JPH11311120A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reliably perform a purification process when HC adsorbed at the start of an internal combustion engine 1 and to prevent the HC from being released to the outside. SOLUTION: An adsorption catalyst device 3 for adsorbing HC in exhaust gas is interposed in an exhaust passage 2 of an internal combustion engine 1. The adsorption catalyst device 3 has a two-layer structure in which an adsorbent layer containing an adsorbent is provided in an inner layer and a catalyst layer is provided in a surface layer, and an exhaust reburner 4 for heating exhaust gas is provided upstream thereof. I have. The exhaust reburner 4 makes the air-fuel ratio rich, reburns combustible exhaust gas generated by adding secondary air, and rapidly raises the temperature of the exhaust gas. After the internal combustion engine 1 is started, the temperature of the exhaust gas is rapidly increased by the exhaust gas reburner 4. Therefore, in the case of the adsorption catalyst, the catalyst layer reaches the activation temperature before the adsorption layer reaches the desorption start temperature, and then desorbs. HC is reliably processed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an exhaust gas purifying apparatus for purifying exhaust gas immediately after starting.

[0002]

2. Description of the Related Art Catalysts carrying noble metals (platinum, palladium, rhodium, etc.) or other metals have conventionally been used for purifying exhaust gases emitted from internal combustion engines of automobiles. Such a catalyst purifies by oxidizing or reducing HC, CO, NOx and the like, which are harmful components in the exhaust gas. By the way, in order to obtain this catalytic action, the exhaust gas temperature must be high. For example, in order to purify HC with a catalyst, a temperature of about 200 to 300 ° C. is generally required. However, immediately after the start of the internal combustion engine, the exhaust gas temperature is low, and the temperature at which the above-mentioned catalyst is activated (for example, 20
(0 ° C. or higher), the HC is hardly purified, resulting in an increase in the amount of HC released into the atmosphere.

[0003] In order to solve the above problem, an HC adsorbent that adsorbs HC under low-temperature conditions is provided in the exhaust system of the internal combustion engine in addition to the conventional catalyst device, so that HC exhausted before the catalyst is activated. Are known (JP-A-6-241028, JP-A-7-144119).
No.). H used in these exhaust gas purification devices
The C adsorbent is, in fact, an adsorption catalyst in which both HC adsorption components such as zeolite and catalyst components such as noble metals are mixed,
It has a self-purifying function of oxidizing a part of the adsorbed HC by catalytic action. This adsorption catalyst is heated by the heat of the exhaust gas or the heat of reaction in a general catalyst device provided on the upstream side, so that the adsorbed HC can be purified with the activity of the catalyst component of the adsorption catalyst.

[0004]

However, the activation temperature of a catalyst using a noble metal or the like is generally at least about 200 ° C., whereas the desorption of HC from the adsorbent starts at about 100 ° C. depending on the component. Therefore, when the temperature of the adsorption catalyst composed of the adsorption component and the catalyst component gradually increases due to the heat of the exhaust gas or the reaction heat in the upstream catalyst device, the HC adsorbed at a low temperature becomes In the early stage, it is inevitable that the catalyst is desorbed before the catalyst becomes active. That is, in the above-mentioned conventional exhaust gas purification device, there is a problem that a part of the adsorbed HC is discharged to the outside without being purified.

An object of the present invention is to provide an exhaust gas purifying apparatus capable of purifying almost all of adsorbed HC simultaneously with desorption.

[0006]

SUMMARY OF THE INVENTION The present invention provides an exhaust gas purifying apparatus for an internal combustion engine in which an adsorption catalyst device for adsorbing HC (hydrocarbon component) in exhaust gas is interposed in an exhaust passage of the internal combustion engine. Wherein the adsorption catalyst device comprises at least two layers of an adsorption catalyst having an inner layer composed of an adsorption layer containing an adsorbent for adsorbing HC and a surface layer composed of a catalyst layer,
An exhaust gas heating means for heating exhaust gas is provided upstream of the adsorption catalyst device.

For example, the above-mentioned adsorption catalyst has a two-layer structure in which a honeycomb carrier is first coated with an adsorption layer, and then a catalyst layer is coated thereon. Exhaust gas heating means for rapidly increasing the temperature of the exhaust gas is provided upstream of the adsorption catalyst.

Here, the exhaust gas heating means includes:
It is important to rapidly raise the temperature of the exhaust gas. For example, an air-fuel ratio control means for temporarily setting the air-fuel ratio of the internal combustion engine to a rich state, and increasing the air concentration in the exhaust gas It comprises an air supply means, and an exhaust reburner provided with an ignition means for reburning the combustible exhaust gas generated by the air-fuel ratio control means and the air supply means. Alternatively, the fuel injection means for re-burning the fuel to the exhaust passage of the internal combustion engine, the air supply means for increasing the air concentration in the exhaust gas, the fuel injection means for re-burning and the air supply And an exhaust reburner provided with ignition means for reburning combustible exhaust gas generated by the means. Further, an electric heating catalyst, an electric heating heater or the like can be used.

A fifth aspect of the present invention is a more specific version of the first aspect.
The invention has an adsorption catalyst temperature detecting means for detecting or indirectly estimating the temperature of the adsorption catalyst, and the operation of the exhaust gas heating means is controlled based on the temperature of the adsorption catalyst. . The temperature of the adsorption catalyst may be estimated from the temperature of the exhaust gas flowing into the adsorption catalyst.

Further, the invention of claim 7 is characterized in that the operation of the exhaust gas heating means is started when the temperature of the adsorption catalyst reaches just before the temperature at which HC desorption starts.

The invention of claim 8 is characterized in that the operation of the exhaust gas heating means is stopped when the temperature of the adsorption catalyst exceeds a catalyst activation temperature by a predetermined value or more.

The applicant of the present invention has proposed a catalyst having a catalyst layer and an adsorption layer.
A bed-type adsorption catalyst has already been filed (Japanese Patent Laid-Open No. 6-17 / 1994).
0234, JP-A-7-124467 and the like).
This two-layer type adsorption catalyst is composed of HC adsorbed in the inner adsorption layer.
When desorbed, it always passes through the surface catalyst layer, so that there is an advantage that the purification performance in the catalyst layer is improved.

In the present invention, in addition to the above, the following effects can be obtained by installing exhaust gas heating means capable of rapidly increasing the temperature of the exhaust gas upstream of the adsorption catalyst. That is, during the temperature rise period of the adsorption catalyst, the temperature of the exhaust gas rapidly rises due to the operation of the exhaust gas heating means,
This hot exhaust gas will flow into the individual cells of the adsorption catalyst. As a result, heat is first supplied to the surface catalyst layer, and then heat is transferred to the inner layer, and a temperature gradient can be positively generated between the surface catalyst layer and the inner adsorption layer. . Therefore, while the surface catalyst layer quickly reaches the activation temperature, the inner adsorbent layer reaches the desorption temperature of HC relatively late, so that at the stage where the desorption of HC from the adsorption layer starts, the surface layer becomes Since the catalyst layer is already active, almost all of the desorbed HC can be purified by the catalyst layer.

Incidentally, even with a two-layer adsorption catalyst,
When heated slowly only by the heat of normal exhaust gas, the temperature of the entire surface of the adsorption catalyst gradually increases, so the temperature difference between the surface catalyst layer and the inner adsorption layer is small. Even if the HC reaches the temperature at which desorption starts, the surface catalyst layer has not yet reached the activation temperature, and the initial desorbed HC is discharged without being purified.

That is, the feature of the present invention is that the exhaust gas whose temperature has been rapidly raised by the exhaust gas heating means is supplied to the adsorption catalyst before HC starts to be desorbed from the adsorption layer. As described above, the activity of the surface catalyst layer can be made earlier than the start of desorption of the inner adsorption layer.

Although the temperature of the exhaust gas also rises by increasing the load and the number of revolutions of the internal combustion engine,
In this case, since the amount of exhaust gas increases significantly, even if the adsorbent has not reached the desorption start temperature, a part of HC is pushed out from the pores of the adsorbent by the increased exhaust gas flow rate,
As a result, they are desorbed and discharged outside without being purified, so that this is not an effective method.

When a general catalytic device is installed immediately upstream of the adsorption catalyst, the temperature of the exhaust gas flowing into the downstream adsorption catalyst rises due to the reaction heat generated by the oxidation of HC and CO at the catalyst. In order to obtain the reaction heat as described above, the catalyst of the upstream catalytic device needs to be active, and the reaction heat cannot be generated until the catalyst temperature reaches at least about 200 ° C. Although the temperature of the adsorption catalyst installed immediately downstream thereof is slightly lower than the temperature of the upstream catalyst, when the temperature of the upstream catalyst reaches 200 ° C. (the temperature immediately before catalytic activity), for example, about 150 ° C. Some of the HCs have already started to desorb because the temperature has risen. At this time, since the surface catalyst layer of the adsorption catalyst has not been activated yet, HC is discharged as it is, which is also not an effective method.

Therefore, the exhaust gas temperature can be rapidly increased without significantly increasing the exhaust gas flow rate when the two-layer adsorption catalyst is at or below the desorption start temperature (about 100 ° C.). This is a necessary function as a means.

As described above, as the exhaust gas heating means that satisfies such demands, as described above, the air-fuel ratio of the internal combustion engine is corrected to be rich, and air is further mixed. For example, an exhaust reburning device that ignites and reburns, a combustion device that supplies fuel and air to the exhaust gas and burns the same, or an electric heating catalyst, an electric heating heater, or the like is effective. Such a device has, for example, the ability to raise the exhaust gas temperature to about 900 ° C. in a few seconds, can start operation regardless of the exhaust gas temperature, and does not increase the exhaust gas flow rate so much. . For example, in order to raise the exhaust gas temperature to 900 ° C. by increasing the load and the rotational speed of the internal combustion engine, the load and the rotational speed are reduced until the exhaust gas amount becomes 10 times or more as compared with the exhaust gas amount under the idle condition. Although it is necessary to raise the exhaust gas amount, when the temperature is raised to about 900 ° C. by the above-described exhaust reburner, the amount of exhaust gas needs to be increased by about two times. Is almost none.

[0020]

According to the exhaust gas purifying apparatus for an internal combustion engine of the present invention,
The adsorption catalyst has at least two layers each having an adsorption layer as an inner layer and a catalyst layer as a surface layer, and is provided with exhaust gas heating means on the upstream side, so that the temperature of exhaust gas flowing into the adsorption catalyst after adsorption of HC is increased. The temperature of the catalyst layer is rapidly increased, the temperature difference between the catalyst layer and the adsorption layer is positively expanded, and the activity of the catalyst layer can be relatively quicker than the start of HC desorption of the adsorption layer. Almost all of the HC can be reliably purified by the catalyst layer. Therefore, the total amount of HC discharged to the outside when the internal combustion engine is started can be reduced as a whole.

According to the seventh aspect of the present invention, when the temperature of the adsorption catalyst reaches just before the desorption start temperature of HC, the operation of the exhaust gas heating means is started, so that the exhaust gas is forcibly heated. The amount of fuel required for the operation can be minimized.

[0022]

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of the first embodiment of the present invention. In the exhaust passage 2 of the internal combustion engine 1, HC in the exhaust gas
An adsorption catalyst device 3 for adsorbing components is interposed, and an exhaust reburner 4 is provided upstream of the adsorption catalyst device 3. The exhaust reburner 4 includes an ignition plug 5 that performs spark discharge by an ignition device 8 including an ignition coil and the like as ignition means. Note that a glow plug can be used as the ignition means. Further upstream of the exhaust reburner 4, a secondary air supply passage 7 from a secondary air pump 6 is connected as air supply means.

The exhaust gas reburner 4 is provided with a reburner temperature sensor 9 for measuring the temperature of the exhaust gas in the reburner 4, and the adsorption catalyst device 3 detects the temperature of the adsorption catalyst. A catalyst temperature sensor 10 is provided. The detection signals of these temperature sensors 9 and 10 are input to the engine control unit 11.

The secondary air pump 6 and the ignition device 8 are connected to the engine control unit 11 respectively.
As described later, the secondary air supply and the spark ignition are performed at the time of exhaust gas reburning, respectively.

A fuel injection device 13 is attached to the intake passage 12 of the internal combustion engine 1 and injects fuel according to an injection signal from the engine control unit 11. This fuel injection amount is basically controlled according to the operating conditions of the internal combustion engine 1, but
At the time of exhaust gas reburning, the air-fuel ratio is kept rich by increasing the fuel injection amount.

FIG. 2 shows a detailed configuration of the adsorption catalyst device 3. This adsorption catalyst device 3 is mainly composed of a honeycomb-shaped carrier 3b made of ceramics or metal having a large number of cells 3a through which exhaust gas passes. As shown in an enlarged view of one cell 3a, the carrier 3b first has, as an inner layer, an adsorbing layer 3 for adsorbing HC.
c is coated. Further, a catalyst layer 3d for purifying exhaust components is coated thereon as a surface layer, and constitutes one cell 3a. A large number of the cells 3a constitute the adsorption catalyst device 3. As the material of the adsorption layer 3c, for example, a material mainly composed of zeolite, or a material obtained by ion-exchanging zeolite with a metal is used. Such HC
The adsorbent generally uses HC up to about 100 ° C. to 200 ° C.
And has the property of desorbing HC at a higher temperature. As the catalyst layer 3d, a material containing a noble metal such as platinum, palladium, and rhodium is used.
The same ones as general three-way catalysts can be used, but those having a higher palladium content and higher low-temperature activity are more effective. Such a catalyst is
Generally, it is activated at about 200 to 300 ° C. and purifies exhaust components.

There is no problem if the adsorption layer 3c contains not only the adsorbent component but also a catalyst component. The adsorbing layer 3c can be formed not only as one layer but also as two or more layers using adsorbing layers having different adsorbent components. Also, the catalyst layer 3d can be configured by two or more catalyst layers 3d formed of different components. In any case, there is a catalyst layer 3d near the surface, and an adsorption layer 3c inside.
If there is.

Next, the basic operation of the exhaust gas reburner 4 will be described. When it is determined that the operating condition of the exhaust reburner 4 is satisfied, the fuel injection device 13 increases the amount of fuel so that the air-fuel ratio becomes very rich (about 9 to 10 in air-fuel ratio) based on a signal from the engine control unit 11. I do. As a result, in the exhaust gas, 12 to 13% of CO and 6 to
7% and 2-3% of HC are contained (all are percentages by volume). At the same time, the engine control unit 11 operates the secondary air pump 6 and the ignition device 8 to start the supply of the secondary air and the spark discharge of the ignition plug 5. The flow rate of the secondary air is set to a flow rate that at least causes an excess of oxygen in a state of being mixed with the rich exhaust gas. This varies depending on the displacement and operating state of the internal combustion engine, and is set in advance to a sufficient flow rate through experiments.
%. As a result, the combustible components (C
O, H2, HC) in a state that contains, then, in the state in which O ₂ is mixed from the secondary air, CO is 7 to 8%, H
2 as a combustible gas containing 3 to 4% and HC of 1 to 2% and supplied to the exhaust gas reburner 4,
The combustion starts due to the sparks. The operation of the exhaust gas reburner 4 is stopped when the temperature of the adsorption catalyst reaches a predetermined temperature as described later.

The above operation will be described in more detail with reference to the flowchart of FIG. This routine is, for example, 1
It is repeatedly executed every 0 msec. First, in step 1, the elapsed time after starting is determined. this is,
Since the operation of the exhaust gas re-combustor 4 is aimed at the early activation of the adsorption catalyst immediately after the start (mainly the early activation of the surface catalyst layer 3d), for example, it is necessary to limit the operation to 60 seconds after the start. Things. Here, if it is determined that the time is within 60 seconds after the start, the process proceeds to step 2, and the adsorption catalyst temperature Tcat is read. In step 3, it is determined whether or not the adsorption catalyst temperature Tcat is lower than the activation temperature of the catalyst layer 3d of the adsorption catalyst (here, 250 ° C.). Proceeding to each step, the operation of the exhaust gas reburner 4 is performed. In step 4, the recombustor temperature Tegc is read. In step 5, the reburner temperature Te
The fuel increase coefficient TFEGC required for the operation of the exhaust gas reburner 4 is set according to gc. As shown in FIG. 4, this is searched from a predetermined table set in such a characteristic that the lower the Tegc, the larger the increase coefficient TFEGC. Here, the lower the reburner temperature Tegc, that is, the lower the temperature of the exhaust gas flowing into the exhaust reburner 4, the more the increase coefficient T
The reason why the FEGC is increased is that the lower the temperature, the higher the concentration of CO, H2, and the like is required for ignition in the exhaust gas reburner 4. This table is set in advance by experiments.

In step 6, the set increase coefficient TF is set.
The fuel injection amount is increased according to the EGC to perform the injection. This is based on the basic fuel injection amount (the injection amount corresponding to the stoichiometric air-fuel ratio), which is generally obtained from the intake air amount and the internal combustion engine speed.
The fuel injection amount is determined by multiplying the increase coefficient TFEGC to perform the fuel injection. As a result, combustible components such as CO and H2 are supplied at a concentration sufficient for combustion in the exhaust gas reburner 4. Next, at step 7, the intake air amount QA is read, and at step 8, the secondary air supply amount QEXAIR is set from the intake air amount QA and the above-mentioned increase coefficient TFEGC. This is searched from a predetermined map having characteristics as shown in FIG. 5, and as the intake air amount QA increases and the increase coefficient TFEGC increases, the secondary air supply amount QEX increases.
It has the property of increasing AIR. This map is set in advance by experiments so that the supply of oxygen is sufficient for the combustion of the supplied combustible components. In step 9, the secondary air pump 6 is driven according to the determined secondary air supply amount QEXAIR to supply necessary secondary air to the exhaust passage 2. As a result, a mixture of combustible exhaust gas and air is created. And in step 10,
The ignition device 8 is operated so as to be ignited by the ignition plug 5 provided in the exhaust gas reburner 4, and the above-mentioned mixture is burned in the exhaust gas reburner 4.

In step 1 or step 3 above, N
If it is determined to be O, the process proceeds to each step after step 11, and a process for terminating the operation of the exhaust gas reburner 4 is performed. First, in step 11, the increase coefficient TFEGC is set to 1,
That is, there is no increase. In step 12, the increasing coefficient T
Normal fuel injection without increasing the amount by FEGC is executed. As a result, surplus combustible components such as CO and H2 are not supplied. In step 13, the secondary air supply amount QEX
AIR is set to 0, and the secondary air pump 6 is stopped in step 14. Further, at step 15, the ignition device 8 of the exhaust gas reburner 4 is stopped. By the above processing, the exhaust reburner 4
Operation stops.

Therefore, in the present embodiment, when the adsorption catalyst device 3 is started at a sufficiently low temperature, the exhaust reburner 4 starts operating immediately after the start. When the exhaust gas recombustor 4 operates in this manner, the temperature of the exhaust gas flowing into the adsorption catalyst device 3 rapidly increases, and for example, the exhaust gas that has reached 700 ° C. or more flows into the catalyst layer 3 on the surface of the adsorption catalyst. 3d raises the temperature first, and then the inner adsorption layer 3c gradually increases the temperature by heat transfer. As a result, the unburned HC that has flowed into the adsorption catalyst device 3 before the activation of the catalyst layer 3d (the unburned HC before the ignition of the exhaust reburner 4 and the unburned HC remaining burned in the exhaust reburner 4) is The catalyst layer 3d of the adsorption catalyst is temporarily adsorbed, and before the adsorption layer 3c reaches the desorption temperature, the surface catalyst layer 3d reaches the activation temperature. Therefore, almost all of the HC desorbed from the adsorption layer 3c due to the temperature rise is purified when passing through the catalyst layer 3d, and is hardly discharged to the outside.

Next, a second embodiment will be described with reference to the flowchart of FIG. This is when the operation of the exhaust gas reburner 4 is started immediately before the start of HC desorption from the adsorption catalyst. Note that the mechanical configuration of the exhaust gas purification device is the same as that of the first embodiment.

The processing flow of this embodiment is basically the same as that of the first embodiment described above. Steps 21 to 35 in the flowchart of FIG. Are equivalent to steps 1 to 15 of the flowchart of FIG. Step 23 corresponds to Step 3 of the first embodiment. In Step 23, the adsorption catalyst temperature Tc
at is the start temperature of HC desorption from the adsorption layer 3c (100 ° C.)
The temperature range immediately before the temperature reaches about 80 ° C. (here, 80 ° C.) and lower than the activation temperature of the catalyst layer 3 d (here, 250 ° C.) are determined. Only in the case of, the process proceeds to each step after step 24 to operate the exhaust gas reburner 4. That is, when the adsorption catalyst temperature Tcat is lower than 80 ° C., the exhaust reburner 4 does not operate.

Therefore, based on the above flowchart,
In the second embodiment, unlike the first embodiment, even when the internal combustion engine 1 is started in a state where the adsorption catalyst device 3 is at a sufficiently low temperature (for example, about 20 ° C.), the exhaust recombustor is in a stage immediately after the start. 4 does not work. Therefore, the temperature of the adsorption catalyst gradually increases in accordance with the normal temperature rise of the exhaust gas. Thereafter, when the temperature of the adsorption catalyst Tcat reaches 80 ° C. before the start of desorption, the operation of the exhaust gas reburner 4 starts, and the temperature of the exhaust gas which is rapidly increased to, for example, 700 ° C. or more is supplied to the adsorption catalyst device 3. Flows in. Thereafter, as in the first embodiment, the surface temperature of the catalyst layer 3d of the adsorption catalyst first rises and reaches the activation temperature.
Almost all of the HC desorbed from the adsorption layer 3c can be purified by the catalyst layer 3d.

In the present embodiment, the operation of the exhaust gas reburner 4 is not performed immediately after the start of the internal combustion engine 1, but the HC from the adsorption catalyst is used.
Immediately before the start of desorption, the reburner temperature Tegc at the start of the operation of the exhaust reburner 4 has increased to some extent. As a result, the fuel increase coefficient T
The value of FEGC is set small. That is, the higher the reburner temperature Tegc is, the more the ignition combustion of the exhaust reburner 4 can be sufficiently performed even if the fuel increase is small, so that the degree of enrichment can be reduced, and as a result, the fuel consumption can be suppressed. Becomes possible.

In the above embodiment, as an exhaust gas heating means, an exhaust reburning device for correcting the air-fuel ratio of the internal combustion engine 1 to be rich, further mixing air, and igniting and burning with an ignition plug 5 in an exhaust reburner 4. However, it is also possible to use a combustion device that supplies fuel and air to the exhaust gas and burn, or an electric heating catalyst or an electric heater.

FIG. 7 shows the configuration of a third embodiment using a combustion device for supplying fuel and air to exhaust gas and burning the exhaust gas. In this embodiment, a reburning fuel injection device 21 is provided as reburning fuel injection means so as to directly inject and supply fuel toward an exhaust reburner 4 provided in the exhaust passage 2. Reference numeral 22 denotes a fuel pipe. A secondary air supply passage 7 from a secondary air pump 6 is connected to the exhaust reburner 4 as air supply means.

The exhaust reburner 4 has a spark plug 9 as an ignition means, and a fuel injection device 21 for reburning.
And the combustible exhaust gas generated by the secondary air pump 6 is reburned.

With the configuration in which fuel and air are supplied to the exhaust gas and burned, the fuel supply means must be added to the exhaust system, but there is no need to change the fuel increase control of the internal combustion engine 1 and the like. That is, since the internal combustion engine 1 itself can be coped with by improving only the exhaust system while including the control system, there is an advantage that it can be easily mounted on various internal combustion engines 1. It should be noted that also in the case of this apparatus, the effect of reducing exhaust gas (the performance of purifying HC desorbed from the adsorption catalyst 3c) can be obtained in the same manner as in the first and second embodiments.

FIG. 8 shows a fourth embodiment in which an electric heating catalyst device 31 is arranged upstream of the adsorption catalyst device 3 in place of the exhaust gas reburner 4. Reference numeral 32 denotes a power supply device for supplying electric power to the adsorption catalyst device 31, and reference numeral 33 denotes an electric heating catalyst temperature sensor for detecting a catalyst temperature of the electric heating catalyst device 31. Here, an electric heater may be used instead of the electric heating catalyst device 31.

The application of the electric heating catalyst device 31 (or electric heater) as the exhaust gas heating means is advantageous, for example, in the case of a hybrid vehicle using both an electric motor and an internal combustion engine as a power source of an automobile. . That is, such a hybrid vehicle can retain sufficient electric power in the battery due to energy recovery at the time of deceleration, and so can heat the electric heating catalyst using this electric power. . Therefore, unnecessary fuel increase and additional fuel supply to the exhaust system are not required, so that fuel consumption can be suppressed. However, in the method using the electric heating catalyst device 31, the effect of reducing the exhaust gas (the effect of purifying the desorbed HC from the adsorption catalyst) may be slightly inferior to those described in the above embodiments. The reason is that the exhaust reburner 4 directly raises the temperature of the exhaust gas by the combustion heat of the combustible components in the exhaust gas, whereas the electric heating catalyst device 31 generates the same amount of heat even when the same amount of heat is generated. This is because the heat capacity of the electric heating catalyst device 31 itself has a slight delay in the temperature rise of the exhaust gas. When the temperature of the exhaust gas rises slowly, the temperature difference between the catalyst layer 3d on the surface of the adsorption catalyst and the adsorption layer 3c on the inner layer decreases, and especially when the adsorption catalyst is deteriorated, the catalyst activation temperature increases, and conversely. Since the desorption temperature tends to decrease, as a result, some HC
May be detached. However, its superiority is apparent as compared with the case where the temperature of the adsorption catalyst is raised only by the heat of the exhaust gas itself without using the exhaust gas heating means.

FIG. 9 shows first to fourth exhaust gas heating means.
When the temperature of the exhaust gas flowing into the adsorption catalyst device 3 is rapidly increased using the exhaust reburner 4 as in the third embodiment (A), the electric heating catalyst device 31 as in the fourth embodiment is used. (B) shows the temperature history of each part in the case where the adsorption catalyst is heated only by the heat of the normal exhaust gas without the exhaust gas heating means (C). Here, (A) and (B) using the exhaust gas heating means show characteristics when heating is started immediately before the start of desorption of the adsorption catalyst.

As shown in (A), when the exhaust gas reburner 4 is used as the exhaust gas heating means, the temperature of the exhaust gas flowing into the adsorption catalyst device 3 rises rapidly, so that the catalyst layer 3d
The temperature difference between the catalyst layer 3c and the adsorption layer 3c increases, and as a result, the time for the catalyst layer 3d to reach the catalyst activation temperature is longer than that in the adsorption layer 3c.
c becomes earlier than the time when the temperature reaches the HC desorption start temperature, and almost all the desorbed HC can be purified by the catalyst layer 3d.

When the electric heating catalyst device 31 is used as the exhaust gas heating means, the temperature of the exhaust gas flowing into the adsorption catalyst device 3 is slightly slower because of the heat capacity of the electric heating catalyst device 31 itself. Become. As a result, the time until the catalyst activity and the time until the start of HC desorption are substantially the same (when the deterioration of the adsorption catalyst is progressing, the time until the start of HC desorption is slightly shorter). Although HC is discharged without being purified at the time of desorption, the amount of HC is suppressed to a very small amount as compared with the case where the exhaust gas heating means is not provided (C).

In the case of (C) in which the exhaust gas heating means is not provided and the adsorption catalyst is heated only by the heat of ordinary exhaust gas, the temperature difference between the catalyst layer 3d and the adsorption layer 3c is small, and the start of HC desorption is caused by the catalyst. Because it is much faster than the activity, a large amount of HC is discharged without being purified at the time of desorption.

HC in the above three cases (A) to (C)
FIG. 10 shows the comparison results of the emission concentrations. As shown in FIG. 10, compared with the case where the temperature of the adsorption catalyst is raised only by the heat of the normal exhaust gas, the use of the exhaust gas heating means makes it possible to greatly reduce the amount of HC emission. When an exhaust reburner is used, the amount of HC emissions can be reduced most.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing a configuration of a first embodiment of the present invention.

FIG. 2 is an enlarged view showing details of an adsorption catalyst device.

FIG. 3 is a flowchart showing a processing flow of the first embodiment.

FIG. 4 shows a recombustor temperature Tegc and a fuel increase coefficient TFEG.
FIG. 4 is a characteristic diagram showing a relationship with C.

FIG. 5 shows a fuel increase coefficient TFEGC and an intake air amount QA and 2
FIG. 9 is a characteristic diagram showing a relationship with a next air supply amount QEXAIR.

FIG. 6 is a flowchart illustrating a flow of a process according to a second embodiment.

FIG. 7 is a configuration explanatory view showing a configuration of a third embodiment of the present invention.

FIG. 8 is a configuration explanatory view showing a configuration of a fourth embodiment of the present invention.

FIG. 9 is a time chart showing the temperature history of each part when the exhaust gas reburner 4 is used (A), when the electric heating catalyst device 31 is used (B), and when no exhaust gas heating means is provided (C). .

FIG. 10 shows a comparison of the amount of HC emission in a case where the exhaust gas reburner 4 is used (A), in a case where the electric heating catalyst device 31 is used (B), and in a case where no exhaust gas heating means is provided (C). Time chart.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Adsorption catalyst device 3c ... Adsorption layer 3d ... Catalyst layer 4 ... Exhaust reburner 5 ... Spark plug 6 ... Secondary air pump

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 9/00 F01N 9/00 Z (72) Inventor Shunichi Shiino 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (8)

[Claims] An exhaust passage for an internal combustion engine is provided with H in the exhaust gas.
In an exhaust gas purifying apparatus for an internal combustion engine provided with an adsorption catalyst device for adsorbing C (hydrocarbon component), the adsorption catalyst device includes an inner layer including an adsorbent layer containing an adsorbent for adsorbing HC and a catalyst. An exhaust gas purifying device for an internal combustion engine, comprising exhaust gas heating means for heating exhaust gas, the exhaust gas purifying device comprising at least two layers of an adsorption catalyst having a surface layer consisting of two layers. . 2. The exhaust gas heating means includes: an air-fuel ratio control means for temporarily setting the air-fuel ratio of the internal combustion engine to a rich state; an air supply means for increasing the air concentration in the exhaust gas; 2. An exhaust reburner provided with ignition means for reburning combustible exhaust gas generated by the air supply means.
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 3. The exhaust gas heating means includes: a reburning fuel injection means for supplying fuel to an exhaust passage of an internal combustion engine; an air supply means for increasing an air concentration in exhaust gas; and the reburning fuel injection means. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising: an exhaust reburner provided with an ignition means for reburning combustible exhaust gas generated by the air supply means. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said exhaust gas heating means comprises an electric heating catalyst or an electric heater. 5. An adsorption catalyst temperature detecting means for detecting or indirectly estimating the temperature of the adsorption catalyst, wherein the operation of the exhaust gas heating means is controlled based on the temperature of the adsorption catalyst. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 4. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 5, wherein the temperature of the adsorption catalyst is estimated from the temperature of the exhaust gas flowing into the adsorption catalyst. 7. The internal combustion engine according to claim 5, wherein the operation of the exhaust gas heating means is started when the temperature of the adsorption catalyst reaches just before the desorption start temperature of HC. Exhaust purification equipment. 8. The method according to claim 5, wherein when the temperature of the adsorption catalyst exceeds a catalyst activation temperature by a predetermined value or more, the operation of the exhaust gas heating means is stopped. An exhaust gas purification device for an internal combustion engine.