JP3512062B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] TECHNICAL FIELD The present invention relates to an air-fuel ratio lean condition.
Related to exhaust gas purification devices for internal combustion engines that burn in the dry state
is there. [0002] 2. Description of the Related Art When the air-fuel ratio of inflow exhaust gas is lean, N
Ox is absorbed and absorbed when the oxygen concentration of the inflowing exhaust gas decreases.
The NOx storage reduction catalyst that releases collected NOx
Due to the high purification rate, in recent years the fuel
NOx purification of exhaust gas discharged from the internal combustion engine to be burned
It is heavily used for [0003] The NOx absorption capacity of the NOx storage reduction catalyst
Has a limit, and the absorbed NOx amount reaches a predetermined allowable amount.
When reached, it saturates and becomes unabsorbable. for that reason,
In an exhaust gas purification device using an NOx storage reduction catalyst, the storage
Appropriate timing of NOx absorbed by the reduced NOx catalyst
Need to be released and reduced. [0004] International Publication Pamphlet WO 93/258
No. 06, when the air-fuel ratio of the inflow exhaust gas is lean
The amount of NOx absorbed by the reduced NOx catalyst is estimated, and this estimation is performed.
When the constant absorption NOx amount exceeds the allowable amount, a predetermined
Period, the air-fuel ratio of the inflowing exhaust gas is made rich,
Technology to release and reduce NOx absorbed in the NOx catalyst
It has been disclosed. In addition, the pamphlet includes
The NOx absorption capacity (allowable amount) of the original NOx catalyst depends on the catalyst temperature.
Or it depends on the exhaust gas temperature.
NO, which is a criterion for changing the air-fuel ratio from lean to rich
x The absorption capacity depends on the catalyst temperature or exhaust gas temperature.
Changes are disclosed. In other words, in the past,
NOx absorption capacity based on catalyst temperature or exhaust gas temperature
The estimated amount of absorbed NOx exceeded the calculated amount.
At times, the air-fuel ratio of the inflowing exhaust gas is made rich. [0005] By the way, the exhaust gas temperature
Changes constantly depending on the load of the internal combustion engine, etc., and the catalyst temperature becomes
Since the catalyst has heat capacity, it is slow to change exhaust gas temperature.
Change. Therefore, for example, when the exhaust gas temperature is N
When the temperature changes in a direction to increase the Ox absorption capacity
Indicates that the estimated absorbed NOx amount is
Even if the corresponding NOx absorption capacity is reached,
Type NOx catalysts can still absorb NOx
It is. [0006] However, in the conventional technique, the exhaust gas
Since the direction of change in gas temperature is not considered, NOx absorption
When the exhaust gas temperature changes in the direction of increasing capacity
Also, the estimated absorbed NOx amount is changed to the current exhaust gas temperature.
When the corresponding NOx absorption capacity is exceeded, the
The air-fuel ratio has been switched to rich, which has
I was invited. [0007] The present invention addresses these problems of the prior art.
The present invention has been made in view of the above, and is intended to be solved by the present invention.
The challenge is to change the direction of the catalyst temperature of the NOx storage reduction catalyst.
Accordingly, the NOx absorbed from the NOx storage reduction catalyst is released.
By correcting the timing of flow-out and reduction, NOx absorption
Prolonged collection time, reduced NOx emission frequency, NOx purification rate
The goal is to improve [0008] The present invention solves the above-mentioned problems.
In order to do so, the following means were adopted. That is, the present invention
NOx is absorbed when the air-fuel ratio of the inflowing exhaust gas is lean.
Absorbed when the oxygen concentration of the exhaust gas collected and reduced
The NOx storage-reduction catalyst that releases NOx is placed in the engine exhaust passage.
NOx amount absorbed by the NOx storage reduction catalyst
Flows into the NOx storage reduction catalyst when the amount exceeds the allowable amount
To make the air-fuel ratio of exhaust gas rich
Internal combustion engine with release means for releasing and reducing NOx from a medium
In the exhaust purification device of Seki, the storage reduction type NOx catalyst
The catalyst temperature at which the NOx absorption capacity is maximized
Catalyst temperature to determine whether it is changing in the approaching direction
Change direction determining means and the catalyst temperature change direction determining means.
Therefore, the catalyst temperature of the NOx storage reduction catalyst is determined by the NOx absorption capacity.
Is changing in a direction approaching the maximum catalyst temperature.
When determined, the air-fuel ratio of exhaust gas by the release means
Release time that is adjusted to delay the time to make it rich
Correction means. The NOx absorption capacity of the NOx storage reduction catalyst is
The contact temperature changes according to the medium temperature and maximizes the NOx absorption capacity.
Medium temperature exists. Therefore, the NOx storage reduction catalyst
The catalyst temperature at which the NOx absorption capacity is maximized
When changing to the approaching direction, the storage reduction type NO
The NOx absorption capacity of the x catalyst also changes in the increasing direction. Therefore, the catalyst temperature change direction determining means is
Therefore, the catalyst temperature of the NOx storage reduction catalyst is determined by the NOx absorption capacity.
Is changing in a direction approaching the maximum catalyst temperature.
When it is determined, the release timing correction means
Time to make the air-fuel ratio of exhaust gas rich by the release means
Exhaust gas flowing into the NOx storage reduction catalyst
By keeping the air-fuel ratio of lean, the occlusion reduction type N
The NOx absorption time of the Ox catalyst is extended, and the NOx stored and reduced
The frequency of releasing NOx from the x catalyst is reduced. This
Therefore, the NOx purification rate of the exhaust gas purification device is improved. As the internal combustion engine, a diesel engine,
Lean burn gasoline engine can be exemplified
You. Judgment of change direction of catalyst temperature of NOx storage reduction catalyst
To detect the catalyst temperature directly,
The direction of change may be determined, or exhaust may be used instead of catalyst temperature.
Detects gas temperature and changes the direction of exhaust gas temperature change in catalyst temperature
The direction may be used. Also, the exhaust gas temperature depends on the operating state of the engine.
From the estimated exhaust gas temperature
May be used as the catalyst temperature change direction. [0012] DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an exhaust gas purifying apparatus according to the present invention will be described.
An embodiment will be described with reference to the drawings of FIGS.
You. FIG. 1 shows the present invention applied to a gasoline engine.
FIG. 3 is a diagram showing a schematic configuration in a case where the device is used. In this figure,
1 is the engine body, 2 is the piston, 3 is the combustion chamber,
Reference numeral 4 is a spark plug, reference numeral 5 is an intake valve, and reference numeral 6 is an intake port.
G, reference numeral 7 denotes an exhaust valve, and reference numeral 8 denotes an exhaust port.
The intake port 6 is connected to the surge tank 1 via the corresponding branch pipe 9.
0, and each branch pipe 9 is directed toward the intake port 6 respectively.
A fuel injection valve 11 for injecting fuel is attached. Sa
The air tank 10 is connected to an air cleaner through an intake duct 12.
13 and a throttle valve 1 in the intake duct 12.
4 are arranged. On the other hand, the exhaust port 8 is an exhaust manifold.
NOx catalyst 1 via the exhaust pipe 15 and the exhaust pipe 16
7 is connected to a casing 18 containing the same. An electronic control unit for engine control
(ECU) 30 is composed of a digital computer,
ROMs (leads) interconnected by a direction bus 31
Only memory) 32, RAM (random access memo)
3) 33, CPU (central processor unit) 3
4, an input port 35 and an output port 36 are provided. Sir
Proportional to the absolute pressure in surge tank 10
Pressure sensor 19 that generates the output voltage
The output voltage of the pressure sensor 19 is supplied to the AD converter 37.
The input is input to the input port 35 via the input port 35. Also throttle
The throttle valve 14 has an idling opening degree for the valve 14.
Idle switch 20 for detecting that
The output signal of the idle switch 20 is input port 35
Is entered. On the other hand, the exhaust pipe 16 upstream of the casing 18
The temperature sensor generates an output voltage proportional to the exhaust gas temperature.
Sensor 25 is attached, and the output power of the temperature sensor 25 is
Is input to the input port 35 via the AD converter 38.
You. The input port 35 has an output parameter representing the engine speed.
A rotation sensor 26 for generating looseness is connected. Output port
The ports 36 are respectively connected to the ignition plugs 4 via corresponding drive circuits 39.
And the fuel injection valve 11. In this gasoline engine, for example,
The fuel injection time TAU is calculated based on this. TAU = TP · K Here, TP indicates the basic fuel injection time, and K is the supplementary fuel injection time.
The positive coefficient is shown. The basic fuel injection time TP is
The air-fuel ratio of the air-fuel mixture supplied into the
3 shows the fuel injection time required for the fuel injection. This basic fuel injection
The firing time TP is determined in advance by an experiment,
2 as a function of the absolute pressure PM and the engine speed N in FIG.
Is stored in advance in the ROM 32 in the form of a map as shown in FIG.
ing. The correction coefficient K is a mixture supplied to the engine cylinder.
A coefficient for controlling the air-fuel ratio of the gas, where K = 1.0
If the mixture supplied to the engine cylinder is stoichiometric
Ratio. On the other hand, if K <1.0,
The air-fuel ratio of the air-fuel mixture supplied into the fan is larger than the stoichiometric air-fuel ratio.
It becomes lean, that is, it becomes lean, and if K> 1.0, the engine
The air-fuel ratio of the mixture supplied to the cylinder is the stoichiometric air-fuel ratio.
, Ie, rich. The value of the correction coefficient K is
Predetermined for the absolute pressure PM and the engine speed N
FIG. 3 shows an example of the value of the correction coefficient K.
You. In this example, the absolute pressure PM in the surge tank 10 is
In a relatively low range, that is, a low-medium load operation range, the correction coefficient
The value of K is assumed to be less than 1.0,
Sometimes the air-fuel ratio of the mixture supplied to the engine cylinder
Lean. On the other hand, the absolute pressure P in the surge tank 10
In the region where M is relatively high, that is, in the engine high load operation region, the correction is performed.
The value of the coefficient K is set to 1.0, and
The air-fuel ratio of the mixture supplied to the Seki cylinder is the stoichiometric air-fuel ratio
It is said. Also, the absolute pressure PM in the surge tank 10 is minimized.
Correction coefficient in the region where
The value of K is set to a value greater than 1.0, and
Sometimes the air-fuel ratio of the mixture supplied to the engine cylinder
It is said to be rich. Internal combustion engines are usually operated at low to medium loads.
Most frequently, and therefore during most of the driving period.
And the lean mixture will be fueled. FIG. 4 shows the exhaust gas discharged from the combustion chamber 3.
1 schematically shows the concentration of a typical component of. This figure
As can be seen, the exhaust gas discharged from the combustion chamber 3
The concentration of unburned HC and CO depends on the mixture supplied to the combustion chamber 3.
Increases as the air-fuel ratio of the fuel becomes rich, and is discharged from the combustion chamber 3.
Oxygen in exhaust gas_TwoIs supplied to the combustion chamber 3
As the air-fuel ratio of the air-fuel mixture becomes leaner, the air-fuel ratio increases. The storage and return housed in the casing 18
The original NOx catalyst 17 uses alumina as a carrier, for example.
On a carrier such as potassium K, sodium Na, and lithium
Li, alkali metal such as cesium Cs, barium
Ba, alkaline earth like calcium Ca, lanthanum
La, a small number selected from rare earths such as yttrium Y
At least one and a noble metal such as platinum Pt
I have. On the engine intake passage and the NOx storage reduction catalyst 17
Air and fuel (hydrocarbons)
Exhaust gas flowing into the NOx storage reduction catalyst 17
(Hereinafter abbreviated as exhaust air-fuel ratio),
The NOx storage reduction catalyst 17 has a lean exhaust air-fuel ratio.
Absorbs NOx and oxygen concentration in the inflow exhaust gas
NOx release and release released NOx
Do The exhaust gas upstream of the NOx storage reduction catalyst 17 is
No fuel (hydrocarbon) or air is supplied into the air passage.
In this case, the exhaust air-fuel ratio is
The air-fuel ratio of the gas, and in this case
The original NOx catalyst 17 is a catalyst for the air-fuel mixture supplied into the combustion chamber 3.
When the air-fuel ratio is lean, NOx is absorbed and the combustion chamber 3
Absorbed when the oxygen concentration in the mixture supplied to
NOx will be released. The above-described NOx storage reduction catalyst 17 is exhausted from the engine.
If disposed in the air passage, the NOx storage reduction catalyst 17
It actually performs the absorption and release of NOx.
Some details are not clear. I
However, this absorption / release effect is not affected by the mechanical mechanism shown in FIG.
It is thought that it is done in the rhythm. Next, this mechanism
Platinum Pt and barium Ba on the carrier
In the following, the case of carrying the precious metal will be explained.
The same applies when using alkali metals, alkaline earths, and rare earths.
It becomes a mechanism. That is, the inflow exhaust gas is considerably lean.
And the oxygen concentration in the inflowing exhaust gas greatly increased, and FIG.
As shown in FIG._Two Is O_Two ^-Or O^2-In the form of
It adheres to the surface of platinum Pt. On the other hand, included in the inflow exhaust gas
NO on the surface of platinum Pt_Two ^-Or O^2-And react
And NO_Two (2NO + O_Two → 2NO_Two ). Next, the generated NO_TwoPart of the platinum
While being oxidized on Pt, it is absorbed into the NOx storage reduction catalyst 17.
While being collected and combined with barium oxide BaO, FIG.
As shown in (A), nitrate ion NO_Three ^-Occlusion in the form of
It diffuses into the original NOx catalyst 17. In this way, NOx
Is absorbed in the NOx storage reduction catalyst 17. As long as the oxygen concentration in the inflowing exhaust gas is high, platinum
NO on Pt surface_TwoIs generated, and the NOx storage reduction catalyst 1
As long as the NOx absorption capacity of NO._TwoIs occluded
Nitrate ion NO absorbed in the primary NOx catalyst 17_Three ^-But
Generated. On the other hand, the oxygen concentration in the inflow exhaust gas
Decreases and NO_TwoThe reaction goes in the reverse direction when the amount of
(NO_Three ^-→ NO_Two), And into the NOx storage reduction catalyst 17.
Nitrate ion NO_Three ^-Is NO_TwoNOx storage-reduction type catalyst
Emitted from 17. That is, the oxygen concentration in the incoming exhaust gas
Is reduced, NOx is released from the NOx storage reduction catalyst 17.
Will be issued. As shown in FIG.
If the degree of leanness of the gas decreases, the acid in the incoming exhaust gas
Element concentration and thus the degree of leanness of the incoming exhaust gas
If the exhaust air-fuel ratio is lean,
NOx is released from the NOx storage reduction catalyst 17 and
Become. On the other hand, at this time, the fuel is supplied into the combustion chamber 3.
When the mixture becomes rich and the exhaust air-fuel ratio becomes rich,
As shown in FIG. 4, a large amount of unburned HC and CO
Are discharged, and the unburned HC and CO are converted to acid on platinum Pt.
Element O_Two ^-Or O^2-And oxidize. When the exhaust air-fuel ratio becomes rich,
Occlusion reduction type because the oxygen concentration in the gas is extremely reduced
NOx from the NOx catalyst 17_TwoIs released and this NO_TwoThe figure
As shown in 5 (B), it reacts with unburned HC and CO and returns
I can be rejected. In this way, N
O_TwoIs no longer present, the NOx storage reduction catalyst 17
NO one after another_TwoIs released. Therefore, exhaust air
When the fuel ratio is made rich, the NOx storage reduction type
NOx is released from the medium 17. That is, first, when the exhaust air-fuel ratio is made rich,
Unburned HC and CO are converted to O on platinum Pt_Two ^-Or O^2-And just
And then oxidized, then O on Pt_Two ^-
Or O^2-Unburned HC and CO still remain even after consumption
If the unburned HC and CO are used, the NOx storage reduction catalyst
NOx emitted from the engine 17 and N emitted from the engine
Ox is reduced. Therefore, if the exhaust air-fuel ratio is made rich,
Is absorbed by the NOx storage reduction catalyst 17 in a short time.
NOx is released, and the released NOx is returned.
To prevent NOx from being released into the atmosphere
Will be able to In addition, the NOx storage reduction type
Since the medium 17 has a function of a reduction catalyst, the exhaust air-fuel ratio
Is released from the NOx storage reduction catalyst 17 even if the stoichiometric air-fuel ratio is
The emitted NOx is reduced. However,
When the air-fuel ratio is set to the stoichiometric air-fuel ratio, the storage reduction type NO
Since NOx is released only gradually from the x catalyst 17,
Releases all NOx absorbed by the storage reduction type NOx catalyst 17
It takes a little longer time to do this. By the way, as described above, the exhaust air-fuel ratio
If the exhaust air-fuel ratio is lean,
NOx is released from the NOx storage reduction catalyst 17
You. Therefore, NOx is stored in the NOx storage reduction catalyst 17.
To release it, lower the oxygen concentration in the incoming exhaust gas.
It would be good. However, the storage reduction type NOx catalyst 17
The exhaust air-fuel ratio is lean even if NOx is released from
NOx is not reduced in the NOx storage reduction catalyst 17,
Therefore, in this case, the storage reduction type NOx catalyst 17
Provide a catalyst capable of reducing NOx in the stream or occlude
It is necessary to supply a reducing agent downstream of the reduced NOx catalyst 17.
is there. Needless to say, below the NOx storage reduction catalyst 17
Although it is possible to reduce NOx in the stream,
Rather, NOx is stored in the NOx storage reduction catalyst 17.
Reduction is preferred. Therefore, in this embodiment,
When NOx is to be released from the storage reduction type NOx catalyst 17
The exhaust air-fuel ratio is enriched, so that the storage reduction type N
NOx released from the Ox catalyst 17 is stored and reduced by NOx catalyst.
The medium 17 is reduced. In the embodiment according to the present invention,
As described above, the fuel is supplied into the combustion chamber 3 during the full load operation.
The mixture is considered rich, and during high-load operation
Since the stoichiometric air-fuel ratio is used, the system operates at full load
Sometimes, NOx is released from the NOx storage reduction catalyst 17.
And However, full load operation or high load operation
If the frequency of rotation is low, full load operation and high load
NOx is released from the NOx storage reduction catalyst 17 only during load operation.
Even if it is delivered, the lean mixture is burned
Of NOx by the NOx storage reduction catalyst 17 during storage
Is saturated, and thus the NOx storage reduction catalyst 17
This makes it impossible to absorb NOx. So, this
In this embodiment, the lean mixture continuously burns.
When the mixture is supplied to the combustion chamber 3 periodically.
Aiki is made rich, and during this time the storage reduction type NOx catalyst 1
7 is designed to release NOx. In this case, the fuel supplied into the combustion chamber 3 is
The longer the mixture is enriched, the longer the mixture
While the combustion of the gas is being performed, the NOx storage reduction catalyst 17
NOx absorption capacity is saturated, thus absorbing NOx.
NOx catalyst 17
Is released into the atmosphere. to this
On the other hand, the engine operating state with a large amount of NOx emitted from the engine
Of the NOx storage reduction catalyst 17 even when
Before the NOx absorption capacity is saturated, the NOx storage reduction catalyst 17
Mixture is enriched so that NOx can be released from
Shortening the cycle will in turn increase fuel consumption
The problem arises. Therefore, in the present invention, the storage reduction type NOx catalyst
17 to determine the amount of NOx absorbed in the storage-reduction type NOx.
The amount of NOx absorbed in the catalyst 17 is set to a predetermined allowable value.
The mixture is made rich when the capacity is exceeded
You. As described above, the NOx catalyst 17
Mixed when the NOx amount exceeds the predetermined allowable amount.
When the aiki is made rich, the NOx of the NOx storage reduction catalyst 17 is increased.
NOx is released to the atmosphere because the absorption capacity does not saturate
And how often the mixture is enriched
The fuel consumption increases.
Can be suppressed. The storage-reduction type NOx catalyst 17
When obtaining the stored NOx amount, occlusion reduction
Directly obtains the amount of NOx absorbed in the type NOx catalyst 17
It is difficult. In the present invention, therefore,
The NOx storage reduction catalyst 17 is determined based on the amount of NOx contained in the exhaust gas.
The amount of NOx absorbed in the inside is estimated. Immediately
That is, as the engine speed N increases, the
Since the amount of exhaust gas discharged to the engine increases, the engine speed N
Emission from the engine per unit time
The NOx amount increases. Also, 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 the combustion chamber 3 increases, and
Since the baking temperature increases, the higher the engine load, that is,
The higher the absolute pressure PM in the surge tank 10, the higher the engine
Therefore, the amount of NOx discharged per unit time increases. FIG. 6A shows the unit time obtained by the experiment.
NOx amount discharged from the engine per hour and surge tank
10 shows the relationship between the absolute pressure PM and the engine speed N.
In FIG. 6A, each curve shows the same NOx amount.
I have. As shown in FIG.
Of NOx discharged from the tank is the absolute pressure in the surge tank 10.
The higher the PM, the higher the number, and the higher the engine speed N.
More. The NOx amount shown in FIG.
In the form of a map as shown in FIG.
Is stored in On the other hand, FIG. 7 shows that the NOx storage reduction catalyst 17 is used.
NOx absorption capacity of NOx that can be absorbed and storage reduction type
Relationship with the exhaust gas temperature T representing the temperature of the NOx catalyst 17
Is shown. The temperature of the NOx storage reduction catalyst 17 is low.
When the exhaust gas temperature T decreases, the oxidation of NOx
For (2NO + O_Two → 2NO_TwoNOx absorption due to weakening)
The capacity NOxCAP decreases, and the NOx storage reduction catalyst 1
7 increases, that is, when the exhaust gas temperature T increases.
NOx absorbed in the NOx storage reduction catalyst 17 is decomposed.
NOx absorption capacity NOxCAP is small
It will be cheap. Therefore, the NOx storage reduction catalyst 17 is
Constant exhaust gas temperature T_a(About 390 ° C in this example)
Thus, the maximum NOx absorption capacity becomes NOxCAPmax. N that can be absorbed by the NOx storage reduction catalyst 17
Ox absorption capacity NOxCAP and storage reduction type NOx catalyst 1
7, that is, the relationship with the exhaust gas temperature T.
Therefore, the exhaust gas temperature T is equal to the predetermined exhaust gas temperature T._a
When it is changing in the direction approaching
The NOx absorption capacity NOxCAP of the Ox catalyst 17 also increases
In a different direction. Therefore, the storage reduction type NO
The estimated value of the amount of NOx absorbed by the x
NOx absorption capacity NOxCAP calculated based on temperature T
Even if the exhaust gas temperature T reaches the predetermined exhaust gas temperature,
T_aOcclusion reduction
The type NOx catalyst 17 can further absorb NOx
You will be in a state. Therefore, in this embodiment,
Estimation of the amount of NOx absorbed by the NOx storage reduction catalyst 17
NOx absorption capacity whose constant value is calculated based on exhaust gas temperature T
When the amount of NOxCAP is exceeded, the exhaust gas temperature T decreases
Constant exhaust gas temperature T_aIs changing in the direction approaching
Is determined, and if YES, the NOx storage reduction catalyst 1
7 continues to absorb NOx, that is, the fuel
The burning is continued, and in the case of NO, the NOx storage reduction catalyst 17 is used.
Release NOx from the fuel, that is, burn a rich mixture.
I'm trying. FIG. 8 shows the NOx storage reduction catalyst 17.
Switching the air-fuel ratio of the incoming exhaust gas from lean to rich
Released from the NOx storage reduction catalyst 17
The experimental results of the amount of Ox are shown. Note that FIG.
The line indicates the temperature of the NOx storage reduction catalyst 17, that is, the exhaust gas temperature.
T indicates a high value, and the broken line indicates the NOx storage reduction type.
This shows a case where the temperature of the medium 17, that is, the exhaust gas temperature T is low.
You. NOx decomposition speed in the NOx storage reduction catalyst 17
The temperature increases as the temperature of the NOx storage reduction catalyst 17 increases.
It becomes. Therefore, as shown by the solid line in FIG.
When the temperature of the primary NOx catalyst 17 is high, that is, when the exhaust gas
When the temperature T is high, a large amount of NOx is absorbed in a short time.
The NOx stored and reduced by the NOx storage reduction catalyst 17
When the temperature of the catalyst 17, that is, the exhaust gas temperature T is low, FIG.
As shown by the dashed line in
Over this period, the NOx catalyst 17 is continuously released.
That is, the higher the exhaust gas temperature T, the more occlusion per unit time
The amount of NOx released from the reduced NOx catalyst 17 increases,
It can be seen that the NOx release time is shortened. By the way, unburned HC discharged from the engine,
The total amount of CO released from the NOx storage reduction catalyst 17
When the amount is smaller than the amount that can reduce NOx, some NOx
Is released into the atmosphere without reduction, whereas
The amount of unburned HC and CO discharged from the engine is stored and reduced N
From the amount that can reduce all NOx released from the Ox catalyst 17
When there is too much, excess unburned HC and CO are released into the atmosphere.
It is. Therefore, NOx and unburned HC and CO
In order to prevent the release into
Just needed to reduce NOx released from x catalyst 17
It is necessary to discharge a large amount of unburned HC and CO from the engine
For that purpose, the unburned H corresponds to the curve shown in FIG.
It is necessary to increase the amounts of C and CO. By the way, as described above,
The amount of unburned HC and CO to be mixed depends on the mixing supplied to the combustion chamber 3.
It is proportional to the degree of Qi richness. Therefore, this fruit
In the present embodiment, as shown in FIG.
The value of the correction coefficient k for P, that is, the degree of richness of the air-fuel mixture
Is as close as possible to the NOx concentration change pattern shown in FIG.
I try to change it with a different pattern. In addition,
Here, the correction coefficient k is between K = 1 and the correction coefficient K described above.
+ K, and therefore mixed when k = 0
The air becomes the stoichiometric air-fuel ratio, and when k> 0, the air-fuel mixture becomes rich.
It becomes j. As shown by the solid line in FIG.
Time when NOx should be released from the primary NOx catalyst 17
C is C₁Until the correction coefficient k reaches α per unit time
And then time C becomes C₁And C_TwoBetween
The positive coefficient k is kept constant, and then the time C becomes C_TwoBeyond
Then, the correction coefficient k decreases by β every unit time.
You. These α, β, C₁, C_TwoIs the change parameter of the correction coefficient k.
Change in NOx concentration whose turn is indicated by the solid line in FIG.
It is set to be as close as possible to the pattern. On the other hand, the temperature of the NOx storage reduction catalyst 17
That is, the change pattern of the correction coefficient k when the exhaust gas temperature T is low.
8, the exhaust gas temperature T indicated by the broken line in FIG.
As close as possible to the change pattern of NOx concentration
Stipulated. In this case, the correction coefficient in FIG.
In order to make the change pattern of k like a broken line, it is shown by a solid line.
Α and β are both smaller than the change pattern
₁, C_TwoIt can be seen that it is sufficient to increase both. That is,
The change pattern of the positive coefficient k is shown in FIG.
To get closer to the pattern, as shown in FIG.
Α and β increase as the temperature T increases, and C₁, C_Two
Should be reduced. Note that C shown in FIG.
₁, C_Two, Α, β and the exhaust gas temperature T are stored in the ROM 3 in advance.
2 is stored. In the embodiment according to the present invention, the exhaust gas
A temperature sensor 25 for detecting the temperature T is provided.
Therefore, the discharge detected by the temperature sensor 25 is
The NOx absorption capacity N shown in FIG. 7 based on the gas gas temperature T
OxCAP and α, β, C shown in FIG.₁, C_TwoBut
It is determined. However, the exhaust gas temperature T is
From the absolute pressure PM in the engine 10 and the engine speed N.
be able to. Therefore, instead of providing the temperature sensor 25,
Instead, the exhaust gas temperature T is calculated in the form of a map as shown in FIG.
It is stored in advance in the ROM 32, and obtained from this map.
NOx absorption capacity NOxCAP based on the exhaust gas temperature T
And α, β, C₁, C_TwoCan also be determined. Next, referring to FIGS. 12 to 14, NO
The x release control will be described. FIG. 12 and FIG.
The time interrupt rule executed by the interrupt every fixed time
Is shown. Referring to FIG. 12 and FIG.
In step 100, the NOx storage reduction catalyst 1
NOx release flag indicating that NOx should be released from
It is determined whether a lag is set. NOx release
If the output flag is not set, step 101
To determine whether the correction coefficient K is smaller than 1.0,
It is determined whether the operating condition is such that the air-fuel mixture should be lean.
It is. When K <1.0, that is, the mixture should be lean
When the vehicle is in the operation state, the process proceeds to step 102 and the count value
D is made zero, and then the routine proceeds to step 103. In step 103, the pressure sensor 19
Pressure PM in the surge tank 10
The unit is calculated from the map shown in FIG.
Calculate the NOx amount Nij emitted from the engine per hour
Is done. Next, at step 104, the NOx amount Nij
Multiply the interrupt time interval Δt, and multiply these products Nij · △
t is added to ΣNOx. Product Nijｊt is interrupt
Indicates the amount of NOx emitted from the engine during the time interval Δt
At this time, NOx exhausted from the engine is stored and reduced.
NOx is stored and reduced because it is absorbed by the type NOx catalyst 17.
The estimated value of the amount of NOx absorbed in the type NOx catalyst 17 is displayed.
You will be doing. Next, at step 105, the temperature sensor 2
5 based on the exhaust gas temperature T detected by FIG.
The NOx absorption capacity NOxCAP is calculated from the relationship. Next
In step 106, the NOx storage reduction catalyst 17
The estimated value of the stored NOx amount ΣNOx is the NOx absorption capacity
It is determined whether or not NOxCAP has been exceeded. ΣNOx ≦ N
In the case of OxCAP, the processing cycle is completed. This and
The lean mixture is being burned during the
The emitted NOx is absorbed by the NOx storage reduction catalyst 17.
You. On the other hand, in step 106 ΣNOx>
If NOxCAP is determined, the process proceeds to step 107.
Then, the current exhaust gas temperature T becomes the maximum NOx absorption capacity.
Exhaust gas temperature T corresponding to NOxCAPmax_aWhether or not
Is determined. Note that the current
The exhaust gas temperature T corresponds to the value detected by the temperature sensor 25.
Value is adopted. In step 107, T ≦ T_aDetermined to be
When it is determined that the routine
Exhaust gas temperature T when executing_iThis routine last time
Exhaust gas temperature T when executed_i-1Whether the difference after subtracting is positive or not
Is determined. T_i−T_i-1Exhaust gas temperature when> 0
T is the exhaust gas temperature T_aChange in the direction approaching
Thus, the processing cycle is completed. At this time
The combustion of the lean mixture will continue, and the engine will
The exhausted NOx is absorbed by the NOx storage reduction catalyst 17.
You. On the other hand, at step 108, T_i−T_i-1≤0
Is determined to be NOx storage NOx storage catalyst 17 NOx storage
Proceeding to step 109 assuming that the
The NOx release flag is set. In step 107, T> T_aIs
When it is determined, the process proceeds to step 110 and
Exhaust gas temperature T when executing routine_iFrom the last book
Exhaust gas temperature T when running_i-1Negative difference
Is determined. T_i−T _i-1Exhaust gas when <0
Exhaust gas temperature T_aChange in the direction approaching
Therefore, the processing cycle is completed. This and
Combustion of the lean mixture continues,
NOx discharged from the storage is absorbed by the NOx storage reduction catalyst 17.
Will be collected. On the other hand, in step 110, T_i−T_i-1≧
If it is determined to be 0, the NOx storage reduction catalyst 17
Assuming that the NOx absorption capacity is saturated, step 109
And the NOx release flag is set. Then, from Step 109 to Step 11
1 and based on the exhaust gas temperature T, the relationship shown in FIG.
La C₁, C_Two, Α, β are calculated and the processing cycle is completed.
You. When the NOx release flag is set, the next processing cycle
In step 100, the process proceeds from step 100 to step 112,
The count value C is incremented by one. Next,
In step 113, the count value C is C₁Is less than
Is determined. C <C₁If so, proceed to step 114
Is added to the correction coefficient k. Then the processing cycle
Complete. The addition effect of α on the correction coefficient k is C ≧ C₁
, And is therefore shown in FIG.
Thus, the value of the correction coefficient k continues to increase during this period. On the other hand, at step 113, C ≧ C₁To
If it is determined that the time has been reached, proceed to step 115 and count
Value C is C_TwoIt is determined whether or not C <
C_TwoIn the case of, the processing cycle is completed. Therefore figure
C ≧ C as shown in FIG._TwoUntil the correction coefficient k becomes
Will be kept constant. Next, at step 115, C ≧ C_TwoTo
If it is determined that the time has become
Β is subtracted from the positive coefficient k. Then in step 117
Is determined whether the correction coefficient k has become zero or negative, and
When k> 0, the processing cycle is completed. Therefore
As shown in FIG. 9, the correction coefficient k decreases until k ≦ 0.
Can be reduced. When k> 0, as described later,
During this time, the air-fuel mixture supplied into the combustion chamber 3 is made rich,
During this time, the degree of richness changes according to the pattern shown in FIG.
I'm sullen. On the other hand, at step 117, k ≦ 0.
If it is determined that NOx has been reached, the routine proceeds to step 118, where NOx is released.
The flag is reset. Next, at step 119,
NOx is set to zero. That is, at this time, the storage reduction type NOx catalyst
It is considered that all NOx absorbed in the medium 17 has been released.
Is absorbed by the NOx storage reduction catalyst 17
The estimated NOx amount ΣNOx is set to zero. Then step 1
At 20 the count value C and the correction coefficient k are zero.
To complete the processing cycle. On the other hand, in step 101, K ≧ 1.0
Is determined, that is, the mixture is rich or
If the engine is operating under the condition that the stoichiometric air-fuel ratio should be set, step 12 is executed.
Proceeds to 1 and the count value D is incremented by 1.
You. Next, at step 122, the count value D becomes a constant value D.
₀It is determined whether or not it has become larger. D> D₀Nana
When the time has elapsed, the routine proceeds to step 123, where the NOx becomes zero.
It is. That is, a rich mixture or a stoichiometric mixture
When combustion of NOx continues for a certain period of time, NOx
Since it is considered that all NOx was released from the medium 17,
Is absorbed by the NOx storage reduction catalyst 17.
The estimated value ΣNOx of the NOx amount is set to zero. FIG. 14 is a calculation routine of the fuel injection time TAU.
This routine is repeatedly executed. Figure
Referring to FIG. 14, first in step 150
The basic fuel injection time TP is calculated from the map shown in FIG.
You. Next, at step 151, according to the operating state of the engine,
The determined correction coefficient K shown in FIG. 3 is calculated. Next,
In step 152, is the NOx release flag set?
The NOx release flag is not set.
If not, the routine proceeds to step 153, where the correction coefficient K is Ki.
Is done. Next, at step 155, the basic fuel injection time T
By multiplying P by Ki, the fuel injection time TAU
Is calculated. Therefore, at this time, the fuel is supplied into the combustion chamber 3.
The fuel-air mixture depends on the operating condition of the engine as shown in FIG.
First, the air-fuel ratio is made lean, stoichiometric, or rich. On the other hand, in step 152, NOx is released.
If it is determined that the flag is set,
Proceeding to step 154, Ki becomes the loop shown in FIGS.
The sum of the correction coefficients k and 1 calculated by the chin (k +
1), and then proceed to step 155. Accordingly
At this time, the mixture supplied to the combustion chamber 3 is rich.
At this time, the degree of richness is determined by the pattern shown in FIG.
You can change it. In this embodiment, the ECU 30
Step 1 of a series of signal processing by the ECU 30
07, Step 108, Step 110
Means for determining catalyst temperature change direction and release timing correction
Means are configured. In the above-described embodiment,
Although the present invention has been described using an example in which the present invention is applied to a gasoline engine,
The present invention can be applied to a diesel engine.
Of course. For diesel engines,
Much more than (A / F = 13-14)
Since combustion is performed in the lean region, the engine is
Is the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 17.
The ratio is very lean, and NOx in exhaust gas is absorbed and returned.
N absorbed by the primary NOx catalyst 17 and released from the catalyst
The amount of Ox is extremely small. In the case of a gasoline engine,
As described above, the mixture supplied to the combustion chamber 3 is made rich.
This makes the exhaust air-fuel ratio rich and increases the oxygen concentration in the exhaust gas.
The NOx catalyst 17
NOx can be released for regeneration.
In the case of diesel engines, the mixture supplied to the combustion chamber is
If it is made rich, soot may be generated during combustion.
Cannot be adopted. Therefore, the present invention
When applied to diesel engines, a mixture for combustion
Separately, a reducing agent (for example, light oil as fuel) is directly stored and returned.
The NOx catalyst 17 is supplied to the primary NOx catalyst 17 and stored and reduced.
NOx is released and reduced. [0060] The present invention provides an exhaust gas purifying apparatus for an internal combustion engine according to the present invention.
According to this, when the air-fuel ratio of the inflowing exhaust gas is lean, N
When the oxygen concentration of the exhaust gas flowing in by absorbing Ox decreases
The NOx storage reduction catalyst that releases the absorbed NOx is exhausted from the engine.
Placed in the air passage and absorbed by the NOx storage reduction catalyst.
NOx catalyst when the NOx amount exceeds the allowable amount
Occlusion reduction type with rich air-fuel ratio of exhaust gas flowing into
Release means for releasing and reducing NOx from the NOx catalyst,
The catalyst temperature of the NOx storage reduction catalyst is determined by the NOx absorption capacity.
Is changing in a direction approaching the catalyst temperature where the maximum is reached
Catalyst temperature change direction determining means for determining whether or not
The temperature change direction determining means determines whether the NOx storage reduction catalyst
The catalyst temperature approaches the catalyst temperature at which the NOx absorption capacity becomes maximum
The release hand when it is determined that the
Delays when the air-fuel ratio of exhaust gas by the stage is enriched
Release time correction means for correcting
The NOx absorption time of the NOx storage reduction catalyst
And release NOx from the NOx storage reduction catalyst.
Frequency can be reduced. This enables exhaust purification
The NOx purification rate of the device can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a gasoline engine to which the present invention is applied. FIG. 2 is a diagram showing an example of a map of a basic fuel injection time. FIG. 3 is a diagram illustrating an example of a correction coefficient. FIG. 4 shows unburned HC in exhaust gas discharged from an engine,
FIG. 3 is a diagram schematically showing the concentrations of CO and oxygen. FIG. 5 is a diagram for explaining the NOx releasing action of a storage reduction type NOx catalyst. FIG. 6 is a diagram showing an example of an NOx amount discharged from an engine. FIG. 7 is a diagram showing an example of the NOx absorption capacity of a storage reduction type NOx catalyst. FIG. 8 is a diagram showing an example of the NOx release characteristics of a storage reduction type NOx catalyst. FIG. 9 is a diagram showing a change in a correction coefficient k in one embodiment of the exhaust gas purification device according to the present invention. FIG. 10 is a diagram showing a relationship between exhaust gas temperature and C ₁ , C ₂ , α, and β in _one embodiment of the exhaust gas purification apparatus according to the present invention. FIG. 11 is a view showing an example of a map of an exhaust gas temperature T; FIG. 12 is a flowchart (No. 1) illustrating a NOx release control procedure in the embodiment of the exhaust gas purification apparatus according to the present invention. FIG. 13 is a flowchart (No. 2) showing a NOx release control procedure in one embodiment of the exhaust gas purification apparatus according to the present invention. FIG. 14 is a flowchart showing a procedure for calculating a fuel injection time TAU in one embodiment of the exhaust gas purification apparatus according to the present invention. [Description of Signs] 1 Gasoline engine (internal combustion engine) 3 Combustion chamber 25 Temperature sensor 16 Exhaust pipe (engine exhaust passage) 17 Storage reduction type NOx catalyst 30 ECU (Catalyst temperature change direction determination means, release timing correction means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/04 ZAB F02D 41/04 ZAB 45/00 312 45/00 312R ZAB ZAB (58) Fields surveyed (Int. Cl. ⁷ , DB name) F01N 3/08-3/36 F02D 41/04 F02D 45/00

Claims (1)

(57) Claims 1. An occlusion-reduction NOx that absorbs NOx when the inflowing exhaust gas has a lean air-fuel ratio and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas decreases. A catalyst is disposed in the engine exhaust passage, and when the NOx amount absorbed by the NOx storage reduction catalyst exceeds an allowable amount, the NOx storage reduction type
In an exhaust purification apparatus for an internal combustion engine including a release unit that releases and reduces NOx from an NOx storage reduction catalyst by enriching an air-fuel ratio of exhaust gas flowing into an Ox catalyst, the catalyst temperature of the NOx storage reduction catalyst is: Catalyst temperature change direction determining means for determining whether or not the NOx absorption capacity changes in a direction approaching the catalyst temperature at which the NOx absorption capacity becomes maximum;
When it is determined that the catalyst temperature of the x catalyst is changing in a direction approaching the catalyst temperature at which the NOx absorption capacity is maximized, correction is made so as to delay the time when the air-fuel ratio of the exhaust gas by the release means is made rich. An exhaust gas purification device for an internal combustion engine, comprising: a discharge timing correction unit.