CATALYST DEVICE

Description

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2024-058338, filed on 30 Mar. 2024, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a catalyst device, and more particularly relates to a catalyst device including a honeycomb core that includes laminated metallic foils supporting a catalyst.

Related Art

Efforts toward mitigating climate change or toward reducing the influence of climate change have continued, and research and development have been conducted to reduce emissions to achieve these objects. Here, a catalyst device that purifies exhaust gas from an internal combustion engine has been known to include a honeycomb core that includes laminated metallic foils supporting a catalyst, such as platinum.

Japanese Patent No. 5199291 discloses a catalyst device including a honeycomb core that includes metallic foils with many through holes for the purpose of reducing the thermal strain phenomena caused by internal temperature variations and the phenomena where the metallic foils are stretched by expansion of the volume of an oxide film formed on the surface of each metallic foil in addition to for the purpose of increasing the surface area of the honeycomb core.

• Patent Document 1: Japanese Patent No. 5199291

SUMMARY OF THE INVENTION

The honeycomb core of Japanese Patent No. 5199291 has a region with the through holes having the same pattern and densely arranged in a grid pattern, and a region without through holes. These regions are in contact with each other. This unfortunately causes the strength of the metallic foils to vary on a boundary region between these regions. Thus, there is a need for devices to maintain the durability of the honeycomb core.

An object of the present invention is to solve the foregoing problem in the known art and to provide a catalyst device that can increase the durability of a honeycomb core while maintaining the performance of purifying exhaust gas. The present invention in turn contributes to mitigation of climate change or reduction in the influence of climate change.

In order to achieve the object, the present invention has the following first feature. Specifically, a catalyst device (30) for purifying exhaust gas (G) by passing the exhaust gas (G) through a honeycomb core (31, 31a, 31b, 31c, 31d) includes: a honeycomb core (31, 31a, 31b, 31c, 31d) including a metallic foil (40) supporting a catalyst and wound. A portion of the metallic foil (40) has a plurality of through holes (H). The honeycomb core (31, 31a, 31b, 31c, 31d) has a dense region (A) where the through holes (H) are densely formed, a zero region (B) where no through hole (H) is formed, and a boundary region (C) between the dense region (A) and the zero region (B) in an axial direction in which the exhaust gas (G) flows. The boundary region (C) is configured such that a total area of the through holes (H) in the boundary region (C) decreases gradually from near the dense region (A) toward the zero region (B).

The present invention has the following second feature. Specifically, the boundary region (C) is only downstream of the dense region (A) along a flow of the exhaust gas (G).

The present invention has the following third feature. Specifically, the boundary region (C) is configured such that a total area of the through holes (H) in the boundary region (C) decreases gradually due to a reduction in the number of the through holes (H) in the boundary region (C).

The present invention has the following fourth feature. Specifically, in the dense region (A), the through holes (H) have an identical diameter, and are equally spaced apart from each other, and the boundary region (C) is configured such that while a layout of the through holes (H) in the dense region (A) is maintained, a total area of the through holes (H) in the boundary region (C) decreases gradually due to a gradual reduction in a diameter of the through holes (H) in the boundary region (C).

The present invention has the following fifth feature. Specifically, in the dense region (A), the through holes (H) have an identical diameter, and are equally spaced apart from each other, the boundary region (C) is configured such that while a layout of the through holes (H) in the dense region (A) is maintained, the total area of the through holes (H) in the boundary region (C) decreases gradually due to a reduction in the number of the through holes (H) in the boundary region (C), and the through holes (H) are not formed around at least one of the through holes (H) closest to the zero region (B).

The present invention further has the following sixth feature. Specifically, the boundary region (C) includes a plurality of boundary regions (C) both upstream and downstream of the dense region (A) along a flow of the exhaust gas (G).

According to the first feature, the catalyst device (30) for purifying the exhaust gas (G) by passing the exhaust gas (G) through the honeycomb core (31, 31a, 31b, 31c, 31d) includes: the honeycomb core (31, 31a, 31b, 31c, 31d) including the metallic foil (40) supporting a catalyst and wound. The portion of the metallic foil (40) has the plurality of through holes (H). The honeycomb core (31, 31a, 31b, 31c, 31d) has

• • the dense region (A) where the through holes (H) are densely formed, the zero region (B) where no through hole (H) is formed, and the boundary region (C) between the dense region (A) and the zero region (B) in the axial direction in which the exhaust gas (G) flows. The boundary region (C) is configured such that a total area of the through holes (H) in the boundary region (C) decreases gradually from near the dense region (A) toward the zero region (B). Thus, the boundary region provided between the dense region and the zero region can keep the strength of a shift region between the dense region and the zero region from being lower than if the dense region and the zero region are in contact with each other, thus enabling an increase in the durability of the honeycomb core.

According to the second feature, the boundary region (C) provided only downstream of the dense region (A) along the flow of the exhaust gas G allows the exhaust gas (G) to diffuse in the dense region (A) to improve the purification efficiency, and can keep the strength of the honeycomb core in the boundary region from decreasing.

According to the third feature, the boundary region (C) is configured such that the total area of the through holes (H) decreases gradually due to a reduction in the number of the through holes (H) in the boundary region (C). Thus, processing pins for forming the through holes in the honeycomb core can be reduced.

According to the fourth feature, in the dense region (A), the through holes (H) have an identical diameter, and are equally spaced apart from each other, and the boundary region (C) is configured such that while a layout of the through holes (H) in the dense region (A) is maintained, a total area of the through holes (H) in the boundary region (C) decreases gradually due to a gradual reduction in a diameter of the through holes (H) in the boundary region (C). Thus, while the diffusion effect caused by the through holes is maintained, the strength of the boundary region of the honeycomb core can be kept from decreasing.

According to the fifth feature, in the dense region (A), the through holes (H) have an identical diameter, and are equally spaced apart from each other, the boundary region (C) is configured such that while the layout of the through holes (H) in the dense region (A) is maintained, the total area of the through holes (H) in the boundary region (C) decreases gradually due to a reduction in the number of the through holes (H) in the boundary region (C), and the through holes (H) are not formed around at least one of the through holes (H) closest to the zero region (B). Thus, not having the through holes formed around the at least one through hole closest to the zero region can keep the strength of the boundary region of the honeycomb core from decreasing.

According to the sixth feature, the boundary region (C) includes a plurality of boundary regions both upstream and downstream of the dense region (A) along a flow of the exhaust gas (G). This can keep the strength of the boundary region of the honeycomb core from decreasing upstream and downstream of the dense region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left side view of a gas exhauster including a catalyst device according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line II-II illustrated in FIG. 1;

FIG. 3 is a perspective view of the catalyst device;

FIG. 4 is a front view illustrating a structure of a honeycomb core;

FIG. 5 is a partial enlarged perspective view illustrating the structure of the honeycomb core;

FIG. 6 is a side view of a honeycomb core according to an embodiment of the present invention;

FIG. 7 is a side view of a honeycomb core according to a first variation of the embodiment;

FIG. 8 is a side view of a honeycomb core according to a second variation of the embodiment;

FIG. 9 is a side view of a honeycomb core according to a third variation of the embodiment; and

FIG. 10 is a partial enlarged side view of a honeycomb core according to a fourth variation of the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a left side view of a gas exhauster 1 including a catalyst device 30 according to an embodiment of the present invention. The direction arrows in each of the drawings correspond to the directions of a vehicle, such as a motorcycle, to which the gas exhauster 1 is attached.

The gas exhauster 1 includes an exhaust pipe 2 attached to a cylinder head of an internal combustion engine (not shown), a catalyst container 4 continuous with the back of the exhaust pipe 2, and a muffler 6 continuous with the back of the catalyst container 4. The catalyst container 4 and the muffler 6 are provided with plate-shaped stays 3 and 5, respectively, for fixing the gas exhauster 1 to the vehicle. Exhaust gas G from the internal combustion engine is sent through the exhaust pipe 2 to the catalyst container 4, and is purified by the catalyst device 30 contained in the catalyst container 4. Thereafter, the purified exhaust gas G is silenced by the muffler 6, and is then discharged backward.

FIG. 2 is a cross-sectional view taken along line II-II illustrated in FIG. 1. FIG. 3 is a perspective view of the catalyst device 30. The same reference numerals as those described above denote the same or equivalent elements. The “front” and “back” indicated by the direction arrows in FIG. 2 correspond to the upstream and downstream sides, respectively, of the flow of the exhaust gas G.

The catalyst device 30 having substantially a circular cylindrical shape includes a tubular outer cylinder 32, and a circular cylindrical honeycomb core 31 contained in the outer cylinder 32. A front taper pipe 9 continuous with the exhaust pipe 2 is connected to a front end portion of the outer cylinder 32. Meanwhile, a back taper pipe 11 continuous with a tailpipe 12 is connected to a back end portion of the outer cylinder 32. The radially outer surface of the outer cylinder 32 is wrapped by a heat insulating pipe 10 forming the catalyst container 4. A front end portion of the heat insulating pipe 10 is connected through an outer taper pipe 8 to the exhaust pipe 2.

FIG. 4 is a front view illustrating a structure of the honeycomb core 31. The honeycomb core 31 has a honeycomb structure obtained by winding a metallic foil 40 a plurality of times. The metallic foil 40 includes a flat foil 41 and a corrugated foil 42 each supporting a catalyst, such as platinum, and overlaid one over the other. The flat foil 41 and the corrugated foil 42 can be configured as, for example, a ferrite stainless steel plate with a thickness of 30 μm to 100 μm. To manufacture the honeycomb core 31, the flat foil 41 and the corrugated foil 42 each having a predetermined portion on which a brazing filler metal, such as a nickel brazing filler metal, is placed are overlaid one over the other to form the metallic foil 40, which is wound and then housed in the outer cylinder 32. The resultant object is heated in a vacuum furnace so as to be subjected to vacuum brazing.

FIG. 5 is a partial enlarged perspective view illustrating the structure of the honeycomb core 31. The same reference numerals as those described above denote the same or equivalent elements. The flat foil 41 and the corrugated foil 42 are joined together at the crests and troughs of the corrugated foil 42 by brazing. The flat foil 41 and the corrugated foil 42 each have a plurality of through holes H. The through holes H are intended to substantially prevent thermal strain phenomena caused by internal temperature variations in the honeycomb core 31 and the phenomena where the metallic foil 40 itself is stretched by expansion of the volume of an oxide film formed on the surface of the metallic foil 40. In addition, this structure can increase the surface area of the catalyst exposed to the exhaust gas, thus contributing also to improvement in the conversion efficiency.

Here, for example, if a region where the through holes H are densely arranged and a region where no through hole H is arranged are in contact with each other, the strength of the metallic foil 40 varies on a boundary region between these regions. Thus, there is a need for devices to maintain the durability of the honeycomb core 31. To satisfy the need, the present invention has the following feature. Specifically, a boundary region is provided between a dense region where the through holes H are densely formed and a zero region where no through hole H is formed, and is configured such that the total area of the through holes H therein decreases gradually from near the dense region toward the zero region. This increases the strength of a shift region between the dense region and the zero region, resulting in an increase in the durability of the honeycomb core.

FIG. 6 is a side view of the honeycomb core 31 according to the embodiment of the present invention. In this embodiment, the circular cylindrical honeycomb core 31 has a dense region A where the through holes H are densely formed, a zero region B where no through hole H is formed, and a boundary region C disposed downstream of the dense region A and between the dense region A and the zero region B in an axial direction in which the exhaust gas G flows. In the dense region A, the plurality of through holes H have the same diameter, and are equally spaced apart from one another. The boundary region C is configured such that the total area of the through holes H therein decreases gradually from near the dense region A toward the zero region B.

More specifically, the boundary region C is configured such that the total area of the through holes H therein decreases gradually due to a reduction in the number of the through holes H therein. This can keep the strength of the shift region between the dense region A and the zero region B from being lower than if the dense region A and the zero region B are in contact with each other, thus enabling an increase in the durability of the honeycomb core 31. The boundary region C provided only downstream of the dense region A along the flow of the exhaust gas G allows the exhaust gas G to diffuse in the dense region A to improve the purification efficiency, and can increase the strength of the boundary region C of the honeycomb core 31. By reducing the number of the through holes H to gradually reduce the total area of the through holes H, processing pins for forming the through holes H in the honeycomb core 31 can be reduced.

Furthermore, in this embodiment, the boundary region C is configured such that the total area of the through holes H therein decreases gradually due to a reduction in the number of the through holes H therein, with the layout of the through holes H in the dense region A maintained. No through hole H is formed around each of the through holes H closest to the zero region B. This can further increase the strength of the boundary region C of the honeycomb core 31.

FIG. 7 is a side view of a honeycomb core 31a according to a first variation of the embodiment. This first variation is different from the embodiment illustrated in FIG. 6 in terms of the manner in which the number of through holes H is reduced in a boundary region C. The manner in which the number of the through holes H is reduced can be modified in various ways. For example, the through holes H may be alternately eliminated, or two adjacent ones of the through holes H may be eliminated.

FIG. 8 is a side view of a honeycomb core 31b according to a second variation of the embodiment. This second variation is also different from the embodiment illustrated in FIG. 6 and the first variation illustrated in FIG. 7 in terms of the manner in which the number of through holes H is reduced in a boundary region C. In this second variation, no through hole H is formed around each of the through holes H closest to the zero region B. The manner in which the number of the through holes H is reduced can be modified in various ways. For example, when the through holes H aligned in the lateral direction in the drawing form a row, the number of the through holes H reduced may be linearly increased in every row from the upstream side toward the downstream side, or may be increased step by step in every two rows.

FIG. 9 is a side view of a honeycomb core 31c according to a third variation of the embodiment. This third variation is characterized in that boundary regions C are provided both upstream and downstream of a dense region A along the flow of exhaust gas G. This can increase the strength of the boundary regions C of the honeycomb core 31c upstream and downstream of the dense region A.

FIG. 10 is a partial enlarged side view of a honeycomb core 31d according to a fourth variation of the embodiment. In this fourth variation, while the layout of through holes H in a dense region A is maintained, a boundary region C is configured such that the total area of the through holes H therein decreases gradually due to a gradual reduction in the diameter of the through holes H (H1, H2, H3) therein. This can increase the strength of the boundary region C of the honeycomb core 31d while the diffusion effect caused by the through holes H is maintained. Also in this variation, the through holes H in the dense region A have the same diameter, and are equally spaced apart from one another. However, the layout of the through holes H in the dense region A can be modified in various ways. The diameter of the through holes H may also be linearly reduced in every row, or may be reduced step by step in every two rows, for example.

The form of a vehicle to which a gas exhauster is attached, the shape and structure of the gas exhauster, the shape and arrangement of a catalyst device, the materials of a flat foil and a corrugated foil forming a metallic foil of a honeycomb core, the shape and structure of the honeycomb core, the pattern in which through holes are arranged, the shape and size of the through holes, the number of the through holes, and any other elements should not be limited to those in the foregoing embodiment, and can be modified in various ways. The shape of the catalyst device should not be limited to a circular cylindrical shape, and the catalyst device may be shaped to have an elliptical cross section, for example. The catalyst device according to the present invention can be used for a gas exhauster not only for motorcycles but also for vehicles, such as a tricycle and a four-wheeled vehicle, and various devices including an internal combustion engine as a power source.

EXPLANATION OF REFERENCE NUMERALS

1 . . . Gas Exhauster, 30 . . . Catalyst Device, 31, 31a, 31b, 31c, 31d . . . Honeycomb Core, 32 . . . Outer Cylinder, 40 . . . Metallic Foil, 41 . . . Flat Foil, 42 . . . Corrugated Foil, A . . . Dense Region, B . . . Zero Region, C . . . Boundary Region, H . . . Through Hole, G . . . Exhaust Gas