Honeycomb unit and catalytic converter

Abstract

The purpose of the present invention is to provide a honeycomb unit in which the axial length of a honeycomb body is longer than the diameter of the honeycomb body and the honeycomb unit has excellent thermal fatigue resistance and vibration resistance. The present invention is a honeycomb unit having a honeycomb body formed by winding a corrugated foil and a flat foil made of metal, and an outer cylinder arranged at a position surrounding the outer circumferential surface of the honeycomb body, in which the length in the axial direction of the honeycomb body is longer than the outer diameter of the honeycomb body, and wherein the honeycomb body and the outer cylinder are joined to each other by an outer cylinder-honeycomb body joint section, the flat foil and the corrugated foil are joined to each other at an end joint section on one end of the honeycomb body and at an outer circumferential joint section connected with the other end of the end joint section, the end joint section is formed over all the layers in the stacking direction of the flat foil and the corrugated foil, the outer circumferential joint section is formed from the other end of the end joint section to the other end of the honeycomb body, the outer circumferential joint section has a first region in which the number of layers from the outermost circumference of the honeycomb body is N and a second region in which the number of layers from the outermost circumference of the honeycomb body is N + 1 (wherein N is any one of 4 to 7) when a set of the corrugated foil and the flat foil sandwiching the corrugated foil in the layering direction is defined as one layer, the number of layers in a region among the first region and the second region in which the occupancy in the circumferential direction of the honeycomb body is high is any one of 5 to 7 layers, the axial length of the outer cylinder-honeycomb body joint section is 5 mm or more, and the honeycomb unit satisfies the formulas (1), (2), and (3) indicated below when the outer diameter of the honeycomb body is denoted by A, the axial length from one end of the honeycomb body to one end of the outer cylinder-honeycomb body joint section is denoted by B, the axial length of the end joint section is denoted by C, the axial length from the other end of the end joint section to the one end of the outer cylinder-honeycomb body joint section is denoted by D, the axial length of the honeycomb body is denoted by E, and the axial length from the other end of the outer cylinder-honeycomb body joint section to the other end of the honeycomb body is denoted by F. Formula (1): A > B. Formula (2): C < D. Formula (3): F ≥ 0.7E - B.

Description

Honeycomb unit and catalytic converter

[0001] The present invention relates to a honeycomb unit and a catalytic converter.

[0002] Honeycomb units, which are composed of a honeycomb body formed by laminating flat foil and corrugated foil and an outer cylinder that houses the honeycomb body, are used as purification devices for purifying exhaust gases emitted from internal combustion engines. Honeycomb bodies are mainly classified into laminated honeycomb bodies and wound honeycomb bodies. Laminated honeycomb bodies are formed by alternately laminating flat foil made of metal foil and corrugated foil made of corrugated metal foil. Wound honeycomb bodies are formed by spirally winding overlapping flat foil and corrugated foil. By placing a honeycomb unit (also called a catalytic converter) including a honeycomb body supporting a catalyst in the exhaust gas path, exhaust gas passing through the catalytic converter comes into contact with the catalyst over a wide area, thereby enabling efficient exhaust gas purification.

[0003] However, because this catalytic converter is used in an environment where high-temperature exhaust gas flows, the honeycomb body expands axially and radially due to the heat from the exhaust gas, resulting in stress concentration at the joint between the outer casing and the honeycomb body. Repeated expansion can lead to separation at the joint between the outer casing and the honeycomb body, making the honeycomb body more susceptible to detachment. Furthermore, air pollutants in the exhaust gas contact and react with the catalyst, generating heat, which increases the temperature closer to the inlet end face of the honeycomb unit. Therefore, for example, if the outer casing and the honeycomb body are joined near the axial inlet end of the honeycomb unit, repeated reaction heat between the air pollutants in the exhaust gas and the catalyst can weaken the joint strength, making the honeycomb body more susceptible to detachment. Thus, if the honeycomb unit does not have sufficient resistance to repeated heating and cooling due to the heat of the exhaust gas and the reaction heat of the catalyst (hereinafter also referred to as thermal fatigue resistance), the honeycomb body may fall off, resulting in damage to the honeycomb unit.

[0004] Therefore, in honeycomb units, the joining position between the outer tube and the honeycomb body is generally set on the outlet side in the axial direction of the honeycomb unit. With this configuration, the joining position between the outer tube and the honeycomb body can be separated from the area of ​​the honeycomb body that is likely to become hot (near the inlet side), thereby reducing the thermal stress applied to the joining portion and the possibility of the honeycomb body falling off.

[0005] For example, Example 5 of Patent Document 1 discloses a honeycomb unit in which an outer cylinder and a honeycomb body are joined from the outlet end in the axial direction to near the center.

[0006] WO 1990 / 03842

[0007] In addition to thermal fatigue resistance, honeycomb units are also required to be vibration resistant so that they can be used in environments where engines and exhaust pipes vibrate violently, such as diesel engines and motorcycles. The honeycomb unit used in Example 5 of Patent Document 1 has a honeycomb body whose axial length is shorter than its diameter. In this honeycomb unit, even if the joining position between the outer tube and the honeycomb body is set on the axial outlet side, the axial distance from the joining position to the inlet end of the honeycomb body is short. Therefore, the honeycomb body vibrates little around the joining point between the outer tube and the honeycomb body, resulting in high vibration resistance.

[0008] On the other hand, in the case of a honeycomb unit in which the axial length of the honeycomb body is longer than the diameter of the honeycomb body, if the joint position between the outer tube and the honeycomb body is set on the axial outlet side, the axial distance from the joint position to the inlet end of the honeycomb body is long, so the vibration of the honeycomb body with the joint between the outer tube and the honeycomb body as the fulcrum becomes larger, and therefore the possibility of the honeycomb body falling off from the outer tube increases.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a honeycomb unit in which the axial length of the honeycomb body is longer than the diameter of the honeycomb body, and which has excellent thermal fatigue resistance as well as vibration resistance.

[0010] In view of the above, the present invention provides (1) a honeycomb unit comprising a honeycomb body formed by winding flat foil and corrugated foil made of metal foil, and an outer cylinder arranged in a position surrounding the outer peripheral surface of the honeycomb body, wherein the axial length of the honeycomb body is longer than the outer diameter of the honeycomb body, the honeycomb body and the outer cylinder are joined to each other by an outer cylinder-honeycomb body joint, the flat foil and the corrugated foil are joined to each other at an end joint at one end of the honeycomb body, and are joined to each other at a peripheral joint that connects to the other end of the end joint, the end joint being formed over all layers in the stacking direction of the flat foil and the corrugated foil, and the peripheral joint being formed from the other end of the end joint to the other end of the honeycomb body, and when a set of the corrugated foil and the flat foil sandwiching it in the stacking direction is defined as one layer, the peripheral joint is a first region having N layers from the outermost periphery of the honeycomb body, and a second region having N+1 layers from the outermost periphery of the honeycomb body (where N is any number from 4 to 7); the number of layers in the region having a high circumferential occupancy rate of the honeycomb body in the first region or the second region is any number from 5 to 7; the axial length of the outer tube-honeycomb body joint is 5 mm or more; and the honeycomb unit satisfies the following formulas (1), (2), and (3), where A is the outer diameter of the honeycomb body, B is the axial length from one end of the honeycomb body to one end of the outer tube-honeycomb body joint, C is the axial length of the end joint, D is the axial length from the other end of the end joint to one end of the outer tube-honeycomb body joint, E is the axial length of the honeycomb body, and F is the axial length from the other end of the outer tube-honeycomb body joint to the other end of the honeycomb body. A>B...(1) C<D...(2) F≧0.7E-B...(3)

[0011] (2) A racetrack-type honeycomb unit having a honeycomb body formed by winding flat foil and corrugated foil made of metal foil, and an outer cylinder arranged in a position surrounding the outer peripheral surface of the honeycomb body, wherein the axial length of the honeycomb body is longer than the minor axis of the honeycomb body when viewed in the axial direction, the honeycomb body and the outer cylinder are joined to each other by an outer cylinder-honeycomb body joint, the flat foil and the corrugated foil are joined to each other at an end joint at one end of the honeycomb body, and are joined to each other at a peripheral joint connected to the other end of the end joint, the end joint is formed over all layers in the stacking direction of the flat foil and the corrugated foil, and the peripheral joint is formed from the other end of the end joint to the other end of the honeycomb body, and when a set of the corrugated foil and the flat foil sandwiching it in the stacking direction is defined as one layer, the peripheral joint is formed over all layers of the honeycomb body a first region having N layers from the outermost periphery of the honeycomb body, and a second region having N+1 layers from the outermost periphery of the honeycomb body (where N is any value from 4 to 7); the number of layers in the region having a high circumferential occupancy rate of the honeycomb body in the first region and the second region is any value from 5 to 7; the axial length of the outer tube-honeycomb body joint is 5 mm or more; and the honeycomb unit satisfies the following formulas (1'), (2'), and (3'), where A' is the minor axis of the honeycomb body when viewed in the axial direction, B' is the axial length from one end of the honeycomb body to one end of the outer tube-honeycomb body joint, C' is the axial length from the other end of the end joint to one end of the outer tube-honeycomb body joint, D' is the axial length of the honeycomb body, E' is the axial length of the honeycomb body, and F' is the axial length from the other end of the outer tube-honeycomb body joint to the other end of the honeycomb body. A'>B'...(1') C'<D'...(2') F'≧0.7E'-B'...(3')

[0012] (3) The honeycomb unit according to (1), further satisfying the following formula (4): E≧1.4A (4)

[0013] (4) The honeycomb unit according to (2), further satisfying the following formula (4'): E'≧1.4A' (4')

[0014] (5) The honeycomb unit according to any one of (1) to (4), characterized in that the number of layers in the region having a high occupancy rate in the circumferential direction of the honeycomb body among the first region and the second region is six.

[0015] (6) A catalytic converter characterized in that a catalyst is supported on the honeycomb body according to any one of (1) to (4).

[0016] (7) A catalytic converter characterized in that a catalyst is carried on the honeycomb body according to (5).

[0017] According to the present invention, it is possible to provide a honeycomb unit in which the axial length of the honeycomb body is longer than the diameter of the honeycomb body, and which has excellent thermal fatigue resistance as well as vibration resistance.

[0018] 1. A perspective view of a honeycomb unit 1 in a first embodiment. An X-X cross-sectional view of the honeycomb unit shown in FIG. 1. A cross-sectional view of the honeycomb unit 1 shown in FIG. 1, cut in a direction perpendicular to the axial direction in a region where a peripheral bonding layer 12 is present. A vertical cross-sectional view of the honeycomb unit shown in FIG. 1. A plan view of a honeycomb unit 1' in a second embodiment. A Y-Y cross-sectional view of the honeycomb unit 1' shown in FIG. 5.

[0019] (First Embodiment) Hereinafter, a first embodiment of a honeycomb unit of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view of a honeycomb unit 1 in the first embodiment. Referring to the same figure, the honeycomb unit 1 includes a honeycomb body 10 and an outer cylinder 20 formed in a cylindrical shape and disposed in a position surrounding the outer surface of the honeycomb body 10 in the radial direction. In the honeycomb unit 1 of this embodiment, the axial length of the honeycomb body 10 is longer than the outer diameter of the honeycomb body 10, and is preferably 1.4 times or more the outer diameter of the honeycomb body 10.

[0020] The honeycomb body 10 is constructed by winding a corrugated foil 30 and a flat foil 40 in an overlapping state around the axial direction and bonding the corrugated foil 30 and the flat foil 40 together with a brazing material. Therefore, the honeycomb body 10 has a configuration in which the corrugated foil 30 and the flat foil 40 are alternately stacked in the radial direction. That is, the radial direction of the honeycomb body 10 coincides with the stacking direction of the corrugated foil 30 and the flat foil 40. This configuration allows for the formation of numerous axially extending gas flow channels (cells) within the honeycomb body 10. The "axial direction" coincides with the flow direction of exhaust gas flowing into the honeycomb body 10. The honeycomb body 10 is inserted into an outer cylinder 20, and the outermost peripheral surface of the honeycomb body 10 is bonded to the inner peripheral surface of the outer cylinder 20 with a brazing material, thereby constructing a honeycomb unit 1. The bonding between the corrugated foil 30 and the flat foil 40 and the bonding between the honeycomb body 10 and the outer cylinder 20 will be described later. The cell density of the honeycomb body 10 is preferably set to 100 to 600 cells per square inch, more preferably 300 to 400 cells per square inch.

[0021] Heat-resistant alloys can be used for the corrugated foils 30 and flat foils 40 that make up the honeycomb body 10. Examples of heat-resistant alloys include alloys containing 15% to 25% by mass of Cr and 2% to 8% by mass of Al, such as an Fe-20Cr-5Al alloy. The thickness of the corrugated foils 30 and flat foils 40 is preferably set to 20 μm to 100 μm, more preferably 30 μm to 50 μm. Ferritic stainless steel containing 13% to 20% by mass of Cr, such as SUS436L, SUS430, or EN Standard 1.4509, can be used for the outer cylinder 20. However, austenitic stainless steels such as SUS315J1 can also be used. The thickness of the outer cylinder 20 is preferably set to 0.5 mm to 3 mm, more preferably 1 mm to 2 mm.

[0022] (Regarding bonding of honeycomb unit 1) Figure 2 is an X-X cross-sectional view of the honeycomb unit shown in Figure 1. Referring to Figure 2, the honeycomb body 10 is formed with an inlet-side joint 11 extending in the axial direction from the inlet-side end of the honeycomb body 10, a peripheral joint 12 extending from the outlet-side end of the inlet-side joint 11 to the outlet-side end of the honeycomb body 10, and an outlet-side joint 13. The honeycomb body 10 and outer cylinder 20 are bonded together by an outer cylinder-honeycomb body joint 50.

[0023] The entry-side joint 11, the outer peripheral joint 12, the exit-side joint 13 and the outer cylinder-honeycomb body joint 50 are formed by brazing (indicated by thick lines in the drawing) using a highly heat-resistant Ni-based brazing material (for example, BNi-5). That is, the corrugated foil 30 and the flat foil 40 are wound around the axial direction in a stacked state to form a wound body, and then a brazing material is disposed on the outer peripheral surface of the wound body or on the inner peripheral surface of the outer cylinder 20 at the intended joining position of the honeycomb body 10 and the outer cylinder 20. After inserting this wound body into the outer cylinder 20, the brazing material is disposed at the intended joining position of the corrugated foil 30 and the flat foil 40, and heated in a vacuum atmosphere, thereby joining the corrugated foil 30 and the flat foil 40 (i.e., forming the entry-side joining portion 11, the outer peripheral joining portion 12, and the exit-side joining portion 13) and joining the honeycomb body 10 and the outer cylinder 20 (i.e., forming the outer cylinder-honeycomb body joining portion 50), thereby producing the honeycomb unit 1. Note that the timing for disposing the brazing material that joins the honeycomb body 10 and the outer cylinder 20 and the brazing material that joins the corrugated foil 30 and the flat foil 40 is not limited to this.

[0024] The inlet-side joint 11 joins the corrugated foil 30 and the flat foil 40 over the entire radial direction of the honeycomb body 10. By providing the inlet-side joint 11, sufficient joint strength can be ensured in the inlet region, which is prone to high temperatures when exhaust gas is passed through and is exposed to exhaust gas pulsation, thereby improving the thermal fatigue resistance of the honeycomb unit 1.

[0025] The peripheral bonding portion 12 bonds a predetermined number of layers of corrugated foils 30 and flat foils 40 from the outermost periphery of the honeycomb body 10 toward the inside in the radial direction. Here, the number of layers bonded by the peripheral bonding portion 12 will be explained in more detail. Figure 3 is a cross-sectional view of the honeycomb unit 1 shown in Figure 1, cut in a direction perpendicular to the axial direction in the region where the peripheral bonding layer 12 exists. In Figure 3, the parts indicated by black dots correspond to the bonding locations, and the region where the black dots exist corresponds to the peripheral bonding portion 12.

[0026] 3 , when a pair of corrugated foil 30 and flat foil 40 sandwiching it is defined as one layer in the radial direction of honeycomb body 10, peripheral joint portion 12 is composed of first region 121 having N layers from the outermost periphery of honeycomb body 10, and second region 122 having N+1 layers from the outermost periphery of honeycomb body 10 (where N is any value from 4 to 7). The number of layers in the region with a high circumferential occupancy rate of honeycomb body 10, either first region 121 or second region 122 (hereinafter also referred to as the representative number of layers of peripheral joint portion 12), is any value from 5 to 7. The reason for this will be described later.

[0027] As an example, in this embodiment, N is set to 5. That is, the first region 121 in the peripheral bonding portion 12 has five layers from the outermost periphery of the honeycomb body 10, and the second region 122 in the peripheral bonding portion 12 has six layers from the outermost periphery of the honeycomb body 10. The representative number of layers is six, which is the number of layers in the region (the second region 122 in this embodiment) that is higher between the occupation ratio L1 of the first region 121 to the outermost periphery of the honeycomb body 10 and the occupation ratio L2 of the second region 122 to the outermost periphery of the honeycomb body 10 in the circumferential direction of the honeycomb body 10.

[0028] (Overall Structure of Honeycomb Unit 1) The overall structure of the honeycomb unit 1 will be described with reference to Fig. 4. Fig. 4 is a vertical cross-sectional view of the honeycomb unit shown in Fig. 1. For ease of explanation, only the inlet-side bonding portion 11, the outer peripheral bonding portion 12, and the outlet-side bonding portion 13 of the honeycomb body 10 in Fig. 4 are shown, and the corrugated foil 30 and the flat foil 40 are not shown.

[0029] The present inventors have conducted extensive research to manufacture a honeycomb unit in which the axial length of the honeycomb body is longer than the diameter of the honeycomb body, and which is excellent in both thermal fatigue resistance and vibration resistance. As a result, it has been found that a honeycomb unit having: (i) a representative number of layers in the outer peripheral joint 12 is any one of 5 to 7 layers, (ii) an axial length of the outer cylinder-honeycomb body joint 50 is 5 mm or more, (iii) an outer diameter of the honeycomb body 10 is A, an axial length from the entry end 14 of the honeycomb body 10 (corresponding to "one end of the honeycomb body" in claim 1) to the entry end 51 of the outer cylinder-honeycomb body joint 50 (corresponding to "one end of the outer cylinder-honeycomb body joint" in claim 1) is B, an axial length of the entry joint 11 (corresponding to "end joint" in claim 1) is C, an exit end 111 of the entry joint 11 (corresponding to "end joint" in claim 1) is D, and an axial length of the entry joint 11 is C. Let D be the axial length from the outer cylinder-honeycomb body joint portion 50 (corresponding to the "other end of the outer cylinder-honeycomb body joint portion" in claim 1) to the inlet end 51 of the outer cylinder-honeycomb body joint portion 50, the axial length of the honeycomb body 10 be E, and the axial length F be from the outlet end 52 of the outer cylinder-honeycomb body joint portion 50 (corresponding to the "other end of the outer cylinder-honeycomb body joint portion" in claim 1) to the outlet end 15 of the honeycomb body 10 (corresponding to the "other end of the honeycomb body" in claim 1). It has been found that by satisfying all of the following formulas (1) to (3), it is possible to achieve both thermal fatigue resistance and vibration resistance by satisfying all of the above requirements (i) to (iii): A>B (1) C<D (2) F≧0.7E-B (3) Each requirement is explained below.

[0030] (Regarding the number of representative layers in the peripheral joint 12) The present inventors conducted extensive research, focusing on the number of representative layers in the peripheral joint 12, in order to manufacture a honeycomb unit that is excellent in both thermal fatigue resistance and vibration resistance. If the number of representative layers in the peripheral joint 12 is four or less, the number of joint layers is too small, making it easier for cracks that occur in the honeycomb body 10 due to vibrations of the engine or exhaust pipe in which the honeycomb unit 1 is installed to penetrate radially through the peripheral joint 12, increasing the risk of the honeycomb body 10 being severed from the outer tube 20 and falling off. On the other hand, if the number of representative layers in the peripheral joint 12 is eight or more, the number of joint layers is too large, making it difficult to release thermal stresses that occur in the honeycomb body 10 during thermal expansion of the honeycomb body 10. This increases the risk of the corrugated foil near the joint in the peripheral joint 12 breaking, causing the honeycomb body 10 to fall off the outer tube 20. In view of these points, the inventors discovered that in order to achieve both thermal fatigue resistance and vibration resistance of the honeycomb unit 1, it is necessary to set the representative number of layers of the outer peripheral joint 12 to anywhere from 5 to 7 layers.

[0031] (Regarding the axial length of the outer tube-honeycomb body joint 50) The axial length of the outer tube-honeycomb body joint 50 is 5 mm or more. If the axial length of the outer tube-honeycomb body joint 50 is less than 5 mm, cracks that occur in the honeycomb body 10 due to vibrations of the engine or exhaust pipe in which the honeycomb unit 1 is installed are likely to penetrate the corrugated foil near the outer peripheral joint 12 in the axial direction due to thermal stress, increasing the risk of the honeycomb body 10 being severed from the outer tube 20 and falling off. Furthermore, while the thermal stress increases as the axial length of the outer tube-honeycomb body joint 50 increases, the axial temperature gradient decreases as the axial length of the honeycomb body 10 increases. Therefore, the upper limit of the axial length of the outer tube-honeycomb body joint 50 depends on the axial length of the honeycomb body 10. For example, the axial length of the outer tube-honeycomb body joint 50 is limited to 30% or less of the axial length of the honeycomb body 10.

[0032] (Regarding A > B and F ≥ 0.7E-B) In the honeycomb unit used in Example 5 of Patent Document 1, the axial length of the honeycomb body is shorter than the diameter of the honeycomb body. In such a honeycomb unit, even if the outer tube-honeycomb body joint is provided on the axial outlet side, the vibration of the honeycomb body with the outer tube-honeycomb body joint as a fulcrum is small, and therefore the vibration resistance is high. On the other hand, in the case of a honeycomb unit (honeycomb unit 1 in this embodiment) in which the axial length of the honeycomb body is longer than the diameter of the honeycomb body, if the outer tube-honeycomb body joint 50 is provided at the outlet end 15 of the honeycomb body 10, the vibration of the honeycomb body 10 with the outer tube-honeycomb body joint 50 as a fulcrum increases. In this case, even a honeycomb unit that satisfies the above (i) and (ii) cannot sufficiently reduce the possibility of the honeycomb body 10 falling off from the outer tube 20. Therefore, by setting F≧0.7E−B and moving the outer casing-honeycomb body joint 50 away from the outlet end 15 of the honeycomb body 10 toward the inlet side, the axial distance from the outer casing-honeycomb body joint 50 to the inlet end 14 of the honeycomb body 10 is narrowed, and vibration of the honeycomb body 10 with the outer casing-honeycomb body joint 50 as a fulcrum can be reduced. However, even when F≧0.7E−B is satisfied, if A≦B, the axial distance from the inlet end 14 of the honeycomb body 10 to the outer casing-honeycomb body joint 50 is not sufficiently short, and therefore sufficient vibration resistance may not be obtained. Therefore, by setting A>B and further narrowing the distance between the inlet end 14 of the honeycomb body 10 and the outer casing-honeycomb body joint 50, the vibration of the honeycomb body 10 can be further reduced and vibration resistance can be sufficiently improved.

[0033] (Regarding C<D) As described above, if the separation distance between the inlet end 14 of the honeycomb body 10 and the outer casing-honeycomb body joint 50 is narrowed with a focus only on vibration resistance, a configuration can be obtained in which the inlet joint 11 and the outer casing-honeycomb body joint 50 overlap, or in which the inlet joint 11 and the outer casing-honeycomb body joint 50 are close to each other in the axial direction. However, in these configurations, thermal stress is concentrated at the outer casing-honeycomb body joint 50 due to expansion and contraction of the inlet joint 11 caused by repeated heating and cooling due to the heat of the exhaust gas and the heat of reaction in the catalyst, making the honeycomb body 10 more likely to fall off. Therefore, by setting C<D and separating the inlet joint 11 and the outer tube-honeycomb body joint 50 by a predetermined amount in the axial direction, it is possible to prevent thermal stress from concentrating at the outer tube-honeycomb body joint 50, thereby improving thermal fatigue resistance and reducing the possibility of the honeycomb body 10 falling off.

[0034] As described above, the honeycomb unit 1 that satisfies all of the above requirements (i) to (iii) can achieve both thermal fatigue resistance and vibration resistance.

[0035] 3, the number of representative layers in the outer peripheral joint portion 12 is preferably six as in this embodiment, which improves the balance between the thermal fatigue resistance and the vibration resistance of the honeycomb unit 1.

[0036] Referring to Figure 4, the axial length C of the inlet-side joint 11 is preferably 5 mm or more and (⅓)E or less. By setting C to 5 mm or more, damage to the corrugated foil 30 and the flat foil 40 due to the pulsating flow of exhaust gas is further suppressed. By setting C to (⅓)E or less, the axial length of the inlet-side joint 11 can be appropriately shortened, which makes it easier to release thermal stress generated in the honeycomb body 10, thereby further reducing the risk of the joint portion of the outer peripheral joint 12 breaking and damaging the honeycomb body 10.

[0037] 2 and 4 , the outlet joint 13 is formed in the outlet region of the honeycomb body 10. The outlet joint 13 joins the corrugated foil 30 and the flat foil 40, which are located radially inward of the outer peripheral joint 12, across the entire radial length of the honeycomb body 10. By providing the outlet joint 13, not only the inlet region but also the outlet region of the honeycomb body 10 are joined, thereby further suppressing damage to the corrugated foil 30 and the flat foil 40 due to exhaust gas pulsation. Because exhaust gas pulsation at the outlet end 15 of the honeycomb body 10 is less severe than at the inlet end 14, the inlet joint 11 must include the inlet end 14 of the honeycomb body 10, but the outlet joint 13 does not necessarily include the outlet end 15. However, the outlet end of the outlet joint 13 is preferably located within a region axially extending 15 mm from the outlet end 15 of the honeycomb body 10. In addition, it is desirable that the axial length of the outlet-side joint portion 13 be set to half or less of the axial length of the inlet-side joint portion 12 .

[0038] To use the honeycomb unit 1 manufactured in this manner as a catalytic converter, a catalyst (not shown) is supported on the corrugated foil 30 and the flat foil 40. The catalyst can be supported by supplying a washcoat liquid (a solution containing gamma alumina, additives, and a precious metal catalyst) to the gas flow passage of the honeycomb body 10 and baking the catalyst onto the foil surface by heat treatment.

[0039] A honeycomb unit carrying a catalyst (i.e., a catalytic converter) can be installed in the exhaust gas path of a vehicle. Vehicles include motorcycles, automobiles, and off-road vehicles. When exhaust gas that has flowed into the gas flow path of the honeycomb body comes into contact with the catalyst, CO, hydrocarbons, and NO contained in the exhaust gas are converted into CO, hydrocarbons, and NO. Ｘ is rendered harmless, and clean gas can be discharged outside the vehicle.

[0040] Second Embodiment The second embodiment differs from the first embodiment in that the shapes of the honeycomb body and the outer cylinder are racetrack shaped (hereinafter also referred to as RT shape) when viewed in the axial direction. Fig. 5 is a plan view of a honeycomb unit 1' in the second embodiment. Note that components that share functions with the first embodiment are given the same names and symbols as in the first embodiment, and descriptions thereof will be omitted as appropriate.

[0041] 5, as described above, the honeycomb body 10' and outer cylinder 20' included in the honeycomb unit 1' in the second embodiment have a racetrack shape when viewed in the axial direction. Here, the "racetrack shape" refers to a shape that imitates a racetrack on a sports field, in which two parallel lines of equal length are drawn, with one end of these lines connected by an arc and the other end of these lines connected by an arc. In the honeycomb unit 1' of this embodiment, the axial length of the honeycomb body 10' is longer than the minor axis A' of the honeycomb body 10', and is preferably 1.4 times or more the minor axis A' of the honeycomb body 10'.

[0042] (Overall Structure of Honeycomb Unit 1') The overall structure of the honeycomb unit 1' will be described with reference to Fig. 6. Fig. 6 is a Y-Y cross-sectional view of the honeycomb unit 1' shown in Fig. 5. For ease of explanation, Fig. 6 shows only the entry-side bonding portion 11', the outer peripheral bonding portion 12', and the exit-side bonding portion 13' of the honeycomb body 10', and does not show the corrugated foil 30 and the flat foil 40.

[0043] The present inventors have conducted extensive research to manufacture a honeycomb unit having an axial length of the honeycomb body longer than its diameter, which is excellent in both thermal fatigue resistance and vibration resistance. As a result, they have found that the honeycomb unit has the following characteristics: (i') the number of representative layers in the outer peripheral joint 12' is any one of 5 to 7 layers, (ii') the axial length of the outer cylinder-honeycomb body joint 50' is 5 mm or more, (iii') In addition to the above-mentioned A', the axial length from the inlet end 14' of the honeycomb body 10' (corresponding to "one end of the honeycomb body" in claim 1) to the inlet end 51' of the outer tube-honeycomb body joint 50' (corresponding to "one end of the outer tube-honeycomb body joint" in claim 1) is B', the axial length of the inlet joint 11' (corresponding to "end joint" in claim 1) is C', the outlet end 111' of the inlet joint 11' (corresponding to "end joint" in claim 1) is C', The inventors have discovered that, when the axial length from an outlet end 52' of the outer cylinder-honeycomb body joint 50' (corresponding to the "other end of the outer cylinder-honeycomb body joint" in claim 1) to an outlet end 15' of the honeycomb body 10' (corresponding to the "other end of the honeycomb body" in claim 1) is defined as D', the axial length of the honeycomb body 10' is defined as E', and the axial length from an outlet end 52' of the outer cylinder-honeycomb body joint 50' (corresponding to the "other end of the outer cylinder-honeycomb body joint" in claim 1) to an outlet end 15' of the honeycomb body 10' (corresponding to the "other end of the honeycomb body" in claim 1) is defined as F', it is possible to achieve both thermal fatigue resistance and vibration resistance by satisfying all of the above requirements (i') to (iii') below: A' > B' (1') C' < D' (2') F' ≧ 0.7E' - B' (3')

[0044] The reasons for the above (i') to (iii') have already been explained in the corresponding (i) to (iii) in the first embodiment, and therefore will not be explained in this embodiment.

[0045] (Examples) Each of the above-described embodiments will be described in more detail with examples. In the examples and comparative examples shown below, SUS436L was used for the outer cylinder. BNi-5 (see JIS Z 3265) powder brazing material was used to join the corrugated foil and flat foil. BNi-5a (AWS standard) foil brazing material with a thickness of 25 μm was used to join the honeycomb body and outer cylinder. The width of the foil brazing material was the value shown in each table.

[0046] First Example First Example (Examples 1 to 42, Comparative Examples 1 to 109) are examples corresponding to the first embodiment described above. Two flat foils made of Fe-20Cr-5Al ferritic stainless steel were prepared, and one of the flat foils was corrugated to form a corrugated foil, while the other flat foil was used as is. After the corrugated foil and flat foil were overlapped and wound around the axial direction to create a wound body, foil brazing material was arranged on the outer surface of the wound body or on the inner surface of the outer tube corresponding to the intended joining position of the honeycomb body and outer tube, and after inserting this wound body into the outer tube, powder brazing material was applied to the intended joining points of the corrugated foil and flat foil, and heat treatment was performed at 1200°C in a vacuum atmosphere, thereby joining the corrugated foil and flat foil (i.e., forming the entry joint 11 and outer peripheral joint 12 in the first embodiment) to produce a honeycomb body, and joining the honeycomb body and outer tube (i.e., forming the outer tube-honeycomb body joint 50 in the first embodiment) to produce a honeycomb unit.

[0047] Thereafter, a washcoat solution containing ceria-zirconia-lanthana-alumina as the main component and 1.25 g of palladium per 100 g was passed through the honeycomb body of the manufactured honeycomb unit, and after removing excess washcoat solution, the honeycomb unit was dried at 180°C for 1 hour and then fired at 500°C for 2 hours to manufacture a honeycomb unit (catalytic converter) carrying a catalyst. The washcoat layer was carried on the corrugated foil and flat foil of this catalytic converter in an amount of 200 g / L of dried weight per volume of the honeycomb body.

[0048] (Evaluation Method) The thermal fatigue resistance and vibration resistance of the catalytic converter were evaluated using a heating / cooling cycle test using a burner test device (not shown). More specifically, the catalytic converter was set in the burner test device, and the number of heating / cooling cycles until the honeycomb body fell off the outer casing (e.g., core displacement) was measured. The burner gas piping and the outer casing were welded via a cone (not shown). The heating / cooling cycle pattern was a temperature pattern in which the inlet gas temperature of the catalytic converter was repeatedly changed between 1000°C and 100°C. Specifically, one cycle consisted of raising the inlet gas temperature to 1000°C in 10 seconds, holding it for 1 minute, and then cooling it to 100°C in 30 seconds. During the test, the catalytic converter was tilted at a 45° angle and continuously subjected to random vibration with an effective acceleration of 60G with a constant acceleration spectral density in the range of 100 Hz to 1000 Hz. Observation was continued up to 2000 cycles, and if the honeycomb body did not fall off up to 2000 cycles, it was evaluated as "◎", if the honeycomb body fell off between 1000 and 2000 cycles, it was evaluated as "◯", and if the honeycomb body fell off less than 1000 cycles, it was evaluated as "×".

[0049] Second Example The second example (Examples 43 to 84, Comparative Examples 110 to 218) corresponds to the second embodiment described above. The test conditions and evaluation method were the same as those of the first example, except that the honeycomb unit constituting the catalytic converter had an RT shape when viewed in the axial direction.

[0050] (Evaluation Results) The parameters and evaluation results of the honeycomb units in the examples and comparative examples are shown in the table.

[0051] In the first example, all catalytic converters using honeycomb units in which (i) the number of representative layers in the outer peripheral joint was between 5 and 7, (ii) the axial length of the outer casing-honeycomb body joint was 5 mm or more, and (iii) all of the following formulas (1) to (3) were evaluated as "○" or better (Examples 1 to 42 of the first example): A>B (1) C<D (2) F≧0.7E-B (3) In particular, among the above examples, the examples in which the number of representative layers in the outer peripheral joint was 6 (Examples 2, 4 to 8, 10, 12 to 17, 19, 21 to 26, 28, 30 to 34, 36, and 38 to 42 of the first example) were evaluated as "◎".

[0052] On the other hand, in the examples (Comparative Examples 1 to 109 of the first example) that did not satisfy at least one of the requirements (i) to (iii) above, the honeycomb body fell off from the outer tube in less than 1000 cycles, and therefore was rated as "X".

[0053] In the second example, all catalytic converters using honeycomb units in which (i') the number of representative layers in the outer peripheral joint was between 5 and 7, (ii') the axial length of the outer casing-honeycomb body joint was 5 mm or more, and (iii') all satisfied the following formulas (1') to (3') were evaluated as "○" or better (Examples 43 to 84 of the second example): A' > B' (1') C' < D' (2') F' ≧ 0.7E' - B' (3') In particular, the examples in which the number of representative layers in the outer peripheral joint was 6 (Examples 44, 46 to 50, 52, 54 to 59, 61, 63 to 68, 70, 72 to 76, 78, 80 to 84 of the second example) were evaluated as "◎".

[0054] On the other hand, in the examples (comparison examples 110 to 218 of the second example) that did not satisfy at least one of the requirements (i') to (iii') above, the honeycomb body fell off from the outer tube in less than 1000 cycles, and therefore was rated as "X".

[0055] (Modifications) In the first embodiment described above, the outlet-side joints 13 are formed on the honeycomb body 10, but the honeycomb body 10 may also be configured not to have the outlet-side joints 13. Similarly, in the second embodiment described above, the honeycomb body 10' is formed with the outlet-side joints 13', but the honeycomb body 10' may also be configured not to have the outlet-side joints 13'.

[0056] 1, 1': Honeycomb unit 10, 10': Honeycomb body 11, 11': Inlet side joint 12, 12': Peripheral joint 20, 20': Outer cylinder 30: Corrugated foil 40: Flat foil 50, 50': Outer cylinder-honeycomb body joint 121: First region 122: Second region

Claims

1. A honeycomb unit comprising a honeycomb body formed by winding flat and corrugated metal foils, and an outer tube arranged in a position surrounding the outer peripheral surface of the honeycomb body, wherein the axial length of the honeycomb body is longer than the outer diameter of the honeycomb body, wherein the honeycomb body and the outer tube are joined to each other at an outer tube-honeycomb body joint, the flat foils and the corrugated foils are joined to each other at an end joint at one end of the honeycomb body, and are joined to each other at a peripheral joint that connects to the other end of the end joint, the end joint is formed over all layers in the stacking direction of the flat foils and the corrugated foils, and the peripheral joint is formed from the other end of the end joint to the other end of the honeycomb body, and when a set of the corrugated foil and the flat foils sandwiching it in the stacking direction is defined as one layer, the outer peripheral joint portion is composed of a first region having N layers from the outermost periphery of the honeycomb body, and a second region having N+1 layers from the outermost periphery of the honeycomb body (where N is any value from 4 to 7); the number of layers in the region having a high circumferential occupancy rate of the honeycomb body among the first region and the second region is any value from 5 to 7; the axial length of the outer tube-honeycomb body joint portion is 5 mm or more; and the honeycomb unit satisfies the following formulas (1), (2), and (3), where A is the outer diameter of the honeycomb body, B is the axial length from one end of the honeycomb body to one end of the outer tube-honeycomb body joint portion, C is the axial length of the end joint portion, D is the axial length from the other end of the end joint portion to one end of the outer tube-honeycomb body joint portion, E is the axial length of the honeycomb body, and F is the axial length from the other end of the outer tube-honeycomb body joint portion to the other end of the honeycomb body. A>B...(1) C<D...(2) F≧0.7E-B...(3) 2. A racetrack-type honeycomb unit having a honeycomb body formed by winding flat and corrugated metal foils, and an outer tube arranged in a position surrounding the outer peripheral surface of the honeycomb body, wherein the axial length of the honeycomb body is longer than the minor axis of the honeycomb body when viewed in the axial direction, wherein the honeycomb body and the outer tube are joined to each other by an outer tube-honeycomb body joint, the flat foils and the corrugated foils are joined to each other at an end joint at one end of the honeycomb body, and are joined to each other at a peripheral joint connected to the other end of the end joint, the end joint is formed over all layers in the stacking direction of the flat foils and the corrugated foils, and the peripheral joint is formed from the other end of the end joint to the other end of the honeycomb body, and when a set of the corrugated foil and the flat foils sandwiching it in the stacking direction is defined as one layer, the peripheral joint portion comprises a first region having N layers from the outermost periphery of the honeycomb body, and a second region having N+1 layers from the outermost periphery of the honeycomb body (where N is any number from 4 to 7); the number of layers in the region having a high circumferential occupancy rate of the honeycomb body in the first region and the second region is any number from 5 to 7; the axial length of the outer tube-honeycomb body joint portion is 5 mm or more; A honeycomb unit that satisfies the following formulas (1'), (2'), and (3'), where A' is the minor axis of the honeycomb body when viewed in the axial direction, B' is the axial length from one end of the honeycomb body to one end of the outer cylinder-honeycomb body joint, C' is the axial length of the end joint, D' is the axial length from the other end of the end joint to one end of the outer cylinder-honeycomb body joint, E' is the axial length of the honeycomb body, and F' is the axial length from the other end of the outer cylinder-honeycomb body joint to the other end of the honeycomb body. A'>B' (1') C'<D' (2') F'≧0.7E'-B' (3') 3. The honeycomb unit according to claim 1, further satisfying the following formula (4): E≧1.4A (4) 4. The honeycomb unit according to claim 2, further satisfying the following formula (4'): E' ≥ 1.4A' (4') 5. A honeycomb unit according to any one of claims 1 to 4, characterized in that the number of layers in the first region and the second region, which have a high circumferential occupancy rate of the honeycomb body, is six.

6. A catalytic converter, characterized in that a catalyst is supported on the honeycomb body according to any one of claims 1 to 4.

7. A catalytic converter, characterized in that a catalyst is supported on the honeycomb body according to claim 5.

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