JP2007255308A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device which achieves excellent NOx purifying performance by supplying a suitable amount of HC to a NOx occlusion catalyst during steady operation or the like, and surely suppresses an HC slip even when a rear stage catalyst is inactivated in the case of transient operation or the like at the time of rich spike for a NOx occlusion catalyst. <P>SOLUTION: An HC supply quantity correction part 103 in an ECU 10 sets a correction coefficient K to a smaller value further from 1.0 as exhaust temperature on an inlet side of a rear stage catalyst 43 falls. The correction coefficient K is multiplied to a basic HC supply quantity set in a basic HC supply quantity setting part so as to reduce and correct a target HC supply quantity. On the basis of the calculated value, a light oil adding injector 50 supplies light oil (HC) into the exhaust. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine having a NOx storage catalyst and a rear catalyst, and more particularly to an exhaust gas purification device that suppresses HC slip that occurs in the rear catalyst during a rich spike that releases and reduces NOx from the NOx storage catalyst. .

In an internal combustion engine that burns in an oxygen-excess atmosphere such as a diesel engine or lean burn engine, NOx (nitrogen oxides) in exhaust gas cannot be sufficiently purified by the conventional three-way catalyst due to its characteristics. However, a NOx storage catalyst capable of purifying NOx is provided. The NOx occlusion catalyst occludes NOx in exhaust gas as nitrate X-NO ₃ in an oxidizing atmosphere having a low reducing component concentration, and the occluded NOx is present in a large amount of HC (hydrocarbon) and CO (carbon monoxide). It is configured as a catalyst having the characteristic of reducing to N ₂ (nitrogen) in a reducing atmosphere.

  In this type of NOx storage catalyst, NOx is stored during normal operation to prevent discharge into the atmosphere, and before the NOx storage catalyst reaches the storage limit, HC and CO (hereinafter, representative) Rich spikes for supplying HC) are periodically performed, whereby NOx stored on the NOx storage catalyst is released and reduced (NOx purge). As the rich spike, for example, in a diesel engine, fuel is supplied from an injector provided in an exhaust passage, or post-injection is performed in an expansion stroke or an exhaust stroke, and in a lean burn engine, an air-fuel ratio is enriched. During these rich spikes, it is difficult to supply HC without excess or deficiency over the entire operating range for NOx purge. Therefore, NOx purge is necessary based on the operating state of the engine (for example, fuel injection amount and rotational speed). HC is supplied slightly larger than the amount, and surplus HC is treated by a subsequent catalyst provided downstream of the NOx storage catalyst.

  By the way, the installation layout of the NOx occlusion catalyst and the rear catalyst under the vehicle floor is limited in terms of space, and the rear catalyst is often separated from the NOx occlusion catalyst. As a result, there has been a problem that a so-called HC slip is generated in which HC passes through the downstream catalyst and is discharged. That is, since the post-catalyst treats surplus HC by an oxidation reaction, the post-catalyst needs to reach the light-off temperature and be activated in order to perform its function. When the engine is in steady operation, it is possible to accelerate the temperature increase of the rear catalyst by controlling the exhaust gas temperature on the engine side. Slip can be prevented. However, for example, as shown in FIG. 4, in the transient operation that shifts from the low load region to the high load region with acceleration, the temperature of the rear catalyst is lowered below the light-off temperature due to the continuation of the low load. As indicated by the thin solid line, the HC supply amount corresponding to the high load range is controlled. As a result, during the period of delay time A from the start of acceleration until the post-catalyst reaches the light-off temperature, as shown by the thick solid line, surplus HC exceeding the processing capacity is supplied to the post-catalyst and the HC slip is not fully processed. There was a problem that it occurred.

On the other hand, various methods for controlling the amount of HC supplied to the exhaust passage by paying attention to the catalyst temperature have been proposed (see, for example, Patent Document 1). The technology of Patent Document 1 focuses on the problem that the catalyst becomes excessively oxygen during the fuel cut of the engine and lowers the purification capacity, and the engine air-fuel ratio is made rich according to the catalyst temperature correlated with the oxygen storage capacity of the catalyst. As a result, the catalyst is restored to an appropriate state and the discharge of surplus HC is prevented.
JP-A-2005-140011

  However, even if the technique of Patent Document 1 is applied to solve the above HC slip problem and the HC supply amount at the time of rich spike is controlled according to the temperature of the NOx storage catalyst, the HC slip cannot be suppressed. . Although the temperature of the NOx storage catalyst is reflected in the temperature of the rear catalyst with a delay corresponding to the exhaust gas temperature of the engine, the exhaust gas flow rate, etc., the exhaust passage from the NOx storage catalyst to the rear catalyst is long, so the temperature of the NOx storage catalyst is An appropriate amount of HC supply, and hence reliable suppression of HC slip, was practically impossible.

  Therefore, in the technique of Patent Document 1, it is necessary to limit the HC supply amount during the rich spike in the entire operation region in order to avoid the HC slip in a very small operation region such as the transient operation. As a result, there is a problem that the HC supply amount is limited even when there is a margin in the HC purification capability of the subsequent catalyst such as during steady operation, and the NOx purification performance is reduced in exchange for HC slip suppression.

  The object of the present invention is to reliably suppress HC slip even when the post-stage catalyst is not activated, such as during transient operation during a rich spike with respect to the NOx storage catalyst. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine which can supply HC and realize a good NOx purification performance.

  In order to achieve the above object, an invention according to claim 1 is an exhaust purification device for an internal combustion engine having a NOx storage catalyst provided in an exhaust passage of the internal combustion engine and a rear stage catalyst disposed downstream of the NOx storage catalyst. When reducing agent supply means for supplying a reducing agent to the upstream side of the NOx storage catalyst in the exhaust passage, downstream catalyst temperature detection means for detecting the temperature of the downstream catalyst, and release reduction of NOx stored in the NOx storage catalyst is required The target supply amount setting means for setting the target supply amount of the reducing agent according to the operating state of the internal combustion engine, and the target supply amount setting means based on the temperature of the rear catalyst detected by the rear catalyst temperature detection means. Supply amount correction means for correcting the target supply amount, NOx release reduction control means for controlling the reducing agent supply means based on the target supply amount corrected by the supply amount correction means and supplying the reducing agent to the exhaust passage, It includes those were.

  Therefore, NOx contained in the exhaust gas of the internal combustion engine is stored in the NOx storage catalyst, and NOx is released and reduced before the NOx storage catalyst reaches the storage limit. When releasing and reducing NOx, the target supply amount setting means sets the target supply amount of the reducing agent according to the operating state of the internal combustion engine, and this target supply amount is supplied based on the temperature detected by the post-catalyst temperature detection means. The reducing agent is supplied to the exhaust passage of the internal combustion engine by the reducing agent supply means which is corrected by the correction means and controlled by the NOx release reduction control means based on the corrected target supply amount. As the reducing agent supply means, for example, fuel supply from an injector provided in the exhaust passage, or post injection in an expansion stroke or an exhaust stroke, enrichment of the air-fuel ratio, etc. are applied, and the reducing agent supplied from the reducing agent supply means As a result, NOx occluded in the NOx occlusion catalyst is released and reduced, and surplus HC due to the reducing agent that has not been consumed in the emission reduction is treated by an oxidation reaction in the subsequent catalyst.

  For example, in a transient operation that shifts from a low load range to a high load range, the operating state of the internal combustion engine is controlled by the target supply amount setting means even though the temperature of the rear catalyst has decreased below the light-off temperature due to continued low load. Therefore, when the supply amount of the reducing agent is controlled based on the target supply amount, surplus HC exceeding the processing capacity is supplied to the post-stage catalyst and processed. A so-called HC slip in which surplus HC passes through without being completely generated occurs.

  In the present invention, since the target supply amount is corrected based on the temperature of the post-catalyst, when the temperature of the post-catalyst catalyst is low and the processing capacity of surplus HC is reduced, the target supply amount is corrected to the decreasing side, so that the post-stage catalyst is corrected. The reducing agent flowing into the catalyst is reduced, and HC slip in the latter catalyst is suppressed. Further, when the temperature of the rear catalyst is not lowered, the target supply amount of the reducing agent is not corrected for reduction, and an appropriate amount of the reducing agent is supplied to the NOx storage catalyst, so that a good NOx purification performance is realized.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine of the first aspect of the present invention, it is possible to reliably suppress HC slip even when the post-stage catalyst is not activated, such as during transient operation, during a rich spike with respect to the NOx storage catalyst. At the same time, in steady operation, an appropriate amount of HC can be supplied to the NOx storage catalyst to achieve good NOx purification performance.

Hereinafter, an embodiment in which the present invention is embodied in an exhaust emission control device for a diesel engine will be described.
FIG. 1 is an overall configuration diagram showing an exhaust emission control device for a diesel engine according to the present embodiment. In this figure, reference numeral 1 indicates an engine, for example, a common rail type diesel engine, and reference numeral 10 indicates an electronic control unit (hereinafter referred to as ECU) that constitutes a main part of the control system of the engine control device and the exhaust purification device.

  Although not shown in detail, the common rail diesel engine 1 is provided with a fuel injector having a needle valve and a fuel chamber and a control chamber provided on the distal end side and the proximal end side of the needle valve for each cylinder. The control chamber is connected to the pressure accumulation chamber via a fuel passage, and the control chamber is connected to the fuel tank via a fuel return passage. Under the control of the ECU 10, when the solenoid valve provided in the fuel injector is opened, the high-pressure fuel supplied from the pressure accumulating chamber is injected into the combustion chamber of the engine 1 through the fuel injector, and when the solenoid valve is closed, the fuel injection is finished. Thus, the fuel injection start / end timing (fuel injection amount) is adjusted by controlling the opening / closing timing of the solenoid valve.

  The engine 1 has an intake pipe 12 connected to the intake manifold 11 and an exhaust pipe 14 (exhaust passage) connected to the exhaust manifold 13. In the middle of the intake pipe 12, a compressor 21, an intercooler 31, and an intake throttle valve 32 of the supercharger 20 are arranged. The opening degree of the intake throttle valve 32 is variably adjusted by the ECU 10 via the intake throttle valve drive unit 33. The exhaust temperature can be raised by reducing the opening of the intake throttle valve 32. On the other hand, a turbine 22 of the supercharger 20, an exhaust brake 15, a light oil addition injector 50, an aftertreatment device 40 and a muffler (not shown) are provided in the middle of the exhaust pipe 14.

  The compressor 21 and the turbine 22 of the supercharger 20 are connected so as to be able to rotate synchronously, and the compressor 21 is rotated by the rotational force of the turbine 22 generated by the flow of exhaust gas discharged from the engine 1 and is pressurized by the compressor 21. Intake air is supplied to the engine 1. At this time, the pressurized and heated air is cooled by the intercooler 31, thereby increasing the density of the intake air and improving the charging efficiency to increase the engine output.

  The supercharger 20 is provided with an exhaust bypass passage (not shown) that bypasses the turbine 22, and the wastegate 23 of the supercharger 20 provided in the middle of the bypass passage is opened during excessive supercharging. In addition to the operation of adjusting the supply pressure, the ECU 10 is forcibly controlled by the ECU 10 via the waste gate drive unit 24 to increase or decrease the pressure of the intake air supplied to the intake pipe 12 by increasing or decreasing the turbine (compressor) rotation. It is like that. The exhaust gas temperature can be raised by opening the supercharger wastegate 23. Similarly, the exhaust brake 15 can be opened and closed by the ECU 10 via the exhaust brake drive unit 16, and the exhaust gas temperature can be raised by closing the exhaust brake 15.

  In FIG. 1, reference numeral 36 indicates an EGR passage extending from the exhaust manifold 13 to the intake pipe 12, and a part of the exhaust gas is supplied to the engine 1 as a recirculation gas via the EGR passage 36. In the middle of the EGR passage 36, an EGR cooler 37 that cools the recirculation gas to increase the gas filling density of the engine 1 and an EGR valve 38 for supplying and shutting off the recirculation gas to the engine 1 are provided. ing. The EGR valve 38 is controlled to be opened or closed or adjusted by the ECU 10 via the EGR valve drive unit 39.

  The aftertreatment device 40 reduces NOx and PM contained in the exhaust gas flowing into the aftertreatment device 40. The post-processing device 40 according to the present embodiment includes a diesel particulate filter (DPF) 41 that collects PM and burns and removes it, and light oil that is disposed in front of the DPF 41 and supplied from a light oil addition injector 50 (reducing agent supply means). A NOx storage catalyst (exhaust gas purification catalyst) 42 that purifies NOx in exhaust gas using (HC) as a reducing agent, and a rear catalyst 43 that is disposed downstream of the DPF 41 and that treats excess HC by an oxidation reaction, for example. Yes.

In this embodiment, the rear catalyst 43 is spaced apart from the NO storage catalyst 42 and the DPF 41 on the rear side from the point on the space under the vehicle floor. As a result, the exhaust pipe 14 connecting the DPF 41 and the rear catalyst 43 has a considerable length, and the exhaust gas that has passed through the NO storage catalyst 42 flows into the rear catalyst 43 with a considerable time delay. .
The light oil addition injector 50 injects light oil (HC) to the NOx storage catalyst 42 and is controlled to be opened and closed by the ECU 10 via the light oil addition injector drive unit 51, and light oil is injected during the valve opening period of the light oil addition injector 50. Is done.

  In FIG. 1, reference numeral 61 is a NOx catalyst temperature sensor provided on the downstream side of the NOx storage catalyst 42 (between the DPF 41), and the exhaust temperature T 1 (the NOx storage catalyst 42 of the NOx storage catalyst 42) on the outlet side of the NOx storage catalyst 42. It correlates with temperature). Reference numeral 62 denotes a rear catalyst temperature sensor (rear catalyst temperature detecting means) provided on the upstream side of the rear catalyst 43, and correlates with the exhaust temperature T2 on the inlet side of the rear catalyst 43 (the temperature of the rear catalyst 43). ) Is detected. The temperature data detected by these sensors 61 and 62 is used for HC supply control for the rich spike of the NOx storage catalyst 42.

Further, various sensors such as a load sensor 71 and a crank angle sensor 72 are connected to the ECU 10. The load sensor 71 detects the amount of depression of an accelerator pedal (not shown), that is, the accelerator opening, as an engine load, and the crank angle sensor 72 detects the rotation of the crankshaft (not shown) of the engine 1 as the engine rotation speed. is there.
The ECU 10 determines the operating region of the engine 1 based on the engine load detected by the load sensor 71 and the engine rotation speed detected by the crank angle sensor 72, and each injector (illustrated) of the engine 1 according to the engine operating region. The fuel injection timing and the fuel injection amount are controlled by turning on and off the abbreviated solenoid valve.

  The diesel engine 1 configured as described above is operated at a lean air-fuel ratio as is well known, and during this lean air-fuel ratio operation, NOx (nitrogen oxide) contained in the exhaust gas discharged from the engine 1 is stored in the NOx storage catalyst 42. Is done. When the NOx occlusion amount increases to a certain level or more, the rich spike operation of the engine 1 is performed, and the NOx occluded in the NOx occlusion catalyst 42 is released and reduced and removed. In the present embodiment, a light spike (HC) is injected into the exhaust gas by the light oil addition injector 50 to execute a rich spike operation. Under the control of the ECU 10, the light oil addition injector 50 is periodically opened at a predetermined duty ratio, for example. Thus, the light oil injected into the exhaust gas has a NOx release / reduction action on the NOx storage catalyst 42 (NOx release / reduction control means). In addition, surplus HC due to light oil that has not been consumed for NOx release reduction on the NOx storage catalyst 42 is treated by an oxidation reaction in the post-stage catalyst 43 to be prevented from being discharged into the atmosphere.

Although the basic part of the HC supply control at the time of the rich spike is not different from the conventional control, the present invention is characterized in that the HC supply amount is corrected according to the temperature of the post-catalyst 43. Hereinafter, the HC supply control will be described. Supply control will be described.
In relation to the HC supply control, as shown in FIG. 1, the ECU 10 includes an HC supply amount setting unit 101 that sets a target HC supply amount. The HC supply amount setting unit 101 includes a basic HC supply amount setting unit 102 (target supply amount setting means) connected to the NOx catalyst temperature sensor 61 and an HC supply amount correction unit 103 (connected to the rear catalyst temperature sensor 62. Supply amount correction means).

  In the present embodiment, the basic HC supply amount setting unit 102 is based on, for example, the engine speed, the fuel injection amount, and the exhaust temperature T1 on the outlet side of the NOx storage catalyst 42 detected by the NOx catalyst temperature sensor 61. The HC supply amount correction unit 103 calculates the basic HC supply amount by a correction coefficient K corresponding to the exhaust gas temperature T2 on the inlet side of the rear catalyst 43 detected by the rear catalyst temperature sensor 62. The target HC supply amount (here, the target injection amount of light oil from the light oil addition injector 50) is obtained by correcting the amount.

  The processing of the HC supply amount correction unit 103 will be described in more detail. The ECU 10 stores a correction coefficient setting map shown in FIG. 2, and the map is a rear catalyst having the light-off temperature T 0 of the rear catalyst 43 as a boundary. When the exhaust gas temperature T2 on the inlet side of 43 is equal to or higher than the light-off temperature T0, the correction coefficient K is set to 1.0. On the other hand, as the exhaust gas temperature T2 falls below the light-off temperature T0, the correction coefficient K becomes 1 according to a predetermined gain. The characteristic is set from 0.0 to the decreasing side.

  The HC supply amount correction unit 103 calculates a correction coefficient K from the exhaust temperature T2 on the inlet side of the rear catalyst 43 based on such a characteristic map, and sets the basic HC supply amount calculated by the basic HC supply amount setting unit 102. The target HC supply amount is obtained by multiplying the correction coefficient K. Note that the map characteristic for setting the correction coefficient K is not limited to that shown in FIG. 2, and gradually increases as the temperature decreases without applying a single gain in the temperature range below the light-off temperature T0, for example. The correction coefficient K may be decreased rapidly by applying a gain.

  Then, the light oil addition injector drive unit 51 operates in accordance with the target light oil injection amount (target HC supply amount), whereby a target amount of light oil (HC) is injected from the light oil addition injector 50 into the exhaust gas. In the present embodiment, the target light oil injection amount is achieved by changing the injection period (that is, the rich period of the exhaust air / fuel ratio) while making the injection flow rate (that is, the rich depth of the exhaust air / fuel ratio) of the light oil addition injector 50 substantially constant. However, the present invention is not limited to this. For example, the injection flow rate may be changed instead of the injection period, or both the injection period and the injection flow rate may be changed. Based on the correction of the target HC supply amount by the HC supply amount correction unit 103, the injection period of the light oil addition injector 50 is controlled to decrease as the rear catalyst 43 falls below the light-off temperature T0. The amount of light oil injected into the engine is reduced.

As described above, the HC supply control is performed at the time of the rich spike, and at this time, the post-stage catalyst 43 performs the process of surplus HC by the oxidation reaction as described below.
When the NOx occlusion amount in the NOx occlusion catalyst 42 increases to a certain level or more, the ECU 10 executes light oil injection into the exhaust gas by the light oil addition injector 50 as a rich spike. FIG. 3 is a time chart showing the HC supply status at the time of rich spike. Light oil is injected into the exhaust every time the gas oil addition injector 50 is periodically opened, and the thin solid line in the figure is the outlet side of the NOx storage catalyst 42. The thick solid line indicates the HC amount on the outlet side of the rear catalyst 43, that is, the HC slip amount.

  Before the start of acceleration in the figure, the temperature of the NOx storage catalyst 42 (correlated with the exhaust gas temperature T1 as described above) and the temperature of the rear catalyst 43 (correlated with the exhaust gas temperature T2 as described above) are maintained by continuing the low load operation. It is falling. At this time, the basic HC supply amount setting unit 102 sets a relatively small value as the basic HC supply amount based on the engine speed, the fuel injection amount, and the exhaust temperature T1 on the outlet side of the NOx storage catalyst 42, and the subsequent stage. In response to the exhaust gas temperature T2 on the inlet side of the catalyst 43 being lower than the light-off temperature T0, the HC supply amount correction unit reduces the target HC supply amount by multiplying the basic HC supply amount by a correction coefficient K less than 1.0. Therefore, as a result, the light oil injection amount of the light oil addition injector 50 is controlled to the decreasing side. In the low load operation, the NOx release reduction reaction on the NOx storage catalyst 42 is not promoted so much, but the amount of HC on the outlet side of the NOx storage catalyst 42 indicated by the thin solid line is suppressed because the light oil injection amount is reduced accordingly. In addition, the rear catalyst 43 is less than the light-off temperature T0 and does not have sufficient HC treatment capacity. However, since the amount of HC flowing into the rear catalyst 43 is originally small, the HC slip amount is low as shown by the thick solid line. It is suppressed.

  When acceleration is started by the driver's accelerator operation, the temperature of the NOx occlusion catalyst 42 rises relatively quickly as the engine load increases. However, the rear catalyst separated from the NOx occlusion catalyst 42 on the rear side. There is a delay in the temperature rise of 43, and a delay time A is required from the start of acceleration for the post-catalyst 43 to reach the light-off temperature T0. In this transient operation, the basic HC supply amount setting unit 102 is based on the engine speed and fuel injection amount after the start of acceleration, and the exhaust temperature T1 on the outlet side of the NOx storage catalyst 42 that is heated prior to the post-stage catalyst 43. Since the basic HC supply amount is set, when this basic HC supply amount is applied as it is to the light oil injection amount of the light oil addition injector 50, as described in [Background Art], the post-stage catalyst 43 can process the surplus HC. An HC slip will occur without this.

  In the present invention, in such a transient operation, the exhaust gas temperature T2 on the inlet side of the rear catalyst 43 is lower than the light-off temperature T0, and the HC supply amount correction unit 103 is less than 1.0 from the map of FIG. A correction coefficient K is set, and the light oil injection amount of the light oil addition injector 50 is controlled to the decrease side based on the target HC supply amount corrected to decrease as a result of multiplication of the correction coefficient K. Therefore, during the period of the delay time A in the figure, as shown by a thin solid line, the amount of HC on the outlet side of the NOx storage catalyst 42, that is, the amount of surplus HC flowing into the rear catalyst 43 decreases, and the HC of the rear catalyst 43 Even if the processing capacity is low, the HC slip amount is suppressed to a low value as shown by a thick solid line.

  After that, when the post-catalyst 43 reaches the light-off temperature T0, the HC supply amount correction unit 103 sets the correction coefficient K to 1.0, and the light oil injection amount by the light oil addition injector 50 as the target HC supply amount increases. Accordingly, the amount of HC flowing into the rear catalyst 43 also increases as shown by a thin solid line. At this time, since the rear catalyst 43 exhibits sufficient HC treatment capacity, an HC slip as shown by a thick solid line is obtained. The quantity keeps the low value.

  Therefore, it is possible to reliably suppress HC slip even when the vehicle shifts to a transient operation such as acceleration during a rich spike and the rear catalyst 43 is not activated. Further, the target HC supply amount, and hence the light oil injection amount of the light oil addition injector 50, is only suppressed by setting the reduction of the correction coefficient K only during transient operation, and the target HC supply amount is limited at all during steady operation. Instead, since an appropriate amount of HC is supplied to the NOx storage catalyst 42 based on the basic HC supply amount set by the basic HC supply amount setting unit 102, good NOx purification performance can be realized.

  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 gas purification device for a diesel engine is embodied. However, a lean burn engine or an in-cylinder injection engine that operates at a lean air-fuel ratio is provided with a NOx storage catalyst 42 and a post-stage catalyst 43. The same operation and effect can be obtained by executing the HC supply control of the above embodiment.

  Further, in the above embodiment, the reducing agent supply means is constituted by the light oil addition injector 50 that injects light oil into the exhaust gas. Instead of this, post-injection is executed in the exhaust stroke or expansion stroke of the engine 1 to perform unburned fuel. May be supplied to the NOx storage catalyst 42, or in the case of a gasoline engine, the HC concentration or CO concentration of the exhaust gas may be increased by enriching the air-fuel ratio.

It is a whole lineblock diagram showing the exhaust gas purification device for diesel engines of this embodiment. It is a figure which shows the map for setting the correction coefficient of HC supply amount. It is a time chart which shows the HC supply condition at the time of rich spike of embodiment. It is a time chart which shows the HC supply condition at the time of the rich spike of a prior art.

Explanation of symbols

1 engine 10 ECU (target supply amount setting means, supply amount correction means, NOx release reduction control means)
14 Exhaust pipe (exhaust passage)
42 NOx storage catalyst 43 Rear catalyst 50 Light oil addition injector (reducing agent supply means)
62 Second-stage catalyst temperature sensor (second-stage catalyst temperature detection means)

Claims (1)

In an exhaust gas purification apparatus for an internal combustion engine having a NOx storage catalyst provided in an exhaust passage of the internal combustion engine and a rear-stage catalyst disposed downstream of the NOx storage catalyst,
Reducing agent supply means for supplying a reducing agent to the upstream side of the NOx storage catalyst in the exhaust passage;
A post-catalyst temperature detecting means for detecting the temperature of the post-catalyst;
A target supply amount setting means for setting a target supply amount of the reducing agent in accordance with an operating state of the internal combustion engine when it is necessary to release and reduce NOx stored in the NOx storage catalyst;
A supply amount correction means for correcting the target supply amount set by the target supply amount setting means based on the temperature of the rear catalyst detected by the latter catalyst temperature detection means;
Exhaust gas purification of an internal combustion engine, comprising: NOx release reduction control means for controlling the reducing agent supply means based on the target supply amount corrected by the supply amount correction means to supply the reducing agent to the exhaust passage apparatus.

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