JP7616983B2 - Catalytic converter - Google Patents

Description

This disclosure relates to catalytic converters.

As described in Patent Document 1, a tandem catalytic converter is known in which two catalysts are arranged side by side inside a cylindrical case along the exhaust flow direction. In the catalytic converter of Patent Document 1, a spacer configured as a screw or the like is arranged between the upstream metal carrier and the downstream metal carrier.

Japanese Patent Application Publication No. 6-241036

In order to comply with environmental regulations, catalytic converters are required to have the catalyst reach its activation temperature as soon as possible after the vehicle engine is started, so that the exhaust gas can be effectively purified. To achieve this, it is necessary to reduce the heat capacity of the catalyst, for example, by making the catalyst smaller or by thinning the walls that form the catalyst (hereafter referred to as "thin-walled").

However, while making the catalyst smaller and thinner-walled improves the purification performance of the catalyst, it may become difficult to keep the catalyst in the designated position inside the case.

One aspect of the present disclosure aims to maintain the position of the catalyst in an excellent manner while improving purification performance.

One aspect of the present disclosure is a catalytic converter comprising a case portion, a first catalyst, a second catalyst, a first holding portion, a second holding portion, and a connecting portion. The case portion is cylindrical and can be arranged in a flow path of exhaust gas from an engine of a vehicle. The first catalyst is arranged inside the case portion. The second catalyst is a portion arranged inside the case portion and located downstream of the first catalyst in the exhaust flow direction. The first holding portion is arranged between the first catalyst and the inner peripheral surface of the case portion, and is configured to generate a first holding force that urges the first catalyst to be held at a predetermined position in the exhaust flow direction. The second holding portion is arranged between the second catalyst and the inner peripheral surface of the case portion, and is configured to generate a second holding force that urges the second catalyst to be held at a predetermined position in the exhaust flow direction. The connecting portion is sandwiched between the first catalyst and the second catalyst, and has air permeability. The first catalyst and the second catalyst satisfy at least one of the first and second conditions. The first condition is that the size of the first catalyst is smaller than the size of the second catalyst. The second condition is that the strength of the first catalyst is lower than the strength of the second catalyst. The second retention force is greater than the first retention force.

According to the above configuration, when the first catalyst, which has been made smaller and/or weaker due to improved purification performance, attempts to displace in the direction of exhaust flow, the first catalyst can be supported by the second catalyst via the connecting portion. This makes it possible to maintain the position of the catalyst with improved purification performance.

In one aspect of the present disclosure, the connecting portion may have cushioning properties.

The above configuration makes it possible to prevent damage to the first and second catalysts due to contact with the connecting portion.

In one aspect of the present disclosure, the connecting portion may be disposed in a region in the space between the first catalyst and the second catalyst inside the case portion where the exhaust flow is concentrated.

The above configuration can prevent the flow of exhaust gas passing through the first and second catalysts from becoming biased. This can prevent the first and second catalysts from being locally loaded and causing partial deterioration.

1 is a cross-sectional view including an axis of a catalytic converter. This is a modified example of the connecting portion. This is a modified example of the connecting portion. This is a modified example of the connecting portion. This is a modified example of the connecting portion. This is a modified example of the connecting portion. 13 is a cross-sectional view including an axis of a connecting portion of a modified example. FIG. 13 is a cross-sectional view including an axis of a connecting portion of a modified example. FIG.

Embodiments of the present disclosure will be described below with reference to the drawings. Note that the embodiments of the present disclosure are not limited to the following embodiments, and may take various forms as long as they fall within the technical scope of the present disclosure.

[1. Catalytic Converter]
The catalytic converter 1 is mounted on a vehicle and purifies exhaust gas from the engine of the vehicle (see FIG. 1). The engine may be, for example, a gasoline engine or a diesel engine. The catalytic converter 1 is configured as a tandem type and includes a case portion 2, first and second catalysts 3, 4, first and second holding portions 5, 6, and a connecting portion 7.

[2. Case part]
As an example, the case portion 2 is formed in a cylindrical shape extending straight along an axis 10 (see FIG. 1 ). The case portion 2 is disposed in a flow path of exhaust from the engine, and an exhaust inlet 20 and an exhaust outlet 21 located at both ends of the case portion 2 are each connected to an exhaust pipe.

The case part 2 is arranged so that the axis 10 coincides with the exhaust flow direction 11, and the cross section perpendicular to the axis 10 (hereinafter also simply referred to as the cross section) is circular, with the axis 10 passing through the center of the cross section. Note that the shape of the case part 2 is not limited to this, and for example, the case part 2 may have a curved shape, or the cross section of the case part 2 may be polygonal.

[3. First and second catalysts]
The first and second catalysts 3, 4 are disposed inside the case portion 2, and are arranged side by side along the exhaust flow direction 11 (see FIG. 1 ). The first catalyst 3 and the second catalyst 4 are arranged with a gap between them, with the first catalyst 3 located upstream of the exhaust flow direction 11 (hereinafter simply referred to as the upstream side), and the second catalyst 4 located downstream of the exhaust flow direction 11 (hereinafter simply referred to as the downstream side).

The first and second catalysts 3, 4 are, for example, cylindrical and are arranged inside the case 2 so as to extend in the exhaust flow direction 11 (in other words, in the direction of the axis 10). Hereinafter, the bottom surfaces located on the upstream side of the first and second catalysts 3, 4 will be referred to as the upstream bottom surfaces 30, 40, and the bottom surfaces located on the downstream side will be referred to as the downstream bottom surfaces 31, 41.

The first and second catalysts 3, 4 have multiple exhaust flow paths (hereinafter also referred to as cells) that extend in the exhaust flow direction 11 from the upstream bottom surface to the downstream bottom surface, and purify the exhaust by modifying or capturing environmental pollutants in the exhaust through contact with the exhaust. Note that the first and second catalysts 3, 4 may have a honeycomb structure, as an example.

In addition, the first catalyst 3 has a lower heat capacity than the second catalyst 4, and when the vehicle engine is started, the first catalyst 3 reaches its activation temperature early and can effectively purify the exhaust gas. In addition, as a result of making the heat capacity of the first catalyst 3 lower than that of the second catalyst 4, the first and second catalysts 3 and 4 satisfy the following first and second conditions.

That is, the first condition is that the size of the first catalyst 3 is smaller than the size of the second catalyst 4. In other words, the size is the area of the outer circumferential surface, and is determined by the length of the first and second catalysts 3, 4 in the direction of the axis 10 (hereinafter simply referred to as the length) and the cross-sectional diameter of the first and second catalysts 3, 4. In this embodiment, as an example, the length of the first catalyst 3 is shorter than the length of the second catalyst 4, and the cross-sectional diameter of the first catalyst 3 is smaller than the cross-sectional diameter of the second catalyst 4. However, this is not limited to this, and the first catalyst 3 may be smaller in size than the second catalyst 4 by having either the length or the diameter smaller than the second catalyst 4.

The second condition is that the strength of the first catalyst 3 is lower than the strength of the second catalyst 4. Specifically, the first catalyst 3 has thinner walls that form each cell and the outer peripheral surface compared to the second catalyst 4, and therefore has a lower strength than the second catalyst 4.

The first and second catalysts 3, 4 may be configured so that the heat capacity of the first catalyst 3 is lower than that of the second catalyst 4 by satisfying one of the first and second conditions.

[4. First and second holding parts]
The first and second holding parts 5, 6 are each configured as a flat mat-shaped cushioning material and are provided so as to surround the outer circumferential surfaces of the first and second catalysts 3, 4 (see FIG. 1 ). The first holding part 5 is disposed between the outer circumferential surface of the first catalyst 3 and the inner circumferential surface of the case part 2, and the second holding part 6 is disposed between the outer circumferential surface of the second catalyst 4 and the inner circumferential surface of the case part 2.

The first and second catalysts 3, 4 may change position in the exhaust flow direction 11 due to exhaust back pressure, vehicle vibration, etc. In response to this, the first holding portion 5 applies a first holding force to the first catalyst 3, encouraging the first catalyst 3 to maintain its position in the exhaust flow direction 11. The first holding force increases as the surface density of the first holding portion 5 and the area of the contact portion between the first holding portion 5 and the first catalyst 3 (hereinafter, contact area) increase. Surface density refers to the weight per unit area.

Similarly, the second holding portion 6 also exerts a second holding force on the second catalyst 4, encouraging the second catalyst 4 to maintain its position in the exhaust flow direction 11. Like the first holding force, the second holding force also increases as the surface density of the second holding portion 6 and the contact area between the second holding portion 6 and the second catalyst 4 increase.

[5. Connection]
The connecting part 7 is made of a breathable material and is disposed in the space between the first catalyst 3 and the second catalyst 4 inside the case part 2 (hereinafter, referred to as the intermediate space 22) and is sandwiched between these catalysts (see FIG. 1 ). The connecting part 7 abuts against the downstream bottom surface 31 of the first catalyst 3 and the upstream bottom surface 40 of the second catalyst 4.

The connecting portion 7 may have cushioning properties, and may be made of wire mesh, for example. The wire mesh may be made of stainless steel, for example. The connecting portion 7 may be arranged so that the fibers of the connecting portion 7, which is a wire mesh, enter the openings of the multiple cells on the downstream bottom surface 31 of the first catalyst 3 and the openings of the multiple cells on the upstream bottom surface 40 of the second catalyst 4. This causes the connecting portion 7 to be caught on the downstream bottom surface 31 and the upstream bottom surface 40. In other words, a part of the connecting portion 7 enters the inside of the cells of the first and second catalysts 3 and 4, and the connecting portion 7 is prevented from shifting in the cross-sectional direction due to frictional force. In other words, the connecting portion 7 connects the first and second catalysts 3 and 4.

In addition, the connecting portion 7 may be made of a porous material such as foam metal, for example.

The connecting portion 7 is also disposed in a region in the intermediate space 22 where the exhaust flow concentrates. In this embodiment, the case portion 2 has a cylindrical shape that extends straight, so the exhaust flow concentrates in the center of the cross section of the case portion 2, and the exhaust flow speed becomes relatively high. For this reason, as an example, the connecting portion 7 is formed in a disk shape and disposed in the center of the cross section of the intermediate space 22. More specifically, the connecting portion 7 is disposed in the intermediate space 22 so that the center of the cross section approximately coincides with the position of the axis 10.

Of course, the area inside the case 2 where the exhaust flow concentrates varies depending on the shape of the case 2 and the shape of the exhaust pipe connected to the upstream side of the case 2. Therefore, the position of the connecting part 7 can be appropriately determined depending on these. In addition, the position of the connecting part 7 may be determined regardless of the exhaust flow.

[6. Modifications of the connecting portion]
By making the air permeability of the portion of the connecting portion 7 where the exhaust flow concentrates lower than the air permeability of the other portions, it is possible to further suppress the bias of the exhaust flow passing through the first and second catalysts 3, 4.

Here, even in the modified example described below, the connecting portion 7 is positioned so that the center of the cross section substantially coincides with the position of the axis 10. In addition, the portion of the connecting portion 7 that is located at the center of the cross section is referred to as the central portion, and the portion surrounding the central portion is referred to as the peripheral portion.

The connecting portion 7 may be formed, for example, in a truncated cone shape (see FIG. 2), or may be formed so that the cross section parallel to the axis 10 is substantially elliptical (see FIG. 3). This results in the connecting portion 7 having relatively thick central portions 70, 72 and peripheral portions 71, 73 whose thickness decreases toward the edge.

As a result, the central portions 70 and 72 have low breathability, while the peripheral portions 71 and 73 have gradually higher breathability toward the edges. Therefore, as described above, when the exhaust flow is concentrated in the center of the cross section of the case portion 2, the exhaust flow passing through the first and second catalysts 3 and 4 can be made more uniform.

For example, in a disk-shaped connecting part 7 made of wire mesh, the density of the wire mesh in the center may be relatively high, while the density of the wire mesh in the peripheral area may be relatively low. For example, in a disk-shaped connecting part 7 made of a porous body, the porosity in the center may be relatively low, while the porosity in the peripheral area may be relatively high. Note that porosity refers to the degree to which an object has gaps such as holes.

This results in lower ventilation in the center and higher ventilation in the periphery. This helps to make the flow of exhaust gas passing through the first and second catalysts 3 and 4 more uniform.

Of course, the part of the connecting part 7 where the exhaust flow concentrates varies depending on the shape of the case part 2, the shape of the exhaust pipe connected to the upstream side of the case part 2, the position of the connecting part 7, etc. Therefore, the air permeability of each part of the connecting part 7 can be adjusted depending on the shape of the case part 2, the position of the connecting part 7, etc.

In addition, for example, the connecting portion 7 may have a cylindrical portion 74 and a plurality of (for example, two) cylindrical portions 75 (see FIG. 4). The cylindrical portion 74 may be arranged to extend along the axis 10, and the plurality of cylindrical portions 75 may be arranged concentrically around the cylindrical portion 74.

Furthermore, the connecting portion 7 may have a cylindrical portion 74 and multiple (three, for example) cylindrical portions 75, and may also have multiple wall portions 76 extending radially to connect these portions (see FIG. 5).

The connecting portion 7 may also have a spiral wall portion 77 that orbits the axis 10 (see Figure 6).

This configuration makes it possible to suppress the increase in pressure loss caused by providing the connecting portion 7.

For example, the connecting portion 7 may include a main body portion 78 and an outer peripheral portion 79 (see Figs. 7 and 8). The main body portion 78 is a disk-shaped portion that covers the entire downstream bottom surface 31 of the first catalyst 3 and the entire upstream bottom surface 40 of the second catalyst 4. The outer peripheral portion 79 is provided on the edge of the main body portion 72 so as to surround the main body portion 72.

The outer peripheral portion 79 may protrude upstream so that the connecting portion 7 fits into the downstream bottom surface 31 of the first catalyst 3, as shown in FIG. 7. The outer peripheral portion 79 may also be sandwiched between the outer peripheral surface of the first catalyst 3 and the inner peripheral surface of the case portion 2. The outer peripheral portion 79 may also protrude downstream instead of upstream.

8, the outer peripheral portion 79 may protrude upstream and downstream so that the connecting portion 7 fits into the downstream bottom surface 31 of the first catalyst 3 and the upstream bottom surface 40 of the second catalyst 4. The outer peripheral portion 79 may be sandwiched between the outer peripheral surface of the first catalyst 3 and the inner peripheral surface of the case portion 2, and may also be sandwiched between the outer peripheral surface of the second catalyst 4 and the inner peripheral surface of the case portion 2.

This configuration can prevent the position of the connecting part 7 from shifting. In addition, it is easier to position the connecting part 7 during the manufacturing process of the catalytic converter 1, making it easier to place the connecting part 7.

In addition, in the connecting portion 7 having the main body portion 78 and the outer peripheral portion 79, if the connecting portion 7 is made of wire mesh, the density of the wire mesh in the center portion may be made relatively high and the density of the wire mesh in the peripheral portion may be made relatively low in the same manner. In addition, in the case where the connecting portion 7 is made of a porous body, the porosity of the center portion may be made relatively low and the porosity of the peripheral portion may be made relatively high in the same manner. This can encourage the flow of exhaust gas passing through the first and second catalysts 3, 4 to become more uniform.

[7. Manufacturing method of catalytic converter]
In the manufacturing process of the catalytic converter, the case portion 2 is formed. Furthermore, a first holding portion 5 is provided so as to cover the outer peripheral surface of the first catalyst 3, and a second holding portion 6 is provided so as to cover the outer peripheral surface of the second catalyst 4. Then, the first catalyst 3 provided with the first holding portion 5, the second catalyst 4 provided with the second holding portion 6, and the connecting portion 7 are all disposed inside the case portion 2. As a result, the connecting portion 7 is sandwiched between the downstream bottom surface 31 of the first catalyst 3 and the upstream bottom surface 40 of the second catalyst 4.

Specifically, first, the second catalyst 4 provided with the second holding portion 6 may be pressed into the case portion 2 from the inlet 20. Then, with the connecting portion 7 sandwiched between the upstream bottom surface 40 and the downstream bottom surface 31, the first catalyst 3 provided with the first holding portion 5 may be pressed into the case portion 2 from the inlet 20, and the second catalyst 4 may be further pressed into the case portion 2 by the first catalyst 3 through the connecting portion 7. After that, when the first catalyst 3 is pressed into a predetermined position, the second catalyst 4 also reaches a predetermined position, and the pressing of the first and second catalysts 3, 4 is completed.

Conversely, the first catalyst 3 provided with the first retaining portion 5 may first be pressed into the case portion 2 from the outlet 21. Then, with the connecting portion 7 sandwiched between the downstream bottom surface 31 and the upstream bottom surface 40, the second catalyst 4 provided with the second retaining portion 6 may be pressed into the case portion 2 from the outlet 21, and the first catalyst 3 may be further pressed in by the second catalyst 4 via the connecting portion 7. After that, when the second catalyst 4 is pressed in to a predetermined position, the first catalyst 3 also reaches a predetermined position, and the pressing in of the first and second catalysts 3, 4 is completed.

This reduces the workload compared to when the first and second catalysts 3, 4 are pressed in twice separately through the inlet 20 and outlet 21 of the case portion 2.

[8. First and second holding forces]
As described above, in order to improve the purification performance of the first catalyst 3 when the vehicle engine is started, the heat capacity of the first catalyst 3 is reduced, and as a result, the size and strength of the first catalyst 3 are smaller than those of the second catalyst 4. As a result, the first holding force is smaller than the second holding force.

That is, the first catalyst 3 has a smaller outer peripheral surface area than the second catalyst 4. Therefore, the contact area between the first catalyst 3 and the first holding portion 5 is smaller than the contact area between the second catalyst 4 and the second holding portion 6, and as a result, the first holding force is smaller than the second holding force.

Here, in order to generate a sufficient first retention force in the first catalyst 3 with a reduced contact area, it is conceivable to increase the first retention force per unit area generated in the first retention portion 5. However, if such a measure is taken, the force required to press the first catalyst 3 with the first retention portion 5 provided on its outer circumferential surface into the case portion 2 during the manufacturing process of the catalytic converter 1 (hereinafter, the pressing load) will increase.

In contrast, the strength of the first catalyst 3 decreases as the heat capacity decreases, and therefore if the pressing load increases, there is a risk that the first catalyst 3 will be damaged when pressed in. For this reason, the first holding portion 5 is configured to have a low first holding force per unit area to enable the first catalyst 3 to be pressed in. As a result, the first holding portion 5 cannot hold the position of the first catalyst 3 in the exhaust flow direction, and there is a risk that the first catalyst 3 will be displaced downstream due to exhaust pressure or vehicle vibration.

On the other hand, the second holding portion 6 has a larger contact area than the first holding portion 5, and the second holding force in the second holding portion 6 is greater than the first holding force. In other words, the second holding portion 6 is configured to compensate for the decrease in the first holding force, and while supporting the second catalyst 4 that tends to be displaced downstream due to back pressure or vehicle vibration, the second holding portion 6 supports the first catalyst 3 that tends to be displaced downstream due to the same factors at the second catalyst 4 via the connecting portion 7. Specifically, the second holding force is large enough to hold the positions of the first and second catalysts 3, 4 in the exhaust flow direction that tend to be displaced downstream.

As an example, the second holding force may be increased by making the surface density of the second holding portion 6 higher than the surface density of the first holding portion 5. Of course, this is not limited to the above, and the second holding force may be increased, for example, by appropriately selecting the material that constitutes the second holding portion 6.

The first catalyst 3 may be smaller than the second catalyst 4 in either size or strength, so that the first holding force is smaller than the second holding force. Similarly, the second holding portion 6 may be configured to generate a second holding force sufficient to hold the positions of the first and second catalysts 3, 4.

[9. Effects]
(1) According to the above embodiment, the first catalyst 3 is made smaller and weaker as a result of reducing the heat capacity of the first catalyst 3 to improve the purification performance at engine start, and as a result, the first holding force is reduced. However, when the first catalyst 3 tries to be displaced in the exhaust flow direction 11, the first catalyst 3 is supported by the second catalyst 4 via the connecting portion 7. Therefore, the position of the first catalyst 3, which has improved purification performance, can be well maintained. In addition, the first and second catalysts 3, 4 can be prevented from contacting each other and causing damage to these catalysts. In addition, by providing the connecting portion 7, the first and second catalysts 3, 4 can be pressed into the case portion 2 together in the manufacturing process of the catalytic converter 1. This reduces the workload.

(2) The connecting portion 7 is made of a wire mesh or the like and has cushioning properties. This prevents damage to the first and second catalysts 3 and 4 caused by contact with the connecting portion 7.

(3) Furthermore, because the connecting portion 7 is disposed in an area where the exhaust flow is concentrated, it is possible to prevent the exhaust flow passing through the first and second catalysts 3, 4 from becoming biased. This prevents the first and second catalysts 3, 4 from being locally loaded and from being partially deteriorated. In addition, the purification performance of the first and second catalysts 3, 4 is improved.

10. Other embodiments
In the above embodiments, multiple functions of one component may be realized by multiple components, or one function of one component may be realized by multiple components. Furthermore, multiple functions of multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Furthermore, part of the configuration of the above embodiments may be omitted. Furthermore, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

1...catalytic converter, 10...axis, 11...exhaust flow direction, 2...case portion, 22...middle area, 3...first catalyst, 31...downstream bottom surface, 4...second catalyst, 40...upstream bottom surface, 5...first holding portion, 6...second holding portion, 7...connecting portion.

Claims (2)

A catalytic converter comprising:
A cylindrical case portion that can be disposed in an exhaust flow path from an engine of a vehicle;
A first catalyst disposed inside the case portion;
a second catalyst that is disposed inside the case portion and is located downstream of the first catalyst in a flow direction of exhaust gas;
a first holding portion disposed between the first catalyst and an inner circumferential surface of the case portion and configured to generate a first holding force that urges the first catalyst to be held at a predetermined position in the exhaust gas flow direction;
a second holding portion disposed between the second catalyst and an inner circumferential surface of the case portion and configured to generate a second holding force that urges the second catalyst to be held at a predetermined position in the exhaust gas flow direction;
a connecting portion that is a fibrous member having air permeability and cushioning properties and is sandwiched between a downstream surface of the first catalyst and an upstream surface of the second catalyst in a flow direction of the exhaust gas ,
The first catalyst and the second catalyst satisfy at least one of a first condition and a second condition,
the first condition is that the size of the first catalyst is smaller than the size of the second catalyst;
the second condition is a condition that the strength of the first catalyst is lower than the strength of the second catalyst;
the second retention force is greater than the first retention force;
A member that abuts against the upstream surface of the first catalyst is not provided,
the surface density of the second holding portion is higher than the surface density of the first holding portion,
The connecting portion is provided in a state in which fibers enter an opening of a cell provided on the downstream surface of the first catalyst and an opening of a cell provided on the upstream surface of the second catalyst.
Catalytic converter. 2. The catalytic converter of claim 1 ,
The connecting portion is disposed in a region in the space between the first catalyst and the second catalyst inside the case portion, where the exhaust flow concentrates.

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