JP2007071024A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of preventing the increase of an NOx exhaust quantity by reducing a lean region in response to deterioration in occluding capacity of an NOx catalyst caused by the sulfur poisoning, and of suppressing bad effect of deterioration in fuel efficiency due to the increase in execution frequency of the stoichiometric operation in accompany with the reduction of the lean region. <P>SOLUTION: At sulfur poisoning of an NOx catalyst, the execution frequency of the stoichiometric operation is increased by reducing a lean region so as to suppress the increase in an NOx exhaust amount into the atmosphere. By setting a timer region between the lean region and stoichiometric region, the lean operation is continued for the prescribed delay time at the time of transition from the lean region to the timer region, thereby extending the lean operation time in total. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust purification device for an internal combustion engine (hereinafter referred to as an engine) provided with a storage type NOx catalyst.

In-cylinder injection engines that inject fuel directly into the cylinder perform lean operation to control the air-fuel ratio to the lean side from the stoichiometric air-fuel ratio (stoichio), so it is possible to purify NOx in exhaust gas even in an oxygen-rich atmosphere An occlusion type NOx catalyst is installed in the exhaust passage. The occlusion type NOx catalyst occludes NOx in exhaust gas as nitrate X-NO ₃ in an oxygen-excess atmosphere with a low reducing component concentration, and once releases the occluded NOx in an oxygen concentration-reduced atmosphere with a large amount of CO (carbon monoxide). It is configured as a catalyst having the property of being reduced to N ₂ (nitrogen) or the like (at the same time, carbonate X-CO ₃ is generated). With respect to the cylinder injection type engine, for example, the NOx purge for controlling the air-fuel ratio to the stoichiometric air-fuel ratio or the rich air-fuel ratio is periodically executed before the NOx occlusion amount of the storage-type NOx catalyst is saturated, thereby flowing into the catalyst. Regeneration is achieved by increasing the CO concentration of the exhaust gas to release and reduce NOx from the NOx catalyst.

  On the other hand, fuel and engine oil contain an S (sulfur) component (sulfur component), which reacts with oxygen to form SOx (sulfur oxide), which is replaced by NOx. There is a problem that the NOx catalyst is occluded as a sulfate and the catalyst carrier is poisoned by SOx, and the NOx catalyst occlusion ability is lowered. It is known that the SOx occluded in this way is removed by supplying a reducing component (CO) to the catalyst and bringing the NOx catalyst into a high temperature state. For example, the estimated value of the SOx occlusion amount is a predetermined amount. After reaching the ignition timing, the fuel is injected during the ignition timing retard or expansion stroke, and the NOx catalyst is brought to a high temperature state by raising the exhaust gas temperature. S purge technology is known that removes SOx by producing.

  However, the NOx catalyst cannot be heated up to a temperature range where SOx can be removed even if the exhaust gas temperature is raised in a low load low rotation range where the engine exhaust temperature is originally low, such as when idling or low speed running continues. . Therefore, in such a case, it is necessary to wait for execution of the S purge until the vehicle is in a driving state where a somewhat high engine exhaust temperature is obtained. However, during this time, the storage capacity of the NOx catalyst decreases due to storage of SOx. Then, since the NOx catalyst does not completely store NOx, the NOx catalyst discharges the NOx catalyst. Therefore, a countermeasure focusing on this problem has been proposed (for example, see Patent Document 1).

In the technique described in Patent Document 1, the stoichiometric operation is performed instead of the lean operation by reducing the region in which the lean operation is performed in accordance with the decrease in the NOx storage capacity of the NOx catalyst. The increase in the NOx emission amount is suppressed until the S purge can be executed.
Japanese Patent No. 3525708

  The reduction of the lean region described in Patent Document 1 is, for example, an operation region map that is set in order of a lean region, a stoichiometric region, and a rich region from the low load low rotation side according to the engine load and the rotational speed, for example. The lean area is reduced to the low load and low rotation side, and the stoichiometric area is expanded to the low load and low rotation side by the reduced amount, but only the operation area is changed, so only the expansion of the stoichiometric area. The execution frequency of stoichio driving increased, fuel consumption deteriorated, and there was room for improvement in fuel consumption.

  The present invention has been made to solve such problems, and the object of the present invention is to reduce NOx emission by reducing the lean region in accordance with the decrease in storage capacity of the NOx catalyst due to sulfur poisoning. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can suppress an increase in the amount of fuel, and can suppress the adverse effects of fuel consumption deterioration due to an increase in the execution frequency of stoichiometric operation as the lean region is reduced.

  In order to achieve the above object, an invention according to claim 1 is provided in an exhaust passage of an internal combustion engine, occludes NOx in exhaust gas in an oxygen-excess atmosphere, and occludes NOx occluded in an oxygen concentration-reduced atmosphere and reduces it. NOx catalyst, NOx purge control means for controlling the air-fuel ratio of the internal combustion engine to the stoichiometric air-fuel ratio or rich air-fuel ratio in the intake stroke injection mode, and releasing and reducing NOx stored in the NOx catalyst; The internal combustion engine is operated at a lean air-fuel ratio when the engine operating region is in a predetermined lean region, while the internal combustion engine is not operated when the operating region of the internal combustion engine is in a non-lean region on the high load high rotation side from the lean region. When the air-fuel ratio control means that operates at a lean air-fuel ratio, the poisoning determination means that determines the sulfur poisoning state of the NOx catalyst, and the sulfur determination of the NOx catalyst is determined by the poisoning determination means, the lean region is reduced. In addition to reducing to the low load rotation side, a timer region is set at the boundary between the lean region and the stoichiometric region, and when the operating region of the internal combustion engine shifts from the lean region to the timer region, the lean air-fuel ratio in the lean region is predetermined. And a poisoning time control means for switching to the stoichiometric air-fuel ratio after continuing the delay time.

  Therefore, the internal combustion engine is operated at the lean air-fuel ratio by the air-fuel ratio control means in the lean region, and is operated at the non-lean air-fuel ratio in the non-lean region. For example, NOx discharged from the internal combustion engine during operation in the lean region is the NOx catalyst. The stored NOx is released and reduced when the exhaust air-fuel ratio of the internal combustion engine is controlled to a non-lean air-fuel ratio, that is, the stoichiometric air-fuel ratio or rich air-fuel ratio by the NOx purge control means.

When the NOx catalyst sulfur poisoning is judged by the poisoning judgment means, the lean area is reduced to the low load low rotation side by the poisoning control means, and a timer area is set at the boundary between the lean area and the stoichiometric area. When the operating region of the internal combustion engine shifts from the lean region to the timer region, the lean air-fuel ratio is switched to the stoichiometric air-fuel ratio after continuing the delay time.
Therefore, even if the NOx storage capacity of the NOx catalyst is reduced due to sulfur poisoning, the frequency of operation at the stoichiometric air-fuel ratio increases due to the reduction of the lean region, resulting in NOx emissions into the atmosphere as a result. An increase in the amount can be suppressed.

  Then, when shifting from the lean region to the timer region, switching to the stoichiometric air-fuel ratio is delayed by an amount corresponding to the delay time, but since the lean operation is continued only for the delay time, the amount of NOx emission to the atmosphere becomes a problem. On the other hand, the total lean operation time is extended due to the delay in switching to the stoichiometric air-fuel ratio, and when returning to the lean region before the delay time elapses, the lean operation is continued. Frequent switching between stoichiometric operation and lean operation is prevented in advance, and the number of tailings for the purpose of suppressing torque steps at the time of operation switching is reduced to reduce fuel consumption during tailing.

According to a second aspect of the present invention, in the first aspect, the poisoning time control means gradually reduces the lean region to the low load and low rotation side in accordance with the progress of sulfur poisoning of the NOx catalyst, and reduces the lean region. The timer area is set following the above.
Accordingly, the lean region is gradually reduced to the low load and low rotation side in accordance with the progress of sulfur poisoning of the NOx catalyst, and the timer region is set following the reduction of the lean region. With respect to the NOx storage capacity of the catalyst, the execution frequency of the stoichiometric operation is increased by reducing the lean region without excess or deficiency, and the increase in NOx emission is suppressed, and the lean operation is executed in an appropriate timer region, The fuel consumption reduction effect by this is acquired reliably.

According to a third aspect of the present invention, in the second aspect, the poisoning time control means sets the reduced amount of the lean region as the timer region.
Therefore, if the lean operation is continued in a region that greatly exceeds the lean region on the high load high rotation side, the NOx emission amount of the engine out increases rapidly, but the reduced amount of the lean region is set as the timer region. Since the upper limit on the high-load high-rotation side is limited, such a problem is prevented in advance.

According to a fourth aspect of the present invention, in the first to third aspects, the NOx purge control means executes the NOx release / reduction process for each first lean continuation time preset in the lean region, and the timer region from the lean region. When the shift is made to, the NOx emission reduction process is executed every second lean duration shorter than the first lean duration.
Therefore, in the timer region, as compared with the lean region, the NOx emission amount of the engine out tends to increase as the engine load and the engine speed increase. Even if the sulfur poisoning situation of the NOx catalyst is the same, NOx Although the NOx occlusion amount of the catalyst saturates earlier, the NOx purge is executed earlier based on the shorter second lean duration in the timer region, so NOx into the atmosphere due to the saturation of the NOx occlusion amount Emission is prevented.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine of the first aspect of the present invention, the NOx emission amount can be increased by reducing the lean region in accordance with the decrease in the storage capacity of the NOx catalyst due to sulfur poisoning. The lean air-fuel ratio is maintained only for the delay time in the timer region set at the boundary between the lean region and the stoichiometric region, so that the total lean operation time can be extended and the stoichiometric and lean operations can be extended. The fuel consumption due to frequent switching between the two can be reduced, and the adverse effect of fuel consumption deterioration due to the increased frequency of stoichiometric operation accompanying the reduction of the lean region can be minimized.

According to the exhaust gas purification apparatus for an internal combustion engine of the invention of claim 2, in addition to claim 1, the lean region and the timer region are optimally set according to the progress of sulfur poisoning of the NOx catalyst. It is possible to suppress the increase in the NOx emission amount by increasing the execution frequency of the operation, and to surely obtain the fuel consumption reduction effect by continuing the lean operation in the timer region.
According to the exhaust emission control device for an internal combustion engine of the invention of claim 3, in addition to claim 2, the timer region is set more appropriately as a reduction of the lean region, and the increase in NOx emission into the atmosphere is more reliably ensured. Can be suppressed.

  According to the exhaust gas purification apparatus for an internal combustion engine of a fourth aspect of the present invention, in addition to the first to third aspects, in the timer region where the NOx emission amount of the engine out tends to increase, the lean continuation time is shortened and the earlier NOx. Since purging is performed, NOx emission into the atmosphere due to saturation of the NOx occlusion amount in the timer region can be more reliably prevented.

Hereinafter, an embodiment of an exhaust emission control device for an internal combustion engine embodying the present invention will be described.
FIG. 1 is an overall configuration diagram showing an exhaust emission control device for an engine according to the present embodiment. The exhaust emission control device according to the present embodiment is configured for an in-cylinder injection type in-line four-cylinder gasoline engine 1. The engine 1 employs a DOHC 4-valve type valve operating mechanism, and an intake camshaft 3 and an exhaust camshaft 4 provided on the cylinder head 2 are rotationally driven by a crankshaft (not shown). 4, the intake valve 5 and the exhaust valve 6 are opened and closed at a predetermined timing.

  The cylinder head 2 is provided with an electromagnetic fuel injection valve 8 (fuel injection means) together with an ignition plug 7 for each cylinder, and high-pressure fuel supplied from a fuel pump (not shown) is combusted in response to opening and closing of the fuel injection valve 8. It is injected directly into the chamber 9. An intake port 10 is formed in each cylinder of the cylinder head 2 so as to pass between the camshafts 3 and 4 in a substantially upright direction. As the intake valve 5 is opened, intake air is supplied from the air cleaner 11 to the throttle valve 12. It is introduced into the combustion chamber 9 through the surge tank 13, the intake manifold 14, and the intake port 10.

  An exhaust port 15 is formed in each cylinder of the cylinder head 2 in a substantially horizontal direction, and an exhaust passage 17 is connected to the exhaust port 15 via an exhaust manifold 16. A catalytic converter 18 is provided at a position corresponding to the floor of the vehicle in the exhaust passage 17, and the catalytic converter 18 includes an occlusion-type NOx catalyst 19 on the exhaust upstream side and a three-way catalyst 20 on the exhaust downstream side. The exhaust gas after combustion in the combustion chamber 9 flows into the catalytic converter 18 via the exhaust manifold 16 and the exhaust passage 17, and after passing through the NOx catalyst 19 and the three-way catalyst 20, is discharged to the outside through the exhaust throttle valve 21. Is done.

The NOx catalyst 19 of the catalytic converter 18 includes, for example, noble metals such as platinum (Pt) and rhodium (Rh), alkali metals such as barium (Ba), potassium (K), and sodium (Na), and NOx of alkaline earth metals. It contains a trapping agent, has a function of occluding NOx in an oxygen-excess atmosphere, and once releasing NOx in an oxygen concentration-reduced atmosphere mainly containing CO and then reducing it to N ₂ (nitrogen) or the like. The three-way catalyst 20 contains a noble metal such as platinum or rhodium, and has a function of purifying HC, CO and NOx in the exhaust gas at the stoichiometric air-fuel ratio.

  In the vehicle, an input / output device (not shown), a storage device (ROM, RAM, etc.) for storing control programs and control maps, an ECU (engine control unit) equipped with a central processing unit (CPU), a timer counter, etc. 31 is installed, and comprehensive control of the engine 1 is performed. Various sensors such as a rotational speed sensor 32 for detecting the rotational speed Ne of the engine 1 and a NOx sensor 34 provided on the downstream side of the NOx catalyst 19 are connected to the input side of the ECU 31, and the fuel is connected to the output side of the ECU 31. Various devices such as an igniter 33 for driving the injection valve 8 and the spark plug 7 are connected.

The ECU 31 determines the ignition timing, the fuel injection amount, and the like from the map based on the detection information from each sensor, and operates the engine 1 by drivingly controlling the fuel injection valve 8 and the igniter 33 based on the determined control amount.
Regarding the fuel injection control, the intake stroke injection mode in which the injection timing is set to the intake stroke and the compression stroke injection mode in which the injection timing is set to the compression stroke are switched according to the operating region of the engine 1, specifically, the throttle. Based on the opening degree θth and the engine speed Ne, a target average effective pressure Pe that correlates with the engine load is obtained, and the fuel to be executed according to the operation region map shown in FIG. 2 from the target average effective pressure Pe and the engine speed Ne. In addition to determining the injection mode, the fuel injection control is executed by determining the fuel injection amount based on the target air-fuel ratio obtained from the target average effective pressure Pe and the engine speed Ne in the determined fuel injection mode.

In the compression stroke injection mode, fuel injection is performed in the compression stroke, and a mixture near the stoichiometric air-fuel ratio is secured around the spark plug 7 using the tumble flow generated by the intake air flowing in from the intake port 10. Thus, stratified combustion is performed that ignites at an extremely lean air-fuel ratio (for example, around 40) as a whole. On the other hand, in the intake stroke injection mode, the fuel injection is performed in the intake stroke, and the fuel spray is sufficiently mixed with the intake air to be burned, and the intake stroke injection mode is performed by an O ₂ sensor (not shown). It is divided into a stoichiometric F / B control mode in which the air-fuel ratio is fed back to the stoichiometric air-fuel ratio based on the output and an O / L control mode in which the air-fuel ratio on the rich side is controlled in an open loop (air-fuel ratio control means).

  As shown in FIG. 2, in the region where the target average effective pressure Pe and the engine rotational speed Ne are low, a lean region in which the lean operation is executed is set by the compression stroke injection mode, and the target average effective pressure Pe and the engine rotational speed Ne are set from the lean region. As it becomes higher, a stoichiometric region (non-lean region) in which stoichiometric operation is executed in the stoichiometric F / B control mode and a rich region (non-lean region) in which rich operation is executed in the O / L control mode are set.

  2 is an initial setting map (hereinafter, the driving area map will be referred to as an initial setting map). In the present embodiment, the characteristics differ in addition to the initial setting map. These three operation region maps (hereinafter referred to as first to third NOx reduction maps) are set, and the operation region map applied to the fuel injection control of the ECU 31 is switched according to the NOx occlusion capacity of the NOx catalyst 19. Yes. First, the characteristics of each operation region map will be described.

  In short, each driving area map is obtained by sequentially reducing the lean area with respect to the initial setting map, and setting a timer area at the boundary between the lean area and the stoichiometric area as necessary. The lean region is reduced at the inner and outer two boundary lines L1 and L2 (see FIGS. 3 and 4) set on the low load and low rotation side from the outline of the lean region of the initial setting map (the boundary between the lean region and the stoichiometric region). As shown in the following).

  First, in the first NOx reduction map shown in FIG. 3, the lean region is reduced to the outer boundary line L1 with respect to the initial setting map, and the lean region is reduced (that is, the outer and outer contours of the lean region of the initial setting map). The area between the boundary line L1) is set as the timer area. As will be described in detail later, the stoichiometric operation is basically executed in the timer area in the same manner as in the stoichiometric area. However, when shifting from the lean area to the timer area, the lean operation is continued only for a predetermined delay time Tdelay. Is set to

In the second NOx reduction map shown in FIG. 4, the lean region is reduced to the inner boundary line L2 with respect to the first NOx reduction map, and the lean region is reduced (that is, between the inner and outer boundary lines L1 and L2). Area) is set as the timer area.
Further, in the third NOx reduction map shown in FIG. 5, the lean region is abolished with respect to the initial setting map (the timer region of the second and third NOx reduction maps is also abolished), and as a result, lower load and lower rotation than the rich region. All sides are set as stoichiometric areas.

  On the other hand, NOx discharged from the engine 1 during lean operation in the lean region is stored in the NOx catalyst 19, and the theoretical air-fuel ratio or rich air-fuel ratio (rich air-fuel ratio (in the intake stroke injection mode) before the NOx storage amount of the NOx catalyst 19 is saturated. A NOx purge that is controlled to a non-lean air-fuel ratio) is periodically executed, whereby NOx is released and reduced from the NOx catalyst 19 due to an increase in the CO concentration of the exhaust gas (NOx purge control means). For example, as shown in FIG. 6, the NOx purge is executed every predetermined first lean continuation time T1lean, and the first lean continuation obtained from the target average effective pressure Pe and the engine speed Ne according to a map (not shown). When the time T1lean elapses, NOx purge is executed to release and reduce NOx, and this NOx occlusion / release reduction is repeated.

  The first lean duration T1lean in the lean region is set as described above, but since the lean operation is continued only in the timer region for the delay time Tdelay, the set delay time Tdelay is long and the lean operation is performed. When the NOx occlusion amount saturates during the continuation of NOx, it is necessary to perform NOx purge. Therefore, although the lean duration is set for the timer region, the engine-out NOx emission increases in the timer region as the target average effective pressure Pe and the engine rotational speed Ne increase as compared with the lean region. In view of this tendency, as shown in FIG. 7, the second lean duration T2lean applied in the timer area is shorter based on a map different from the first lean duration T1lean in the lean area. Set to time.

  The NOx catalyst 19 also stores SOx generated from the S component in the fuel and engine oil together with NOx. Since the SOx cannot be removed only in an oxygen concentration-decreasing atmosphere in which the CO concentration is increased, the SOx occlusion amount is reduced. When the estimated value reaches a predetermined amount, fuel is injected during the ignition timing retard and expansion stroke, and the NOx catalyst 19 is brought to a high temperature state by raising the exhaust gas temperature. S purge that generates a concentration-reduced atmosphere is executed, thereby removing SOx from the NOx catalyst 19.

  In a low load range where the exhaust temperature of the engine 1 is originally low, such as when idling or low speed running continues, the NOx catalyst 19 cannot be raised to a temperature range where SOx can be removed even if the exhaust temperature is raised. Therefore, until shifting to an engine operating state where S purge can be executed, a measure for reducing the NOx emission amount of the engine out by increasing the execution frequency of the stoichiometric operation by reducing the lean region, as in the technique of Patent Document 1. Have taken. In addition to this, in the present embodiment, the lean operation is continued in the timer region, thereby suppressing the deterioration of fuel consumption due to the increase in the execution frequency of the stoichiometric operation. Hereinafter, the execution state of the S purge will be described in detail. .

The ECU 31 executes the S purge control / map switching routine shown in FIG. 8 at predetermined control intervals while the engine 1 is in operation. Now, for convenience of explanation, the initial setting map of FIG. 2 is set as the operation region map. It is assumed that the fuel injection control is executed by the ECU 31 based on the fuel injection mode determined from the initial setting map.
First, the ECU 31 determines in step S2 whether or not the interval time for estimating the SOx occlusion amount has elapsed. When the determination is No (negative), the routine is terminated. If the determination in step S2 becomes Yes (positive) due to the elapse of the interval time, the amount of SOx stored in the NOx catalyst 19 is estimated in the subsequent step S4 (poisoning determination means). The estimation process is performed, for example, by estimating the SOx amount contained in the exhaust gas at that time based on the operating state of the engine 1 and sequentially integrating the estimated SOx amount from the previous execution of the S purge. The integrated value of the SOx amount is regarded as the SOx amount occluded in the current NOx catalyst 19.

  Thereafter, in step S6, it is determined whether or not the SOx amount is equal to or greater than a predetermined SOx determination value. When the determination is No, the routine is terminated because it is not necessary to perform the S purge. Further, when the determination in step S6 is Yes, it is determined that execution of S purge is required, and the process proceeds to subsequent step S8. In step S8, whether or not S purge can be executed based on the current operating state of the engine 1, that is, to a temperature range in which SOx can be removed by exhaust temperature rise such as ignition timing retard or fuel injection in the expansion stroke. It is determined whether or not the temperature of the NOx catalyst 19 can be raised.

  For example, in an operation region where the target average effective pressure Pe and the engine rotational speed Ne are relatively high, such as during high-speed driving, S purge can be executed, a Yes determination is made in step S8, and the flow proceeds to step S10 to perform S purge. The routine is terminated after the initial setting map is set as the operation region map in the subsequent step S12. Since the initial setting map has already been set as described above, this map setting state is maintained at this time.

  On the other hand, in an operation state where the target average effective pressure Pe and the engine rotational speed Ne are relatively low as in the case where idle operation or low-speed traveling continues, S purge cannot be executed, and No is determined in step S8. Then, the first NOx reduction map is set as the operation region map. In the subsequent step S16, it is determined whether or not the output of the NOx sensor 34 is equal to or greater than the first NOx determination value. When the determination is No, that is, NOx leaking downstream without being stored in the NOx catalyst 19 is acceptable. If it is estimated that the sulfur poisoning of the NOx catalyst 19 is not progressing so much, the process directly returns to step S8. Therefore, in this case, the first NOx reduction map in which the lean region is reduced instead of the initial setting map is applied to the fuel injection control, and the stoichiometric engine exhaust amount of NOx that decreases as the lean region decreases as will be described later. NOx reduction is achieved by increasing the frequency of operation (poisoning control means).

  In addition, when the determination in step S16 becomes Yes despite the NOx reduction due to the application of the first NOx reduction map, the NOx emission amount of the NOx into the atmosphere is reduced in the first NOx reduction map due to sulfur poisoning of the NOx catalyst 19. It is considered that the increase cannot be suppressed, and the second NOx reduction map is set as the operation region map in step S18. In subsequent step S20, it is determined whether or not the output of the NOx sensor 34 is equal to or greater than the second NOx determination value. If the determination is no, the process returns to step S8. Therefore, in this case, the second NOx reduction map in which the lean region is further reduced instead of the first NOx reduction map is applied to the fuel injection control, and the NOx emission amount of the engine out is further reduced. The second NOx determination value may be the same value as the first NOx determination value or may be set separately.

  In addition, when the determination in step S20 becomes Yes despite the NOx reduction due to the application of the second NOx reduction map, the second NOx reduction map considers that the increase in the NOx emission amount cannot be suppressed, and the operation is performed in step S22. After setting the third NOx reduction map as the region map, the process returns to step S8. Therefore, in this case, the third NOx reduction map that eliminates the lean region is applied to the fuel injection control, and the NOx emission amount of the engine out is further reduced.

  On the other hand, when such an operation region map is sequentially switched, when the NOx catalyst 19 is shifted to an engine operation state in which the temperature can be raised and the determination in step S8 becomes Yes, the S purge is immediately performed in step S10. In step S12, the operation region map is returned to the initial setting map. As a result, sulfur poisoning of the NOx catalyst 19 is eliminated, and the operation region map returns to the initially set initial map.

Next, the execution state of the fuel injection control accompanying the switching of the operation region map by the ECU 31 will be described.
In the first NOx reduction map of FIG. 3 that is switched from the initial setting map of FIG. 2 when the S purge cannot be executed as described above, the reduced amount of the lean area with respect to the initial setting map is set as the timer area. Since the stoichiometric operation is basically performed in the timer area in the same manner as the stoichiometric area, the frequency of the stoichiometric operation is increased, resulting in a decrease in engine-out NOx emissions compared to lean operation, and sulfur poisoning. As a result, even if the NOx storage capacity of the NOx catalyst 19 is reduced, an increase in the amount of NOx discharged into the atmosphere can be suppressed.

  Further, when the first NOx reduction map is applied, when the engine 1 shifts from the lean region side to the timer region with a change in the operation state, the lean operation is continued for a preset delay time Tdelay and then the stoichiometric operation is continued. On the other hand, if the operation is switched to the timer region but returns to the lean region before the delay time Tdelay elapses, the lean operation is continued without being switched to the stoichiometric operation. As a result, the stoichiometric operation and the lean operation are performed. Frequent switching between and is prevented.

  The delay time Tdelay is the NOx occlusion capacity of the current NOx catalyst 19, more specifically, until the NOx emission amount of the engine out increases due to the shift to the timer region, and the NOx catalyst 19 begins to exhaust the NOx without being occluded. Therefore, even if the operation shifts to the timer region while the lean operation is being performed, the NOx emission amount to the atmosphere does not increase so as to cause a problem until the delay time Tdelay elapses.

  In addition, by delaying the switching to the stoichiometric operation by an amount corresponding to the delay time Tdelay in this way, the total lean operation time can be extended, and when returning to the lean region before the delay time Tdelay elapses To prevent frequent switching between stoichiometric operation and lean operation by continuing lean operation, and to reduce the number of tailings for the purpose of suppressing torque steps during operation switching and to execute tailing Can save fuel consumption. In addition, in a short-time stoichiometric operation in the timer region, NOx that has started to be released from the NOx catalyst 19 is discharged without sufficient time to reduce, so from this point of view, a short-time stoichiometric operation can be prevented. preferable.

  Therefore, according to the exhaust gas purification apparatus for the engine 1 of the present embodiment, the NOx storage capability of the NOx catalyst 19 is increased by sulfur poisoning by increasing the execution frequency of the stoichiometric operation by reducing the lean region as in the technique of Patent Document 1. In addition to being able to suppress an increase in NOx emissions into the atmosphere even when there is a decrease, the total lean operation time is extended by continuing lean operation only in the timer region for the delay time Tdelay. In addition, fuel consumption due to frequent switching between stoichiometric operation and lean operation can be reduced, thereby minimizing the adverse effects of fuel consumption deterioration due to the increase in the frequency of stoichiometric operation as the lean region is reduced. can do.

Further, when the increase in the NOx emission amount cannot be suppressed even when the first NOx reduction map is applied, the second NOx reduction map in which the lean region is further reduced is applied, and the second NOx reduction map also has the same timer as the first NOx reduction map. In the region, the lean operation is continued only for the delay time Tdelay, and the same fuel consumption reduction effect is obtained.
Then, the lean region is gradually reduced from the initial setting map to the first NOx reduction map and the second NOx reduction map in accordance with the decrease in the NOx storage capacity of the NOx catalyst 19 due to sulfur poisoning, while the lean region is reduced. The timer area is always positioned on the high load high rotation side of the lean area.

  Therefore, with respect to the NOx storage capacity of the NOx catalyst 19 at that time, it is possible to suppress the increase in NOx emission by increasing the execution frequency of stoichiometric operation by reducing the lean region without excessive or insufficient, for example, reducing the excessive lean region. Thus, it is possible to prevent deterioration of fuel consumption when the frequency of execution of stoichiometric operation increases or increase in NOx emission when stoichiometric operation is not executed due to insufficient reduction of the lean region.

Also, following the reduction of the lean region, the timer region is always set to the high load high rotation side of the lean region, i.e., the NOx emission amount of the engine out increases, but it is set to a region where lean operation can be performed for a short time. The lean operation can be continued based on the delay time Tdelay in an appropriate timer region, and the fuel consumption reduction effect can be reliably obtained.
Here, the continuation of the lean operation limited to the delay time Tdelay can be executed in a region slightly exceeding the lean region toward the high load and high rotation side, but in the region significantly exceeding the lean region, the NOx emission amount of the engine out is reduced due to the lean operation. Since it increases rapidly, there is a possibility of increasing NOx emissions into the atmosphere. In this embodiment, since the reduced amount of the lean region is set as the timer region in the first and second NOx reduction maps, the timer region is necessarily reduced together with the reduction of the lean region, and the upper limit on the high load high rotation side is limited. As a result, it is possible to set a more appropriate timer area that does not cause the above-described problem.

For example, the outer area of the timer area may be left as the outer boundary line L1 without reducing the timer area together with the lean area.
On the other hand, in the lean region of the first and second NOx reduction maps, NOx discharged from the engine 1 during lean operation is occluded in the NOx catalyst 19, and NOx purging is performed for each first lean duration T1lean. The stored NOx is released and reduced. Such NOx occlusion / release reduction is continued as long as the lean operation is continued even after the transition from the lean region to the timer region. In the timer region, the second lean continuation time shorter as shown in FIG. A NOx purge is executed every T2lean.

  Here, in the timer region, as compared with the lean region, the NOx emission amount of the engine-out increases with the increase of the target average effective pressure Pe and the engine rotational speed Ne, so the sulfur poisoning situation of the NOx catalyst 19 is the same. Even if the NOx occlusion amount of the NOx catalyst 19 is saturated earlier, the NOx purge is also performed earlier in the timer region based on the shorter second lean duration T2lean as described above. As a result, NOx emission into the atmosphere due to saturation of the NOx occlusion amount in the timer region can be more reliably prevented.

This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the exhaust purification device of the in-cylinder in-line four-cylinder gasoline engine 1 is embodied. However, the present invention is not limited to this, and the exhaust purification device may be embodied, for example, for a diesel engine.
In the above embodiment, the first to third NOx reduction maps in which the lean region is reduced stepwise in addition to the initial setting map are applied. However, the number of NOx reduction maps is not limited to this, for example, the third NOx reduction The map may be omitted, or a number of more detailed NOx reduction maps may be applied.

1 is an overall configuration diagram illustrating an engine exhaust gas purification apparatus according to an embodiment. It is a figure which shows an initial setting map. It is a figure which shows a 1st NOx reduction map. It is a figure which shows a 2nd NOx reduction map. It is a figure which shows a 3rd NOx reduction map. It is a time chart which shows the execution situation of NOx purge in the lean region. It is a time chart which shows the execution condition of NOx purge in the timer area. 4 is a flowchart showing a SOx purge control / map switching routine executed by an ECU.

Explanation of symbols

1 engine (internal combustion engine)
17 Exhaust passage 19 NOx catalyst 31 ECU (NOx purge control means, air-fuel ratio control means, poisoning determination means,
Control means during poisoning)

Claims (4)

An occlusion type NOx catalyst that is provided in an exhaust passage of an internal combustion engine, occludes NOx in exhaust gas in an oxygen-excess atmosphere, and releases and reduces NOx occluded in an oxygen-concentrated atmosphere;
NOx purge control means for controlling the exhaust air-fuel ratio of the internal combustion engine to a theoretical air-fuel ratio or a rich air-fuel ratio, and releasing and reducing NOx stored in the NOx catalyst;
When the internal combustion engine is operated at a lean air-fuel ratio when the operation region of the internal combustion engine is in a predetermined lean region, while the operation region of the internal combustion engine is in a non-lean region on the high-load high-rotation side from the lean region Air-fuel ratio control means for operating the internal combustion engine at a non-lean air-fuel ratio;
Poisoning judging means for judging the sulfur poisoning state of the NOx catalyst;
When the poisoning determination means determines that the NOx catalyst is poisoned by sulfur, the lean region is reduced to a low load and low rotation side, and a timer region is set at the boundary between the lean region and the non-lean region. And a poisoning time control means for switching the lean air-fuel ratio in the lean region to the non-lean air-fuel ratio after continuing the predetermined delay time when the operating region of the internal combustion engine shifts from the lean region to the timer region. An exhaust emission control device for an internal combustion engine, comprising:   The poisoning time control means gradually reduces the lean area to the low load and low rotation side in accordance with the progress of sulfur poisoning of the NOx catalyst, and follows the reduction of the lean area to reduce the timer area. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is set.   3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the poisoning time control means sets the reduced amount of the lean region as the timer region.   The NOx purge control means executes the NOx release reduction process for each first lean continuation time set in advance in the lean region, and when the transition from the lean region to the timer region is performed, the first lean The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the NOx emission reduction process is executed every second lean continuation time shorter than the continuation time.

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