JPH0994433A - Exhaust gas cleaner for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively eliminate an HC component contained in exhaust gas while power consumption of a battery is suppressed. SOLUTION: An HC adsorbent 3 for adsorbing the HC component is arranged in the exhaust gas system consisting of an exhaust gas pipe 2 and also an electrically heated catalyst 4 is arranged on the down stream thereof. The HC adsorbent 3 is composed of a raw material such as a β type zeolite having such characteristic that desorbing temp. of the HC component having better ignitability, consisting of 5-8C paraffins, etc., is lower than the desorbing temp. of the HC component having worse ignitability, consisting of olefins and aromatics, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, which purifies HC components contained in the exhaust gas of the internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, as disclosed in, for example, Japanese Patent Laid-Open No. 6-33747, an electrically heated catalyst (with a heater) is installed between an unburned gas adsorbent installed in an engine exhaust system and an exhaust purification catalyst. (Catalyst) is installed, and the unburned gas desorbed from the adsorbent is purified by the electrically heated catalyst from the time the engine is started to the time when the exhaust purification catalyst is activated. There has been proposed an engine exhaust gas purification device configured to reduce the amount of unburned gas emitted.

The adsorbent is made of activated carbon, silica gel, zeolite or the like, and is configured to gradually release the adsorbed unburned gas when the exhaust gas temperature reaches a desorption temperature of about 140 ° C. In addition, the electrically heated catalyst is used as a heater until it is confirmed that the exhaust gas purifying catalyst has been activated from the time when the engine is started, or until a time sufficient for the exhaust gas purifying catalyst to be activated has elapsed. Is energized to purify unburned gas such as HC component desorbed from the adsorbent.

[0004]

In the exhaust gas purification device configured to purify the HC components and the like gradually released from the adsorbent by the electric heating catalyst as described above, the purification of the HC components by the electric heating catalyst is performed. Since the amount of heat generated at times is small, it is necessary to continue energizing the heater of the electrically heated catalyst from the time the engine is started until the exhaust gas purification catalyst is activated, which causes a problem of significant battery power consumption. Further, since various HC components are released from the adsorbent, there is a problem that it is difficult to purify all HC components by the electrically heated catalyst.

The present invention has been made in view of the above points, and exhaust gas of an internal combustion engine capable of effectively purifying HC components contained in exhaust gas while suppressing power consumption of a battery. A purification device is provided.

[0006]

The invention according to claim 1 is
An exhaust purification device installed in an exhaust system of an internal combustion engine,
An HC adsorbent that adsorbs the HC component in the exhaust gas is arranged in the exhaust system, and an electric heating catalyst is arranged in the downstream thereof, and the desorption temperature of the HC component with good ignitability is H with poor ignitability.
The HC adsorbent is composed of a material having a characteristic that it is lower than the desorption temperature of the C component.

According to this structure, after the HC component in the exhaust gas discharged immediately after the start of the internal combustion engine is adsorbed by the HC adsorbent in the upstream portion, when the HC adsorbent rises to a predetermined temperature, The HC component having good ignitability is desorbed from the HC adsorbent and is purified by the electrically heated catalyst. After that, when the HC adsorbent rises to the desorption temperature of the HC component with poor ignitability, the HC component with poor ignitability begins to desorb from the HC adsorbent.

According to a second aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, the desorption temperature of the HC component composed of C _{5 to} C ₈ paraffin is higher than that of the HC component composed of olefin and aroma. The HC adsorbent is composed of a material having a characteristic of being lower than the desorption temperature.

According to this structure, among the HC components adsorbed by the HC adsorbent, the C _{5 to} C ₈ paraffins, which have the property of having a good ignition temperature, are used at an early stage after the internal combustion engine is started. After desorbing from the HC adsorbent, the HC component composed of the above-mentioned olefin and aroma having a low ignition temperature becomes H.
It will be desorbed from the C adsorbent.

According to a third aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, the HC adsorbent is composed of β-type zeolite.

According to this structure, the β-type zeolite has a large number of substantially elliptical pores having different vertical and horizontal bores,
Since various HC components are effectively adsorbed and the HC component having poor ignitability among the adsorbed HC components has a high holding power, the HC component having poor ignitability is It will be retained for a long time by the HC adsorbent composed of type zeolite.

[0014] The invention according to claim 4 is the above-mentioned claims 1-3.
In the exhaust gas purification device for an internal combustion engine according to any one of
When it is confirmed that the HC component having good ignitability starts to be desorbed from the HC adsorbent, the electrically heated catalyst is brought into a heated state.

According to this structure, when it is confirmed that the HC adsorbent reaches the desorption temperature of the HC component having good ignitability and the HC component starts to desorb from the HC adsorbent,
The electric heating catalyst is energized, and the HC component is purified by the electric heating catalyst.

According to a fifth aspect of the present invention, in the exhaust gas purifying apparatus for an internal combustion engine according to the fourth aspect, the HC according to the detection signal of the oxygen concentration detecting means for detecting the oxygen concentration of the exhaust gas.
A control means is provided for determining whether or not the HC component having good ignitability starts to be desorbed from the adsorbent, and controlling the electrically heated catalyst according to the determination result.

According to this structure, when it is confirmed that the HC component having good ignitability starts to be desorbed from the HC adsorbent according to the detection signal of the oxygen concentration detecting means, the electric heating catalyst is energized. The electric heating catalyst purifies the HC component.

[0016] The invention according to claim 6 is, in the exhaust gas purification apparatus for an internal combustion engine according to claim 4 or 5, when it is confirmed that HC components having good ignitability have started to desorb from the HC adsorbent. Secondary air supply means for supplying secondary air is provided upstream of the electrically heated catalyst.

According to this structure, the HC component having good ignitability desorbed from the HC adsorbent is purified by the electric heating catalyst, and the purifying action is performed by the secondary air supplied from the secondary air supply means. Will be promoted by

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an exhaust emission control system for an internal combustion engine according to the present invention. This exhaust gas purification device includes an HC adsorbent 3 provided in an exhaust passage 2 of an internal combustion engine 1 and an electric heating catalyst (EHC) installed in a downstream portion thereof.
4 and an exhaust gas purifying catalyst 5 disposed downstream thereof
A secondary air supply means 6 for supplying secondary air to the exhaust passage between the HC adsorbent 3 and the electrically heated catalyst 4, and a control means for controlling the electrically heated catalyst 4 and the secondary air supply means 6. 7 and 7.

The HC adsorbent 3 is composed of β-type zeolite (PQB) in which a large number of substantially oval pores having different vertical and horizontal caliber are formed. This β-type zeolite has a strong holding power for HC components having a high ignition temperature and poor ignitability among HC components in exhaust gas, and a weak holding power for HC components having a low ignition temperature and good ignitability. There is a characteristic that the desorption temperature of the HC component having good ignitability is lower than the desorption temperature of the HC component having poor ignitability.

That is, as shown in Table 1 below, among various HC components, ethylene (CH ₂ = CH ₂ ), propylene (CH ₃ CH = CH ₂ ) and 1-butene, that is, ethylethylene (CH ₃ CH ₂ ). C ₂ -C consisting of ₂ CH = CH ₂ ).
The olefin of ₄ (unsaturated hydrocarbon having a double bond represented by C _n H _2n , that is, alkene) has an ignition temperature of 490 ° C, 458 ° C and 443 ° C, respectively,
Since this ignition temperature is relatively high, it has a property of poor ignitability.

Among various HC components, benzene (C ₆ H ₆ ), toluene, that is, methylbenzene (C ₆ H ₅ C)
C ₆ consisting of H ₃ ) and xylene [C ₆ H ₄ (CH ₂ ) ₂ ].
~ C ₈ aroma (aromatic hydrocarbon having a benzene ring,
In other words, the firing temperature of each arene is 580 °
C, 552 ° C. and 496 ° C., and has a property of poor ignitability.

Among various HC components, methane (C
H _4), ethane (CH ₃ CH _3), propane (CH ₃ CH ₂
CH ₁ ) and butane (CH ₃ CH ₂ CH ₂ CH ₃ ) C _{1 to} C ₄ paraffins (saturated chain hydrocarbons having the general formula of C _n H _{2n + 2} ) have an ignition temperature of 632, respectively.
° C, 490 ° C, 504 ° C, and 428 ° C, and has the property of poor ignitability.

On the other hand, n-pentane [CH ₃ (C
H _{2) 3} CH = CH _2], hexane [CH ₃ (CH _{2) 4} CH
= CH _2], heptane _{[CH 3 (CH 2) 5 CH} = CH 2 ]
And octane _{[CH 3 (CH 2) 6 CH} = CH 2 ] paraffins consisting C ₅ -C _8, the ignition temperature is respectively 2
The temperatures are 90 ° C., 248 ° C., 230 ° C. and 210 ° C. Since the ignition temperature is relatively low, it has the property of good ignitability.

[0024]

[Table 1]

Then, after adsorbing the above-mentioned various HC components to the HC adsorbent composed of β-type zeolite, the HC adsorbent is heated to gradually raise its temperature, and the desorption amount of the HC component is increased. When we conducted an experiment to measure
As shown in FIG. 2, a two-step peak is formed in the vicinity of 200 ° C. and 300 ° C., and at the first peak in the vicinity of 200 ° C., HC having good ignitability mainly composed of C _{5 to} C ₈ paraffins is formed. It was confirmed that the components were desorbed, and at the second peak near 300 ° C., the HC components mainly composed of the above-mentioned olefin and aroma and having poor ignitability were desorbed.

A similar experiment was carried out using an HC adsorbent composed of Y-type zeolite (USY), and as shown in FIG. 3, one large peak was formed near 200 ° C. Almost no change was observed depending on the difference in ignitability as in the above β-type zeolite.

The electrically heated catalyst 4 has an electric heater 8 which is heated by electric power supplied from a power source (not shown),
Catalyst component mainly composed of palladium etc. which is activated at low temperature 9
And is configured to activate the catalyst component 9 by heating the electric heater 8 in an energized state in response to a control signal output from the control means 7.

The control means 7 includes a first oxygen concentration detecting means 10 including an O ₂ sensor for detecting the oxygen concentration of the exhaust gas discharged from the internal combustion engine 1, and the HC adsorbent 3
According to the detection signal output from the second oxygen concentration detection means 11 including an O ₂ sensor for detecting the oxygen concentration of the exhaust gas derived from the H adsorbent 3 which has a good ignitability.
It is determined whether or not the C component has started to desorb, and a control signal corresponding to the result of this determination is output to the electrically heated catalyst 4.

That is, the control means 9 controls the oxygen concentration on the upstream side of the HC adsorbent 3 detected by the first oxygen concentration detecting means 10 and the HC adsorbent 3 detected by the second oxygen concentration detecting means 11. When it is confirmed that the oxygen concentration in the downstream side of the HC adsorbent 3 is lower than that in the upstream side, the HC adsorbent 3 has a high ignitability. It is configured to output a control signal for determining that the components have begun to be desorbed and bringing the electrically heated catalyst 4 into a heating state.

The exhaust gas purifying catalyst 5 has excellent purifying performance for HC components and has an activation temperature of 2
A catalyst component composed mainly of palladium (Pd) set at a low temperature of about 50 ° C., to which a noble metal such as platinum (Pt) or rhodium (Rh) is added, is used as a catalyst component. It is formed by being supported on a honeycomb carrier made of a duerite ceramic material or the like. The honeycomb carrier may have a structure in which a platinum-rhodium-based three-way catalyst is mainly supported.

The secondary air supply means 6 is composed of an air pump driven in response to a control signal output from the control means 7. When it is confirmed by the control means 7 that the HC component having good ignitability starts to desorb from the HC adsorbent 3, the electric heating catalyst 4 is heated and at the same time the secondary air supply means is supplied. 6 is driven and the above H
Secondary air is supplied to the exhaust passage between the C adsorbent 3 and the electrically heated catalyst 4.

In the above structure, a large amount of the HC component discharged immediately after the start of the internal combustion engine 1 is first adsorbed by the HC adsorbent 3 arranged in the upstream portion of the exhaust system. This HC adsorbent 3 has a characteristic that the desorption temperature of the HC component having good ignitability is lower than the desorption temperature of the HC component having poor ignitability, as shown in FIG. To
At a time t1 when a predetermined time has passed after the start of the internal combustion engine, HC components having a good ignitability start to be desorbed, and at a time t2 after a predetermined time has elapsed, a HC component having a poor ignitability starts to desorb. .

Then, at the time t1 when it is confirmed by the control means 7 that the HC component having good ignitability starts to be desorbed from the HC adsorbent 3, the electric heater 8 of the electric heating catalyst 4 is brought into the heating state. , The secondary air supply means 6
A control signal for activating is output, as shown in FIG.
The temperature of the electrically heated catalyst 4 (EHC) rises and the catalyst component 9 is activated.

When the catalyst component 9 of the electrically heated catalyst 4 is activated, the HC component having good ignitability desorbed from the HC adsorbent 3 is purified by the catalyst component 9 and the purification action is It is promoted by the secondary air supplied from the secondary air supply means 6. And the above H
The heat generated during purification of the C component is transferred to the downstream side, so that the exhaust gas purification catalyst 5 is activated, and the HC component with poor ignitability discharged thereafter is converted into the exhaust gas purification catalyst 5 described above.
Will be surely purified by.

As described above, the HC adsorbent 3 for adsorbing the HC component in the exhaust gas is arranged in the exhaust system, and the electric heating catalyst 4 is arranged in the downstream thereof, and the C _{5 to} C ₈ paraffin or the like is provided. The HC adsorbent 3 is made of a material having a characteristic that the desorption temperature of the HC component having good ignitability composed of is lower than the desorption temperature of the HC component having poor ignitability composed of an olefin and an aroma. At a time point t1 when the adsorbent 3 reaches the desorption temperature of the HC component having good ignitability, the electric heater 8 is energized to bring the electrically heated catalyst 4 into a heating state, thereby desorbing from the HC adsorbent 3. The HC components having good ignitability can be collectively burned and purified by the electrically heated catalyst 4.

Since the HC component having good ignitability, such as C _{5 to} C ₈ paraffin, has a low ignition temperature, the HC component of the electric heating catalyst 4 is reliably burned without heating it to such a high temperature. Can be made. Therefore,
As shown in FIG. 5, the temperature of the electrically heated catalyst 4 is increased without excessively increasing the amount of electricity supplied to the electrically heated catalyst 4 or starting heating the electrically heated catalyst 4 from the start of the internal combustion engine 1. The catalyst component 9
Also, the exhaust gas purifying catalyst 5 can be instantly activated, and the HC component having poor ignitability such as olefin and aroma desorbed from the HC adsorbent 3 by the electrically heated catalyst 4 and the exhaust gas purifying catalyst 5. Can be reliably burned and purified, and the amount of HC components discharged into the atmosphere can be reliably reduced.

In particular, as shown in the above embodiment, when the HC adsorbent 3 is composed of β-type zeolite, the β-type zeolite has a large number of substantially elliptical pores having different vertical and horizontal bores. In addition to being able to effectively adsorb various HC components, it is also possible to adsorb various HC components once adsorbed.
Among the components, since it has a characteristic that it has a high holding power for HC components having poor ignitability, such as the above-mentioned olefins and aromas, the HC components having poor ignitability adsorbed on the HC adsorbent 3 can be used for a long time. Can be held over. Therefore, before the electric heating catalyst 4 or the exhaust gas purifying catalyst 5 is activated, the HC component having poor ignitability is desorbed from the HC adsorbent 3 and passes through the installation portion of the electric heating catalyst 4 or the like. It is possible to reliably prevent the occurrence of a situation.

A conventional device in which an HC adsorbent composed of Y-type zeolite having pores having a relatively large pore size is disposed upstream of the electrically heated catalyst 4 and the HC adsorbent 3 is constituted by the β-type zeolite. And the exhaust gas purifying apparatus according to the embodiment of the present invention
The following data were obtained when an experiment was conducted to measure the component amounts.

In the above-mentioned conventional apparatus, as shown by the broken line in FIG. 6, it is impossible to prevent a large amount of HC components from being discharged into the atmosphere immediately after the internal combustion engine is started. Β consisting of β-type zeolite on the upstream side of
In the embodiment of the present invention in which the HC adsorbent 3 is arranged, as shown by the solid line in FIG. 6, the amount of HC components discharged from the exhaust gas purifying catalyst 5 into the atmosphere is significantly reduced. It was confirmed that

Further, as shown in the above embodiment,
At time t1 when it is confirmed by the control means 7 that the HC component having high ignitability starts to desorb from the HC adsorbent 3 in response to the detection signals of the second oxygen concentration detection means 10 and 11,
When the electrically heated catalyst 4 is configured to be in a heated state, the electrically heated catalyst 4 can be accurately heated and activated at the desorption timing of the HC component. Thus, the HC component can be surely purified. Moreover, since it is not necessary to bring the electrically heated catalyst 4 into a heated state more quickly than necessary, there is an advantage that the power consumption of the battery can be effectively suppressed.

Further, in the above embodiment, when it is confirmed by the control means 7 that the HC component having good ignitability starts to be desorbed from the HC adsorbent 3, the secondary air is provided upstream of the electrically heated catalyst 4. Since the secondary air supply means 6 for supplying the HC is provided, the HC desorbed from the HC adsorbent 3 and having good ignitability
Since the purifying action of the electrically heated catalyst 4 for purifying the components can be promoted by the secondary air supplied from the secondary air supply means 6, the amount of the HC component discharged into the atmosphere is further effective. There is an advantage that it can be reduced.

In the above embodiment, the first and second
According to the detection signals of the oxygen concentration detecting means 10 and 11, the above H
Although it is configured to determine whether or not the HC component having poor ignitability starts to be desorbed from the C adsorbent 3, instead of this configuration, a detection signal of a temperature sensor that detects the temperature of the HC adsorbent 3 is used. Accordingly, it may be configured to determine whether or not the HC component having poor ignitability starts to be desorbed from the HC adsorbent 3.

[0043]

As described above, according to the present invention, the HC adsorbent for adsorbing the HC component in the exhaust gas is arranged in the exhaust system, and the electric heating catalyst is arranged in the downstream portion thereof to improve the ignitability. Since the HC adsorbent is composed of a material having a characteristic that the desorption temperature of a good HC component having a good ignition temperature is lower than the desorption temperature of an HC component having a poor ignitability, the HC adsorbent is C ₅
When it becomes the desorption temperature of the ignitability good HC component comprising paraffins of -C _8, by an electric heating catalyst and heated state, a predetermined amount of the HC component desorbed from the HC absorbent The electrically heated catalyst can be burned together.

Therefore, while suppressing the power consumption of the battery, the temperature of the electrically heated catalyst is rapidly raised to activate it instantaneously, and thereafter the ignition of olefins and aromas etc. desorbed from the HC adsorbent is carried out. It is possible to reliably burn and purify HC components having poor properties by the above-mentioned electrically heated catalyst or the exhaust gas purifying catalyst disposed on the downstream side thereof, and to reliably reduce the amount of HC components discharged into the atmosphere. is there.

[Brief description of drawings]

FIG. 1 is an overall explanatory view showing an embodiment of an exhaust emission control device according to the present invention.

FIG. 2 Temperature and H of HC adsorbent composed of β-type zeolite
It is a graph which shows the relationship with the desorption amount of C component.

FIG. 3: Temperature and H of HC adsorbent composed of Y-type zeolite
It is a graph which shows the relationship with the desorption amount of C component.

FIG. 4 is a time chart showing a change state of the desorption amount of the HC component desorbed from the HC adsorbent.

FIG. 5 is a time chart showing a temperature change state of an electrically heated catalyst.

FIG. 6 is a time chart showing a change state of the amount of HC component discharged into the atmosphere.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Exhaust Pipe (Exhaust System) 3 HC Adsorbent 4 Electric Heating Catalyst 6 Secondary Air Supply Means 7 Control Means 10, 11 Oxygen Concentration Detection Means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Ichikawa 3-1, Shinchi Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Yuki Kokuda 3-1-1 Shinchu, Fuchu-cho, Hiroshima Prefecture Mazda Stock In the company

Claims (6)

[Claims] 1. An exhaust gas purification device installed in an exhaust system of an internal combustion engine, wherein an HC adsorbent for adsorbing HC components in exhaust gas is provided in the exhaust system, and an electrically heated catalyst is provided at a downstream portion thereof. The exhaust gas of an internal combustion engine, wherein the HC adsorbent is composed of a material that is disposed and has a characteristic that the desorption temperature of the HC component having good ignitability is lower than the desorption temperature of the HC component having poor ignitability. Purification device. 2. The HC adsorbent is composed of a material having a characteristic that the desorption temperature of the HC component composed of C _{5 to} C ₈ paraffin is lower than the desorption temperature of the HC component composed of olefin and aroma. The exhaust emission control device for an internal combustion engine according to claim 1. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the HC adsorbent is composed of β-type zeolite. 4. The electrically heated catalyst is configured to be in a heating state at the time when it is confirmed that the HC component having good ignitability starts to be desorbed from the HC adsorbent. 2. An exhaust gas purification device for an internal combustion engine according to any one of 1. 5. It is determined whether or not the HC component having a good ignitability starts to be desorbed from the HC adsorbent according to the detection signal of the oxygen concentration detection means for detecting the oxygen concentration of the exhaust gas, and according to this determination result. An exhaust purification system for an internal combustion engine according to claim 4, further comprising control means for controlling the electrically heated catalyst. 6. A secondary air supply means for supplying secondary air to the upstream part of the electrically heated catalyst at the time when it is confirmed that HC components having good ignitability have started to desorb from the HC adsorbent. The exhaust emission control device for an internal combustion engine according to claim 4 or 5,