JP2001304016A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of early activating a catalyst, after preventing deterioration of fuel consumption by enriching of exhaust air/fuel ratio and preventing increase in a drive loss by an air pump, at cold starting time or the like. SOLUTION: A catalyst activated at a low temperature by making CO and O2 in exhaust gas react is provided, two-step injection executing fuel injection divided into a compression stroke and an expansion stroke is executed (step S6) when cold starting is decided (step S2 is YES). In this two-step injection, O2 by combustion of excessive oxygen in the compression stroke and CO by incomplete combustion in the expansion stroke are simultaneously generated, these CO and O2 are supplied with exhaust gas onto the catalyst, by heat of reaction thereof, a temperature of the catalyst is increased. Accordingly, necessity for enriching for supplying CO and necessity for supplying secondary air for supplying O2 are eliminated.

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 (hereinafter referred to as an engine) provided with a catalyst which activates at a low temperature by reacting unburned components in exhaust gas with O _2. .

[0002]

2. Related Background Art In order to comply with recent strict exhaust gas regulations, it is important to reduce the amount of hydrocarbon (HC) emission particularly at the time of a cold start. An exhaust gas purifying apparatus described in SAE 980421 has been proposed. This exhaust gas treatment device comprises a water (H ₂ O) trap, an HC
A trap and a low-temperature active catalyst are arranged, and secondary air can be supplied from an air pump into an exhaust passage on the upstream side of the H ₂ O trap. The low-temperature active catalyst supports a catalyst made of a platinum-based noble metal oxide such as palladium (Pd), and has a property of allowing CO and O ₂ to react on the catalyst even at room temperature.

[0003] During a cold start, the air-fuel ratio of the exhaust gas is enriched and secondary air is supplied from an air pump, and the enriched CO and O ₂ generated by the secondary air react on the low-temperature active catalyst, thereby causing the engine to operate at a low temperature. Before the exhaust temperature rises due to warm-up, the temperature of the low-temperature active catalyst is quickly raised to exert its purifying action. The HC trap temporarily adsorbs HC to prevent its emission to the atmosphere when the temperature of the low-temperature active catalyst at the very beginning of the cold start has not yet risen, and prevents the H ₂ O trap from being discharged into the atmosphere. _{It functions} to adsorb ₂ O and prevent adverse effects on HC traps and low-temperature active catalysts.

[0004] By the way, the storage NOx catalyst used in lean burn engines and the like has a purifying action by temporarily storing nitrogen oxides (NOx) generated under a lean air-fuel ratio. There is a problem called so-called sulfur poisoning, in which sulfur oxide (SOx) in which the component (S) has reacted with oxygen is occluded instead of NOx, thereby lowering purification efficiency. It has been confirmed that the same phenomenon occurs in the low-temperature active catalyst described above, and there is a problem that the sulfur-poisoning degrades the active function at normal temperature.

As a countermeasure against sulfur poisoning of the NOx catalyst, for example, Japanese Patent Application Laid-Open No. 7-217474 discloses a method in which the temperature of the catalyst is raised to a high temperature (for example, about 600 to 700 ° C.) by raising the temperature of exhaust gas such as retard of ignition timing. Thus, a regeneration treatment technique for removing SOx by generating a CO-rich reducing atmosphere by enriching the air-fuel ratio has been disclosed, and it is conceivable to apply the same treatment to a low-temperature active catalyst.

[0006]

The above-mentioned exhaust gas treatment apparatus has the following problems. First, since at the time of cold start, the exhaust air-fuel ratio for the supply of CO over that would fuel efficiency deteriorates because you are rich, and actuates the air pump for supplying O _2, There is a problem that the drive loss cannot be avoided.

When the sulfur-poisoned low-temperature active catalyst is regenerated, the temperature of the H ₂ O trap and the HC trap on the upstream side together with the low-temperature active catalyst is increased by raising the temperature of the exhaust gas. Since it has a crystal structure of alumina (Al ₂ O ₃ ) and silica (SiO ₂ ) for adsorbing H ₂ O and HC, the crystal structure collapses when the temperature is raised to the above temperature, and its adsorption action A problem occurs that is greatly deteriorated.

On the other hand, the low-temperature active catalyst poisons HC as well as S. Therefore, in order to prevent this HC poisoning,
It is necessary to always keep the air-fuel ratio of the exhaust gas to which the low-temperature active catalyst is exposed to about 15, and since the air pump is operated at a considerable frequency to satisfy this condition, not only at the above-mentioned cold start, Even during the subsequent normal operation, the driving loss of the air pump was not negligible.

Therefore, claims 1, 2, and 5 are provided.
It is an object of the present invention to provide an internal combustion engine capable of activating a low-temperature active catalyst at an early stage while preventing fuel consumption deterioration due to rich exhaust air-fuel ratio and an increase in drive loss due to an air pump at a cold start or the like. An object of the present invention is to provide an exhaust gas purifying apparatus. Another object of the present invention is to provide an internal combustion engine capable of regenerating a sulfur-poisoned low-temperature active catalyst without deteriorating an upstream H ₂ O trap or an HC trap. An exhaust gas purifying apparatus for an engine is provided.

It is a further object of the present invention to reduce the operating frequency of an air pump for maintaining the atmosphere of a low-temperature active catalyst on the lean side, thereby reducing the driving loss thereof. Is to provide.

[0011]

Means for Solving the Problems To achieve the above object,
According to the first aspect of the present invention, the fuel is directly injected into the combustion chamber.
In a cylinder injection type internal combustion engine,
Provided, unburned components and O _TwoActive at low temperature when supplied
Exhaust purification catalyst and the internal combustion engine at cold start
Cold start determining means for determining that
Determines that the internal combustion engine is in a cold start
And the mode in which fuel injection is performed after the main combustion stroke
And the unburned components and O_TwoTo the catalyst to promote activity
And a cold start control means for moving forward.

Accordingly, at the time of cold-start, the fuel injection is performed after main combustion stroke by cold start control means, the oxygen excess combustion in the main combustion stroke with O ₂ is produced, in the subsequent injection The unburned components (eg, CO and HC) are generated by the incomplete combustion, and these unburned components and O ₂ are supplied onto the catalyst together with the exhaust gas to react with each other, and the heat of the reaction raises the temperature of the catalyst. Since O ₂ and the unburned component are generated in this way, it is not necessary to enrich the air-fuel ratio for supplying the unburned component.
O ₂ is not necessary to operate the air pump for supplying.

According to a second aspect of the present invention, in a cylinder injection type internal combustion engine for directly injecting fuel into a combustion chamber, a low temperature is provided in an exhaust passage of the internal combustion engine so that unburned components and O ₂ are supplied. The exhaust gas purifying catalyst activated in the above, a cold start determining means for determining that the internal combustion engine is in a cold start, and a cold start determining means determining that the internal combustion engine is in a cold start. By selecting the compression stroke injection mode in which fuel is injected in the compression stroke, and changing the target air-fuel ratio in the compression stroke injection mode to a more enriched side than the target air-fuel ratio selected except during a cold start, A cold start control means for supplying unburned components and O ₂ to the catalyst to promote the activity is provided.

Accordingly, at the time of cold start, the compression stroke injection mode is selected by the cold start control means, and the target air-fuel ratio is changed to a more enriched side than the target air-fuel ratio other than at the time of cold start ( The enrichment side at this time is not limited to the rich side than the stoichiometric side.If the target air-fuel ratio is a lean side except during a cold start, the lean target air-fuel ratio is also used during a cold start. In some cases). In this situation,
Since the vicinity of the spark plug is locally in a rich air-fuel ratio state where the fuel concentration is extremely high and O ₂ is insufficient, the fuel causes incomplete combustion and unburned components (eg, CO and HC)
Is relatively large, while in other areas, excess O
₂ is generated, and these unburned components and O ₂ are supplied onto the catalyst together with the exhaust gas to react with each other, and the heat of the reaction raises the temperature of the catalyst. Since O ₂ and the unburned component are generated in this manner, it is not necessary to enrich the air-fuel ratio for supplying the unburned component, and the air pump is operated to supply O ₂ . Eliminates the need.

Further, according to the third aspect of the present invention, in an in-cylinder injection type internal combustion engine for directly injecting fuel into a combustion chamber, an H ₂ O trap and / or an H ₂ O trap provided in an exhaust passage of the internal combustion engine are provided.
The C trap, a catalyst for exhaust gas purification provided at the downstream side of the trap in the exhaust passage, and activated at a low temperature when unburned components and O ₂ are supplied, and the timing at which the catalyst should be regenerated for sulfur poisoning. When it is determined that the regeneration should be performed by the regeneration timing determination means and the regeneration timing determination means, a mode in which fuel injection is performed after the main combustion stroke is selected.
A catalyst regenerating means for regenerating the catalyst by supplying the unburned component and O ₂ to the catalyst was provided.

Therefore, at the time of the catalyst regeneration processing, fuel injection is performed by the catalyst regeneration means after the main combustion stroke, and O ₂ is generated due to excessive oxygen combustion in the main combustion stroke.
Unburned components (eg, CO and HC) are generated by incomplete combustion in the subsequent fuel injection, and these unburned components and O ₂ are supplied to the catalyst together with the exhaust gas to react, and the reaction heat causes the catalyst to react. It is heated and regenerated. Since the temperature of the catalyst is raised by utilizing the heat of reaction between the unburned components and O ₂ , as in the case where the exhaust gas temperature is raised by ignition timing retard or the like, the upstream H ₂ gas and the catalyst are heated together. O trap and HC
The trap does not heat up.

According to a fourth aspect of the present invention, in a cylinder injection type internal combustion engine for directly injecting fuel into a combustion chamber, an H ₂ O trap and / or H ₂ O provided in an exhaust passage of the internal combustion engine is provided.
The C trap, a catalyst for exhaust gas purification provided at the downstream side of the trap in the exhaust passage, and activated at a low temperature when unburned components and O ₂ are supplied, and the timing at which the catalyst should be regenerated for sulfur poisoning. When it is determined that the regeneration is to be performed by the regeneration timing determination means and the regeneration timing determination means, the compression stroke injection mode for performing fuel injection in the compression stroke is selected, and the target air-fuel ratio in the compression stroke injection mode is set. A catalyst regenerating means for regenerating the catalyst by supplying the unburned component and O ₂ to the catalyst by changing the target air-fuel ratio to a richer side than the target air-fuel ratio selected except during regeneration of the catalyst.

Therefore, during the catalyst regeneration process, the compression stroke injection mode is selected by the catalyst regeneration means, and the target air-fuel ratio is changed to a more enriched side than the target air-fuel ratio when the catalyst is not being regenerated (at this time). The enrichment side is not limited to the rich side than the stoichiometric side.If the target air-fuel ratio is a lean side except at the time of catalyst regeneration, the lean-side target air-fuel ratio is obtained even during a cold start. There is). In this situation, since the vicinity of the ignition plug is locally in a rich air-fuel ratio state having a very high fuel concentration and O ₂ is insufficient, the fuel causes incomplete combustion and unburned components (for example, CO and H 2).
While relatively large amounts of C) are generated, excess O ₂ is generated in other regions, and these unburned components and O ₂ are supplied to the catalyst together with the exhaust gas to react, and the heat of the reaction causes the catalyst to rise. Regenerate being heated. Since the temperature of the catalyst is raised by utilizing the heat of reaction between the unburned components and O ₂ ,
Unlike the case where the exhaust gas temperature is raised by ignition timing retard or the like, the temperature of the upstream H ₂ O trap or HC trap is not raised together with the catalyst.

According to a fifth aspect of the present invention, the internal combustion engine according to any one of the first to fourth aspects further includes a secondary air supply means for supplying secondary air to an upstream side of the catalyst. When it is determined that the air-fuel ratio is in the enriched side, the secondary air supply means is operated to supply the secondary air into the exhaust gas. Therefore, when the catalyst is at or above the predetermined temperature and in the enriched air-fuel ratio atmosphere, the air-fuel ratio is suppressed to the lean side by the supply of the secondary air.
This condition is prevented from being satisfied, and as a result, catalyst deterioration due to sintering or the like occurring under this condition is avoided. Then, since the secondary air supply means is operated only when the condition is satisfied, the operation frequency is reduced.

Further, according to the present invention, in a lean-burn internal combustion engine capable of executing a lean operation with the air-fuel ratio set to a lean side, an unburned component and O ₂ are provided in an exhaust passage of the internal combustion engine. The exhaust gas purifying catalyst which is activated at a low temperature when supplied, secondary air supply means for supplying secondary air to the upstream side of the catalyst to maintain the atmosphere of the catalyst at a lean air-fuel ratio, and the internal combustion engine operates in a lean operation. And a secondary air suppression unit for suppressing the operation of the secondary air supply unit in the operation region where

Accordingly, in order to prevent HC poisoning or the like which occurs when the atmosphere of the catalyst reaches the enriched side air-fuel ratio, secondary air is supplied by the secondary air supply means so that the atmosphere of the catalyst is constantly maintained. It is kept at the lean air-fuel ratio. Then, in the operating region where the internal combustion engine performs the lean operation, since the atmosphere of the catalyst is originally the lean air-fuel ratio, there is no risk of HC poisoning or the like, and the operation of the secondary air supply means is suppressed, and the operation frequency is reduced. Decrease.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] Hereinafter, a first embodiment in which the present invention is embodied in an exhaust gas purifying apparatus for a direct injection internal combustion engine will be described.
An embodiment will be described. This embodiment corresponds to the first, third, fifth, and sixth aspects of the present invention.

FIG. 1 is an overall configuration diagram showing an exhaust gas purifying apparatus for an internal combustion engine according to a first embodiment. As shown in FIG.
The engine 1 is configured as an in-cylinder injection spark ignition type in-line four-cylinder gasoline engine. The cylinder head of the engine 1 is provided with an electromagnetic fuel injection valve 3 together with an ignition plug 2 for each cylinder, and fuel is directly injected from the fuel injection valve 3 into the combustion chamber. The intake port 4a is provided in the cylinder head in a substantially upright direction for each cylinder.
These intake ports 4a are connected to a throttle valve 5 via an intake manifold 4, and the throttle valve 5 is connected to an intake passage (not shown).

An exhaust port 7a is formed substantially horizontally in the cylinder head.
Is connected to an exhaust manifold 7 having a three-way catalyst 8. An exhaust passage 6 is connected to the exhaust manifold 7, and an H ₂ O trap 9, an HC trap 10, a first low-temperature active catalyst 11, and a second low-temperature active A catalyst 12 is provided.
On the upstream side of the H ₂ O trap 9, an air pump 15 as secondary air supply means is connected to the exhaust passage 6 via a check valve 13 and a cutoff valve 14.

Here, the HC trap 10 is, for example, 30
It has the property of adsorbing HC at low temperatures and desorbing the adsorbed HC at high temperatures around 0 ° C. Further, the low-temperature active catalysts 11 and 12 carry a catalyst made of a platinum-based noble metal oxide such as palladium (Pd), and have the property of allowing CO and O ₂ to react on the catalyst at room temperature. on the other hand,
An ECU (electronic control unit) including an input / output device, a storage device (ROM, RAM, nonvolatile RAM, and the like), a central processing unit (CPU), a timer counter, and the like in the vehicle interior.
21 are installed. On the input side of the ECU 21, a throttle sensor 22 for detecting the opening degree θth of the throttle valve 5, a rotation speed sensor 23 for detecting the rotation speed Ne of the engine 1, a water temperature sensor 24 for detecting the cooling water temperature Tw, an air-fuel ratio sensor 25, 26 are connected, and detection information from these sensors is input. The output side of the ECU 21 is connected to the ignition plug 2, the fuel injection valve 3, the cutoff valve 14, the air pump 15, and the like.

Then, the ECU 21 executes comprehensive control of the exhaust gas purifying apparatus including the engine 1 according to the present invention based on information input from each sensor. Regarding the fuel injection amount control, for example, according to the control map shown in FIG. The fuel ratio is determined. For example, in a low-load low-speed range such as during idling or low-speed running, a compression stroke lean mode in which the target air-fuel ratio is set to the lean side and fuel injection is performed in the compression stroke is selected, and the target average effective pressure Pe The fuel injection is executed in the intake stroke with the increase of the engine rotation speed Ne and the air-fuel ratio is stoichiometrically controlled based on the signal from the air-fuel ratio sensor 25.
/ B mode, and sequentially switches to the intake stroke rich mode in which the target air-fuel ratio is set to the rich side and fuel injection is performed in the intake stroke.

Since the fuel injection timing can be freely set in the in-cylinder injection type engine 1 as described above, the in-cylinder injection type engine 1 can be used at the time of cold start and the regeneration processing of the low-temperature active catalysts 11 and 12 described later.
A so-called two-stage injection in which fuel injection is divided into a compression stroke and an expansion stroke and executed is performed. In this two-stage injection, fuel injected in a compression stroke (hereinafter, referred to as main injection) is burned in a combustion chamber, and additional injection (hereinafter, referred to as “injection”) in an expansion stroke is performed by using a preflame reaction product remaining after combustion. The fuel is fired by self-ignition.

In this two-stage injection, O ₂ due to excessive oxygen combustion in the compression stroke and C ₂ due to incomplete combustion in the expansion stroke
Since O is generated at the same time, O ₂ and CO in the exhaust gas can be increased without necessarily making the overall air-fuel ratio (air-fuel ratio of the main injection and the sub-injection combined) rich. ₂ and the amount of CO generated include, for example, the total air-fuel ratio, the fuel ratio between the main injection and the sub-injection, the timing of the sub-injection, the amount of ignition retard performed for self-igniting the fuel of the sub-injection, etc. ), The above control parameters are set such that a large amount of surplus CO and surplus O ₂ remain in the exhaust gas.

Next, in the exhaust gas purifying apparatus for a direct injection type internal combustion engine configured as described above, a process performed to raise the temperature of the low temperature active catalysts 11 and 12 when the engine 1 is cold started will be described. I do. This processing corresponds to the first aspect of the present invention. The ECU 21 executes a start-time control routine shown in FIG. 3 at a predetermined control interval when the engine 1 is started. First, in step S2, it is determined whether or not a cold start is performed based on, for example, the cooling water temperature Tw (cold start determination means). If the engine 1 is already warm and a determination of NO (No) is made, The process proceeds to step S4 to execute normal fuel injection control. For example, a fuel injection mode is set according to the cooling water temperature Tw at that time, and a main operation is performed in a stroke (compression stroke or intake stroke) according to the mode. The engine 1 is started by performing only the injection.

When the engine 1 is cold at the time of starting and a determination of YES (Yes) is made in step S2,
The process proceeds to step S6 to execute two-stage injection (cold start control means). As described above, the two-stage injection at this time is as follows.
The above-described control parameters are set so that a large amount of surplus CO and surplus O ₂ are contained in the exhaust gas, and the main injection is executed in the compression stroke and the sub-injection is executed in the expansion stroke based on these parameters. Next, the ECU 21 determines in step S8 whether or not the condition for terminating the temperature raising process has been satisfied. For example, when the temperature Tcata of the low-temperature active catalysts 11 and 12 reaches a predetermined value set as the temperature raising completion temperature, or when the temperature rise slows down to an equilibrium state, it is determined that the termination condition is satisfied. At this time, the catalyst temperature T
For cata, an actual value measured by a sensor or an estimated value based on a time change of the engine rotation speed Ne or the engine load is applied. When the determination in step S8 is NO, the process returns to step S6 to continue the two-stage injection, and when the determination is YES, the process proceeds to step S4 to execute the normal fuel injection control and terminate the routine.

A large amount of O ₂ and CO remain in the exhaust gas after combustion by the two-stage injection in step S6, and these O ₂ and CO are removed from the first and second low-temperature active catalysts 11 and 12 together with the exhaust gas. And reacts on these catalysts 11 and 12. This reaction heat causes the low-temperature active catalysts 11 and 12
Is heated before the three-way catalyst 8, the H ₂ O trap 9, and the HC trap 10 on the upstream side, and the activation temperature (250 to 300
° C.) is reached, the three-way catalyst 8 and at a Atsushi Nobori action of the exhaust heat H ₂ O trap 9, HC trap 10 is to be heated subsequently.

In the very early stage of the cold start, the low-temperature active catalyst 11,
When the temperature of the exhaust gas 12 has not been raised yet, HC in the exhaust gas is H
The H ₂ O in the exhaust gas is adsorbed by the H ₂ O trap 9 and adsorbed by the C trap 10 to prevent discharge into the exhaust gas.
The adverse effect of H ₂ O on H ₂ O is prevented. When the temperature of the HC trap 10 is increased by the exhaust heat, the HC separated from the HC trap 10 is purified by the first and second low-temperature active catalysts 11 and 12 on the downstream side.

As described above, in the exhaust gas purifying apparatus of the present embodiment, O ₂ and CO are generated by two-stage injection utilizing the characteristics of the in-cylinder injection type engine 1, and the low-temperature active catalysts 11 and 12 at the time of a cold start. Because the overall air-fuel ratio does not necessarily need to be enriched in this two-stage injection, the fuel injection amount can be reduced as compared with the conventional example in which CO is generated by enriching the exhaust air-fuel ratio. Become. Further, since it is not necessary to operate the air pump 15 for supplying O ₂ , the air pump 15 may be kept stopped during the cold start.
Therefore, it is possible to activate the low-temperature active catalysts 11 and 12 at an early stage while preventing the fuel efficiency deterioration due to the richer exhaust air-fuel ratio and the increase in drive loss due to the air pump 15 (the operation of the invention of claim 1). Corresponding to the effect).

On the other hand, since the low-temperature active catalysts 11 and 12 accumulate SOx with use and reduce the purifying action,
It is necessary to execute a regeneration process for purging Ox, and the regeneration process will be described below. This processing corresponds to the third aspect of the present invention. The ECU 21 periodically executes a process of estimating the amount of SOx (poisoned S amount Qs) accumulated in the low-temperature active catalysts 11 and 12 (regeneration timing determining means), and when the poisoned S amount Qs reaches a predetermined value. The SOx purge routine shown in FIG. 4 is executed at a predetermined control interval. The poisoning S amount Qs is estimated based on the air-fuel ratio A / F and the S
Low temperature active catalyst 1 corrected according to content, catalyst temperature, etc.
It is obtained by calculating the amount of SOx adsorbed on the elements 1 and 12 and successively integrating the values.

When the SOx purge routine is started, E
The CU 21 resets the regeneration counter C in step S12, and determines the regeneration time Tpurge for continuing the SOx purge in the following step S14. That is, since the release / reduction speed of SOx changes according to the operating state of the engine 1, the regeneration time Tpurge is set according to a map set in advance according to the engine rotation speed Ne and the engine load. For example, since the release / reduction speed of SOx increases with an increase in the engine rotation speed Ne and the target average effective pressure Pe, the regeneration time Tpurge is set to decrease accordingly.

Thereafter, in step S16, two-stage injection is executed. In the two-stage injection at this time, as in the case of the cold start described above, the control parameters are set so that a large amount of excess CO and excess O ₂ contributing to the temperature rise remain in the exhaust gas. _A rapid temperature rise is achieved by the reaction of ₂ on the low temperature active catalysts 11,12. Subsequent step S
At 18, it is determined whether or not the temperature Tcata of the low-temperature active catalysts 11 and 12 has reached a preset regeneration start temperature T0. Note that, as the catalyst temperature Tcata at this time, an actually measured value or an estimated value by the sensor is applied.

Here, the low-temperature active catalysts 11 and 12 are supplied with SO
To purge x, it is necessary to satisfy any of the following conditions, and the condition under which the regeneration process is performed is selected in advance. The regeneration start temperature T0 is set at the catalyst temperature condition (700 ° C. or 600 ° C.) specified in the selected condition.
° C). That is, step S18
When the determination of YES is made, the low-temperature active catalyst 1
1 and 12 indicate that SOx can be purged. a) The low-temperature active catalysts 11 and 12 are maintained at 700 ° C. or higher and are exposed to exhaust gas having an air-fuel ratio of about 15 (hereinafter, this condition is referred to as high-temperature lean). b) The low-temperature active catalysts 11 and 12 are maintained at 600 ° C. or higher. Then, it is exposed to exhaust gas having an air-fuel ratio of about 13 (hereinafter, this condition is referred to as medium temperature rich). When the determination in step S18 is NO, step S16
Then, the two-stage injection is continued, and if the determination is YES, the control content of the two-stage injection is switched in step S20. That is, since the low-temperature active catalysts 11 and 12 have reached the purging temperature at this point, the air-fuel ratio condition (15 or 13) of a) or b) is continued while maintaining the temperature thereafter. Then, each control parameter is reset (reproduction control means). For example, in a high-temperature lean operation, it is necessary to realize a leaner exhaust air-fuel ratio as compared with a medium-temperature rich operation. Therefore, the control parameters are set so that a combustion state in which a larger amount of O ₂ is generated is obtained.

Thereafter, in step S22, the reproduction counter C
Is incremented, and in step S24, the reproduction counter C
Has reached the value Cpurge corresponding to the reproduction time Tpurge. When the determination is NO, the process returns to step S20 to continue the two-stage injection, and when the determination is YES, the routine ends. Therefore, thereafter, the control returns to the normal fuel injection control according to the operation state of the engine 1.

As described above, in the exhaust gas purifying apparatus of the present embodiment, the two-stage injection is used even when the low-temperature active catalysts 11 and 12 are regenerated, and the low-temperature activation is performed by the reaction between O ₂ and CO generated by the two-stage injection. The catalysts 11 and 12 are heated to a condition of high temperature lean or medium temperature rich and purged with SOx. As a result, unlike the conventional case where the exhaust gas temperature is raised by ignition timing retard or the like, the upstream H ₂ O trap 9 and the HC trap 10 are maintained at the allowable temperature limit or lower during the SOx purge. Is done. Therefore, the sulfur-poisoned low-temperature active catalysts 11 and 12 can be regenerated without deteriorating the H ₂ O trap 9 or the HC trap 10 on the upstream side (corresponding to the operation and effect of the invention of claim 3). .

In addition, even when the SOx purge is performed at a high temperature lean, the air-fuel ratio condition (15 or more) at that time can be realized by O ₂ supply by two-stage injection.
Therefore, there is also an advantage that no secondary air supply is required at all and the driving loss can be reduced. By the way, the low-temperature active catalysts 11 and 12 need to always maintain the exhaust air-fuel ratio at about 15 in order to prevent poisoning by HC. On the other hand, the SOx purging or the like requires a high-temperature lean temperature condition (700 ° C. or more). When the exhaust air-fuel ratio fluctuates to the rich side (less than 15) (hereinafter, referred to as
It is necessary to prevent the so-called sintering (a phenomenon that causes the activation temperature to decrease due to coarsening of particles) that occurs under this condition called a high temperature rich condition.
Lean correction is performed by the supply of the next air.
The control will be described. These processes are described in claim 5
And the invention according to claim 6.

The ECU 21 executes the air pump control routine shown in FIG. 5 at predetermined control intervals. First, in step S32, it is determined whether or not the regeneration processing of the low-temperature active catalysts 11, 12 is being executed. Step S
At 34, the air-fuel ratio A / F on the outlet side of the low-temperature active catalysts 11 and 12
It is determined whether out (that is, the air-fuel ratio of the exhaust gas to which the low-temperature active catalysts 11 and 12 are exposed) is less than 15. Judgment is N
If O, the routine is terminated, and if the determination is YES, the air pump 15 is operated in step S36, and then the routine is terminated. Secondary air is supplied into the exhaust passage 6 by the operation of the air pump 15, whereby the outlet side air-fuel ratio A / Fout is suppressed to a lean side of 15 or more, and poisoning of the low-temperature active catalysts 11 and 12 by HC is prevented. Is prevented.

On the other hand, when the determination in step S32 is YES, it is determined in step S38 whether the above-described high temperature rich condition is satisfied, and when the determination is NO, the routine ends. YES in step S38
In step S36, the process proceeds to step S36, where the air pump 1
Activate 5 Outlet air-fuel ratio A by supply of secondary air
/ Fout is suppressed to the lean side of 15 or more, so that the condition of high temperature lean is satisfied, and the lowering of the activation temperature due to sintering of the low temperature active catalysts 11 and 12 is prevented.

As described above, in the exhaust gas purifying apparatus of this embodiment, the outlet air-fuel ratio A / Fout is always kept at about 15 by the supply of the secondary air from the air pump 15. Then, as is apparent from the control map in FIG. 2, since the condition of step S32 is not satisfied in the region of the compression stroke lean mode, there is no need to operate the air pump 15 (secondary air suppression means). That is, since the operation frequency of the air pump 15 is reduced by the region corresponding to the compression stroke lean mode as compared with a normal engine that does not perform the lean operation, the drive loss thereof can be significantly reduced (claim 6). Corresponds to the function and effect of the invention).

During the regeneration treatment of the low-temperature active catalysts 11 and 12, the outlet air-fuel ratio A / Fout is suppressed to the lean side of 15 or more by the supply of the secondary air from the air pump 15, and the high-temperature rich condition is satisfied. Is prevented. And
When the regeneration process is performed under normal high-temperature lean or medium-temperature rich conditions as described above, secondary air supply by the air pump 15 is not required at all. It is only necessary to operate the air pump 15 when the condition is satisfied, and the above-mentioned drive loss can be further reduced (corresponding to the function and effect of the invention of claim 5). Second Embodiment Next, a second embodiment in which the present invention is embodied in another exhaust gas purifying apparatus for a direct injection internal combustion engine will be described. This embodiment corresponds to the second, fourth, fifth, and sixth aspects of the present invention.

Here, the configuration of the exhaust gas purifying apparatus of the present embodiment is the same as that of the first embodiment, except for the temperature increase processing of the low temperature active catalysts 11 and 12 performed at the time of cold start.
And a regeneration process for purging SOx. Therefore, the differences will be mainly described. The ECU 21 executes a start control routine shown in FIG. 6 at a predetermined control interval when the engine 1 is started. As is clear from the comparison between FIG. 3 and FIG. 6, in the present embodiment, instead of the two-stage injection in step S4 of the first embodiment, a compression bright lean (compression S / L) mode is executed in step S102. (Cold start control means). In the compression S / L mode, the air-fuel ratio in the compression stroke is slightly leaner than the stoichiometric air-fuel ratio (for example, a value of 14.7 to a value of 20, preferably a value of 1).
This is a mode in which control is performed from 4.7 to 16).

In this compression S / L mode, the vicinity of the ignition plug 2 is locally in a rich air-fuel ratio state having a very high fuel concentration, and O ₂ becomes insufficient. Is relatively common,
Excess O ₂ is generated in other areas. That is, referring to FIG. 8, the O ₂ concentration and the CO concentration when the compression stroke injection is performed while changing the air-fuel ratio A / F are shown by solid lines, and the intake stroke injection is performed while changing the air-fuel ratio A / F. A similar result for the case is shown in dash-dot line comparison, thus:
It can be seen that in the compression stroke injection, the CO concentration is significantly higher in all the air-fuel ratio regions including the stoichiometric ratio than in the intake stroke injection.

Therefore, even in the compression S / L mode, a large amount of O ₂ and CO remain in the exhaust gas after combustion, as in the two-stage injection performed in the first embodiment, and these O ₂ and CO are removed. The exhaust gas reaches the first and second low-temperature active catalysts 11 and 12 together with the exhaust gas, and reacts on the catalysts 11 and 12 to exert a temperature increasing action. As described above, in the exhaust gas purifying apparatus of the present embodiment, O ₂ and CO are generated by the compression S / L mode utilizing the characteristics of the in-cylinder injection type engine 1 so that the low-temperature active catalysts 11 and 12 at the time of the cold start are formed. In this compression S / L mode, since the air-fuel ratio is slightly leaner than the stoichiometric mode, the fuel injection amount can be reduced as compared with the conventional example in which CO is generated by enriching the exhaust air-fuel ratio. Become. Further, since it is not necessary to operate the air pump 15 for supplying O ₂ , the air pump 15 may be kept stopped during the cold start. Therefore, it is possible to activate the low-temperature active catalysts 11 and 12 at an early stage, while preventing the deterioration of fuel efficiency due to the rich exhaust air-fuel ratio and the increase in driving loss due to the air pump 15 (the operation of the invention of claim 2). Corresponding to the effect).

On the other hand, the ECU 21 controls the low-temperature active catalysts 11, 1
When the poisoning S amount Qs of No. 2 reaches a predetermined value (regeneration timing determining means), the SOx purge routine shown in FIG. 7 is executed at a predetermined control interval. As is clear from the comparison between FIG. 4 and FIG. 7, also in this case, the compression S / L mode is executed in steps S104 and S106 instead of the two-stage injection in steps S16 and S20 of the first embodiment. (Catalyst regeneration means). Therefore, this compression S
In the / L mode, a large amount of O ₂ and CO remain in the exhaust gas and is supplied to the low-temperature active catalysts 11 and 12, and the low-temperature active catalysts 11 and 12 are brought into a state of satisfying the condition of high-temperature lean or medium-temperature rich by the reaction heat. The SOx purge is performed while being held.

As described above, in the exhaust gas purifying apparatus of the present embodiment, even when the low-temperature active catalysts 11 and 12 are regenerated, the compression S / L
Mode, and O generated in the compressed S / L mode
By the reaction between ₂ and CO, the low-temperature active catalysts 11 and 12 are heated to a high-temperature lean or medium-temperature rich condition and purged with SOx. As a result, unlike the conventional case where the exhaust gas temperature is raised by ignition timing retard or the like, the upstream H ₂ O trap 9 and the HC trap 10 are maintained at the allowable temperature limit or lower during the SOx purge. Is done. Therefore, the sulfur-poisoned low-temperature active catalysts 11 and 12 can be regenerated without deteriorating the upstream H ₂ O trap or the HC trap (corresponding to the operation and effect of the invention of claim 4).

On the other hand, although not described in detail, the exhaust gas purifying apparatus of the present embodiment also executes the air pump control routine of FIG. 5 described in the first embodiment. The side air-fuel ratio A / Fout is always maintained at about 15, and the low-temperature active catalysts 11, 1
At the time of the regeneration process 2, the high temperature rich condition which causes sintering is prevented from being satisfied. In addition, since it is not necessary to operate the air pump 15 in the region of the compression stroke lean mode (secondary air suppression means), the operation frequency can be reduced and the driving loss can be greatly reduced. In addition, since the air pump 15 may be operated only when the high temperature rich condition is satisfied at the time of catalyst regeneration, the drive loss can be further reduced (the operation and effect of the invention of claim 5). Correspondence).

Although the embodiment has been described above, aspects of the present invention are not limited to the first and second embodiments. For example, in each of the above embodiments, the exhaust gas purifying apparatus for the in-cylinder injection type engine 1 has been embodied. However, the type of the engine to be applied is not limited to this. For example, only the function and effect of the invention of claim 6 are described. If desired, it may be embodied as an exhaust gas purification device for a lean burn engine. That is, even in this case, in the lean operation range, there is no possibility that the low-temperature active catalysts 11 and 12 are poisoned by HC, so that it is not necessary to operate the air pump 15 and the operation frequency can be reduced.

In each of the above embodiments, even at room temperature,
CO and O_TwoLow-temperature active catalysts 11 and 12 capable of reacting
The exhaust gas purification device was equipped with
Properties are not required, and the activity of the upstream three-way catalyst 8
CO and O as soon as possible _TwoThe temperature rises by the reaction of
If it can be activated, its activation temperature is higher than room temperature.
Is also good.

Further, in the first embodiment, the control for performing the main injection in the compression stroke and the sub-injection in the expansion stroke as the two-stage injection is executed. However, the process for executing the main injection and the sub-injection is not necessarily performed as described above. The present invention is not limited to this, and it is only necessary to be able to simultaneously generate O ₂ due to excessive oxygen combustion and CO due to incomplete combustion. Therefore, for example, the main injection is performed in a compression stroke, the sub-injection is performed in an exhaust stroke, or the main injection is performed in a compression stroke, and the sub-injection is performed in an expansion stroke and an exhaust stroke.
Further, the main injection may be performed in the intake stroke, and the sub-injection may be performed in the expansion stroke.

On the other hand, the low-temperature active catalysts 11 and 1 during the cold start
2 and the SOx purge regeneration process in the first
In the embodiment, the injection is realized by the two-stage injection, and in the second embodiment, the injection is realized by the compression S / L mode. For example, the two-stage injection is applied to the temperature increasing process at the cold start, and the compression S / L is applied to the regeneration process. / L mode may be applied or vice versa. In the regeneration treatment of the low-temperature active catalysts 11 and 12,
Temperature rising stage of the low-temperature active catalysts 11 and 12 (Step S in FIG. 4)
16, in step S104 in FIG. 7, two-stage injection is applied, and the subsequent SOx purging step (step S2 in FIG. 4)
0, in step S106 in FIG. 7, the compression S / L mode may be applied or vice versa.

[0055]

As described above, according to the exhaust gas purifying apparatus for an internal combustion engine according to the first and second aspects of the present invention, at the time of a cold start or the like, the fuel efficiency deteriorates due to the enrichment of the exhaust air-fuel ratio and the driving loss due to the air pump. The catalyst can be activated at an early stage after preventing the increase in the temperature.

According to the exhaust gas purifying apparatus for an internal combustion engine according to the third and fourth aspects of the present invention, the sulfur-poisoned catalyst is regenerated without deteriorating the upstream H ₂ O trap, the HC trap, and the like. be able to. Further, according to the exhaust gas purifying apparatus for an internal combustion engine according to the fifth aspect of the present invention, in addition to the first to fourth aspects of the present invention, the operation frequency of the secondary air supply means is reduced to further reduce the driving loss. can do.

On the other hand, according to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, the operation frequency of the secondary air supply means for maintaining the atmosphere of the catalyst at the lean air-fuel ratio is reduced, and the driving loss is reduced. Can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram illustrating an exhaust gas purifying apparatus for a direct injection internal combustion engine according to a first embodiment.

FIG. 2 is an explanatory diagram showing a control map for determining a fuel injection mode.

FIG. 3 is a flowchart illustrating a start-time control routine executed by an ECU.

FIG. 4 is a flowchart illustrating a SOx purge routine executed by an ECU.

FIG. 5 is a flowchart illustrating an air pump control routine executed by the ECU.

FIG. 6 is a flowchart illustrating a start-time control routine executed by an ECU according to a second embodiment.

FIG. 7 is a flowchart illustrating a SOx purge routine executed by the ECU.

FIG. 8 is an explanatory diagram showing the O ₂ concentration and the CO concentration when the air-fuel ratio is changed between the compression stroke injection and the intake stroke injection.

[Explanation of symbols]

1 engine (internal combustion engine) 6 exhaust passage 9 H ₂ O trap 10 HC trap 11, 12 low temperature active catalyst 15 air pump (secondary air supply means) 21 ECU (cold start determining means, cold start control means, regeneration timing determination Means, catalyst regeneration means, secondary air suppression means)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F01N 3/24 F01N 3/24 RE F F02D 41/02 335 F02D 41/02 335 41/20 335 41/20 335 41 / 34 41/34 H (72) Inventor Osamu Nakayama 5-33-8 Shiba, Minato-ku, Tokyo F-term in Mitsubishi Motors Corporation (Reference) 3G091 AA02 AA12 AA17 AA24 AA28 AB03 AB08 AB10 BA03 BA11 BA14 BA15 BA19 BA33 CA23 CA24 CB02 CB03 CB08 DA01 DA02 DB06 DB10 EA01 EA07 EA16 EA18 EA30 EA34 FA02 FA04 FA12 FA13 FB02 FB10 FB11 FB12 FC02 FC07 GB05W GB06W GB07W HA03 HA19 HA20 HA36 HA37 HA42 HA47 3G301 HA01 HA04 KA01 JA08 ND NE01 NE13 PA11Z PB05Z PD02Z PD04Z PD11Z PE01Z PE06Z PE08Z

Claims (6)

[Claims] 1. An in-cylinder injection type internal combustion engine for directly injecting fuel into a combustion chamber, the exhaust purification system being provided in an exhaust passage of the internal combustion engine and being activated at a low temperature when unburned components and O ₂ are supplied. A catalyst, a cold start determining means for determining that the internal combustion engine is in a cold start, and a cold start determining means for determining that the internal combustion engine is in a cold start. By selecting a mode in which fuel injection is performed after the combustion stroke, the unburned component and O ₂
An exhaust gas purifying apparatus for an internal combustion engine, comprising: 2. An in-cylinder injection type internal combustion engine for directly injecting fuel into a combustion chamber, provided in an exhaust passage of the internal combustion engine and activated at a low temperature when unburned components and O ₂ are supplied. When the internal combustion engine is determined to be in a cold start by the cold start determination means for determining that the internal combustion engine is in a cold start, compression is performed. By selecting the compression stroke injection mode in which fuel is injected during the stroke, and changing the target air-fuel ratio in the compression stroke injection mode to a more enriched side than the target air-fuel ratio selected except during cold start, An exhaust gas purifying apparatus for an internal combustion engine, comprising: a cold start control unit that supplies a fuel component and O ₂ to the catalyst to promote the activity. 3. An in-cylinder injection type internal combustion engine for directly injecting fuel into a combustion chamber, wherein: an H ₂ O trap and / or an HC trap provided in an exhaust passage of the internal combustion engine; and a downstream of the trap in the exhaust passage. A catalyst for exhaust purification that is provided on the side and that is activated at a low temperature when unburned components and O ₂ are supplied; regeneration timing determination means for determining when regeneration of sulfur poisoning of the catalyst should be performed; When it is determined by the regeneration timing determination means that regeneration is to be performed, a mode in which fuel injection is performed after the main combustion stroke is selected to supply the unburned components and O ₂ to the catalyst to regenerate the catalyst. An exhaust gas purifying apparatus for an internal combustion engine, comprising: 4. An in-cylinder injection type internal combustion engine for directly injecting fuel into a combustion chamber, wherein an H ₂ O trap and / or an HC trap provided in an exhaust passage of the internal combustion engine, and a portion of the exhaust passage downstream of the trap. A catalyst for exhaust purification that is provided on the side and that is activated at a low temperature when unburned components and O ₂ are supplied; regeneration timing determination means for determining when regeneration of sulfur poisoning of the catalyst should be performed; If it is determined by the regeneration timing determination means that regeneration is to be performed, a compression stroke injection mode in which fuel is injected in the compression stroke is selected, and the target air-fuel ratio in the compression stroke injection mode is set to a value other than during the regeneration of the catalyst. An internal combustion engine comprising: catalyst regeneration means for supplying the unburned component and O ₂ to the catalyst by regenerating the catalyst by changing the target air-fuel ratio to a richer side than the selected target air-fuel ratio. Exhaust gas Purifying device. 5. The internal combustion engine further includes secondary air supply means for supplying secondary air to an upstream side of the catalyst, and it is determined that the catalyst is at a predetermined temperature or higher and is in an enriched air-fuel ratio atmosphere. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein when activated, the secondary air supply means is operated to supply secondary air into the exhaust gas. 6. A lean-burn internal combustion engine capable of performing a lean operation with an air-fuel ratio set to a lean side, provided in an exhaust passage of the internal combustion engine, and activated at a low temperature when unburned components and O ₂ are supplied. Exhaust gas purification catalyst, secondary air supply means for supplying secondary air to the upstream side of the catalyst to maintain the atmosphere of the catalyst at a lean air-fuel ratio, and the internal combustion engine performs a lean operation. An exhaust gas purifying apparatus for an internal combustion engine, comprising: a secondary air suppressing means for suppressing an operation of the secondary air supplying means in an operation region.