Patent Publication Number: US-2023151785-A1

Title: Air cleaner

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on Japanese Patent Application No. 2021-185548 filed on Nov. 15, 2021, the contents of which are incorporated herein by way of reference. 
     TECHNICAL FIELD 
     The present invention relates to an air cleaner. 
     BACKGROUND 
     There has been a straddle-type vehicle in which an air cleaner is disposed behind an engine (for example, see Patent Literature 1). In the air cleaner disclosed in Patent Literature 1. an inlet tube is attached to a rear surface of an air cleaner case, and an outlet tube is attached to a front surface of the air cleaner case. Air is taken into the air cleaner case from the inlet tube, and the air is filtered by an air filter disposed in the air cleaner. Then, the clean air enters the outlet tube from the air cleaner, and the clean air is sent out to a throttle body through the outlet tube. 
     Patent Literature 1: JP4J21392B 
     The air cleaner described in Patent Literature 1 is disposed below the seat, and a suction port of the inlet tube is open to the inside of the vehicle body frame. In order to improve the flow of air, it is necessary to increase the opening area of the suction port of the inlet tube. However, when water intrudes into the air cleaner from the suction port and the air filter is moistened by the water, the air flow may be deteriorated. Although it is conceivable to suppress the intrusion of water by bending the inlet tube, bending of the inlet tube may be steep due to the narrow space inside the vehicle body frame, which increases the intake resistance. 
     The present invention has been made in view of the above, and an object of the present invention is to provide an air cleaner capable of smoothly flowing air while suppressing adhesion of water to an air filter. 
     SUMMARY 
     An air cleaner according to an aspect of the present invention is an air cleaner configured to be disposed inside a vehicle body frame, the air cleaner including: an air cleaner case in which an intake chamber is formed; an air filter disposed in the intake chamber; an inlet tube configured to take in air to the intake chamber; and an outlet tube configured to send out the air from the intake chamber. The inlet tube extends in a front-rear direction. The inlet tube has a bottom wall curved downward in a side view to form a concave curved portion below a discharge port of the inlet tube. The concave curved portion is formed with a drain hole. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a left side view of a straddle-type vehicle according to the present embodiment. 
         FIG.  2    is a left side view of the periphery of an engine according to the present embodiment. 
         FIG.  3    is a top view of the periphery of the engine according to the present embodiment. 
         FIG.  4    is a side view of an air cleaner according to the present embodiment. 
         FIG.  5    is a top view of the air cleaner of the present embodiment. 
         FIG.  6    is a cross-sectional view of the air cleaner of  FIG.  5    taken along a line A-A. 
         FIG.  7    is a cross-sectional view of the air cleaner of  FIG.  5    taken along a line B-B. 
         FIG.  8    is a cross-sectional view of the periphery of the engine of  FIG.  3    taken along a line C-C. 
         FIGS.  9 A and  9 B  are diagrams showing a flow of air and water in the air cleaner according to the present embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An air cleaner according to an aspect of the present invention is disposed inside a vehicle body frame. An intake chamber is formed in an air cleaner case of the air cleaner, and an air filter is disposed in the intake chamber. Air is taken into the intake chamber through an inlet tube, and air is sent out from the intake chamber through an outlet tube. The inlet tube extends in a front-rear direction, and the inlet tube has a bottom wall curved downward in a side view to form a concave curved portion. The concave curved portion is located below the discharge port of the inlet tube, and water intruding the inlet tube is blocked by the concave curved portion and is less likely to head for the air filter of the intake chamber. The concave curved portion is formed with a drain hole. Water in the inlet tube is likely to gather in the drain hole due to the concave curved portion, and water can be drained from the inside of the inlet tube through the drain hole. In addition, the concave curved portion of the inlet tube does not interfere with the flow of air from the inlet tube toward the air filter. Therefore, even if the opening area of the suction port of the inlet tube is increased, the adhesion of water to the air filter is suppressed, and the air in the air cleaner can flow smoothly. 
     Embodiments 
     Hereinafter, an embodiment will be described in detail with reference to the accompanying drawings.  FIG.  1    is a left side view of a straddle-type vehicle according to the present embodiment. In addition, in the drawings to be described later, an arrow FR indicates a vehicle front side, an arrow RE indicates a vehicle rear side, an arrow L indicates a vehicle left side, and an arrow R indicates a vehicle right side. 
     As shown in  FIG.  1   , a straddle-type vehicle  1  is formed by mounting various components such as an engine  40  and an electrical system on a diamond-type vehicle body frame  10  formed of a pipe and a sheet metal. The vehicle body frame  10  includes a pair of main frames  12  that are branched off from a head pipe  11  to the left and right and extend rearward, and a pair of down frames  13  that are branched off from the head pipe  11  to the left and right and extend downward. A rear portion of the engine  40  is supported by the pair of main frames  12 . and a front portion of the engine  40  is supported by the pair of down frames  13 . By supporting the engine  40  with the vehicle body frame  10 , the rigidity of an entire vehicle is secured. 
     A front side portion of the main frame  12  is a tank rail  14  located above the engine  40 , and a fuel tank  31  is supported from below by the tank rail  14 . A rear side portion of the main frame  12  is a body frame  15  located behind the engine  40 , and a swing arm  25  is swingably supported by a lower half portion of the body frame  15 . A seat rail  21  including an upper rail  22  and a lower rail  23  is attached to an upper half portion of the body frame  15 . A rider seat  32  and a pillion seat  33  are supported on an upper portion of the upper rail  22  at the rear of the fuel tank  31 . 
     A pair of front forks  34  are steerably supported by the head pipe  11  via a steering shaft (not shown). A front wheel  35  is rotatably supported by lower portions of the front forks  34 , and an upper portion of the front wheel  35  is covered with a front fender (not shown). The swing arm  25  extends rearward from the body frame  15 . A rear wheel  36  is rotatably supported at a rear end of the swing arm  25 , and the upper side of the rear wheel  36  is covered with a rear fender (not shown). The engine  40  is coupled to the rear wheel  36  via a chain drive type transmission mechanism, and power from the engine  40  is transmitted to the rear wheel  36  via the transmission mechanism. 
     An air cleaner  50  is disposed behind the engine  40 , and an inlet tube  62  of the air cleaner  50  extends rearward. In order to enlarge the suction port of the inlet tube  62  to improve the flow of air in the air cleaner  50 , it is necessary to suppress intrusion of water into the air cleaner  50  so that the air filter  57  (see  FIG.  6   ) is not moistened. In a narrow space behind the engine  40 , it is difficult to direct the orientation of the suction port to the upper side, the lateral side, or the like to suppress the intrusion of water from the rear of the vehicle. Therefore, in the air cleaner  50  of the present embodiment, an inlet tube  62  capable of capturing and draining water heading for the air filter  57  without interrupting the flow of air is used. 
     A peripheral configuration of the engine and the air cleaner will be described with reference to  FIGS.  2  to  8   .  FIG.  2    is a left side view of the periphery of the engine according to the present embodiment.  FIG.  3    is a top view of the periphery of the engine according to the present embodiment.  FIG.  4    is a side view of the air cleaner according to the present embodiment.  FIG.  5    is a top view of the air cleaner according to the present embodiment.  FIG.  6    is a cross-sectional view of the air cleaner of  FIG.  5    taken along a line A-A.  FIG.  7    is a cross-sectional view of the air cleaner of  FIG.  5    taken along a line B-B.  FIG.  8    is a cross-sectional view of the periphery of the engine of  FIG.  3    taken along a line C-C. 
     As shown in  FIGS.  2  and  3   , the engine  40  is a two-cylinder engine, and includes a crankcase  41  having an upper-lower divided structure. A cylinder  42 , a cylinder head  43 , and a cylinder head cover  44  are attached to an upper portion of the crankcase  41 . A magneto cover  45  that covers a magneto (not shown) from a side is attached to a left side surface of the crankcase  41 . A sprocket cover  46  that covers a drive sprocket (not shown) from the side is attached to the rear of the magneto cover  45 . A clutch cover  47  that covers a clutch (not shown) from the side is attached to a right side surface of the crankcase  41 . 
     A throttle body  48  is connected to a rear surface of the cylinder head  43 , and the air cleaner  50  is connected to an upstream side (rear side) of the throttle body  48 . The air cleaner  50  is disposed behind the engine  40  and inside the pair of main frames  12  and the pair of seat rails  21 . As described above, the rear portions of the pair of main frames  12  are the pair of body frames  15 , and a front end portion of the air cleaner  50  is located inside the pair of body frames  15 . The upper half portion of the body frame  15  is inclined obliquely downward toward the rear, and an air cleaner case  51  behind the body frame  15  is also inclined obliquely downward. 
     An upper bracket  16  and a lower bracket  17  are formed at a rear edge of the upper half portion of the body frame  15 . The upper rail  22  of the seat rail  21  is connected to the upper bracket  16 , and the lower rail  23  of the seat rail  21  is connected to the lower bracket  17 . The upper rail  22  extends rearward across a side of an upper half portion of the air cleaner case  51 , and the lower rail  23  extends obliquely rearward across a side of a lower half portion of the air cleaner case  51 . Front sides of the upper rail  22  and the lower rail  23  are coupled to each other via a bridge pipe  24 , and rear sides of the upper rail  22  and the lower rail  23  are coupled to each other at a vehicle rear portion. 
     A front portion of the air cleaner case  51  protrudes upward from the upper rail  22 , and a protruding portion of the front portion is accommodated in a space inside the rider seat  32  (see  FIG.  1   ). A rear portion of the air cleaner case  51  protrudes downward from the lower rail  23 , and a protruding portion of the rear portion serves as an expansion portion  65  that expands an intake chamber  56  (see  FIG.  6   ) in the air cleaner case  51 . The expansion portion  65  of the air cleaner case  51  is located above the swing arm  25  (see  FIG.  1   ), and the expansion portion  65  extends rearward so as to avoid a swing range of the swing arm  25 . A volume of the air cleaner case  51  is expanded by using a lower space of the seat rail  21 . 
     A battery case  38  and a battery  37  are disposed above the expansion portion  65  of the air cleaner case  51 . The battery case  38  is supported by the pair of seat rails  21  via a bridge  19 . The battery case  38  is formed in a box shape having an open upper surface, and a rectangular parallelepiped battery  37  is held inside the battery case  38 . In a top view, the pair of inlet tubes  62  of the air cleaner  50  are curved, and the battery  37  is located between the pair of inlet tubes  62 . A space for arranging the battery  37  is secured by using a space above the expansion portion  65  of the air cleaner  50 . 
     As shown in  FIGS.  4  to  6   , the air cleaner case  51  of the air cleaner  50  includes an upper case  52  and a lower case  53  which are divided in an upper-lower direction, and a filter cover  54  attached to a rear surface of the upper case  52 . The upper case  52  and the lower case  53  extend obliquely downward from the front to the rear, and the filter cover  54  bulges in a dome shape on a rear side of the upper case  52 . Internal spaces of the upper case  52  and the lower case  53  and an internal space of the filter cover  54  are connected to each other through an opening  55  formed in the rear surface of the upper case  52 , and an intake chamber  56  is formed inside the air cleaner case  51 . 
     An air filter  57  is disposed in the opening  55  in the rear surface of the upper case  52 , and the air filter  57  is covered by the filter cover  54  from behind. The air filter  57  is inclined along an upper surface of the upper case  52  such that an upper portion of the air filter  57  is located closer to the vehicle front side than a lower portion. Due to the air filter  57 , the intake chamber  56  is divided into a dirty side  58  and a clean side  59 . That is, the dirty side  58  is formed by the filter cover  54  on the upstream side of the air filter  57 , and the clean side  59  is formed by the upper case  52  and the lower case  53  on the downstream side of the air filter  57 . 
     A pair of inlet tubes  62  are attached to left and right side walls  61  of the filter cover  54 . The pair of inlet tubes  62  extend from the left and right side walls  61  of the filter cover  54  toward the vehicle rear side, and air is taken into the dirty side  58  from the rear of the vehicle by the pair of inlet tubes  62 . A suction port  63  of each inlet tube  62  is directed toward the rear of the vehicle, and a discharge port  64  of the inlet tube  62  is directed inward in the vehicle width direction. The pair of inlet tubes  62  are located inside the pair of seat rails  21  (see  FIG.  3   ), and an interval between the pair of inlet tubes  62  is substantially equal to a lateral width of the expansion portion  65 . 
     A pair of outlet tubes  82  are attached to a front wall  81  of the lower case  53 . The pair of outlet tubes  82  penetrate the front wall  81  of the lower case  53  and extend in a front-rear direction, and air is sent out from the clean side  59  to the engine  40  (see  FIG.  1   ) by the pair of outlet tubes  82 . A suction port  83  of each outlet tube  82  is directed toward the rear of the vehicle, and a discharge port  84  of the outlet tube  82  is directed toward the front of the vehicle. The pair of outlet tubes  82  are located inside the pair of main frames  12  (see  FIG.  3   ), and the pair of outlet tubes  82  are connected to a pair of intake passages of the throttle body  48 . 
     The inlet tubes  62  and the outlet tubes  82  are attached to the upper side of the air cleaner case  51 . As described above, the inlet tubes  62  are attached to the filter cover  54 , the outlet tubes  82  are attached to the front wall  81  of the lower case  53 . and the filter cover  54  and the front wall  81  of the lower case  53  face each other in the front-rear direction via the air filter  57  in a side view. Since the discharge port  64  of each inlet tube  62  and the suction port  83  of each outlet tube  82  are located at substantially the same height, air easily flows directly from the inlet tube  62  to the outlet tube  82 . 
     In addition, a breather nipple  85  is formed at a front portion of the upper case  52 , and a breather hose (not shown) extending from the engine  40  is connected to the breather nipple  85 . An intake air temperature sensor  86  is attached to the vicinity of the breather nipple  85 , and a detection result of the intake air temperature sensor  86  is used for fuel injection amount control with respect to the engine  40  (see  FIG.  1   ). A secondary air nipple  87  is formed at a front portion of the lower case  53 , and a secondary air hose (not shown) extending to an exhaust system is connected to the secondary air nipple  87 . A drain plug  88  is provided at the bottom portion of the lower case  53 , and water in the air cleaner case  51  is discharged from the drain plug  88 . 
     As shown in  FIG.  7   , the bottom wall and the upper wall of each inlet tube  62  are curved in a manner warped downward. The bottom wall of the inlet tube  62  is curved downward to form a concave curved portion  71  below the discharge port  64 , and the upper wall of the inlet tube  62  is curved downward to form a convex curved portion  73 . The lowest position of the concave curved portion  71  is located below a lower edge of the discharge port  64  (see  FIG.  6   ) of the inlet tube  62 , and the lowest position of the convex curved portion  73  is located below an upper edge of the discharge port  64  of the inlet tube  62 . The air in the inlet tube  62  smoothly flows toward the discharge port  64 , but water adhering to the wall surface of the inlet tube  62  is less likely to flow toward the discharge port  64 . 
     A drain hole  72  penetrating the bottom wall of the inlet tube  62  is formed in the concave curved portion  71 , and water captured by the concave curved portion  71  is likely to gather in the drain hole  72 . The convex curved portion  73  is located above the drain hole  72 . Water captured by the convex curved portion  73  falls into the concave curved portion  71 , and water is likely to gather in the drain hole  72 . Water is discharged through the drain hole  72 , which improves the drainage performance of the inlet tube  62 . Since water intruding the inlet tube  62  is less likely to head for the air filter  57  (see  FIG.  6   ), the adhesion of water to the air filter  57  is suppressed, and the air flow in the air cleaner  50  is smooth. 
     At this time, the concave curved portion  71  and the convex curved portion  73  are curved at a curvature that does not interfere with the flow of the air from the suction port  63  toward the discharge port  64 , and the intake resistance of the inlet tube  62  does not significantly increase due to the concave curved portion  71  and the convex curved portion  73 . Although some of the air flows out from the inlet tube  62  through the drain hole  72 , the drain hole  72  is formed with an inner diameter small enough so as not to excessively affect the flow of the air from the suction port  63  toward the discharge port  64 . In addition, the suction port  63  of the inlet tube  62  is formed to be larger than the discharge port  64 , and air is likely to enter the inlet tube  62  from the suction port  63 . 
     The suction port  63  of the inlet tube  62  has a lower edge located below the drain hole  72 . The bottom wall of the inlet tube  62  protrudes upward between the drain hole  72  and the lower edge of the suction port  63  to form a convex portion  75 . The convex portion  75  is curved in a manner warped upward in the vicinity of the lower edge of the suction port  63 , and even if the opening area of the suction port  63  of the inlet tube  62  is increased, intrusion of water is hindered by the convex portion  75  in the vicinity of the suction port  63 . When water is captured by the convex portion  75  in the vicinity of the suction port  63  of the inlet tube  62 , some of the water moves from the convex portion  75  toward the concave curved portion  71 , and water gathers in the drain hole  72 , which improves the drainage performance of the inlet tube  62 . 
     Further, as in the present embodiment, when the air cleaner  50  is disposed inside the pair of seat rails  21  where the height is limited, the positions of the air filter  57  (see  FIG.  6   ) and the discharge port  64  of the inlet tube  62  cannot be shifted in the height direction. Therefore, the drain hole  72  of the inlet tube  62  is located below the center of the air filter  57  in the height direction. Even when water accumulated in the concave curved portion  71  moves toward the discharge port  64  (see  FIG.  6   ) together with the flow of air, water hardly adheres to a position higher than the center of the air filter  57  in the height direction. Therefore, water totally does not adhere to the air filter  57 , and the air flow is not hindered by the moistened air filter  57 . 
     As shown in  FIG.  8   , in a cross-sectional view orthogonal to the extending direction of the inlet tube  62 , the inlet tube  62  has a cross-sectional shape of a right-angled trapezoid with an acute-angled portion facing downward. The acute-angled portion of the right-angled trapezoid is located on the inner side in the vehicle width direction, and due to the acute-angled portion of the right-angled trapezoid, the bottom wall of the concave curved portion  71  is formed in a valley shape. The drain hole  72  is formed in the valley bottom of the concave curved portion  71 , and water gathers in the drain hole  72  due to the valley shape of the concave curved portion  71 , thereby improving the drainage performance of the inlet tube  62 . In the side view and the cross-sectional view, the drain hole  72  is formed at the lowest position of the concave curved portion  71 . 
     The battery  37  is located on the inner side in the vehicle width direction of the inlet tubes  62 . As described above, the battery  37  is held by the box-shaped battery case  38 . Flanges  39  extend outward in the vehicle width direction from an outer edge of the battery case  38 , and each flange  39  is located below the drain hole  72  of the inlet tube  62 . The inlet tube  62  and the flange  39  face each other with a slight gap therebetween, and the drain hole  72  of the inlet tube  62  is covered from the lower side by the flange  39 . An intrusion path into the drain hole  72  is blocked by the flange  39 , thereby suppressing intrusion of water from the drain hole  72  into the inlet tube  62 . 
     The flow of air and water in the air cleaner will be described with reference to  FIGS.  9 A and  9 B .  FIGS.  9 A and  9 B  are diagrams showing the flow of air and water in the air cleaner according to the present embodiment.  FIG.  9 A  is a side view of the flow of air and water in the air cleaner, and  FIG.  9 B  is a rear view of the flow of air and water in the air cleaner. 
     As shown in  FIG.  9 A , the upper portion of the air filter  57  is inclined so as to be closer to the vehicle front side than the lower portion in a side view. The discharge port  64  of the inlet tube  62  faces the center of the front surface of the air filter  57 , and the suction port  83  of the outlet tube  82  faces the upper portion of the back surface of the air filter  57 . Since the center of the front surface and the upper portion of the back surface of the inclined air filter  57  have substantially the same height, the discharge port  64  of the inlet tube  62  and the suction port  83  of the outlet tube  82  face each other with the air filter  57  interposed therebetween. The suction port  63  of the inlet tube  62  is formed wide, and air can be easily taken in from the suction port  63 . 
     The bottom wall of the inlet tube  62  is formed with the concave curved portion  71 , and the upper wall of the inlet tube  62  is formed with the convex curved portion  73 . The concave curved portion  71  and the convex curved portion  73  are curved gently, so that even when the air is taken into the suction port  63  of the inlet tube  62 , the flow of air is not hindered by the curved shapes of the concave curved portion  71  and the convex curved portion  73 . Therefore, the air smoothly flows from the suction port  63  of the inlet tube  62  toward the discharge port  64 . In rainy weather or the like, water is taken into the suction port  63  of the inlet tube  62  together with air, but water is captured by the curved shapes of the concave curved portion  71  and the convex curved portion  73 . 
     In the bottom wall of the inlet tube  62 , the upstream side of the concave curved portion  71  from the convex portion  75  to the drain hole  72  is a downward slope, and the downstream side of the concave curved portion  71  from the drain hole  72  to the discharge port  64  is an upward slope. When water adheres to the downward slope on the upstream side of the concave curved portion  71 , water moves toward the downstream side (front side) from the downward slope toward the drain hole  72  as indicated by the arrow A1. When water adheres to the upward slope on the downstream side of the concave curved portion  71 , water moves toward the upstream side (rear side) from the upward slope toward the drain hole  72  as indicated by the arrow A2. In addition, water is less likely to enter the vicinity of the suction port  63  of the inlet tube  62  due to the convex portion  75  as indicated by the arrow A3. 
     In the upper wall of the inlet tube  62 , the upstream side of the convex curved portion  73  from the suction port  63  to a top  74  is a downward slope, and the downstream side of the convex curved portion  73  from the top  74  to the discharge port  64  is an upward slope. When water adheres to the downward slope on the upstream side of the convex curved portion  73 , water moves toward the downstream side (front side) from the downward slope toward the top  74  as indicated by the arrow A4. When water adheres to the upward slope on the downstream side of the convex curved portion  73 , water moves toward the upstream side (rear side) from the upward slope toward the top  74  as indicated by the arrow A5. In addition, water flows down from the top  74  of the convex curved portion  73  toward the concave curved portion  71 . and water moves toward the drain hole  72  of the concave curved portion  71 . 
     As shown in  FIG.  9 B , in a cross-sectional view orthogonal to the inlet tube  62 , the bottom wall of the inlet tube  62  is inclined in a manner descending from the outer side in the vehicle width direction toward the inner side in the vehicle width direction. In the cross-sectional view, the concave curved portion  71  is formed in a V-shaped valley shape, and the drain hole  72  is formed in the valley bottom of the valley shape. Therefore, when water adheres to the inclined surface of the concave curved portion  71 , water moves inward in the vehicle width direction from the inclined surface toward the drain hole  72  as indicated by the arrow A6. As indicated by the arrows A1 to A6, water is collected in the drain hole  72  by the concave curved portion  71  and the convex curved portion  73 , and water is effectively drained from the inlet tube  62  through the drain hole  72 . 
     As shown in  FIG.  9 A , the lower edge of the discharge port  64  of the inlet tube  62  is located below the center of the air filter  57  in the height direction. Therefore, even if water flows along the upward slope on the downstream side of the concave curved portion  71  and water is discharged from the discharge port  64  toward the air filter  57 , water is less likely to adhere to the upper side of the center of the air filter  57  in the height direction as indicated by the arrow A7. That is, water adheres to the air filter  57  at a position avoiding a main flow F of the air flowing from the discharge port  64  of the inlet tube  62  toward the suction port  83  of the outlet tube  82 . Therefore, the main flow F of the air in the air cleaner  50  is not hindered by the moistened air filter  57 . 
     As described above, according to the present embodiment, since the bottom wall and the upper wall of the inlet tube  62  are curved downward, water intruding the inlet tube  62  is less likely to head for the air filter  57  of the intake chamber  56 . Water in the inlet tube is likely to gather in the drain hole  72 . and water is drained from the inside of the inlet tube through the drain hole  72 . In addition, the curved shape of the inlet tube  62  does not interfere with the flow of air from the inlet tube  62  toward the air filter  57 . Therefore, even if the opening area of the suction port  63  of the inlet tube  62  is increased, the adhesion of water to the air filter  57  is suppressed, and the air in the air cleaner  50  can flow smoothly. 
     In the present embodiment, a two-cylinder engine is exemplified as the engine, but the type of the engine is not particularly limited. 
     In the present embodiment, the air cleaner includes a pair of inlet tubes and a pair of outlet tubes, but the numbers of inlet tubes and outlet tubes are not limited. For example, the air cleaner may include a single inlet tube and a single outlet tube, or the air cleaner may include three or more inlet tubes and three or more outlet tubes. 
     The convex curved portion is formed on the upper wall of the inlet tube in the present embodiment, but the convex curved portion may be not formed on the upper wall of the inlet tube as long as the concave curved portion is formed at least on the bottom wall of the inlet tube. 
     In the present embodiment, the inlet tube is formed in a right-angled trapezoidal shape in the cross-sectional view orthogonal to the extending direction of the inlet tube, but the cross-sectional shape of the concave curved portion of the inlet tube may be formed in a valley shape in the cross-sectional view. 
     In the present embodiment, the drain hole is formed at the lowest position of the concave curved portion of the inlet tube in a side view, but the drain hole may be formed at a position other than the lowest position as long as the drain hole is in the concave curved portion. 
     In the present embodiment, the air filter is disposed to be inclined, but the air filter may be not inclined. For example, the air filter may be disposed vertically. 
     In the present embodiment, the drain hole is located below the center of the air filter in the height direction, but the positional relationship in the height direction between the center of the air filter in the height direction and the drain hole is not particularly limited. 
     In the present embodiment, the convex portion is formed in the vicinity of the suction port of the inlet tube, but the convex portion may be not formed in the inlet tube. 
     In the present embodiment, the air cleaner case is formed with the expansion portion obtained by expanding the intake chamber, but the air cleaner case may be not provided with the expansion portion. As long as the air cleaner case is formed with an intake chamber, the shape of the air cleaner case is not particularly limited. 
     In addition, the air cleaner may be applied not only to the straddle-type vehicle shown in the drawings, but also to other types of straddle-type vehicles. The straddle-type vehicle is not limited to general vehicles on which a rider rides in a posture of straddling a seat, and includes a small-sized scooter-type vehicle on which a rider rides without straddling a seat. 
     As described above, the air cleaner ( 50 ) according to the present embodiment is an air cleaner configured to be disposed inside a vehicle body frame ( 10 ), the air cleaner including: an air cleaner case ( 51 ) in which an intake chamber ( 56 ) is formed; an air filter ( 57 ) disposed in the intake chamber; an inlet tube ( 62 ) configured to take in air to the intake chamber; and an outlet tube ( 82 ) configured to send out the air from the intake chamber. The inlet tube extends in a front-rear direction. The inlet tube has a bottom wall curved downward in a side view to form a concave curved portion ( 71 ) below a discharge port of the inlet tube. The concave curved portion is formed with a drain hole ( 72 ). According to this configuration, since the inlet tube has the bottom wall curved downward to form the concave curved portion below the discharge port ( 64 ) of the inlet tube, water intruding the inlet tube is blocked by the concave curved portion and is less likely to head for the air filter of the intake chamber. Water in the inlet tube is likely to gather in the drain hole due to the concave curved portion, and water can be drained from the inside of the inlet tube through the drain hole. In addition, the concave curved portion of the inlet tube does not interfere with the flow of air from the inlet tube toward the air filter. Therefore, even if the opening area of the suction port of the inlet tube is increased, the adhesion of water to the air filter is suppressed, and the air in the air cleaner can flow smoothly. 
     In the air cleaner of the present embodiment, the inlet tube has an upper wall curved downward in the side view to form a convex curved portion ( 73 ), and the drain hole is located below the convex curved portion. According to this configuration, since the upper wall of the inlet tube is curved downward to form the convex curved portion, water intruding the inlet tube is less likely to head for the air filter of the intake chamber. Water adhering to the convex curved portion falls into to the concave curved portion, and water is likely to gather in the drain hole, which further improves the drainage performance. 
     In the air cleaner of the present embodiment, the drain hole is located below a center of the air filter in a height direction. According to this configuration, even when water accumulated in the concave curved portion moves toward the discharge port together with the flow of air, water hardly adheres to a position higher than the center of the air filter in the height direction. Therefore, water totally does not adhere to the air filter, and the air flow is less likely to be hindered by the moistened air filter. 
     In the air cleaner of the present embodiment, a suction port ( 63 ) of the inlet tube has a lower edge located below the drain hole, and the bottom wall of the inlet tube protrudes upward between the drain hole and the lower edge of the suction port to form a convex portion ( 75 ). According to this configuration, even if the opening area of the suction port of the inlet tube is increased, water is less likely to intrude the inner side of the suction port due to the convex portion. In addition, due to the convex portion and the concave curved portion, water is likely to gather in the drain hole, which further improves the drainage performance. 
     In the air cleaner of the present embodiment, the concave curved portion is formed in a valley shape in the cross-sectional view orthogonal to an extending direction of the inlet tube, and the drain hole is formed in the valley bottom of the concave curved portion. According to this configuration, due to the valley shape of the concave curved portion, water is likely to gather in the drain hole, which further improves the drainage performance. 
     In the air cleaner of the present embodiment, a battery ( 37 ) is located on a lateral side of the inlet tube. The battery is held by a battery case ( 38 ). The drain hole is covered from below by a flange ( 39 ) on an outer edge of the battery case. According to this configuration, the flanges can suppress water from intruding the inlet tube from the drain hole. 
     Although the present embodiment has been described, the above-described embodiment and modifications may be combined entirely or partially as another embodiment. 
     The technique of the present invention is not limited to the above-described embodiment, and various changes, substitutions, and modifications may be made without departing from the spirit of the technical concept of the present invention. The present invention may be implemented by other methods as long as the technical concept can be implemented by the methods through advance of the technique or other derivative techniques. Therefore, the claims cover all embodiments that may be included within the scope of the technical concept.