JP4244510B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus for an internal combustion engine having a storage type NOx catalyst in an exhaust passage.
[0002]
[Prior art]
In recent years, lean combustion internal combustion engines in which an internal combustion engine is operated at a lean air-fuel ratio to improve fuel efficiency have been put into practical use. In this lean combustion internal combustion engine, when operating at a lean air-fuel ratio, there is a problem that the three-way catalyst cannot sufficiently purify NOx (nitrogen oxide) in the exhaust gas due to its purification characteristics. Recently, for example, at a lean air-fuel ratio, A storage-type NOx catalyst that stores or adsorbs NOx in exhaust gas during operation (hereinafter simply referred to as storage) and releases and reduces NOx stored during operation at a stoichiometric or rich air-fuel ratio is provided. Exhaust gas purification catalyst devices have been adopted.
[0003]
This occlusion-type NOx catalyst converts NOx in exhaust gas to nitrate (X-NO) in an oxygen excess state of an internal combustion engine. _Three ) Adsorbed and occluded, and the occluded NOx is released mainly in an excess state of carbon monoxide (CO) to form nitrogen (N ₂ ) To reduce (at the same time carbonate X-CO _Three Is produced). Therefore, in practice, when the lean air-fuel ratio operation continues for a predetermined time, the exhaust air-fuel ratio is controlled to the stoichiometric air-fuel ratio or the rich air-fuel ratio by switching the air-fuel ratio in the combustion chamber or supplying the reducing agent to the exhaust pipe. Switching to rich air-fuel ratio operation periodically (this is called a rich spike), thereby creating a reducing atmosphere with a large amount of CO in an atmosphere with a low oxygen concentration, and releasing the stored NOx and purifying and reducing (NOx purge). The type NOx catalyst can be regenerated. Such a technique is disclosed in, for example, Japanese Patent No. 2586738.
[0004]
By the way, in such a storage type NOx catalyst, there is a limit to the amount of NOx that can be stored on the catalyst, and when the amount of NOx stored by the storage type NOx catalyst reaches the limit amount, as described above, rich spike is performed, The rich air-fuel ratio operation is performed for a predetermined time under a predetermined rich air-fuel ratio.
[0005]
However, when the NOx occlusion amount in the occlusion type NOx catalyst reaches the limit and the rich spike is required, the operation of the internal combustion engine that affects the deterioration degree of the NOx purification efficiency of the occlusion type NOx catalyst and the flow rates of NOx and CO is affected. Varies depending on conditions. For example, Japanese Patent Application Laid-Open No. 7-166681 discloses that the NOx amount occluded by such an occlusion-type NOx catalyst is detected and regenerated.
[0006]
The “exhaust gas purification device” disclosed in this publication arranges a NOx absorbent in an exhaust passage of an internal combustion engine, arranges a NOx sensor downstream of the NOx absorbent, and detects a detected value ( When the concentration of the NOx component) exceeds the determination value, regeneration control (NOx purge) is performed in which the exhaust air-fuel ratio is made rich and the NOx is released from the catalyst.
[0007]
[Problems to be solved by the invention]
By the way, the regulation value by the NOx emission regulation of the countries of the world is, for example, the total NOx emission amount with respect to a predetermined travel distance. In the above-described conventional “exhaust gas purification device”, the regeneration control is executed by detecting the concentration of the NOx component in a certain short period of each lean operation section. Therefore, the determination value is set depending on how the driver operates. If the margin is small, there is a possibility that a desired NOx emission amount, for example, a regulation value cannot be surely cleared when viewed at every predetermined travel distance.
[0008]
That is, in the above-described “exhaust gas purification device”, it is not known whether the total NOx emission amount for a predetermined travel distance exceeds a desired value, for example, a regulation value during operation. Even when the operation is performed, the above determination value for starting the regeneration control (NOx purge) is set sufficiently low with a sufficient margin so that the total NOx emission amount at the predetermined travel distance is less than the predetermined value. It is necessary to keep. By setting the determination value in this manner, the frequency of regeneration control (NOx purge) that makes the air-fuel ratio rich or stoichiometric increases by a sufficient margin, and fuel efficiency deteriorates. That is, CO ₂ This causes a problem that the amount of discharge increases.
[0009]
In addition, as what controls NOx discharge | emission amount per predetermined travel distance within a predetermined value, for example, there is what was disclosed in Japanese Patent No. 2503387, and “electronic internal combustion engine control device” disclosed in this gazette Since the NOx emission amount is controlled by controlling the ignition timing and EGR amount only in the stoichiometric operation region, when applied to the lean combustion internal combustion engine that operates at the lean air-fuel ratio as described above, the air-fuel ratio is always maintained. It must be in the stoichi driving range and fuel consumption cannot be improved.
[0010]
A lean combustion internal combustion engine equipped with an occlusion-type NOx catalyst is required to improve both fuel efficiency and exhaust performance. For example, it is conceivable that the lean air-fuel ratio is set even in the operating region during acceleration. However, if the lean air-fuel ratio region is increased, the NOx emission amount may increase and the exhaust performance may deteriorate.
[0011]
Thus, in a lean combustion internal combustion engine equipped with an occlusion-type NOx catalyst, it is important to comprehensively manage and improve both fuel efficiency and exhaust performance.
[0012]
The present invention has been made in view of the above situation, and it is possible to reliably suppress the NOx emission amount to a desired amount by directly managing the NOx emission amount released into the atmosphere even under an acceleration operation condition without causing deterioration of fuel consumption. NOx emission reduction and CO ₂ It is an object of the present invention to provide an exhaust emission control device for an internal combustion engine that can achieve both reductions in emissions.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust emission control device for an internal combustion engine according to claim 1 of the present invention is provided in an exhaust passage of the internal combustion engine and stores NOx in exhaust gas when the exhaust air-fuel ratio is a lean air-fuel ratio. And an exhaust purification device that reduces and purifies the stored NOx when the exhaust air-fuel ratio is a stoichiometric air-fuel ratio or a rich air-fuel ratio; In accordance with a lean zone map divided into an acceleration lean operation permission region and an acceleration lean operation prohibition region, it is determined whether or not to permit operation at a lean air-fuel ratio during engine acceleration operation, Calculate the total NOx emissions and the relationship between the total NOx emissions and the distance traveled by the vehicle When the total emission increases from the predetermined relationship, the acceleration lean operation permission area of the lean zone map becomes narrower. Control means for permitting operation at a lean air-fuel ratio even during acceleration operation when the total emission amount has a margin due to the relationship between the total NOx emission amount and the travel distance of the vehicle. Balance total emissions management.
[0014]
An internal combustion engine exhaust gas purification apparatus according to claim 1 of the present invention is also provided. , N The NOx occlusion performance is efficiently recovered by increasing the NOx reduction opportunities at the same time as efficiently suppressing the total amount of Ox emissions.
[0015]
Further, the claims of the present invention 2 In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the vehicle is distance If it is derived that the total amount of NOx emissions exceeds the predetermined amount before reaching the value, it has a function of stopping or suppressing the operation at the lean air-fuel ratio in all regions except during acceleration operation, distance The total NOx emission amount is reliably suppressed within a predetermined value.
[0016]
The travel distance is preferably applied to the travel period of the vehicle, and the total NOx emission amount is preferably calculated based on the NOx concentration (detected value or estimated value) of the exhaust discharged into the atmosphere.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic configuration of an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention, FIGS. 2 to 6 are control flowcharts of the exhaust gas purification apparatus for an internal combustion engine of the present embodiment, and FIG. FIG. 8 shows a lean zone map based on the engine speed and the target average effective pressure. FIG. 9 shows the required output for the travel distance, the air-fuel ratio mode, and the total NOx emission. A time chart showing the relationship, FIG. 10 shows a NOx purge time chart.
[0018]
The internal combustion engine (hereinafter referred to as an engine) according to the present embodiment, for example, by switching the fuel injection mode (operation mode), the fuel injection in the intake stroke (intake stroke injection mode) or the fuel injection in the compression stroke ( This is an in-cylinder injection type spark ignition type in-line four-cylinder gasoline engine capable of performing a compression stroke injection mode). The in-cylinder injection type engine can easily operate at a stoichiometric air-fuel ratio (stoichiometric), operation at a rich air-fuel ratio (rich air-fuel ratio operation), or an operation at a lean air-fuel ratio (lean air-fuel ratio operation). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.
[0019]
In this embodiment, as shown in FIG. 1, an electromagnetic fuel injection valve 14 is attached to the cylinder head 12 of the engine 11 together with a spark plug 13 for each cylinder, and combustion is performed by the fuel injection valve 14. Fuel can be directly injected into the chamber 15. A fuel supply device (fuel pump) is connected to the fuel injection valve 14 via a fuel pipe (not shown), and the fuel in the fuel tank is supplied at a high fuel pressure. The fuel is supplied from the fuel injection valve 14 to the combustion chamber. 15 is injected at a desired fuel pressure. At this time, the fuel injection amount is determined from the fuel discharge pressure of the fuel pump and the valve opening time (fuel injection time) of the fuel injection valve 14.
[0020]
An intake port is formed in the cylinder head 12 in a substantially upright direction for each cylinder, and one end of an intake manifold 16 is connected so as to communicate with each intake port. A drive-by-wire (DBW) type electric throttle valve 17 is connected to the other end of the intake manifold 16, and the throttle valve 17 is provided with a throttle sensor 18 for detecting a throttle opening θth. Further, an exhaust port is formed in the cylinder head 12 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 19 is connected to communicate with each exhaust port.
[0021]
The engine 11 is provided with a crank angle sensor 20 that detects a crank angle. The crank angle sensor 20 can detect the engine rotational speed Ne. Note that the above-described in-cylinder injection engine 11 is already known, and a detailed description thereof will be omitted here.
[0022]
An exhaust pipe (exhaust passage) 21 is connected to the exhaust manifold 19 of the engine 11, and the exhaust pipe 21 is illustrated via a small three-way catalyst 22 and an exhaust purification catalyst device 23 close to the engine 11. No muffler is connected. A portion of the exhaust pipe 21 between the three-way catalyst 22 and the exhaust purification catalyst device 23 is located immediately upstream of the exhaust purification catalyst device 23, that is, immediately upstream of the storage type NOx catalyst 25 described later. A high temperature sensor 24 for detecting the exhaust temperature is provided.
[0023]
This exhaust purification catalyst device 23 has a NOx reduction function for storing NOx in the exhaust gas when the exhaust air-fuel ratio is a lean air-fuel ratio, and a harmful substance (HC) in the exhaust gas when the exhaust air-fuel ratio is close to the theoretical air-fuel ratio. , CO, NOx) in order to have a redox function for purifying the catalyst, the storage NOx catalyst 25 and the three-way catalyst 26 are provided, and the three-way catalyst 26 is the storage type. It is disposed downstream of the NOx catalyst 25.
[0024]
The three-way catalyst 26 also serves to reduce NOx that could not be reduced by the storage NOx catalyst 25 itself when NOx stored from the storage NOx catalyst 25 is released. The exhaust purification catalyst device 23 has a sufficient function of a three-way catalyst (herein referred to as a three-way function) that reduces the NOx and oxidizes HC and CO by the occlusion-type NOx catalyst 25. The occlusion-type NOx catalyst and the three-way catalyst may be integrated with the occlusion-type NOx catalyst 25 alone.
[0025]
This NOx storage catalyst 25 temporarily stores NOx in an oxidizing atmosphere (NOx reduction function), releases NOx in a reducing atmosphere mainly containing CO, and N ₂ It has a reducing function of reducing to (nitrogen) or the like. Specifically, the storage-type NOx catalyst 25 is configured as a catalyst having platinum (Pt), rhodium (Rh) or the like as a noble metal, and the storage material is made of an alkali metal such as barium (Ba) or an alkaline earth metal. It has been adopted. A NOx sensor 27 that detects the NOx concentration is provided downstream of the exhaust purification catalyst device 23.
[0026]
Further, an ECU (electronic control unit) 28 is provided as a control means having an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like. Thus, comprehensive control of the exhaust emission control device of the present embodiment including the engine 11 is performed. That is, various sensors such as the high temperature sensor 24 and the NOx sensor 27 described above are connected to the input side of the ECU 28, and detection information from these sensors is input.
[0027]
On the other hand, the ignition plug 13 and the fuel injection valve 14 described above are connected to the output side of the ECU 28 via an ignition coil. The ignition coil, the fuel injection valve 14 and the like are detected information from various sensors. The optimum values such as the fuel injection amount and ignition timing calculated based on the above are output. Accordingly, an appropriate amount of fuel is injected from the fuel injection valve 14 at an appropriate timing, and ignition is performed at an appropriate timing by the spark plug 13.
[0028]
Actually, in the ECU 28, the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure Pe, based on accelerator opening information from an accelerator opening sensor (not shown) and engine rotational speed information Ne from the crank angle sensor 20. Further, the fuel injection mode is set from a map (not shown) according to the target average effective pressure Pe and the engine rotational speed information Ne. For example, when both the target average effective pressure Pe and the engine rotational speed Ne are small, the fuel injection mode is set to the compression stroke injection mode, and fuel is injected in the compression stroke, while the target average effective pressure Pe increases, or the engine When the rotational speed Ne increases, the fuel injection mode is changed to the intake stroke injection mode, and fuel is injected in the intake stroke.
[0029]
Then, a target air-fuel ratio (target A / F) as a control target is set from the target average effective pressure Pe and the engine speed Ne, and an appropriate amount of fuel injection is determined based on the target A / F. Further, the catalyst temperature Tcat is estimated from the exhaust gas temperature information detected by the high temperature sensor 24. Specifically, in order to correct an error caused by the high temperature sensor 24 and the storage-type NOx catalyst 25 being somewhat apart from each other, the temperature is determined according to the target average effective pressure Pe and the engine rotational speed information Ne. The difference map is set in advance by experiments or the like, and the catalyst temperature Tcat is uniquely estimated when the target average effective pressure Pe and the engine rotational speed information Ne are determined.
[0030]
Hereinafter, the operation of the exhaust gas purification apparatus for an internal combustion engine of the present embodiment configured as described above will be described.
[0031]
In the occlusion type NOx catalyst 25 of the exhaust purification catalyst device 23, NOx in the exhaust is occluded as nitrate in an oxygen excess atmosphere as in the super lean combustion operation in the lean mode, and the exhaust gas is purified. On the other hand, in an atmosphere where the oxygen concentration is reduced, the nitrate stored in the storage-type NOx catalyst 25 reacts with the CO in the exhaust to generate carbonate and release NOx. Therefore, when NOx storage into the storage-type NOx catalyst 25 proceeds, CO is supplied by reducing the oxygen concentration by enriching the air-fuel ratio or performing additional fuel injection, and the NOx is stored from the storage-type NOx catalyst 25. Release and maintain function.
[0032]
In the present embodiment, the vehicle travel distance is detected based on a signal from the vehicle speed sensor as a parameter value correlated with the travel distance of the vehicle, while the NOx concentration released from the NOx storage catalyst 25 by the NOx sensor 27 is detected. The ECU 28 calculates the total NOx emission amount that can be released into the atmosphere based on the output of the NOx sensor 27. Further, before the ECU 28 reaches a predetermined travel distance, the total NOx emission amount is a predetermined value. The exhaust air-fuel ratio is changed to the stoichiometric air-fuel ratio or the rich air-fuel ratio when exceeding the above, so that NOx is released from the storage-type NOx catalyst 25 and reduced and purified (NOx purge), and NOx emission thereafter is suppressed. I have to.
[0033]
In the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the total NOx emission amount is calculated, and the NOx total emission amount and the required output are calculated based on the relationship between the total NOx emission amount and the travel distance as the travel period of the vehicle. When there is a margin in the travel distance, even when the engine 11 is accelerating, it can be operated at a lean air-fuel ratio if NOx can be stored. When the NOx total emission amount is in an increasing state, the operating range at the lean air-fuel ratio during the acceleration operation of the engine 11 is narrowed to efficiently suppress the NOx total emission amount and simultaneously reduce and purify the stored NOx. While increasing the opportunity to efficiently restore the NOx storage performance, the NOx emission is suppressed. Further, if it is derived that the total NOx emission exceeds the predetermined value before the vehicle reaches the predetermined travel distance, the operation at the lean air-fuel ratio is limited in all operation regions, and the NOx total emission is within the predetermined travel distance. The discharge amount is surely suppressed within a predetermined value.
[0034]
Here, this NOx emission amount control will be described based on the flowcharts of FIGS.
[0035]
As shown in FIG. 2, the operation region is recognized in step S1. That is, in step S1, acceleration stoichiometric determination and steady lean determination are performed, and it is recognized whether acceleration operation or steady operation. After the acceleration operation or the steady operation is recognized, the air-fuel ratio mode (A / F mode) determination by the allowable breakthrough inspection is performed in step S2 (details will be described later with reference to FIG. 4). When the lean operation is continued and the NOx emission amount is greatly deteriorated, that is, after the allowable breakthrough (forced) NOx purge is performed, in step S2, the A / F mode determination by the allowable breakthrough inspection ( Lean prohibition or permission determination) is performed.
[0036]
After the A / F mode determination by the allowable breakthrough inspection, the A / F mode determination by the discharge amount inspection is performed in step S3 (details will be described later based on FIG. 5). A / F mode determination (stoichiometric operation or lean operation, or other than lean operation or lean operation) is performed according to the required output to the engine 11. In this determination, even during acceleration operation, stoichiometric operation (including rich operation) is prohibited and lean operation can be performed (operation with a lean air-fuel ratio is permitted). Accordingly, since the lean air-fuel ratio operation can be performed even during acceleration operation, fuel efficiency is improved.
[0037]
In step S4, it is determined whether or not the lean operation (W / lean) is switched to a mode other than the lean operation (W / O lean). If it is determined that the mode is switched to a mode other than the lean operation, the lean continuation time is determined in step S5. It is determined whether or not T1 is exceeded. If it is determined in step S5 that the lean continuation time exceeds the determination value T1, NOx purge is started in step S6 (details will be described later with reference to FIG. 6).
[0038]
After the NOx purge, the lean continuation time is reset in step S7. If it is determined in step S5 that the lean continuation time is equal to or less than the determination value T1, the lean continuation time is reset in step S7. The lean continuation time determination value T1 is set to, for example, a short time of about 5 seconds, and prevents NOx purge from being performed more frequently than necessary immediately after switching from lean operation to non-lean operation. Yes. If it is determined in step S4 that the operation has not been switched to other than the lean operation, or after the lean duration time is reset in step S7, the process returns.
[0039]
In the present embodiment, as shown in FIG. 3, the NOx emission amount and the travel distance during the lean operation are detected by a control by a subroutine. The detection of the NOx emission amount and the travel distance will be described.
[0040]
As shown in FIG. 3, it is determined in step S11 whether the elapsed time after the start of lean exceeds a predetermined value t. Since the output of the NOx sensor 27 may not be stable immediately after switching from stoichiometric operation or rich operation to lean operation, the output of the NOx sensor 27 is not seen for a predetermined value t after the start of lean operation. The masked state. Therefore, if the elapsed time after the start of lean does not exceed the predetermined value t in step S11, the output of the NOx sensor 27 is set to M1 in step S12, and the NOx value until the output of the NOx sensor 27 becomes stable is a temporary value. Let M1.
[0041]
As a method for setting the value of M1, immediately after lean switching, all NOx is occluded in the occlusion-type NOx catalyst 25, and almost no NOx may be discharged, and may be set to zero. Further, based on the output Nt of the NOx sensor 27 at the time t after the start of the lean operation, the discharge amount of the NOx sensor 27 between t is expressed as Nt × t × 1/2 (linearly NOx from the start of lean to the time t has elapsed. NOx sensor 27 is calculated based on the output Nt, and the amount of NOx sensor 27 discharged during t is Nt x t x 1/3 (NOx increases in a convex curve from the start of lean until t elapses) (Assuming that).
[0042]
When it is determined in step S11 that the elapsed time after the start of lean exceeds the predetermined value t, or after the output of the NOx sensor 27 is set to M1 in step S12, the process proceeds to step S13 to calculate the NOx emission value. . The NOx emission value can be calculated by the following equation (1).
NOx emission value = NOx sensor 27 output x intake air amount x coefficient x calculation cycle (1)
However, the coefficient is for adjusting the unit.
Then, after calculating the NOx emission value in step S13, the total NOx emission amount is calculated in step S14. The total NOx emission amount can be calculated by the following equation (2).
Total NOx emissions = previous total NOx emissions + NOx emissions value (2)
Further, the travel distance is calculated in step S15. The travel distance can be calculated by the following equation (3).
Travel distance = previous travel distance + vehicle speed x calculation cycle (3)
[0043]
Since the output of the NOx sensor 27 is the NOx concentration (ppm), when calculating the exhaust amount from the concentration, here the product of the intake air amount is taken as a representative of the exhaust amount. The intake air amount may be set by a preset load / rotation speed map of the engine 11 or the exhaust flow rate may be directly obtained.
[0044]
An acceleration stoichiometric permission line map PS1 (described later) is set based on the total NOx emission amount and the travel distance obtained by the equations (2) and (3), and the required output is PS1 of the lean zone map (described later) at that time. The stoichiometric operation or lean operation (other than lean operation or lean operation) is determined by comparing with the value of.
[0045]
After calculating the travel distance, it is determined whether or not the travel distance has reached the management travel distance L1 in step S16. If it is determined that the travel distance has reached the management travel distance L1, the travel distance and the total NOx emission amount are determined in step S17. Is set to 0 (reset) and the calculation is repeated again (return). If it is determined in step S16 that the management travel distance L1 has not been reached, the process returns as it is.
[0046]
The acceleration stoichiometric permission line map PS1 will be described with reference to FIG. The acceleration stoichiometric permission line map PS1 sets a lean operation upper limit output line during acceleration.
[0047]
As shown in FIG. 7, the acceleration stoichiometric permission line map PS1 is divided into a plurality of regions in which the horizontal axis is the travel distance and the vertical axis is the NOx total discharge amount. Here, the NOx total discharge is performed at the management travel distance L1. The lower side of the line passing through the point where the amount becomes a predetermined amount is PS1 = A. In the zone of PS1 = A, if the increasing pace of the NOx emission amount is equal to or less than this pace, the total NOx emission amount at the management travel distance L1 does not exceed the predetermined amount. Here, the areas that are partitioned by a plurality of lines substantially parallel to A and the total NOx emission amount is lower than the predetermined amount are PS1 = B, C, and D regions, respectively, and the total NOx emission amount = predetermined amount (management) The outside (upper side) of the NOx emission amount line is the PS1 = E region. Therefore, the lean operation upper limit output line at the time of acceleration is set according to which region of the acceleration stoichiometric permission line map PS1 the intersection of the current travel distance and the total NOx emission amount is.
[0048]
In addition, since there is a margin to the predetermined amount of the total NOx emission amount for the portion where the travel distance is short, it is also possible to raise the line to the side where the total NOx emission amount is large in order to increase the lean frequency. The management travel distance L1 can be set to, for example, 1 km or the exhaust gas mode travel distance. The predetermined amount of total NOx emission may be set to the exhaust gas mode regulation value per km when the management travel distance L1 is 1 km, and per 1 km when the management travel distance L1 is the exhaust gas mode travel distance. The exhaust gas mode regulation value may be multiplied by the exhaust gas mode travel distance. Further, the predetermined amount of the total NOx emission amount may be a value obtained by multiplying the above value by a margin rate.
[0049]
The lean zone map will be described with reference to FIG. The lean zone map is used to determine whether or not to permit lean during acceleration operation with respect to the current required output.
[0050]
As shown in FIG. 8, the lean zone map includes a plurality of equal output lines (A to D) connecting points where the engine output is equal in a region where the horizontal axis is the engine rotation speed Ne and the vertical axis is the target average effective pressure Pe. ), The inside of each line is an acceleration stoichiometric (including rich) prohibition area (acceleration lean operation permission area), and the outside is an acceleration operation permission area in W / O lean (stoichiometry or rich). Then, it is determined whether or not the acceleration stoichiometric operation is possible (acceleration lean permission) by referring to the lean zone map and PS1 in FIG. The lines A to D may be an equal engine out NOx amount line or an equal tail pipe NOx amount line. In this case, whether or not the acceleration stoichiometric operation is possible is determined based on the engine-out NOx amount (comparison between the map value of the engine speed Ne and the target average effective pressure Pe and PS1, or the tail pipe NOx emission amount (output value of the NOx sensor 27)). The number of iso-output lines may be larger or smaller than A to D.
[0051]
In the lean zone map, for example, the outermost line A indicating the initial acceleration stoichiometric permission zone is set so that the lean operating region can be widened as much as possible from the combustion surface or the like without concern for fuel consumption. By doing so, the high load region also becomes a lean operation region, and lean operation is possible even at high acceleration. In actual operation, steady operation (generally lean operation) is small, and transient operation (generally, stoichiometric or rich operation during acceleration operation) is high. As a result, the lean frequency is improved and fuel efficiency is improved. As a result, all-lean driving is possible in the general driving range, and fuel efficiency is greatly improved. In the lean zone map, the lean operation region becomes narrower as PS1 changes from A to D. When PS1 is D, accelerated lean operation is prohibited in the entire region. When PS1 is E, all lean operations are prohibited in the entire region including those other than the acceleration operation such as during steady operation.
[0052]
Based on the acceleration stoichiometric permission line map PS1 shown in FIG. 7 and the lean zone map shown in FIG. 8, PS1 is obtained from the acceleration stoichiometric permission line map in the current vehicle state, and the requested output and PS1 are compared with the lean zone map. It is determined whether to permit acceleration stoichiometry or prohibit acceleration stoichiometry in the current vehicle state, that is, to allow acceleration lean, and execute an acceleration lean operation.
[0053]
Therefore, when lean operation is permitted during acceleration operation and fuel efficiency is improved, and the relationship between the total NOx emission amount and the travel distance is higher than the predetermined relationship, the operation at the lean air-fuel ratio during acceleration operation is performed. Since the region is narrowed, the total NOx emission amount can be efficiently suppressed, and at the same time, the NOx occlusion capacity can be efficiently recovered by increasing opportunities for reduction and purification of NOx occluded in the occlusion-type NOx catalyst 25. The improvement and the management of the total NOx emission amount can be efficiently made compatible. Further, when PS1 is E (when the management travel distance L1 exceeds a predetermined amount), all lean operations are prohibited in the entire area including the acceleration operation, so the total NOx up to the management travel distance L1, which is a predetermined period, is prohibited. The emission amount can be reliably suppressed to less than a predetermined amount that is the total management NOx emission amount.
[0054]
The allowable breakthrough inspection in step S2 will be described based on FIG.
[0055]
As shown in FIG. 4, it is determined in step S21 whether or not the lean continuation time exceeds a predetermined value T2, and if it is determined that it exceeds the predetermined value T2, lean is prohibited in step S22. The predetermined value T2 is larger than the above-described determination value T1, and is set to 30 seconds, for example. If it is determined in step S21 that the lean continuation time does not exceed the predetermined value T2, it is determined in step S23 whether the NOx average concentration is equal to or greater than the predetermined value M2. If it is determined in step S23 that the NOx average concentration is below the predetermined value M2, lean is permitted in step S24, and if it is determined in step S23 that the NOx average concentration is greater than or equal to the predetermined value M2, the process proceeds to step S22. Transition and lean are prohibited.
[0056]
The NOx average concentration is an average value between the predetermined values T2 of the NOx sensor 27. The NOx average concentration may be an instantaneous value when the predetermined value T2 has elapsed. The predetermined value M2 is preset by a map of the engine speed Ne and the target average effective pressure Pe. As a method for setting the predetermined value M2, when considering the NOx purge so as to ensure the purification efficiency of the storage-type NOx catalyst 25, for example, 50%, the engine-out NOx concentration is multiplied by 0.5. That's fine. If NOx breakthrough from the storage-type NOx catalyst 25 is not allowed, the predetermined value M2 may be set to a value close to 0. In this case, the predetermined value M2 may not be used as a map.
[0057]
That is, when the lean operation continues beyond the predetermined value T2, that is, when it is estimated that the NOx emission amount is greatly deteriorated and the catalyst temperature is lowered and the HC purification efficiency is deteriorated due to the continued lean operation. Forbids lean operation and forcibly performs NOx purge. When the NOx average concentration during the predetermined lean continuation time (until the predetermined value T2) is equal to or greater than the predetermined value M2, the NOx breakthrough state in which the NOx storage leaks because the NOx storage catalyst 25 cannot store NOx any more. After the allowable breakthrough, the lean operation is prohibited and NOx purge control is performed.
[0058]
The discharge amount inspection in step S3 will be described based on FIG.
[0059]
As shown in FIG. 5, in step S31, the required output is calculated by the following equation (4).
Required output = Target average effective pressure Pe x Engine rotation speed Ne x Coefficient (4)
After the requested output is calculated, it is determined in step S32 whether the requested output exceeds PS1. That is, the output line in FIG. 8 corresponding to PS1 (= A to E) obtained from the acceleration stoichiometric permission line map shown in FIG. 7 is compared with the required output, and the required output exceeds the PS1-compatible output. It is determined whether or not. For example, from the relationship between the travel distance and the total NOx emission amount, when the acceleration stoichiometric permission line map PS1 shown in FIG. 7 is set to PS1 = B, it is determined whether the requested output is inside or outside the line B in FIG. The
[0060]
If it is determined in step S32 that the required output exceeds PS1, since the required output is outside the line in FIG. 8, acceleration stoichiometry (including rich) is permitted in step S33, and the required output is less than PS1. If it is determined that there is, the requested output is inside the line in FIG. 8, and therefore, the acceleration stoichiometry (including rich) is prohibited in step S34, that is, acceleration lean is permitted. That is, lean operation is possible during acceleration operation, and fuel consumption can be improved. Next, in step S35, it is determined whether PS1 = E. If it is determined that PS1 = E, the lean operation is prohibited not only in the acceleration operation but also in the entire region including the steady operation, and the return becomes the PS1 = E. If it is determined that this is not the case, the process returns as it is.
[0061]
In the emission inspection, the required output is compared with PS1 of the lean zone map at that time (the value of PS1 is obtained from the acceleration stoichiometric permission line map PS1), and stoichiometric operation or lean operation (W / O lean operation or W / lean). Driving). When the total NOx emission amount reaches a predetermined amount in the acceleration stoichiometric permission line map, PS1 = E is set to prohibit the whole area acceleration lean and prohibit the steady lean, thereby prohibiting the whole area lean. When switching from W / lean operation to W / O lean operation, NOx purge control may be performed. Depending on the characteristics of the catalyst, the W / O lean operation (stoichiometric operation or rich operation) may be performed without performing the NOx purge control at the time of switching.
[0062]
As shown in FIG. 9, until the total NOx emission amount reaches the upper limit of the A zone (up to the travel distance La), the acceleration stoichiometric operation is permitted only for the required output exceeding PS1 = A, and the A / F The mode is stoichiometric (d portion), and the rest (a, b, c portion) is inhibited from acceleration stoichiometry and becomes lean. Until the total NOx emission reaches the upper limit of the B zone (up to the travel distance Lb), acceleration stoichiometry is permitted for the required output exceeding PS1 = B and the A / F mode is stoichiometric (corresponding to the example shown in the figure) None), otherwise (b portion), the acceleration stoichiometry is prohibited and the acceleration becomes lean. Until the total NOx emission reaches the upper limit of the C zone (up to the travel distance Lc), the acceleration stoichiometry is permitted for the required output exceeding PS1 = C, and the A / F mode becomes stoichiometric (parts c and d). In other cases (portion a), acceleration stoichiometry is prohibited and acceleration leans.
[0063]
When the required output is b, the acceleration stoichiometry is prohibited up to the travel distance Lb and the acceleration becomes lean. However, when the travel distance Lb is exceeded, the acceleration stoichiometry is permitted and the A / F mode is Become. Until the total NOx emission exceeds the upper limit of the C zone and reaches a predetermined amount (up to the travel distance Ld), the acceleration stoichiometry is permitted for the required output exceeding PS1 = D and the A / F mode becomes stoichiometric. (B, c part). Further, when the total NOx emission reaches a predetermined value, PS1 = E and the whole area lean is prohibited until the management travel distance L1, and the A / F mode becomes stoichiometric throughout the entire area, and the travel distance and the total NOx emission are reset. (See step S17).
[0064]
The NOx purge in step S6 will be described based on FIG. The NOx purge is a control for switching the air-fuel ratio A / F from lean operation to rich operation as NOx release control.
[0065]
As shown in FIG. 6, it is confirmed in step S61 that the rich purge is not completed and the NOx purge is not completed. In step S62, it is determined whether the rich purge is completed. Since the purge is not completed at first, the process proceeds to step S63, where it is determined whether the rich continuation time has exceeded t1. t1 is set by a function of the storage parameter and SV (Space Velocity: space velocity = gas flow rate / catalyst capacity).
[0066]
The storage parameter is a value that correlates with the amount of NOx stored in the storage-type NOx catalyst 25 and can be obtained from the output of the NOx sensor 27. For example, the stored NOx amount is calculated from the difference between the upstream and downstream NOx amounts of the storage-type NOx catalyst 25. In this case, the NOx amount upstream of the storage type NOx catalyst 25 may be obtained from a map with respect to the engine rotational speed Ne and the target average effective pressure Pe, or a new NOx sensor may be installed (see Japanese Patent Laid-Open No. 7-166681). . Further, the storage parameter may be obtained simply by a map with respect to the engine speed Ne and the target average effective pressure Pe, and the rich continuation time or the stoichiometric continuation time becomes longer as the amount of NOx stored in the storage type NOx catalyst 25 increases. Is set as follows.
[0067]
Since the purged NOx amount is greatly affected by the CO amount, SV is used as a representative of the CO amount supplied to the storage-type NOx catalyst 25. Since the amount of generated CO is also affected by the air-fuel ratio A / F, when the air-fuel ratio A / F at the time of the rich purge is made variable according to the operating conditions or the like, the air-fuel ratio A / F in addition to the SV is also rich duration time It is preferable to add to this function.
[0068]
In step S63, since it is initially determined that the rich continuation time does not exceed t1, the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 25 after the rich purge is executed in step S64 is a predetermined air-fuel ratio richer than the stoichiometric ratio. To control. In the rich purge, the air-fuel ratio A / F is controlled by a map for the engine speed Ne and the target average effective pressure Pe, the throttle opening is controlled by a map for the engine speed Ne and the target average effective pressure Pe, The ignition timing is controlled based on the map for the speed Ne and the energization state. After the rich purge is started in step S64, it is determined in step S65 whether or not the target air-fuel ratio A / F (target A / F) is smaller than the pulse injection start air-fuel ratio AF1. This is a timing determination process for executing pulse injection at a predetermined timing at which the air-fuel ratio gradually changes by tailing toward a predetermined rich air-fuel ratio. Specifically, the pulse injection start air-fuel ratio AF1 may be a stoichiometric or rich A / F from which a large amount of NOx is released from the storage-type NOx catalyst 25.
[0069]
When it is determined in step S65 that the target air-fuel ratio A / F (target A / F) is smaller than AF1, that is, when the A / F passes AF1 during tailing from the lean operation to the rich purge operation, step S67. In step S68, it is determined whether or not the pulse duration is shorter than t2. Since it is not initially pulse-injected, it is determined that the pulse duration is shorter than t2, and pulse injection is started in step S68. In the pulse injection, since a large amount of NOx is released in the first period of the rich purge, the fuel injection in the expansion stroke is executed in order to supply HC that reduces NOx to the catalyst. The pulse injection duration t2 is set by a function of the storage parameter and SV. When the pulse injection duration exceeds t2, the process proceeds to step S62.
[0070]
If it is determined in step S63 that the rich continuation time has exceeded t1, it is determined in step S66 that the rich purge is complete. Thereafter, in step S62, it is determined that the rich purge is completed. The determination of the completion of the rich purge is performed by an O (not shown) downstream of the storage type NOx catalyst 25. ₂ When the sensor output changes from lean output to rich output (when it becomes V1 or more), it may be determined that the rich purge is complete (in principle, see No. 2692380). In this case, O ₂ A linear A / F sensor may be used instead of the sensor, and when a signal equivalent to these is output from the NOx sensor, the signal can also be used. Further, the upstream of the NOx storage type catalyst 25 is also O ₂ Install upstream sensor and always show rich output during rich purge. ₂ Downstream of the sensor ₂ The sensor output changes from lean output to rich output. ₂ It is also possible to determine that the rich purge is complete when the sensor outputs match.
[0071]
If it is determined in step S62 that the rich purge is completed, it is determined in step S69 whether or not the stoichiometric duration is shorter than t3. Initially, it is determined that the stoichiometric duration is shorter than t3, and in step S70, stoichiometric purge with the air-fuel ratio as the stoichiometric air-fuel ratio is executed. The stoichiometric purge may be executed by making the air-fuel ratio slightly richer than the stoichiometric air-fuel ratio by making the feedback gain differently set, and making it rich rich. Then, the stoichiometric purge time t3 is set by the occlusion parameter and the SV function, similarly to the above-described t1 and t2. When the stoichiometric duration exceeds t3, the routine proceeds to step S71 where the NOx purge is completed and a return is returned.
[0072]
In the NOx purge, the rich duration, the stoichiometric duration, and the pulse injection duration may be variable depending on the degree of catalyst deterioration. That is, as the catalyst deteriorates, the rich duration time and the pulse injection duration time are shortened and the stoichiometric duration time is lengthened. Further, the degree of deterioration may be determined as a function of the travel distance, or may be determined from the output of the NOx sensor (refer to Toku No. 2888124, etc.).
[0073]
As shown in FIG. 10, in the above-described NOx purge, when the air-fuel ratio A / F is switched from the lean operation to the rich operation, in order to mainly supply CO to the storage type NOx catalyst 25, for example, A / F = 12. From 1 to 5 seconds (t1). Since a large amount of NOx is released at the beginning of the rich period, HC that reduces NOx is supplied to the occlusion-type NOx catalyst 25. Therefore, when A / F reaches a predetermined value (when it passes AF1), for example, Pulse injection for injecting fuel in the expansion stroke for 0.1 to 0.5 seconds (t2) is executed. After that, since NOx is released slowly, it is only necessary to supply a small amount of CO and HC, so switching to stoichiometric operation (slight rich) with the air-fuel ratio as the stoichiometric air-fuel ratio, about 0-50% of the previous lean time For the time (t3). During the stoichiometric operation period, O (not shown) ₂ Feedback control by a sensor may be performed.
[0074]
For rich operation, pulse injection, and stoichiometric (slight rich) operation in NOx purge, the combination of each time and operation mode can be selected and changed depending on the release characteristics of the storage type NOx catalyst 25, the combination with the three-way catalyst, and the like. However, the present invention is not limited to the embodiment described above.
[0075]
In the above-described embodiment, when acceleration lean is permitted in step S35 in FIG. 5 during acceleration operation, the lean operation is continued until the acceleration operation ends. Only a part of the vehicle may be operated lean. For example, the transmission is shifted during acceleration, but a determination may be made as to whether or not to perform lean operation depending on the gear position. Specifically, even when acceleration lean is permitted, a determination condition may be added so that the acceleration stoichiometric operation is performed at a low gear and the acceleration lean operation is permitted only at a high gear. That is, even during a certain acceleration operation, the acceleration stoichiometric operation is performed during a low gear position, and the acceleration lean operation is performed when the gear is shifted to a high gear position. Further, even when acceleration lean is permitted depending on the vehicle speed or the engine rotation speed, a determination condition as to whether or not to actually perform acceleration lean may be added.
[0076]
Further, the first several percent of the acceleration operation and the remaining several percent may be divided into lean operation and stoichiometric operation. For example, during a certain acceleration operation, the first 50% may be a lean operation and the remaining 50% may be a stoichiometric operation. Conversely, the first 50% may be stoichiometric and the remaining 50% may be lean. In this case, it may be allocated according to time, or may be allocated according to the output between the output before acceleration and the required output (output assumed to arrive after acceleration). Further, this ratio may be a fixed value or may be determined based on the acceleration stoichiometric permission line map of FIG. That is, for example, as the total NOx emission in the B zone increases, each zone is further subdivided so that the lean operation ratio is reduced and the stoichiometric operation ratio is increased during a certain continuous acceleration operation. What is necessary is just to determine the ratio of driving | operation and stoichiometric operation. Also, instead of suddenly shifting from the C zone to the D zone, where leaning of the entire acceleration range is prohibited, a plurality of new zones are set between the C zone and the D zone, and as the total NOx emission increases, there is a certain continuous During acceleration operation, the zone setting may be such that the lean operation ratio is decreased and the stoichiometric operation ratio is increased.
[0077]
Further, the determination itself as to whether or not only a part of the continuous acceleration operation as described above is the lean operation may be included in the acceleration stoichiometric permission line map of FIG. That is, for example, when the total NOx emission amount in the B zone increases, each zone is further subdivided and only a part is made lean operation, such that only a part is made lean operation during a certain continuous acceleration operation. The determination itself may be made. Also, instead of suddenly shifting from the C zone to the D zone where leaning of the entire acceleration range is prohibited, a new zone is set between the C zone and the D zone, and only a part of the vehicle is leaned during a certain acceleration operation. You may make it drive.
[0078]
As described above, by making only part of the acceleration operation lean, the fuel consumption can be improved more optimally and the total NOx emission can be managed, and drivability can be improved.
[0079]
In the above-described embodiment, during acceleration operation, whether or not acceleration lean is permitted is determined only by comparing the output request and PS1 in step S32 in FIG. A condition of whether or not may be added. For example, the degree of acceleration is determined based on the accelerator depressing speed (speed of change in throttle opening). If the degree of acceleration is large, acceleration lean is prohibited and acceleration stoichiometry is set. Instead of acceleration, a change degree of the vehicle speed and a change degree of the engine rotation speed may be used.
[0080]
Further, NOx is discharged during acceleration in lean operation, the total NOx emission amount increases, the value of the acceleration stoichiometric permission line map PS1 in FIG. 7 is changed (for example, changed from B to C), and the lean zone in FIG. If the map line is changed (for example, changed from B to C as described above), and the required output enters the acceleration lean prohibition area (acceleration stoichiometric permission area), The lean operation may be stopped and the remaining acceleration operation may be changed to the stoichiometric operation.
[0081]
As described above, even when accelerating, permitting accelerated lean operation in accordance with the situation makes it possible to more optimally improve fuel efficiency and manage total NOx emissions, and also improve drivability.
[0082]
In the above-described embodiment, the NOx emission control is performed using the NOx sensor 27. However, the total NOx emission is calculated based on the engine operating state without using the NOx sensor 27, and the NOx emission control is performed. It can also be done. In this case, the NOx sensor 27 is not used, which is advantageous in terms of cost.
[0083]
The NOx emission value varies depending on the purification efficiency of the catalyst. In particular, the purification efficiency is significantly lowered when the storage NOx catalyst 25 is poisoned by S in the fuel, that is, sulfur (sulfur). On the other hand, if the catalyst whose purification efficiency is reduced by S poisoning is made rich at a high temperature (for example, 550 ° C. or higher), the S component accumulated in the catalyst is released and the catalyst is regenerated to restore the purification efficiency. (S regeneration). Therefore, when the total NOx emission amount A is obtained without using the NOx sensor 27, it is considered how much S is accumulated in the catalyst and the purification efficiency is lowered, that is, how much S regeneration is performed. May be.
[0084]
The above-described exhaust gas purification apparatus for an internal combustion engine changes the lean operation range in accordance with the NOx emission status, and therefore can optimally achieve both fuel consumption reduction and NOx emission reduction. That is, the acceleration stoichiometry is prohibited even during the acceleration operation according to the required output to the engine 11 and the lean operation can be performed (operation with a lean air-fuel ratio is permitted), and NOx is exhausted in the whole or part of the acceleration region. Since lean operation is performed according to the situation, it is possible to reliably reduce the NOx emission amount to a predetermined amount or less while increasing the lean operation region as much as possible to reduce fuel consumption. Further, since the operation permission at the lean air-fuel ratio is determined based on the total NOx emission amount (accumulation of NOx value) for a predetermined period, both fuel consumption reduction and NOx emission reduction can be reliably achieved. Further, since the NOx sensor 27 is used, the control can be performed more accurately and is not affected by catalyst deterioration. Furthermore, since the NOx sensor 27 is arranged on the most downstream side of the catalyst, it is possible to directly manage the NOx emission amount (NOx emission regulation value) from the tail pipe to the atmosphere.
[0085]
Further, lean operation is permitted during acceleration operation and fuel efficiency is improved, and the relationship between the total NOx emission amount and the travel distance is higher than the predetermined relationship, that is, from the A region to the B region to E in FIG. On the region side, as shown in FIG. 8, the lean zone based on the relationship between the target average effective pressure Pe and the engine rotational speed Ne is limited to narrow the operation region at the lean air-fuel ratio during acceleration operation. Therefore, the total NOx emission amount can be efficiently suppressed, and at the same time, the NOx occlusion capacity can be efficiently recovered by increasing the NOx occlusion capacity occluded in the occlusion-type NOx catalyst 25, thereby improving fuel efficiency and total NOx emission. It is possible to achieve both efficient management of quantity. Further, as shown in FIG. 8, in the lean zone map, an area E that prohibits all lean operations is set in the entire area, so that the total NOx emission amount up to the management travel distance L1 that is a predetermined period is predetermined. It can be reliably suppressed to be less than a predetermined amount within the range.
[0086]
In the above-described embodiment, the exhaust purification catalytic device having an occlusion type NOx catalyst has been described. However, the present invention generally enables lean operation by determining whether to perform stoichiometric or lean at the time of acceleration, which is generally stoichiometric operation. The catalyst is not limited to the type and arrangement of the catalyst. For example, the proximity three-way catalyst may be an exhaust manifold integrated type, or the proximity three-way catalyst may be absent. In the present embodiment, an occlusion type NOx catalyst is used for the exhaust purification catalyst device. However, an adsorption type NOx catalyst that directly reduces NOx adsorbed on the catalyst may be used. Furthermore, the engine type is not limited as long as the engine is capable of lean operation, and an intake pipe injection type lean burn engine or a diesel engine may be used.
[0087]
【The invention's effect】
An exhaust gas purification apparatus for an internal combustion engine according to a first aspect of the present invention is provided in an exhaust passage of the internal combustion engine and stores NOx in the exhaust gas when the exhaust air-fuel ratio is a lean air-fuel ratio, and the exhaust air-fuel ratio is the stoichiometric air-fuel ratio. Or an exhaust purification device that reduces and purifies the stored NOx when the air-fuel ratio is rich; In accordance with a lean zone map divided into an acceleration lean operation permission region and an acceleration lean operation prohibition region, it is determined whether or not to permit operation at a lean air-fuel ratio during engine acceleration operation, Calculate the total NOx emissions and the relationship between the total NOx emissions and the distance traveled by the vehicle When the total emission increases from the predetermined relationship, the acceleration lean operation permission area of the lean zone map becomes narrower. Control means for controlling the total NOx emissions and vehicle travel distance Therefore, it is possible to determine whether the stoichiometric operation or the lean operation is performed and to operate at the lean air-fuel ratio even during the acceleration operation. As a result, both improvement in fuel consumption and management of total NOx emission can be achieved.
[0088]
According to claim 1 of the present invention, there is provided an exhaust emission control device for an internal combustion engine. , N It is possible to efficiently reduce the NOx occlusion performance by efficiently suppressing the total amount of Ox emission and increasing the NOx reduction opportunities.
[0089]
Claim 2 In the exhaust emission control device for an internal combustion engine according to the present invention, the control means includes a distance If it is derived that the total amount of NOx emissions exceeds the predetermined amount before reaching the value, it has a function to stop or suppress the operation at the lean air-fuel ratio even during acceleration operation, distance It is possible to reliably suppress the total NOx emission amount within the standard.
[0090]
Therefore, the exhaust gas purification apparatus for an internal combustion engine according to the present invention can reliably suppress the NOx emission amount to a desired amount by directly managing the NOx emission amount released into the atmosphere even under accelerated operation conditions without causing deterioration of fuel consumption. NOx emission reduction and CO ₂ It is possible to achieve both reduction in emission amount.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a control flowchart of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment.
FIG. 3 is a control flowchart of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment.
FIG. 4 is a control flowchart of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment.
FIG. 5 is a control flowchart of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment.
FIG. 6 is a control flowchart of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment.
FIG. 7 is a lean zone map based on travel distance and total NOx emission.
FIG. 8 is a lean zone map based on the engine rotation speed and the target average effective pressure.
FIG. 9 is a time chart showing the relationship between the required output, the air-fuel ratio mode, and the total NOx emission amount with respect to the travel distance.
FIG. 10 is a time chart of NOx purge.
[Explanation of symbols]
11 engine
21 Exhaust pipe (exhaust passage)
22, 26 Three-way catalyst
23 Exhaust purification catalytic equipment
25 NOx storage type catalyst
27 NOx sensor
28 ECU (Electronic Control Unit)

Claims (2)

Provided in the exhaust passage of the internal combustion engine and stores NOx in the exhaust gas when the exhaust air-fuel ratio is a lean air-fuel ratio, and reduces and purifies the stored NOx when the exhaust air-fuel ratio is the stoichiometric or rich air-fuel ratio An exhaust purification device;
In accordance with the lean zone map divided into the acceleration lean operation permission region and the acceleration lean operation prohibition region, it is determined whether or not the operation at the lean air-fuel ratio at the time of engine acceleration operation is permitted, and the total NOx emission amount is calculated and the NOx is calculated. and wherein <br/> the relationship between the travel distance of the total emissions and vehicle and control means for narrowing the acceleration lean operation permission region of the lean zone map to become total emissions increase side than the predetermined relationship An exhaust purification device for an internal combustion engine. 2. The control unit according to claim 1, wherein when the total NOx emission amount is derived to exceed a predetermined amount before the vehicle reaches a predetermined travel distance, the operation at the lean air-fuel ratio is stopped even during acceleration operation. Alternatively, an exhaust purification device for an internal combustion engine, which is provided with a function to suppress.

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