Patent Publication Number: US-7895984-B2

Title: Intake device of internal combustion engine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an intake device provided in an internal combustion engine and more particularly to a waterproof construction provided in an intake device which is provided with a negative pressure outlet port for taking out negative pressure generated in an intake passage for preventing water from entering into the negative pressure outlet port. 
     2. Description of Related Art 
     In an intake device of an internal combustion engine, sometimes moisture which is present in air flowing through an intake passage formed by passage walls adheres to inner surfaces of the passage walls in the form of water drops. In this case, the water drops may flow along the inner surfaces to enter into a negative pressure passage from a negative pressure outlet port which opens to the intake passage and become frozen due to a reduction in atmospheric temperature when the internal combustion engine is stopped. Thus, a negative pressure is prevented from taking-out from the negative pressure outlet port immediately after the internal combustion engine is started to operate. To address these problems, there are known various waterproof constructions for suppressing the entering of water drops into the negative pressure outlet port. For example, refer to Japanese Unexamined Patent Publications JP-A-2007-40142 and JP-A-2004-124831. 
     In a waterproof construction in which inner surfaces of passage walls which form an intake passage extend in a vertical direction and a negative pressure outlet port opens to a projecting portion which is provided on the inner surface so as to project into the intake passage, water drops which flow downwards along the inner surface is guided so as not to reach the negative pressure outlet port by a rising surface of the projecting portion. However, since the projecting portion which projects into the intake passage hinders the flow of intake air, the passage resistance of the intake passage is increased and intake efficiency is lowered. 
     In addition, in a waterproof construction in which a recessed portion is provided on an inner surface of passage walls, although the increase in passage resistance of the intake passage is suppressed compared with the waterproof construction in which the projecting portion is provided, a projecting portion (for example, a baffle plate) which projects towards an opening formed in the recessed portion so as to prevent the entering of water drops into a negative pressure outlet port needs to be provided within the recessed portion so as to surround the negative pressure outlet port. Accordingly, the recessed portion is enlarged and the disposition of the negative pressure outlet port in the intake device becomes restricted. In addition, the construction of the recessed portion becomes complex and the production costs of the intake device increases. 
     In addition, in the passage wall, because the projecting portion may be damaged when handling the passage wall, depending upon locations where the projecting portion is provided which makes up the waterproof construction, it is desirable to avoid such damage. 
     SUMMARY OF THE INVENTION 
     The invention has been made in view of these situations. In a waterproof construction for suppressing the entering of water drops into a negative pressure outlet port in an intake device, wherein the water proof construction is made up of a recessed portion and a projecting portion which are provided on passage walls which form an intake passage, the present invention aims to suppress the increase in passage resistance of the intake passage and to reduce the production costs. In addition, the present invention also aims to increase further the effect of preventing the entering of water drops into the negative pressure outlet port by the waterproof construction. Further, the present invention aims to avoid the damage to the protrusion formed on the passage walls during handling. 
     According to the first aspect of the invention, there is provided an intake device of an internal combustion engine, including: 
     an upper passage wall and a lower passage wall which are disposed next to each other in a vertical direction and are connected together to form an intake passage, wherein 
     the lower passage wall has a recessed portion, which is recessed in a horizontal direction, in part of an inner surface thereof, 
     in a deep portion in the horizontal direction, the recessed portion has a recessed surface to which a negative pressure outlet port for taking out negative pressure generated in the intake passage opens, 
     an opening which opens upwards is provided in a position which opposes to the upper passage wall in the vertical direction at an upper portion of the recessed portion, 
     the upper passage wall has a projecting portion which extends further downwards than a mating surface between the upper passage wall and the lower passage wall and which projects into the recessed portion through the opening, 
     the projecting portion is positioned above the negative pressure outlet port and also positioned between the negative pressure outlet port and the inner surface in the horizontal direction, and 
     a lower end portion of the projecting portion is formed into an arc shape in which a central portion in a direction which is perpendicular to the horizontal direction as viewed from a vertical direction projects downwards. 
     Further, according to the second aspect of the invention, as set forth in the first aspect of the invention, it is advantageous that 
     the recessed surface has a deep surface which opposes to the projecting portion in the horizontal direction, 
     the negative pressure outlet port opens to the deep surface and 
     a gap is provided in the horizontal direction between the deep surface and the projecting portion. 
     According to the invention, water drops falling along the inner surface of the upper passage wall towards the negative pressure outlet port flow downwards along the projecting portion which is situated closer to the intake passage side than the negative pressure outlet port and fall from the lower end portion of the projecting portion towards therebelow. Therefore, water drops are restrained from entering into the negative pressure outlet port which lies deeper than the projecting portion within the recessed portion. Accordingly, the reduction in performance of the function of taking out negative pressure is prevented which would otherwise be caused by water drops which have entered from the negative pressure outlet port and become frozen. 
     Further, the projecting portion is accommodated within the recessed portion and does not project into the intake passage from the inner surface. Therefore, the increase in passage resistance in the intake passage by the water proof construction made up of the recessed portion and the projecting portion is suppressed, and the intake efficiency is increased by such an extent that the increase in passage resistance is so suppressed. 
     Furthermore, the waterproof construction is formed by connecting the lower passage wall having the recessed portion in which the negative pressure outlet port and the upwardly opened opening are provided with the upper passage wall having the projecting portion which extends downwards; and accommodating the projecting portion so as to project from the opening into the recessed portion. Therefore, since the lower passage wall and the upper passage wall which have the recessed portion and the projecting portion, respectively, are separate members, the respective constructions of the recessed portion and the projecting portion are simplified and the respective members are able to be more easily molded. Therefore, the production costs of the intake device can be reduced. 
     Furthermore, the projecting portion which is situated within the recessed portion is positioned between the inner surface and the negative pressure outlet port in the horizontal direction which is the direction in which the recessed portion is recessed relative to the inner surface of the lower passage wall and the projecting portion is not required to surround the negative pressure outlet port. Therefore, the recessed portion is made smaller in size. Thus, the degree of freedom in disposing the negative pressure outlet port is increased and the lower passage wall can be made smaller in size and lighter in weight. 
     In addition, the projecting portion is positioned above the negative pressure outlet port and the projecting portion does not cover the negative pressure outlet port in the horizontal direction in which the recessed portion is recessed relative to the inner surface of the lower passage wall. Therefore, since a negative pressure is not hindered from taking-out from the negative pressure outlet port even if the projecting portion and the negative pressure outlet port are positioned close to each other in the horizontal direction, the negative pressure taking-out function can be ensured while making the waterproof construction smaller in size in the horizontal direction. 
     Furthermore, the projecting portion which is provided on the upper passage wall only has to be situated further upwards than the negative pressure outlet port. Thus, a vertical length of the projecting portion can be shortened, and a central portion of a lower end portion of the projecting portion is formed into an arc-like shape in which it projects downwards. Therefore, when the upper passage wall is temporarily placed with its mating surface oriented downwards before it is connected to the lower passage wall, breaking of the projecting portion which projects further downwards than the mating surface can be avoided. 
     Since the projecting portion situated within the recessed portion extends downwards to cover the recessed portion, a turbulent flow of intake air caused by the recessed portion is suppressed. Thus, the increase in passage resistance in the intake passage due to the recessed portion is suppressed further. 
     According to another invention, water drops falling along the projecting portion are prevented from continuing to fall from the lower end portion of the projecting portion to the deep surface to which the negative pressure outlet port opens by the gap defined in the horizontal direction between the projecting portion and the deep surface. Therefore, the entering of water drops into the negative pressure outlet port can be suppressed further, thereby improving the effect of preventing the entering of water drops into the negative pressure outlet port by the waterproof construction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an exploded view of an intake manifold of an intake device of the invention when a lower case of the intake manifold is seen from a mating surface; 
         FIG. 1B  is an exploded view of an intake manifold of an intake device of the invention when an upper case of the intake manifold is seen from a mating surface; 
         FIG. 1C  is an enlarged view of a portion c in  FIG. 1A ; 
         FIG. 2  is a view of a main part resulting when the intake manifold in  FIG. 1A  is viewed from thereabove in a vertical direction; 
         FIG. 3A  is a sectional view taken along the line IIIA-IIIA in  FIG. 2 ; and 
         FIG. 3B  is a sectional view taken along the line IIIB-IIIB in  FIG. 3A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the invention will be described by reference to  FIGS. 1A to 3B . 
       FIGS. 1A to 3B  are drawings describing a first embodiment. 
     Referring to  FIG. 1 , an intake device  1  of the present invention is provided in a single-cylinder or multi-cylinder internal combustion engine mounted on a vehicle, or in this embodiment, an inline four-cylinder spark ignition type internal combustion engine. 
     The intake device includes an air cleaner  2  for cleaning air induced thereinto, a throttle device  3  including a throttle valve  3   a  for controlling flow rate of intake air including the air from the air cleaner  2 , and an intake pipe for guiding intake air that has flowed through the throttle device  3  to respective combustion chambers. The intake pipe is made up of an intake manifold  4  which is connected to a downstream of the throttle device  3  and a downstream side intake pipe  5  which is connected to the intake manifold  4 . Note that the terms of upstream and downstream are used in relation to the flow of intake air. 
     In addition, the intake air that has flowed through an intake passage formed by the intake device  1  (hereinafter, referred to simply as an “intake passage”) is sucked into the respective combustion chambers through intake ports provided in a cylinder head of the internal combustion engine. In addition, the throttle valve  3   a  controls the flow rate of intake air flowing through the intake passage downstream of the throttle valve  3   a  in accordance with its opening degree. By the air sucked into cylinders being reduced by the throttle valve  3   a , a negative pressure is generated at downstream side of the throttle valve  3   a.    
     The intake manifold  4  includes an inlet port  4   a  which forms an inlet passage  31  into which intake air from the throttle device  3  is allowed to flow, a merged portion  4   b  which forms a merged passage  32  into which intake air from the inlet passage  31  is allowed to flow, and a branch portion  4   c  which forms branch passages  33  which branch from the merged passage  32  for guiding intake air individually to the respective combustion chambers. 
     The downstream side intake pipe  5  which forms a plurality of downstream side branch passages  5   p  which communicate with the corresponding branch passages  33  is connected to a flange portion  4   d  which constitutes a downstream end portion of the branch portion  4   c . A downstream end of the downstream side intake pipe  5  is connected to the cylinder head. 
     Depending upon types of internal combustion engines, the flange portion  4   d  may be connected directly to the cylinder head without being connected thereto by the downstream side intake pipe  5 . 
     The merged passage way  32  is an enlarged chamber whose passage area is larger than those of the inlet passage  31  and the respective branch passages  33 . 
     The intake passage is made up of an air chamber  2   p  formed by an air cleaner casing  2   a  of the air cleaner  2 , an in-throttle body intake passage  3   p  which is formed by a throttle body  3   b  which is a body of the throttle device  3  and in which the throttle valve  3   a  is disposed, the inlet passage  31 , the merged passage  32  and the respective branch passages  33  which are formed by the intake manifold  4  and the respective downstream side branch passages  5   p.    
     Here, the intake passage includes passage components including the air cleaner  2 , the throttle device  3 , the intake manifold  4  and the downstream side intake pipe  5 . In addition, respective inner surfaces of the air cleaner casing  2   a , the throttle body  3   b , the intake manifold  4  and the downstream side intake pipe  5  constitutes a passage wall surface. 
     Referring to  FIGS. 1A ,  1 B,  2 ,  3 A and  3 B, the intake manifold  4  is a passage component having a separate element assembling construction which is formed by connecting together a plurality of passage walls including at least an upper passage wall and a lower passage wall which are disposed next to each other in a vertical direction A 0 . In this embodiment, the intake manifold  4  includes a lower case  10  functioning as the upper passage wall and an upper case  20  functioning as the lower passage wall which is disposed above the lower case, and both the cases  10 ,  20  are configured so as to be connected to each other such that the connection is air tight at mating surfaces  10   a ,  20   a . Here, next to each other in the vertical direction A 0  means above and below in the vertical direction A 0 . 
     The lower case  10  and the upper case  20  are each a single member which is molded integrally from a synthetic resin by using a molding die. Edge portions  10   b ,  20   b  thereof which have the mating surfaces  10   a ,  20   a , respectively, are connected directly to each other by thermal welding as a fastening means. 
     In addition, the lower case  10  and the upper case  20  may be connected to each other indirectly by bolts as a fastening means via a member separate from both the cases  10 ,  20  such as a seal member. In addition, the intake manifold  4  may be formed from materials other than resin such as metal and the like. 
     The lower case  10  includes a lower inlet portion  11  which is part of the inlet portion  4   a , a lower merged portion  12  which is part of the merged portion  4   b  and branch pipes  13  which are connected to the lower merged portion  12 . The lower merged portion  12  has a bottom wall  15  and a lower side wall which surrounds the bottom wall  15  and has an edge portion  10   b . The lower side wall has a side wall  16  to which the branch passages  33  open and a side wall  17  having an inner surface  17   a  which opposes to the side wall  16  across the merged passage  32 . 
     The upper case  20  includes an upper inlet portion  21  which is part of the inlet portion  4   a  and is connected with the lower inlet portion  11  to make up the inlet port  4   a  and an upper merged portion  22  which is part of the merged portion  4   b  and is connected with the lower merged portion  12  to make up the merged portion  4   b . The upper merged portion  22  has a ceiling wall  25  and an upper side wall which surrounds the ceiling wall  25  and has an edge portion  20   b . The upper side wall has a side wall  27  which is connected to the side wall  17  and which has an inner surface  27   a  extending in the vertical direction A 0 . 
     Here, the surface extends in the vertical direction A 0  means that the surface extends over different positions in the vertical direction A 0  so that water drops adhering to the surface flow downwards irrespective of the fact that the surface is a planar or curved surface or the fact that the surface is parallel to the vertical direction A 0  or inclined relative to the vertical direction A 0 . 
     Referring also to  FIG. 1C , in the lower case  10  which forms, in cooperation with the upper case  20 , the merged passage  32  which constitutes the intake passage lying further downstream than the throttle valve  3   a , a negative pressure outlet portion  40 , which forms a negative pressure passage  41  having a negative pressure outlet port  42  from which negative pressure generated in the merged passage  32  is taken out, is provided on the side wall  17  of the lower case  10  so as to be molded integrally therewith. 
     A hole in a straight line which constitutes the negative pressure passage  41  is formed in the negative pressure outlet portion  40  having a pipe joint shape. A negative pressure conduit pipe  48  which forms a negative pressure passage  48   a  for guiding a negative pressure to a negative pressure utilization device  49  is connected to the hole. 
     The negative pressure utilization device  49 , which is a device that operates by the negative pressure guided by both the negative pressure passages  41 ,  48   a  which are connected to each other, is, in this embodiment, a brake booster for increasing the brake effort exerted on a brake device, and the negative pressure conduit pipe  48  is connected to a negative pressure tank of the brake booster. In addition, the negative pressure utilization device  49  may be a negative pressure-type actuator other than the brake booster and furthermore it may be a negative pressure sensor. 
     Referring to  FIGS. 1C ,  2 ,  3 A and  3 B, the side wall  17  of the lower case  10  has a recessed portion  50  which is recessed towards an outer surface  17   b  side of the side wall  17  in a first horizontal direction A 1  in part of the inner surface  17   a  which extends in the vertical direction A 0 . The recessed portion  50 , which is molded integrally with the side wall  17  and is also molded integrally with the negative pressure outlet portion  40 , forms a horizontal opening  51  which opens to the merged passage  32  in the horizontal direction A 1  in a position which opposes to the negative pressure outlet port  42  and a deep surface  53 , which will be described later, in the horizontal direction A 1 . The opening  51  is defined by a circumferential edge portion  18  which is part of the inner surface  17   a  to open to the inner surface  17   a.    
     The recessed portion  50  has a recessed surface which is made up of the deep surface  53  and a depth surface  54 . The deep surface  53  is positioned deep in the horizontal direction A 1 , extends in the horizontal direction A 0  and the negative pressure outlet port  42  opens to the deep surface  53 . The depth surface  54  extends from the deep surface  53  towards the opening  51  in a depth direction (one of which is the direction in which the recessed portion  50  is recessed relative to the circumferential edge portion  18 ) which is the horizontal direction A 1  and continues to the circumferential edge portion  18 . Accordingly, the recessed surface of the recessed portion  50  constitutes a surface which recedes from the circumferential edge portion  18  relative to the merged passage  32 . In addition, in the merged passage  32 , intake air flows across the opening  51  and along the inner surface  17   a.    
     In addition, the depth surface  54  has a lower depth surface  54   a  which lies further downwards than the negative pressure outlet port  42 . The lower depth surface  54   a  is inclined obliquely downwards to continue smoothly to an inner surface  15   a  of the bottom wall  15 . 
     A vertical opening  52   a  is provided on the recessed portion  50  in a position which opposes to the mating surface  20   a  of the side wall  27  of the upper case  20  in the vertical direction A 0  so as to open to the mating surface  10   a  and to open upwards. The opening  52  is provided so as to extend between the deep surface  53  and the opening  51  in the horizontal direction A 1  and continues to the opening  51 . 
     The side wall  27  of the upper case  20  has a projecting portion  60 , which extends downwards towards the negative pressure outlet port  42  and projects into the recessed portion  50  through the opening  52  in the vertical direction A 0 , in a position which aligns with the recessed portion  50  in the vertical direction A 0  in a state that both the cases  10 ,  20  are connected together (hereinafter, referred to as a “connected state”). The projecting portion  60  is molded integrally on the side wall  27  and extends from the mating surface  20   a  to project further downwards than the mating surface  20   a.    
     In the connected state, the projecting portion  60  is positioned such that entire thereof is positioned between the deep surface  53  or the negative pressure outlet port  42  and the circumferential edge portion  18  in the horizontal direction A 1  and has a shape such that entire thereof is accommodated within the recessed portion  50 . The projecting portion  60  has a front surface  61  and a rear surface  62 . The front surface  61  faces the merged passage  32 , continues smoothly to the inner surface  27   a  and extends in the vertical direction A 0 . The a rear surface  62  opposes to the deep surface  53  in the horizontal direction A 1 . In addition, in a state that the projecting portion  60  is accommodated within the recessed portion  50 , the projecting portion  60  covers part of the deep surface  53  from a merged passage  32  side, and the front face  61  is positioned on substantially the same plane as the circumferential edge portion  18  or occupies a position which recedes further than the circumferential edge portion  18 . Therefore, the projecting portion  60  is situated in a position where the projecting portion  60  does not project from the circumferential edge portion  18  to the merged passage  32  side in the horizontal direction A 1 . Consequently, the projecting portion  60  does not project from the circumferential edge  18  to the merged passage  32 . 
     A gap  71  is formed in the horizontal direction A 1  between the rear surface  62  of the projecting portion  60  and the deep surface  53 . A width w 1  of the gap  71  in the horizontal direction A 1 , a thickness w 2  of the projecting portion  60  in the horizontal direction A 1  and a distance w 3  between the deep surface  53  and the front surface  61  in the horizontal direction are, even at their maximums, smaller than widths w 7 , w 8  of the negative pressure outlet port  42 , which will be described later. In this embodiment, the thickness w 1 , w 2  and w 3  are equal to or less than one half of the widths w 7 , w 8 . According to these dimensional relations, the depth of the recessed portion  50  in the horizontal direction A 1  can be reduced, and the recessed portion  50  can be made smaller in size in the horizontal direction A 1 . 
     In this embodiment, the projecting portion  60  has a flat plate-like shape when viewed from a front direction (hereinafter, referred to as “as viewed from the front”), the thickness w 2  in the depth direction (also the horizontal direction A 1 ) is smaller than width w 6  in second horizontal direction A 2  and length w 5  in the vertical direction A 0  and has substantially quadrangular shape as viewed from the front. 
     Here, the “front direction” means a direction which is substantially perpendicular to the opening  51  on a horizontal plane or the circumferential edge portions  18   a ,  18   b  holding the opening  51  in the horizontal direction A 2  and also a direction in which the recessed portion  50  and the projecting portion  60  are viewed from the merged passage  32  side. A front direction A 3  is exemplified in  FIGS. 1C and 3A . 
     In addition, the front direction A 3  is parallel to center axis L of the straight-line negative pressure passage  41  and the horizontal direction A 1  and also perpendicular to the negative pressure outlet port  42 . In addition, as viewed from the vertical direction A 0 , the horizontal direction A 1  is perpendicular to the horizontal direction A 2 . 
     As viewed from the front, the width w 7  of the negative pressure outlet port  42  (in this embodiment, the diameter of the negative pressure outlet port  42 ) which is measured between end portions  44 ,  45  of the negative pressure outlet port  42  in the horizontal direction A 2  is smaller than the width w 6  of the projecting portion  60 . The negative pressure outlet port  42  is disposed within the range of the projecting portion  60  in the horizontal direction A 2 . 
     Furthermore, widths w 11 , w 12  of respective gaps  72 ,  73  between the circumferential edge portion  18  and the projecting portion  60  in the horizontal direction A 2  are, even at their maximums, smaller than the width w 6  of the projecting portion  60  and the width w 7  of the negative pressure outlet port  42 . 
     In addition, in order to suppress the increase in passage resistance in the merged passage  32  by the recessed portion  50 , the respective widths w 11 , w 12  are preferably smaller. 
     A lower end portion  63  of the projecting portion  60  is positioned above the negative pressure outlet port  42  which exhibits a circular shape as viewed from the front. In addition, in the horizontal direction A 1 , the projecting portion  60  extends downwards from the opening  52  or the mating surface  10   a  to cover the recessed portion  50  and also to cover the deep surface  53  above the negative pressure outlet port  42 . In addition, as viewed from the front, the projecting portion  60  is symmetry with respect to a straight line which passes through the center axis L and which is parallel to the vertical direction A 0 . In addition, the lower end portion  63  is formed into an arc-like shape in which a central portion  65  in the horizontal direction A 2  projects downwards. 
     A length w 5  of the projecting portion  60  is smaller than a width w 6  thereof. In addition, a space w 4  between a lowermost portion  64  and an uppermost portion  43  of the lower end portion  63  in the vertical direction A 0  is substantially equal to a width w 7  and a maximum width w 8  of the negative pressure outlet port  42  in the vertical direction A 0  (either of the widths w 7 , w 8  is the diameter of the negative pressure outlet port  42  in this embodiment) or less than the respective widths w 7 , w 8 . 
     The negative pressure outlet port  42  is not covered by the projecting portion  60  which lies above the negative pressure outlet port  42  in the horizontal direction A 1  with respect to the merged passage  32 , and the negative pressure outlet port  42  is opened towards the merged passage  32  so as not to be hindered by the projecting portion  60  in the front direction or the horizontal direction A 1 . By this configuration, since an airflow which flows out from the negative pressure outlet port  42  towards the merged passage  32  is not hindered by the projecting portion  60 , the efficiency of taking out the negative pressure in the merged passage  32  can be increased. 
     There may be a situation where moisture which is present in air flowing in the intake passage adheres to the inner surfaces of the lower case  10  and the upper case  20  in the form of water drops when the internal combustion engine is driven. 
     At driving or stopping of the internal combustion engine, water drops, which are adhered to the inner surface  27   a  of the side wall  27  of the upper case  20  and flow down inner surface  27   a  towards the negative pressure outlet port  42 , fall downwards from the lower end portion  63  of the projecting portion  60  along the front surface  61  of the projecting portion  60 , adhere to the lower depth surface  54   a  which is inclined downwards towards the bottom wall  15  and flow down along the lower depth surface  54   a  to flow out to the bottom wall  15  smoothly. Accordingly, water is prevented from remaining on the lower depth surface  54   a.    
     When water drops fall from the projecting portion  60  while being guided by the projecting portion  60 , since the negative pressure outlet port  42  lies in the position which recedes further backwards towards a deep surface  53  side of the recessed portion  50  than the lower end portion  63  in the horizontal direction A 1 , the water drops falling from the lower end portion  63  are made difficult to enter into the negative pressure outlet port  42 . Therefore, the water drops are restrained or prevented from entering into the negative pressure passage  41  from the negative pressure outlet port  42 . Thus, the waterproof construction for preventing or suppressing the entering of water drops into the negative pressure outlet port  42  is made up of the recessed portion  50  and the projecting portion  60 . 
     Next, the functions and advantages of the above described embodiment will be described. 
     The recessed portion  50 , which is recessed in the horizontal direction A 1 , is provided on part of the inner surface  17   a  of the side wall  17  of the lower case  10 . The recessed portion  50  has, in its deep portion, the deep surface  53  to which the negative pressure outlet port  42  opens, and the opening  51  opened upwards is provided in the upper portion of the recessed portion  50  in the position which opposes to the upper case  20  in the vertical direction A 0 . The upper case  20  has the projecting portion  60  which extends further downward towards the negative pressure outlet port  42  than the mating surfaces  10   a ,  20   a  and projects into the recessed portion  50  through the opening  52 , and the projecting portion  60  is positioned above the negative pressure outlet port  42  and between the negative pressure outlet port  42  and the inner surface  17  in the horizontal direction A 1 . The lower end portion  63  of the projecting portion  60  is formed into the arc-like shape in which the central portion  65  in the horizontal direction A 2  projects downwards. 
     Accordingly, the water drops, which flow down towards the negative pressure outlet port  42  along the inner surface  27   a  of the side wall  27 , flow down along the projecting portion  60  which lies closer to the merged passage  32  side than the negative pressure outlet port  42  to fall downwards from the lower end portion  63  of the projecting portion  60 . Therefore, the entering of water drops into the negative pressure outlet port  42  which lies deeper than the projecting portion  60  in the recessed portion  50  is suppressed. Accordingly, the reduction in performance of the function of taking-out the negative pressure can be prevented which would otherwise be caused by water drops which have entered from the negative pressure outlet port  42  become frozen. 
     Further, since the projecting portion  60  is accommodated within the recessed portion  50  and hence does not project from the inner surface  17   a  into the merged passage  32 , the increase in passage resistance in the merged passage  32  by the waterproof construction made up of the recessed portion  50  and the projecting portion  60  is suppressed, and the intake efficiency is increased by such an extent that the increase in passage resistance is so suppressed. 
     Furthermore, the waterproof construction is configured by connecting to each other the lower case  10 , which has the recessed portion  50  on which the negative pressure outlet port  42  and the opening  52  opened upwards are provided, and the upper case  20 , which has the projecting portion  60  extending downwards, while accommodating the projecting portion  60  so as to project from the opening  52  into the recessed portion  52 . Therefore, since the lower case  10  and the upper case  20  which have the recessed portion  50  and the projecting portion  60 , respectively, are separate members, the respective constructions of the recessed portion  50  and the projecting portion  60  are simplified. Further, their easiness of molding process is increased including a case where the recessed portion  50  and the projecting portion  60  are molded integrally on the lower case  10  and the upper case  20 , respectively. Therefore, the production costs of the intake device  1  can be reduced. 
     The projecting portion  60  which is situated within the recessed portion  50  is positioned between the inner surface  17   a  and the negative pressure outlet port  42  in the horizontal direction A 1  which is also the direction in which the recessed portion  50  is recessed relative to the inner surface of the lower case  10 . Therefore, the projecting portion  60  is not required to surround the negative pressure outlet port  42 . Accordingly, the recessed portion  50  is made smaller in size, which increases the degree of freedom in disposing the negative pressure outlet port  42 , and the lower case  10  can be made smaller in size and lighter in weight. Since the negative pressure outlet port  42  opens to the deep surface  53 , compared with a case where the negative pressure outlet port  42  opens to the depth surface  54  of the recessed portion  50 , the recessed portion  50  can be made small in size in the horizontal direction A 1 . 
     In addition, the projecting portion  60  is positioned above the negative pressure outlet port  42  and is not positioned further downwards than the negative pressure outlet port  42 . Thus, the projecting portion  60  does not cover the negative pressure outlet port  42  in the horizontal direction A 1  which is also the direction in which the recessed portion  50  is recessed relative to the inner surface  17   a . Therefore, even if the projecting portion  60  and the negative pressure outlet port  42  are positioned closed to each other in the horizontal direction A 1 , a negative pressure is not prevented from taking-out from the negative pressure outlet port  42  by the projecting portion  60 . Thus, the negative pressure taking-out function can be ensured while making the waterproof construction small in size in the horizontal direction A 1 . 
     Furthermore, since the projecting portion  60  provided on the upper case  20  only has to lie further upwards than the negative pressure outlet port  42 , for example, the length w 5  of the projecting portion  60  can be made shorter than the width w 6  so as to shorten the length w 5  of the projecting portion  60  in the vertical direction A 0 , and the lower end portion  63  is formed into the arc-like shape in which the central portion  65  projects downwards. Therefore, the damage to the projecting portion  60 , such as a case where the projecting portion  60  is broken which would otherwise occur when the upper case  20  is placed temporarily with its mating surface  20   a  oriented downwards before it is connected to the lower case  10 , can be avoided. 
     Since the projecting portion  60  situated within the recessed portion  50  extends downwards to cover the recessed portion  50 , the turbulent flow of intake air caused by the recessed portion  50  is suppressed. Therefore, the increase in passage resistance in the intake passage due to the recessed portion  50  is suppressed further. Moreover, the adhesion of water drops to the recessed surface, which includes the deep surface  53  above the negative pressure outlet port,  42  is suppressed. Thus, the effect of preventing the entering of water drops into the negative pressure outlet port  42  is improved. 
     The recessed surface of the recessed portion  50  has the deep surface  53  which opposes to the projecting portion  60  in the horizontal direction A 1 , and the negative pressure outlet port  42  opens to the deep surface  53 . By the gap  71  provided between the deep surface  53  and the projecting portion  60  in the horizontal direction, water drops falling along the projecting portion  60  are prevented from continuing to fall from the lower end portion  63  of the projecting portion  60  to the deep surface  53  opened to the negative pressure outlet port  42  by the gap  71  provided between the projecting portion  60  and the deep surface  53  in the horizontal direction A 1 . Consequently, the entering of water drops into the negative pressure outlet port  42  can be suppressed further. Thus, the effect of preventing the entering of water drops into the negative pressure outlet port  42  by the waterproof construction is improved. 
     Next, modifications to the above-described exemplary embodiments will be described. In the following embodiments, the configurations in the above-described embodiments are partially modified. 
     In an intake device  1 , passage components other than an intake manifold  4  which makes up an intake passage may be made up of a plurality of passage walls which include at least a lower passage wall and an upper passage wall, and a recessed portion, a projecting portion and a negative pressure outlet portion  42  may be provided in the passage components. 
     A recessed portion  50  or a projecting portion  60  may be a separate member from a side wall  17  of a lower case  10  or a side wall  27  of an upper case  20  and may be made up of a passage wall which is may be attached and/or detached to the side walls  17 ,  27 . In addition, a negative pressure outlet portion  40  may be a separate member from the recessed portion  50 . 
     A gap  71  may be formed so that a rear surface  62  of a projecting portion  60  and a deep surface  53  are in contact with each other via a projecting portion which is provided on the rear surface  62  or the deep surface  53 . Furthermore, the rear surface  62  and the deep surface  53  may be in surface contact with each other over substantially the whole area thereof. 
     The shape of the negative pressure outlet port  42  may take other shapes than the circular shape. In the embodiments, while the negative pressure outlet port  42  opens only to the deep surface  53 , the negative pressure outlet port  42  may also open to a range between the deep surface  53  and the depth surface  54  or only to the depth surface  54 . 
     Further, it is adaptable that the throttle device  3  is a carburetor. 
     Furthermore, the intake manifold  4  which is other than the merged portion  4   b  such as the branch portion  4   c  or the passage components which makes up the intake device  1  and is other than the intake manifold  4  (for example, the throttle body  3   b  of the throttle device  3 ) may include an upper passage wall having a recessed portion  50  and an upper passage wall having a projecting portion  60 . 
     The internal combustion engine may be a compression ignition type internal combustion engine or an internal combustion engine that is used for a marine propulsion system such as a marine outboard engine which includes a crankshaft directed in a vertical direction A 0 . 
     While the invention has been described in connection with the exemplary embodiments, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the present invention, and it is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of the present invention.