Duct structure

Abstract

To provide a duct structure which enables improvement of rigidity of a duct member formed of non-woven fabric.SOLUTION: An air intake duct 13 is provided within a battery pack 1 mounted on a vehicle V and connects an intake port 17a of the battery pack 1 with a fan 12 which blows cooling air to a battery module 11. The air intake duct 13 includes a downstream side duct member 40 formed of non-woven fabric. The downstream side duct member 40 has a horizontal flow passage 410 disposed above the fan 12 and extending in a horizontal direction. A thickness t1 of a standing wall part 411, which extends in a vertical direction, of a wall part defining the horizontal flow passage 410 is smaller than a thickness t2 of a horizontal wall part 412 extending in the horizontal direction.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a duct structure including a duct member formed from a nonwoven fabric. [Background technology]

[0002] In recent years, research and development has been conducted into secondary cells (also called batteries) that contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] As the drive source of a vehicle becomes electric, the vehicle is equipped with a battery that supplies power to the motor, etc. The battery generates heat when supplying power or when charging, so the battery needs to be cooled. For example, Patent Document 1 describes a configuration for blowing cooling air to a battery mounted on an automobile to cool the battery.

[0004] Patent Document 1 also describes a ventilation duct that is connected to a battery case or a blower fan and sends cooling air to the battery. The ventilation duct in Patent Document 1 is a member that is integrated by combining a pair of halves in which nonwoven fabric is shaped by press processing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-99367 A Summary of the Invention [Problem to be solved by the invention]

[0006] Nonwoven fabric has excellent sound absorbing properties, and by forming a ventilation duct from nonwoven fabric as in Patent Document 1, it is expected that the driving noise of a fan or the like can be absorbed. On the other hand, nonwoven fabric has low rigidity compared to resin, metal, etc. With regard to duct members formed from nonwoven fabric, there is room for improvement in terms of rigidity.

[0007] The present invention provides a duct structure that can improve the rigidity of a duct member made of nonwoven fabric, which in turn contributes to improving energy efficiency. [Means for solving the problem]

[0008] The present invention relates to A duct structure provided inside a battery pack mounted on a vehicle, connecting an intake port of the battery pack and a fan that blows cooling air to the battery, A duct member formed of a nonwoven fabric, the duct member is disposed above the fan and has a flow passage extending in a horizontal direction, Among the walls that define the flow path and extend in the horizontal direction, a thickness of a first wall portion that extends in the vertical direction is greater than a thickness of a second wall portion that extends in the horizontal direction. Make it smaller by compressing it . Effect of the Invention

[0009] According to the present invention, the rigidity of a duct member made of nonwoven fabric can be improved. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view of a battery pack 1 equipped with an intake duct 13 that is one embodiment of the duct structure of the present invention. [Diagram 2] FIG. 2 is an exploded oblique view of the battery pack 1. [Diagram 3] 2 is a perspective view of an intake duct 13 connected to a fan 12. FIG. [Figure 4] 2 is a perspective view of a downstream duct member 40. FIG. [Diagram 5] 5 is a cross-sectional view taken along line AA in FIG. 4, showing a part of the cross section of horizontal flow channel 410. FIG. [Figure 6] 1 is a graph showing the relationship between the thickness of a member formed from a nonwoven fabric and the compression and tensile stiffness. [Figure 7]1 is a graph showing the relationship between the thickness and bending rigidity of a member formed of nonwoven fabric. [Figure 8] 5 is a schematic diagram of a fixing portion 13a provided with part B in FIG. 4, viewed from the horizontal direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the duct structure of the present invention will be described with reference to the attached drawings. The drawings are to be viewed in the direction of the reference symbols. In this specification and the like, for the sake of simplicity and clarity, the front / rear, left / right, and up / down directions are described according to the direction as seen by the driver of the vehicle, and in the drawings, the front of the vehicle is indicated as Fr, the rear as Rr, the left as L, the right as R, the top as U, and the bottom as D.

[0012] [Battery pack] First, a battery pack 1 equipped with an intake duct 13 which is one embodiment of the duct structure of the present invention will be described. As shown in Fig. 1, the battery pack 1 is equipped in a vehicle V. The vehicle V is an electric vehicle such as a hybrid vehicle or an electric car, and is configured to be able to run by driving a motor with electricity stored in the battery pack 1. The battery pack 1 is placed on and fixed to a floor panel 2 between a pair of left and right skeletal frame members 3 extending along the front-rear direction. The floor panel 2 forms the floor of the vehicle interior and luggage compartment, and a rear seat (not shown) is disposed above the battery pack 1.

[0013] As shown in FIG. 2, the battery pack 1 includes a battery module 11, a fan 12, an intake duct 13, an air blower duct 14, a battery ECU (Electronic Control Unit) 15, a junction board 16, and a battery case 17 that houses these components.

[0014] The battery case 17 has a base plate 171 and a cover 172 that covers the base plate 171 from above. The battery module 11, the fan 12, and the air duct 14 are placed on the base plate 171. The cover 172 covers the base plate 171 and is fixed to the floor panel 2. An air intake 17a is formed in the front surface of the cover 172, and the air intake 17a is covered by a ventilated grill 18.

[0015] The battery module 11 has a generally rectangular parallelepiped shape that is long in the vehicle width direction, and is fixed to a base plate 171. The battery module 11 has a plurality of battery cells stacked in the vehicle width direction. Inter-cell flow paths (not shown) are formed between adjacent battery cells, and the battery module 11 is cooled by the cooling air sent out from the air duct 14 flowing through the inter-cell flow paths.

[0016] The fan 12 is fixed to a base plate 171. The fan 12 is, for example, a sirocco fan. The fan 12 draws in cooling air from an inlet 12a provided in the rotation axis direction (vertical direction in this embodiment) and blows the cooling air from an outlet 12b provided in the centrifugal direction to the air duct 14.

[0017] 2 and 3, the intake duct 13 connects an intake port 17a provided in the cover 172 to an inlet port 12a of the fan 12. The intake duct 13 guides the air in the vehicle compartment as cooling air from the intake port 17a to the fan 12.

[0018] The intake duct 13 includes an upstream duct member 30 and a downstream duct member 40. The upstream duct member 30 is connected to the intake port 17a and is disposed above the battery module 11. The downstream duct member 40 is connected to the suction port 12a of the fan 12 and is disposed to the right of the battery module 11. Details of the intake duct 13 will be described later.

[0019] The air supply duct 14 is provided between the battery module 11 and the fan 12, and is connected to the air outlet 12b of the fan 12. The air supply duct 14 sends out the cooling air blown out from the air outlet 12b along the lower surface of the battery module 11. The cooling air sent out below the battery module 11 flows from the bottom to the top through the inter-cell flow paths, cools the battery module 11, and is discharged from the upper surface of the battery module 11. The cooling air then flows inside the battery case 17 and is discharged to the outside of the battery case 17 as indicated by the arrow in FIG. 1.

[0020] The battery ECU 15 controls charging and discharging of the battery module 11. The battery ECU 15 is placed on a bracket 19 attached to the battery module 11, and is disposed between the upstream duct member 30 and the battery module 11. The battery ECU 15 includes a processor, a memory, an interface, and the like.

[0021] The junction board 16 electrically connects the battery module 11 to an external device (not shown) and includes wiring components through which charging power and discharging power of the battery module 11 flows. The junction board 16 is disposed above the downstream duct member 40 and to the right of the upstream duct member 30. The junction board 16 is placed on a bracket 60 provided above the downstream duct member 40.

[0022] [Intake duct] Next, the intake duct 13 will be described in detail with reference to FIGS.

[0023] As described above, the intake duct 13 is provided inside the battery pack 1 mounted on the vehicle V. The intake duct 13 connects the intake port 17a of the battery pack 1 and the fan 12.

[0024] 3, the intake duct 13 includes an upstream duct member 30 and a downstream duct member 40. The upstream duct member 30 and the downstream duct member 40 are connected by inserting an end of the upstream duct member 30 into an end of the downstream duct member 40 from above.

[0025] The upstream duct member 30 is a duct that is substantially L-shaped when viewed from the front. The upstream duct member 30 is formed of, for example, resin. The upstream duct member 30 is provided with an intake port connection part 30a that opens forward, and the intake port connection part 30a connects to the intake port 17a from the inside of the cover 172.

[0026] The upstream duct member 30 has a horizontal portion 31, a vertical portion 32, and a bent portion 33. The horizontal portion 31 extends horizontally along the upper surface of the battery module 11. The vertical portion 32 extends vertically along the right surface of the battery module 11. The lower end of the vertical portion 32 opens downward and connects to the downstream duct member 40. The bent portion 33 connects the horizontal portion 31 and the vertical portion 32. The bent portion 33 changes the direction of travel of the cooling air flowing inside the horizontal portion 31 from the horizontal direction to the vertical direction, and guides the cooling air to the vertical portion 32.

[0027] The downstream duct member 40 is a duct that is substantially L-shaped when viewed from the front. The downstream duct member 40 is provided with a fan connection part 40a (see FIG. 4) that opens downward, and the fan connection part 40a is connected to the intake port 12a of the fan 12 from above.

[0028] The downstream duct member 40 is composed of an upper member 40A and a lower member 40B. The lower member 40B has the above-mentioned fan connection portion 40a and is connected to the fan 12. The upper member 40A is attached to the lower member 40B from above. The upper member 40A and the lower member 40B abut on their outer edges extending in the horizontal direction and are joined by an adhesive or the like to define an intake flow path communicating with the fan 12.

[0029] 3 and 4, the downstream duct member 40 has a horizontal portion 41, a vertical portion 42, and a bent portion 43. The horizontal portion 41 extends horizontally above the fan 12. The vertical portion 42 extends vertically along the right surface of the battery module 11. The upper end of the vertical portion 42 opens upward and connects to the upstream duct member 30. The bent portion 43 connects the horizontal portion 41 and the vertical portion 42. The bent portion 43 changes the direction of the cooling air flowing through the vertical portion 42 from the vertical direction to the horizontal direction, and guides the cooling air to the horizontal portion 41.

[0030] Here, the horizontal flow passage 410 formed inside the horizontal portion 41 of the flow passages formed inside the downstream duct member 40 will be described with reference to Fig. 5. Fig. 5 is a cross-sectional view taken along the line AA in Fig. 4.

[0031] The horizontal flow path 410 extends horizontally above the fan 12. The horizontal flow path 410 is defined by an upright wall portion 411 extending vertically and a horizontal wall portion 412 extending horizontally. The horizontal wall portion 412 is connected to the upper and lower ends of the upright wall portion 411 and extends horizontally.

[0032] Moreover, the horizontal flow passage 410 is divided into a plurality of passages in a direction perpendicular to the flow direction (front-rear direction in this embodiment). In this embodiment, the horizontal flow passage 410 is divided into three passages, and each horizontal flow passage 410 is also formed by a vertical wall portion 411 and a horizontal wall portion 412. In other words, the vertical wall portion 411 is provided between adjacent horizontal flow passages 410, and the rigidity of the downstream duct member 40 against a load input from the vertical direction is improved. The three horizontal flow passages 410 extend in the left-right direction and join together in the vicinity of the fan connection portion 40a.

[0033] The vertical wall portion 411 that defines each horizontal flow path 410 will be described in detail. The upper member 40A is provided with two upper recesses 41A recessed toward the lower member 40B, and the lower member 40B is provided with two lower recesses 41B recessed toward the upper member 40A and abutting the upper recesses 41A. The upper recesses 41A and the lower recesses 41B have vertical wall portions 411 that define each horizontal flow path 410. The number of upper recesses 41A and the number of lower recesses 41B are determined according to the number of divided horizontal flow paths 410. For example, when the horizontal flow path 410 is divided into two, the number of upper recesses 41A and the number of lower recesses 41B are one each.

[0034] The downstream duct member 40 is made of nonwoven fabric. Specifically, a sheet-like nonwoven fabric is pressed to form an upper member 40A and a lower member 40B, and the upper member 40A and the lower member 40B are joined to form the downstream duct member 40. Nonwoven fabric has excellent sound absorbing properties and absorbs acoustic energy of the driving sound generated when the fan 12 is driven and the fluid sound generated when the cooling air flows. By forming the downstream duct member 40 communicating with the fan 12 from nonwoven fabric, the driving sound of the fan 12 can be absorbed and the driving sound leaking from the intake port 17a into the vehicle interior through the intake duct 13 can be reduced.

[0035] On the other hand, nonwoven fabric has low rigidity and is easily deformed compared to resin, metal, etc. In this embodiment, the downstream duct member 40 is disposed sandwiched between the junction board 16 and the base plate 171 in the vertical direction. When a vertical load is input to the downstream duct member 40 from the junction board 16 and the base plate 171, the downstream duct member 40 may deform. Therefore, it is preferable that the downstream duct member 40 has a configuration that is not easily deformed by a load input from the vertical direction, that is, a configuration with high rigidity.

[0036] Fig. 6 is a graph showing the relationship between the thickness of a member made of nonwoven fabric (hereinafter also referred to as a nonwoven fabric member) and the compression and tensile stiffness. Here, the thickness of the nonwoven fabric member changes when the nonwoven fabric member is compressed by press processing or the like. When the thickness of the nonwoven fabric member is small, the nonwoven fabric member is compressed to a high density state, and the compression and tensile stiffness are high. On the other hand, when the thickness of the nonwoven fabric member is large, the nonwoven fabric member is not compressed (or is compressed to a small extent) and is in a low density state, and the compression and tensile stiffness are low.

[0037] 7 is a graph showing the relationship between the thickness and bending rigidity of a nonwoven fabric member. When the thickness of a nonwoven fabric member is small, the bending rigidity of the nonwoven fabric member is low, but as the thickness increases, the bending rigidity of the nonwoven fabric member increases.

[0038] Returning to FIG. 5, in this embodiment, among the walls that define the horizontal flow path 410, the thickness t1 of the vertical wall portion 411 extending in the vertical direction is smaller than the thickness t2 of the horizontal wall portion 412 extending in the horizontal direction. In FIG. 5, the thickness of the rearmost vertical wall portion 411 of the lower member 40B is given the symbol t1, and the thickness of the horizontal wall portion 412 of the lower member 40B is given the symbol t2. However, even if the thicknesses of the other vertical wall portions 411 that define each horizontal flow path 410 are given the symbol t1, and the thickness of the horizontal wall portion 412 of the upper member 40A is given the symbol t2, the thickness t1 of the vertical wall portion 411 is smaller than the thickness t2 of the horizontal wall portion 412. For example, the thickness t2 of the horizontal wall portion 412 is about 2 to 4 times the thickness t1 of the vertical wall portion 411.

[0039] Specifically, when the downstream duct member 40 is formed from nonwoven fabric, pressing or the like is performed so that the compression ratio is locally increased in the portion corresponding to the vertical wall portion 411. Since the thickness t1 of the vertical wall portion 411 is smaller than the thickness t2 of the horizontal wall portion 412, the compression and tensile rigidity of the vertical wall portion 411 is higher than that of the horizontal wall portion 412. Therefore, the vertical wall portion 411 is less likely to be compressed even when a load is input from the vertical direction, and the intake duct 13 is less likely to be crushed.

[0040] Conversely, since thickness t2 of horizontal wall portion 412 is greater than thickness t1 of standing wall portion 411, horizontal wall portion 412 has a higher bending rigidity than standing wall portion 411. Therefore, horizontal wall portion 412 is less likely to bend even when a load is input from the vertical direction, and intake duct 13 is less likely to bend.

[0041] As described above, during molding, the portion of the nonwoven fabric material corresponding to the standing wall portion 411 is compressed to reduce the thickness, so that the downstream duct member 40 is configured so that the density of the nonwoven fabric in the standing wall portion 411 is higher than the density of the nonwoven fabric in the horizontal wall portion 412. In this way, by increasing the density of the nonwoven fabric in the standing wall portion 411 by compression, the thickness of the standing wall portion 411 can be made smaller than the thickness of the horizontal wall portion 412.

[0042] Returning to Figs. 3 and 4, three fixing portions 13a are provided on the abutting portion 44 at the outer edge of the upper member 40A and the lower member 40B of the downstream duct member 40. The fixing portions 13a have insertion holes through which fastening means such as a pin-shaped clip (not shown) can be inserted. The downstream duct member 40 is fixed to the base plate 171 by inserting a clip between the fixing portions 13a and a fixing portion (not shown) provided on the base plate 171. The fastening means may be a bolt or the like. Furthermore, the fixing of the downstream duct member 40 to the base plate 171 is not limited to these, and any fixing method can be adopted.

[0043] Fig. 8 is a schematic diagram of the fixing portion 13a provided with the portion B in Fig. 4, viewed from the horizontal direction. As shown in Fig. 8, the thickness of the fixing portion 13a is smaller than the thickness of the abutting portion 44 excluding the fixing portion 13a. The abutting portions 44 of the upper member 40A and the lower member 40B locally reduce the thickness of the fixing portion 13a, making it easier to fix the downstream duct member 40 to the base plate 171 with a clip or the like. In addition, the abutting portions 44 excluding the fixing portion 13a have a large thickness, so that the bending rigidity of the abutting portions 44 is high, and it is possible to configure the abutting portions 44 to be less likely to bend under a load input from the vertical direction.

[0044] Incidentally, since the thickness of the horizontal wall portion 412 of the downstream duct member 40 is large, the sound absorbing performance of the horizontal wall portion 412 is high. In particular, since the driving sound of the fan 12 first travels from the bottom to the top of the downstream duct member 40, the sound absorbing performance of the downstream duct member 40 can be improved by increasing the thickness of the horizontal wall portion 412 of the upper member 40A of the downstream duct member 40.

[0045] As described above, according to the downstream duct member 40 of this embodiment, it is possible to improve the sound absorbing performance and to provide a structure with high rigidity against a load input from the outside.

[0046] Although one embodiment of the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such an embodiment. It is clear that a person skilled in the art can come up with various modified or revised examples within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present invention. In addition, the components in the above embodiment may be arbitrarily combined within the scope of the invention.

[0047] For example, in the above-described embodiment, the horizontal flow path 410 is divided into a plurality of parts, but it does not have to be divided. That is, the upper recess 41A and the lower recess 41B do not have to be provided.

[0048] This specification describes at least the following items. In parentheses, components corresponding to the above-described embodiments are shown as examples, but the present invention is not limited to these.

[0049] (1) A duct structure (intake duct 13) is provided inside a battery pack (battery pack 1) mounted on a vehicle (vehicle V) and connects an intake port (intake port 17a) of the battery pack to a fan (fan 12) that blows cooling air to a battery (battery module 11), The downstream duct member 40 is made of a nonwoven fabric. The duct member has a flow passage (horizontal flow passage 410) disposed above the fan and extending horizontally, Among the walls that define the flow path extending in the horizontal direction, a thickness of a first wall portion (standing wall portion 411) extending in the vertical direction is smaller than a thickness of a second wall portion (horizontal wall portion 412) extending in the horizontal direction. Duct structure.

[0050] The compressive and tensile rigidity of a member formed from nonwoven fabric increases as the thickness decreases, and the bending rigidity decreases as the thickness increases. According to (1), since the thickness of the first wall portion extending in the vertical direction is smaller than the thickness of the second wall portion extending in the horizontal direction, the compressive and tensile rigidity of the first wall portion increases, resulting in a duct structure that is less likely to be compressed by a load input from the vertical direction. Furthermore, since the thickness of the second wall portion is greater than the thickness of the first wall portion, the bending rigidity of the second wall portion increases, resulting in a duct structure that is less likely to bend by a load input from the vertical direction.

[0051] (2) A duct structure according to (1), The duct member is configured such that the density of the nonwoven fabric in the first wall portion is higher than the density of the nonwoven fabric in the second wall portion. Duct structure.

[0052] According to (2), by increasing the density of the nonwoven fabric in the first wall portion by compression compared to the density of the nonwoven fabric in the second wall portion, the thickness of the first wall portion can be made smaller than the thickness of the second wall portion.

[0053] (3) A duct structure according to (1) or (2), The duct member includes an upper member (upper member 40A) and a lower member (lower member 40B), The upper member and the lower member have outer edges that abut against each other, and the flow path is defined and formed between the upper member and the lower member, The abutment portion (abutment portion 44) of the upper member and the lower member has a fixing portion (fixing portion 13a) that is fixed to another member (base plate 171) by a fastening means, The thickness of the fixing portion is smaller than the thickness of the contact portion excluding the fixing portion. Duct structure.

[0054] According to (3), since the fixing portion is thinner than the other portions, fixing by the fastening means is easy. Meanwhile, since the thickness of the contact portion excluding the fixing portion is thicker than the fixing portion, the bending rigidity of the contact portion is increased, and the structure can be made such that the contact portion is less likely to bend when subjected to a load input from the vertical direction.

[0055] (4) A duct structure according to (1) or (2), The flow path is divided into a plurality of paths in a direction perpendicular to the flow direction, Among the walls that define each flow path, the thickness of the first wall portion that extends in the vertical direction is smaller than the thickness of the second wall portion that extends in the horizontal direction. Duct structure.

[0056] According to (4), since the flow path is divided into a plurality of flow paths, a plurality of first walls are also provided to define each flow path. By making the thickness of each first wall smaller than that of the second wall, the compressive and tensile rigidity of each first wall can be increased, resulting in a duct structure that is less likely to be compressed by a load input from the vertical direction.

[0057] (5) The duct structure according to (4), The duct member includes an upper member (upper member 40A) and a lower member (lower member 40B), The upper member and the lower member are in contact with each other at their outer edges, and each flow path is defined and formed between the upper member and the lower member, The upper member is provided with at least one upper recess (upper recess 41A) recessed toward the lower member, The lower member is provided with at least one lower recess (lower recess 41B) that is recessed toward the upper member and abuts against the upper recess, The upper recess and the lower recess have the first wall portion that defines each flow path. Duct structure.

[0058] According to (5), each flow path of the duct member can be formed by abutting an upper recess and a lower recess provided in an upper member and a lower member, respectively. The upper recess and the lower recess have a first wall portion that is thinner than a second wall portion extending in a horizontal direction, so that the duct structure is unlikely to be compressed by a load input from a vertical direction. [Explanation of symbols]

[0059] 1 Battery pack 11 Battery module (battery) 12 Fan 13 Intake duct (duct structure) 13a Fixed part 17a Air intake 171 Base plate (other parts) 40 Downstream duct component (duct component) 40A Upper member 40B Lower part 41A Upper recess 41B Lower recess 44 Contact part 410 Horizontal Channel (Channel) 411 Vertical wall section (first wall section) 412 Horizontal wall (second wall) V Vehicle

Claims

1. A duct structure provided inside a battery pack mounted on a vehicle, connecting an intake port of the battery pack and a fan that blows cooling air to the battery, A duct member formed of a nonwoven fabric, the duct member is disposed above the fan and has a flow passage extending in a horizontal direction, Among the walls that define the flow path extending in the horizontal direction, a thickness of a first wall portion extending in a vertical direction is made smaller by compression than a thickness of a second wall portion extending in the horizontal direction. Duct structure.

2. The duct structure according to claim 1, The duct member is configured such that a density of the nonwoven fabric in the first wall portion is higher than a density of the nonwoven fabric in the second wall portion. Duct structure.

3. The duct structure according to claim 1 or 2, The duct member includes an upper member and a lower member, The upper member and the lower member have outer edges that abut against each other, and the flow path is defined and formed between the upper member and the lower member, the abutment portions of the upper member and the lower member have fixing portions that are fixed to other members by fastening means; The thickness of the fixing portion is smaller than the thickness of the contact portion excluding the fixing portion. Duct structure.

4. The duct structure according to claim 1 or 2, The flow path is divided into a plurality of paths in a direction perpendicular to the flow direction, Among the wall portions that define each flow path, a thickness of the first wall portion extending in a vertical direction is made smaller than a thickness of the second wall portion extending in the horizontal direction by compression. Duct structure.

5. The duct structure according to claim 4, The duct member includes an upper member and a lower member, The upper member and the lower member are in contact with each other at their outer edges, and each flow path is defined and formed between the upper member and the lower member, The upper member is provided with at least one upper recess recessed toward the lower member, The lower member is provided with at least one lower recess that is recessed toward the upper member and abuts against the upper recess, The upper recess and the lower recess have the first wall portion that defines each flow path by compression. Duct structure.

6. A duct structure according to claim 1 or 2, The thickness of the second wall portion is 2 to 4 times greater than the thickness of the first wall portion; Duct structure.

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