JP5751198B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device mounted on an internal combustion engine such as a diesel engine for automobiles, and particularly relates to an exhaust purification device having a NOx occlusion material and a PM filter in an exhaust passage.

  Conventionally, a lean NOx catalyst capable of purifying NOx (nitrogen oxide) even in exhaust gas having a high oxygen concentration, as an exhaust gas purification device for a diesel engine (hereinafter sometimes simply referred to as an engine) mounted on an automobile or the like, A PM filter that collects particulate matter (PM) contained in exhaust gas is known (see, for example, Patent Document 1 below).

  Among the lean NOx catalysts, the NOx storage reduction type (NOx Storage Reduction: NSR) catalyst stores NOx in a state where the oxygen concentration in the exhaust gas is high, in other words, in a state where the air-fuel ratio (A / F) of the exhaust gas is lean. Has occlusion material. Then, NOx released from the NOx occlusion material as the oxygen concentration decreases, that is, the air-fuel ratio becomes richer, reacts with HC (hydrocarbon), CO (carbon monoxide), etc. in the exhaust to reduce and purify. .

  In such NSR, as the NOx occlusion amount increases, the ability to occlude NOx in the exhaust gas decreases, so if the occlusion amount reaches a predetermined threshold, the exhaust air-fuel ratio is intentionally enriched and occluded. NOx reduction control is performed to release and reduce the NOx that has been discharged. Specifically, for example, a fuel addition valve is provided in the exhaust system to supply fuel, or a small amount of fuel is injected (post-injection) after main fuel injection into the combustion chamber to enrich the air-fuel ratio of the exhaust NSR can be reduced to a reducing atmosphere.

  On the other hand, as the PM filter, various structures have been proposed for efficiently scavenging (collecting) PM from the flow of exhaust gas passing therethrough, such as DPF (Diesel Particulate Filter) and DPNR (Diesel Particulate-). This is known as NOx Reduction. In the filter that collects PM in this way, the collected PM accumulates on the wall surface, thereby increasing the ventilation resistance of the filter and eventually causing clogging.

  Therefore, when the amount of PM collected (deposited amount) in the filter reaches a predetermined threshold value, fuel supply to the exhaust system, post-injection, etc. are performed in the same manner as in the NOx reduction control, and thus the fuel supplied into the exhaust gas. The filter regeneration control is performed to oxidize (burn) and remove the accumulated PM by raising the filter temperature to a predetermined level or higher by combustion of.

JP 2007-107474 A

  However, since the driving state of an automobile engine is strongly influenced by the driver's will and driving environment, the NOx reduction control and the filter regeneration control may not be sufficiently performed. In other words, the diesel engine has higher thermal efficiency, and the exhaust temperature is lower than that of the gasoline engine. Therefore, if the traveling speed continues at a very low speed such as a congested road, the temperature of the NSR and PM filter will be considerably lower. .

  In such a low temperature state, the PM filter cannot be raised to a temperature at which PM burns easily, and the NSR is also low in activity at a low temperature, so that NOx can be released and reduced sufficiently. Absent. In particular, in the case of filter regeneration control, since it takes a relatively long time to burn out the PM of the filter, once control is started, control must be interrupted halfway due to changes in the operating state of the engine. Sometimes you don't get.

  Therefore, in the automobile having a high frequency of low-speed driving as described above, there is a situation that effective filter regeneration control cannot be performed for a long period of time, and the amount of accumulated PM in the PM filter is not decreased. Further, if the PM accumulation amount exceeds an allowable upper limit value, the filter temperature may become too high due to PM combustion when the filter regeneration control is subsequently performed.

  On the other hand, the NOx reduction control can be executed even when the temperature of the NSR is lower than the filter regeneration control, and the NOx release and reduction purification can be completed in a short time. There is a possibility that effective control cannot be performed and the NOx occlusion amount exceeds the allowable upper limit value.

  In view of this point, the object of the present invention is to stabilize the exhaust purification performance by increasing the execution opportunities of the control (NOx reduction control and filter regeneration control) for recovering the purification performance of the NSR and PM filters in the exhaust purification device as much as possible. It is to secure it.

  In order to achieve the above object, the inventors of the present invention have verified that NOx reduction control and filter regeneration control are actually performed in a diesel engine mounted on an automobile. As a result, the PM filter is excessive as described above. Even when the PM accumulated state, the NOSR occlusion capacity of NSR often has a margin, and the exhaust gas purification apparatus that combines the two has realized that the capacity is not fully exhibited.

  Based on this knowledge, the inventor performs NOx reduction control based only on the state of the NSR as in the past, and does not perform filter regeneration control based only on the state of the PM filter, but rather the NOx occlusion amount and PM trapping. In consideration of the balance of the collection amount, the combustion state of the internal combustion engine is controlled so that only one of them does not become excessive.

-Solution-
Specifically, the present invention includes a NOx occlusion material that is disposed in an exhaust passage of an internal combustion engine and occludes NOx in exhaust gas in a predetermined state, and a PM filter that collects PM contained in the exhaust gas. The exhaust gas purification apparatus is an object, and the internal combustion engine is provided with a burned gas amount adjusting means capable of adjusting the burned gas amount remaining or recirculated in the combustion chamber. In this case, when the storage amount of NOx in the NOx storage material reaches a predetermined threshold value, or the amount of PM trapped in the PM filter reaches a predetermined threshold value, the combustion chamber Control means for performing correction control to increase or decrease the burned gas amount by the burned gas amount adjusting means so that the generated amount of the NOx and PM that have reached the threshold value is reduced. It is provided.
Further, the control means determines the amount of burned gas by the burned gas amount adjusting means according to the margin to the threshold of the stored amount of NOx and the collected amount of PM that has not reached the threshold. The degree of increase or decrease correction is changed.

  Due to this specific matter, NOx and PM generated in the combustion chamber during operation of the internal combustion engine are respectively stored in the NOx storage material of the exhaust purification device, and are collected and removed by the PM filter. When either the NOx occlusion amount or the PM trapping amount reaches a predetermined threshold value, the amount that has reached this threshold value is reduced or the residual amount that has already been returned to the combustion chamber of the internal combustion engine is reduced. The amount of fuel gas (hereinafter collectively referred to as EGR) is increased or decreased.

  That is, for example, if the amount of PM collected by the PM filter reaches a threshold value, EGR is reduced, and the amount of PM produced due to combustion decreases. Therefore, the period until the PM accumulation amount of the PM filter exceeds the allowable upper limit value is increased. As a result, it is possible to increase the opportunities for executing filter regeneration control. Similarly, if the NOx occlusion amount reaches the threshold value, the EGR is increased and the NOx generation amount decreases. Therefore, the period until the NOx occlusion amount of the NOx occlusion material exceeds the allowable upper limit value is extended, and the NOx reduction control is executed. Opportunities can be increased.

In other words, by correcting and controlling EGR so that only one of the NOx occlusion amount and the PM trapping amount does not increase too much, the balance between the NOx and PM generation amounts accompanying the combustion of the internal combustion engine can be corrected. . Thereby, the period until the capacity of the NOx occlusion material and the PM filter is saturated is extended as much as possible, and each capacity is fully exhibited, and the exhaust purification performance can be stably secured.
In particular, the control means determines the amount of burned gas (EGR) by the burned gas amount adjusting means according to the margin to the threshold of the stored amount of NOx and the collected amount of PM that has not reached the threshold. For example, when the amount of PM trapped reaches the threshold, if the margin to the NOx occlusion amount is large, the EGR reduction correction amount is increased accordingly. By doing so, it is possible to sufficiently extend the period until the amount of PM trapped exceeds the allowable upper limit.

  As a preferred mode, the timing for starting the EGR correction control as described above may be the same as the timing for starting the NOx reduction control or the filter regeneration control. That is, when the amount of PM collected in the PM filter reaches a threshold value, the control means is as described above if the internal combustion engine is in a predetermined operation state, that is, an operation state in which it is difficult to raise the temperature of the PM filter. The correction control of the burnt gas (EGR) amount is performed.

  On the other hand, if the internal combustion engine is not in the predetermined operating state, filter regeneration control is performed, the temperature of the PM filter is increased, and the collected PM is burned and removed, thereby recovering the filter's collection ability. In other words, the EGR reduction correction described above is performed only when PM cannot be burned and removed despite the fact that the amount of PM trapped has increased to the extent that filter regeneration control should be performed. That is, the EGR amount appropriately set according to the engine operating state or the like is not changed as much as possible, and the effect of reducing pump loss by EGR can be sufficiently obtained.

  The control means performs correction control of the burnt gas (EGR) amount if the internal combustion engine is in a predetermined operation state when the NOx storage amount in the NOx storage material reaches a threshold value. If the operating state is not, the air-fuel ratio of the exhaust gas flowing into the NOx storage material may be enriched to perform NOx reduction control for reducing and purifying the stored NOx.

  If it carries out like this, also about NOx occlusion material, NOx reduction | restoration control can be performed as needed and NOx occlusion capability can be recovered | restored appropriately. In addition, the EGR amount that is appropriately set according to the engine operating state or the like is obtained by performing the EGR increase correction only when the NOx reduction control cannot be performed in spite of the situation where the NOx reduction control should be performed. As much as possible, the deterioration of the combustion state accompanying the increase in EGR can be suppressed.

  Specifically, the control means controls the burned gas amount adjusting means so that the burned gas (EGR) amount remaining or recirculated in the combustion chamber of the internal combustion engine becomes a target value corresponding to the operating state. As the correction control, the target value of the burnt gas amount may be increased or decreased.

  In general, in diesel engines, the amount of NOx and PM produced by combustion is affected by EGR, and although the amount of NOx can be suppressed by increasing EGR, PM tends to increase, and conversely, if EGR is reduced Although there is less PM, NOx generation tends to increase. Therefore, NOx and PM in the exhaust gas can be reduced in a well-balanced manner by appropriately controlling EGR according to the engine operating state.

  According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, EGR correction control is performed in consideration of the NOx occlusion amount of the NOx occlusion material and the PM trapping amount of the PM filter, and the amount of NOx and PM produced by combustion is controlled. By correcting the balance, the period until the capacity of the NOx storage material or PM filter is saturated can be extended as much as possible. Thereby, the ability of the NOx occlusion material and the PM filter can be fully exhibited, and the exhaust purification performance can be secured stably.

It is a figure which shows schematic structure of the diesel engine which concerns on embodiment, and its control system. It is a block diagram which shows the structure of control systems, such as ECU. It is explanatory drawing which shows the aspect of the fuel injection by an injector typically. It is a figure which shows an example of the basic control map of EGR control. FIG. 9 is a timing chart schematically showing a state in which the PM accumulation amount and the NOx occlusion amount increase as the automobile travels, with respect to a conventional example in which the PM accumulation amount increases beyond the regeneration threshold and reaches an allowable upper limit value. . FIG. 5 is a flowchart showing EGR correction control for increasing the chances of NOx reduction and DPF regeneration. FIG. 6 is a diagram corresponding to FIG. 5 when the PM accumulation amount reaches a threshold value and the EGR is corrected to decrease. FIG. 6 is a diagram corresponding to FIG. 5 when the NOx occlusion amount reaches a threshold value and the EGR is increased and corrected.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (for example, in-line 4-cylinder) diesel engine (internal combustion engine) mounted on an automobile will be described.

-Engine configuration-
First, a schematic configuration of a diesel engine according to the present embodiment will be described with reference to FIG. 1. In this diesel engine 1 (hereinafter, also simply referred to as an engine 1), nozzle holes are respectively provided in combustion chambers in the cylinders 1a. The injector 2 is arranged facing it. The injector 2 for each cylinder 1a is connected to a common rail 11 common to all the cylinders 1a, and receives supply of fuel sent from the upstream supply pump 10 via the common rail 11.

  The supply pump 10 pressurizes the fuel pumped from the fuel tank and then supplies the fuel to the common rail 11 through the fuel passage 10a. The common rail 11 has a function as a pressure accumulation chamber that relaxes fluctuations in fuel discharged from the supply pump 10 and maintains (accumulates) the fuel pressure at a predetermined value, and distributes the accumulated fuel to each injector 2. The injector 2 is an electromagnetically driven on / off valve that opens when a predetermined voltage is applied and injects fuel into the cylinder 1a. The opening / closing control of the injector 2, that is, the control of the fuel injection amount and the injection timing is performed by an ECU (Electronic Control Unit) 100 as a control means.

  An intake passage 3 and an exhaust passage 4 are connected to the engine 1. In the intake passage 3, an air cleaner 9, an air flow meter 33, a compressor 63 of the turbocharger 6, an intercooler 8, and a throttle valve 5 are arranged in this order from the upstream portion (upstream portion in the intake air flow direction) to the downstream side. Has been. The throttle valve 5 is adjusted in opening degree by a throttle motor 51. This throttle opening is detected by a throttle opening sensor 41. The intake passage 3 is branched corresponding to each cylinder 1a in an intake manifold 3a arranged on the downstream side of the throttle valve 5.

  On the other hand, the exhaust passage 4 collects exhaust flows from the plurality of cylinders 1a into one by an exhaust manifold 4a connected to each cylinder 1a of the engine 1. In the exhaust passage 4 downstream of the exhaust manifold 4a, a NOx occlusion reduction type catalyst (NOx) capable of purifying NOx even when the exhaust air-fuel ratio (A / F) is lean (the oxygen concentration in the exhaust gas is high). Storage Reduction (hereinafter referred to as NSR 21) and a DPF (Diesel Particulate Filter) 22 that collects PM (particulate matter) contained in the exhaust gas are sequentially arranged.

  As an example, the NSR 21 is a general three-way catalyst in which alkalis, alkaline earths, and rare earth oxides are supported as NOx storage materials, and the exhaust air air-fuel ratio (A / F) is in a lean state. While NOx is occluded by the NOx occlusion material, when the air-fuel ratio of the exhaust gas becomes rich, NOx released from the NOx occlusion material reacts with HC (hydrocarbon), CO (carbon monoxide), etc. in the exhaust gas, and is reduced. Purify.

  On the other hand, the DPF 22 is a porous ceramic structure such as cordierite or silica as an example, and has a large number of elongated cells extending in the exhaust flow direction. The front end and rear end of adjacent cells are alternately sealed, and the exhaust flowing into the open cell at the front end passes through the porous wall between the adjacent cells. PM is collected. In addition, a noble metal such as platinum is supported on the DPF 22 of the present embodiment, and functions as an oxidation catalyst that promotes an oxidation reaction of the deposited PM during DPF regeneration control described later.

  An A / F sensor 36 and a first exhaust temperature sensor 37 are arranged in the exhaust passage 4 upstream of the NSR 21 (upstream of the exhaust flow), and flows into the NSR 21 by an output signal of the first exhaust temperature sensor 37. The temperature of the exhaust can be detected. A second exhaust temperature sensor 38 is disposed in the exhaust passage 4 between the NSR 21 and the DPF 22, and the temperature of the exhaust gas flowing into the DPF 22 can be detected by an output signal of the second exhaust temperature sensor 38. . Further, a differential pressure sensor 39 for detecting a differential pressure between the upstream pressure and the downstream pressure of the DPF 22 is also provided.

  The engine 1 of this embodiment is equipped with a turbocharger 6. The turbocharger 6 is formed by connecting a turbine 62 in the exhaust passage 4 and a compressor 63 in the intake passage 3 via a rotor shaft 61, and rotates the compressor 63 using an exhaust flow (exhaust pressure) received by the turbine 62. In this way, the intake air is supercharged. The intake air supercharged by the turbocharger 6 is cooled by the intercooler 8 disposed in the intake passage 3.

  Furthermore, the engine 1 of this embodiment is equipped with an EGR device 7. The EGR device 7 recirculates a part of the exhaust from the exhaust passage 4 to the intake passage 3 and recirculates it to the combustion chamber of each cylinder 1a. As an example, the EGR device 7 includes an EGR passage 71 that connects the intake manifold 3a and the exhaust manifold 4a. The EGR passage 71 cools exhaust gas that is recirculated to the intake side (hereinafter also referred to as EGR gas). EGR cooler 73 and EGR valve 72 are provided.

  Since the flow rate of the EGR gas is adjusted according to the opening degree of the EGR valve 72, in this embodiment, the amount of burned gas to be recirculated to the combustion chamber in the cylinder 1a can be adjusted by the EGR passage 71 and the EGR valve 72. A burned gas amount adjusting means is configured. And according to the control command from ECU100 described below, the actuator (not shown) of EGR valve 72 is operated, and the opening degree is adjusted.

-ECU-
As shown in FIG. 2, the ECU 100 includes a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like. The ROM 102 stores various control programs, maps that are referred to when the control programs are executed, and the like. The CPU 101 executes arithmetic processing based on various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores calculation results of the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a non-volatile memory that stores data to be saved when the engine 1 is stopped. is there.

  The CPU 101, ROM 102, RAM 103, and backup RAM 104 are connected to each other via a bus 107, and are connected to an input interface 105 and an output interface 106.

  The input interface 105 includes an engine speed sensor 31 that detects the rotation speed of the crankshaft that is the output shaft of the engine 1, a water temperature sensor 32 that detects the engine water temperature (cooling water temperature), an air flow meter 33 that detects the intake air flow rate, An intake air temperature sensor 34 disposed in the intake manifold 3a, an intake pressure sensor 35 disposed in the intake manifold 3a, the A / F sensor 36, a first exhaust temperature sensor 37, a second exhaust temperature sensor 38, a differential pressure sensor 39, A rail pressure sensor 40 for detecting the pressure of the high-pressure fuel in the common rail 11, a throttle opening sensor 41, an accelerator opening sensor 42, a vehicle speed sensor 43, and the like are connected, and signals from these sensors are sent to the ECU 100. Entered.

  On the other hand, the output interface 106 is connected to the injector 2, the supply pump 10, the throttle motor 51 of the throttle valve 5, the actuator of the EGR valve 72, and the like. The ECU 100 controls the opening degree of the throttle valve 5 of the engine 1, the fuel injection control (control of the injection amount / injection timing) by the injector 2, and the control of the EGR gas amount based on the output signals of the various sensors described above. Various controls of the engine 1 including the above are executed.

  As an example, the ECU 100 executes pilot injection, main injection (fuel injection contributing mainly to torque generation of the engine 1), and post injection as fuel injection control by the injector 2 as schematically shown in FIG. As is well known, pilot injection burns a small amount of fuel injected prior to main injection, thereby shortening the ignition delay time of fuel subsequently injected from main injection and preventing initial combustion from becoming excessively intense. To do.

  Further, as is well known, post-injection is performed at a timing at which fuel injected after main injection does not burn in the cylinder 1a. It is used to enrich the air-fuel ratio and make the atmosphere around the NSR 21 a reducing atmosphere. The post injection is also used to raise the temperature of the DPF 22 in the DPF regeneration control (filter regeneration control) described below.

  Further, the ECU 100 controls the opening degree of the EGR valve 72 in accordance with the operating state of the engine 1 to adjust the ratio of EGR gas in the intake air that is filled in the cylinder 1a. That is, in general, the amount of NOx and PM generated by combustion in the diesel engine 1 is affected by EGR. When the ratio of EGR gas is large, NOx decreases, but PM tends to increase. Conversely, when the ratio of EGR gas is small, PM decreases, but NOx tends to increase.

  In the present embodiment, the opening degree of the EGR valve 72 is basically controlled according to the operating state of the engine 1 based on, for example, an EGR control map as shown in FIG. The illustrated control map is a map of a value egr (corresponding to the target value of the EGR gas amount) obtained by experiment / calculation etc. with a suitable opening degree of the EGR valve 72 using the engine speed NE and the fuel injection amount Qv as parameters. And is stored in the ROM 102 of the ECU 100. In the map of FIG. 4, the EGR valve 72 is set to be closed (egr is zero) when the engine speed NE is high or the fuel injection amount Qv is large.

-Control operation of exhaust gas purification device-
Hereinafter, the NOx reduction control, the DPF regeneration control, and the EGR control for coordinating them with the exhaust purification device of the present embodiment will be described. First, the well-known NOx reduction control and DPF regeneration control in a diesel engine will be described, and then EGR correction control will be described.

(NOx reduction control)
In general, in the diesel engine 1, the air-fuel ratio of the exhaust gas is a lean air-fuel ratio in most of the operation region, and in the normal operation state, the ambient atmosphere of the NSR 21 is in a high oxygen concentration state, and the NOx in the exhaust gas is NSR21. Occluded. And since there are very few situations where the ambient atmosphere of the NSR 21 has a low oxygen concentration, the NOx occlusion amount gradually increases, and accordingly, the NOx occlusion capacity of the NSR 21 decreases.

  Therefore, when the NOx occlusion amount estimated based on the engine operating state or the like reaches a predetermined threshold (hereinafter also referred to as a reduction threshold), fuel is supplied into the exhaust by post injection from the injector 2, The air-fuel ratio (A / F) is temporarily enriched. As a result, the NOx stored in a reducing atmosphere around the NSR 21 is released and reduced and purified. And NOSR occlusion ability of NSR21 is recovered.

  As a method for estimating the NOx occlusion amount, the NOx occlusion amount corresponding to the engine speed and the fuel injection amount from the injector 2 is obtained in advance through experiments or the like and mapped, and the NOx occlusion amount obtained from this map. The method of integrating | accumulating is mentioned.

(DPF regeneration control)
In general, in the diesel engine 1, PM contained in the exhaust is collected by the DPF 22, but the collected PM accumulates on the wall surface of the cell and obstructs the flow of the exhaust, and the ventilation resistance increases. go. Accordingly, the differential pressure between the exhaust pressure upstream of the DPF 22 and the exhaust pressure downstream of the DPF 22 increases, so that the PM accumulation amount of the DPF 22 can be estimated from the differential pressure.

  Therefore, the ECU 100 estimates a PM accumulation amount in the DPF 22 by referring to the map based on the differential pressure obtained from the output signal of the differential pressure sensor 39. The map used for estimating the PM accumulation amount is a map of values adapted by experiments and calculations in consideration of the correlation between the differential pressure before and after the DPF 22 and the PM accumulation amount. Stored in the ROM 102.

  When the estimated accumulation amount (collected amount) of PM reaches a predetermined threshold value (hereinafter also referred to as a regeneration threshold value), the ECU 100 supplies fuel into the exhaust gas by post-injection from the injector 2, thereby accumulating in the DPF 22. DPF regeneration control is performed to burn and remove the PM. That is, the post-injected fuel reaches the NSR 21 together with the exhaust gas, and components such as HC and CO are oxidized, and the exhaust gas temperature rises due to heat generated by this oxidation reaction, and the temperature of the DPF 22 rises.

  If the temperature of the DPF 22 is raised to a temperature at which PM burns (for example, 600 ° or more), the PM deposited on the DPF 22 starts to burn, and the temperature of the DPF 22 further rises due to heat generated by this combustion. If such a state can be maintained for a predetermined time (for example, about 10 minutes), the deposited PM is removed, and the PM collecting ability of the DPF 22 is restored.

(EGR correction control)
By the way, since the driving state of the diesel engine 1 mounted on the automobile is strongly influenced by the driver's will and the driving environment as in the present embodiment, the NOx reduction control and the DPF regeneration control may not be sufficiently performed. possible. That is, since the diesel engine 1 has a high thermal efficiency, the temperature of the exhaust gas is relatively low, for example, about 200 to 400 °. Therefore, if the traveling speed is very low such as a traffic jam road, the temperature of the NSR 21 and the DPF 22 Will drop considerably.

  As described above, it is difficult to raise the temperature of the DPF 22 in a low temperature state so that the PM burns as described above, and it is more difficult to maintain such a high temperature state. That is, even if the DPF regeneration control is started once and the DPF 22 is brought into a high temperature state, if the driver stops the vehicle after that, the control must be interrupted on the way.

  For this reason, in an automobile with a high frequency of low-speed traveling, effective DPF regeneration control cannot be performed for a long time, and the amount of PM accumulated in the DPF 22 sometimes exceeds the regeneration threshold. As an example, as shown in FIG. 5, when the amount of accumulated PM in the DPF 22 further exceeds the regeneration threshold and exceeds the allowable upper limit value, the PM becomes excessively intense when the DPF regeneration control is performed thereafter. By burning, the DPF 22 may be temporarily overheated.

  Here, in the example of FIG. 5, even when the PM accumulation amount of the DPF 22 reaches the regeneration threshold, the NOx storage capacity of the NSR 21 has a large margin, and when the allowable upper limit is exceeded as described above, the NOx There is still a margin in storage capacity. In other words, even if the DPF 22 is overheated, it can be said that the exhaust purification device including the NSR 21 is not fully capable.

  Therefore, in the present embodiment, not only the conventional NOx reduction control and DPF regeneration control are performed individually, but also only one of them is considered in consideration of the balance between the NOx occlusion amount in the NSR 21 and the PM accumulation amount in the DPF 22. EGR is corrected and controlled so that it does not increase too much. By so doing, the so-called NOx reduction control and the DPF regeneration control can be coordinated, and the exhaust gas purification apparatus combined with both the NSR 21 and the DPF 22 can fully exhibit their capabilities.

  Hereinafter, a specific procedure of EGR correction control will be described with reference to the flowchart of FIG. Note that the processing shown in this flowchart is repeatedly executed by the ECU 100 at a predetermined cycle after the operation of the engine 1 is started.

  First, in step S1, it is determined whether or not the NOx reduction control can be executed based on the current temperature state of the NSR 21, the driving state of the automobile, the driving history, and the like. The temperature state of the NSR 21 may be detected by an output signal of the first exhaust temperature sensor 37, or may be detected by output signals of both the first exhaust temperature sensor 37 and the second exhaust temperature sensor 38.

  The NOx reduction control cannot be executed when the NSR 21 is in a low activity state where the temperature state of the NSR 21 is very low and effective NOx release and reduction cannot be performed, or when the traveling speed is very low, such as on a congested road. It determines with (NO in step S1), and progresses to step S9 mentioned later. On the other hand, if NOx reduction control can be executed (YES in step S1), the process proceeds to step S2, and it is determined whether or not the NOx occlusion amount in the NSR 21 is less than a preset reduction threshold.

  The reduction threshold is appropriately set as a value such that the NOx occlusion capacity in the exhaust gas by the NSR 21 decreases to a predetermined value or less as the NOx occlusion amount increases. If the NOx occlusion amount reaches the reduction threshold, NO is stored. The process proceeds to step S3, where NOx reduction post-injection is started and the NOx reduction control is executed. On the other hand, if the NOx occlusion amount is less than the reduction threshold value (that is, if the reduction threshold value has not been reached), the determination is YES, and NOx reduction control is not necessary yet. Judge whether or not.

  Whether or not the DPF regeneration control can be executed is determined based on the temperature state of the DPF 22, the driving state of the automobile, the driving history, and the like as in the case of the NSR 21 described above. For example, the current temperature state of the DPF 22 can be detected by the output signal of the second exhaust temperature sensor 38. It is also preferable to consider whether the temperature state of the NSR 21 is suitable for DPF regeneration control based on the output signal of the first exhaust temperature sensor 37.

  If it is determined that the DPF regeneration control cannot be performed (NO in step S4), the process proceeds to step S7 described later. If YES, the process proceeds to step S5, and the PM accumulation amount in the DPF 22 is determined in advance. It is determined whether it is less than the set reproduction threshold. The accumulation amount of PM is calculated (estimated) with reference to a map based on the differential pressure obtained from the output signal of the differential pressure sensor 39. Further, the regeneration threshold is appropriately set as a value such that the pressure loss of the exhaust passing therethrough becomes greater than a predetermined value due to the PM accumulated in the DPF 22.

  If the PM accumulation amount is equal to or greater than the regeneration threshold value (that is, reaches the regeneration threshold value), if NO is determined in step S5, the process proceeds to step S6, where post injection for DPF regeneration is started and the DPF regeneration control is executed. . On the other hand, if the PM accumulation amount is less than the regeneration threshold value (that is, if the regeneration threshold value has not been reached), it is determined YES in step S5, and DPF regeneration control is not necessary yet, and the process returns.

  In other words, in a situation where both NOx reduction control and DPF regeneration control can be performed, NOx reduction control is executed when the NOx occlusion amount reaches the reduction threshold, and DPF regeneration control is performed when the PM accumulation amount reaches the regeneration threshold. As a result, the respective capacities of the NSR 21 and the DPF 22 can be restored.

  On the other hand, if it is determined in step S4 that the DPF regeneration control cannot be executed, the process proceeds to step S7, and it is determined whether the PM deposition amount of the DPF 22 is less than the regeneration threshold, as in step S5. If this determination is YES and the PM accumulation amount is less than the regeneration threshold (that is, if the regeneration threshold has not been reached), the process returns.

On the other hand, if it is determined in step S7 that the PM accumulation amount is equal to or greater than the regeneration threshold (NO), that is, it has reached the regeneration threshold, the process proceeds to step S8, and the EGR reduction correction is executed. For example, it correct | amends so that the control target value egr of the opening degree of the EGR valve 72 read from the control map illustrated in FIG. 4 may be decreased. In the present embodiment, it is the correction amount as a variable.

That is, in accordance with allowance to the NOx occlusion amount of the reducing threshold NSR21, the correction amount of the opening degree of the EGR valve 72, so as to change the degree of other words EGR gas amount decreasing correction. For that purpose, for example, according to the margin of the NOx occlusion amount when the PM accumulation amount reaches the regeneration threshold as described above, and the pace (increase amount per mileage) at which the NOx occlusion amount increases until that point. The correction amount obtained in advance may be obtained by experiment or the like and mapped, and the correction amount obtained from this map may be subtracted from the control target value of the opening degree of the EGR valve 72.

That is, when the PM accumulation amount has increased to such an extent that DPF regeneration control should be performed originally, but the PM accumulated in the DPF 2 cannot be removed by combustion, the amount of EGR gas to be recirculated to the combustion chamber in the cylinder 1a is set. By reducing (increase NO ₂ ), the amount of PM produced by combustion is reduced. In this way, as shown in an example in FIG. 7, the pace at which the PM accumulation amount increases after the regeneration threshold is exceeded, so that the automobile can travel a longer distance before the PM accumulation amount exceeds the allowable upper limit value. As a result, opportunities for executing DPF regeneration control can be increased.

  If the EGR gas amount is reduced as described above, the amount of NOx generated increases as the combustion temperature rises, and the pace at which the NOx occlusion amount increases as shown in the figure increases, but the reduction threshold is reached. Since there is no allowance, there is no problem. FIG. 7 shows a case where the correction amount of EGR is changed in accordance with the margin of the NOx occlusion amount, whereby the PM accumulation amount and the NOx occlusion amount reach the allowable upper limit value at substantially the same time. It becomes like this.

  By the way, if it is determined in step S1 that NOx reduction control cannot be executed (NO), DPF regeneration control cannot usually be executed. In this case, in step S9, the PM accumulation amount is regenerated as in steps S5 and S7. It is determined whether it is less than the threshold value. If the regeneration threshold has been reached (determination is NO), the process proceeds to step S10 to determine whether or not the NOx occlusion amount of the NSR 21 is less than the reduction threshold. Proceeding to S8, EGR reduction correction is executed.

  On the other hand, if the determination in step S10 is NO and the NOx occlusion amount of the NSR 21 has reached the reduction threshold, that is, if there is no allowance for the NOx occlusion amount (determination is NO), the EGR reduction correction is not executed. In this case, since it is necessary to take some measures before the PM accumulation amount of the DPF 22 further increases and reaches the allowable upper limit value, the process proceeds to step S11, and predetermined notification processing to the driver such as lighting of the mill illumination is performed. Go and return.

  If it is determined in step S9 that the PM accumulation amount has not reached the regeneration threshold value, the process proceeds to step S12, where it is determined whether the NOx storage amount of the NSR 21 is less than the reduction threshold value. If this determination is YES and the NOx occlusion amount has not reached the reduction threshold value, the process returns. On the other hand, if the NOx occlusion amount has reached the reduction threshold value, the routine proceeds to step S13, where EGR increase correction is performed.

  In other words, when the NSR storage amount of the NSR 21 is originally increased to the extent that the NOx reduction control is performed and the NOx reduction control cannot be performed, the NOGR generation amount is decreased by the EGR increase correction. In this case, as shown in an example in FIG. 8, the pace at which the NOx occlusion amount increases after the regeneration threshold is exceeded, and the vehicle can travel a longer distance before it exceeds the allowable upper limit. In addition, the opportunity for executing the NOx reduction control can be increased.

  Therefore, according to the exhaust gas purification apparatus of the present embodiment, not only the NOx reduction control is performed based on the state of the NSR 21 disposed in the exhaust system of the diesel engine 1, and the DPF regeneration control is performed based on the state of the DPF 22, In consideration of the balance between the NOx occlusion amount in the NSR 21 and the PM accumulation amount in the DPF 22, EGR correction control is performed so that only one of them does not increase excessively.

  That is, when the amount of accumulated PM in the DPF 22 reaches the regeneration threshold, the EGR is corrected to decrease, and the amount of PM generated due to combustion is decreased, thereby extending the period until the amount of accumulated PM exceeds the allowable upper limit value, and DPF regeneration. Opportunities for control can be increased. Similarly, when the NOx occlusion amount of the NSR 21 reaches the reduction threshold, the EGR is increased and corrected, and the NOx occlusion amount is reduced to extend the period until the NOx occlusion amount exceeds the allowable upper limit value, and the execution of the NOx reduction control is performed. Opportunities can be increased.

  In other words, by appropriately changing the EGR gas amount that is suitably set according to the operating state of the engine 1, the balance of the NOx and PM generation amounts can be corrected according to the margin of the NSR 21 and the DPF 22. it can. As a result, the period until the capacity of either NSR21 or DPF22 saturates can be extended as much as possible, and the opportunity to recover the capacity can be increased. The performance can be secured stably.

  Moreover, such EGR gas amount correction control is performed when the DPF regeneration control cannot be executed even though the PM accumulation amount has reached the regeneration threshold, and when the NOx occlusion amount has reached the reduction threshold. When reduction control cannot be performed, it is performed only in either case. Therefore, it is possible to minimize adverse effects such as a reduction in pump loss by reducing the amount of EGR gas that is suitably set, and deterioration of the combustion state due to an increase in EGR.

-Other embodiments-
The embodiment described above has been described with respect to the case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder diesel engine 1 mounted on an automobile. The present invention is not limited to this, and can also be applied to a diesel engine mounted other than an automobile. Further, the present invention is applicable not only to diesel engines but also to gasoline engines.

  In the above-described embodiment, the amount of EGR gas that recirculates the EGR passage 71 is adjusted by the EGR valve 72. However, the present invention is not limited to this. For example, the opening / closing timings of the intake valve and the exhaust valve are changed. Thus, the present invention can be applied to the one that adjusts the amount of burnt gas remaining in the cylinder 1a or recirculated directly from the exhaust passage 4.

  Further, in the above embodiment, the NOx reduction control and the DPF regeneration control are performed by the post injection from the injector 2, but the present invention is not limited to this, for example, from a fuel addition valve provided in the exhaust passage 4. The present invention is also applicable when NOx reduction control or DPF regeneration control is performed by adding fuel.

  In the above embodiment, the case where the present invention is applied to both NOx reduction control and DPF regeneration control has been described. However, the present invention is not limited to this, and only one of NOx reduction control or DPF regeneration control is used. Is also applicable. However, considering the risk of DPF overheating when the PM accumulation amount exceeds the allowable upper limit value, it is preferable to apply the present invention to at least DPF regeneration control.

  Further, in the above-described embodiment, the system including the DPF 22 is described as a filter for collecting PM. However, the present invention can be applied to a system including the DPNR.

  INDUSTRIAL APPLICABILITY The present invention can fully exhibit the ability of an exhaust purification device including a NOx occlusion material and a PM filter, and is particularly useful when applied to a diesel engine or the like mounted on an automobile.

1 engine (internal combustion engine)
1a cylinder (combustion chamber)
4 Exhaust passage 21 NSR (NOx storage material)
22 DPF (PM filter)
71 EGR passage (burned gas amount adjusting means)
72 EGR valve (burned gas amount adjusting means)
100 ECU (control means)

Claims (4)

An exhaust purification device comprising a NOx occlusion material that is disposed in an exhaust passage of an internal combustion engine and occludes NOx in the exhaust in a predetermined state, and a PM filter that collects PM contained in the exhaust,
The internal combustion engine is provided with a burnt gas amount adjusting means capable of adjusting a burnt gas amount that remains or recirculates in the combustion chamber,
It is generated in the combustion chamber when either the NOx occlusion amount in the NOx occlusion material reaches a predetermined threshold value or the PM collection amount in the PM filter reaches a predetermined threshold value. Control means for performing correction control to increase or decrease the amount of burned gas by the burned gas amount adjusting means so that the amount of NOx and PM that has reached the threshold value decreases ,
The control means is configured to increase the amount of burned gas by the burned gas amount adjusting means according to the margin to the threshold of the stored amount of NOx and the collected amount of PM that has not reached the threshold, or An exhaust purification device for an internal combustion engine, characterized in that the degree of weight reduction correction is changed . The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The control means performs correction control of the burnt gas amount if the internal combustion engine is in a predetermined operation state when the amount of collected PM in the PM filter reaches the threshold value, while the predetermined operation state If not, the exhaust gas purifying apparatus for an internal combustion engine that performs filter regeneration control for increasing the temperature of the PM filter and burning and removing the collected PM. The exhaust emission control device for an internal combustion engine according to claim 1 or 2,
When the NOx occlusion amount in the NOx occlusion material reaches the threshold value, the control means performs correction control of the burned gas amount if the internal combustion engine is in a predetermined operation state, while the predetermined operation state If not, an exhaust gas purification apparatus for an internal combustion engine that performs NOx reduction control for reducing and purifying the stored NOx by enriching the air-fuel ratio of the exhaust gas flowing into the NOx storage material. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3,
The control means controls the burned gas amount adjusting means so that the burned gas amount remaining or recirculated in the combustion chamber of the internal combustion engine becomes a target value corresponding to the operating state, and the correction control includes the An exhaust purification device for an internal combustion engine that corrects the target value of the burned gas amount to increase or decrease .

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