JPH1182111A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device for an internal combustion engine that can purify desorbed HC satisfactorily in a three-way catalyst layer even in case of using an HC adsorbing catalyst. SOLUTION: During desorption of HC (S1-S3), a target air-fuel ratio TFBYA at an outlet of an HC adsorbing catalyst is controlled to the lean side taking account of the diffusion speed of HC, desorbed from HC adsorbing material, to a three-way catalyst layer, and the intake speed of oxygen in exhaust gas into the three-way catalyst layers in S5. The target air-fuel ratio TFBYA is variably set according to the temperature Tc of an HC adsorbing catalyst. In S6, feedback control based on a detection signal of an air-fuel ratio sensor 21 is performed so as to attain the target air-fuel ratio TFBYA. This flow is completed when the HC desorption quantity becomes the HC adsorption quantity (S4, S7, S8). On required for oxidation of desorbed HC can therefore be adsorbed well to the surface of the three-way catalyst layer, so that desorbed HC can be purified satisfactorily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio control device for an internal combustion engine.

[0002]

2. Description of the Related Art A conventional air-fuel ratio control device for an internal combustion engine is disclosed, for example, in JP-A-6-81637. In this type, an HC adsorbent is interposed in an exhaust passage of an internal combustion engine, and the HC in the exhaust gas at the time of cooling is removed by the HC.
After the warm-up is completed, the HC adsorbent absorbs H
C is desorbed, and the desorbed HC is purified by a three-way catalyst disposed downstream of the HC adsorbent in the exhaust gas. At the time of the desorption, the air-fuel ratio of the air-fuel mixture sucked into the internal combustion engine is controlled to the lean side by the fuel injection amount from the fuel injection valve according to the elapsed time from the start of the desorption, whereby the three-way catalyst is controlled. Of the air-fuel ratio at the entrance of the vehicle.

[0003]

However, FIG.
As shown in (A), a so-called HC adsorption catalyst in which a three-way catalyst layer is coated on the upper layer of an HC adsorbent is used to adsorb HC to the HC adsorbent at the time of cooling, and after the warming-up is completed, the HC adsorbs from the HC adsorbent. When the desorbed HC is purified by the three-way catalyst layer, the following fears may be caused.

That is, HC desorbed from the HC adsorbent is
When purifying with the three-way catalyst layer, the HC adsorbent
The rate at which the desorbed HC diffuses into the three-way catalyst layer and the exhaust gas
Oxygen (O_Two) Is taken into the three-way catalyst layer (adsorbed
Speed) and the conventional air-fuel ratio
The O required for the oxidation of the desorbed HC_TwoThree-way catalyst
Not fully adsorbed on the layer surface
HC content and O on the surface of the medium layer _TwoThe balance with the quantity is lost,
HC desorbed from HC adsorbent cannot be purified well
There was fear.

[0005] The present invention has been made in view of such circumstances, and even when an HC adsorbing catalyst is used, the desorbed H is used.
It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine in which C can be favorably purified by a three-way catalyst layer.

[0006]

Therefore, an air-fuel ratio control apparatus for an internal combustion engine according to the first aspect of the present invention includes a three-way catalyst layer as an upper layer of an HC adsorbent as shown in FIG. An air-fuel ratio control device for an internal combustion engine having an HC adsorption catalyst arranged in an exhaust passage, wherein the exhaust air-fuel ratio at an outlet of the HC adsorption catalyst is adjusted during desorption of HC from the HC adsorbent. An air-fuel ratio control means for controlling the air-fuel ratio of the intake air-fuel mixture of the internal combustion engine so as to achieve a fixed amount of lean is provided.

[0007] With this configuration, when the HC adsorbing catalyst having the three-way catalyst layer on the upper layer of the HC adsorbing material is used, the HC desorbed from the HC adsorbing material during the desorption of HC. In consideration of the difference between the speed of diffusion into the three-way catalyst layer and the speed of oxygen (O ₂ ) in the exhaust gas being taken into (adsorbed into) the three-way catalyst layer, the air at the outlet of the HC adsorption catalyst is taken into account. since the ratio was set to be controlled to a predetermined amount lean, the O ₂ required for the oxidation of HC desorbed can be adsorbed more on the surface of the three-way catalyst layer, desorbed from the HC adsorbent me than HC Can be satisfactorily purified.

That is, there is a concern in the case where the air-fuel ratio at the inlet of the three-way catalyst (layer) is made lean by the amount of desorbed HC as in the prior art, that is, HC desorbed from the HC adsorbent.
The rate at which oxygen diffuses into the three-way catalyst layer and the oxygen (O
Due to the difference between the rate at which ₂ ) is taken into (adsorbed to) the three-way catalyst layer, the amount of O ₂ required for the oxidation of the desorbed HC cannot be sufficiently adsorbed on the surface of the three-way catalyst layer, Accordingly, it is possible to suppress the fear that the balance between the amount of HC and the amount of O _{2 on the} surface of the three-way catalyst layer is lost and the HC desorbed from the HC adsorbent cannot be sufficiently purified.

According to the present invention, the air-fuel ratio of the intake air-fuel mixture of the internal combustion engine is determined based on a detection value of an air-fuel ratio sensor provided at an outlet of the HC adsorption catalyst.
During the desorption of HC from the adsorbent, feedback control is performed so that the exhaust air-fuel ratio at the outlet of the HC adsorption catalyst becomes lean by a predetermined amount. With this configuration, the air-fuel ratio of the intake air-fuel mixture of the internal combustion engine is adjusted so that the exhaust air-fuel ratio at the outlet of the HC adsorption catalyst becomes a predetermined amount during the desorption of HC from the HC adsorbent. Since feedback control can be performed, O ₂ required for oxidation of the desorbed HC can be adsorbed on the surface of the three-way catalyst layer with high accuracy even if there is a change over time or disturbance. HC desorbed from the HC adsorbent can be satisfactorily purified.

According to the third aspect of the present invention, the air-fuel ratio of the intake air-fuel mixture of the internal combustion engine is such that the exhaust air-fuel ratio at the outlet of the HC adsorbing catalyst varies during the desorption of HC from the HC adsorbent. It was configured to be feed-forward controlled so as to achieve a quantitative lean. With such a configuration, O ₂ required for the oxidation of the desorbed HC can be adsorbed on the surface of the three-way catalyst layer with a relatively simple configuration, whereby the HC desorbed from the HC adsorbent can be removed. Good purification can be achieved. It is also possible to adopt a configuration in which feedforward control is performed immediately after the start of HC desorption, and then feedback control is performed.

[0011] In the invention according to claim 4, the predetermined amount is set in accordance with the temperature of the HC adsorption catalyst. That is, the desorption concentration (speed) of HC has a characteristic that it increases (increases) with the temperature of the HC adsorption catalyst.
Depending on the temperature of the adsorption catalyst, if to vary the predetermined amount, always, the O ₂ required for the oxidation of HC desorbed can be adsorbed on the surface of the three-way catalyst layer, I than HC HC desorbed from the adsorbent can be satisfactorily purified.

[0012] In the invention described in claim 5, the temperature of the HC adsorption catalyst is estimated based on the operating state of the internal combustion engine. With such a configuration, a sensor for detecting the temperature of the HC adsorption catalyst can be omitted, so that product cost can be reduced. In the invention described in claim 6, the temperature of the HC adsorption catalyst is estimated based on the integrated value of the fuel injection amount or the intake air flow rate of the internal combustion engine.

With this configuration, a sensor for detecting the temperature of the HC adsorption catalyst can be omitted, so that the product cost can be reduced, and a relatively simple configuration can be used with high accuracy. It is possible to estimate the temperature of the HC adsorption catalyst.

[0014]

According to the first aspect of the present invention, when an HC adsorbing catalyst having a three-way catalyst layer on the upper layer of the HC adsorbing material is used, the HC adsorbing is performed during the desorption of HC. In consideration of the difference between the rate at which HC desorbed from the material diffuses into the three-way catalyst layer and the rate at which oxygen in exhaust gas is taken in (adsorbed) into the three-way catalyst layer, the outlet of the HC adsorption catalyst is considered. since so as to control the air-fuel ratio to a predetermined amount lean in part, de-a O ₂ required for the oxidation of HC desorbed can be adsorbed more on the surface of the three-way catalyst layer, from the HC adsorbent me than The separated HC can be satisfactorily purified.

That is, there is a concern in the case where the air-fuel ratio at the inlet of the three-way catalyst (layer) is made lean by the amount of desorbed HC as in the prior art, that is, HC desorbed from the HC adsorbent.
The difference between the rate at which oxygen diffuses into the three-way catalyst layer and the rate at which oxygen in the exhaust gas is taken into (adsorbed to) the three-way catalyst layer reduces the amount of O ₂ necessary for the oxidation of the desorbed HC by three. Cannot be sufficiently adsorbed on the surface of the three-way catalyst layer, and thus the balance between the amount of HC and the amount of O _{2 on the} surface of the three-way catalyst layer is lost.
The concern that HC desorbed from the C adsorbent cannot be satisfactorily purified can be suppressed.

According to the second aspect of the present invention, O ₂ required for the oxidation of the desorbed HC can be adsorbed on the surface of the three-way catalyst layer with high accuracy even if there is a temporal change or disturbance. Thus, HC desorbed from the HC adsorbent can be satisfactorily purified. According to the third aspect of the present invention, O ₂ required for the oxidation of the desorbed HC can be adsorbed on the surface of the three-way catalyst layer with a relatively simple configuration, so that the HC adsorbent can be removed from the HC adsorbent. The desorbed HC can be satisfactorily purified.

According to the fourth aspect of the present invention, the predetermined amount is changed in accordance with the temperature of the HC adsorption catalyst, so that O ₂ necessary for oxidizing the desorbed HC is always ternary. HC can be adsorbed on the surface of the catalyst layer, so that HC desorbed from the HC adsorbent can be satisfactorily purified. According to the fifth aspect of the present invention, since a sensor for detecting the temperature of the HC adsorption catalyst can be omitted, product cost can be reduced.

According to the invention described in claim 6, the cost of the product can be reduced, and the temperature of the HC adsorption catalyst can be estimated with high accuracy with a relatively simple configuration.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.
Description will be given based on the attached drawings. 2, an air flow meter 13 for detecting an intake air flow rate Qa and a throttle valve 14 for controlling the intake air flow rate Qa in conjunction with an accelerator pedal are provided in an intake passage 12 of an engine 11 in FIG. An electromagnetic fuel injection valve 15 is provided for each cylinder in the downstream manifold portion. 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 described later, and is pressure-fed from a fuel pump (not shown) to pressure regulator (not shown).
Injects and supplies fuel controlled to a predetermined pressure. A water temperature sensor 1 is provided facing the cooling jacket of the engine 11 and detects a cooling water temperature Tw in the cooling jacket.
6 are provided.

On the other hand, an oxygen sensor 18 is provided in the exhaust passage 17 near the manifold collecting portion to detect the concentration of a specific component (for example, oxygen) in the exhaust gas to detect the rich / lean air-fuel ratio of the intake air-fuel mixture. On the downstream side, in the vicinity of the stoichiometric air-fuel ratio {λ = 1, A / F (air weight / fuel weight) {14.7}, CO and HC in the exhaust gas are oxidized and NO _x is reduced to reduce the exhaust gas. A three-way catalyst (so-called manifold catalyst) 19 as an exhaust gas purifying catalyst for purifying is interposed.

In this embodiment, the HC adsorbent 20A as shown in FIG.
An HC adsorption catalyst 20 coated with a three-way catalyst layer (three-layer) 20B or the like is interposed in the upper layer, and adsorbs HC in the exhaust gas to the HC adsorbent 20A during cooling.
Reference II, after the warm-up is completed, the HC is desorbed from the HC adsorbent 20A and the desorbed HC is transferred to the three-way catalyst layer 20B.
(See FIG. 3 (C)).

At the outlet of the HC adsorption catalyst 20, the air-fuel ratio of the intake air-fuel mixture can be detected linearly from a lean region to a rich region by detecting the concentration of a specific component (eg, oxygen) in the exhaust gas. An air-fuel ratio sensor 21 is provided. The distributor (not shown in FIG. 2) has a built-in crank angle sensor 22.
The engine rotation speed Ne can be detected by counting a crank unit angle signal output in synchronization with the engine rotation for a certain period of time, or by measuring the cycle of the crank reference angle signal.

By the way, CPU, ROM, RAM, A /
The control unit 50 including a microcomputer including a D converter and an input / output interface receives input signals from various sensors, and in a normal state (at the time of non-desorption), as described below, The injection amount of the fuel injection valve 15 (and hence the air-fuel ratio) is controlled. That is, the basic fuel injection pulse width (corresponding to the fuel injection amount) Tp = c × from the intake air flow rate Qa obtained from the voltage signal from the air flow meter 13 and the engine rotation speed Ne obtained from the signal from the crank angle sensor 22. While calculating Qa / Ne (c is a constant), a water temperature correction coefficient Kw that forcibly corrects to a rich side at a low water temperature, a startup and post-start increase correction coefficient Kas, and an air-fuel ratio feedback correction coefficient LAMD1
The final effective fuel injection pulse width Te = Tp ×
(1 + Kw + Kas +...) × LAMD1 + Ts is calculated. Ts is a voltage correction amount.

The effective fuel injection pulse width Te is sent to the fuel injection valve 15 as a drive pulse signal.
Fuel adjusted to a predetermined amount is injected and supplied.
The air-fuel ratio feedback correction coefficient LAMD1 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 three-way catalyst 19, and is controlled based on this. In the unit 50, the basic fuel pulse width Tp is corrected, and the air-fuel ratio of the combustion air-fuel mixture is feedback-controlled near the target air-fuel ratio (the stoichiometric air-fuel ratio).

By the way, using the HC adsorption catalyst 20,
Then, the desorbed HC is purified by the three-way catalyst layer 20B.
In this case, the HC desorbed from the HC adsorbent 20A is
The speed of diffusion into the medium layer 20B and the oxygen in the exhaust gas
(O_Two) Is taken into (adsorbed to) the three-way catalyst layer 20B.
Speed), there is a difference between the
By simply controlling the air-fuel ratio at the inlet of the medium 20 to lean,
O necessary for oxidation of desorbed HC _TwoThe amount is three-way catalyst layer 20B
Can not be sufficiently adsorbed on the surface of
HC amount and O on the surface of the medium layer 20B_TwoBalance with quantity
Has been disintegrated, and the HC desorbed from the HC adsorbent 20A is satisfactorily purified.
There is a risk that the system will not be able to be converted (see Fig. 3 (C)).

For this reason, in this embodiment, the HC adsorbent 2
The difference between the rate at which HC desorbed from 0A diffuses into the three-way catalyst layer 20B and the rate at which oxygen (O ₂ ) in exhaust gas is taken in (adsorbed) into the three-way catalyst layer 20B is taken into account. By controlling the air-fuel ratio, the amount of HC and the amount of O _{2 on} the surface of the three-way catalyst layer 20B are balanced, whereby the HC
HC desorbed from the adsorbent 20A can be satisfactorily purified.

That is, when the HC is desorbed, the control unit 50 according to the present embodiment receives input signals from various sensors and executes a flowchart as shown in FIG. And thus the air-fuel ratio). Note that, as described below, the function as the air-fuel ratio control means according to the present invention is provided by the control unit 50 as software. FIG.
The flowchart of FIG. 5 is executed every time the engine 11 is started.

That is, in step (denoted by S in the figure, hereinafter the same), it is determined whether or not the cooling water temperature Tw <the cold (cooler) determination temperature A. If YES, the process proceeds to step 2 because it is a cold (cold) time. If the determination is NO, this 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 basic fuel injection amount Tp (or intake air flow rate Qa) is integrated or weighted average by a method similar to the conventional method, and the temperature Tc of the HC adsorption catalyst 20 is calculated.
Is estimated. For example, the amount of heat ΔTp (or Qa) generated by combustion and given to the HC adsorption catalyst 20 via exhaust gas
And the amount of heat removed from the HC adsorption catalyst 20 by the exhaust gas {correlated to the exhaust gas flow rate (intake air flow rate Qa)}, etc.
The catalyst temperature Tc can be estimated, and the outside air temperature and the water temperature T can be estimated.
Considering w and the like, the estimation accuracy can be further improved.

Further, the fuel injection amount Tp, the engine speed Ne,
From the above, the equilibrium catalyst temperature when the operation state is continued is estimated, and the current catalyst temperature Tc is estimated based on the estimated value and the operation continuation time (or time constant) in the operation state. And so on. Note that a configuration may be employed in which the catalyst temperature Tc is directly detected via the catalyst temperature sensor 23 shown in FIG.

In step 3, it is determined whether or not the catalyst temperature Tc> HC desorption start temperature T1. If YES, the temperature of the HC adsorbing catalyst 20 rises, and the HC adsorbed at the time of cooling is desorbed from the HC adsorbent 20A, so that the HC desorbed from the HC adsorbent 20A diffuses to the three-way catalyst layer 20B. Velocity and oxygen (O ₂ ) in exhaust gas are converted to three-way catalyst layer 2
The process proceeds to step 4 in order to execute the air-fuel ratio control in consideration of the difference between the speed taken in (absorbed) by 0B. On the other hand, if NO, the process returns to step 2.

In step 4, the amount of HC adsorbed by the 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 (Tp integrated value × α). In the next step 5, the target air-fuel ratio TFBYA (the target air-fuel ratio at the outlet of the HC adsorption catalyst 20, which is set to the lean side) is calculated. Here, the target air-fuel ratio TFBYA is calculated by the following equation.

That is, TFBYA = Tc × γ where Tc: temperature of the HC adsorption catalyst 20, γ: target air-fuel ratio coefficient That is, as shown in FIG. 5, the desorption concentration (speed) of HC depends on the catalyst temperature Tc. Determined (substantially proportional to the catalyst temperature)
The target air-fuel ratio coefficient γ {“the speed at which oxygen (O ₂ ) is taken into the three-way catalyst layer 20B” / “the HC desorption speed”}
Is multiplied, it is possible to obtain a target air-fuel ratio TFBYA (air weight / fuel weight), that is, an amount of oxygen necessary for purifying HC properly according to the catalyst temperature. The target air-fuel ratio TFBYA may be set in accordance with the temperature Tc of the HC adsorption catalyst 20 with reference to a table as shown in FIG.

Then, in the control unit 50,
Final effective fuel injection pulse width Te = Tp × (1 + Kw
+ Kas +...) × 1 / TFBYA + Ts, the effective fuel injection pulse width Te is sent to the fuel injection valve 15 as a drive pulse signal, and the fuel adjusted to a predetermined amount is injected and supplied. In step 6, based on the air-fuel ratio detected by the air-fuel ratio sensor 21 provided at the outlet of the HC adsorption catalyst 20, the air-fuel ratio at the outlet of the HC adsorption catalyst 20 is calculated as
The fuel injection amount is feedback-controlled so that the target air-fuel ratio becomes TFBYA (set to the lean side).

That is, Te = Tp × (1 + Kw + Kas +
..) × 1 / TFBYA × LAMD2 + Ts, the effective fuel injection pulse width Te is sent to the fuel injection valve 15 as a drive pulse signal, and the air-fuel ratio at the outlet of the HC adsorption catalyst 20 becomes the target air-fuel ratio TFBYA. The feedback control is performed so that The air-fuel ratio feedback correction coefficient LAMD2 is proportionally integrated based on an air-fuel ratio detection signal (output as a linear signal with respect to the air-fuel ratio) of an air-fuel ratio sensor 21 provided on the downstream side of the HC adsorption catalyst 20. (PI) It is set to increase or decrease by control or the like.

In step 7, the HC desorption amount of the adsorbent 20A is integrated. The HC desorption amount can be estimated and calculated by, for example, the following equation. HC desorption amount = Qa × Tc × β where Qa: intake air flow rate, β; desorption amount conversion coefficient That is, as shown in FIG. 5, the desorption concentration of HC (%, pp
m) is determined by the catalyst temperature, so that the desorption concentration of HC according to the catalyst temperature can be calculated from Tc × β, and the desorption concentration of HC can be calculated based on the intake air flow rate Qa (l / min or g / min) ｛exhaust flow rate (l / min or g / mi)
The desorption amount of HC can be obtained by multiplying n) by a value correlated with 相関.

In step 8, the integrated value of the HC desorption amount obtained in step 7 is compared with the HC adsorption amount.
If the integrated value of the HC desorption amount ≧ the HC adsorption amount, it is determined that the HC desorption process has been completed, and the process shifts to the normal (non-desorption) air-fuel ratio control. On the other hand, if the integrated value of the HC desorption amount is smaller than the HC adsorption amount, the air is still being desorbed, and the air-fuel ratio control by this flow needs to be continued. The process returns to step 5 until the amount of adsorption is reached.

As described above, according to the present embodiment, when the HC adsorption catalyst 20 is used, during the desorption of HC, H
The difference between the rate at which HC desorbed from the C adsorbent 20A diffuses into the three-way catalyst layer 20B and the rate at which oxygen (O ₂ ) in the exhaust gas is taken into (adsorbed to) the three-way catalyst layer 20B is determined. Considering the air-fuel ratio at the outlet of the HC adsorption catalyst 20, the amount of O ₂ required for the oxidation of the desorbed HC is
Target air-fuel ratio T that can be sufficiently adsorbed on the 0B surface
Since it is controlled to FBYA (lean air-fuel ratio),
HC desorbed from the HC adsorbent can be satisfactorily purified.

Step 6 in the flowchart of FIG. 4 is omitted, and the air-fuel ratio at the outlet of the HC adsorption catalyst 20 is controlled to the target air-fuel ratio TFBYA (lean air-fuel ratio) by so-called open control (feedforward control). You can also. In this case, the air-fuel ratio sensor 21 may be omitted. By the way, when a three-way catalyst is provided independently of the HC adsorbent on the downstream side of the HC adsorbent as in the related art, the air-fuel ratio at the inlet of the three-way catalyst is changed during HC desorption. Lean according to the amount of separation (in this case, the air-fuel ratio at the outlet of the three-way catalyst is controlled near the stoichiometric air-fuel ratio)
On the other hand, according to the present invention, when the HC adsorption catalyst 20 is used, during the desorption of HC, the rate at which HC desorbed from the HC adsorbent 20A is diffused into the three-way catalyst layer 20B is reduced. In consideration of the low rate at which oxygen (O ₂ ) is taken up (adsorbed) into the three-way catalyst layer 20B, H
The air-fuel ratio at the outlet of the C adsorption catalyst 20 is made lean to balance the amount of HC and the amount of O _{2 on} the surface of the three-way catalyst layer 20B so that the HC desorbed from the HC adsorbent 20A can be satisfactorily purified. It was done.

In other words, the present invention provides the HC adsorption catalyst 2
0 during the HC desorption, the three-way catalyst layer 20
In order to balance the amount of HC and the amount of O _{2 on} the surface of B, the essential point is to control the air-fuel ratio at the outlet of the HC adsorption catalyst 20 to the lean side. That is,
The present embodiment describes a case where the target air-fuel ratio TFBYA is set to an optimal value in order to more effectively purify the desorbed HC, and the present invention is not limited to this. HC adsorption catalyst 2 during HC desorption
By simply controlling the air-fuel ratio at the outlet of 0 to the lean side, it is possible to satisfactorily purify the desorbed HC as compared with the prior art. The one that controls the air-fuel ratio at the outlet of 20 to the lean side is included in the scope of the present invention.

[Brief description of the drawings]

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

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

FIG. 3A is a diagram illustrating a structure of an HC adsorption catalyst.
(B) is a diagram for explaining the function of the HC adsorption catalyst at the time of cold (at the time of cold). (C) is a diagram for explaining the function of the HC adsorption catalyst during warm-up (hot).

FIG. 4 is a flowchart for explaining air-fuel ratio control in the embodiment.

FIG. 5 is a timing chart for explaining the relationship between the desorbed HC concentration and the HC adsorption catalyst temperature.

FIG. 6 is an example of a table showing a relationship between a desorbed HC concentration and an HC adsorption catalyst temperature.

[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 Three-way catalyst (manifold catalyst) 20 HC adsorption catalyst 21 Air-fuel ratio sensor (linear sensor) 22 Crank angle sensor 50 Control unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 45/00 312 F02D 45/00 312R 364 364N 366 366F

Claims (6)

[Claims] 1. An air-fuel ratio control device for an internal combustion engine having an HC adsorbent, which is provided with a three-way catalyst layer above a HC adsorbent, interposed in an exhaust passage, comprising: During desorption, the exhaust air-fuel ratio at the outlet of the HC adsorption catalyst becomes lean by a predetermined amount,
An air-fuel ratio control device for an internal combustion engine, comprising air-fuel ratio control means for controlling an air-fuel ratio of an intake air-fuel mixture of the internal combustion engine. 2. An air-fuel ratio of an intake air-fuel mixture of the internal combustion engine, based on a detection value of an air-fuel ratio sensor provided at an outlet of the HC adsorption catalyst, during the desorption of HC from the HC adsorbent. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein feedback control is performed such that the exhaust air-fuel ratio at the outlet of the HC adsorption catalyst becomes lean by a predetermined amount. 3. An air-fuel ratio of an intake air-fuel mixture of the internal combustion engine is set so that an exhaust air-fuel ratio at an outlet of the HC adsorbing catalyst becomes lean by a predetermined amount during desorption of HC from the HC adsorbing material. 2. The feedforward control is performed.
Or an air-fuel ratio control device for an internal combustion engine according to claim 2. 4. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the predetermined amount is set according to the temperature of the HC adsorption catalyst. 5. The system according to claim 1, wherein the temperature of the HC adsorption catalyst is estimated based on an operation state of the internal combustion engine.
An air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 4. 6. The method according to claim 1, wherein the temperature of the HC adsorption catalyst is estimated based on an integrated value of a fuel injection amount or an intake air flow rate of the internal combustion engine. An air-fuel ratio control device for an internal combustion engine according to the above.