JPH0719034A - Current-supplying heating type catalyst - Google Patents

Abstract

PURPOSE:To heat catalyst partially, and prevent oxidation reaction heat from escaping outside. CONSTITUTION:Current-carrying heating type catalyst 9 composed of a layered structure body of metallic thin plates and metallic corrugated plates in formed of an upstream catalyst 14 and a downstream catalyst 15. The outer peripheral part of the upstream catalyst 14 is connected to an electrode 19, and an electric surrent is supplied to the downstram catalyst 15 from the upstream catalyst 14 through the central part 13 of the layered structure body. At this time, only a heating area 27 positioned in the vicinity of the upstream end surface of the upstream catalyst 14 is partially heated.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electrically heated catalyst.

[0002]

2. Description of the Related Art A catalyst for purifying harmful components in exhaust gas does not exert a purifying action unless it reaches an activation temperature or higher. Therefore, in order to start the purifying action by the catalyst early after the engine is started, the catalyst must be activated. It is necessary to raise to the activation temperature as soon as possible. Therefore, a laminated structure of a metal thin plate and a metal corrugated plate supporting a catalyst is placed in the exhaust passage, and an electric current is passed through the laminated structure to heat the entire laminated structure to thereby generate a catalyst supported by the laminated structure. An electrically heated catalyst is known in which the temperature is raised to the activation temperature within a short time (see Japanese Patent Application Laid-Open No. 3-246315).

However, in such a laminated structure, the catalyst in a partial region of the laminated structure reaches the activation temperature and unburned H
When the oxidation reaction of C, CO, etc. is started, the catalyst of the entire laminated structure reaches the activation temperature within a short time due to the heat of the oxidation reaction. Therefore, in such a laminated structure, in order to raise the temperature of the entire catalyst to the activation temperature in a short time, it is sufficient to raise only a part of the temperature of the laminated structure at an early stage. It is meaningless to heat the entire laminated structure like a catalyst because it wastes electric power.

By the way, the oxidation reaction of unburned HC, CO, etc. becomes more active as the amount of exhaust gas in contact with the catalyst increases, and the heat of oxidation reaction generated with it increases. Therefore, in order to quickly raise the entire catalyst to the activation temperature by causing a part of the laminated structure to generate heat, it is preferable to generate heat in the part of the laminated structure having a large amount of exhaust gas flowing. In this case, it is considered that the laminated structure portion having the largest amount of exhaust gas flowing therein is the central portion of the laminated structure located in the central portion of the exhaust passage.

Therefore, in order to locally generate heat in the central portion of the laminated structure, a center electrode is arranged in the central portion of the laminated structure,
An electrically heated catalyst is known in which a current is supplied from the central electrode to the central portion of the laminated structure to generate heat only in the central portion of the laminated structure (see Japanese Patent Laid-Open No. 48-54312).

[0006]

However, when the center electrode is provided in this way and heat is generated only from the center part of the laminated structure from the center electrode, the unburned HC and CO are oxidized when the oxidation reaction is started. There is a problem that the heat of reaction escapes to the outside through the center electrode, and thus it takes time for the entire catalyst to reach the activation temperature.

[0007]

In order to solve the above problems, according to the present invention, in an electrically heated catalyst arranged in an engine exhaust passage, the catalyst is passed from the outer peripheral portion of the catalyst through the central portion of the catalyst and then again. A current path reaching the outer peripheral portion of the catalyst is formed, and only a part of the catalyst area along the current path is a heat generating area and the remaining catalyst area is a non-heat generating area that does not substantially generate heat.

Further, according to the present invention, in order to solve the above problems, an insulating region extending from the outer peripheral portion of the catalyst toward the central portion of the catalyst is formed in the catalyst, and a current path is formed around this insulating region. However, at least a part of the catalyst portion located upstream of the insulating area is a heat generating area, and the catalyst portion downstream of the insulating area is a non-heat generating area that does not substantially generate heat.

[0009]

According to the first aspect of the invention, the catalyst region, which should generate heat, is locally energized and heated by the current supplied from the outer peripheral portion of the catalyst. In the second aspect of the invention, the catalyst portion located on the upstream side is electrically heated, and the heat of oxidation reaction in this catalyst portion is carried by the exhaust gas to the catalyst portion located on the downstream side to heat the catalyst portion on the downstream side.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is an engine body, 2 is an exhaust manifold, 3 is a catalytic converter, 4 is an exhaust pipe, 5 is a secondary air supply device provided as necessary, and 2 respectively.
The secondary air supply device 5 includes an engine-driven air pump 6 and a control valve 7 that controls the amount of secondary air to be supplied into the exhaust manifold 2. An electrically heated catalyst 9 is arranged in a casing 9 of the catalytic converter 3, and a main catalyst 10 made of a three-way catalyst is arranged in a casing 8 downstream of the electrically heated catalyst 9.

FIG. 2 shows a first embodiment of the electrically heated catalyst 9 arranged in the catalytic converter 3. As shown in FIG. 3, the electrically heated catalyst 9 has a laminated structure in which a metal thin plate 11 made of a resistor and a metal thin plate 12 made of a resistor are alternately wound around a central axis. As shown in FIG. 2, this laminated structure has a common laminated structure central portion 13 and a casing 8 extending radially outward from the laminated structure central portion 13 on the upstream side of the laminated structure central portion 13.
Of the upstream laminated structure 14 extending to the vicinity of the inner peripheral surface of the laminated structure, and the laminated structure central part 1 on the downstream side of the laminated structure central part 13.
3 and the downstream side laminated body 15 extending outward in the radial direction to the inner peripheral surface of the casing 8. The upstream-side laminated structure 14 and the downstream-side laminated structure 15 have a disk shape having a substantially uniform axial width over the entire length in the radial direction, and the upstream-side laminated structure 14 and the downstream-side laminated structure. A disk-shaped insulating space 16 extending outward from the outer peripheral surface of the laminated structure central portion 13 is formed between the portions 15.

The outer peripheral portion of the upstream side laminated structure 14 is welded and fixed to the inner peripheral surface of the metallic cylindrical body 17, and the metallic cylindrical body 17 protrudes to the outside of the casing 3 via the insulator 18. Is connected to the electrode 19. On the other hand, the downstream laminated structure 15
The outer peripheral portion of is fixed to the inner peripheral surface of the casing 3 by welding. As shown in FIG. 1, the electrode 19 is connected to the positive side of the power source 21 via the switch 20, and the negative side of the power source 21 is connected to the casing 8.

Both sides of the metal thin plate 11 and the metal corrugated plate 12 constituting the laminated structure central portion 13, the upstream laminated structure 14 and the downstream laminated structure 15 are covered with an alumina oxide layer which is an electrical insulator. Further, three-way catalyst particles are carried on both surfaces of the metal thin plate 11 and the metal corrugated plate 12. Therefore, the laminated structure serves as a catalyst, and hence the upstream laminated structure 14 is referred to as an upstream catalyst and the downstream laminated structure 15 is referred to as a downstream catalyst.

As described above, since both surfaces of the metal thin plate 11 and the metal corrugated plate 12 are covered with the alumina oxide layer made of an electric insulator, when the switch 20 is turned on, a current flows from the metal cylindrical body 17 to the metal. Circularly flows in the thin plate 11 and the metal corrugated plate 12 to reach the laminated structure central portion 13, and then in the metal thin plate 11 and the metal corrugated plate 12 that constitute the downstream side catalyst 15 in the circumferential direction. It flows and reaches the casing 3. At this time, as described above, since the metal thin plate 11 and the metal corrugated plate 12 are made of resistors, the entire laminated structure will generate heat. However, in the present invention, not only the entire laminated structure is heated but only a part of the laminated structure is partially heated. Therefore, in the first embodiment shown in FIG. 2, only a part of the upstream side catalyst 14 is partially heated. Since a special treatment is applied to heat the sheet, the special treatment will be described below.

That is, both end face portions 22 and 23 of the downstream side catalyst 15 shown by dots in FIG. 2 are the end face portions of the metal thin plate 11 and the metal corrugated plate 1 as shown in FIG. 4 (B).
The portions 24 of the two end face portions that contact each other are melted together by electrical discharge machining. Thus, the contact portion 24
Is melted, the alumina oxide layer is destroyed, so that the metal thin plate 11 and the metal corrugated plate 12 adjacent to each other are short-circuited, so that the electric current flows in the radial direction in the downstream catalyst 15 through these short-circuited portions. It will be. In this case, the current flows in the metal thin plate 11 and the metal corrugated plate 12 while flowing from the short-circuited portion to the adjacent short-circuited portion, but this distance is short, and therefore the downstream side catalyst 15 is substantially resistant to the radial direction. There is no conduction. Therefore, the downstream catalyst 1
No. 5 does not substantially generate heat.

On the other hand, both end surface portions 25 of the outer peripheral portion of the upstream side catalyst 14 and both end surface portions 26 of the central portion of the upstream side catalyst 14 which are shown by dots in FIG. 2 also contact each other as shown in FIG. 4 (B). The parts 24 to be melted are melted by electric discharge machining. Therefore, the outer peripheral portion and the central portion of the upstream side catalyst 14 are also brought into a conductive state with substantially no resistance in the radial direction, so that the outer peripheral portion and the central portion of the upstream side catalyst 14 do not substantially generate heat.

On the other hand, in the region surrounded by the broken line 27 in FIGS. 2 and 3, when the metal thin plate 11 and the metal corrugated plate 12 are wound, the metal thin plate 11 is denoted by reference numeral 28 in FIG. And a part of the contact portion of the metal corrugated plate 12 is bonded to each other using a laser beam. The joint portion 28 formed by such a laser beam is shown in FIG.
As shown in FIG. In this way, the metal thin plate 11 and the metal corrugated plate 1 are formed by using the laser beam.
When the two are joined to each other, the alumina oxide layer of the joint portion 28 is destroyed, the metal thin plate 11 and the metal corrugated plate 12 are electrically connected, and the resistance value of the joint portion 28 becomes considerably small. Therefore, the amount of current flowing in the joint portion 28 is much larger than the amount of current flowing in the metal thin plate 11 and the metal corrugated plate 12 in the circumferential direction. as a result,
Even if the resistance value of the joint portion 28 is small, the Joule heat generated is much larger than the Joule heat generated in the metal thin plate 11 and the metal corrugated plate 12. Therefore, when an electric current is passed through the upstream side catalyst 14, the joint portion 28 Will generate heat.

As described above, when a current is applied to the laminated structure shown in FIG. 2, only the area surrounded by the broken line 27 generates heat, and the remaining area does not substantially generate heat. Figure 2
As can be seen from the above, the heat generating region 27 is formed slightly behind the upstream end face of the upstream catalyst 14, but the heat generating region 27 can also be formed on the upstream end face of the upstream catalyst 14. In any case, in the first embodiment shown in FIG. 2, when the switch 20 is turned on, the heat generating area 27 located in the intermediate portion of the upstream end surface excluding the outer peripheral portion and the central portion of the upstream catalyst 14 becomes a donut shape. You will get a fever.

The energization heating type catalyst 9 shown in FIG. 2 is energized as soon as the engine is started. When energization is started, the heat generation region 27 generates heat and the temperature of the three-way catalyst in the heat generation region 27 rises to the activation temperature in a short time. When the air-fuel mixture is made rich for a while after the engine is started, a large amount of unburned HC and CO are discharged from the engine, but the oxygen concentration in the exhaust gas is extremely low. Even when the activation temperature is reached, the unburned HC and CO are hardly oxidized. Therefore, when the air-fuel mixture is made rich for some time after the engine is started, as soon as the three-way catalyst reaches the activation temperature in order to start the oxidation action of unburned HC and CO, the secondary air supply devices 5 to 2 Next air is supplied.

When the secondary air is supplied to start the oxidation reaction of unburned HC and CO in the heat generation region 27, this unburned H
The heat of oxidation reaction due to the oxidation reaction of C and CO is extremely large,
Therefore, when the oxidation reaction of unburned HC and CO is started, the heating effect of the exhaust gas also assists and the entire upstream side catalyst 14 reaches the activation temperature in a short time. When the temperature of the upstream side catalyst 14 rises, the heat of the upstream side catalyst 14 is carried by the exhaust gas and transferred to the downstream side catalyst 15, thus the downstream side catalyst 1
5 also rises in temperature and reaches the activation temperature. Therefore, the upstream side catalyst 14 and the downstream side catalyst 15 can be arranged within a short time after the engine is started.
At this point, the purification action of unburned HC and CO is started.

When the oxidation reaction is started in the upstream side catalyst 14 in this way, the temperature of the upstream side catalyst 14 starts to rise due to the heat of the oxidation reaction, so that the energization to the electrically heated catalyst 9 is stopped. Then, after a while, the main three-way catalyst 10 also reaches the activation temperature, and the main three-way catalyst 10 also has unburned HC and CO.
The purification action of is started. Note that the amount of exhaust gas is small during the fast idling operation immediately after the engine is started, and unburned HC and CO discharged from the engine at this time are the electrically heated catalyst 9
It can be purified sufficiently by itself. After that, when the vehicle starts traveling, the main three-way catalyst 10 has reached the activation temperature, so that the main three-way catalyst 10 mainly performs the exhaust gas purification action at this time.

When the air-fuel mixture is made lean or at the stoichiometric air-fuel ratio immediately after the engine is started, it is not necessary to provide the secondary air supply device 5 because there is sufficient oxygen in the exhaust gas. Further, when the oxidation action of unburned HC and CO is started immediately after the engine is started, the electric heating type catalyst 9 is started before the engine is started.
Should be heated by energization. By the way, the oxidation reaction of unburned HC and CO is actively performed in a region where the amount of unburned HC and CO is large, that is, in a region where the amount of exhaust gas flowing through the electrically heated catalyst 9 is large. In the catalytic converter 3, the amount of exhaust gas flowing in the central portion is larger than that in the peripheral portion, so that the upstream side catalyst 1
In No. 4, unburned HC and CO in the central part rather than the peripheral part
The oxidation reaction of is activated. Therefore, in the upstream side catalyst 14, a larger amount of heat of oxidation reaction is generated in the central portion than in the peripheral portion thereof, and it is preferable that the heat of the oxidation reaction can be used for heating the downstream side catalyst 15 without being released to the outside. In the present invention, the electrode 19 is connected to the outer peripheral portion of the upstream side catalyst 14 which generates a small amount of heat of oxidation reaction, and therefore the heat of oxidation reaction escaping to the outside via the electrode 19 is extremely small. Therefore, most of the oxidation reaction heat generated in the upstream side catalyst 14 can be used for heating the downstream side catalyst 15, thus raising the whole of the electrically heated catalyst 9 to the activation temperature in a short time. It will be possible. Also, the electrode 1
Since 9 does not hinder the exhaust gas flowing into the upstream side catalyst 14, the unburned HC,
The CO oxidation reaction can be initiated.

Further, in order to perform a good purification action in the electrically heated catalyst 9, it is necessary that the electrically heated catalyst 9 has a surface area of a certain value or more. For that purpose, the electrically heated catalyst 9 has a shaft of a certain value or more. It is necessary to have a directional length. In this case, if the electrically heated catalyst 9 is separated into the upstream side catalyst 14 and the downstream side catalyst 15 with the insulating space 16 provided therebetween while ensuring a certain axial length or more, the following advantages can be obtained.

That is, first of all, in order to reduce the power consumption, it is necessary to increase the overall resistance value of the electrically heated catalyst 9, and as in the present invention, a part of the electrically heated catalyst 9 is locally removed. In the case where heat is generated, it is necessary to increase the resistance value of the part where heat is generated. By the way, in this case, when the electrically heated catalyst 9 is separated into the upstream catalyst 14 and the downstream catalyst 15 as shown in FIG. 2, the axial width of the heat generating region other than the peripheral portion and the central portion of the upstream catalyst 14 is narrow. Therefore, the resistance value of the heat generation region of the upstream side catalyst 14 can be increased. As a result, it is possible to reduce the amount of power consumption necessary for electrically heating the electrically heated catalyst 9.

Secondly, when the electrically heated catalyst 9 is electrically heated, a large difference in thermal expansion occurs between the electrically heated catalyst 9 and the casing 3. In this case, the shaft of the joint between the electrically heated catalyst 9 and the casing 3 is made. If the directional length is long, a large axial shearing force is generated at this joint. However, when the electrically heated catalyst 9 is separated into the upstream side catalyst 14 and the downstream side catalyst 15 as shown in FIG. 2, only the outer peripheral portion of the downstream side catalyst 15 can be joined to the casing 3. The axial length of the joint portion between the equation catalyst 9 and the casing 3 can be shortened. As a result, the axial shearing force generated at the joint between the downstream side catalyst 15 and the casing 3 becomes small, and therefore the joint can be prevented from being damaged.

Further, the temperature of the exhaust gas gradually lowers while flowing through the exhaust passage, so that the temperature of the upstream end surface of the upstream catalyst 14 rises most due to the exhaust gas. Therefore, if the upstream end surface of the upstream catalyst 14 is heated, a part of the electrically heated catalyst 9 can be raised to the activation temperature in the shortest time as compared with the case where the other regions are heated. Therefore, FIG.
In the first embodiment, as shown in FIG.
A heat generating region 27 is provided near the upstream end face of the. In this case, as described above, the heat generating area 27 can be formed on the upstream end surface of the upstream catalyst 14.

Further, the metal thin plate 11 and the metal corrugated plate 12
In a laminated structure in which and are alternately wound around the central axis, if the metal thin plates 11 and the metal corrugated plates 12 adjacent to each other are not constrained to each other, the metal thin plates 11 and the metal corrugated plate 12 adjacent to each other Moves relative to the axial direction, and as a result, the central portion of the laminated structure projects in the axial direction like the telescopic inner tube of the telescope. However, as shown in FIG. 2, in the first embodiment, the metal thin plates which are adjacent to each other at both end face portions 22 and 23 of the downstream side catalyst 15 and both end face portions 25 and 26 of the peripheral portion and the central portion of the upstream side catalyst 14. 14 and the metal corrugated plate 15 are firmly joined by electric discharge machining, and the heat generation area 2 of the upstream side catalyst 14
7 also adjoins the metal thin plate 11 and the metal corrugated plate 1
There is no risk of the central part of the laminated structure protruding in the axial direction, since 2 and 2 are partially connected to each other using a laser beam.

FIGS. 5 to 33 show various examples in which the electrically heated catalyst 9 shown in FIG. 2 is modified, and these various examples will be sequentially described. Note that FIG.
33 to 33, components similar to those in the first embodiment shown in FIG. 2 are designated by the same reference numerals. In the second embodiment shown in FIG. 5, the electrode 19 extends straight from the outer peripheral surface of the metal tubular body 17 toward the radial outside of the upstream catalyst 14. When such an electrode 19 is used, the heat capacity of the electrode 19 becomes small, and thus the amount of heat escaping to the outside via the electrode 19 can be reduced.

In the third embodiment shown in FIG. 6, the axial width of the heat insulating space 16 between the upstream side catalyst 14 and the downstream side catalyst 15 is made considerably large. When the axial width of the adiabatic space 16 is increased in this way, the exhaust gases that have passed through the upstream catalyst 14 are mixed with each other in the radial direction while flowing through the insulating space 16, and the amount of exhaust gas flowing into the downstream catalyst 15 and The exhaust gas temperature is made uniform. As a result, the downstream catalyst 1
In No. 5, the whole reaches the activation temperature in a short time, and the unburned HC and CO are uniformly oxidized in the whole downstream catalyst 15.

In the fourth embodiment shown in FIG. 7, the axial length of the downstream side catalyst 15 is greatly lengthened so that the downstream side catalyst 15 plays the role of the main catalyst 10 shown in FIG. Therefore, in the fourth embodiment, it is not necessary to separately provide the main catalyst 10 shown in FIG. Also in the fifth embodiment shown in FIG. 8, the axial length of the downstream catalyst 15 is set so that the downstream catalyst 15 plays the role of the main catalyst 10 shown in FIG. 1 similarly to the fourth embodiment shown in FIG. It is made very long. However, in the fifth embodiment, unlike the fourth embodiment, the outer diameter of the downstream side catalyst 15 is smaller than the inner diameter of the casing 8, and the downstream side catalyst 15
Is supported by the casing 10 by a plurality of strip-shaped stress absorbing plates 30. These stress absorbing plates 30
Are arranged so that the stress absorbing plates 30 adjacent to each other at equal angular intervals around the downstream side catalyst 15 are in close contact with each other.
The upstream end of each stress absorption plate 30 is welded and fixed to the upstream end of the outer peripheral surface of the downstream side catalyst 15, and the downstream end of each stress absorption plate 30 is welded and fixed to the inner peripheral surface of the casing 8. When such a stress absorbing plate 30 is used, the downstream side catalyst 15 can freely expand in the radial direction and the axial direction when the temperature of the downstream side catalyst 15 becomes high, and thus the downstream side catalyst 15 can be expanded. It is possible to prevent a large stress from being generated in 15.

In the sixth embodiment shown in FIGS. 9 and 10, the heat generating area 27 of the upstream catalyst 14 is formed only in the upper half area of the upstream catalyst 14. That is, the velocity distribution of the exhaust gas in the casing 8 may be influenced by the shape of the exhaust passage upstream of the casing 8 to have a velocity distribution as shown by S in FIG. 9, for example. In such a case, even if the temperature of the entire upstream side catalyst 14 is raised to the activation temperature, most of the unburned HC and CO oxidation reaction is caused by the upstream side catalyst 1.
4 is carried out in the upper half region of the upstream side catalyst 14 where the amount of exhaust gas flowing into the No. 4 is large, so that most of the heat of oxidation reaction is generated in the upper half region of the upstream side catalyst 14. In such a case, even if the lower half of the upstream side catalyst 14 is heated, almost no heat of oxidation reaction is generated in the lower half region of the upstream side catalyst 14, so that even if the lower half of the upstream side catalyst 14 is heated, the electric power is not generated. It only makes sense to consume. Therefore, in FIGS. 9 and 10, the heat generation region 27 is formed only in the upper half region of the upstream side catalyst 14 where the amount of exhaust gas flowing into the upstream side catalyst 14 is large in order to effectively use the electric power.

In the seventh embodiment shown in FIG. 11, a large number of louvers 31 for guiding exhaust gas are formed on the metal thin plate 11 and the metal corrugated plate 12 in the axial center region of the downstream side catalyst 15. 12A shows an enlarged view of a region A surrounded by a chain line in FIG. 11, and FIG. 12B shows FIG. 12A.
FIG. As can be seen from FIG. 12, area A
In this case, each louver 31 is formed by cutting and raising a part of the metal thin plate 11 and the metal corrugated plate 12 downward. Therefore, in the region A, the exhaust gas is flowed by each louver 31 as indicated by the arrow X. Is deflected radially outward.

On the other hand, in a region B surrounded by a chain line in FIG. 11, a part of the metal thin plate 11 and the metal corrugated plate 12 is shown in FIG.
It is cut and raised upward in the direction opposite to (A) and (B), so that in the region B, the exhaust gas flow direction is deflected radially inward by the louvers 31 as shown by the arrow Y. . Further, each of these louvers 31 has a symmetrical shape with respect to the axis of the downstream side catalyst 15. Therefore, in the seventh embodiment, the exhaust gas heated by the heat of the oxidation reaction in the heat generation region 27 of the upstream side catalyst 14 is used as the downstream side catalyst 1.
Therefore, it is possible to raise the temperature of the entire downstream side catalyst 15 to the activation temperature in a short time and to carry out a good oxidation reaction of unburned HC and CO in the entire downstream side catalyst 15. .

In the eighth embodiment shown in FIG. 13, the heat generation area 27
Is formed in the vicinity of the downstream end surface of the upstream catalyst 14, and is formed on the metal thin plate 11 and the metal corrugated plate 12 between the upstream end surface of the upstream catalyst 14 and the heat generation area 27 in the same manner as the louver 31 shown in FIG. A large number of louvers 31 having a shape are formed. In the eighth embodiment, the louver 31 in the area A is formed so that the exhaust gas flow direction is deflected radially outward X, and the louver 31 in the area B has the exhaust gas flow direction in the radial direction. The louvers 31 are formed so as to be deflected inward Y, and each louver 31 has a symmetrical shape with respect to the axis of the upstream catalyst 14. Therefore, in the eighth embodiment, the exhaust gas flowing into the upstream side catalyst 14 is collected in the heat generation area 27,
Thus, the heating action of the exhaust gas can rapidly raise the temperature of the exothermic region 27 to the activation temperature, and after the activation temperature is reached, a large amount of heat of oxidation reaction is generated. The activation temperature can be raised in a short time.

In the ninth embodiment shown in FIG. 14, the upstream catalyst 1
The cross-sectional shape of the heat insulating space 16 is formed in a dogleg shape so that the axial width of 4 becomes smaller in the heat generating region 27. In this way, the heat capacity around the heat generating area 27 becomes small,
Thus, it is possible to shorten the time required for the heat generating region 27 to reach the activation temperature. In the tenth embodiment shown in FIG. 15, the insulating space 16 is obliquely extended so that the axial width of the upstream side catalyst 14 becomes gradually narrower radially outward.
By doing so, the cross-sectional area of the heat radiation path for the heat that escapes toward the electrode 19 becomes small, so the amount of heat that escapes to the outside via the electrode 19 decreases, and thus the time until the heat generating region 27 reaches the activation temperature. Can be shortened.

In the eleventh embodiment shown in FIG. 16, the insulating space 16 is obliquely provided so that the axial width of the upstream side catalyst 14 becomes gradually narrower inward in the radial direction. In this way, the cross-sectional area of the heat dissipation path for the heat escaping toward the laminated structure central portion 13 is reduced, so the amount of heat escaping to the laminated structure central portion 13 is reduced, and thus the heat generating region 27 reaches the activation temperature. The time to reach can be shortened.

In the twelfth embodiment shown in FIG. 17, the insulating space 16 is formed so that the axial width of the upstream side catalyst 14 becomes gradually narrower from the central portion of the heat radiating region 27 toward both the radially outer side and the radially inner side. The cross-sectional shape of is formed in a dogleg shape.
In this way, both the amount of heat escaping to the outside via the electrode 19 and the amount of heat escaping to the central portion 13 of the laminated structure are reduced, so that the time until the heat generating region 27 reaches the activation temperature can be further shortened. .

In the thirteenth embodiment shown in FIG. 18, the heat generation area 2
The upstream end surface of the upstream catalyst 14 has a triangular cross-section so that the central portion of the upstream end 7 protrudes to the upstream side. As described above, the temperature of the exhaust gas gradually decreases while flowing through the exhaust passage, and therefore, in order to promote the temperature rise of the heat generating region 27, it is better to position the heat generating region 27 as upstream as possible. Therefore, in the thirteenth embodiment, the heat generation area 27
The upstream end surface portion of the upstream catalyst 14 in which is formed is projected to the upstream side.

In the fourteenth embodiment shown in FIG. 19 as in the thirteenth embodiment shown in FIG. 18, the upstream end face portion of the upstream catalyst 14 in which the heat generating region 27 is formed is further projected to the upstream side. In the fourteenth embodiment, the exhaust gas flow flowing through the center of the casing 3 is deflected toward the heat generating area 27,
That is, an exhaust gas guide pin 32 having a conical tip portion is attached on the central axis of the electrically heated catalyst 9 in order to collect the exhaust gas in the heat generating region 27 and raise the temperature of the heat generating region 27 as quickly as possible.

In the fifteenth embodiment shown in FIG. 20, the heat generation area 2
The upstream end face of the upstream catalyst 14 has a conical shape in which the upstream end face of the upstream catalyst 14 projects toward the upstream side so that the exhaust gas having a high temperature flows into the heat generation region 27 by arranging 7 as far upstream as possible. In the sixteenth embodiment shown in FIG. 21, the upstream catalyst 14 is provided only in the upper half region of the electrically heated catalyst 9.
The cross-sectional shape of the upstream end surface of the upstream catalyst 14 is triangular so that the center of the heat generating region 27 is located on the most upstream side. In the sixteenth embodiment, most of the exhaust gas has a heat generation region 2 even if the velocity distribution of the exhaust gas in the casing 8 is offset as shown by the arrow S in FIG.
The upstream-side catalyst 14 is arranged in a region where the flow rate of exhaust gas is large so that the catalyst 14 flows into the upstream side catalyst 7.

In the seventeenth embodiment shown in FIG. 22, the heat generation area 2
7 so that the center of 7 is located on the most downstream side.
The upstream end face of the surrounding upstream catalyst 14 is recessed in a V shape. In this way, the exhaust gas collects in the heat generating area 27, so that the temperature rise of the heat generating area 27 can be promoted. In the eighteenth embodiment shown in FIG. 23, the upstream end surface of the upstream catalyst 14 is formed into a concave conical shape in order to collect the exhaust gas in the heat generating area 27 and promote the temperature rise of the heat generating area 27. Further, in this eighteenth embodiment, the downstream side catalyst 15
In order to reduce the shearing force generated at the joint between the outer peripheral portion of the casing and the casing 8, the annular space 1 is provided around the downstream side catalyst 15.
6a is formed, and the end surface portions 22a and 23a of the downstream side catalyst 15 facing the annular space 16a are melt-bonded by electric discharge machining.

In the nineteenth embodiment shown in FIG. 24, as in the eighteenth embodiment shown in FIG. 23, the upstream end surface of the upstream catalyst 14 is formed into a concave conical shape. The axial length of the downstream side catalyst 15 is greatly lengthened so that the downstream side catalyst 15 plays the role of the main catalyst 10 shown in FIG. FIG. 25 shows a twentieth embodiment of the electrically heated catalyst 9 which is suitable when the casing 8 is bent in an L shape. In this case, the upstream end surface of the upstream catalyst 14 is inclined with respect to the axis of the electrically heated catalyst 9 so that the exhaust gas uniformly flows into the entire area of the upstream catalyst 14, especially the heat generation area 27. There is.

FIGS. 26 and 27 show a twenty-first embodiment of the electrically heated catalyst 9 suitable for the case where the casing 8 has a pair of exhaust gas inlets 33a and 33b. In the twenty-first embodiment, each exhaust gas inlet 33a, 3a
The upstream side catalyst 1 into which the exhaust gas flowing in from 3b most flows in
4, a heat generating region 27 is formed in each of the upstream side catalyst 14 facing the exhaust gas inlets 33a and 33b.

FIG. 28 shows a twenty-second embodiment of an electrically heated catalyst 9 suitable for a case where a pair of catalytic converters 3a and 3b are arranged in parallel. In the twenty-second embodiment, the electrically heated catalyst 9 composed of the upstream catalyst 14 and the downstream catalyst 15 is arranged in each of the catalytic converters 3a and 3b, but the metal tubular body 17 of each upstream catalyst 14 is arranged. On the other hand, a common electrode 19 is used.

Each of the embodiments shown in FIGS. 29 to 31 is basically the same as the embodiment shown in FIG. 2 in that an upstream side catalyst 14 and a downstream side catalyst 15 are provided with an insulating space 16 therebetween. However, in each of the embodiments shown in FIGS. 29 to 31, the downstream side catalyst 15 functions as the main catalyst 10 shown in FIG. 1, and the joining method of the metal thin plate 11 and the metal corrugated plate 12 is shown in FIG. It is slightly different from the example shown.

That is, in the embodiment shown in FIG. 29 to FIG. 31, the metal thin plate 11 and the metal corrugated plate 12 of the downstream side catalyst 15 are centered without forming an electrically insulating layer composed of an alumina oxide layer on both side surfaces thereof. It is wound alternately around the axis.
Therefore, in these embodiments, the electric current flows in the radial direction in the downstream side catalyst 15, so that the downstream side catalyst 15 does not substantially generate heat. Further, in these examples, the metal thin plate 11 and the metal corrugated plate 1 which constitute the downstream side catalyst 15 are formed.
The upstream end surface portion indicated by the dot 2 is joined to each other by brazing, and the outer peripheral surface region 41 indicated by the dot of the downstream catalyst 15 is joined to the inner peripheral surface of the casing 8 by brazing. . Further, the metal thin plate 11 and the metal corrugated plate 12 are joined to each other by brazing also in the outer peripheral portion 42 indicated by the dot of the laminated structure central portion 13 bridging the downstream side catalyst 15 and the upstream side catalyst 14. There is.

The structure of the downstream side catalyst 15 and the structure of the central portion 13 of the laminated structure described above are the same in each of the embodiments shown in FIGS. 29 to 31, but the structure of the upstream side catalyst 14 is in each of the embodiments. Slightly different. Therefore, the structure of the upstream side catalyst 14 in each embodiment will be sequentially described. Second
Referring to FIG. 29 showing the third embodiment, in this embodiment, the metal thin plate 11 and the metal corrugated plate 12 of the upstream side catalyst 14 also have a central axis without forming an electric insulating layer made of an alumina oxide layer on both side surfaces thereof. The windings are alternately wound around each other, so that in this embodiment, the electric current flows in the radial direction in the upstream side catalyst 14. Further, in this embodiment, the upstream catalyst 14 has a wide portion 14a having a large axial length in its peripheral portion, and a small axial length is provided between the wide portion 14a and the laminated structure central portion 13. To form a narrow portion 14b. The metal thin plate 11 and the metal corrugated plate 12 of the narrow portion 14b are joined to each other on both sides by brazing, and the metal thin plate 11 and the metal corrugated plate 12 of the wide portion 14a are indicated by dots. The inner peripheral portion of the wide portion 14a and the downstream end face portion 43 are joined together by brazing. Further, an outer peripheral portion 44 indicated by a dot of the wide portion 42a is a metal cylindrical body 17 connected to the electrode 19.
It is joined by brazing to.

In this embodiment, the resistance value of the narrow portion 14b is considerably larger than that of the other portions. Therefore, when the electrically heated catalyst 9 is energized, only the narrow portion 14b substantially generates heat. . Therefore, in this embodiment, when electricity is supplied to the electrically heated catalyst 9, only the upstream end surface of the annular intermediate portion of the upstream catalyst 14 excluding the peripheral portion and the central portion is caused to generate heat.

Referring to the twenty-fourth embodiment shown in FIG. 30, also in this embodiment, the upstream side catalyst 14 is provided between the wide portion 14a formed in the peripheral portion thereof and the wide portion 14a and the central portion 13 of the laminated structure. And a narrow portion 14b formed in. Further, in this embodiment, the metal thin plate 11 of the wide portion 14a and the metal corrugated plate 12 are joined together by brazing at the upstream end face portion 45 shown by a dot. In this connection by brazing, a brazing material is applied to a portion to be brazed when the metal thin plate 11 and the metal corrugated plate 12 are wound around the central axis, and the laminated structure is formed after the winding is completed. It is performed by heating and melting the brazing material.

In the twenty-fourth embodiment, the metal thin plate 1 is used.
1 and the metal corrugated plate 12 are wound around the central axis, the space between the metal thin plate 11 and the metal corrugated plate 12 forming the narrow portion 14b is burnt when heated like paper, for example. A member or material that inserts a small gap between the thin plate 11 and the metal corrugated plate 12 is inserted. If such a member or material is inserted, when the laminated structure is heated after winding is completed, all of the metal thin plate 11 and the metal corrugated plate 12 in the region where such a member or material was inserted are heated. An oxide film serving as an electrical insulating layer is formed on the surface, and no oxide film is formed on the contact surface between the metal thin plate 11 and the metal corrugated plate 12 in a region where such a member or material is not inserted. become. Therefore, in the embodiment shown in FIG. 30, the narrow portion 1
An oxide film serving as an electrical insulating layer is formed on the entire surfaces of the metal thin plate 11 and the metal corrugated plate 12 of 4b.
4a and the contact surface between the metal thin plate 11 and the metal corrugated plate 12 in the central portion 13 of the laminated structure are not provided with an oxide film serving as an electrical insulating layer.

Therefore, in this embodiment, when the electrically heated catalyst 9 is energized, the wide portion 14a does not substantially generate heat because the current flows in the radial direction. On the other hand, since the current flows only in the circumferential direction in the narrow portion 14b, the resistance value of the narrow portion 14b becomes much larger than that of the other portions. You will get a fever. Therefore, also in this embodiment, the electrically heated catalyst 9 is used.
When electricity is applied to the upstream side catalyst, only the upstream end surface of the annular intermediate portion excluding the peripheral portion and the central portion of the upstream side catalyst 14 is made to generate heat.

In the twenty-fifth embodiment shown in FIG. 31, the entire upstream catalyst 14 is formed narrow. In this embodiment, the metal thin plate 11 and the metal corrugated plate 12 of the upstream side catalyst 14 are joined by brazing over the whole. Therefore, in this embodiment, when electricity is applied to the electrically heated catalyst 9, the central portion of the laminated structure is The entire upstream side catalyst 14 except 13 is made to generate heat. FIG. 32 shows the 26th embodiment. In this embodiment, the upstream side catalyst 50, the downstream side catalyst 51, the upstream side catalyst 50 and the downstream side catalyst 51 are arranged around the common laminated structure 13, and the upstream side catalyst 50 and the downstream side catalyst 51 An intermediate catalyst 54 is formed so as to be separated from each other by insulating spaces 52 and 53, and a heat generating region 27 is formed in this intermediate catalyst 54. Note that, in this embodiment as well, the area indicated by a dot indicates a joining area by electric discharge machining, and therefore, in this embodiment, only the heat generating area 27 of the intermediate catalyst 54 is substantially caused to generate heat.

FIG. 33 shows a twenty-seventh embodiment. In this embodiment, an upstream catalyst 61 and a downstream catalyst 62 are formed around the common laminated structure 13 with an insulating space 60 therebetween, and a heat generating region 27 is formed in the downstream catalyst 62. In this embodiment as well, the area indicated by the dot indicates the joining area by electric discharge machining, and therefore, in this embodiment, only the heat generating area 27 of the downstream side catalyst 62 is substantially heated.

As shown in FIGS. 32 and 33, the catalysts 54 and 62 in which the heat generating region 27 is formed are the electrically heated catalyst 9
It is not always necessary to arrange the heat generating area 27 in the innermost part of the catalyst, but as shown in the first to twenty-fifth embodiments, when the heat generating region 27 is formed in the most upstream catalyst part 14 in the electrically heated catalyst 9. Since the oxidation reaction heat generated in the heat generation region 27 is carried by the exhaust gas flow to the downstream side catalyst 15, there is an advantage that the downstream side catalyst 15 can be raised to the activation temperature in a short time.

[0055]

EFFECTS OF THE INVENTION When a part of an electrically heated catalyst is made to partially generate heat, it is not necessary to dispose an electrode in the center of the catalyst, so that heat of oxidation reaction is prevented from escaping to the outside through the electrode. It is possible to raise the temperature of the entire catalyst to the activation temperature in a short time. Further, when the catalyst is composed of the upstream side catalyst and the downstream side catalyst to heat the upstream side catalyst, the heat generated in the upstream side catalyst is transferred to the downstream side catalyst by the exhaust gas, so the downstream side catalyst is The activation temperature can be raised early.

[Brief description of drawings]

FIG. 1 is a diagram showing an engine exhaust passage.

FIG. 2 is a side sectional view of a first embodiment of an electrically heated catalyst.

3 is a cross-sectional view of the upstream side catalyst taken along the line III-III in FIG.

FIG. 4 is a diagram for explaining a method of joining a metal thin plate and a metal corrugated plate.

FIG. 5 is a side sectional view showing a second embodiment of the electrically heated catalyst.

FIG. 6 is a side sectional view showing a third embodiment of an electrically heated catalyst.

FIG. 7 is a side sectional view showing a fourth embodiment of an electrically heated catalyst.

FIG. 8 is a side sectional view showing a fifth embodiment of an electrically heated catalyst.

FIG. 9 is a side sectional view showing a sixth embodiment of an electrically heated catalyst.

FIG. 10 is a sectional view taken along line IX-IX in FIG.

FIG. 11 is a side sectional view showing a seventh embodiment of an electrically heated catalyst.

FIG. 12 is a diagram for explaining a louver formed on a metal thin plate and a metal corrugated plate.

FIG. 13 is a side sectional view showing an eighth embodiment of the electrically heated catalyst.

FIG. 14 is a side sectional view showing a ninth embodiment of the electrically heated catalyst.

FIG. 15 is a side sectional view showing a tenth embodiment of an electrically heated catalyst.

FIG. 16 is a side sectional view showing an eleventh embodiment of an electrically heated catalyst.

FIG. 17 is a side sectional view showing a twelfth embodiment of the electrically heated catalyst.

FIG. 18 is a side sectional view showing a thirteenth embodiment of the electrically heated catalyst.

FIG. 19 is a side sectional view showing a fourteenth embodiment of an electrically heated catalyst.

FIG. 20 is a side sectional view showing a fifteenth embodiment of an electrically heated catalyst.

FIG. 21 is a side sectional view showing a sixteenth embodiment of the electrically heated catalyst.

FIG. 22 is a side sectional view showing a seventeenth embodiment of the electrically heated catalyst.

FIG. 23 is a side sectional view showing an eighteenth embodiment of the electrically heated catalyst.

FIG. 24 is a side sectional view showing a nineteenth embodiment of the electrically heated catalyst.

FIG. 25 is a side sectional view showing a twentieth embodiment of an electrically heated catalyst.

FIG. 26 is a side sectional view showing a twenty-first embodiment of an electrically heated catalyst.

27 is a front view of the upstream side catalyst shown in FIG. 26. FIG.

FIG. 28 is a side sectional view showing a twenty-second embodiment of the electrically heated catalyst.

FIG. 29 is a side sectional view showing a twenty-third embodiment of the electrically heated catalyst.

FIG. 30 is a side sectional view showing a twenty-fourth embodiment of an electrically heated catalyst.

FIG. 31 is a side sectional view showing a twenty-fifth embodiment of the electrically heated catalyst.

FIG. 32 is a side sectional view showing a twenty-sixth embodiment of the electrically heated catalyst.

FIG. 33 is a side sectional view showing a twenty-seventh embodiment of the electrically heated catalyst.

[Explanation of symbols]

 3 ... Catalytic converter 9 ... Electric heating type catalyst 10 ... Main catalyst 14, 50, 61 ... Upstream catalyst 15, 51, 62 ... Downstream catalyst 16, 16a, 52, 53, 60 ... Insulation space 19 ... Electrode

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B01J 35/04 321 A 8017-4G F01N 3/20 ZAB H (72) Inventor Yoshiaki saki ▼ Koji Toyota, Aichi Prefecture City, Toyota-Cho, Toyota Automobile Co., Ltd. (72) Inventor, Toru Yoshinaga, 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Stock Company Japan Automotive Parts Research Institute (72) Inventor, Seihiko Watanabe Iwatani, Shimohakaku-cho, Nishio-shi, Aichi No. 14 Inside Japan Auto Parts Research Institute, Inc.

Claims (2)

[Claims] 1. An electric heating type catalyst disposed in an engine exhaust passage, wherein a current path is formed from the outer peripheral portion of the catalyst through the central portion of the catalyst to the outer peripheral portion of the catalyst again, and a current path along the current path is formed. An electrically heated catalyst in which only the catalyst region of a certain portion is a heat generating region and the remaining catalyst region is a non-heat generating region that does not substantially generate heat. 2. An insulating region extending from the outer peripheral portion of the catalyst toward the central portion of the catalyst is formed in the catalyst to form the current path around the insulating region, and the insulating region is located upstream of the insulating region. An electrically heated catalyst in which at least a part of the catalyst portion to be heated is a heat generating area and a catalyst portion located downstream of the insulating area is a non-heat generating area that does not substantially generate heat.