EXHAUST GAS CONTROL DEVICE

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2024-197087 filed on Nov. 12, 2024. The disclosure of the above-identified application, including the specification, drawings, and claims, is incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a device that controls exhaust gas by supporting a catalyst on a substrate and causing the exhaust gas to flow along the substrate, and more particularly, to a structure of a substrate that carries a catalyst.

2. Description of Related Art

Exhaust gas generated by internal combustion engines of vehicles contains pollutants such as carbon monoxide (CO) and hydrocarbons (HC). Catalytic converters are installed in exhaust systems of internal combustion engines to oxidize or reduce these pollutants, thereby making them harmless. To control exhaust gas using a catalyst, it is necessary to actively bring the exhaust gas into contact with the catalyst. Hitherto, various structures for this purpose have been proposed.

Japanese Unexamined Patent Application Publication No. 11-290699 (JP 11-290699 A) discloses a honeycomb catalyst for flue gas denitration. The honeycomb catalyst is mainly composed of a honeycomb structure supporting a catalyst, and a large number of holes formed inside the honeycomb structure serve as gas channels. When the gas channel is long, a boundary film grows along the inner surface of the hole to increase the diffusion resistance of the exhaust gas over the catalyst. In the honeycomb catalyst described in JP 11-290699 A, a large number of cutouts are provided across the gas channel with mutual intervals of 300 mm or less.

Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-511699 (JP 2007-511699 A) discloses an exhaust gas control converter for an internal combustion engine that uses a panel made of metal fibers supporting a catalyst. In the exhaust gas control converter disclosed in JP 2007-511699 A, a metal sheet is sandwiched between the panels to form a single stack, and a plurality of stacks is layered and housed in a housing. In each stack, exhaust gas flows between the panels and also through the panels to come into contact with the catalyst. Thus, the exhaust gas is controlled. To secure a channel for such exhaust gas, the metal sheet is provided with wings protruding from one surface thereof. The wing is a bent piece obtained by cutting part of the metal sheet, for example, at three sides of a rectangle. The wing is bent at the remaining side out of the four sides of the rectangle to protrude from one surface of the metal sheet. The rectangular portion has a hole.

SUMMARY

In an exhaust gas control device, the temperature of exhaust gas to be treated is high. In addition, oxidation and reduction reactions occur for pollutants in the exhaust gas. Therefore, heat generated by the reactions may cause an increase in temperature. When the device is mounted on a vehicle, the device may vibrate significantly while the vehicle is traveling. The exhaust gas control device is inevitably subjected to such thermal stress and external force. For example, in the configuration disclosed in JP 11-290699 A, the honeycomb structure is interrupted at the slits, and the strength of these portions is low. As a result, the honeycomb structure is deformed or displaced due to the thermal stress or vibration, thereby causing frictional contact or collision between the honeycomb structures. Furthermore, the honeycomb structures may be damaged.

In the exhaust gas control converter described in JP 2007-511699 A, exhaust gas flows across the panels each made of metal fibers supporting the catalyst, and the exhaust gas comes into contact with the catalyst. Thus, the exhaust gas is controlled. Since the panels are disposed parallel to the exhaust gas flow direction, it is desirable to disperse the exhaust gas over the entire surfaces of the panels. For this purpose, the metal sheet is disposed between the panels, and the wings are provided to function as spacers. That is, the metal sheet in the exhaust gas control converter described in JP 2007-511699 A is a member for securing the distance between the panels, and does not particularly function to control the exhaust gas. Therefore, the exhaust gas control converter disclosed in JP 2007-511699 A has a large number of components. Thus, the size of the overall device configuration may increase. In particular, the number of metal sheets increases along with an increase in the number of stacks, thereby causing an increase in weight and furthermore an increase in costs.

The present disclosure has been made in view of the above technical issues, and has an object to provide an exhaust gas control device in which the number of required components can be reduced, the strength is excellent, and the exhaust gas control efficiency can be improved by sufficiently securing an exhaust gas channel.

In order to achieve the above object, the present disclosure provides an exhaust gas control device configured to control exhaust gas generated by combustion by causing the exhaust gas to flow along a metal sheet that is a substrate supporting catalysts. The exhaust gas control device includes: protrusions each serving as a gas channel and protruding such that a strip piece defined by two front and rear cut portions in a longitudinal direction of the metal sheet in which the exhaust gas flows is bent or curved to a front surface side that is one surface side of the metal sheet; and recesses each serving as a gas channel and receding such that another strip piece defined by two other front and rear cut portions in the longitudinal direction of the metal sheet in which the exhaust gas flows is bent or curved to a back surface side that is the other surface side of the metal sheet. A portion defined by the cut portions is a through hole. The protrusions and the recesses are alternately arranged in at least one of the longitudinal direction and a lateral direction perpendicular to the longitudinal direction via predetermined flat connecting portions. A plurality of the metal sheets with the catalysts attached to the front surface side including the protrusions and the back surface side including the recesses is stacked such that the protrusions are offset from each other in the lateral direction and the recesses are offset from each other in the lateral direction. The metal sheets adjacent to each other in a stacking direction are joined and connected at least by the flat connecting portions.

In the present disclosure, a top surface of each of the protrusions may be joined to the flat connecting portion of another of the metal sheets that is located upward in the stacking direction, and a bottom surface of each of the recesses may be joined to the flat connecting portion of still another of the metal sheets that is located downward in the stacking direction.

In the present disclosure, the protrusions and the recesses of the metal sheet may be alternately arranged in the lateral direction, and the protrusions and the recesses may be alternately arranged in the longitudinal direction and offset from each other in the lateral direction.

In the present disclosure, the protrusions of the metal sheet may be arranged in a plurality of rows in the lateral direction, and the recesses may be arranged in the lateral direction between the rows of the protrusions.

In the present disclosure, a length of the flat connecting portion in the longitudinal direction may be a predetermined length with an upper limit that is a length Le determined by the following expression, and a length of each of the protrusions and the recesses in the longitudinal direction may be a predetermined length with an upper limit that is half the length Le determined by the following expression:

Le = { dH / 9.28 × √ ( ρ · u / μ ) } 2

• • where dH is a hydraulic diameter expressed in units of meter, ρ is a gas density expressed in units of kg/m³, u is a gas flow rate expressed in units of m/s, and μ is a gas viscosity expressed in units of Pas.

In the present disclosure, the metal sheet that is the substrate supports the catalysts. Therefore, the exhaust gas is controlled by coming into contact with the catalysts while flowing along the front and back surfaces of the metal sheet. In particular, the recesses and the protrusions serve as the gas channels that pass through the recesses and the protrusions in the longitudinal direction in which the exhaust gas flows. The protrusions and the recesses are arranged in the longitudinal direction in which the exhaust gas flows, and are offset from each other in the lateral direction. Therefore, the gas channels are interrupted at the points where they are offset in the lateral direction. That is, each gas channel is a short channel corresponding to the distance between the two cut portions that define the protrusion or recess, or the width of the strip piece. Therefore, the channel can be made less susceptible to the influence of boundary film diffusion resistance, and the exhaust gas control efficiency can be improved. Since the metal sheets supporting the catalysts are stacked, the strength in the stacking direction can be secured. Since the stacked metal sheets are fixed inside a predetermined housing or casing, the strength in the lateral direction can be secured. Since the protrusions or recesses arranged in the longitudinal direction are offset relatively in the lateral direction, the protrusions or recesses are engaged in the longitudinal direction to prevent movement of the metal sheets. Thus, the strength in the longitudinal direction can be secured. As a result, it is possible to avoid or suppress abnormalities such as damage to the metal sheets supporting the catalysts even if the metal sheets are subjected to thermal deformation or external force caused by vibration. The flat connecting portions are provided between the protrusions and the recesses, and the stacked metal sheets are connected together by joining the top surfaces of the protrusions or the bottom surfaces of the recesses to the connecting portions. Therefore, the metal sheets for forming the channels also function to join the metal sheets together. Thus, the number and types of required components can be reduced to simplify the configuration, reduce the weight, and also reduce the costs.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

FIG. 1 is a schematic sectional view of an exhaust gas control device according to an embodiment of the present disclosure, with a housing cut away to show the internal structure of the exhaust gas control device;

FIG. 2 is an enlarged sectional view of part of a metal sheet;

FIG. 3 is a perspective view showing part of the metal sheet;

FIG. 4 is an end view of the metal sheet cut along a plane in a lateral direction;

FIG. 5 is an end view taken along line V-V in FIG. 3;

FIG. 6 is an end view showing the shape of an end face when two metal sheets are stacked and cut along a plane in the lateral direction;

FIG. 7 is a sectional view showing the end face when the two metal sheets are stacked and cut along the plane in the lateral direction, and other protrusions and recesses arranged in a longitudinal direction;

FIG. 8 is an end view similar to FIG. 6, showing another stacking form of the metal sheets; and

FIG. 9 is a perspective view showing another array pattern of the protrusions and recesses on the metal sheet.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the present disclosure will be described with reference to the accompanying drawings. The embodiment described below is merely one example of the case where the present disclosure is carried out, and is not intended to limit the present disclosure.

FIG. 1 shows an example of the embodiment of the present disclosure. FIG. 1 is a schematic sectional view of an exhaust gas control device 1, with a housing 2 cut away to show the internal structure of the exhaust gas control device 1. The housing 2 includes tapered portions 4, 5 integrally provided forward and rearward of a cylindrical portion 3, an inlet pipe 6 provided to the one tapered portion 4, and an outlet pipe 7 provided to the other tapered portion 5. The exhaust gas control device 1 is used by being incorporated into an exhaust system of an internal combustion engine (not shown). Exhaust gas G generated by combustion is introduced through the inlet pipe 6, controlled, and discharged through the outlet pipe 7 toward a filter (not shown) etc.

A catalyst unit 8 is housed inside the cylindrical portion 3. The catalyst unit 8 includes a plurality of stacked metal sheets 9. The metal sheets 9 are fastened to each other and fixed to the inner surface of the cylindrical portion 3. As shown in a partially enlarged view of FIG. 2, the metal sheet 9 supports catalysts 10 on both front and back surfaces, and serves as a so-called catalyst substrate. In the following description, the metal sheet 9 may be referred to as “catalyst.”

The metal sheet 9 includes a large number of protrusions 11 and recesses 12 that define gas channels P through which the exhaust gas G flows. In the following description, a portion protruding upward in the drawing is referred to as “protrusion 11” and a portion receding downward is referred to as “recess 12.” An upper surface in the drawing is referred to as “front surface” of the metal sheet 9 and a lower surface is referred to as “back surface” of the metal sheet 9. The metal sheet 9 including the protrusions 11 and the recesses 12 is shown in FIGS. 3 to 5. FIG. 3 is a perspective view showing part of the metal sheet 9. A direction shown by arrows is a direction in which the exhaust gas G flows, and this direction is referred to as “longitudinal direction.” Therefore, a direction perpendicular to the longitudinal direction on the surface of the metal sheet 9 is referred to as “lateral direction.” FIG. 4 is an end view taken along a plane in the lateral direction. FIG. 5 is an end view taken along a plane in the longitudinal direction.

In the metal sheet 9 shown in FIGS. 3 to 5, the protrusions 11 and the recesses 12 are alternately formed side by side in the lateral direction. A predetermined distance is set between the protrusion 11 and the recess 12, and a portion therebetween is a flat connecting portion 13. Although the protrusions 11 and the recesses 12 are arranged in the longitudinal direction, they are relatively offset from each other in the lateral direction. The protrusions 11 and the recesses 12 are offset in any way. In the example shown in FIGS. 3 to 5, the protrusion 11 and the recess 12 adjacent to each other in the longitudinal direction are offset so as not to overlap each other in the longitudinal direction. More specifically, the protrusion 11 and the recess 12 are offset by the length of each of the protrusion 11 and the recess 12 in the lateral direction.

The lengths of the protrusion 11 and the recess 12 in the longitudinal direction will be described. The protrusion 11 and the recess 12 are portions serving as the gas channels P as described later. Similarly, part of the connecting portion 13 also serves as the gas channel. The length of the gas channel P may be set as appropriate based on, for example, pressure loss and efficiency of control on the exhaust gas G. The lengths of the protrusion 11 and the recess 12 in the longitudinal direction can be set in consideration of boundary film diffusion resistance. A boundary film in the gas channel starts to grow at a position that is a predetermined distance from the inlet of the gas channel. The thickness of the boundary film eventually reaches half the bore diameter or the channel width of the gas channel. Thus, the boundary film significantly impedes the diffusion of gas toward the inner surface of the gas channel. A length Le from the inlet to the point where the thickness of the boundary film reaches half the bore diameter or the channel width of the gas channel is given by the following expression.

Le =   ( dH 2 × 4.64 ⁢ ρ ⁢ u μ ) 2 Expression ⁢ 1

In Expression 1, dH is a hydraulic diameter (m), ρ is a gas density (kg/m³), u is a gas flow rate (m/s), and μ is a gas viscosity (Pas).

As described above, the protrusion 11 and the recess 12 are arranged in the longitudinal direction. Therefore, the longest portion of the above flat connecting portion 13 in the longitudinal direction has a length obtained by combining the length of the protrusion 11 and the length of the recess 12 in the longitudinal direction, that is, twice the length of the protrusion 11 or the recess 12 in the longitudinal direction. In consideration that the longest portion of the connecting portion 13 also serves as the gas channel, the length of this portion is set to the length Le obtained by the above expression, and accordingly, a length L of each of the protrusion 11 and the recess 12 in the longitudinal direction is set to “Le/2.”

Although there is no particular limitation, the protrusions 11 and the recesses 12 are formed by deforming part of the metal sheet 9. For example, two cut portions 14 parallel to each other and extending in the lateral direction are provided on the metal sheet 9. A strip piece 15 between the cut portions 14 is caused to protrude to the front side of the metal sheet 9 to form the protrusion 11, and is caused to recede toward the back side to form the recess 12. As a result, the portion from which the strip piece 15 has come out is a through hole 16. The shapes of the protrusion 11 and the recess 12 may be any shapes in which the channel is formed through the protrusion 11 and the recess 12 in the longitudinal direction, and may be set as appropriate depending on need. In the example shown in FIGS. 3 to 5, the protrusion 11 and the recess 12 have the same shape except for the difference in their up and down orientations. The shape is an isosceles trapezoid shape in which the length of the upper base is half the length of the lower base and the upper base and the right and left legs have equal lengths. When the protrusions 11 and the recesses 12 vertically overlapping each other are viewed in the longitudinal direction, the protrusions 11 and the recesses 12 appear to form a regular hexagon.

The gas channels P through which the exhaust gas G flows are formed by stacking the metal sheets 9 such that the protrusions 11 and the recesses 12 cooperate with the other upper or lower metal sheet 9. In other words, the metal sheets 9 are stacked with the positions of the protrusions 11 and the recesses 12 shifted such that each of the protrusions 11 and the recesses 12 forms the gas channel P. That is, the relative positions of the metal sheets 9 are shifted such that the protrusions 11 and the recesses 12 of the upper and lower metal sheets 9 are not fitted together. In the illustrated example, each of the protrusions 11 and the recesses 12 has the isosceles trapezoid shape that corresponds to half of the regular hexagon. Therefore, the metal sheets 9 are stacked such that the protrusion 11 and the recess 12 at the top and bottom (top and bottom in the stacking direction of the metal sheets 9) are in consecutive positions and cooperatively form the regular hexagon (or a regular hexagon with one side missing).

An example of the stacked state is shown in FIG. 6. FIG. 6 is an end view showing the shape of an end face when two metal sheets 9 are stacked and cut along a plane in the lateral direction. In FIG. 6, the other protrusions 11 and recesses 12 arranged in the longitudinal direction are omitted. In the example shown in FIG. 6, the protrusions 11 and the recesses 12 are adjacent to each other in the lateral direction and are consecutive vertically.

More specifically, the edge on the lower base side of the upper protrusion 11 coincides with the edge on the upper base side (top surface 11a) of the lower protrusion 11. Therefore, the slope corresponding to one leg of the trapezoid in the lower protrusion 11 and the flat connecting portion 13 connected to the slope form a regular hexagon together with the upper protrusion 11. The regular hexagon has one open side as shown by the dashed lines in FIG. 6.

Similarly, the edge on the bottom side of the upper recess 12 coincides with the edge on the opening side (through hole 16 side) of the lower recess 12. Therefore, the slope corresponding to one leg of the trapezoid in the upper recess 12 and the flat connecting portion 13 connected to the slope form a regular hexagon together with the lower recess 12. The regular hexagon has one open side. The two channels each having the regular hexagonal shape with one open side are connected by the channel formed by the upper and lower connecting portions 13 between them, thereby forming a unit as a channel. That is, this is a compartment that may be referred to as “unit cell.” By setting the channel length of the unit cell to be equal to or less than “Le/2” as described above, the influence of the diffusion resistance due to the boundary film can be suppressed. In this case, the hydraulic diameter that determines the channel length may be a diameter obtained based on the sectional area of the channel formed by the two regular hexagons with open sides and the channel formed by the upper and lower connecting portions 13 between them, and the length of the contour (perimeter) that determines the sectional shape of the channel, that is, the “wetted perimeter length.”

As described above, the protrusions 11 and the recesses 12 are connected vertically to form the gas channels P each having a predetermined opening shape (sectional shape). Therefore, the top surface 11a of the protrusion 11 (upper base of the trapezoid) comes into contact with the connecting portion 13 of the upper metal sheet 9, and the two portions are joined at this point. Similarly, the bottom surface of the recess 12 (lower base of the inverted trapezoid) comes into contact with the connecting portion 13 of the lower metal sheet 9, and the two portions are joined at this point. Therefore, the area over which the stacked metal sheets 9 are joined increases sufficiently, and the number of joining points is large. Thus, the metal sheets 9 can firmly be joined together, thereby increasing the strength of the catalyst unit 8 or the exhaust gas control device 1 in the stacking direction.

As described above, the protrusions 11 and the recesses 12 that form the gas channels P are arranged alternately in the longitudinal direction of the metal sheet 9 and are offset from each other in the lateral direction. The metal sheets 9 are stacked such that the protrusions 11 and the recesses 12 are not arranged in a straight line in the longitudinal direction. Therefore, when the stacked metal sheets 9 are cut along a plane in the lateral direction and viewed in the longitudinal direction, the shape of the cut end face is as shown in FIG. 6. Since the other protrusions 11 and recesses 12 are arranged in the longitudinal direction from the end face and form the gas channels P, the sectional shape shows the other protrusions 11 and recesses 12 arranged in the longitudinal direction. Part of the sectional shape is shown in FIG. 7. In FIG. 7, the hatched portion is the cut end face, and the non-hatched portions are the end faces of the protrusions 11 and the recesses 12 that are spaced away from the cut end face in the longitudinal direction. Therefore, the protrusions 11 and the recesses 12 of the stacked metal sheets 9 partially overlap each other in the longitudinal direction. Since the overlapping portions are engaged in the longitudinal direction, the metal sheets 9 mutually prevent movement of the metal sheets 9 in the longitudinal direction. As a result, the strength of the metal sheet 9 or the catalyst unit 8 in the longitudinal direction is increased.

The flat connecting portion 13 functions to form or separate the gas channels above and below, and also functions to join the metal sheets 9 together at a predetermined distance. Since the exhaust gas control device 1 or the catalyst unit 8 is formed using the metal sheets 9 having the same uneven shape as the components, the number or types of components can be reduced to simplify the configuration, manufacturing, and assembling.

By stacking the metal sheets 9, the protrusions 11 and the recesses 12 form the gas channels P, and the exhaust gas G introduced through the inlet pipe 6 flows through the gas channels P. An example of how the exhaust gas G flows is shown by arrows in FIG. 3. For example, the gas channel P is formed by one inclined surface (leg of the trapezoid) of the upper protrusion 11 and the lower recess 12 separated across the through hole 16 and the connecting portion 13. Since the gas channel P is interrupted at the length of the protrusion 11 or the recess 12 in the longitudinal direction, the exhaust gas enters the next gas channel. In this case, the flat connecting portion 13 is present at the outlet of each gas channel P. Therefore, the exhaust gas separately flows up and down. The protrusions 11 and the recesses 12 arranged in the longitudinal direction are offset relatively in the lateral direction. Therefore, a vertical wall of another gas channel (portion corresponding to the leg of the trapezoid) is present at the outlet of each gas channel P. Thus, the exhaust gas separately flows right and left.

In this way, the exhaust gas flows in the longitudinal direction while entering and exiting the short gas channels and merging and diverging. During this process, the exhaust gas comes into contact with the catalysts 10 attached to the surfaces of the protrusions 11 and the recesses 12, and the pollutants are oxidized or reduced via the catalysts 10. Thus, the exhaust gas is controlled. As described above, the length of each of the protrusion 11 and the recess 12 in the longitudinal direction is small in consideration of the generation of the boundary film. Therefore, the boundary film diffusion resistance in each gas channel P is small, and the catalytic reaction, that is, the control on the exhaust gas, can be performed efficiently.

Other embodiments of the present disclosure will be described. In the embodiment of the present disclosure, the gas channels P formed by the protrusions 11 and the recesses 12 are not arranged in a straight line in the longitudinal direction in which the exhaust gas flows, but are offset from each other in the lateral direction. Therefore, each gas channel P is interrupted at the length of the protrusion 11 or the recess 12. Such a configuration can be achieved by stacking the metal sheets 9 in a different way from that shown in FIG. 6.

FIG. 8 is an end view similar to FIG. 6, showing another stacking form of the metal sheets 9. In this example, one inclined surface (leg of the trapezoid) forming the recess 12 of the upper metal sheet 9 is brought into close contact with one parallel inclined surface (leg of the trapezoid) forming the protrusion 11 of the lower metal sheet 9, and the top surface 11a of the protrusion 11 and a bottom surface 12a of the recess 12 are brought into close contact with the connecting portions 13 of the mating metal sheets 9. Thus, the metal sheets 9 are joined at least at the connecting portions 13. In the example shown in FIG. 8, the spaces between the metal sheets 9 serve as the gas channels. In particular, as shown by dashed lines in FIG. 8, the gas channels each having a hexagonal sectional shape are formed below the protrusions 11 or above the recesses 12.

The protrusions 11 and the recesses 12 in the embodiment of the present disclosure may be arrayed in a different pattern from that shown in FIGS. 3 to 5. FIG. 9 shows an example in which the protrusions 11 and the recesses 12 are arrayed in a straight line with predetermined intervals in the lateral direction. The pitch of the protrusions 11 and the recesses 12 in the lateral direction is, for example, the length of each of the protrusions 11 and the recesses 12 in the lateral direction. In the longitudinal direction, the protrusions 11 and the recesses 12 are adjacent to each other, and are arrayed alternately. The protrusion 11 and the recess 12 adjacent to each other are offset by half the pitch in the lateral direction. In this configuration, the metal sheets 9 are stacked and joined by the connecting portions 13 such that the upper protrusions 11 cover the lower recesses 12. Thus, the gas channels P passing through the protrusions 11 and the recesses 12 in the longitudinal direction are formed by the protrusions 11 and the recesses 12. The gas channels P are offset by half the pitch in the lateral direction. Thus, the exhaust gas flows while being separated in the vertical direction and the lateral direction every time it enters and exits the gas channels. That is, each gas channel is interrupted before the thickness of the boundary film reaches half the bore diameter of the gas channel. Therefore, an increase in boundary film diffusion resistance can be suppressed.

The protrusions 11 and the recesses 12 of the metal sheet 9 can be formed by, for example, pressing. In this case, the shapes of the protrusions 11 and the recesses 12 can be set as appropriate depending on the shape of a mold. In the above embodiment, the opening shape (or the sectional shape) of each of the protrusion 11 and the recess 12 is the isosceles trapezoid shape. Instead, the shape may be an isosceles triangle shape, a rectangular shape, a semicircular arc shape, a semi-elliptical arc shape, etc. In the case of an isosceles triangle shape, the opening shape of the gas channel formed by the protrusion 11 and the recess 12 is a rhombus shape. Depending on the height of the triangle, the rhombus becomes a rhombus pointed at the top and bottom, or a rhombus that is wide laterally. In the case of a rectangular shape, the opening shape of the gas channel is a rectangular or square shape. In the case of a semicircular arc shape, the opening shape of the gas channel is a circular shape. In the case of a semi-elliptical arc shape, the opening shape of the gas channel is an elliptical shape.

Since the opening shape of the gas channel P formed by the protrusion 11 and the recess 12 is related to the pressure loss and contactability of the flowing exhaust gas, it is preferable to determine the shapes of the protrusion 11 and the recess 12 in consideration of the required pressure loss, contactability, etc. The term “contactability” refers to the number of times (frequency) of contact of the pollutants contained in the exhaust gas G with the inner surface of the gas channel P or the catalyst 10 per unit time. As a result of investigations conducted by the inventors of the present disclosure, it was found that the pressure loss was smaller and the contactability was higher in the order of rhombus, square, and regular hexagon. It was found that, as for the rhombus, the pressure loss was smaller and the contactability was higher as the ratio of the diagonal lengths was closer to “1.”

The present disclosure is not limited to the above embodiments. The directions such as “longitudinal direction,” “lateral direction,” and “vertical direction” in the above embodiments are directions for the convenience of description based on the drawings. The installation orientation of the metal sheet 9, the catalyst unit 8, or the exhaust gas control device 1 is not limited to the orientation described in the above embodiments. In the above embodiments, the protrusion 11 and the recess 12 have the same shape except that they are inverted upside down. In the present disclosure, the heights or shapes may be different on the front and back sides. In this case, the metal sheets may be stacked such that the surfaces with the protrusions face each other or the surfaces with the recesses face each other. In the exhaust gas control device of the present disclosure, the exhaust gas may flow between the flat connecting portions of the upper and lower stacked metal sheets. Therefore, the portion between the connecting portions also serves as the gas channel.