JPH11200852A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform effectively the desorption and reduction treatment of an NOx absorbing catalyst while improving fuel consumption and the like. SOLUTION: A three way catalyst 3 is interposed in an exhaust passage 2 for the right bank (RH) of a V-type internal combustion engine 1, and jointed with an exhaust passage 4 for a left bank (LH) in the exhaust downstream of the three way catalyst 3, and after that, connected to a turbo supercharger 5. A precatalyst (NOx absorbing catalyst) 7 and an underfloor catalyst 8 are interposed in an exhaust passage 6 on the outlet side of the turbo supercharger 5. In this case, when the NOx absorbing amount of the precatalyst 7 reaches a saturation amount by continuation of lean combustion, an air-fuel ratio in a right bank cylinder is not made rich and an air-fuel ratio in a left bank cylinder (specific cylinder) only is made rich. Hereby, the precatalyst 7 can be effectively desorbed and reduced while improving fuel consumption and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for an internal combustion engine, and more particularly, to a control device for an internal combustion engine having a NOx absorption catalyst.

[0002]

2. Description of the Related Art Conventionally, a NOx absorption catalyst that absorbs NOx in exhaust gas when the exhaust air-fuel ratio is lean and desorbs and reduces the absorbed NOx when the exhaust air-fuel ratio is rich has been used. NOx absorbed by the NOx absorption catalyst during lean combustion (also referred to as lean operation) by temporarily shifting the air-fuel ratio to a rich spike or rich shift.
There is known a lean-burn engine configured to perform a desorption / reduction process (see, for example, JP-A-06-066).
No. 135).

[0003]

Further, for example, the exhaust gas from the right (RH) bank and the exhaust gas from the left (LH) bank of a V-type engine are introduced into a single turbocharger while being merged. After that, in the exhaust gas purifying apparatus in which exhaust gas is caused to flow into the pre-catalyst and the underfloor catalyst, a delay in activation of each of the catalysts (a long exhaust passage to the pre-catalyst,
Alternatively, in order to suppress an increase in the emission of harmful exhaust components (especially, HC and CO) due to the exhaust gas not being able to achieve a good temperature increase due to the heat capacity of the turbocharger, for example, the right bank A three-way catalyst is provided between the turbocharger and the turbocharger, and the exhaust from the right bank is purified by the three-way catalyst, which can be relatively quickly activated, and then combined with the exhaust from the left bank. There is.

However, when applying a NOx absorption catalyst to a precatalyst of such an exhaust gas purification device, a three-way catalyst is newly provided upstream of the NOx absorption catalyst (precatalyst) in the exhaust gas. Therefore, the following situation may occur. That is, by temporarily enriching the air-fuel ratio to increase HC and CO in the exhaust gas, an oxygen-deficient state is created, and the NOx absorbed by the NOx absorbent is created.
And using the increased HC and CO as a reducing agent, the three-way catalyst portion of the NOx absorption catalyst (pre-catalyst) and the underfloor catalyst (three-way catalyst) to remove NOx (NO
x (including NOx desorbed from the absorbent). However, if a new three-way catalyst is provided between the right bank and the turbocharger, the air-fuel ratio is temporarily enriched and the exhaust gas is reduced. Even if the amount of HC and CO in the air is increased, the three-way catalyst will purify (convert and oxidize) these gases. Therefore, even if the air-fuel ratio is made rich, the NOx absorption catalyst (pre-catalyst) There is a possibility that the reducing agent (HC, CO) for the NOx reduction treatment cannot be satisfactorily provided to the three-way catalyst section and the underfloor catalyst (three-way catalyst).

[0005] The above description is not limited to the V-type engine but also applies to the horizontally opposed engine. In an in-line type engine, the cylinders of the engine are divided into a plurality of cylinder groups, and the exhaust gas is NOx-absorbed for each cylinder group. The same applies to the case where the reaction is led to the catalyst. The same result is obtained when no turbocharger is provided. The present invention has been made in view of such a conventional situation, and includes a plurality of cylinders, in which exhaust gas from at least one specific cylinder among the plurality of cylinders is introduced into a NOx absorption catalyst without being introduced into an exhaust purification catalyst, In the case where exhaust gas from a cylinder other than the specific cylinder is introduced into the exhaust purification catalyst and then introduced into the NOx absorption catalyst, the air-fuel ratio at the time of performing the desorption / reduction processing of the NOx absorption catalyst is reduced. An object of the present invention is to provide a control device for an internal combustion engine that can effectively perform a desorption / reduction process of a NOx absorption catalyst while improving fuel efficiency and the like by devising a rich process.

[0006]

Therefore, according to the first aspect of the present invention, as shown in FIG. 1, a plurality of cylinders are provided, and exhaust gas from at least one specific cylinder among the plurality of cylinders is purified. A control device for an internal combustion engine, wherein the control device is configured to introduce the exhaust gas from a cylinder other than the specific cylinder into the exhaust purification catalyst and then introduce the exhaust gas from the cylinder other than the specific cylinder into the NOx absorption catalyst without introducing the NOx into the catalyst. During the lean combustion, when the exhaust air-fuel ratio is enriched to perform the desorption / reduction processing of the NOx absorbed by the NOx absorption catalyst, only the at least one of the specific cylinders is mixed with suction. A specific cylinder air-fuel ratio control means for enriching the air-fuel ratio of the air to enrich the exhaust air-fuel ratio is included.

With this configuration, the air-fuel ratio of the intake air-fuel mixture is enriched only in at least one of the specific cylinders, and the NOx absorbed by the NOx absorption catalyst is increased.
The desorption / reduction process of NOx is effectively performed while suppressing wasteful consumption of fuel (improvement of fuel efficiency) and deterioration of the exhaust gas purification catalyst as in the related art. It is possible to make it. The exhaust purification catalyst may be a three-way catalyst or an oxidation catalyst, that is, any catalyst that can oxidize at least HC and CO in exhaust gas.

According to the invention described in claim 2, the internal combustion engine includes a plurality of cylinders, and at least one of the plurality of cylinders is provided.
Exhaust gas from the specified cylinder is introduced into the exhaust supercharger without being introduced into the exhaust purification catalyst, and then introduced into the NOx absorption catalyst,
After the exhaust gas from the cylinders other than the specific cylinder is introduced into the exhaust purification catalyst, the exhaust gas is introduced into the exhaust supercharger, and then the NO.
An internal combustion engine is designed to be introduced into the x-absorption catalyst.

According to this configuration, the NOx absorption catalyst is caused by the fact that the exhaust gas cannot achieve a good temperature rise due to the heat capacity of the exhaust turbocharger (exhaust turbocharger, complex supercharger, etc.). Increase in emissions of exhaust harmful components (especially HC and CO) due to delay in activation of
By providing the exhaust purification catalyst, the exhaust gas can be suppressed, and in the exhaust supercharger, the exhaust gas from the specific cylinder and the exhaust gas from the cylinders other than the specific cylinder can be satisfactorily mixed. The separation / reduction treatment can be performed more favorably.

That is, it can be said that the use value of the present invention can be further enhanced when the exhaust supercharger is provided, as compared with the case where the exhaust supercharger is not provided. According to the third aspect of the present invention, at least one of the specific cylinders is controlled by the specific cylinder air-fuel ratio control means as shown by a broken line in FIG.
When the air-fuel ratio of the intake air-fuel mixture is enriched only for the cylinders, the output air-fuel ratio of the intake air-fuel mixture is enriched. I did it.

With this configuration, it is possible to suppress an increase in the output of a cylinder whose air-fuel ratio is enriched, and it is possible to suppress a variation in output from other cylinders.
While effectively performing the NOx desorption / reduction process, it also suppresses the vehicle longitudinal shock (output shock) and the vibration / noise of the internal combustion engine that may occur with the start of the air-fuel ratio enrichment process. Thus, it is possible to maintain good operability.

The output suppression control means includes ignition timing retard control, swirl suppression (over-swirl in some cases) control, and fuel injection rate reduction control. Further, according to the invention as set forth in claim 5, a plurality of cylinders are provided, and exhaust gas from at least one specific cylinder among the plurality of cylinders is introduced into the NOx absorption catalyst without being introduced into the exhaust purification catalyst. The control device for an internal combustion engine, wherein the exhaust gas from the cylinder is introduced into the exhaust purification catalyst and then into the NOx absorption catalyst.
Includes stoichiometric control means for controlling the exhaust air-fuel ratio of cylinders other than the specific cylinder to stoichiometric when the exhaust air-fuel ratio of the specific cylinder is enriched in order to perform the desorption / reduction processing of NOx absorbed by the x-absorption catalyst. It was made to consist of.

With this configuration, the same operation and effect as those of the first aspect of the present invention can be more effectively achieved, and the number of opportunities for performing the enrichment process can be increased. It is possible to reduce the amount of NOx absorbed by the absorption catalyst, and further reduce the chance of performing the enrichment process during lean operation, that is, further reduce the adverse effects on drivability and exhaust performance and fuel efficiency. Can be.

[0014]

According to the first aspect of the present invention, the NOx absorption catalyst is effectively prevented while suppressing wasteful consumption of fuel (improvement of fuel efficiency) and deterioration of the exhaust purification catalyst as in the prior art. NOx desorption / reduction treatment can be performed. According to the second aspect of the present invention, the NOx desorption / reduction process can be performed more favorably.
The utility value of the present invention can be further enhanced.

According to the third aspect of the present invention, the output variation between the cylinders can be suppressed, so that good operability can be maintained. According to the fourth aspect of the invention, it is possible to perform highly accurate output suppression control with a relatively simple configuration without significantly deteriorating flammability.
According to the fifth aspect of the invention, the same operation and effect as those of the first aspect of the invention can be more effectively achieved, and further, the chance of performing the enrichment processing can be increased. In addition, the amount of NOx absorbed by the NOx absorption catalyst can be kept low, which further reduces the opportunity for performing the enrichment process during lean operation, that is, the adverse effect on drivability and the exhaust performance and fuel efficiency. can do.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 showing the first embodiment of the present invention shows a V-type internal combustion engine 1 including an exhaust turbocharger 5 to which the present invention is applied. Right bank (RH) of V-type internal combustion engine (hereinafter also simply referred to as internal combustion engine) 1
A three-way catalyst 3 is disposed in the exhaust passage 2 as an exhaust gas purifying catalyst, and is joined to the left bank (LH) exhaust passage 4 on the downstream side of the exhaust gas. Note that the three-way catalyst 3 may be an oxidation catalyst. That is, the exhaust purification catalyst according to the present invention corresponds to the three-way catalyst (or oxidation catalyst) 3, in other words, a catalyst capable of oxidizing at least HC and CO in exhaust gas.

Then, the combined exhaust gas is introduced into an exhaust turbine (not shown) of the exhaust turbocharger 5, and the exhaust turbine is rotated at an exhaust flow pressure, whereby
The compressor (not shown), which is coaxially connected to the internal combustion engine and is interposed in the intake passage, is rotationally driven to reduce the intake air to the internal combustion engine 1.
Pressure supply (supercharging). The pre-catalyst ｛NO is provided in the exhaust passage 6 on the exhaust turbine outlet side of the exhaust turbocharger 5.
An x-absorption catalyst (NOx absorbent + three-way catalyst) # 7 is interposed, and an underfloor catalyst (three-way catalyst) is provided downstream of the exhaust gas.
8 are interposed. The three-way catalyst oxidizes and removes HC and CO in the vicinity of the stoichiometric air-fuel ratio, and reduces NOx.
Is reduced and removed.

When the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the NOx absorbing catalyst 7 absorbs NOx in the exhaust gas (by the NOx absorbent), and the exhaust air-fuel ratio becomes higher than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio. Is also rich when the absorbed N
Ox is released for reduction (with a catalyst). As shown in FIG. 3, while the intake air amount of the internal combustion engine 1 is controlled by a throttle valve 9, each cylinder of the internal combustion engine 1 is provided with a fuel injection valve 10 for injecting fuel into a combustion chamber. The air-fuel mixture is formed in the combustion chamber by the fuel injection by the fuel injection valve 10. The fuel injection valve 10
Is a configuration that directly injects and supplies fuel to the combustion chamber, and may be an engine that performs stratified lean combustion.

Here, the internal combustion engine 1 according to the present embodiment
Is capable of performing homogeneous lean combustion (including stratified lean combustion in the case of direct fuel injection and supply to the combustion chamber). In the engine control unit 50 incorporating a microcomputer, the target air-fuel ratio The fuel injection amount of the fuel injection valve 10 is controlled to form an air-fuel mixture (in the case of stratified lean combustion, the injection timing is also controlled).

The mixture formed by the fuel injection from the fuel injection valve 10 is ignited and burned by spark ignition by a spark plug. The crankshaft (or camshaft) is provided with a crank angle sensor 11, and the control unit 50 counts a crank unit angle signal output from the crank angle sensor 11 in synchronization with the engine rotation for a certain period of time. Alternatively, the engine rotation speed Ne can be detected by measuring the cycle of the crank reference angle signal.

Incidentally, the control unit 50
Comprises a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, a timer, and the like.
, Input signals from various sensors are input. The various sensors include, in addition to the crank angle sensor 11, an air flow meter 1 that detects an intake air flow rate Qa of the internal combustion engine 1.
2, a water temperature sensor 13 for detecting a cooling water temperature TW of the internal combustion engine 1, an air-fuel ratio sensor 14 for detecting an exhaust air-fuel ratio between the NOx absorption catalyst 7 and the underfloor catalyst 8, and the like.

The air-fuel ratio sensor 14 is a sensor capable of detecting the exhaust air-fuel ratio over a wide range based on the oxygen concentration in the exhaust gas, and is capable of obtaining a larger output value as the exhaust air-fuel ratio is richer. Can be. The air-fuel ratio sensor 14 may output a rich / lean signal with respect to a stoichiometric air-fuel ratio based on the oxygen concentration in the exhaust gas.

As described above, the NOx absorption catalyst 7 is
During lean combustion, NOx is absorbed and NOx is not desorbed and reduced, so when the NOx absorption amount reaches a saturation amount, NOx discharged from the internal combustion engine 1 is directly discharged without being purified. (Three-way catalyst does not work well during lean). Therefore, when the lean combustion continues and the NOx absorption amount reaches the saturation amount, the air-fuel ratio is temporarily made rich, and the desorbed and reduced NOx absorbed up to that time is performed, and the NOx absorption capacity is increased. Need to be resurrected.

For this reason, the control unit 50 in this embodiment gives a rich spike (or rich shift) for the desorption / reduction as shown in the flowchart of FIG. As described below, the functions of the specific cylinder air-fuel ratio control unit and the output suppression control unit according to the present invention are provided in the control unit 50 by software.

In the flowchart of FIG. 4, first, in step 1 (indicated as S1 in the figure, the same applies hereinafter), it is determined whether or not the internal combustion engine 1 is currently performing lean combustion. If the determination is YES, the process proceeds to S2. If the determination is NO, the air-fuel ratio feedback control (λ control) is performed based on the detection result of the normal air-fuel ratio sensor 14 so that the actual exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio. This flow ends.

In step 2, it is determined whether or not conditions for causing the NOx absorption catalyst 7 to desorb and reduce NOx are satisfied. The desorption / reduction conditions are, for example, when lean combustion is being performed and the NOx absorption amount estimated from the engine load and the engine speed has reached a predetermined saturation amount.

When the desorption / reduction conditions are satisfied, the routine proceeds to step 3, where the air-fuel ratio of the combustion mixture is enriched, and the desorption / reduction of NOx absorbed by the NOx absorption catalyst 7 is performed. In order to perform the reduction, the fuel injection amount increase correction (rich spike or rich shift) is started. In the present embodiment, since the three-way catalyst 3 is interposed in the right bank (RH) exhaust passage 2, the air-fuel ratio of the cylinder on the right bank (RH) side is made rich. However, the NO absorbed in the NOx absorption catalyst 7
This is not effective for the desorption / reduction treatment of x, and may lead to deterioration of fuel efficiency or deterioration of the three-way catalyst 3.

Therefore, in this embodiment, the right bank (R
No air-fuel ratio enrichment is performed for the cylinder on the H) side.
Only for the cylinders on the left bank (LH) side (specific cylinders, or at least one of the left bank side cylinders), the fuel injection amount is increased (for example, increased in advance according to the operating state, etc.). Correction amount), that is, enrichment of the air-fuel ratio, thereby suppressing deterioration of fuel efficiency and deterioration of the three-way catalyst 3, and effectively desorbing and removing NOx absorbed by the NOx absorption catalyst 7. A reduction treatment is performed.

The fuel injection amount may be increased at a fixed rate until the stop condition of the increase correction is detected in step 5 described later. In the next step 4, the output of the air-fuel ratio sensor 14 after the start of the increase correction is monitored to determine whether or not the rich spike (or the rich shift amount) has reached a predetermined value. Note that it may be determined whether a predetermined time has elapsed since the start of the rich spike (rich shift), or whether the output of the air-fuel ratio sensor 14 is a rich output or the output of the air-fuel ratio sensor 14 is It is also possible to determine whether or not a predetermined time has elapsed since the output became rich.

That is, whether a rich spike (or a rich shift) that can complete the desorption / reduction process of the NOx absorbed in the NOx absorption catalyst 7 successfully can be provided. It is only necessary to determine whether or not the desorption / reduction processing of the NOx absorbed in 7 has been completed (terminated). If the determination is YES, the process proceeds to step 5, where the rich spike (or rich shift) for the cylinder on the left bank (LH) side started in step 3 is canceled (fuel increase correction is stopped) and the original lean operation is started. Return to the combustion state (all cylinders lean).

If NO, the process returns to step 4. As described above, according to the present embodiment, the pre-catalyst (NO
x Delay of activation of the absorption catalyst 7 and the underfloor catalyst (three-way catalyst) 8 (a good temperature rise cannot be achieved by exhaust due to the long exhaust passage or the heat capacity of the turbocharger 5). For example, in order to suppress an increase in emissions of exhaust harmful components (especially, HC and CO) caused by the
H) and the three-way catalyst 3 in the exhaust passage 2 between the turbocharger 5
When the lean combustion continues and the NOx absorption amount of the pre-catalyst (NOx absorption catalyst) 7 reaches the saturation amount in the internal combustion engine, the cylinder group on the exhaust upstream side of the three-way catalyst 3 (right While the air-fuel ratio is not enriched with respect to the three-way catalyst 3 and the three-way catalyst 3 is maintained in a lean combustion state, the left bank cylinder group (specific cylinder) which is not on the exhaust upstream side of the three-way catalyst 3
The defueling / reducing process of the NOx absorbed by the pre-catalyst (NOx absorbing catalyst) 7 is performed by enriching the air-fuel ratio only for the Improvement), deterioration of the three-way catalyst 3, etc., while effectively performing the NOx desorption / reduction treatment (see FIG. 10).

As shown in the flowchart of FIG. 5, during the rich shift control of the air-fuel ratio of the combustion mixture to the cylinder group (specific cylinder) on the left bank side in step 3 of the flowchart of FIG. The ignition timing may be retarded for a certain cylinder. Such a processing operation corresponds to output suppression control means according to the present invention.

With this configuration, it is possible to suppress an increase in the output of the cylinder in which the air-fuel ratio is richly shifted.
Since the output variation with other cylinders maintained in the lean combustion state can be suppressed, the desorption / reduction process of NOx can be effectively performed, and the air-fuel ratio enrichment process is started. The vehicle longitudinal shock (output shock) and the vibration and noise of the internal combustion engine, which may occur, can be suppressed, and the engine operability can be maintained satisfactorily.

Not only the ignition timing retard, but also a control capable of suppressing the output, for example, a swirl suppression (in some cases, an overswirl) control, a fuel injection rate reduction control, an injection timing retard control (fuel atomization). As a result, control for lowering the mixing of fuel and air may be performed. Further, these output suppression controls may be performed alone or in combination as appropriate.

Next, a second embodiment of the present invention will be described. In the second embodiment, the flowchart of FIG. 6 is executed instead of the flowchart of FIG. 4 in the first embodiment. Note that other configurations are the same as those of the first embodiment, and a description thereof will not be repeated. That is, in the second embodiment, the control unit 50 performs the rich spike (or rich shift) processing for the desorption / reduction as shown in the flowchart of FIG. That is, as described below, the functions of the specific cylinder air-fuel ratio control unit, the output suppression control unit, and the stoichiometric control unit according to the present invention are provided by the control unit 50 as software.

In this embodiment, the three-way catalyst 3
Simply giving a rich shift to a specific cylinder that is not on the exhaust upstream side of the exhaust gas (exhaust gas is not introduced into the three-way catalyst 3) will result in NOx
This is an example of a case where there is a possibility that the exhaust air-fuel ratio cannot be made rich enough to perform the desorption / reduction processing of NOx absorbed in the absorption catalyst 7. That is, NOx
If a rich spike (or rich shift) is applied only to a specific cylinder as in the first embodiment in order to enrich the exhaust air-fuel ratio sufficient to perform the desorption / reduction processing of the specific cylinder, In some cases, it is necessary to make the air-fuel ratio excessively rich, so that the combustion of the specific cylinder becomes excessively deteriorated, which may rather deteriorate the drivability, the exhaust performance, the exhaust black smoke concentration, and the like ( If the enrichment exceeds a certain level, the combustion stability, the exhaust performance, the exhaust black smoke concentration, etc. of the cylinder may be exponentially deteriorated).

Therefore, in the present embodiment, as described below, when a rich shift is given to a specific cylinder, other cylinders (all the first to fifth cylinders, or at least one of these cylinders. , The same), the air-fuel ratio is operated in the rich direction (stoichiometric air-fuel ratio). That is, in the flowchart of FIG. 6, first, at step 11, similarly to S1 of the flowchart of FIG. 4, it is determined whether or not the internal combustion engine 1 is currently performing lean combustion.
If ES, proceed to S12; if NO, step 1
Proceed to 7.

In step 12, the NOx absorption amount is estimated from the engine load and the engine speed by the same method as in the prior art. In step 13, it is determined whether or not the estimated NOx absorption amount is the saturated absorption amount. YE
If S, NOx needs to be desorbed / reduced. If NO, at this stage
It is determined that there is no need to perform the NOx desorption / reduction treatment yet, and this flow ends.

In step 14, the fuel injection amount is increased with respect to the specific cylinder in order to make the air-fuel ratio of the combustion air-fuel mixture rich and perform the desorption and reduction of the NOx absorbed by the NOx absorption catalyst 7. Correction (rich spike or rich shift) is started. Further, in this embodiment, the air-fuel ratios of the other cylinders (first to fifth cylinders) are stoichiometrically controlled in order to suppress the occurrence of an adverse effect when a rich spike (or rich shift) is given only to a specific cylinder. To do. Such a processing operation corresponds to a stoichiometric control unit according to the present invention.

The fuel injection amount can be increased at a constant rate until the stop condition of the increase correction is detected in step 15 described later. In the next step 15, the output of the air-fuel ratio sensor 14 after the start of the increase correction is monitored to determine whether or not the rich spike (or the rich shift amount) has become a predetermined value. Note that it may be determined whether a predetermined time has elapsed since the start of the rich spike (rich shift), or whether the output of the air-fuel ratio sensor 14 is a rich output or the output of the air-fuel ratio sensor 14 is It is also possible to determine whether or not a predetermined time has elapsed since the output became rich.

That is, whether a rich spike (or a rich shift) that can complete the desorption / reduction process of the NOx absorbed in the NOx absorption catalyst 7 successfully can be given (and, consequently, the NOx absorption catalyst). 7 has been completed). If YES, step 1
Proceed to 6 to return to the original lean combustion state (all cylinders lean).

If NO, the process returns to step S14. In step 17, it is determined whether or not the operation has been switched from the lean operation to the stoichiometric operation due to a change in the operation state or the like. If YES, the process proceeds to step 18, and if NO, the present flow is terminated. In step 18, the amount of NOx absorption during the previous lean operation is estimated.

In step 19, the currently absorbed NOx is determined based on the NOx absorption amount estimated in step 18.
A rich spike (rich shift) is set such that the desorption / reduction processing of the cylinder can be satisfactorily completed, and while this is given to a specific cylinder, the other cylinders are operated in stoichiometric operation. In addition,
The processing operation for causing the other cylinder to perform the stoichiometric operation corresponds to a stoichiometric control unit according to the present invention.

That is, when shifting from the lean operation to the stoichiometric operation due to an increase in the required torque or the like, regardless of whether the NOx absorption amount has become the saturated absorption amount during the previous lean operation,
Shift to stoichiometric operation while giving a predetermined rich shift. In this manner, the rich shift can be satisfactorily provided without affecting the drivability (without giving a sense of incongruity to the driver), and the chance of giving the rich shift can be increased. Therefore, there is an advantage that it is possible to reduce the chances of giving a rich shift during lean operation (that is, adverse effects on drivability and exhaust performance, fuel efficiency, etc.). .

In step 20, it is determined whether or not the NOx desorption / reduction process has been completed by the same method as described above. If YES, the process proceeds to step 21, the rich shift for the specific cylinder is released, all-cylinder stoichiometric operation is performed, and this flow ends. If NO, the process returns to step S19.

As described above, according to the second embodiment, the same operation and effect as the first embodiment can be obtained while further suppressing the influence on the drivability (discomfort to the driver). In addition to being able to play more effectively,
In addition, since the chance of giving a rich shift can be increased, the NOx absorption amount can be kept low. As a result, the opportunity of giving a rich shift during lean operation, that is, adverse effects on drivability, exhaust performance, The adverse effect on fuel efficiency and the like can be further reduced.

By the way, as shown in the flowchart of FIG. 7, the flowchart of FIG.
19A, 16A, and 21A are added to retard the ignition timing during the air-fuel ratio rich shift processing in steps 14 and 19, and release the air-fuel ratio rich shift processing and the ignition timing retard after completion of desorption. It can also be done. In particular, step 14
In A, since the retard amount of the specific cylinder is set larger than that of the other cylinders, the torque of each cylinder can be made uniform. Steps 14A and 19A for retarding the ignition timing in the flowchart of FIG. 7 correspond to the output suppression control means of the present invention.

By doing so, output variations (or output steps) can be suppressed, and therefore NOx
While effectively performing the desorption / reduction process of the vehicle, and at the same time, suppresses the vehicle longitudinal shock (output shock) and the vibration and noise of the internal combustion engine that may occur with the start of the air-fuel ratio enrichment process. As a result, it is possible to maintain good engine operability.

Not only the ignition timing retard but also an output that can suppress the output, for example, a swirl control (in some cases, an overswirl) control, a fuel injection rate reduction control, an injection timing retard control (fuel atomization). As a result, control for lowering the mixing of fuel and air may be performed. Further, these output suppression controls may be performed alone or in combination as appropriate.

Next, a third embodiment of the present invention will be described. In the third embodiment, as shown in FIG.
With respect to the system configuration in the embodiment, after the exhaust from the fourth cylinder and the fifth cylinder passes through the three-way catalyst 15,
The exhaust gas from the sixth cylinder is merged with the exhaust gas. That is, a three-way catalyst 15 as an exhaust purification catalyst is interposed in an exhaust passage between the fifth cylinder and the sixth cylinder. Other configurations are the same as those shown in FIGS. 2 and 3, and therefore, the same reference numerals are given and the description is omitted.

In the third embodiment, the control unit 50 gives a rich spike (or rich shift) for the desorption / reduction as shown in the flowchart of FIG. In the present embodiment, the specific cylinder that is not on the exhaust gas upstream side of the three-way catalyst 3 or the exhaust catalyst 15 (exhaust gas is not introduced into the three-way catalyst 3 or the exhaust catalyst 15) is only the sixth cylinder. There is a high possibility that the exhaust air-fuel ratio cannot be made rich enough to perform the desorption / reduction processing of NOx absorbed in the absorption catalyst 7. That is, when a rich spike (or rich shift) is given only to the sixth cylinder, the air-fuel ratio of the sixth cylinder may need to be excessively rich, so that the combustion of the sixth cylinder is excessively deteriorated. On the contrary, the drivability, the exhaust performance, the exhaust black smoke concentration, etc. may be deteriorated. (If the enrichment exceeds a certain level, the combustion stability, the exhaust performance, the exhaust black smoke concentration, etc. of the cylinder will become worse. Exponentially worse).

Therefore, in the present embodiment, as described below, at the time of the rich shift with respect to the sixth cylinder, the air-fuel ratio is operated in the rich direction also for the other cylinders (first to fifth cylinders). It has become. That is, in the flowchart of FIG. 9, first, at step 31, it is determined whether or not the internal combustion engine 1 is currently performing lean combustion as described above.
If S, proceed to S32; if NO, step 37
Proceed to.

In step 32, the NOx absorption amount is estimated from the engine load, the engine speed and the like by the same method as in the prior art. In step 33, it is determined whether or not the estimated NOx absorption amount is the saturated absorption amount. YE
If it is S, the process proceeds to step 34 because the NOx needs to be desorbed and reduced. If NO, at this stage
It is determined that there is no need to perform the NOx desorption / reduction treatment yet, and this flow ends.

In step 34, the air-fuel ratio of the combustion air-fuel mixture is made rich, and the amount of fuel injected into the sixth cylinder is reduced in order to perform the desorption and reduction of NOx absorbed by the NOx absorption catalyst 7. The increase correction (rich spike or rich shift) is started. Further, in the present embodiment, the air-fuel ratios of the other cylinders (first to fifth cylinders) are stoichiometrically controlled in order to suppress the occurrence of an adverse effect when a rich spike (or rich shift) is given only to the sixth cylinder. I do.
Such a processing operation corresponds to a stoichiometric control unit according to the present invention.

It should be noted that the fuel injection amount can be increased at a fixed rate until the stop condition of the increase correction is detected in step 35 described later. Then, in step 34A, the ignition timing is retarded for all cylinders in order to suppress output variations (or output steps). At this time, the specific cylinder (sixth cylinder) has a greater degree of enrichment as compared with the other cylinders (first to fifth cylinders), so that the output increase margin is also large, so that the specific cylinder (sixth cylinder) is ignited. It is preferable that the timing retard amount is set to be larger than the ignition timing retard amounts of the other cylinders (first to fifth cylinders).

In the next step 35, it is determined whether or not the desorption / reduction process of NOx absorbed in the NOx absorption catalyst 7 has been successfully completed. When the determination is YES, the process proceeds to step 36, where the engine is returned to the original lean combustion state (all cylinders lean), and the retard control of the ignition timing is released. If NO, the process returns to step 34.

In step 37, it is determined whether or not the operation has been switched from the lean operation to the stoichiometric operation due to a change in the operation state or the like. If yes, step 3
Then, if NO, the flow ends. In step 38, the amount of NOx absorbed during the previous lean operation is estimated. In step 39, the NOx estimated in step 38
Based on the absorbed amount, the desorption of NOx currently absorbed
A rich spike (rich shift) is set such that the reduction process can be completed satisfactorily, and the other cylinders are stoichiometrically operated while giving the rich spikes to the sixth cylinder. The processing operation for causing the other cylinder to perform the stoichiometric operation corresponds to the stoichiometric control unit according to the present invention.

That is, when shifting from the lean operation to the stoichiometric operation due to an increase in the required torque (load) or the like, regardless of whether the NOx absorption amount has become the saturated absorption amount during the previous lean operation, Shift to stoichiometric operation while giving a rich shift of. In this manner, the rich shift can be satisfactorily provided without affecting the drivability (without giving a sense of incongruity to the driver), and the chance of giving the rich shift can be increased. Therefore, there is an advantage that it is possible to reduce the chances of giving a rich shift during lean operation (that is, adverse effects on drivability and exhaust performance, fuel efficiency, etc.). .

In step 39A, the ignition timing is retarded for the specific cylinder (sixth cylinder) in order to suppress the output variation (or the output step). In addition,
In addition to the ignition timing retard, if the output can be suppressed, for example, a swirl suppression (or overswirl in some cases) control, a reduction control of the fuel injection rate or an injection timing retard control (the atomization of the fuel, Control for lowering the mixing of air) may be used. Further, these output suppression controls may be performed alone or in combination as appropriate. Step 39A
Corresponds to the output suppression control means of the present invention.

In step 40, it is determined whether or not the NOx desorption / reduction process has been completed by the same method as described above. If YES, the process proceeds to step 41, in which the rich shift for the specific cylinder (the sixth cylinder) is released, and the retard control of the ignition timing is released to shift the specific cylinder (the sixth cylinder) to the stoichiometric operation. The cylinder stoichiometric operation is performed, and this flow ends. If NO, the process returns to step 39.

As described above, according to the third embodiment, the pre-catalyst (NOx absorption catalyst) 7 and the underfloor catalyst (three-way catalyst) 8
Harmful components (especially, H) due to the activation delay of the exhaust gas (a good exhaust gas temperature cannot be achieved due to the long exhaust passage or the heat capacity of the turbocharger 5).
For example, in order to suppress an increase in the emission amount of C, CO), for example, the exhaust passage 2 between the right bank (RH) and the turbocharger 5
In the internal combustion engine in which the three-way catalyst 3 is provided and the three-way catalyst 15 is provided in the exhaust passage between the fifth cylinder and the sixth cylinder, lean combustion continues and the pre-catalyst (NOx absorption catalyst) When the NOx absorption amount of No. 7 reaches the saturation amount, the air-fuel ratio enrichment process is performed on the sixth cylinder (cylinder not on the exhaust upstream side of the three-way catalyst 3 or the three-way catalyst 15; specific cylinder). At the same time, the air-fuel ratio is stoichiometrically controlled for the other cylinders, and the desorption / reduction processing of the NOx absorbed by the pre-catalyst (NOx absorption catalyst) 7 is performed. It is feared that the combustion of the sixth cylinder is excessively deteriorated, as in the case where a rich spike (or rich shift) is given only to the cylinder, and the driving performance, exhaust performance, exhaust black smoke concentration, etc. are rather deteriorated. Maximum waste It is possible to effectively perform the NOx desorption / reduction process while suppressing the consumption of fuel (improvement of fuel efficiency), the deterioration of the three-way catalyst 3 and the three-way catalyst 15, and the like.

Further, at the time of the transition from the lean operation to the stoichiometric operation, regardless of whether the NOx absorption amount becomes the saturated absorption amount during the previous lean operation, the operation is shifted to the stoichiometric operation while giving a predetermined rich shift. In addition, since the rich shift can be satisfactorily given while further suppressing the influence on the driving performance (uncomfortable feeling for the driver), and the chance of giving the rich shift can be increased, the NOx can be improved.
The amount of absorption can be kept low, and the chance of giving a rich shift during lean operation, that is, adverse effects on drivability, exhaust performance, fuel efficiency, and the like can be further reduced.

Further, since the ignition timing is retarded during the air-fuel ratio enrichment processing, the output variation (or the output step) can be suppressed.
While effectively performing the desorption / reduction treatment of x, and
The vehicle longitudinal shock (output shock) and the vibration and noise of the internal combustion engine, which may occur with the start of the air-fuel ratio enrichment process, can be suppressed, and the engine operability can be maintained satisfactorily.

The three-way catalyst 3 and the three-way catalyst 15
The catalyst is not limited to a catalyst supported on a carrier separate from the exhaust passage. For example, a catalyst layer may be coated on the inner surface of the exhaust passage (exhaust manifold or the like).
In each of the above embodiments, the case where the turbocharger 5 is provided has been described. However, the present invention is not limited to this. Instead of the turbocharger 5, a so-called complex supercharger ｛exhaust gas is used. The present invention can be applied to a case where a supercharger 利用 utilizing a pressure wave (pressure wave) is used, and also to an internal combustion engine in which the turbocharger 5 in FIGS. 2 and 8 is omitted.

In this case, although the mixing performance of the exhaust from the enriched cylinder and the exhaust from the other cylinders is slightly lowered, the exhaust passage 2 from the right bank (RH) and the left It is also possible to connect to the pre-catalyst 7 without merging with the exhaust passage 4 from the bank (LH). Further, for example, after connecting to the pre-catalyst 7, the exhaust from the exhaust passages 2 and 4 may be combined within the case of the pre-catalyst 7.

When the turbocharger 5 and the like are provided, the pre-catalyst (NOx absorption catalyst) can not be heated due to the heat capacity of the turbocharger 5. ) 7 and the delay of activation of the underfloor catalyst (three-way catalyst) 8 can suppress an increase in the emission of exhaust harmful components (especially, HC and CO) and the like. The exhaust from the selected cylinder and the exhaust from other cylinders can be satisfactorily mixed.
This has the advantage that the desorption / reduction treatment can be performed more favorably. That is, it can be said that the use value of the present invention can be further enhanced when the turbocharger 5 is provided, as compared with the case where the turbocharger 5 is not provided.

The present invention is not limited to the V-type engine,
The same applies to horizontally opposed engines. In addition, the present invention divides the cylinders of the engine into a plurality of cylinder groups in the in-line type engine and emits NOx for each cylinder group.
The present invention can be similarly applied to a case where a three-way catalyst is interposed between any one of the cylinder groups and the NOx absorption catalyst while leaving at least one cylinder group by leading to the absorption catalyst.

Further, as described above, the present invention can be similarly applied to a case where a turbocharger is not provided. That is, what has been described in each of the above embodiments is an example, and the present invention
It is not limited to this. That is, the present invention includes a plurality of cylinders, and allows the exhaust gas from at least one specific cylinder of the plurality of cylinders to be introduced into the NOx absorption catalyst without being introduced into the exhaust purification catalyst, and the exhaust gas from the cylinders other than the specific cylinder to be exhausted. Is introduced into the exhaust purification catalyst and then into the NOx absorption catalyst (including not including an exhaust supercharger, a horizontally opposed or in-line engine, and The present invention is also applicable to a case where exhaust gas and exhaust gas from a cylinder other than the specific cylinder are not merged before introducing the NOx absorption catalyst.) At least one of the specific cylinders (this cylinder is the first embodiment) The present invention is not limited to the specific cylinder described in the second embodiment, but may be any cylinder as long as it satisfies the requirements for the specific cylinder.
The air-fuel ratio of the intake air-fuel mixture is enriched to make the exhaust air-fuel ratio rich,
The present invention can be applied to all the devices that perform the desorption / reduction process of NOx absorbed by the NOx absorption catalyst.

[Brief description of the drawings]

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

FIG. 2 is a system configuration diagram (part 1) according to the first embodiment of the present invention;

FIG. 3 is a system configuration diagram (part 2) according to the first embodiment of the present invention;

FIG. 4 is a flowchart for explaining NOx desorption control and air-fuel ratio control according to the embodiment.

FIG. 5 is a flowchart for explaining output suppression control according to the embodiment;

FIG. 6 is a flowchart for explaining NOx desorption control and air-fuel ratio control according to a second embodiment of the present invention.

FIG. 7 is a flowchart for explaining NOx desorption control, air-fuel ratio control, and output suppression control according to the embodiment.

FIG. 8 is a system configuration diagram according to a third embodiment of the present invention.

FIG. 9 is a flowchart for explaining NOx desorption control, air-fuel ratio control, and output suppression control according to the embodiment.

FIG. 10 is a timing chart illustrating the operation and effect according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 2 exhaust passage (for right bank) 3 three-way catalyst (exhaust purification catalyst) 4 exhaust passage (for left bank) 5 turbocharger 7 precatalyst (NOx absorption catalyst) 8 underfloor catalyst 9 throttle valve 10 fuel injection Valve 11 Crank angle sensor 12 Air flow meter 50 Control unit

──────────────────────────────────────────────────の Continuation of front page (51) Int.Cl. ⁶ Identification code FI F02D 41/04 ZAB F02D 41/04 ZAB 305 305A 43/00 301 43/00 301E 301B

Claims (5)

[Claims] An exhaust system comprising a plurality of cylinders, wherein exhaust gas from at least one specific cylinder among the plurality of cylinders is introduced into a NOx absorption catalyst without being introduced into an exhaust purification catalyst, and exhaust gas from a cylinder other than the specific cylinder is exhausted. A control device for an internal combustion engine, which is introduced into the exhaust purification catalyst and then introduced into the NOx absorption catalyst, wherein during lean combustion, the exhaust air-fuel ratio is enriched and the NOx is reduced.
When performing the desorption / reduction processing of NOx absorbed by the absorption catalyst, the air-fuel ratio of the intake air-fuel mixture is made rich only in at least one of the specific cylinders, and the exhaust air-fuel ratio is made rich. A control device for an internal combustion engine, comprising a specific cylinder air-fuel ratio control means. 2. An internal combustion engine comprising a plurality of cylinders, wherein exhaust gas from at least one specific cylinder among the plurality of cylinders is introduced into an exhaust supercharger without being introduced into an exhaust purification catalyst, and then the NOx absorbing catalyst is introduced. After the exhaust from the cylinders other than the specific cylinder is introduced into the exhaust purification catalyst, the exhaust gas is introduced into the exhaust supercharger, and then the NO.
The control device for an internal combustion engine according to claim 1, wherein the control device is an internal combustion engine that is introduced into an x-absorption catalyst. 3. When the air-fuel ratio of the intake air-fuel mixture is enriched only in at least one of the specific cylinders by the specific cylinder air-fuel ratio control means, the air-fuel ratio of the intake air-fuel mixture is increased. The control device for an internal combustion engine according to claim 1 or 2, further comprising output suppression control means for performing output suppression control on a cylinder to be enriched. 4. The output suppression control means includes means for retarding the ignition timing of a cylinder whose air-fuel ratio of the intake air-fuel mixture is enriched.
A control device for an internal combustion engine according to any one of claims 1 to 3. 5. An exhaust system comprising a plurality of cylinders, wherein exhaust gas from at least one specific cylinder among the plurality of cylinders is introduced into a NOx absorption catalyst without being introduced into an exhaust purification catalyst, and exhaust gas from a cylinder other than the specific cylinder is exhausted. A control device for an internal combustion engine, which is introduced into the exhaust purification catalyst and then introduced into the NOx absorption catalyst, wherein a specific cylinder is provided for performing a desorption / reduction process of NOx absorbed by the NOx absorption catalyst. A stoichiometric control means for stoichiometrically controlling the exhaust air-fuel ratio of a cylinder other than the specific cylinder when enriching the exhaust air-fuel ratio of the internal combustion engine.