JP2000084365A - Purifying device for exhaust from internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely purify, at the time of desorbing, a hydrocarbon adsorbed at the start of an internal combustion engine to prevent it from releasing to the outside. SOLUTION: An adsorption catalytic device 13 for adsorbing the hydrocarbon in an exhaust gas is interposingly mounted in an exhaust passage 18 of the internal combustion engine 1. The adsorption catalytic device 13 has a double layer structure of an adsorption layer containing adsorbent as an upper layer and a catalytic layer as a surface layer and in the catalytic layer, an oxide or the like generating heat by the irradiation with electromagnetic wave is blended. An electromagnetic wave generator 12 for emitting electromagnetic wave is provided in the inlet side of the adsorption catalytic device 13. After the start of the internal combustion engine 1, the electromagnetic generator 12 is operated to selectively cause the catalytic layer to generate heat when the tamp. of the catalyst is low. Then the catalyst reaches activation temp. before the adsorption layer reaches desorption start temp., and after that, the desorbed hydrocarbon is surely treated.

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 (hydrocarbon), CO, NOx, and the like, which are harmful components in exhaust gas. By the way, in order to obtain this catalytic action, the exhaust temperature must be high.
A temperature of about 00 ° C. is required. However, immediately after the start of the internal combustion engine, the exhaust gas temperature is low and does not reach the temperature at which the above-mentioned catalyst is activated (for example, 200 ° C. or higher). The result is an increase.

[0003] In order to solve the above-mentioned problem, in addition to a conventional catalyst, a hydrocarbon adsorbent for adsorbing hydrocarbons at low temperature conditions is provided in the exhaust system of an internal combustion engine, so that the carbon dioxide discharged before the catalytic activity is activated. A device that adsorbs hydrogen is known (Japanese Patent Application Laid-Open No. 6-241033). The hydrocarbon adsorbent used in these exhaust purification devices is actually an adsorption catalyst in which both a hydrocarbon adsorbent such as zeolite and a catalyst component such as a noble metal are mixed, and a part of the adsorbed hydrocarbon is used. Has a self-purifying function of oxidizing by a catalytic action. This adsorption catalyst is heated by the heat of the exhaust gas or the reaction heat of a general catalyst device provided on the upstream side, and when the temperature of the catalyst component reaches the activation temperature, the temperature of the adsorption catalyst increases. Purification of desorbed hydrocarbons becomes possible.

[0004] In addition, in order to ensure that the catalyst is activated at the time of desorbing hydrocarbons, various types having a heating means such as an electrothermal catalyst have been proposed.

[0005]

However, in general, the activation temperature of a catalyst using a noble metal or the like is at least about 200 ° C., whereas the desorption of hydrocarbons from an adsorbent is about 100 ° C. depending on the component. Begin. Therefore, not only when the temperature of the adsorption catalyst gradually rises due to the heat of the exhaust gas, but also when the adsorption catalyst is heated to some extent suddenly by a heating means such as an electrothermal catalyst, the amount of the hydrocarbon adsorbed by the adsorption component is reduced. In the early stage when desorption starts, it is inevitable that hydrocarbons are desorbed while the catalyst component has not reached a sufficiently active state. That is, in the above-described conventional adsorption catalyst device, when the catalyst is heated and activated early in order to purify the desorbed hydrocarbons, the adsorbed components are also heated at the same time, and the desorption starts early, Also, a part of the desorbed hydrocarbon is easily discharged to the outside without being purified.

[0006] It is an object of the present invention to provide an exhaust gas purifying apparatus which can surely purify adsorbed hydrocarbons simultaneously with desorption.

[0007]

According to the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine, wherein an adsorption catalyst device for adsorbing a hydrocarbon component in exhaust gas is interposed in an exhaust passage of the internal combustion engine. The adsorption catalyst device is composed of at least two layers of an adsorption catalyst having a lower layer composed of an adsorption layer containing an adsorbent for adsorbing hydrocarbons and a surface layer composed of a catalyst layer, and generates heat by irradiation of the catalyst layer with electromagnetic waves. It is characterized in that the substance is mixed and electromagnetic wave irradiation means for irradiating the adsorption catalyst with electromagnetic waves is provided.

According to a second aspect of the present invention, the catalyst layer is formed by adding platinum, palladium, rhodium as a catalyst component to a powder containing at least one of activated ceria and alumina as a main component. And at least one noble metal selected from the group consisting of: and a substance that generates heat when irradiated with electromagnetic waves. For example, a catalyst layer is formed by coating a slurry made of these materials on the adsorption layer.

The substance generating heat upon irradiation with the electromagnetic wave is, for example, at least one oxide selected from perovskite-type composite oxides, iron oxides, manganese oxides and cobalt oxides. is there.

[0010] 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 has an advantage that when hydrocarbons adsorbed in the lower adsorption layer desorb, they always pass through the surface catalyst layer, so that the purification performance in the catalyst layer is improved. . Also, considering the temperature rise due to the exhaust gas, since the surface catalyst layer is exposed to the exhaust gas, the temperature of the catalyst layer rises before the lower adsorbent layer, and the start of desorption of hydrocarbons The delay of the catalyst activity is suppressed.

In the present invention, in addition to this, the catalyst layer of the adsorption catalyst is mixed with a substance that generates heat by irradiation with electromagnetic waves, and the catalyst layer is selectively heated by irradiating the mixture with electromagnetic waves. Is possible. That is, during the temperature rising period of the adsorption catalyst such as immediately after the cold start of the engine, the electromagnetic wave irradiation means irradiates the adsorption catalyst with electromagnetic waves, so that the surface catalyst layer generates heat and the temperature rises. The part transfers heat to the lower adsorption layer. Therefore, a temperature gradient can be positively generated between the surface catalyst layer and the lower adsorption layer. Therefore, while the surface catalyst layer quickly reaches the activation temperature, the lower adsorption layer relatively delays in reaching the hydrocarbon desorption temperature, so that at the stage when the desorption of hydrocarbons from the adsorption layer starts. Since the surface catalyst layer is already active, almost all of the desorbed hydrocarbons can be purified by the catalyst layer.

Further, the invention of claim 4 has an adsorption catalyst temperature detecting means for detecting or indirectly estimating the temperature of the adsorption catalyst, and the operation of the electromagnetic wave irradiation means is controlled based on the temperature of the adsorption catalyst. It is characterized by being done.

The temperature of the adsorption catalyst can be directly detected using, for example, a temperature sensor. In addition, the temperature of the adsorption catalyst can be determined based on engine operating conditions such as cooling water temperature, engine speed, load, etc., and elapsed time after starting. Indirectly. The heating by the irradiation of the electromagnetic wave is performed, for example, at a stage when the temperature of the adsorption catalyst is low after the engine is started cold, and is stopped when the temperature reaches a predetermined temperature.

The invention according to claim 5 is characterized in that the irradiation of the electromagnetic wave is stopped when the temperature of the adsorption catalyst does not reach the predetermined temperature even after the irradiation with the electromagnetic wave for a predetermined time or more. That is, when the temperature of the adsorption catalyst does not rise due to some abnormality, the irradiation of the electromagnetic wave is stopped in order to avoid unnecessary power consumption.

Further, the invention according to claim 6 is characterized in that the operation of the electromagnetic wave irradiation means is prohibited based on the number of times of stopping the irradiation of the electromagnetic wave. For example, if the number of times the irradiation of the electromagnetic wave is stopped without reaching the predetermined temperature even after the irradiation of the electromagnetic wave reaches the predetermined number of times, or if such a situation continues a predetermined number of times, the failure of the electromagnetic wave irradiation means, etc. Therefore, the operation of the electromagnetic wave irradiation means is prohibited in advance. It is preferable to display some kind of warning at the same time.

[0016]

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 a lower layer and a catalyst layer as a surface layer, and only the surface catalyst layer is selectively heated by electromagnetic wave irradiation means. The temperature difference between the active layer and the catalytic layer can be positively expanded to make the activity of the catalyst layer relatively faster than the start of hydrocarbon desorption in the adsorption layer, and the desorbed hydrocarbons are reliably purified by the catalyst layer. be able to. Therefore, the total amount of hydrocarbons discharged to the outside when the internal combustion engine is started can be reduced as a whole.

[0017]

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

FIG. 1 shows an example of an embodiment of the present invention. The internal combustion engine 1 is a direct injection type gasoline engine, and includes a piston 2 and a crankshaft 3, and also includes a fuel injection valve 9 and a spark plug 10 toward a combustion chamber 11. Reference numeral 5 denotes a crank angle sensor for detecting the rotation speed of the crankshaft 3, and reference numeral 6 denotes a water temperature sensor for detecting the temperature of the cooling water.

In the intake passage 17 of the internal combustion engine 1, for example, a hot-wire type air flow meter 4 for detecting an intake air amount is interposed, and a throttle valve 7a is disposed downstream thereof. The opening of the throttle valve 7a is detected by the throttle opening sensor 7. The exhaust passage 18 of the internal combustion engine 1 is provided with an adsorption catalyst device 13 for adsorbing hydrocarbon components in the exhaust gas.
An oxygen sensor 8 for detecting the oxygen concentration in the exhaust gas is provided upstream of the adsorption catalyst device 13. A resonator 15 made of the same casing as the adsorption catalyst device 13 is provided on the inlet side of the adsorption catalyst device 13, and the electromagnetic wave generator 12 is connected to the resonator 15. That is, in this embodiment, the resonator 15
An electromagnetic wave irradiating means is constituted by the electromagnetic wave generator 12, and the electromagnetic wave generated by the electromagnetic wave generator 12 resonates with the resonator 15 and irradiates the adsorption catalyst of the adsorption catalyst device 13. Further, the adsorption catalyst device 13 is provided with a catalyst temperature sensor 14 for detecting the temperature.

Detection signals from various sensors such as the above-described crank angle sensor 5, water temperature sensor 6, air flow meter 4, throttle opening sensor 7, oxygen sensor 8, and catalyst temperature sensor 14 are input to an engine control unit 16. . The engine control unit 16 controls the fuel injection amount and the injection timing of the fuel injection valve 9, the ignition timing of the ignition plug 10, and the like based on these detection signals. 12
Controls the start and stop of.

FIG. 2 shows a detailed configuration of the adsorption catalyst device 13. The adsorption catalyst device 13 is mainly composed of a honeycomb-shaped carrier 20 made of ceramics or metal having many cells 23 through which exhaust gas passes. As one cell 23 is shown in an enlarged manner, the carrier 20 is firstly coated with an adsorption layer 21 for adsorbing hydrocarbons as a lower layer. Further, a catalyst layer 22 for purifying exhaust components is coated thereon as a surface layer, and constitutes one cell 23.
Then, a large number of the cells 23 are assembled and the adsorption catalyst device 13
Is composed. The material of the adsorption layer 21 is, for example, a component mainly composed of zeolite, and is coated with a slurry. Such a hydrocarbon adsorbent component has a property of adsorbing hydrocarbons at a low temperature, for example, about 100 ° C. to 200 ° C., and desorbing the hydrocarbons at a temperature higher than that. As the catalyst layer 22, a powder containing a noble metal such as platinum, palladium, and rhodium as a catalyst component in a powder containing one or both of activated ceria and alumina as a main component is used.
Further, one or more oxides selected from perovskite-type composite oxides, iron oxides, manganese oxides, and cobalt oxides are blended as heat generating substances due to electromagnetic waves. The material of the catalyst layer 22 is also formed as a slurry, and is coated on the adsorption layer 21.

The adsorbent layer 21 may contain not only the adsorbent component but also a catalyst component. The adsorbing layer 21 can be formed not only as one layer but also as two or more layers including adsorbing layers having different adsorbent components. Further, the catalyst layer 22 can also be constituted by two or more layers composed of different components.

Next, the operation of the electromagnetic wave generator 12 will be described with reference to the flowchart of FIG. The routine in FIG. 3 is repeatedly executed, for example, at regular intervals. First, at step 10, the state of the electromagnetic wave generator operation inhibition flag FLGCAT is determined. This will be "1" at the time of some kind of failure, as will be described later. If this is "1", the process proceeds to step 17, where the electromagnetic wave generator 12 is kept stopped. Flag FL
If GCAT is "0", the routine proceeds to step 11, where the catalyst temperature TCAT detected by the catalyst temperature sensor 14 is read. In step 12, this adsorption catalyst temperature TCA
It is determined whether T is equal to or lower than a predetermined temperature SLT1.
The predetermined temperature SLT1 is set corresponding to the activation temperature of the catalyst layer 22, and the catalyst temperature TCAT is set to the predetermined temperature SL.
If it is equal to or less than T1, go to step 13 and go to step 1
In step 4, the electromagnetic wave generator 12 is turned on, and the heating of the catalyst layer 22 using the electromagnetic waves is started. The irradiation of the electromagnetic wave causes the catalyst layer 22 in the adsorption catalyst device 13 to generate heat, and only the catalyst layer 22 is selectively heated.

Therefore, before the lower adsorbent layer 21 reaches the desorption temperature, the surface catalyst layer 22 surely reaches the activation temperature, and the hydrocarbon desorbed from the adsorbent layer 21 as the temperature rises increases. Almost the entire amount is purified when passing through the catalyst layer 22, and is hardly discharged to the outside.

The operation of the electromagnetic wave generator 12 is as follows.
The process ends when T1 is reached. On the other hand, in step 13, the operation time TM1 of the electromagnetic wave generator 12 is set to the predetermined time TM
If it is determined that the temperature has become 0 or more, and if the catalyst temperature TCAT becomes equal to or more than the predetermined time TM0 before reaching the predetermined temperature SLT1, the routine proceeds to step 15, where 1 is added to the value of the counter n. Note that the initial value of the counter n is 0.
Then, the process proceeds to step 17 via step 16, and the electromagnetic wave generator 12 is turned off. That is, when the temperature does not rise to the predetermined temperature within the predetermined time despite the irradiation of the electromagnetic wave, the irradiation of the electromagnetic wave is stopped in order to avoid excessive consumption of battery power.

In step 16, the number of times the operation is stopped, that is, the value of the counter n is set to a predetermined reference number S.
If the number is greater than the reference number SLn compared to Ln, the routine proceeds to step 18, where the electromagnetic wave generator operation inhibition flag FLGCAT is set to "1". In other words, in this case, since it is considered that some failure has occurred, the operation of the electromagnetic wave generator 12 is prohibited from the next start. At the same time, some kind of abnormal display such as turning on a warning light is performed,
It is desirable to warn the driver of the abnormality.

Here, when the total number of times the irradiation of the electromagnetic wave generator 12 is stopped is SLn times, it is determined that the abnormality is abnormal. An abnormality may be determined only when a certain number of consecutive times have occurred.

Since the rise in the temperature of the adsorption catalyst device 13 is affected by the outside air temperature and the initial temperature at the time of starting the engine, the reference number SLn is varied by calculation or table lookup as a function of the outside air temperature and the initial temperature. You may make it set dynamically.

Next, based on the flowchart of FIG.
An embodiment will be described. This is to estimate the temperature of the adsorption catalyst device 13 based on engine operating conditions, and does not include the above-described catalyst temperature sensor 14.

First, at step 21, it is determined whether the internal combustion engine 1 is rotating. If not, the routine proceeds to step 28, where the electromagnetic wave generator 12 is turned off. Next, in step 22, it is determined whether or not a starter switch (not shown) has changed from ON to OFF. In other words, only after the internal combustion engine 1 has been started and the starter switch has changed from ON to OFF, the process proceeds to step 23 and thereafter, and otherwise, the process proceeds to step 28.

In step 23, the engine operating conditions, specifically, the engine speed Ne and the load are read. As the load, a value of the basic fuel injection amount Tp calculated from the intake air amount and the engine speed Ne is used. Then, in step 24, based on the engine speed Ne and the load Tp, the exhaust gas temperature TEX is referred to with reference to a predetermined exhaust gas temperature map.
Find H. If the exhaust gas temperature map is created for each cooling water temperature (for example, every 10 ° C.) and the map corresponding to the cooling water temperature at that time is used, the accuracy of estimating the exhaust gas temperature is further improved.

Next, at step 25, the exhaust gas temperature TEX
Using H and the previous catalyst temperature TCAT (n-1), the current catalyst temperature TCAT (n) is obtained from the following equation: TCAT (n) = TCAT (n-1) + (TEXH-T
CAT (n−1)) × k At the first time, for example, the cooling water temperature may be used as the catalyst temperature TCAT (n−1).

In step 26, it is determined whether the estimated catalyst temperature TCAT is equal to or higher than a predetermined temperature SLT2.
If the temperature is lower than the predetermined temperature SLT2, the electromagnetic wave generator 12 is turned on in step 27, and if the temperature is equal to or higher than the predetermined temperature SLT2, the electromagnetic wave generator 12 is turned off in step 28. Since the process returns from step 27 to step 23, the operation of the electromagnetic wave generator 12 is continued until the temperature reaches the predetermined temperature SLT2.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory diagram 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 the flow of processing according to the first embodiment;

FIG. 4 is a flowchart illustrating a flow of a process according to the second embodiment;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 12 ... Electromagnetic wave generator 13 ... Adsorption catalyst device 14 ... Catalyst temperature sensor 15 ... Resonator 21 ... Adsorption layer 22 ... Catalyst layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/20 F01N 3/20 D 3/24 3/24 ECL 3/28 301 3/28 301P F Term (reference) 3G091 AA02 AA17 AA24 AB01 AB10 BA03 BA15 BA22 CA01 CB02 CB03 CB05 DB06 DB10 DB13 EA01 EA05 EA07 EA16 EA18 EA30 EA34 FA02 FA04 FB02 FC07 GA06 GB01X GB05W GB06W GB07W GB09A GBA18AGBX18A03A BA19X BA28X BA30X BA31X BA32X BA36X BA37X BA39X BA41X BB02 BB16 CC43 CC53 DA01 DA02 DA13 EA03 EA04 4G069 AA01 AA03 AA08 BA01A BA01B BB04A BB04B BB06A BB06B BB06A BB06B BC43A BC43B BCBC BCA BCBC BCA BCBC

Claims (6)

[Claims] 1. An exhaust purification device for an internal combustion engine, comprising an adsorption catalyst device for adsorbing hydrocarbon components in exhaust gas disposed in an exhaust passage of the internal combustion engine. A material composed of at least two layers of an adsorption catalyst having a lower layer composed of an adsorption layer containing an adsorbent to be adsorbed and a surface layer composed of a catalyst layer, and a substance that generates heat by irradiation with electromagnetic waves is mixed in the catalyst layer, An exhaust gas purifying apparatus for an internal combustion engine, comprising an electromagnetic wave irradiating means for irradiating an electromagnetic wave to the adsorption catalyst. 2. The catalyst layer according to claim 1, wherein the catalyst layer contains at least one of activated ceria and alumina as a main component and at least one noble metal selected from the group consisting of platinum, palladium and rhodium as a catalyst component. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a substance that generates heat by irradiation with electromagnetic waves is mixed therein. 3. The substance that generates heat upon irradiation with the electromagnetic wave is at least one oxide selected from perovskite-type composite oxides, iron oxide, manganese oxide, and cobalt oxide. Item 3. An exhaust gas purifying apparatus for an internal combustion engine according to item 1 or 2. 4. An adsorption catalyst temperature detecting means for detecting or indirectly estimating the temperature of the adsorption catalyst, wherein the operation of the electromagnetic wave irradiation means is controlled based on the temperature of the adsorption catalyst. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 4, wherein the irradiation of the electromagnetic wave is stopped when the temperature of the adsorption catalyst does not reach the predetermined temperature even if the electromagnetic wave is irradiated for a predetermined time or more. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 5, wherein the operation of the electromagnetic wave irradiation means is prohibited based on the number of times of stopping the irradiation of the electromagnetic wave.