JP2002266629A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately determine deterioration of an NOX absorbent. SOLUTION: At least one of a maximum NOX absorbing amount of the NOX absorbent and an NOX absorption rate in the NOX absorbent is calculated by using an output of a sensor 29 capable of detecting an NOX concentration placed downstream of the NOX absorbent 23. In such manner, when the calculated maximum NOX absorbing amount or the NOX absorption rate is smaller than a determination value, it is determined that the NOX absorbent is deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art Exhaust gas discharged from a combustion chamber of an internal combustion engine
Nitrogen oxides (NO_X NO for purifying)_X Purification
An exhaust purification device in which a catalyst is disposed in an engine exhaust passage is known.
It is. NO_X As a purification catalyst, the exhaust gas
NO when fuel ratio is lean_X Absorbs and flows in
NO absorbed when the air-fuel ratio of exhaust gas becomes rich_X Exhaust
NO released and reduced by the reducing agent contained in the gas
_X Absorbents are known. Such NO_X Absorbent
NO that can be absorbed_X The amount of
NO_X There is a limit to absorption. And NO_X Absorbent
NO contained _X Is the maximum NO_X Exceeds absorption
NO_X Absorbent is no longer NO_X Can absorb
No, NO_X NO to downstream of absorbent_X Leaked out
I will. So NO_X NO absorbed by absorbent_X Amount of
Is the maximum NO_X NO before exceeding absorption_X Flows into the absorbent
Switching the air-fuel ratio of exhaust gas from lean to rich
_X NO from absorbent_X Need to be released and reduced. Only
While max NO_X When the absorption becomes very low
Frequently uses hydrocarbon (fuel) as a reducing agent for NO_X Absorbent
Must be supplied to the vehicle, resulting in poor fuel economy. In this case
In order to prevent deterioration of fuel economy, some measures must be taken.
O_X Must be applied to the absorbent, but some action
NO to determine whether or not to apply_X Poor absorbent
It is necessary to determine whether or not it has become.

[0003] The system for determining the deterioration of the NO _X absorbent is known a system disclosed in JP-A-2000-104536. The NO _X sensor capable of detecting the concentration of NO _X in the exhaust gas in _the NO _X storage catalyst downstream arranged according to the publication, when the NO _X concentration detected by the NO _X sensor has reached a predetermined value In a system in which the air-fuel ratio of the exhaust gas flowing into the NO _X storage catalyst is switched from lean to rich, the NO _X storage time is shortened by executing a process for switching the air-fuel ratio of the exhaust gas from lean to rich. It is determined that the catalyst has deteriorated.

[0004]

According to Japanese Patent Application Laid-Open No. 2000-104536, the presence or absence of deterioration of the NO _X storage catalyst is determined based on the interval at which the process for switching the air-fuel ratio of the exhaust gas from lean to rich is executed. Although it is determined, the execution interval of the process of switching the air-fuel ratio of the exhaust gas from lean to rich is, for example, NO _X flowing into the NO _X storage catalyst.
Is large, even if the NO _X storage catalyst has not deteriorated. Therefore, in the system of this publication, N
O _X can not be determined accurately the deterioration of the storage catalyst.
An object of the present invention view of these circumstances is to accurately determine the deterioration of the NO _X absorbent.

[0005]

Absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean in the A solving means for] the first in order to solve the above problems the invention, when the air-fuel ratio of the inflowing exhaust gas becomes rich the absorbed NO _X released by a reducing agent contained in the exhaust gas is disposed in the reduction to _the NO _X absorbent to the engine exhaust passage, NO _X concentration in the exhaust gas to the _the NO _X absorbent engine exhaust passage downstream of in the exhaust purification apparatus arranged an internal combustion engine the sensor capable of detecting, the estimated value of the maximum NO _X absorption amount is estimated to be absorbed in the NO _X absorbent by utilizing the output of the sensor, _the NO _X absorbent air-fuel ratio of the inflowing exhaust gas to calculate at least one of the estimated value of the NO _X absorption rate into _the NO _X absorbent which is estimated to be achieved by _the NO _X absorbent when is lean, and thus the maximum NO _X absorption is calculated Te When the estimated value of the estimated value or NO _X absorption rate is less than the determination value is determined as _the NO _X absorbent is deteriorated. That is, NO _{X in} exhaust gas
The maximum NO _X absorption amount or NO _{X of the} NO _X absorbent calculated using the output of the sensor capable of detecting the concentration
Deterioration of the NO _X absorbent is determined based the NO _X absorption rate into the absorbent.

In the second invention, in the first invention, N
O_X NO flowing out of the absorbent_X And the amount of NO_X Absorbent
Maximum NO_X Absorption and NO_X NO in absorbent_X Sucking
A relational expression that holds between the rate of acquisition and that of
_X NO flowing out of the absorbent _X Output of the above sensor
Is calculated on the basis of_X Up the amount of
Maximum NO by substituting_X Estimation of absorption
Value and NO_X An estimated value of the absorption rate is calculated.

[0007] In the third invention, N in the first invention
Absorbed in _the NO _X absorbent by the air-fuel ratio of the exhaust gas flowing into the O _X absorbent integrating the amount of the NO _X absorbed in the NO _X absorbent is calculated based on the engine operating state when it is lean comprising a NO _X absorption amount estimation means for estimating the amount of the NO _X that is, flows into _the NO _X absorbent when the NO _X absorbed amount estimated by the NO _X absorption amount estimation means exceeds the allowable value The air-fuel ratio of the exhaust gas is switched from lean to rich.

[0008] In the fourth invention, the above is the third invention.
Note NO_X NO_X Absorbed by absorbent
NO_X When estimating the amount of
NO _X Absorption and NO_X The absorption rate is used. The above issues
In order to solve this problem, the fifth aspect of the present invention discloses that the exhaust gas
NO when fuel ratio is lean_X Absorbs and flows in
NO absorbed when the air-fuel ratio of exhaust gas becomes rich_X Exhaust
NO released and reduced by the reducing agent contained in the gas
_X An absorbent is disposed in the engine exhaust passage, and the NO._X Downstream of absorbent
Detects ammonia concentration in exhaust gas in engine exhaust passage
A possible sensor, NO_X Exhaust gas flowing into the absorbent
NO when the air-fuel ratio of the engine is changed from lean to rich_X Sucking
NO from collector_X Not used to release and reduce
Surplus reducing agent in the form of ammonia_X Flow from absorbent
Out, and NO by the above sensor_X Exhaust from the absorbent
NO when the ammonia concentration in the gas exceeds the judgment value_X 
NO from absorbent_X That the release and reduction of
In the exhaust gas purifying apparatus for an internal combustion engine,_X Sucking
When the air-fuel ratio of the exhaust gas flowing into the absorbent is lean
Is NO calculated based on the engine operating state_X Absorbed by absorbent
NO collected_X Is integrated, and NO_X Flows into the absorbent
NO when the air-fuel ratio of the exhaust gas is rich_X Absorbent
NO in_X Calculated based on the reduction speed of NO_X 
NO reduced in the absorbent_X To subtract the amount of
More NO_X NO absorbed by absorbent_X Estimate the amount of
NO_X Equipped with absorption amount estimation means, NO_X From the absorbent
NO_X When it is determined that the release / reduction of
NO_X NO estimated by absorption amount estimation means_X Absorption
When it is out of the reference value, the above NO_X Estimated amount of absorption
NO used in stages_X Correct the reduction rate and thus supplement
Corrected NO_X When the reduction speed is lower than the determination value, N
O_X It is determined that the absorbent has deteriorated. Ie ammonia
NO based on output of sensor capable of detecting concentration_X Absorbent
NO in_X The release and reduction of
NO_X NO estimated by absorption amount estimation means_X Absorption
NO corrected based on_X NO based on reduction rate_X 
The deterioration of the absorbent is determined.

In the sixth invention, N in the fifth invention
N the release and reduction of the NO _X from O _X absorbent is estimated by NO _X absorption amount estimation means when it is determined to be complete
When O _X absorption amount is larger than the reference value is corrected so as to increase the NO _X reduction rate used in NO _X absorption amount estimation means, when less than the reference value corrected so as to slow down the NO _X reduction rate I do.

[0010] 7-th in the invention NO as the engine operating state when the NO _X absorption amount estimation means for estimating the amount of the NO _X that is absorbed in the NO _X absorbent in the fifth invention
NO _X to maximum NO _X absorption and _the NO _X absorbent for _X absorbent
And the absorption rate.

[0011]

FIG. 1 shows a case where the present invention is applied to a direct injection type spark ignition engine. However, the present invention can also be applied to a compression ignition type internal combustion engine. Figure 1
1 is an engine body, 2 is a cylinder block, 3
Is a piston that reciprocates in the cylinder block 2, 4 is a cylinder head fixed on the cylinder block 2, 5 is a combustion chamber formed between the piston 3 and the cylinder head 4, 6 is an intake valve, 7 is intake air. Port 8 indicates an exhaust valve, and 9 indicates an exhaust port. As shown in FIG. 1, an ignition plug 10 is arranged at the center of the inner wall surface of the cylinder head 4, and a fuel injection valve 11 is arranged around the inner wall surface of the cylinder head 4. A cavity 12 is formed on the top surface of the piston 3 and extends from below the fuel injection valve 11 to below the ignition plug 10.

An intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake branch pipe 13, and the surge tank 14 is connected to an intake duct 15 and an air flow meter 16
Through an air cleaner (not shown). A throttle valve 18 driven by a step motor 17 is arranged in the intake duct 15. On the other hand, the exhaust port 9 of each cylinder is connected to an exhaust manifold 19, and the exhaust manifold 19 has a catalyst converter 21 containing an oxidation catalyst or a three-way catalyst 20 and a casing containing a NO _X absorbent 23 via an exhaust pipe 22. 24. The exhaust manifold 19 and the surge tank 14 are connected to each other via a recirculated exhaust gas (hereinafter, referred to as EGR gas) conduit 26, and an EGR gas control valve 27 is disposed in the EGR gas conduit 26.

The electronic control unit 31 is composed of a digital computer, and is connected to a RAM (random access memory) 33 and a ROM via a bidirectional bus 32.
(Read only memory) 34, CPU (microprocessor) 35, input port 36 and output port 37. The air flow meter 16 generates an output voltage proportional to the amount of intake air, and the output voltage
8 to the input port 36. An air-fuel ratio sensor 28 for detecting an air-fuel ratio is attached to the exhaust manifold 19, and an output signal of the air-fuel ratio sensor 28 is input to an input port 36 via a corresponding AD converter 38. The exhaust pipe 25 connected to the outlet of the casing 24 containing the NO _X absorbent 23 contains NO _X in the exhaust gas.
The concentration and ammonia concentration together detectable NO _X ammonia sensor 29 is disposed and the air-fuel ratio sensor 30,
The output signals of the NO _X ammonia sensor 29 and the air-fuel ratio sensor 30 are input to the input port 36 via the corresponding AD converter 38.

A load sensor 41 for generating an output voltage proportional to the amount of depression of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is supplied to an input port 36 via a corresponding AD converter 38. Will be entered. The crank angle sensor 42 generates an output pulse every time the crankshaft rotates 30 degrees, for example, and this output pulse is input to the input port 36. The CPU 35 calculates the engine speed from the output pulse of the crank angle sensor 42. On the other hand, the output port 37 is connected to the corresponding drive circuit 3
9, the ignition plug 10, the fuel injection valve 11, the step motor 17, and the EGR control valve 27 are connected.

Next, the NO _X shown in FIG. 1 with reference to FIG.
The structure of the sensor section of the ammonia sensor 29 will be briefly described. Referring to FIG. 2 NO _X ammonia sensor 2
The sensor section 9 comprises six oxygen ion conductive solid electrolyte layers such as zirconia oxide laminated on each other.
The first solid electrolyte layer is referred to as a first layer L ₁ , a second layer
The layers are referred to as a layer L ₂ , a third layer L ₃ , a fourth layer L ₄ , a fifth layer L ₅ , and a sixth layer L ₆ .

Referring to FIG. 2, the first layer L ₁ and the third layer L ₃
A first diffusion-controlling member 50 and a second diffusion-controlling member 51 having, for example, a porous or fine pore are disposed between the first and second diffusion-controlling members 50 and 51. chamber 52 is formed, the second diffusion-controlling member 51 is provided between the second layer L ₂ is formed with a second chamber 53. Third
Between the layers L ₃ and the fifth layer L ₅ atmospheric chamber 54 communicating with the outside air are formed. On the other hand, the first diffusion-controlling member 5
0 is in contact with the exhaust gas. Therefore, the exhaust gas flows into the first chamber 52 via the first diffusion-controlling member 50, and thus the first chamber 52 is filled with the exhaust gas.

Meanwhile, the first layer inner circumferential surface on the L ₁ that faces the first chamber 52 the cathode side first pump electrode 55 is formed, the first
An anode-side first pump electrode 56 is formed on the outer peripheral surface of the layer L ₁ , and a voltage is applied between the first pump electrodes 55 and 56 by a first pump voltage source 57. When a voltage is applied between the first pump electrodes 55 and 56, oxygen contained in the exhaust gas in the first chamber 52 is changed to the cathode-side first pump electrode 5.
5 and becomes oxygen ions.
The inside layer L ₁ flows toward the anode side first pump electrode 56.
Therefore, oxygen contained in the exhaust gas in the first chamber 52 moves in the first layer L ₁ and is pumped out. At this time, the amount of oxygen pumped out is reduced by the first pump voltage source 57. Increases as the voltage of the signal increases.

Meanwhile, reference electrode 58 is formed on the inner surface of the third layer L ₃ that faces the atmospheric chamber 54. By the way, in the oxygen ion conductive solid electrolyte, if there is a difference in oxygen concentration on both sides of the solid electrolyte layer, oxygen ions move in the solid electrolyte layer from the high oxygen concentration side to the low oxygen concentration side. In the example shown in FIG. 2, the oxygen concentration in the atmosphere chamber 54 is higher than the oxygen concentration in the first chamber 52. And this oxygen ion is in the third layer L
_3, the second layer L ₂ and the first layer L ₁ moves, releasing the charge at the cathode side first pump electrode 55. as a result,
A voltage V ₀ indicated by reference numeral 59 is generated between the reference electrode 58 and the first pump electrode 55 on the cathode side. This voltage V ₀ is proportional to the oxygen concentration difference between the atmospheric pressure chamber 54 and the first chamber 52.

In the example shown in FIG. 2, the voltage of the first pump voltage source 57 is feedback-controlled so that the voltage V ₀ coincides with the voltage generated when the oxygen concentration in the first chamber 52 is 1 ppm. . That is, the oxygen in the first chamber 52 is
Oxygen concentration in 2 is pumped through the first layer L ₁ so that 1P.Pm, whereby the oxygen concentration in the first chamber 52 is maintained at 1P.Pm.

[0020] Note that the cathode material having a low reducibility to the first pump electrode 55 is NO _X, for example, gold Au and are formed of an alloy of platinum Pt, thus NO _X contained in the exhaust gas is first It is hardly reduced in the one room 52. Therefore, this NO _X flows into the second chamber 53 through the second diffusion-controlling member 51. On the other hand, on the inner surface of the first layer L ₁ that faces the second chamber 53 the cathode side second pump electrode 6
0 is formed, and a voltage is applied between the cathode-side second pump electrode 60 and the anode-side first pump electrode 56 by a second pump voltage source 61. These pump electrodes 60,
When the voltage across 56 is applied oxygen contained in the exhaust gas in the second chamber 53 becomes oxygen ions in contact with the cathode side second pump electrode 60, the oxygen ions anode the first layer L ₁ It flows toward the first side pump electrode 56. Therefore, the oxygen contained in the exhaust gas in the second chamber 53 moves in the first layer L ₁ and is pumped out. At this time, the amount of oxygen pumped out is reduced by the second pump voltage source 61. Increases as the voltage of the signal increases.

On the other hand, as described above, in the oxygen ion conductive solid electrolyte, if there is a difference in oxygen concentration on both sides of the solid electrolyte layer, the oxygen ion conducts in the solid electrolyte layer from the high oxygen concentration side to the low oxygen concentration side. Moves. In the example shown in FIG. 2, the oxygen concentration in the atmosphere chamber 54 is higher than the oxygen concentration in the second chamber 53, so that the oxygen in the atmosphere chamber 54 contacts the reference electrode 58 to receive a charge and generate oxygen ions. The oxygen ions move in the third layer L ₃ , the second layer L _2, and the first layer L ₁ , and discharge charges at the cathode-side second pump electrode 60. As a result, the voltage V indicated by reference numeral 62 is applied between the reference electrode 58 and the cathode-side second pump electrode 60.
₁ occurs. This voltage V ₁ is proportional to the oxygen concentration difference between the atmospheric pressure chamber 54 and the second chamber 53.

In the example shown in FIG. 2, the voltage of the second pump voltage source 61 is controlled by feedback so that the voltage V ₁ coincides with the voltage generated when the oxygen concentration in the second chamber 53 is 0.01 ppm. Is done. That oxygen in the second chamber 53 the oxygen concentration in the second chamber 53 is pumped through the first layer L ₁ so that 0.01P.Pm, whereby the second chamber 53
The oxygen concentration inside is maintained at 0.01 ppm.

The cathode side second pump electrode 60 is also NO_X To
On the other hand, materials having low reducibility such as gold Au and platinum Pt
Alloys and therefore contained in exhaust gas
NO_X Is in contact with the cathode-side second pump electrode 60
Hardly reduced. On the other hand, the third facing the second chamber 53
Layer L_Three NO on the inner circumference_X Cathode side pump electrode for detection
63 are formed. This cathode side pump electrode 63 is N
O_X Materials that have a strong reducibility against, for example, rhodium
It is made of Rh or platinum Pt. Therefore the second room
NO in 53_X In fact, most of the NO is on the cathode side
N on the pump electrode 63_Two And O_Two And is decomposed into
As shown in FIG. 2, the cathode side pump electrode 63 and the reference
A constant voltage 64 is applied between the pole 58 and
As a result, it was decomposed and generated on the cathode side pump electrode 63.
O_Two Is oxygen ions and the third layer L_Three Inside reference electrode 58
Move towards. At this time, the cathode side pump electrode 63 and the base
A sign proportional to the amount of oxygen ions between the quasi-electrode 58
Current I shown at 65 ₁ Flows.

As described above, NO _X is hardly reduced in the first chamber 52, and oxygen is hardly present in the second chamber 53. Thus current I ₁ is proportional to the NO _X concentration in the exhaust gas, it becomes possible to detect the concentration of NO _X in the exhaust gas from the current I ₁ and thus. On the other hand, ammonia NH ₃ contained in exhaust gas is decomposed into NO and H ₂ O in the first chamber 52 (4NH
₃ + 5O ₂ → 4NO + 6H ₂ O), this decomposed NO
Flows into the second chamber 53 through the second diffusion-controlling member 51. This NO is N ₂ on the cathode side pump electrode 63.
And is decomposed into O _2, O ₂ produced decomposition moves toward the reference electrode 58 of the third layer L ₃ becomes oxygen ions. Also at this time, the current I ₁ is reduced to the NH contained in the exhaust gas.
₃ proportional to the concentration and thus the current I ₁
The H ₃ concentration can be detected.

FIG. 3 shows the current I₁ And NO in exhaust gas_X concentration
And NH_Three The relationship with the concentration is shown. From Figure 3 the current
I₁ Is NO in exhaust gas_X Concentration and NH_Three Proportional to concentration
You can see that it is doing. On the other hand, the oxygen concentration in the exhaust gas
The higher the air-fuel ratio, the leaner the air-fuel ratio,
The amount of oxygen pumped out from 2 increases, and
The current I indicated by _Two Increase. Therefore, this current I_Two 
Thus, the air-fuel ratio of the exhaust gas can be detected.

Note that N is provided between the fifth layer L ₅ and the sixth layer L _6.
O _X ammonia and an electric heater 67 for heating the sensor portion of the sensor 29 is disposed, the electric heater 67
Sensor portion of the NO _X ammonia sensor 29 by 70
Heated from 0 ° C to 800 ° C. Figure 4 is _the NO _X absorbent 2
3 shows the output voltage E (V) of the air-fuel ratio sensor 30 disposed in the exhaust pipe 25 downstream of the exhaust pipe 25, that is, the output signal level of the air-fuel ratio detection means in a general expression. As can be seen from FIG. 4, the air-fuel ratio sensor 30 generates an output voltage of about 0.9 (V) when the air-fuel ratio of the exhaust gas is rich,
When the air-fuel ratio of the exhaust gas is lean, an output voltage of about 0.1 (V) is generated. That is, in the example shown in FIG. 4, the output signal level indicating rich is 0.9 (V), and the output signal level indicating lean is 0.1 (V).
(V).

On the other hand, it is also possible to use a NO _X from the current I ₂ of the ammonia sensor 29 can detect the air-fuel ratio of the exhaust gas, thus NO _X ammonia sensor 29 as an air-fuel ratio detecting means as described above. In this case, there is no need to provide the air-fuel ratio sensor 30. Next, FIG.
The fuel injection control of the internal combustion engine shown in FIG. 1 will be described with reference to FIG. In FIG. 5A, the vertical axis represents engine load Q / N (intake air amount Q / engine speed N).
The horizontal axis represents the engine speed N.

[0028] Figure 5 in the operating region of lower load than the solid line X ₁ in (A) has a stratified charge combustion is performed. That is, at this time, as shown in FIG.
The fuel F is injected from 1 into the cavity 12.
This fuel is guided by the inner peripheral surface of the cavity 12 to form an air-fuel mixture around the ignition plug 10.
0 causes ignition combustion. At this time, the average air-fuel ratio in the combustion chamber 5 is lean.

On the other hand, in the region of the high load side than the solid line X ₁ in FIG. 5 (A) the fuel from the fuel injection valve 11 is injected during the intake stroke, uniform mixture combustion is performed at this time. In still between solid X ₁ and a chain line X ₂ is performed homogeneous mixture combustion under a lean air-fuel ratio, the uniform mixture combustion under a stoichiometric air-fuel ratio between the chain line X ₂ and the chain line X ₃ Done,
Uniform mixture combustion under a rich air-fuel ratio in the high load side is performed than the chain line X _3.

In the present invention, the basic fuel injection amount TAU required to make the air-fuel ratio the stoichiometric air-fuel ratio is represented by a map as a function of the engine load Q / N and the engine speed N as shown in FIG. The basic fuel injection amount TAU is basically multiplied by a correction coefficient K (in some cases, a correction coefficient K
_The final fuel injection amount TAUO (= K · TAU) is calculated by further multiplying _S. The correction coefficient K is stored in the ROM 34 in advance in the form of a map as a function of the engine load Q / N and the engine speed N as shown in FIG.

The value of the correction coefficient K is smaller than 1.0 in an operation region on the lower load side than the dashed line X _{2 in} FIG. It is larger than 1.0 even in the operating range of the high load side than the chain line X ₃ shown in FIG. 5 (a) where combustion takes place under. The correction coefficient K is in the operating region between the chain line X ₂ and a chain line X ₃ is 1.0, the air-fuel ratio at this time is feedback controlled based on the output signal of the air-fuel ratio sensor 28 so that the theoretical air-fuel ratio Is done.

[0032] and _the NO _X absorbent 23 disposed in the engine exhaust passage, for example alumina as carrier, for example potassium K on the carrier, sodium Na, lithium Li, cesium Cs, barium Ba, calcium Ca And at least one selected from the group consisting of alkaline earths, rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. In this case, to place the particulate filter consisting of a casing 24 in the example cordierite, alumina on the particulate filter can be supported to _the NO _X absorbent 23 to a carrier.

[0033] Any engine intake passage even when the, the ratio of the amount of air to the amount of fuel supplied to the combustion chamber 5 and _the NO _X absorbent 23 in the exhaust passage upstream of (hydrocarbon) N
O _X absorbent Toko called air-fuel ratio of the exhaust gas flowing into 23 NO _X absorbent 23 absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, the air-fuel ratio of the inflowing exhaust gas or the stoichiometric air-fuel ratio carry out the absorption and release action of NO _X to release the NO _X absorbed and become rich.

[0034] While performing the absorbing and releasing action of the NO _X when the absorbent 23 be disposed in the engine exhaust passage _the NO _X absorbent 23 actually NO _X is also not clear portion detailed mechanism of action out this absorbing . However, it is considered that this absorption / release action is performed by the mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

In the internal combustion engine shown in FIG.
Combustion with lean air-fuel ratio in most operating conditions
Is performed. In this way, combustion occurs when the air-fuel ratio is lean.
If this is done, the oxygen concentration in the exhaust gas is high,
At this time, as shown in FIG._Two But
O_Two ^-Or O^2-On the surface of platinum Pt. one
On the other hand, NO in the inflowing exhaust gas becomes O on the surface of platinum Pt._Two ^-Ma
Or O^2-Reacts with NO _Two (2NO + O_Two → 2N
O_Two ). NO generated next_Two Part of is on platinum Pt
Barium oxide BaO being absorbed in the absorbent while being oxidized
6A, the nitrate ion N is combined as shown in FIG.
O_Three ^-Diffuses into the absorbent in the form of NO in this way_X 
Is NO_X It is absorbed in the absorbent 23. In the incoming exhaust gas
NO on the surface of platinum Pt as long as oxygen concentration is high_Two Is generated
NO_X NO unless absorption capacity is saturated_Two But
Nitrate ion NO absorbed in the absorbent_Three ^-Is generated.

On the other hand, when the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas decreases, and as a result,
The amount of NO ₂ generated on the surface of platinum Pt decreases. NO ₂
And the amount of production is reduced reaction backward (NO ₃ ^- → NO ₂₎
The process proceeds, thus nitrate ions to the absorber NO ₃ ^- is NO ₂
Released from the absorbent in the form of At this time, _the NO _X absorbent 2
NO _X released from 3 large amount of unburned HC contained in the inflowing exhaust gas as shown in FIG. 6 (B), is caused to reduction by reaction with CO. In this way, when NO ₂ is no longer present on the surface of platinum Pt, N ₂ is successively removed from the absorbent.
O ₂ is released. Therefore NO _X from _the NO _X absorbent 23 in a short time when the air-fuel ratio of the inflowing exhaust gas is made rich is released, yet NO _X is discharged into the atmosphere to the released NO _X is reduced It will not be done.

In this case, the air-fuel ratio of the inflowing exhaust gas is controlled.
NO even if stoichiometric_X NO from absorbent 23_X Is released
It is. However, the air-fuel ratio of the incoming exhaust gas is
NO if set to_X NO from absorbent 23_X Gradually
NO because it is not released_XAbsorbed by absorbent 23
All NO_X It takes a slightly longer time to release. When
NO at the time_X NO of absorbent 23_X The absorption capacity is limited
And therefore NO _X NO of absorbent 23_X I'm tired of absorption
NO before summing_X NO from absorbent 23_X Must be released
It is necessary. But NO_X Absorbent 23 is NO_X Absorption capacity
Is sufficient, almost all N contained in exhaust gas
O_X Absorbs NO_X Partial when approaching the limit of absorption capacity
NO_X Can no longer be absorbed, and thus NO_X Absorbent 2
3 is NO_X NO when approaching the limit of absorption capacity_X Absorbent 23
NO that flows downstream from_X The volume starts to increase.

[0038] Therefore, in the first embodiment of the present invention estimates the NO _X absorption of the total, which is absorbed in the NO _X absorbent 23, NO _X when the NO _X absorption amount close to the maximum NO _X absorption It is from _the NO _X absorbent 23 so as to release the NO _X fuel ratio of the exhaust gas flowing into the absorbent 23 temporarily rich. In this case, the method of the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 23 rich There are various ways. For example, the air-fuel ratio of the exhaust gas can be made rich by making the average air-fuel ratio of the air-fuel mixture in the combustion chamber 5 rich, and the exhaust gas can be made rich by injecting additional fuel at the end of the expansion stroke or during the exhaust stroke. the air-fuel ratio can either be rich or air-fuel ratio of the exhaust gas by injecting additional fuel to _the NO _X absorbent 23 in the exhaust passage upstream of it is also possible to rich. In the embodiment of the present invention, the first method, that is, the air-fuel ratio of the exhaust gas is made rich by performing uniform mixture combustion under the rich air-fuel ratio.

The exhaust gas contains SO _X , and the NO _X absorbent 23 contains not only NO _X but also SO _X
Is also absorbed. It is considered that the mechanism of absorbing SO _X into the NO _X absorbent 23 is the same as the mechanism of absorbing NO _X. That is, the case where platinum Pt and barium Ba are carried on the carrier as in the description of the NO _X absorption mechanism will be described as an example. As described above, when the air-fuel ratio of the inflowing exhaust gas is lean, oxygen O ₂ becomes O _{2. 2} ^-
Or O ²⁻ is attached to the surface of platinum Pt in the form of O ²⁻ , and SO ₂ in the inflowing exhaust gas is converted to O ₂ ⁻ or O ₂ on the surface of platinum Pt.
Reacts with ^2- to form SO ₃ . Next, a part of the generated SO ₃ is further oxidized on the platinum Pt, absorbed in the absorbent and combined with barium oxide BaO, and diffused into the absorbent in the form of sulfate ion SO ₄ ²⁻ , thereby stabilizing. Sulfate Ba
Generate SO ₄ .

However, the sulfate BaSO ₄ is stable and hard to decompose, and the sulfate BaSO ₄ remains without being decomposed simply by making the air-fuel ratio of the inflowing exhaust gas rich. _The NO _X absorbent 23 as thus NO _X in the absorbent 23 hours will be sulfate BaSO ₄ increases as elapses, thus to time has elapsed
Will decrease the amount of NO _X that can be absorbed. That will be _the NO _X absorbent 23 deteriorates over time.

However, in this case, NO_X Absorbent 23 temperature
NO when the temperature exceeds a certain temperature, for example, 600 ° C._X absorption
Sulfate BaSO in agent 23_Four Decomposes, at this time
NO _X Rich air-fuel ratio of exhaust gas flowing into absorbent 23
NO_X Absorbent 23 to SO_X Releasing
Can be. Therefore, in the embodiment of the present invention, NO_X Absorbent 23
To SO_X To release NO_X Temperature of absorbent 23
NO if high_XOf the exhaust gas flowing into the absorbent 23
NO with rich air-fuel ratio_X Absorbent 23 to SO_X Release
Let out, SO_X To release NO_X Absorbent 23
NO if temperature is low_X Raise the temperature of the absorbent 23
And NO_X Air-fuel ratio of exhaust gas flowing into absorbent 23
Is made rich.

[0042] Then outflow from the amount and _the NO _X absorbent 23 of the reducing agent when the air-fuel ratio of the exhaust gas flowing from _the NO _X absorbent 23 in the NO _X absorbent 23 to be released NO _X rich downstream The relationship with the concentration of ammonia NH ₃ in the exhaust gas will be described. First, the amount of the reducing agent will be described. Excess fuel to the fuel quantity required for the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 23 to the stoichiometric air-fuel ratio of the excess fuel because it is used for release and reduction of the NO _X the amount is equal to the amount of reducing agent used in the release and reduction of NO _X. This is _the NO _X absorbent 2
3 from the air-fuel ratio of the mixture in the combustion chamber 5 when releasing the NO _X even when the rich, even when injecting additional fuel during the expansion stroke end or exhaust stroke, NO
_This is true even when additional fuel is injected into the exhaust passage upstream of the _X absorbent 23.

Next, the concentration of ammonia will be described.
When the air-fuel ratio is lean, that is, in an oxidizing atmosphere
Ammonia NH_Three Rarely occurs. However, air fuel
Inhalation when the ratio becomes rich, that is, when the atmosphere becomes a reducing atmosphere
Nitrogen N in air or exhaust gas_Two Is an oxidation catalyst or three
Reduced by the hydrocarbon HC in the primary catalyst 20,
Monia NH_Three Is generated. However, the air-fuel ratio
NO_X NO from absorbent 23_X Is released and raw
Ammonia NH formed_Three Is this NO_X To reduce
NO because it is used for_X NO from absorbent 23_X Is released
While the supplied reducing agent is NO_X Release
And NO while used for reduction_X Absorbent 2
Ammonia NH downstream from 3_Three Does not leak. Against this
NO _X NO from absorbent 23_X After the release of
If the air-fuel ratio is made rich, more precisely, N
O_X NO from absorbent 23_X Used to release and reduce
If excess reducing agent not supplied is supplied, ammonia NH_Three 
Is no longer_X Will not be consumed for the reduction of
Therefore, at this time NO_X Downstream from absorbent 23
Ammonia NH_Three Will be leaked.

[0044] This is caused even when the oxidation catalyst or three-way catalyst 20 upstream of _the NO _X absorbent 23 is not provided. That is, since the NO _X absorbent 23 also includes a catalyst such as platinum Pt having a reducing function, ammonia NH ₃ may be generated in the NO _X absorbent 23 when the air-fuel ratio becomes rich. However, even if ammonia NH
_{Even if 3} is produced, this ammonia NH ₃ is NO _X
Since it is used to reduce NO _X released from the absorbent 23, ammonia NH ₃ does not flow downstream from the NO _X absorbent 23. N However, from _the NO _X absorbent 23
O ammonia NH _{3 X} from _the NO _X absorbent 23 as excess of the reducing agent that is not used has been described above as being provided to release reduced to downstream will flow out.

As described above, when the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 23 is made rich, the NO _X absorbent 2
3 from the excess of the reducing agent that is not used to release and reduce NO _X is supplied the excess of the reducing agent flows out from _the NO _X absorbent 23 downstream in the form of ammonia NH _3, ammonia flowing out at this time The amount is proportional to the amount of excess reducing agent. Therefore, the amount of excess reducing agent can be determined from the amount of ammonia flowing out at this time. The amount of ammonia is capable of detecting the ammonia concentration NO _X ammonia sensor 29
Is detected by In this case, the integrated value of the ammonia concentration is considered to represent the surplus reducing agent amount, and therefore, it can be said that the integrated value of the ammonia concentration is a representative value indicating the surplus reducing agent amount. Further, it can be considered that the maximum value of the ammonia concentration represents the surplus reducing agent amount, and therefore, it can be said that the maximum value of the ammonia concentration is a representative value representing the surplus reducing agent amount.

Next, a first embodiment of the control of the supply of the reducing agent will be described with reference to FIG. Referring to FIG. 7, ΣNO
X is the total being absorbed in the NO _X absorbent 23 NO
_{The X} amount (total NO _X absorption amount) is shown, and I ₁ is the detection current of the NO _X ammonia sensor 29. FIG. 7
NO _X and NH ₃ shows respectively the change of the detection current of the NO _X ammonia sensor 29 due to the change of the NO _X concentration and the NH ₃ concentration in the exhaust gas, detected both of these detection currents of the NO _X ammonia sensor 29 in Current I ₁
Appears in. E indicates the output voltage of the air-fuel ratio sensor 30, and A / F indicates the average air-fuel ratio of the air-fuel mixture in the combustion chamber 5.

As shown in FIG. 7, the total NO _X absorption amountΣNO
X is detected current I ₁ of the NO _X ammonia sensor 29 so approaches the absorption capacity limit of the NO _X absorbent 23 from _the NO _X absorbent 23 NO _X starts to flow out to the downstream begins to rise increases. In the embodiment shown in FIG. 7 NO _X absorbent 2
Estimating the total NO _X absorption amount of 3, on the basis of the rich time interval air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 23 to be re-rich after the rich to the estimated value of the total NO _X absorption Control. That is, in the first embodiment, NO
_The amount of NO _X in the total absorbed in the _X absorbent 23 is provided with a total NO _X absorption amount estimation means for estimating,
As shown in FIG. 7, the total NO _X absorption amount ΣNOX estimated by the total NO _X absorption amount estimating means is equal to the allowable value NOXmax−α.
Is exceeded, the air-fuel ratio is temporarily switched from lean to rich. Here, NOx _max is the maximum NO _X absorption amount that can be absorbed by the NO _X absorbent 23.

[0048] Immediately after the air-fuel ratio A / F is switched to rich so the exhaust gas of a rich air-fuel ratio be the air-fuel ratio A / F is switched from lean to rich to reach _the NO _X absorbent 23 is time-consuming _the amount of NO _X continues to increase flowing out from _the NO _X absorbent 23 to downstream. Then NO _X does not flow out from _the NO _X absorbent 23 to the reducing action of the NO _X with a reducing agent contained in the exhaust gas of a rich air-fuel ratio is started downstream. Therefore the air-fuel ratio after rising short time is switched from lean to rich detected current I ₁ of the NO _X ammonia sensor 29 decreases to zero. On the other hand, when the air-fuel ratio is switched from lean to rich _the NO _X absorbent 2
3 begins to release NO _X , and thus NO _X
The amount of NO _X ΣNOX absorbed in the absorbent 23 gradually decreases.

Next, in the first embodiment, the total NO_X Of absorption
The calculation method will be described. NO_XFlows into the absorbent 23
Exhaust gas (hereinafter referred to as inflow exhaust gas)
NO per unit time when lean_X Absorbent 23
NO absorbed by_X (Hereinafter, unit NO_X Absorbed amount
You. ) Is NO_X NO that can be maximally absorbed by the absorbent 23 _X 
(The maximum NO_X It is called the amount of absorption. ) And NO_X Sucking
NO to collector 23_X Coefficient for the rate at which
Bottom, NO_X Absorption rate) and NO in the inflowing exhaust gas _X concentration
(Hereafter, inflow NO_X It is called concentration. ) And NO_X Absorbent 2
3 Total NO currently absorbed_X Amount (total NO
_X (The amount of absorption).

Then, these parameters, ie, the unit N
O_X Absorption amount and maximum NO_X Absorption and NO_X Absorption speed
And inflow NO_X Concentration and total NO_X Between absorption
A certain relationship holds. Therefore, in this embodiment,
The relational expression that holds between the data
The maximum NO in the relational expression at predetermined time intervals_X Absorption
And NO_X Absorption speed and inflow NO_X Concentration and total NO_X Sucking
Substitute the yield and unit NO _X Calculate the amount of absorption, and thus
Unit NO calculated_X By integrating the absorption amount, the total N
O_X Calculate the absorption. Note that in this example,
The relational expression obtained is the expression shown in FIG. Figure
In the relational expression shown, Aabc is a unit NO._XAbsorption, N
OXmax is the maximum NO_X Absorption amount, Kab is NO_X Absorption speed
Degree, Cnox is inflow NO_X Concentration, ΣNOX is total NO_X absorption
Quantity.

Here, as the initial values of the maximum NO _X absorption amount and the NO _X absorption speed, values obtained in advance by experiments are used.
These maximum NO _X absorption amount and NO _X absorption speed are NO _X
As long as the absorbent 23 does not deteriorate, it is substantially constant irrespective of the change in the engine operating state. However, NO _X
With the use of absorbent 23 is started _the NO _X absorbent 23 is S
Gradually deteriorated due O _X heat of absorption and exhaust gas, the maximum NO _X absorption and NO _X absorption rate varies. Therefore, in this embodiment, the maximum NO
_{The X} absorption amount and the NO _X absorption speed are appropriately corrected. on the other hand,
The inflow NO _X concentration changes with a change in the engine operating state,
Since the total NO _X absorption amount also changes over time, the inflow NO _X concentration and the total NO _X absorption amount are expressed in unit NO.
_When calculating the amount of _X absorption, use the value calculated each time.

[0052] The inlet NO _X concentration Cnox is calculated as follows. That amount of the NO _X flowing per unit time in the NO _X absorbent 23 (hereinafter, referred to as a unit NO _X inflow.) Figure unit NO _X flow rate NA since the function of the engine speed and engine load As shown in FIG. 9, the ROM 3 is previously stored in the form of a map using a function of the engine speed N and the engine load Q / N.
4, and the inflow NO _X concentration can be calculated by dividing the unit NO _X inflow amount NA calculated based on the map by the intake air amount per unit time.

As described above, the maximum NO _X absorption amount gradually decreases with the deterioration of the NO _X absorbent 23,
NO _X absorption rate gradually slows down. In this case, the maximum N
Even if the unit NO _X absorption amount is calculated using the O _X absorption amount and the NO _X absorption speed as they are, an accurate unit NO _X absorption amount is not calculated. Therefore, in the present embodiment, the maximum NO _X absorption amount and the NO _X absorption speed are appropriately corrected by the following method, thereby obtaining the accurate maximum NO _X absorption amount and the NO _X absorption speed.

That is, NO _X is located downstream of the NO _X absorbent 23.
Concentration of NO _X in the exhaust gas flowing out from the absorbent 23 (hereinafter, the outflow NO _X concentration referred.) By using the output of the NO _X ammonia sensor 29 as it can detect the NO _X ammonia sensor 29 is disposed N per unit time
The amount of NO _X flowing out of the O _X absorbent 23 (hereinafter, unit N
It is referred to as O _X outflow. ) Aouts can be calculated. As described above, the unit NO _X inflow amount NA is shown in FIG.
Map so it can be calculated from the unit by subtracting the thus was units NO _X outflow Aouts from the unit NO _X flow rate NA which is calculated according to the relationship shown in FIG. 8 (B) NO _X of
The absorption amount Aabs is calculated. Unit NO _X outflow A
out it is calculated by multiplying a predetermined coefficient K ₁ to the output current I ₁ of the NO _X ammonia sensor 29.

The unit NO _X absorption amount (hereinafter referred to as an actually measured value) Aabs thus calculated and the unit NO _X absorption amount (hereinafter referred to as a theoretical value) A calculated based on the above relational expression.
If _the NO _X absorbent 23 is not deteriorated when compared with the abc these measured values Aabs and the theoretical value Aabc is substantially equal. However, these measured values when the _the NO _X absorbent 23 has deteriorated Aabs and the theoretical value Aabc
And it is considerably different. So in this case,
Before calculating the theoretical value Aabc using the above relational expression, the unit NO _X absorption amount, the inflow NO _X concentration, and the total NO _X absorption amount used when calculating the theoretical value Aabc are stored. The measured values of the inflow NO _X concentration, the total NO _X absorption amount, and the unit NO _X absorption amount used when the theoretical value Aabc was calculated using the above relational expression this time are respectively substituted into the above relational expression to obtain the maximum NO. _X absorption amount NO
To again calculate the Xmax and the NO _X absorption rate Kab. That is, in this embodiment, the maximum NO _X absorption amount NOXmax
_{The X} absorption speed Kab is corrected by the output of the NO _X ammonia sensor 29. According to this the maximum NO _X absorption and NO _X absorbing rate of the NO _X absorbent 23 can be accurately grasped.

[0056] Incidentally excess fuel air-fuel ratio is switched from lean to rich, i.e. reducing agent an air-fuel ratio of the exhaust gas flowing out from _the NO _X absorbent 23 because they are consumed for the reduction of NO _X downstream almost It becomes the stoichiometric air-fuel ratio. In this case, the reason why this is so becomes the air-fuel ratio is only slightly lean of the exhaust gas is not clear when the NO _X absorbent 23 has not deteriorated flowing out from _the NO _X absorbent 23 to downstream, _the NO _X absorbent NO if 23 deteriorates
The air-fuel ratio of the exhaust gas flowing downstream from the _X absorbent 23 tends to be slightly rich. However, in any case, when the action of releasing NO _X from the NO _X absorbent 23 is completed, the air-fuel ratio of the exhaust gas flowing downstream from the NO _X absorbent 23 becomes rich.

[0057] Figure 7 shows the case where the air-fuel ratio of the exhaust gas flowing out from _the NO _X absorbent 23 when the air-fuel ratio is switched from lean to rich to downstream and has a just slightly lean, NO _X absorption When the release action of NO _X from the agent 23 is completed, that is, the total NO _X absorption amount ΣNO
It can be seen that when X approaches zero, the output voltage E of the air-fuel ratio sensor 30 changes toward the output signal level indicating that it is rich, that is, rises. This change in the output signal level E has a good response, so that the output signal level E
It can be switched air-fuel ratio when the releasing action of the NO _X from _the NO _X absorbent 23 be switched to the air-fuel ratio from rich to lean has been completed from rich to lean based on the change.

Therefore, in the embodiment shown in FIG. 7, a reference voltage E _S is set for the output voltage E of the air-fuel ratio sensor 30. That is, using a general expression, the output signal level E of the air-fuel ratio detecting means is obtained. and the air-fuel ratio from rich to switch to a lean when previously set the reference level E _S, the output signal level E exceeds the reference level E _S against.

The output voltage E of the air-fuel ratio sensor 30 changes with a good response to the completion of the NO _X releasing operation. However, the output voltage E varies due to variations in the performance of the air-fuel ratio sensor 30 and the NO _X absorbent 23 or changes over time. E changes in various ways. Therefore, if the reference level E _S not be switched air-fuel ratio from rich to lean upon completion of release of the NO _X it is fixed to a constant value arises.

On the other hand, if an excess reducing agent not used for releasing and reducing NO _X is supplied from the NO _X absorbent 23 when the air-fuel ratio is switched from lean to rich, at this time, the NO _X absorbent 23 since ammonia NH ₃ flows out to the downstream from the detection current I ₁ of the NO _X ammonia sensor 29 as shown in FIG. 7 is increased. In this case, the maximum value Imax of the integrated value ΣI and detected current I ₁ of the detected current I ₁ indicated by hatching in FIG. 7 represents the excess of reducing agent amount.

Although the detection current I ₁ of the NO _X ammonia sensor 29 has a response delay with respect to the completion of the NO _X release, the surplus reducing agent amount can be accurately obtained from the detection current I ₁ . Therefore, in the present invention, the detection current I ₁ of the NO _X ammonia sensor 29 is used.
The reference level E _S is changed based on the change in the exhaust gas, that is, the air-fuel ratio of the exhaust gas is switched from rich to lean when the release of NO _X from the NO _X absorbent 23 is completed based on the change in the ammonia concentration. I try to make it.

More specifically, the integrated value of the detected current I ₁ Σ
I, or set in advance the target value of the smaller value relative to the maximum value Imax of detected current I _1, when ΣI or Imax becomes greater than the target value, i.e. from rich when the amount of reducing agent excess is large The reference level E _S is lowered so that the air-fuel ratio switching time to lean is advanced so that the surplus reducing agent amount becomes _small , that is, the reference level E _S is changed to the output signal level indicating lean, and ΔI Alternatively, when Imax becomes smaller than the target value, that is, when the surplus reducing agent amount is zero or close to zero, the switching timing of the air-fuel ratio from rich to lean is delayed so that the surplus reducing agent amount is not increased. E _S is increased, that is, the reference level E _S is changed to an output signal level indicating richness.

By the way NO _X reducing agent in the exhaust gas being absorbed in the NO _X absorbent 23 when the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 23 is switched from lean to rich (i.e. hydrocarbon) Released and reduced by It should gradually decrease the total NO _X absorption amount ΣNOX therefore. So then the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 23 in this embodiment will be described the method for calculating the total NO _X absorption amount ΣNOX of time is rich.

When the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 23 is lean, the amount of NO _X released / reduced from the NO _X absorbent 23 per unit time (hereinafter referred to as unit N
Referred to as O _X reduction amount. ) Is a coefficient relating to the speed at which NO _X is released and reduced from the NO _X absorbent 23 (hereinafter referred to as the NO _X reduction speed), and the concentration of the reducing agent in the inflowing exhaust gas (hereinafter referred to as the inflow reducing agent concentration). ) And the total amount of NO _X currently absorbed by the NO _X absorbent 23 (total NO _X absorption amount).

Then, these parameters, ie, the unit N
And O _X reduction amount, and NO _X reduction rate, the inflow reducing agent concentration,
A certain relationship is established between the total NO _X absorption amount.
Therefore the NO _X reduction rate equation that holds between these parameters obtained in advance by empirical formula, on the relational expression at predetermined time intervals in the present embodiment, the inflow reducing agent concentration,
Substituting the total NO _X absorption to calculate the unit NO _X reduction amount, calculates the total NO _X absorption by subtracting the thus was units NO _X reduction amount calculated from the total NO _X absorption amount at that time I do. Note that the relational expression obtained by the experiment in the present embodiment is the expression shown in FIG. In the relational expression shown, Are is a unit NO _X reduction amount, Kre is a NO _X reduction speed, Chc is an inflow reducing agent concentration, and ΔNOX is a total NO _X.
It is the amount of absorption.

Here, as the initial value of the NO _X reduction rate, a value obtained in advance by an experiment is used. This NO _X reduction speed is almost constant irrespective of a change in the engine operating state as long as the NO _X absorbent 23 does not deteriorate. However, when the use of the NO _X absorbent 23 is started, the NO _X absorbent 2
3 gradually deteriorates due to absorption of SO _X and heat of exhaust gas, and the NO _X reduction rate changes. Therefore, in this embodiment, the NO _X reduction speed is appropriately corrected by a method described later. On the other hand, the inflow reducing agent concentration depends on the engine operating state, specifically, the amount of air introduced into the combustion chamber 5 and the fuel injection valve 1.
Since it changes with the change of the amount of fuel injected from 0 and the total NO _X absorption also changes over time, the inflow reducing agent concentration and the total NO _X absorption are expressed in the unit NO _X.
When calculating the reduction amount, the value calculated each time is used.

As described above, the NO _x reduction rate K
re gradually decreases with the deterioration of the NO _x absorbent 23. In this case, even if the unit NO _X reduction amount Are is calculated using the NO _X reduction speed Kre as it is, an accurate unit NO
_X reduction amount is not calculated. Therefore Correct appropriately NO _X reduction rate Kre by the following method in the present embodiment, thereby acquiring an accurate NO _X reduction rate.

That is, NO _X is provided downstream of the NO _X absorbent 23.
N capable of detecting the ammonia concentration in the exhaust gas flowing out of the absorbent 23 (hereinafter, referred to as the outflowing ammonia concentration).
Since O _X ammonia sensor 29 is disposed the N
O _X ammonia release and reduction of the NO _X in _the NO _X absorbent 23 by using the output of the sensor 29 can know the completion. Here, if the NO _X reduction rate used for calculating the total NO _X absorption amount is a true value while the air-fuel ratio of the inflowing exhaust gas is rich, the NO _X ammonia sensor 29 detects the NO in the NO _X absorbent 23. Before detecting that the release / reduction of _X is completed, the total NO _X absorption amount does not become zero, and is at least larger than a certain value.
On the other hand, NO _X ammonia sensor 29 is _the NO _X absorbent 23
When it is detected that the release and reduction of NO _{X in} the above is completed, the total NO _X absorption amount should be zero, or at least be smaller than a certain value.

[0069] In other words NO _X ammonia sensor 29
Before detecting that the NO _X release / reduction in the NO _X absorbent is completed, the total NO _X absorption amount becomes zero,
Alternatively, when the value becomes smaller than a certain value, the total NO
Since it can be determined that the NO _X reduction speed used for calculating the _X absorption amount is too fast, in this embodiment, the currently used NO _X reduction speed is reduced by a predetermined value in this embodiment. The predetermined value here may be a constant value, or
When O _X absorption amount becomes zero, or it is detected that the release and reduction of the NO _X in _the NO _X absorbent 23 is completed by NO _X ammonia sensor 29 when it becomes less than a certain value It may be a value that becomes larger as the time is longer based on the time up to.

[0070] On the other hand, NO _X ammonia sensor 29 is NO
Or total NO _X absorption when it is detected that the release and reduction of the NO _X in the _X absorbent 23 has been completed is not the zero, or still when more than a certain value of total NO _X absorption Since it can be determined that the NO _X reduction speed used for the calculation is too slow, in this embodiment, the NO _X reduction speed currently used is increased by a predetermined value in this case. Predetermined value here may be a constant value, or _the NO _X absorbent 23 by NO _X ammonia sensor 29
Based on the total NO _X absorption at the time when it is detected that the release and reduction of the NO _X has been completed in the total NO _X
It may be a value that increases as the amount of absorption increases. As described above, in the present embodiment, the NO _X reduction rate is determined by the NO _X ammonia sensor 2.
9 will be corrected. According to this, N
The O _X reduction rate can be accurately grasped.

As described above, in the present embodiment, the maximum NO _X absorption amount, NO _X absorption speed, and NO _X reduction speed used in the above relational expression are modified in accordance with the degree of deterioration of the NO _X absorbent 23. Can be In other words, the degree of deterioration of the NO _X absorbent 23 can be known from the maximum NO _X absorption amount, the NO _X absorption speed, and the NO _X reduction speed.
That is, when less than the amount the maximum NO _X absorption which is allowed modifications would deterioration of the NO _X absorbent 23 is achieved if within tolerance, or was allowed to fix N
O _X absorption rate or NO _X reduction rate is likewise _the NO _X absorbent 23 is deteriorated in this embodiment when the degree of deterioration of _the NO _X absorbent 23 is slower than the rate that would have been achieved if within tolerance Diagnose that you have done it. According to this deterioration of the NO _X absorbent 23 can be accurately diagnosed.

FIG. 10 is a flow chart for executing the first embodiment.
Shows Chin. Referring to FIG.
The map shown in FIG.
The fuel injection amount TAU is calculated. Then step 101
Then NO_X NO from absorbent 23_X Indicates that
NO_X It is determined whether the release flag is set.
It is. NO_X When the release flag is not set
Proceeding to Step 102,
Total NO calculated by routine_X Absorption ΣNOX is the highest
Large NO_X Exceeds a value smaller than the absorption amount NOXmax by the value α.
It is determined whether or not it has been received. ΣNOX ≦ NOXmax -α
Time, that is, NO_X NO of absorbent 23 _X Not in absorption capacity
If there is enough time, the process jumps to step 104.
In step 104, correction is performed from the map shown in FIG.
A coefficient K is calculated. Next, at step 105, the basic fuel
Multiplying the fuel injection amount TAU by the correction coefficient K
The final fuel injection amount TAUO (= K · TAU) is calculated.
The fuel injection is performed with the injection amount TAUO.
Next, at step 106, NO_X SO from absorbent 23
_X To release SO_X Whether or not to perform the release process
Is determined. SO_X When it is not necessary to perform release processing
Complete the processing cycle.

On the other hand, in step 102 ΣNOX>
When a determination is made that the NOXmax-.alpha. is set NO _X release flag proceeds to step 103, and then NH ₃ detection flag is set the routine proceeds to step 103a. Next, the routine proceeds to step 104. If NO _X release flag is set step, at the next processing cycle 101
Then, the routine proceeds to step 108, where the rich correction coefficient K _R is calculated. Next, at step 109, the basic fuel injection amount TA
U is multiplied by a rich correction coefficient K _R and a rich correction coefficient K _S to obtain a final fuel injection amount TAUO (= K _R
.TAU · K _S ) is calculated, and fuel injection is performed with this injection amount TAUO. Note that the rich correction coefficient K _S is a coefficient calculated as the NO _X reduction speed is corrected in the routines of FIG. 11 and FIG. Step 1
According to 09 is switched from the uniform mixture combustion under stratified combustion or a lean air-fuel ratio at a lean air-fuel ratio uniform mixture combustion under a rich air-fuel ratio, whereby _the NO _X absorbent The release action of NO _X from 23 is started.

Next, at step 110, the air-fuel ratio sensor 3
0 of the output voltage E is whether exceeds the reference voltage E _S is determined. Proceeds to step 106 when the E ≦ E _S. On the other hand, if E> E _S , the process proceeds to step 111 and NO
_{The X} release flag is reset. When the NO _X release flag is reset, the air-fuel ratio is switched from rich to lean. On the other hand, if it is determined in step 106 that the SO _X release process should be performed, the process proceeds to step 107 and N
A process of releasing SO _X from the O _X absorbent 23 is performed. That is, the air-fuel ratio is made rich while maintaining the temperature of the NO _X absorbent 23 at about 600 ° C. or higher.

FIGS. 11 and 12 show the total NO _X of this embodiment.
2 shows a routine for calculating an absorption amount ＸNOX. In FIG. 11, first in step 200, NO
It is determined whether or not the air-fuel ratio of the exhaust gas flowing into the _X absorbent 23 is lean. When it is determined in step 200 that the air-fuel ratio of the inflowing exhaust gas is lean, the engine speed N, the engine load L, and the intake air amount Q are calculated in step 201, and then in step 202, the map shown in FIG. the amount NA of the NO _X flowing into _the NO _X absorbent 23 on the basis of the engine speed N and the engine load L is calculated. Then _the NO _X absorbent 23 in step 203
NO _X concentration Cnox in the exhaust gas flowing is calculated,
Then theoretical Aabc of the amount of absorbed NO _X in _the NO _X absorbent 23 per unit time from the equation shown in FIG. 8 (A) (unit NO _X absorption amount) is calculated in step 204. Then 8 (B) in and 8 units NO _X absorption from relational expression (C) Found Aabs is calculated in step 205.

Next, at step 207, the theoretical value Aa
It is determined whether the difference between bc and the measured value Aabs is within the range of the predetermined value β. In step 207, Aa
When it is determined that bs−β <Aabc <Aabs + β, the values of the maximum NO _X absorption amount NOXmax and the NO _X absorption speed Kab used in the relational expression shown in FIG. 8A are true values. In step 208, the theoretical value Aabc is adopted as the unit NO _X absorption amount Aab, and in step 209, the unit NO _X absorption amount Aa
b is added to the current total NO _X absorption amount ΣNOX, and a new total NO _X absorption amount ΣNOX is calculated.
09a, the maximum NO at the time of execution of the current routine
And _X absorption NOXmax, NO _X concentration C in the inflowing exhaust gas
and nox, and a unit NO _X absorption Aab stored.

On the other hand, in step 207, Aabs-
β ≧ Aabc or Aabc ≧ Aabs + β
When they are separated, they are used in the relational expression shown in FIG.
Maximum NO_X NOXmax or NO_X Absorption speed
It is determined that the value of Kab is not a true value, and step 211
Unit NO in_X Measured value Aa as absorption amount Aab
bs, and then at step 212
Unit saved in step 209a before
NO_X Absorption amount Aab and NO in inflow exhaust gas _X Concentration C
nox and total NO_X FIG. 8A shows the absorption amount ΣNOX.
Was obtained by substituting into the equation
NO when executing the routine_X Absorption amount Aab;
NO in inflow exhaust gas_X Concentration Cnox and total NO_X Absorption
Similarly, ΣNOX is substituted into the relational expression shown in FIG.
To get another one equation and from these two equations
The two calculated values NOXmax and Kab are newly updated.
Maximum NO_X Absorption and NO_X By setting the absorption rate
After correcting these parameters, the process proceeds to step 209.

If it is determined in step 200 that the air-fuel ratio of the inflowing exhaust gas is rich, the engine speed N, the engine load L, and the intake air amount Q are calculated in step 213 in FIG. Based on the engine speed N, the engine load L, and the intake air amount Q, the concentration Chc of the reducing agent, that is, the hydrocarbon in the exhaust gas flowing into the NO _X absorbent 23 is calculated. That is, the amount of fuel injected from the fuel injection valve 10 is determined based on the engine speed N and the engine load L, and the amount of fuel not combusted in the combustion chamber 5 among the fuel injection amounts determined in this manner. By dividing by the intake air amount Q, the concentration of the reducing agent in the inflowing exhaust gas is calculated, so that the engine speed N, the engine load L,
The reducing agent concentration Chc in the inflowing exhaust gas can be calculated based on the intake air amount Q.

Next, at step 215, FIG.
The unit NO _X reduction amount Are is calculated from the relational expression shown in (2), and then, in step 216, the unit NO _X reduction amount Are is subtracted from the current total NO _X absorption amount ΣNOX, and a new total NO _X absorption amount ΣNOX is calculated. , Step 2
Proceed to 17. Output current I ₁ in step 217 the NO _X ammonia sensor 29 whether exceeds the reference value It is determined. NO _X releasing flag proceeds to step 218 when it is I _1> It is reset at step 217. Here, in step 111 of FIG.
O _X release flag is step if it is not reset 2
Air-fuel ratio of the exhaust gas NO _X release flag is flowing into _the NO _X absorbent 23 by being reset at 18 is lean from rich, thus releasing and reduction of the NO _X from _the NO _X absorbent 23 is 10 The process is forcibly terminated instead of according to the flowchart.

[0080] The total NO _X absorbed amount ΣNOX in step 219 and then whether greater than the determination value A is determined. If ΣNOX ≦ A in step 219, FIG.
It is determined that the value of the NO _X reduction speed Kre used in the relational expression (D) is a true value, and the routine is terminated without correcting the currently used NO _X reduction speed. On the other hand, when it is determined in step 219 that ΣNOX> A, the process proceeds to step 220 and FIG.
When the NO _X reduction speed Kre used in the relational expression (D) is increased by a predetermined value, and then the air-fuel ratio of the inflowing exhaust gas is made rich in step 221, FIG.
In step 109 of 0, the rich correction coefficient K _S used is corrected so that the rich degree increases.

On the other hand, at step 217, I ₁ ≦ It
When it is judged that the total NO _X absorption ΣNOX in step 222 whether less than the determination value A is determined. The value of the NO _X reduction rate Kre used in relation to FIG. 8 (D) when it is judged that .SIGMA.NOX ≧ A in step 222 determines that the true value, NO _X currently in use The routine ends without correcting the reduction speed. On the other hand, step 222
NO _X reduction rate Kre used in relation to FIG. 8 (D) proceeds to step 223 is made to slow down by a predetermined value when it is judged that .SIGMA.NOX <A in,
Next, at step 224, when the air-fuel ratio of the inflowing exhaust gas is made rich, the rich correction coefficient K _S used at step 109 of FIG. 10 is corrected so that the degree of richness becomes small.

FIG. 13 shows the target level E._S To calculate
Shows a routine. Referring first to FIG.
In step 300, NH_Three The detection flag is set
Is determined. This NH_Three Figure shows detection flag
In step 102 of 10 ΣNOX> NOXmax−
Set when it becomes α. NH_Three If the detection flag is
If so, the routine proceeds to step 301 where NH_Three 
The elapsed time t since the detection flag was set is a fixed time
t₁ Is determined. This fixed time t₁ Is
NO after air-fuel ratio is made rich from lean_X Ammoni
Detection current I of the sensor 29₁ Until it has dropped to zero
It's time. t> t₁ , The process proceeds to step 302.
At NH_Three The elapsed time t since the detection flag was set is
Fixed time t_Two Is determined. At this fixed time
Interval t_Two Is NO_X Ammonia flows downstream from absorbent 23
No matter what amount of ammonia_X A
Although the ammonia sensor 29 can detect the ammonia concentration
That's enough time. t ≦ t _Two Step 303
Proceed to.

[0083] detected current I ₁ of the step 303 NO _X ammonia sensor 29 is calculated. Then step 3
04 In the integrated value ΣI of detected current by adding the detected current I ₁ in ΣI is calculated. Then whether the integrated value ΣI of detected current proceeds to step 305 is larger than the target value Sr when it is determined that becomes t> t ₂ in step 302 is determined. When ΣI> Sr, the routine proceeds to step 306, where the target level E _S is decreased by a predetermined set value a, and then the routine proceeds to step 308. On the other hand, if ΣI ≦ Sr, the routine proceeds to step 307, where the target level E _S is increased by a predetermined set value a, and then the routine proceeds to step 308. At step 308, ΔI is cleared and the NH ₃ detection flag is reset.

FIG. 14 shows another example of a routine for calculating the target level E _S. Referring to FIG. 14, first, at step 400, it is determined whether or not the NH ₃ detection flag is set. This NH ₃ detection flag is determined in step 102 of FIG.
Set when Xmax-α. When NH ₃ detection flag has been set is determined whether the elapsed time t from being set NH ₃ detection flag goes to step 401 exceeds a predetermined time t ₁ is. This fixed time t ₁ is a time from when the air-fuel ratio is made rich to lean as described above, until the detection current I ₁ of the NO _X ammonia sensor 29 ends to drop to zero. t> whether becomes to t ₁ NH ₃ detection flag goes to step 402 the elapsed time t after the set exceeds a predetermined time t ₂ is determined. This fixed time t ₂ is equal to NO _X as described above.
Whatever the amount of ammonia when ammonia absorber 23 to the downstream flows out NO _X ammonia sensor 29 also is a sufficient time to be detected ammonia concentration. When t ≦ t _2, the process proceeds to step 403.

At step 403, the detected current I₁ Is Imax
It is determined whether or not it is greater than I₁ When> Imax
Proceeds to step 404 and₁ Is the maximum value of the detection current I
max. Next, at step 402, t> t_Two 
When it is determined that the condition has been reached, the process proceeds to step 405.
Whether the maximum value Imax of the detection current is larger than the target value Imaxr
It is determined whether it is not. Step if Imax> Imaxr
Proceeding to 406, target level E_S Is a predetermined setting value
a, and then go to step 408.
On the other hand, when Imax.ltoreq.Imaxr, step 407 is executed.
Go to target level E_S Is only a predetermined set value a
Is increased, and then go to step 408. Step
In step 408, Imax is cleared and NH_Three Detection flag
Reset.

[0086] Figure 15 shows a routine for determining the deterioration of the NO _X absorbent 23. In FIG. 15, first, at step 500, it is determined whether or not the maximum NO _X absorption amount NOXmax is larger than the determination value C. At step 501, it is determined whether or not the NO _X absorption speed Kab is larger than the determination value D. In step 502 NO _X reduction rate Kre
Is larger than a predetermined value E. The NOXmax, Kab, and Kre used here are shown in FIG.
Alternatively, it is a parameter used in the relational expression shown in FIG.

[0087] is determined NOXmax> C in step 500, and in step 501 it is determined that Kab> D, and when it is determined that Kre> E in step 502 NO _X absorbent proceeds to step 503 2
The deterioration flag indicating that 3 is deteriorated is turned off. On the other hand, it is determined in step 500 that NOXmax ≦ C, or in step 501, Kab ≦ D
Or Kre in step 502
If it is determined that ≦ E, the routine proceeds to step 504, where the deterioration flag is turned on.

In the above-described embodiment, the maximum NO _X absorption amount NOXmax, NO _X absorption speed Kab, NO _X reduction speed K
unused N as the initial value of parameters such as re
O _X absorbent values employed in, but so as to overlap the modification from the start is used NOXmax, Kab, K
re may be considering the temperature of the NO _X absorbent in the embodiments described above so also vary according to the temperature of the NO _X absorbent 23. Specifically, for example _the NO _X absorbent 23
The initial value of each parameter determined according to the temperature is previously obtained and stored in the ROM 34. For the correction of each parameter described above, a correction coefficient for each parameter is calculated, and the unit NO _X absorption amount Aab or the unit NO _X reduction Correct this correction factor to the initial value of each parameter calculated by the temperature of the NO _X absorbent 23 when calculating the amount are, shows a modified and thus the parameters in FIG. 8 (a) or FIG. (D) It may be used in a relational expression.

In the above embodiment, NO_X Absorbent 23
In exhaust gas flowing into_X Concentration Cnox to engine speed
N, the engine load L, and the intake air amount Q.
NO_X NO on the upstream side of the absorbent 23_X Ammoni
A sensor is arranged and this NO _X With ammonia sensor
NO_X The concentration Cnox may be directly detected. Ma
NO_X NO of absorbent 23_X When the reduction ability is insufficient
NO if_X NO downstream of ammonia sensor 29_X Reducing ability
You may make it arrange | position a catalyst with high power.

The corrected parameters (ie, the maximum NO _X absorption amount and NO _X absorption speed) are not compared with the determination values, but are calculated using the initial values as they are and using the relational expression of FIG. NO _X based on the unit NO _X absorption
The amount of NO _X flowing downstream of the absorbent is calculated, and the NO _X amount thus calculated is compared with the amount of NO _X flowing downstream of the NO _X absorbent calculated from the output of the NO _X ammonia sensor 29, when there is a large isolation between them it may be determined that _the NO _X absorbent 23 is deteriorated.

[0091]

According to the first aspect of the present invention, NO in exhaust gas
Maximum NO _X absorption amount of NO _X absorbent by utilizing the output of the sensor which can detect the _X concentration, or rate of absorption of NO _X into _the NO _X absorbent is calculated, these maximum NO _X absorption or NO The deterioration of the NO _X absorbent is determined based on the _X absorption speed. As described above, since the parameters such as the maximum NO _X absorption amount or the NO _X absorption speed calculated using the actually measured value of the NO _X concentration in the exhaust gas, that is, the value that is not the estimated value, are used, the deterioration of the NO _X absorbent is accurately determined. Can be determined.

[0092] The fifth of the NO _X absorbing amount estimation means in the completion timing of the release and reduction of the NO _X in _the NO _X absorbent which is determined based on the output of a sensor capable of detecting the ammonia concentration in the exhaust gas according to the invention deterioration of the NO _X absorbent is determined based to the NO _X reduction rate in _the NO _X absorbent to be corrected on the basis of the NO _X absorbent amount estimated by. As described above, the NO calculated using the measured value of the ammonia concentration in the exhaust gas, that is, the value that is not the estimated value
Since utilizing parameters such _X reduction rate can be determined accurately the deterioration of the NO _X absorbent.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing a structure of a sensor section of the NO _X ammonia sensor.

FIG. 3 is a diagram showing a current detected by a NO _X ammonia sensor.

FIG. 4 is a diagram showing an output voltage of an air-fuel ratio sensor.

FIG. 5 is a diagram showing a basic fuel injection amount, a correction coefficient, and the like.

FIG. 6 is a diagram for explaining the NO _X absorbing / releasing action of the NO _X absorbent.

FIG. 7 is a time chart showing an output voltage of an air-fuel ratio sensor, a detection current of a NO _X ammonia sensor, and the like.

FIG. 8 is a diagram showing a relational expression for calculating a unit NO _X absorption amount and the like.

FIG. 9 is a view showing a map of an NO _X inflow amount.

FIG. 10 is a flowchart for controlling engine operation.

FIG. 11 is a flowchart for calculating a total NO _X absorption amount.

FIG. 12 is a flowchart for calculating a total NO _X absorption amount.

13 is a flow chart for calculating a target level E _S.

14 is a flow chart for calculating a target level E _S.

FIG. 15 is a flowchart for determining deterioration of the NO _X absorbent.

[Explanation of symbols]

11 ... Fuel injection valve 23 ... NO _X absorbent 29 ... NO _X ammonia sensor 30 ... air-fuel ratio sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 305 F02D 41/04 305A 45/00 314 45/00 314Z (72) Inventor Yasuyuki Irisawa Aichi 1 Toyota Town, Toyota City Toyota Motor Corporation F-term (reference) 3G084 BA09 BA13 BA24 DA10 DA27 EA11 EB11 FA10 FA18 FA26 FA28 FA29 FA33 3G091 AB02 AB03 AB09 BA33 DB05 DB06 DB07 DB10 DC01 EA01 EA03 EA07 EA33 EA34 FB10 GB12 GB GB04W GB04X HA19 HA36 HA37 3G301 HA01 JA15 JA21 JB09 JB10 LB01 MA01 MA11 NA04 NA05 ND01 NE13 NE15 NE19 PA11Z PA17Z PD01Z PD02Z PE01Z PF03Z

Claims (7)

[Claims] 1. A absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, and releasing the reducing agent an air-fuel ratio of the inflowing exhaust gas contained in the exhaust gas absorbed NO _X and becomes rich the _the NO _X absorbent to reduce disposed engine exhaust passage, the exhaust purification system of an internal combustion engine arranged a sensor capable of detecting concentration of NO _X in the exhaust gas to the _the NO _X absorbent downstream of the engine exhaust passage, NO _X when the estimated value of the maximum NO _X absorption amount is estimated to be absorbed in the NO _X absorbent by utilizing the output of the sensor, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is lean at least one calculates, thus estimated value of the maximum NO _X absorption amount calculated or NO _X absorption of the estimated value of the NO _X absorption rate into _the NO _X absorbent which is estimated to be achieved in absorbent Speed estimated value is smaller than judgment value Sometimes an exhaust purifying apparatus for an internal combustion engine which is adapted to determine that _the NO _X absorbent is deteriorated. The amount of wherein _the NO _X absorbent NO _X flowing out to the downstream, previously obtained the maximum NO _X absorption of the NO _X absorbent, the relational expression holds between the NO _X absorption rate in _the NO _X absorbent In advance, the amount of NO _X flowing downstream of the NO _X absorbent is calculated based on the output of the sensor, and the thus calculated amount of NO _X is substituted into the above relational expression to obtain the maximum N N
O _X absorption of the estimated value and the exhaust gas control apparatus according to claim 1 which is adapted to calculate the estimated value of the NO _X absorbing rate. 3. NO by the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is integrating the amount of the NO _X absorbed in the NO _X absorbent is calculated based on the engine operating state when it is lean comprising a NO _X absorption amount estimation means for estimating the amount of the NO _X absorbed in the _X absorbent, NO _X when the NO _X absorbed amount estimated by the NO _X absorption amount estimation means exceeds the allowable value 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio of the exhaust gas flowing into the absorbent is switched from lean to rich. 4. A claim using the maximum NO _X absorption and NO _X absorbing rate as the engine operating condition when estimating the amount of the NO _X which the NO _X absorbed amount estimating means is absorbed in _the NO _X absorbent 4. The exhaust gas purification device for an internal combustion engine according to 3. 5. The air-fuel ratio of the inflowing exhaust gas is lean.
NO when_X And the air-fuel ratio of the inflowing exhaust gas
NO absorbed when becomes rich_X The exhaust gas contains
NO released and reduced by a reducing agent_X Exhaust absorbent
Placed in the air passage and the NO_X In the engine exhaust passage downstream of the absorbent
A sensor that can detect the concentration of ammonia in exhaust gas
Place, NO_X The air-fuel ratio of the exhaust gas flowing into the absorbent is
NO when enriched_X NO from absorbent_X To
Surplus reductant not used to release and reduce
NO in the form of ammonia_X Spilled from the absorbent and the above sensor
NO_X Ammonium in exhaust gas flowing out of absorbent
NO when the concentration exceeds the judgment value_X NO from absorbent
_X Internal combustion engine that determines that the release and reduction of fuel has been completed
In the Seki exhaust purification system, NO_X Exhaust flowing into the absorbent
When the air-fuel ratio of the gas is lean, the engine
NO calculated based on_X NO absorbed by the absorbent_X of
Integrate the amount, NO_X Air-fuel ratio of exhaust gas flowing into the absorbent
Is rich when NO_X NO in absorbent_X of
NO calculated based on reduction speed _X Return on absorbent
NO_X NO by subtracting the amount of_X Absorbent
NO absorbed in_X NO to estimate the amount of_X Absorption amount
Equipped with a_X NO from absorbent_X Release / return
NO when it is determined that the original is completed_X Absorption estimation
NO estimated by means_X Absorption amount deviates from the reference value
NO when above _X Used by absorption amount estimation means
NO_X The reduction rate is corrected and the NO thus corrected_X Return
NO when the original speed is lower than the judgment value_X Absorbent deteriorates
An exhaust gas purifying apparatus for an internal combustion engine, which is configured to determine that exhaust gas has been exhausted. 6. when NO _X absorption amount estimated by the NO _X absorbent amount estimating means when the release and reduction of the NO _X from _the NO _X absorbent is determined to be completed is greater than the reference value NO _X absorbent correction so as to increase the NO _X reduction rate used in an amount estimating means, the reference value exhaust purification system of an internal combustion engine according to claim 5 for correcting to slow the NO _X reduction rate when less than . 7. A maximum NO _X absorption of the NO _X absorbent as the engine operating condition when estimating the amount of the NO _X which the NO _X absorbed amount estimating means is absorbed in the NO _X absorbent and NO _X
An exhaust purification system of an internal combustion engine according to claim 5 using the rate of absorption of the NO _X in the absorbent.