JP2586739B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas purification device for an internal combustion engine.

The engine exhaust passage for purifying NO _X in the Background diesel engine branches to the pair of exhaust branch passages, is arranged a switching valve to the branch portions of the exhaust branch passages, by switching the switching valve whenever the predetermined period has elapsed alternately electrically sawn exhaust gases either one of the exhaust branch passage, a diesel engine is arranged a catalyst capable of oxidizing absorb respectively NO _X in the exhaust branch passages is well known (JP 62-106826 JP ). In this diesel engine, NO _X in the exhaust gas led into one exhaust branch passage is oxidized and absorbed by a catalyst arranged in the exhaust branch passage. During this time, the flow of exhaust gas into the other exhaust branch passage is stopped, and a gaseous reducing agent is supplied into the exhaust branch passage, and the reducing agent accumulates in the catalyst disposed in the exhaust branch passage. NO _X is reduced. Then, after a certain period of time, the switching action of the switching valve stops the introduction of the exhaust gas into the exhaust branch passage from which the exhaust gas has been guided, and the introduction into the exhaust branch passage from which the introduction of the exhaust gas has been stopped. Exhaust gas introduction is resumed. That is, in this diesel engine, regarding each exhaust branch passage, exhaust gas is circulated for a certain period of time, and during this period, NO _X in the exhaust gas is oxidized and absorbed by the catalyst, and then the exhaust gas is stopped for a certain period of time. The reducing agent is supplied, and the NO _X stored in the catalyst is reduced.

However, the amount of NO _X emitted from the engine varies depending on the operating state of the engine, and therefore the amount of NO _X oxidized and absorbed by the catalyst during a certain period during which exhaust gas is circulated varies depending on the operating state of the engine during that period. I do. Therefore a large amount of NO _X
There becomes saturated is NO _X oxide absorption capacity of the catalyst within a fixed period in which the exhaust gas is caused to flow in the case where the operating state of the engine is discharged to continue, the NO _X oxidize absorbed catalyst and thus This causes the problem that NO _X is released into the atmosphere.

On the other hand, if the operating state of the engine that emits a small amount of NO _X continues, only a small amount of NO _X is oxidized and absorbed by the catalyst within a certain period during which the exhaust gas is circulated. Therefore, in this case, the reducing agent is not used for the reduction of part of the reducing agent only NO _X becomes excessive when the inflow of exhaust gas is supplied reducing agent is stopped, the excess of reducing agent is air The problem is that it is released into the interior.

DISCLOSURE OF THE INVENTION An object of the present invention is to provide an exhaust gas purification apparatus capable of satisfactorily reducing harmful components released into the atmosphere irrespective of the amount of NO _X discharged from an engine.

According to the present invention, absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, the engine and _the NO _X absorbent to release the NO _X absorbed to decrease the oxygen concentration in the exhaust gas flowing It was disposed in the exhaust passage, and is absorbed in the NO _X absorbent N
And _the amount of NO _X estimating means for estimating a O _X amount, NO by NO _X estimating means
_When the NO _X amount estimated to be absorbed by the _X absorbent exceeds a predetermined allowable amount, the oxygen concentration in the exhaust gas flowing into the NO _X absorbent is reduced, and NO from the NO _X absorbent is reduced. exhaust purification system for an internal combustion engine and a NO _X emission means for emitting _X is provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall view of an internal combustion engine, FIG. 2 is a view showing a map of basic fuel injection time, FIG. 3 is a view showing a correction coefficient K, and FIG. unburned HC in the gas, the diagram showing the concentration schematically CO and oxygen, FIG. 5 is a diagram for explaining the absorbing and releasing action of NO _X, FIG. 6 is the NO _X amount exhausted from the engine shown figure, FIG. 7 is graph showing the NO _X absorbing capacity of the NO _X absorbent, Figure 8 Figure showing the release profile of the NO _X, FIG. FIG. 9 is showing a change of a correction coefficient k, Fig. 10 Are C ₁ , C ₂ , α, β
FIG. 11 is a diagram showing a map of exhaust gas temperature T,
12 and 13 are flowcharts showing a time interruption routine, FIG. 14 is a flowchart for calculating a fuel injection time TAU, FIGS. 15 and 16 are flowcharts showing a time interruption routine of another embodiment, From Fig. 17
FIG. 19 is a flowchart for calculating a fuel injection time TAU of another embodiment, FIG. 20 is a diagram showing a correction coefficient _Kt, and FIG.
FIG. 22 is an overall view of an internal combustion engine showing another embodiment, FIG. 22 is an overall view of a diesel engine showing still another embodiment, FIG. 23 is a view showing the amount of NO _X exhausted from the engine, FIG. Is the NO _X absorbent
NO _X absorption characteristics shows a diagram, FIG. 25 is a line diagram showing a residual ratio of the NO _X remaining in _the NO _X absorbent, Figure 26 is a flowchart showing the NO _X release control, FIG. 27 is yet another An overall view of a diesel engine showing an embodiment, and FIGS. 28 to 30 are flowcharts showing NO _X release control.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 shows a case where the present invention is applied to a gasoline engine.

Referring to FIG. 1, 1 is an engine body, 2 is a piston,
Reference numeral 3 denotes a combustion chamber, 4 denotes a spark plug, 5 denotes an intake valve, 6 denotes an intake port, 7 denotes an exhaust valve, and 8 denotes an exhaust port. The intake port 6 is connected to a surge tank 10 via a corresponding branch pipe 9, and a fuel injection valve 11 for injecting fuel toward the intake port 6 is attached to each branch pipe 9. The surge tank 10 is connected to an air cleaner 13 via an intake duct 12, and a throttle valve 14 is arranged in the intake duct 12. On the other hand, the exhaust port 8 is connected through the exhaust manifold 15 and the exhaust pipe 16.
It is connected to a casing 18 containing a NO _X absorbent 17.

The electronic control unit 30 is composed of a digital computer, and a ROM (read-on memory) 32, a RAM (random access memory) 3
3, a CPU (microprocessor) 34, an input port 35 and an output port 36 are provided. A pressure sensor 19 that generates an output voltage proportional to the absolute pressure in the surge tank 10 is mounted in the surge tank 10, and the output voltage of the pressure sensor 19 is
The signal is input to the input port 35 via the AD converter 37. Also,
An idle switch 21 for detecting that the throttle valve 14 is at an idling opening is attached to the throttle valve 14, and an output signal of the idle switch 20 is supplied to an input port 35.
Is input to

On the other hand, a transmission, for example, an automatic transmission 22, is connected to the crankshaft 21. The automatic transmission 22 is provided with a gear position detector 23 for detecting a transmission gear position and a vehicle speed sensor 24 for detecting a vehicle speed. The outputs of the gear position detector 23 and the vehicle speed sensor 24 are provided. The signal is input to the input port 35. Also, the exhaust pipe upstream of the casing 18
A temperature sensor 25 for generating an output voltage proportional to the exhaust gas temperature is mounted in the unit 16, and the output voltage of the temperature sensor 25 is
The signal is input to the input port 35 via the AD converter 38. Also,
The input port 35 is connected to a rotation speed sensor 26 that generates an output pulse representing the engine rotation speed. On the other hand, output port 36
Are connected to the ignition plug 4 and the fuel injection valve 11 via corresponding drive circuits 39, respectively.

In the internal combustion engine shown in FIG. 1, the fuel injection time TAU is calculated based on, for example, the following equation.

TAU = TP · K Here, TP indicates a basic fuel injection time, and K indicates a correction coefficient. The basic fuel injection time TP indicates a fuel injection time required for setting the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder to the stoichiometric air-fuel ratio. The basic fuel injection time TP is obtained in advance by an experiment, and is stored in advance in the ROM 32 in the form of a map as shown in FIG. 2 as a function of the absolute pressure PM in the surge tank 10 and the engine speed N. The correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder. If K = 1.0, the air-fuel mixture supplied to the engine cylinder has the stoichiometric air-fuel ratio. On the other hand, when K <1.0, the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder becomes larger than the stoichiometric air-fuel ratio, that is, lean, and when K> 1.0, the air-fuel ratio supplied to the engine cylinder becomes Is smaller than the stoichiometric air-fuel ratio, that is, rich.

The value of the correction coefficient K is predetermined with respect to the absolute pressure PM in the surge tank 10 and the engine speed N, and FIG. 3 shows an example of the value of the correction coefficient K. In the embodiment shown in FIG. 3, in the region where the absolute pressure PM in the surge tank 10 is relatively low, that is, in the low engine load operation region, the value of the correction coefficient K is set to a value smaller than 1.0. The air-fuel ratio of the air-fuel mixture supplied into the cylinder is made lean. On the other hand, in a region where the absolute pressure PM in the surge tank 10 is relatively high, that is, in a high engine load operation region, the value of the correction coefficient K is set to 1.0. It is assumed to be the air-fuel ratio. Also, the region where the absolute pressure PM in the surge tank 10 is highest,
That is, in the engine full load operation region, the value of the correction coefficient K is set to a value larger than 1.0, and at this time, the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder is made rich. In an internal combustion engine, low-medium load operation is usually most frequent, so that the lean mixture is burned during most of the operation.

FIG. 4 schematically shows the concentration of typical components in the exhaust gas discharged from the combustion chamber 3. As can be seen from FIG. 4, unburned HC and CO in the exhaust gas discharged from the combustion chamber 3
Is increased as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes richer, and the oxygen O ₂ in the exhaust gas discharged from the combustion chamber 3 becomes the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3. It increases as the fuel ratio becomes leaner.

Casing _the NO _X absorbent 17 contained in the 18 as a carrier, for example alumina, such as the carrier on, for example, potassium K, sodium Na, lithium Li, cesium Cs, barium Ba, calcium Ca At least one selected from alkaline earths, rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt are supported. Engine intake passage and _the NO _X absorbent is supplied to the 17 exhaust passage upstream of the air and fuel (hydrocarbons)
The _the NO _X absorbent 17 of Toko to refer to the ratio of the air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent 17 absorbs the NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, the oxygen concentration in the inflowing exhaust gas performing absorption and release action of the NO _X to release the absorbed and reduced NO _X. The air-fuel ratio of the inflowing exhaust gas when the NO _X absorbent 17 in the exhaust passage upstream of the fuel (hydrocarbon) or the air-fuel ratio is not supplied coincides with the air-fuel ratio of the mixture supplied into the combustion chamber 3 , therefore this case _the NO _X absorbent 17 absorbs NO _X when the air-fuel ratio of the mixture supplied into the combustion chamber 3 of the lean, the oxygen concentration in the mixture fed into the combustion chamber 3 It will release the absorbed and reduced NO _X.

If the above-mentioned NO _X absorbent 17 is arranged in the engine exhaust passage, the NO _X absorbent 17 actually performs the NO _X absorption / release operation, but there are some parts where the detailed mechanism of this absorption / release operation is not clear. However, it is considered that this absorption / release action is performed by a 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.

That is, the oxygen concentration of the inflowing exhaust gas inflow exhaust gas becomes considerably lean, increases by a large margin, with these oxygen O ₂ is O _2- or O ^2- in the form as shown in FIG. 5 (A) Attaches to the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas reacts with O ₂₋ or O ²⁻ on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2N
O ₂ ). Next, a part of the generated NO ₂ is absorbed in the absorbent while being oxidized on the platinum Pt and combined with the barium oxide BaO to form nitrate ion NO ₃₋ as shown in FIG. 5 (A). Diffuses into absorbent. In this way, NO _X is absorbed into the NO _X absorbent 17.

As long as the oxygen concentration in the incoming exhaust gas is high,
As long as NO ₂ is produced and the NO _X absorption capacity of the absorbent is not saturated
NO ₂ is absorbed in the absorbent to generate nitrate ion NO ₃₋ . On the other hand, the oxygen concentration in the exhaust gas
When the production amount of NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ → NO ₂ ), and thus nitrate ion NO ₃₋ in the absorbent is released from the absorbent in the form of NO ₂ . Namely, when the oxygen concentration in the inflowing exhaust gas is released NO _X from _the NO _X absorbent 17 when lowered. As shown in FIG. 4, when the degree of lean of the inflowing exhaust gas decreases, the oxygen concentration in the inflowing exhaust gas decreases,
Thus the inflowing exhaust gas lean degree of the lower them For example inflow air-fuel ratio of the exhaust gas is a lean also _the NO _X absorbent 17
NO _X is to be released from the.

On the other hand, at this time, when the mixture supplied to the combustion chamber 3 is made rich and the air-fuel ratio of the inflowing exhaust gas becomes rich, the fourth
As shown in the figure, a large amount of unburned HC and CO is emitted from the engine, and the unburned HC and CO react with oxygen O ₂₋ or O ²⁻ on platinum Pt to be oxidized. Further, the air-fuel ratio of the inflowing exhaust gas is NO ₂ is released from the absorbent in the oxygen concentration in the inflowing exhaust gas becomes rich is extremely lowered, so that the NO ₂ is shown in FIG. 5 (B) Reacts with unburned HC and CO and is reduced. In this way, when NO ₂ is no longer present on the surface of platinum Pt, NO ₂ is released from the absorbent one after another. Therefore NO _X from _the NO _X absorbent 17 in a short time when the air-fuel ratio of the inflowing exhaust gas is made rich, that is released.

That is, when the air-fuel ratio of the inflowing exhaust gas is made rich, first, unburned HC and CO immediately react with O ₂₋ or O ²⁻ O ₂₋ on platinum Pt to be oxidized, and then O ₂ on platinum Pt is oxidized. If unburned HC and CO still remain even if _2- or O ^2- is consumed, this unburned HC,
NO _X discharged from the released NO _X and the engine from the absorbent by CO is made to reduction. _The NO _X absorbent 17 is therefore in a short period of time if the air-fuel ratio of the inflowing exhaust gas is made rich
NO _X being absorbed is released, yet NO _X is able to be prevented from being discharged into the atmosphere to the released NO _X is reduced to. In addition, NO _X absorbent 17
N is released from _the NO _X absorbent 17 even if the theoretical air-fuel ratio of the inflowing exhaust gas because it has the function of a reduction catalyst
O _X is reduced. However to release all NO _X that is absorbed in the NO _X absorbent 17 to NO _X from _the NO _X absorbent 17 is not only released gradually when the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio It takes a little longer time.

Incidentally NO _X is released from even _the NO _X absorbent 17 air-fuel ratio of lower them For example inflowing exhaust gas lean degree of the air-fuel ratio of the inflowing exhaust gas as described above is a lean. Therefore, in order to release NO _X from the NO _X absorbent 17, the oxygen concentration in the inflowing exhaust gas needs to be reduced. However, NO
_{Even if} NO _X is released from the _X absorbent 17, if the air-fuel ratio of the inflowing exhaust gas is lean, NO _X is not reduced in the NO _X absorbent 17, and in this case, NOx is downstream of the NO _X absorbent 17. _It is necessary to provide a catalyst capable of reducing _X or to supply a reducing agent downstream of the NO _X absorbent 17. Course toward Although it is possible to reduce NO _X in the downstream of the thus _the NO _X absorbent 17 for reducing NO _X in _the NO _X absorbent 17, rather than being preferred. In the embodiment according to the present invention is therefore _the NO _X absorbent 1
Air-fuel ratio of the inflowing exhaust gas when the 7 should be released NO _X is rich, so that the reduction of NO _X to thereby released from _the NO _X absorbent 17 in _the NO _X absorbent 17.

By the way, in the embodiment according to the present invention, as described above, the mixture supplied to the combustion chamber 3 is made rich at the time of full load operation, and the mixture is made the stoichiometric air-fuel ratio at the time of high load operation. during high load operation _the NO _X absorbent 17
NO _X is to be released from the. However, such in lean mixture is burned as full load or high load operation NO _X from _the NO _X absorbent 17 only at full load operation The less frequency and high load operation to be performed has been released no longer able to absorb NO _X by NO _X absorbing capacity of the NO _X by the absorbent 17 is saturated, NO _X absorbent 17 and thus while in. Therefore, in the embodiment according to the present invention, when the lean air-fuel mixture is continuously combusted, the air-fuel mixture periodically supplied to the combustion chamber 3 is made rich, during which the NO _X absorbent 17 releases NO _X. I try to make it.

Incidentally in this case, is NO _X absorbing capacity of the NO _X absorbent 17 during the air-fuel mixture fed into the combustion chamber 3 cycles to be rich is being performed is long and lean mixture combustion becomes saturated , there arises a problem that thus to NO _X to _the NO _X absorbent 17 NO _X to become E absorbed into from being released into the atmosphere.
Releasing NO _X from _the NO _X absorbent 17 before the amount of NO _X discharged from the engine, on the contrary many engine operating condition where NO _X absorbing capacity of even if continued _the NO _X absorbent 17 becomes saturated If the period in which the air-fuel mixture is enriched is shortened, the fuel consumption will increase.

Therefore seek amount of NO _X is absorbed in the NO _X absorbent 17 in the present invention, the air-fuel mixture when exceeding the allowable amount of _the amount of NO _X is absorbed in the NO _X absorbent 17 is predetermined for the rich I am trying to do it. Thus, the N absorbed in the NO _X absorbent 17
Since NO _X absorbing capacity of the O when _X amount is the mixture when exceeding the allowable amount predetermined for the rich _the NO _X absorbent 17 will not be saturated prevents the NO _X is released into the atmosphere, Further, since the frequency of enriching the air-fuel mixture can be reduced, the increase in fuel consumption can be suppressed.

Meanwhile determining the amount of NO _X is absorbed in the NO _X absorbent 17 in the case of obtaining the amount of NO _X is absorbed in the NO _X absorbent 17 directly it is difficult. Therefore, in the present invention so as to estimate the amount of NO _X absorbed in _the NO _X absorbent 17 from the amount of NO _X in the exhaust gas discharged from the engine. That is, as the engine speed N increases, the amount of exhaust gas discharged from the engine per unit time increases. Therefore, as the engine speed N increases, the amount of NO _X discharged from the engine per unit time increases. Further, as the engine load increases, that is, as the absolute pressure PM in the surge tank 10 increases, the amount of exhaust gas discharged from each combustion chamber 3 increases, and the combustion temperature increases. As the absolute pressure PM in the tank 10 increases, the amount of NO _X discharged from the engine per unit time increases.

FIG. 6 (A) shows the relationship between the NO _X amount discharged from the engine per unit time determined by the experiment, the absolute pressure PM in the surge tank 10, and the engine speed N. In (A), each curve shows the same NO _X amount. Sixth
As shown in FIG. 1A, the NO _X amount discharged from the engine per unit time increases as the absolute pressure PM in the surge tank 10 increases, and increases as the engine speed N increases. The NO _X amount shown in FIG. 6 (A) is stored in advance in the ROM 32 in the form of a map as shown in FIG. 6 (B).

On the other hand, FIG. 7 shows the relationship between the absorption capacity NO _X CAP of the NO _X that can be absorbed by _the NO _X absorbent 17, the exhaust gas temperature T representative of the temperature of the NO _X absorbent 17. When the temperature of the NO _X absorbent 17 becomes low, i.e., oxidation of the exhaust gas temperature T becomes lower NO _X (2
(NO + O ₂ → 2NO ₂ ) is weakened, the NO _X absorption capacity NO _X CAP decreases, and when the temperature of the NO _X absorbent 17 increases, that is, when the exhaust gas temperature T increases, the NO _X absorbent 17 is absorbed by the NO _X absorbent 17. NO _X
Is decomposed and released spontaneously, so that the NO _X absorption capacity NO _X CAP becomes smaller. Therefore, the NO _X absorption capacity NO _X CAP increases when the exhaust gas temperature T is between approximately 300 ° C. and approximately 500 ° C.

On the other hand, _the NO _X absorbent when FIG. 8 is switched to the rich air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 17 from lean 17
Shows the experimental results of the amount of NO _X released from. In addition,
In FIG. 8, the solid line indicates the case where the temperature of the NO _X absorbent 17, that is, the exhaust gas temperature T is high, and the broken line indicates the case where the temperature of the NO _X absorbent 17, that is, the exhaust gas temperature T is low. NO _X
The degradation rate of the NO _X in the absorbent 17 becomes faster as the temperature of the NO _X absorbent 17 becomes higher. Thus when the temperature of _the NO _X absorbent 17 is high as indicated by the solid line in Figure 8, that is within a large amount of the NO _X is short when a high exhaust gas temperature T NO _X
Are released from the absorbent 17, the temperature of the NO _X absorbent 17, that is, when a low exhaust gas temperature T from _the NO _X absorbent 17 a small amount of the NO _X as indicated by broken lines over a long period of time in Figure 8 Continue to be released. That is, as the exhaust gas temperature T increases, the amount of NO _X released from the NO _X absorbent 17 per unit time increases,
It turns out that the release time of _X becomes short.

By the way, when the amount of unburned HC and CO discharged from the engine is smaller than the amount that can reduce all the NO _X released from the NO _X absorbent 17, some NO _X is released to the atmosphere without being reduced. On the other hand, when the amount of unburned HC and CO discharged from the engine is larger than the amount that can reduce all the NO _X released from the NO _X absorbent 17, excess unburned HC and CO Will be released. Therefore, in order to prevent NO _X and unburned HC and CO from being released into the atmosphere, the amount of unburned HC and CO just required to reduce NO _X released from the NO _X absorbent 17 is reduced. It is necessary to discharge from the engine, and for that purpose, it is necessary to increase the amount of unburned HC and CO corresponding to the curve shown in FIG.

By the way, as described above, unburned HC and C discharged from the engine
The amount of O is proportional to the degree of richness of the air-fuel mixture supplied into the combustion chamber 3. NO _X in the embodiment according to the present invention thus indicating the value of the correction coefficient k for the basic fuel injection time TP as shown in FIG. 9, i.e. the degree of rich mixture in FIG. 8
The density is changed by a pattern as close as possible to the change pattern. Here, the correction coefficient k has a relationship of K = 1 + k with the above-described correction coefficient k. Therefore, when k = 0, the air-fuel mixture becomes the stoichiometric air-fuel ratio, and when k> 0, the air-fuel mixture becomes rich. .

Correction coefficient k from _the NO _X absorbent 17 as indicated by the solid line until the time when it should be released NO _X is C reaches C ₁ is raised by α at each unit time in FIG. 9, then the time C in between C ₁ and C ₂ are held in the correction coefficient k is constant, then the time C is a correction coefficient k exceeding C ₂ is moved down by β for each unit time. The values of α, β, C ₁ , and C ₂ are determined so that the change pattern of the correction coefficient k is as close as possible to the change pattern of the NO _X concentration shown by the solid line in FIG.

On the other hand, the change pattern of the correction coefficient k when the temperature of the NO _X absorbent 17, that is, the exhaust gas temperature T is low, can be changed to the change pattern of the NO _X concentration when the exhaust gas temperature T shown by the broken line in FIG. 8 is low. It is determined to be close. In this case, in order to make the change pattern of the correction coefficient k as shown by a broken line in FIG. 9, both α and β should be smaller and both C ₁ and C ₂ should be larger than the change pattern shown by the solid line. You can see that. That is, the change pattern of the correction coefficient k in the Keru not a near-change pattern of the NO _X concentration shown in Figure 8 to increase alpha and β as the exhaust gas temperature T, as shown in FIG. 10 becomes high, C _It suffices to reduce ₁ and C ₂ . Note that the relationship between C ₁ , C ₂ , α, β and the exhaust gas temperature T shown in FIG. 10 is stored in the ROM 32 in advance.

In the embodiment according to the present invention, a temperature sensor 25 for detecting the exhaust gas temperature T is provided, so that the seventh temperature is detected based on the exhaust gas temperature T detected by the temperature sensor 25.
The NO _X 2 absorption capacity NO _X CAP shown in the figure and α, β, C ₁ and C ₂ shown in FIG. 10 are determined. However, the exhaust gas temperature T can be estimated from the absolute pressure PM in the surge tank 10 and the engine speed N. Thus is stored in advance in the ROM32 of the exhaust gas temperature T instead of providing the temperature sensor 25 in the form of a map as shown in FIG. 11, NO _X absorption amount based on the exhaust gas temperature T obtained from the map NO _X CAP and α,
β, C ₁ and C ₂ can also be determined.

Next, a first embodiment of the NO _X release control will be described with reference to FIG. 12 to FIG.

FIG. 12 and FIG. 13 show a time interruption routine executed by interruption every predetermined time.

Referring to FIGS. 12 and 13, the first step is
NO _X releasing flag showing that from _the NO _X absorbent 17 should release the NO _X in 100 whether it is set or not. Whether the correction coefficient K proceeds to step 101 is less than 1.0 when the NO _X release flag is not set, that is, whether the air-fuel mixture is an operation state should lean or not. When K <1.0, that is, when the air-fuel mixture is lean, the routine proceeds to step 102, where the count value D is made zero, and then proceeds to step 103.

Figure 6 based on the absolute pressure PM and the engine speed N in the surge tank 10 detected by the pressure sensor 19 in step 103 (B) NO _X amount Nij discharged from unit time per engine from the map shown in the calculation Is done. Next, at step 104, N
O to _X amount Nij multiplied by the interruption time interval Delta] t, these products Nij
Δt is added to ΣNO _X. The product Nij · Δt represents the NO _X amount discharged from the engine during the interruption time interval Δt. At this time, the NO _X discharged from the engine is absorbed by the NO _X absorbent 17, so that ΣNO _X is NO _X NO _X absorbed in absorbent 17
This represents an estimate of the quantity.

Then NO _X absorption capacity NO _X CAP is calculated from the relationship shown in FIG. 7 based on the exhaust gas temperature T detected by the temperature sensor 25 at step 105. Then whether the estimated value ShigumaNO _X of the NO _X that is absorbed in the NO _X absorbent 17 in step 106 exceeds the NO _X absorption capacity NO _X CAP is determined. ΣNO _X ≦ NO _X CAP
In the case of, the processing cycle is completed. At this time, the lean air-fuel mixture is being burned, and the NO
_X is absorbed in the NO _X absorbent 17.

On the other hand, if it is determined that ΣNO _X> NO _X CAP in step 106, i.e., _the NO _X absorbent 17 NO _X absorption capacity NO _X release flag proceeds to when it is determined step 107 and the saturation is set You. Next, at step 108, C ₁ , C ₂ , α, β are calculated from the relationship shown in FIG.
Complete the processing cycle. If NO _X release flag is set step by step 100, at the next processing cycle 109
And the count value C is incremented by one.
Then whether step 110 the count value C is smaller than C ₁ is determined. Is α to the correction coefficient k proceeds to step 111 is added when C <of C _1. Then the processing cycle is completed. The addition effect of α on the correction coefficient k is C ≧
Until C ₁ is performed continuously, therefore the value of this period correction coefficient k as shown in FIG. 9 continues to increase.

On the other hand, when it is determined that now C ≧ C ₁ in step 110 the count value C proceeds to step 112 is determined whether it is smaller than C ₂ is, the processing cycle is completed when the C <C _2. Therefore, as shown in FIG.
Correction coefficient k until the C ₂ is to be kept constant.

Next, when it is determined in step 112 that C ≧ C ₂ , the routine proceeds to step 113, where β is subtracted from the correction coefficient k. Next, at step 114, it is determined whether or not the correction coefficient k has become zero or negative. When k> 0, the processing cycle is completed. Therefore, as shown in FIG.
The correction coefficient k is reduced until ≦ 0. In addition,
As will be described later, when k> 0, the air-fuel mixture supplied into the combustion chamber 3 is made rich during this time, and the degree of the air-fuel mixture is changed according to the pattern shown in FIG. 9 during this time.

On the other hand, if it is determined in step 114 that k ≦ 0, the routine proceeds to step 115, where the NO _X release flag is reset. Next, at step 116, ΣNO _X is made zero. That is, at this time, it is considered that all the NO _X absorbed in the NO _X absorbent 17 has been released, so the N absorbed in the NO _X absorbent 17
Estimate ShigumaNO _X of O _X is zero. Next, at step 117, the count value C and the correction coefficient k are made zero, and the processing cycle is completed.

On the other hand, when it is determined in step 101 that k ≧ 1.0, that is, when the engine is in the engine operating state in which the mixture is to be rich or the stoichiometric air-fuel ratio, the routine proceeds to step 118, where the count value D is incremented by one. Then step 119
In whether the count value D is greater than a predetermined value D _O is determined. When it becomes D> D _O is ShigumaNO _X is zero proceeds to step 120. That is, when the combustion of the rich mixture or the stoichiometric mixture continues for a certain period of time.
Since NO _X from the absorbent 17 total NO _X is considered to have been released estimate ShigumaNO _X of _the amount of NO _X is absorbed in the NO _X absorbent 17 at this time it is made zero.

FIG. 14 shows a routine for calculating the fuel injection time TAU, and this routine is repeatedly executed.

Referring to FIG. 14, first, at step 150, the basic fuel injection time TP is calculated from the map shown in FIG. Next, at step 151, the compensation coefficient K shown in FIG. 3 determined according to the operating state of the engine is calculated. Next, at step 152 NO _X release flag is discriminated whether it is set, the correction coefficient K proceeds to step 153 when the NO _X release flag is not set is set to K _t. Then, the fuel injection time TAU is calculated by multiplying the K _t the basic fuel injection time TP in step 155. Accordingly, at this time, the air-fuel mixture supplied into the combustion chamber 3 is made lean, stoichiometric or rich according to the operating state of the engine as shown in FIG.

On the other hand, K _t the routine proceeds to step 154 when the NO _X release flag is judged as being set in step 152
Is the sum (k + 1) of the correction coefficient k and 1 calculated by the routines shown in FIGS. 12 and 13, and then proceeds to step 155. Accordingly, at this time, the air-fuel mixture supplied into the combustion chamber 3 is made rich, and at this time, the degree of the rich is changed according to the pattern shown in FIG.

15 to 20 show a second embodiment. N in the first embodiment as described above, which is absorbed in the NO _X absorbent 17
NO of O _X of the estimated value ShigumaNO _X is _the NO _X absorbent 17 _X absorption capacity NO _X CAP
Even when exceeding the air ratio of the mixture supplied is switched from lean to rich _the NO _X absorbent 17 from the NO _X is to be in more of engine high load operation, and the engine full load operation discharged into the combustion chamber 3 the The release action of NO _X from the NO _X absorbent 17 is performed. Is NO _X release action from _the NO _X absorbent 17 is air-fuel mixture is rich in the engine operating condition other than the time and the engine full load operation of engine high load operation is performed in the second embodiment, this time NO _X when all NO _X which has been absorbed into the absorbent 17 is considered to have been released estimate ShigumaNO _X of _the amount of NO _X is absorbed in the NO _X absorbent 17 is made zero.

That is, in the first embodiment, as can be seen from FIG. 3, when the acceleration operation in which the engine load is increased in the low load region is performed, that is, when the gentle acceleration operation is performed, the air-fuel mixture is maintained lean. When an acceleration operation in which the engine load is changed from a low load to a high load is performed, that is, when a rapid acceleration operation is performed, the air-fuel mixture is switched from lean to the stoichiometric air-fuel ratio. In the second embodiment with respect to this mixture to the time of the rapid acceleration operation to ensure a good acceleration operation is a rich mixture in accordance with the degree of acceleration, releasing action of the NO _X is carried out at this time.

When the downshift is performed in the automatic transmission 22, the engine speed increases. At this time, if there is a delay in the increase in the engine speed, a torque shock occurs when the downshift is performed. Therefore, in the second embodiment, when the downshift is performed, the air-fuel mixture is made rich to immediately increase the engine speed, thereby preventing the occurrence of torque shock. NO _{X at} this time
Release action is performed.

In the first embodiment it is absorbed in the NO _X absorbent 17 N
NO _X absorbing capacity NO _X CAP represented estimate ShigumaNO _X of O _X is in Figure 7
NO _X in is the air-fuel mixture is the action of releasing switched to NO _X from lean to rich is performed second embodiment upon reaching
When the estimated value NONO _X of the NO _X absorbed in the absorbent 17 reaches 70% of the NO _X absorption capacity NO _X CAP shown in FIG. 7, the mixture is switched from lean to rich and the NO _X A release action takes place.

In the second embodiment, the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is set to the stoichiometric air-fuel ratio during the idling operation and the deceleration operation in which the throttle valve 14 is at the idling opening. Incidentally fuel is better to switch between the air-fuel ratio of the mixture the stoichiometric air-fuel ratio and richer than switching between the air-fuel ratio of the mixture lean and rich when the air-fuel mixture in order to release the NO _X rich The consumption is small and the fluctuation of the torque is small. Therefore N in order in the second embodiment to increase the opportunity to release NO _X by switching the air-fuel ratio of the mixture from the stoichiometric air-fuel ratio to the rich
The estimated value of the amount of NO _X absorbed by the O _X absorbent 17 ΣNO _X is the seventh
When the NO _X absorption capacity NO _X CAP shown in the figure exceeds 30%, the air-fuel mixture is temporarily made rich when the throttle valve 14 reaches the idling opening degree to release the NO _X. I have to. In this case, the mixture is maintained at the stoichiometric air-fuel ratio when the NO _X releasing action is completed.

Next, a second embodiment of the NO _X release control will be described with reference to FIG. 15 to FIG.

FIGS. 15 and 16 show a time interruption routine executed by interruption every predetermined time.

Referring to FIGS. 15 and 16, the first step is
NO _X releasing flag showing that from _the NO _X absorbent 17 should release the NO _X in 200 whether it is set or not. Whether the correction coefficient K proceeds to step 201 is less than 1.0 when the NO _X release flag is not set, that is, whether the air-fuel mixture is an operation state should lean or not. When K <1.0, that is, when the air-fuel mixture is in an operating state in which the mixture is to be lean, the process proceeds to step 202.

Figure 6 based on the absolute pressure PM and the engine speed N in the surge tank 10 detected by the pressure sensor 19 in step 202 NO _X amount Nij discharged is calculated from the map shown in (B) from the unit time per engine Is done. Next, in step 203, N
O to _X amount Nij multiplied by the interruption time interval Delta] t, these products Nij
Δt is added to ΣNO _X. This ΔNO _X represents an estimated value of the amount of NO _X absorbed by the NO _X absorbent 17 as described above. Next, at step 204, the estimated value ΣNO _X of the amount of NO _X absorbed by the NO _X absorbent 17 is changed to the NO _X absorption capacity N shown in FIG.
O _X CAP 30% a is greater or not than 30% CAP in is determined. ΣNO permission flag proceeds to step 205 when the _X ≦ 30% CAP is reset, then the processing cycle is completed. On the other hand, when ΣNO _X > 30% CAP, step
Proceed to 206, the permission flag is set, then step 2
Go to 07.

Estimates of _the amount of NO _X is absorbed in the NO _X absorbent 17 in step 207 ΣNO _X 70% of the NO _X absorbent capacity NO _X CAP shown in FIG. 7
It is determined whether or not 70% CAP has been exceeded. ΣNO _X ≦ 70
At the time of% CAP, the processing cycle is completed.

On the other hand, if it is determined that ΣNO _X> 70% CAP in step 207, i.e., when NO _X in the absorbent 17 NO _X 70% or more of the NO _X absorbent capacity is determined to be absorbed in the step 208 The NO _X release flag is set. Then step 2
In 09, based on the exhaust gas temperature T, C ₁ ,
C ₂ , α, β are calculated, and the processing cycle is completed. NO _X
When the release flag is set, the process proceeds from step 200 to step 210 in the next processing cycle, and the count value C is incremented by one. Then whether or not the count value C in step 211 is smaller than C ₁ is determined. Is α to the correction coefficient k proceeds to step 212 is added when C <of C _1. Then the processing cycle is completed. Adding the action of α with respect to the correction coefficient k is performed continuously until C ≧ C _1,
Therefore, as shown in FIG. 9, the value of the correction coefficient k continues to increase during this time.

On the other hand, when it is determined that now C ≧ C ₁ in step 211 the count value C proceeds to step 213 is determined whether it is smaller than C ₂ is, the processing cycle is completed when the C <C _2. Therefore, as shown in FIG.
Until C ₂ correction coefficient k is kept constant.

Next, when it is determined in step 213 that C ≧ C ₂ , the routine proceeds to step 214, where β is subtracted from the correction coefficient k. Next, at step 215, it is determined whether or not the correction coefficient k has become zero or negative. When k> 0, the processing cycle is completed. Therefore, as shown in FIG.
The correction coefficient k is reduced until ≦ 0. In addition,
As will be described later, when k> 0, the air-fuel mixture supplied into the combustion chamber 3 is made rich during this time, and the degree of the air-fuel mixture is changed according to the pattern shown in FIG. 9 during this time.

On the other hand, the routine proceeds to step 216 where it is determined that k ≧ 0 in step 215, and the NO _X release flag is reset. Next, at step 217, ΣNO _X is made zero. That is,
Estimate ShigumaNO _X at this time NO _X total NO _X which has been absorbed in the absorbent 17 is absorbed in the NO _X absorbent 17 since it is considered to have been released NO _X is made zero. Next, at step 218, the count value C and the correction coefficient k are made zero, and the processing cycle is completed.

On the other hand, when it is determined in step 201 that k ≧ 1.0, that is, when the engine is in the engine operating state in which the air-fuel mixture is to be rich or the stoichiometric air-fuel ratio, the routine proceeds to step 219, where the vehicle speed V is constant from the output signal of the vehicle speed sensor 24 A value, for example, 130 km / h or more is determined. If the vehicle speed V exceeds 130 km / h, NO _X is completely released from the NO _X absorbent 17. At this time, the routine proceeds to step 221 and the NO _X amount absorbed by the NO _X absorbent 17 estimate ShigumaNO _X of is made zero. On the other hand, when V ≦ 130 km / h, the routine proceeds to step 220, where it is determined whether or not a predetermined time has elapsed since k ≧ 1.0. Step 221 when a certain time has elapsed
ΣNO _X is made zero. That is, NO combustion of the mixture of the rich mixture or stoichiometric air-fuel ratio it is considered that the total NO _X from _the NO _X absorbent 17 is released when continued for a certain time at this time is absorbed in the NO _X absorbent 17 _X The quantity estimate 量 NO _X is set to zero.

17 to 19 show a routine for calculating the fuel injection time TAU, and this routine is repeatedly executed.

Referring to FIGS. 17 to 19, first, step 25 is executed.
At 0, the basic fuel injection time TP is calculated from the map shown in FIG.
Is calculated. Next, at step 251, a correction coefficient K shown in FIG. 3 determined according to the operating state of the engine is calculated.
Next, at step 252, it is determined whether or not the throttle valve 14 is at the idling opening based on the output signal of the idle switch 20. When the throttle valve 14 is not at the idling opening, the routine proceeds to step 261 to reset the rich flag, and then proceeds to step 262.

In step 262, it is determined whether or not the correction coefficient K is smaller than 1.0. When K ≧ 1.0, that is, when the air-fuel ratio of the air-fuel mixture is to be rich or stoichiometric, the process jumps to step 268. On the other hand, when K ≦ 1.0, that is, when the air-fuel ratio of the air-fuel mixture should be lean, the routine proceeds to step 263, where the current absolute pressure PM in the surge tank 10 and the surge tank 10 detected in the previous processing cycle are detected. Absolute pressure PM
The pressure difference ΔPM from ₁ is calculated. Then whether the pressure difference .DELTA.PM step 264 is greater than the predetermined value X _o, that is, whether the rapid acceleration operation is being performed is determined, when the .DELTA.PM ≦ X _o, i.e. the rapid acceleration operation is not being performed Sometimes step
Proceed to 268.

In step 268, it is determined whether or not the downshift operation of the automatic transmission 22 is performed based on the output signal of the gear position detector 23. If the downshift operation is not performed, the process jumps to step 272. NO _{X in} step 272
It is determined whether or not the release flag is set, and NO _X
If the release flag is not set, step 273
Willing correction coefficient K is set to K _t. Then step 275
In the fuel injection time TAU is calculated by multiplying the K _t the basic fuel injection time TP. Therefore, at this time, the combustion chamber 3
As shown in FIG. 3, the air-fuel mixture supplied to the inside is made lean, stoichiometric or rich depending on the operating state of the engine.

On the other hand, when it is determined in step 274 that the NO _X release flag is set, the process proceeds to step 274, where K _t
Is the sum (k + 1) of the correction coefficient k and 1 calculated by the routine shown in FIGS. 15 and 16, and then the routine proceeds to step 275. Accordingly, at this time, the air-fuel mixture supplied into the combustion chamber 3 is made rich, and at this time, the degree of the rich is changed according to the pattern shown in FIG.

On the other hand, when it is determined in step 252 that the throttle valve 14 is at the idling opening, the routine proceeds to step 253, where it is determined whether or not the rich flag is set. If the rich flag has not been set, the routine proceeds to step 254, where it is determined whether the permission flag has been set. Permission flag is rich flag is set the routine proceeds to step 255 when it is set, then the correction coefficient K _t in step 256 is set to 1.2. Next, the routine proceeds to step 275. On the other hand, when the permission flag is not set, the routine proceeds to step 260, where the correction coefficient K
_t is set to 1.0, and then the routine proceeds to step 275.

Thus if permission flag is set when the throttle valve 14 becomes idle opening degree, i.e. _the NO _X absorbent 1
When the 7 in the NO _X absorbent capacity NO _X 30% or more of the NO _X in the CAP is absorbed is the air-fuel mixture rich, this time _the NO _X absorbent 1
When the NO _X amount absorbed in 7 is 30% or less of the NO _X absorption capacity NO _X CAP, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio.

When the rich flag is set, the process proceeds from step 253 to step 257, where it is determined whether a predetermined time has elapsed since the rich flag was set. When the predetermined time has elapsed, the routine proceeds to step 258, where the rich flag is reset. Next, in step 259, the estimated value ΣNO _X of the NO _X amount absorbed by the NO _X absorbent 17 is set to zero. Next, at step 260, the correction coefficient _Kt is set to 1.0. When ΣNO _X is made zero in step 259, FIGS. 15 and 16
Since the permission flag is reset in the routine shown in the figure, the process proceeds to step 260 via steps 253 and 254 in the next processing cycle. Therefore NO which is absorbed in the NO _X absorbent 17
_When the estimated value XNO _X of the _X amount is 30% or more of the NO _X absorption capacity NO _X CAP, the air-fuel mixture is temporarily made rich, and then the air-fuel ratio of the air-fuel mixture is made the stoichiometric air-fuel ratio.

On the other hand, when it is judged that .DELTA.PM> X _o in step 264, i.e., at the time of the rapid acceleration operation is absorbed in the NO _X absorbent 17 on the basis of the relationship shown in FIG. 20 proceeds to step 265 N
O _X amount estimate ShigumaNO _X from the correction coefficient K _t is calculated. 20th
Correction coefficient K _t is larger than 1.0 as shown in FIG, also the correction coefficient K _t becomes larger as the estimated value ShigumaNO _X increases. Therefore, when the rapid acceleration operation is performed, the air-fuel mixture is made rich. Then a step 266 in .DELTA.PM> X _o it is determined whether the elapsed et predetermined time, the estimated value of the amount of NO _X is absorbed in the NO _X absorbent 17 proceeds to step 267 after a certain period of time ΣNO _X is set to zero.

On the other hand, when it is determined in step 268 that the downshift operation is being performed in the automatic transmission 22, the process proceeds to step 269, where the correction coefficient _Kt is set to 1.2. Therefore, it is understood that the air-fuel mixture is enriched immediately after the downshift operation is performed. Then it is determined whether the shift-down action in step 270 has elapsed a predetermined time from the start is constant when the time has elapsed the estimation of the amount of NO _X is absorbed in the NO _X absorbent 17 proceeds to step 271 Value Σ NO
_X is set to zero.

Incidentally, NO _X absorbent and at each step 259,267,271 mixture is in the predetermined time rich to release the NO _X 17
Although estimates ShigumaNO _X of the NO _X amount which is absorbed is made zero without zero estimate ShigumaNO _X this time, the estimated value ΣNO _X NO _X absorption capacity NO _X CAP 30% about or less and the You can also.

FIG. 21 shows another embodiment of the internal combustion engine. In this embodiment, the outlet side of the caging 18 is connected via an exhaust pipe 27 to a catalytic converter 29 containing a three-way catalyst 28.
While exhibiting a high purification efficiency with respect to CO, HC and NO _X when the air-fuel ratio is maintained near the stoichiometric air-fuel ratio as the three-way catalyst 28 it is well known ternary catalyst 28 is empty It has high purification efficiency for NO _X even when the fuel ratio is rich to some extent. In the embodiment shown in FIG. 21, a three-way catalyst 28 is provided downstream of the NO _X absorbent 17 in order to purify NO _X utilizing this characteristic.

That is, when the air-fuel mixture fed into the engine cylinder so as to release the NO _X from _the NO _X absorbent 17 as described above to the rich
NO _X that is absorbed in the NO _X absorbent 17 is abruptly released from _the NO _X absorbent 17. At this time, NO _X is reduced at the time of release, but not all NO _X may be reduced. However N
O _X NO _X which has not been reduced during the NO _X release previously arranged three-way catalyst 28 downstream of the absorbent 17 will be reduced by the three-way catalyst 28. Thus downstream of _the NO _X absorbent 17 three way catalyst 2
By arranging 8, the purification performance of NO _X can be further improved.

Previously alkali metal as _the NO _X absorbent in the embodiment described, alkaline earth, _the NO _X absorbent 17 which carries the one with a noble metal on alumina at least a rare earth is used. However composite oxide of alkaline-earth and copper, instead of using such _the NO _X absorbent 17, namely Ba-Cu-
It is also possible to use O-based of the NO _X absorbent. Such composite oxides of alkaline earth and copper include, for example, MnO ₂ BaCu
O ₂ can be used, and in this case, platinum Pt or cerium Ce can be added. NO of this MnO ₂・ BaCuO ₂ system
_{In the X} absorbent, copper Cu is the platinum Pt of the NO _X absorbent 17 described so far.
Performs the same catalytic action as above, and when the air-fuel ratio is lean, copper
NO _X is oxidized by Cu (2NO + O ₂ → 2NO ₂ ) and nitrate ion
It diffuses into the absorbent in the form of NO _3- .

On the other hand, if the air-fuel ratio is made rich, NO _X
Is released, and this NO _X is reduced by the catalytic action of copper Cu. However, the NO _X reducing power of copper Cu is the same as that of platinum Pt
Weaker than the O _X reducing power, in the case of using Ba-Cu-O system absorbent is thus compared to _the NO _X absorbent 17 mentioned heretofore NO _X
The amount of NO _X that is not reduced during release increases slightly. Therefore Ba
When a -Cu-O-based absorbent is used, a three-way catalyst 28 is preferably disposed downstream of the absorbent as shown in FIG.

FIG. 22 and FIG. 27 show a case where the present invention is applied to a diesel engine. 22. In FIG. 22 and FIG. 22, the same components as those in FIG. 1 are indicated by the same reference numerals.

Normally, a diesel engine is burned with an excess air ratio of 1.0 or more, that is, an average air-fuel ratio of the air-fuel mixture in the combustion chamber 3 in a lean state in any operating state. Therefore, the NO _X discharged at this time is absorbed by the NO _X absorbent 17. On the other hand, NO from _X absorbent 17 when releasing the NO _X is hydrocarbon fed into the engine exhaust passage upstream _the NO _X absorbent 17, whereby the air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent 17 rich To be.

Referring to FIG. 22, in this embodiment, the accelerator pedal 50
Sensor that generates an output voltage proportional to the amount of depression
The output voltage of this load sensor 51 is provided by an AD converter.
The data is input to the input port 35 via 40. Further, in this embodiment, an intake shutoff valve 52 is arranged in the intake duct 12, and this intake shutoff valve 52 is a diaphragm of a negative pressure diaphragm device 53.
Connected to 54. The diaphragm negative pressure chamber 55 of the negative pressure diaphragm device 53 is connected to the atmosphere or a negative pressure tank via an electromagnetic switching valve 56.
57, while the output port 36 of the electronic control unit 30 is connected to the electromagnetic switching valve 56 via the corresponding drive circuit 39.
Connected to. The diaphragm chamber 55 is normally open to the atmosphere, and at this time, the intake shutoff valve 52 is held at the fully open position as shown in FIG.

Further, a reducing agent supply valve 58 is disposed in the exhaust pipe 16, and the reducing agent supply valve 58 is connected to a reducing agent tank 60 via a supply pump 59. The output port 36 of the electronic control unit 30 is connected to the reducing agent supply valve 58 through the corresponding drive circuit 39.
And the supply pump 59. The reducing agent tank 60 is filled with hydrocarbons such as gasoline, isooctane, hexane, heptane, light oil and kerosene, or hydrocarbons such as butane and propane which can be stored in a liquid state.

_The amount of NO _X absorbed in _the NO _X absorbent 17 from _the amount of NO _X in the exhaust gas discharged from the engine in the diesel engine shown in FIG. 22 is estimated. That is, even in a diesel engine, the higher the engine speed N, the greater the amount of exhaust gas discharged per unit time from the engine. Therefore, the higher the engine speed N, the larger the NO _X amount discharged from the engine per unit time. . Further, as the engine load increases, that is, as the depression amount of the accelerator pedal 50 increases, the amount of exhaust gas discharged from each combustion chamber 3 increases, and the combustion temperature increases, so that the engine load increases, that is, the accelerator pedal increases. As the stepping amount of 50 increases, the amount of NO _X emitted from the engine per unit time increases.

FIG. 23 (A) shows the relationship between the NO _X amount exhausted from the engine per unit time, the depression amount Acc of the accelerator pedal 50, and the engine speed N obtained by the experiment. In A), each curve shows the same NO _X amount. 23rd
As shown in FIG. 7A, the NO _X amount discharged from the engine per unit time increases as the accelerator pedal depression amount Acc increases, and increases as the engine speed N increases.
The NO _X amount shown in FIG. 23 (A) is stored in advance in the ROM 32 in the form of a map as shown in FIG. 23 (B).

In a diesel engine, the air-fuel mixture in the combustion chamber 3 is burned under excess air, that is, in a state in which the average air-fuel ratio is lean. At this time, NO _X discharged from the engine is NO _X
Absorbed by the absorbent 17. Figure 24 shows the relationship between the concentration of NO _X exhaust gas flowing out from the NO _X absorption and _the NO _X absorbent 17 to _the NO _X absorbent 17. In FIG. 24, the NO _X absorption amount A indicates an allowable absorption limit amount at which the NO _X absorbent 17 can favorably absorb NO _X.

When less than approximately allowable absorption limit amount A in NO _X absorption amount as can be seen from Fig. 24 total NO _X in the exhaust gas is absorbed in the NO _X absorbent 17, thus flowing out from the time _the NO _X absorbent 17 The NO _X concentration in the exhaust gas is zero. This When NO _X absorption exceeds the allowable absorption limit amount A NO _X absorption is reduced NO _X absorption rate gradually as it increases for, thus to exhaust gas flowing out from _the NO _X absorbent 17 of NO _X concentration becomes gradually higher. Absorbed amount of NO _X in the exhaust gas flowing into the NO _X absorbent 17 at this time in H ₁ (= 1.0) to the K of the _{NO X 1 / H 1 (K} 1) only _the NO _X absorbent 17 Will be done.

On the other hand, in this embodiment, when the deceleration operation is performed, NO _X
Release action is performed. That is, when the deceleration operation is performed, the diaphragm chamber 53 is connected to the negative pressure tank 57 by the switching operation of the switching valve 56, and thereby the intake shutoff valve 52 is closed to almost fully closed. At the same time, the supply pump 61 is driven and the reducing agent supply valve 58 is opened, whereby the hydrocarbon filled in the reducing agent tank 60 is supplied from the reducing agent supply valve 58 into the exhaust pipe 16. Feed amount of hydrocarbons in this case is determined so that the air-fuel ratio of the inflowing exhaust gas flowing into the NO _X absorbent 17 becomes rich, thus NO _X is released from _the NO _X absorbent 17 at this time Will be.

Air-fuel ratio of the exhaust gas amount of exhaust gas such intake shutoff valve 52 is discharged from the caused to closed engine is reduced, flows into _the NO _X absorbent 17 by supplying a small amount of the reducing agent and thus Can be rich. That is, NO _X
By closing the intake shut-off valve 52 when performing the discharge operation of, the amount of consumption of the reducing agent can be reduced. Also, closing the intake shut-off valve 52 does not affect the operating state of the engine only during deceleration operation, and when the intake shut-off valve 52 is closed at this time, the engine brake acts strongly. . In the embodiment according to the present invention thus closes the intake shutoff valve 52 at the time of deceleration operation, and to perform the releasing action of the time NO _X.

FIG. 25 shows the rate of residual NO _X remaining in the NO _X absorbent 17 after the release of NO _X was started. 25th
As shown by the solid line in the figure, when the release action of NO _X is started, the residual NO _X rate gradually decreases. In this case, the 25th
NO _X remaining amount as indicated by the solid line in FIG rather than decreases uniformly been accompanied over time, NO _X remaining amount decreases relatively fast initial of the NO _X release action, late Decreases relatively slowly. Further, when a relatively low-volatility reducing agent such as light oil or kerosene is used, it takes time for the reducing agent to evaporate, so that the reducing agent is supplied as shown by the broken line in FIG. 25. The NO _X releasing action is not performed immediately, so that it takes time for all the NO _{X to} be released.

Almost all NO _X when releasing action of the NO _X is made approximately t _o times as can be seen from Fig. 25 is released from _the NO _X absorbent 17, therefore when the deceleration operation is started in the embodiment according to the present invention
intake cutoff valve 52 over a t _o time is made to closed, the reducing agent is supplied into the exhaust pipe 16 over a t _o time. But N While deceleration period shorter kite NO _X remaining rate is not zero
Releasing action of O _X from being stopped. In such a case,
NO _X estimate ShigumaNO _X is allowable absorption limit amount A of the NO _X that releasing action is absorbed in the NO _X absorbent 17 is judged complete (Part 24
Figure) becomes saturated absorption capacity of the NO _X absorbent 17 before performing the action of releasing again NO _X NO _X when to perform the action of releasing upon reaching, thus a large amount of the NO _X in the atmosphere Will be released inside.

Incidentally short deceleration period, thus NO _X residual ratio of NO _X remaining rate in deceleration immediately before if not zero H ₂ (1 = 1.0) to the NO NO release when action has completed the the _{X X} residual rate is represented by K ₂ / H ₂ (= K ₂ ). Still therefore K ₂ · ΣNO _X qs of the NO _X when the entire NO _X is not released upon release of the NO _X in the embodiment according to the invention
It is estimated that it remains in the NO _X absorbent 17, so that the next release time of NO _X is advanced.

Next, referring to controlled release of the NO _X to Figure 26 will be described. The NO _X release control routine shown in FIG. 26 is executed by interruption every predetermined time.

Referring to FIG. 26, first, in step 300, the NO _X amount Nij discharged from the engine per unit time is calculated from the map shown in FIG. 23 (B) based on the depression amount of the accelerator pedal 50 and the engine speed N. Is done. Then step 301
Then, the estimated value of the amount of NO _X absorbed by the NO _X absorbent 17 ΣNO _X
Is greater than the allowable absorption limit A (FIG. 24). When ΣNO _X ≦ A, the routine proceeds to step 302, where the NO _X amount N
ij is multiplied by the interrupt time interval Δt, and the product Nij · Δ
t is added to ΣNO _X. The product Nij · Δt represents the amount of NO _X exhausted from the engine during the interruption time interval Δt, and thus ΔNO _X represents an estimated value of the amount of NO _X absorbed by the NO _X absorbent 17. Then the execution permission flag F ₁ is allowed to execute the action of releasing step 303 NO _X is reset, then the routine proceeds to step 306.

On the other hand, when it is determined in step 301 that ΣNO _x > A, the process proceeds to step 304 and Nij · Δt is set to K ₁ (the
Product K ₁ · Nij · Δt multiplied by the 24 view) is added to ΣNO _X. Next, the routine proceeds to step 305, where the execution permission flag is set, and then the routine proceeds to step 306. In step 306, it is determined whether or not the execution permission flag has been set.
Step if the execution permission flag is not set
Proceeding to 314, the count value T is made zero, and then the processing cycle is completed.

On the other hand, if it is determined in step 306 that the execution permission flag is set, the process proceeds to step 307 to determine whether or not the condition for performing the NO _X release action, that is, whether the regeneration condition for the NO _X absorbent 17 is satisfied. Is determined. In this case, when the depression amount of the accelerator pedal 50 is zero and the engine speed N is higher than a predetermined speed, that is, NO
It is determined that the regeneration condition of _X absorbent 17 is satisfied. In this case, it can be added to the reproduction condition that the exhaust gas temperature is a temperature above which can the temperature of the NO _X absorbent 17 to the activation temperature.

When the regeneration condition is determined to be satisfied in step 307 the reproduction of _the NO _X absorbent 17 proceeds to step 308 is executed. That is, the intake shutoff valve 52 is closed, and the reducing agent is supplied from the reducing agent supply valve 58. Then step 30
At 9, the interruption time interval Δt is added to the count value T. Next, at step 310, it is determined whether or not the elapsed time T from the start of reproduction has _{exceeded to} (FIG. 25).
At time t _o , the processing cycle is completed. On the other hand, T
≧ regenerative action of t _o to become the _the NO _X absorbent 17 is stopped, the estimated value ShigumaNO _X of _the amount of NO _X is absorbed in the NO _X absorbent 17 proceeds to step 312 is made zero. Next, the processing cycle is completed through step 314.

On the other hand, whether the elapsed time T from the start of the playback proceeds to step 311 when the regeneration condition is not satisfied exceeds the predetermined time t _A is determined. The predetermined time t _A represents a time a little shorter time than t _o NO _X remaining rate is to be regarded as zero as shown in FIG. 25. Thus T> T _A NO _X amount estimate ShigumaNO _X that is absorbed in the NO _X absorbent 17 proceeds to step 312 when the is made zero.

When this respect is determined that T ≦ t _A in step 311, i.e., when the deceleration operation period remains the NO _X is still in _the NO _X absorbent 17 Te short Step 3
Estimate ShigumaNO _X of _the amount of NO _X is absorbed in the NO _X absorbent 17 proceeds to 13 are multiplied by the K ₂ (Figure 25) to ΣNO _X.
Therefore, in the next interrupt routine, Nij · Δt is added to に NO _X in step 302.

_The NO _X absorbent 17 downstream of the exhaust passage 6 in the embodiment shown in FIG. 27
NO _X concentration sensor 62 is disposed in the 0. The NO _X concentration sensor 62 generates an output voltage proportional to the concentration of NO _X in the exhaust gas flowing out from _the NO _X absorbent 17, the output voltage AD converter 41
Through the input port 35. Also, output port
36 is connected to a warning light 63 via a corresponding drive circuit 39.

Also in this embodiment, basically, when the estimated value ΣNO _X of the NO _X amount absorbed by the NO _X absorbent 17 exceeds the allowable absorption limit amount A, the regeneration of NO _X is executed when the regeneration condition is satisfied. . Further, in this embodiment, the NO _X amount actually absorbed is larger than the estimated value ΣNO _{X, the} NO _X absorbent 17 is deteriorated, or the absorption capacity of the NO _X absorbent 17 is reduced due to other reasons. detects that the absorption capacity of the NO _X absorbent 17 is so as to promote regeneration action of _the NO _X absorbent 17 by increasing the playing time of, for example _the NO _X absorbent 17 when lowered.

Next, the NO _X release control will be described with reference to FIGS. 28 to 30. The NO _X release control routine shown in FIGS. 28 to 30 is executed by interruption every predetermined time.

Referring to FIGS. 28 to 30, first, step 40
0 NO _X amount Nij discharged from depression amount and the engine speed N Figure 23 (B) per unit time engine from the map shown in based on the accelerator pedal 50 is calculated in. Next, at step 401, it is determined whether or not the estimated value ΣNO _X of the NO _X amount absorbed by the NO _X absorbent 17 has exceeded the allowable absorption limit amount A (FIG. 24). When ΣNO _X ≦ A, the routine proceeds to step 402, where the NO _X amount Nij is multiplied by the interruption time interval Δt, and the product Nij · Δt is added to ΣNO _X. The product Nij · Δt represents the amount of NO _X exhausted from the engine during the interruption time interval Δt, and thus ΔNO _X represents the estimated amount of NO _X absorbed by the NO _X absorbent 17. Then the execution permission flag F ₁ is allowed to execute the action of releasing step 403 NO _X is reset, then the routine proceeds to step 415.

On the other hand, when it is determined in step 401 that ΣNO _X > A, the routine proceeds to step 404, where the NO _X concentration NOR detected by the NO _X concentration sensor 62 is read. Then NO _X concentration NOR step 405 whether greater than a predetermined value W _O is determined. When the NOR ≦ W _O is not deteriorated _the NO _X absorbent 17, hence NO _X estimates ShigumaNO _X reason is considered to have been absorbed in the NO _X absorbent 17 Step 4
Reset regeneration-promoting flag F ₂ indicating that proceed to 06 should promote the regeneration of _the NO _X absorbent 17. Next, at step 407, the count value C is set to zero.
Now, the product K ₁ · Nij · Δ obtained by multiplying Nij · Δt by K ₁ (Fig. 24)
t is added to ΣNO _X. Next, the routine proceeds to step 409, where the execution permission flag is set, and then the routine proceeds to step 415. At step 415, it is determined whether or not the execution permission flag is set. If the execution permission flag has not been set, the routine proceeds to step 423, where the count value T is set to zero, and then the processing cycle is completed.

On the other hand, if it is determined in step 415 that the execution permission flag is set, the process proceeds to step 416 to determine whether or not the condition for performing the NO _X release action, that is, whether the regeneration condition for the NO _X absorbent 17 is satisfied. Is determined. In this case, when the amount of depression of the accelerator pedal 50 is higher than the rotational speed of zero and is and the engine speed N has been determined in advance as described above, i.e., reproducing conditions of the NO _X absorbent 17 during deceleration operation is established Is determined to be.

If it is determined in step 416 that the regeneration condition has been satisfied, the flow advances to step 417 to determine whether or not the regeneration promotion flag has been set. Regeneration of _the NO _X absorbent 17 is performed proceeds to step 148 when the regeneration-promoting flag is not set. That is, the intake shutoff valve 52 is closed, and the reducing agent is supplied from the reducing agent supply valve 58. Next, at step 419, the interruption time interval Δ
t is added. Next, at step 420, it is determined whether or not the elapsed time T from the start of the reproduction has exceeded t _O (FIG. 25). When T <t _O , the processing cycle is completed. On the other hand, when T ≧ t _O , the regeneration action of the NO _X absorbent 17 is stopped, and the routine proceeds to step 422, where the estimated value ΣNO _X of the NO _X amount absorbed in the NO _X absorbent 17 is made zero. . Then step
The processing cycle is completed via 423.

On the other hand, whether the elapsed time T from the start of the playback proceeds to step 416 when the regeneration condition is not satisfied exceeds the predetermined time t _A is determined. The predetermined time t _A is a somewhat shorter time than t _O as described above NO _X remaining rate represents the time may be considered to be zero. Thus T> T _A NO _X amount estimate ShigumaNO _X that is absorbed in the NO _X absorbent 17 proceeds to step 422 when the is made zero.

When it is determined that the contrast is T ≦ t _A in step 421, i.e., when the deceleration operation period remains NO _X is still in _the NO _X absorbent 17 Te short Step 4
Is intended to estimate ShigumaNO _X of _the amount of NO _X is absorbed in the NO _X absorbent 17 proceeds to 24 multiplied by K ₂ (Figure 25) to ΣNO _X.

On the other hand, if it is determined in step 405 that NOR> W _O, that is, if it is determined that the NO _X concentration is high, the process proceeds to step 410, where the regeneration promotion flag F ₂ is set, and
At 411, the count value C is incremented by one. Next, at step 412, it is determined whether or not the count value C has become larger than the fixed value C _O. When C ≦ C _O , the routine proceeds to step 408. Next, the routine proceeds to step 416 via steps 409 and 415.

Next, when it is determined in step 416 that the reproduction condition is satisfied, the process proceeds to step 405 via step 417, and a reproduction promotion process is performed. In the regeneration promoting process, for example, the voltage applied to the supply pump 59 is increased, and the supply amount of the reducing agent is increased. Or the temperature of placing the burner (not shown) in the NO _X absorbent 17 in the exhaust passage upstream of the exhaust gas by the burner is raised. Then summed interrupt time interval Δt is the count at step 426 value T, then the elapsed time T from the start of the step in 427 regeneration promoting process whether it is greater than the predetermined time t ₁ is determined. This fixed time t ₁ is a time longer than t _O in step 420. Become T ≧ t ₁ and _the NO _X absorbent 1
The regeneration promotion process of step 7 is stopped, and the routine proceeds to step 428, where NO _X
The estimated value ΣNO _{X of the} amount of NO _X absorbed in the absorbent 17 is set to zero.

Unless the NO _X absorbent 17 is deteriorated or abnormal, once the regeneration promoting process is performed, or when the regeneration promoting process is repeated several times, ΣNO _X ≧ A
At step 405 when it becomes to be determined that NOR ≦ W _O. However, even repeated many times the reproduction process and _the NO _X absorbent 17 is deteriorated or or abnormality occurs Step 40
In step 5, it is determined that NOR> W _O and therefore step 41
In 2, it is determined that C> C _O. In this case, the process proceeds to step 413, for example, the reproduction execution flag F ₁
Is reset and abnormal processing such as prohibiting useless reproduction processing is performed. Next, at step 414, for example, the warning lamp 63 is turned on to notify the driver that the NO _X absorbent 17 is abnormal.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display F02D 41/14 310 F02D 41/14 310L (72) Inventor Tomohiro Oda Miyoshi-cho, Nishi-kamo-gun, Aichi prefecture 34-1 Yufunagayu (72) Inventor Fumiyasu Murakami 527 Imazato, Susono-shi, Shizuoka (56) References JP-A-2-149715 (JP, A) JP-A-3-194113 (JP, A) 1-56816 (JP, B2)

Claims (37)

(57) [Claims] 1. A absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, the engine exhaust to _the NO _X absorbent to release the NO _X absorbed to decrease the oxygen concentration in the exhaust gas flowing placed in the passageway, NO and _the amount of NO _X estimating means for estimating the amount _of NO _{X X} absorbed in the absorbent, NO _X by the amount of NO _X estimating means
Which reduce the oxygen concentration in the exhaust gas flowing into the NO _X absorbent _the NO _X absorbent from NO _X when the amount of NO _X and the estimated absorbed in the absorbent exceeds an allowable amount predetermined exhaust purification system for an internal combustion engine and a NO _X emission means to emit. Wherein an internal combustion according to claim 1 for estimating the NO _X which the amount of NO _X estimating means is absorbed in the NO _X absorbent based on _the amount of NO _X discharged into the engine exhaust passage from the combustion chamber Engine exhaust purification device. 3. A said amount of NO _X estimating means calculates the NO _X amount exhausted per unit time in the engine exhaust passage from the engine in response to engine load and engine speed _the amount of NO _X calculating means, the NO _X 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, comprising an integrating means for integrating the NO _X amount calculated by the amount calculating means. 4. A comprising a memory for pre-recording as the amount of NO _X calculating means the NO _X amount exhausted per unit time in the engine exhaust passage from the engine the engine load and engine speed function, the cumulative means an exhaust purification system of an internal combustion engine according to claim 3 for integrating the amount of NO _X which is determined from the memory to be stored and the engine load and engine speed. 5. The engine according to claim 3, further comprising a throttle valve disposed in the engine intake passage for controlling the engine load, wherein a negative pressure in the engine intake passage downstream of the throttle valve is used as a representative value of the engine load. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, further comprising an accelerator pedal for controlling an engine load, and using a depression amount of the accelerator pedal as a representative value of the engine load. 7. The exhaust gas control apparatus according to claim 1 which is the maximum NO _X absorbing capacity of the allowable amount _the NO _X absorbent. 8. An exhaust purification system of an internal combustion engine according to claim 1, wherein the absorption defined smaller advance than the maximum NO _X absorbing capacity of the allowable amount _the NO _X absorbent. 9. An exhaust purification system of an internal combustion engine according to claim 1 which is a function of the temperature at which the allowable amount is representative of the temperature of the NO _X absorbent. 10. An exhaust purification system of an internal combustion engine according to claim 9 in which the temperature representative of the temperature of the NO _X absorbent is the exhaust gas temperature. 11. The NO _X release means is an air-fuel ratio of the exhaust gas flowing into the period _the NO _X absorbent predetermined when _the amount of NO _X was estimated by the amount of NO _X estimating means exceeds the allowable value The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas is switched from lean to rich. 12. The NO _X release means is an air-fuel ratio of the mixture amount of NO _X which is estimated by the amount of NO _X estimating means is supplied in a predetermined period the combustion chamber when it exceeds the allowable value 12. The exhaust gas purification device for an internal combustion engine according to claim 11, wherein the device is switched from lean to rich. 13. comprising a reducing agent supply means for supplying a reducing agent to _the NO _X absorbent in the engine exhaust passage upstream of said NO _X
Amount of NO _X which is estimated by the release means the amount of NO _X estimating means the reducing agent from a predetermined time period _the NO _X absorbent reducing agent supply means to the engine exhaust passage upstream of the time exceeding the allowable value 12. The exhaust gas purification device for an internal combustion engine according to claim 11, which is supplied. 14. The method according to claim 13, wherein said reducing agent comprises a hydrocarbon.
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 15. The exhaust gas purifying apparatus for an internal combustion engine according to claim 14, wherein said hydrocarbon comprises at least one selected from gasoline, isooctane, hexane, heptane, butane, propane, light oil, and kerosene. 16. The NO _X release means of the exhaust gas flowing into the period _the NO _X absorbent predetermined during deceleration operation when said amount of NO _X NO _X estimated by the estimating means exceeds the allowable value 12. The exhaust gas purification device for an internal combustion engine according to claim 11, wherein the air-fuel ratio is switched from lean to rich. 17. An engine shut-off valve which is normally fully opened and closed during deceleration operation is disposed in an engine exhaust passage.
16. The exhaust gas purification device for an internal combustion engine according to item 16. 18. The amount of NO _X estimating means, N is estimated to be absorbed in _the NO _X absorbent when the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is a period rich predetermined
An exhaust purification system of an internal combustion engine according to claim 11, O _X amount to zero. 19. The amount of NO _X estimating means is NO _X in the NO _X absorbent when the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is in short periods richer than the period of said predetermined 12. The exhaust gas purification device for an internal combustion engine according to claim 11, wherein the device is estimated to remain. 20. is absorbed in the NO _X absorbent taking into account the amount of NO _X is the amount of NO _X estimating means for remaining in _the NO _X absorbent
An exhaust purification system of an internal combustion engine according to claim 19 for estimating the amount of NO _X. 21. The time the air-fuel ratio of the exhaust gas is the amount of NO _X estimating means for flowing into _the NO _X absorbent is made rich is more shorter
20. The exhaust gas purifying apparatus for an internal combustion engine according to claim 19, wherein the amount of NO _X estimated to remain in the NO _X absorbent is increased. 22. The relationship between the time when the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is enriched and the residual ratio of NO _X estimated to remain in the NO _X absorbent is stored in advance. A memory, wherein the NO _X amount estimating means is configured to store the N _X stored in the memory.
O _X exhaust purification system of an internal combustion engine according to claim 21 for estimating the amount of NO _X remaining in _the NO _X absorbent based on residual ratio of. NO _X of 23. _the NO _X absorbent exhaust gas flowing out from the
The N when the NO _X concentration detecting means for detecting the concentration, amount of NO _X which is estimated by the amount of NO _X estimating means exceeds the allowable amount
O _X concentration exhaust purification system of an internal combustion engine according to claim 11 comprising a NO _X emission promoting means promotes the release action of the NO _X from _the NO _X absorbent when higher than a predetermined concentration . 24. The internal combustion engine according to claim 23, wherein said NO _X release promoting means promotes the NO _X release action by extending the time for enriching the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent. Exhaust purification equipment. 25. An exhaust system for an internal combustion engine according to claim 23, wherein said NO _X release promoting means promotes the NO _X release effect by increasing the degree of richness of the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent. Purification device. 26. Even if the NO _X release promoting action of the NO _X release promoting means is performed a predetermined number of times or more,
Degradation amount of NO _X which is estimated by the amount of NO _X estimating means judges that _the NO _X absorbent when higher than the concentration of the NO _X concentration is predetermined when it exceeds the allowable amount is degraded 24. The exhaust gas purification device for an internal combustion engine according to claim 23, further comprising a determination unit. 27. The amount of NO _X estimating means for estimating an amount of NO _X absorbed in _the NO _X absorbent taking into account the reduction of the NO _X absorbing capacity when the NO _X absorbing capacity of the NO _X absorbent is lowered Claim 1
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 28. comprising time and the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is lean, the previously stored memory the relationship between the NO _X absorbing capacity of the NO _X absorbent, the NO _X the amount estimation means exhaust gas control apparatus according to claim 27 for estimating the amount of NO _X absorbed in _the NO _X absorbent based to the NO _X absorption capacity stored in the memory. 29. The amount of NO _X was estimated by the estimation means NO _X
2. The internal combustion engine according to claim 1, further comprising air-fuel ratio control means for enriching the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber according to the operating state of the engine regardless of whether the amount exceeds the allowable value. Exhaust purification equipment. 30. An exhaust purification system for an internal combustion engine according to claim 29, wherein said air-fuel ratio control means makes the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber rich when the engine load is higher than a predetermined load. apparatus. 31. An exhaust gas purifying apparatus for an internal combustion engine according to claim 29, wherein said air-fuel ratio control means temporarily makes the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber rich when the engine shifts to idling operation. 32. The exhaust gas purification of an internal combustion engine according to claim 29, wherein said air-fuel ratio control means makes the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber rich during acceleration operation in which the acceleration is greater than a predetermined value. apparatus. 33. The exhaust gas purifying apparatus for an internal combustion engine according to claim 29, wherein said air-fuel ratio control means enriches the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber during a shift-down operation of the transmission. 34. A claim for the amount of NO _X to zero, which is estimated to be absorbed in _the NO _X absorbent when the amount of NO _X estimating means the air-fuel ratio of the mixture a predetermined time or more has been rich Item 30. An exhaust gas purification device for an internal combustion engine according to item 29. Potassium 35. _the NO _X absorbent is sodium, lithium, alkali metal consisting of cesium, barium, alkaline earth consisting of calcium, lanthanum, with one least selected from rare earth consisting of yttrium, and a platinum The exhaust gas purification device for an internal combustion engine according to claim 1. 36. _the NO _X absorbent is barium, the exhaust purification system of an internal combustion engine according to claim 1 comprising a composite oxide of copper. 37. An exhaust purification system of an internal combustion engine according to claim 1 placing the three-way catalyst in the NO _X absorbent downstream of the engine exhaust passage.