JP2007303306A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of inhibiting deterioration of NOx emissions of the internal combustion engine caused by slippage of calculated sulfur poisoning quantity from actual sulfur poisoning quantity. <P>SOLUTION: Sulfur poisoning quantity S is calculated with including not only variable poisoning quantity Si changing according to air fuel ratio of exhaust gas and catalyst bed temperature of a NOx catalyst but also sulfur remaining quantity SX which is quantity of SOx always remaining in the NOx catalyst. Slippage of the calculated sulfur poisoning quantity S from the actual sulfur poisoning quantity due to shortage of actual sulfur remaining quantity by sulfur remaining quantity SZ, thereby, can be inhibited. Consequently, a phenomenon that the actual sulfur poisoning quantity is allowable value or higher although the calculated sulfur poisoning quantity S is less than the allowable value can be inhibited and deterioration of NOx emission of the internal combustion engine 10 caused by the phenomenon can be inhibited. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  As an exhaust emission control device applied to an internal combustion engine, a catalyst converter is provided in an exhaust system of the engine, and a NOx storage reduction catalyst that performs exhaust gas purification on nitrogen oxide (NOx) is supported on the catalytic converter. It has been.

  In such an exhaust purification device, the NOx occlusion capacity of the NOx catalyst is reduced by occlusion of sulfur oxide (SOx) or the like in the NOx catalyst. Therefore, many of this type of exhaust gas purification apparatuses obtain an S poison amount that is the amount of SOx stored in the NOx catalyst, as shown in Patent Document 1, for example, and the S poison amount exceeds an allowable value. In some cases, S poison recovery control is performed to release SOx from the NOx catalyst in order to recover the NOx storage capability of the NOx catalyst that has been reduced by the storage of SOx. 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 exhaust air-fuel ratio is made rich at that high temperature. The release of SOx from the NOx catalyst and its reduction are promoted to restore the NOx storage capacity.

Here, calculation of the S poisoning amount in Patent Document 1 will be described.
In Patent Document 1, the S poisoning amount Qs is calculated at a predetermined calculation cycle using the equation “Qs = previous Qs + ΔQf · Ks−Rs”. In this equation, the term “ΔQf · Ks” represents the S inflow amount that is the amount of SOx stored in the NOx catalyst from the previous calculation of the S poison amount Qs to the current calculation of the S poison amount Qs. The term “Rs” represents the S release amount, which is the amount of SOx released from the NOx catalyst from the previous calculation of the S poison amount Qs to the current calculation of the S poison amount Qs.

  The S inflow amount ΔQf · Ks is related to the fuel injection amount ΔQ by the fuel injection performed from the previous calculation of the S poison amount Qs to the calculation of the current S poison amount Qs. It increases almost in proportion to the increase of ΔQ. This is because the sulfur content in the fuel is stored in the NOx catalyst as SOx, and the more fuel consumed in the internal combustion engine, the more SOx stored in the NOx catalyst. Accordingly, the S inflow amount ΔQf · Ks is calculated by multiplying the fuel injection amount ΔQ by the S poisoning coefficient Ks. The S poisoning coefficient Ks is a coefficient for converting the fuel injection amount ΔQf of the internal combustion engine into the amount of SOx stored in the NOx catalyst by the amount of fuel consumption.

  The S release amount Rs is calculated at a predetermined calculation cycle using the formula “Rs = α · R1 · R2 · R3 · dt”. In this equation, “α” is a fixed value representing the regeneration rate from S poisoning per unit time in the NOx catalyst, and “dt” represents the calculation period of the S release amount Rs. “R1” in the above formula is a regeneration capacity coefficient that increases as the catalyst bed temperature increases. “R2” in the above equation is a regeneration capacity coefficient that becomes constant at a large value when the air-fuel ratio is rich, and decreases when the air-fuel ratio is lean. Furthermore, “R3” in the above equation is a regeneration capacity coefficient that increases as the S poison amount Qs increases in the NOx catalyst.

  Therefore, in a normal engine operation state, the catalyst bed temperature does not become extremely high and the exhaust air-fuel ratio does not become rich unlike when the S poison recovery control is executed. “0”. On the other hand, the S inflow amount ΔQf · Ks increases with the fuel consumption of the internal combustion engine regardless of whether or not the S poison recovery control is executed. For this reason, in a normal engine operating state where S poison recovery control is not performed, the S poison amount Qs calculated using the equation “Qs = previous Qs + ΔQf · Ks−Rs” gradually increases. It will be.

When the S poisoning amount Qs becomes equal to or greater than the allowable value and the S poisoning recovery control is started, the catalyst bed temperature becomes high and the air-fuel ratio of the exhaust gas becomes rich, so the S release amount Rs becomes the S inflow amount. It becomes larger than ΔQf · Ks. As a result, the S poisoning amount Qs calculated using the expression “Qs = previous Qs + ΔQf · Ks−Rs” gradually decreases. Thereafter, when the S poisoning amount Qs decreases to, for example, “0”, the S poisoning recovery control is ended.
JP 2002-256858 A (paragraphs [0057] to [0071])

  By the way, in calculating the S release amount Rs used in the expression “Qs = previous Qs + ΔQf · Ks−Rs”, a capacity coefficient R3 that increases as the S poison amount Qs in the NOx catalyst increases is used. This corresponds to the fact that the more SOx occluded in the NOx catalyst, the faster the regeneration rate from S poisoning in the NOx catalyst, in other words, the SOx release rate, during execution of the S poison recovery control. This is to change the S release amount Rs. Accordingly, the calculated S release amount Rs becomes a value corresponding to the SOx release rate affected by the S poison amount Qs in the NOx catalyst at that time.

  However, the S release amount Rs is calculated as a theoretical value. Of the SOx contained in the S release amount Rs, the S poison recovery control cannot actually be released from the NOx catalyst. There exists SOx that remains in the catalyst. The existence of such SOx is assumed to be due to the following reasons [1] and [2].

  [1] On the surface of the NOx catalyst, noble metals (Pt and the like) for NOx purification are provided at intervals, and when SOx adheres to the catalyst surface at a position away from the noble metals, The SOx cannot be released even if the exhaust air-fuel ratio is enriched at high temperatures by S poison recovery control.

  [2] In the vicinity of the outer peripheral surface of the catalytic converter, heat exchange with the exhaust gas is frequently performed and the catalyst bed temperature hardly rises. Therefore, the SOx adhering to the NOx catalyst in that portion is kept at a high temperature by S poison recovery control. It is not always possible to release the exhaust air when the exhaust air-fuel ratio is enriched.

  As described above, in the calculation of the S poison amount Qs in Patent Document 1, the equation “Qs = previous Qs + ΔQf · Ks−Rs” in spite of the presence of SOx that always remains in the NOx catalyst. As is apparent from the above, the S poisoning amount Qs is calculated without considering the above-mentioned SOx. For this reason, the calculated S poisoning amount Qs is smaller than the actual S poisoning amount by the amount not considering SOx that always remains in the NOx catalyst, and a deviation occurs between the two. Become.

  As a result, after the start of the S poisoning recovery control, when the S poisoning amount Qs decreases to “0” and the S poisoning recovery control is terminated, the actual S poisoning amount decreases to “0”. The SOx remains in the NOx catalyst to some extent. Then, as the use period of the NOx catalyst becomes longer and the amount of SOx that always remains in the catalyst increases, the difference between the calculated S poison amount Qs and the actual S poison amount increases. The amount of SOx that remains in the NOx catalyst at the end of the poison recovery control increases. Under such circumstances, there is a high possibility that the calculated S poisoning amount Qs is less than the allowable value but the actual S poisoning amount is not less than the allowable value. As a result, the NOx emission of the internal combustion engine may be deteriorated.

  The present invention has been made in view of such circumstances, and its object is to suppress NOx emission deterioration of the internal combustion engine caused by the difference between the calculated S poisoning amount and the actual S poisoning amount. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine.

In the following, means for achieving the above object and its effects are described.
In order to achieve the above object, an invention according to claim 1 is provided with an NOx storage reduction catalyst provided in an exhaust system of an internal combustion engine, and an S poisoning amount that is a storage amount of sulfur oxide in the NOx catalyst. S is calculated, and when the S poison amount S exceeds an allowable value, S poison recovery control for releasing sulfur oxide from the NOx catalyst is started, and the S poison amount S is more than the allowable value. In the exhaust gas purification apparatus for an internal combustion engine that terminates the S poison recovery control when the value is also reduced to a small predetermined value or less, the amount of sulfur oxide that can be reduced by the S poison recovery control with the NOx catalyst The poisoning amount Si is defined as the previously calculated variable poisoning amount Si-1 and the S inflow which is the amount of sulfur oxide occluded in the NOx catalyst from the previous calculation of the fluctuation poisoning amount to the current calculation of the variable poisoning amount. Amount SU and the current fluctuation from the previous fluctuation poisoning amount calculation Based on the S release amount SD, which is the amount of sulfur oxide released from the NOx catalyst until the poison amount is calculated, a first calculation is performed at a predetermined calculation cycle using the formula “Si = Si−1 + SU−SD”. In addition to calculating the S residual amount SZ, which is the amount of sulfur oxide remaining in the NOx catalyst without being released from the NOx catalyst by the calculation means and the S poison recovery control, in a predetermined calculation cycle, And a second calculating means for calculating the S poisoning amount S using the formula “S = Si + SZ” based on the S residual amount SZ and the variable poisoning amount Si.

  During normal operation of the internal combustion engine, the variable poisoning amount Si at the NOx catalyst increases by the S inflow amount SU, and when the S poisoning recovery control is executed, the variable poisoning amount Si decreases by the S release amount SD. . According to the above configuration, since the S poison amount S is calculated including not only the variable poison amount Si calculated as described above but also the S residual amount SZ, the calculated S poison amount S is the S residual amount. It is possible to suppress the occurrence of a shift between the two due to the amount SZ being smaller than the actual S poisoning amount. If a deviation occurs between the calculated S poison amount S and the actual S poison amount, the calculated S poison amount S is less than the allowable value, but the actual S poison amount is There is a high possibility that the phenomenon of exceeding the allowable value will occur. As a result, the NOx emission of the internal combustion engine may be deteriorated. However, the deterioration of the NOx emission of the internal combustion engine is suppressed.

  According to a second aspect of the present invention, in the first aspect of the present invention, the second calculation means includes a fixed value S1 determined by the specifications of the catalytic converter on which the NOx catalyst is supported, the S residual amount SZ, The calculation is based on the catalyst bed temperature of the NOx catalyst and the fluctuation value S2 updated in accordance with the air-fuel ratio of the exhaust.

  Sulfur oxide adhering to a position away from the noble metals on the catalyst surface of the NOx catalyst always remains without being released by the S poison recovery control. The amount of sulfur oxide adhering to the position is determined by the specifications of the catalytic converter. Further, the sulfur oxide attached to the NOx catalyst in the vicinity of the outer peripheral surface of the catalytic converter is always left without being released by the S poison recovery control. The amount of sulfur oxide adhering to the position varies depending on the catalyst bed temperature and the air-fuel ratio of the exhaust. According to the above configuration, the fixed value S1 is set as a value corresponding to the amount of sulfur oxide attached to the catalyst surface of the NOx catalyst away from the noble metals, and the fluctuation value S2 is set to NOx near the outer peripheral surface of the catalytic converter. By calculating as a value corresponding to the sulfur oxide adhering to the catalyst, the S residual amount SZ calculated based on the fixed value S1 and the fluctuation value S2 can be an accurate value.

  According to a third aspect of the invention, in the first or second aspect of the invention, the second calculation means stores the fluctuation value S2 in the nonvolatile memory for each update, and the first S residual amount SZ after battery replacement. At the time of calculation, the residual S amount SZ is calculated using the fluctuation value S2 stored in the nonvolatile memory.

According to the above configuration, it is possible to avoid the fluctuation value S2 being returned to the initial value by the battery replacement, and thereby the S residual amount calculated at the first time after the battery replacement becomes inaccurate.
In the invention according to claim 4, in the invention according to any one of claims 1 to 3, the S poison amount S is greater than or equal to a threshold value that is larger than the allowable value during the S poison recovery control. The control means for executing the forced poisoning recovery process for more powerfully releasing the sulfur oxide from the NOx catalyst when the NOx catalyst is reached.

  If the S residual amount SZ in the NOx catalyst increases, the S poisoning amount S does not decrease so much even if the S poison recovery control is executed, and good S poison recovery of the NOx catalyst cannot be expected. However, according to the above-described configuration, when the S poison amount S exceeds a threshold value that is larger than the allowable value in such a situation, more powerful sulfur oxide is released from the NOx catalyst through the execution of the forced poisoning recovery process. It is done. Thereby, the S residual amount SZ in the NOx catalyst can be reduced, and good S poison recovery of the NOx catalyst by the S poison recovery control can be ensured.

  According to a fifth aspect of the present invention, in the fourth aspect of the present invention, as the S poisoning recovery control, the control means controls the catalyst bed temperature of the NOx catalyst to a target bed temperature by supplying fuel to the NOx catalyst. As the temperature increases, the air-fuel ratio of the exhaust gas becomes the target air-fuel ratio set to a richer side than the stoichiometric air-fuel ratio, and as the forced poisoning recovery process, the target bed temperature is changed to the higher side and the target At least one of the change to the rich side of the air-fuel ratio is performed.

  According to the above configuration, the forced poisoning recovery control performs at least one of increasing the catalyst bed temperature of the NOx catalyst and making the air-fuel ratio of the exhaust gas richer. Thus, more powerful release of sulfur oxides from the NOx catalyst can be accurately performed.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the control means determines that the forced coverage is only when it is determined that the NOx catalyst has changed from a new state to a state that has deteriorated to some extent. The poison recovery process was to be executed.

  If the target bed temperature is changed to the rising side or the air-fuel ratio of the exhaust gas is changed to the rich side by the forced poisoning recovery process, the NOx catalyst will be more or less thermally deteriorated with the temperature increase of the NOx catalyst. The degree of thermal deterioration of the NOx catalyst accompanying such a temperature increase becomes large from when the catalyst is in a new state until it is thermally deteriorated to some extent. According to the above configuration, only when it is determined that the NOx catalyst has changed from a new state to a state in which the NOx catalyst has deteriorated to some extent, a change to the target bed temperature due to the forced poisoning recovery process or an exhaust air exhaust is performed. Since the fuel ratio is changed to the rich side, the S residual amount SZ can be reduced while suppressing the thermal deterioration of the NOx catalyst accompanying them.

  According to a seventh aspect of the invention, in the invention according to any one of the first to sixth aspects, the S poison recovery control is not executed, and the S poison amount S is larger than the threshold value. A judgment means is further provided for judging that an abnormality has occurred when the threshold value is equal to or greater than another threshold value.

  When the S residual amount SZ is increased, if the execution condition of the S poison recovery control is not satisfied and the execution frequency of the control becomes low, it will hinder the storage of nitrogen oxide (NOx) in the NOx catalyst. There is a risk, and some measures need to be taken. According to the above configuration, the S poison recovery control is not executed and the S poison amount S is larger than the other threshold value, which hinders NOx occlusion in the NOx catalyst. It is possible to determine that an abnormality has occurred and to take measures against the abnormality.

  According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, the second calculating means calculates the S residual amount SZ from the various catalytic converters on which the NOx catalyst is supported. It is calculated based on a fixed value S1 determined by the original and a fluctuation value S2 updated in accordance with the catalyst bed temperature of the NOx catalyst and the air-fuel ratio of the exhaust, and it is determined that the NOx catalyst is in a new state. In addition, there is further provided prohibiting means for prohibiting execution of the S poison recovery control while the cumulative value of the S inflow amount SU is less than the fixed value S1.

  During the engine operation with the NOx catalyst in a new state, until the cumulative value of the S inflow amount SU reaches the fixed value S1, the part of the catalyst surface of the NOx catalyst away from noble metals or the vicinity of the outer peripheral surface of the catalytic converter There is a high possibility that the sulfur oxide will adhere to a portion where the sulfur oxide always remains, such as NOx catalyst. For this reason, even if the S poison recovery control is executed during such a period, the sulfur oxide cannot be effectively released from the NOx catalyst, and the S poison recovery control is executed wastefully. The accompanying deterioration in fuel consumption of the internal combustion engine is inevitable. According to the above configuration, wasteful execution of the S poison recovery control during such a period is prohibited, so that deterioration in fuel consumption of the internal combustion engine can be suppressed.

Hereinafter, an 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 the intake system of the internal combustion engine 10 and an exhaust passage 14 constituting the exhaust system of the engine 10 are each connected to a combustion chamber 13 of a cylinder of the internal combustion engine 10. An air flow meter 16 and an intake throttle valve 19 are provided in the intake passage 12. 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 of the exhaust are arranged on the exhaust gas upstream side of the NOx catalytic converter 25 and between the PM filter 26 and the oxidation catalytic converter 27, respectively. It is installed.

  Further, the internal combustion engine 10 is provided with an exhaust gas recirculation (hereinafter referred to as EGR) device that recirculates a part of the exhaust gas to the air in the intake passage 12. The EGR device includes an EGR passage 33 that allows the exhaust passage 14 and the intake passage 12 to communicate with each other. The most upstream part of the EGR passage 33 is connected to the exhaust passage 14. An EGR valve 36 is provided in the EGR passage 33. The most downstream portion of the EGR passage 33 is connected to the downstream side of the intake throttle valve 19 in the intake passage 12.

  On the other hand, an injector 40 for injecting fuel to be used for combustion in the combustion chamber 13 is disposed in the combustion chamber 13 of each cylinder of the internal combustion engine 10. 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 a throttle valve sensor that detects the opening of the intake throttle valve 19. 53, an intake air temperature sensor 54 for detecting the intake air temperature of the internal combustion engine 10, a water temperature sensor 55 for detecting the cooling water temperature of the engine 10, and the like are connected. The output port of the electronic control unit 50 is connected to drive circuits such as the intake throttle valve 19, the EGR valve 36, 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. Thus, the opening control of the intake throttle valve 19, EGR control based on the opening control of the EGR valve 36, control of the fuel injection amount, fuel injection timing, and fuel injection pressure from the injector 40, Various controls such as fuel addition control are performed by the electronic control unit 50.

  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 oxide (SOx) or the like in the NOx catalyst, is performed. Such S poison recovery control is started when the S poison amount S, which is the SOx occlusion amount of the NOx catalyst calculated based on the history of the engine operating state, exceeds the allowable value.

  In this S poison recovery control, temperature increase control is first performed to raise the temperature of the catalyst to, for example, about 600 to 700 ° C. through the supply of the unburned fuel component to the NOx catalyst, and then the temperature is lowered after the temperature increase control. Thus, S release control is performed to promote the release and reduction of SOx from the NOx catalyst by making the exhaust air-fuel ratio rich. Thus, by performing the temperature rise control and the S release control in the S poison recovery control, the NOx storage capability of the NOx catalyst can be 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 is reduced 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 terminated.
Next, the outline of the S poison recovery control will be described with reference to the time charts of FIGS. 2 and 3 separately for the above-described temperature rise control and S release control.

[Temperature control]
In the temperature increase control in the S poison recovery control, the target bed temperature Tt of the NOx catalyst is set to be gradually increased to, for example, 700 ° C., and the catalyst is obtained based on detection signals from the inlet gas temperature sensor 28 and the outlet gas temperature sensor 29. The unburned fuel component is supplied to the NOx catalyst through fuel addition from the addition valve 46 so that the bed temperature T rises toward the target bed temperature Tt.

  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 time a and the fuel addition stop time b in such fuel addition are the temperature difference ΔT between the target bed temperature Tt and the catalyst bed temperature T, and the gas flow rate of the internal combustion engine 10 detected by the air flow meter 16. It is set based on Ga (corresponding to the exhaust flow rate of the engine 10). Then, the intensive intermittent fuel addition started as described above is continued until a predetermined number of times of fuel addition is executed, and is stopped after the number of fuel additions is made (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. This 16 ms exothermic fuel amount Q is integrated for each calculation based on the formula “ΣQ ← previous ΣQ + Q (1)”, so that 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 from the start to the end of fuel addition, as shown by the solid line in FIG. The increase during the fuel addition suspension period B is suppressed.

  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. The 16 ms required fuel amount Qr, which is the amount of fuel added necessary for this, 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 integrated for each calculation based on the formula “ΣQr ← previous ΣQr + Qr (2)”, so that the average value of the catalyst bed temperature T is required to be the target bed temperature Tt. A required fuel amount integrated value ΣQr representing the 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 indicated by a 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 temperature increase control in the S poison recovery control.

  During the temperature rise control, the 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 integrated value ΣQr is calculated. Increases rapidly. As a result, the time required for the required fuel amount integrated value ΣQr to be equal to or greater than the exothermic fuel amount integrated value ΣQ is shortened and the pause 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 of the catalyst bed temperature T that changes and increases or decreases is controlled to the target bed temperature Tt. Thus, by supplying the unburned fuel component to the catalyst so that the catalyst bed temperature T becomes the target bed temperature Tt which is set to be gradually increased to 700 ° C., the catalyst bed temperature T of the NOx catalyst is about 700 ° C. Can be raised.

[S release control]
When the catalyst bed temperature T of the NOx catalyst is raised to about 700 ° C. through the temperature raising control, the S release control that promotes the release and reduction of SOx from the NOx catalyst by making the exhaust air-fuel ratio rich at that high temperature. Executed. In this S release control, intensive intermittent fuel addition from the addition valve 46 is performed in order to perform fuel addition in an amount substantially equal to the total fuel addition amount during the addition period A (FIG. 2) in the temperature increase control. The exhaust air / fuel ratio is made richer than the stoichiometric air / fuel ratio.

  However, if such intensive intermittent fuel addition is continued, the catalyst bed temperature T of the NOx catalyst may be excessively increased. For this reason, as described above, after performing intensive intermittent fuel addition in a period shorter than the addition period A in the temperature rise control, a period longer than the pause period B (FIG. 2) in the temperature rise control, The intensive intermittent fuel addition is stopped, and the intensive intermittent fuel addition and the stop of the fuel addition are repeated, thereby suppressing an excessive increase in the catalyst bed temperature T.

  The reason for stopping the intensive intermittent fuel addition is longer than the pause period B for the following reason. That is, since the catalyst bed temperature T rises more rapidly and to a higher value due to the intensive intermittent fuel addition, in order to keep the average value of the catalyst bed temperature T constant at the target bed temperature Tt, the intermittent fuel addition is performed. It is necessary to increase the decrease width of the catalyst bed temperature T by extending the stop period.

Here, the fuel addition mode in the S release control and the fuel addition stop mode will be described in detail.
Concentrated intermittent fuel addition in the S release control is also performed at the timing (time T4) of the addition permission flag F shown in FIG. Start based on. When the intensive intermittent fuel addition is started, the 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.

  Also in the S release control, the 16 ms exothermic fuel amount Q and the exothermic fuel amount integrated value ΣQ shown in FIG. The 16 ms exothermic fuel amount Q calculated in this way is the 16 ms exothermic fuel in the addition period A (FIG. 2) in the temperature increase control in the addition period A (T4 to T5) in which the intensive intermittent fuel addition is performed. It becomes larger than the quantity Q. Therefore, the exothermic fuel amount integrated value ΣQ obtained by integrating the 16 ms exothermic fuel amount Q based on the above formula (1) every time the calculation is performed, as shown by the solid line in FIG. It increases more rapidly than the heat generation fuel amount integrated value ΣQ during the addition period A (FIG. 2).

  By performing intensive intermittent fuel addition as described above, the air-fuel ratio of the exhaust gas is set to a target air-fuel ratio AFt that is richer than the stoichiometric air-fuel ratio, as shown at timings T4 to T5 in FIG. . As a result, the exhaust air-fuel ratio is enriched at a high catalyst bed temperature T of the NOx catalyst of about 700 ° C., thereby promoting the release and reduction of SOx from the NOx catalyst.

  On the other hand, after the start of the intensive intermittent fuel addition, the 16 ms required fuel amount Qr is also calculated as in the temperature raising control. The 16 ms required fuel amount Qr becomes smaller as the catalyst bed temperature T shown in FIG. 3C is higher than the target bed temperature Tt (the temperature difference ΔT is larger). The temperature difference ΔT under the situation where the catalyst bed temperature T is higher than the target bed temperature Tt is the temperature difference ΔT (FIG. 2 (b)). As a result, the 16 ms required fuel amount Qr when the catalyst bed temperature T is higher than the target bed temperature Tt tends to be smaller than the 16 ms required fuel amount Qr (FIG. 2C) in the temperature increase control. is there.

  For this reason, the required fuel amount integrated value ΣQr obtained by integrating the 16 ms required fuel amount Qr based on the above equation (2) for each calculation is calculated by the temperature increase control as shown by the broken line in FIG. It increases slowly compared to the required fuel amount integrated value ΣQr in the idle period B (FIG. 2). As a result, the required fuel amount integrated value ΣQr becomes equal to or greater than the exothermic fuel amount integrated value ΣQ (timing T6), and the timing at which the addition permission flag F changes to “1 (permitted)”, that is, the end timing of the suspension period B is Slower than temperature rise control. From the above, the suspension period B during the S release control is made longer than the suspension period B (FIG. 2) in the temperature rise control.

  When the addition permission flag F changes to “1 (permission)”, intensive intermittent fuel addition is started again. At this time, similar to the temperature increase control, the heat generating 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 the intensive intermittent fuel addition, the operation shifts again to the addition period A. When the addition period A ends, the operation shifts to the suspension period B. Therefore, the addition period A and the rest period B described above are repeated also in the S release control, so that the fluctuation center of the catalyst bed temperature T is controlled to the target bed temperature Tt (about 700 ° C.) as in the temperature rise control. Become.

  Thus, the addition period A and the rest period B are repeated, and during the addition period A, the release and reduction of SOx from the NOx catalyst are promoted, so that the storage amount of SOx in the NOx catalyst is reduced and the NOx is reduced. Recovery of the NOx storage capacity of the catalyst is achieved. When the S poison amount S, which is the amount of SOx stored in the NOx catalyst, decreases to the above-described predetermined value, the S release control (S poison recovery control) is terminated.

  Next, the detailed calculation procedure of the S poison amount S will be described with reference to the flowchart of FIG. 4 showing the S poison amount calculation routine. This S poison amount calculation routine is executed through the electronic control unit 50 for each fuel injection from the injector 40, for example.

  In the S poison amount calculation routine, first, the S inflow amount SU, which is the amount of SOx stored in the NOx catalyst from the previous fuel injection to the current fuel injection, is calculated (S101). More specifically, a fuel value that is a predetermined value with respect to the command value Qfin of the fuel injection amount calculated before fuel injection from the injector 40, that is, the command value of the fuel amount injected in one fuel injection. A value (N / 100) obtained by dividing the sulfur concentration N therein by “100” is multiplied. A value (Qfin · (N / 100)) obtained as a result is a value corresponding to the amount of sulfur contained in the fuel injected by one fuel injection from the injector 40. By multiplying this value (Qfin · (N / 100)) by a coefficient K for converting a parameter of sulfur amount into a parameter of S poison amount, the S inflow amount SU is obtained. 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.

  Subsequently, the S release amount SD, which is the amount of SOx released from the NOx catalyst from the previous fuel injection to the current fuel injection, is calculated (S102). The S release amount SD is obtained based on the air-fuel ratio and the catalyst bed temperature of the NOx catalyst, and represents the amount of decrease in the S poison amount at the NOx catalyst when the air-fuel ratio and the catalyst bed temperature are the same. The S release amount SD becomes a value larger than “0” as the catalyst bed temperature becomes higher and richer when the air-fuel ratio is richer than the theoretical air-fuel ratio (here 14.5). When the air-fuel ratio is a value leaner than the stoichiometric air-fuel ratio, it is maintained at “0”.

  Then, based on the S inflow amount SU and the S release amount SD, the variable poisoning amount Si is calculated using the following equation “Si = Si−1 + SU−SD (3)” (S103). The term “Si−1” in the equation (3) represents the variable poisoning amount at the time of the previous calculation, and is set to “0” when the first variable poisoning amount Si is calculated. The variable poisoning amount Si thus calculated gradually increases by the amount of the S inflow amount SU as fuel is consumed during normal engine operation, and during the S poisoning recovery control (particularly during the S release control). Decreases by the amount of S released SD. Therefore, the variable poisoning amount Si is a value that increases or decreases with the inflow of SOx into the NOx catalyst accompanying fuel consumption in normal engine operation and the release of SOx from the NOx catalyst during the S poisoning recovery control. It will be.

  Here, if the variable poisoning amount Si calculated through the processing of steps S101 to S103 is used as it is as the S poisoning amount S that is the storage amount of SOx in the NOx catalyst, the calculated S poisoning amount S is obtained. It becomes less than the actual S poisoning amount. This is because, among the SOx contained in the S release amount SD, in reality, there is SOx that cannot be released from the NOx catalyst in the S poison recovery control and remains in the catalyst. This is because the calculation of the variable poisoning amount Si does not take into account the SOx as apparent from the equation (3). Note that the SOx that always remains in the NOx catalyst exists because of the reasons [1] and [2] described in the [Problems to be solved by the invention] column.

  However, when the calculated S poisoning amount S is smaller than the actual S poisoning amount, the calculated S poisoning amount S is shown in FIG. 5 after the start of the S poisoning recovery control. (Solid line) and actual S poisoning amount (two-dot chain line) decrease as shown in the figure. When the calculated S poisoning amount S decreases to a predetermined value (for example, “0”) smaller than the allowable value and the S poisoning recovery control is finished, the actual S poisoning amount indicated by a two-dot chain line Does not decrease to the predetermined value, and SOx remains in the NOx catalyst to some extent. Then, as the use period of the NOx catalyst becomes longer and the amount of SOx that always remains in the catalyst increases, the difference between the calculated S poisoning amount S and the actual S poisoning amount increases. The amount of SOx that remains in the NOx catalyst at the end of the poison recovery control increases. Under such circumstances, there is a high possibility that the calculated S poisoning amount S is less than the allowable value, but the actual S poisoning amount is not less than the allowable value. As a result, the NOx emission of the internal combustion engine 10 may be deteriorated.

  Therefore, in this embodiment, the S residual amount SZ, which is the amount of SOx that cannot be released in the S poison recovery control and remains in the catalyst, is calculated at the same timing as the calculation timing of the variable poisoning amount Si. The value obtained by calculating and adding the S residual amount SZ to the variable poisoning amount Si is defined as the S poisoning amount S. In this way, by calculating the S poison amount S including not only the variable poison amount Si but also the S residual amount SZ, the calculated S poison amount S is the actual S residual amount by the amount of the S residual amount SZ. It is possible to suppress the occurrence of a shift between the two. Therefore, the deterioration of the NOx emission of the internal combustion engine 10 as described above can be suppressed. Note that the S residual amount SZ is a fixed value S1 corresponding to the amount of SOx that is attached to a position away from noble metals on the catalyst surface of the NOx catalyst and always remains, and the NOx catalyst on which the NOx catalyst is supported. It is calculated by adding the fluctuation value S2 corresponding to the amount of SOx that is attached to the vicinity of the outer peripheral surfaces of the converter 25 and the PM filter 26 and always remains.

  In the S poisoning amount calculation routine of FIG. 4, the fluctuation value S2 is calculated in the processes of steps S104 to S107. Specifically, on the condition that the first S residual amount SZ after the battery replacement is not calculated (S104: NO), the fluctuation value S2 is calculated based on the exhaust air-fuel ratio and the catalyst bed temperature of the NOx catalyst. 25 and the PM filter 26 are updated so as to have a value corresponding to the amount of SOx that is attached to the vicinity of the outer peripheral surface and always remains (S105). The amount of SOx varies according to the exhaust air / fuel ratio and the catalyst bed temperature, and increases as the exhaust air / fuel ratio becomes leaner and increases as the catalyst bed temperature decreases. The update amount of the fluctuation value S2 in step 105 is changed based on the exhaust air-fuel ratio and the catalyst bed temperature so that the fluctuation value S2 changes corresponding to such fluctuation. That is, the renewal amount or the like of the S poison amount S is changed so that the fluctuation value S2 increases as the exhaust air-fuel ratio becomes leaner or the catalyst bed temperature decreases. Further, the magnitude of the change such as the renewal amount based on the changes in the exhaust air-fuel ratio and the catalyst bed temperature at this time is determined in advance by experiments.

  Then, the fluctuation value S2 updated as described above is stored in the nonvolatile memory 56 (FIG. 1) provided in the electronic control unit 50 (S106). Thus, the fluctuation value S2 stored in the nonvolatile memory 56 for each update is acquired when an affirmative determination is made in step S104, that is, when the first S residual amount SZ after the battery replacement is calculated (S107). , And is used as a fluctuation value S2 for calculating the S residual amount SZ.

  After the fluctuation value S2 is calculated by the processing of steps S104 to S107, the S residual amount SZ is calculated using the equation “SZ = S1 + S2 (4)” based on the fluctuation value S2 and the fixed value S1. (S108). The fixed value S1 of the equation (4) is set to a value corresponding to the amount of SOx that is attached to a position away from the noble metals on the catalyst surface of the NOx catalyst and always remains. Since the amount of SOx is determined by the specifications of the NOx catalytic converter 25 and the PM filter 26, the fixed value S1 is obtained and fixed in advance. Then, based on the S residual amount SZ and the variable poisoning amount Si, the S poisoning amount S is calculated using the formula “S = Si + SZ (5)” (S109).

  Next, a detailed execution procedure of the S poison recovery control will be described with reference to the flowchart of FIG. 6 showing the S poison recovery routine. This S poison recovery routine is executed through the electronic control unit 50 at predetermined time intervals such as every 16 ms.

  In the S poison recovery routine, S poison recovery control for releasing SOx occluded in the NOx catalyst is performed, and the S residual amount SZ increases and the S poison amount S increases during the execution of the control. In such a case, a forced poisoning recovery process is performed to release SOx more strongly from the NOx catalyst. If the forced poisoning recovery process is not performed, the S residual amount SZ increases. In a state where the S residual amount SZ is large, even if the S poison recovery control is executed, the S poison amount S does not decrease so much, so that it is impossible to expect a good S poison recovery of the NOx catalyst. However, the S residual amount SZ can be reduced by executing the forced poisoning recovery process, and good S poison recovery control of the NOx catalyst by the S poison recovery control can be secured.

  In the S poison recovery routine, it is determined in step S201 that the forced poisoning recovery flag F1 for determining whether or not the forced poisoning recovery process is being executed is “0 (stopped)”. Then, the process of step S202-S204 for starting S poison recovery control is performed. That is, it is determined whether or not the S poisoning amount S is greater than or equal to an allowable value (S202). If the determination is affirmative, it is determined whether or not the execution condition for the S poisoning recovery control is satisfied (S202). S203).

Incidentally, in the present embodiment, the establishment of the execution condition of the S poison recovery control is determined when all of the following conditions are established.
No abnormality has occurred in the addition valve 46, the inlet gas temperature sensor 28, the outlet gas temperature sensor 29, the air-fuel ratio sensors 31, 32, and the like.

  The detection value (input gas temperature thci) of the input gas temperature sensor 28 is equal to or higher than the lower limit temperature (for example, 150 ° C.) at which the catalyst temperature can be raised in the S poison recovery control. Further, the catalyst bed temperature in the NOx catalyst estimated from the history of the engine operation state, the detected value of the inlet gas temperature sensor 28, and the detected value of the outlet gas temperature sensor 29 can be increased in the S poison recovery control. Above the minimum temperature limit. These lower limit temperatures are respectively set to an exhaust temperature and a lower limit value of the catalyst bed temperature that can cause an oxidation reaction sufficient to raise the catalyst bed temperature with the supply of the unburned fuel component.

The detection value of the inlet gas temperature sensor 28 is less than the upper limit value of the temperature range in which overheating of the catalyst due to heat generation due to S poison recovery control can be avoided.
The detection value of the outgas temperature sensor 29 is less than the upper limit value of the temperature range in which overheating of the catalyst due to heat generation accompanying the S poison recovery control can be avoided.

  • Supply of unburned fuel components to the exhaust is permitted. That is, the engine is in an operating state that allows the supply of unburned fuel components to the catalyst. In the internal combustion engine 10, if the engine is not stalled, the cylinder discrimination is completed, and the accelerator opening is not limited, the supply of the unburned fuel component to the catalyst is permitted. ing.

  When the S poisoning amount S is equal to or larger than the allowable value and the execution condition of the S poisoning recovery control is satisfied, the S poisoning recovery control is started and the above-described temperature increase control and S release control are performed. Are performed in order (S204).

  The processes in steps S205 to S211 in the S poison recovery routine are for executing the forced poison recovery process. That is, S release control is being performed (S205: YES), the S poison amount S is greater than or equal to the threshold value sk1 (S206: YES), and the travel distance from when the NOx catalyst is new is 5000 km or more. On the condition that it is (S207: YES), the forced poisoning recovery process is executed (S208).

  Specifically, as the forced poisoning recovery process, the target bed temperature Tt during the S release control shown in FIG. 3C is changed to the rising side by a predetermined amount X, and the process shown in FIG. The target air-fuel ratio AFt during the S release control shown is changed to the rich side by a predetermined amount Y.

  When the target bed temperature Tt during the S release control is changed to the rising side, the period during which the catalyst bed temperature T is lower than the target bed temperature Tt becomes longer, and based on the temperature difference ΔT between the two during that period. The changing 16 ms required fuel amount Qr becomes large. As a result, based on the 16 ms required fuel amount Qr, the increase in the required fuel amount integrated value ΣQr calculated using the above equation (2) becomes faster, and the required fuel amount integrated value ΣQr becomes equal to or greater than the exothermic fuel amount integrated value ΣQ. Thus, the timing when the addition permission flag F changes to “1 (permission)”, that is, the end timing of the suspension period B is advanced. Then, when the end timing of the suspension period B is advanced and the suspension period B is shortened, the catalyst bed temperature T is increased, and the fluctuation center of the catalyst bed temperature T is changed to the rising side by the predetermined amount X. The target bed temperature Tt is controlled.

  When the target air-fuel ratio AFt during the S release control is changed to the rich side, the fuel addition time a from the addition valve 46 during the addition period A is lengthened and the fuel addition pause time b is shortened. Furthermore, the number of times of fuel addition is increased and the addition period A is lengthened. As a result, the air-fuel ratio detected by the air-fuel ratio sensors 31 and 32 is adjusted to approach the target air-fuel ratio AFt that has been changed to the rich side by the predetermined amount Y.

  As described above, the forced poisoning recovery process is performed to further increase the catalyst bed temperature of the NOx catalyst and change the exhaust air-fuel ratio to a richer side, thereby releasing more powerful SOx from the NOx catalyst. In this way, the SOx that adheres to the vicinity of the outer peripheral surfaces of the NOx catalytic converter 25 and the PM filter 26 and remains in a constant state is released. The predetermined value X corresponding to the amount of increase in the catalyst bed temperature and the predetermined amount Y corresponding to the change amount of the exhaust air-fuel ratio to the rich side are set to optimum values obtained in advance by experiments. Further, during the execution of the forced poisoning recovery process, the fluctuation value S2 indicating the amount of SOx adhering to the vicinity of the outer peripheral surface is small based on the air-fuel ratio accompanying the increase in the catalyst bed temperature and the richness of the exhaust air-fuel ratio. Therefore, the S residual amount SZ calculated based on the fluctuation value S2 and the like is reduced according to the release of the SOx, and as a result, the S poisoning amount S is reduced.

  Note that, when the forced poisoning recovery process is executed, the catalyst bed temperature of the NOx catalyst rises, so it is inevitable that the NOx catalyst is thermally deteriorated. FIG. 7 is a graph showing changes in the degree of deterioration of the NOx catalyst with respect to changes in the travel distance from when the NOx catalyst is new. As can be seen from the figure, when the travel distance is short and the NOx catalyst is not deteriorated so much, the progress of thermal deterioration of the NOx catalyst with respect to the increase of the travel distance becomes remarkable. In such a case, if the catalyst bed temperature is raised through the execution of the forced poisoning recovery process, the thermal degradation of the NOx catalyst proceeds rapidly, so the degree of thermal degradation of the NOx catalyst with respect to the rise of the catalyst bed temperature is large. It becomes.

  Therefore, in the forced poisoning recovery process, the S residual amount SZ can be reduced by executing the forced poisoning recovery process while suppressing the thermal deterioration of the NOx catalyst accompanying the execution of the forced poisoning recovery process. Only when an affirmative determination is made in step S207, it is executed. Therefore, the determination that the travel distance from the new NOx catalyst in this step S207 is 5000 km or more means the determination that the NOx catalyst has changed to a state in which the NOx catalyst has been thermally degraded to some extent. Specifically, this means that the NOx catalyst has been changed to a state in which the thermal degradation is not significant to the extent that the thermal degradation accompanying the increase in the catalyst bed temperature is not significant. The travel distance “5000 km” is a value for determining whether or not the NOx catalyst has changed to a state in which the thermal degradation has not become noticeable as the catalyst bed temperature increases. Yes, it can be appropriately changed according to the specifications of the NOx catalyst.

  When the above-described forced poisoning recovery process is being executed, the forced poisoning recovery flag F1 is set to “1 (running)” (S209). For this reason, after the forced poisoning recovery process is started, a negative determination is made in step S201, and the process of step S208 is executed by skipping the processes of steps S202 to S207. When the S poisoning amount S is reduced by the execution of the forced poisoning recovery process and becomes equal to or less than the value obtained by subtracting the predetermined value h from the threshold value sk1 (“sk1-h”) (S210: YES), the forced poisoning recovery is performed. The flag F1 is set to “0 (stopped)” (S211). Further, when the S poison amount S becomes a predetermined value smaller than the allowable value, for example, a value (“S1-H”) smaller than the fixed value S1 by the predetermined value H (S212: YES), the S poison recovery control is performed. The process is terminated (S213).

  In the S poison recovery routine, when a negative determination is made in step S203, that is, it is determined that the execution condition of the S poison recovery control described above is not satisfied, and the S poison recovery control is not executed. In step S214, it is determined whether or not the S poison amount S is equal to or greater than a threshold sk2, which is another threshold larger than the threshold sk1. Here, the affirmative determination means that the S poison amount S increases as the S residual amount SZ increases in a state in which the S poison recovery control cannot be executed, and the NOx catalyst is caused accordingly. This means that an abnormality has occurred that interferes with NOx storage. Therefore, if an affirmative determination is made in step S214, it is determined that an abnormality has occurred, the abnormality flag F2 is set to “1 (abnormal)” (S215), and then a warning lamp provided in the driver's seat of the automobile is displayed. Lights up (S216).

  Next, the procedure for prohibiting the wasteful execution of the S poison recovery control will be described with reference to the flowchart of FIG. 8 showing the S poison recovery prohibit routine. This S poison recovery prohibition routine is executed at predetermined time intervals such as every 16 ms through the electronic control unit 50.

  When the engine is operated in a new state of the NOx catalyst, SOx always remains in a state where the NOx catalyst is separated from noble metals on the catalyst surface, or in the vicinity of the outer peripheral surfaces of the NOx catalyst converter 25 and the PM filter 26. There is a high possibility that SOx will adhere to the portion. Even if the S poison recovery control is executed in such a case, SOx cannot be effectively released from the NOx catalyst, and the S poison recovery control is executed unnecessarily. It is inevitable that fuel consumption will deteriorate.

  In the S poisoning recovery prohibition routine, the new touch flag F3 for determining whether or not the NOx catalyst is in a new state is “1 (new touch)” for the purpose of avoiding the above-described problems. On the condition of (S301: YES), the processing of steps S302 to S304 for prohibiting the execution of the S poison recovery control is executed. The new touch flag F3 is set to “1 (new touch)” when an abnormality diagnosis is made before the first running in the automobile or after replacement of the NOx catalyst (NOx catalytic converter 25 and PM filter 26).

  In a series of processes of steps S302 to S305 for prohibiting the execution of S poison recovery control, first, the S inflow amount SU is added to the previously calculated total S inflow amount ΣSU, thereby accumulating the S inflow amount SU. A total S inflow amount ΣSU, which is a value, is calculated (S302). Then, during the engine operation from the new state of the NOx catalyst and until the total S inflow amount ΣSU reaches the fixed value S1 (S303: YES), the execution of the S poison recovery process is prohibited (S304). ).

  If it is determined in step S303 that the total S inflow amount ΣSU is greater than or equal to the fixed value S1, the execution of the S poison recovery process is not prohibited, and the new touch flag F3 is set to “0 (new Is not touched ”(S305). Subsequently, the total S inflow amount ΣSU is reset to “0” (S206).

According to the embodiment described in detail above, the following effects can be obtained.
(1) The S poison amount S is not only the variable poison amount Si that changes according to the air-fuel ratio of the exhaust gas and the catalyst bed temperature of the NOx catalyst, but also the amount of SOx that always remains in the NOx catalyst. It is calculated including the residual amount SZ. For this reason, it is possible to prevent the calculated S poisoning amount S from being smaller than the actual S residual amount by the amount of the S residual amount SZ and causing a shift between the two. Therefore, it is possible to suppress the phenomenon that the calculated S poisoning amount S is less than the allowable value but the actual S poisoning amount is not less than the allowable value, and the internal combustion engine 10 is caused by the phenomenon. It is possible to suppress the deterioration of NOx emissions.

  (2) The SOx that always remains in the NOx catalyst includes SOx adhering to a position away from the precious metals on the catalyst surface of the NOx catalyst, and the outer periphery of the NOx catalyst converter 25 and the PM filter 26 on which the NOx catalyst is supported. SOx adhering to the vicinity of the surface can be used. The fixed value S1 used for the calculation of the S residual amount SZ is set to a value corresponding to the amount of SOx that is attached to a position away from the noble metals on the catalyst surface of the NOx catalyst and always remains. . Similarly, the fluctuation value S2 used for calculating the S residual amount SZ is a value corresponding to the amount of SOx that is attached to the vicinity of the outer peripheral surfaces of the NOx catalytic converter 25 and the PM filter 26 and always remains. It is updated according to the air-fuel ratio of the exhaust and the catalyst bed temperature of the NOx catalyst. Accordingly, the S residual amount SZ calculated based on the fixed value S1 and the fluctuation value S2 can be an accurate value.

  (3) The fluctuation value S2 is stored in the non-volatile memory 56 for each update, and the fluctuation value S2 stored in the non-volatile memory 56 is used to calculate the S residual quantity SZ when calculating the first S residual quantity SZ after battery replacement. Used. Therefore, it can be avoided that the fluctuation value S2 is returned to the initial value (for example, “0”) by the battery replacement, and the S residual amount SZ calculated at the first time after the battery replacement becomes inaccurate.

  (4) When the S residual amount SZ in the NOx catalyst increases, the S poison recovery amount does not decrease so much even if the S poison recovery control (S release control) is executed. Under these circumstances, when the S poison amount S becomes greater than the threshold value sk1 during the S release control, more powerful SOx is released from the NOx catalyst through the execution of the forced poisoning recovery process. As a result, the S residual amount SZ in the NOx catalyst can be reduced, and good S poison recovery in the S poison recovery control can be ensured.

  (5) In the forced poisoning recovery process, the catalyst bed temperature T is raised and the air-fuel ratio of the exhaust gas is increased by the change of the target bed temperature Tt during the S release control to the increase side and the change of the target air-fuel ratio AFt to the rich side. Is enriched. Thereby, more powerful release of SOx from the NOx catalyst can be accurately performed.

  (6) When the catalyst bed temperature of the NOx catalyst rises due to the execution of the forced poisoning recovery process, the thermal degradation of the NOx catalyst is caused more or less accordingly. The degree of thermal deterioration of the NOx catalyst accompanying such increase in the catalyst bed temperature becomes large from when the catalyst is new to when it is thermally degraded to some extent. Therefore, the forced poisoning recovery process is performed only when it is determined that the NOx catalyst has deteriorated to some extent, that is, only when the travel distance from a new NOx catalyst is 5000 km or more. Accordingly, when the forced poisoning recovery process is executed, the S residual amount SZ in the NOx catalyst can be reduced while suppressing the thermal deterioration of the NOx catalyst.

  (7) If the S poison recovery control execution condition is not satisfied when the S residual amount SZ is large and the execution frequency of the control is low, there is a risk of hindering NOx storage in the NOx catalyst. Yes, it is necessary to increase some countermeasures such as exchanging the NOx catalyst or forcibly setting the internal combustion engine 10 to an engine operating state in which S poison recovery control can be executed. Here, when the S poisoning recovery control is not executed and the S poisoning amount S is equal to or larger than the threshold value sk2, which is another threshold value larger than the threshold value sk1, the S poisoning recovery control cannot be executed. In this state, the S poison amount S increases as the S residual amount SZ increases, and it is determined that an abnormality has occurred that hinders NOx storage in the NOx catalyst. This makes it possible to accurately determine that the abnormality has occurred and to take measures against the abnormality.

  (8) At the time of engine operation from a new state of the NOx catalyst, more specifically, until the total S inflow amount ΣSU reaches the fixed value S1, the portion of the NOx catalyst on the catalyst surface away from noble metals, the NOx catalytic converter 25 and the NOx catalyst in the vicinity of the outer peripheral surface of the PM filter 26 and the like, there is a high possibility that SOx adheres to a portion where SOx always remains. At this time, even if the S poison recovery control is executed, SOx cannot be effectively released from the NOx catalyst. However, since the execution of the S poison recovery control is prohibited in such a case, it is possible to avoid a deterioration in fuel consumption of the internal combustion engine 10 due to the wasteful execution of the control.

In addition, the said embodiment can also be changed as follows, for example.
It is not always necessary to prohibit the execution of the S poison recovery control during the engine operation from a new NOx catalyst state until the total S inflow amount ΣSU reaches the fixed value S1.

  Judgment as to whether or not the S poisoning amount S increases as the S residual amount SZ increases in a state where the S poisoning recovery control cannot be executed, in other words, step S214 in the S poisoning recovery routine of FIG. It is not always necessary to execute the processes of .about.S216.

  The forced poisoning recovery process is performed only when it is determined that the NOx catalyst has deteriorated to some extent, that is, when an affirmative determination is made in step 207 in the S poison recovery routine of FIG. It is not always necessary to perform the process in step S207.

As the forced poisoning recovery process, only one of the change to the increase side of the target bed temperature Tt and the change to the rich side of the target air-fuel ratio AFt may be performed.
When the S poisoning amount S becomes greater than or equal to the threshold sk1 during the S release control, a lamp or the like warns that the S poisoning amount S has exceeded the threshold sk1 instead of executing the forced poisoning recovery process. You may do it.

  It is not always necessary to store the fluctuation value S2 used for calculating the S residual amount SZ in the nonvolatile memory 56.

1 is a schematic diagram showing an entire internal combustion engine to which an exhaust emission control device of an embodiment is applied. (A)-(d) are the change of the addition pulse for driving the addition valve during the temperature rise control in the S poison recovery control, the change of the catalyst bed temperature T, the change of the integrated values ΣQr, ΣQ, and 4 is a time chart showing how to set an addition permission flag F. (A)-(e) are the change of the addition pulse for driving the addition valve during the S release control in the S poison recovery control, the change of the exhaust air-fuel ratio, the change of the catalyst bed temperature T, the integrated value ΣQr, The time chart which shows transition of (SIGMA) Q and the setting aspect of the addition permission flag F. FIG. The flowchart which shows the calculation procedure of S poisoning amount. The time chart which shows transition of S poisoning amount calculated at the time of S poisoning recovery control, and actual S poisoning amount. The flowchart which shows the execution procedure of S poison recovery control. The graph which showed the change of the deterioration degree of a NOx catalyst with respect to the change of the travel distance from the new NOx catalyst. The flowchart which shows the procedure which prohibits execution of S poison recovery control.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 12 ... Intake passage, 13 ... Combustion chamber, 14 ... Exhaust passage, 16 ... Air flow meter, 19 ... Intake throttle valve, 25 ... NOx catalytic converter, 26 ... PM filter, 27 ... Oxidation catalytic converter, 28 ... Inlet gas temperature sensor, 29 ... outlet gas temperature sensor, 30 ... differential pressure sensor, 31, ... 32 air-fuel ratio sensor, 33 ... EGR passage, 36 ... EGR valve, 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 (control means, prohibition means), 50 ... Electronic control device (first calculation means, second calculation means, control) Means, determination means, prohibition means), 51 ... NE sensor, 52 ... accelerator sensor, 53 ... throttle valve sensor, 54 ... intake air temperature sensor, 55 ... water temperature sensor, 56 ... non-volatile memory

Claims (8)

An NOx storage reduction catalyst provided in an exhaust system of an internal combustion engine is provided, and an S poison amount S, which is a storage amount of sulfur oxide in the NOx catalyst, is calculated, and the S poison amount S exceeds an allowable value. S poison recovery control for releasing sulfur oxide from the NOx catalyst is started, and when the S poison amount S is reduced below a predetermined value smaller than the allowable value, the S poison recovery is started. In the exhaust gas purification apparatus for an internal combustion engine that ends control,
The variable poisoning amount Si, which is the amount of sulfur oxide that can be reduced by the S poison recovery control with the NOx catalyst, is calculated from the previously calculated variable poisoning amount Si-1 and the previous variable poisoning amount calculation. S inflow amount SU, which is the amount of sulfur oxide occluded in the NOx catalyst before the calculation of the variable poisoning amount, and the NOx catalyst released from the previous calculation of the variable poisoning amount to the current calculation of the variable poisoning amount First calculation means for calculating at a predetermined calculation period using the formula “Si = Si−1 + SU−SD” based on the S emission amount SD which is the amount of sulfur oxide to be produced;
The S residual amount SZ, which is the amount of sulfur oxide that cannot be released from the NOx catalyst depending on the S poison recovery control and remains in the NOx catalyst, is calculated at a predetermined calculation cycle, and the S residual amount A second calculating means for calculating the S poisoning amount S using the formula “S = Si + SZ” based on SZ and the variable poisoning amount Si;
An exhaust gas purification apparatus for an internal combustion engine. The second calculation means determines the S residual amount SZ in accordance with a fixed value S1 determined by the specifications of the catalytic converter on which the NOx catalyst is supported, the catalyst bed temperature of the NOx catalyst, and the air-fuel ratio of the exhaust. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is calculated based on the updated fluctuation value S2. The second calculation means stores the fluctuation value S2 in the nonvolatile memory for each update, and uses the fluctuation value S2 stored in the nonvolatile memory when calculating the first S residual amount SZ after battery replacement. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the S residual amount SZ is calculated. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3,
During the S poison recovery control, when the S poison amount S becomes equal to or greater than a threshold value that is larger than the allowable value, the forced poisoning for more powerful release of the sulfur oxide from the NOx catalyst. An exhaust purification device for an internal combustion engine, further comprising control means for executing poison recovery processing. As the S poison recovery control, the control means raises the catalyst bed temperature of the NOx catalyst to the target bed temperature by supplying fuel to the NOx catalyst, and the air-fuel ratio of the exhaust is richer than the stoichiometric air-fuel ratio. The target air-fuel ratio set on the side is set, and as the forced poisoning recovery process, at least one of changing the target bed temperature to the rising side and changing the target air-fuel ratio to the rich side is performed. 5. An exhaust emission control device for an internal combustion engine according to 4. The exhaust purification of an internal combustion engine according to claim 5, wherein the control means executes the forced poisoning recovery process only when it is determined that the NOx catalyst has changed from a new state to a state that has deteriorated to some extent. apparatus. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 6,
When the S poisoning recovery control is not executed and the S poisoning amount S is equal to or greater than another threshold value that is larger than the threshold value, it further includes a determination unit that determines that an abnormality has occurred. An exhaust purification device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 7,
The second calculation means determines the S residual amount SZ in accordance with a fixed value S1 determined by the specifications of the catalytic converter on which the NOx catalyst is supported, the catalyst bed temperature of the NOx catalyst, and the air-fuel ratio of the exhaust. Which is calculated based on the updated variation value S2,
While the NOx catalyst is determined to be in a new state and the cumulative value of the S inflow amount SU is less than the fixed value S1, the apparatus further comprises prohibiting means for prohibiting execution of the S poison recovery control. An exhaust purification device for an internal combustion engine.

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