JP3186730B2 - Exhaust gas purification device for internal combustion engine - Google Patents

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 an exhaust gas purifying apparatus provided with a catalyst for reducing NOx using HC in an exhaust passage, in which the NOx reducing performance of the catalyst is maintained. For technology.

[0002]

2. Description of the Related Art Conventionally, as an exhaust gas purifying apparatus for an internal combustion engine,
There has been one disclosed in Japanese Patent No. 26000492.

In this system, a NOx absorbent that absorbs NOx when the air-fuel ratio of exhaust gas is lean and releases the absorbed NOx when the oxygen concentration in the exhaust gas decreases is disposed in the exhaust passage of the engine. On the other hand, from the NOx absorbent, N
When Ox is to be released, the air-fuel ratio of the exhaust gas is set to a stoichiometric air-fuel ratio or rich, and under the reducing atmosphere, the released NOx is reacted with HC to perform a reduction process.

[0004]

The above-mentioned NOx
In order to make the air-fuel ratio of the exhaust gas flowing into the absorbent rich in the stoichiometric air-fuel ratio or rich, the above-mentioned conventional device performs the increase correction of the fuel injection amount. However, since the fuel injection amount of all cylinders is equally increased and corrected. , The amount of increase in each cylinder becomes a very small amount.

[0005] However, the control for increasing the minute fuel amount is inferior in control stability, and it is difficult to control the actual injection amount with high accuracy. In addition, NOx released from the NOx absorbent may be discharged without being sufficiently reduced due to insufficient increase in amount, or conversely, the amount of HC may increase due to excessive increase in amount.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to reliably increase an amount of fuel injection required for NOx reduction processing and to improve exhaust purification performance and fuel efficiency. It is intended to provide a device.

[0007]

The invention according to claim 1 is configured as shown in FIG. In FIG.
The fuel injection means is means for injecting and supplying fuel for each cylinder, and the exhaust purification catalyst is interposed in the exhaust passage and adsorbs HC.
Capable of reducing NOx in the presence of HC .

Here, the HC increase request detecting means detects a state in which an increase in the amount of HC in the exhaust is required in order to secure the amount of HC required for the reduction of NOx by the exhaust purification catalyst. The air-fuel ratio enrichment means forcibly increases and corrects the amount of fuel injected and supplied to the specific cylinder for a predetermined period when the state where an increase in the amount of HC is required is detected by the HC increase request detecting means. This makes the air-fuel ratio of the specific cylinder only richer than the target air-fuel ratio ,
The specific cylinder whose ratio is to be enriched is
To sequentially switch to different cylinders.

On the other hand, when the air-fuel ratio of the specific cylinder is enriched by the air-fuel ratio enrichment means, the generated torque control means controls the generated torque of the specific cylinder to match the generated torque of another cylinder. The control target other than the air-fuel ratio related to the generated torque in the specific cylinder is controlled.

According to such a configuration, in order to secure the amount of HC required for the reduction of NOx by the exhaust purification catalyst,
When the increase in the amount of HC in the exhaust gas is required, the amount of the HC in the exhaust gas is increased by forcibly increasing and correcting the fuel amount for a predetermined period, but the increase in the amount of fuel is performed only in a specific cylinder. br /> allowed Wa, and especially for enriching the air-fuel ratio in the fuel quantity increasing
The constant cylinder is sequentially switched to a different cylinder within the predetermined period.
Replace it. In addition, by increasing the fuel only in the specific cylinder, the control target other than the air-fuel ratio in the cylinder is reduced in the generated torque so that the generated torque in the cylinder does not become larger than the other cylinders. Control in the direction.

In the invention according to claim 2, the generated torque control means suppresses an increase in generated torque by controlling the ignition timing in the specific cylinder.
According to such a configuration, in the specific cylinder for which the fuel is increased, the ignition timing is, for example, retarded, so that the increase in the torque generated by the increase in the fuel is offset, and the generated torque is made equal to the torque generated in other cylinders.

[0012]

[0013] In the invention according to claim 3 , the air-fuel ratio enriching means changes the number of cylinders for enriching the air-fuel ratio in accordance with the acceleration state of the engine. According to such a configuration, for example, at the time of gentle acceleration, the air-fuel ratio is enriched in a small number of cylinders, whereas at the time of rapid acceleration, the number of cylinders for which the air-fuel ratio is enriched is increased, so that the necessary increase can be completed in a short time. I do.

The invention according to claim 4 is configured as shown in FIG. In FIG. 2, the rapid acceleration detecting means detects the rapid acceleration state of the engine, and the rapid acceleration enrichment means detects the HC increase request when the rapid acceleration detecting means detects the rapid acceleration state of the engine. If the means detects a state in which an increase in the amount of HC is required, the air-fuel ratio of all cylinders is made richer, prior to the air-fuel ratio enriching means. Here, the sudden acceleration generated torque control means, when the air-fuel ratio of all cylinders is enriched by the rapid acceleration enrichment means,
In order to make the generated torque of all cylinders equal to the generated torque corresponding to the target air-fuel ratio, control targets other than the air-fuel ratio related to the generated torque of all cylinders are individually controlled.

With this configuration, when the vehicle is not undergoing rapid acceleration, only the air-fuel ratio of the specific cylinder is enriched, and the NOx
The amount of HC used for the reduction is ensured, but at the time of rapid acceleration, the air-fuel ratio of all cylinders is made rich, and when the enrichment is performed for all cylinders, the generated torque is suppressed for all cylinders. Is performed so that the same torque as before the increase correction is obtained.

According to the fifth aspect of the present invention, the torque generating means at the time of rapid acceleration controls at least one of the ignition timing and the exhaust gas recirculation amount to suppress an increase in the generated torque.

With this configuration, when the air-fuel ratio is made rich in all the cylinders, the ignition timing in all the cylinders is retarded and / or the exhaust gas recirculation amount is changed.
The same torque as before the increase correction is obtained in each cylinder.

[0018]

According to the first aspect of the present invention, the cylinder for which the air-fuel ratio is enriched by increasing the fuel amount is limited to a part of the cylinders, so that the fuel increase per cylinder is increased and the control stability is improved. It is possible to ensure that the amount of HC required for the NOx reduction process can be reliably obtained and to make it rich.
Since the cylinders are sequentially switched to different cylinders, some cylinders
The combustion temperature remains low and the wall temperature continues to drop,
The thermal stress of the solder can be prevented from becoming unbalanced.
Furthermore, since the generated torque of the enriched cylinder is suppressed, there is an effect that it is possible to prevent the occurrence of imbalance in the generated torque between the cylinders.

According to the second aspect of the present invention, the correction of the ignition timing cancels out the increase in the generated torque due to the increase in the amount of fuel and makes it equal to the generated torque of the other cylinders. There is an effect that balance can be prevented.

[0020]

According to the third aspect of the present invention, when the air-fuel ratio enrichment for NOx treatment is to be completed in a short time at the time of rapid acceleration, the number of cylinders to be enriched is increased to increase the necessary HC. There is an effect that the amount can be increased in a short time.

According to the fourth aspect of the invention, when the air-fuel ratio enrichment for NOx treatment is to be completed in a short time at the time of rapid acceleration, the required amount of HC is increased by enriching all the cylinders. Is increased in a short time, and a sudden increase in generated torque due to the enrichment can be prevented.

According to the fifth aspect of the present invention, by controlling the ignition timing and / or the exhaust gas recirculation amount, the increase in the generated torque due to the increase in the fuel in all the cylinders can be offset, and the sudden increase in the generated torque due to the richness can be prevented. This has the effect.

[0024]

Embodiments of the present invention will be described below.
In FIG. 3 showing a system configuration of the embodiment, air is sucked into an internal combustion engine 1 through an air cleaner 2, an intake duct 3, a throttle chamber 4, and an intake manifold 5.

The intake duct 3 is provided with an air flow meter 6 for detecting an intake air flow rate Q of the engine 1. The throttle chamber 4 is provided with a butterfly type throttle valve 7 for adjusting an intake air amount.
The throttle valve 7 is provided with a potentiometer type throttle sensor 8 for detecting the opening TVO.

In order to control the amount of auxiliary air supplied to the engine by bypassing the throttle valve 7, an idle control valve 9 whose opening is controlled, a fast opening / closing valve which opens and closes in response to an air conditioner signal. An idle control valve (FICD) 10 and an air regulator 11 for adjusting the amount of auxiliary air according to the cooling water temperature are provided.

On the other hand, an electromagnetic injector for intermittently injecting fuel supplied from a fuel tank (not shown) and adjusted to a predetermined pressure by a pressure regulator into the engine 1 is supplied to each branch of the intake manifold 5. The fuel injection amount, and hence the air-fuel ratio of the engine intake air-fuel mixture, can be controlled via the valve opening time of the injector 12.

Further, the ignition plug 13 faces the combustion chamber of each cylinder.
A high voltage generated by an ignition coil 14 in response to an ignition timing control signal is distributed and supplied to the ignition plug 13 via a distributor 15.

The distributor 15 has a built-in crank angle sensor 16.
Outputs a detection signal every predetermined crank angle. The engine speed is calculated based on the detection signal from the crank angle sensor 16.

The exhaust gas from the engine 1 is supplied to the exhaust manifold 1
7, the exhaust duct 18, the lean NOx catalyst 19 (exhaust gas purifying catalyst), and the muffler 20 are discharged into the atmosphere. The exhaust duct 18 is provided with an oxygen sensor 21 for detecting the oxygen concentration in the exhaust gas, which is closely related to the air-fuel ratio of the engine intake air-fuel mixture.

An exhaust temperature sensor 22 for detecting the exhaust gas temperature is provided downstream of the lean NOx catalyst 19.
The lean NOx catalyst 19 is made of zeolite supporting a transition metal or a noble metal, and has an HC adsorption capacity (HC
It has a storage effect) and a function of reducing NOx in the presence of HC in an oxidizing atmosphere.

A control unit 23 incorporating a microcomputer inputs detection signals from a water temperature sensor 24 for detecting a cooling water temperature of the engine, a knock sensor 25 for detecting knocking vibration of the engine, and the like, in addition to the various sensors.
It has a function of controlling the fuel injection amount by the injector 12, the ignition timing by the ignition plug 13, the auxiliary air amount adjusted by the idle control valve 9, and the like.

In FIG. 3, reference numeral 26 denotes a canister, which adsorbs and collects the evaporated fuel in a fuel tank (not shown), and desorbs and supplies the adsorbed and collected evaporated fuel to an engine intake system.

The control unit 23 sets the target air-fuel ratio of the engine intake air-fuel mixture to an output air-fuel ratio range near the stoichiometric air-fuel ratio and larger than the stoichiometric air-fuel ratio in accordance with the operating conditions detected by the various sensors. The air-fuel ratio is switched to a lean air-fuel ratio region near the combustion stability limit (air-fuel ratio of about 20 to 22), and the fuel injection amount is controlled according to the target air-fuel ratio set by the switching. Therefore, the engine 1 of the present embodiment is a so-called lean burn engine.

Here, as described above, the lean NOx catalyst is for reducing NOx by using HC, so if the amount of HC is insufficient, the NOx reducing performance is reduced. In particular, when the air-fuel ratio is gradually changed between the output air-fuel ratio range and the lean air-fuel ratio range as described above, as shown in FIG. 4, the air-fuel ratio range (the air-fuel ratio 16 to 18), but at this time HC / NO
The x ratio becomes small, and NO in the lean NOx catalyst 19
Since the reduction process of x cannot be expected, a large amount of NOx may be emitted into the atmosphere when switching the air-fuel ratio.

Therefore, in the present embodiment, at the time of switching the air-fuel ratio, the HC amount is secured as described below so that the NOx reduction performance can be maintained. The flowchart of FIG. 5 shows the control for switching the target air-fuel ratio between the output air-fuel ratio range (substantially the stoichiometric air-fuel ratio) and the lean air-fuel ratio range. In the present embodiment, the engine 1 is an in-line four-cylinder engine.

The routine shown in the flowchart of FIG.
This is executed every cycle. First, information such as the engine load, the rotation speed, and the coolant temperature is read (S1).
1). The engine load is calculated by another routine based on an intake air flow rate Q detected by the air flow meter 6 and an engine rotation speed Ne calculated based on a detection signal from the crank angle sensor 16. Injection amount Tp (←
K × Q / Ne: K is a constant).

Based on the information on the engine load and the rotational speed, it is determined whether or not the current operating condition is included in a preset lean operating region. By determining whether or not the condition is such that the vehicle is operable, it is determined whether or not the lean operation is possible (S12).

If it is determined that the lean operation is possible, the lean determination flag FLEAN indicating the switching state of the target air-fuel ratio is set to 1 (S13). When it is necessary to perform combustion (stoichiometric operation) in the fuel ratio range (stoichiometric air-fuel ratio),
The lean determination flag FLEAN is set to 0 (S
14).

Next, the lean determination flag FLEAN set this time is compared with the lean determination flag FLEAN (= FL-OLD) set at the time of the previous execution of this program (S15).

Here, when the lean determination flag FLEAN set this time is different from the previous value, in other words,
Switching from lean air-fuel ratio range to output air-fuel ratio range, or
When switching from the output air-fuel ratio range to the lean air-fuel ratio range is performed, the enrichment flag FRICH is set to 1 (S16).

The enrichment flag FRICH is a flag indicating a state in which combustion is performed at a richer air-fuel ratio than the air-fuel ratio before switching for a predetermined period before actually switching the air-fuel ratio (see FIG. 9).

On the other hand, if the lean determination flag FLEAN is the same as the previous one, the process proceeds without setting the enrichment flag FRICH. Then, the lean determination flag FLEAN set this time is set to the previous value FL-OLD for the determination in S15 at the next execution of this program (S17).

Next, in response to the result of the determination as to whether or not the lean operation is possible, an actual target air-fuel ratio is set (S18). Details of the setting of the target air-fuel ratio in S18 are shown in the flowcharts of FIGS. still,
In the present embodiment, the functions of the HC increase request detection means, the air-fuel ratio enrichment means, and the generated torque control means are provided by software in the control unit 23 as shown in the flowcharts of FIGS. .

In the flowcharts of FIGS. 6 and 7, first, the enrichment flag FRICH is determined (S201). When the enrichment flag FRICH is 1, the flag FR-OLD for judging the initial state of the control for enriching the air-fuel ratio is judged (S202).

Here, it is determined that the flag FR-OLD is 0, and when the enrichment control is in the initial state, the flag FR-OLD is set to 1 (S20).
3) As shown in FIG. 8, a period TR for forcibly enriching the air-fuel ratio before actually switching the air-fuel ratio is read from a map previously allocated based on the engine load and the engine rotation speed (S204). Then, the timer tR for measuring the enrichment period TR is counted up by a predetermined value Δt (S205), and the measurement of the enrichment period is started.

That is, even if the switching of the air-fuel ratio between the output air-fuel ratio range and the lean air-fuel ratio range is set, the switching is not immediately started but the switching start of the air-fuel ratio is delayed by the enrichment period TR. During the delay period, a large amount of HC is discharged by burning at an air-fuel ratio richer than the air-fuel ratio before switching, and lean N
The maximum amount of HC within a possible range is adsorbed on the Ox catalyst 19 (see FIG. 9).

In the lean NOx catalyst 19, the total amount MO of adsorbable HC is determined by the amount of the catalyst carried. Therefore, the amount of HC discharged from the engine is obtained from the operating conditions and the air-fuel ratio setting. The time required for the amount of adsorption to reach the adsorbable amount MO is determined, and this time is defined as the enrichment period TR. Since the amount of HC emission increases as the load becomes higher and the engine speed increases, the enrichment period TR is set to a shorter period as the engine load and the engine speed increase, in other words, a longer period as the engine load and the engine speed decrease. Is set to be Therefore, if the predetermined enrichment process is performed only during the enrichment period TR, it is predicted that the maximum amount of HC that can be adsorbed to the lean NOx catalyst 19 will be adsorbed.

Next, a map of the air-fuel ratio / ignition timing for normal operation assigned based on the engine load and the engine speed is referred to based on the lean determination flag FLEAN, and the reference values are respectively referred to as MKMR and MADV. (S206).

As shown in FIG. 10, the air-fuel ratio / ignition timing map for normal operation is prepared in advance for the output air-fuel ratio range (stoichiometric) and the lean air-fuel ratio range. One of the maps is selected based on the lean determination flag FLEAN, and the target lean air-fuel ratio and ignition timing are referenced from the selected map based on the engine load and rotation at that time.

The reference values MKMR and MADV are assigned to KMR (i) and ADV (i) assigned to each cylinder.
(I = 1 to 4) (S207). Here, the lean determination flag FLEAN is inverted with respect to the previous time, and if the lean determination flag FLEAN is 1, the lean determination flag FLEAN is normally referred to a map for a lean air-fuel ratio range (lean operation). If the flag FLEAN is 0, a map for the output air-fuel ratio range (stoichiometric operation) is referred to.

However, in the present embodiment, the switching of the air-fuel ratio is delayed during the enrichment period TR (while the flag FRICH is 1), and the lean determination flag FLE
The air-fuel ratio is switched only after the enrichment period TR has elapsed since the inversion of AN (see FIG. 9).

Therefore, as described above, the enrichment flag F
In S206, which is the enrichment period TR in which RICH is determined to be 1, if the lean determination flag FLEAN is to be switched from the lean air-fuel ratio range of 0 to the output air-fuel ratio range, the lean air-fuel ratio range before switching is set. Refer to the map for
When switching from the output air-fuel ratio range (the stoichiometric air-fuel ratio) in which the lean determination flag FLEAN is 1 to the lean air-fuel ratio range, the map for the output air-fuel ratio range before switching is referred to.

In the above description, the normal data corresponding to the air-fuel ratio setting before switching is set as the air-fuel ratio and ignition timing of all cylinders. However, in S208 to S212 , only the air-fuel ratio of the specific cylinder is enriched. Then, a process of rewriting the air-fuel ratio / ignition timing setting of the specific cylinder is performed.

That is, when an instruction is given to switch the air-fuel ratio between the output air-fuel ratio range and the lean air-fuel ratio range, the start of the actual switching control is simply delayed for the cylinders other than the specific cylinder. Is to enrich more than at least other cylinders in order to forcibly discharge more HC within the delay period.

As shown in FIGS. 10 (c) and 10 (d), the control unit 23 stores the air-fuel ratio / ignition timing map for enriching the specific cylinder in advance from the output air-fuel ratio range (stoichiometric). A map used when switching to the air-fuel ratio range and a map used when switching to the opposite direction are provided.For example, in the enrichment period when switching from the output air-fuel ratio range to the lean air-fuel ratio range, other maps are used. For the specific cylinder, the map of FIG. 10C is used.

Here, the map shown in FIG. 10A and the map shown in FIG.
10 (b) and FIG. 10 (d), when the control is performed using data Sij and S ′ ij or Lij and L ′ ij corresponding to the same load and rotation. The same generated torque can be obtained.

In the enrichment period TR, only the specific cylinder is enriched. Therefore, if only the setting of the air-fuel ratio is made different between the cylinders, the generated torque becomes larger in the specific cylinder, and the generated torque between the cylinders becomes larger. The torque becomes unbalanced. Therefore, even if the air-fuel ratio is enriched, a map in which the ignition timing is corrected is set to an air-fuel ratio / ignition timing map for enrichment so that the generated torque does not become larger than that of other cylinders due to the enrichment. Set as (Figure
11), the generated torque of a specific cylinder to be enriched is equal to the generated torque of another cylinder that is not enriched.

That is, as shown in FIG. 11, when the air-fuel ratio of a specific cylinder is greatly increased to about 9 with respect to other cylinders burned at a predetermined lean air-fuel ratio (air-fuel ratio = about 21), With the enrichment, only the generated torque of the enriched cylinder increases. Therefore, data of the air-fuel ratio and the ignition timing that can offset the increase in the torque generated by the enrichment by setting the retard of the ignition timing (retard) is obtained by an experiment in advance, and this is set as a map for enrichment. The generated torque in the cylinder controlled using the normal map and the generated torque in the cylinder controlled using the enrichment map are made substantially equal under the same load and rotation conditions.

In S208, the enrichment air-fuel ratio / ignition timing map set as described above is referred to according to the air-fuel ratio switching direction, and the enrichment cylinder counter CY is referred to.
Enrich specific cylinder specified by LN (initial value = 1)
As the cylinder, the air-fuel ratio KMR for this enriched cylinder
(CYL-N) and the ignition timing ADV (CYL-N).
To make a decision. The air-fuel ratio KMR (CY
LN) and the ignition timing ADV (CYL-N)
Control according to the air-fuel ratio setting before switching to normal without being changed
The cylinder is rich in air-fuel ratio,
This is equivalent to the generated torque.

In this embodiment, as shown in FIG. 9, the air-fuel ratio is controlled to about 14 to 16 in the output air-fuel ratio range, and is controlled to about 20 to 22 in the lean air-fuel ratio range. On the other hand, when switching from the output air-fuel ratio range to the lean air-fuel ratio range, the air-fuel ratio of the specific cylinder is reduced (enriched) to about 10 to 12 for a predetermined period, and then the actual switching is started.
When switching from the lean air-fuel ratio range to the output air-fuel ratio range, the actual switching is started after the air-fuel ratio of the specific cylinder is reduced (enriched) to about 8 to 10 for a predetermined period.

In the predetermined period TR immediately before switching the air-fuel ratio as described above, only the air-fuel ratio of the specific cylinder is generated with respect to the target air-fuel ratio before switching (the air-fuel ratio of another cylinder) without increasing the generated torque. Air-fuel ratio to be enriched
When the ignition timing is set, in S209, the above set
The air-fuel ratio KMR (CYL-N) and the ignition timing ADV (CYL
-N) with the previous value in the enriched cylinder CYL-N.
KMR-OLD (CYL-N), ADV-OLD
(CYL-N). Next, in S210,
The enriched cylinder counter CYL-N is incremented by one, and S2
At 11, the incremented enriched cylinder counter becomes 4
If it is determined that the value has exceeded
1 is reset. Therefore, the rich
The cylinder counter CYL-N is 1 → 2 → 3 every cycle.
→ 4 → 1 changes, and specific air enriched accordingly
The cylinder is # 1 → # 2 → # 3 → # 4 → # 1 in each cycle
It will change next. When the air-fuel ratio is enriched,
Although the temperature of the combustion chamber wall of the cylinder decreases, it is enriched as described above.
If the configuration is such that the cylinders are sequentially changed, the wall temperature of one cylinder
And the thermal stress of the cylinder becomes unbalanced
Nothing.

Next, it is determined whether or not a predetermined enrichment period TR has elapsed based on the time measured by the timer tR (S213) . If the enrichment period TR has not elapsed, the process directly proceeds to the target air-fuel ratio setting step after S217 , but if it is determined that the enrichment period TR has elapsed, the flag FRICH,
FR-OLD and timer tR are reset to zero (S2
14) The switching of the air-fuel ratio delayed by the enrichment period TR is started.

When the enrichment flag FRICH is reset to zero, the lean determination flag FLEAN will be
When the flag FLEAN is 0, a normal map for the output air-fuel ratio range (FIG. 10A) is referred to, and when the flag FLEAN is 1, a normal map for the lean air-fuel ratio range (see FIG. 10A). 10 (b)), a common air-fuel ratio / ignition timing for each cylinder is set (S215, S2).
16) .

S 217 to S 225 are performed when the air-fuel ratio is switched between the output air-fuel ratio range and the lean air-fuel ratio range.
This is a step for gradually changing the air-fuel ratio before the switching to the air-fuel ratio after the switching, and setting the target air-fuel ratio so as not to cause a sudden output change accompanying the switching of the air-fuel ratio.

First, the air-fuel ratio KMR (i) set with reference to the current map and the previous air-fuel ratio KMR-OLD (i)
Then, it is determined whether or not the air-fuel ratio is set to be increased (S217) .

Here, when it is determined that the set air-fuel ratio is increasing and changing, the data obtained by adding a predetermined step amount ΔRMR to the previous value KMR-OLD (i) and the current set air-fuel ratio KMR (i) is compared, and the smaller data is set as the final target air-fuel ratio TMR (i).
Accordingly, when shifting from the output air-fuel ratio range to the lean air-fuel ratio range, the air-fuel ratio does not change from near the stoichiometric air-fuel ratio to the final lean air-fuel ratio at once, but gradually changes by the step amount ΔRMR.

On the other hand, if the set air-fuel ratio obtained by referring to the map has not changed or has decreased, the data obtained by subtracting the predetermined step amount ΔLMR from the previous value KMR-OLD (i) is used. , The current set air-fuel ratio KMR
(I) is compared, and the larger data is set as the final target air-fuel ratio TMR (i). Therefore, when shifting from the lean air-fuel ratio region to the output air-fuel ratio region, the air-fuel ratio does not change from the lean air-fuel ratio to near the stoichiometric air-fuel ratio at once, but gradually changes by the step amount ΔLMR.

When the set air-fuel ratio obtained by referring to the map has not changed, that is, in the stable stoichiometric air-fuel ratio or lean air-fuel ratio operating state, or in the enrichment period TR, the map reference value Is directly set as the target air-fuel ratio TMR (i).

In S220 to S222 , the ignition timing TADV is set in the same manner as the setting of the target air-fuel ratio TMR (i).
A process for gradually changing (i) is performed. The setting of the target air-fuel ratios TMR (i) and TADV (i) is performed for each cylinder. S217 to S222
Is completed, the cylinder counter i (initial value = 1) is incremented by one. And this counter i
Until the target air-fuel ratio TMR (i) and TADV (i) have been set for all the cylinders, and the processing of S217 to S222 is repeated.

The target air-fuel ratio TMR (i) and TADV
When the setting of (i) is completed for all cylinders, the counter i is reset to 0, which is an initial value (S225) .
The target air-fuel ratio TMR (i) and TADV (i) are passed to an air-fuel ratio / ignition timing control routine ( not shown) (S22).
6) The injection amount control corresponding to the target air-fuel ratio TMR (i) and the ignition timing control corresponding to TADV (i) are performed.

The control shown in the flowcharts of FIGS. 6 and 7 will be described briefly. When switching between the output air-fuel ratio range (stoichiometric operation) and the lean air-fuel ratio range (lean operation), the switching is performed. For a predetermined period TR,
In the switching delay period, only the air-fuel ratio of the specific cylinder is enriched. When the air-fuel ratio is enriched, the ignition timing is set to be retarded as compared with the other cylinders in order to suppress an increase in the generated torque due to the enrichment, and is set to the same level as the generated torque of the other cylinder.

When the specific cylinder is enriched as described above, the amount of HC contained in the exhaust gas from the specific cylinder can be forcibly increased. By setting the period TR, the maximum amount of HC that can be adsorbed to the lean NOx catalyst 19 can be adsorbed within the air-fuel ratio switching delay period. Then, after the enrichment period TR has elapsed, the lean NOx catalyst
After the state where it is estimated that the maximum amount of HC is adsorbed in 19, the actual air-fuel ratio switching is started.

Here, in the air-fuel ratio range (air-fuel ratio 16 to 18) between the output air-fuel ratio range near the stoichiometric air-fuel ratio and the lean air-fuel ratio range (air-fuel ratio 20 to 22), the NOx emission from the engine 1 is determined. However, if a large amount of HC is positively adsorbed on the lean NOx catalyst 19 immediately before the start of the air-fuel ratio switching as described above, a large amount of NOx is actually discharged from the engine. When the fuel ratio state is reached, NOx can be reduced using the adsorbed HC.

Therefore, according to the present embodiment, when the target air-fuel ratio is switched between the output air-fuel ratio range (the stoichiometric air-fuel ratio) and the lean air-fuel ratio range, the output is gradually reduced to avoid a rapid change in the output. Even when the air-fuel ratio is changed, it is possible to satisfactorily reduce NOx discharged in the air-fuel ratio range during switching, and to maintain NOx while maintaining operability.
An increase in emissions can be avoided.

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

In the above-described embodiment, only one of the four cylinders is forcibly enriched in order to secure the amount of HC. However, two or three cylinders or all cylinders are switched before the air-fuel ratio switching. May be configured to be enriched within the predetermined period.

For example, when switching from lean operation to output air-fuel ratio (stoichiometric air-fuel ratio) for rapid acceleration, there are cases where air-fuel ratio switching must be performed in a relatively short time. In order to shorten the period for enriching temporarily (enrichment period TR) as the air-fuel ratio is rapidly switched, it is necessary to increase the HC concentration in the enrichment period. Therefore, at the time of rapid acceleration, it is considered that the number of cylinders to be temporarily enriched is increased to cope with it. Depending on the required HC concentration, it is possible to temporarily enrich all cylinders.

FIG. 12 is a flowchart showing a control for enriching not only one cylinder but all cylinders when the engine 1 is rapidly accelerated.
In the flowchart of FIG.

That is, when the timer tR for measuring the enrichment period TR immediately before switching of the air-fuel ratio is counted up (S205), the opening TVO of the throttle valve 7 detected by the throttle sensor 8 is read (S1001).

Then, the difference ΔTVO between the currently read opening TVO and the previous value TVO-OLD, that is, the amount of change in the opening TVO during one cycle is calculated (S1002).
Based on the TVO, it is determined whether or not the throttle valve 7 is being opened at a predetermined rate or more (rapid acceleration) (S1003: rapid acceleration detection means).

Here, if the vehicle is not in the rapid acceleration state, S20
Proceeding to 6, the process for enriching only one specific cylinder is performed as described above. On the other hand, if it is determined that the vehicle is accelerating rapidly, the process of adsorbing the required HC amount to the lean NOx catalyst 19 needs to be completed immediately. Therefore, the enrichment map is referred to to enrich all the cylinders. To set the air-fuel ratio and ignition timing of all cylinders (S1004, S1005:
Rich acceleration means at the time of rapid acceleration, generated torque control means at the time of rapid acceleration).

Here, if the configuration is such that all cylinders are enriched at the same time as described above, the generated torque does not vary among the cylinders. However, if only the process for enriching the air-fuel ratio is performed, The generated torque will increase rapidly. However, the enrichment map enriches the air-fuel ratio. However, by setting the ignition timing to be retarded, it is possible to obtain substantially the same generated torque as when the control is performed using the normal air-fuel ratio / ignition timing map. Since it is set, even if the enrichment is performed for all cylinders, the generated torque does not suddenly increase.

Although not shown in the flowchart of FIG. 12 , when the all-cylinder enrichment process is performed in response to the rapid acceleration determination, the enrichment period TR is shortened compared to the case where only one cylinder is enriched. Good.

If the configuration in which all the cylinders are enriched as described above is employed, there is no imbalance in the shaft exciting force between the cylinders, which is advantageous in terms of vibration and durability. Since the maximum amount of HC can be adsorbed to the lean NOx catalyst 19, the enrichment period can be shortened.

In the above description, in the process for enriching the air-fuel ratio for a predetermined period before the start of the air-fuel ratio switching, all cylinders are enriched during rapid acceleration, and only one cylinder is used except during rapid acceleration. However, the acceleration may be determined to be rapid acceleration or moderate acceleration. For example, only one cylinder may be enriched except during acceleration, two cylinders may be enriched during gentle acceleration, and all cylinders may be enriched during rapid acceleration. Furthermore,
When the two or three cylinders are enriched, the cylinder group to be enriched may be sequentially changed.

In the above embodiment, the engine 1 provided with a lean NOx catalyst 19 containing zeolite as a main component in its exhaust passage.
However, if the catalyst has the ability to adsorb HC and reduces NOx in the presence of HC, by increasing the amount of HC upstream of the catalyst immediately before switching the air-fuel ratio as described above,
Before the switching is started, a sufficient amount of HC can be adsorbed to the catalyst for the NOx processing, so that the NOx processing capacity in the middle of the switching can be increased, so that the catalyst is not limited to the lean NOx catalyst. A three-way catalyst may be used.

Further, in the above-described embodiment, the increase in the torque generated by enriching the air-fuel ratio is offset by setting the ignition timing to be retarded. However, particularly in the case of rapid acceleration in which all cylinders are enriched, By controlling the exhaust gas recirculation amount, an increase in generated torque due to enrichment can be suppressed. Furthermore, a configuration in which an increase in generated torque is suppressed by a combination of the ignition timing and the exhaust gas recirculation amount may be adopted.

The HC adsorbing capacity of the lean NOx catalyst depends on not only the HC concentration and the gas flow rate but also the exhaust temperature (catalyst temperature).
The enrichment period TR may be changed according to the exhaust gas temperature detected by the exhaust gas temperature sensor 22.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the invention described in claim 1.

FIG. 2 is a block diagram showing a basic configuration of the invention according to claim 5;

FIG. 3 is a schematic diagram illustrating a system configuration according to the embodiment;

FIG. 4 is a diagram showing a state of a change in the emission amount of NOx and HC with respect to an air-fuel ratio.

FIG. 5 is a flowchart showing air-fuel ratio switching control.

FIG. 6 is a flowchart showing HC increase control at the time of air-fuel ratio switching.

FIG. 7 is a flowchart showing HC increase control at the time of air-fuel ratio switching.

FIG. 8 is a diagram showing a map of a HC increase control (enrichment) period.

FIG. 9 is a time chart showing how the air-fuel ratio changes in the embodiment.

FIG. 10 is a diagram showing an air-fuel ratio / ignition timing map in the embodiment.

FIG. 11 is a diagram showing a relationship between an air-fuel ratio / ignition timing and a generated torque.

FIG. 12 is an embodiment in which all cylinders are enriched during rapid acceleration .
5 is a flowchart showing the process .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 6 Air flow meter 12 Injector 16 Crank angle sensor 22 Lean NOx catalyst 23 Control unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 21/08 301 F02D 21/08 301C 301G 41/14 310 41/14 310A 41/36 41/36 B 43/00 301 43 / 00G 301B 301H 301N 45/00 301 45/00 301G F02M 25/07 550 F02M 25/07 550R F02P 5/15 F02P 5/15 B JP-A-62-75043 (JP, A) JP-A-60-79139 (JP, A) JP-A-6-10725 (JP, A) JP-A-6-129246 (JP, A) A) JP-A-4-81539 (JP, A) JP-A-7-208151 (JP, A) JP-A-3-217640 (JP, A) JP-A-3-229914 (JP, A) JP-A-3 -242415 (JP, A) 234891 (JP, A) WO 93/7363 (WO, A1) WO 93/8383 (WO, A1) (58 ) investigated the field (Int.Cl. ^7, DB name) F02D 41/00 - 41/40 F02D 43/00-45/00 F02P 5/145-5/155 F01N 3/00-3/38 F01N 9/00

Claims (5)

(57) [Claims] 1. An exhaust gas purifying apparatus for an internal combustion engine, comprising a fuel injection means for injecting and supplying fuel for each cylinder, wherein the exhaust gas purifying apparatus is provided in an exhaust passage and has an HC adsorbing ability and is provided with an HC.
An exhaust purification catalyst for reducing NOx by using the catalyst, and HC required for NOx reduction by the exhaust purification catalyst.
In order to secure the amount, the HC increase request detecting means for detecting a state in which the amount of HC in the exhaust gas is required to be increased, and when the state in which the amount of HC is required to be increased is detected by the HC increase request detecting means, By enriching the amount of fuel injected and supplied to the specific cylinder only for a predetermined period to make the air-fuel ratio of the specific cylinder richer than the target air-fuel ratio , and a specific cylinder that makes the air-fuel ratio richer, Previous
Air-fuel ratio enrichment means for sequentially switching to a different cylinder within the predetermined period; and when the air-fuel ratio of the specific cylinder is enriched by the air-fuel ratio enrichment means, the torque generated in the specific cylinder is generated by another cylinder. And a generated torque control means for controlling a control target other than the air-fuel ratio related to the generated torque in the specific cylinder so as to match the torque. 2. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said generated torque control means controls an ignition timing in said specific cylinder to suppress an increase in generated torque. 3. The air-fuel ratio enrichment means includes means for accelerating an engine.
Change the number of cylinders to enrich the air-fuel ratio according to the state
The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2, wherein: 4. A rapid acceleration detecting means for detecting a rapid acceleration state of an engine.
And the rapid acceleration state of the engine is detected by the rapid acceleration detecting means.
The amount of HC is detected by the HC increase
When a state in which an increase is required is detected, the air-fuel ratio
The air-fuel ratio of all cylinders is
Means for enriching the air-fuel ratio of all cylinders by the enrichment means at the time of sudden acceleration.
When the torque is changed to the target air-fuel ratio,
In order to match the generated torque of the cylinders,
Control targets other than air-fuel ratio related to raw torque
And during rapid acceleration torque control means for controlling any one of claims 1 to 3, characterized in that the provided
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 5. The control apparatus according to claim 1, wherein said sudden acceleration generated torque control means includes:
To control at least one of the timing and the exhaust gas recirculation amount
Therefore, it is possible to suppress an increase in generated torque.
The exhaust gas purification device for an internal combustion engine according to claim 4 .