JP4178864B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention stores NOx when the air-fuel ratio of the exhaust gas is leaner than the state corresponding to the stoichiometric air-fuel ratio, while releasing the stored NOx in response to the enrichment of the air-fuel ratio and reducing it. The present invention relates to an exhaust gas purification apparatus for an internal combustion engine including a NOx occlusion type catalyst to be purified, and particularly belongs to the field of control technology for appropriately dealing with deterioration of the catalyst. Incidentally, various types of NOx occlusion type catalysts are already known, and they are sometimes called NOx absorption type or NOx adsorption type. However, in this specification, when referred to as a NOx occlusion type catalyst, Any name shall be included.
[0002]
[Prior art]
  Conventionally, as an exhaust purification device of this type, as disclosed in, for example, Japanese Patent No. 2888124, a NOx occlusion type catalyst is disposed in the exhaust passage of an internal combustion engine, and the NOx concentration disposed downstream of the catalyst. A device that detects the deterioration of a catalyst based on a signal from a sensor is known. That is, in the NOx storage type catalyst, the internal combustion engine is operated at an air / fuel ratio leaner than the stoichiometric air / fuel ratio (hereinafter also referred to as lean operation), and the exhaust air / fuel ratio is leaner than the state corresponding to the stoichiometric air / fuel ratio. NOx is occluded when the engine is in the normal state, while the operating air-fuel ratio of the internal combustion engine becomes the stoichiometric air-fuel ratio or richer (hereinafter also referred to as rich operation), and the air-fuel ratio of the exhaust becomes the stoichiometric air-fuel ratio or higher. If the state becomes rich (hereinafter also simply referred to as rich state), the stored NOx is released and reduced and purified.
[0003]
  In the exhaust purification apparatus of the conventional example, the release of NOx stored by the catalyst by the rich operation of the internal combustion engine is completed, and then the internal combustion engine is switched to the lean operation, and the catalyst stores NOx in the exhaust gas. If the time until the NOx concentration downstream of the catalyst reaches the predetermined value is short when the operation is restarted, it is determined that the NOx storage capacity is reduced due to the deterioration of the catalyst. The passenger is informed of the deterioration of the catalyst and prompted to replace the catalyst.
[0004]
[Problems to be solved by the invention]
  By the way, in general, as a NOx occlusion type catalyst, a carrier in which a NOx occlusion material such as barium oxide and a noble metal such as platinum and palladium are supported is used. As a deterioration state of such a catalyst, Exposure to high-temperature exhaust from an internal combustion engine reduces the function of the noble metal and NOx storage material (thermal degradation), and the sulfur component contained in the exhaust gas strongly binds to the NOx storage material, thereby reducing NOx storage capacity. Inhibiting (sulfur poisoning) is known.
[0005]
  When the catalyst is in the sulfur poisoning state, for example, in the case of a gasoline engine, the exhaust gas temperature is increased by retarding the ignition timing, etc. By maintaining the catalyst at a predetermined level or higher, the sulfur component can be released from the NOx storage material of the catalyst, and thereby the NOx storage capacity can be recovered.
[0006]
  However, since the exhaust gas purification apparatus of the conventional example merely detects the deterioration of the catalyst and issues an alarm to the vehicle occupant, it is a case of sulfur poisoning that can recover the function of the catalyst as described above. However, a warning is given to the passenger, and this warning becomes extremely complicated.
[0007]
  In view of such a problem, the inventors of the present application have intensively studied the identification of the cause of deterioration of the NOx occlusion type catalyst. As a result, the catalyst once completed the release of the occluded NOx, and then the exhaust gas is exhausted. When the NOx occlusion in the gas was resumed, it was found that the state of change in the NOx concentration on the downstream side of the catalyst was greatly different between the case of thermal deterioration and the case of sulfur poisoning, which led to the completion of the invention. It was.
[0008]
  That is, the object of the present invention is to automatically specify not only the deterioration of this catalyst but also the cause thereof in an exhaust purification device provided with a NOx occlusion type catalyst in the exhaust passage of the internal combustion engine. It is to enable appropriate countermeasures.
[0009]
[Means for Solving the Problems]
  In order to achieve the above object, according to the solution means of the present invention, a NOx concentration sensor is disposed in the exhaust passage on the downstream side of the catalyst, and when the deterioration of the catalyst is detected, the NOx occluded by the catalyst is released. When the NOx occlusion in the exhaust gas is resumed after completion, the cause of catalyst deterioration is determined based on the temporal change rate of the NOx concentration detected by the NOx concentration sensor.
[0010]
  Specifically, in the first aspect of the present invention, the NOx is stored when the air-fuel ratio of the exhaust gas is leaner than the state corresponding to the stoichiometric air-fuel ratio. NOx occlusion type catalyst that releases and reduces and purifies NOx in response to enrichment of the air-fuel ratio, and an exhaust passage downstream of the catalystArranged inIn exhaust gasNOxDetect the concentration ofNOx concentration sensorAnd at least saidNOx concentration sensorAn exhaust purification device for an internal combustion engine is provided on the premise of including a catalyst deterioration detecting means for detecting deterioration of the catalyst based on the detection value obtained by the above. And,in frontNOx detected by the NOx concentration sensor when the catalyst deterioration is detected by the catalyst deterioration detecting means when the release of the NOx stored by the catalyst is completed and the storage of NOx in the exhaust gas is resumed. Determining the time change rate of the concentration, and a deterioration cause determination means for determining that the influence of sulfur poisoning on the catalyst cause of deterioration is large if the time change rate is equal to or higher than a preset reference value; To do.
[0011]
  With the above configuration, first, when the internal combustion engine is lean operated and the air-fuel ratio of the exhaust gas becomes leaner than the stoichiometric air-fuel ratio, NOx in the exhaust gas in an oxygen-excess atmosphere is occluded by the NOx occlusion type catalyst. Is done. On the other hand, when the internal combustion engine is richly operated, the air-fuel ratio of the exhaust gas also becomes rich. At this time, NOx stored in the catalyst is released and reduced and purified.
[0012]
  Here, when the catalyst deteriorates, its NOx occlusion ability decreases. For example, even if the catalyst once releases all of the occluded NOx by the rich operation of the internal combustion engine, the internal combustion engine then switches to the lean operation. When NOx occlusion in the exhaust gas by the catalyst is resumed, the concentration of NOx downstream of the catalyst increases relatively quickly. At this time, when the catalyst is thermally deteriorated, the rise in the increase in NOx concentration is relatively slow, whereas in the case of sulfur poisoning, the rise in the increase in NOx concentration is relatively steep. It will be something.
[0013]
  Therefore, according to the present invention, when the NOx occlusion stored by the catalyst is completed and NOx occlusion in the exhaust gas is resumed, the time change rate of the NOx concentration detected by the NOx concentration sensor downstream of the catalyst is calculated. In other words, if the rate of change with time is equal to or greater than a preset reference value, it is determined that the influence of sulfur poisoning on the cause of catalyst deterioration is significant. This makes it possible to accurately determine whether the catalyst is deteriorated due to heat deterioration or sulfur poisoning, and it is possible to take appropriate measures according to the deterioration state based on the determination result. become.
[0014]
  Specifically, as in the invention of claim 2, when it is determined by the deterioration cause determination means that the influence of sulfur poisoning on the cause of deterioration of the catalyst is large, the detachment of the sulfur component from the catalyst is promoted. It is preferable to provide a deterioration control means for controlling the operating state of the internal combustion engine.
[0015]
  In this way, when the influence of sulfur poisoning on the cause of catalyst deterioration is large, the deterioration time control means, for example, makes the air-fuel ratio state of the exhaust gas rich and the temperature state of the exhaust gas higher than a predetermined value. Thus, the operating state of the internal combustion engine is controlled. Thereby, the separation of the sulfur component from the NOx storage type catalyst is promoted, and the NOx storage ability of the catalyst is recovered.
[0016]
  In the invention of claim 3, the deterioration cause determination means in the invention of claim 2 is detected by the NOx concentration sensor when the release of NOx occluded by the catalyst is completed and occlusion of NOx in the exhaust gas is resumed. If the time change rate of the NOx concentration is smaller than the set reference value, it is determined that the influence of sulfur poisoning on the cause of catalyst deterioration is small, and further catalyst deterioration is detected by the catalyst deterioration detecting means, and When the deterioration cause determining means determines that the influence of sulfur poisoning is small, it is provided with notifying means for notifying deterioration of the catalyst.
[0017]
  Thus, when catalyst deterioration is detected and it is determined that the influence of sulfur poisoning on the cause of deterioration is small, the catalyst is thermally deteriorated and cannot restore NOx storage capacity. The notification means notifies the deterioration of the catalyst. And a catalyst is replaced | exchanged rapidly, and the deterioration of an exhaust state is prevented beforehand. On the other hand, when it is determined that the influence of sulfur poisoning is great, the notification is not immediately performed, and thus the complexity of the notification is eliminated.
[0018]
  In the fourth aspect of the invention, when the deterioration of the catalyst is detected by the catalyst deterioration detecting means after the control of the internal combustion engine by the deterioration time control means, the notification means in the invention of the third aspect is determined. The deterioration of the catalyst is notified regardless of the result of determination by the means.
[0019]
  Thus, even if the cause of deterioration of the catalyst is erroneously determined to be due to sulfur poisoning, the deterioration of the catalyst is notified when further deterioration of the catalyst is detected. Therefore, the catalyst can be quickly replaced to prevent the exhaust state from deteriorating.
[0020]
  In the invention of claim 5, when the release of NOx occluded by the catalyst is completed and occlusion of NOx in the exhaust gas is resumed, the rate of change of NOx concentration detected by the NOx concentration sensor is higher than the set reference value. If it is greater than another large set value, it is provided with sulfur poisoning reduction control means for controlling the operating state of the internal combustion engine so as to promote the separation of the sulfur component from the catalyst.
[0021]
  That is, when the NOx occlusion type catalyst resumes occlusion of NOx in the exhaust gas, the time change rate of the NOx concentration detected by the NOx concentration sensor is large, which means that the NOx occlusion ability of the catalyst is lowered. Therefore, at this time, even if the catalyst deterioration detection means has not detected the deterioration of the catalyst, the sulfur poisoning mitigation control hand promotes the removal of the sulfur component from the catalyst. Control the operating state. Thereby, the recovery of the NOx occlusion ability by the catalyst is achieved.
[0022]
  In the invention of claim 6,The NOx is stored when the air-fuel ratio of the exhaust gas is leaner than the state corresponding to the stoichiometric air-fuel ratio, while the stored NOx is stored in the exhaust passage of the internal combustion engine in response to the enrichment of the air-fuel ratio. NOx occlusion type catalyst that releases and reduces and purifies, an oxygen concentration sensor that is disposed in an exhaust passage downstream of the catalyst and detects the concentration of oxygen in the exhaust gas, and at least the oxygen concentration sensor An exhaust gas purifying apparatus for an internal combustion engine is provided on the premise of including catalyst deterioration detection means for detecting catalyst deterioration based on the detected value.
[0023]
  When the deterioration of the catalyst is detected by the NOx concentration sensor disposed in the exhaust passage on the downstream side of the catalyst and detecting the concentration of NOx in the exhaust gas, and the catalyst deterioration detecting means, the catalyst When the NOx occlusion is completed and NOx occlusion in the exhaust gas is resumed, the time change rate of the NOx concentration detected by the NOx concentration sensor is obtained, and this time change rate is a preset reference. If it is equal to or greater than the value, deterioration cause determination means for determining that the influence of sulfur poisoning on the cause of deterioration of the catalyst is great is provided.
[0024]
  In this case, the same effect as the invention of claim 1 can be obtained.Downstream from the catalystAcidElemental concentration sensorIn order to detect catalyst deterioration based on the detected value byAn oxygen concentration sensor is also arranged in the exhaust passage upstream of the catalyst,ThemDetects catalyst deterioration based on signals from oxygen concentration sensors upstream and downstream of the catalyst(Invention of claim 7).
[0025]
  That is, for example, when NOx in the exhaust gas is stored in a NOx storage type catalyst, oxygen in the exhaust gas is consumed and the oxygen concentration decreases, and conversely, NOx is released from the catalyst. As a result, the oxygen concentration in the exhaust gas increases. For this reason, when the operating air-fuel ratio of the internal combustion engine changes between a lean state and a rich state, the output of the oxygen concentration sensor on the upstream side of the catalyst and the oxygen concentration sensor on the downstream side are stored by the storage or release of NOx by the catalyst. Deviation occurs with respect to the output of the catalyst, and the magnitude of this deviation varies depending on the NOx storage capacity of the catalyst. Therefore, the deterioration of the catalyst can be detected based on the signals from the upstream and downstream oxygen concentration sensors.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0027]
  FIG. 1 shows the overall configuration of an in-cylinder direct injection gasoline engine 1 (internal combustion engine) to which an exhaust emission control device according to the present invention is applied. In FIG. 1, an engine 1 includes a cylinder block 3 in which a plurality of cylinders 2, 2,... (Only one is shown) are provided in series, and a cylinder head 4 disposed on the cylinder block 3. A piston 5 is fitted in each cylinder 2 so as to be able to reciprocate. A combustion chamber 6 is defined in the cylinder 2 between the crown surface of the piston 5 and the lower surface of the cylinder head 4. The reciprocating motion of the piston 5 is converted into a rotational motion of the crankshaft 8 through the connecting rod 7 and output by the crankshaft 8. The cylinder block 3 includes an electromagnetic crank angle sensor 9 for detecting the rotation angle at one end of the crankshaft 8 and a knock for detecting knocking based on fluctuations in combustion pressure for each cylinder 2. A sensor 10 and an engine water temperature sensor 11 for detecting the temperature of the cooling water (engine water temperature) facing the inside of a water jacket (not shown) are provided.
[0028]
  In the cylinder head 4, two intake ports 12 and two exhaust ports 13 are opened for each cylinder 2 so as to face the ceiling surface of the combustion chamber 6, and intake and exhaust are provided in the respective port openings. Valves 14 and 15 are arranged. The intake valve 14 and the exhaust valve 15 are opened and operated in synchronism with the rotation of the crankshaft 8 by intake and exhaust camshafts (not shown) pivotally supported in the cylinder head 4, respectively. It has become. Further, an electromagnetic cam angle sensor 16 for detecting the rotation angle is attached to the intake side camshaft. A spark plug 17 is disposed for each cylinder 2 so as to penetrate the cylinder head 4 in the vertical direction and be surrounded by the intake and exhaust valves 14 and 15. The electrode at the tip of the spark plug 17 protrudes downward from the ceiling surface of the combustion chamber 6 by a predetermined distance. The base end portion of the spark plug 17 is connected to an ignition circuit 18 (igniter) disposed so as to penetrate the head cover.
[0029]
  The crown surface of the piston 5 serving as the bottom of the combustion chamber 6 has an outer peripheral portion substantially parallel to the ceiling surface of the combustion chamber 6, while the piston 5 has a substantially central portion of the crown surface in plan view. Lemon-shaped recesses are provided. In addition, an injector (fuel injection valve) 20 is disposed with the injection port facing the peripheral edge of the combustion chamber 6 on the intake side. The injector 20 may be, for example, a known swirl injector that ejects fuel as a swirling flow from a nozzle hole at the tip facing the combustion chamber 6 and injects it in a hollow cone shape along the direction in which the axis extends. However, the present invention is not limited to this, and a slit type or multi-injector type injector may be used, or a core valve may be operated by a piezoelectric element.
[0030]
  The proximal end side of the injector 20 is connected to a fuel distribution pipe 21 common to all cylinders 2, 2,..., And fuel discharged from the high-pressure fuel pump 22 through the fuel distribution pipe 21 is injected into each cylinder 2. 20 are distributed. When fuel is injected by the injector 20 in the compression stroke of the cylinder 2, the fuel spray is decelerated by the intake air flow in the combustion chamber 6, and an air-fuel mixture in an appropriate concentration state is formed around the spark plug 17. To do. The fuel distribution pipe 21 is provided with a fuel pressure sensor 23 for measuring the pressure state (fuel injection pressure) of the fuel injected from the injector 20.
[0031]
  An intake passage 25 is connected to one side surface (the right side surface in the figure) of the engine 1 so as to communicate with the intake port 12 of each cylinder 2. This intake passage 25 supplies the intake air filtered by the air cleaner 26 to the combustion chamber 6 of the engine 1 and is a hot for detecting the intake air amount to the engine 1 in order from the upstream side to the downstream side. A wire type air flow sensor 27, an electric throttle valve 28 for changing the cross-sectional area of the intake passage 25, a throttle sensor 29 for detecting the position thereof, and a surge tank 30 are provided. The throttle valve 28 is not mechanically connected to an accelerator pedal (not shown), and is opened and closed by an electric motor (not shown). The surge tank 30 is provided with a boost sensor 31 that detects the pressure in the intake passage 25 downstream of the throttle valve 28.
[0032]
  Further, the intake passage 25 on the downstream side of the surge tank 30 is an independent passage branched for each cylinder 2, and the downstream end portion of each independent passage is further divided into two to be individually connected to the intake port 12. It is a branch road that communicates with In this branch path or independent path, a throttle valve 32 (TSCV) for adjusting the strength of the intake air flow in the combustion chamber 6 is disposed, and is opened and closed by, for example, a stepping motor or the like. Actuated. The valve body of the TSCV 32 has a notch in a part thereof, and in the fully closed state, intake air flowing downstream only from the notch portion generates a strong in-cylinder flow in the combustion chamber 6. On the other hand, as the TSCV 32 is opened, the intake air circulates from other than the notch, and the strength of in-cylinder flow gradually decreases.
[0033]
  An exhaust passage 34 for discharging burned gas (exhaust gas) from the combustion chamber 6 in the cylinder 2 is connected to the other side surface (the left side surface in the figure) of the engine 1. The upstream end side of the exhaust passage 34 is constituted by an exhaust manifold 35 connected to the exhaust port 13 for each cylinder 2. The exhaust passage 34 downstream of the exhaust manifold 35 is a harmful component in the exhaust gas. Two catalytic converters 36 and 37 for purifying hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (NOx) are arranged in series.
[0034]
  Although not shown in detail, the upstream catalytic converter 36 accommodates a honeycomb structure carrier in a casing, and a so-called three-way catalyst layer is formed on the wall surface of each through hole of the carrier. This three-way catalyst (hereinafter also referred to as upstream side three-way catalyst 36) is HC, CO, NOx when the air-fuel ratio of the exhaust gas is in a predetermined state including a substantially stoichiometric air-fuel ratio, as is conventionally known. Can be purified almost completely.
[0035]
  Further, the downstream catalytic converter 37 accommodates two carriers in series in one casing, and forms a so-called NOx occlusion type catalyst layer on the wall surface of each through hole of the upstream carrier, so that the upstream side In addition to the NOx catalyst 38, a NOx occlusion type catalyst layer is formed on the downstream carrier in the same manner to constitute the downstream NOx catalyst 39. Here, the NOx catalysts 38 and 39 are formed by, for example, supporting a NOx occlusion material such as barium oxide and a noble metal such as platinum or palladium on a base coat such as zeolite, and the air-fuel ratio state of the exhaust gas corresponds to the stoichiometric air-fuel ratio. In this state, NOx in the exhaust gas is occluded when it is leaner than the state to be released, while the NOx occluded in this way is released in accordance with the enrichment of the air-fuel ratio, and is reduced and purified.
[0036]
  Specifically, the mechanism by which NOx in the exhaust gas is occluded or released by the NOx occlusion type catalyst is considered as follows. That is, as schematically shown in FIG. 2 (a), when the air-fuel ratio of the exhaust gas is lean, NOx (NO in the illustrated example) in the exhaust gas in an oxygen-excess atmosphere is converted to the catalyst metal (in the illustrated example). Pt) reacts with oxygen O2 and is occluded as nitrate NO3 while part of it is bonded to barium. On the other hand, if the air-fuel ratio of the exhaust gas is substantially the stoichiometric air-fuel ratio or richer than that, the reaction proceeds in the opposite direction, and NO2 away from the barium becomes HC, CO in the exhaust gas. It reacts (reduction reaction) and decomposes into nitrogen N2 and oxygen O2.
[0037]
  An oxygen concentration sensor 40 for detecting the oxygen concentration in the exhaust gas is disposed in the vicinity of the collecting portion of the exhaust manifold 35 of the engine 1, and the air-fuel ratio of the engine 1 is mainly based on a signal from the oxygen concentration sensor 40. Feedback control is performed. Further, between the two catalytic converters 36 and 37, an oxygen concentration sensor 41 for determining the deterioration state of the upstream three-way catalyst 36, and an exhaust temperature for detecting the temperature of the exhaust gas flowing into the NOx catalyst 38 are provided. Further, a NOx concentration sensor 43 that detects the concentration of NOx in the exhaust gas is disposed between the two NOx catalysts 38 and 39. The NOx concentration sensor 43 takes a part of the exhaust gas flowing through the exhaust passage 34 into a closed space, and from there, the oxygen concentration is almost zero by an oxygen pump (for example, 10^-3Oxygen is pumped out until it becomes less than or equal to ppm), thereby promoting the decomposition of NOx in the exhaust gas and measuring the concentration of oxygen newly obtained by the decomposition of the NOx, thereby reducing the NOx concentration in the exhaust gas. It is to detect.
[0038]
  Further, an upstream end of an exhaust gas recirculation passage 45 (hereinafter referred to as an EGR passage) that recirculates a part of the exhaust gas to the intake passage 25 so as to branch from the exhaust passage 34 downstream of the exhaust manifold 35. Are communicating. The downstream end of the EGR passage 45 is open facing the inside of the surge tank 30, and an EGR valve 46 comprising a duty solenoid valve is disposed in the EGR passage 45 near the downstream end. The recirculation amount of the exhaust gas in the EGR passage 45 is adjusted by the EGR valve 46. Reference numeral 47 denotes a purge passage that guides blow-by gas leaking from the combustion chamber 6 of each cylinder 2 to the surge tank 30.
[0039]
  The ignition circuit 18, the injector 20, the high-pressure fuel pump 22, the throttle valve 28, the TSCV 32, the EGR valve 46, and the like described above are all controlled by an engine control unit 50 (hereinafter referred to as an ECU). On the other hand, the ECU 50 includes at least the crank angle sensor 9, the knock sensor 10, the water temperature sensor 11, the air flow sensor 27, the throttle sensor 29, the two oxygen concentration sensors 40 and 41, the exhaust temperature sensor 42, the NOx concentration sensor 43, and the like. Output signals from the accelerator opening sensor 51 for detecting the amount of operation of the accelerator pedal (hereinafter referred to as accelerator opening), and the engine rotational speed (the rotational speed of the crankshaft 8). An output signal from the rotational speed sensor 52 to be detected and an output signal from the vehicle speed sensor 53 are input.
[0040]
  That is, the ECU 50 controls the intake air amount to the engine 1, the fuel injection amount for each cylinder 2, the injection timing, and the ignition timing based on the signals input from the sensors, and further the intake air flow in the cylinder 2 Control the exhaust gas recirculation ratio. Specifically, as shown in an example of the control map in FIG. 3, for example, a stratified combustion region (S) is set in advance on the low-speed and low-load side in the entire operating region of the engine 1. Then, the fuel is injected by the injector 20 in the compression stroke of the cylinder 2 to enter the stratified combustion mode in which the air-fuel mixture unevenly distributed around the electrode of the spark plug 17 is combusted. At this time, the throttle valve 28 is greatly opened to reduce pump loss. As a result, the average air-fuel ratio in the combustion chamber 6 of each cylinder 2 is significantly leaner than the stoichiometric air-fuel ratio (for example, A / F> 30).
[0041]
  On the other hand, a region other than the stratified combustion region (S) is a so-called uniform combustion region (H). Here, fuel is injected by the injector 20 mainly in the intake stroke of the cylinder 2, and the intake air and fuel are separated in the combustion chamber 6. The mixture is sufficiently mixed to form a uniform combustion mode in which a substantially uniform mixture is formed in the entire combustion chamber 6 and then burned. In most of the uniform combustion region (H), the fuel injection amount, the opening degree of the throttle valve 28, etc., the air-fuel ratio of the air-fuel mixture becomes substantially the stoichiometric air-fuel ratio (A / F≈14.7). However, particularly in the vicinity of the full load, control is performed so that the state is richer than the stoichiometric air-fuel ratio (for example, A / F = 12 to 14) so that a large output corresponding to a high load can be obtained. .
[0042]
  That is, the engine 1 of this embodiment basically operates in a stratified combustion mode, that is, in a state where the air-fuel ratio of the air-fuel mixture is significantly leaner than the stoichiometric air-fuel ratio, depending on the load state (target torque) and the engine speed. The lean operation state is switched to the uniform combustion mode, that is, the rich operation state in which the operation is performed in a substantially stoichiometric air-fuel ratio or a richer state.
[0043]
  In addition to such basic operation control, in order to maintain the NOx occlusion ability of the NOx catalyst 38 at a predetermined level or more, the lean operation of the engine 1 is continued for a certain degree or more, and the NOx by the NOx catalyst 38 is continued. When the amount of occlusion increases, the operation is temporarily switched to rich operation to release NOx from the NOx catalyst 38 and reduce and purify it (so-called NOx purge). That is, first, when the engine 1 is switched from the rich operation to the lean operation, and the air-fuel ratio state of the exhaust gas flowing into the NOx catalyst 38 changes from the rich state to the lean state, it is released from the exhaust passage 34 into the atmosphere. The concentration of NOx in the exhaust gas to be gradually increased as the NOx occlusion amount in the NOx catalyst 38 increases as shown in FIG. This is because almost all of the NOx in the exhaust gas is occluded by the NOx catalyst 38 while the NOx occlusion amount of the NOx catalyst 38 is small, but when the amount of occlusion of NOx increases to some extent, new NOx occlusion is performed thereafter. Is limited. When the NOx occlusion amount reaches the maximum occlusion amount determined by the capacity of the NOx catalyst 38 or the like, NOx cannot be occluded any more.
[0044]
  Therefore, in consideration of the characteristics of the NOx catalyst 38, in this embodiment, when the NOx concentration in the exhaust gas becomes higher than a predetermined level based on a signal from the NOx concentration sensor 43 provided downstream of the catalyst. A NOx purge is performed, whereby NOx occluded from the NOx catalyst 38 is released and reduced and purified to recover its NOx occlusion ability.
[0045]
  By the way, in the NOx catalyst 38 having the above-described configuration, a slight sulfur component (for example, sulfur oxide S0x) contained in the exhaust gas is gradually occluded in barium by the same mechanism as that of NOx. Is stronger than that of barium and NOx, the storage amount of the sulfur component in the NOx catalyst 38 gradually increases with time, and this causes a phenomenon that the NOx storage capacity decreases (sulfur cover). poison).
[0046]
  In contrast, if the NOx catalyst 38 is maintained at a high temperature above a predetermined level in a rich atmosphere, SOx can be released from the barium of the catalyst and reduced by HC and CO in the exhaust gas as in the case of NOx. Thus, if the sulfur component is released from the NOx catalyst 38 in this way, the NOx occlusion ability of the NOx catalyst 38 can be recovered (so-called sulfur purge, hereinafter also referred to as S purge).
[0047]
  On the other hand, the NOx catalyst 38 is exposed to high-temperature exhaust gas and undergoes so-called thermal degradation in which the NOx occlusion ability gradually decreases. In this case, the NOx occlusion ability is restored as in the case of sulfur poisoning. Can not be replaced, so if the degree of deterioration increases, it must be replaced with a new one.
[0048]
  Therefore, in this embodiment, during the operation of the engine 1, the deterioration state of the NOx catalyst 38 is determined based on a signal from the NOx concentration sensor 43 disposed in the exhaust passage 34 downstream of the NOx catalyst 38, When the deterioration of the catalyst 38 is mainly caused by sulfur poisoning, an S purge is performed to recover the NOx storage capacity of the catalyst 38, and the NOx storage catalyst 38 mainly causes thermal deterioration. If this is the case, this fact is notified, and the replacement of the catalyst 38 is urged.
[0049]
  Hereinafter, a specific control procedure of the engine 1 by the ECU 50 will be described based on flowcharts shown in FIGS.
[0050]
  First, in step SA1 after the start in the main flow shown in FIG. 5, the crank angle sensor 9, the water temperature sensor 11, the cam angle sensor 16, the air flow sensor 27, the oxygen concentration sensor 40, the accelerator opening sensor 51, the rotation speed sensor 52, and the like. An output signal is input, and data temporarily stored in the RAM of the ECU 50 is read. Subsequently, in step SA2, the current operation mode of the engine 1 is determined from the control map as shown in FIG. 3 based on the target torque of the engine 1 and the engine speed. Note that the target torque corresponds to the load state of the engine 1. For example, the target torque is determined in advance based on the engine rotation speed detected by the rotation speed sensor 52 and the accelerator opening detected by the accelerator opening sensor 51. What is necessary is just to read from the map set experimentally.
[0051]
  Subsequently, in step SA3, it is determined whether or not the stratified combustion mode is set. If this determination is NO and the uniform combustion mode is selected, the process proceeds to step SA4 to control the injector 20, the throttle valve 28, etc. so that the engine 1 is in a uniform combustion state, and then returns, while the determination is YES and stratified combustion If it is the mode, the process proceeds to step SA5, and it is determined whether or not the condition for setting the NOx purge mode is satisfied. In this determination, for example, when the NOx concentration detected by the NOx concentration sensor 43 exceeds the set value, the NOx purge mode condition is satisfied until the engine 1 continues to perform rich operation for a predetermined time thereafter. If you are doing.
[0052]
  If the NOx purge mode condition is satisfied and YES, the routine proceeds to step SA6, where the engine 1 is uniformly at the stoichiometric air fuel ratio or an air fuel ratio richer than that (for example, A / F = 12.0 to 14.7). The NOx purge is performed by controlling the injector 20, the throttle valve 28, etc. so as to be in a combustion state, and then the process returns. On the other hand, if the NOx purge mode condition is not satisfied in step SA5 and it is determined NO, the process proceeds to step SA7.
[0053]
  In step SA7, it is determined whether a condition for setting the S purge mode is satisfied. The specific contents of this determination will be described later. If it is determined YES when the S purge mode condition is satisfied, the routine proceeds to step SA8, where the injector 20, the throttle valve 28, etc. are controlled so that the engine 1 is in a uniform combustion state. At the same time, the air-fuel ratio of the air-fuel mixture is made the stoichiometric air-fuel ratio or richer and the ignition timing is significantly retarded to greatly increase the temperature while enriching the air-fuel ratio of the exhaust gas (S purge execution), Then return. As a result, the temperature of the NOx catalyst 38 is maintained at a predetermined temperature or higher, and the separation of SOx from barium is promoted in a rich atmosphere.
[0054]
  On the other hand, if the S purge mode condition is not satisfied in step SA7 and the determination is NO, the process proceeds to step SA9 to control the injector 20, the throttle valve 28, etc. so that the engine 1 enters the stratified combustion state, and then returns. .
[0055]
  (Determining the deterioration state of the NOx catalyst)
  Next, conditions for executing the S purge mode in step SA7 of the main flow will be described. First, the flow shown in FIG. 6 is for determining conditions for accurately determining the sulfur poisoning of the NOx catalyst 38. In step SB1 after the start, the engine 1 changes from the NOx purge mode to the stratified combustion mode. It is determined whether or not it is within a predetermined period since the transition to. That is, in this embodiment, only when the NOx occlusion stored by the NOx catalyst 38 is completed and occlusion of NOx in the exhaust gas is resumed, the sulfur poisoning of the NOx catalyst 38 is determined. .
[0056]
  If the determination in step SB1 is NO, it means that the condition for determination of sulfur poisoning is not satisfied, and thus the process proceeds to step SB8, and the flag F1 indicating that the determination condition for sulfur poisoning is satisfied is turned off (F1 ← 0). On the other hand, if the determination in step SB1 is YES, the process proceeds to step SB2, and this time it is determined whether the engine water temperature is equal to or higher than a predetermined value. This is for confirming the warm-up of the engine 1. For example, if the engine water temperature is 45 ° C. or less (determination is NO), the process proceeds to step SB8. If the engine water temperature is higher than that, the process proceeds to step SB3. move on.
[0057]
  In step SB3, it is determined whether or not the engine speed is equal to or less than a predetermined value. If this determination is NO, the process proceeds to step SB8. If the determination is YES, the process proceeds to step SB4, and the target torque of the engine 1 is predetermined. Determine if it is less than or equal to the value. If this determination is NO, the process proceeds to step SB8, whereas if the determination is YES, the process proceeds to step SB5. That is, when at least one of the target torque or the rotational speed of the engine 1 is higher than a predetermined value and the flow rate of the exhaust gas is higher than a certain level, the accuracy of the detected value by the NOx concentration sensor 43 is considered to be slightly lower. Sulfur poisoning is not judged.
[0058]
  In step SB5, based on the output from the exhaust temperature sensor 42, it is determined whether the temperature of the NOx catalyst 38 is within a predetermined temperature range where the activity is high. If this determination is NO, the process proceeds to step SB8, while the determination is made. If YES, the routine proceeds to step SB6, where it is determined whether the engine 1 is other than the acceleration operation. If this determination is NO, the process proceeds to step SB8. If the determination is YES, the process proceeds to step SB7, and the flag F1 is turned on (F1 ← 1), assuming that the sulfur poisoning determination condition is satisfied. It should be noted that the determination is not performed during the acceleration operation because the flow rate of the exhaust gas and the gas component concentration inside the engine 1 fluctuate transiently and greatly by the NOx concentration sensor 43 when the operating state of the engine 1 changes greatly. This is because the accuracy of the detected value is considered to be slightly lowered.
[0059]
  Next, the flow shown in FIG. 7 shows a procedure for actually determining the state of sulfur poisoning of the NOx catalyst 38 on the premise that the sulfur poisoning determination condition is satisfied. In SC1, the value of the flag F1 is read to determine whether the sulfur poisoning determination condition is satisfied. If the flag F1 is off (F1 = 0) and NO, the process proceeds to step SC8, the flag F2 indicating sulfur poisoning of the NOx catalyst 38 is turned off (F2 ← 0), and then the process returns. On the other hand, if the determination in step SC1 is YES, the process proceeds to step SC2, and the output of the NOx concentration sensor 43 is read. In the subsequent step SC3, the time change rate of the output value of the NOx concentration sensor 43 (time change rate of NOx concentration). Is calculated. Specifically, the previous value may be subtracted from the current value of the sensor output.
[0060]
  Subsequently, in step SC4, the deterioration of the NOx catalyst 38 is determined based on the output from the NOx concentration sensor 43. That is, after the engine 1 shifts from the NOx purge mode to the stratified combustion mode, the time until the detected value of the NOx concentration sensor 43 exceeds a predetermined value is measured first. Is shorter, it is determined that the NOx catalyst 38 has deteriorated (YES). At this time, the process proceeds to step SC5, where it is determined whether or not the time change rate of the NOx concentration calculated in step SC3 is equal to or higher than a preset first reference value (set reference value). If this determination is NO, the process proceeds to step SC8. If the determination is YES, the process proceeds to step SC6 to turn on the flag F2 (F2 ← 1), and then returns.
[0061]
  That is, when the NOx catalyst 38 deteriorates, as shown in an example in FIG. 10, when the operating state of the engine 1 is switched from the rich operation to the lean operation, and the NOx catalyst 38 resumes storing NOx in the exhaust gas. Thereafter, the time until the NOx concentration starts increasing downstream of the catalyst 38 is shortened. At this time, comparing the case of thermal degradation indicated by the broken line in the figure with the case of sulfur poisoning indicated by the one-point difference line, the NOx concentration increases faster than the new catalyst (shown by the solid line in the figure). However, the state of the increase change is clearly different, and the rise of the NOx concentration in the case of sulfur poisoning is sharper than that in the case of thermal deterioration.
[0062]
  In other words, when the NOx occlusion of the NOx catalyst 38 is completed and the NOx occlusion in the exhaust gas is resumed, the temporal change rate of the NOx concentration in the exhaust gas downstream of the catalyst is the case of sulfur poisoning. In this embodiment, the first reference value is set so that the two can be distinguished from each other, and the temporal change rate of the NOx concentration is the first reference as in step SC3. When the value is greater than or equal to the value, it is determined that the cause of deterioration of the catalyst 38 is mainly due to sulfur poisoning. Like to do.
[0063]
  On the other hand, if it is determined in step SC4 that the NOx catalyst 38 has not deteriorated, the process proceeds to step SC7, where the temporal change rate of the NOx concentration calculated in step SC3 is the first reference value (step It is determined whether or not the second reference value (another set value) is larger than SC5). If this determination is NO, the process proceeds to step SC8, whereas if the determination is YES, the process proceeds to step SC7. That is, even when the deterioration of the NOx catalyst 38 is not judged, when the NOx catalyst 38 resumes storing NOx in the exhaust gas after the NOx purge, the temporal change rate of the NOx concentration downstream of the catalyst is extremely high. If it is larger, the sulfur poisoning of the NOx catalyst 38 is determined, and S purge is performed as will be described later.
[0064]
  Next, the flow shown in FIG. 8 shows a procedure for determining whether or not the engine 1 is in a state where the S purge can be performed. In step SD1 after the start, it is determined whether or not the engine water temperature is equal to or higher than a predetermined value. If this determination is NO, the process proceeds to step SD6, the flag F3 indicating that the S purge execution condition is satisfied is turned off (F3 ← 0), and then the process returns. If the determination is YES, the process proceeds to step SD2. It is determined whether the engine speed is equal to or higher than a predetermined value. If this determination is NO, the process proceeds to step SD6, whereas if the determination is YES, the process proceeds to step SD3.
[0065]
  In step SD3, it is determined whether or not the target torque of the engine 1 is greater than or equal to a predetermined value. If this determination is NO, the process proceeds to step SD6. If the determination is YES, the process proceeds to step SD4, and this time the vehicle speed is predetermined. Determine if it is greater than or equal to the value. If the determination is NO, the process proceeds to step SD6. If the determination is YES, the process proceeds to step SD5, and the flag F3 is turned on (F3 ← 1), assuming that the S purge execution condition is satisfied. Return later.
[0066]
  That is, the engine 1 is completely warmed up (for example, the engine water temperature is 80 ° C. or higher), the temperature of the NOx catalyst 38 is relatively high, the target torque of the engine 1 or the engine rotational speed is high, and the exhaust gas flow rate is high. It is determined that the S purge can be executed when there are relatively many states and the vehicle speed is relatively high.
[0067]
  Then, the sulfur poisoning of the NOx catalyst 38 is determined in the flow shown in FIG. 7, the flag F2 is turned on (F2 ← 1), and it is determined that the S purge can be executed in the flow shown in FIG. If the flag F3 is also turned on (F3 ← 1), it is determined at this time that the S purge mode condition is satisfied (YES) in step SA7 of the main flow in FIG. 5, and the engine 1 is operated in the S purge mode. As a result, sulfur poisoning of the NOx catalyst 38 is reduced or eliminated, and the NOx storage capacity is restored.
[0068]
  Next, the flow shown in FIG. 9 shows a procedure for detecting the deterioration of the NOx catalyst 38 and notifying the vehicle occupant accordingly, and in step SE1 after the start, the steps of the flow shown in FIG. Similarly to SC4, the deterioration of the NOx catalyst 38 is determined. If this judgment is NO, it will progress to Step SE5 and will return, without notifying a crew member. As a notification method, for example, a deterioration notification lamp (not shown) disposed on the instrument panel of the vehicle may be turned on.
[0069]
  On the other hand, when the deterioration of the NOx catalyst 38 is determined in step SE1 (determination is YES), the sulfur poisoning of the NOx catalyst 38 is determined in the subsequent step SE2. This determination is made based on the value of the flag F2 set in steps SC6 and SC8 of the flow shown in FIG. 7. If the flag F2 is off (F2 = 0) and the determination is YES, the process proceeds to step SE3. , Perform notification (for example, turn on the deterioration notification lamp), and then return. If the flag F2 is on (F2 = 1) in step SE2 and the determination is NO, the process proceeds to step SE4, where it is determined whether or not the control of the S purge mode is performed in the previous control cycle. If this determination is NO, the process proceeds to step SE5, while if the determination is YES, the process proceeds to step SE3 to notify the occupant and then returns.
[0070]
  That is, when the deterioration of the NOx catalyst 38 is detected and it is determined that the main cause is not sulfur poisoning, the NOx catalyst 38 is thermally deteriorated and it is difficult to restore the NOx storage capacity. Is notified to the vehicle occupant to encourage replacement of the NOx catalyst 38. On the other hand, if it is determined that the deterioration of the NOx catalyst 38 is mainly due to sulfur poisoning, the notification is not immediately performed. Even at that time, the notification is performed when further deterioration of the catalyst is detected after the S purge.
[0071]
  The control procedures in the flowcharts of FIGS. 5 to 9 described above are realized by a plurality of programs electronically stored in the memory of the ECU 50 being executed by the CPU, whereby the ECU 50 Has the following constituent features of the invention in terms of software.
[0072]
  That is, when the release of NOx occluded by the NOx catalyst 38 is completed and occlusion of NOx in the exhaust gas is resumed by step SC4 of the flow shown in FIG. 7 and step SE1 of the flow shown in FIG. A catalyst deterioration detecting means 50a for detecting deterioration of the NOx catalyst 38 based on a signal from the NOx concentration sensor 43 is configured.
[0073]
  When the deterioration of the NOx catalyst 38 is detected as described above in step SC5 of the flow of FIG. 7, the release of the NOx occluded by the catalyst 38 is completed and the occlusion of NOx in the exhaust gas is resumed. When the time change rate of the NOx concentration detected by the NOx concentration sensor 43 is obtained, and the time change rate is equal to or higher than a preset first reference value, the catalyst 38 is sulfur poisoned (NOx catalyst). The deterioration cause determining means 50b is determined to determine that the influence of sulfur poisoning on the cause of deterioration 38 is large). If the NOx concentration change rate with time is smaller than the first reference value, the deterioration cause determining means 50b is not sulfur poisoned (the influence of sulfur poisoning on the cause of deterioration of the NOx catalyst 38 is small). Is).
[0074]
  Further, when it is determined in steps SA7 and SA8 in the flow shown in FIG. 5 that the NOx catalyst 38 has deteriorated due to sulfur poisoning, the separation of the sulfur component (SOx) from the NOx catalyst 38 is promoted. Deterioration control means 50c for operating the engine 1 in the S purge mode is configured. In steps SA7 and SA8, when the NOx occlusion stored by the NOx catalyst 38 is completed and NOx occlusion in the exhaust gas is resumed, the time change rate of the NOx concentration detected by the NOx concentration sensor 43 is increased. If it is equal to or greater than a second reference value (another set value) that is greater than the first reference value, the sulfur poisoning reduction control means 50d that operates the engine 1 in the S purge mode so as to promote the removal of SOx from the NOx catalyst 38. Is also configured.
[0075]
  Further, the deterioration of the NOx catalyst 38 is determined by step SE3 of the flow shown in FIG. 9 and, for example, a vehicle deterioration notification lamp, and the catalyst 38 is not sulfur poisoning (the influence of sulfur poisoning is small). When the determination is made, the notification means 50e is configured to notify the vehicle occupant of the deterioration of the NOx catalyst 38. According to the notification means 50e, when the deterioration of the NOx catalyst 38 is detected even when the S purge is performed, the deterioration of the NOx catalyst 38 is notified regardless of the result of the determination by the deterioration cause determination means 50b. It is like that.
[0076]
  Therefore, according to the exhaust gas purification apparatus for an internal combustion engine according to this embodiment, first, the engine 1 is in the stratified combustion region (S) on the low speed and low load side, and the average air-fuel ratio of the combustion chamber 6 of each cylinder 2 is When the air-fuel ratio is much leaner than the stoichiometric air-fuel ratio, the air-fuel ratio of the exhaust gas also becomes lean, and NOx in the exhaust gas is occluded by the NOx catalyst 38. On the other hand, when the engine 1 is in the uniform combustion region (H) and the average air-fuel ratio of the combustion chamber 6 of each cylinder 2 becomes substantially stoichiometric or richer than that, the exhaust gas air-fuel ratio is also rich. At this time, NOx stored in the NOx catalyst 38 is released and reduced and purified.
[0077]
  Further, when the lean operation in the stratified combustion region (S) of the engine 1 continues and the NOx occlusion amount in the NOx catalyst 38 increases, the NOx occlusion ability of the NOx catalyst decreases in accordance with the increase in the NOx occlusion amount. The NOx concentration of the exhaust gas exhausted into the atmosphere gradually increases, but if the detected value by the NOx concentration sensor 43 exceeds a predetermined value, the NOx purge is performed and the NOx occlusion ability by the NOx catalyst 38 is recovered. Is planned.
[0078]
  Further, when the NOx purge is completed and the engine 1 shifts from the rich operation in the NOx purge mode to the lean operation in the stratified combustion mode, the NOx catalyst 38 completes the release of the stored NOx, and in the exhaust gas The NOx occlusion is resumed. At this time, assuming that a predetermined condition is satisfied, the deterioration of the NOx catalyst 38 is determined based on the signal from the NOx concentration sensor 43, and further, the NOx concentration is further increased. Based on the time change rate, it is determined whether the cause of deterioration of the NOx catalyst 38 is mainly due to sulfur poisoning or heat deterioration.
[0079]
  If it is determined that the cause of deterioration is mainly sulfur poisoning, the operation mode of the engine 1 is switched to the S purge mode on the premise that a predetermined condition is satisfied, and SOx is released from the NOx catalyst 38. The NOx occlusion ability of the NOx catalyst 38 is recovered by being promoted. On the other hand, when the thermal deterioration of the NOx catalyst 38 is determined, this is notified to the vehicle occupant, and the NOx catalyst 38 is quickly replaced, so that the exhaust state is prevented from deteriorating.
[0080]
  That is, when the deterioration of the NOx catalyst 38 is detected, if it is a thermal deterioration, the passenger is immediately notified. On the other hand, if the deterioration is caused by sulfur poisoning, the passenger is not notified, and the NOx occlusion ability is obtained by S purge. Thus, appropriate measures are taken according to the state of deterioration such as recovery of the problem, and this eliminates the complexity of the notification.
[0081]
  In addition, even if it is erroneously determined that the thermal deterioration is due to sulfur poisoning, when the deterioration of the NOx catalyst 38 is further detected after the S purge, an immediate notification is made, resulting in erroneous determination. As a result, the exhaust state is not deteriorated.
[0082]
  In addition, the structure of this invention is not limited to the thing of the said embodiment, It includes other various structures. For example, in the embodiment, the downstream side of the NOx catalyst 38 is used.NAlthough the Ox concentration sensor 43 is provided and the deterioration of the NOx catalyst 38 is detected based only on the output from the sensor 43 (see SC4 in FIG. 7), this is not restrictive. That is, for example, an oxygen concentration sensor is provided between the NOx catalyst 38 and the downstream side three-way catalyst 39 separately from the NOx concentration sensor 43, and the oxygen concentration sensor 41 and the oxygen concentration sensor 41 upstream of the NOx catalyst 38. The deterioration of the NOx catalyst 38 may be detected based on the output signals.
[0083]
  Specifically, when the exhaust gas is lean and NOx is occluded by the NOx catalyst 38, oxygen is consumed for this purpose. On the contrary, NOx is released from the NOx catalyst 38 in a rich state and reduced. When this is done, the oxygen concentration in the exhaust gas will increase. Therefore, for example, when the engine 1 shifts between the lean operation and the rich operation, the output of the oxygen concentration sensor 41 on the upstream side of the catalyst 38 and the oxygen on the downstream side in accordance with the storage or release of NOx by the NOx catalyst 38. Deviation occurs from the output of the density sensor. Since the magnitude of the misalignment increases as the NOx storage capacity of the NOx catalyst 38 increases, the deterioration of the NOx catalyst 38 can be detected based on the signals from the two oxygen concentration sensors.
[0084]
  In the above embodiment, the two NOx catalysts 38 and 39 are accommodated in one casing to constitute the downstream catalytic converter 37. However, without such a configuration, for example, different casings are used. Needless to say, it may be accommodated in the room.
[0085]
  Further, it goes without saying that the present invention can be applied to other than the direct injection gasoline engine as in the above-described embodiment, and that the average air-fuel ratio of the cylinder is leaner than the stoichiometric air-fuel ratio. As long as the internal combustion engine can be switched to a substantially stoichiometric air-fuel ratio or a rich operation state richer than that, it is possible to obtain the same effects as described above regardless of whether the engine is a gasoline engine or a diesel engine.
[0086]
【The invention's effect】
  As described above, claim 1, 6ofeachAccording to the exhaust gas purification apparatus for an internal combustion engine according to the invention, when the NOx concentration sensor is disposed in the exhaust passage downstream of the NOx occlusion type catalyst and the deterioration of the catalyst is detected, the NOx occluded by the catalyst is stored. When the NOx concentration in the exhaust gas is restarted and the NOx concentration sensor detects the cause of deterioration of the catalyst based on the NOx concentration temporal change rate detected by the NOx concentration sensor. It is possible to determine not only the deterioration but also whether the deterioration is due to thermal deterioration or sulfur poisoning. Based on this determination result, an appropriate countermeasure according to the deterioration state of the catalyst can be taken.
[0087]
  According to the invention of claim 2, when it is determined that the influence of sulfur poisoning on the cause of catalyst deterioration is great, the operating state of the internal combustion engine is controlled so as to promote the detachment of the sulfur component from the catalyst. The NOx occlusion ability can be recovered.
[0088]
  According to the invention of claim 3, when the thermal deterioration of the catalyst is determined, this is notified, and the deterioration of the exhaust state can be prevented beforehand by exchanging the catalyst. On the other hand, when the deterioration due to sulfur poisoning is determined, notification is not performed, so that the complexity of the notification can be eliminated.
[0089]
  According to the invention of claim 4, even if it is erroneously determined that the deterioration is due to sulfur poisoning, the deterioration of the exhaust state caused by the erroneous determination can be prevented by performing notification when further detecting the deterioration of the catalyst.
[0090]
  According to the invention of claim 5, even when the deterioration of the catalyst is not detected, if the sulfur poisoning of the catalyst is determined, the operating state of the internal combustion engine is set so as to promote the separation of the sulfur component from the catalyst. Control to recover NOx storage capacity of the catalyst.
[0091]
According to the invention of claim 7, it is possible to detect the deterioration of the catalyst based on the signals from the oxygen concentration sensors respectively arranged on the upstream side and the downstream side of the catalyst.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of a control system for an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a mechanism of NOx occlusion and release by a NOx catalyst.
FIG. 3 is a diagram showing an example of a control map in which operating regions in which the engine is in a stratified combustion state or a uniform combustion state are set.
FIG. 4 is an explanatory diagram showing a change in the NOx occlusion amount of the NOx catalyst and the downstream NOx concentration in association with each other after the exhaust gas is switched from the rich state to the lean state.
FIG. 5 is a flowchart of a main flow showing an outline of engine control.
FIG. 6 is a flowchart of control for determining whether a determination condition for sulfur poisoning is satisfied.
FIG. 7 is a flowchart of control for determining sulfur poisoning.
FIG. 8 is a flowchart of control for determining an execution condition of S purge.
FIG. 9 is a flowchart of control for notifying deterioration of the NOx catalyst.
FIG. 10 shows how NOx concentration in the exhaust gas changes when NOx occlusion is completed by the NOx catalyst and when NOx concentration in the exhaust gas is restarted, in the case of thermal deterioration and sulfur poisoning. It is explanatory drawing shown in contrast with.
[Explanation of symbols]
1 engine (internal combustion engine)
34 Exhaust passage
38 NOx catalyst (NOx storage type catalyst)
41 Oxygen concentration sensor
43 NOx concentration sensor
50 ECU (Engine Control Unit)
50a Catalyst deterioration detection means
50b Deterioration cause determination means
50c Deterioration control means
50d Sulfur poisoning reduction control means
50e Notification means

Claims (7)

The NOx is stored when the air-fuel ratio of the exhaust gas is leaner than the state corresponding to the stoichiometric air-fuel ratio, while the stored NOx is stored in the exhaust passage of the internal combustion engine in response to the enrichment of the air-fuel ratio. NOx occlusion type catalyst that releases and reduces and purifies,
A NOx concentration sensor that is disposed in the exhaust passage downstream of the catalyst and detects the concentration of NOx in the exhaust gas;
In an exhaust gas purification apparatus for an internal combustion engine, comprising at least catalyst deterioration detection means for detecting catalyst deterioration based on a detection value by the NOx concentration sensor ,
When the catalyst deterioration is detected by the catalyst deterioration detecting means, the NOx concentration detected by the NOx concentration sensor is detected when the release of NOx stored by the catalyst is completed and the storage of NOx in the exhaust gas is resumed. A deterioration cause determining means for determining a time change rate of the concentration and determining that the influence of sulfur poisoning on the cause of deterioration of the catalyst is large if the time change rate is equal to or greater than a preset reference value; An exhaust gas purification apparatus for an internal combustion engine characterized by the above. In claim 1,
When the deterioration cause determining means determines that the influence of sulfur poisoning on the cause of deterioration of the catalyst is large, the deterioration control means for controlling the operating state of the internal combustion engine so as to promote the separation of the sulfur component from the catalyst is provided. An exhaust emission control device for an internal combustion engine. In claim 2,
When the NOx stored in the exhaust gas is resumed after the release of NOx stored by the catalyst is completed, the deterioration cause determination means determines that the rate of change of NOx concentration detected by the NOx concentration sensor is smaller than the set reference value. For example, it is determined that the influence of sulfur poisoning on the cause of catalyst deterioration is small.
And a notification means for notifying the deterioration of the catalyst when the deterioration of the catalyst is detected by the catalyst deterioration detecting means and the influence of the sulfur poisoning is determined to be small by the deterioration cause determining means. An exhaust purification device for an internal combustion engine. In claim 3,
The notification means notifies the catalyst deterioration regardless of the result of the determination by the deterioration cause determination means when the deterioration of the catalyst is detected by the catalyst deterioration detection means even after the internal combustion engine is controlled by the deterioration control means. An exhaust emission control device for an internal combustion engine, characterized in that In claim 1,
When the NOx occluded by the catalyst is released and occlusion of NOx in the exhaust gas is resumed, the NOx concentration change rate detected by the NOx concentration sensor is greater than another set value that is greater than the set reference value. If present, an exhaust purification device for an internal combustion engine, comprising sulfur poisoning reduction control means for controlling the operating state of the internal combustion engine so as to promote the separation of the sulfur component from the catalyst. The NOx is stored when the air-fuel ratio of the exhaust gas is leaner than the state corresponding to the stoichiometric air-fuel ratio, while the stored NOx is stored in the exhaust passage of the internal combustion engine in response to the enrichment of the air-fuel ratio. NOx occlusion type catalyst that releases and reduces and purifies,
An oxygen concentration sensor that is disposed in the exhaust passage downstream of the catalyst and detects the concentration of oxygen in the exhaust gas;
In an exhaust gas purification apparatus for an internal combustion engine comprising at least catalyst deterioration detection means for detecting catalyst deterioration based on a detection value by the oxygen concentration sensor,
A NOx concentration sensor that is disposed in the exhaust passage downstream of the catalyst and detects the concentration of NOx in the exhaust gas;
When the catalyst deterioration is detected by the catalyst deterioration detecting means, the NOx concentration detected by the NOx concentration sensor is detected when the release of NOx stored by the catalyst is completed and the storage of NOx in the exhaust gas is resumed. A deterioration cause determining means for determining a time change rate of the concentration and determining that the influence of sulfur poisoning on the cause of deterioration of the catalyst is large if the time change rate is equal to or greater than a preset reference value ; An exhaust gas purification apparatus for an internal combustion engine characterized by the above. In claim 6 ,
An oxygen concentration sensor is also disposed in the exhaust passage upstream of the catalyst,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the catalyst deterioration detecting means is configured to detect catalyst deterioration based on signals from oxygen concentration sensors upstream and downstream of the catalyst.

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