JP2001115827A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress NOx reduction treatment to the minimum, and improve fuel consumption performance while achieving an intended NOx purifying performance by estimating a NOx absorbing quantity of a NOx absorbing catalyst on a downstream side of an exhaust system in an internal combustion engine capable of operating in a lean condition with a good efficiency on the basis of a purifying ratio of a selective reduction catalyst of the upstream side, in a device wherein the selective reduction catalyst is arranged on the upstream side and the NOx absorbing catalyst is disposed on the downstream side. SOLUTION: A NOx delivery quantity X of an engine, and an FNOMPL (D) are calculated from engine rotating speed by a map retrieval (S16, S18), a NOx purifying ratio is calculated from a catalyst temperature TCAT by a table retrieval (S22), it is corrected by a target air-fuel ratio KCMD (S24), a NOx adsorbing quantity Q. NOx is calculated (S26), an integrated value ΣQ.NOx is calculated (S28), it is compared with a prescribed value, and then, it is judged whether a NOx reduction treatment is carried out or not (S30 to S34).

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 system in which two types of NOx purifying catalysts are arranged in series, and a downstream NOx purifying catalyst is provided based on a purifying efficiency of an upstream catalyst. In which the NOx adsorption amount of the catalyst is accurately calculated to improve fuel efficiency.

[0002]

2. Description of the Related Art In recent years, lean air-fuel ratios such as lean-burn engines or direct-injection engines have been developed, and it is desired to further improve the purification performance of NOx (nitrogen oxide) components in an oxidizing atmosphere. Japanese Patent Laid-Open Publication No.
The technique described in Japanese Patent Publication No. 2508 can be mentioned.

[0003] In this prior art, in an exhaust gas purifying apparatus for an internal combustion engine capable of lean operation, a zeolite type NOx catalyst in which a transition metal is supported on zeolite is arranged in an exhaust system of the internal combustion engine, and downstream of the NOx catalyst. To
NOx when the air-fuel ratio of the inflowing exhaust gas is lean
When the oxygen concentration in the inflowing exhaust gas decreases, the NOx absorbent (NO
x adsorption catalyst).

That is, in this prior art, the NOx adsorbing catalyst (NOx absorbent) has to saturate the NOx adsorbing performance in a short period of time and must supply a reducing agent (HC (hydrocarbon) or the like) frequently. In order to eliminate the inconvenience, a zeolite-based NOx catalyst is provided upstream of the NOx catalyst, NOx is reduced and purified by the NOx catalyst at a lean air-fuel ratio, and the remaining NOx is adsorbed by the subsequent NOx adsorption catalyst to reduce the time until saturation. And make the NO of the downstream from the accumulated value of the engine speed.
The NOx adsorption amount of the x-adsorption catalyst is estimated, and when the accumulated value exceeds the upper limit, the NOx reduction purification process for switching the air-fuel ratio to the rich or the stoichiometric air-fuel ratio is performed.

[0005]

As described above, in the prior art, the amount of NOx adsorbed on the downstream NOx adsorbing catalyst is simply estimated from the engine speed, but the amount of NOx adsorbed fluctuates only depending on the operating state. However, it also depends on the purification rate of the upstream NOx catalyst.

Therefore, when simply estimating the NOx adsorption amount as in the prior art, it is necessary to set the upper limit value to a relatively small value and perform the NOx reduction process for enriching the air-fuel ratio with a considerable frequency. There is a disadvantage that fuel efficiency is impaired. On the other hand, when importance is placed on fuel economy performance, it becomes difficult to achieve intended NOx purification performance.

Accordingly, an object of the present invention is to provide an upstream NO
It is possible to accurately estimate the NOx adsorption amount of the downstream NOx adsorption catalyst based on the purification rate of the x catalyst and to minimize the NOx reduction process, thereby improving the fuel consumption performance while achieving the intended NOx purification performance. To provide an exhaust gas purification device for an internal combustion engine.

[0008]

In order to achieve the above object, according to the present invention, in an exhaust gas purifying apparatus for an internal combustion engine capable of lean operation, the exhaust gas purifying apparatus is disposed in an exhaust system of the internal combustion engine. NOx using HC as a reducing agent in a lean atmosphere
A selective reduction catalyst for selectively reducing NOx, a NOx adsorption catalyst for adsorbing NOx in a lean atmosphere disposed downstream of the selective reduction catalyst, and reducing NOx adsorbed at a stoichiometric air-fuel ratio or a rich air-fuel ratio lower than the stoichiometric air-fuel ratio. NOx emission calculating means for detecting an operating state of the internal combustion engine including an engine speed and a load, and calculating an NOx emission discharged from the internal combustion engine in accordance with the detected operating state, NOx purification of the selective reduction catalyst NOx to calculate rate
Purification rate calculation means, the calculated NOx emission amount and NOx
The NOx adsorption amount of the NOx adsorption catalyst based on the purification rate,
More specifically, the system includes a NOx adsorption amount calculating unit that calculates an NOx adsorption amount that would have been adsorbed by the NOx adsorption catalyst, and a NOx reduction processing unit that performs a NOx reduction process based on the calculated NOx adsorption amount. Configured.

The amount of NOx discharged from the internal combustion engine is calculated in accordance with the detected operating condition, the NOx purification rate of the selective reduction catalyst is calculated, and the NOx emission and NOx are calculated.
Based on the purification rate, the NOx adsorbing catalyst would have adsorbed N
The Ox adsorption amount is calculated, and NO is determined based on the NOx adsorption amount.
Since the configuration is such that the x reduction process is performed, the NOx reduction process can be minimized, and the fuel consumption performance can be improved while achieving the intended NOx purification performance.

[0010] In the present invention, the selective reduction catalyst is an iridium-based selective reduction catalyst.

Iridium-based selective reduction catalyst and downstream NO
Since the x adsorption catalyst has a different NOx purification function or characteristic, the purification rate can be optimized. That is, the iridium-based selective reduction catalyst on the upstream side reacts NOx with the multiple bond HC at a lean air-fuel ratio (oxidizing atmosphere) to purify NOx, and the downstream NOx adsorption catalyst adsorbs NOx at a lean air-fuel ratio. (Or occlusion), and NOx is reduced and purified by a reducing agent at a stoichiometric air-fuel ratio or a rich air-fuel ratio. As described above, since the two have different purification functions or characteristics, by combining them, the purification rate can be increased to the maximum.

An iridium-based selective reduction catalyst and NO
In both x-adsorption catalysts, the purification performance (purification rate) is maximized at around 400 ° C. at the catalyst temperature. For example, when the catalyst temperature is around that, the lean air-fuel ratio is supplied, or By controlling so that
It is also possible to increase the NOx purification rate.

Further, in the case of an iridium-based selective reduction catalyst, since the dependence on the space velocity is extremely small, the catalyst capacity can be reduced to reduce the heat capacity, which is advantageous during a cold start. . In addition, the activation of the downstream NOx adsorption catalyst can be accelerated, and the burden can be reduced.

Further, by purifying NOx with the iridium-based selective reduction catalyst on the upstream side and reducing the NOx concentration, the time until the NOx adsorption catalyst on the downstream side reaches the saturation point can be prolonged. The reduction processing time can be reduced. In that sense, fuel efficiency can be improved.

As described above, the NOx adsorption catalyst on the downstream side has an excellent NOx purification performance (adsorption performance) at a lean air-fuel ratio.
Iridium-based selective reduction catalyst and NO
By arranging the x adsorption catalysts in series, the NOx purification performance at a lean air-fuel ratio can be improved.

Further, the iridium-based selective reduction catalyst is N
Since the HC purification performance in the Ox purification temperature range is lower than that of a three-way catalyst or the like, the reduction components such as HC necessary for the downstream NOx adsorption catalyst to reduce NOx adsorbed at the stoichiometric air-fuel ratio or the rich air-fuel ratio are reduced. It can be supplied to the NOx adsorption catalyst without purification, and the NOx purification rate of the NOx adsorption catalyst can be improved at a stoichiometric air-fuel ratio or a rich air-fuel ratio.

Further, by using an iridium-based selective reduction catalyst, the durability of the catalyst itself can be improved.

According to a third aspect of the present invention, the NOx purification rate calculation means is configured to calculate the NOx purification rate of the selective reduction catalyst based on the temperature of the selective reduction catalyst.

Although the NOx purification rate of the selective reduction catalyst changes depending on its temperature, this configuration makes it possible to calculate the NOx purification rate with high accuracy, and thus to achieve the intended NOx purification rate.
x The fuel consumption performance can be further improved while achieving the purification performance.

Preferably, the NOx purification rate calculating means includes catalyst temperature calculating means for calculating a temperature of the selective reduction catalyst based on at least the detected operating state. The NOx purification rate of the selective reduction catalyst is calculated based on the temperature of the selective reduction catalyst.

Since the configuration is such that the temperature of the selective reduction catalyst is calculated based on the detected operating state, in addition to the above-mentioned effects, a temperature sensor is not required, and the configuration of the apparatus can be simplified.

According to a fifth aspect of the present invention, the NOx purification rate calculating means corrects the NOx purification rate of the selective reduction catalyst based on an air-fuel ratio supplied to the internal combustion engine.

By correcting the NOx purification rate of the selective reduction catalyst based on the air-fuel ratio supplied to the internal combustion engine, when the selective reduction catalyst has a characteristic dependent on oxygen concentration, NO
The x purification rate can be calculated with higher accuracy, and the fuel consumption performance can be further improved while achieving the intended NOx purification performance.

According to a sixth aspect of the present invention, the NOx reduction processing means includes a comparing means for comparing the calculated NOx adsorption amount with a predetermined value, and the calculated NOx adsorption amount exceeds the predetermined value. At this time, it was configured to perform the NOx reduction processing.

As a result, the execution time of the NOx reduction process can be accurately determined, and the fuel consumption performance can be further improved while achieving the intended NOx purification performance.

Further, there is provided an in-cylinder injection type spark ignition type internal combustion engine in which the internal combustion engine is operated in one of an ultra lean combustion mode and a premixed combustion mode by directly injecting gasoline fuel into a cylinder combustion chamber. , The NOx emission calculating means,
Operating mode determining means for determining in which of the operating modes the internal combustion engine is operated, and calculating an NOx emission amount discharged from the internal combustion engine according to the determined operating mode and the detected operating state It was configured so that

As a result, the NOx emission amount can be calculated with higher accuracy, and the fuel consumption performance can be further improved while achieving the intended NOx purification performance.

[0028]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention.

FIG. 1 is an overall view schematically showing the apparatus.

In the drawing, reference numeral 10 denotes an OHC in-line four-cylinder internal combustion engine (hereinafter referred to as “engine”), and intake air introduced from an air cleaner 14 disposed at the tip of an intake pipe 12 passes through a surge tank 16. Each cylinder (cylinder; only one cylinder 22 is shown) via an intake (intake) manifold 20 and two intake valves (not shown) while the flow rate is adjusted by a throttle valve 18.
Flows into.

Each of the cylinders is provided with a piston 24 movably, and a recess is formed at the top thereof. A gap is formed between the top of the piston 24 and the inner wall of the cylinder head 26.
A combustion chamber 28 is formed. An injector (fuel injection valve) 30 is provided near the center of the position facing the combustion chamber 28.

The injector 30 is connected to a fuel supply pipe 34, through which a fuel tank (not shown) is connected.
When the valve is opened, the fuel is injected into the combustion chamber 28 when the fuel (gasoline fuel) pressurized by a fuel pump (not shown) is supplied.

An ignition plug 36 is disposed in the combustion chamber 28 of each cylinder 22. The ignition plug 36 receives supply of ignition energy from an ignition device (not shown) including an ignition coil, and ignites a mixture of injected fuel and intake air at a predetermined ignition timing. The ignited mixture burns and explodes, driving the piston 24.

As described above, the engine 10 according to this embodiment is a direct injection type spark ignition type internal combustion engine in which gasoline fuel is directly injected into the combustion chamber 28 of each cylinder 22 via the injector 30. .

The exhaust gas after the combustion is discharged to an exhaust (exhaust) manifold 40 through two exhaust valves (not shown), and travels through an exhaust pipe 42 to the first catalytic device 4.
4 and the second catalytic device 46, where they are purified and discharged to the atmosphere. These first and second catalyst devices will be described later.

Downstream of the exhaust manifold 40, the exhaust pipe 42 is connected to the intake pipe 12 via the EGR pipe 50, and recirculates a part of the exhaust gas to the intake system. The EGR pipe 50 has an EGR valve 5 near the connection to the intake pipe 12.
2 is provided to adjust the EGR reflux amount.

The throttle valve 18 is not mechanically connected to an accelerator pedal (not shown) arranged on the floor of the driver's seat of the vehicle. The throttle valve 18 is connected to a pulse motor 54 and is driven by its output. To open and close the intake pipe 12. As described above, the throttle valve 18
Driven in a manner.

The piston 24 is connected to a crankshaft 56, and a crank angle sensor 62 is arranged near the crankshaft 56. Crank angle sensor 62
Is a pulsar 62 attached to the crankshaft 56.
a and a magnetic pickup 62b disposed opposite thereto
Consists of

The crank angle sensor 62 detects the crank angle 7
A CYL signal for cylinder discrimination every 20 degrees, a TDC signal for each cylinder BTDC predetermined crank angle, TDC
The signal interval is subdivided into six.
An RK signal is output.

Returning to the description of FIG. 1, a throttle opening sensor 64 is connected to the pulse motor 54, and outputs a signal corresponding to the opening TH of the throttle valve 18 through the pulse motor rotation amount.

An absolute pressure (MAP) sensor 66 is provided near the position of the throttle valve 18 in the intake pipe 12.
The intake pressure downstream of the throttle is introduced through a passage (not shown) to output a signal corresponding to the intake pipe absolute pressure PBA.
An intake air temperature sensor 68 is provided in the intake pipe 12 upstream of the position where the throttle valve 18 is disposed, and outputs a signal corresponding to the intake air temperature TA.

A water temperature sensor 70 is provided near the cylinder 22, and outputs a signal corresponding to the engine cooling water temperature TW. A wide-range air-fuel ratio sensor 72 is provided in the exhaust pipe 42 upstream of the catalyst devices 44 and 46, and outputs a signal proportional to the exhaust air-fuel ratio, and downstream of the first and second catalyst devices 44 and 46. An O ₂ sensor 74 is provided, and outputs a signal indicating that the exhaust air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.

Further, an accelerator opening sensor 76 is provided near the accelerator pedal, and outputs a signal corresponding to an accelerator opening (accelerator pedal depression amount) θAP operated by the driver.

These sensor outputs are sent to an electronic control unit (hereinafter referred to as “ECU”) 80.

The ECU 80 includes a microcomputer including a CPU, a ROM, a RAM, and the like, and a counter (not shown). The ECU 80 counts the CRK signal output from the crank angle sensor 62 to detect the engine speed NE, and NOx to be described later. Calculation of the amount of adsorption and NOx reduction processing are performed.

Here, the above-mentioned catalyst will be described. The first catalyst device 44 on the upstream side is provided with iridium (I
r) as an active species and an iridium-based selective reduction catalyst for selectively reducing NOx with HC as a reducing agent in a lean atmosphere, specifically, a perovskite-type double oxide (LaCo
O ₃ ), more specifically, a catalyst in which iridium, which is an active species, and a perovskite-type double oxide are supported together, or a catalyst in which an iridium catalyst is coated with a perovskite-type double oxide (eg, LaCoO ₃ ) Is provided.

The iridium-based selective reduction catalyst 44 comprises:
In an oxidizing atmosphere (lean air-fuel ratio), NOx is reduced and purified by reacting (reducing) HC and NOx.

The second catalytic device 46 on the downstream side is provided with a NOx adsorption catalyst that adsorbs NOx in a lean atmosphere and reduces and purifies NOx adsorbed at a stoichiometric air-fuel ratio or a rich air-fuel ratio lower than the stoichiometric air-fuel ratio.

As a NOx adsorption catalyst, JP-A-6-88
Any of the so-called occlusion type catalysts proposed in Japanese Patent Application Publication No. 518 and the like, and the so-called adsorption type catalysts proposed by the present applicant in Japanese Patent Application No. 10-124317 may be used.

In both the storage type catalyst and the adsorption type catalyst, the oxygen concentration in the exhaust gas is high and N
It has a characteristic of storing (or adsorbing) Ox, reducing NOx stored (or adsorbed) in a rich atmosphere having a relatively low oxygen concentration and a large amount of HC and CO with HC and CO.
HC and CO are oxidized and released as water vapor and carbon dioxide.

As described above, in this embodiment,
First catalytic device 4 comprising an iridium-based selective reduction catalyst
No. 4 and a second catalyst device 46 composed of a NOx adsorption catalyst are arranged in series.

That is, the iridium-based selective reduction catalyst and the downstream NOx adsorption catalyst have different NOx purification functions or characteristics, so that the purification rate can be optimized. That is, the iridium-based selective reduction catalyst on the upstream side reacts NOx with the multiple bond HC at a lean air-fuel ratio (oxidizing atmosphere) to produce NOx.
And the NOx adsorption catalyst on the downstream side adsorbs (or stores) NOx at a lean air-fuel ratio and reduces and purifies NOx with a reducing agent at a stoichiometric air-fuel ratio or a rich air-fuel ratio. As described above, since the two have different purification functions or characteristics, by combining them, the purification rate can be increased to the maximum.

An iridium-based selective reduction catalyst and NO
In both x-adsorption catalysts, the purification performance (purification rate) is maximized at around 400 ° C. at the catalyst temperature. For example, when the catalyst temperature is around that, the lean air-fuel ratio is supplied, or By controlling so that
It is also possible to increase the NOx purification rate.

Further, in the case of an iridium-based selective reduction catalyst, since the dependence on the space velocity is extremely small, the catalyst capacity can be reduced to reduce the heat capacity, which is advantageous during a cold start. . In addition, the activation of the downstream NOx adsorption catalyst can be accelerated, and the burden can be reduced.

Furthermore, by purifying NOx with the iridium-based selective reduction catalyst on the upstream side and reducing the NOx concentration, the time until the NOx adsorption catalyst on the downstream side reaches the saturation point can be extended, and NOx can be extended. The reduction processing time can be reduced. Therefore, fuel efficiency can be improved in that sense.

Further, since the NOx adsorption catalyst on the downstream side has an excellent NOx purification performance (adsorption performance) at a lean air-fuel ratio, the lean iridium-based selective reduction catalyst and the NOx adsorption catalyst are arranged in series, so that the lean air-fuel ratio is reduced. The NOx purification performance at the fuel ratio can be improved.

Further, the iridium-based selective reduction catalyst is N
Since the HC purification performance in the Ox purification temperature range is lower than that of a three-way catalyst or the like, the reduction components such as HC necessary for the downstream NOx adsorption catalyst to reduce NOx adsorbed at the stoichiometric air-fuel ratio or the rich air-fuel ratio are reduced. It can be supplied to the NOx adsorption catalyst without purification, and the NOx purification rate of the NOx adsorption catalyst can be improved at a stoichiometric air-fuel ratio or a rich air-fuel ratio.

Further, by using an iridium-based selective reduction catalyst for the first catalyst device 44, the durability of the catalyst device can be improved.

Next, the operation of the exhaust gas purifying apparatus for an internal combustion engine according to this embodiment will be described.

FIG. 2 is a flow chart showing the operation. The illustrated program is executed, for example, every 50 msec.

The operation will be described below. EM
It is determined whether or not OD is 0. S. EMOD is a variable that is set in an appropriate area in the RAM of the ECU 80 and indicates the operation mode of the engine.

That is, S.I. When the value of EMOD is 0, the average in-cylinder air-fuel ratio is set at or near the stoichiometric air-fuel ratio. When the value of EMOD is 1, the average air-fuel ratio is set at a lean air-fuel ratio larger than the stoichiometric air-fuel ratio, for example, at or near 22: 1. , A target air-fuel ratio (hereinafter referred to as “KCMD”; the target air-fuel ratio is indicated by an equivalence ratio), and the engine 10 is operated according to the set target air-fuel ratio to generate a premixed combustion. Means that.

Further, S.I. When the value of EMOD is 2, a target air-fuel ratio (hereinafter, referred to as “KCMD”) is set so as to be a larger lean air-fuel ratio, for example, 60: 1 or in the vicinity thereof, and according to the set target air-fuel ratio. Means that the engine 10 is operated to generate an ultra-lean combustion or a stratified charge combustion (Direct Injection Stratified Charge).

The setting of the target air-fuel ratio KCMD and fuel injection are performed by another routine (not shown). S1
0 is set in the routine. EMOD
The operation mode is determined by searching the value of.

When the result in S10 is affirmative, the engine 10 is operated at the stoichiometric air-fuel ratio, and the calculation of the NOx adsorption amount is unnecessary. Therefore, the subsequent processing is skipped. And the detected engine cooling water temperature TW becomes the predetermined value X. It is determined whether the temperature exceeds TWNOx, for example, 80 ° C., and if not, the subsequent processing is skipped.

That is, since the purification rate of the first catalyst device 44 varies greatly depending on its temperature, and the purification rate is low at low temperatures, the engine cooling water temperature is low when the first catalyst device 44 is at low temperature and the purification rate is low. When it is sufficient to indicate, the following processing is skipped to simplify the calculation.

When the result in S12 is affirmative, the program proceeds to S14,
The S.S. It is determined whether or not the value of EMOD is 1.
When the result in S12 is affirmative, it is determined that the engine is in the premixed lean operation, and the program proceeds to S16, in which a map (not shown) preset from the detected engine speed NE and the intake pipe absolute pressure PBA (engine load) is displayed. Searching for the NOx emissions X.X that the engine 10 would have emitted in its premixed lean operation. Calculate FNOMPL.

On the other hand, if the result in S14 is NO, since the determination in S10 has been made, it is determined that the engine is in stratified charge combustion operation, and the routine proceeds to S18, in which the detected engine speed NE and the calculated target torque PMCMDREG ( A second preset map (not shown) is searched from the calculated engine speed NE and the accelerator opening θAP), and similarly, the NOx emission amount X that would have been emitted by the engine 10 during the stratified combustion operation thereof. . Calculate FNOMPD.

In each of the above maps, the NOx emission amount that will be emitted by the engine 10 in a predetermined cycle is determined in advance by an experiment.

Then, the program proceeds to S20, in which the temperature of the selective reduction catalyst of the first catalyst device 44 (catalyst bed temperature, hereinafter referred to as "catalyst temperature TCAT") is calculated in accordance with the detected operating state and the like. Specifically, the heat transfer of the selective reduction catalyst is obtained and calculated based on a thermodynamic equation based on the detected operating state.

More specifically, the specific heat, the heat transfer coefficient, and the specific heat of the selective reduction catalyst are determined according to the characteristics set in advance based on the engine rotational speed NE, the intake pipe absolute pressure PBA, the target air-fuel ratio KCMD, and the engine coolant temperature TW. The exhaust system temperature and the like are obtained, and the catalyst temperature TCAT is calculated using the mass and cross-sectional area of the selective reduction catalyst stored in advance.

The details of the method of calculating the catalyst temperature TCAT have been previously proposed by the present applicant in Japanese Patent Application Laid-Open No. H11-62656, and thus the description will be limited to this extent.

Then, the program proceeds to S22, in which the calculated catalyst temperature T is calculated.
3 is searched from the CAT, and the NOx purification rate X.C. of the selective reduction catalyst of the first catalyst device 44 is searched. I
Calculate NO. The NOx purification rate X. INO is shown in%.

Then, the program proceeds to S24, in which a table showing the characteristics shown in FIG. 4 is retrieved from the target air-fuel ratio KCMD set in another routine (not shown), and the NOx purification rate correction coefficient X. Calculate KINO.

Then, the program proceeds to S26, in which the calculated NOx purification rate X. NOx purification rate correction coefficient X. The NOx purification rate is corrected by multiplying by the KINO, and the difference (indicating the unpurified rate) obtained by subtracting the correction value from 1 is calculated as the calculated NOx emission amount X.
FNOMPL (or X. FNOMPD) multiplied by N
Ox adsorption amount Q. The NOx, more specifically, the NOx adsorption amount of the NOx adsorption catalyst of the second catalyst device 46, more specifically, the NOx adsorption amount that would have been adsorbed by the NOx adsorption catalyst is calculated.

That is, the first catalyst device 44
By multiplying by the unpurified rate of the selective reduction catalyst, the NOx adsorption catalyst could not be purified by the selective reduction catalyst of the first catalyst device 44 and sent to the downstream second catalyst device 46 to adsorb the NOx adsorption catalyst. The NOx adsorption amount is calculated.

Then, the program proceeds to S28, in which the calculated NOx adsorption amount is integrated, and the NOx adsorption amount integrated value {Q. Find NOx,
Proceeding to S30, the obtained NOx adsorption amount integrated value {Q. NOx
Is a predetermined value X. It is determined whether or not NOLT is exceeded. The predetermined value X. NOLT is N of the NOx adsorption catalyst of the second catalyst device.
A value sufficient to indicate that the Ox adsorption amount is saturated is appropriately determined by experiment and set.

When the result in S30 is affirmative, the program proceeds to S32, where
Flag F. Set the bit of NOLT to 1 and
If not, the process proceeds to S34, and the flag F. The bit of NOLT is reset to 0.

Here, the flag F. Set NOLT bit to 1
Setting the flag F. indicates that the NOx reduction process needs to be performed. Resetting the NOLT bit to 0 means that it is unnecessary.

FIG. 5 is a flow chart showing the NOx reduction processing performed in parallel with the flow chart of FIG. The illustrated program is also executed at time intervals similar to those in FIG.

The following is a description. If NOLT is 1 and flag F. NOLTlast (the value at the time of the previous loop in the flow chart of FIG. 5) is 0, that is,
In the current program loop, the flag F. It is determined whether the bit of the NOLT has been inverted from 0 to 1.

When the result in S100 is affirmative, the program proceeds to S102, in which the detected engine speed NE and the intake pipe absolute pressure P
Target air-fuel ratio KCMD according to appropriate characteristics based on BA
Is set to the stoichiometric air-fuel ratio while the engine 10 is operated. Set STSMP.

Next, the routine proceeds to S104, where a timer (down counter) T. NOP set stoichiometric air-fuel ratio operation duration X. STSMP is set, and a down count (time measurement) is started.

After affirming in S100, in the next program loop, the determination in S100 is denied, and the routine proceeds to S106, where the flag F. If NOLT is 1 and timer T. It is determined whether the value of NOP exceeds zero.

When the result in S106 is affirmative, the program proceeds to S108, in which S. Set the value of EMOD to 0. Thus, in another routine (not shown), the target air-fuel ratio KCMD
Is set to the stoichiometric air-fuel ratio, the engine 10 is operated, and N
The Ox reduction process is performed, and the NOx adsorbed on the second catalyst device 46 is reduced to HC and CO in the exhaust gas and purified. At this time, the target air-fuel ratio KCMD may be a rich air-fuel ratio less than the stoichiometric air-fuel ratio.

Next, the routine proceeds to S110, where the timer T. NOP
Is decremented by a predetermined amount.

In the next and subsequent program loops, S
If the result in S100 is NO, the program proceeds to S106, and if the result in S106 is NO, the NOx reduction process ends and the adsorbed N
When it is determined that Ox has been purified, the process proceeds to S112, and the flag F. The bit of NOLT is reset to 0, and the routine proceeds to S114, where the NOx adsorption amount integrated value {Q. Set NOx to zero.

In this embodiment, as described above, the engine 1
NO discharged from the engine 10 according to the operating state of 0
x emissions x. FNOMPL (or X. FNOMP
D) is calculated, and the catalyst temperature TCAT of the first catalyst device 44 is calculated.
Is calculated, and then the NOx purification rate X. Calculate INO,
Further, the unpurified rate is obtained by correcting with the target air-fuel ratio KCMD,
Multiplying the NOx emission amount by the NOx adsorption amount Q.O. NOx was calculated.

Further, the NOx adsorption amount integrated value {Q. NO
x is calculated and a predetermined value X. Compared to the NOLT, when the predetermined value is exceeded, the operation is performed at the stoichiometric air-fuel ratio to perform the NOx reduction process. Therefore, the NOx adsorption amount of the second catalyst device 46 is accurately calculated (or estimated). And N
Ox reduction treatment can be minimized. Therefore, fuel efficiency can be improved while achieving the intended NOx purification performance.

As described above, in this embodiment, in the exhaust gas purifying apparatus for an internal combustion engine (engine 10) capable of lean operation, HC is used as a reducing agent in a lean atmosphere disposed in the exhaust system of the internal combustion engine. Catalyst (first catalyst device 44) for selectively reducing NOx, adsorbs NOx in a lean atmosphere disposed downstream of the selective reduction catalyst, and adsorbs NOx at a stoichiometric air-fuel ratio or a rich air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio. NOx adsorbing catalyst (second catalytic device 46) for reducing at least the engine speed (engine speed NE) and load (intake pipe absolute pressure PB
A) NOx emission amount calculating means (crank) for detecting an operating state of the internal combustion engine including A) and calculating an NOx emission amount (X.FNOMPL, X.FNOMPD) discharged from the internal combustion engine according to the detected operating state. Angle sensor 62, absolute pressure sensor 66, ECU 80, S10 to S18), NOx purification rate calculation means (ECU 80, S20 to S2) for calculating the NOx purification rate (X.INO) of the selective reduction catalyst.
4), the calculated NOx emission amount (X. FNOMP)
L, X. FNOMPD) and NOx purification rate (1-XINO)
× X. KINO) based on the NOx of the NOx adsorption catalyst.
x adsorption amount, more specifically, the NOx adsorption amount that would have been adsorbed by the NOx adsorption catalyst (Q.NOx, ΔQ.NOx)
NOx adsorption amount calculating means (ECU 80, S26
To S28) and a NOx reduction processing means (EC) for performing a NOx reduction process based on the calculated NOx adsorption amount.
U80, S30 to S34, and S100 to S114).

Further, the selective reduction catalyst is configured to be an iridium-based selective reduction catalyst.

Further, the NOx purification rate calculating means calculates the NOx purification rate of the selective reduction catalyst based on the temperature of the selective reduction catalyst (catalyst temperature TCAT) (ECU 8).
0, S22).

The NOx purification rate calculating means includes catalyst temperature calculating means (ECU 80, S20) for calculating the temperature of the selective reduction catalyst based on the detected operating state. Calculating the NOx purification rate of the selective reduction catalyst based on the temperature of the catalyst (ECU
80, S22).

Further, the NOx purification rate calculation means is configured to correct the NOx purification rate of the selective reduction catalyst based on the air-fuel ratio (target air-fuel ratio KCMD) supplied to the internal combustion engine (ECU 80, S24). .

Further, the NOx reduction processing means sets the calculated NOx adsorption amount (ΣQ.NOx) to a predetermined value (X.NO.
NOLT) (ECU 80, S30)
When the calculated NOx adsorption amount exceeds the predetermined value, a NOx reduction process is performed (ECU 80, S3
2) It was constituted as follows.

Further, there is provided an in-cylinder injection type spark ignition type internal combustion engine in which the internal combustion engine is operated in an operation mode of either ultra-lean combustion or premixed combustion by directly injecting gasoline fuel into a cylinder combustion chamber. , The NOx emission calculating means,
An operation mode determination unit (E) that determines which of the operation modes (S.EMOD) the internal combustion engine is operating in;
CU80, S14), and calculates the NOx emission amount discharged from the internal combustion engine according to the determined operation mode and the detected operation state (ECU80, S1).
6, S18).

In the above description, a cylinder injection type spark ignition type internal combustion engine has been described as an example. However, an internal combustion engine which performs only premix combustion between a lean air-fuel ratio or a stoichiometric air-fuel ratio (and a rich air-fuel ratio) is described. It may be.

[0098]

According to the first aspect of the present invention, the amount of NOx discharged from the internal combustion engine is calculated according to the detected operating state, the NOx purification rate of the selective reduction catalyst is calculated, and the amount of NOx discharged is calculated. And the NOx adsorption amount that would have been adsorbed by the NOx adsorption catalyst is calculated based on
Since the NOx reduction processing is configured to be performed based on the Ox adsorption amount, the NOx reduction processing can be minimized, and the fuel consumption performance can be improved while achieving the intended NOx purification performance.

In the second aspect, the iridium-based selective reduction catalyst and the downstream NOx adsorption catalyst have different NOx purification functions or characteristics, so that the purification rate can be optimized. That is, the iridium-based selective reduction catalyst on the upstream side reacts NOx with the multiple bond HC at a lean air-fuel ratio (oxidizing atmosphere) to purify NOx, and the downstream NOx adsorption catalyst adsorbs NOx at a lean air-fuel ratio. (Or occlusion)
Then, NOx is reduced and purified by a reducing agent at a stoichiometric air-fuel ratio or a rich air-fuel ratio. As described above, since the two have different purification functions or characteristics, by combining them, the purification rate can be increased to the maximum.

Further, an iridium-based selective reduction catalyst and NO
In both x-adsorption catalysts, the purification performance (purification rate) is maximized at around 400 ° C. at the catalyst temperature. For example, when the catalyst temperature is around that, the lean air-fuel ratio is supplied, or By controlling so that
It is also possible to increase the NOx purification rate.

Further, in the case of an iridium-based selective reduction catalyst, since the dependence on the space velocity is extremely small, the catalyst capacity can be reduced to reduce the heat capacity, which is advantageous at the time of a cold start and the like. . In addition, the activation of the downstream NOx adsorption catalyst can be accelerated, and the burden can be reduced.

Further, by purifying NOx with the iridium-based selective reduction catalyst on the upstream side and reducing the NOx concentration, it is possible to extend the time until the NOx adsorption catalyst on the downstream side reaches the saturation point. The reduction processing time can be reduced. Therefore, fuel efficiency can be improved in that sense.

As described above, the NOx adsorption catalyst on the downstream side has an excellent NOx purification performance (adsorption performance) at a lean air-fuel ratio.
Iridium-based selective reduction catalyst and NO
By arranging the x adsorption catalysts in series, the NOx purification performance at a lean air-fuel ratio can be improved.

Further, the iridium-based selective reduction catalyst is N
Since the HC purification performance in the Ox purification temperature range is lower than that of a three-way catalyst or the like, the reduction components such as HC necessary for the downstream NOx adsorption catalyst to reduce NOx adsorbed at the stoichiometric air-fuel ratio or the rich air-fuel ratio are reduced. It can be supplied to the NOx adsorption catalyst without purification, and the NOx purification rate of the NOx adsorption catalyst can be improved at a stoichiometric air-fuel ratio or a rich air-fuel ratio.

Further, by using an iridium-based selective reduction catalyst, the durability as a catalyst can be improved.

According to a third aspect of the present invention, the amount of N
Although the Ox purification rate changes depending on the temperature, the above configuration makes it possible to calculate the NOx purification rate with high accuracy, thereby further improving the fuel economy performance while achieving the intended NOx purification performance. it can.

According to the fourth aspect of the present invention, the temperature of the selective reduction catalyst is calculated based on at least the detected operating condition. Can be simplified.

According to the present invention, the NOx purification rate can be calculated with higher accuracy by correcting the NOx purification rate of the selective reduction catalyst based on the air-fuel ratio supplied to the internal combustion engine. Therefore, the fuel consumption performance can be further improved while achieving the intended NOx purification performance.

According to the present invention, the execution time of the NOx reduction process can be determined accurately, and the fuel consumption performance can be further improved while achieving the intended NOx purification performance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an exhaust gas purifying apparatus for an internal combustion engine according to the present application as a whole.

FIG. 2 is a flowchart showing the operation of the apparatus in FIG. 1;

FIG. 3 shows a NOx purification rate X.R. It is an explanatory graph which shows the table characteristic of INO.

FIG. 4 shows a NOx purification rate correction coefficient X. It is an explanatory graph which shows the table characteristic of KINO.

FIG. 5 is a flowchart showing a NOx reduction process executed in parallel with the flowchart of FIG. 2;

[Explanation of symbols]

 Reference Signs List 10 internal combustion engine (engine) 12 intake pipe 22 cylinder (cylinder) 28 combustion chamber 30 injector (fuel injection valve) 44 first catalyst device (selective reduction catalyst) 46 second catalyst device (NOx adsorption catalyst) 62 crank angle sensor 66 Absolute pressure (MAP) sensor 76 Accelerator opening sensor 80 Electronic control unit (ECU)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 305 B01D 53/36 101B 45/00 360 102B B01J 23/56 301A F-term (Reference) 3G084 BA09 BA24 DA02 DA10 FA02 FA10 FA11 FA20 FA27 FA29 FA38 3G091 AA11 AA12 AA17 AA24 AA28 AB05 AB06 BA00 BA14 CB02 DB06 DB10 DB13 DC01 EA01 EA06 EA07 EA16 EA18 EA33 EA34 FB11 FB12 GB10W HA36 HA01 HA04 LA03 PD03Z PD04Z PD08Z PE01Z PE03Z PE05Z PE08Z PF03Z 4D048 AA06 AB02 BA18X BA33X BA37X BA42X CA01 CC32 CD01 DA02 DA08 EA04 4G069 AA02 AA03 BB06B BC42B BC67B BC74A BC74B CA03 CA08 CA13 EC23 EE08

Claims (6)

[Claims] An exhaust gas purifying apparatus for an internal combustion engine capable of lean operation, comprising: a. A selective reduction catalyst for selectively reducing NOx using HC as a reducing agent in a lean atmosphere disposed in an exhaust system of the internal combustion engine; b. NO that adsorbs NOx in a lean atmosphere disposed downstream of the selective reduction catalyst and reduces the adsorbed NOx at a stoichiometric air-fuel ratio or a rich air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio
x adsorption catalyst, c. NOx for detecting an operating state of the internal combustion engine including at least an engine speed and a load and calculating a NOx emission amount discharged from the internal combustion engine in accordance with the detected operating state
Means for calculating emissions, d. NOx for calculating the NOx purification rate of the selective reduction catalyst
Purification rate calculating means, e. NO for calculating the NOx adsorption amount of the NOx adsorption catalyst based on the calculated NOx emission amount and NOx purification rate
x adsorption amount calculation means; and f. An exhaust purification device for an internal combustion engine, comprising: NOx reduction processing means for performing a NOx reduction process based on the calculated NOx adsorption amount. 2. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said selective reduction catalyst is an iridium-based selective reduction catalyst. 3. The internal combustion engine according to claim 1, wherein the NOx purification rate calculating means calculates a NOx purification rate of the selective reduction catalyst based on a temperature of the selective reduction catalyst. Exhaust gas purification device. 4. The NOx purification rate calculating means comprises: g. Catalyst temperature calculating means for calculating the temperature of the selective reduction catalyst based on at least the detected operating state, and calculating the NOx purification rate of the selective reduction catalyst based on the calculated temperature of the selective reduction catalyst. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein: 5. The NOx purification rate calculating means for correcting the NOx purification rate of the selective reduction catalyst based on an air-fuel ratio supplied to the internal combustion engine. An exhaust purification device for an internal combustion engine according to any one of the above. 6. The NOx reduction processing means includes: h. 6. A comparison means for comparing the calculated NOx adsorption amount with a predetermined value, wherein a NOx reduction process is performed when the calculated NOx adsorption amount exceeds the predetermined value. An exhaust gas purification device for an internal combustion engine according to any one of the above items.