JPH11210446A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain HC purification effect to the maximum extent while suppressing NOx exhaust by providing lean NOx catalyst and HC adsorption catalyst in the order from the upstream side in an exhaust passage and controlling an air-fuel ratio of mixed air to a lean state while lean NOx catalyst is active and HC is removed from an HC adsorption material. SOLUTION: In an exhaust manifold of an air exhaust passage 17, an oxygen sensor 18 detecting rich or lean state of an air-fuel ratio is provided, a lean NOx catalyst 19 is provided on the downstream side thereof, and an HC adsorption catalyst 20 provided with a ternary catalyst layer on an upper layer of an HC adsorption material is provided on the downstream side furthermore. This HC adsorption catalyst 20 absorbs HC in exhaust air into the HC adsorption material when an internal combustion engine is cold and removes HC from the HC adsorption material upon completion of warming up the engine to purify the removed HC by oxygen in the ternary catalyst layer. In this case, an air-fuel ratio of mixed air is controlled to a lean state while lean NOx catalyst 19 is activated and HC is removed from the HC adsorption material. Consequently, it is possible to securely supply oxygen required for HC purification to the ternary catalyst layer and increase the purification efficiency of HC.

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, and more particularly, to HC in exhaust gas in a cold state.
After being warmed up, the HC adsorbent adsorbs H
The present invention relates to an exhaust gas purification device for an internal combustion engine having a configuration for removing and purifying C.

[0002]

2. Description of the Related Art Conventionally, an HC adsorbent is interposed in an exhaust passage of an internal combustion engine so that HC in exhaust gas is adsorbed by the HC adsorbent during a cold period, and HC is desorbed from the HC adsorbent after completion of warm-up. There is known an exhaust gas purifying apparatus having a configuration in which the desorbed HC is oxidized and purified by a three-way catalyst (Japanese Patent Laid-Open No. 6-8 / 1994).
No. 1637).

[0003] The applicant of the present invention has an HC adsorbing catalyst comprising a three-way catalyst layer on an upper layer of an HC adsorbing material in an exhaust passage, so that the HC adsorbing material is removed during the desorption of HC from the HC adsorbing material. An exhaust gas purifying device having a configuration in which the fuel injection amount is controlled so that the exhaust air-fuel ratio at the outlet of the catalyst becomes lean by a predetermined amount has been previously proposed (see Japanese Patent Application No. 9-246409).

[0004]

The above-mentioned lean control aims at securing oxygen necessary for oxidizing the desorbed HC. The lean control is performed by performing the lean combustion.
However, at the time of lean combustion, the NOx conversion rate in the three-way catalyst is reduced, so that leaning is restricted to suppress NOx emissions, and the effect of HC purification by the lean control is maximized. There was a possibility that it could not be demonstrated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an exhaust gas purifying apparatus capable of securing oxygen necessary for HC oxidation while suppressing NOx emission. The purpose is to be able to make the most of it.

[0006]

Therefore, an exhaust gas purifying apparatus for an internal combustion engine according to the first aspect of the present invention includes, in an exhaust passage, an HC adsorbing catalyst comprising a three-way catalyst layer above an HC adsorbing material. In addition, a lean NOx catalyst having NOx purification performance in a lean combustion region is provided in an exhaust passage on the upstream side of the HC adsorption catalyst, and the lean NOx catalyst is in an active state, and HC is desorbed from the HC adsorbent. During the operation, the air-fuel ratio of the combustion mixture of the engine is controlled lean.

With this configuration, the lean NOx catalyst provided on the upstream side of the HC adsorption catalyst purifies NOx in the exhaust gas during the lean control if it is in an active state. Therefore, if lean control for oxidizing HC desorbed from the HC adsorbent in the three-way catalyst layer is performed in the activated state of the lean NOx catalyst, NOx is purified by the lean NOx catalyst. Lean control for supplying oxygen necessary for purifying HC to the catalyst layer can be performed without being limited by the NOx emission amount.

The lean NOx catalyst is a so-called NOx storage-reduction type three-way catalyst that temporarily stores NOx in exhaust gas in a lean combustion region into a NOx storage material and performs a reduction process when the stoichiometric air-fuel ratio is approached. A catalyst can be used, or a zeolite-type three-way catalyst that uses zeolite for a part of the base material and can reduce NOx even in a lean combustion region (oxidizing atmosphere) (the same applies hereinafter).

According to a second aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine, wherein an HC adsorbing catalyst constituted by providing a three-way catalyst layer on an upper layer of an HC adsorbing material is provided in an exhaust passage,
In the exhaust passage on the upstream side of the C adsorption catalyst, N
Equipped with a lean NOx catalyst having Ox purification performance, and
The desorption of HC from the HC adsorbent is started after the activation of the lean NOx catalyst, and the air-fuel ratio of the combustion mixture of the engine becomes lean during the desorption of HC from the HC adsorbent. It was configured to control.

According to this configuration, the desorption of HC from the HC adsorbent of the HC adsorbing catalyst is started after the lean NOx catalyst is activated. NOx is lean N from the beginning of control
It will be purified by the Ox catalyst. The exhaust gas purifying apparatus for an internal combustion engine according to the third aspect of the present invention is configured as shown in FIG.

In FIG. 1, the HC adsorbing catalyst is a catalyst comprising a three-way catalyst layer on an upper layer of an HC adsorbing material.
On the upstream side of the HC adsorption catalyst, NO
A lean NOx catalyst having x purification performance is provided. On the other hand, the activity judging means judges the activation state of the lean NOx catalyst, and the desorption judging means judges the amount of HC from the HC adsorbent.
Is determined.

The lean control means determines that the lean NOx catalyst is in an active state by the activity determining means, and indicates a state in which HC is desorbed from the HC adsorbent by the desorption determining means. Is determined, the air-fuel ratio of the combustion mixture of the engine is controlled lean. According to such a configuration, when it is determined that the lean NOx catalyst has been activated and it is determined that the HC is desorbed from the HC adsorbent, the HC adsorbing catalyst is reset. The air-fuel ratio is controlled lean so as to secure oxygen necessary for the oxidation treatment of HC in the source catalyst layer. Accordingly, NOx is reduced by lean control on the upstream side while promoting oxidation of HC in the three-way catalyst layer of the HC adsorption catalyst by lean control.
It will be purified in the catalyst.

[0013] In the invention described in claim 4, the lean NO
In order to start the desorption of HC from the HC adsorbent after the activation of the x catalyst, exhaust cooling means for cooling exhaust gas between the lean NOx catalyst and the HC adsorption catalyst is provided. According to such a configuration, after the exhaust gas that has passed through the lean NOx catalyst is cooled by the exhaust gas cooling means,
By being introduced into the adsorption catalyst, the temperature rise of the HC adsorption catalyst (HC adsorbent) is delayed more than the temperature rise of the lean NOx catalyst, and after the lean NOx catalyst is activated, HC
The temperature of the adsorbent is raised to the desorption temperature of HC.
Thus, when the desorption of HC from the HC adsorbent is started, the lean NOx catalyst has already been activated and the NOx can be purified in the lean combustion region. Control will be performed.

The exhaust cooling means includes a lean N
In addition to a configuration in which a heat mass (heat capacity) composed of a cooling fin or a honeycomb structure is interposed between the Ox catalyst and the HC adsorption catalyst, a method of cooling with a coolant such as water may be used. According to a fifth aspect of the present invention, the lean control means performs feedback control so that the exhaust air-fuel ratio at the outlet of the HC adsorption catalyst matches the target lean air-fuel ratio.

According to this configuration, the balance between the HC amount and the oxygen amount in the HC adsorption catalyst is controlled by performing feedback control so that the exhaust air-fuel ratio at the outlet of the HC adsorption catalyst becomes the target lean air-fuel ratio. In the invention described in claim 6, the lean control means controls the target lean air-fuel ratio in accordance with the temperature of the HC adsorption catalyst.

According to this configuration, by setting the target lean air-fuel ratio in accordance with the temperature of the HC adsorption catalyst (HC adsorbent) related to the desorbed concentration of HC, oxygen can be supplied in accordance with the amount of HC desorbed. Aim.

[0017]

According to the invention described in claim 1 or 3,
In the active state of the lean NOx catalyst that can purify NOx in the lean combustion region, lean control for purifying HC desorbed from the HC adsorbent of the HC adsorbing catalyst is performed, so leaning is performed to suppress NOx emissions. Without being restricted,
Oxygen required for purifying HC can be reliably supplied to the three-way catalyst layer of the HC adsorption catalyst, and there is an effect that HC desorbed from the HC adsorbent can be maximally purified while suppressing NOx emission.

According to the second or fourth aspect of the invention, the desorption of HC from the HC adsorbent is started after the activation of the lean NOx catalyst. There is an effect that it is possible to perform lean control that can secure the oxygen amount. According to the fifth aspect of the present invention, the balance between the amount of HC and the amount of oxygen in the three-way catalyst layer of the HC adsorption catalyst is kept constant by feedback-controlling the exhaust air-fuel ratio at the outlet of the HC adsorption catalyst to the target lean air-fuel ratio. There is an effect that can be controlled.

According to the sixth aspect of the present invention, it is possible to set a target lean air-fuel ratio in accordance with the concentration of desorbed HC from the HC adsorbent, and it is possible to supply oxygen necessary for oxidizing HC without excess or deficiency. .

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 2 showing the configuration of the embodiment of the present invention, an intake passage 12 of an internal combustion engine 11 controls an intake air flow rate Qa in conjunction with an air flow meter 13 for detecting an intake air flow rate Qa of the engine 11 and an accelerator pedal. A throttle valve 14 is provided, and an electromagnetic fuel injection valve 15 is provided for each cylinder in a downstream intake manifold section.
Is provided. The fuel injection valve 15 may be configured to face the combustion chamber of each cylinder, and the internal combustion engine according to the present embodiment may be a so-called direct injection type internal combustion engine.

The fuel injection valve 15 is driven to open by a drive pulse signal set in the control unit 50 as will be described later. The fuel is supplied from a fuel pump (not shown) under pressure and controlled to a predetermined pressure by a pressure regulator. Inject supply. Further, a water temperature sensor 16 is provided facing the water jacket of the engine 11 and detects a cooling water temperature Tw in the water jacket.

On the other hand, an oxygen sensor 1 for detecting rich / lean exhaust air-fuel ratio by detecting oxygen concentration in exhaust gas is provided in the exhaust passage 17 near the exhaust manifold gathering portion.
8 are provided. A lean NOx catalyst 19 is interposed in the exhaust passage 17 downstream of the oxygen sensor 18. The lean NOx catalyst 19, CO in the exhaust at near the stoichiometric air-fuel ratio, which has a purification performance as the three-way catalyst for purifying exhaust by performing the reduction of oxidation and NO _X of HC, NOx occluding substance in the lean combustion region A known NOx storage-reduction type having NOx purification performance in a lean combustion region by temporarily storing NOx and reducing and purifying the stored NOx by the three-way catalyst when the stoichiometric air-fuel ratio is approached. It is a three-way catalyst.

As the lean NOx catalyst 19, zeolite is used as a part of the base material, and HC trapped in the fine pores of the zeolite reacts with NOx, so that NOx can be reduced and purified even in the lean combustion region. A zeolite-type three-way catalyst may be used. Further, on the downstream side of the lean NOx catalyst 19, an HC adsorption catalyst 20 having a three-way catalyst layer 20B on an upper layer of the HC adsorbent 20A as shown in FIG. The HC in the exhaust gas is
After adsorbing onto the C adsorbent 20A (see FIG. 3 (B)), after the warm-up is completed, HC is desorbed from the HC adsorbent 20A, and the desorbed HC is oxidized and purified by the three-way catalyst layer 20B. (See FIG. 3C).

At the outlet of the HC adsorption catalyst 20, there is provided an air-fuel ratio sensor 21 capable of linearly detecting the exhaust air-fuel ratio from a lean region to a rich region by detecting the oxygen concentration in the exhaust gas. . Further, a crank angle sensor 22 for extracting a detection signal from the crankshaft or the camshaft is provided. The control unit 50 counts a crank unit angle signal output from the crank angle sensor 22 in synchronization with the engine rotation for a predetermined time. do it,
Alternatively, the engine rotation speed Ne can be detected by measuring the cycle of the crank reference angle signal.

In the exhaust passage 17 between the lean NOx catalyst 19 and the HC adsorption catalyst 20, a lean NOx catalyst 19
A heat mass 24 is provided as exhaust cooling means for cooling the exhaust gas that has passed through the lean NOx catalyst 19 so that the desorption of HC from the HC adsorption catalyst 20 (HC adsorbent 20A) is started after the activation. That is, the heat mass 24
, The temperature of the exhaust gas introduced into the HC adsorption catalyst 20 is positively lowered, and the upstream lean NOx catalyst 1
The activation of the HC adsorbent 9 ensures that the HC adsorbent 20A does not reach the desorption start temperature.

As the heat mass 24, for example, FIG.
A bellows-like flexible tube as shown in the inside can be used, and a honeycomb carrier (one that does not support a noble metal) manufactured for a catalyst is interposed,
As shown in FIG. 4, a pipe in which a plurality of cooling fins are provided radially in parallel with the axis on the inner wall of the pipe can be used. The operation region in which the exhaust is desired to be cooled by the heat mass 24 is in a transitional state from cooling to complete warming, and it is required that the heat of the exhaust be absorbed by the pipe, so that it comes into contact with the exhaust in the exhaust passage 17. It is preferable to increase the area. For example, it is preferable to provide a honeycomb carrier or a cooling fin in the pipe to increase the heat absorption performance, rather than providing a cooling fin or the like outside the pipe.

In addition, as the exhaust cooling means, in addition to the heat mass 24, a coolant such as cooling water for the engine 11 is circulated through the exhaust passage 17 between the lean NOx catalyst 19 and the HC adsorption catalyst 20 to circulate the internal gas. A configuration for cooling the exhaust gas may be used. The lean NOx catalyst 1 for the exhaust passage 17
9. The position of the HC adsorption catalyst 20 and the lean NOx catalyst 1
9. Considering the volume of the HC adsorption catalyst 20, etc.,
By simply interposing the lean NOx catalyst 19 upstream of the HC adsorption catalyst 20, the lean NOx catalyst 19
Is obtained before the start of the desorption of HC, the exhaust cooling means such as the heat mass 24 can be omitted.

By the way, CPU, ROM, RAM, A /
The control unit 50 including a microcomputer including a D converter, an input / output interface, and the like receives input signals from various sensors, and normally (after HC adsorption and desorption processing at the time of starting), The injection amount of the fuel injection valve 15 (and thus the air-fuel ratio) is controlled as described below.

That is, the basic fuel injection pulse width Tp = k × Qa / from the intake air flow rate Qa obtained based on the detection signal from the air flow meter 13 and the engine rotation speed Ne obtained based on the signal from the crank angle sensor 22. Ne
(K is a constant), a water temperature correction coefficient Kw for forcibly correcting to a rich side at low water temperature, a start and post-start increase correction coefficient Kas, and an air-fuel ratio feedback correction coefficient L
The final fuel injection pulse width Ti = Tp × (1 + Kw + Kas +...) × by AMD1 and the voltage correction Ts.
Calculate LAMD1 + Ts.

Then, the fuel injection pulse width Ti is output to the fuel injection valve 15 as a drive pulse signal, and an amount of fuel proportional to the injection pulse width Ti is injected and supplied. The air-fuel ratio feedback correction coefficient LAMD
1 is increased or decreased by proportional integration (PI) control or the like based on the rich / lean inversion output of the oxygen sensor 18 provided on the upstream side of the lean NOx catalyst 19, and based on this, the basic fuel injection pulse width Tp , The air-fuel ratio of the combustion air-fuel mixture is feedback-controlled near the target air-fuel ratio (stoichiometric air-fuel ratio).

On the other hand, at the time of starting (at the time of cooling), the injection amount (and hence the air-fuel ratio) of the fuel injection valve 15 is controlled as follows. As described below, the functions of the activity determination unit, the desorption determination unit, and the lean control unit according to the present invention are provided as software in the control unit 50. The flowchart of FIG.
It is executed every time the engine is started.

In step (denoted by S in the figure, hereinafter the same), in step 1, it is determined whether or not the cooling water temperature Tw is lower than a predetermined cooling determination temperature A. If Tw <A, the process proceeds to step 2 because the engine is cold. Tw ≧
If the answer is A, the flow is terminated in order to perform the normal air-fuel ratio control described above assuming that the normal operation is being performed. In step 2, the temperature Tc of the HC adsorption catalyst 20 is estimated from engine operating conditions such as the basic fuel injection amount Tp and the engine speed Ne. Here, if the outside air temperature, the water temperature Tw, and the like are considered, the estimation accuracy can be further improved.

Further, the temperature Tc of the HC adsorption catalyst 20 may be directly detected via the catalyst temperature sensor 23 shown in FIG. In step 3, it is determined whether or not the estimated or directly detected temperature Tc of the HC adsorption catalyst 20 exceeds a preset HC desorption start temperature T1. If Tc> T1, the HC adsorption catalyst 20
Temperature rises, and the HC adsorbed at the time of cooling becomes HC adsorbent 2
It is determined that it is in a state of desorption from 0A (desorption determination means), and the process proceeds to step 4. On the other hand, if Tc ≦ T1,
Since it is not in a state where HC is desorbed, the process returns to step 2.

In step 4, similarly to step 2, the temperature Tc2 of the lean NOx catalyst 19 is obtained by estimation based on the engine operating conditions or by direct detection by the catalyst temperature sensor 26. In step 5, it is determined whether or not the temperature Tc2 of the lean NOx catalyst 19 obtained in step 4 exceeds a preset activation determination temperature T2.
It is determined whether the lean NOx catalyst 19 is active (activity determining means). If Tc2> T2, the lean NOx catalyst 19 has been activated, and the process proceeds to step 6. On the other hand, if Tc2 ≦ T2, the lean NOx catalyst 1
Since it is in the inactive state of No. 9, the process returns to Step 4.

By providing the heat mass 24, normally, when the HC desorption of the HC adsorption catalyst 20 from the HC adsorbent 20A is started,
This means that the lean NOx catalyst 19 has reached the activation temperature. In step 6, the HC adsorption amount of the HC adsorbent 20A is calculated. The HC adsorption amount can be estimated and calculated by, for example, multiplying the integrated value of the basic fuel injection amount Tp (or the intake air flow rate Qa) by the adsorption efficiency α.

In the following step 7, the target equivalent ratio TFB
YA (a value indicating the target air-fuel ratio at the outlet of the HC adsorption catalyst 20, which is set to be leaner than the stoichiometric air-fuel ratio) is calculated according to the temperature Tc of the HC adsorption catalyst 20. Since the desorption concentration (speed) of HC increases as the catalyst temperature Tc increases, as shown in FIG.
The higher the c (the higher the desorption concentration), the higher the HC
The target equivalence ratio TFBYA is calculated so that the target air-fuel ratio at the outlet of the adsorption catalyst 20 becomes leaner (so that the oxygen concentration in the exhaust gas of the HC adsorption catalyst 20 becomes higher).

The exhaust air-fuel ratio is made lean (as an oxidizing atmosphere) by injection amount control based on the target equivalent ratio TFBYA (target lean air-fuel ratio), and HC desorbed from the HC adsorbent 20A is removed by the three-way catalyst layer 20B. Oxygen required for oxidizing and purifying is supplied so that oxidizing and purifying of HC is performed favorably. The target equivalent ratio TF
By the air-fuel ratio control based on the BYA (target lean air-fuel ratio), lean combustion in which the NOx conversion rate in the three-way catalyst is reduced is performed.
x is performed under the condition of the activity of the catalyst 19,
From the upstream lean NOx catalyst 19
Will be purified (occluded). Therefore, it is not necessary to limit the lean operation to suppress the NOx emission amount, and it is possible to secure the oxygen necessary for the oxidative purification of HC, and to achieve the lean N operation.
Leaning can be further promoted as compared with the case where the Ox catalyst 19 is not provided.

Therefore, according to the present embodiment, as shown in FIGS. 7 and 8, the amount of oxygen required for the oxidation treatment of the desorbed HC is secured while the amount of NOx is suppressed, thereby reducing the amount of HC emission. Can be minimized. In step 8, based on the exhaust air-fuel ratio detected by the air-fuel ratio sensor 21 provided at the outlet of the HC adsorption catalyst 20, the exhaust air-fuel ratio at the outlet of the HC adsorption catalyst 20 is changed to a target equivalent ratio TFBYA (target lean air-fuel ratio). ) So that the air-fuel ratio feedback correction coefficient LAM
While setting D2, the final fuel injection pulse width Ti
Ti = Tp × (1 + Kw + Kas +...) × TFBYA
XLAMD2 + Ts, and outputs the fuel injection pulse width Ti to the fuel injection valve 15 as a drive pulse signal (lean control means).

In step 9, the HC of the HC adsorbent 20A is
Integrate the desorption amount. The HC desorption amount can be estimated and calculated by, for example, the following equation. HC desorption amount = Qa × Tc × β (β: desorption amount conversion coefficient) As described above, since the desorption concentration of HC is determined by the catalyst temperature Tc, the desorption of HC according to the catalyst temperature is determined by Tc × β. The desorption concentration can be calculated, and the desorption amount of HC can be obtained by multiplying the desorption concentration of HC by the intake air flow rate Qa (a value correlated with the exhaust flow rate).

In step 10, the HC desorption amount estimated in step 9 is compared with the HC adsorption amount estimated in step 6, and if HC desorption amount ≧ HC adsorption amount, HC is detected.
It is determined that the desorption process has been completed, and the process shifts to normal air-fuel ratio control. On the other hand, if HC desorption amount <HC adsorption amount,
Since the HC is still being desorbed, it is necessary to continue the lean air-fuel ratio control by this flow.
The process returns to step 7 until the suction amount is reached.

As described above, according to the present embodiment, control is performed so that the exhaust air-fuel ratio at the outlet of the HC adsorption catalyst 20 becomes the target lean air-fuel ratio corresponding to the HC desorption concentration.
HC desorbed from the HC adsorbent 20A is converted to the three-way catalyst layer 20B.
And the oxygen in the exhaust gas is diffused into the three-way catalyst layer 20.
In consideration of the difference between the rate of being taken in (adsorbed) by B and the oxygen required for the oxidation of the desorbed HC, the three-way catalyst layer 20
HC can be sufficiently adsorbed on the B surface, and HC desorbed from the HC adsorbent can be satisfactorily purified.

Step 8 in the flowchart of FIG. 5 is omitted, and the so-called open control (feedforward control) is used to reduce the air-fuel ratio at the outlet of the HC adsorption catalyst 20 to the target equivalent ratio TFBYA (target lean air-fuel ratio).
Can also be controlled. In this case, the air-fuel ratio sensor 2
1 may be omitted. Further, when the desorption of HC is started in the HC adsorption catalyst 20 before the lean NOx catalyst 19 is activated, the target lean air-fuel ratio is set by restricting the NOx emission to a range that can suppress the NOx emission to an allowable level. When the lean NOx catalyst 19 is activated, lean combustion may be performed by setting a target lean air-fuel ratio as required to ensure the amount of oxygen necessary for HC oxidation purification.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a system configuration diagram according to the embodiment of the present invention.

3A and 3B are diagrams illustrating an HC adsorption catalyst according to an embodiment, wherein FIG. 3A is a diagram illustrating the structure of the HC adsorption catalyst, and FIG.
FIG. 3 is a diagram for explaining an HC adsorption function at the time of cold operation, and FIG.

FIG. 4 is a cross-sectional view of an exhaust passage showing another example of the heat mass in the embodiment.

FIG. 5 is a flowchart for explaining air-fuel ratio control in the embodiment.

FIG. 6 is a diagram showing a correlation between the temperature of the HC adsorption catalyst and a target lean air-fuel ratio in the embodiment.

FIG. 7 is a timing chart for explaining the effect of reducing the amount of HC emission.

FIG. 8 is a timing chart for explaining the effect of reducing NOx emission.

[Explanation of symbols]

 11 Internal combustion engine 12 Intake passage 13 Air flow meter 14 Throttle valve 15 Fuel injection valve 17 Exhaust passage 18 Oxygen sensor 19 Lean NOx catalyst 20 HC adsorption catalyst 21 Air-fuel ratio sensor 22 Crank angle sensor 50 Control unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/04 ZAB F02D 41/04 ZAB 305 305A 41/14 ZAB 41/14 ZAB 310 310F

Claims (6)

[Claims] An exhaust gas passage is provided with an HC adsorption catalyst comprising a three-way catalyst layer on an upper layer of an HC adsorbent.
In the exhaust passage on the upstream side of the C adsorption catalyst, N
A lean NOx catalyst having an Ox purification performance, wherein the lean NOx catalyst is in an active state and the air-fuel ratio of the combustion mixture of the engine is lean while the HC is being desorbed from the HC adsorbent. An exhaust purification device for an internal combustion engine. 2. An exhaust passage having an HC adsorbing catalyst comprising a three-way catalyst layer on an upper layer of an HC adsorbing material.
In the exhaust passage on the upstream side of the C adsorption catalyst, N
Equipped with a lean NOx catalyst having Ox purification performance, and
The desorption of HC from the HC adsorbent is started after the activation of the lean NOx catalyst, and the air-fuel ratio of the combustion mixture of the engine becomes lean during the desorption of HC from the HC adsorbent. An exhaust gas purifying apparatus for an internal combustion engine, characterized by controlling. 3. An exhaust gas passage having an HC adsorbing catalyst comprising a three-way catalyst layer on an upper layer of an HC adsorbing material.
In the exhaust passage on the upstream side of the C adsorption catalyst, N
An activation determining unit that determines an activation state of the lean NOx catalyst; a desorption determination unit that determines a desorption state of HC from the HC adsorbent; and an activation determination. Means determines that the lean NOx catalyst is in an active state, and the desorption determining means determines that the H
And a lean control means for leanly controlling the air-fuel ratio of the combustion mixture of the engine when it is determined that the HC is desorbed from the C adsorbent. Purification device. 4. An exhaust cooling means for cooling exhaust gas between the lean NOx catalyst and the HC adsorption catalyst so as to start desorption of HC from the HC adsorbent after the activation of the lean NOx catalyst has started. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein: 5. An exhaust gas for an internal combustion engine according to claim 3, wherein said lean control means performs feedback control so that an exhaust air-fuel ratio at an outlet of said HC adsorption catalyst coincides with a target lean air-fuel ratio. Purification device. 6. The exhaust gas purification of an internal combustion engine according to claim 3, wherein said lean control means controls a target lean air-fuel ratio in accordance with a temperature of said HC adsorption catalyst. apparatus.