JPH11336535A - Catalyst structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make uniform the linear velocity distribution inside a catalyst structure for accelerating the activation of a catalyst, wherein the catalyst structure consists of a plurality of monolith catalyst pieces arranged in series in the exhaust gas flowing direction. SOLUTION: A catalyst structure 1 includes two catalyst pieces 2 and 3 consisting of honeycomb structure composed of bulkheads 21 and 31 of a constant thickness installed at a certain spacing in matrix arrangement formed from lines and columns and cell holes 22 and 32 partitioned by the bulkheads 21 and 31, and these catalyst pieces 2 and 3 are arranged adjoiningly in series in the exhaust gas flowing direction G inside an exhaust pipe 4, wherein the bulkhead 31 of the downstream catalyst 3 has one smaller number of lines and columns than those of the upstream catalyst 2. The positional relationship between the bulkheads 21 and 31 of the two catalysts 2 and 3 is such that the degree of positioning of the downstream bulkhead 31 within the cell holes 22 in the upstream catalyst 2 is greater in the central part of the cross-section of the exhaust gas flow in the exhaust pipe 4 and becomes smaller as going toward the periphery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst structure used in a catalytic converter for treating exhaust gas discharged from an internal combustion engine.

[0002]

2. Description of the Related Art In general, a catalytic converter uses a catalyst (monolith catalyst) in which a catalyst such as platinum is supported on a honeycomb structure made of cordierite or the like as a catalyst structure, and this catalyst structure is placed in an exhaust pipe. It will be stored. Here, the exhaust gas flows through the cell holes along the exhaust gas flow direction of the monolith catalyst, and the flow is in a laminar flow state because the gas flow velocity (hereinafter, referred to as linear velocity) in the cell holes is small.

[0003] Therefore, in a catalyst structure (integrated converter) composed of one monolithic catalyst, the gas near the center of the gas flow is unlikely to react due to a low probability of contact with the cell hole wall, and the gas is difficult to react in the latter half of the cell hole. A catalytic reaction (especially an exothermic reaction due to an oxidation reaction) does not easily occur, and the temperature of the catalyst structure does not easily rise. For this reason, in the catalytic converter, the substantial volume of the exhaust gas treatment is small and the purification capacity is low.

Therefore, as a device for improving the purification ability of the catalyst, a catalyst structure in which a plurality of monolithic catalysts are arranged in series along the flow direction of exhaust gas in an exhaust pipe has been proposed. For example, Japanese Patent Application Laid-Open No.
No. 7113 and JP-A-63-18123. According to these, it is said that two monolith catalysts are arranged in series with a gap therebetween and turbulence is generated in the gap, so that a catalytic reaction can be effectively performed by the downstream monolith catalyst.

[0005]

However, the inventors of the present invention have made a prototype of a catalyst structure in which two monolith catalysts are arranged in series based on each of the above-mentioned conventional publications, and have studied. It was found that the monolith catalyst was limited to the central part of the monolith catalyst (particularly the upstream monolith catalyst), and it was not possible to use substantially the entire monolith catalyst. It is considered that such a bias in the activation region is caused by the non-uniform linear velocity distribution in the catalyst structure. However, in each of the above-mentioned conventional publications, the linear velocity distribution in the catalyst structure is specifically described. There is no description.

The present inventors have investigated and studied the linear velocity distribution, and as a result, it has been found that the linear velocity is high at the center of the cross section of the exhaust pipe perpendicular to the exhaust gas flow, and low at the peripheral part. Accordingly, since the exhaust gas mainly flows in the central part of the catalyst structure, the catalytic activity in the peripheral part is delayed or not generated, and the SV (space velocity) is substantially increased, and a sufficient purification capacity is obtained. Can not do.

SUMMARY OF THE INVENTION In view of the above problems, the present invention relates to a catalyst structure comprising a plurality of monolithic catalysts arranged in series along the flow direction of exhaust gas. The purpose is to make the distribution uniform.

[0008]

In order to make the linear velocity distribution inside the catalyst structure using a monolithic catalyst uniform,
It is conceivable to control the distribution of airflow resistance inside the catalyst structure by changing the thickness or the interval of the partition walls of the honeycomb structure. However, in general, the partition walls are formed at a constant thickness and a constant interval in one honeycomb structure, and forming the partition walls with a partially changed thickness or interval requires a complicated manufacturing method. .

The present invention is not a honeycomb structure having a special structure but a conventional honeycomb structure having a plurality of cell holes defined by a plurality of partition walls formed at a constant thickness and a constant interval. In a catalyst structure in which a plurality of media, that is, so-called monolithic catalysts are arranged in series along the exhaust gas flow direction in the exhaust pipe, the relative positional relationship between the monolithic catalysts when viewed from the exhaust gas flow direction of the honeycomb partition walls is devised. It is made by paying attention to this.

That is, according to the first aspect of the present invention, the relative position of the partition walls (21, 31) in the two adjacently disposed catalyst bodies (2, 3) as viewed from the exhaust gas flow direction is determined by the upstream catalyst body. The degree to which the partition wall (31) of the downstream catalyst body (3) is located within the cell hole (22) of (2) depends on the cross section of the exhaust pipe (4) at right angles to the exhaust gas flow (hereinafter simply referred to as right angle cross section). Is characterized in that it is defined so as to be large at the center and smaller as it goes to the periphery.

As a result, the two adjacent catalyst bodies (2,
When 3) is viewed from the exhaust gas flow direction, the partition wall (3) of the downstream catalyst body (3) is arranged so as to block the flow of exhaust gas passing through the cell holes (22) of the upstream catalyst body (2) at the center of the perpendicular cross section.
As 1) is located and goes to the periphery of the right-angled cross section, the partition walls (21, 31) of both catalyst bodies (2, 3) can be positioned so as to approach the same plane with respect to the exhaust gas flow.

Therefore, according to the present invention, in the catalyst structure, the ventilation resistance is large at the center of the right-angled cross section, and small at the periphery of the right-angled cross section. A linear velocity distribution can be realized. Therefore, activation can be promoted over the entire catalyst structure, and a catalytic converter having excellent starting performance can be provided.

According to the second aspect of the present invention, the opening ratio of each catalyst body (2, 3) is defined as the ratio of the opening area of the plurality of cell holes (21, 31) to the area of the right-angled cross section. When defined, the aperture ratio B / A based on the aperture ratio A of the upstream catalyst body (2) and the aperture ratio B of the downstream catalyst body (3) is set to 0.
It is characterized by being in the range of 8 to 1.2. The reason why the aperture ratio B / A is set in such a range is as follows. In general, the opening ratio of the monolith catalyst is practically certain (for example, 60 to 70) so as not to hinder the exhaust gas flow.
%) Or less, and the thickness of the partition walls cannot be reduced too much. Here, if B / A is too different, the aperture ratio of one of the monolithic catalysts becomes extremely large, or the other one becomes extremely small.

Therefore, when the aperture ratio becomes extremely large,
The honeycomb structure has an extremely thin partition wall, and the strength of the monolith catalyst deviates from a practical level. On the other hand, when the opening ratio becomes extremely small, the partition wall becomes thick and the pressure loss of the monolith catalyst increases, which adversely affects the engine output. According to the second aspect of the present invention, by defining the ratio B / A within the above range, a catalyst structure having suitable strength and pressure loss can be provided.

According to the third aspect of the present invention, when the upstream and downstream catalyst bodies (2, 3) have the same cross-sectional area parallel to the right-angle cross section, the upstream catalyst body (2, 3) in the exhaust gas flow direction. 2) The volume ratio M / L based on the length L and the length M of the downstream catalyst body (3) is in the range of 0.3 to 1.8. That is, if the ratio M / L is too different, one of the catalyst bodies becomes slender or thin, and the strength of the catalyst body becomes weak. In the present invention, by defining the ratio M / L in the above range, a catalyst structure having practical strength can be provided.

According to the fourth aspect of the present invention, the interval between the upstream and downstream catalyst bodies (2, 3) is not more than 10 times the interval between the partition walls (21, 31) of one of the catalyst bodies. It is characterized by being restricted to the distance of. If the two catalysts are too far apart, the effect of the partition wall of the downstream catalyst blocking the flow of exhaust gas passing through the cell holes of the upstream catalyst will be weak. By restricting the voids, the two catalyst bodies are connected to each other, so that the above-described effect can be reliably achieved.

According to the fifth aspect of the present invention, the outer peripheral shapes of the cross sections parallel to the right-angled cross section of the upstream and downstream catalyst bodies (2, 3) have the same shape and the same size, and both the catalyst bodies (2, 3) ) Are arranged in a matrix composed of rows and columns in a cross section parallel to the right-angled cross section, and the downstream catalyst body (2) is further compared with the upstream catalyst body (2). 3) The number of rows and columns of the matrix arrangement is increased by one or decreased by one.

The present invention provides specific means according to the first aspect of the present invention, wherein the catalysts (2, 3) having the matrix arrangement are arranged in series, whereby the partition walls (21, 2) are arranged. 31) can be realized. In the invention according to claim 6, the relative positional relationship between the partition walls (21, 31) is shifted by displacing one of the upstream and downstream catalyst bodies (2, 3). It is characterized by having a displacement means (6), and can change the ventilation resistance of the entire catalyst structure and the linear velocity distribution according to the degree of activation of the catalyst of the catalyst structure or the engine output. Specifically, the displacement means (6) can be the same as the invention according to claim 7.

The symbols in parentheses above indicate the correspondence with specific means described in the embodiments described later.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) In a first embodiment, a catalyst structure of the present invention will be described as being used in a catalytic converter for purifying exhaust gas from a gasoline or diesel engine. The structure of the catalyst structure according to the present embodiment is shown in the schematic diagram of FIG. In FIG.
(A) shows the catalyst structure 1 of the present embodiment, and (b) shows, as a comparative example, the present invention based on the above-mentioned conventional gazette (Japanese Patent Laid-Open No. 4-47113) described in the above-mentioned subject column. 1 shows a catalyst structure 100 prototyped by the present inventors.

As shown in FIG. 1A, a catalyst structure 1 according to the present embodiment comprises catalysts 2, 3 for purifying exhaust gas.
Two are arranged in series along the exhaust gas flow direction in the exhaust pipe (converter shell) 4 (indicated by an arrow G in FIG. 1A). The catalyst structure 1 is fixedly arranged in the exhaust pipe 4 and is configured as a catalytic converter. Hereinafter, the catalyst body 2 located on the exhaust gas flow upstream side (left side in FIG. 1A) of the exhaust pipe 4 is the upstream catalyst body, and the catalyst body 3 located on the downstream side (right side in FIG. 1A) is downstream. It is called the side catalyst.

Here, FIG. 2 is a schematic view showing the structure of the catalyst structure 1 viewed from the exhaust gas flow direction G in FIG. 1A, wherein FIG. 2A shows the upstream catalyst body 2 alone, and FIG. Represents the downstream catalyst body 3 alone, and (c) shows a configuration in which both catalyst bodies 2 and 3 are combined, that is, the overall configuration of the catalyst structure 1. Each of the catalyst bodies 2 and 3 is formed of a columnar honeycomb structure which is molded from cordierite or the like.
And are arranged in parallel.

In this embodiment, the shape relationship between the two catalyst bodies 2 and 3 is as follows. The lengths L and M in the axial direction (exhaust gas flow direction G) of the cylinder shown in FIG. 1 are the same. FIG.
As shown in the figure, the outer peripheral shape of the radial cross section (the cross section parallel to the cross section perpendicular to the exhaust gas flow of the exhaust pipe 4) is the same circular shape and the same size for both catalyst bodies 2, 3, and both catalyst bodies 2, 3 The volume of 3 is also equivalent. For example, the lengths L and M are both about 12c.
m, the area of the cross section in the radial direction is about 110 cm ² , and the volume is about 1.3 liters.

As shown in FIG. 2, both the catalyst bodies 2 and 3 have a plurality of partitions 21 and 31 and these partitions 21 and 31
A plurality of cell holes 2 defined in parallel with the exhaust gas flow direction G
2, 32. Each of the plurality of partition walls 21 and 31 has a constant thickness (for example, 0.1 mm) when viewed from the exhaust gas flow direction G.
15 to 0.17 μm) and at regular intervals (that is, at a constant cell hole pitch, for example, about 1.3 mm),
They are arranged in a matrix composed of rows and columns in a radial cross section.

Here, a noble metal catalyst made of Pt or the like for purifying exhaust gas is carried on the inner surface of each of the plurality of cell holes 22 and 32. The ratio of the opening area of the cell holes to the area of the radial cross section in the catalyst body, that is, the opening ratio,
In this example, the opening ratio A of the upstream catalyst body 2 and the opening ratio B of the downstream catalyst body 3 are the same, and are set to a level (for example, about 60 to 70%) at which an appropriate engine output can be obtained.

Further, in each of the partitions 21 and 31 arranged in a matrix, the partitions 21 of the upstream catalyst 2 are arranged in m rows and n columns, and the partitions 31 of the downstream catalyst 3 are placed in the upstream catalyst 2.
The number of rows and columns is one more or one less than the side, that is, the arrangement configuration is m ± 1 rows and n ± 1 columns. In each of the catalyst bodies 2 and 3, the same number of rows and columns (m = n)
It may be.

Therefore, the partition wall 31 of the downstream catalyst body 3 is m-
When the arrangement is one row and n-1 rows, the downstream catalyst body 3
The thickness of the partition wall 31 is made thicker and / or the interval (pitch) is made narrower than that of the upstream catalyst body 2. When the partition walls 31 of the downstream catalyst body 3 are arranged in m + 1 rows and n + 1 rows, The catalyst body 3 makes the partition wall 31 thinner and / or makes the interval (pitch) wider than the upstream catalyst body 2.

In practice, the cell holes 2 of each of the catalyst bodies 2 and 3
The numbers 2, 32 are about 400 pieces / square inch, for example, about 20 rows and 20 columns per square inch (about 25.4 cm × 25.4 cm). However, in FIG. The upstream catalyst body 2 shown in FIG.
Is 28 rows × 28 columns, and the downstream catalyst body 3 shown in FIG.
Are arranged in a matrix of 27 rows × 27 columns, one row and one column smaller than the upstream catalyst body 2.

FIG. 2C shows the catalyst structure 1 in which the catalyst bodies 2 and 3 are arranged in series as viewed from the exhaust gas flow direction G. FIG. 2A and FIG. Are equivalent to those obtained by superimposing. The composite pitch resulting from the superposition of both figures is narrow near the center of the radial cross section and wide at the periphery.
That is, as shown by dashed lines D1 and D2 in FIG. 1A, the partition wall 31 of the downstream catalyst body 3 is cut off at the center of the radial cross section so as to block the flow of exhaust gas passing through the cell holes 22 of the upstream catalyst body 2.
And the partition walls 21 and 31 of the catalyst bodies 2 and 3 are located closer to the same plane with respect to the flow of exhaust gas toward the peripheral portion.

Here, as described above, the relative positional relationship is such that the number of rows and columns in the matrix arrangement of the downstream catalyst 3 is one more or one less than that of the upstream catalyst 2 as described above. (In this example, one less), this realizing means has partition walls formed with a constant thickness and a constant interval, and the outer peripheral shape of the radial cross section is the same shape and the same size. The present inventors have made intensive studies on a combination of a certain pair of catalyst bodies, and as a result, have uniquely found them.

As described above, the degree to which the partition wall 31 of the downstream catalyst body 3 is located in the cell hole 22 of the upstream catalyst body 2 is large (that is, the pitch is narrow) at the center of the radial cross section.
Since the diameter becomes smaller toward the periphery of the radial cross section (that is, the pitch becomes wider), the ventilation resistance increases near the center where the pitch is small, and decreases in the periphery where the pitch is large.

If the two catalysts 2 and 3 are too far apart, the effect of blocking the flow of exhaust gas passing through the cell holes 22 of the upstream catalyst 2 by the partition walls 31 of the downstream catalyst 3 becomes weak. Therefore, both catalyst bodies 2 shown in FIG.
3 is one of the distance between the partition walls 21 and 31 of one of the catalyst bodies 2 and 3 (one pitch of the cell holes 22 and 32).
The distance is limited to 0 times or less. In addition, both catalyst bodies 2,
3 does not need to provide a gap as in the related art, and may be in contact.

Here, FIG. 3 shows this embodiment and FIG.
FIGS. 7A and 7B are diagrams showing a difference in the operation and effect from the comparative example shown in FIG. 7 as a change in an active region in a low temperature state of exhaust gas. FIG. 7A shows this embodiment, and FIG. As described above, the catalyst structure 100 of the comparative example is disclosed in the above-mentioned conventional publication (Japanese Unexamined Patent Application Publication No.
No.-47113), which was prototyped by the present inventors and has a catalyst body (monolith catalyst) 200 having an equal volume.
Two 300s are arranged in series with a gap along the exhaust gas flow direction G.

Since the flow of the exhaust gas in the exhaust pipe 4 is originally large at the center in the cross section perpendicular to the flow of the exhaust gas in the pipe and small at the periphery, in the present embodiment, the above-described configuration of the ventilation resistance makes the linear velocity distribution unbalanced. Can be made uniform without generation of blemishes. Therefore, as shown in FIG. 3A, the temperature distribution of the catalyst structure 1 due to the heating of the exhaust gas can be made uniform over a wide range up to the peripheral portion, and the active region is expanded uniformly.

On the other hand, as shown in FIG. 3B, in the comparative example, as described in Japanese Patent Application Laid-Open No. 4-47113, turbulence is newly generated at the inlet of the catalyst body 300 on the downstream side. The temperature of the inlet surface rises as compared with the vicinity of the outlet of the upstream catalyst body 200, and the temperature of the downstream catalyst body 30 rises.
At 0, the active area can be expanded to some extent uniformly. However, particularly in the upstream catalyst body 200, due to the bias of the linear velocity distribution, the high-activity portion is biased toward the center portion, and the low-activity portion toward the peripheral portion, and further the inactive region, Occurs.

As described above, in the present embodiment, in the catalyst structure 1, the exhaust gas is difficult to pass near the center of the exhaust pipe 4 at a cross section perpendicular to the exhaust gas flow, and the gas is easy to pass in the peripheral portion. The linear velocity distribution can be corrected and a uniform linear velocity distribution can be realized. Therefore, activation can be promoted over the entire catalyst structure 1, and a catalytic converter excellent in starting performance and exhaust gas processing ability can be provided.

Next, the effect of the uniformized linear velocity distribution on the activation of the catalyst in the catalyst structure 1 will be described more specifically. Here, FIGS. 4 and 5 are diagrams showing the catalytic activity effect of the present embodiment, respectively. FIG. 4 shows a case where the present invention is used for a catalytic converter of a gasoline engine.
Indicates a case where the catalyst is used for a catalytic converter of a diesel engine.

FIG. 4 shows an example in which the effect is examined in the LA # 4 mode using the three-way catalyst of a gasoline engine.
Shows the transition of the activity ratio with respect to the elapsed time as an index of the activity effect, and (b) shows the LA # 4 mode. Here, the activity ratio (%) is a ratio of the active region volume (the temperature in the region where the catalyst bed temperature is 200 ° C. or higher) to the catalyst structure volume (converter volume).

In the comparative example, as shown in FIG. 3B, the temperature rises around the center of the inlet of the catalyst structure 100, and it takes time for the entire catalyst structure 100 to become catalytically active. About 280 sec when the activity ratio exceeds 20%
Take it. On the other hand, in this embodiment, it is faster (about 2).
30 sec) Since the activity ratio exceeds 20%, the startability of the converter is excellent, and the emission of HC can be suppressed and the emission can be reduced accordingly.

FIG. 5 shows the relationship between the throttle lever opening (vertical axis) and the engine rotation state (horizontal axis) and the ratio of the active state of the catalyst structure. Here, the active state is an operation region in which the volume of the region of the catalyst structure where the catalyst bed temperature is 200 ° C. or more exceeds 80% of the total volume of the catalyst structure. In FIG. 5, a one-way hatched portion indicates a comparative example, and a cross-hatched portion indicates a region in an active state further enlarged according to the present embodiment.

In a diesel engine, since there is a low temperature condition in which the exhaust gas temperature is 200 ° C. or less (100 ° C. or more) and catalytic activity does not occur, for example, when starting and accelerating after idling operation, a highly active Pt-based catalyst is used. Even if is used, the active temperature range of the catalyst is 200 ° C. or higher, so that the emission reduction ability is exhibited only in the operating region where the catalyst is in the active state. As shown in FIG. 5, in the present embodiment, the catalyst structure 1 can be activated with a smaller throttle lever opening and a smaller engine speed than in the comparative example.

By the way, since PM (suspended particles) composed of a soot component containing graphite and the like is present in the exhaust gas from the diesel engine, the PM adheres to the cell pore wall of the monolith catalyst, and finally becomes clogged. It is known from the examination and examination by the present inventors that this will be achieved. Further, according to tests and studies by the present inventors, this adhesion of PM occurs when the cell hole wall temperature decreases.
It is known that this is likely to occur when the linear flow velocity decreases.

Here, FIG. 6 (this embodiment) and FIG. 7 (comparative example) show the inside of the catalyst structure 1, 100 when the catalyst structure 1, 100 is used as a catalyst (oxidation catalyst) for a diesel engine. 3 shows the PM accumulation distribution of the sample. Here, in both figures, (b) shows the catalyst structure 1 shown in (a),
100 cross sections perpendicular to the exhaust gas flow direction (observation planes P1, P2,
P3, P4) shows the PM deposition distribution in the radial direction from the central part to the peripheral part of each catalyst structure 1, 100 as hatched portions. The symbol K indicates a center line of a cross section of the catalyst structure perpendicular to the exhaust gas flow direction.

In the present embodiment, since the exhaust gas easily flows in the peripheral portion of the catalyst structure 1, the cell hole wall temperature rises as compared with the conventional monolith catalyst, so that the amount of deposited PM in the peripheral portion is greatly increased. Has been reduced. As a result, the entire monolith catalyst can be used, and the durability is improved. As described above, the present embodiment also has an effect of suppressing cell hole blockage due to PM in the diesel engine.

As described above, according to the present embodiment, instead of a honeycomb structure having a special structure, a catalyst body (monolith) having a plurality of partition walls formed at a certain thickness and at a certain interval is not used. In the catalyst structure 1 in which two catalysts 2 and 3 are arranged in series, a simple method is used in which the numbers of rows and columns of the partition walls 21 and 31 between the catalysts 2 and 3 are different from each other by one. Thus, the relative positional relationship between the partition walls can be realized, and a uniform linear velocity distribution can be realized.

According to the present embodiment, the opening ratios A and B are equal (that is, the opening ratio B / A is about 1) in the two catalyst bodies 2 and 3 having the same shape and the same cross-sectional area in the radial direction. .0) and the axial lengths L and M of the cylinders are equal (that is, the volume ratio M / L is about 1.0), so that the catalyst structure is made of a honeycomb structure having practically suitable strength and pressure loss. Can be provided. According to the study by the present inventors,
The opening ratio B / A is in the range of 0.8 to 1.2, and the volume ratio M /
L is preferably in the range of 0.3 to 1.8.

According to the present embodiment, both catalysts 2
3, the spacing R of either one of the catalyst bodies,
Since the distance is limited to 10 times or less of the 31 interval, both catalyst bodies 2 and 3 are connected. Therefore, FIG.
The effect of uniformizing the linear velocity distribution due to the arrangement relationship of the partition walls 21 and 31 of the catalyst bodies 2 and 3 shown in (c) can be smoothly exerted.

(Second Embodiment) FIG. 8 shows a catalytic converter according to a second embodiment of the present invention. The present embodiment is characterized by having a displacement means 6 for displacing one of the upstream and downstream catalyst bodies 2 and 3 to shift the relative positional relationship between the partition walls 21 and 31. I have. Hereinafter, parts different from the first embodiment will be mainly described, and the same parts will be denoted by the same reference numerals in the drawings and description thereof will be omitted.

As shown in FIG. 8, the upstream catalyst body 2 is fixed to an exhaust pipe (converter shell) 4 via a fixing member 5, and the downstream catalyst body 3 is fixed via the displacement means 6. It is fixed to the exhaust pipe 4. The displacement means 6 has at least one deformable member 6a such as a bimetal or a shape memory alloy that expands and contracts due to thermal expansion accompanying a change in exhaust gas temperature in the exhaust pipe 4.

Here, FIG. 9 is an enlarged view taken in the direction of arrow C in FIG. The deformable member 6 a is welded to the metal ring 7 fixedly installed on the outer periphery of the downstream catalyst body 3 with the downstream catalyst body 3, and is welded to the inner wall of the exhaust pipe 4 with the exhaust pipe 4. It extends by thermal expansion and rotates the downstream catalyst body 3 counterclockwise about the center line K when viewed from the exhaust gas flow direction G.

Next, the operation of the displacement means 6 will be described with reference to FIG.
However, the arrangement relationship of the partition walls of the catalyst bodies 2 and 3 shown in FIG. 10 is an example, and the present invention is not limited to this. Now, when the incoming gas temperature and the temperature of the catalytic converter are low and the catalyst is not activated or hardly activated, the positional relationship between the upstream catalyst body 2 and the downstream catalyst body 3 is as shown in FIG.
As shown in FIG. 2A, in FIG.
Counterclockwise, the downstream side catalyst body 3 is arranged to be rotated by a half pitch with respect to the cell hole pitch (partition space) on the outer periphery.

FIG. 10A also shows that the upstream catalyst 2
The degree to which the partition wall 31 of the downstream-side catalyst body 3 is located in the cell hole 22 is large at the center of the radial cross section and becomes smaller toward the peripheral part of the radial cross section. It becomes large, and the ventilation resistance is small in the peripheral portion where the pitch is wide. Therefore, in the catalyst structure 1, a uniform linear velocity distribution can be realized, and activation can be promoted.

Next, when the output of the engine is high (high engine speed and high torque), the deformable member 6a becomes hot and extends, causing the downstream catalyst structure 3 to rotate. Then, by adjusting the phases of the cell holes 22 and 32 near the center in the radial cross section of the two catalyst structures 2 and 3 to reduce the pressure loss of the catalytic converter, the drivability of the engine is not impaired. To

Specifically, from the state shown in FIG.
The downstream side catalyst structure 3 is rotated counterclockwise about the center line K by an angle corresponding to a desirable 1/2 pitch or (1/2 + integer) pitch of the cell holes on the outer periphery. Note that FIG. 10B is an example of rotation by one pitch from the state of FIG. 2C, and FIG. 10C is an example of rotation of 3/2 pitch from the state of FIG. is there.

As described above, according to the present embodiment, the displacement means 6 changes the distribution of the synthesized pitch shown in FIG. 2 (c), thereby changing the activation degree of the catalyst and the state of the engine output. In addition, the linear velocity distribution in the catalyst structure 1 can be changed so as to move the portion where the gas flow passes most easily and the portion where the gas flow hardly passes. This change in the linear velocity distribution can be achieved by designing in advance the degree of expansion and contraction due to thermal expansion of the deformable member 6a.

The present embodiment is more effective for removing PM. In a conventional catalytic converter, the linear velocity distribution (gas flow velocity distribution) changes in a similar manner depending on the engine speed, so that the effect that PM desorption can be expected is limited to the vicinity of the center. However, in this embodiment, since the portion where the linear velocity becomes the highest can be moved to the peripheral portion of the converter and the like, the PM that has accumulated up to that point can be efficiently blown off, and the catalyst performance can be recovered.

The effect of reducing the pressure loss due to the phase shift of the synthetic pitch is described in FIG. 2 (c).
From the state, in the row and / or column direction of the matrix array,
It can also be realized by moving by (1/2 + integer) pitch. 11A and 11B show an example of a synthetic pitch in a state where the output of the engine is large. FIG. 11A shows an example in which the matrix is moved by 行 pitch in the row direction of the matrix, and FIG.
Is an example in which the matrix is moved by ピ ッ チ pitch in the row and column directions, respectively.

The displacement means 6 shown in FIGS. 8 and 9 displaces the downstream catalyst structure 3, but the upstream catalyst structure 2 or both of the catalyst bodies 2, 3 are displaced by the displacement means. 6, it may be rotated in the circumferential direction or shifted in the radial direction. (Other Embodiments) The catalyst structure may be one in which three or more catalyst bodies (monolithic catalysts) are arranged in series along the exhaust gas flow direction in the exhaust pipe. In this case, the relative positional relationship of the partition walls viewed from the exhaust gas flow direction in the two catalyst bodies disposed adjacent to each other depends on the degree to which the partition wall of the downstream catalyst body is located in the cell hole of the upstream catalyst body. The linear velocity distribution inside the catalyst structure can be made uniform as long as it is specified so that it is large at the center of the cross section perpendicular to the exhaust gas flow and becomes smaller toward the periphery.

In the present invention, the partition wall thickness or the partition wall width (cell hole width) of the two catalyst bodies is set so as to realize the relative positional relationship of the partition walls in the two catalyst bodies arranged adjacent to each other. The configuration such as the other configuration, the cross-sectional shape of both catalyst bodies, the arrangement of the partition walls, and the like may be changed as appropriate. For example, in the upstream catalyst body and the downstream catalyst body, the outer peripheral shape of the cross section parallel to the cross section of the exhaust pipe at right angles to the exhaust gas flow may be different in shape and size, and the partition walls are not a matrix arrangement, They may be arranged so as to form hexagonal cell holes. In these cases, the relative positional relationship between the partition walls can be realized by appropriately defining the partition wall thickness or the partition wall width (cell hole width) of both catalyst bodies.

Further, the displacement means may be a means for mechanically displacing the catalyst body using an external control means. For example, using an actuator,
At least one of the two catalyst bodies 2 and 3 may be rotated around the center line K by a stepping motor.

[Brief description of the drawings]

FIG. 1 is a schematic structural view of a catalyst structure, (a) shows a first embodiment of the present invention, and (b) shows a prototype of the present inventors.

FIGS. 2A and 2B are schematic diagrams of the structure of the catalyst structure viewed from the exhaust gas flow direction in FIG. 1A, wherein FIG. 2A is a single upstream catalyst body, FIG. 2B is a single downstream catalyst body, and FIG. 1 shows the configuration of the entire catalyst structure.

FIG. 3 is a diagram showing a change in an active region in a low temperature state of exhaust gas.

FIG. 4 is a diagram showing a catalytic activity effect when the catalyst structure according to the first embodiment is used for a catalytic converter of a gasoline engine.

FIG. 5 is a diagram showing a catalytic activity effect when the catalyst structure according to the first embodiment is used for a catalytic converter of a diesel engine.

FIG. 6 is a diagram showing PM in the catalyst structure according to the first embodiment.
It is a figure which shows a deposition distribution.

FIG. 7 is a diagram showing a PM deposition distribution in a catalyst structure in a comparative example.

FIG. 8 is a schematic structural diagram illustrating a catalytic converter according to a second embodiment of the present invention.

FIG. 9 is an enlarged view as viewed from an arrow C in FIG. 8;

FIG. 10 is an explanatory diagram showing an example of the operation of the second embodiment.

FIG. 11 is an explanatory diagram showing another example of the operation of the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Catalyst structure, 2 ... Upstream catalyst body, 3 ... Downstream catalyst body, 4 ... Exhaust pipe, 6 ... Displacement means, 6a ... Deformable member, 21
... Partition walls of upstream catalyst body, 22 ... Partition walls of downstream catalyst body, 3
1 ... cell hole of upstream catalyst body, 32 ... cell hole of downstream catalyst body.

 ──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Shigeki Omichi 14 Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Pref.Japan Automobile Parts Research Institute (72) Inventor Yoshimichi Ito 14 Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Pref. (72) Inventor Shinya Hirota 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (7)

[Claims] 1. A catalyst for purifying exhaust gas (2,
3) are arranged in series along the flow direction of the exhaust gas in the exhaust pipe (4), and each of the catalyst bodies (2, 3) is formed with a constant thickness and a constant interval. A catalyst structure (1) constituted by a honeycomb structure having partition walls (21, 31) and a plurality of cell holes (22, 32) defined by the partition walls (21, 31) and through which the exhaust gas flows; The relative positional relationship of the partition walls (21, 31) viewed from the exhaust gas flow direction in the two catalyst bodies (2, 3) disposed adjacent to each other is as follows: the cell hole (22) of the upstream catalyst body (2). The degree that the partition wall (32) of the downstream catalyst body (3) is located inside the exhaust pipe (4) is large at the center of the cross section of the exhaust pipe (4) at right angles to the exhaust gas flow, and becomes smaller toward the periphery. A catalyst structure characterized in that: 2. An opening ratio of each of the catalyst bodies (2, 3) is a ratio of an opening area of the plurality of cell holes (22, 32) to an area of a cross section of the exhaust pipe (4) at right angles to an exhaust gas flow. And an opening ratio B / A based on the opening ratio A of the upstream catalyst body (2) and the opening ratio B of the downstream catalyst body (3) is 0.8 to 0.8.
The honeycomb structure according to claim 1, wherein the honeycomb structure is 1.2. 3. The upstream catalyst body (2) and the downstream catalyst body (3) have the same area of a cross section parallel to a cross section of the exhaust pipe (4) at right angles to the exhaust gas flow. A volume ratio M / L of a length L of the upstream catalyst body (2) and a length M of the downstream catalyst body (3) in a direction is 0.3 to 1.8. The catalyst structure according to claim 1. 4. An arrangement interval between the upstream catalyst body (2) and the downstream catalyst body (3) is equal to an interval between the partition walls (21, 31) of one of the two catalyst bodies (2, 3). The catalyst structure according to any one of claims 1 to 3, wherein the distance is limited to 10 times or less. 5. The upstream and downstream catalyst bodies (2, 3).
In the exhaust pipe (4), the outer peripheral shape of a cross section parallel to a cross section perpendicular to the exhaust gas flow has the same shape and the same size, and the partition wall (2) of the upstream and downstream catalyst bodies (2, 3) has the same shape.
1, 31) are arranged in a matrix composed of rows and columns, respectively, in a cross section parallel to a cross section of the exhaust pipe (4) at right angles to the flow direction of the exhaust gas, and the partition walls (21) are arranged in the matrix. , 31)
In the above, the upstream catalyst body (2) side is m rows and n columns,
The said downstream side catalyst body (3) side has an m +/- 1 row and n +/- 1 column arrangement structure.
The catalyst structure according to any one of the above. 6. The upstream and downstream catalyst bodies (2, 3).
6. A displacement means (6) for displacing one of the catalyst bodies to shift a relative positional relationship between the partition walls (21, 31). 4. The catalyst structure according to any one of the above. 7. The displacement means (6) includes a member (6a) deformed by thermal expansion accompanying a change in exhaust gas temperature in the exhaust pipe (4). 3. The catalyst structure according to 1.