JP2009057851A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain a learning value calculated in temperature rise control from becoming an improper value as a value corresponding to a steady difference between the catalyst bed temperature and the target bed temperature due to progress of the deterioration in a catalyst. <P>SOLUTION: In the temperature rise control, the learning value K is calculated as the value corresponding to the steady difference between a catalyst bed temperature average value Tave and the target bed temperature Tt. A calculation of such a learning value K is permitted by the realization of a calculation permitting condition in the temperature rise control. Among the calculation permitting condition, on a condition related to an increase in the catalyst bed temperature average value Tave, when a deterioration degree of an NOx catalyst is large, the permitting condition is made severer than when the degree is small. Thus, when an increase in the catalyst bed temperature average value Tave becomes slow in the temperature rise control when the deterioration in the NOx catalyst advances, the calculation permitting condition is realized in the same timing as a deterioration not-so-much advancing state, and permission of the calculation of the learning value K is restrained before stabilizing the increasing catalyst bed temperature average value Tave. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  Conventionally, as an exhaust gas purification device applied to an internal combustion engine such as a vehicle-mounted diesel engine, a PM filter that collects particulates (PM) mainly containing soot and exhaust gas purification related to nitrogen oxide (NOx) are performed. 2. Description of the Related Art An exhaust system provided with a catalytic converter that supports an NOx storage reduction catalyst is known. In such an exhaust purification device, temperature increase control is performed to raise the temperature of the catalyst to a target bed temperature through the supply of unburned fuel components to the catalyst for the purpose of recovering the exhaust purification capability.

  For example, in the PM filter and the catalytic converter, clogging due to accumulation of fine particles occurs, so that the fine particles are burned (oxidized) to perform filter regeneration to eliminate the clogging. Control is implemented. In this temperature rise control, components such as hydrocarbons (HC) and carbon monoxide (CO) are oxidized in the exhaust or on the catalyst by supplying unburned fuel components to the catalyst, and accompanying the oxidation reaction. The catalyst bed temperature is raised to the target bed temperature by heat generation. As the catalyst bed temperature rises in this way, the particulates deposited when the PM filter and the catalytic converter are placed in a high temperature environment are removed, and the particulate collection ability of the PM filter is recovered.

  By the way, when the temperature increase control is executed, even if an attempt is made to raise the catalyst bed temperature to the target bed temperature by supplying the unburned fuel component to the catalyst, the catalyst bed temperature may not reach the target bed temperature. For example, when the fuel supply system for supplying the unburned fuel component to the catalyst is clogged, the supply amount of the unburned fuel component to the catalyst is deviated from an appropriate value and the deviation is reduced. It appears as a steady deviation between the catalyst bed temperature and the target bed temperature.

  In order to eliminate such a steady shift between the catalyst bed temperature and the target bed temperature, as shown in Patent Document 1, the steady shift between the two is based on the catalyst bed temperature and the target bed temperature during the temperature rise control. It is conceivable that a learned value is calculated as a corresponding value, and the learned value is reflected in the supply of the unburned fuel component to the catalyst in the temperature raising control. In this case, the supply amount of the unburned fuel component to the catalyst is corrected by the learning value, and the deviation from the appropriate value of the supply amount is suppressed. Therefore, the catalyst bed temperature and the target bed temperature during the temperature rise control The steady deviation between the two is suppressed.

The learning value is calculated when the calculation permission condition is satisfied, and is prohibited when the condition is not satisfied. Such calculation permission conditions include, for example, conditions related to an increase in the catalyst bed temperature. Incidentally, in Patent Document 1, the target bed temperature is increased stepwise during the temperature rise control, and as a condition related to the increase in the catalyst bed temperature, the target bed temperature becomes higher than before. The condition that the time required for the stabilization of the catalyst bed temperature that rises following the passage has been included. Therefore, the calculation of the learning value is prohibited during the period from when the target bed temperature becomes high until the above time elapses, and the calculation of the learning value is permitted under other circumstances. As a result, the learning value is calculated before the catalyst bed temperature rising toward the target bed temperature is stabilized, and the learned value is inappropriate as a value corresponding to a steady deviation between the target bed temperature and the catalyst bed temperature. It is made so that it will not become a bad value.
JP 2006-291827 A (paragraphs [0054], [0059], [0066], FIG. 9)

  By the way, since the reaction rate of the unburned fuel component in the catalyst decreases as the deterioration of the catalyst proceeds with respect to the new article, the increase in the catalyst bed temperature during temperature increase control tends to be gradually slowed down. . For this reason, in a state where the deterioration of the catalyst has progressed, the calculation permission condition (including the condition related to the increase of the catalyst bed temperature) during the rise of the catalyst bed temperature toward the target bed temperature in the temperature rise control Even if the calculation of the learning value is permitted, the catalyst bed temperature rising toward the target bed temperature is not stable at that time. In other words, this situation is a process in which the catalyst bed temperature is increasing at a large rate toward the target bed temperature, and is a situation before the catalyst bed temperature is stabilized. Therefore, when the learning value is calculated in such a situation, the learning value is calculated as a value corresponding to the difference between the target bed temperature and the catalyst bed temperature in the rising process. May be too large for a steady deviation between the catalyst bed temperature and the target bed temperature. When the learning value that is too large as the value corresponding to the steady deviation between the catalyst bed temperature and the target bed temperature is reflected in the supply of unburned fuel components to the catalyst in the temperature rise control, the catalyst The amount of unburned fuel component supplied to the catalyst may be excessive, leading to an excessive increase in the catalyst bed temperature.

  The present invention has been made in view of such circumstances, and its purpose is to obtain a learning value calculated during the temperature rise control due to the progress of catalyst deterioration between the catalyst bed temperature and the target bed temperature. An object of the present invention is to provide a control device for an internal combustion engine that can suppress an inappropriate value as a value corresponding to a steady deviation.

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, temperature increase control is performed to raise the temperature of the catalyst to the target bed temperature by supplying unburned fuel components to the catalyst provided in the exhaust system. A learning value is calculated as a value corresponding to the difference between the catalyst bed temperature and the target bed temperature when the calculation permission condition is satisfied during temperature control, and the learning value is prohibited when the calculation permission condition is not satisfied. In the control device for an internal combustion engine that reflects the calculated learned value in the supply of the unburned fuel component to the catalyst, when the deterioration determination means for determining the degree of deterioration of the catalyst and the degree of deterioration of the catalyst are large, Compared with a case where the degree of deterioration is small, a condition variable means for making the condition variable is provided so that a condition related to the increase in the catalyst bed temperature among the calculation permission conditions becomes stricter.

  According to the above configuration, in other words, when the catalyst bed temperature rises toward the target bed temperature when the catalyst bed temperature rises slowly during the temperature rise control due to deterioration of the catalyst, the catalyst bed temperature is not stable. For example, in a situation where the catalyst bed temperature is not stabilized, the calculation permission condition is prevented from being satisfied and the learning value is not permitted to be calculated. This is because when the degree of deterioration of the catalyst is large, conditions related to the increase in the catalyst bed temperature are made stricter among the calculation permission conditions than when the degree of deterioration is small. Therefore, by calculating the learning value under the above-described situation, it is suppressed that the learning value becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature. It becomes like this. On the other hand, after the conditions are tightened as described above, the calculation permission condition is established under the condition that the catalyst bed temperature rising toward the target bed temperature is stable, and the calculation of the learning value is permitted based on the condition. Then, the learning value is calculated. The learning value calculated at this time is an appropriate value as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature.

  In the invention of claim 2, in the invention of claim 1, the calculation permission condition is that the catalyst bed temperature is equal to or higher than a determination temperature that is lower than the target bed temperature, and the rate of increase of the catalyst bed temperature. Including a condition that the elapsed time from the time point when the value becomes equal to or lower than a predetermined determination speed is equal to or greater than the stability determination time, and the condition variable means has the same deterioration when the deterioration degree of the catalyst is large. The gist is that the stability determination time is set to a longer value than when the degree is small.

  According to the above configuration, as a condition related to the increase in the catalyst bed temperature among the calculation permission conditions, the catalyst bed temperature is equal to or higher than the determination temperature that is lower than the target bed temperature, and the rate of increase in the catalyst bed temperature is The condition that the elapsed time from when the speed becomes equal to or lower than a predetermined determination speed is equal to or longer than the stability determination time is employed. In this case, by setting the stability determination time to a long value, a condition related to the increase in the catalyst bed temperature among the calculation permission conditions becomes strict, and the establishment of the calculation permission condition is delayed and the learning value is calculated. The timing at which is permitted is also delayed. Therefore, when catalyst deterioration progresses and the rise in catalyst bed temperature during temperature rise control becomes slow, the catalyst bed temperature that rises toward the target bed temperature is not stable. Under the condition before the temperature stabilizes, the calculation permission condition is satisfied and the learning value is not permitted to be calculated. For this reason, by calculating the learning value under the above-described situation, it becomes possible to prevent the learning value from becoming inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature. . On the other hand, after the conditions are tightened as described above, when the calculation permission condition is satisfied and the learning value is permitted to be calculated, the catalyst bed temperature rising toward the target bed temperature is stable, The learning value is calculated under the circumstances. The learning value calculated at this time is an appropriate value as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature.

  In the invention of claim 3, in the invention of claim 2, the condition variable means makes the stability determination time a longer value as the degree of deterioration of the catalyst increases, and regarding the stability determination time, The initial value is a length value suitable when the catalyst is new, and the maximum value is an appropriate value as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature. The gist is to set the value of the length to obtain the calculation frequency of the same learning value necessary for maintaining the above.

  The longer the stability determination time is, the more severe the conditions related to the rise in the catalyst bed temperature among the calculation permission conditions, the later the establishment of the calculation permission conditions is delayed, and the timing at which the calculation of the learning value is permitted. It will be late. When the catalyst bed temperature rises toward the target bed temperature during temperature increase control, if the learning value is allowed to be calculated for the rise too early, the calculated learning value will be the catalyst bed temperature and the target bed temperature. As a value corresponding to a steady deviation from Further, if the learning value calculation is permitted too late for the catalyst bed temperature to rise, the learning value calculation frequency holds the learning value at an appropriate value as a value corresponding to the steady deviation. It may be too small.

  According to the above configuration, when the catalyst is new and the stability determination time becomes the initial value, the initial value is set to a value that is suitable for when the catalyst is new. The conditions associated with increased bed temperature are not too loose or too severe. Therefore, the calculated learning value does not become too early or too late when the calculation permission condition is satisfied and the learning value is permitted to be calculated, and the calculated learning value is a steady deviation between the catalyst bed temperature and the target bed temperature. It can be suppressed that the value becomes inappropriate as a corresponding value, and that the learning value calculation frequency becomes too small to hold the learning value as an appropriate value as a value corresponding to the steady deviation.

  Then, as the deterioration of the catalyst proceeds, the stability determination time is lengthened, and the same time is continued to be increased according to the progress of the degree of deterioration of the catalyst until the stability determination time reaches the maximum value. It should be noted that the maximum value is set to a length value at which the learning value is obtained as an appropriate value as a value corresponding to the steady deviation, and is necessary to obtain the same learning value calculation frequency. Thus, by making the stability determination time variable according to the degree of deterioration of the catalyst, the calculated learning value becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature. While appropriately suppressing, increase the learning value calculation frequency as much as possible, and keep the learning value calculation frequency necessary to keep the learning value as a value corresponding to the steady deviation. Can be secured.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the calculation permission condition is a condition that an exhaust temperature of the internal combustion engine is equal to or higher than a predetermined minimum temperature. The condition variable means is characterized in that when the degree of deterioration of the catalyst is large, the minimum temperature is set to a higher value than when the degree of deterioration is small.

  Between the exhaust temperature of the internal combustion engine and the catalyst bed temperature during the temperature rise control, the lower the exhaust temperature of the engine, in other words, the lower the temperature of the exhaust gas passing through the catalyst, the lower the catalyst bed temperature in the temperature rise control. There is a relationship that the rising speed of the slow.

  According to the above configuration, the condition that the exhaust temperature of the internal combustion engine is equal to or higher than a predetermined minimum temperature is adopted as a condition related to the increase in the catalyst bed temperature among the calculation permission conditions. In this case, since the minimum temperature is set to a high value, the conditions related to the increase in the catalyst bed temperature among the calculation permission conditions are stricter, and the situation where the exhaust gas temperature is higher, in other words, the increase in the catalyst bed temperature is increased. The calculation permission condition is satisfied only under a situation where the speed is more easily secured. Therefore, when the catalyst deterioration progresses and the increase in the catalyst bed temperature during the temperature increase control is delayed, the minimum temperature is set to a higher value, so that the rate of increase in the catalyst bed temperature is more easily secured. The calculation permission condition is only satisfied under the circumstances. If the minimum temperature is not set to a high value, the catalyst bed temperature rising toward the target bed temperature is not stable due to a delay in the rise of the catalyst bed temperature due to catalyst deterioration. In other words, under the situation before the catalyst bed temperature is stabilized, the calculation permission condition is satisfied and the calculation of the learning value is permitted. As a result, the calculated learning value becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature. However, since the minimum temperature is set to a high value as described above, the calculation permission condition is not satisfied under such circumstances, and the calculated learning value is a value corresponding to the steady deviation. Occurrence of the above-described problem of inappropriateness is suppressed.

  On the other hand, after the conditions are tightened as described above, when the calculation permission condition is satisfied and the calculation of the learning value is permitted, the exhaust temperature of the internal combustion engine is high (it is easy to ensure the rate of increase of the catalyst bed temperature). Therefore, the catalyst bed temperature rising toward the target bed temperature is stable. Since the learning value is calculated under the circumstances, the calculated learning value is an appropriate value as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature.

  According to a fifth aspect of the present invention, in the fourth aspect of the invention, the condition varying means sets the minimum temperature to a higher value as the exhaust temperature of the internal combustion engine increases, and the minimum temperature is an initial value. Is a height value suitable for a new catalyst, and the maximum value is held at an appropriate value as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature. The gist is that it is set to a height value at which the necessary calculation frequency of the learning value is obtained.

  The higher the minimum temperature, the more severe the conditions related to the increase in the catalyst bed temperature among the calculation permission conditions, and the calculation permission conditions are less likely to be satisfied, and the calculation of the learning value is less permitted. Become. Here, if the minimum temperature is too low, if the catalyst is in a state of advanced deterioration, the deterioration of the catalyst bed temperature will be delayed due to the deterioration, and it will be difficult to secure the rate of increase of the catalyst bed temperature. Value calculation is allowed. As a result, the learning value is calculated under the condition that the catalyst bed temperature rising toward the target bed temperature is not stable, in other words, the situation before the catalyst bed temperature is stabilized, and the learning value is calculated. Becomes an inappropriate value as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature. Also, if the minimum temperature is too high, the calculation permission condition is not easily satisfied, and the learning value calculation frequency is small to maintain the learning value at an appropriate value as a value corresponding to the steady deviation. There is a risk of becoming too much.

  According to the above configuration, when the catalyst is new and the minimum temperature is the initial value, the initial value is set to a value suitable for when the catalyst is new. Conditions associated with elevated temperatures are never too loose or too severe. Therefore, the calculation permission condition including the above-described condition related to the exhaust temperature of the internal combustion engine is not easily established or difficult to establish. For this reason, the calculated learning value becomes inappropriate as a value corresponding to the steady deviation between the catalyst bed temperature and the target bed temperature, and the learning value calculation frequency is different from the steady deviation. It can be suppressed that the value corresponding to the value becomes too small in maintaining an appropriate value.

  The minimum temperature is increased as the catalyst deteriorates, and the minimum temperature is continuously increased according to the progress of the degree of deterioration of the catalyst until the minimum temperature reaches the maximum value. It should be noted that the maximum value is set to a height value at which the learning value is obtained as an appropriate value as a value corresponding to the steady deviation, and a necessary calculation frequency of the learning value is obtained. Thus, by making the minimum temperature variable according to the degree of deterioration of the catalyst, it is ensured that the calculated learning value becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature and the target bed temperature. The learning value calculation frequency is increased as much as possible, and the same learning value calculation frequency necessary to keep the learning value as an appropriate value corresponding to the steady deviation is secured. can do.

[First Embodiment]
A first embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 shows a configuration of an internal combustion engine 10 to which the control device of the present embodiment is applied. The internal combustion engine 10 is a diesel engine for automobiles 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 for detecting the air-fuel ratio based on the oxygen concentration in the exhaust gas are provided upstream of the NOx catalytic converter 25 in the exhaust passage 14 and between the PM filter 26 and the oxidation catalytic converter 27. , 32 are respectively arranged.

  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, in order to prevent clogging due to PM in the NOx catalytic converter 25 and the PM filter 26, PM accumulated in the exhaust system such as the NOx catalytic converter 25 and the PM filter 26 is burned ( Filter regeneration is performed by oxidizing and purifying. In order to perform such filter regeneration, it is necessary to sufficiently raise the temperature of the NOx catalytic converter 25 and the PM filter 26. For this reason, when filter regeneration is performed, the unburnt fuel component is supplied to the NOx catalyst of the NOx catalytic converter 25 and the PM filter 26, so that the catalyst bed temperature is a value necessary for the combustion of the PM (for example, 600 to 700 ° C.). The temperature raising control is performed to raise the temperature to. Note that the supply of the unburned fuel component to the catalyst in the temperature rise control is performed by adding fuel to the exhaust from the addition valve 46 or the like.

Incidentally, in the present embodiment, the temperature increase control for filter regeneration is started when all of the following conditions are satisfied.
-When filter regeneration is requested. The filter regeneration request here is made when the PM accumulation amount in the exhaust system estimated from the engine operating state exceeds an allowable value, and it is confirmed that clogging occurs in the PM filter 26 and the like.

  -The detection value (input gas temperature thci) of the said input gas temperature sensor 28 is more than the minimum temperature (for example, 150 degreeC) of temperature rise control implementation. Further, the catalyst bed temperature of 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 is equal to or higher than the lower limit temperature of the temperature increase control. 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 C of the temperature range in which the catalyst can be prevented from being overheated due to heat generation accompanying the temperature rise control.
The detection value of the outgas temperature sensor 29 is less than the upper limit value D of the temperature range that can avoid the excessive temperature rise of the catalyst due to the heat generation accompanying the temperature rise control.

  ・ Addition of fuel to the exhaust is permitted. In other words, the engine is in an operating state in which exhaust fuel addition can be allowed. In this internal combustion engine 10, addition of exhaust fuel is permitted if the cylinder discrimination is completed and the output is not limited when the engine is not stalling.

  When the PM regeneration amount is reduced to a predetermined value (for example, “0”) by executing the filter regeneration through the temperature increase control, it is determined that the filter regeneration is completed, and the temperature increase control for the filter regeneration is completed. Be made.

Next, an outline of the temperature rise control will be described with reference to the time chart of FIG.
The catalyst bed temperature T during the temperature rise control is a value that is increased by the amount of heat generated by the oxidation reaction based on the fuel addition from the addition valve 46 with respect to the catalyst inlet exhaust temperature Tb that is the exhaust temperature upstream of the NOx catalytic converter 25. It will be. In the temperature increase control, the target bed temperature Tt of the catalyst is increased stepwise such as 605, 630, 650, and 670 ° C., and the addition valve is set so that the catalyst bed temperature T increases toward the target bed temperature Tt. The unburned fuel component is supplied to the catalyst through the fuel addition from 46. However, when the exhaust temperature of the internal combustion engine 10 is low and the exhaust flow rate is small, the oxidation reaction of the unburned fuel component does not proceed even if the fuel addition from the addition valve 46 is increased, and the catalyst bed temperature T may be raised. Therefore, the target bed temperature Tt may be temporarily lowered to prevent unnecessary fuel addition from the addition valve 46.

  Fuel addition from the addition valve 46 is started based on a change (timing T1) of the addition permission flag F1 to “1 (permitted)” shown in FIG. The addition permission flag F1 is set to “0” after being set to “1”. When fuel addition from the addition valve 46 is started, 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 intermittent fuel addition are the temperature difference ΔTb between the target bed temperature Tt and the catalyst inlet exhaust temperature Tb and the internal combustion engine detected by the air flow meter 16. 10 gas flow rate Ga (corresponding to the exhaust flow rate of the internal combustion engine 10). As the catalyst inlet exhaust temperature Tb, for example, a value estimated based on detection values of the inlet gas temperature sensor 28 and the outlet gas temperature sensor 29 can be used. The 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 fuel addition is performed for 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 this 16 ms exothermic fuel amount Q based on the equation “ΣQ ← previous ΣQ + Q (1)” for each calculation, the total addition amount from the addition valve 46 from the fuel addition start time (T1), in other words, For example, an exothermic fuel amount integrated value ΣQ representing the total fuel amount contributing to the heat generation due to the oxidation reaction is calculated. The exothermic fuel amount integrated value ΣQ calculated in this way increases rapidly during 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 reaches the target bed temperature Tt. A required fuel amount Qr of 16 ms, which is the amount of fuel added necessary for the control, is calculated. This 16 ms required fuel amount Qr is calculated using the temperature difference ΔTb between the target bed temperature Tt and the catalyst inlet exhaust temperature Tb and the gas flow rate Ga of the internal combustion engine 10. The calculated 16 ms required fuel amount Qr increases as the catalyst inlet exhaust temperature Tb indicated by the solid line L2 in FIG. 2B is lower 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 (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 calculated required fuel amount integrated value ΣQr increases gradually 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 F1 changes to “1 (permission)”, and intermittent fuel addition from the addition valve 46 is performed. Be started. At this time, since the addition of the fuel for the heat generation fuel amount integrated value ΣQ after the timing T1 has been completed from the addition valve 46, the heat generation fuel amount integration value ΣQ is subtracted from the required fuel amount integration value ΣQr. Furthermore, the exothermic fuel amount integrated value ΣQ is cleared and becomes “0”. Then, along with the start of intermittent fuel addition from the addition valve 46, the process shifts again to the addition period A. When the addition period A ends, the process shifts to the pause period B. Therefore, the addition period A and the pause period B are repeated during the temperature rise control.

  During the temperature increase control, the 16 ms required fuel amount Qr is calculated to be larger as the catalyst inlet exhaust temperature Tb is further away from the target bed temperature Tt. The integrated value ΣQr 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 suspension period B is shortened. Further, the 16 ms required fuel amount Qr is calculated to be smaller as the catalyst inlet exhaust temperature Tb 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 be equal to or greater than the exothermic fuel amount integrated value ΣQ becomes longer, and the suspension period B becomes longer.

  As described above, by changing the length of the suspension period B according to the deviation state of the catalyst inlet exhaust temperature Tb from the target bed temperature Tt, the average amount of fuel added from the addition valve 46 per unit time is changed accordingly. The value changes. As a result, the catalyst bed temperature T changes, for example, as indicated by the solid line L1 in FIG. 2B, and the fluctuation center of the catalyst bed temperature T that increases or decreases is controlled to the target bed temperature Tt.

  Next, the fuel addition control procedure by the addition valve 46 during the temperature rise control will be described with reference to the flowcharts of FIGS. 3 and 4 showing the fuel addition control routine. This fuel addition control routine is periodically executed through the electronic control unit 50, for example, with a time interruption every predetermined time (in this embodiment, 16 ms).

  In this routine, it is first determined in step S101 in FIG. 3 whether or not the temperature raising control is being performed. If the determination is affirmative, the routine proceeds to step S102, where the 16 ms required fuel amount Qr is calculated based on the temperature difference ΔTb between the target bed temperature Tt and the catalyst inlet exhaust temperature Tb and the gas flow rate Ga. The subsequent processes in steps S103 and S104 are for correcting the 16 ms required fuel amount Qr by the learned value K for eliminating the steady deviation between the catalyst bed temperature T and the target bed temperature Tt.

  Specifically, as the process of step S103, the learning value K stored in the nonvolatile RAM of the electronic control device 50 is read. This learning value K is calculated as a value corresponding to a steady deviation between the catalyst bed temperature T and the target bed temperature Tt by another routine, and is stored in the nonvolatile RAM. In the process of step S104, a value obtained by multiplying the 16 ms required fuel amount Qr by the learning value K is set as a new 16 ms required fuel amount Qr.

  The 16 ms required fuel amount Qr calculated by the processing of steps S102 to S104 is accumulated based on the equation “ΣQr ← previous ΣQr + Qr (2)” in step S105. By this accumulation, the required fuel amount integrated value ΣQr described above can be obtained. Then, it progresses to step S106 of FIG.

  In the process of step S106, the 16 ms exothermic fuel amount Q is calculated based on the driving state of the addition valve 46. Subsequently, as the processing of step S107, the calculated 16 ms exothermic fuel amount Q is accumulated based on the formula “ΣQ ← previous ΣQ + Q (1)”. As a result of this accumulation, the above-mentioned heat generating fuel amount integrated value ΣQ can be obtained.

  In the process of step S108, it is determined whether or not the required fuel amount integrated value ΣQr is equal to or greater than the exothermic fuel amount integrated value ΣQ. If the determination is affirmative, the process proceeds to step S109, and the addition permission flag F1 is set to “1 (permitted)”. As a result, intermittent fuel addition from the addition valve 46 is started. Thereafter, as a process of step S110, a value obtained by subtracting the exothermic fuel amount integrated value ΣQ from the required fuel amount integrated value ΣQr is set as a new required fuel amount integrated value ΣQr. Furthermore, the heat generation fuel amount integrated value ΣQ is cleared and set to “0” in the process of step S111.

Next, an outline of a procedure for calculating the learning value K used in step S103 of FIG. 3 will be described with reference to FIGS.
FIG. 5 shows a state in which a steady shift occurs between the catalyst bed temperature T and the target bed temperature Tt during the temperature rise control, and the catalyst bed temperature T (solid line) does not rise to the target bed temperature Tt (broken line). ing. The reason why such a steady deviation occurs is, for example, a deviation from an appropriate value of the fuel addition amount due to an abnormality such as clogging of the addition valve 46, or a deviation from an appropriate value of the gas flow rate Ga due to an abnormality in the air flow meter 16. can give.

  The learning value K is calculated as a value corresponding to a steady deviation between the catalyst bed temperature T (catalyst bed temperature average value Tave) and the target bed temperature Tt, and is used to correct the 16 ms required fuel amount Qr. . When the 16 ms required fuel amount Qr is corrected using the learning value K, the increase in the required fuel amount integrated value ΣQr is accelerated or delayed, so that the required fuel amount integrated value ΣQr becomes greater than or equal to the exothermic fuel amount integrated value ΣQ. The timing that changes. As a result, the pause period B increases and decreases, and the average value of the amount of fuel added from the addition valve 46 per unit time changes. Thus, the learning value K is reflected in the supply of unburned fuel components to the catalyst.

  Here, when a steady shift between the catalyst bed temperature average value Tave and the target bed temperature Tt as shown in FIG. 5 occurs, the learning value K corresponding to the shift is used as an unburned fuel component for the catalyst. FIG. 6 and FIG. 7 show the difference between the case where it is not reflected and the case where it is reflected.

  The broken line in FIG. 6 shows the transition of the required fuel amount integrated value ΣQr when the learned value K is not reflected. In this case, the learning value K is not multiplied by the 16 ms required fuel amount Qr, and the 16 ms required fuel amount Qr includes a deviation from an appropriate value due to clogging of the addition valve 46 or an abnormality of the air flow meter 16. . As a result, the required fuel amount integrated value ΣQr gradually increases by the amount of deviation from the appropriate value of the 16 ms required fuel amount Qr, and the required fuel amount integrated value ΣQr becomes equal to or greater than the exothermic fuel amount integrated value ΣQ. Will be late. As described above, the pause period B becomes longer and the average value of the amount of fuel added from the addition valve 46 per unit time becomes smaller, and the catalyst bed temperature average value Tave and the target bed temperature Tt as shown in FIG. There will be a steady shift between the two.

  On the other hand, the broken line in FIG. 7 shows the transition of the required fuel amount integrated value ΣQr when the learned value K is reflected. In this case, the learning value K is multiplied by the 16 ms required fuel amount Qr, and the deviation from the appropriate value due to the clogging of the addition valve 46 or the abnormality of the air flow meter 16 is removed from the 16 ms required fuel amount Qr. As a result, the required fuel amount integrated value ΣQr does not gradually increase by the amount of deviation from the appropriate value of the 16 ms required fuel amount Qr, and increases more rapidly than the broken line in FIG. The timing at which becomes the heat generation fuel amount integrated value ΣQ or more is advanced. As described above, the pause period B is shortened, the average value of the amount of fuel added from the addition valve 46 per unit time is increased, the catalyst bed temperature average value Tave is increased, and the catalyst bed temperature average value Tave and the target bed are increased. The steady deviation from the temperature Tt is eliminated.

  FIG. 8 is a time chart showing how the learning value K changes when the steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt is eliminated. Now, as indicated by the broken line and the alternate long and short dash line in FIG. 8A, it is assumed that there is a steady deviation that the catalyst bed temperature average value Tave becomes a lower value with respect to the target bed temperature Tt.

The learning value K as a value corresponding to such a deviation is calculated using the 16 ms required fuel amount Qr (see FIG. 2C) and the 16 ms estimated heat generation fuel amount Q ′.
Here, the 16 ms estimated exothermic fuel amount Q ′ is calculated every 16 ms, and is obtained from the addition valve 46 during 16 ms in order to obtain the increase amount ΔT ′ of the catalyst bed temperature T from the catalyst inlet exhaust temperature Tb. This is an estimated value of the added fuel amount, in other words, an estimated value of the fuel amount that contributed to the heat generation in 16 ms for obtaining the increase amount ΔT ′. The 16 ms estimated exothermic fuel amount Q ′ is calculated based on the increase amount ΔT ′ that is the difference between the catalyst bed temperature T and the catalyst inlet exhaust temperature Tb, and the gas flow rate Ga. As the catalyst bed temperature T, for example, a value estimated based on detection values of the inlet gas temperature sensor 28 and the outlet gas temperature sensor 29 can be used. The 16 ms required fuel amount Qr represents the amount of fuel to be added from the addition valve 46 during 16 ms in order to raise the catalyst bed temperature T from the catalyst inlet exhaust temperature Tb to the target bed temperature Tt. As described above, it is calculated based on the temperature difference ΔTb between the bed temperature Tt and the catalyst inlet exhaust temperature Tb and the gas flow rate Ga.

  The ratio Qr / Q ′ between the 16 ms required fuel amount Qr and the 16 ms estimated exothermic fuel amount Q ′ is the catalyst bed relative to the target bed temperature Tt at the time of calculation of the 16 ms required fuel amount Qr and the 16 ms estimated exothermic fuel amount Q ′. The value corresponds to the temperature T shift. Therefore, by calculating an average value of the ratio Qr / Q 'over a predetermined period, the average value becomes a value corresponding to a steady deviation of the catalyst bed temperature average value Tave from the target bed temperature Tt. An average value of the ratio Qr / Q ′ over a predetermined period is calculated as a learned value K, and the learned value K is non-volatile based on the target bed temperature Tt being in a stable state at a value that allows PM combustion. Stored (updated) in RAM.

  If the learning value K is updated at the timings T4, T5, and T6 in the drawing, for example, the learning value K stored in the non-volatile RAM changes as shown in FIG. 8B. In addition, the pause period B in the temperature rise control is gradually shortened. As a result, the average value of the amount of fuel added from the addition valve 46 becomes large, and the catalyst bed temperature average value Tave rises to the target bed temperature Tt as shown in FIG. The gap is resolved.

  Next, a detailed procedure for calculating and updating the learning value K will be described with reference to a flowchart of FIG. 9 showing a learning value updating routine. This learning value update routine is periodically executed through the electronic control unit 50, for example, with a time interrupt every predetermined time (16 ms in the present embodiment).

  In this routine, first, it is determined whether or not the calculation of the learning value K is permitted (S201), that is, whether or not the calculation permission condition is satisfied. If a negative determination is made in step S201, calculation of the learning value K is prohibited (S206). If the determination is affirmative, the ratio Qr / Q ′ of both is obtained based on the 16 ms required fuel amount Qr and the 16 ms estimated heat generation fuel amount Q ′ calculated every 16 ms, and the ratio Qr / Q ′ is determined within a predetermined period. The average value is calculated as the learning value K (S202). When the calculation of the learning value K continues for a predetermined time or longer (S203: YES), and the target bed temperature Tt is in a stable state at a value not lower than the combustible value of PM (for example, 600 ° C. or higher) (S204: YES), the calculated learning value K is stored (updated) in a non-volatile RAM provided in the electronic control unit 50. Thus, the learning value K stored in the nonvolatile RAM is reflected in the fuel addition from the addition valve 46.

Here, the calculation permission conditions in step S201 related to permission and prohibition of calculation of the learning value K will be described in detail.
The determination as to whether or not the calculation permission condition is satisfied is made based on whether or not all of the following conditions (a) to (j) are satisfied, for example.

(A) Temperature rise control is being performed.
(B) The state where the gas flow rate Ga is low does not continue for a long time such as 50 s.
(C) Not immediately after the target bed temperature Tt becomes higher than before.

(D) Immediately after updating the learning value K, in other words, not immediately after reflecting the new learning value K on the fuel addition.
(E) The target bed temperature Tt does not continue to decrease, for example, the target bed temperature Tt continues to decrease for less than 15 seconds.

(F) The fuel addition from the addition valve 46 is not prohibited. The fuel addition is prohibited, for example, when the catalyst bed temperature T is excessively increased.
(G) The inlet gas temperature sensor 28 and the outlet gas temperature sensor 29 are not abnormal.

  (I) Determination that the catalyst bed temperature T is equal to or higher than a determination temperature (for example, 600 ° C.) that is lower than the target bed temperature Tt, and the rate of increase of the catalyst bed temperature T (catalyst bed temperature average value Tave) is determined in advance. The elapsed time after the speed falls below the stability judgment time. Here, the stability determination time is because the catalyst bed temperature average value Tave, which rises toward the target bed temperature Tt during the temperature rise control, is in a state suitable for stably calculating the learning value K. It is the time required.

  (J) The exhaust temperature of the internal combustion engine 10 (catalyst inlet exhaust temperature Tb) is equal to or higher than the minimum temperature. Note that the catalyst inlet exhaust temperature Tb decreases between the catalyst inlet exhaust temperature Tb and the catalyst bed temperature average value Tave, in other words, the NOx catalyst carried on the PM filter 26 and the NOx catalyst converter 25 passes. There is a relationship that as the temperature of the exhaust gas becomes lower, the rate of increase of the catalyst bed temperature average value Tave in the temperature rise control becomes slower. The minimum temperature is an exhaust temperature at which the rising speed of the catalyst bed temperature average value Tave in the temperature rise control can be set to a minimum level necessary for calculating the learning value K.

  If any one of the above conditions (a) to (i) is not satisfied, it is determined that the calculation permission condition is not satisfied and the calculation of the learning value K is prohibited. If all the conditions (a) to (i) are satisfied, it is determined that the calculation permission condition is satisfied, and the calculation of the learning value K is permitted. Of the above conditions (a) to (i), (i) and (j) are conditions related to an increase in the catalyst bed temperature T (catalyst bed temperature average value Tave). This means that the calculation permission condition includes a condition related to an increase in the average catalyst bed temperature value Tave.

  By the way, the NOx catalyst gradually deteriorates as it is used, and the deterioration affects the increase of the catalyst bed temperature average value Tave during the temperature rise control. That is, with respect to the NOx catalyst, as the deterioration progresses with respect to the new one, the increase in the catalyst bed temperature average value Tave during the temperature increase control tends to be gradually delayed. Here, FIG. 10 shows the transition of the catalyst bed temperature average value Tave during the temperature increase control between the state in which the deterioration of the NOx catalyst has not progressed so much and the state in which the deterioration has advanced.

  As can be seen from the figure, after the temperature increase control for filter regeneration is started, for example, when the calculation permission condition is satisfied at timing Tk1, calculation of the learning value K is permitted and calculation of the learning value K is performed. Will come to be. In a state where the deterioration of the NOx catalyst has not progressed so much, the catalyst bed temperature average value Tave quickly rises toward the target bed temperature Tt as shown by the solid line L3 in the figure by the temperature rise control. For this reason, the catalyst bed temperature average value Tave rising toward the target bed temperature Tt is stable at the timing Tk1, and the calculated learning value K is a steady state between the catalyst bed temperature average value Tave and the target bed temperature Tt. It becomes an appropriate value as a value corresponding to the shift.

  On the other hand, in a state in which the deterioration of the NOx catalyst has advanced, the catalyst bed temperature average value Tave rises gradually toward the target bed temperature Tt only as shown by the solid line L4 in the figure by the temperature rise control. For this reason, the catalyst bed temperature average value Tave rising toward the target bed temperature Tt is not stable at the timing Tk1, in other words, the catalyst bed temperature average value Tave increases at a large rate toward the target bed temperature Tt. This is the situation before the catalyst bed temperature average value Tave is stabilized. Therefore, when the learning value K is calculated at the timing Tk1, the learning value K is calculated as a value corresponding to the difference between the target bed temperature Tt and the catalyst bed temperature average value Tave in the rising process. The learning value K may be too large for the steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. When the learning value K that is too large is reflected in the supply of the unburned fuel component to the NOx catalyst in the temperature raising control, the supply amount of the unburned fuel component to the NOx catalyst becomes excessive, and the catalyst bed temperature T There is also a risk of over-rising.

  Therefore, in the present embodiment, the degree of deterioration of the NOx catalyst is determined. When the degree of deterioration is large, a condition related to the increase in the average catalyst bed temperature Tave among the calculation permission conditions is compared with when the degree of deterioration is small. The condition is made variable so that becomes more severe.

  As a result, when the deterioration of the NOx catalyst progresses and the increase in the catalyst bed temperature average value Tave during the temperature increase control becomes slow as indicated by the solid line L4, the calculation permission condition is satisfied at the timing Tk1, and the learning value K It is suppressed that calculation is permitted. In other words, the calculation is permitted under the condition that the catalyst bed temperature average value Tave rising toward the target bed temperature Tt is not stable, in other words, before the catalyst bed temperature average value Tave is stable. It is suppressed that the calculation of the learning value K is permitted when the condition is satisfied. Therefore, when the learning value is calculated under the above-described situation, the learning value K becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. It will be suppressed.

  On the other hand, after the conditions are tightened as described above, the calculation permission condition is established under the condition that the catalyst bed temperature average value Tave rising toward the target bed temperature Tt is stable, and the learning value K And the learning value K is calculated. The learning value K calculated at this time is an appropriate value as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt.

  Incidentally, in the present embodiment, the above condition (i) is adopted as the above condition that becomes strict when the degree of deterioration of the NOx catalyst becomes large. Hereinafter, a specific example of tightening this condition will be described with reference to FIGS. FIG. 11 shows the transition of the catalyst bed temperature average value Tave during the temperature increase control in a state where the deterioration of the NOx catalyst has not progressed, and FIG. 12 shows the temperature increase control during the temperature increase control with the deterioration of the NOx catalyst advanced. It shows the transition of the catalyst bed temperature average value Tave.

  As shown in FIG. 11, when the catalyst bed temperature T becomes equal to or higher than the determination temperature and the rising speed of the catalyst bed temperature average value Tave becomes lower than the determination speed during the temperature increase control (timing Ts), the time is measured from that point. Is started. When the elapsed time from the timing Ts reaches the stability determination time (t1 in the example in this figure) (timing Te), it is determined that the condition (i) is satisfied. In a state in which the deterioration of the NOx catalyst has not progressed, the rise in the catalyst bed temperature average value Tave during the temperature rise control does not slow down, so the catalyst bed temperature average value that rises toward the target bed temperature Tt at the timing Te. Tave is stable. That is, the stability determination time (t1) is set so as to achieve such a situation at the timing Te. Therefore, when the calculation permission condition is satisfied based on the condition (i) being satisfied at the timing Te, the learning value K calculated based on the condition is constant between the catalyst bed temperature average value Tave and the target bed temperature Tt. It becomes an appropriate value as a value corresponding to the deviation.

  On the other hand, in a state in which the deterioration of the NOx catalyst has progressed, the increase in the catalyst bed temperature average value Tave during the temperature increase control is delayed as shown in FIG. Therefore, during the temperature increase control, the elapsed time from when the catalyst bed temperature T becomes equal to or higher than the determination temperature and the rising speed of the catalyst bed temperature average value Tave becomes equal to or lower than the determination speed, that is, the elapsed time from the timing Ts is “t1”. It is highly possible that the catalyst bed temperature average value Tave that increases toward the target bed temperature Tt is not yet stable at the time point (Te). In this way, when the calculation permission condition is satisfied and the learning value K is calculated under the situation before the catalyst bed temperature average value Tave is stabilized, the learning value K becomes the catalyst bed temperature T and the target bed temperature Tt. There is a risk that the value will be too large for the steady deviation of. In order to cope with such a problem, when the degree of deterioration of the NOx catalyst is large, the stability determination time under the condition (i) is increased compared to when the degree of deterioration is small (t2 in this example).

  By increasing the stability determination time in this manner, the above condition (i) becomes stricter, and the establishment of the same condition, and hence the establishment of the calculation permission condition, is delayed, for example, from the timing Ter, and the timing at which the learning value K is calculated is also increased. Become slow. Therefore, when calculation of the learning value K is permitted and calculation of the learning value K is performed (Ter), the catalyst bed temperature average value Tave rising toward the target bed temperature Tt becomes stable. That is, the stability determination time (t2) is set so as to achieve such a situation at the timing Ter. As a result, the calculated learning value K is suppressed from being too large with respect to the steady deviation between the catalyst bed temperature T and the target bed temperature Tt, and is a value corresponding to the steady deviation. Appropriate value.

  Next, a procedure for increasing the stability determination time under the above condition (i) to make the condition stricter will be described with reference to a flowchart of FIG. 13 showing a condition variable routine. This condition variable routine is periodically executed through the electronic control unit 50, for example, with a time interrupt at predetermined time intervals.

  In this routine, first, the degree of deterioration of the NOx catalyst is determined (S301). The degree of deterioration of the NOx catalyst is the cumulative value of the catalyst bed temperature T from the time when the vehicle is delivered (when the NOx catalyst is new) and the catalyst bed temperature T from when the NOx catalyst is new during the engine operation. Since ΣT increases as it increases, the degree of deterioration of the NOx catalyst is obtained in step S301 with reference to a map or the like based on these parameters. As shown in FIG. 14, the degree of deterioration of the NOx catalyst obtained in this way increases as the travel distance increases, and increases as the cumulative value ΣT increases.

  The map used when determining the degree of deterioration of the NOx catalyst defines the relationship between the travel distance and the cumulative value ΣT and the degree of deterioration of the NOx catalyst, and is set in the following procedure. That is, the relationship between the travel distance and the cumulative value ΣT and the purification rate of the NOx catalyst is obtained by experiments or the like. FIG. 15 shows the relationship between the travel distance thus obtained and the purification rate of the NOx catalyst. Then, the relationship between the travel distance and the cumulative value ΣT and the degree of deterioration of the NOx catalyst is obtained from the relationship between the travel distance and the cumulative value ΣT obtained through experiments or the like and the purification rate of the NOx catalyst. The map is set based on the relationship.

  In the condition variable routine of FIG. 13, after determining the deterioration degree of the NOx catalyst in step S102, the stability determination time under the condition (i) is made variable based on the deterioration degree (S102). That is, the greater the degree of deterioration of the NOx catalyst, the longer the stability determination time under the above condition (i). Thus, when the degree of deterioration of the NOx catalyst is large, the stability determination time under the condition (i) is set to a longer value than when the degree of deterioration is small.

  Here, with respect to the stability determination time, the longer the calculation permission condition (i), the more severe the calculation permission condition, the later the establishment of the calculation permission condition is delayed, and the learning value calculation is permitted. Will be late. When the catalyst bed temperature average value Tave rises toward the target bed temperature Tt during the temperature increase control, if the learning value K is allowed to be calculated too early with respect to the rise, the calculated learned value K becomes the catalyst. It becomes an inappropriate value as a value corresponding to a steady deviation between the bed temperature average value Tave and the target bed temperature Tt. Further, if the timing at which the learning value K is permitted to be calculated with respect to the increase in the catalyst bed temperature average value Tave is too late, the calculation frequency of the learning value K sets the learning value K as a value corresponding to the steady deviation. It may be too small to keep it at an appropriate value.

  In consideration of this, with respect to the above-described determination determination time that is variable in step S102, the initial value is a value that is suitable for a new NOx catalyst, and the maximum value is the learning value K that is the catalyst bed temperature average. The value is set to a length value at which the calculation frequency of the learning value K necessary for maintaining an appropriate value as a value corresponding to a steady deviation between the value Tave and the target bed temperature Tt is obtained.

  As a result, when the NOx catalyst is new and the stability determination time becomes the initial value, the initial value is set to a value suitable for the new NOx catalyst. The conditions are not too loose or too strict. Therefore, the timing at which the calculation permission condition is satisfied and the calculation of the learning value K is permitted is neither too early nor too late. For this reason, the calculated learning value K becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt, and the calculation value of the learning value K is the same learning value. It is possible to prevent K from becoming too small in maintaining an appropriate value as a value corresponding to the steady deviation.

  Then, as the deterioration of the NOx catalyst proceeds, the stability determination time is lengthened. Until the stability determination time reaches the maximum value, the same time is continuously lengthened according to the progress of the degree of deterioration of the NOx catalyst. Note that the maximum value is set to a length value that can be used to obtain a calculation frequency of the learning value necessary to hold the learning value as an appropriate value corresponding to the steady deviation. As described above. By making the stability determination time variable in this way, it is accurately determined that the calculated learned value K becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. While suppressing, increase the calculation frequency of the learning value K as much as possible, and secure the calculation frequency of the learning value K necessary to hold the learning value K at a value corresponding to the steady deviation. Can do.

According to the embodiment described in detail above, the following effects can be obtained.
(1) During the temperature rise control, the learning value K is calculated as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. Such calculation of the learning value K is permitted when a calculation permission condition is satisfied during the temperature rise control. Among the calculation permission conditions, the condition relating to the increase in the average catalyst bed temperature value Tave, that is, the condition (i), is greater when the degree of deterioration of the NOx catalyst is larger than when the degree of deterioration is small. Be strict. Specifically, the stability determination time under the above condition (i) is set to a longer value than when the degree of deterioration of the NOx catalyst is small. By increasing the stability determination time in this manner, the condition (i) becomes stricter, and the establishment of the same condition, and hence the establishment of the calculation permission condition is delayed, and the timing at which the learning value K is calculated is also delayed. Accordingly, when the deterioration of the NOx catalyst is advanced and the increase in the catalyst bed temperature average value Tave in the temperature rise control is delayed, the calculation of the learning value K is permitted and the learning value K is calculated. Then, the catalyst bed temperature average value Tave rising toward the target bed temperature Tt becomes stable. As a result, the calculated learning value K is suppressed from being too large with respect to the steady deviation between the catalyst bed temperature T and the target bed temperature Tt, and is a value corresponding to the steady deviation. Appropriate value.

  (2) The change of the stability determination time under the condition (i) according to the degree of deterioration of the NOx catalyst is specifically performed as follows. That is, the greater the degree of deterioration of the NOx catalyst, the longer the stability determination time becomes. The initial value of the stability determination time that is variable is set to a value that is suitable for a new NOx catalyst. The maximum value of the stability determination time is necessary to maintain the calculated learned value K at an appropriate value as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. The learning value K is set to a length value that provides the calculation frequency. As described above, by making the stability determination time variable, it is accurately determined that the calculated learned value K becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. The learning value calculation frequency is increased as much as possible, and the learning value K necessary for maintaining the learning value K at a value corresponding to the steady deviation is ensured. Can do.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS.
Also in this embodiment, the degree of deterioration of the NOx catalyst is determined, and when the degree of deterioration is large, among the calculation permission conditions, the condition related to the increase in the catalyst bed temperature average value Tave is compared to when the degree of deterioration is small. The conditions are made variable so as to be severe. However, the condition (j) is adopted instead of the condition (i) as in the first embodiment as the condition that becomes strict when the degree of deterioration of the NOx catalyst becomes large. Hereinafter, a specific example of tightening this condition will be described with reference to FIGS. FIG. 16 shows the transition of the catalyst bed temperature average value Tave during the temperature rise control in a state where the NOx catalyst has not deteriorated, and FIG. 17 shows the temperature rise control in the state where the NOx catalyst has deteriorated. It shows the transition of the catalyst bed temperature average value Tave.

  In FIG. 16, when the calculation permission condition (including the condition (j) above) is satisfied during the temperature rise control (timing Tk2), the calculation of the learning value K is permitted and the learning value K is calculated. Become. In a state in which the deterioration of the NOx catalyst has not progressed so much, the catalyst bed temperature average value Tave during the temperature rise control quickly rises toward the target bed temperature Tt. Therefore, at the timing Tk2, the catalyst bed temperature average value Tave rising toward the target bed temperature Tt is in a stable state, and the calculated learning value K is a steady state between the catalyst bed temperature average value Tave and the target bed temperature Tt. It becomes an appropriate value as a value corresponding to the shift.

  On the other hand, in a state in which the deterioration of the NOx catalyst has progressed, the catalyst bed temperature average value Tave during the temperature rise control increases only gradually toward the target bed temperature Tt as shown in FIG. For this reason, the catalyst bed temperature average value Tave that increases toward the target bed temperature Tt is not stable at the timing Tk2, in other words, the process in which the catalyst bed temperature T increases at a large speed toward the target bed temperature Tt. Therefore, this is a situation before the catalyst bed temperature T is stabilized. Therefore, when the learning value K is calculated at the timing Tk2, the learning value K is calculated as a value corresponding to the difference between the target bed temperature Tt and the catalyst bed temperature T in the rising process. There is a possibility that the value K is too large for the steady deviation between the catalyst bed temperature T and the target bed temperature Tt.

  In order to deal with such problems, when the degree of deterioration of the NOx catalyst is large, the minimum temperature of the exhaust temperature (catalyst inlet exhaust temperature Tb) of the internal combustion engine 10 under the condition (j) is higher than when the degree of deterioration is small. Is raised.

  Here, between the catalyst inlet exhaust temperature Tb and the catalyst bed temperature average value Tave during the temperature increase control, the lower the catalyst inlet exhaust temperature Tb, in other words, the lower the temperature of the exhaust gas passing through the NOx catalyst, the higher the temperature. There is a relationship that the rate of increase of the catalyst bed temperature average value Tave in the temperature control becomes slow.

  Therefore, by increasing the minimum temperature, the condition (i) is made stricter, and the situation where the catalyst inlet exhaust temperature Tb is higher, in other words, the rate of increase of the catalyst bed temperature average value Tave is more easily secured. The calculation permission condition is satisfied only under the condition. Accordingly, when the deterioration of the NOx catalyst progresses and the increase in the catalyst bed temperature average value Tave during the temperature increase control becomes slow, the minimum temperature is set to a higher value, thereby increasing the catalyst bed temperature average value Tave. However, the calculation permission condition can be satisfied only under a situation where it is easier to ensure, for example, a situation where the transition of the catalyst bed temperature average value Tave indicated by the solid line in FIG.

  If the minimum temperature is not set to a high value, a catalyst that rises toward the target bed temperature Tt due to a delay in the rise of the catalyst bed temperature average value Tave indicated by a solid line in FIG. 17 due to deterioration of the NOx catalyst. Under conditions where the bed temperature average value Tave is not stable, in other words, under conditions before the catalyst bed temperature average value Tave is stabilized, the calculation permission condition is satisfied and the calculation of the learning value K is permitted. . As a result, the calculated learned value K becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. However, since the minimum temperature is set to a high value as described above, the calculation permission condition is not satisfied under such a situation, and the calculated learning value K is a value corresponding to the steady deviation. As a result, the occurrence of the above-described inconvenience that the value becomes too large is suppressed.

  On the other hand, after the conditions are tightened as described above, when the calculation permission condition is satisfied and the learning value K is permitted to be calculated, the catalyst inlet exhaust temperature Tb is high (the rate of increase of the catalyst bed temperature average value Tave is ensured). Therefore, the catalyst bed temperature average value Tave rising toward the target bed temperature Tt is stable. Since the learning value K is calculated under the circumstances, the calculated learning value K is an appropriate value as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. It becomes.

  Next, a procedure for increasing the minimum temperature under the above condition (j) and tightening the condition will be described with reference to the flowchart of FIG. 18 showing a condition variable routine. This condition variable routine is periodically executed through the electronic control unit 50, for example, with a time interrupt at predetermined time intervals.

  In this routine, first, the degree of deterioration of the NOx catalyst is determined (S401), and the minimum temperature under the condition (j) is made variable based on the degree of deterioration and the gas flow rate Ga (corresponding to the exhaust flow rate of the internal combustion engine 10). (S402). That is, under the condition that the degree of deterioration of the NOx catalyst is constant, as shown in FIG. 19, the minimum temperature of the condition (j) is increased as the gas flow rate Ga is increased. This is because, in the region where the catalyst inlet exhaust temperature Tb is low, the amount of heat removed from the NOx catalyst increases as the gas flow rate Ga increases, and the average catalyst bed temperature Tave becomes difficult to increase. Further, under the condition where the gas flow rate Ga is constant, the minimum temperature is increased as the degree of deterioration of the NOx catalyst increases. That is, as the degree of deterioration of the NOx catalyst increases, the minimum temperature of the condition (j) is set to a higher value. Thereby, when the deterioration degree of the NOx catalyst is large, the minimum temperature under the condition (j) is set to a higher value than when the deterioration degree is small.

  The higher the minimum temperature, the more severe the condition (j) of the calculation permission conditions, and the calculation permission condition is less likely to be satisfied, and the learning value K is less likely to be calculated. Here, if the minimum temperature is too low, in the state in which the deterioration of the NOx catalyst has progressed, the increase in the catalyst bed temperature average value Tave is delayed due to the deterioration, and further the rate of increase in the catalyst bed temperature average value Tave. The learning value K is allowed to be calculated in a situation where it is difficult to secure the value. As a result, the catalyst bed temperature average value Tave, which increases toward the target bed temperature Tt, is not stable, in other words, the learning value K under the condition before the catalyst bed temperature average value Tave is stabilized. Calculation is performed, and the learning value K becomes an inappropriate value as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. In addition, if the minimum temperature is too high, the calculation permission condition is not easily satisfied, and the calculation frequency of the learning value K holds the learning value K at an appropriate value as a value corresponding to the steady deviation. It may be too small.

  Taking this into consideration, the initial value of the minimum temperature that can be changed in step S202 is set to a value that is suitable for a new NOx catalyst, and the learned value K that is calculated as the maximum value is used as the catalyst bed temperature. The value is set to a height value at which the calculation frequency of the learning value K necessary for maintaining an appropriate value as a value corresponding to a steady deviation between the average value Tave and the target bed temperature Tt is obtained.

  As a result, when the NOx catalyst is new and the minimum temperature is the initial value, the initial value is set to a height value suitable for the new NOx catalyst. The conditions are not too loose or too strict. Therefore, the calculation permission condition including the condition (j) is not easily established or difficult to be established. For this reason, the calculated learning value K becomes inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt, and the calculation value of the learning value K is the same learning value. It is possible to prevent K from becoming too small in order to maintain an appropriate value as a value corresponding to the steady deviation.

  Then, as the NOx catalyst deteriorates, the minimum temperature is raised. Until the minimum temperature reaches the maximum value, the minimum temperature is continuously increased according to the progress of the degree of deterioration of the NOx catalyst. It should be noted that the maximum value is set to a height value at which the learning frequency K is obtained as an appropriate value as a value corresponding to the steady deviation, and a necessary calculation frequency of the learning value K is obtained. This is as described above. By making the minimum temperature variable in this way, the calculated learned value K is accurately suppressed from becoming inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. However, the calculation frequency of the learning value K is increased as much as possible, and the calculation frequency of the learning value K necessary for holding the learning value K at a value corresponding to the steady deviation is ensured. it can.

According to the embodiment described in detail above, the following effects can be obtained.
(3) Among the calculation permission conditions for permitting the calculation of the learning value K, the condition relating to the increase in the catalyst bed temperature average value Tave, that is, the condition (j) above, is when the degree of deterioration of the NOx catalyst is large. The degree of deterioration is stricter than when the degree of deterioration is small. Specifically, the minimum temperature under the condition (j) is set to a higher value than when the degree of deterioration of the NOx catalyst is small. By increasing the minimum temperature in this way, the condition (j) is made stricter, and the situation where the catalyst inlet exhaust temperature Tb is higher, in other words, the rate of increase of the catalyst bed temperature average value Tave is more easily secured. The calculation permission condition is not satisfied only with. Therefore, even when the NOx catalyst has been deteriorated, when the learning value K is allowed to be calculated and the learning value K is calculated, the catalyst bed temperature average value Tave that increases toward the target bed temperature Tt. Becomes a stable situation. As a result, the calculated learning value K is suppressed from being too large with respect to the steady deviation between the catalyst bed temperature T and the target bed temperature Tt, and is a value corresponding to the steady deviation. Appropriate value.

  (4) The variable according to the degree of deterioration of the NOx catalyst at the lowest temperature under the condition (j) is specifically performed as follows. That is, the lower the NOx catalyst, the higher the minimum temperature. Note that the initial value of the minimum temperature that can be made variable is a value suitable for a new NOx catalyst. The maximum value of the minimum temperature is the same as that necessary for maintaining the calculated learned value K as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. It is set to a height value at which the learning frequency K is calculated. As described above, by making the minimum temperature variable, the calculated learned value K is appropriately determined to be inappropriate as a value corresponding to a steady deviation between the catalyst bed temperature average value Tave and the target bed temperature Tt. While suppressing, the calculation frequency of the learning value is increased as much as possible, and the calculation frequency of the learning value K necessary for holding the learning value K at a value corresponding to the steady deviation is ensured. it can.

[Other Embodiments]
In addition, each said embodiment can also be changed as follows, for example.
-You may implement combining 1st Embodiment and 2nd Embodiment.

In the first and second embodiments, the degree of deterioration of the NOx catalyst is determined based on both the travel distance and the cumulative value ΣT, but either can be determined using only one of them.
In the first and second embodiments, the supply of the unburned fuel component to the exhaust system is performed by the sub-injection performed in the exhaust stroke or the expansion stroke after the fuel supplied from the injector 40 to the combustion in the combustion chamber 13 is injected. You may go by. In this case, the addition valve 46 may be omitted.

  In the first embodiment, the stability determination time under the condition (i) may be changed stepwise instead of gradually with respect to the change in the degree of deterioration of the NOx catalyst. For example, the stability determination time may be extended in multiple stages as the degree of deterioration of the NOx catalyst increases. It is also possible to make the stability determination time longer not in multiple stages but in two stages.

In the first embodiment, the determination temperature under the condition (i) may be a value other than 600 ° C.
-In 2nd Embodiment, it is not essential regarding the change of the minimum temperature according to gas flow rate Ga.

  In the second embodiment, the change of the minimum temperature under the condition (j) may be performed stepwise instead of gradually with respect to the change in the degree of deterioration of the NOx catalyst. For example, the minimum temperature may be increased in multiple stages as the degree of deterioration of the NOx catalyst increases. It is also possible to increase the minimum temperature not in multiple stages but in two stages.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the whole internal combustion engine to which the control apparatus of 1st Embodiment is applied. (A)-(d) are the change of the addition pulse for driving the addition valve during the temperature rise control for filter regeneration, the change of the catalyst bed temperature T and the catalyst inlet exhaust temperature Tb, and the integrated values ΣQr and ΣQ. The time chart which shows transition and the setting aspect of the addition permission flag F1. The flowchart which shows the control procedure of the fuel addition by the addition valve in temperature rising control. The flowchart which shows the control procedure of the fuel addition by the addition valve in temperature rising control. 4 is a time chart showing a state in which a steady deviation occurs between a catalyst bed temperature T (catalyst bed temperature average value Tave) and a target bed temperature Tt during temperature rise control. The time chart which shows transition of integrated value (SIGMA) Qr and (SIGMA) Q when the learning value K is not reflected. The time chart which shows transition of integrated value (SIGMA) Qr and (SIGMA) Q when the learning value K is reflected. (A) is a time chart showing the transition of both the catalyst bed temperature average value Tave and the target bed temperature Tt by the learning value K and the transition of the catalyst inlet exhaust temperature Tb when the steady deviation is eliminated. (B) is a time chart which shows the change mode of the learning value K at that time. The flowchart which shows the learning value update routine for memorize | storing the learning value K in non-volatile RAM. The graph which shows transition of the catalyst bed temperature average value Tave in temperature rising control with the state in which deterioration of the NOx catalyst has not progressed much and the state in which the deterioration has advanced. The graph which shows transition of the catalyst bed temperature average value Tave in temperature rising control in the state in which deterioration of a NOx catalyst is not progressing. The graph which shows transition of the catalyst bed temperature average value Tave during temperature rising control in the state in which deterioration of the NOx catalyst has advanced. The flowchart which shows the procedure for lengthening the stability determination time on the conditions of (i) and making the conditions severe. The graph which shows the change of the deterioration degree of a NOx catalyst with respect to the change of the travel distance and the cumulative value of catalyst bed temperature. The graph which showed the relationship between a travel distance and the purification rate of a NOx catalyst. The graph which shows transition of the catalyst bed temperature average value Tave in temperature rising control in the state in which deterioration of a NOx catalyst has not progressed so much. The graph which shows transition of the catalyst bed temperature average value Tave during temperature rising control in the state in which deterioration of the NOx catalyst has advanced. The flowchart which shows the procedure for raising the minimum temperature on the conditions of (j) in 2nd Embodiment, and making the conditions severe. The graph which shows the change of the minimum temperature with respect to the deterioration degree of NOx catalyst, and the change of gas flow rate.

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 ... Air-fuel ratio sensor, 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, 50 ... Electronic control device (degradation judgment means, condition variable means), 51 ... NE sensor, 52 ... Accelerator sensor, 53 ... throttle valve sensor, 54 ... intake air temperature sensor, 55 ... water temperature sensor.

Claims (5)

A temperature increase control for raising the temperature of the catalyst to a target bed temperature by supplying an unburned fuel component to the catalyst provided in the exhaust system is performed, and when the calculation permission condition is satisfied during the temperature increase control, The learning value is calculated as a value corresponding to the difference between the two based on the target bed temperature, and the calculation of the learning value is prohibited when the calculation permission condition is not satisfied, and the calculated learning value is used as unburned fuel for the catalyst. In a control device for an internal combustion engine to be reflected in the supply of components,
A deterioration determining means for determining the degree of deterioration of the catalyst;
When the degree of deterioration of the catalyst is large, the condition variable means for making the condition variable so that the condition related to the increase of the catalyst bed temperature becomes stricter among the calculation permission conditions than when the degree of deterioration is small. When,
A control device for an internal combustion engine, comprising: The calculation permission condition is that the elapsed time from the time when the catalyst bed temperature is equal to or higher than a determination temperature that is lower than the target bed temperature and the rate of increase of the catalyst bed temperature is equal to or lower than a predetermined determination speed. Including the condition that is more than the stability judgment time,
2. The control device for an internal combustion engine according to claim 1, wherein the condition varying means sets the stability determination time to a longer value when the degree of deterioration of the catalyst is large than when the degree of deterioration is small. The condition variable means sets the stability determination time to a longer value as the degree of deterioration of the catalyst increases.
With respect to the stability determination time, the initial value is set to a value suitable for when the catalyst is new, and the maximum value is set to a steady deviation between the catalyst bed temperature and the target bed temperature. The control apparatus for an internal combustion engine according to claim 2, wherein the control value is set to a length value at which a calculation frequency of the learning value necessary to hold an appropriate value as a corresponding value is obtained. The calculation permission condition includes a condition that the exhaust temperature of the internal combustion engine is equal to or higher than a predetermined minimum temperature,
The internal combustion engine according to any one of claims 1 to 3, wherein the condition variable means sets the minimum temperature to a higher value when the degree of deterioration of the catalyst is large than when the degree of deterioration is small. Engine control device. The condition variable means increases the minimum temperature as the exhaust temperature of the internal combustion engine increases.
Regarding the minimum temperature, the initial value is set to a value suitable for a new catalyst, and the maximum value corresponds to a steady deviation between the catalyst bed temperature and the target bed temperature. The control device for an internal combustion engine according to claim 4, wherein the control value is set to a height value at which a calculation frequency of the learning value necessary for holding the value at an appropriate value is obtained.

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