JP3334635B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to a technique for removing NOx stored in a storage NOx catalyst.

[0002]

[Related Background Art] In recent years, due to good fuel efficiency and low CO ₂ emission, etc., the air-fuel ratio has been changed to the stoichiometric air-fuel ratio (value 1).
4.7) An internal combustion engine (lean burn engine) that can be controlled to a target value on the leaner side (lean side) than that of 4.7) and realizes not only stoichiometric air-fuel ratio operation and rich air-fuel ratio operation but also lean air-fuel ratio operation has been developed. It has been put to practical use as an internal combustion engine.

However, if the air-fuel ratio is set to a lean air-fuel ratio, there is a problem that the conventional three-way catalyst cannot sufficiently purify NOx (nitrogen oxide) in exhaust gas due to its purification characteristics. N even in excessive atmosphere
A storage NOx catalyst capable of purifying Ox has been developed and put into practical use. Occlusion-type NOx catalyst, the oxygen excess state occluded by attaching NOx in the exhaust gas as nitrate X-NO ₃ in (an oxidizing atmosphere), N ₂ a suction built the NOx with CO (carbon monoxide) over state (reduction atmosphere) (Nitrogen) (at the same time, carbonate X-CO ₃ is generated). Therefore, Patent Registration No. 25
As disclosed in US Patent No. 86738, in practice,
When the lean air-fuel ratio operation continues for a predetermined time, the air-fuel ratio is periodically switched to a rich air-fuel ratio operation in which the air-fuel ratio is controlled to a stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio (this is referred to as a rich spike). Is generated, and the stored NOx is purified and reduced (NOx purge) to store the stored NOx.
x We are trying to regenerate the catalyst.

[0004] However, if the lean air-fuel ratio operation is switched to the rich air-fuel ratio operation periodically when the lean air-fuel ratio operation continues for a predetermined time, a large amount of fuel is suddenly injected, and the lean air-fuel ratio operation is normally continuous. Therefore, there is a problem that when the driver does not operate the accelerator and unexpectedly, the torque fluctuates and a torque shock occurs. On the other hand, there is a patent for a technology that temporarily executes a rich air-fuel ratio operation when the operating state is switched from a lean air-fuel ratio operation to a stoichiometric air-fuel ratio operation (this is referred to as stoichiometric operation) under specific operating conditions. It is disclosed in Registration No. 2692530. In this method, for example, when an accelerator operation for acceleration or the like based on the driver's intention is performed as a specific driving condition, the NOx purge is performed at the same time. As expected, no torque shock contrary to the driver's intention will occur.

[0005]

However, normally, stoichiometric operation is not performed unless the driver depresses the accelerator pedal to perform an accelerating operation. When the lean air-fuel ratio operation is continued for a long period of time, such as when traveling at a constant speed, the rich air-fuel ratio operation cannot be easily performed, and the NOx purge cannot be satisfactorily performed. There is. If the NOx purge is not performed for a long time, the NOx storage capacity of the storage NOx catalyst reaches the limit, and NOx may be diffused into the atmosphere, which is not preferable.

The present invention has been made to solve such a problem, and an object thereof is to provide a storage type N.
In an exhaust gas purification device provided with an Ox catalyst, the storage NOx
The NOx stored in the catalyst is efficiently and reliably removed, and the torque shock when switching the operation state to the rich air-fuel ratio operation is reduced as much as possible to reduce the NOx of the storage NOx catalyst.
An object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine capable of always maintaining a good purifying ability.

[0007]

According to the first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine equipped with a storage type NOx catalyst, wherein the operating state switching means is operated under a specific operating condition. N when the operation state is switched from the lean air-fuel ratio operating state to the operating state at the stoichiometric air-fuel ratio by
The NOx storage amount estimated by the Ox storage amount estimation means is equal to the first
The air-fuel ratio is corrected to a predetermined rich air-fuel ratio when the air-fuel ratio is equal to or more than a predetermined value (first rich correction means). Further, the NOx storage amount estimated by the NOx storage amount estimation means under the lean air-fuel ratio operating state The air-fuel ratio is corrected to the above-mentioned rich air-fuel ratio when the air-fuel ratio reaches a second predetermined value larger than the first predetermined value (second rich correction means).

Accordingly, for example, when the occlusion type NOx catalyst does not occlude so much NOx in the exhaust gas, the operating state is set under specific operating conditions such as acceleration by accelerator operation based on the driver's intention. when switching from the lean air-fuel ratio operation on the operating state of the stoichiometric air-fuel ratio, will be air-fuel ratio is a suitable rich air-fuel ratio to the NOx purge, a driver or the like by an unexpected change in torque of the driver feels a sense of discomfort NOx reduction and removal is performed satisfactorily, a high NOx purification rate is maintained, and the operating state is not switched, and the lean air-fuel ratio operating state continues for a long time. Also occlusion type NO
NOx can be reliably reduced and removed before the NOx storage capacity of the x catalyst reaches the limit.

Further, according to the invention of claim 2, according to claim 1,
It limits the specific operating conditions in the invention of
In the above, the specific operating condition is a vehicle equipped with an internal combustion engine.
Switching the air conditioner installed in the car from off to on
The automatic transmission shift position from neutral to dry.
When switching to the Evrange or when the driver
It is characterized by being at the time of acceleration by a steering operation. Therefore,
For example, a rich spike occurs when the operating state of the air conditioner is switched from lean air-fuel ratio operation to stoichiometric air-fuel ratio operation due to switching of the operating state of the air conditioner, switching of the shift position of the automatic transmission, or operation of the accelerator pedal by the driver. would happens is that when the driver unexpected change in torque by reduction removal of NOx without the driver or the like feels discomfort is satisfactorily carried out a high NOx purification rate of Ru is retained. Thereby, it is possible to realize a suitable exhaust gas purification apparatus which always has a high NOx purification capability, in which the driver does not feel discomfort such as torque shock generated when the air-fuel ratio is set to a rich air-fuel ratio appropriate for NOx purge. You.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the accompanying drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention mounted on a vehicle. Hereinafter, the configuration of the exhaust gas purifying apparatus according to the present invention will be described with reference to FIG.

Engine body (hereinafter simply referred to as engine) 1
For example, in-cylinder injection spark ignition capable of performing fuel injection in an intake stroke (intake stroke injection mode) or fuel injection in a compression stroke (compression stroke injection mode) by switching a fuel injection mode (operation mode), for example. It is an inline 4-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric ratio), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.

As shown in FIG. 1, an electromagnetic fuel injection valve 6 is attached to a cylinder head 2 of an engine 1 together with a spark plug 4 for each cylinder, whereby fuel is injected into a combustion chamber 8. Direct injection is possible. A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, whereby the fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. From the fuel injection valve 6 into the combustion chamber at a desired fuel pressure.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10. The throttle valve 11 is provided with a throttle sensor 11a for detecting a throttle opening θth.

An exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port. Reference numeral 13 in the figure denotes a crank angle sensor for detecting a crank angle, and the crank angle sensor 13 is capable of detecting an engine rotation speed Ne.

The in-cylinder injection type engine 1 is already known, and a detailed description of its configuration is omitted here. As shown in FIG. 1, an exhaust pipe (exhaust passage) 14 is connected to the exhaust manifold 12, and a small close three-way catalyst 20 and an exhaust purification catalyst device 30 close to the engine 1 are connected to the exhaust pipe 14. A muffler (not shown) is connected via the terminal. The exhaust pipe 14 is provided with a high temperature sensor 16 for detecting the exhaust gas temperature.

The exhaust purification catalyst device 30 is provided with two catalysts, that is, a storage type NOx catalyst 30a and a three-way catalyst 30b, and the three-way catalyst 30b has a storage type NOx catalyst 3a.
0a is disposed downstream. The storage NOx catalyst 30a temporarily stores NOx in an oxidizing atmosphere,
It has a function of reducing NOx to N ₂ (nitrogen) or the like mainly in a reducing atmosphere where CO is present. More specifically, the storage NOx catalyst 30a is configured as a catalyst having platinum (Pt), rhodium (Rh), or the like as a noble metal, and an alkali metal such as barium (Ba) or an alkaline earth metal as a storage material. Has been adopted.

A NOx sensor 32 for detecting the NOx concentration is provided between the storage type NOx catalyst 30a and the three-way catalyst 30b.
Is provided. Further, an input / output device, a storage device (R
OM, RAM, nonvolatile RAM, etc.), central processing unit (C
PU), an ECU (electronic control unit) 40 including a timer counter and the like.
With 0, comprehensive control of the exhaust gas purification apparatus according to the present invention including the engine 1 is performed. Various sensors such as the high-temperature sensor 16 and the NOx sensor 32 described above are connected to the input side of the ECU 40, and detection information from these sensors is input.

On the other hand, the output side of the ECU 40 is connected to the above-described ignition plug 4 and the fuel injection valve 6 via an ignition coil. The ignition coil, the fuel injection valve 6 and the like are connected to various sensors. The optimum values such as the fuel injection amount and the ignition timing calculated based on the detection information are output.
As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and ignition is performed by the spark plug 4 at an appropriate timing.

In practice, the ECU 40 determines the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure, based on the throttle opening information θth from the throttle sensor 11a and the engine rotation speed information Ne from the crank angle sensor 13. Pe is obtained, and further, according to the target average effective pressure Pe and the engine rotation speed information Ne,
The fuel injection mode is set from a fuel injection mode setting map (not shown). For example, when the target average effective pressure Pe and the engine rotation speed Ne are both small, the fuel injection mode is a compression stroke injection lean mode, that is, a compression lean mode, and fuel is injected in a compression stroke below a lean air-fuel ratio. When the target average effective pressure Pe increases or the engine speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and fuel is injected in the intake stroke. In the intake stroke injection mode, the lean air-fuel ratio is assumed to be the lean air-fuel ratio, and the stoichiometric air-fuel ratio (stoichio)
There is a stoichiometric feedback mode, and an open loop mode (O / L mode), which is a rich air-fuel ratio (operating state switching means).

The target air-fuel ratio (target A / A) is set as a control target based on the target average effective pressure Pe and the engine speed Ne.
F) is set, and the appropriate amount of fuel injection is set to the target A /
It is determined based on F. Further, the catalyst temperature Tcat is estimated from the exhaust gas temperature information detected by the high temperature sensor 16. More specifically, in order to correct an error caused by the inability to directly install the high-temperature sensor 16 on the storage NOx catalyst 30a, the temperature is previously determined by an experiment or the like in accordance with the target average effective pressure Pe and the engine rotation speed information Ne. A difference map (not shown) has been set and therefore the catalyst temperature Tcat
Is uniquely estimated when the target average effective pressure Pe and the engine speed information Ne are determined.

Hereinafter, the operation of the exhaust gas purification apparatus thus configured according to the present invention will be described. That is, the NOx purge control of the storage NOx catalyst 30a according to the present invention will be described. Referring to FIG. 2, there is shown a flowchart of a NOx purge control routine according to the present invention, which will be described below with reference to the flowchart. Here, for convenience, as an example of the specific operation condition, as an example of the specific operation condition, the driver depresses the accelerator pedal during the lean air-fuel ratio operation, and the operation state is switched from the lean air-fuel ratio operation to the stoichiometric operation based on the fuel injection mode setting map. Let's talk about it.

First, in step S10, an integrated NOx amount Q (n) is calculated. That is, the current NOx storage amount stored in the storage NOx catalyst 30a is obtained by calculation from the following equation (1) (NOx storage amount estimation means). Q (n) = Q (n-1) + q1-q2 (1) where Q (n-1) is the NOx integrated amount at the time of the previous execution of the routine, and q1 is a new value for the storage NOx catalyst 30a. Indicates the amount of adsorbed NOx stored in the storage NOx catalyst, and q2 indicates the storage NOx catalyst 30.
The figure shows the amount of desorbed NOx removed from a.

The amount of adsorbed NOx q1, ie, the amount of N that is discharged from the engine 1 and flows into the storage-type NOx catalyst 30a and is adsorbed
It means the amount of Ox, and can be easily obtained based on the target average effective pressure Pe and the engine speed information Ne.
Actually, as shown in FIG. 3, the adsorbed NOx amount q1 is mapped based on the target average effective pressure Pe and the engine rotation speed information Ne, and is read from the map. However, during stoichiometric or rich air-fuel ratio operation other than the lean air-fuel ratio operation, the adsorbed NOx amount q1 is set to the value 0.

The desorbed NOx amount q2 is obtained from the following equation (2). q2 = q2 '· Qa (2) Here, q2' is a desorbed NOx amount per unit intake air amount (unit desorbed NOx amount), and Qa is an intake air amount.
Actually, as shown in FIG. 4, the unit desorption NOx amount q2 'is mapped in advance based on the target A / F, and is read out from the map. In other words, the unit desorbed NOx amount q2 'is set to a larger value as the degree of richness increases in the range of the rich air-fuel ratio where the target A / F is smaller than the stoichiometric ratio, and the desorbed NOx amount q2 becomes smaller as the target A / F becomes smaller. The larger the intake air amount Qa, the larger the value.

In this way, the adsorbed NOx amount q1 and the desorbed NO
The NOx integrated amount Q (n) is obtained according to the increase / decrease amount with respect to the x amount q2. However, at this time, since the lean air-fuel ratio operation is still performed, the NOx is actually stored in the storage type NOx catalyst 30a. While it is not removed, so the desorbed NO
The x amount q2 is set to a value 0 based on the map of FIG.
The integrated amount Q (n) increases without decreasing.

In step S12, it is determined whether the operating state is other than the lean air-fuel ratio operation (stoichiometric operation or rich air-fuel ratio operation). Here, as described above, since it is assumed that the operation state has been switched from the lean operation to the stoichiometric operation, the determination result is true (Yes), and the process proceeds to step S14. In step S14, the NOx integrated amount Q (n) is a predetermined value Q2 (first predetermined value) which is one of the NOx purge execution determination values.
It is determined whether or not this is the case. Note that the predetermined value Q2
Is smaller than a predetermined value Q1 described later (Q2
<Q1).

In practice, as shown in FIG. 5, the predetermined value Q2 is set and mapped in advance so that the value becomes smaller as the vehicle speed, that is, the vehicle speed V increases. Normal,
When the vehicle speed V increases, that is, the target average effective pressure Pe and the engine rotation speed information Ne increase, and the storage NOx catalyst 3
As the temperature of the exhaust gas flowing through the exhaust gas 0a increases, the exhaust gas flow rate increases, and the catalyst temperature Tcat rises. NOx catalyst 3
The NOx storage capacity of Oa decreases. Further, the vehicle speed V includes an influence on the catalyst temperature Tcat due to the catalyst cooling of the traveling wind, or a direct influence on the NOx storage capacity due to an increase in the exhaust gas flow rate.

Therefore, in consideration of the above, here, when the vehicle speed V increases, the NOx purge execution determination value is reduced so that the NOx purge is easily performed early. Although FIG. 2 also shows the relationship between the predetermined value Q1 and the vehicle speed V, the predetermined value Q1 is set to a smaller value as the vehicle speed V increases.

The determination result of step S14 is false (No)
If the NOx integrated amount Q (n) is smaller than the predetermined value Q2, the process proceeds to step S16. Here, referring to FIG. 6, when the NOx purge control routine is executed, the vehicle speed V (a), the target A / F (b), and the adsorbed NOx amount q1
(C) and a time chart of the NOx integrated amount Q (n) (d) are shown, which will be described below with reference to FIG. In addition,
In the same figure, the above-mentioned predetermined value Q2 and the predetermined value Q1, which change according to the vehicle speed V, are also indicated by a chain line.

In step S16, as will be described later in detail, it is determined whether or not the flag F set to the value 1 when the rich spike is executed is the value 1. At this point, since the rich spike has not been performed yet, the flag F has a value of 0, and the determination result is false (No). That is, as shown by timing A in FIG. 6, when the stoichiometric operation is started and the NOx integrated amount Q (n) has not yet reached the predetermined value Q2, the NOx purge is particularly performed. Without this, the integration of the NOx integrated amount Q (n) is continued as it is.

On the other hand, if the result of the determination in step S12 is true (Y
es), the stoichiometric operation is started and step S
If the determination result of 14 is true (Yes) and it is determined that the NOx integrated amount Q (n) is equal to or more than the predetermined value Q2, then step S1 is performed.
Proceed to 8. In step S18, rich correction (rich spike) is performed. That is, as shown by timing B or timing C in FIG. 6, when the stoichiometric operation is started and the NOx integrated amount Q (n) is equal to or more than the predetermined value Q2, the target A / F (here, stoichiometric ), The operation state is switched to the rich air-fuel ratio operation, whereby a reducing atmosphere is formed in the storage NOx catalyst 30a and N
Ox purge is performed (first rich correction means). In the rich air-fuel ratio operation in the rich spike, the air-fuel ratio is set to, for example, a value of 12.

Then, in the next step S20, a value 1 is set to the flag F to store that the rich spike is being executed (F = 1). When the rich spike is executed and the NOx purge is started, the NOx integrated amount Q
(n) decreases, and the determination result of step S14 becomes false (N
At this point, the value of the flag F is 1, so the result of the determination in step S16 is true (Yes), and the process proceeds to step S22.

In step S22, the NOx purge proceeds due to the execution of the rich spike, and the storage NOx catalyst 30a
The NOx occluded in the NOx is completely removed, and as shown in FIG. 6D, the NOx integrated amount Q (n) exceeding the predetermined value Q2 is reduced to a value 0 based on the calculation of the above equation (1). It is determined whether or not the number has decreased. If the determination result is false (No), the NOx integrated amount Q
If it is determined that (n) has not yet decreased to the value 0, the rich spike is continuously performed in step S18.

On the other hand, if the result of the determination in step S22 is true (Y
If it is determined in es) that the NOx integrated amount Q (n) has decreased to the value 0, the process proceeds to step S24, and the flag F set to the value 1 is reset to the value 0. When the flag F is set to the value 0 in this manner, the next time step S16 is executed, the determination result becomes false (No), so that the rich spike is not performed, and thus NOx
Purging ends.

As described above, if the rich spike is performed in accordance with the stoichiometric operation based on the driver's intention, torque shock unintended by the driver does not occur, and the driving fee is reduced. The deterioration of the ring is suitably prevented. That is, when the accelerator operation is performed for acceleration by the driver's intention and the driving state is switched from the lean air-fuel ratio operation to the stoichiometric operation, the driver originally expects a torque shock due to an increase in torque. By performing the rich spike in accordance with the situation, the torque shock can be made inconspicuous, and the driver and the occupant do not feel uncomfortable.

In the rich spike in accordance with the execution of the stoichiometric operation, the NOx purge execution determination value such as the predetermined value Q2 is set to a relatively small value with respect to a predetermined value Q1, which will be described later, so that the rich spike is easily performed. However, this is done so that the rich spike is performed as much as possible when switching to the stoichiometric operation by the driver's accelerator operation, and to the rich air-fuel ratio operation during the continuous lean air-fuel ratio operation described later. This is for minimizing the chance of unexpected torque shock by the driver due to the switching.

If the determination result of step S12 in FIG. 2 is false (N
In the case of o), when the operation state is neither the stoichiometric operation nor the rich air-fuel ratio operation, that is, in the case of the lean air-fuel ratio operation, the process proceeds to step S28. In step S28, the N
It is determined whether or not the Ox integrated amount Q (n) is equal to or larger than the above-described predetermined value Q1 (second predetermined value) which is one of the NOx purge execution determination values. Note that, as described above, the predetermined value Q1 is also:
As shown in FIG. 5, the map is set in advance so that the value becomes smaller as the vehicle speed, that is, the vehicle speed V increases.

The determination result of step S28 is false (No)
If it is determined that the NOx integrated amount Q (n) has not yet reached the predetermined value Q1, the process proceeds to step S16 described above,
It is determined whether or not the flag F has the value 1. Since the flag F has the value 0 unless the rich spike is executed,
In this case, the determination result is false (No), and the process exits the routine without doing anything. That is, in the case of the lean air-fuel ratio operation, this route is always selected, and only the integration of the NOx integrated amount Q (n) is continuously performed.

On the other hand, if the decision result in the step S28 is true (Y
If it is determined in es) that the NOx integrated amount Q (n) is equal to or greater than the predetermined value Q1, the process proceeds to step S18, where a rich spike is performed. That is, as shown by the timing D in FIG. 6, even during the lean air-fuel ratio operation, the NOx integrated amount Q
When (n) is equal to or more than the predetermined value Q1, the operating state is switched to the rich air-fuel ratio operation regardless of the target A / F (here, the lean air-fuel ratio).
A NOx purge is performed by forming a reducing atmosphere in (a) (second rich correction means).

Step S20 and subsequent steps are as described above, and a description thereof will be omitted. That is, also in this case, when the rich spike is executed and the NOx purge is started, N
The integrated amount of Ox Q (n) will decrease, but as described above, N
The Ox purge is satisfactorily continued until the integrated NOx amount Q (n) becomes zero. That is, in order to eliminate the torque shock during the execution of the rich spike, it is preferable to perform the rich spike at the time when the stoichiometric operation is performed based on the driver's intention as described above. In the case where the stoichiometric operation is not easily performed as in the case where the vehicle is traveling at a high speed, the NOx storage capacity of the storage NOx catalyst 30a reaches the limit, that is, N
When the integrated amount of Ox Q (n) reaches a predetermined value Q1 closer to the storage limit value, rich spike is performed and NOx purge is performed. Thereby, even if the stoichiometric operation is not performed, the storage NO
x catalyst 30a is always maintained in a state capable of storing NOx,
NOx is reliably prevented from being inadvertently discharged into the atmosphere.

[0041]

[0042] As described above, in the exhaust purification system of an internal combustion engine of the present invention is as NOx purge is performed is rich spike is performed in accordance with the timing at which stoichiometric OPERATION is performed, further, stoichiometric luck Even if the lean air-fuel ratio operation is continued without the rotation being performed, the NOx accumulation amount Q (n) must be reached before the NOx integrated amount Q (n) reaches the storage limit value.
Purging is performed.

[0043] Therefore, usually, as when accelerated by the driver's intention, the driver is a NOx purge is seamlessly be implemented in the original switching to stoichiometric OPERATION to anticipate torque shock due to the torque increase and, surely even when the stoichiometric OPERATION is not performed nO
By purging x, the NOx storage capacity of the storage NOx catalyst 30a can always be kept good.

Further, in the present invention, the predetermined value Q2 for the NOx purge execution determination is set smaller than the predetermined value Q1,
So that NOx purge is performed in switching to the utmost stoichiometric OPERATION. Therefore, the chance of purging NOx during the lean air-fuel ratio operation is reduced, and it is possible to more suitably prevent the driver or the like from feeling uncomfortable.

In the above embodiment, the NOx integrated amount Q
Although the rich spike is performed and the NOx purge is performed until the value of (n) becomes 0, the lower limit and the upper limit of the execution time of the rich spike are set to prevent insufficient or excessive execution of the rich spike. You may. That is, the execution time of the rich spike may be limited to a predetermined time range.

In the above embodiment, the predetermined values Q1 and Q2 are variable values with respect to the vehicle speed V.
It may be a variable value for the engine speed or load, or a fixed value. Further, in the above-described embodiment, the NOx purge execution determination value is set to two predetermined values Q1 and Q2. However, three or more execution determination values are set and used depending on the operation state and the like. Is also good.

In the present embodiment, the accelerator operation (acceleration) of the driver is raised as an example of the specific driving condition. However, for example, the air conditioner is turned on from OFF, or the shift position of the automatic transmission is set to N (neutral). ) Range to D
Even if the range is changed to the (drive) range, the load required on the engine side increases, and the air-fuel ratio switches to an air-fuel ratio other than the lean air-fuel ratio. You may make it implement.

In the above-described embodiment, the engine 1 is a direct-injection spark ignition type in-line four-cylinder gasoline engine. However, if the air-fuel ratio can be switched between a lean air-fuel ratio and a rich air-fuel ratio, the engine 1 1 may be an intake pipe injection type lean burn engine or the like.

[0049]

As described above in detail, according to the exhaust gas purifying apparatus for an internal combustion engine of the present invention , the NOx storage catalyst is
If the Ox is switched to the operating state of the operation state in particular operating conditions at the stoichiometric air-fuel ratio from the lean air-fuel ratio operation when not so much occluded, for example, air conditioning, Oh
The shift position of the automatic transmission when switching from off to on
When switching from neutral to drive range, or
When the vehicle is accelerated by operating the accelerator pedal, the air-fuel ratio is set to a rich air-fuel ratio, so that not only the driver and the like can perform the reduction and removal of NOx without feeling uncomfortable, but also the operation state is not switched and the lean operation is performed. Even when the air-fuel ratio operation state continues for a long period of time and a large amount of NOx is stored in the NOx storage catalyst, the N
NOx can be reliably reduced and removed before the Ox storage capacity reaches its limit.

[0050] Because less be uncomfortable to the driver or the like by a torque shock generated an air-fuel ratio upon an appropriate rich air-fuel ratio to the NOx purging feel, a consistently high suitable exhaust gas purification device of NOx purification capability implemented can do.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an exhaust gas purification device for an internal combustion engine according to the present invention.

FIG. 2 is a flowchart showing a control routine of NOx purge control according to the present invention.

FIG. 3 shows a target average effective pressure Pe and engine speed information Ne.
4 is a map showing the relationship between the amount of adsorption NOx and q1.

FIG. 4 is a map showing a relationship between a target A / F and a unit desorbed NOx amount q2 ′.

FIG. 5 is a map showing a relationship between a vehicle speed V and a NOx purge execution determination value.

FIG. 6 is a time chart showing a control result of the NOx purge control of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine (internal combustion engine) 4 Spark plug 6 Fuel injection valve 11 Throttle valve 11a Throttle sensor 13 Crank angle sensor 30a Storage type NOx catalyst 40 Electronic control unit (ECU)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-254135 (JP, A) JP-A-6-58185 (JP, A) JP-A-8-260948 (JP, A) 272540 (JP, A) JP-A-9-137738 (JP, A) JP-A-6-280550 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/04 F01N 3 / 08-3/36

Claims (2)

(57) [Claims] An operating state switching means for switching an operating state of an internal combustion engine between a lean air-fuel ratio operating state and an operating state at a stoichiometric air-fuel ratio; and an operating state switching means provided in an exhaust passage of the internal combustion engine. When in the fuel ratio operation state, NOx in the exhaust gas is stored,
NOx stored in the rich air-fuel ratio operating state
A NOx storage catalyst for reducing NOx storage amount, NOx storage amount estimating means for estimating the NOx storage amount stored in the storage NOx catalyst, and an operating state switching means for operating the lean air-fuel ratio under specific operating conditions. The air-fuel ratio is corrected to a predetermined rich air-fuel ratio when the NOx storage amount estimated by the NOx storage amount estimating means at the time of switching from the state to the operation state at the stoichiometric air-fuel ratio is equal to or more than a first predetermined value. First rich correction means, and when the NOx storage amount estimated by the NOx storage amount estimation means in the lean air-fuel ratio operating state reaches a second predetermined value larger than the first predetermined value, the air-fuel ratio And a second rich correction means for correcting the predetermined rich air-fuel ratio to the predetermined rich air-fuel ratio. 2. The method according to claim 1, wherein the specific operating condition is that the internal combustion engine is mounted.
The air conditioner installed on a damaged vehicle from off to on
The automatic transmission's shift position
To the drive range, or when the driver
The accelerator pedal is operating at the time of acceleration.
The exhaust gas purifying apparatus for an internal combustion engine according to claim 1.