JP4258639B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to a technique for improving the exhaust gas purification performance of a catalytic converter by controlling the combustion air-fuel ratio of the internal combustion engine.

A three-way catalytic converter for purifying exhaust gas using a noble metal such as platinum (Pt) has an oxidant storage function that occludes or adsorbs (hereinafter simply “occludes”) an oxidant such as oxygen (O ₂ ). When the exhaust air-fuel ratio is a lean air-fuel ratio (oxidizing atmosphere), O ₂ is occluded to suppress the generation of NOx, while when the exhaust air-fuel ratio is a rich air-fuel ratio (reducing atmosphere), the occluded O _{2 is} stored. It is possible to promote the oxidation of HC and CO by releasing (supplying) the exhaust gas, thereby realizing the NOx reduction reaction and the HC and CO oxidation reaction in a wide air-fuel ratio range, thereby improving the exhaust purification performance. .

  Recently, a catalytic converter having a reducing agent storage function for storing a reducing agent such as HC as well as an oxidizing agent storage function has been developed. In the catalytic converter, when the exhaust air-fuel ratio is a rich air-fuel ratio. Occludes the reducing agent to suppress the generation of HC, etc., while when the exhaust air-fuel ratio is a lean air-fuel ratio, the stored HC, etc. is released (supplied) to promote the oxidation of NOx, thereby improving the exhaust purification performance. Can be further improved.

For this reason, for example, the air-fuel ratio (combustion air-fuel ratio) in the combustion chamber of the internal combustion engine is switched between a lean air-fuel ratio and a rich air-fuel ratio at regular intervals with a predetermined center air-fuel ratio (for example, stoichiometric) in between. Automobiles have been developed that improve the exhaust gas purification performance of catalytic converters by modulating (perturbation) the fuel ratio into a lean air-fuel ratio and a rich air-fuel ratio, and repeatedly storing and releasing oxidants and reductants (Patent Literature) 1 etc.).
Japanese Patent Laid-Open No. 10-159629

  By the way, for example, due to variations in intake air amount sensors, fuel injection valves, etc., fuel supply amount error in the cylinder due to fuel adhesion, fuel amount calculation error, etc., the rich side piece amplitude, lean side piece amplitude or rich side The actual exhaust air-fuel ratio is biased toward the rich air-fuel ratio side or lean air-fuel ratio side as a whole with respect to the predetermined center air-fuel ratio, and either the rich air-fuel ratio side or the lean air-fuel ratio side of the exhaust air-fuel ratio changes. On the other hand, the modulation amplitude of one of them may be reduced.

On the other hand, depending on the exhaust system volume between the internal combustion engine and the catalytic converter installed in the exhaust system, the modulation of the exhaust air / fuel ratio (hereinafter referred to as exhaust air / fuel ratio modulation) tends to attenuate with respect to the modulation of the combustion air / fuel ratio. is there.
Therefore, when the modulation amplitude of either the rich air-fuel ratio side or the lean air-fuel ratio side of the exhaust air-fuel ratio becomes small as described above, the exhaust air-fuel ratio modulation is further attenuated on the air-fuel ratio side where the modulation amplitude is reduced, There arises a problem that the oxidant and the reductant cannot be fully occluded and released.

As described above, when the oxidant and the reducing agent cannot be sufficiently stored and released, the balance between the storage and release of the oxidant and the reducing agent is lost, and the exhaust gas purification performance of the catalytic converter is improved. It is not preferable because it cannot be done.
The present invention has been made to solve such problems, and an object of the present invention is to provide exhaust air that accompanies a bias of the exhaust air / fuel ratio at the time of air / fuel ratio modulation toward the rich air / fuel ratio side or lean air / fuel ratio side. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that suppresses the attenuation of the fuel ratio modulation and optimizes the exhaust gas purification performance in the catalytic converter.

In order to achieve the above-mentioned object, in the exhaust gas purification apparatus for an internal combustion engine according to claim 1, a rich air can be applied across a predetermined center air-fuel ratio between the catalytic converter provided in the exhaust passage of the internal combustion engine and the combustion air-fuel ratio of the internal combustion engine. Air-fuel ratio modulation that periodically modulates the air-fuel ratio of the exhaust gas flowing into the catalytic converter into a rich air-fuel ratio side and a lean air-fuel ratio side periodically with a predetermined period by modulating the fuel-fuel ratio side and the lean air-fuel ratio side periodically And an exhaust air / fuel ratio detecting means for detecting the air / fuel ratio of the exhaust gas upstream of the catalytic converter , wherein the air / fuel ratio modulating means modulates the combustion air / fuel ratio from the rich air / fuel ratio side to the lean air / fuel ratio side. to time, discontinue modulating exhaust air-fuel ratio to the lean air-fuel ratio side to the rich air-fuel ratio when the exhaust air-fuel ratio detected by the exhaust air-fuel ratio detection means is not in the rich air-fuel ratio Li Holds the modulation in Chi air side is characterized by increasing the modulation amplitude of the rich air-fuel ratio side.

In the exhaust gas purification apparatus for an internal combustion engine according to claim 2 , the rich air-fuel ratio side and the lean air-fuel ratio side of the catalytic converter provided in the exhaust passage of the internal combustion engine and the combustion air-fuel ratio of the internal combustion engine straddling a predetermined center air-fuel ratio The air-fuel ratio modulation means for periodically modulating the air-fuel ratio of the exhaust gas flowing into the catalytic converter into a rich air-fuel ratio side and a lean air-fuel ratio side at a predetermined period by periodically modulating the air-fuel ratio of the catalytic converter, Exhaust air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust upstream of the exhaust, and the air-fuel ratio modulation means adjusts the combustion air-fuel ratio from the rich air-fuel ratio side to the lean air-fuel ratio side when the exhaust air-fuel ratio is modulated holding a modulation at a rich air-fuel ratio side exhaust air-fuel ratio detected by the detection means to stop the modulation to the lean air-fuel ratio side to the exhaust air-fuel ratio becomes a rich air-fuel ratio when not become rich air-fuel ratio It is characterized by decreasing the modulation amplitude of the lean air-fuel ratio side immediately after the discontinuation while.

In the exhaust gas purification apparatus for an internal combustion engine according to claim 3 , the rich air-fuel ratio side and the lean air-fuel ratio side of the catalytic converter provided in the exhaust passage of the internal combustion engine and the combustion air-fuel ratio of the internal combustion engine straddling a predetermined center air-fuel ratio The air-fuel ratio modulation means for periodically modulating the air-fuel ratio of the exhaust gas flowing into the catalytic converter into a rich air-fuel ratio side and a lean air-fuel ratio side at a predetermined period by periodically modulating the air-fuel ratio of the catalytic converter, Exhaust air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas upstream of the exhaust gas, and the air-fuel ratio modulation means adjusts the combustion air-fuel ratio from the lean air-fuel ratio side to the rich air-fuel ratio side when the exhaust air-fuel ratio is modulated holding a modulation at a lean air-fuel ratio side exhaust air-fuel ratio detected by the detection means to stop the modulation to the rich air-fuel ratio side to the exhaust air-fuel ratio becomes a lean air-fuel ratio when it is not already lean air-fuel ratio It is characterized by increasing the modulation amplitude of the lean air-fuel ratio side as well as.

Further, in the exhaust purification system of an internal combustion engine according to claim 4, a catalytic converter provided in an exhaust passage of an internal combustion engine, a rich air-fuel ratio side and a lean air-fuel ratio side combustion air-fuel ratio of the internal combustion engine across a predetermined center air-fuel ratio The air-fuel ratio modulation means for periodically modulating the air-fuel ratio of the exhaust gas flowing into the catalytic converter into a rich air-fuel ratio side and a lean air-fuel ratio side at a predetermined period by periodically modulating the air-fuel ratio of the catalytic converter, Exhaust air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas upstream of the exhaust gas, and the air-fuel ratio modulation means adjusts the combustion air-fuel ratio from the lean air-fuel ratio side to the rich air-fuel ratio side when the exhaust air-fuel ratio is modulated holding a modulation at a lean air-fuel ratio side exhaust air-fuel ratio detected by the detection means to stop the modulation to the rich air-fuel ratio side to the exhaust air-fuel ratio becomes a lean air-fuel ratio when it is not already lean air-fuel ratio It is characterized by decreasing the modulation amplitude of the rich air-fuel ratio side immediately after the discontinuation while.

According to the exhaust gas purification apparatus for an internal combustion engine of claim 1, when the combustion air-fuel ratio is modulated from the rich air-fuel ratio side to the lean air-fuel ratio side, the exhaust air-fuel ratio on the exhaust upstream side of the catalytic converter is not the rich air-fuel ratio. Sometimes, the modulation to the lean air-fuel ratio side is stopped until the exhaust air-fuel ratio becomes the rich air-fuel ratio, and the modulation on the rich air-fuel ratio side is held, so that the deviation of the exhaust A / F to the lean A / F side occurs. Even if it corrects combustion A / F suitably, the said bias | bias can be suppressed and by extension, the attenuation | damping of exhaust A / F modulation accompanying the said bias | bias can be suppressed. Thereby, optimization of the exhaust gas purification performance in the catalytic converter can be achieved.

Furthermore, when modulating the combustion air-fuel ratio from the rich air-fuel ratio side to the lean air-fuel ratio side, the modulation amplitude of the rich air-fuel ratio side when the exhaust air-fuel ratio of the exhaust gas upstream of the catalytic converter is not in the rich air-fuel ratio Therefore, even if the exhaust A / F leans to the lean A / F side, the combustion A / F is positively corrected, and the attenuation of the exhaust A / F modulation caused by the bias is more quickly suppressed. can do. Thereby, further optimization of the exhaust gas purification performance in the catalytic converter can be achieved.

Further, according to the exhaust purification system of an internal combustion engine according to claim 2, when modulating the combustion air-fuel ratio from the rich air-fuel ratio side to the lean air-fuel ratio side, the exhaust gas air-fuel ratio of the exhaust gas upstream of the catalytic converter in a rich air-fuel ratio If not, the modulation to the lean air-fuel ratio side is stopped until the exhaust air-fuel ratio becomes the rich air-fuel ratio, the modulation on the rich air-fuel ratio side is held, and the modulation amplitude on the lean air-fuel ratio side immediately after the cancellation is held Therefore, even if a deviation of the exhaust A / F to the lean A / F side occurs, the combustion A / F is positively corrected, and the attenuation of the exhaust A / F modulation caused by the deviation is more promptly corrected. Can be suppressed. Thereby, the exhaust gas purification performance in the catalytic converter can be further optimized.

According to the exhaust gas purification apparatus for an internal combustion engine according to claim 3 , when the combustion air-fuel ratio is modulated from the lean air-fuel ratio side to the rich air-fuel ratio side, the exhaust air-fuel ratio on the exhaust upstream side of the catalytic converter becomes the lean air-fuel ratio. If not, the modulation to the rich air-fuel ratio side is stopped until the exhaust air-fuel ratio becomes the lean air-fuel ratio, and the modulation on the lean air-fuel ratio side is maintained, so that the deviation of the exhaust A / F to the rich A / F side is maintained. Even if the combustion A / F occurs, the combustion A / F can be corrected as appropriate to suppress the bias, and thus the exhaust A / F modulation attenuation associated with the bias can be suppressed. Thereby, optimization of the exhaust gas purification performance in the catalytic converter can be achieved.

Furthermore, when modulating the combustion air-fuel ratio from the lean air-fuel ratio side to the rich air-fuel ratio side, the modulation amplitude of the lean air-fuel ratio side when the exhaust air-fuel ratio of the exhaust gas upstream of the catalytic converter is not in the lean air-fuel ratio Because it increases, even if the exhaust A / F is biased toward the rich A / F side, the combustion A / F is positively corrected, and the attenuation of the exhaust A / F modulation caused by the bias is suppressed more quickly. can do. Thereby, further optimization of the exhaust gas purification performance in the catalytic converter can be achieved.

Further, according to the exhaust purification system of an internal combustion engine according to claim 4, when modulating the combustion air-fuel ratio from the lean air-fuel ratio side to the rich air-fuel ratio side, the exhaust gas air-fuel ratio of the exhaust gas upstream of the catalytic converter in a lean air-fuel ratio If not, the modulation to the rich air-fuel ratio side is stopped until the exhaust air-fuel ratio becomes the lean air-fuel ratio, the modulation on the lean air-fuel ratio side is held, and the modulation amplitude on the rich air-fuel ratio side immediately after the cancellation is held Therefore, even if the exhaust A / F is biased toward the rich A / F side, the combustion A / F is positively corrected, and the exhaust A / F modulation accompanying the bias is more quickly attenuated. Can be suppressed. Thereby, the exhaust gas purification performance in the catalytic converter can be further optimized.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention mounted on a vehicle. Hereinafter, the configuration of the exhaust gas purification apparatus will be described.
As shown in the figure, an intake pipe injection (MPI) gasoline engine is adopted as an engine body (hereinafter simply referred to as an engine) 1 that is an internal combustion engine.

A spark plug 4 is attached to each cylinder of the cylinder head 2 of the engine 1, and an ignition coil 8 that outputs a high voltage is connected to the spark plug 4.
In the cylinder head 2, an intake port is formed for each cylinder, and one end of an intake manifold 10 is connected so as to communicate with each intake port. An electromagnetic fuel injection valve 6 is attached to the intake manifold 10, and a fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. .

  An electromagnetic throttle valve 14 for adjusting the amount of intake air is provided upstream of the fuel injection valve 6 of the intake manifold 10 and a throttle position sensor (for detecting the valve opening θth of the throttle valve 14). TPS) 16 is provided. Further, an air flow sensor 18 for measuring the intake air amount is interposed upstream of the throttle valve 14. A Karman vortex airflow sensor is used as the airflow sensor 18.

The cylinder head 2 has an exhaust port for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port.
Since the MPI engine is a known one, the detailed description of its configuration is omitted.
An exhaust pipe 20 is connected to the other end of the exhaust manifold 12, and a three-way catalyst (catalytic converter) 30 is interposed in the exhaust pipe 20 as an exhaust purification catalyst device.

The three-way catalyst 30 has copper (Cu), cobalt (Co), silver (Ag), platinum (Pt), rhodium (Rh), or palladium (Pd) as an active noble metal on a support. In addition to the case where an oxygen storage material such as cerium (Ce) or zirconia (Zr) is included, the active noble metal has an oxygen storage function (O ₂ storage function, oxidant storage function) even when the oxygen storage material is not included. Have. Therefore, when the three-way catalyst 30 occludes oxygen (O ₂ ) in an oxidizing atmosphere in which the exhaust air / fuel ratio (exhaust A / F) is a lean air / fuel ratio (lean A / F), the exhaust A / F becomes a rich air / fuel ratio. It retains its O ₂ until the (rich a / F) becomes a reducing atmosphere as a storage O _2, by the release of the storage O ₂ (supplied), also HC (hydrocarbon) in a reducing atmosphere state and CO (carbon monoxide ) Can be removed by oxidation. That is, the three-way catalyst 30 not only can purify HC and CO in an oxidizing atmosphere, but also suppresses the generation of NOx to some extent, and not only purifies NOx in the reducing atmosphere but also stores HC and CO by O ₂ stored. Can be purified to some extent.

Further, an O ₂ sensor (exhaust air / fuel ratio detecting means) that detects and determines whether the exhaust A / F is rich A / F or lean A / F immediately upstream of the three-way catalyst 30 of the exhaust pipe 20. ) 22 is provided.
The ECU (electronic control unit) 40 includes an input / output device, a storage device (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like. Overall control of the exhaust emission control device is performed.

Various sensors such as a crank angle sensor 42 for detecting the crank angle of the engine 1 are connected to the input side of the ECU 40 in addition to the TPS 16, the air flow sensor 18 and the O ₂ sensor 22 described above. Detection information is input. The engine speed Ne is calculated based on information from the crank angle sensor 42.
On the other hand, various output devices such as the fuel injection valve 6, the ignition coil 8, and the throttle valve 14 are connected to the output side of the ECU 40. These various output devices are operated based on detection information from various sensors. The fuel injection amount, fuel injection timing, ignition timing, etc., are output. Specifically, the air-fuel ratio is set to an appropriate target air-fuel ratio (target A / F) based on detection information from various sensors, and an amount of fuel corresponding to the target A / F is injected at the appropriate timing. The throttle valve 14 is adjusted to an appropriate opening, and spark ignition is performed at an appropriate timing by the spark plug 4.

More specifically, in the exhaust purification device, since the three-way catalyst 30 has the O ₂ storage function, the ECU 40 sets the air-fuel ratio during normal operation in order to fully demonstrate the ability of the three-way catalyst 30. Forcible modulation control is performed in which the center A / F (predetermined center air-fuel ratio, for example, stoichiometric) is periodically and forcibly alternately swung between the rich A / F and the lean A / F. That is, the air-fuel ratio (combustion A / F) in the combustion chamber is set to a predetermined amplitude (predetermined rich side piece amplitude dr and predetermined lean side piece amplitude dl), a predetermined period (predetermined rich side period tr and predetermined lean side). Modulation control is performed between a predetermined rich A / F and a predetermined lean A / F with a period tl), and the exhaust A / F is forcibly modulated between the rich A / F and the lean A / F (empty). Fuel ratio modulation means).

Here, the center A / F is, for example, stoichiometric, but other operating conditions (engine speed, volume efficiency, exhaust flow rate, intake air flow rate, exhaust temperature, catalyst temperature, elapsed time after start-up) are used for the center A / F. The cooling water temperature, the hydraulic oil temperature, the air-fuel ratio fluctuation amount, etc.) may be changed.
As a result, in an oxidizing atmosphere in which the exhaust A / F is lean A / F, HC and CO are well purified and O ₂ is occluded by the O ₂ storage function of the three-way catalyst 30 to suppress generation of NOx to some extent. In a reducing atmosphere where the exhaust A / F is rich A / F, NOx is purified well and HC and CO are continuously purified to some extent by the stored storage O ₂ , and the exhaust of the three-way catalyst 30 The purification performance is improved.

  By the way, as described above, the actual exhaust A / F is center A / F due to variations in the air flow sensor 18, the fuel injection valve 6, etc., the fuel supply amount error in the cylinder due to fuel adhesion, the fuel amount calculation error, and the like. On the air / fuel ratio side where the modulation amplitude of the exhaust A / F has become smaller and the exhaust A / F modulation amplitude has become smaller as a whole, the exhaust gas is exhausted by the exhaust system volume between the engine 1 and the three-way catalyst 30. The modulation of A / F (hereinafter referred to as exhaust A / F modulation) is further attenuated, and the exhaust purification performance of the three-way catalyst 30 may not be improved.

Therefore, in the exhaust emission control device according to the present invention, in the air-fuel ratio modulation control, attenuation of the exhaust air-fuel ratio modulation accompanying such a bias of the exhaust A / F toward the rich A / F side or lean A / F side is suppressed. Hereinafter, air-fuel ratio modulation control according to the present invention will be described.
Referring to FIG. 2, a control routine for air-fuel ratio modulation control according to the present invention is shown in a flowchart, and with reference to FIG. 3, each modulation of combustion A / F and exhaust A / F by the air-fuel ratio modulation control is shown. The waveform is shown, and will be described along the flowchart with reference to FIG.

In step S10, it is determined whether or not the current air-fuel ratio modulation mode is in effect, that is, whether or not modulation control is being performed. If the determination result is true (Yes) and it is determined that modulation control is being performed, the process proceeds to step S12.
In step S12, first, it is determined whether or not the reducing agent total amount (for example, HC, CO amount) in the modulation to the rich A / F side is smaller than a preset target reducing agent total amount.

  In the air-fuel ratio modulation control, when the total amount of reducing agent reaches the target total amount of reducing agent during modulation on the rich A / F side, switching to modulation on the lean A / F side is performed, and oxidation is performed during modulation on the lean A / F side. When the total amount of the agent reaches the target total amount of oxidant, the modulation is changed to the modulation to the rich A / F side, and the predetermined modulation period (the predetermined rich side period tr and the predetermined lean side period tl) is set. In this case, it is determined here whether or not the rich side period is within a range of a predetermined rich side period tr corresponding to the target reducing agent total amount.

Specifically, for example, the determination is made based on the following equation (1).
∫ (modulation amplitude (t) x catalyst inflow exhaust flow rate (t)) dt
<∫ (basic modulation amplitude (t) x basic catalyst inflow and exhaust flow rate) dt (1)
Here, the modulation amplitude (t) is a command value from the ECU 40, and the catalyst inflow / exhaust flow rate (t) is a value estimated based on information from the airflow sensor 18, for example. Further, the basic modulation amplitude (t) is, for example, the predetermined rich side piece amplitude dr, and the basic catalyst inflow exhaust flow rate corresponds to the predetermined rich side period tr and corresponds to the engine exhaust amount and the engine rotational speed Ne. The value is determined accordingly. If detectable, the reducing agent concentration may be used instead of the modulation amplitude (t) and the basic modulation amplitude (t).

When the determination result of step S12 is true (Yes) and it is determined that the total amount of reducing agent is smaller than the target total amount of reducing agent, the process proceeds to step S14 and modulation to the rich A / F side (rich modulation) is continued. At the same time, the reducing agent total amount is updated in step S16.
If the determination result in step S12 is false (No) and it is determined that the total amount of reducing agent is equal to or greater than the target total amount of reducing agent, the process proceeds to step S18.

In step S18, it is determined whether the exhaust A / F detected and determined by the O ₂ sensor 22 is rich A / F or lean A / F. If it is determined that the exhaust A / F is lean A / F, the process proceeds to step S20 to perform enrichment correction.
That is, if the exhaust A / F fluctuates in accordance with the modulation of the combustion A / F as shown by the broken line in FIG. 3, the actual exhaust A / F is centered as described above. In the case where the A / F as a whole is biased toward the rich A / F side or lean A / F side, as shown by the solid line in FIG. Even when the rich side period tr elapses, the exhaust A / F may remain lean A / F and does not become rich A / F. In such a case, the exhaust A / F moves to the lean A / F side. Judgment is biased, and rich correction is performed. Specifically, as shown in FIG. 3, the modulation to the lean A / F side is stopped, and the combustion A / F is held at a predetermined rich A / F as it is.

If it is determined in step S18 that the exhaust A / F has become rich A / F, the enrichment correction is terminated, modulation to the lean A / F side is permitted, and the process proceeds to step S22. Thus, the predetermined rich side period tr is extended by a period of Δtr as shown in FIG.
In step S22, in the same manner as in step S12, this time, whether or not the total amount of oxidant (for example, O ₂ amount) in the modulation to the lean A / F side is smaller than a preset target oxidant total amount, in other words, Then, whether or not the lean side period is within the range of the predetermined lean side period tl corresponding to the target oxidant total amount is determined based on, for example, the above formula (1). In this case, the basic modulation amplitude (t) is, for example, the predetermined lean side piece amplitude dl, and the basic catalyst inflow / exhaust flow rate corresponds to the predetermined lean side period tl. Further, if detectable, the oxidant concentration may be used instead of the modulation amplitude (t) and the basic modulation amplitude (t).

If the determination result in step S22 is true (Yes) and it is determined that the total amount of oxidant is smaller than the target total amount of oxidant, the process proceeds to step S24 and modulation to the lean A / F side (lean modulation) is continued. At the same time, the total amount of oxidant is updated in step S26.
If the determination result of step S22 is false (No) and it is determined that the total amount of oxidant is equal to or greater than the target total amount of oxidant, the process proceeds to step S28.

In step S28, as in step S18, it is determined whether the exhaust A / F detected and determined by the O ₂ sensor 22 is rich A / F or lean A / F. If it is determined that the exhaust A / F is rich A / F, the process proceeds to step S30, and lean correction is performed.
That is, as in the case of the enrichment correction, the exhaust A / F remains lean A / F and the lean A / F even when the predetermined lean side period tl elapses when the total amount of oxidant is equal to or greater than the target total oxidant amount. If not, it is determined that the exhaust A / F is biased toward the rich A / F side, and lean correction is performed. More specifically, the modulation to the rich A / F side is stopped as in the case of the enrichment correction, and the combustion A / F is held at a predetermined lean A / F as it is.

If it is determined in step S28 that the exhaust A / F has become lean A / F, the lean correction is terminated and the modulation to the rich A / F side is permitted, and the process proceeds to step S32.
In step S32, both the reducing agent total amount and the oxidizing agent total amount used in step S12 and step S22 are reset to prepare for the next modulation, and the process returns to step S10.

  As described above, in the air-fuel ratio modulation control according to the present invention, the exhaust A / F is adjusted even when the predetermined rich-side period tr in which the total amount of the reducing agent becomes equal to or larger than the total amount of the reducing agent when modulating to the rich A / F side. Is a lean A / F and does not become a rich A / F, or when a predetermined lean side period tl in which the total amount of oxidant becomes equal to or greater than the total amount of target oxidant during modulation to the lean A / F side However, if the exhaust A / F remains rich A / F and does not become lean A / F, the modulation to the lean side is stopped until the exhaust A / F becomes rich A / F, and the rich A / F. The modulation on the rich side is held until the lean A / F is reached, and the modulation on the lean A / F side is held until the lean A / F is reached. Therefore, even if the deviation of the exhaust A / F toward the lean A / F side or the deviation toward the rich A / F side occurs, the combustion A / F is appropriately corrected according to the deviation, and the exhaust A / F is corrected accordingly. The deviation of F to the lean A / F side or the rich A / F side is suppressed, and consequently, the attenuation of the exhaust A / F modulation accompanying the deviation is suppressed.

As a result, the O ₂ storage function can be sufficiently exhibited, and the exhaust purification performance of the three-way catalyst 30 can be optimized.
4 and 5, there are shown modulation waveforms of combustion A / F and exhaust A / F by air-fuel ratio modulation control according to another embodiment of the present invention. Other embodiments will be described with reference to FIG. The other embodiment is different from the control routine of the air-fuel ratio modulation control only in the execution contents of the enrichment correction in step S20 and the leaning correction in step S30, and the description of the control routine is omitted here.

First, the case of FIG. 4 will be described.
In the case of FIG. 4, at the time of modulation to the rich A / F side, the exhaust A / F remains lean A / F even when a predetermined rich side period tr in which the total amount of reducing agent becomes equal to or greater than the target total amount of reducing agent has elapsed. If not rich A / F, the modulation to the lean side is stopped until the exhaust A / F becomes rich A / F, the modulation on the rich A / F side is held, and the rich A / F is held. The modulation amplitude of the modulation on the F side (rich side half amplitude) is increased by, for example, Δdr. Although the amplitude is gradually increased in FIG. 4, it may be increased stepwise.

The same applies to the modulation to the lean A / F side, and the description is omitted here.
Thus, the combustion A / F is positively corrected to the rich A / F side or the lean A / F side with respect to the deviation of the exhaust A / F toward the lean A / F side or the bias toward the rich A / F side. Further, the attenuation of the exhaust A / F modulation accompanying the deviation of the exhaust A / F from the center A / F toward the lean A / F side or the rich A / F side is more quickly suppressed, and the three-way catalyst 30 Further optimization of the exhaust gas purification performance can be achieved.

  In the case of FIG. 5, the exhaust A / F remains lean A / F even when a predetermined rich-side period tr when the total amount of reducing agent becomes equal to or greater than the target total amount of reducing agent during modulation to the rich A / F side. If it is not rich A / F, the modulation to the lean side is stopped until the exhaust A / F becomes rich A / F, the modulation on the rich A / F side is held, and the lean side is The modulation amplitude on the lean side (lean side half amplitude) immediately after the modulation is stopped is reduced by, for example, Δdl.

The modulation amplitude may be decreased only once as shown in FIG. 5, or the modulation amplitude may be decreased a plurality of times or constantly. Furthermore, the enrichment correction shown in FIG. 4 may be used in combination.
The same applies to the modulation to the lean A / F side, and the description is omitted here.
Even in this case, the combustion A / F is positively applied to the rich A / F side or the lean A / F side with respect to the deviation of the exhaust A / F to the lean A / F side or the rich A / F side. The correction is greatly made, and the attenuation of the exhaust A / F modulation accompanying the deviation of the exhaust A / F from the center A / F toward the lean A / F side or the rich A / F side is suppressed more quickly. Further optimization of the exhaust gas purification performance of the original catalyst 30 can be achieved.

Although the description of the embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention is finished above, the embodiment is not limited to the above.
For example, in the above embodiment, the predetermined period of modulation (the predetermined rich side period tr and the predetermined lean side period tl) is the relationship between the reducing agent total amount and the target reducing agent total amount, and the total oxidizing agent amount and the target oxidizing agent total amount. It is set based on the relationship, but is not limited to this, and the predetermined cycle may be a fixed value (for example, 0.8 sec), and is optimally set in advance according to the operating conditions. It may be a map value.

Moreover, in the said embodiment, although the modulation waveform of combustion A / F was made into the square wave, it is not restricted to this, A triangular wave, a sawtooth wave, and a wavy wave may be sufficient.
In the above embodiment, the three-way catalyst 30 having an O ₂ storage function (oxidant storage function) has been described as an example. However, a catalytic converter having a reducing agent storage function for storing and releasing HC, CO, etc. It goes without saying that the present invention can be similarly applied to a catalytic converter having both an oxidizing agent storage function and a reducing agent storage function.

  Moreover, in the said embodiment, although the engine 1 was made into the intake pipe injection type gasoline engine, it may be a cylinder injection type gasoline engine.

1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention mounted on a vehicle. 3 is a flowchart showing a control routine of air-fuel ratio modulation control according to the present invention. It is a figure which shows each modulation waveform of combustion A / F and exhaust A / F by the air fuel ratio modulation control which concerns on this invention. It is a figure which shows each modulation waveform of combustion A / F and exhaust A / F by the air fuel ratio modulation control which concerns on other embodiment of this invention. It is a figure which shows each modulation waveform of combustion A / F and exhaust A / F by the air fuel ratio modulation control which concerns on other embodiment of this invention.

Explanation of symbols

1 Engine Body 6 Fuel Injection Valve 22 O ₂ Sensor (Exhaust Air / Fuel Ratio Detection Means)
30 Three-way catalyst (catalytic converter)
40 ECU (Electronic Control Unit)

Claims (4)

A catalytic converter provided in an exhaust passage of the internal combustion engine;
By periodically modulating the combustion air-fuel ratio of the internal combustion engine between the rich air-fuel ratio side and the lean air-fuel ratio side across the predetermined center air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the catalytic converter is adjusted to the rich air-fuel ratio side and the lean air-fuel side. Air-fuel ratio modulation means for periodically modulating the fuel ratio side with a predetermined cycle;
An exhaust air-fuel ratio detecting means for detecting an air-fuel ratio of the exhaust on the exhaust upstream side of the catalytic converter ;
The air-fuel ratio modulation means includes
When the combustion air-fuel ratio is modulated from the rich air-fuel ratio side to the lean air-fuel ratio side, if the exhaust air-fuel ratio detected by the exhaust air-fuel ratio detection means is not the rich air-fuel ratio, the exhaust air-fuel ratio becomes the rich air-fuel ratio. An exhaust emission control device for an internal combustion engine, wherein the modulation to the lean air-fuel ratio side is stopped, the modulation on the rich air-fuel ratio side is maintained, and the modulation amplitude on the rich air-fuel ratio side is increased . A catalytic converter provided in an exhaust passage of the internal combustion engine;
By periodically modulating the combustion air-fuel ratio of the internal combustion engine between the rich air-fuel ratio side and the lean air-fuel ratio side across the predetermined center air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the catalytic converter is adjusted to the rich air-fuel ratio side and the lean air-fuel side. Air-fuel ratio modulation means for periodically modulating the fuel ratio side with a predetermined cycle;
An exhaust air-fuel ratio detecting means for detecting an air-fuel ratio of the exhaust on the exhaust upstream side of the catalytic converter;
The air-fuel ratio modulation means includes
When the combustion air-fuel ratio is modulated from the rich air-fuel ratio side to the lean air-fuel ratio side, if the exhaust air-fuel ratio detected by the exhaust air-fuel ratio detection means is not the rich air-fuel ratio, the exhaust air-fuel ratio becomes the rich air-fuel ratio. An exhaust gas purification apparatus for an internal combustion engine, wherein the modulation to the lean air-fuel ratio side is stopped to maintain the modulation on the rich air-fuel ratio side, and the modulation amplitude on the lean air-fuel ratio side immediately after the stop is reduced . A catalytic converter provided in an exhaust passage of the internal combustion engine;
By periodically modulating the combustion air-fuel ratio of the internal combustion engine between the rich air-fuel ratio side and the lean air-fuel ratio side across the predetermined center air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the catalytic converter is adjusted to the rich air-fuel ratio side and the lean air-fuel side. Air-fuel ratio modulation means for periodically modulating the fuel ratio side with a predetermined cycle;
An exhaust air-fuel ratio detecting means for detecting an air-fuel ratio of the exhaust on the exhaust upstream side of the catalytic converter ;
The air-fuel ratio modulation means includes
When the combustion air-fuel ratio is modulated from the lean air-fuel ratio side to the rich air-fuel ratio side, if the exhaust air-fuel ratio detected by the exhaust air-fuel ratio detecting means is not the lean air-fuel ratio, the exhaust air-fuel ratio becomes the lean air-fuel ratio. An exhaust emission control device for an internal combustion engine, wherein the modulation to the rich air-fuel ratio side is stopped, the modulation on the lean air-fuel ratio side is maintained, and the modulation amplitude on the lean air-fuel ratio side is increased . A catalytic converter provided in an exhaust passage of the internal combustion engine;
By periodically modulating the combustion air-fuel ratio of the internal combustion engine between the rich air-fuel ratio side and the lean air-fuel ratio side across the predetermined center air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the catalytic converter is changed to the rich air-fuel ratio side and the lean air-fuel side. Air-fuel ratio modulation means for periodically modulating the fuel ratio side with a predetermined cycle;
An exhaust air-fuel ratio detecting means for detecting an air-fuel ratio of the exhaust on the exhaust upstream side of the catalytic converter;
The air-fuel ratio modulation means includes
When the combustion air-fuel ratio is modulated from the lean air-fuel ratio side to the rich air-fuel ratio side, if the exhaust air-fuel ratio detected by the exhaust air-fuel ratio detecting means is not the lean air-fuel ratio, the exhaust air-fuel ratio becomes the lean air-fuel ratio. An exhaust emission control device for an internal combustion engine, wherein the modulation to the rich air-fuel ratio side is stopped to maintain the modulation on the lean air-fuel ratio side, and the modulation amplitude on the rich air-fuel ratio side immediately after the cancellation is reduced .

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