JP2003227378A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine to improve exhaust purification efficiency in a cold state. <P>SOLUTION: When the internal combustion engine is in the cold state and a three-way catalytic converter is not yet functioning at low temperature of the catalyst, NOx is stored into an occlusion type NOx catalytic converter. When the temperature correlation value (TW) of the three-way catalytic converter is within a predetermined range (T<SB>2</SB><TW<T<SB>3</SB>initial semi activation state) (S14) and an exhaust flow rate is predetermined low flow (S20), an exhaust air-fuel ratio in the exhaust passage is controlled to a first exhaust air-fuel ratio (G=G<SB>b</SB>×1.5) close to rich air-fuel ratio rather than a second exhaust air-fuel ratio (G=G<SB>b</SB>) (S24) when the temperature correlation value of the three-way catalytic converter is over the predetermined range or when the exhaust flow is over the predetermined low flow rate. <P>COPYRIGHT: (C)2003,JPO

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 an exhaust gas purifying technology at a cold start.

[0002]

Related Background Art Normally, a three-way catalytic converter is provided in an exhaust passage of an internal combustion engine (engine) mounted on a vehicle, and the three-way catalytic converter causes harmful substances (HC, CO, NOx, etc.) is purified. However, since the three-way catalytic converter cannot sufficiently perform the purifying function unless it is activated by the temperature rise, when the engine is in a cold state such as at the time of starting, harmful substances (HC, CO, NOx) are generated. Etc.) purification efficiency decreases.

In this case, it is conceivable to set the combustion air-fuel ratio to a lean air-fuel ratio at the time of cold start of the engine to reduce HC and CO. However, if the combustion air-fuel ratio is made to be a lean air-fuel ratio in this way, on the other hand There is a problem that a large amount of NOx is generated as the combustion temperature and exhaust temperature rise. Therefore, NOx is stored in a lean atmosphere where the exhaust air-fuel ratio is the lean air-fuel ratio, and the stored NOx is released and reduced (NOx purge) in a predetermined atmosphere where the exhaust air-fuel ratio is the theoretical air-fuel ratio or the rich air-fuel ratio. It is considered that the storage type NOx catalytic converter having the above configuration is arranged in series with the three-way catalytic converter, and the storage type NOx catalytic converter purifies NOx.

[0004]

By the way, the occlusion type NO
The NOx storage capacity of the x catalytic converter is determined according to the size (trap site amount) of the region (trap site) capable of storing NOx, and the NOx purge is sufficiently performed to increase the trap site amount. The higher the price.

However, the NOx storage capacity tends to decrease as the catalyst temperature becomes lower as in the cold start, and even if the trap site amount is the same, the NOx storage capacity is lower in the cold start than in the warm operation. However, the NOx storage amount decreases. In other words, even if the amount of trap sites is small during warm operation, N
While it is possible to satisfactorily store Ox, it is necessary to secure the amount of trap sites as much as possible at the cold start to compensate for the decrease in NOx storage capacity.

In order to secure a sufficient amount of trap sites, the NOx purge should be performed almost completely during normal temperature operation so that the engine does not stop with a small amount of trap sites. This is sufficient, so that a sufficient amount of trap sites is always secured even during cold start. However, in order to perform NOx purging with the exhaust air-fuel ratio as the stoichiometric air-fuel ratio or the rich air-fuel ratio, in general, the fuel supply amount must be frequently increased so that the combustion air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, In a warm state operation in which NOx can be sufficiently stored even if the amount of trap sites is small, excessive NOx purge is performed, which leads to deterioration of fuel efficiency and is not preferable.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine which improves exhaust gas purification efficiency in a cold state without deteriorating fuel consumption. To provide.

[0008]

In order to achieve the above object, according to the invention of claim 1, a three-way catalytic converter provided in an exhaust passage of an internal combustion engine and the exhaust gas in series with the three-way catalytic converter are provided. A storage type NOx catalytic converter that is provided in the passage and that stores NOx in the exhaust gas in a lean atmosphere and that releases the stored NOx in a predetermined atmosphere, and a catalyst temperature correlation that detects the temperature correlation value of the three-way catalytic converter. A value detecting means, an exhaust low flow rate detecting means for detecting that the flow rate of the exhaust gas flowing through the exhaust passage is a predetermined low flow rate, and a temperature correlation value of the three-way catalytic converter is predetermined by the catalyst temperature correlation value detecting means. When it is detected that it is within the range and the predetermined low flow rate is detected by the low exhaust flow rate detection means, the exhaust air-fuel ratio in the exhaust passage is set to the three-way catalytic converter. Exhaust air that is controlled to a first exhaust air-fuel ratio that is closer to the rich air-fuel ratio than the second exhaust air-fuel ratio when the temperature correlation value exceeds the predetermined range or the flow rate of exhaust exceeds the predetermined low flow rate And a fuel ratio control means.

That is, when the internal combustion engine is in a cold state and the three-way catalytic converter is still not functioning at a low temperature of the catalyst, NOx is stored in the storage type NOx catalytic converter. When the correlation value is within the predetermined range (initial half-active state) and the exhaust flow rate is at the predetermined low flow rate, the exhaust air-fuel ratio in the exhaust passage is such that the temperature correlation value of the three-way catalytic converter exceeds the predetermined range. When the flow rate of the exhaust gas exceeds a predetermined low flow rate, the first exhaust air-fuel ratio is controlled to be closer to the rich air-fuel ratio than the second exhaust air-fuel ratio, and therefore the Nx stored in the NOx catalytic converter is controlled.
Ox is satisfactorily purged, a sufficient trap site amount is secured, and NOx can be sufficiently stored even when the NOx catalytic converter has a low temperature and a low NOx storage capacity.

As a result, excessive N
Ox purging is performed, and NOx emissions are favorably prevented when the catalyst temperature is low, that is, when the catalyst is cold, and exhaust purification efficiency is improved without deteriorating fuel efficiency. Further, in the invention of claim 2, the catalyst temperature correlation value detecting means includes a temperature of the three-way catalytic converter, a temperature of the occlusion type NOx catalytic converter, a cooling water temperature of the internal combustion engine, an elapsed time after starting the internal combustion engine, and One of the amounts of NOx flowing into the storage type NOx catalytic converter is detected as a temperature correlation value of the three-way catalytic converter.

Therefore, the temperature correlation value of the three-way catalytic converter becomes one of the temperature of the three-way catalytic converter, the temperature of the occlusion type NOx catalytic converter, the cooling water temperature of the internal combustion engine, and the elapsed time after starting the internal combustion engine. Easily detected based on Further, there is a correlation between the NOx purification performance of the three-way catalytic converter and the temperature of the three-way catalytic converter, and the temperature correlation value of the three-way catalytic converter is the amount of NOx downstream of the three-way catalytic converter, that is, the storage type NOx. NO upstream of catalytic converter
It is also easily detected from the amount of x.

According to the invention of claim 3, the three-way catalytic converter provided in the exhaust passage of the internal combustion engine, and the three-way catalytic converter provided in the exhaust passage in series with the three-way catalytic converter, NOx in the exhaust gas in a lean atmosphere. A storage type NOx catalytic converter for storing the stored NOx and releasing the stored NOx under a predetermined atmosphere, a catalyst semi-active state detecting means for detecting that the three-way catalytic converter is in a semi-active state, and a flow through the exhaust passage. An exhaust gas low flow rate detection means for detecting that the flow rate of exhaust gas is a predetermined low flow rate, and the catalyst semi-active state detection means detects that the three-way catalytic converter is in the semi-active state and the exhaust gas low flow rate detection means. When the predetermined low flow rate is detected by the means, the exhaust air-fuel ratio in the exhaust passage is changed to the three-way catalyst converter for a predetermined period corresponding to the initial state of the semi-active state. An exhaust air-fuel ratio control means for controlling the exhaust gas to a first exhaust air-fuel ratio closer to the rich air-fuel ratio than the second exhaust air-fuel ratio when the exhaust gas flow rate exceeds the predetermined low flow rate. It is characterized by having.

That is, when the internal combustion engine is in a cold state and the three-way catalytic converter is still not functioning at a low temperature of the catalyst, NOx is stored in the storage type NOx catalytic converter. The exhaust air-fuel ratio in the exhaust passage has the temperature correlation value of the three-way catalytic converter exceeding the predetermined range for a predetermined period (the initial state of the semi-active state) after becoming the active state and the exhaust flow rate becoming the predetermined low flow rate. At this time, or when the flow rate of the exhaust gas exceeds a predetermined low flow rate, the first exhaust air-fuel ratio is controlled to be closer to the rich air-fuel ratio than the second exhaust air-fuel ratio, and therefore the NOx stored in the NOx catalytic converter is improved. Even if the NOx catalytic converter is at a low temperature and has a low NOx storage capacity, it is possible to store NOx sufficiently even if the NOx catalytic converter is purged and a sufficient trap site amount is secured.

As a result, excessive N
Ox purging is performed, and NOx emissions are favorably prevented when the catalyst temperature is low, that is, when the catalyst is cold, and exhaust purification efficiency is improved without deteriorating fuel efficiency. Further, in the invention of claim 4, the catalyst semi-active state detecting means includes a temperature of the three-way catalytic converter, a temperature of the occlusion type NOx catalytic converter, a cooling water temperature of the internal combustion engine, an elapsed time after starting the internal combustion engine, and The semi-active state of the three-way catalytic converter is detected based on any one of the amounts of NOx flowing into the storage type NOx catalytic converter.

Therefore, the semi-active state of the three-way catalytic converter becomes one of the temperature of the three-way catalytic converter, the temperature of the occlusion type NOx catalytic converter, the temperature of the cooling water of the internal combustion engine, and the elapsed time after starting the internal combustion engine. Easily detected based on Further, there is a correlation between the NOx purification performance of the three-way catalytic converter and the temperature of the three-way catalytic converter, and the semi-active state of the three-way catalytic converter is the amount of NOx downstream of the three-way catalytic converter, that is, the storage type NOx. NO upstream of catalytic converter
It is also easily detected from the amount of x.

Further, the invention of claim 5 is characterized in that the second exhaust air-fuel ratio is a stoichiometric air-fuel ratio or a substantially stoichiometric air-fuel ratio. Therefore, when the three-way catalytic converter is in the fully active state or when the flow rate of the exhaust gas exceeds the predetermined low flow rate, the exhaust air-fuel ratio is set to the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio, that is, the combustion air-fuel ratio is the theoretical air-fuel ratio. The fuel ratio or the approximately stoichiometric air-fuel ratio is set, the warm-up of the internal combustion engine is promoted, the temperature of the cooling water rises, and the heater performance is secured even in the cold state.

Further, the invention of claim 6 is characterized in that the first exhaust air-fuel ratio is a stoichiometric air-fuel ratio or a rich air-fuel ratio. Therefore, when the three-way catalytic converter is in the initial half-active state, the exhaust air-fuel ratio is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio, and the NOx purge is efficiently and sufficiently performed.

Further, in the invention of claim 7, the exhaust air-fuel ratio control means controls the exhaust air-fuel ratio in the exhaust passage to a lean air-fuel ratio before controlling to the first exhaust air-fuel ratio. I am trying. Therefore, when the three-way catalytic converter is inactive until it becomes semi-active, the exhaust temperature is low and N
Ox is scarcely generated, and the exhaust air-fuel ratio is made to be a lean air-fuel ratio so that sufficient oxygen is supplied to the exhaust gas, so that the emission of HC and CO is also suppressed satisfactorily.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments 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 emission control system for an internal combustion engine according to the present invention. Hereinafter, the configuration of the exhaust emission control system for the internal combustion engine will be described. As shown in FIG. 1, an engine body (hereinafter, simply referred to as an engine) 1 which is an internal combustion engine has a fuel injection in an intake stroke (intake stroke injection) and a fuel injection in a compression stroke (intake stroke injection) by switching a fuel injection mode. (Compression stroke injection)
A cylinder injection type spark ignition type gasoline engine capable of implementing the above is adopted. This in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (Stoichio) or at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio operation). Can be easily realized.

As shown in the figure, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, whereby the fuel is directly injected into the combustion chamber. It is possible. An ignition coil 8 that outputs a high voltage is connected to the spark plug 4. A fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, which supplies the fuel in the fuel tank to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. Can be injected from the fuel injection valve 6 toward 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 so as to communicate with each intake port. The intake manifold 10 is provided with an electromagnetic throttle valve 14 that adjusts the intake air amount and a throttle position sensor (TPS) 16 that detects the opening degree θth of the throttle valve 14.

Further, the cylinder head 2 is formed with an exhaust port in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected so as to communicate with each exhaust port. Since the in-cylinder injection type engine 1 is already known, the detailed description of its configuration will be omitted.

An exhaust pipe (exhaust passage) 20 is connected to the exhaust manifold 12, and the exhaust pipe 20 is located near the exhaust manifold 12 as an exhaust purification catalyst device (catalytic converter) and is a three-way catalytic converter in a front stage. (FC
C, hereinafter, front stage three-way catalyst) 22 is interposed and the underfloor catalytic converter (UCC) 30 is located under the floor of the vehicle.
Is installed.

The underfloor catalytic converter 30 is a storage type NOx.
A catalytic converter (hereinafter, occlusion type NOx catalyst) 32 and a rear stage three-way catalytic converter (hereinafter, rear stage three-way catalyst) 34 are arranged in this order from the upstream side. The storage type NOx catalyst 32 has a lean air-fuel ratio (lean atmosphere).
The NOx component in the exhaust gas is stored at the time of, and when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or a rich air-fuel ratio (predetermined atmosphere) that is richer than the stoichiometric air-fuel ratio, the stored NOx component is released and reduced. It is a catalyst having a characteristic of (NOx purging).

As described above, the NOx storage capacity of the storage type NOx catalyst 32 changes according to the size (trap site amount) of the region (trap site) capable of storing NOx, and the NOx purge is performed. Is increased and the amount of trap sites is increased, the temperature is increased. On the other hand, the lower the catalyst temperature is, such as when the engine 1 is cold-started, the lower the overall temperature tends to be. That is, the storage type NOx catalyst 32 is
Even if the trap site amount is the same, the NOx storage amount is smaller at the cold start than at the warm operation.

The front stage three-way catalyst 22 and the rear stage three-way catalyst 34 are
Copper (Cu), cobalt (C) as an active noble metal on the carrier
o), silver (Ag), platinum (Pt), rhodium (Rh),
It has one of palladium (Pd) and is configured to be able to remove HC, CO and NOx in an active state (fully active state). Further, as shown in FIG.
_In addition to an O ₂ sensor 24 that detects the exhaust air-fuel ratio based on the ₂ concentration, an exhaust temperature sensor 25 that detects the exhaust temperature is provided.

The ECU 60 includes an input / output device and a storage device (R
OM, RAM, non-volatile RAM, etc., central processing unit (C
PU), a timer counter, etc.
With 0, comprehensive control of the exhaust emission control device including the engine 1 is performed. On the input side of the ECU 60, the above-mentioned T
Other than PS16, O ₂ sensor 24, exhaust temperature sensor 25, idle switch (idle SW, exhaust low flow rate detection means)
62, various sensors such as a water temperature sensor (catalyst temperature correlation value detection means, catalyst semi-active state detection means) 64 that detects the cooling water temperature Tw (temperature correlation value) of the engine 1 are connected, and these sensors are connected. The detection information of is input. The idle SW 62 detects an idle operation state of the engine 1, and may detect whether the engine rotation speed Ne is equal to or lower than a predetermined idle rotation speed Ni.

On the other hand, the output side of the ECU 60 is connected with various output devices such as the above-mentioned fuel injection valve 6, ignition coil 8, throttle valve 14 and the like, and detection information from various sensors is connected to these various output devices. The fuel injection amount, the fuel injection timing, the ignition timing, etc., which are calculated on the basis of the above, are output respectively, whereby the fuel injection valve 6 injects an appropriate amount of fuel at an appropriate timing, and the spark plug 4 at an appropriate timing. Ignition is performed, and the throttle valve 14 is opened / closed at appropriate timing.

The operation of the exhaust gas purifying apparatus according to the present invention thus constructed will be described below. Referring to FIG. 2, a control routine of the cold NOx purge control according to the present invention is shown in a flow chart, and referring to FIG. 3, the exhaust air-fuel ratio when the cold NOx purge control is executed. , HC emission amount and NOx emission amount are shown in a time chart, which will be described below with reference to FIG.

First, in step S10, it is determined whether the engine 1 is in the starting mode. What is the start mode?
Immediately after the engine 1 is started (several seconds), the combustion air-fuel ratio is set to the rich air-fuel ratio, which is an operation mode for ensuring the start. When the determination result is true (Yes) and it is determined that the vehicle is currently in the starting mode, nothing is done and the routine exits. On the other hand, when the determination result is false (No) and it is determined that the start mode is exited, the process proceeds to step S12.

In step S12, the cooling water temperature Tw detected by the water temperature sensor 64 is the predetermined temperature T1 (for example, 7
6 ° C.) or higher. Here, the predetermined temperature T1 is set to, for example, a temperature at which a heater unit (not shown) that uses the heat of the cooling water of the engine 1 for heating can sufficiently function. When the determination result of step S12 is false (No) and it is determined that the cooling water temperature Tw is equal to or lower than the predetermined temperature T1, the process proceeds to step S14.

In step S14, it is determined whether the cooling water temperature Tw is within a range (T2 <Tw <T3) (within a predetermined range) from a predetermined temperature T2 (for example, 29 ° C.) to a predetermined temperature T3 (for example, 37 ° C.). Determine whether. That is, here, by determining the cooling water temperature Tw, it is determined whether or not the front stage three-way catalyst 22 is in the initial stage of the semi-active state. Immediately after the cold start of the engine 1, the cooling water temperature Tw does not normally reach the predetermined temperature T2, and the determination result of step S14 is false (No). In this case, the process proceeds to step S16. move on.

In step S16, the cooling water temperature T
It is determined whether w is below a predetermined temperature T2 (Tw≤T2). That is, it is determined whether or not the former three-way catalyst 22 is in the inactive state. Immediately after the cold start of the engine 1, the determination result is true (Yes), and the process proceeds to step S18.
In step S18, the exhaust air-fuel ratio F / B gain ratio G (G = rich air-fuel ratio / lean air-fuel ratio) of the air-fuel ratio feedback (F / B) control by the O ₂ sensor 24 is calculated based on the following equation (G = rich air-fuel ratio / lean air-fuel ratio). Set from 1).

G = Gb × 0.5 (1) Here, the base gain ratio Gb is a preset value and is stoichio (value 14.7) or substantially stoichio (for example, a slightly lean air-fuel ratio). The value is 14.8,
(It may be a little rich air-fuel ratio). That is, when the cooling water temperature Tw is equal to or lower than the predetermined temperature T2, the exhaust air-fuel ratio F / B gain ratio G is made smaller than the base gain ratio Gb based on the above equation (1), and the exhaust air-fuel ratio, that is, the F / B control The control value should be close to the lean air-fuel ratio as a whole.

In this way, the cooling water temperature Tw is the predetermined temperature T2.
When the exhaust air-fuel ratio is leaned toward the lean air-fuel ratio in the following cases,
When the amount of oxygen (O ₂ ) in the exhaust gas increases, the oxidation reaction is promoted and the production of HC and CO is suppressed, and as shown by the solid line in FIG. 3, for example, when the exhaust air-fuel ratio is kept stoichiometric (dashed line) Compared with, the emission amount of HC and CO immediately after the cold start is reduced. Further, since the exhaust temperature is also low at this time, NOx is hardly generated as shown in FIG. 3, and the exhaust purification efficiency is improved as a whole.

When the temperature of the cooling water rises, the determination result of step S14 becomes true (Yes), and it is determined that the cooling water temperature Tw is within the range of the predetermined temperature T2 to the predetermined temperature T3, step S20. Proceed to. In step S20,
It is determined whether the idle SW is on and is currently in the idle operation state. That is, it is determined whether or not the exhaust gas flow rate is a predetermined low flow rate by detecting the idle operation state. If the determination result is true (Yes) and it is determined that the vehicle is currently in the idle operation state, the process proceeds to step S22.

In step S22, the exhaust air-fuel ratio F / B gain ratio G (G = rich air-fuel ratio / lean air-fuel ratio) is set based on the base gain ratio Gb by the following equation (2) (exhaust air-fuel ratio control means). . G = Gb × 1.5 (2) That is, the cooling water temperature Tw changes from the predetermined temperature T2 to the predetermined temperature T3.
When the pre-stage three-way catalyst 22 is in the initial half-active state and the exhaust flow rate is a predetermined low flow rate within the range of, the exhaust air-fuel ratio is calculated based on the above equation (2). The F / B gain ratio G is made larger than the base gain ratio Gb so that the exhaust air-fuel ratio, that is, the control value of the F / B control is closer to the rich air-fuel ratio as a whole. Specifically, since the base gain ratio Gb is a value corresponding to stoichio or substantially stoichio as described above, the exhaust air-fuel ratio becomes stoichio or becomes a rich air-fuel ratio (first exhaust air-fuel ratio) as shown in FIG. To do so.

As described above, when the pre-stage three-way catalyst 22 is in the initial half-active state and the exhaust flow rate is a predetermined low flow rate, the exhaust air-fuel ratio is stoichiometric or rich over a predetermined period corresponding to the initial half-active state. When the air-fuel ratio is set, the NOx purging is efficiently and sufficiently performed in the occlusion type NOx catalyst 32, and the NOx stored in the occlusion type NOx catalyst 32 is released all at once and is reduced and removed.

As a result, the amount of trap sites in the storage-type NOx catalyst 32 is increased, and the storage-type NOx catalyst 32 has an increased NOx storage capacity and can store NOx sufficiently. When the temperature of the cooling water further rises and the cooling water temperature Tw becomes equal to or higher than the predetermined temperature T3 and the determination result of step S14 becomes false (No) again, or the determination result of step S20 is false (No) and idle. If it is determined that the vehicle is not in the operating state, step S1
In step 6, it is determined whether the cooling water temperature Tw is equal to or lower than the predetermined temperature T2.

Since the cooling water temperature Tw is higher than the predetermined temperature T2 this time, the determination result of step S16 is false (No).
Then, the process proceeds to step S24. In step S24, the exhaust air-fuel ratio F / B gain ratio G (G = rich air-fuel ratio /
Set the lean air-fuel ratio) to the base gain ratio Gb (G =
Gb). That is, when the cooling water temperature Tw becomes higher than the predetermined temperature T3 and the pre-stage three-way catalyst 22 has left the initial stage of the semi-active state, or even in the initial stage of the semi-active state, the exhaust flow rate seems to be large. In this case, the NOx purge is ended or not performed, and the exhaust air-fuel ratio F / B gain ratio G is set as the base gain ratio Gb so that the exhaust air-fuel ratio becomes stoichiometric or substantially stoichiometric (for example, slightly lean air-fuel ratio). (Second exhaust air-fuel ratio).

When the exhaust flow rate is large, NO
The reason why the x purging is not performed is to avoid wasteful NOx purging in the state where the catalyst performance is deteriorated at the time of high SV, and to suppress the emission of HC and CO at the time of semi-activation. As described above, when the exhaust air-fuel ratio is stoichiometric or substantially stoichiometric (for example, a slightly lean air-fuel ratio), warming up of the engine 1 in the cold state is promoted and the rise of the cooling water temperature is accelerated, so that the heater unit. The heater performance is secured from the cold state.

Even if the cooling water temperature Tw becomes higher than the predetermined temperature T3, NOx increases as the exhaust gas temperature rises. However, at this stage, the pre-stage three-way catalyst 22 is still in the semi-active state, and the NOx concerned is still present. Can not be purified enough. However, in the present invention, as described above, the occlusion type NO
Since the x-catalyst 32 is in a state capable of sufficiently storing NOx by performing NOx purging just before it is necessary to store NOx, even if the pre-stage three-way catalyst 22 is still in the semi-active state, NOx will be emitted. The occlusion-type NOx catalyst 32 is satisfactorily occluded, and the NOx emission in the cold state is preferably prevented. In other words, as shown by the solid line in FIG. 3, when the NOx purge is performed immediately before the NOx storage is required, the front three-way catalyst 22 is in a half-active state as compared with the case where the NOx purge is not performed (dashed line). It is possible to significantly reduce the NOx emission amount. As a result, the exhaust gas purification efficiency in the cold state can be improved.

If NOx purging of the NOx storage catalyst 32 is performed immediately before NOx needs to be stored in this way, the NOx purge is always performed during the temperature operation to secure an excessive trap site amount. You do n’t have to
The period during which the combustion air-fuel ratio is changed to stoichiometric or rich air-fuel ratio for NOx purging can be significantly reduced.
As a result, it is possible to minimize the implementation of the NOx purge and prevent the fuel consumption from being deteriorated.

After the pre-stage three-way catalyst 22 leaves the semi-active state and becomes active (completely active state), the pre-stage three-way catalyst 2
In this case, the emission amounts of HC, CO, and NOx are sufficiently suppressed, as shown in FIG. Then, the cooling water temperature further rises, and the determination result of step S12 is true (Yes),
When it is determined that the cooling water temperature Tw has become higher than the predetermined temperature T1, the process proceeds to step S30 and normal operation control is performed. That is, after the warm-up of the engine 1 is completed, the normal operation in the warm state, for example, the lean air-fuel ratio operation is performed.

Although the description is finished above, the embodiment of the present invention is not limited to the above embodiment. For example, in the above-described embodiment, whether or not the pre-stage three-way catalyst 22 is in the initial half-active state is detected based on the cooling water temperature information Tw from the water temperature sensor 64.
The temperature T of the three-way catalyst 22 of the front stage estimated based on the output of FIG.
You may make it detect from tcat (temperature correlation value),
If a temperature sensor is provided in the front-stage three-way catalyst 22, the front-stage three-way catalyst 2
The temperature may be directly detected from the temperature Ttcat (temperature correlation value) of 2 or a temperature sensor may be provided in the occlusion type NOx catalyst 32 to detect from the temperature Tncat (temperature correlation value) of the occlusion type NOx catalyst 32. Exhaust temperature sensor 2
The temperature may be detected from the temperature Tncat (temperature correlation value) of the storage type NOx catalyst 32 estimated based on the output of No. 5, or may be estimated from the elapsed time tst (temperature correlation value) after the start of the engine 1. Good. In this case, instead of the determination in step S14, the determination condition is, for example, 300 ° C.
<Ttcat or Tncat <400 ° C, 30 seconds <tst <5
0 seconds. The same applies to step S16. However, it is preferable that the discriminating threshold value is appropriately set to an optimum value according to the system.

Further, since there is a correlation between the NOx purification performance of the pre-stage three-way catalyst 22 and the temperature of the pre-stage three-way catalyst 22, the amount of NOx upstream of the occlusion type NOx catalyst 32 and the pre-stage three-way catalyst 22. Therefore, for example, a NOx sensor is provided upstream of the storage-type NOx catalyst 32 to determine whether or not the front three-way catalyst 22 is in the initial half-active state.
It can also be detected from the amount Qnox (temperature correlation value) of NOx flowing into the x catalyst 32. In this case, instead of the determination in step S14, the determination condition is, for example, 10 ppm <Q
Set to nox. The same applies to step S16. However, it is preferable that the discriminating threshold value is appropriately set to an optimum value according to the system.

The cooling water temperature information T from the water temperature sensor 64 indicates whether the front-stage three-way catalyst 22 is in the initial half-active state.
w, temperature information Ttcat of the front-stage three-way catalyst 22, temperature information Tncat of the occlusion type NOx catalyst 32, elapsed time information tst after startup, Nst
Any two or more of the Ox amount information Qnox may be combined and detected. Further, in the above-described embodiment, the timing for canceling the enrichment of the exhaust air-fuel ratio is determined based on the temperature correlation value of the front stage three-way catalyst 22, but the enrichment is canceled when the enrichment is executed for a predetermined period. You may do it.

Further, in the above embodiment, the front-stage three-way catalyst 2 is used.
When 2 is in the inactive state, the exhaust air-fuel ratio is set to the lean air-fuel ratio (step S18), but the effect of the present invention can be obtained without necessarily setting the lean air-fuel ratio. Further, in the above-described embodiment, the exhaust air-fuel ratio is changed by the air-fuel ratio feedback (F / B) control by the O ₂ sensor 24, but the present invention is not limited to this, and any control can be adopted as long as the exhaust air-fuel ratio can be changed. Good.

Further, in the above embodiment, the idle SW6
Although the exhaust flow rate is detected to be a predetermined low flow rate based on the information of No. 2, it can be obtained from the intake air amount information from an air flow sensor (not shown) (exhaust low flow rate detection means). Further, in the above embodiment, the engine 1
As the cylinder injection type spark ignition type gasoline engine, the engine 1 may be an intake pipe injection type gasoline engine or a diesel engine.

[0050]

As described in detail above, according to the exhaust gas purifying apparatus for an internal combustion engine according to claim 1 of the present invention, the catalyst is such that the internal combustion engine is in a cold state and the three-way catalytic converter is not yet functioning. At low temperatures, the storage type NOx catalytic converter has N
Ox is occluded, but when the temperature correlation value of the three-way catalytic converter is within a predetermined range (initial half-active state) and the exhaust flow rate is a predetermined low flow rate, the exhaust air-fuel ratio in the exhaust passage becomes three. When the temperature correlation value of the original catalytic converter exceeds a predetermined range or when the flow rate of exhaust gas exceeds a predetermined low flow rate, the first air-fuel ratio closer to the rich air-fuel ratio than the second exhaust air-fuel ratio
Since the exhaust air-fuel ratio is controlled, NOx stored in the NOx catalytic converter can be satisfactorily purged and a sufficient trap site amount can be secured. Even if the NOx catalytic converter is at a low temperature and the NOx storage capacity is low, NOx storage capacity is low. It becomes possible to store NOx sufficiently in the catalytic converter.

As a result, excessive N
It is possible to prevent NOx from being discharged satisfactorily at a low temperature of the catalyst, that is, in a cold state, and to improve exhaust gas purification efficiency without deteriorating fuel efficiency by performing Ox purging. According to the exhaust gas purifying apparatus for an internal combustion engine of claim 2, the temperature of the three-way catalytic converter, the temperature of the occlusion type NOx catalytic converter,
The temperature correlation value of the three-way catalytic converter can be easily detected based on the cooling water temperature of the internal combustion engine, the elapsed time after the internal combustion engine has started, or the amount of NOx flowing into the occlusion type NOx catalytic converter.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 3, when the temperature of the catalyst is low such that the internal combustion engine is in a cold state and the three-way catalytic converter is not yet functioning, the storage type NO
NOx is stored in the x-catalytic converter, but the exhaust air-fuel ratio in the exhaust passage is maintained for a predetermined period (initial half-active state) after the three-way catalytic converter is in the semi-active state and the exhaust flow rate is the predetermined low flow rate. Is the first exhaust air-fuel ratio closer to the rich air-fuel ratio than the second exhaust air-fuel ratio when the temperature correlation value of the three-way catalytic converter exceeds a predetermined range or when the flow rate of exhaust exceeds a predetermined low flow rate. Therefore, the NOx stored in the NOx catalytic converter can be satisfactorily purged and a sufficient trap site amount can be secured. Even if the NOx catalytic converter has a low temperature and has a low NOx storage capacity,
It becomes possible to store NOx sufficiently in the Ox catalytic converter.

As a result, excessive N
It is possible to prevent NOx from being discharged satisfactorily at a low temperature of the catalyst, that is, in a cold state, and to improve exhaust gas purification efficiency without deteriorating fuel efficiency by performing Ox purging. According to the exhaust gas purifying apparatus for an internal combustion engine of claim 4, the temperature of the three-way catalytic converter, the temperature of the occlusion type NOx catalytic converter,
The semi-active state of the three-way catalytic converter can be easily detected based on the cooling water temperature of the internal combustion engine, the elapsed time after the internal combustion engine has started, or the amount of NOx flowing into the NOx storage converter.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 5, the exhaust air-fuel ratio is theoretical when the three-way catalytic converter is in a completely active state or when the flow rate of exhaust gas exceeds a predetermined low flow rate. Since the air-fuel ratio or the approximate stoichiometric air-fuel ratio is used, the combustion air-fuel ratio becomes the stoichiometric air-fuel ratio or the approximate stoichiometric air-fuel ratio, the warm-up of the internal combustion engine is promoted, the cooling water temperature rises, and the heater performance is secured from the cold state. can do.

Further, according to the exhaust purification system of the internal combustion engine of claim 6, when the three-way catalytic converter is in the initial state of the semi-active state, the exhaust air-fuel ratio is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio. Can be efficiently and sufficiently performed. Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 7, when the three-way catalytic converter is inactive before the semi-active state, the exhaust air-fuel ratio is set to the lean air-fuel ratio and sufficient oxygen is supplied into the exhaust gas. In addition to producing almost no NOx at low temperatures, HC and CO emissions can be suppressed well.

[Brief description of drawings]

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

FIG. 2 is a flow chart showing a control routine of NOx purge control during cold state according to the present invention.

FIG. 3 is a time chart showing changes over time in the exhaust air-fuel ratio, the HC emission amount, and the NOx emission amount when the cold NOx purge control is executed.

[Explanation of symbols]

1 Engine Body 6 Fuel Injection Valve 12 Exhaust Manifold 20 Exhaust Pipe 22 Front Stage Three-Way Catalyst (FCC) 24 O ₂ Sensor 30 Underfloor Catalyst Unit (UCC) 32 Storage NOx Catalyst 34 Rear Stage Three-Way Catalyst 60 ECU (Electronic Control Unit) 62 Idle SW 64 water temperature sensor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/28 301 F01N 3/28 301C 301E F02D 41/14 310B F02D 41/14 310 B01D 53/36 103B 101B F-term (reference) 3G091 AA02 AA12 AA17 AA24 AA28 AB03 AB06 BA03 BA14 BA15 BA19 CB02 CB03 CB05 CB07 CB08 DA01 DA02 DC01 EA01 EA07 EA16 EA17 EA26 EA30 EA34 FA02 FA04 FA12 FA13 FB02 FB10 FB11 FB12 FC07 GB01W GB05W GB06W GB07W HA08 HA09 HA10 HA12 HA36 HA37 3G301 HA01 HA04 HA06 HA15 HA16 JA02 JA25 JA26 JB09 KA02 KA05 LA03 LB04 MA01 MA11 MA26 NA01 NA06 NA07 NA08 NC04 ND01 NE01 NE06 NE13 NE14 NE15 PA01B PA01Z PA11B PA11Z PD02B PD02Z PD11B PD11Z PD12B PD12Z PE02B PE02Z PE03B PE03Z PE08B PE08Z 4D048 AA06 AA13 AA18 AB05 BA30X BA31X BA33X BA34X BA35X BA37X CC32 CC46 DA01 DA02 DA03 DA05 DA08 DA13 DA20 EA04

Claims (7)

[Claims] 1. A three-way catalytic converter provided in an exhaust passage of an internal combustion engine, and a three-way catalytic converter provided in the exhaust passage in series with the three-way catalytic converter to occlude and occlude NOx in exhaust under a lean atmosphere. A storage-type NOx catalytic converter that releases NOx in a predetermined atmosphere, a catalyst temperature correlation value detection unit that detects a temperature correlation value of the three-way catalytic converter, and a flow rate of exhaust gas that flows through the exhaust passage is a predetermined low flow rate. That the temperature correlation value of the three-way catalytic converter is detected to be within a predetermined range by the exhaust gas low flow rate detection means and the catalyst low temperature flow rate detection means, and the exhaust gas low flow rate detection means detects the predetermined low value. When the flow rate is detected, the exhaust air-fuel ratio in the exhaust passage is controlled when the temperature correlation value of the three-way catalytic converter exceeds the predetermined range or when the exhaust flow rate is Exhaust gas purification of an internal combustion engine, comprising: exhaust air-fuel ratio control means for controlling to a first exhaust air-fuel ratio closer to a rich air-fuel ratio than a second exhaust air-fuel ratio when a predetermined low flow rate is exceeded. apparatus. 2. The catalyst temperature correlation value detecting means, the temperature of the three-way catalytic converter, the temperature of the occlusion type NOx catalytic converter, the cooling water temperature of the internal combustion engine, the elapsed time after the start of the internal combustion engine and the occlusion type NOx. The exhaust emission control device for an internal combustion engine according to claim 1, wherein any one of the amounts of NOx flowing into the catalytic converter is detected as a temperature correlation value of the three-way catalytic converter. 3. A three-way catalytic converter provided in an exhaust passage of an internal combustion engine, and a three-way catalytic converter provided in the exhaust passage in series with the three-way catalytic converter for storing NOx in the exhaust in a lean atmosphere and storing the NOx. A storage-type NOx catalytic converter that releases NOx in a predetermined atmosphere, a catalyst semi-active state detection means that detects that the three-way catalytic converter is in a semi-active state, and a flow rate of exhaust gas that flows through the exhaust passage is a predetermined low level. A low exhaust flow rate detection means for detecting that the flow rate is a flow rate, and the catalyst semi-active state detection means detects that the three-way catalytic converter is in a semi-active state, and the low exhaust flow rate detection means provides the predetermined low flow rate. Is detected, the exhaust air-fuel ratio in the exhaust passage is set to the fully active state for a predetermined period corresponding to the initial state of the semi-active state. Or an exhaust air-fuel ratio control means for controlling to a first exhaust air-fuel ratio closer to the rich air-fuel ratio than the second exhaust air-fuel ratio when the flow rate of the exhaust gas exceeds the predetermined low flow rate. An exhaust emission control device for an internal combustion engine. 4. The catalyst semi-active state detecting means includes a temperature of the three-way catalytic converter, a temperature of the occlusion type NOx catalytic converter, a cooling water temperature of an internal combustion engine, an elapsed time after starting the internal combustion engine and the occlusion type NOx. The exhaust emission control device for an internal combustion engine according to claim 3, wherein the half-active state of the three-way catalytic converter is detected based on any one of the amounts of NOx flowing into the catalytic converter. 5. The first exhaust air-fuel ratio is a stoichiometric air-fuel ratio or a substantially stoichiometric air-fuel ratio.
9. An exhaust gas purification device for an internal combustion engine according to any one of 1. 6. The first exhaust air-fuel ratio is a stoichiometric air-fuel ratio or a rich air-fuel ratio.
9. An exhaust gas purification device for an internal combustion engine according to any one of 1. 7. The exhaust air-fuel ratio control means controls the exhaust air-fuel ratio in the exhaust passage to a lean air-fuel ratio before controlling to the first exhaust air-fuel ratio.
7. An exhaust gas purification device for an internal combustion engine according to any one of items 6 to 6.