904  facing the outlet  902 B. 
     Here, it should be noted that the portion of the air flow distributer  903  facing the outlet  902 B may have any shape as long as capable of changing the direction of flow of the air discharged from the outlet  902 B to spread over the entirety of the main surface of the filter  904 . For example, the portion of the air flow distributer  903  facing the outlet  902 B may have any one of the shapes illustrated in  FIGS. 8, 9, 10 . 
       FIG. 8  is a schematic illustrating air flow from the air duct  902  to the filter  904  when the portion of the air flow distributer  903  facing the outlet  902 B has a flat plate-like shape (in  FIG. 8 , the portion of the air flow distributer  903  facing the outlet  902 B has a circular disk-like shape). In  FIG. 8 , reference symbols  901 ,  902 ,  902 A,  902 B,  903 ,  904 , and  905  respectively indicate the fan, the air duct, the inlet of the air duct, the outlet of the air duct, the air flow distributer, the filter, and the housing. Further, in  FIG. 8 , air flow is indicated by using arrows, and the white arrow indicated by reference symbol F indicates the direction in which the air is discharged from the fan  901  to the air duct  902 . The above explanations similarly apply to each of  FIGS. 9 and 10 . 
     As illustrated in  FIG. 8 , the air guided to the outlet  902 B collides with and spreads along the flat surface of the portion of the air flow distributer  903  facing the outlet  902 B, thereby spreading over the entirety of the surface of the filter  904 . Although not illustrated in  FIG. 8 , it should be noted that due to collision with the inner wall of the housing  905 , the surface of the filter  904 , etc., and the consequent change in flow direction, some of the air also reaches the area of the filter  904  facing a rear surface of the air flow distributer  903 , however smaller the amount of the air reaching this area of the filter  904  may be than the amount of the air reaching other areas of the filter  904 . This similarly applies to each of  FIGS. 9 and 10 , description related to which is provided in the following. 
       FIG. 9  is a schematic illustrating air flow from the air duct  902  to the filter  904  when the portion of the air flow distributer  903  facing the outlet  902 B has a symmetrical conical shape. Similar to the configuration illustrated in  FIG. 8 , in the configuration illustrated in  FIG. 9 , the air guided to the outlet  902 B collides with and spreads along the inclined lateral surface of the conical portion of the air flow distributer  903  facing the outlet  902 B, thereby spreading over the entirety of the main surface of the filter  904 . In addition, providing the portion of the air flow distributer  903  facing the outlet  902 B with a conical shape reduces pressure loss of the air discharged from the outlet  902 B compared to when the portion has a flat surface, and thereby improves discharge efficiency, due to the air discharged from the outlet  902 B being distributed to the entirety of the main surface of the filter  904  through collision with the inclined lateral surface of the conical portion of the air flow distributer  903  facing the outlet  902 B. 
       FIG. 10  is a schematic illustrating air flow from the air duct  902  to the filter  904  when the portion of the air flow distributer  903  facing the outlet  902 B has an asymmetric conical shape. Here, the flow distributer  903  is disposed such that the apex of the conical portion facing the outlet  902 B is offset in the direction F, in which the air is discharged from the outlet  902 B, with respect to the center of the outlet  902 B (i.e., with respect to the apex of the conical portion of the flow distributor  903  illustrated in  FIG. 9 ). Similar to the configuration illustrated in  FIG. 9 , in the configuration illustrated in  FIG. 10 , the air guided to the outlet  902 B collides with and spreads along the inclined lateral surface of the conical portion of the air flow distributer  903  facing the outlet  902 B, thereby spreading over the entirety of the main surface of the filter  904 . In addition, providing the portion of the air flow distributer  903  facing the outlet  902 B with a conical shape reduces pressure loss of the air discharged from the outlet  902 B compared to when the portion has a flat surface, and thereby improves discharge efficiency, due to the air discharged from the outlet  902 B being distributed to the entirety of the main surface of the filter  904  through collision with the inclined lateral surface of the conical portion of the air flow distributer  903  facing the outlet  902 B. 
     In addition, in the configuration illustrated in  FIG. 10 , a portion of the inclined lateral surface of the conical portion of the air flow distributer  903  that extends from the apex towards the direction opposite the direction F (referred to in the following as reverse-direction inclined surface portion) has greater surface area than a portion of the inclined lateral surface of the conical portion of the air flow distributer  903  that extends from the apex towards the discharge direction F (referred to in the following as forward-direction inclined surface portion). Accordingly, the air discharged from the outlet  902 B is more likely to be guided towards the reverse-direction inclined surface portion than towards the forward-direction inclined surface portion. Thus, the air flow distributer  903  is capable of changing the direction of air flow so that air flow is not biased towards the discharge direction F. 
     Here, it should be noted that the air is discharged from the outlet  902 B towards the discharge direction F. Thus, when surface area of the reverse-direction inclined surface portion is equal to the surface area of the forward-direction inclined surface portion, the amount of the discharged air arriving at the forward-direction inclined surface portion would be greater than the amount of the discharged air arriving at the reverse-direction inclined surface portion. This results in the amount of undesirable airborne substances captured differing between an area of the main surface of the filter  904  that is located in the discharge direction F from the area of the main surface of the filter  904  facing the outlet  902 B and an area of the main surface of the filter  904  that is located in the direction opposite the discharge direction F from the area of the main surface of the filter  904  facing the outlet  902 B. 
     In view of this, providing the portion of the air flow distributer  903  facing the outlet  902 B with an asymmetric conical shape as illustrated in  FIG. 10  suppresses such difference in the amount of undesirable airborne substances captured by different areas of the filter  904 . This further prevents a difference in filter performance occurring between different areas of the filter  904 . 
     As such, in the present embodiment, the distance between the outlet  902 B of the air duct  902  and where the filter  904  is located in the housing  905  is relatively small. Further, the air cleaner  90  has an air flow path having greater cross-sectional area in the housing  905 , into which the air discharged from the outlet  902 B is input, than at the outlet  902 B, and the air flow distributer  903  is disposed between the outlet  902 B and the filter  904 , near a downstream side of the outlet  902 B in the direction of air flow. As already described above, the air flow distributer  903  distributes the air discharged from the outlet  902 B by changing the direction of air flow. Due to this, the direction of air flow from the outlet  902 B into the housing  905 B is changed so that air flow is not intensified towards the area of the main surface of the filter  904  facing the outlet  902 B and the discharged air arrives at areas of the main surface of the filter  904  other than the area facing the outlet  902 B. 
     This prevents a rapid decrease in filter performance from occurring at the area of the main surface of the filter  904  facing the outlet  902 B. Thus, clogging of the area of the main surface of the filter  904  facing the outlet  902 B is suppressed, and, a shortening of lifetime of the filter  904  is prevented. That is, the present embodiment suppresses a local decrease in filter performance, and thereby extends the lifetime of the filter  904 . 
     (Modifications) 
     In the above, the technology pertaining to the present disclosure is described based on a specific form of embodiment thereof. However, needless to say, the embodiment merely provides a non-limiting example of how the technology pertaining to the present disclosure may be implemented, and it should be construed that the present disclosure encompasses in the spirit and scope thereof, for example, the modifications described in the following. 
     (1) In the embodiment, a conical shape is discussed as one specific example of a shape of the portion of the air flow distributer  903  facing the outlet  902 B that reduces pressure loss occurring when the air comes in contact with the air flow distributer  903 . However, as long as the air flow distributer  903  is capable of reducing such pressure loss, the portion of the air flow distributer  903  facing the outlet  902 B may have any shape forming a mountain-shaped protrusion, such as a pyramid shape, a frustum shape, and a circular truncated cone shape. 
     When making such a modification, in order to achieve a further reduction in pressure loss, a slope of the mountain-shaped protrusion may be curved to form a concave shape. 
     (2) The portion of the air flow distributer  903  facing the outlet  902 B may have one or more through-holes formed therein. This allows the air discharged from the outlet  902 B to reach the area of the main surface of the filter  904  that faces the rear surface of the air flow distributer  903  (i.e., a portion of the air flow distributer  903  not facing the outlet  902 B). This reduces a difference in the amount of air flow reaching the area of the main surface of the filter  904  facing the rear surface of the air flow distributer  903  and the amount of air flow reaching other areas of the main surface of the filter  904 . Accordingly, the risk is reduced of a difference in filter performance occurring between the area of the main surface of the filter  904  facing the rear surface of the air flow distributer  903  and other areas of the main surface of the filter  904 . 
     (3) In the embodiment, the filter  904  is implemented by using an electrostatic-type filter having a pleated shape. However, needless to say, the air flow distributer  903  pertaining to the embodiment is usable in combination with other filters, including electrostatic-type filters not having a pleated shape and filters of types other than the electrostatic-type. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. 
     Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.