JP4158475B2 - Apparatus and method for exhaust gas purification of internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust purification device and method for an internal combustion engine having a three-way catalyst in an exhaust passage.
[0002]
[Prior art]
Conventionally, in order to purify exhaust gas discharged from an internal combustion engine, a three-way catalyst that performs feedback control so that the air-fuel ratio becomes a stoichiometric air-fuel ratio (stoichiometric), and also performs oxidation of HC and CO and reduction of NOx A system in which is disposed in the exhaust passage has been widely put into practical use. When the three-way catalyst is exposed to the air-fuel ratio rich state, the purification processing capacity is reduced (temporary deterioration), and exhaust deterioration is caused. Therefore, in Patent Document 1, the three-way catalyst is subjected to temporary deterioration recovery processing by performing the air-fuel ratio leaning operation for a predetermined time, and immediately after that, control is performed to return to normal operation.
[0003]
[Patent Document 1]
Japanese Patent No. 2996084 [0004]
[Problems to be solved by the invention]
Here, the air-fuel ratio leaning operation can recover the temporary deterioration of the three-way catalyst by supplying oxygen to the three-way catalyst. However, during the air-fuel ratio leaning operation, the NOx emission amount increases, so the air-fuel ratio leaning operation needs to be performed at the minimum necessary.
[0005]
Further, the air-fuel ratio leaning operation stores oxygen until the three-way catalyst reaches the upper limit of its oxygen storage capacity, and even if the air-fuel ratio lean operation is returned to the normal operation, the three-way catalyst cannot reduce NOx. Since this is a state, the amount of NOx emission increases.
In view of such problems, the present invention performs an air-fuel ratio leaning operation to recover the temporary deterioration of the three-way catalyst, discharge the accumulated oxygen, create an atmosphere in which NOx can be reduced, and NOx The purpose is to switch the air-fuel ratio appropriately so as to minimize the amount of exhaust gas discharged.
[0006]
[Means for Solving the Problems]
Therefore, in the present invention, the air-fuel ratio leaning operation of the internal combustion engine is performed at a timing to recover the temporary deterioration of the three-way catalyst, and the air-fuel ratio downstream of the three-way catalyst in this air-fuel ratio leaning operation is higher than the predetermined air-fuel ratio. When lean , the air-fuel ratio leaning operation is switched to the air-fuel ratio enriching operation, and when the air-fuel ratio change downstream of the three-way catalyst in the air-fuel ratio enrichment operation is reversed from the lean direction to the rich direction, It is configured to return from the fuel ratio enrichment operation to the normal operation.
[0007]
【The invention's effect】
According to the present invention, the temporary deterioration of the three-way catalyst is recovered by the air-fuel ratio leaning operation, the three-way catalyst is made in a state capable of reducing NOx by the air-fuel ratio enrichment operation, and the NOx emission amount is minimized by the normal operation. To the limit.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an exhaust purification device for an internal combustion engine.
An intake throttle passage 2 of the engine 1 is provided with an electric throttle valve 3 that controls the amount of intake air.
[0009]
A fuel injection valve 4 is provided for each cylinder in the intake manifold / branch portion of the intake passage 2 downstream of the electric throttle valve 3. These fuel injection valves 4 may be arranged directly facing the combustion chamber of each cylinder.
In the exhaust passage 5 of the engine 1, as an exhaust purification device, a pre-catalyst 6 is disposed just below the exhaust manifold, and a rear catalyst 7 is disposed below the vehicle floor. The pre-catalyst 6 and the rear catalyst 7 are both three-way catalysts that can reduce NOx at the same time as oxidizing HC and CO in the exhaust when the exhaust air-fuel ratio is in the vicinity of stoichiometric.
[0010]
The operation of the electric throttle valve 3 and the fuel injection valve 4 is controlled by an engine control unit (ECU) 10. For this control, the ECU 10 includes an accelerator opening sensor 11, a crank angle sensor 12, an air flow meter 13, Signals are input from the first to third air-fuel ratio sensors 14 to 16, the odometer 17, and the like.
The accelerator opening sensor 11 outputs a signal corresponding to an accelerator pedal depression amount (accelerator opening) APO.
[0011]
The crank angle sensor 12 outputs a crank angle signal in synchronization with engine rotation, and can detect the engine rotation speed Ne based on this signal.
The air flow meter 13 is provided upstream of the electric throttle valve 3 in the intake passage 2 and outputs a signal corresponding to the intake air amount Qa.
The odometer 17 outputs a signal corresponding to the cumulative mileage of the vehicle.
[0012]
The first to third air-fuel ratio sensors 14 to 16 are respectively provided upstream of the pre-catalyst 6, downstream of the pre-catalyst 6 and downstream of the rear catalyst 7 in the exhaust passage 5, and output signals corresponding to the exhaust air-fuel ratio. The first to third air-fuel ratio sensors 14 to 16 may be so-called wide-area air-fuel ratio sensors or rich-lean inversion oxygen sensors.
The ECU 10 determines a required fuel amount corresponding to the required engine torque based on the accelerator opening APO and the engine speed Ne, determines a required air amount from the required fuel amount and the target air-fuel ratio, and realizes the required air amount. The opening TVO of the electric throttle valve 3 is controlled.
[0013]
Further, based on the actual intake air amount Qa detected by the air flow meter 13, a basic fuel injection amount TP = K × Qa / Ne (K is a constant) equivalent to stoichiometry is determined, and this is expressed as The final fuel injection amount TI is calculated by correcting from the target equivalent ratio TFBYA corresponding to the fuel ratio or by correcting with the air-fuel ratio feedback correction coefficient LAMBDA.
[0014]
TI = TP × TFBYA × LAMBDA
Here, the target equivalent ratio TFBYA can be expressed by the following equation when the stoichiometric ratio is 14.7.
TFBYA = 14.7 / target air-fuel ratio feedback correction coefficient LAMBDA is controlled to increase or decrease based on the signal from the first air-fuel ratio sensor 14 when the target air-fuel ratio is stoichiometric, but the signal from the second air-fuel ratio sensor 15 Correction is made based on Here, the three-way catalyst performs oxidation of HC and CO and reduction of NOx, but oxidation of HC and CO is easier than reduction of NOx due to the presence of oxygen stored in the three-way catalyst. Therefore, the correction based on the signal of the second air-fuel ratio sensor 15 is performed so that the exhaust air-fuel ratio becomes somewhat rich.
[0015]
For this reason, the rear catalyst 7 is often exposed to a rich air-fuel ratio, which causes temporary deterioration.
That is, when the three-way catalyst is exposed to a high-temperature exhaust atmosphere at an air-fuel ratio richer than stoichiometric, the noble metal component (for example, palladium) in the three-way catalyst is reduced, and palladium oxide is converted to metal palladium (metalation). Reduction of the purification capacity of the original catalyst, that is, temporary deterioration occurs. The temporary deterioration of the three-way catalyst is promoted by accumulation of sulfur components in the fuel on the three-way catalyst base (sulfur poisoning).
[0016]
Since exhaust gas deterioration occurs when temporary deterioration progresses, it is necessary to control the exhaust air-fuel ratio flowing into the three-way catalyst to be lean for the purpose of recovering the temporary deterioration. And since the temporary deterioration of the three-way catalyst proceeds continuously in normal operation, it is necessary to periodically recover. Furthermore, if the air-fuel ratio leaning operation for the temporary deterioration recovery process of the three-way catalyst is not performed at an appropriate air-fuel ratio, NOx is exhausted, so it is necessary to control the leaning by detecting the air-fuel ratio. is there. Furthermore, since the upper limit of the oxygen storage capacity of the three-way catalyst is reached during the air-fuel ratio leaning operation, the reduction performance is reduced, and NOx cannot be purified immediately after returning to normal operation, It is necessary to perform an enrichment operation for setting the air-fuel ratio after the lean operation to an appropriate state, that is, for consuming temporarily stored oxygen.
[0017]
Therefore, temporary deterioration recovery control performed by the ECU 10 will be described with reference to FIG. 2 and FIG.
FIG. 2 is a flowchart showing temporary deterioration recovery control. FIG. 3 is a timing chart of the temporary deterioration recovery control. These controls are performed while the engine 1 is operating.
[0018]
In step 1 (shown as S1 in the figure, the same applies hereinafter), based on the output of the third air-fuel ratio sensor 16 installed downstream of the rear catalyst 7, while the air-fuel ratio described later is in a rich state over a predetermined air-fuel ratio, that is, the third air-fuel ratio RO2SV detected based on the output of the air-fuel ratio sensor 16 is a second predetermined air-fuel ratio VSLL2 least 3 between (RO2SV ≧ VSLL2) is, the fuel injection amount counter value TPCNT the following equation Count up.
[0019]
TPCNT = TPCNT (-1) + TP
That is, the basic fuel injection amount TP is added to the previous value TPCNT (−1) of the fuel injection amount counter value to calculate the fuel injection amount counter value (temporary deterioration estimated amount) TPCNT.
The metallization and sulfur poisoning, which are considered to be the main causes of the temporary deterioration of the rear catalyst 7, occur in correlation with the cumulative value of the fuel injection amount, and therefore the degree of temporary deterioration can be estimated based on the fuel injection amount. For this reason, the counter value TPCNT for estimating the temporary deterioration amount is a fuel injection amount counter based on the fuel injection amount. Alternatively, temporary deterioration can be estimated by using the intake air amount or the vehicle travel distance as a counter parameter instead of the fuel injection amount.
[0020]
In step 2, it is determined whether or not the fuel injection amount counter value TPCNT is equal to or greater than a predetermined counter value TPSLL (TPCNT ≧ TPSLL). Note that this predetermined value TPSLL is a range in which emission deterioration does not occur and frequent deterioration recovery control is frequently performed when traveling under conditions where steady running or fuel cut control is not performed, and exhaust purification performance deteriorates. Set the value obtained by experiment etc. so that it does not occur. This is because the air-fuel ratio in the pre-catalyst 6 is out of the purifiable range, particularly during the leaning operation and the riching operation that are performed during the temporary deterioration recovery control described later. This is because the deterioration recovery control is desirably suppressed to as few times as possible (and in a short time). If the counter value TPCNT is less than the predetermined value TPSLL (TPCNT <TPSLL), the process proceeds to step 3. On the other hand, if the value is equal to or greater than the predetermined value TPSLL (TPCNT ≧ TPSLL), the process proceeds to step 6 described later.
[0021]
In step 3, it is determined whether the air-fuel ratio RO2SV based on the output of the third air-fuel ratio sensor 16 is leaner than the second predetermined air-fuel ratio VSLL2 (RO2SV <VSLL2). When the air-fuel ratio RO2SV is leaner than the second predetermined air-fuel ratio VSLL2 (RO2SV <VSLL2), the routine proceeds to step 4. On the other hand, if it is richer than the second predetermined air-fuel ratio VSLL2 (RO2SV ≧ VSLL2), the process returns to step 1.
[0022]
The second predetermined air-fuel ratio VSLL2 is determined within a predetermined air-fuel ratio range. This is because if the second predetermined air-fuel ratio VSLL2 is set larger than the stoichiometric value to the rich side, the estimation accuracy of the temporary deterioration is lowered, and the sufficient effect of the temporary deterioration recovery control cannot be obtained, while it is set to the lean side. If excessively, the temporary deterioration recovery control is frequently performed, which may worsen the emission, and the lean catalyst has an upper limit of the oxygen storage capacity range (purifying range) during the lean control. This is because NOx may be discharged without being purified immediately after the lean control is stopped. For this reason, the second predetermined air-fuel ratio VSLL2 needs to sufficiently obtain the effects of suppressing the NOx emission amount and recovering from the temporary deterioration, and is desirably set to an optimum value through experiments or the like. Note that the optimum value of VSLL2 obtained through experiments or the like does not become leaner than at least stoichiometric, and is a stoichiometric or rich value.
[0023]
Step 4 is a case where the air-fuel ratio RO2SV detected by the third air-fuel ratio sensor 16 is leaner than the second predetermined air-fuel ratio VSLL2 (RO2SV <VSLL2), and it is determined that the temporary deterioration of the rear catalyst 7 has been recovered. Then, the fuel injection amount counter value TPCNT is reset (see point A in FIG. 3). Such an example is applicable to a case where fuel cut conditions such as deceleration are satisfied and fuel cut is performed. In FIG. 3, there is a time difference between the time when the fuel cut is started and the time when the output RO2SV of the third air-fuel ratio sensor 16 is lowered between the fuel injection valve 4 and the third air-fuel ratio sensor 16. This is because, in addition to being influenced by the arrangement position, the oxygen storage capacity of the catalyst delays the arrival of the lean atmosphere at the air-fuel ratio sensor downstream of the catalyst.
[0024]
In step 5, it is determined whether or not the air-fuel ratio RO2SV based on the output of the third air-fuel ratio sensor 16 is richer than the second predetermined air-fuel ratio VSLL2 (RO2SV ≧ VSLL2). When the air-fuel ratio RO2SV is leaner than the second predetermined air-fuel ratio VSLL2 (RO2SV <VSLL2), the routine returns to step 4 and the fuel injection amount counter value TPCNT is reset to zero. On the other hand, when the second predetermined air-fuel ratio is equal to or higher than VSLL2 (RO2SV ≧ VSLL2), the fuel injection amount counter value TPCNT is counted up again in step 1 (see point B in FIG. 3).
[0025]
Further, the case where the fuel injection amount counter value TPCNT is equal to or greater than the counter predetermined value TPSLL (TPCNT ≧ TPSLL) in step 2 and the process proceeds to step 6 will be described.
In step 6, the fuel injection amount counter value TPCNT is reset (see point C in FIG. 3). Then, at the timing when the fuel injection amount counter value TPCNT of the rear catalyst 7 exceeds the counter predetermined value TPSLL, in order to recover the temporary deterioration of the rear catalyst 7, an operation for decreasing the target equivalent ratio TFBYA, that is, an air-fuel ratio leaning operation ( First control) is performed.
[0026]
In step 7, the target equivalent ratio TFBYA is set to a predetermined target equivalent ratio KL that is leaner than the stoichiometry, and the fuel injection valve 4 is controlled based on this to start the air-fuel ratio leaning operation (C in FIG. 3). Point).
Here, when the air-fuel ratio leaning operation is performed on the lean side larger than the stoichiometry, the lean air-fuel ratio is easily prolonged even after exceeding the oxygen storage capacity of the rear catalyst 7, and until the lean air-fuel ratio is eliminated. NOx cannot be purified. On the other hand, if the degree of lean (shift amount) is too small, the time required to depart from the purifiable range in the pre-catalyst 6 becomes longer, and the possibility of worsening of emissions arises. For this reason, it is desirable to set the optimal lean-side predetermined target equivalent ratio KL by experiments or the like.
[0027]
In step 8, it is determined whether the air-fuel ratio RO2SV based on the output of the third air-fuel ratio sensor 16 is leaner than the first predetermined air-fuel ratio VSLL (RO2SV <VSLL). If the value of VSLL is set too high, the leaning (described later) time in the temporary deterioration recovery control becomes too short, the enriching (described later) time becomes too long, and if set too low, the opposite result Therefore, the optimum value is obtained by experimentation and set. The first predetermined air-fuel ratio VSLL and the second predetermined air-fuel ratio VSLL2 may be set separately, but may be the same value, taking into account the above points for VSLL and VSLL2, respectively. FIG. 3 shows an example in which the control is simplified as the same value.
[0028]
If the air-fuel ratio RO2SV is leaner than the predetermined air-fuel ratio VSLL (RO2SV <VSLL), the process proceeds to step 9. On the other hand, when the air-fuel ratio is equal to or higher than the predetermined air-fuel ratio VSLL (RO2SV ≧ VSLL), the routine returns to step 6 and the air-fuel ratio leaning operation (target equivalent ratio TFBYA = KL) is continued (see points C to D in FIG. 3).
In step 9, the target equivalent ratio TFBYA is set to a predetermined target equivalent ratio KR on the rich side, the fuel injection amount of the fuel injection valve 4 is increased, and the control (second control) for instantly performing the enrichment operation (second control) is started ( (See point D in FIG. 3).
[0029]
Here, when the air-fuel ratio enrichment operation is performed on the rich side larger than the stoichiometry, the rear catalyst 7 cannot oxidize HC and CO in the exhaust, and the emission deteriorates. On the other hand, if the degree of richness (shift amount) is too small, the time that is out of the purifiable range in the pre-catalyst 6 becomes longer, and the possibility of worsening of emission arises. For this reason, it is desirable to set the optimal rich side predetermined target equivalent ratio KR through experiments or the like.
[0030]
In step 10, it is determined whether the air-fuel ratio RO2SV based on the third air-fuel ratio sensor 16 is richer (RO2SV> RO2SV (-1)) than the previous air-fuel ratio RO2SV (-1). This is to determine when the air-fuel ratio RO2SV becomes greater than the previous air-fuel ratio RO2SV (−1) (RO2SV> RO2SV (−1)), that is, when the air-fuel ratio is switched from the lean direction to the rich direction. Since the purpose of this step is to detect air-fuel ratio inversion switching, switching may be determined when the slope of the air-fuel ratio change exceeds a predetermined value (negative or positive). If the air-fuel ratio RO2SV is richer than the previous air-fuel ratio RO2SV (-1) (RO2SV> RO2SV (-1)) (see point E in FIG. 3), the process proceeds to step 11. On the other hand, if the previous air-fuel ratio RO2SV (-1) is greater than or equal to (RO2SV ≦ RO2SV (-1)), the process returns to step 9 to continue the air-fuel ratio enrichment operation (TFBYA = KR) (from point D in FIG. 3). (See point E).
[0031]
In step 11, the target equivalent ratio TFBYA is set to the normal target equivalent ratio KS, and based on this, the fuel injection valve 4 is controlled to start normal operation (third control). Thereby, the air-fuel ratio rich operation (TFBYA = KR) is switched to the normal operation (TFBYA = KS) (see point E in FIG. 3). The target equivalent ratio TFBYA during normal operation is such that the target equivalent ratio based on the third air-fuel ratio sensor 16 is slightly richer than stoichiometric (TFBYA = KS) in order to minimize the NOx emission amount during normal operation. Performs air-fuel ratio feedback control.
[0032]
In step 12, it is determined whether or not the air-fuel ratio RO2SV based on the output of the third air-fuel ratio sensor 16 is equal to or greater than a predetermined air-fuel ratio VSLL (RO2SV ≧ VSLL). When the air-fuel ratio is leaner than the predetermined air-fuel ratio VSLL (RO2SV <VSLL), the process returns to step 11 and the normal operation (TFBYA = KS) is continued. On the other hand, when the air-fuel ratio is equal to or higher than the predetermined air-fuel ratio VSLL (see point F in FIG. 3), the process returns to step 1 again.
[0033]
Here, when the shift amount of the target equivalent ratio TFBYA described so far is small, the deterioration of operability such as a torque step can be minimized, but the switching of the air-fuel ratio in the catalyst is slow, and after passing through the rear catalyst 7 When the air-fuel ratio RO2SV becomes lean or rich, the air-fuel ratio in the pre-catalyst 6 greatly deviates from the purifiable range, and the emission may deteriorate. On the other hand, when the shift amount of the target equivalent ratio TFBYA is large, the switching of the air-fuel ratio in the catalyst is quick, the control time can be shortened, and the deterioration of the emission can be suppressed. It will affect the worsening of. Therefore, in consideration of these points, it is desirable to appropriately set the maximum shift amount that does not deteriorate the emission and drivability by experiments.
[0034]
According to this embodiment, the exhaust passage 5 is provided with the rear catalyst 7, and the air-fuel ratio of the engine 1 is made lean at the timing at which the third air-fuel ratio sensor 16 provided downstream thereof and the temporary deterioration of the rear catalyst 7 are recovered. First control means (step 7) for performing the operation (TFBYA = KL), based on the detection of the first predetermined air-fuel ratio by the third air-fuel ratio sensor 16 (step 8), the air-fuel ratio leaning operation (TFBYA = KL) Based on the second control means (step 9) for switching from the air-fuel ratio enrichment operation (TFBYA = KR) and the third air-fuel ratio sensor 16 to detect the change of the air-fuel ratio RO2SV from the lean direction to the rich direction (step 10). , Rear catalyst temporary deterioration times provided with third control means (step 11) for returning from air-fuel ratio enrichment operation (TFBYA = KR) to normal operation (TFBYA = KS). Configured to include a control means. Therefore, the temporary deterioration of the rear catalyst 7 can be appropriately recovered by the air-fuel ratio leaning operation (TFBYA = KL), and the rear catalyst 7 can be reduced to NOx by the air-fuel ratio leaning operation (TFBYA = KR). It is possible to reduce the emission (HC, CO, NOx) emission amount by normal operation (TFBYA = KS).
[0035]
Further, according to the present embodiment, the rear catalyst temporary deterioration recovery control means includes temporary deterioration estimation means (step 1) for estimating the temporary deterioration of the rear catalyst 7, and the temporary deterioration estimated amount TPCNT estimated by the estimation means is provided. When the fixed amount TPSLL is exceeded, the air-fuel ratio leaning operation (TFBYA = KL) by the first control means is started (step 7). Therefore, the air-fuel ratio leaning operation (TFBYA = KL) can be performed at an appropriate timing based on the temporary deterioration estimated amount TPCNT, and the temporary deterioration of the rear catalyst 7 can be appropriately recovered.
[0036]
Further, according to the present embodiment, the temporary deterioration estimating means (step 1) is temporarily executed when the air-fuel ratio RO2SV by the third air-fuel ratio sensor 16 is richer than the second predetermined air-fuel ratio VSLL2 (steps 5 and 12). The count value TPCNT for estimating the deterioration is counted, and the predetermined amount TPSLL of the temporary deterioration is set to a predetermined count value when the second predetermined air-fuel ratio VSLL2 is rich. Therefore, the second predetermined air-fuel ratio VSLL2 can be set within a predetermined range of the air-fuel ratio RO2SV based on the output of the third air-fuel ratio sensor 16, and the temporary deterioration amount TPCNT can be estimated based on the air-fuel ratio VSLL2.
[0037]
Further, according to the present embodiment, the second predetermined air-fuel ratio VSLL2 is the same as the first predetermined air-fuel ratio VSLL, so that the control can be simplified.
Further, according to the present embodiment, the count value TPCNT is reset when the air-fuel ratio RO2SV by the third air-fuel ratio sensor 16 is leaner than the second predetermined air-fuel ratio VSLL2 (VSLL) (step 3) (step 3). 4). Therefore, it is possible to correctly determine that the fuel injection amount count value (temporal deterioration estimated amount) TPCNT has reached the allowable upper limit from the air-fuel ratio RO2SV and the second predetermined air-fuel ratio VSLL2 (VSLL) by the third air-fuel ratio sensor 16. Can do.
[0038]
Further, according to the present embodiment, the count value TPCNT estimates temporary deterioration based on the fuel injection amount. For this reason, temporary deterioration that is considered to be caused mainly by metallization of the catalyst and sulfur poisoning is estimated by using a cumulative value of the fuel injection amount (or intake air amount, travel distance) correlated with these main factors. Therefore, the temporary deterioration of the rear catalyst 7 can be accurately estimated.
[0039]
According to this embodiment, the normal operation by the third control means (step 11) is performed in a state where the air-fuel ratio RO2SV after passing through the rear catalyst 7 is slightly richer than stoichiometric (TFBYA = KS). For this reason, the NOx emission amount can be minimized during normal operation (TFBYA = KS).
Further, according to the present embodiment, the engine 1 includes the pre-catalyst 6 upstream of the rear catalyst 7, and in the normal operation by the third control means (step 11), the air-fuel ratio RO2SV after passing through the rear catalyst 7 is slightly higher than the stoichiometric ratio. This is performed in a rich state (TFBYA = KS). For this reason, even if there are a plurality of catalysts, the temporary deterioration can be appropriately recovered.
[0040]
Further, according to the present embodiment, the air-fuel ratio RO2SV is detected downstream of the rear catalyst 7 provided in the exhaust passage 5, while the air-fuel ratio leaning operation of the engine 1 is performed at the timing to recover the temporary deterioration of the rear catalyst 7 ( (TFBYA = KL) is performed (step 7), and based on the detection of the predetermined air-fuel ratio VSLL (step 8), the air-fuel ratio leaning operation (TFBYA = KL) is switched to the air-fuel ratio enriching operation (TFBYA = KR) (step 9). ) Based on detection of switching of the air-fuel ratio RO2SV from the lean direction to the rich direction (step 10), the air-fuel ratio enrichment operation (TFBYA = KR) is returned to the normal operation (TFBYA = KS) (step 11). For this reason, the temporary deterioration of the rear catalyst 7 can be appropriately recovered by the air-fuel ratio leaning operation (TFBYA = KL), and the three-way catalyst can be made in a state capable of reducing NOx by the enrichment operation (TFBYA = KR). The deterioration of emission (HC, CO, NOx) emissions can be reduced by normal operation (TFBYA = KS).
[0041]
In FIG. 1, the case where there are two three-way catalysts has been described. However, even when one three-way catalyst is arranged, the present invention can be applied using an air-fuel ratio sensor arranged on the downstream side thereof. It is. For this reason, the system configuration is simplified.
Further, the catalysts 6 and 7 may have an HC trap function. In this case, the amount of HC emission can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram of an exhaust purification device for an internal combustion engine. FIG. 2 is a flowchart showing temporary deterioration recovery control. FIG. 3 is a timing chart of temporary deterioration recovery control.
1 Engine 2 Intake passage 3 Electric throttle valve 4 Fuel injection valve 5 Exhaust passage 6 Pre-catalyst 7 Rear catalyst 10 ECU
11 Accelerator opening sensor 12 Crank angle sensor 13 Air flow meter 14 First air-fuel ratio sensor 15 Second air-fuel ratio sensor 16 Third air-fuel ratio sensor 17 Odometer

Claims (10)

An exhaust purification device for an internal combustion engine comprising a three-way catalyst in an exhaust passage,
An air-fuel ratio detecting means provided downstream of the three-way catalyst;
The first control means for performing the air-fuel ratio leaning operation of the internal combustion engine at the timing for recovering the temporary deterioration of the three-way catalyst, and the air-fuel ratio detected by the air-fuel ratio detecting means in the air-fuel ratio leaning operation is when it is leaner than the first predetermined air-fuel ratio, a second control means for switching from the air-fuel ratio leaner operation to enriching the air-fuel ratio operation, and by the air-fuel ratio detecting means in the air-fuel ratio rich operation Three-way catalyst temporary deterioration recovery control means comprising third control means for returning from the air-fuel ratio enrichment operation to the normal operation when the detected air-fuel ratio change is reversed from the lean direction to the rich direction. An exhaust emission control device for an internal combustion engine. The three-way catalyst temporary deterioration recovery control means,
Comprising temporary deterioration estimating means for estimating temporary deterioration of the three-way catalyst;
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein when the temporary deterioration estimated by the estimating means exceeds a predetermined amount, the air-fuel ratio leaning operation by the first control means is started. The temporary deterioration estimation means counts the temporary deterioration count value when the air-fuel ratio by the air-fuel ratio detection means is rich beyond a second predetermined air-fuel ratio,
3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the predetermined amount of temporary deterioration is a predetermined count value when the engine is richer than the second predetermined air-fuel ratio. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the second predetermined air-fuel ratio is the same as the first predetermined air-fuel ratio. The exhaust gas purification of an internal combustion engine according to claim 3 or 4, wherein the count value is reset when the air-fuel ratio by the air-fuel ratio detection means is leaner than the second predetermined air-fuel ratio. apparatus. The count value is a value calculated based on at least one of a fuel injection amount, an intake air amount, and a travel distance, and temporary deterioration is estimated. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. 7. The internal combustion engine according to claim 1, wherein the normal operation by the third control unit is performed in a state where the air-fuel ratio after passing through the three-way catalyst is slightly richer than stoichiometric. Engine exhaust purification system. The internal combustion engine includes another three-way catalyst upstream of the three-way catalyst,
The normal operation by the third control means is performed in a state where the air-fuel ratio after passing through the upstream three-way catalyst is slightly richer than the stoichiometric state. An exhaust gas purification apparatus for an internal combustion engine as described. The exhaust purification apparatus for an internal combustion engine according to any one of claims 1 to 8, wherein the three-way catalyst has an HC trap function. An exhaust purification method for an internal combustion engine having a three-way catalyst in an exhaust passage,
While detecting the air-fuel ratio downstream of the three-way catalyst,
At the timing of recovering the temporary deterioration of the three-way catalyst, the air-fuel ratio leaning operation of the internal combustion engine is performed,
When the air-fuel ratio downstream of the three-way catalyst in the air-fuel ratio leaning operation becomes leaner than a predetermined air-fuel ratio, the air-fuel ratio leaning operation is switched to the air-fuel ratio enriching operation,
The exhaust of the internal combustion engine, wherein when the air-fuel ratio change downstream of the three-way catalyst is reversed from the lean direction to the rich direction in the air-fuel ratio enrichment operation, the air-fuel ratio enrichment operation is returned to the normal operation. Purification method.

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