JP3287082B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to an exhaust purifying apparatus for an internal combustion engine, to effectively removable exhaust purification system the NO _X contained in exhaust gas of an internal combustion engine causing combustion of lean air-fuel ratio in detail .

[0002]

2. Description of the Related Art As an exhaust gas purifying apparatus for an internal combustion engine of this type, the present applicant has filed International Application No. PCT / JP9310.
No. 0778 proposes. The exhaust gas purification apparatus proposed in the above, NO air-fuel ratio of the exhaust flowing absorbs NO _X in the exhaust gas when the lean, the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed when reduced the _X absorbent disposed in an exhaust passage of an internal combustion engine, typically operating the internal combustion engine at a lean air-fuel ratio, NO in the exhaust to the _the NO _X absorbent
Absorb _X. In addition, lean air-fuel ratio operation continues, and NO
_{If the} amount of NO _X absorbed by the _X absorbent exceeds a predetermined amount, the operating air-fuel ratio of the internal combustion engine is switched from a lean air-fuel ratio to a rich or stoichiometric air-fuel ratio to lower the oxygen concentration in the exhaust gas, thereby reducing the NO _X absorption. together to release the absorbed NO _X from the agent, unburned HC, CO in the exhaust gas with this released NO _X
And so as to reduce and purify by components of equal (in this specification, the reduction and release of the NO _X from the _the NO _X absorbent, it referred to the operation of cleaning the "regenerating operation of the NO _X absorbent").

[0003] Further, in the above apparatus, NO in _the NO _X absorbent to _the NO _X absorbent estimates the NO _X absorption amount absorbed
The NO _X absorption amount counter representing the _X absorption provided engine when it is operated at a lean air-fuel ratio, a predetermined addition amount determined in accordance with the engine operating condition in the NO _X absorption counter at predetermined time intervals summed, to when the engine is operated in a rich or stoichiometric air-fuel ratio, thereby reducing the value of the NO _X absorbing amount counter according to the operating time.

That is, during operation of the engine, load from the engine,
NO in an amount corresponding to engine operating conditions such as the number of revolutions_XOccurs
Is running at a lean air-fuel ratio (i.e.
C, NO_XThe air-fuel ratio of the exhaust flowing into the absorbent is lean
), The generated NO _XA certain percentage of the quantity is N
O_XNO is absorbed by the absorbent_XAbsorbed in absorbent
NO_XIs the NO of the institution_XIncrease according to the amount generated
You. Also, if the engine is running at rich or stoichiometric
NO_XNO from absorbent_XWas released
No_XNO absorbed in the absorbent_XThe amount of the institution
Depending on how long the vehicle is running at rich or stoichiometric
Decrease. In the above device, the engine operating air-fuel ratio
When the ratio is reached, a predetermined amount is added at regular intervals, and the engine is operated.
Depending on operating time when air-fuel ratio is rich or stoichiometric
NO where the predetermined amount is subtracted_XProvision of an absorption counter
NO by_XAbsorbent NO_XThe amount of absorption is estimated.

[0005]

[SUMMARY OF THE INVENTION However, reducing the value of the absorption amount counter of the NO _X absorbent and the authorities based only on the operation time if it is operated at a rich or stoichiometric air-fuel ratio as described above of the apparatus If it has, there is a problem of causing an error between the actual value of the amount of NO _X and NO _X absorption counter that is absorbed in the NO _X absorbent.

[0006] sand, the amount of the NO _X released from _the NO _X absorbent per unit time (NO _X release rate) is not always constant, as will be described later, in the temperature or the exhaust of the NO _X absorbent It changes according to the amount of components such as unburned HC and CO contained. Therefore, based on only the operation time of the rich or stoichiometric air-fuel ratio as described above of the device (i.e., assuming the NO _X release rate from _the NO _X absorbent is constant) decreases the value of the NO _X absorption counter The engine operating state and N
O _X absorbent actually N and decrease of the counter depending on the temperature
A large error may occur between the amount of NO _X released from the O _X absorbent.

[0007] In the above described exhaust gas purifying device determines the amount of the NO _X absorption counter value NO _X absorbed in the NO _X absorbent with a predetermined NO _X absorption during the lean air-fuel ratio operation is increased If it exceeds the value by switching the air-fuel ratio forcibly engine to a rich air-fuel ratio, and to perform the reproducing operation of the NO _X absorbent. Therefore, NO
When causing an error between the value of the NO _X amount and the NO _X absorbing amount counter which is absorbed into the _X absorbent, there is no need to perform actually NO _X absorption is small regenerating operation of the NO _X absorbent despite deteriorates fuel economy switching is performed for the values of the NO _X absorption counter to the rich air-fuel ratio operation to exceeds a predetermined value, conversely, actually the NO _X absorption of the NO _X absorbent However, the regeneration operation is not performed because the value of the NO _X absorption amount counter does not exceed a predetermined value, and the absorption capacity of the NO _X absorbent decreases, and which may cause a problem such as can not absorb NO _X.

[0008] The present invention has been developed in order to solve the above problem.
It is an object of the present invention to provide means capable of accurately estimating the amount of NO _X absorbed in an _X absorbent.

[0009]

According to the Summary of the Invention The present invention as set forth in claim 1, disposed in an exhaust passage of an internal combustion engine, the air-fuel ratio of the exhaust gas absorbs NO _X in the exhaust gas when the lean exhaust predetermined addition amount and _the NO _X absorbent oxygen concentration emits NO _X absorbed when reduced, when the internal combustion engine is operated at a lean air-fuel ratio, which is determined according to the engine operating state during It said added to the NO _X absorption counter indicating the NO _X absorption of _the NO _X absorbent at predetermined intervals, when the internal combustion engine is operated at a rich or stoichiometric air-fuel ratio, a certain time a predetermined subtraction amount by the subtracting from the NO _X absorption counter for each, and the absorption amount estimation means for estimating the NO _X absorption of the _the NO _X absorbent, when the engine is operated at a rich air-fuel ratio, the engine air-fuel ratio Required to make the stoichiometric air-fuel ratio And an excess fuel quantity detecting means for detecting the amount of fuel supplied to the over-engine beyond the amount, when the engine is operated in a rich air-fuel ratio, of the NO _X absorption counter on the basis of the excessive fuel amount An exhaust gas purification device for an internal combustion engine, comprising: a subtraction amount setting means for determining the subtraction amount.

[0010] According to the present invention described in claim 2,
Disposed in an exhaust passage of an internal combustion engine, the air-fuel ratio of the exhaust gas absorbs NO _X in the exhaust gas when the lean and _the NO _X absorbent to the oxygen concentration in the exhaust gas to release NO _X absorbed when reduced the when the internal combustion engine is operated at a lean air-fuel ratio, N representing the NO _X absorption of the _the NO _X absorbent at regular time intervals a predetermined addition amount determined in accordance with the engine operating condition
O _X is added to the absorption amount counter, when the internal combustion engine is operated at a rich or stoichiometric air-fuel ratio, by subtracting from the NO _X absorption counter a predetermined subtraction amount for each predetermined time, the NO _X absorption amount estimation means for estimating the NO _X absorption amount of the absorbent, a temperature detecting means for detecting a temperature of the _the NO _X absorbent when the engine is operated in a rich air-fuel ratio, the _the NO _X absorbent temperature And a subtraction amount setting means for determining the subtraction amount of the NO _X absorption amount counter based on the following.

According to the third aspect of the present invention,
Disposed in an exhaust passage of an internal combustion engine, the air-fuel ratio of the exhaust gas absorbs NO _X in the exhaust gas when the lean and _the NO _X absorbent to the oxygen concentration in the exhaust gas to release NO _X absorbed when reduced the when the internal combustion engine is operated at a lean air-fuel ratio, N representing the NO _X absorption of the _the NO _X absorbent at regular time intervals a predetermined addition amount determined in accordance with the engine operating condition
O _X is added to the absorption amount counter, when the internal combustion engine is operated at a rich or stoichiometric air-fuel ratio, by subtracting from the NO _X absorption counter a predetermined subtraction amount for each predetermined time, the NO _X absorption amount estimation means for estimating the NO _X absorption amount of the absorbent, the means for detecting the engine intake air quantity, means for detecting the operating air-fuel ratio of the engine, the NO
Means for detecting the temperature of the _X absorbent, and when the engine is operated at a rich air-fuel ratio, the engine intake air amount;
Wherein the engine operating air-fuel ratio, the _the NO _X absorbent temperature and exhaust gas purification apparatus for an internal combustion engine having a subtraction amount setting means for determining the subtraction amount of the NO _X absorption counter based on is provided.

[0012]

NO _X release rate from _the NO _X absorbent when the [action] engine is operated at a rich or stoichiometric air-fuel ratio, as the temperature of the NO _X absorbent is high, as explained later, also in _the NO _X absorbent The larger the amount of supplied reducing components such as CO and unburned HC, the larger the value. Therefore, decrease per unit of time _the amount of NO _X is absorbed in _the NO _X absorbent when the engine is operated at a rich or stoichiometric air-fuel ratio (i.e. NO _X release amount per unit time), the exhaust Unburned HC inside,
Higher CO component is great, also larger as the temperature of _the NO _X absorbent is high. On the other hand, the concentrations of unburned HC and CO in the exhaust gas increase as the operating air-fuel ratio of the engine decreases (ie, as the air-fuel ratio becomes rich). That is, fuel that is excessively supplied to the engine in excess of the amount required to operate the engine at the stoichiometric air-fuel ratio is discharged together with exhaust gas from the engine as unburned HC and CO. unburned HC amount of fuel is supplied as the NO _X absorbent increases, the amount of CO is increased.

[0013] In the present invention according to claim 1, the amount of fuel that has been excessively supplied to the engine, namely unburned HC supplied to _the NO _X absorbent, as the amount of CO is large, NO _X absorption counter Is set to be large. Therefore, NO
In fact of NO _X absorption amount counter subtraction amount NO _X absorbent
Would correspond to the _X release rate, a large error does not occur between the amount of NO _X in the actual of the NO _X absorbent and the value of the NO _X absorption counter.

Further, in the present invention according to claim 2, NO
_The higher the temperature of the _X absorbent, the larger the subtraction amount of the NO _X absorption amount counter is set. For this reason, NO _X
In fact of the NO _X subtraction amount of absorption counter of the NO _X absorbent
Would correspond to the absorbent release rate, a large error does not occur between the amount of NO _X in the actual of the NO _X absorbent and the value of the NO _X absorption counter.

Further, as described above, the engine operating air-fuel ratio is low.
The concentration of unburned HC and CO in the exhaust gas increases. here
Since the exhaust flow increases in proportion to the amount of intake air,
NO if Seki operation air-fuel ratio and intake air amount are determined_XFor absorbent
The amounts of unburned HC and CO to be supplied are determined. Contract
According to the present invention described in claim 3, in the engine operating air-fuel ratio and the intake air
The amounts of unburned HC and CO are determined by detecting
Therefore, the greater the amount of unburned HC and CO, the more NO_XSucking
The higher the temperature of the absorbent, the higher the NO_XThe subtraction amount of the absorption counter is
Set to a large value. Thereby, NO_XAbsorption counter
Is NO_XThe actual NO of the absorbent _XCorresponds to release speed
Amount.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall view of an internal combustion engine to which the exhaust gas purification device of the present invention is applied. In FIG. 1, reference numeral 1 denotes an internal combustion engine such as a gasoline engine that performs combustion at a lean air-fuel ratio, 2 denotes a piston of the engine 1, 3 denotes a combustion chamber, and 4 denotes a spark plug.
Reference numeral 6 denotes an intake port of the engine, 5 denotes an intake valve, 8 denotes an exhaust port, 7 denotes an exhaust valve, and each intake port 6 is an intake branch pipe 9.
The fuel injection valve 11 is connected to the surge tank 10 through the fuel injection valve 10 and injects fuel to each intake port 6 in each branch pipe 9.

The surge tank 10 is connected to an air cleaner 13 via an intake passage 12, and in the intake passage 12, a throttle valve 14 having an opening corresponding to a driver's operation of an accelerator pedal (not shown) is provided. Are located. Also,
The surge tank 10 is provided with an intake pressure sensor 15 that generates an output voltage proportional to the absolute pressure in the surge tank 10.

On the other hand, the exhaust port 8 of the engine 1 is connected to an exhaust passage 17 via an exhaust manifold 16, and a casing 19 containing a NO _X absorbent 18 described later is connected to the exhaust passage 17. In FIG. 1, what is indicated by 30 is
2 is an electronic control circuit of the engine 1. The electronic control circuit 30 is RO
M (read only memory) 32, RAM (random access memory) 33, CPU (microprocessor) 3
4, a digital computer having a well-known configuration in which an input port 35 and an output port 36 are respectively connected by a bidirectional bus 31 to perform basic control such as fuel injection amount control and ignition timing control of the engine 1; functions as a subtraction amount setting means for determining an absorption amount estimation means and the counter subtraction amount that is according to claims 1 to 3 for estimating the NO _X absorption of _the NO _X absorbent 17 performs an operation of the NO _X absorption counter in the example Plays.

For the above purpose, a voltage signal from the intake pressure sensor 15 and a NO signal are input to the input port 35 of the control circuit 30.
A voltage signal corresponding to the exhaust gas temperature is output from an exhaust gas temperature sensor 20 provided in the exhaust passage on the downstream side of the _X absorbent 18, respectively.
In addition to being input via the converter 37, a pulse signal representing the engine speed is also input from an engine speed sensor 21 provided in a distributor (not shown) of the engine.

The output port 36 of the control circuit 30
The fuel injection valve 11 is connected via the corresponding drive circuit 38.
And the ignition plug 4, and controls the fuel injection from the fuel injection valve 11 and the ignition timing of the ignition plug 4. _The NO _X absorbent 18 built in the casing 19, for example using a carrier such as alumina, alkali metal, 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. This NO _X
The absorbent 18 absorbs the NO _X when the air-fuel ratio of the exhaust gas flowing is lean, the oxygen concentration is carried out to absorbing and releasing action of the NO _X that releases NO _X when lowered.

The above-described exhaust air-fuel ratio is defined as N
O _X absorbent 18 upstream of the exhaust passage and the engine combustion chamber is intended to mean the ratio of the sum of the sum and fuel respectively to the intake passage or the like supplied air quantity. Therefore, NO _X absorbent 1
When no fuel or air is supplied to the upstream exhaust passage 8, the exhaust air-fuel ratio becomes equal to the air-fuel ratio of the engine (air-fuel ratio in combustion in the engine combustion chamber).

In this embodiment, since an engine that performs combustion at a lean air-fuel ratio is used, the exhaust air-fuel ratio during normal operation is lean, and the NO _X absorbent 18 absorbs NO _{X in} the exhaust gas. Further, when the air-fuel ratio of the engine is the oxygen concentration in the exhaust gas is switched from the lean air-fuel ratio to the rich or the stoichiometric air-fuel ratio decreases, NO _X absorbent 18 performs the release of the absorbed reducing agent.

The detailed mechanism of the absorption / release action is not clear in some parts. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, regarding this mechanism, platinum P
The case where t and barium Ba are supported will be described as an example, but other noble metals, alkali metals, alkaline earths,
The same mechanism is obtained even when rare earth elements are used.

That is, the inflow exhaust gas becomes considerably lean.
And the oxygen concentration in the inflow and exhaust gas greatly increased, as shown in Fig. 2 (A).
These oxygen O_TwoIs O_Two ^-Or O^2-In the form of
It adheres to the surface of platinum Pt. On the other hand, NO in the inflow exhaust gas is
This O on the surface of platinum Pt_Two ^-Or O^2-Reacts with N
O_Two(2NO + O_Two→ 2NO_Two ). Then generated
NO_TwoSome of the oxygen is oxidized on platinum Pt and
FIG. 2 shows that while being absorbed by and combined with barium oxide BaO.
As shown in (A), nitrate ion NO_Three ^-Absorbent in the form of
Spreads in. NO in this way_XIs NO_XAbsorbent 1
8 is absorbed.

Therefore, as long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- is generated. Institution 1
When the air-fuel ratio is switched to rich or stoichiometric,
The oxygen concentration in the inflow exhaust gas decreases, and the amount of generated NO ₂ decreases. As a result, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and nitrate ions NO ₃ ⁻ in the absorbent are released from the absorbent in the form of NO ₂ . On the other hand, unburned HC,
When components such as CO are present, these components are oxidized by reacting with oxygen O ₂ ^- or O ^2-on platinum Pt,
Consume the above oxygen. Further, NO ₂ released from the NO _X absorbent 18 is reduced by reacting with HC and CO as shown in FIG. 2 (B). In this way, N on the surface of platinum Pt
When the O ₂ is no longer present, NO _{2 is} successively removed from the absorbent.
Is released.

That is, HC and CO in the inflow exhaust gas are
O on platinum Pt_Two ^-Or O^2-Reacts immediately with acid
And then O on platinum Pt_Two ^-Or O^2-Is consumed
If HC and CO still remain,
Therefore, NO released from the absorbent_X, And with the exhaust
NO flowing into_XIs reduced. Therefore, the platinum Pt
If the amount of HC and CO supplied is large, on the platinum Pt surface
NO_TwoConsumption from the sorbent
NO issued_XAlso increases. That is, NO_Xabsorption
The larger the amount of HC and CO components supplied to the agent, the more NO_XSucking
NO from collector _XThe release will increase.

Further, HC flowing into _the NO _X absorbent with exhaust amount of CO component, from the amount of fuel supplied to the engine, the amount of fuel required to operate the engine at the stoichiometric air-fuel ratio It increases in proportion to the subtracted fuel amount, that is, the excess fuel amount. Therefore, NO _X amount discharged from _the NO _X absorbent per unit time (NO _X release rate) increases with the amount of excess fuel supplied to the engine unit time.

FIG. 3 shows the amount of excess fuel supplied to the engine per unit time and the amount of NO disposed in the engine exhaust passage.
An example of the relationship with the amount of NO _X released from the _X absorbent (NO _X release speed) is shown. As shown in FIG. 3, NO _X release rate from _the NO _X absorbent and substantially proportional to the excess fuel amount increases.
Therefore, it is possible to know the NO _X release rate from _the NO _X absorbent by detecting the amount of excess fuel supplied per unit time to the engine.

On the other hand, NO _X release rate from _the NO _X absorbent, other than the amount of excess fuel supplied to _the NO _X absorbent,
Influenced by the temperature of _the NO _X absorbent, the maximum value of the NO _X release rate by _the NO _X absorbent temperature substantially determined. FIG.
Is NO when the amount of excess fuel in the engine is sufficiently large
Is a graph showing the relationship between the temperature and the NO _X release rate of the _X absorbent. As shown in FIG. 4, in the presence of sufficient excess fuel, N
O _X release rate tends to increase as the temperature of the NO _X absorbent becomes higher. Thus, the NO _X release rate increases in both temperature rise, bound nitrate ions is considered to become easy to separate the temperature of the NO _X absorbent becomes high as BaO in the absorbent.

[0030] Therefore, the lower the temperature of the NO _X absorbent at most the amount of excess fuel supplied to the engine, NO _X release rate of the NO _X absorbent becomes smaller, the temperature of the NO _X absorbent conversely be higher, NO _X release rate of the NO _X absorbent the less amount of excess fuel supplied to the engine will be reduced. Therefore, in order to know the NO _X release rate from _the NO _X absorbent in the rich or stoichiometric air-fuel ratio during operation in precisely, NO
It is necessary to detect both the temperature of the _X absorbent and the amount of excess fuel supplied to the engine. In this embodiment, as described below, was detected using an exhaust gas temperature sensor 20 provided with _the NO _X absorbent temperature on the downstream side exhaust passage of the NO _X absorbent 18, the amount of excess fuel supplied to the engine, It is detected using the engine operating air-fuel ratio and the engine intake air amount.

Next, the air-fuel ratio control of the engine according to the present embodiment will be described. In this embodiment, the above-mentioned International Application No. PC
The same air-fuel ratio control as in T / JP93100778 is performed.
Hereinafter, the air-fuel ratio control will be briefly described. In this embodiment, the fuel injection amount from the fuel injection valve 11, that is, the valve opening time of the fuel injection valve 11 during fuel injection (fuel injection time)
The TAU is, for example, TAU = TP ×
It is calculated as K.

Here, TP indicates a fuel injection time required to make the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber a stoichiometric air-fuel ratio, that is, a basic fuel injection time, and is detected by the intake pressure sensor 15. As a function of the determined absolute pressure PM in the surge tank 10 and the engine speed N, it is obtained in advance by an experiment or the like, and stored in the ROM 32 of the control circuit 30 in the form of a numerical table as shown in FIG.

K is a correction coefficient for controlling the engine air-fuel ratio. When K = 1.0, the engine air-fuel ratio becomes the stoichiometric air-fuel ratio. If K> 1.0, the engine air-fuel ratio is smaller than the stoichiometric air-fuel ratio (that is, the rich air-fuel ratio).
When K <1.0 is set, the engine air-fuel ratio becomes larger than the stoichiometric air-fuel ratio (that is, lean air-fuel ratio). The value of the correction coefficient K is given as a function of the absolute pressure PM in the surge tank 10 and the engine speed N, for example, by a function as shown in FIG. That is, as shown in FIG. 6, in the present embodiment, the region where the PM is relatively low (engine low / medium load operation region).
, The correction coefficient K is set smaller than 1.0, and the engine is operated at a lean air-fuel ratio. In a region where the PM is relatively high (engine high load operation region), the value of the correction coefficient K is set to 1.0, and the engine is operated at the stoichiometric air-fuel ratio. In addition, PM
Is high (engine full load operation range), the value of the correction coefficient K is set to be larger than 1.0, and the engine is operated at a rich air-fuel ratio. Particularly, in a vehicle engine or the like, the low-medium load operation is usually performed most frequently. Therefore, the engine is operated at a lean air-fuel ratio during most of the operation.

[0034] As described above, NO NO _X absorbent engine absorbs NO _X in the exhaust gas when being operated at a lean air-fuel ratio, the engine is absorbed when being operated at a rich or stoichiometric air-fuel ratio _X Release. Therefore, if the operation of the rich or stoichiometric air-fuel ratio is appropriately performed, NO in _the NO _X absorbent
_{The X} absorption does not increase beyond a certain level and no special regeneration operation is required. However, when the engine operating conditions it may as operation at a lean air-fuel ratio continues for a long time, NO _X absorption of the NO _X absorbent increases, NO
_X absorption capacity may be saturated.

[0035] In this embodiment, when the absorbed amount of NO _X by integrating, NO _X absorption of the NO _X absorption counter by _the NO _X absorbent 18 to be described is equal to or greater than a predetermined amount below,
Despite the region of FIG. 6, by setting the value of the predetermined time correction coefficient K to 1.0 or more (e.g., K = 1.2), and operating the engine at a rich air-fuel ratio, the regenerating operation of the NO _X absorbent NO _X absorption of the NO _X absorbent is prevented from being saturated by performing.

Next, the estimation of the NO _X absorption amount using the NO _X absorption amount counter of this embodiment will be described. As described above, when the engine is operating at a lean air-fuel ratio, N
The O _x absorbent absorbs NO _x in the exhaust gas and the N _{x of} the NO _x absorbent
O _X absorption amount is increased. At this time, N per unit time
_The amount of NO _X O _X absorbent absorbs, i.e. amount of increase per unit time of the NO _X absorbed in _the NO _X absorbent, the amount of NO _X contained in the exhaust, i.e. engine generated per unit time It is considered to be proportional to the amount of NO _X Therefore, if the engine is operating at a lean air-fuel ratio,
Engine is absorbed _the NO _X absorbent by integrating the amount obtained by multiplying a constant factor in _the amount of NO _X generated every predetermined time N
The total amount of O _X can be calculated.

Further, NO Conversely engine when it is operating at a rich or stoichiometric air-fuel ratio, NO _X absorbent which has absorbed
Releasing _X, NO _X absorption of the NO _X absorbent is reduced.
Here, the amount of NO _X released from the NO _X absorbent per unit time is an amount determined by the air-fuel ratio of the engine, the temperature of the NO _X absorbent, and the like. Therefore, when the engine is operated at a rich or stoichiometric air-fuel ratio, released from _the NO _X absorbent by integrating the amount corresponding to the NO _X emissions from _the NO _X absorbent at predetermined time intervals NO The total amount of _X can be calculated.

[0038] Therefore, NO _X and NO _X absorption amount counter representing the NO _X absorption amount of the absorbent is provided, when the engine is operated at a lean air-fuel ratio, a certain time an addition amount which is proportional to the NO _X generation amount of the engine adding the NO _X absorption counter for each,
When the reverse the engine is operated in a rich or stoichiometric air-fuel ratio, by subtracting from the NO _X absorption counter subtraction amount corresponding to the NO _X release amount per unit time from _the NO _X absorbent at predetermined time intervals , it is possible to accurately estimate the amount of the NO _X absorbed in the current _the NO _X absorbent.

The engine NO during lean air-fuel ratio operation
_{The X} generation amount increases as the engine load (that is, the intake pressure PM) increases and as the engine speed N increases. Further, the engine NO _X generation amount also changes depending on the engine operating air-fuel ratio.
In this embodiment, (see FIG. 6) because it is determined as a function of the engine operating air-fuel ratio the intake pressure PM and the engine speed N, eventually, NO _X generation amount of engine intake pressure PM and the engine speed N
Only function. Therefore, in this embodiment, the engine NO _X
By experiment or the like generated amount, advance determined as a function of the intake pressure PM and the engine speed N, the addition amount of the NO _X absorption amount counter of every fixed time are multiplied by certain coefficients in the NO _X generation amount The (NO _X absorption amount) α is stored in the ROM 32 in the form of a numerical table as shown in FIG. The engine when the being operated at a lean air-fuel ratio, read the value of the addition amount α from this numerical table using the values of the intake pressure PM and the engine speed N, of the NO _X absorption amount counter at predetermined time intervals The addition amount α is added to the value.

Next, a description will be given estimates of the NO _X release rate from _the NO _X absorbent in the rich or stoichiometric air-fuel ratio during operation in this embodiment. As described above, in order to accurately determine the NO _X release rate from _the NO _X absorbent, it is necessary to know the temperature of the amount and _the NO _X absorbent 18 of the excess fuel supplied to the engine, this embodiment NO _X and _the NO _X absorbent temperature T in the example
Exhaust gas temperature sensor 2 provided in the exhaust passage on the downstream side of absorbent 18
0 to detect the amount of excess fuel supplied to the engine,
It is detected using the engine operating air-fuel ratio and the engine intake air amount. That is, the exhaust gas temperature detected by the exhaust temperature sensor 20 is a temperature of the exhaust gas that has passed through the _the NO _X absorbent 18, it is considered to be equal to approximately _the NO _X absorbent 18 temperature itself, NO _X temperature of the NO _X absorbent 18 by detecting the exhaust gas temperature by absorbent 18 downstream of the exhaust gas temperature sensor 20 can be detected.

Since the reciprocal of the engine operating air-fuel ratio represents the amount of fuel supplied per unit amount of the intake air amount, a value obtained by multiplying the reciprocal of the engine operating air-fuel ratio by the intake air amount is supplied to the engine. It becomes the total amount of fuel. In addition, the amount of fuel required to bring the engine to the stoichiometric air-fuel ratio is also a value obtained by multiplying the reciprocal of the stoichiometric air-fuel ratio by the amount of engine intake air. The amount is expressed as {(1 / operating air-fuel ratio)-(1 / theoretical air-fuel ratio)} × intake air amount using the engine operating air-fuel ratio and the intake air amount.

On the other hand, the engine intake air amount Q is determined by the engine intake pressure PM and the engine speed N, and the engine operating air-fuel ratio is determined by the aforementioned fuel injection amount correction coefficient K.
Therefore, in the present embodiment, the engine intake intake air amount Q is obtained in advance by an experiment or the like as a function of the intake pressure PM and the rotational speed N, and stored in the ROM 32 in the form of a numerical table as shown in FIG. The engine intake air amount Q is determined from this numerical table using the pressure PM and the rotation speed N.

In the above equation, ｛(1 / operating air-fuel ratio) − (1
/ (Theoretical air-fuel ratio)} can be calculated as (K−1.0) × A using the value of the correction coefficient K (A is a constant coefficient). Therefore, the NO _X release rate calculated from the amount of excess fuel is expressed as {(K−1.0) × A} × Q.

In this embodiment, the above (K
−1.0) × A is calculated in advance, and the actual N
O_XRelease rate is NO_XConvert to absorption counter value
In ROM32 as numerical value FADJ multiplied by a constant value
It is stored in the form of a numerical table as shown in FIG. Follow
Thus, in the present embodiment, NO calculated from the amount of excess fuel _X
The subtraction amount of the absorption amount counter is determined by Q obtained from FIG.
Multiplied by FADJ, expressed as FADJ × Q
You.

[0045] Further, as described above, NO in _the NO _X absorbent
_X release rate affected by _the NO _X absorbent temperature,
A low temperature of the NO _X absorbent even much amount of excess fuel supplied to the engine, NO _X release rate of the NO _X absorbent becomes smaller, even at high temperature of the NO _X absorbent is reversed, the engine the less the amount of excess fuel supplied to the NO _X absorbent N
O _X release rate decreases. That, NO _X release rate of the NO _X absorbent when the amount of excess fuel is sufficiently large N
It is determined by the temperature of the O _X absorbent, NO _X release rate of the NO _X absorbent when the amount of excess fuel is small will be determined by the amount of excess fuel.

Therefore, in the present embodiment, N in each temperature condition under the condition where the excess fuel is sufficiently present as shown in FIG.
O _X release advance determined by the speed of advance through experiments or the like, subtraction amount TDEC of the NO _X absorption counter corresponding to this release rate
Is stored in the ROM 32 in the form of a numerical table using the exhaust gas temperature T in the form shown in FIG. 10, and is obtained from the value of the counter subtraction amount FADJ × Q obtained from the excess fuel amount and the exhaust gas temperature. The smaller value of the counter subtraction amount TDEC and the smaller value is adopted as the counter subtraction amount.

FIG. 11 is a flowchart showing the operation of the NO _X absorption amount counter described above. This routine is executed by the control circuit 30 at regular intervals. FIG.
1 and the routine starts, step 110
In 1, the intake pressure PM, the engine speed N, NO _X absorbent temperature T, and the value of the aforementioned correction coefficient K is read from the RAM 33. Intake air pressure PM, engine speed N, the sensor 1 value of the NO _X absorbent temperature T respectively corresponding to predetermined time intervals
5, 20, 21 and the latest value is always R
It is stored in AM33. Next, at step 1103, it is determined from the value of the correction coefficient K whether the engine is currently operating at a lean air-fuel ratio or at a rich air-fuel ratio or a stoichiometric air-fuel ratio. And step 1
If the engine is operating at a lean air-fuel ratio at 103 (K
<Proceeds to step 1105 in the case of 1.0), NO _X absorption amount at the time of the lean air-fuel ratio operation from the numerical table of Figure 7 which is stored in ROM32 with the value of the intake pressure PM and the engine speed N The counter addition amount α is determined, and step 1
The addition amount α found by the adding the value of the NO _X absorption counter C at 109. Step 110 after α addition
In steps 9 and 1111, the value of the NO _x absorption counter C is guarded by the maximum value CF. Here, CF is a counter value corresponding to the maximum NO _X amount that can be absorbed by the NO _X absorbent.
That is, when the NO _X absorbent absorbs NO _X to the maximum, it becomes impossible to absorb NO _X any more, and the addition of the counter is stopped.

If K ≧ 1.0 in step 1103, that is, if the engine is operating at the rich air-fuel ratio or the stoichiometric air-fuel ratio, steps 1113 to 1123 are executed, and the value of the NO _X absorption amount counter C becomes It is subtracted according to the amount of excess fuel supplied to the engine. That is, step 11
At 13, the values of the intake pressure PM and the engine speed N read at step 1101 are stored in the ROM 32 as shown in FIG.
The engine intake air amount is read using the numerical table of
In step 1115, the FAD is calculated from the value of the correction coefficient K using the numerical value table of FIG.
J is read. In step 1117, from the numerical table of Figure 10 stored in ROM32 with _the NO _X absorbent temperature T read in step 1101, N
O _X absorbent based on the temperature counter subtraction amount TDEC is read out.

[0049] Then, in step 1119, the value of the counter subtraction amount Q × FADJ based on excessive fuel amount calculated from the values of Q and FADJ determined by the, the NO _X absorbent temperature T obtained by the The values of the counter subtraction amount TDEC are compared with each other.
In 23, the smaller value of the value of Q × FADJ and the value of TDEC is adopted as the counter subtraction amount NOXDEC.

[0050] At step 1125, the subtraction amount NOXDEC determined by the is subtracted from the NO _X absorption counter C, step 1127, the value of the NO _X absorption counter C is guarded by a minimum value of zero. Incidentally, C = zero, NO _X absorbent it is meant that the released the entire amount of the absorbed NO _X. Thus, when the engine is operated in a rich air-fuel ratio or stoichiometric air-fuel ratio, the amount of excess fuel supplied to the engine (i.e., unburned HC supplied to _the NO _X absorbent, the amount of CO) to by setting the subtraction of the value of the NO _X absorption counter based, since the value of the NO _X absorption counter is reduced exactly according to the engine operating state to the rich or the stoichiometric air-fuel ratio during operation, NO _X absorption it is possible to estimate the NO _X absorption of exactly _the NO _X absorbent by using the value of the counter.

Next, the execution timing of the regeneration operation of the NO _X absorbent of this embodiment will be described. In this embodiment, NO
_If the value of the _X absorption amount counter exceeds a predetermined value,
The value of the air-fuel ratio correction coefficient K is set to 1.0 or more (for example, about K = 1.2) for a fixed time (about several seconds) regardless of the operation region in FIG. 6, and the engine is operated at a rich air-fuel ratio. performing of the NO _X absorbent regenerating operation. FIG. 12 is a flowchart showing an operation of setting the control flag FR for executing the reproduction operation. This routine is executed by the control circuit 30 at regular intervals.

In FIG. 12, at step 1201,
NO calculated by routine 11_XAbsorption counter
The value of C is read from the RAM 33. Then step
At 1203, the reproduction operation control flag FR is set (= 1).
It is determined whether or not the operation has been performed.
If the reproduction operation is not currently being executed, step 120
5 and NO_XThe value of the absorption counter C is a predetermined value C₀Or more
No, that is, whether the playback operation needs to be performed
Is determined. Here, the predetermined value C₀Is the aforementioned NO _Xabsorption
Maximum NO of agent_XTo about 70% of the absorption CF
Is set.

If C ≧ C ₀ in step 1205, it is necessary to perform a NO _X absorbent regeneration operation.
At step 1209, the reproduction operation control flag FR is set (= 1). Here, the flag FR is set, the fuel injection control routine separately executed, the value of the air-fuel ratio correction coefficient K is set to K> 1.0, the engine air-fuel ratio is switched to rich, NO _X absorption Release of NO _X from the agent and reduction purification are started. Step 120
If C <C ₀ in 5, the routine ends without changing the value of the flag FR.

If FR = 1 in step 1203, the counter CT representing the elapsed time from the start of the reproduction operation is incremented by one in step 1209, and in step 1211 the elapsed time C after the start of the reproduction operation is counted.
T is determined whether reaches a predetermined time CT _0, elapsed time when the case has not been reached CT ₀ of (CT <CT ₀₎ ends the routine. If the predetermined time has elapsed after the start of the reproduction operation in step 1211 (CT ≧ CT ₀ ), the reproduction operation flag FR is reset (= 0) in step 1213. This allows
In the separately executed fuel injection control routine, the value of the air-fuel ratio correction coefficient K is determined based on the operating region of FIG.
_{The X} absorbent regeneration operation ends. Then step 121
At 5, the value of the elapsed time counter CT is cleared (= 0), and this routine ends.

As described above, in this routine, once NO _X
When the value of the absorption amount counter regenerating operation of the NO _X absorbent exceeds the predetermined value C ₀ is started, the value of the counter by a routine executed subsequent Figure 11 is a predetermined time CT ₀ even when it becomes smaller than C ₀ During that time, a playback operation is performed. Note that N
Since the release speed of NO _X from the O _X absorbent is extremely high, the regeneration operation execution time CT ₀ of the NO _X absorbent is set to a relatively short time, and is set to, for example, about 1 second in this embodiment. Furthermore, since the routine of FIG. 11 is executed also during playback operation, when the value of the NO _X absorption counter by reproducing operation is performed is reduced, which is completely regenerated in _the NO _X absorbent was performed Means that the value of the counter C becomes 0 (FIG. 1
1 step 1127, 1129).

[0056] The exhaust in the present embodiment, the temperature of the NO _X absorbent is detected by the exhaust temperature sensor 20 installed in an exhaust passage of the NO _X absorbent 18 downstream, once the load condition of the engine since the temperature (NO _X absorbent temperature) is substantially determined, stored in advance by experiments or the like, the ROM32 in the form of a numerical table over and determined as a function of the load condition of the exhaust temperature engine (intake pressure PM and the engine speed N) If the exhaust gas temperature is determined based on the intake pressure PM and the engine speed N, the exhaust gas temperature sensor 20 can be omitted.

[0057] In the routine of FIG. 11, obtains a counter subtraction amount TDEC based on the counter subtraction amount Q × FADJ and _the NO _X absorbent temperature based on excessive fuel amount individually, it adopted the smaller the subtraction amount NOXDEC are, but for example, NOXDEC = (Q × FADJ) a Q × FADJ in the form of -TADJ, NO _X absorbent in the form of correcting the temperature correction amount TADJ set by the temperature subtraction amount NO
XDEC may be set.

[0058] Further, as described above in this embodiment, determines the counter subtraction amount NOXDEC based on both the excess fuel amount and _the NO _X absorbent temperature, counter subtraction amount Q × based on excessive fuel amount FADJ, or _the NO _X absorbent performs calculation either only one of the counter subtraction amount TDEC based on the temperature, it is possible to simplify the operation be adopted as the value of the counter subtraction amount NOXDEC.

In this embodiment, NO_XAbsorbent NO_X
Maximum absorption amount (corresponding to CF in step 1109 in FIG. 11)
And NO_XNO to execute absorbent regeneration operation_XAbsorption
(FIG. 12, C in step 1205)₀Is a constant value
But NO_XAbsorbent NO_XMaximum absorption is NO_X
Since it changes depending on the temperature of the absorbent, NO_XAbsorbent
CF and C depending on the temperature₀Change the value of
Then, a more appropriate NO _XIt is possible to perform the regeneration operation of the absorbent
it can.

[0060]

According to the exhaust purification system of the present invention, as described above, the excess of the engine is supplied to the engine of the subtraction amount of the NO _X absorption counter when it is operated at a rich or stoichiometric air-fuel ratio by you be set based on the fuel amount and _the NO _X absorbent temperature, it becomes possible to accurately estimate the NO _X absorption of real of the NO _X absorbent, appropriate reproduction of the NO _X absorbent There is an advantage that the operation can be performed.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine showing an embodiment of an exhaust gas purification apparatus of the present invention.

FIG. 2 is a diagram for explaining the NO _X absorption / release mechanism of the NO _X absorbent used in the present invention.

FIG. 3 is a diagram showing a relationship between the amount of excess fuel supplied to the engine and the NO _X release speed of the NO _X absorbent.

FIG. 4 is a diagram showing the relationship between the NO _X absorbent temperature and the NO _X release speed.

FIG. 5 is a diagram showing a form of a numerical value table used for determining a basic fuel injection amount of the engine of FIG. 1;

FIG. 6 is a diagram showing a setting example of a correction coefficient K for a fuel injection amount.

FIG. 7 is a diagram showing a form of a numerical value table used for determining an addition amount of a NO _X absorption amount counter during a lean air-fuel ratio operation.

FIG. 8 is a diagram showing a form of a numerical value table used for determining an engine intake air amount.

FIG. 9 is a diagram showing a form of a numerical value table used for determining a coefficient FADJ for calculating an excess fuel amount.

FIG. 10 is a diagram showing a form of a numerical value table used for determining a coefficient TDEC for calculating a NO _X release speed based on the temperature of the NO _X absorbent.

FIG. 11 is a flowchart showing a calculation operation of a NO _X absorption amount counter.

FIG. 12 is a flowchart showing a setting operation of a NO _X absorbent regeneration operation control flag.

[Explanation of symbols]

1 ... engine 10 ... surge tank 11: fuel injection valve 15 ... intake air pressure sensor 17 ... exhaust passage 18 ... NO _X absorbent 20 ... exhaust temperature sensor 21 ... speed sensor 30 ... electronic control circuit

────────────────────────────────────────────────── ─── front page continued (51) Int.Cl. ⁷ identifications FI F01N 3/28 ZAB F01N 3/28 ZAB F02D 41/14 310 F02D 41/14 310A 45/00 314 45/00 314R 366 366F (58 ) Field surveyed (Int. Cl. ⁷ , DB name) F01N 3/08-3/28 F02D 41/14 F02D 45/00

Claims (3)

(57) [Claims] 1. An exhaust system disposed in an exhaust passage of an internal combustion engine.
NO in the exhaust when the air-fuel ratio is lean_XAbsorb and exhaust
NO absorbed when the oxygen concentration in the air decreases_XRelease
NO_XAn absorbent, when the internal combustion engine is operating at a lean air-fuel ratio,
When a predetermined amount of addition determined according to the engine operating state is constant
NO at every interval_XAbsorbent NO_XNO for absorption_XSucking
The internal combustion engine is rich or logical
When operating at the stoichiometric air-fuel ratio, the predetermined subtraction amount is constant.
No. every time_XTo subtract from the absorption counter
From the NO_XAbsorbent NO_XAbsorption to estimate absorption
Means for estimating the amount of the engine,
The amount of fuel required to bring the air-fuel ratio to the stoichiometric air-fuel ratio
Excess excess to detect the amount of fuel supplied to the engine in excess
Fuel amount detecting means; and when the engine is operated at a rich air-fuel ratio,
NO based on fuel amount _XThe subtraction amount of the absorption amount counter
Exhaust gas purification of an internal combustion engine provided with a subtraction amount setting means for determining
apparatus. Wherein disposed in an exhaust passage of an internal combustion engine, the air-fuel ratio of the exhaust gas absorbs NO _X in the exhaust gas when the lean, the oxygen concentration in the exhaust gas to release NO _X absorbed when reduced and _the NO _X absorbent, when the internal combustion engine is operated at a lean air-fuel ratio,
The added to the NO _X absorption counter indicating the NO _X absorption of _the NO _X absorbent to predetermined addition amount determined at regular intervals in accordance with the engine operating conditions, operating the internal combustion engine is rich or the stoichiometric air-fuel ratio when it is, by subtracting from the NO _X absorption counter a predetermined subtraction amount at predetermined time intervals, and the absorption amount estimation means for estimating the NO _X absorption of the _the NO _X absorbent, the NO _X absorbent Temperature detection means for detecting the temperature of the agent; and when the engine is operated at a rich air-fuel ratio, the NO
Exhaust purification apparatus for an internal combustion engine having a subtraction amount setting means for determining the subtraction amount of the NO _X absorption counter based on the _X absorbent temperature. 3. disposed in an exhaust passage of an internal combustion engine, the air-fuel ratio of the exhaust gas absorbs NO _X in the exhaust gas when the lean, the oxygen concentration in the exhaust gas to release NO _X absorbed when reduced and _the NO _X absorbent, when the internal combustion engine is operated at a lean air-fuel ratio,
The added to the NO _X absorption counter indicating the NO _X absorption of _the NO _X absorbent to predetermined addition amount determined at regular intervals in accordance with the engine operating conditions, operating the internal combustion engine is rich or the stoichiometric air-fuel ratio when it is, by subtracting from the NO _X absorption counter a predetermined subtraction amount at predetermined time intervals, and the absorption amount estimation means for estimating the NO _X absorption of the _the NO _X absorbent, the engine intake air means for detecting the amount, and means for detecting the operating air-fuel ratio of the engine, means for detecting the temperature of the _the NO _X absorbent, when the engine is operated at a rich air-fuel ratio, the engine intake air Amount, the engine operating air-fuel ratio, and the NO _X
Exhaust purification apparatus for an internal combustion engine having a subtraction amount setting means for determining the subtraction amount of the NO _X absorption counter on the basis of the absorbent temperature.