Patent Publication Number: US-11035329-B2

Title: Air intake apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an air intake apparatus, and more particularly, it relates to an air intake apparatus including a plurality of pieces joined to each other. 
     BACKGROUND ART 
     In general, an air intake apparatus including a plurality of pieces joined to each other is known. Such an air intake apparatus is disclosed in Japanese Patent Laid-Open No. 2006-90210, for example. 
     Japanese Patent Laid-Open No. 2006-90210 discloses an intake manifold (air intake apparatus) including first and second divided case components (intermediate piece), a third divided case component (first piece), and a fourth divided case component (second piece). In this intake manifold, the third divided case component is welded on the engine (internal combustion engine) side and the lower side of the second divided case component. Furthermore, the fourth divided case component is welded on the opposite side to the engine and the upper side of the second divided case component. The first divided case component and an engine-side portion of the second divided case component define a protrusion extending toward the engine and connected to the engine. 
     In the intake manifold disclosed in Japanese Patent Laid-Open No. 2006-90210, a joining position (first joining position) at the upper ends of the second divided case component and the third divided case component is provided on the lower side of a base of the protrusion. Furthermore, a joining position (second joining position) at the upper ends of the second divided case component and the fourth divided case component is provided on the upper side of the base of the protrusion. The first joining position and the second joining position are both located on a straight line that extends in a direction orthogonal to an intake air flow direction. 
     When an external force is applied to the intake manifold from the opposite side to the engine while the intake manifold is fixed to the engine, the external force and a reaction force from the engine that resists the external force are applied to the intake manifold. At this time, a moment of a couple about the lower base of the protrusion connected to the engine may be generated in the intake manifold. In this case, at the joining position (second joint position) at the upper ends of the second divided case component and the fourth divided case component, a force in a direction away from the second divided case component is applied to the fourth divided case component based on the moment of a couple. 
     PRIOR ART 
     Patent Document 
     Patent Document 1: Japanese Patent Laid-Open No. 2006-90210 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the intake manifold disclosed in Japanese Patent Laid-Open No. 2006-90210, the first joining position and the second joining position are both located on the straight line that extends in the direction orthogonal to the intake air flow direction, and thus the first joining position and the second joining position are close to each other. The force based on the moment of a couple increases as it gets closer to the rotation center, and thus the force in the direction away from the second divided case component applied to the fourth divided case component increases at the second joining position close to the first joining position. Consequently, there is a problem that a joint between the fourth divided case component and the second divided case component is easily separate. A fuel supply component that supplies fuel to the engine is likely to be disposed in the vicinity of the fourth divided case component provided on the upper side in the intake manifold. In this case, when the fourth divided case component is separate from the second divided case component, the fourth divided case component may interfere with the fuel supply component. 
     The present invention has been proposed in order to solve the aforementioned problems, and an object of the present invention is to provide an air intake apparatus in which separation of joints between a plurality of pieces that form a main body of the air intake apparatus can be significantly reduced or prevented. 
     Means for Solving the Problems 
     In order to attain the aforementioned object, an air intake apparatus according to an aspect of the present invention includes an intermediate piece including a protrusion that protrudes from an air intake apparatus main body toward an intake port of an internal combustion engine, and an intake port connection configured to connect to the intake port of the internal combustion engine, a first piece joined to one side of the intermediate piece, the first piece as well as the intermediate piece defining an upstream side of an air intake passage, and a second piece joined to the other side of the intermediate piece, the second piece as well as the intermediate piece defining a downstream side of the air intake passage. Furthermore, a first joining position between the intermediate piece and the first piece in a vicinity of a base of the protrusion of the intermediate piece opposite to the intake port is misaligned along an intake air flow direction with respect to a second joining position between the intermediate piece and the second piece in the vicinity of the base of the protrusion of the intermediate piece. 
     In the air intake apparatus according to this aspect of the present invention, as described above, the first joining position between the intermediate piece and the first piece in the vicinity of the base of the protrusion of the intermediate piece opposite to the intake port is misaligned along the intake air flow direction with respect to the second joining position between the intermediate piece and the second piece in the vicinity of the base of the protrusion of the intermediate piece. Accordingly, the first joining position in the vicinity of the base serving as a rotation center at which a moment of a couple is generated is misaligned along the intake air flow direction with respect to the second joining position such that as compared with the case in which the first joining position and the second joining position are located at the same position in the intake air flow direction, the second joining position can be moved away from the first joining position and the base. Consequently, when an external force is applied to the air intake apparatus main body from the opposite side to the internal combustion engine, a force based on the moment of a couple at the second joining position can be decreased, and thus a force applied to the second piece in a direction away from the intermediate piece can be decreased. Therefore, separation of a joint between a plurality of pieces (the intermediate piece and the second piece) that constitute the air intake apparatus main body can be significantly reduced or prevented. Thus, even when a fuel supply component is arranged in the vicinity of the second piece of the air intake apparatus main body, interference of the second piece with the fuel supply component can be significantly reduced or prevented when the external force is applied to the air intake apparatus main body from the opposite side to the internal combustion engine. 
     Furthermore, in the aforementioned air intake apparatus according to this aspect, the first joining position between the intermediate piece and the first piece is located in the vicinity of the base of the protrusion of the intermediate piece. Accordingly, the first joining position between the intermediate piece and the first piece is located in the vicinity of the base serving as the rotation center of the moment of a couple, and thus when the external force is applied to the air intake apparatus main body from the opposite side to the internal combustion engine, the force based on the moment of a couple applied to the intermediate piece and the first piece can be substantially zero or very small. Consequently, separation of a joint between the plurality of pieces (the intermediate piece and the first piece) that constitute the air intake apparatus main body can be significantly reduced or prevented. Therefore, in the air intake apparatus in which the intermediate piece, the first piece, and the second piece are joined to each other, separation of the joint between the plurality of pieces that constitute the air intake apparatus main body can be significantly reduced or prevented when the external force is applied to the air intake apparatus main body from the opposite side to the internal combustion engine. 
     In the aforementioned air intake apparatus according to this aspect, the first joining position is preferably located further away from the intake port connection than the second joining position in the intake air flow direction. 
     According to this structure, the first joining position can be easily provided in an inner portion of the air intake apparatus main body, and thus as compared with the case in which the first joining position is located closer to the intake port connection than the second joining position (in an outer portion of the air intake apparatus main body), an unnecessary portion (waste portion) generated in at least one of the first piece and the intermediate piece in order to locate the first joining position can be reduced. Consequently, the weight of the air intake apparatus can be decreased. 
     In this case, the protrusion preferably extends obliquely downward toward the intake port, the first joining position is preferably provided below the base of the protrusion, the second joining position is preferably provided above the base of the protrusion, and a shortest distance from an end face of the intake port connection to the first joining position is preferably larger than a shortest distance from the end face of the intake port connection to the second joining position. 
     According to this structure, when the first joining position is provided below the base of the protrusion, and the second joining position is provided above the base of the protrusion, the first joining position can be easily located further away from the intake port connection than the second joining position. 
     In the aforementioned structure in which the first joining position is located further away from the intake port connection than the second joining position, in a vehicle mounted state, the air intake apparatus main body is preferably disposed in front of the internal combustion engine, the second piece as well as the intermediate piece that constitutes a resonance tube in the air intake passage is preferably disposed on a front end side of the air intake apparatus main body, and the first joining position is preferably located further away from the internal combustion engine than the second joining position. 
     According to this structure, when the front of the vehicle collides with an obstacle in the vehicle mounted state, and the external force is applied to the air intake apparatus main body such that the second piece is pushed from the front side opposite to the internal combustion engine toward the internal combustion engine (rearward), separation of the joint between the intermediate piece and the second piece can be significantly reduced or prevented. 
     In the aforementioned air intake apparatus according to this aspect, a joining surface at the second joining position preferably extends along a direction parallel to an end face of the intake port connection, and the first joining position and the second joining position are preferably set in such a manner that a straight line that connects the first joining position to the second joining position is inclined with respect to a direction in which the joining surface at the second joining position extends. 
     According to this structure, the straight line that connects the first joining position to the second joining position is inclined with respect to the direction in which the joining surface at the second joining position extends such that when the external force is applied to the air intake apparatus main body from the opposite side to the internal combustion engine, a portion of the force based on the moment of a couple at the second joining position can be released in a direction parallel to the joining surface. Consequently, the force applied to the second piece in the direction away from the intermediate piece can be further decreased, and thus separation of the joint between the intermediate piece and the second piece can be further significantly reduced or prevented. 
     In the aforementioned air intake apparatus according to this aspect, in a vehicle mounted state, the second joining position is preferably located in a vicinity of a fuel supply component. 
     In this structure in which in the vehicle mounted state, the second joining position is located in the vicinity of the fuel supply component, the first joining position is misaligned along the intake air flow direction with respect to the second joining position such that separation of the joint between the intermediate piece and the second piece can be significantly reduced or prevented. Thus, when the external force is applied to the air intake apparatus main body from the opposite side to the internal combustion engine, interference of the second piece with the fuel supply component can be significantly reduced or prevented. 
     In the aforementioned air intake apparatus according to this aspect, the first piece, the intermediate piece, and the second piece are preferably made of resins weldable to each other. 
     In this air intake apparatus in which the first piece, the intermediate piece, and the second piece are welded to each other, it is possible to make it difficult to cause breakage due to the separation when the external force is applied to the air intake apparatus main body from the opposite side to the internal combustion engine and to realize weight reduction. 
     In the aforementioned air intake apparatus according to this aspect, the first piece as well as the intermediate piece preferably defines the air intake passage on a side of the internal combustion engine, and the second piece as well as the intermediate piece preferably defines the air intake passage on an opposite side to the internal combustion engine. 
     According to this structure, the entire air intake passage can be defined by the three pieces (the first piece, the intermediate piece, and the second piece), and thus complicated manufacturing of each of the three pieces can be significantly reduced or prevented as compared with the case in which the entire air intake passage is defined by only one or two pieces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A diagram schematically showing a vehicle equipped with an air intake apparatus according to an embodiment of the present invention. 
         FIG. 2  A schematic view schematically showing arrangements of the air intake apparatus and an engine according to the embodiment of the present invention. 
         FIG. 3  A perspective view of the air intake apparatus according to the embodiment of the present invention. 
         FIG. 4  An exploded perspective view of the air intake apparatus according to the embodiment of the present invention. 
         FIG. 5  A sectional view of the air intake apparatus according to the embodiment of the present invention. 
         FIG. 6  An enlarged sectional view of the vicinity of a protrusion in the air intake apparatus according to the embodiment of the present invention. 
         FIG. 7  An enlarged sectional view of the vicinity of a protrusion in an air intake apparatus according to a conventional example. 
         FIG. 8  A sectional view of an air intake apparatus according to a modified example of the embodiment of the present invention. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     An embodiment of the present invention is hereinafter described on the basis of the drawings. 
     The structure of a vehicle  120  equipped with an air intake apparatus  100  according to the embodiment of the present invention is now described with reference to  FIGS. 1 and 2 . 
     As shown in  FIG. 1 , the air intake apparatus  100  according to the embodiment of the present invention is mounted in an engine room  120   a  of the vehicle  120  while being fixed to an engine  110  (an example of an internal combustion engine). In  FIGS. 1 to 8 , in the forward-rearward direction (X-axis direction) of the vehicle  120 , the engine room  120   a  side is defined as the front side (X 1  direction), and the side of the vehicle  120  opposite to the engine room  120   a  is defined as the rear side (X 2  direction). In a vertical direction (Z-axis direction), an upward direction is defined as a Z 1  direction, and a downward direction is defined as a Z 2  direction. A direction orthogonal to the X-axis direction and the Z-axis direction is defined as a Y-axis direction. 
     The air intake apparatus  100  is disposed in front of the engine  110  in the engine room  120   a  (in a vehicle mounted state). 
     The engine  110  is an in-line four-cylinder engine including four cylinders  110   a , as shown in  FIG. 2 . The four cylinders  110   a  are arranged side by side in the Y-axis direction. The engine  110  includes a cylinder head  111 , a cylinder block  112  below the cylinder head  111 , a crankcase  113  below the cylinder block  112 , and a head cover  114  above the cylinder head  111 . The engine  110  includes injectors, for example, and a fuel supply component  110   b  that supplies fuel to each cylinder  110   a  is attached. A portion of the fuel supply component  110   b  is located above the air intake apparatus  100 . 
     The air intake apparatus  100  constitutes a portion of an air intake system that supplies air to the engine  110 . The air intake apparatus  100  includes an air intake apparatus main body  30  provided with an air intake passage I including a surge tank  10  and a plurality of (four) resonance tubes  20  formed on the downstream side of the surge tank  10 . The four resonance tubes  20  are aligned in the Y-axis direction in which the cylinders  110   a  are aligned. 
     In the air intake apparatus  100 , intake air (incoming air) that reaches a surge tank inlet  10   a  (see  FIG. 2 ) flows into the surge tank  10  via an air cleaner  130  and a throttle valve  140   a  of a throttle body  140 . Then, the intake air is introduced from the surge tank  10  through the four resonance tubes  20  to each of four intake ports  110   c  (see  FIG. 5 ) of the engine  110 . Thereafter, in the air intake apparatus  100 , the intake air is introduced into each of the four cylinders  110   a  (see  FIG. 2 ). 
     (Detailed Structure of Air Intake Apparatus Main Body) 
     The detailed structure of the air intake apparatus  100  is now described with reference to  FIGS. 3 to 6 . 
     The air intake apparatus main body  30  is formed by joining three pieces made of resins (polyamide resins, for example) weldable to each other. Specifically, as shown in  FIGS. 3 and 4 , an upper piece  40  (an example of a second piece) disposed on the front end  30   a  side of the air intake apparatus main body  30  and a middle piece  50  (an example of an intermediate piece) are integrally joined to each other by vibration welding on the front side (X 1  direction side) of the air intake apparatus main body  30 . Furthermore, the middle piece  50  and a lower piece  60  (an example of a first piece) arranged on the rear end side of the air intake apparatus main body  30  are integrally joined to each other by vibration welding on the rear side (X 2  direction side) of the air intake apparatus main body  30 . Thus, the air intake passage I including the surge tank  10  and the four resonance tubes  20  is provided in the air intake apparatus main body  30 . The upper piece  40 , the middle piece  50 , and the lower piece  60  are each formed by injection molding. 
     The four resonance tubes  20  are set to a predetermined tube length such that so-called Helmholtz resonance can be used. 
     As shown in  FIG. 5 , the downstream side (engine  110  side) of the resonance tubes  20  in the air intake passage I is curved with a bow shape that protrudes forward away from the engine  110 . Furthermore, the upstream side (surge tank  10  side) of the resonance tubes  20  in the air intake passage I is curved with a bow shape that protrudes rearward toward the engine  110 . 
     The resonance tubes  20  in the air intake passage I are spirally formed as viewed from the side in the Y-axis direction. Specifically, in each of the resonance tubes  20 , a length from the center of a spiral shape inside the air intake apparatus main body  30  to a line (centerline CL) that passes through the center of the resonance tube  20  is gradually decreased from the downstream side toward the upstream side, as viewed from the side in the Y-axis direction. That is, each of the resonance tubes  20  has a spiral shape in which the diameter is larger on the downstream side of the resonance tube  20  having a bow shape that protrudes forward than on the upstream side of the resonance tube  20  having a bow shape that protrudes rearward. Consequently, it is possible to easily ensure the sufficient tube length of the resonance tube  20  as compared with the case in which the resonance tube  20  is linear. Furthermore, the resonance tube  20  has a spiral shape such that the upstream side of the air intake passage I defined by the lower piece  60  and the middle piece  50  is located closer to an inner portion of the air intake apparatus main body  30  than the downstream side of the air intake passage I. 
     The upper piece  40  is arranged at a position that overlaps with a portion of the fuel supply component  110   b  in a top view. Accordingly, it is not necessary to arrange the air intake apparatus  100  while avoiding the fuel supply component  110   b  as compared with the case in which the entire air intake apparatus is arranged at a position that does not overlap with the fuel supply component in the top view, and thus the engine  110  and the air intake apparatus  100  can be easily arranged in a limited space of the engine room  120   a.    
     The upper piece  40  constitutes the front sides (X 1  direction sides) of downstream portions of the resonance tubes  20 . As shown in  FIGS. 3 to 5 , the upper piece  40  includes four air intake passage constituent portions  41  that constitute the downstream portions of the resonance tubes  20 , and a flange  42  that surrounds the outer peripheries of the four air intake passage constituent portions  41 . The four air intake passage constituent portions  41  are recessed forward, and are partitioned from each other by walls  41   a.    
     The upper piece  40  is joined (welded) to a joining surface  52   a  (described below) of the middle piece  50  on its entire joining surface  42   a  formed on the rear side (X 2  direction side). Of the joining surface  42   a , a joining surface  42   b  at the upper end of the flange  42  extends along an A 1  line (see  FIG. 6 ) that extends in a direction orthogonal to an intake air flow direction. 
     The middle piece  50  constitutes the rear sides of the downstream portions of the resonance tubes  20 . The middle piece  50  includes four downstream air intake passage constituent portions  51  that constitute the downstream portions of the resonance tubes  20  and a flange  52  that circumferentially surrounds each of the four downstream air intake passage constituent portions  51 . The four downstream air intake passage constituent portions  51  are recessed rearward, and are partitioned from each other by walls  51   a.    
     The middle piece  50  is joined (welded) to the joining surface  42   a  of the upper piece  40  over the entire joining surface  52   a  formed on the front side. Moreover, of the joining surface  52   a , a joining surface  52   b  at the upper end of the flange  52  extends in an A 1  direction similarly to the joining surface  42   a  of the upper piece  40 . 
     The middle piece  50  constitutes the front sides of upstream portions of the resonance tubes  20  and the surge tank  10 . The middle piece  50  includes four upstream air intake passage constituent portions  53  that constitute the upstream portions of the resonance tubes  20 , a surge tank constituent portion  54  that constitutes the surge tank  10 , and a flange  55  that circumferentially surrounds the four upstream air intake passage constituent portions  53  and the surge tank constituent portion  54 . The upstream air intake passage constituent portions  53  and the surge tank constituent portion  54  are formed in such a manner that each resonance tube  20  and the surge tank  10  communicate with each other. The four upstream air intake passage constituent portions  53  are recessed forward, and are partitioned from each other by walls  53   a . Moreover, the surge tank constituent portion  54  is recessed forward. 
     The middle piece  50  is joined (welded) to a joining surface  63   a  (described below) of the lower piece  60  over its entire joining surface  55   a  formed on the rear side. 
     The lower piece  60  constitutes the rear sides of the upstream portions of the resonance tubes  20  and the surge tank  10 . The lower piece  60  includes four air intake passage constituent portions  61  that constitute the upstream portions of the resonance tubes  20 , a surge tank constituent portion  62  that constitutes the surge tank  10 , and a flange  63  that circumferentially surrounds the four air intake passage constituent portions  61  and the surge tank constituent portion  62 . The air intake passage constituent portions  61  and the surge tank constituent portion  62  are formed in such a manner that each resonance tube  20  and the surge tank  10  communicate with each other. The four air intake passage constituent portions  61  and the surge tank constituent portion  62  are recessed rearward. Furthermore, the four air intake passage constituent portions  61  are partitioned from each other by walls  61   a.    
     The lower piece  60  is joined (welded) to the joining surface  55   a  of the middle piece  50  over the entire joining surface  63   a  formed on the front side. 
     The middle piece  50  constitutes the most downstream portions of the resonance tubes  20 . The middle piece  50  includes a protrusion  56  that extends from the joining surface  52   b  toward the engine  110  on the upper side and extends from the vicinity of the joining surface  55   b  toward the engine  110  side on the lower side. Consequently, the joining surface  42   b  at the upper end of the upper piece  40  and the joining surface  52   b  at the upper end of the middle piece  50  are joined to each other in the vicinity of the upper side of a base  56   a  formed on the upper side of the protrusion  56  so as to form a joint. That is, a joining position P 1  (an example of a second joining position) at the upper ends of the upper piece  40  and the middle piece  50  is provided in the vicinity of the upper side of the base  56   a  on the upper side of the protrusion  56 . The joining position P 1  is provided above each of the four resonance tubes  20 . 
     The joining surface  55   b  at the upper end of the middle piece  50  and a joining surface  63   b  at the upper end of the lower piece  60  are joined to each other in the vicinity of the lower side of a base  56   b  on the lower side of the protrusion  56  to form a joint. That is, a joining position P 2  (an example of a first joining position) at the upper ends of the middle piece  50  and the lower piece  60  is provided in the vicinity of the lower side of the base  56   b  on the lower side of the protrusion  56 . A distance D between the base  56   b  and the joining position P 2  is about ⅕ or less of tmin described below, for example, and is sufficiently small. 
     The protrusion  56  constitutes the four resonance tubes  20  independently. Furthermore, as shown in  FIG. 5 , the protrusion  56  extends obliquely rearward and downward toward the intake ports  110   c . The protrusion  56  extends linearly toward the intake ports  110   c.    
     The protrusion  56  includes a flange  56   c  (an example of an intake port connection) configured to connect to the intake ports  110   c  of the engine  110 . As shown in  FIGS. 3 and 4 , the flange  56   c  is circumferentially formed so as to surround the four resonance tubes  20  at an end of the protrusion  56  on the engine  110  side (the end on the X 2  direction side) and its periphery. A plurality of insertion holes  56   d  into which fastening members (not shown) are inserted are provided in the flange  56   c . Consequently, the air intake apparatus  100  is fixed to the engine  110  by the fastening members. At this time, an end face (joining surface  56   e ) of the flange  56   c  on the engine  110  side comes into contact with the outer surface of the engine  110 . The joining surfaces  42   b  and  52   b  that extend along the A 1  line extend along a direction substantially parallel to the joining surface  56   e.    
     In this embodiment, as shown in  FIG. 6 , the joining position P 2  between the middle piece  50  and the lower piece  60  in the vicinity of the lower base  56   b  of the protrusion  56  of the middle piece  50  opposite to the intake port  110   c  is misaligned along the intake air flow direction with respect to the joining position P 1  between the upper piece  40  and the middle piece  50  in the vicinity of the base  56   a  of the protrusion  56  of the middle piece  50 . Specifically, the joining position P 2  and the lower base  56   b  in the vicinity of the joining position P 2  are located on the front side (X 1  direction), which is a position further away from the flange  56   c  and the intake port  110   c  than the joining position P 1  in the intake air flow direction. 
     In this embodiment, the air intake apparatus main body  30  is formed in such a manner that the thickness t of the air intake apparatus main body  30  in the direction orthogonal to the intake air flow direction is minimized (tmin) at the lower base  56   b . Thus, the lower base  56   b  becomes a rotation center O at which a moment of a couple is generated. 
     The shortest distance L 2  from the joining surface  56   e  of the flange  56   c  on the engine  110  side to the joining position P 2  is larger than the shortest distance L 1  from the joining surface  56   e  of the flange  56   c  to the joining position P 1 . Similarly, the shortest distance from the joining surface  56   e  of the flange  56   c  to the base  56   b  is larger than the shortest distance from the joining surface  56   e  of the flange  56   c  to the base  56   a . In addition, the lower side of the base  56   b  of the protrusion  56  at which the joining position P 2  is located is provided at a position at which the length of the protrusion  56  is minimized in a direction orthogonal to the joining surface  56   e  of the flange  56   c.    
     An A 2  line that passes through the lower base  56   b  as the rotation center O and the joining position P 1  intersects with the A 1  line along which the joining surfaces  42   b  and  52   b  extend. Consequently, an A 2 α line that passes through the joining position P 2  located in the vicinity of the lower base  56   b  and the joining position P 1  also intersects with the A 1  line along which the joining surfaces  42   b  and  52   b  extend. An angle θ defined by the A 1  line and the A 2  line is preferably about 20 degrees or more in order to sufficiently space the base  56   a  apart from the joining position P 1 . Note that when the angle θ defined by the A 1  line and the A 2  line is excessively large, the air intake apparatus main body  30  is increased in size, and thus the angle θ is preferably about 60 degrees or less. The angle θ defined by the A 1  line and the A 2  line is only required to be an acute angle, and may be more than about 0 degrees and less than about 20 degrees or may be more than about 60 degrees. 
     As shown in  FIGS. 3 and 4 , a flange  58  to which a flange  140   b  (see  FIG. 2 ) of the throttle body  140  is connected is integrally formed on one side of the middle piece  50  in the Y-axis direction. The flange  58  surrounds the surge tank inlet  10   a . As shown in  FIG. 3 , the flange  58  is provided below the joining position P 2  and in the vicinity of the joining position P 2 , as viewed from the side in the Y-axis direction. The flange  58  is integrally formed on the middle piece  50  such that the mechanical strength (rigidity) around the flange  58  can be improved, and thus it is possible to significantly reduce or prevent the occurrence of inconveniences, such as distortion and breakage, in the air intake apparatus  100  due to the weight of the throttle body  140 . 
     (Mechanical Explanation at Time of Collision) 
     The case in which an external force is applied to the air intake apparatus main body  30  is now described with reference to  FIG. 1  and  FIGS. 5 to 7 . 
     When the front side (X 1  direction) of the vehicle  120  collides with a colliding object such as a wall, a collision intruder  150  intrudes into the engine room  120   a  (see  FIG. 1 ), as shown in  FIG. 5 . At this time, an external force F 1  directed rearward (X 2  direction) is applied to the front side of the air intake apparatus main body  30  disposed in front of the engine  110 . Note that the external force F 1  is applied to the upper piece  40  located at the front end  30   a  in the air intake apparatus main body  30 . 
     The air intake apparatus main body  30  is fixed to the engine  110  at the flange  56   c , and thus when the external force F 1  is applied to the air intake apparatus main body  30 , a reaction force F 2  directed forward from the engine  110  is applied to the air intake apparatus main body  30  so as to resist the external force F 1 . At this time, the reaction force F 2  is opposite to the external force F 1  and has the same magnitude. That is, the external force F 1  and the reaction force F 2  are couples. 
     Consequently, a moment M of a couple resulting from the external force F 1  and the reaction force F 2  is generated with the lower base  56   b  at which the thickness t of the air intake apparatus main body  30  is minimized (tmin) as the rotation center O. Thus, as shown in  FIG. 6 , a force G based on the moment M of a couple is generated at a predetermined position of the air intake apparatus main body  30 . When a distance from the rotation center O to the predetermined position is set to L, the force G acting on the predetermined position of the air intake apparatus main body  30  is G=M/L. 
     In this embodiment, as described above, the joining position P 2  and the base  56   b  in the vicinity the joining position P 2  are located further away from the flange  56   c  than the joining position P 1  in the intake air flow direction. A force G 1  acting on the joining position P 1  is G 1 =M/L 1  when a distance from the rotation center O (base  56   b ) to the joining position P 1  is set to L 1 . 
     In an air intake apparatus  100   a  shown as a conventional example in  FIG. 7 , a case is assumed in which a joining position P 2   a  is located at substantially the same position (on an A 1  line) as a joining position P 1  in an intake air flow direction. At this time, a distance L 2   a  from a rotation center Oa to the joining position P 1  is smaller than the shortest distance L 1  in this embodiment. In the conventional example, a force G 1   a  acting on the joining position P 1  is G 1   a =M/L 2   a . The shortest distance L 1  is larger than the distance L 2   a , and thus the force G 1  becomes smaller than the force G 1   a . That is, the force G 1  acting on the joining position P 1  in this embodiment is smaller than the force G 1   a  acting on the joining position P 1  (force that causes the upper piece to separate from the middle piece) in the conventional example. 
     In this embodiment, as shown in  FIG. 6 , the A 2  line that passes through the lower base  56   b  as the rotation center O and the joining position P 1  intersects with the A 1  line along which the joining surfaces  42   b  and  52   b  extend. Thus, the force G 1  acting on the joining position P 1  is decomposed into a force G 2  acting in an A 3  direction orthogonal to the joining surfaces  42   b  and  52   b  (force that causes the upper piece  40  to separate from the middle piece  50 ) and a force G 3  acting in the A 1  direction in which the joining surfaces  42   b  and  52   b  extend. Specifically, the force G 2  that causes the upper piece  40  to separate from the middle piece  50  satisfies G 2 =G 1  sin θ, and the force G 3  acting in the A 1  direction in which the joining surfaces  42   b  and  52   b  extend satisfies G 3 =G 1  cos θ. Consequently, the force G 2  that causes the upper piece  40  to separate from the middle piece  50  becomes even smaller than the force G 1   a  (see  FIG. 7 ) that causes the upper piece to separate from the middle piece in the conventional example. Specifically, the force G 2  is further decreased such that G 2 /G 1   a  satisfies G 2 /G 1   a =L 1  cos θ/L 1   a.    
     Therefore, even when a force sufficient to separate the upper piece from the middle piece in the conventional example is applied to the air intake apparatus  100  in this embodiment, the force G 2  that causes the upper piece  40  to separate the middle piece  50  becomes sufficiently small. Consequently, in the air intake apparatus  100  in this embodiment, separation of the joint between the upper piece  40  and the middle piece  50  due to separate of the upper piece  40  from the middle piece  50  is effectively significantly reduced or prevented. Therefore, interference of the upper piece  40  with the fuel supply component  110   b  disposed above the upper piece  40  is significantly reduced or prevented. 
     On the joining position P 2  located in the vicinity of the base  56   b  (rotation center O), the force that causes the lower piece  60  to separate from the middle piece  50  hardly acts. Thus, separation of the lower piece  60  from the middle piece  50  is also effectively significantly reduced or prevented. Consequently, in the air intake apparatus  100  in which the middle piece  50 , the lower piece  60 , and the upper piece  40  are joined to each other, it is possible to make it difficult to cause breakage due to the separation when the external force F 1  is applied to the air intake apparatus main body  30  from the opposite side to the engine  110 . 
     Advantageous Effects of this Embodiment 
     According to this embodiment, the following advantageous effects are achieved. 
     According to this embodiment, as described above, the joining position P 2  between the middle piece  50  and the lower piece  60  in the vicinity of the base  56   b  of the protrusion  56  of the middle piece  50  opposite to the intake port  110   c  is misaligned along the intake air flow direction with respect to the joining position P 1  between the middle piece  50  and the upper piece  40  in the vicinity of the base  56   a  of the protrusion  56  of the middle piece  50 . Accordingly, the joining position P 2  in the vicinity of the base  56   b  serving as the rotation center O at which the moment of a couple is generated is misaligned along the intake air flow direction with respect to the joining position P 1  such that as compared with the case in which the joining position P 2  and the joining position P 1  are located at the same position in the intake air flow direction, the joining position P 1  can be moved away from the joining position P 2  and the base  56   b . Consequently, when the external force F 1  is applied to the air intake apparatus main body  30  from the opposite side to the engine  110 , the force G 1  based on the moment M of a couple at the joining position P 1  can be decreased, and thus the force G 2  (G 1 ) applied to the upper piece  40  in a direction away from the middle piece  50  can be decreased. Therefore, separation of the upper piece  40  from the middle piece  50  (separation of the joint between the upper piece  40  and the middle piece  50 ) can be significantly reduced or prevented, and thus when the external force F 1  is applied to the air intake apparatus main body  30  from the opposite side to the engine  110 , interference of the upper piece  40  with the fuel supply component  110   b  can be significantly reduced or prevented. 
     Furthermore, the joining position P 2  between the middle piece  50  and the lower piece  60  is located in the vicinity of the base  56   b  of the protrusion  56  of the middle piece  50 . Accordingly, the joining position P 2  between the middle piece  50  and the lower piece  60  is located in the vicinity of the base  56   b  serving as the rotation center O of the moment of a couple, and thus when the external force F 1  is applied to the air intake apparatus main body  30  from the opposite side to the engine  110 , the force based on the moment M of a couple applied to the middle piece  50  and the lower piece  60  can be substantially zero or very small. Consequently, separation of the middle piece  50  from the lower piece  60  (separation of the joint between the middle piece  50  and the lower piece  60 ) can be reliably significantly reduced or prevented. Therefore, in the air intake apparatus  100  in which the middle piece  50 , the lower piece  60 , and the upper piece  40  are joined to each other, separation of the joint between the plurality of pieces that constitute the air intake apparatus main body  30  can be significantly reduced or prevented when the external force F 1  is applied to the air intake apparatus main body  30  from the opposite side to the engine  110 . 
     According to this embodiment, the joining position P 2  in the vicinity of the base  56   b  of the protrusion  56  is located further away from the flange  56   c  than the joining position P 1  in the intake air flow direction such that the joining position P 2  can be provided in the inner portion of the air intake apparatus main body  30 . Accordingly, as compared with the case in which the joining position P 2  is located closer to the flange  56   c  than the joining position P 1  (in an outer portion of the air intake apparatus main body  30 ), an unnecessary portion (waste portion) generated in at least one of the lower piece  60  and the middle piece  50  in order to locate the joining position P 2  can be reduced. Consequently, the weight of the air intake apparatus  100  can be decreased. 
     According to this embodiment, the protrusion  56  extends obliquely downward toward the intake ports  110   c . Furthermore, the joining position P 2  is provided below the base  56   b  of the protrusion  56 , and the joining position P 1  is provided above the base  56   a  of the protrusion  56 . In addition, the shortest distance L 2  from the joining surface  56   e  of the flange  56   c  to the joining position P 2  is larger than the shortest distance L 1  from the joining surface  56   e  of the flange  56   c  to the joining position P 1 . Accordingly, the joining position P 2  can be easily located further away from the flange  56   c  than the joining position P 1 . 
     According to this embodiment, in the vehicle mounted state, the air intake apparatus main body  30  is disposed in front of the engine  110 . Furthermore, the upper piece  40  as well as the middle piece  50  that constitutes the resonance tubes  20  in the air intake passage I is disposed on the front end  30   a  side of the air intake apparatus main body  30 . In addition, the joining position P 2  is located further away from the engine  110  than the joining position P 1 . Accordingly, when the front of the vehicle  120  collides with an obstacle in the vehicle mounted state, and the external force F 1  is applied to the air intake apparatus main body  30  such that the upper piece  40  is pushed from the front side (X 1  direction) opposite to the engine  110  toward the engine  110  (rearward, X 2  direction), separation of the upper piece  40  from the middle piece  50  can be significantly reduced or prevented. 
     According to this embodiment, the straight line A 2 α that connects the joining position P 2  located in the vicinity of the rotation center O to the joining position P 1  is inclined with respect to the direction in which the joining surface  42   b  ( 52   b ) at the joining position P 1  extends (the direction in which the A 1  line extends). Accordingly, when the external force F 1  is applied to the air intake apparatus main body  30  from the opposite side to the engine  110 , a portion of the force G 1  based on the moment M of a couple at the joining position P 1  can be released in a direction parallel to the joining surface  42   b  ( 52   b ). Consequently, the force G 2  applied to the upper piece  40  in the direction away from the middle piece  50  can be further decreased, and thus separation of the upper piece  40  from the middle piece  50  can be further significantly reduced or prevented. 
     According to this embodiment, in the structure in which the joining position P 1  is located in the vicinity of the fuel supply component  110   b , the joining position P 2  is misaligned along the intake air flow direction with respect to the joining position P 1 . Accordingly, separation of the upper piece  40  from the middle piece  50  can be significantly reduced or prevented, and thus when the external force F 1  is applied to the air intake apparatus main body  30  from the opposite side to the engine  110 , interference of the upper piece  40  with the fuel supply component  110   b  can be significantly reduced or prevented. 
     According to this embodiment, the lower piece  60 , the middle piece  50 , and the upper piece  40  are made of resins weldable to each other. Accordingly, in the air intake apparatus  100  in which the lower piece  60 , the middle piece  50 , and the upper piece  40  are welded to each other, it is possible to make it difficult to cause breakage due to the separation when the external force F 1  is applied to the air intake apparatus main body  30  from the opposite side to the engine  110  and to realize weight reduction. 
     According to this embodiment, the lower piece  60  as well as the middle piece  50  defines the air intake passage I on the engine  110  side, and the upper piece  40  as well as the middle piece  50  defines the air intake passage I on the opposite side to the engine  110 . Accordingly, the entire air intake passage I can be defined by the three pieces, and thus complicated manufacturing of each of the three pieces can be significantly reduced or prevented as compared with the case in which the entire air intake passage is defined by only one or two pieces. 
     MODIFIED EXAMPLES 
     The embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The scope of the present invention is not shown by the above description of the embodiment but by the scope of claims for patent, and all modifications (modified examples) within the meaning and scope equivalent to the scope of claims for patent are further included. 
     For example, while the example in which the joining position P 2  and the lower base  56   b  in the vicinity of the joining position P 2  are located further away from the flange  56   c  than the joining position P 1  in the air intake air flow direction has been shown in the aforementioned embodiment, the present invention is not restricted to this. In the present invention, like an air intake apparatus  200  according to a modified example of this embodiment in  FIG. 8 , a joining position P 3  (an example of a first joining position) and a base  256   b  on the lower side of a protrusion  256  of a middle piece  250  (an example of an intermediate piece) in the vicinity of the joining position P 3  may be located closer to a flange  56   c  than a joining position P 1  in an intake air flow direction. Even in this case, the joining position P 3  is misaligned along the intake air flow direction with respect to the joining position P 1 , and thus when an external force is applied to an air intake apparatus main body  230 , a force based on a moment M of a couple at the joining position P 1  can be decreased. Thus, a force applied to an upper piece  40  in a direction away from the middle piece  250  can be decreased. Consequently, separation of the upper piece  40  from the middle piece  250  (separation of a joint between the upper piece  40  and the middle piece  250 ) can be significantly reduced or prevented. In this case, it is possible to improve the mechanical strength around the joining position P 3  between the middle piece  250  and a lower piece  260  (an example of a first piece) (a flange connected to a heavy throttle body, for example). 
     While the example in which the joining position P 2  (first joining position) at which the middle piece  50  (intermediate piece) and the lower piece  60  (first piece) are joined to each other is located in the vicinity of the lower side of the base  56   b  on the lower side of the protrusion  56  has been shown in the aforementioned embodiment, the present invention is not restricted to this. In the present invention, the first joining position at which the intermediate piece and the first piece are joined to each other may be located at the position of the base on the lower side of the protrusion. Thus, the force based on the moment of a couple acting on the first joining position can be zero, and thus separation of the joint between the intermediate piece and the first piece can be reliably significantly reduced or prevented. 
     While the example in which the lower piece  60  (first piece), the middle piece  50  (intermediate piece), and the upper piece  40  (second piece) are made of resins weldable to each other has been shown in the aforementioned embodiment, the present invention is not restricted to this. In the present invention, the first piece, the intermediate piece, and the second piece may be made of materials other than the resins such as metal materials. In this case, in an air intake apparatus having the structure according to the present invention, separation of a fastening portion between an intermediate piece and a second piece fastened to each other by fastening members can be significantly reduced or prevented. Alternatively, any one or two of the first piece, the intermediate piece, and the second piece may be made of resins, and the remainder of the first piece, the intermediate piece, and the second piece may be made of a metal material. 
     While the example in which the resonance tubes  20  in the air intake passage I are spirally formed has been shown in the aforementioned embodiment, the present invention is not restricted to this. In the present invention, the shapes of the resonance tubes in the air intake passage are not limited to spiral shapes. For example, the resonance tubes in the air intake passage may be S-shaped. 
     In addition to the structure of the air intake apparatus  100  according to the aforementioned embodiment, a piece that defines an EGR passage and a piece that defines a blow-by gas passage may be attached to the air intake apparatus main body  30 , for example. That is, the number of pieces constituting the air intake apparatus is not limited to three (the first piece, the second piece, and the intermediate piece), but may be four or more. 
     In addition to the structure of the air intake apparatus  100  according to the aforementioned embodiment, valves that can vary the lengths of the resonance tubes may be provided in the resonance tubes, for example, such that the air intake length in the air intake apparatus can be varied. 
     While the example in which the joining surface  42   b  of the upper piece  40  (second piece) and the joining surface  52   b  of the middle piece  50  (intermediate piece) extend along the A 1  line that extends in the direction orthogonal to the intake air flow direction has been shown in the aforementioned embodiment, the present invention is not restricted to this. In the present invention, the joining surface of the second piece and the joining surface of the intermediate piece may extend along a straight line that extends in a direction that intersects not only with the intake air flow direction but also with the direction orthogonal to the intake air flow direction. The straight line described above preferably extends in a direction that intersects with the straight line (the A 2  line in  FIG. 6 ) that passes through the base and the second joining position. 
     While the example in which the upper piece  40  (second piece) is arranged at the position that overlaps with a portion of the fuel supply component  110   b  in the top view has been shown in the aforementioned embodiment, the present invention is not restricted to this. In the present invention, the second piece may be arranged in a position that does not overlap with the fuel supply component in the top view. Accordingly, when an external force is applied to the air intake apparatus main body from the opposite side to the internal combustion engine, interference of the second piece with the fuel supply component can be more effectively significantly reduced or prevented. 
     While the present invention is applied to the air intake apparatus  100  mounted on the in-line four-cylinder engine  110  has been shown in the aforementioned embodiment, the present invention is not restricted to this. That is, the air intake apparatus according to the present invention may be applied to a multi-cylinder engine other than an in-line four-cylinder engine, a V-type multi-cylinder engine, or the like. Alternatively, the present invention may be applied to an air intake apparatus of an internal combustion engine (engine) mounted in an equipment instrument other than an automobile, for example. The present invention may be applied to any of a gasoline engine, a diesel engine, a gas engine, etc. as the internal combustion engine. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               20 : resonance tube 
               30 ,  230 : air intake apparatus main body 
               40 : upper piece (second piece) 
               50 ,  250 : middle piece (intermediate piece) 
               56 ,  256 : protrusion 
               56   a : (upper) base 
               56   b ,  256   b : (lower) base 
               56   c : flange (intake port connection) 
               56   e : joining surface (end face) 
               60 ,  260 : lower piece (first piece) 
               100 ,  200 : air intake apparatus 
               110 : engine (internal combustion engine) 
               110   c : intake port 
             I: air intake passage 
             P 1 : joining position (second joining position) 
             P 2 , P 3 : joining position (first joining position)