JP4396760B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  As an exhaust purification device applied to an internal combustion engine such as an automobile engine, a catalytic converter is provided in the exhaust system of the engine, and a NOx storage reduction catalyst that performs exhaust purification on nitrogen oxide (NOx) is provided in the catalytic converter. A supported one is known.

  In such an exhaust purification device, the NOx occlusion capacity of the NOx catalyst is reduced by occlusion of sulfur components such as sulfur oxides in the NOx catalyst. Therefore, many exhaust purification apparatuses of this type obtain an S poison amount that is the amount of sulfur component stored in the NOx catalyst, as shown in Patent Document 1, for example, and the S poison amount exceeds an allowable value. In this case, the S poison recovery control for releasing the sulfur component from the NOx catalyst is performed in order to recover the NOx storage capability of the NOx catalyst that has been reduced by the storage of the sulfur component. In this S poison recovery control, the temperature of the NOx catalyst is raised to, for example, about 600 to 700 ° C. through the supply of unburned fuel components to the exhaust system catalyst, and the atmosphere around the catalyst is richly burned at that high temperature. In this state (hereinafter referred to as a rich combustion atmosphere), the release of the sulfur component from the NOx catalyst and its reduction are promoted to restore the NOx storage capacity. When the sulfur poisoning amount in the NOx catalyst decreases to a predetermined value (for example, “0”) smaller than the allowable value by executing the sulfur poisoning recovery control, the sulfur poisoning recovery control is terminated.

Note that the estimated value estimated based on the engine operation state or the like is used for the S poison amount in Patent Document 1, and when the S poison recovery control is not executed, the previous S poison recovery control is performed. This is calculated based on the amount of fuel consumed since the end of S, and is calculated in consideration of the amount of sulfur component released from the NOx catalyst during the S poison recovery control.
JP-A-2005-90253 (paragraphs [0003], [0033], [0037])

  Incidentally, the S poisoning amount of the NOx catalyst estimated in Patent Document 1 is calculated in consideration of the release amount of the sulfur component from the NOx catalyst during the execution of the S poisoning recovery control. It is unclear whether the release amount of sulfur component considered in the above corresponds to the actual release amount.

  When a theoretical value is used as the amount of sulfur component released, among the sulfur components contained in the amount released, the sulfur poisoning recovery control cannot actually be released from the NOx catalyst. Some of the catalyst remains in the state, and the amount of released sulfur component considered is deviated from the actual amount of release. Note that the sulfur component remains in the NOx catalyst as described above. In the catalytic converter, there is a portion where the catalyst bed temperature is difficult to rise, such as the upstream end of the exhaust gas, and the NOx catalyst in that portion is occluded. It is presumed that the sulfur component is not necessarily released when the rich combustion atmosphere around the NOx catalyst at high temperature is achieved by the S poison recovery control.

  Thus, in the NOx catalyst, sulfur components that cannot be released by the S poison recovery control remain, and as a result, there exist sulfur components that always remain on the catalyst. Accordingly, the amount of sulfur component released from the NOx catalyst in the S poison recovery control considered when estimating the amount of S poison is a value that takes into account the amount of sulfur components that cannot be released from the NOx catalyst by the control. Otherwise, the estimated amount of S poisoning is smaller than the actual amount of S poisoning, resulting in a deviation between the two values.

  As a result, after the start of the S poisoning recovery control, when the estimated S poisoning amount is reduced to “0” and the S poisoning recovery control is terminated, the actual S poisoning amount is reduced to “0”. The sulfur component remains in the NOx catalyst to some extent. Then, as the use period of the NOx catalyst becomes longer and the sulfur component that always remains in the catalyst increases, the difference between the estimated S poisoning amount and the actual S poisoning amount increases, and the S coverage becomes larger. The amount of sulfur component that remains in the NOx catalyst at the end of the poison recovery control increases.

  In particular, under the conditions shown in [1] to [3] below, the estimated S poisoning amount deviates from the actual S poisoning amount, and more specifically, the actual S poisoning amount is estimated. It becomes remarkable that it becomes more than poisoning amount.

  [1] In the case of a driver who drives an automobile only for a short time, the exhaust temperature of the internal combustion engine does not rise so much, so there is a high possibility that the catalyst bed temperature of the NOx catalyst will remain low. Execution opportunities are reduced, and even if executed, the catalyst bed temperature during control is less likely to increase. As a result, the release rate of the sulfur component from the NOx catalyst deteriorates, and the amount of the sulfur component that always remains in the NOx catalyst increases.

  [2] In the case of a driver who consumes a lot of fuel in an internal combustion engine, such as frequently starting a car, the amount of sulfur component flowing into the NOx catalyst increases as the fuel is consumed. Is easily occluded, and the amount of sulfur component always remaining in the catalyst also increases.

  [3] When a fuel having a sulfur concentration higher than the standard value is used, the amount of sulfur components flowing into the NOx catalyst is larger than when using a fuel having a standard sulfur concentration. Therefore, the sulfur component is easily occluded in the catalyst, and the amount of the sulfur component always remaining in the catalyst increases.

  As described above, the sulfur poisoning recovery control is executed under the situation where the amount of the sulfur component always remaining in the NOx catalyst is increased and the actual sulfur poisoning amount is larger than the estimated sulfur poisoning amount. Even if the process is completed, the NOx occlusion ability of the NOx catalyst remains lowered due to the sulfur component remaining in the catalyst, which may deteriorate the NOx emission of the internal combustion engine. Note that such a problem is actually caused by increasing the catalyst bed temperature in the S poison recovery control to more effectively release the sulfur component from the NOx catalyst and reducing the amount of the sulfur component always remaining in the catalyst. It is possible to suppress this by bringing the S poisoning amount close to the estimated S poisoning amount. However, if the catalyst bed temperature is always set high in the S poison recovery control, the catalyst bed temperature excessively increases in the NOx catalyst, and the NOx emissions of the internal combustion engine may be deteriorated due to the accompanying thermal deterioration. is there.

  The present invention has been made in view of such circumstances, and its object is to suppress the excessive increase in the catalyst bed temperature in the NOx catalyst, while reducing the amount of sulfur component always remaining in the catalyst, An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can suppress deterioration of NOx emission of the internal combustion engine due to the remaining sulfur component.

In the following, means for achieving the above object and its effects are described.
In order to achieve the above object, according to the first aspect of the present invention, the NOx storage reduction catalyst provided in the exhaust system of the internal combustion engine and the sulfur poisoning amount that is the storage amount of the sulfur component in the NOx catalyst are estimated. And an estimation means for raising the catalyst bed temperature to the target bed temperature through the supply of the unburned fuel component to the NOx catalyst when the estimated S poisoning amount exceeds a permissible value and the NOx catalyst. The execution of the S poison recovery control for setting the surrounding atmosphere to the state at the time of rich combustion is started to release the sulfur component from the NOx catalyst, and the S poison amount after the start of the S poison recovery control is In the exhaust gas purification apparatus for an internal combustion engine that terminates the control when the value becomes equal to or less than a predetermined value smaller than the value, a high temperature time cumulative value that is a cumulative value of the time when the NOx catalyst becomes high temperature is used as the thermal deterioration of the NOx catalyst. Equivalent to degree And a standard value calculating means for calculating a standard value of the cumulative value of the high temperature time in the total operating time of the engine based on a value corresponding to the total operating time of the internal combustion engine. The control at the catalyst bed temperature higher than the S poison recovery control is performed only when the high temperature time cumulative value calculated by the cumulative value calculation means is equal to or less than the standard value calculated by the standard value calculation means. And high temperature S poisoning recovery control.

  In the case of a driver who drives an automobile only for a short time, the exhaust temperature of the internal combustion engine is difficult to rise, so the catalyst bed temperature of the NOx catalyst is likely to remain low, and the chance of executing the S poison recovery control is small. Even if it is executed, the catalyst bed temperature during the control is hardly increased. As a result, the release rate of the sulfur component from the NOx catalyst deteriorates, and the amount of the sulfur component that always remains in the NOx catalyst increases. In particular, when a fuel having a sulfur concentration higher than the standard value is used, the amount of sulfur component flowing into the NOx catalyst is larger than when a fuel having a standard sulfur concentration is used. The sulfur component is easily stored in the catalyst, and the increase in the sulfur component always remaining in the catalyst becomes remarkable.

  According to the above configuration, when the automobile is operated as described above, the high temperature time cumulative value, which is a cumulative value of the time when the NOx catalyst has become high temperature, remains small, and the high temperature time cumulative value is There is a high possibility of being below the standard value. Only when the accumulated value of the high temperature time becomes below the standard value, the high temperature S poisoning recovery control is performed to efficiently release the sulfur component from the NOx catalyst, and thereby always remain in the NOx catalyst. The amount of sulfur component is reduced. As described above, while suppressing an excessive increase in the catalyst bed temperature of the NOx catalyst due to the execution of the high temperature S poisoning recovery control, the amount of the sulfur component always remaining in the catalyst is reduced, and the internal combustion caused by the remaining sulfur component It is possible to suppress the deterioration of NOx emission of the engine.

  According to a second aspect of the present invention, in the first aspect of the present invention, the control means performs the high temperature S poisoning recovery control in accordance with an increase in the amount of deviation of the high temperature time cumulative value with respect to the standard value toward the lower side. The gist was to increase the catalyst bed temperature.

  As the accumulated value of the high temperature time deviates greatly from the standard value, the amount of sulfur component always remaining in the NOx catalyst increases, and even if an attempt is made to increase the catalyst bed temperature in the S poison recovery control, the catalyst bed temperature is increased. Is difficult to increase, and it is difficult to effectively release the sulfur component always remaining in the NOx catalyst. In other words, this state can be said to be a state in which an excessive increase in the catalyst bed temperature hardly occurs. According to the above configuration, the catalyst bed temperature in the high temperature S poisoning recovery control is increased with an increase in the amount of divergence toward the lower side of the high temperature time cumulative value with respect to the standard value. It is possible to achieve both a high level of suppression of excessive rise in the catalyst bed temperature of the NOx catalyst and effective release of the sulfur component always remaining in the NOx catalyst by the same control.

  The invention according to claim 3 comprises an NOx storage reduction catalyst provided in an exhaust system of an internal combustion engine, and an estimation means for estimating an S poison amount that is a storage amount of a sulfur component in the NOx catalyst, When the estimated amount of sulfur poisoning exceeds an allowable value, the catalyst bed temperature is raised to the target bed temperature through the supply of unburned fuel components to the NOx catalyst and the atmosphere around the NOx catalyst is richly burned. The S poison recovery control is started to release the sulfur component from the NOx catalyst, and after the S poison recovery control is started, the S poison amount is less than a predetermined value smaller than the allowable value. In the exhaust gas purification apparatus for an internal combustion engine that terminates the control when the engine reaches the inflow amount, an inflow amount equivalent value calculating means for obtaining a total S inflow amount equivalent value corresponding to the total amount of sulfur components flowing into the NOx catalyst, and the internal combustion engine Total operating time Based on this value, a standard value calculating means for calculating a standard value of the total S inflow equivalent value for the total operating time of the engine at that time, and a total S inflow amount calculated by the inflow equivalent value calculating means Only when the equivalent value is equal to or greater than the standard value calculated by the standard value calculating means, the control for performing the high temperature S poisoning recovery control which is the same control at the catalyst bed temperature higher than the S poisoning recovery control. Means.

  In the case of a driver with heavy fuel consumption of an internal combustion engine, for example, when the vehicle is suddenly started suddenly, the amount of sulfur component flowing into the NOx catalyst increases as the fuel is consumed, so the sulfur component is occluded in the catalyst. The amount of sulfur component that always remains in the catalyst increases. In particular, when a fuel having a sulfur concentration higher than the standard value is used, the amount of sulfur component flowing into the NOx catalyst is larger than when a fuel having a standard sulfur concentration is used. The sulfur component is easily stored in the catalyst, and the increase in the sulfur component always remaining in the catalyst becomes remarkable.

  According to the above configuration, when the automobile is operated as described above, the total S inflow equivalent value, which is a value corresponding to the total amount of sulfur components flowing into the NOx catalyst, quickly increases, and the total S inflow amount is the same. The possibility that the equivalent value is equal to or higher than the standard value is increased. Only when the total S inflow equivalent value is equal to or higher than the standard value, the high temperature S poisoning recovery control is performed to efficiently release the sulfur component from the NOx catalyst. The amount of residual sulfur component is reduced. As described above, while suppressing an excessive increase in the catalyst bed temperature of the NOx catalyst due to the execution of the high temperature S poisoning recovery control, the amount of the sulfur component always remaining in the catalyst is reduced, and the internal combustion caused by the remaining sulfur component It is possible to suppress the deterioration of NOx emission of the engine.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the control means controls the high temperature S poisoning recovery control as the deviation amount increases toward the increase side of the total S inflow equivalent value with respect to the standard value. The main point was to increase the catalyst bed temperature in the reactor.

  The more the total S inflow equivalent value is greatly deviated from the standard value, the larger the amount of sulfur component that always remains in the NOx catalyst. Even if an attempt is made to increase the catalyst bed temperature in the S poison recovery control, the same catalyst is used. The bed temperature is unlikely to rise, and it is difficult to release the sulfur component that always remains in the NOx catalyst. In other words, this state can be said to be a state in which an excessive increase in the catalyst bed temperature hardly occurs. According to the above configuration, the catalyst bed temperature in the high temperature S poisoning recovery control is increased as the amount of deviation from the standard value to the increase side of the total S inflow equivalent value increases. Suppressing the excessive rise in the catalyst bed temperature of the NOx catalyst in the control and effective release of the sulfur component always remaining in the NOx catalyst by the control can be achieved at a high level.

  According to a fifth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the third or fourth aspect, when the high-temperature S poisoning recovery control is executed, the total S inflow equivalent value relative to the total operation time equivalent value Further, a correction means for correcting the magnitude of is adjusted to the standard value side is further provided.

  When the high-temperature S poisoning recovery control is performed, the amount of sulfur component that always remains in the NOx catalyst decreases, and accordingly, the execution frequency of the high-temperature S poisoning recovery control may be reduced accordingly. This is preferable from the viewpoint of suppressing an excessive increase in the catalyst bed temperature. According to the above configuration, when the high-temperature S poisoning recovery control is performed, the magnitude of the total S inflow equivalent value relative to the total operation time equivalent value is corrected to the standard value side. As a result, the transition of the total S inflow equivalent value with respect to the change in the total operation time equivalent value shifts to the standard value side. It becomes difficult to implement the control, and the above-described excessive increase in the catalyst bed temperature can be suppressed.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the control means controls the NOx catalyst based on the catalyst bed temperature when the catalyst bed temperature is to be increased. It is determined whether or not the deterioration due to heat and sulfur component remains advanced, and the high temperature S poisoning recovery control is performed only when it is determined that the NOx catalyst is in a state of advanced deterioration. The summary.

  The deterioration of the NOx catalyst due to heat and sulfur component residue is in a state where it is difficult for the NOx catalyst to increase in temperature even if the catalyst bed temperature is increased by implementing S poison recovery control or the like. It means that. According to the above configuration, since the high temperature S poisoning recovery control is performed only in such a state, it is possible to more appropriately suppress the excessive increase in the temperature of the NOx catalyst accompanying the execution of the control. be able to.

[First Embodiment]
Hereinafter, a first embodiment in which the present invention is applied to an internal combustion engine for an automobile will be described with reference to FIGS.

  FIG. 1 shows the configuration of an internal combustion engine 10 to which the exhaust purification system of this embodiment is applied. The internal combustion engine 10 is a diesel engine equipped with a common rail fuel injection device.

  An intake passage 12 constituting an intake system of the internal combustion engine 10 and an exhaust passage 14 constituting an exhaust system of the engine 10 are connected to the combustion chambers 13 of the respective cylinders in the internal combustion engine 10. The intake passage 12 is provided with an air flow meter 16, and the exhaust passage 14 is provided with a NOx catalytic converter 25, a PM filter 26, and an oxidation catalytic converter 27 in order from the upstream side.

  The NOx catalytic converter 25 carries an NOx storage reduction catalyst. The NOx catalyst stores NOx in the exhaust when the oxygen concentration of the exhaust is high, and releases the stored NOx when the oxygen concentration of the exhaust is low. Further, the NOx catalyst reduces and purifies the released NOx if there is sufficient unburned fuel component as a reducing agent at the time of releasing the NOx.

  The PM filter 26 is made of a porous material and collects fine particles (PM) mainly composed of soot in the exhaust gas. Similarly to the NOx catalytic converter 25, the PM filter 26 also carries an NOx storage reduction catalyst so that NOx in the exhaust gas can be purified. Further, the collected PM is burned (oxidized) and removed by a reaction triggered by the NOx catalyst.

The oxidation catalyst converter 27 carries an oxidation catalyst. This oxidation catalyst oxidizes and purifies hydrocarbons (HC) and carbon monoxide (CO) in the exhaust.
In addition, on the upstream side and the downstream side of the PM filter 26 in the exhaust passage 14, an inlet gas temperature sensor 28 that detects the inlet gas temperature that is the temperature of the exhaust gas flowing into the PM filter 26, and the exhaust gas after passing through the PM filter 26. An outgas temperature sensor 29 for detecting an outgas temperature, which is a temperature, is provided. The exhaust passage 14 is provided with a differential pressure sensor 30 for detecting a differential pressure between the exhaust upstream side of the PM filter 26 and the exhaust downstream side thereof. Further, two air-fuel ratio sensors 31 and 32 for detecting the air-fuel ratio are disposed on the exhaust passage 14 upstream of the NOx catalytic converter 25 and between the PM filter 26 and the oxidation catalytic converter 27, respectively. ing.

  In the combustion chamber 13 of each cylinder of the internal combustion engine 10, an injector 40 for injecting fuel to be used for combustion in the combustion chamber 13 is disposed. The injector 40 of each cylinder is connected to a common rail 42 via a high pressure fuel supply pipe 41. High pressure fuel is supplied to the common rail 42 through a fuel pump 43. The pressure of the high-pressure fuel in the common rail 42 is detected by a rail pressure sensor 44 attached to the common rail 42. Further, low pressure fuel is supplied from the fuel pump 43 to the addition valve 46 through the low pressure fuel supply pipe 45.

  Various controls of the internal combustion engine 10 are performed by the electronic control unit 50. The electronic control unit 50 includes a CPU that executes various arithmetic processes related to engine control, a ROM that stores programs and data necessary for the control, a RAM that temporarily stores CPU arithmetic results, and signals between the outside The input / output port for inputting / outputting is provided.

  In addition to the above-described sensors, the input port of the electronic control unit 50 includes an NE sensor 51 that detects the engine speed, an accelerator sensor 52 that detects the accelerator operation amount, and an intake air temperature sensor 54 that detects the intake air temperature of the internal combustion engine 10. , And a water temperature sensor 55 for detecting the cooling water temperature of the engine 10 is connected. The output port of the electronic control unit 50 is connected to drive circuits such as the injector 40, the fuel pump 43, and the addition valve 46.

  The electronic control unit 50 outputs a command signal to the drive circuit of each device connected to the output port according to the engine operating state grasped from the detection signal input from each sensor. In this way, the electronic control unit 50 performs various controls such as control of the fuel injection amount, fuel injection timing, and fuel injection pressure related to the fuel injected from the injector 40, and control of fuel addition from the addition valve 46.

  In the present embodiment configured as described above, the S poison recovery control for recovering the NOx occlusion ability of the NOx catalyst, which has been reduced by occlusion of sulfur components such as sulfur oxide (SOx) in the NOx catalyst, is performed. . Such S poison recovery control is started when the S poison amount S, which is the stored amount of the sulfur component in the NOx catalyst calculated (estimated) based on the history of the engine operating state, exceeds the allowable value. .

  In this S-poisoning recovery control, the temperature of the catalyst is raised to, for example, about 600 to 700 ° C. through the supply of the unburned fuel component to the NOx catalyst, and the atmosphere around the NOx catalyst at the high temperature is in a state during rich combustion ( Hereinafter, the rich combustion atmosphere) promotes the release and reduction of the sulfur component from the NOx catalyst, and the NOx storage capacity of the NOx catalyst is recovered. Note that the supply of the unburned fuel component to the NOx catalyst in the S poison recovery control is performed by adding fuel to the exhaust from the addition valve 46 or the like.

When the S poisoning amount S decreases to a predetermined value (for example, “0”) smaller than the allowable value through the execution of the S poisoning recovery control, the S poisoning recovery control is ended.
Next, a detailed calculation procedure of the S poison amount S used for the start / end of the S poison recovery control will be described.

  The S poison amount S is, for example, for each fuel injection from the injector 40, the S inflow amount SU, which is the amount of sulfur component stored in the NOx catalyst from the previous fuel injection to the current fuel injection, and the previous fuel injection. Based on the S release amount SD, which is the amount of the sulfur component released from the NOx catalyst from the injection to the current fuel injection, it is calculated using the following equation (1).

Si = Si-1 + SU-SD (1)
Si: S poison amount this time
Si-1: Previous amount of sulfur poisoning
SU: S inflow
SD: S discharge amount The S inflow amount SU in the equation (1) is a fuel injection amount command value Qfin calculated before fuel injection from the injector 40, that is, fuel injected by one fuel injection from the injector 40. It is calculated using the command value of quantity. Specifically, by multiplying the command value Qfin by a value (N / 100) obtained by dividing the sulfur concentration N, which is a standard value of the sulfur concentration of the fuel, by “100”, a single fuel from the injector 40 is obtained. The amount of sulfur component contained in the fuel injected by injection is determined. Then, the above-mentioned multiplied value “Qfin · (N / 100)” which is a value corresponding to the amount of this sulfur component is multiplied by a coefficient K for converting a parameter of sulfur amount into a parameter of S poisoning amount. Thus, the S inflow amount SU is calculated. The coefficient K is obtained by referring to a map based on the air-fuel ratio detected by the air-fuel ratio sensors 31 and 32 and the catalyst bed temperature, and the air-fuel ratio is the stoichiometric air-fuel ratio (14 in this case). .5) or “0” when the air-fuel ratio is rich, and when the air-fuel ratio is on the lean side of the stoichiometric air-fuel ratio, the air-fuel ratio becomes leaner and becomes larger as the catalyst bed temperature becomes higher.

  The S emission amount SD of the formula (1) is released from the NOx catalyst when the atmosphere around the NOx catalyst is brought into a state corresponding to the air-fuel ratio at the catalyst bed temperature at that time based on the air fuel fire and the catalyst bed temperature. Calculated as the theoretical amount of sulfur component. Regarding the S release amount SD thus calculated, when the air-fuel ratio is a richer value than the stoichiometric air-fuel ratio (here, 14.5), the catalyst bed temperature is higher and becomes a value larger than “0” as it becomes richer. Thus, when the air-fuel ratio is a value leaner than the stoichiometric air-fuel ratio, it is maintained at “0”.

  Accordingly, the S poisoning amount S (the current S poisoning amount Si) calculated using the equation (1) gradually increases by the amount of the S inflow amount SU as the fuel is consumed during normal engine operation. Then, during the S poison recovery control, the amount decreases by the amount of S released SD. From this, the sulfur poisoning amount S is accompanied by the inflow of the sulfur component into the NOx catalyst accompanying fuel consumption in normal engine operation and the release of the sulfur component from the NOx catalyst during the S poison recovery control, It will be a value that increases or decreases.

Next, the S poison recovery control that is started and ended based on the S poison amount S will be described in detail with reference to the time chart of FIG.
In the S poison recovery control, the target bed temperature in which the average value of the catalyst bed temperature T of the NOx catalyst is increased stepwise to, for example, 700 ° C. through supply of unburned fuel components to the NOx catalyst by addition of fuel from the addition valve 46. While raising the temperature toward Tt, a rich combustion atmosphere is made around the NOx catalyst at the high temperature.

  Fuel addition from the addition valve 46 is started based on a change (timing T1) of the addition permission flag F to “1 (permitted)” shown in FIG. The addition permission flag F is set to “0” after being set to “1”. When fuel addition from the addition valve 46 is started, intensive intermittent fuel addition from the addition valve 46 is performed according to the addition pulse shown in FIG.

  The fuel addition mode in such intensive intermittent fuel addition, for example, the fuel addition time a, the fuel addition stop time b, and the number of fuel additions, is determined based on whether the air-fuel ratio detected by the air-fuel ratio sensors 31 and 32 is the theoretical sky. Adjustment is made so as to approach the target air-fuel ratio AFt set on the richer side than the fuel ratio. That is, the pause time b (fuel addition interval) is made shorter as the air-fuel ratio detected by the air-fuel ratio sensors 31 and 32 becomes leaner than the target air-fuel ratio AFt, and the air-fuel ratio sensor 31 for the addition time a. , 32, the air / fuel ratio is made longer as the air / fuel ratio becomes leaner than the target air / fuel ratio AFt. The number of times of addition is increased as the air-fuel ratio detected by the air-fuel ratio sensors 31 and 32 is leaner than the target air-fuel ratio AFt.

  Then, the intensive intermittent fuel addition started as described above is continued until the fuel addition of the number of times determined based on the target air-fuel ratio AFt is executed, and stopped after the fuel addition is made by that number of times. (Timing T2).

  After the start of fuel addition from the addition valve 46, every time a predetermined time, for example, 16 ms elapses based on the drive state of the addition valve 46, 16 ms exothermic fuel that is the amount of fuel added from the addition valve 46 during the 16 ms. A quantity Q is calculated. By accumulating the 16 ms exothermic fuel amount Q based on the formula “ΣQ ← previous ΣQ + Q (2)” for each calculation, the total fuel addition amount from the fuel addition start time (T1), in other words, due to the oxidation reaction A heat generation fuel amount integrated value ΣQ representing the total fuel amount contributing to heat generation is calculated. The exothermic fuel amount integrated value ΣQ calculated in this way rapidly increases in the addition period A, which is the period (T1 to T2) from the start to the end of fuel addition, as shown by the solid line in FIG. However, the increase is suppressed in the rest period B of the fuel addition thereafter.

  On the other hand, after the start of fuel addition from the addition valve 46, the amount of fuel to be added from the addition valve 46 during the predetermined time (16 ms), in other words, the catalyst bed temperature T is brought closer to the target bed temperature Tt. Therefore, a required fuel amount Qr of 16 ms, which is the amount of fuel added for the purpose, is calculated. The calculation of the 16 ms required fuel amount Qr is performed using the temperature difference ΔT between the catalyst bed temperature T and the target bed temperature Tt and the gas flow rate Ga of the internal combustion engine 10. The 16 ms required fuel amount Qr calculated in this way increases as the catalyst bed temperature T is lower than the target bed temperature Tt, and conversely decreases as it is higher than the target bed temperature Tt. Then, the 16 ms required fuel amount Qr is accumulated every calculation based on the formula “ΣQr ← previous ΣQr + Qr (3)”, so that the average value of the catalyst bed temperature T is necessary to be the target bed temperature Tt. A required fuel amount integrated value ΣQr representing the total fuel amount from the fuel addition start time (T1) is calculated. The required fuel amount integrated value ΣQr calculated in this way gradually increases as compared with the increase (solid line) of the exothermic fuel amount integrated value ΣQ, as shown by the broken line in FIG.

  When the required fuel amount integrated value ΣQr becomes equal to or greater than the exothermic fuel amount integrated value ΣQ (timing T3), the addition permission flag F changes to “1 (permitted)”, and concentrated intermittent fuel addition from the addition valve 46 is performed. Is started. At this time, since the addition of fuel for the exothermic fuel amount integrated value ΣQ after timing T1 has been completed from the addition valve 46, the exothermic fuel amount integrated value ΣQ is subtracted from the required fuel amount integrated value ΣQr. Furthermore, the exothermic fuel amount integrated value ΣQ is cleared and becomes “0”. Then, along with the start of intensive intermittent fuel addition from the addition valve 46, the process shifts again to the addition period A, and when the addition period A ends, the process shifts to the suspension period B. Therefore, the addition period A and the pause period B are repeated during the S poison recovery control.

  During the S poison recovery control, the 16 ms required fuel amount Qr is calculated to be larger as the catalyst bed temperature T is further away from the target bed temperature Tt, and the required fuel amount integration is performed. The value ΣQr increases rapidly. As a result, the time required for the required fuel amount integrated value ΣQr to become equal to or greater than the exothermic fuel amount integrated value ΣQ is shortened, and the suspension period B is shortened, so the average value of the fuel addition amount from the addition valve 46 per unit time Becomes big. In this way, by increasing the average value of the fuel addition amount, the catalyst bed temperature T that is separated from the target bed temperature Tt toward the lower side can be increased toward the target bed temperature Tt.

  Then, the 16 ms required fuel amount Qr is calculated to be smaller as the catalyst bed temperature T approaches the target bed temperature Tt, and the increase in the required fuel amount integrated value ΣQr is moderated. As a result, the time required for the required fuel amount integrated value ΣQr to become equal to or greater than the exothermic fuel amount integrated value ΣQ becomes longer, and the suspension period B becomes longer. Therefore, the average value of the fuel addition amount from the addition valve 46 per unit time Becomes small. Thus, by reducing the average value of the fuel addition amount, the catalyst bed temperature T is prevented from excessively exceeding the target bed temperature Tt.

  As described above, by changing the length of the pause period B according to the deviation state of the catalyst bed temperature T from the target bed temperature Tt, the catalyst bed temperature T is, for example, as shown by a solid line in FIG. The fluctuation center (average value) of the catalyst bed temperature T that changes and increases or decreases is controlled to the target bed temperature Tt. Then, the unburnt fuel component is supplied to the catalyst so that the average value of the catalyst bed temperature T becomes the target bed temperature Tt which is set to be gradually increased to 700 ° C. Thus, the catalyst bed temperature of the NOx catalyst. T can be raised to about 700 ° C.

  Further, when concentrated intermittent fuel addition from the addition valve 46 in the addition period A is performed at a high temperature of the NOx catalyst in which the average value of the catalyst bed temperature T is increased to the target bed temperature Tt, the NOx catalyst around As shown in FIG. 2B, the atmosphere is set to the same state as that at the time of combustion at the air-fuel ratio corresponding to the target air-fuel ratio AFt (rich) (during rich combustion). When the atmosphere around the NOx catalyst is changed to a rich combustion atmosphere in this way, the release of the sulfur component from the NOx catalyst and the reduction thereof are promoted. Then, in the process of repeating the addition period A and the rest period B, the release of SOx from the NOx catalyst and the reduction thereof are promoted during the addition period A, so that the storage amount of the sulfur component in the NOx catalyst is reduced. The NOx storage capacity of the NOx catalyst can be recovered. When the sulfur poisoning amount S, which is the amount of sulfur component stored in the NOx catalyst, decreases to the predetermined value (in this example, “0”), the sulfur poisoning recovery control is terminated.

  By the way, regarding the S poison amount S of the NOx catalyst calculated (estimated) using the equation (1), the S release amount SD which is the amount of sulfur component released from the NOx catalyst during the execution of the S poison recovery control. Is calculated in consideration of However, the S release amount SD does not necessarily correspond to the actual release amount of the sulfur component from the NOx catalyst. This is because the S release amount SD is only calculated as the theoretical amount of sulfur component released from the NOx catalyst during the S poison recovery control, and among the sulfur components contained in the S release amount SD, This is because, in actuality, the S poison recovery control cannot be released from the NOx catalyst and remains in the catalyst. It should be noted that the sulfur component remaining in the NOx catalyst as described above exists in the NOx catalyst where the catalyst bed temperature is difficult to rise, such as the upstream end of the NOx catalytic converter 25, under the high temperature by the S poison recovery control. Even if a rich combustion atmosphere is created around the NOx catalyst, the sulfur component occluded in the catalyst is not necessarily released.

  Thus, regarding the S release amount SD used for calculating the S poison amount S, the sulfur component from the NOx catalyst during the S poison recovery control is equivalent to the sulfur component remaining in the NOx catalyst. There is a possibility that the value will deviate from the amount of release. More specifically, there is a possibility that the S release amount SD is shifted to a lower side than the actual release amount of the sulfur component from the NOx catalyst during the S poison recovery control. When such a deviation occurs, the S poisoning amount S calculated using the S release amount SD is also the actual S poisoning amount due to a decrease in the S release amount SD with respect to the actual release amount. The difference between the two values will occur.

  When the calculated (estimated) S poison amount S deviates from the actual S poison amount, the S poison amount S decreases to “0” after the start of the S poison recovery control, and the S poison amount is reduced. When the poison recovery control is terminated, the actual S poison amount is not reduced to “0”, and the sulfur component remains to some extent in the NOx catalyst. The difference between the calculated S poisoning amount S and the actual S poisoning amount increases as the sulfur component that remains in the catalyst always increases as the use period of the NOx catalyst increases. The amount of sulfur component that remains in the NOx catalyst at the end of the poisoning recovery control increases. Incidentally, the situation of [1] to [3] described in the column of [Problems to be solved by the invention] can be given as the situation where the amount of sulfur component remaining in the NOx catalyst increases. Thus, under the situation where the amount of sulfur component that always remains in the NOx catalyst increases, even if the sulfur poisoning recovery control is executed and completed, the NOx storage capacity of the NOx catalyst remains in the catalyst. Since it remains lowered due to the components, the NOx emission of the internal combustion engine 10 may be deteriorated.

  Note that such a problem is caused by setting the target bed temperature Tt to a higher value in the S poison recovery control, for example, a value higher than 700 ° C., and setting the average value of the catalyst bed temperature T to a higher value. It is possible to suppress this by releasing the sulfur component more effectively. As described above, this is to reduce the amount of sulfur component always remaining on the catalyst by more effectively releasing the sulfur component from the NOx catalyst, in other words, to calculate the actual S poisoning amount. This is because the S poisoning amount S can be approached. However, if the target bed temperature Tt in the S poison recovery control is always set higher, the excessive increase in the catalyst bed temperature T in the NOx catalyst becomes severe, and the accompanying heat deterioration causes the internal combustion engine 10 to There is a risk of NOx emissions getting worse.

  Next, the process for suppressing the occurrence of the above-described problem will be described in detail with reference to the flowchart of FIG. 3 showing the S poison recovery control execution routine. This S poisoning recovery control execution routine is periodically executed through the electronic control unit 50, for example, with a time interrupt at predetermined intervals.

  The routine determines whether or not the amount of the sulfur component that always remains in the NOx catalyst increases. Only when it is determined that the situation is higher, the routine is higher than the normal S poison recovery control. This is for performing high temperature S poisoning recovery control, which is the same control at the catalyst bed temperature. By performing the high-temperature S poisoning recovery control in this way, the amount of sulfur component always remaining in the NOx catalyst is reduced while suppressing an excessive increase in the NOx catalyst due to the execution of the control, and the residual sulfur component is the cause. The deterioration of the NOx emission of the internal combustion engine 10 can be suppressed.

  In this routine, first, a high temperature time cumulative value Σt and a standard value Bh used to determine whether or not the amount of sulfur component always remaining in the NOx catalyst is increased are calculated (S101, S102).

  Specifically, as the processing of step S101, by accumulating the time when the catalyst bed temperature T has become a high temperature of, for example, 600 ° C. or higher, the accumulated time is a value corresponding to the degree of thermal deterioration of the NOx catalyst. Calculated as the cumulative value Σt (S101). The high temperature time cumulative value Σt calculated in this way becomes a small value while the degree of thermal deterioration of the NOx catalyst is small, and becomes a large value as the degree of thermal deterioration increases.

  Further, as a process of step S102, based on the travel distance of the vehicle at that time, a standard value Bh that is a standard value of the high temperature time cumulative value Σt at the travel distance is calculated. The travel distance is a value corresponding to the total operation time of the internal combustion engine 10 (hereinafter simply referred to as a total operation time value), and is a value that increases as the total operation time of the engine 10 increases. . For the calculation of the standard value Bh, for example, a map may be used. That is, the relationship between the travel distance and the standard value Bh is determined in advance by experiments or the like, and a map that defines the relationship is stored in the ROM of the electronic control unit 50. Then, the standard value Bh is calculated with reference to the map based on the travel distance. The standard value Bh calculated in this way is increased as shown by a broken line in FIG. 4, for example, as the travel distance increases.

  After the calculation of the high temperature time cumulative value Σt and the standard value Bh, it is determined whether or not it is a time when an execution request for the S poison recovery control is made (S103 in FIG. 3). The execution request for the S poison recovery control is performed when the S poison amount S calculated using the above formula (1) exceeds the allowable value and various execution conditions for the S poison recovery control are satisfied. Is called. If an affirmative determination is made in step S103, whether or not the high-temperature time accumulated value Σt is equal to or less than the standard value Bh is determined as a determination as to whether or not the amount of the sulfur component that always remains in the NOx catalyst increases. Is determined (S104).

  Here, in the case of a driver who drives the automobile only for a short time, since the exhaust temperature of the internal combustion engine 10 is difficult to rise, the catalyst bed temperature T of the NOx catalyst is likely to remain low. Is less likely to occur, and even if it is executed, the catalyst bed temperature T during control is less likely to increase. As a result, the release rate of the sulfur component from the NOx catalyst deteriorates, and the amount of the sulfur component that always remains in the NOx catalyst increases. In particular, when a fuel having a sulfur concentration higher than a standard value (in this example, a sulfur concentration N) is used, sulfur flowing into the NOx catalyst is compared with a case where a fuel having a standard sulfur concentration is used. Since the amount of the component is increased, the sulfur component is easily stored in the catalyst, and the increase in the sulfur component always remaining in the catalyst becomes remarkable.

  When the operation as described above is performed, the high temperature time cumulative value Σt is difficult to increase, so the transition of the high temperature time cumulative value Σt with respect to the increase in travel distance is as shown by the solid line in FIG. There is a high possibility that it is determined in step S104 in FIG. 3 that the high-temperature time cumulative value Σt is equal to or less than the standard value Bh. When it is determined that the high-temperature time cumulative value Σt is larger than the standard value Bh, it is determined that the amount of sulfur component remaining in the NOx catalyst is not always increased, and normal S poison recovery control is performed. The process is started (S106). On the other hand, when it is determined in step S104 that the high temperature time cumulative value Σt is equal to or less than the standard value Bh, it is determined that the amount of sulfur component always remaining in the NOx catalyst is increased, and the above-described high temperature S The poisoning recovery control is started (S105).

  In this high temperature S poison recovery control, the maximum value of the target bed temperature Tt during the control is made higher than the maximum value (700 ° C. in this example) of the target bed temperature Tt in the normal S poison recovery control. Realized. In the high temperature S poisoning recovery control, first, the target bed temperature Tt is increased stepwise in the same manner as in the normal S poisoning recovery control. Thereafter, when the target bed temperature Tt reaches the maximum value (700 ° C.) in the normal S poisoning recovery control, the target bed temperature Tt is set on condition that the average value of the catalyst bed temperature T does not increase beyond that value. Is raised to a value higher than the maximum value (700 ° C.). Such an increase in the target bed temperature Tt is smaller than an increase to a value that leads to thermal damage of the NOx catalytic converter 25, and is a deviation amount KA of the high temperature time cumulative value Σt with respect to the standard value Bh (see FIG. 4). ) With an increasing range that is variably set so as to increase as the value increases. Then, by increasing the average value of the catalyst bed temperature T through the increase of the target bed temperature Tt, the sulfur component is efficiently released from the NOx catalyst, and thereby the amount of sulfur component that always remains in the NOx catalyst. Less.

  After the start of execution of the high-temperature S poisoning recovery control and the normal S poisoning recovery control, the S poisoning amount S decreases to the predetermined value (in this example, “0”) through the same control. Thus, the control is terminated. When the high-temperature S poisoning recovery control is executed, the increase in the high-temperature time cumulative value Σt is promoted. Therefore, after the end of the control, the magnitude of the high-temperature time cumulative value Σt with respect to the travel distance is the standard value Bh (see FIG. 4). (Close to the broken line).

According to the embodiment described in detail above, the following effects can be obtained.
(1) When the high temperature time cumulative value Σt becomes equal to or less than the standard value Bh, in other words, the sulfur component release rate from the NOx catalyst in the S poison recovery control deteriorates depending on how the driver operates the vehicle. Only when the amount of the sulfur component that always remains in the catalyst increases, the high-temperature S poisoning recovery control is performed to efficiently release the sulfur component from the NOx catalyst. By carrying out such high temperature S poisoning recovery control, the amount of sulfur component that always remains in the NOx catalyst is reduced. As described above, while suppressing an excessive increase in the catalyst bed temperature T of the NOx catalyst due to the execution of the high-temperature S poisoning recovery control, the amount of the sulfur component that always remains in the catalyst is reduced, and the sulfur component that remains is the cause. It becomes possible to suppress the deterioration of NOx emission of the internal combustion engine.

  (2) As the high temperature time cumulative value Σt greatly deviates from the standard value Bh and decreases, the amount of sulfur component always remaining in the NOx catalyst increases, and the S poison recovery control is performed. Even if an attempt is made to raise the catalyst bed temperature T through the supply of the unburned fuel component to the NOx catalyst, it is difficult to realize that it always releases the sulfur component remaining in the catalyst. In other words, it can be said that when the catalyst bed temperature T is made higher by the high-temperature S poisoning recovery control, an excessive increase in the catalyst bed temperature T is unlikely to occur. In consideration of these points, in the high temperature S poisoning recovery control, the maximum value of the target bed temperature Tt is increased as the deviation amount KA increases toward the decrease side of the high temperature time cumulative value Σt with respect to the standard value Bh. Based on this, an attempt is made to make the catalyst bed temperature T higher. For this reason, it is possible to achieve both high-level suppression of excessive increase in the catalyst bed temperature T of the NOx catalyst in the high-temperature S poisoning recovery control and effective release of the sulfur component always remaining in the NOx catalyst by the control. Can do.

  (3) When the sulfur concentration of the fuel used is higher than the standard value (sulfur concentration N), the amount of the sulfur component always remaining in the NOx catalyst tends to increase. However, even in such a case, the sulfur component that always remains in the NOx catalyst can be effectively removed while suppressing an excessive increase in the catalyst bed temperature T through the execution of the high-temperature S poisoning recovery control described above.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS.
This embodiment is different from the first embodiment in how to determine whether or not the amount of sulfur component always remaining in the NOx catalyst increases when executing the high temperature S poisoning recovery control. Specifically, the total S inflow amount ΣSU, which is the total amount of sulfur components flowing into the NOx catalyst starting from the start of use of the internal combustion engine 10, and the standard of the total S inflow amount ΣSU at the vehicle travel distance at that time Based on the standard value Bsu, which is a typical value, it is determined whether or not the amount of the sulfur component always remaining in the NOx catalyst is large.

  Here, the relationship between the travel distance of the automobile, the standard value Bsu, and the total S inflow amount ΣSU is shown in FIG. The standard value Bsu increases as the travel distance of the automobile increases as shown by the solid line in FIG. In addition, the total S inflow amount ΣSU increases as the travel distance increases, but in the case of a driver with heavy fuel consumption of the internal combustion engine 10 such as frequent start of an automobile, the NOx catalyst is changed along with the fuel consumption. Since the amount of inflowing sulfur component (S inflow amount SU) increases, the sulfur component is easily stored in the catalyst, and the amount of sulfur component remaining in the catalyst also increases. In particular, when a fuel having a sulfur concentration higher than a standard value (in this example, a sulfur concentration N) is used, sulfur flowing into the NOx catalyst is compared with a case where a fuel having a standard sulfur concentration is used. Since the amount of the component is increased, the sulfur component is easily stored in the catalyst, and the increase in the sulfur component always remaining in the catalyst becomes remarkable. When the operation as described above is performed, the total S inflow amount ΣSU is likely to increase. Therefore, the transition of the total S inflow amount ΣSU with respect to the increase in travel distance is as shown by a solid line in FIG. .

  Therefore, when the total S inflow amount ΣSU (solid line) is equal to or larger than the standard value Bsu (broken line) at the travel distance at that time, it is determined that the amount of the sulfur component always remaining in the NOx catalyst is increased. The high temperature S poison recovery control is started based on the request for execution of the poison recovery control.

  FIG. 6 is a flowchart showing the S poison recovery control execution routine of this embodiment. The S poisoning recovery control execution routine is also periodically executed through the electronic control unit 50, for example, at an angle interruption for each predetermined crank angle.

  In this routine, first, the total S inflow amount ΣSU, which is the accumulated value of the S inflow amount SU, is calculated by accumulating the S inflow amount SU at every calculation timing (each fuel injection timing) (S201). Thereafter, based on the current travel distance, a standard value Bsu which is a standard value of the total S inflow amount ΣSU at the travel distance is calculated (S202). The standard value Bsu calculated in this way changes as shown by a broken line in FIG. When the total S inflow amount ΣSU and the standard value Bsu are calculated, it is determined whether or not it is a time when an execution request for S poison recovery control is made (S203). If an affirmative determination is made in step S203, whether or not the total S inflow amount ΣSU is greater than or equal to the standard value Bsu as a determination as to whether or not the amount of the sulfur component that always remains in the NOx catalyst increases. Is determined (S204).

  If it is determined in step S204 that the total S inflow amount ΣSU is less than the standard value Bsu, it is determined that the amount of sulfur component remaining in the NOx catalyst is not always increased, and normal S poisoning recovery is performed. Control is started (S206). Further, when it is determined in step S204 that the total S inflow amount ΣSU is equal to or greater than the standard value Bsu, it is determined that the amount of sulfur component always remaining in the NOx catalyst is increased, and the high temperature S poisoning is determined. Recovery control is started (S205).

  In the high temperature S poisoning recovery control, the target bed temperature Tt during the control is raised to a value higher than the maximum value of the target bed temperature Tt in the normal S poisoning recovery control. In this case, the increase of the target bed temperature Tt with respect to the maximum value is smaller than the increase to the value that leads to thermal damage of the NOx catalytic converter 25, and is a divergence of the high-temperature time accumulated value Σt from the standard value Bh. This is performed with an increase width that is variably set so as to increase as the amount KA (see FIG. 5) increases. Then, by increasing the average value of the catalyst bed temperature T through the increase of the target bed temperature Tt, the sulfur component is efficiently released from the NOx catalyst, and thereby the amount of sulfur component that always remains in the NOx catalyst. Less.

  After the start of execution of the high-temperature S poisoning recovery control and the normal S poisoning recovery control, the S poisoning amount S decreases to the predetermined value (in this example, “0”) through the same control. Thus, the control is terminated. When the high-temperature S poisoning recovery control is executed, the amount of sulfur component that always remains in the NOx catalyst decreases, and accordingly, the frequency of executing the high-temperature S poisoning recovery control may be reduced accordingly. Is preferable from the viewpoint of suppressing an excessive increase in the catalyst bed temperature T. For this reason, based on the total S inflow correction routine shown in FIG. 7, when the high temperature S poison recovery control is completed (S301: YES), the total S inflow ΣSU is corrected to the standard value Bsu side. Is performed (S302). As the correction amount of the total S inflow amount ΣSU at this time, an optimum value determined in advance through experiments or the like is used. By such correction, the magnitude of the total S inflow amount ΣSU with respect to the travel distance is corrected to the standard value Bsu side, and the transition of the total S inflow amount ΣSU with respect to the change in travel distance shifts to the standard value Bsu (broken line in FIG. 5) side. . Therefore, thereafter, the total S inflow amount ΣSU is less likely to be equal to or greater than the standard value Bsu, and the high temperature S poisoning recovery control is difficult to be executed, and the above-described excessive increase in the catalyst bed temperature T is suppressed.

According to the embodiment described above in detail, the following effects can be obtained in addition to the effect (3) of the first embodiment.
(4) When the total S inflow amount ΣSU becomes equal to or greater than the standard value Bsu, in other words, the amount of fuel consumption (S inflow amount SU) in the internal combustion engine 10 increases due to the manner in which the driver operates the automobile, and becomes a NOx catalyst. Only when the amount of the remaining sulfur component is always increased, the high-temperature S poisoning recovery control is performed to efficiently release the sulfur component from the NOx catalyst. By carrying out such high temperature S poisoning recovery control, the amount of sulfur component that always remains in the NOx catalyst is reduced. As described above, while suppressing an excessive increase in the catalyst bed temperature T of the NOx catalyst due to the execution of the high-temperature S poisoning recovery control, the amount of the sulfur component that always remains in the catalyst is reduced, and the sulfur component that remains is the cause. It becomes possible to suppress the deterioration of NOx emission of the internal combustion engine.

  (5) As the total S inflow amount ΣSU largely deviates from the standard value Bsu and increases, the amount of sulfur component always remaining in the NOx catalyst increases, and the S poison recovery control is performed. Even if an attempt is made to raise the catalyst bed temperature T through the supply of the unburned fuel component to the NOx catalyst, it is difficult to realize that it always releases the sulfur component remaining in the catalyst. In other words, it can be said that when the catalyst bed temperature T is made higher in the high temperature S poisoning recovery control, an excessive increase in the catalyst bed temperature T is unlikely to occur. In consideration of this, in the high temperature S poisoning recovery control, the maximum value of the target bed temperature Tt is further increased with the increase in the deviation amount KA to the increase side of the total S inflow amount ΣSU with respect to the standard value Bsu, Based on this, an attempt is made to make the catalyst bed temperature T higher. For this reason, it is possible to achieve both high-level suppression of excessive increase in the catalyst bed temperature T of the NOx catalyst in the high-temperature S poisoning recovery control and effective release of the sulfur component always remaining in the NOx catalyst by the control. Can do.

  (6) When the high temperature S poisoning recovery control is executed, the amount of sulfur component always remaining in the NOx catalyst is reduced, and accordingly, the execution frequency of the high temperature S poisoning recovery control is reduced accordingly. This is preferable from the viewpoint of suppressing an excessive increase in the catalyst bed temperature T in the NOx catalyst. Considering this, when the high-temperature S poisoning recovery control is executed, the total S inflow amount ΣSU is corrected to the standard value Bsu side when the control is completed. As a result, the transition of the total S inflow amount ΣSU with respect to the change in the travel distance shifts to the standard value Bsu side, and the total S inflow amount ΣSU is less likely to be greater than the standard value Bsu, making it difficult to execute the high temperature S poison recovery control. The above-described excessive increase in the catalyst bed temperature T can be suppressed.

[Other Embodiments]
In addition, each said embodiment can also be changed as follows, for example.
In the first and second embodiments, the high-temperature S poisoning recovery control may be performed only when the NOx catalyst is in a state where deterioration due to heat and sulfur component remains advanced. It should be noted that whether or not the NOx catalyst has deteriorated due to heat and sulfur component residue is the same as when the catalyst bed temperature T is to be raised, such as when normal S poisoning recovery control is performed. It can be determined based on the average value of the catalyst bed temperature T.

  FIG. 8 shows the catalyst bed temperature in each part from the exhaust upstream end side to the exhaust downstream end side in the NOx catalytic converter 25 in the state where the deterioration of the NOx catalyst has not progressed (solid line) and the deterioration of the NOx catalyst. It is the graph shown separately by the state (dashed line) which advanced. As can be seen from the figure, when the above-described deterioration of the NOx catalyst progresses, even if the catalyst bed temperature T is to be increased by implementing S poison recovery control or the like, the exhaust downstream end from the exhaust upstream end side of the NOx catalyst associated therewith is increased. The catalyst bed temperature is hardly increased at each part toward the side. Therefore, when trying to increase the average value of the catalyst bed temperature T toward the target bed temperature Tt by performing the S poison recovery control or the like, the average value of the catalyst bed temperature T is predetermined with respect to the target bed temperature Tt. If it is lower than the determined value, it can be determined that the NOx catalyst is in a state of advanced deterioration due to heat and sulfur component residue.

  By performing the high temperature S poisoning recovery control only in such a state, it is possible to more accurately suppress the excessive increase in the temperature of the NOx catalyst accompanying the execution of the control. .

  -In 2nd Embodiment, the magnitude | size of the total S inflow amount (SIGMA) SU with respect to travel distance is correct | amended to the standard value Bsu side by correct | amending a travel distance to the increase side at the time of completion of high temperature S poisoning recovery control, and travel distance The transition of the total S inflow amount ΣSU with respect to the change of may be shifted to the standard value Bsu side. Also in this case, an effect equivalent to the above (6) in the second embodiment can be obtained.

  In the second embodiment, the fuel injection amount cumulative value that is a value obtained by accumulating the fuel injection amount command value Qfin from the start of use of the internal combustion engine 10 at each fuel injection timing corresponds to the total S inflow amount ΣSU. As the value corresponding to the total S inflow amount, it may be used instead of the total S inflow amount ΣSU. Further, the number of executions of the S poison recovery control from the start of use of the internal combustion engine 10 may be used as the total S inflow amount equivalent value instead of the total S inflow amount ΣSU.

  In the first and second embodiments, regarding the range of increase when the target bed temperature Tt in the high temperature S poison recovery control is higher than the maximum value of the target bed temperature Tt in the normal S poison recovery control, It does not necessarily have to increase as the deviation amount KA increases. For example, an optimum value (fixed value) determined in advance through experiments or the like may be used as the increase range.

  In the first and second embodiments, instead of the travel distance of the automobile 1, the total operation time from the start of use of the internal combustion engine 10 may be used. Further, the cumulative value of the rotational speed from the use start point of the internal combustion engine 10 is used as a total operation time equivalent value that is a value corresponding to the total operation time from the use start point of the internal combustion engine 10 instead of the travel distance. May be.

  The unburned fuel component may be supplied to the NOx catalyst by fuel injection from the injector 40 during the exhaust stroke.

1 is a schematic diagram showing an entire internal combustion engine to which an exhaust emission control device of a first embodiment is applied. (A)-(e) are the change of the addition pulse for driving the addition valve during the S poison recovery control, the change of the atmosphere around the NOx catalyst, the change of the catalyst bed temperature T, the transition of the integrated values ΣQr, ΣQ And a time chart showing how to set the addition permission flag F. The flowchart which shows the procedure of execution start of S poison recovery control. The graph which shows the change of high temperature time accumulation value (SIGMA) t and standard value Bh with respect to the change of a travel distance. The graph which shows the change of the total S inflow amount (SIGMA) SU and the standard value Bsu with respect to the change of a travel distance. The flowchart which shows the procedure of the execution start of S poison recovery control in 2nd Embodiment. The flowchart which shows the correction | amendment procedure of total S inflow amount (SIGMA) SU after completion | finish of high temperature S poisoning recovery control. The graph which shows the catalyst bed temperature of each site | part from the upstream end side of a NOx catalytic converter to the downstream end side.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 12 ... Intake passage, 13 ... Combustion chamber, 14 ... Exhaust passage, 16 ... Air flow meter, 25 ... NOx catalytic converter, 26 ... PM filter, 27 ... Oxidation catalytic converter, 28 ... Incoming gas temperature sensor, 29 DESCRIPTION OF SYMBOLS ... Outgas temperature sensor, 30 ... Differential pressure sensor, 31 ... Air-fuel ratio sensor, 32 ... Air-fuel ratio sensor, 40 ... Injector, 41 ... High pressure fuel supply pipe, 42 ... Common rail, 43 ... Fuel pump, 44 ... Rail pressure sensor, 45 ... Low pressure fuel supply pipe, 46 ... Addition valve, 50 ... Electronic control device (estimating means, cumulative value calculating means, standard value calculating means, control means, inflow equivalent value calculating means, correcting means), 51 ... NE sensor, 52 ... Accelerator sensor, 54 ... Intake air temperature sensor, 55 ... Water temperature sensor.

Claims (6)

An NOx storage reduction catalyst provided in an exhaust system of an internal combustion engine, and an estimation means for estimating an S poisoning amount that is a storage amount of a sulfur component in the NOx catalyst, wherein the estimated S poisoning amount is S poison recovery to raise the catalyst bed temperature to the target bed temperature through the supply of unburned fuel components to the NOx catalyst when the value exceeds the allowable value and to bring the atmosphere around the NOx catalyst into the rich combustion state The control is started to release the sulfur component from the NOx catalyst, and the control is performed when the S poisoning amount becomes equal to or less than the predetermined value after the start of the S poison recovery control. In the exhaust gas purification device of the internal combustion engine to be finished,
A cumulative value calculating means for calculating a high temperature time cumulative value, which is a cumulative value of the time when the NOx catalyst has become high temperature, as a value corresponding to the degree of thermal degradation of the NOx catalyst;
Based on a value corresponding to the total operating time of the internal combustion engine, a standard value calculating means for calculating a standard value of the accumulated high temperature time in the total operating time of the engine at that time;
Only when the high-temperature time cumulative value calculated by the cumulative value calculation means is equal to or less than the standard value calculated by the standard value calculation means, the same control at a catalyst bed temperature higher than the S poison recovery control is performed. Control means for performing certain high temperature S poisoning recovery control;
An exhaust emission control device for an internal combustion engine, comprising: 2. The internal combustion engine according to claim 1, wherein the control means increases the catalyst bed temperature in the high temperature S poisoning recovery control with an increase in the amount of deviation of the high temperature time cumulative value toward the decrease side with respect to the standard value. Exhaust purification equipment. An NOx storage reduction catalyst provided in an exhaust system of an internal combustion engine, and an estimation means for estimating an S poisoning amount that is a storage amount of a sulfur component in the NOx catalyst, wherein the estimated S poisoning amount is S poison recovery that raises the catalyst bed temperature to the target bed temperature through the supply of unburned fuel components to the NOx catalyst when the value exceeds the allowable value and makes the atmosphere around the NOx catalyst a rich combustion state The control is started to release the sulfur component from the NOx catalyst, and the control is performed when the S poisoning amount falls below a predetermined value smaller than the allowable value after the start of the S poison recovery control. In the exhaust gas purification device of the internal combustion engine to be finished,
An inflow equivalent value calculating means for obtaining a total S inflow equivalent value corresponding to the total amount of sulfur components flowing into the NOx catalyst;
Based on a value corresponding to the total operating time of the internal combustion engine, a standard value calculating means for calculating a standard value of the total S inflow equivalent value in the total operating time of the engine at that time;
Only when the total S inflow equivalent value calculated by the inflow amount equivalent value calculating means is not less than the standard value calculated by the standard value calculating means, the catalyst bed temperature is higher than that in the S poison recovery control. Control means for performing high temperature S poisoning recovery control, which is the same control as
An exhaust emission control device for an internal combustion engine, comprising: The control means increases the catalyst bed temperature in the high temperature S poisoning recovery control as the amount of deviation toward the increase side of the total S inflow equivalent value with respect to the standard value increases. An exhaust purification device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 3 or 4,
When the high temperature S poisoning recovery control is executed, the internal combustion engine further comprises correction means for correcting the magnitude of the total S inflow equivalent value with respect to the total operation time equivalent value to the standard value side. Exhaust purification equipment. The control means determines whether or not the NOx catalyst has deteriorated due to heat and sulfur component residue based on the catalyst bed temperature when attempting to increase the catalyst bed temperature, and the NOx catalyst The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein the high-temperature S poisoning recovery control is performed only when it is determined that the deterioration is advanced.

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