JP6150339B2 - Duct connection structure - Google Patents

Description

  According to the present invention, a second duct formed into a tubular shape by blow molding is provided inside one end of a first duct formed by fixing a groove-shaped member having a downward groove opening on the upper surface of a ceiling interior material of a vehicle. The present invention relates to a duct connecting structure that connects to a fitted state.

  Conventionally, on the upper surface of the ceiling interior material, a flange projecting outward from the groove opening edge of the groove-shaped member is bonded to form a bonded duct having an air passage between the ceiling interior material and the groove-shaped member, There is known one in which the bonded duct is a ceiling duct of a vehicle (see, for example, Patent Document 1).

Japanese Patent Laying-Open No. 2008-44422 ([0011], FIG. 1)

  However, the above-described ceiling duct has a problem that it is difficult to connect to a pillar duct that sends air from an air conditioner provided in a vehicle to a bonding duct. Moreover, when unevenness and a slope are formed in the bonding part with the groove-shaped member in a ceiling interior material, there also existed a problem that an air leak tends to arise in the part with the unevenness and the slope. Therefore, the inventor of the present application separately attached the blow duct to the upper surface of the ceiling interior material, and connected the blow duct and the bonded duct to form a ceiling interior material with a new duct that constitutes the ceiling duct. It came to develop. According to this novel ceiling duct, the above-mentioned problem can be solved by replacing the connection portion with the pillar duct in the conventional ceiling duct and the portion where it is difficult to bond the groove-shaped member with the blow duct.

  However, it has been found that in the above-described novel ceiling duct, air leakage is likely to occur at the connection portion between the bonded duct and the blow duct. Specifically, as in the ceiling duct 110 shown in FIG. 7, the end of the groove side wall 23 of the channel member 20 and the cylindrical side wall 132 of the blow duct 130 on the ceiling interior material 11 side approaches the ceiling interior material 11. When the curved shapes are curved so as to be separated from each other, a triangular gap 136 is formed between the groove side wall 23 and the cylindrical side wall 132. For this reason, it is necessary to seal the gap 136 using a sealing material 137 such as urethane slab, and there is a problem that the cost increases.

  This invention is made | formed in view of the said situation, and aims at provision of the duct connection structure which can aim at cost reduction.

  In order to achieve the above object, the duct connection structure according to the first aspect of the present invention is an end portion of a first duct formed by fixing a groove-shaped member having a downward groove opening on an upper surface of a ceiling interior material of a vehicle. A duct connection structure for connecting the end of a second duct blow-molded into a tubular shape to the inner side of the tube, wherein the lower end portion of the pair of groove side walls is folded outward on the channel member. And a pair of side gaps sandwiched between the bending curved portion on the base end side of each flange and the ceiling interior material are formed on both sides of the first duct. A pair of side projections projecting into a pair of side gaps from the lower ends on both sides in the width direction are molded into two ducts, and a blow molding mold parting line is formed at the ends of the pair of side projections. It has the feature in place.

  The duct connection structure according to the invention of claim 2 is blow-molded in a cylindrical shape inside the end portion of the first duct formed by fixing a groove-shaped member having a downward groove opening on the upper surface of a ceiling interior material of a vehicle. A duct connection structure for connecting the end of the second duct in a fitted state, and projecting outward from the lower end of both sides in the width direction along the upper surface of the ceiling interior material. A pair of flange pieces are formed, and a parting line of a blow mold is arranged at the tip of the pair of flange pieces, and the lower end portions of the pair of groove side walls are bent outward on the channel member. A pair of flanges are provided, and each flange part is formed with a flange overlapping part that floats from the top surface of the ceiling interior material in a stepped manner and is superimposed on the flange piece, and the base end part of each flange piece Includes a bending curved portion formed on the base end side of the collar portion and Protruding portion protruding upward to fill the proximal end gaps formed between has characterized in that provided.

  According to a third aspect of the present invention, in the duct connection structure according to the second aspect, the overlapping surface of the flange piece and the flange overlapping portion is provided with a positioning protrusion and a positioning recess that engage with each other. Have

  According to a fourth aspect of the present invention, in the duct connection structure according to any one of the first to third aspects, the cylinder bottom wall that is directed to the upper surface of the ceiling interior material at the end of the second duct is arranged vertically. It has a feature in that it has an undulating shape and a concave groove extending in the duct running direction is formed on the bottom surface of the cylinder bottom wall.

[Invention of Claim 1]
According to the first aspect of the present invention, the pair of side protrusions formed in the second duct are bent curved portions formed on the base end sides of the pair of flanges in the channel-shaped member and the upper surface of the ceiling interior material. Projecting toward the pair of side gaps sandwiched between the second duct and the groove-shaped member, the gap formed between the second duct and the channel-shaped member can be reduced. Thereby, sealing materials, such as a urethane slab, are not used or the usage-amount can be reduced, and cost reduction is achieved. In addition, since the parting line of the blow-molded mold is arranged at the tip of the side protrusion, the mold structure of the mold can be simplified and the mold can be easily removed.

[Invention of claim 2]
According to the second aspect of the present invention, the grooved duct can be easily aligned with the second duct by overlapping the flange overlapping portion of the grooved member on the flange piece of the second duct. In addition, since the parting line of the blow-molded mold is arranged at the tip of the flange piece, the mold structure of the mold can be simplified and the mold can be easily removed. Here, a base end gap is generated in a portion sandwiched between the bending curved portion formed on the base end side of the flange portion and the base end portion of the flange piece, but in the present invention, it is formed at the base end portion of the flange piece. The proximal gap can be filled by the protruding portion. Thereby, the clearance gap produced between a 2nd duct and a channel-shaped member can be made small, sealing materials, such as a urethane slab, can be used, or the usage-amount can be reduced, and cost reduction is achieved.

[Invention of claim 3]
According to the invention of claim 3, the flange overlap portion formed on the flange portion is positioned with respect to the flange piece by the concave-convex engagement of the positioning protrusion and the positioning recess, so the second duct and the channel member The connection is stabilized.

[Invention of claim 4]
According to the invention of claim 4, when the cylinder bottom wall is pressed against the upper surface of the ceiling interior material and bonded, the adhesive can be received in the groove formed on the lower surface of the cylinder bottom wall. Thereby, the adhesion area of the adhesive contributing to the adhesion between the ceiling interior material and the cylinder bottom wall can be increased, and the adhesion can be stabilized. Moreover, since the concave groove extends in the duct running direction, it is possible to suppress the undulating shape of the cylinder bottom wall from becoming the resistance of air passing through the second duct.

The top view of the ceiling duct which concerns on 1st Embodiment Side sectional view of channel member and blow duct Front sectional view of channel member and blow duct Enlarged view around the side protrusion in Fig. 3 Blow mold (A) Side view, (B) Plan view (A) Flat cross-sectional view of blow mold in mold closed state, (B) Flat cross-sectional view of blow mold and blow duct Front sectional view of blow duct and channel member without side protrusions The exploded perspective view of the ceiling duct concerning a 2nd embodiment Front sectional view of channel member and blow duct according to second embodiment Enlarged view around the flange piece in FIG. Front sectional view of side projection according to modification Front sectional view of channel member and blow duct according to modification

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a ceiling duct 10 formed integrally with a ceiling interior material 11 of a vehicle. As shown in FIG. 2, this ceiling duct 10 is a blow duct that is blow-molded into a cylindrical shape at the end of a bonded duct 20 formed by bonding a groove-shaped member 21 to the upper surface 11M of the ceiling interior material 11. 30 end portions are connected. And this invention is applied to the connection structure of this bonding duct 20 and the blow duct 30. FIG.

  Specifically, a pillar duct 80 that sends air from an air conditioner (not shown) is connected to the ceiling duct 10, and a connection portion of the ceiling duct 10 with the pillar duct 80 is configured by the blow duct 30. The other part is composed of the bonded duct 20. In the present embodiment, the bonding duct 20 corresponds to the “first duct” of the present invention, and the blow duct 30 corresponds to the “second duct” of the present invention.

  The bonding duct 20 is formed as follows. That is, as shown in FIG. 3, the groove-shaped member 21 has a reverse groove shape having a groove opening downward, and a pair of flanges formed by bending the lower ends of the pair of groove side walls 23 outward. 22. And this brim part 22 was adhere | attached on the upper surface 11M of the ceiling interior material 11 with the hot-melt-adhesive 40, and it had the ventilation path 20A (refer FIG. 2) between the groove-shaped member 21 and the ceiling interior material 11. A bonding duct 20 is formed.

  As shown in FIG. 2, the blow duct 30 is fixed to the upper surface 11 </ b> M of the ceiling interior material 11 by the tube bottom wall 31 being bonded to the upper surface 11 </ b> M of the ceiling interior material 11 with a hot melt adhesive 40. As shown in the figure, the cylinder bottom wall 31 has an overall shape along the upper surface 11M of the ceiling interior material 11, and the blow duct 30 extends along the upper surface 11M of the ceiling interior material 11. It is arranged to extend.

  As shown in FIG. 3, a plurality of concave grooves 34 extending in the duct running direction (the depth direction in the drawing of FIG. 3) are formed on the lower surface 31 </ b> M of the tube bottom wall 31. Thereby, the hot melt adhesive 40 is received in the plurality of concave grooves 34, and the bonding area of the hot melt adhesive 40 contributing to the adhesion between the blow duct 30 and the ceiling interior material 11 can be increased. The strength is improved. As a result, lifting of the blow duct 30 from the ceiling interior material 11 is prevented. The concave groove 34 is formed by forming the cylindrical bottom wall 31 into a shape that undulates in the vertical direction (for example, a mountain wave shape, a zigzag shape, or the like).

  The blow duct 30 is connected in a state of being fitted inside the bonding duct 20. Specifically, the cylinder side wall 32 and the cylinder ceiling wall 35 of the blow duct 30 are bonded to the inner surface of the groove-shaped member 21 with the hot melt adhesive 40 described above. In FIG. 3, the hot melt adhesive 40 used for the bonding is omitted.

  Here, the fitting of the groove member 21 and the blow duct 30 may be performed by first fixing the blow duct 30 to the ceiling interior material 11 and covering the groove member 21 from above the blow duct 30. The groove member 21 may be fixed to the ceiling interior material 11 first, and the blow duct 30 may be inserted into the end portion of the bonding duct 20.

  By the way, as shown in FIG. 4, a bent curved portion 24 that is curved outward toward the lower side is formed on the proximal end portion of the flange portion 22 in the groove-shaped member 21. And in the both sides of the 1st duct 20, the side gaps 25 and 25 of the tapered shape pinched | interposed between the bending curved part 24 and the ceiling interior material 11 (FIG. 4 shows only one side gap. Is formed).

  Here, when the side gaps 25 and 25 are large, it is difficult to seal the side gap 25 only with the hot melt adhesive 40 that bonds the inner surface of the channel member 21 and the outer surface of the blow duct 30. In addition, as in the ceiling duct 110 shown in FIG. 7, when the lower corners of the blow duct 130 have an R shape that is curved so as to face the inner side in the width direction as it goes downward, the groove side wall 23 and the cylindrical side wall A triangular gap 136 larger than the side gap 25 is formed between the gap 132 and the hot melt adhesive 40 alone makes it difficult to seal the gap 136. When it is difficult to seal with only the hot melt adhesive 40 as described above, it is necessary to fill the side gap 25 or the gap 136 with a sealing material 137 such as a urethane slab as shown in FIG. FIG. 7 shows an example in which the gap 136 is filled.

  On the other hand, the blow duct 30 of the present embodiment has side protrusions 33 and 33 projecting into the side gaps 25 and 25 from the lower ends of the cylindrical side walls 32 and 32 as shown in FIGS. 3 and 4. Therefore, the gap generated between the groove side wall 23 and the cylinder side wall 32 can be reduced, and the gap between the groove side wall 23 and the cylinder side wall 32 can be sealed only by the hot melt adhesive 40.

  Next, blow molding of the blow duct 30 will be described. In order to blow-mold the blow duct 30, first, as shown in FIGS. 5A and 5B, a cylindrical parison 61 extruded from the head 60 </ b> H of the extruder 60 is sandwiched between the blow molding dies 50. Come on. Next, the cylindrical blow duct 30 is formed by blowing air into the inside of the parison 61 and pressing the parison 61 against the molding surface 50 </ b> M of the blow molding die 50.

  The blow molding die 50 is composed of a first die 51 and a second die 52 that are opposed to each other so as to sandwich the parison 61 and are in contact with and away from each other. As shown in FIG. The cylinder bottom wall 31 of the blow duct 30 is molded by the second molding surface 52M of the mold 52, and the portion (except for the cylinder bottom wall 31 of the blow duct 30 is removed by the first molding surface 51M of the first mold 51). That is, the cylinder side walls 32, 32 and the cylinder ceiling wall 35) are formed.

  As shown in FIG. 6A, the entire second molding surface 52M is planar, and the parting line PL of the blow molding die 50 is disposed on the extension of the second molding surface 52M. . And the unevenness | corrugation extended along the parting line PL is formed in the 2nd shaping | molding surface 52M along the parting line PL, raising and lowering so that it may contact / separate with respect to the 1st metal mold | die 51. A concave groove 34 extending along the duct running direction is formed (see FIG. 6B).

  Moreover, as shown to FIG. 6 (A), in the part which shape | molds the lower end part of the cylinder side walls 32 and 32 among the 1st shaping | molding surfaces 51M, it is the 2nd shaping | molding surface as it goes to the center side of the width direction in the blow duct 30. Side curved surfaces 51S and 51S are provided so as to be gradually separated from 52M (FIG. 6 (A) shows only one side curved surface). And the side protrusion 33 which protruded outside from the lower end part of the cylinder side wall 32 is shape | molded by side recessed part 50A, 50A formed between these side curved surfaces 51S and 51S and the 2nd shaping | molding surface 52M (FIG. 6 (B)). Thus, in the blow duct 30, the parting line PL in the blow molding die 50 is disposed at the tip of the side protrusion 33.

  Here, in blow molding, since the blow duct 30 is molded with the parison 61 sandwiched between the parting lines PL of the blow molding die 50, excess resin is likely to gather near the parting line PL in the blow duct 30. Yes. In the blow mold 50 according to the present embodiment, the side recesses 50A and 50A for forming the side protrusions 33 are disposed at the part where the parting line PL is disposed. The excess resin that collects can be effectively used for forming the side protrusions 33.

  This completes the description of the structure of the duct connection structure according to the present embodiment. Next, the effect of this embodiment is demonstrated. According to the present embodiment, the pair of side protrusions 33, 33 formed on the blow duct 30 is formed on the base end side of the pair of flanges 22, 22 in the channel-shaped member 21. , 24 and the upper surface 11M of the ceiling interior material 11 project between the pair of side gaps 25, 25, so that the gap generated between the blow duct 30 and the channel member 21 is reduced. Can do. Thereby, sealing materials, such as a urethane slab, are not used or the usage-amount can be reduced, and cost reduction is achieved. Moreover, since the parting line PL in the blow molding die 50 is arranged at the tip of the side projection 33, the tip of the side projection 33 can be made thin, and the bending curve portion 24 of the channel member 21 can be reduced. The tapered side gap 25 sandwiched between the ceiling interior material 11 can be filled. Furthermore, the mold structure of the blow molding die 50 can be simplified, and the mold can be easily removed.

  In this embodiment, when the tube bottom wall 31 of the blow duct 30 is pressed against the upper surface 11M of the ceiling interior material 11 and bonded, hot melt bonding is performed on the groove 34 formed on the lower surface 31M of the tube bottom wall 31. Agent 40 can be received. Thereby, the quantity of the adhesive agent which contributes to adhesion | attachment with the ceiling interior material 11 and the cylinder bottom wall 31 can be increased, and stabilization of adhesion | attachment is achieved. Further, since the concave groove 34 extends in the duct running direction, it is possible to suppress the undulating shape of the tube bottom wall 31 from becoming the resistance of air passing through the blow duct 30.

[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 8, in the ceiling duct 10V of the present embodiment, the structures of the groove-shaped member 21V and the blow duct 30V are different from those of the first embodiment. Specifically, a pair of flange pieces 33 </ b> F and 33 </ b> F projecting outward from the lower ends of the pair of cylindrical side walls 32 and 32 along the upper surface of the ceiling interior material 11 are provided at the end of the blow duct 30 </ b> V. ing. As in the first embodiment, the mold parting line for blow-molding the blow duct 30 is arranged at the tip of the flange piece 33F, thereby simplifying the mold structure and simplifying the die-cutting operation. Is planned.

  As shown in FIG. 10, the flange piece 33 </ b> F has a flat lower surface and is bonded to the upper surface 11 </ b> M of the ceiling interior material 11. The front end portion of the flange piece 33F is provided with a flat portion 33H having a uniform thickness in the vertical direction, and a positioning projection 38 is formed on the upper surface of the flat portion 33H. Further, the base end portion of the flange piece 33F is a protruding portion 39 that is thicker than the flat portion 33H and protrudes upward. The protruding portion 39 is curved and formed in a shape along the bending curve portion 24 of the groove-shaped member 21V. Further, the upper surface of the protruding portion 39 is curved so as to go upward as it goes toward the base end side, and continues to the outer surface of the cylindrical side wall 32.

  As shown in FIG. 8, flange flanges 33 </ b> V at the end of the channel-shaped member 21 </ b> V have flange overlaps that are raised in a stepped manner from the ceiling interior material 11 so that the flange piece 33 </ b> F is received between the ceiling interior material 11. A portion 27 is provided. As shown in FIG. 9, the flange overlapping portion 27 is overlapped on the flange piece 33 </ b> F in a state where the groove-shaped member 21 </ b> V is fitted in the blow duct 30 </ b> V. The grooved member 21V is positioned with respect to the blow duct 30V because the positioning hole 28 penetrating the flange overlapping portion 27 vertically engages with the positioning protrusion 38 of the flange piece 33F. Yes.

  By the way, if the base end portion of the flange piece 33F is the same as the thickness of the flat portion 33H, that is, if the thickness of the flange piece 33F is uniform, it is formed on the base end side of the flange portion 22V. A proximal gap 26 sandwiched between the bending curved portion 24 and the flange piece 33F is generated, and the hot melt adhesive 40 that bonds the cylindrical sidewall 32 and the groove sidewall 23 alone can seal the proximal gap 26. It becomes difficult. On the other hand, in the blow duct 30V of the present embodiment, the proximal end gap 26 can be filled by the protruding portion 39 formed at the proximal end portion of the flange piece 33F. Thereby, the clearance gap produced between the blow duct 30V and the channel-shaped member 21V can be made small, sealing materials, such as a urethane slab, can be used, or the usage-amount can be reduced, and cost reduction is achieved. In FIG. 10, the outer surface of the blow duct 30V when the thickness of the base end portion of the flange piece 33F is the same as the thickness of the flat portion 33H is indicated by a two-dot chain line.

  In the present embodiment, the flange overlapped portion 27 is provided in the flange portion 22, so that the gap sandwiched between the step portion 22D (see FIG. 8) of the flange portion 22V and the flange piece 33F in the duct traveling direction. However, this gap can be sealed only by the hot melt adhesive 40 by making the end face shape of the flange piece 33F into a shape matching the stepped portion 22D.

  Since the other configuration of the present embodiment is the same as that of the first embodiment, description thereof is omitted by attaching the same reference numerals. Next, the effect of this embodiment is demonstrated.

  In this embodiment, by aligning the flange overlapping portion 27 of the groove member 21V on the flange piece 33F of the blow duct 30V, the alignment of the groove member 21V with respect to the blow duct 30V is facilitated. In addition, since the flange overlap portion 27 formed on the flange portion 22V is positioned with respect to the flange piece 33F by the concave and convex engagement between the positioning protrusion 38 and the positioning hole 28, the connection between the blow duct 30V and the channel member 21V is achieved. Is stabilized.

  Moreover, in this embodiment, the thickness of the flange piece 33F is uniform by the protruding part 39 formed in the base end part of the flange piece 33F and formed in the shape along the bending curve part 24 of the channel-shaped member 21V. It is possible to fill the base end gap 26 that occurs in the case of the occurrence. Thereby, the clearance gap produced between the blow duct 30V and the channel-shaped member 21V can be made small, sealing materials, such as a urethane slab, can be used, or the usage-amount can be reduced, and cost reduction is achieved.

[Other Embodiments]
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various modifications are possible within the scope of the invention other than the following. It can be changed and implemented.

  (1) In the said embodiment, although the cylinder bottom wall 31 was the shape which undulated up and down over the whole width direction, the shape which only the part of the width direction undulated may be sufficient. In this case, the concave groove 34 may be plural or only one.

  (2) In the above embodiment, the portion where the blow duct 30 is disposed in the ceiling duct 10 is a connection portion with the pillar duct 80. For example, the upper surface 11M of the ceiling interior material 11 in the ceiling duct 10 is inclined. It is good also as a part addressed to a part. In this case, the blow duct 30 is disposed at the end portion of the ceiling duct 10, but may be disposed at an intermediate portion.

  (3) In the above embodiment, only the hot melt adhesive 40 is used for the seal between the channel member 21 and the blow duct 30, but a sealing material such as urethane slab is used in addition to the hot melt adhesive 40. It may be used. Even in this case, it is possible to reduce the cost by reducing the amount of the sealing material used.

  (4) In the first embodiment, the side protrusion 33 has a solid structure, but may have a hollow structure like the side protrusion 33W shown in FIG. Similarly, the protruding portion 39 of the flange piece 33F of the second embodiment may have a hollow structure.

  (5) As shown in FIG. 12, a positioning protrusion and a positioning recess may be provided on the cylindrical ceiling wall 35 of the blow duct 30X and the ceiling wall 21T of the channel member 21X. FIG. 12 shows an example in which the positioning projection 35T is provided on the cylindrical ceiling wall 35 and the positioning recess 21A is provided on the ceiling wall 21T.

  (6) In the second embodiment, the positioning protrusion 38 may be provided in the flange overlapping portion 27 and the positioning hole 28 may be provided in the flange piece 33. Specifically, the positioning protrusion 38 may protrude from the lower surface of the flange overlapping portion 27 and the positioning hole 28 may penetrate the flange piece 33F.

  (7) In the second embodiment, the positioning protrusion 38 and the positioning hole 28 may not be provided. Even in this case, the positioning of the groove-shaped member 21V with respect to the blow duct 30V can be easily performed.

10,10V Ceiling duct 11 Ceiling interior material 20,20V Bonding duct (first duct)
21, 21 V groove-shaped member 22, 22 V collar 23 groove side wall 24 bending curved part 25 side gap 26 base end gap 28 positioning recess 30, 30 V blow duct (second duct)
31 Cylinder bottom wall 32 Cylinder side wall 33, 33W Side protrusion 33F Flange piece 34 Concave groove 38 Positioning protrusion 39 Projection part

Claims (4)

The end portion of the second duct blow-molded into a cylindrical shape is fitted inside the end portion of the first duct formed by fixing a groove-shaped member having a downward groove opening on the upper surface of the ceiling interior material of the vehicle. A duct connection structure connected to a state,
The groove-shaped member is provided with a pair of flanges formed by bending the lower ends of the pair of groove sidewalls outward, and the proximal side of each flange is bent on both sides of the first duct. A pair of side gaps are formed between the curved portion and the ceiling interior material,
In the second duct, a pair of side projections projecting from the lower end portions on both sides in the width direction into the pair of side gaps are molded, and the blow molding die is formed at the tip of the pair of side projections. Duct connection structure characterized by arranging parting lines. The end portion of the second duct blow-molded into a cylindrical shape is fitted inside the end portion of the first duct formed by fixing a groove-shaped member having a downward groove opening on the upper surface of the ceiling interior material of the vehicle. A duct connection structure connected to a state,
A pair of flange pieces projecting outward along the upper surface of the ceiling interior material from the lower end portions on both sides in the width direction are formed at the end portions of the second duct, and the blow pieces are formed at the ends of the pair of flange pieces. Place the parting line of the molding mold,
The groove-shaped member is provided with a pair of eaves formed by bending the lower ends of the pair of groove side walls outward, and each eaves is raised in a stepped manner from the upper surface of the ceiling interior material. A flange overlap portion is formed on the flange piece;
The proximal end portion of each flange piece was provided with a protruding portion that protruded upward so as to fill a proximal end gap formed between the bent curved portion formed on the proximal end side of the flange portion. A duct connection structure characterized by   The duct connecting structure according to claim 2, wherein a positioning projection and a positioning recess that engage with each other are provided on the overlapping surface of the flange piece and the flange overlapping portion.   A cylindrical bottom wall addressed to the upper surface of the ceiling interior material is formed in an up-down direction at the end of the second duct, and a concave groove extending in the duct running direction is formed on the lower surface of the cylindrical bottom wall. The duct connection structure according to any one of claims 1 to 3, wherein the duct connection structure is provided.

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