JP2005105871A - Catalyst control device and catalyst deterioration determining device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable highly accurate sulfur poisoning restoring control without putting a catalyst bed temperature into an overheated condition even when the degree of deterioration of an exhaust gas purifying catalyst for an internal combustion engine is changed. <P>SOLUTION: The catalyst base temperature of the exhaust gas purifying catalyst is fluctuated up and down by the intermittent supply of fuel during sulfur poisoning restoring control, and so an amplitude Ampin occurs in an exhaust temperature. The amplitude Ampin is used in detecting the degree of deterioration of the exhaust gas purifying catalyst. When that the deterioration of the exhaust gas purifying catalyst is not in progress is detected in accordance with the amplitude Ampin, a rich time Rt is set to be shorter, thus preventing the maximum value for the catalyst bed temperature from being in an overheat region. When that the deterioration is in progress is determined in accordance with the amplitude Ampin, the rich time Rt is set to be longer, thus preventing the lowering of the catalyst bed temperature and maintaining the efficiency of releasing sulfur components. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a catalyst control device and a catalyst deterioration determination device for an exhaust purification catalyst disposed in an exhaust system of an internal combustion engine.

  Exhaust gas purification catalysts, particularly NOx occlusion reduction catalysts are poisoned by sulfur components contained in the fuel, and the NOx occlusion reduction capability decreases when the degree of poisoning increases. For this reason, when sulfur components are accumulated in the NOx occlusion reduction catalyst to some extent, the sulfur is released from the NOx occlusion reduction catalyst by increasing the temperature in the temperature raising process and enriching the exhaust air-fuel ratio. The poison recovery control is executed.

However, if the enrichment of the air-fuel ratio is continuously performed during the sulfur poisoning recovery control, the sulfur component is also continuously released, so that the concentration of the sulfur component in the exhausted gas becomes high and a strange odor is generated. In order to reduce the concentration of the exhausted sulfur component, the rich time is intermittently executed at intervals, thereby repeating the rich time and the rich pause time, thereby suppressing the concentration of the sulfur component in the exhaust gas from increasing. A technique has been proposed (see, for example, Patent Document 1).
JP 2000-274232 A (page 4-5, FIG. 2)

  In the control of the above prior art, the catalyst bed temperature rises because the fuel is oxidized inside the exhaust purification catalyst during the rich time and generates heat, and the heat generation stops during the rich pause time, so the catalyst bed temperature is cooled by the exhaust gas. Descends. Accordingly, the catalyst bed temperature periodically rises and falls in response to intermittent enrichment. For this reason, even if the target catalyst bed temperature is controlled on average, if the degree of increase in the catalyst bed temperature during the rich time is high, the catalyst bed temperature temporarily becomes overheated and the exhaust purification catalyst causes thermal deterioration. There is a fear.

  Normally, in order to prevent the catalyst bed temperature from becoming overheated during such a rich time, the rich time is set so that the maximum value of the catalyst bed temperature due to the rich time is lower than the temperature at which thermal degradation starts. ing.

  However, when the exhaust purification catalyst is new and when the exhaust purification catalyst is deteriorated due to use, even if the same enrichment is performed, the temperature rise behavior of the catalyst bed temperature is different. In the new exhaust purification catalyst, the maximum value of the bed temperature due to enrichment becomes higher than that of the deteriorated exhaust purification catalyst. Therefore, in the sulfur poisoning recovery control in which the rich time is set so as to be compatible with the catalyst after a certain degree of deterioration, there is a risk that when the exhaust purification catalyst is new, the catalyst bed temperature becomes overheated due to the enrichment and causes early deterioration. is there.

  Also, when the rich time is set so that the catalyst bed temperature does not become overheated with the new exhaust purification catalyst, if the exhaust purification catalyst has deteriorated due to use, the catalyst bed temperature will still reach the overheat state. Although there is a sufficient margin, the rich time is completed in a short time. For this reason, the catalyst bed temperature is lowered, and the sulfur component is not released efficiently. For this reason, there is a possibility that emissions deteriorate due to a decrease in the accuracy of the sulfur poisoning recovery control, and that fuel consumption deteriorates due to a prolonged sulfur poisoning recovery control.

  The present invention relates to a catalyst control device for an internal combustion engine that does not cause an overheated state of the catalyst bed temperature even if the deterioration degree of the exhaust purification catalyst changes, and is capable of highly accurate sulfur poisoning recovery control, and such catalyst control. It is an object of the present invention to provide a catalyst deterioration determination device for determining the degree of deterioration of an exhaust purification catalyst.

In the following, means for achieving the above object and its effects are described.
According to a first aspect of the present invention, there is provided a catalyst control apparatus for an internal combustion engine, wherein an air-fuel ratio of exhaust flowing into the exhaust purification catalyst is reduced by intermittently supplying fuel from upstream of an exhaust purification catalyst disposed in an exhaust system of the internal combustion engine. An internal combustion engine that performs sulfur poisoning recovery control for recovering the exhaust purification catalyst from a sulfur poisoning state by repeating a rich time that is reduced to stoichiometric or less with fuel supply and a rich pause time that occurs when fuel supply is stopped A deterioration degree detecting means for detecting a deterioration degree of the exhaust purification catalyst, and a relative value of the rich time to the rich pause time in accordance with the deterioration degree detected by the deterioration degree detecting means. And a sulfur poisoning recovery control correcting means for correcting an appropriate length.

  Considering that the sulfur poisoning recovery control correcting means directly corrects the length of the rich time, the deterioration degree detecting means detects that the degree of deterioration of the exhaust purification catalyst is not large, that is, the deterioration is not progressing. In this case, the sulfur poisoning recovery control correcting means can set the rich time short. As a result, it is possible to prevent the maximum value of the catalyst bed temperature accompanying the enrichment from entering the overheating region. When the deterioration degree detection means detects that the degree of deterioration of the exhaust purification catalyst is large, that is, the deterioration is progressing, the sulfur poisoning recovery control correcting means corresponds to the degree of deterioration and the catalyst bed temperature is adjusted. The rich time can be lengthened by preventing the maximum value from entering the overheating region. As a result, a decrease in the catalyst bed temperature can be prevented and the sulfur component release efficiency can be maintained, so that the accuracy of the sulfur poisoning recovery control does not decrease.

  Further, it is considered that the sulfur poisoning recovery control correcting means corrects the relative length of the rich time with respect to the rich down time by correcting the length of the rich down time. In this case, the sulfur poisoning recovery control correcting means may set the rich time in advance so that the maximum value of the catalyst bed temperature at which deterioration has not progressed does not become an overheating region. When the deterioration has progressed, the sulfur poisoning recovery control correcting means can shorten the rich pause time corresponding to the degree of deterioration. As a result, a decrease in the catalyst bed temperature can be prevented and the sulfur component release efficiency can be maintained, so that the accuracy of the sulfur poisoning recovery control does not decrease. Since the rich time is maintained, the maximum value of the catalyst bed temperature does not enter the overheating region.

  Further, the sulfur poisoning recovery control correcting means may correct the relative length of the rich time with respect to the rich pause time by correcting both the rich time and the rich pause time. In this case, when the deterioration degree of the exhaust purification catalyst is small, the rich time and the rich pause time are set from the viewpoints of both overheating prevention and catalyst bed temperature maintenance. If the degree of deterioration of the exhaust purification catalyst increases, the rich time is lengthened and the rich pause time is shortened. This makes it possible to prevent overheating and maintain the catalyst bed temperature even when deterioration progresses.

Therefore, even if the degree of deterioration of the exhaust purification catalyst changes, the catalyst bed temperature is not overheated, and highly accurate sulfur poisoning recovery control is possible.
The catalyst control apparatus for an internal combustion engine according to claim 2, wherein the sulfur poisoning recovery control correcting means according to claim 1 is configured such that the greater the degree of deterioration detected by the deterioration degree detecting means, the larger the relative time of the rich time. It is characterized by adding a modification to increase the typical length.

By doing so, even if the deterioration degree of the exhaust purification catalyst changes as described above, the catalyst bed temperature is not overheated, and highly accurate sulfur poisoning recovery control is possible.
The catalyst control apparatus for an internal combustion engine according to claim 3, wherein the sulfur poisoning recovery control includes the exhaust temperature flowing into the exhaust purification catalyst, the supply amount of the fuel, and the exhaust purification catalyst. The catalyst bed temperature of the exhaust purification catalyst is estimated by adjusting the relative length of the rich time by estimating the catalyst bed temperature of the exhaust purification catalyst based on the calorific value obtained from the fuel purification rate at And the sulfur poisoning recovery control correcting means corrects the relative length of the rich time by correcting the fuel purification rate in accordance with the deterioration degree detected by the deterioration degree detecting means. It is characterized by doing.

  In this way, the sulfur poisoning recovery control correcting means can correct the relative length of the rich time by correcting the fuel purification rate according to the deterioration degree detected by the deterioration degree detecting means.

  Since the fuel purification rate becomes lower due to the deterioration of the exhaust purification catalyst, the catalyst bed temperature estimated using this fuel purification rate is accurately corrected by correcting the fuel purification rate according to the degree of deterioration. . This correction corrects the relative length of the rich time to an accurate state. By doing so, even if the deterioration degree of the exhaust purification catalyst changes as described above, the catalyst bed temperature is not overheated, and highly accurate sulfur poisoning recovery control is possible.

  The catalyst control device for an internal combustion engine according to claim 4, further comprising catalyst bed temperature detecting means for detecting a physical quantity reflecting an actual catalyst bed temperature of the exhaust purification catalyst according to any one of claims 1 to 3, The deterioration degree detecting means is characterized in that the deterioration degree is larger as the fluctuation range of the actual catalyst bed temperature appearing in the physical quantity detected by the catalyst bed temperature detecting means with the intermittent supply of the fuel is smaller. And

  The catalyst bed temperature oscillates due to the intermittent supply of fuel, that is, the repetition of the rich time and the rich pause time, resulting in an amplitude. The extent of the fluctuation that appears in this amplitude and the like becomes smaller as the exhaust purification catalyst deteriorates. For this reason, the deterioration degree detecting means can assume that the deterioration degree is larger as the fluctuation range of the actual catalyst bed temperature is smaller.

  The catalyst control device for an internal combustion engine according to claim 5, further comprising catalyst bed temperature detecting means for detecting a physical quantity reflecting an actual catalyst bed temperature of the exhaust purification catalyst according to any one of claims 1 to 3, The deterioration degree detecting means is characterized in that the deterioration degree is larger as the rate of increase of the actual catalyst bed temperature that appears in the physical quantity detected by the catalyst bed temperature detecting means after the fuel is supplied is smaller.

  The actual catalyst bed temperature rises after the fuel is supplied to form the rich time, but the rate of increase becomes smaller as the exhaust purification catalyst deteriorates. For this reason, the deterioration degree detecting means can determine that the deterioration degree is larger as the rate of increase in the actual catalyst bed temperature is smaller.

  The catalyst control apparatus for an internal combustion engine according to claim 6, wherein the deterioration degree detection means is based on a relative length of the rich time corresponding to an undegraded state of the exhaust purification catalyst. When the fuel is intermittently supplied, the degree of deterioration is detected by a physical quantity detected by the catalyst bed temperature detecting means.

  In this way, intermittent supply of fuel is executed based on the relative length of the rich time corresponding to the undegraded state of the exhaust purification catalyst, and thereby the degree of deterioration is determined by the physical quantity detected by the catalyst bed temperature detecting means. May be detected. As a result, since the degree of deterioration is detected in a relative length state of a certain rich time, the degree of deterioration can be detected with higher accuracy. Furthermore, since the exhaust purification catalyst is based on the relative length of the rich time corresponding to the undegraded state, the degree of deterioration can be detected with the fuel supply amount being at a minimum, and the exhaust gas can be detected even at the time of detection. The purification catalyst is not overheated.

  The catalyst control apparatus for an internal combustion engine according to claim 7, wherein the catalyst bed temperature detecting means is an exhaust temperature sensor provided on the downstream side of the exhaust purification catalyst, and the catalyst The physical quantity detected by the bed temperature detecting means is the exhaust temperature detected by the exhaust temperature sensor.

  Since the actual catalyst bed temperature is reflected in the exhaust temperature discharged from the exhaust purification catalyst, an exhaust temperature sensor is provided downstream of the exhaust purification catalyst as catalyst bed temperature detection means, and the exhaust temperature sensor detects this exhaust temperature sensor. The degree of deterioration may be detected by the magnitude of the temperature fluctuation range or the rate of increase.

An internal combustion engine catalyst control apparatus according to an eighth aspect of the present invention is characterized in that, in any one of the first to seventh aspects, the exhaust purification catalyst is a NOx storage reduction catalyst.
As the exhaust purification catalyst, a NOx occlusion reduction catalyst can be exemplified. As described above, even if the deterioration degree of the NOx occlusion reduction catalyst changes, the catalyst bed temperature does not overheat, and the sulfur poisoning recovery control is highly accurate. Is possible.

The catalyst control device for an internal combustion engine according to claim 9 is characterized in that in any one of claims 1 to 8, the internal combustion engine is a diesel engine.
An example of the internal combustion engine is a diesel engine. As described above, even if the degree of deterioration of the exhaust purification catalyst is changed, the catalyst bed temperature is not overheated, and highly accurate sulfur poisoning recovery control is possible.

  In the catalyst control apparatus for an internal combustion engine according to claim 10, in any one of claims 1 to 9, the fuel is supplied to the exhaust system by an addition valve, or into the combustion chamber in an expansion stroke or an exhaust stroke. It is made by fuel injection.

  Examples of the fuel supply for forming the rich time include addition to an exhaust system by an addition valve, or fuel injection into a combustion chamber in an expansion stroke or an exhaust stroke. By correcting the addition amount, the fuel injection amount, or the interval between them as described above, even if the deterioration degree of the exhaust purification catalyst changes, the catalyst bed temperature is not overheated and the sulfur poisoning is recovered with high accuracy. Control becomes possible.

  An internal combustion engine catalyst deterioration determination device according to claim 11 is a catalyst deterioration determination device for an internal combustion engine that detects a deterioration degree of an exhaust purification catalyst disposed in an exhaust system of the internal combustion engine. A fuel supply means for intermittently supplying fuel from upstream of the disposed exhaust purification catalyst, a catalyst bed temperature detection means for detecting a physical quantity reflecting an actual catalyst bed temperature of the exhaust purification catalyst, and the fuel supply means A deterioration degree determining means for determining that the degree of deterioration is larger as the fluctuation range of the actual catalyst bed temperature that appears in the physical quantity detected by the catalyst bed temperature detecting means, which is caused by intermittent supply of fuel, is smaller. It is characterized by that.

  By intermittently supplying the fuel, the catalyst bed temperature vibrates and generates an amplitude. The degree of fluctuation appearing in the amplitude or the like becomes smaller as the exhaust purification catalyst deteriorates. For this reason, the deterioration degree determination means can determine that the deterioration degree is larger as the fluctuation range of the actual catalyst bed temperature is smaller.

  The catalyst deterioration determination device for an internal combustion engine according to claim 12, wherein the catalyst bed temperature detection means is an exhaust temperature sensor provided downstream of the exhaust purification catalyst, and the catalyst bed temperature detection means. The physical quantity detected at is the exhaust temperature detected by the exhaust temperature sensor.

  Since the actual catalyst bed temperature is reflected in the exhaust temperature discharged from the exhaust purification catalyst, an exhaust temperature sensor is provided on the downstream side of the exhaust purification catalyst, and the fluctuation range of the exhaust temperature detected by the exhaust temperature sensor is large. From this, the degree of deterioration may be determined.

According to a thirteenth aspect of the present invention, there is provided the catalyst deterioration determination device for an internal combustion engine according to the thirteenth or twelfth aspect, wherein the exhaust purification catalyst is a NOx storage reduction catalyst.
Examples of the exhaust purification catalyst include a NOx occlusion reduction catalyst, and the degree of deterioration can be determined as described above.

[Embodiment 1]
FIG. 1 is a block diagram illustrating a schematic configuration of a vehicle diesel engine to which the above-described invention is applied and a control system that functions as a catalyst control device and a catalyst deterioration determination device. The present invention can also be applied to a case where a similar catalyst configuration is adopted for a lean combustion gasoline engine or the like.

  The diesel engine 2 includes a plurality of cylinders, here, four cylinders # 1, # 2, # 3, and # 4. The combustion chambers 4 of the cylinders # 1 to # 4 are connected to a surge tank 12 via an intake port 8 and an intake manifold 10 that are opened and closed by an intake valve 6. The surge tank 12 is connected via an intake passage 13 to an intercooler 14 and a supercharger, here, an outlet side of a compressor 16 a of an exhaust turbocharger 16. The inlet side of the compressor 16 a is connected to an air cleaner 18. The surge tank 12 has an EGR gas supply port 20 a of an exhaust gas recirculation (hereinafter referred to as “EGR”) path 20. A throttle valve 22 is disposed in the intake path 13 between the surge tank 12 and the intercooler 14, and an intake air amount sensor 24 and an intake air temperature sensor 26 are disposed between the compressor 16 a and the air cleaner 18. .

  The combustion chambers 4 of the cylinders # 1 to # 4 are connected to the inlet side of the exhaust turbine 16b of the exhaust turbocharger 16 via an exhaust port 30 and an exhaust manifold 32 that are opened and closed by an exhaust valve 28, and the outlet of the exhaust turbine 16b. The side is connected to the exhaust path 34. The exhaust turbine 16b introduces exhaust from the fourth cylinder # 4 side in the exhaust manifold 32.

  In the exhaust path 34, three catalytic converters 36, 38 and 40 in which an exhaust purification catalyst is housed are arranged. The most upstream first catalytic converter 36 houses a NOx storage reduction catalyst 36a. When the exhaust gas is in an oxidizing atmosphere (lean) during normal operation of the diesel engine 2, NOx is stored in the NOx storage reduction catalyst 36a. In the reducing atmosphere (stoichiometric or air / fuel ratio lower than stoichiometric), the NOx occluded in the NOx occlusion reduction catalyst 36a is released as NO and is reduced by HC or CO. In this way, NOx is purified.

  The second catalytic converter 38 arranged second is accommodated with a filter 38a having a wall portion formed in a monolith structure, and exhaust gas passes through the minute holes in the wall portion. Since the layer of the NOx occlusion reduction catalyst is formed by coating on the micropore surface of the filter 38a as the substrate, the NOx purification is performed as described above. Furthermore, particulate matter in the exhaust (hereinafter referred to as “PM”) is trapped in the filter wall, so that oxidation of PM is started by active oxygen generated when NOx is occluded in a high-temperature oxidizing atmosphere. The whole PM is oxidized by oxygen. Thus, the purification of PM is performed together with the purification of NOx. Here, the first catalytic converter 36 and the second catalytic converter 38 are integrally formed.

The most downstream third catalytic converter 40 contains an oxidation catalyst 40a, where HC and CO are oxidized and purified.
A first exhaust temperature sensor 44 is disposed between the NOx storage reduction catalyst 36a and the filter 38a. Further, between the filter 38a and the oxidation catalyst 40a, a second exhaust temperature sensor 46 is disposed near the filter 38a, and an air-fuel ratio sensor 48 is disposed near the oxidation catalyst 40a.

  The air-fuel ratio sensor 48 is a sensor that detects the air-fuel ratio of the exhaust based on the exhaust component and linearly outputs a voltage signal proportional to the air-fuel ratio. The first exhaust temperature sensor 44 and the second exhaust temperature sensor 46 detect the exhaust temperatures Texin and Texout at their respective positions.

  Piping of the differential pressure sensor 50 is provided on the upstream side and the downstream side of the filter 38a, respectively, and the differential pressure sensor 50 is located upstream and downstream of the filter 38a in order to detect the degree of clogging of the filter 38a, that is, the degree of PM accumulation. Is detected.

  The exhaust manifold 32 has an EGR gas inlet 20b of the EGR path 20 opened. The EGR gas inlet 20b is open on the first cylinder # 1 side, and is on the opposite side to the fourth cylinder # 4 side where the exhaust turbine 16b introduces exhaust.

  In the middle of the EGR path 20, an iron-based EGR catalyst 52 for reforming EGR gas is disposed from the EGR gas inlet 20b side, and an EGR cooler 54 for cooling the EGR gas is further provided. The EGR catalyst 52 also has a function of preventing the EGR cooler 54 from being clogged. An EGR valve 56 is disposed on the EGR gas supply port 20a side. By adjusting the opening degree of the EGR valve 56, the amount of EGR gas supplied from the EGR gas supply port 20a to the intake system can be adjusted.

  A fuel injection valve 58 disposed in each cylinder # 1 to # 4 and directly injecting fuel into each combustion chamber 4 is connected to a common rail 60 via a fuel supply pipe 58a. Fuel is supplied into the common rail 60 from an electrically controlled discharge variable fuel pump 62, and the high-pressure fuel supplied from the fuel pump 62 into the common rail 60 is supplied to each fuel injection valve 58 through each fuel supply pipe 58a. Distributed supply. A fuel pressure sensor 64 for detecting the fuel pressure is attached to the common rail 60.

  Further, low pressure fuel is separately supplied from the fuel pump 62 to the addition valve 68 via the fuel supply pipe 66. The addition valve 68 is provided in the exhaust port 30 of the fourth cylinder # 4, and adds fuel into the exhaust by injecting fuel toward the exhaust turbine 16b. The catalyst control mode described later is executed by this fuel addition.

  An electronic control unit (hereinafter referred to as “ECU”) 70 is mainly configured by a digital computer including a CPU, a ROM, a RAM, and the like, and a drive circuit for driving various devices. The ECU 70 includes the intake air amount sensor 24, the intake air temperature sensor 26, the first exhaust temperature sensor 44, the second exhaust temperature sensor 46, the air-fuel ratio sensor 48, the differential pressure sensor 50, the EGR opening sensor in the EGR valve 56, Signals from the fuel pressure sensor 64 and the throttle opening sensor 22a are read. Further, signals are read from an accelerator opening sensor 74 that detects the amount of depression of the accelerator pedal 72 (accelerator opening ACCP) and a cooling water temperature sensor 76 that detects the cooling water temperature THW of the diesel engine 2. Further, signals are read from an engine speed sensor 80 that detects the rotational speed NE of the crankshaft 78, and a cylinder discrimination sensor 82 that detects the rotation phase of the crankshaft 78 or the rotation phase of the intake cam and performs cylinder discrimination.

  Based on the engine operating state obtained from these signals, the ECU 70 executes fuel injection amount control and fuel injection timing control by the fuel injection valve 58. Further, the opening control of the EGR valve 56, the throttle opening control by the motor 22b, the discharge amount control of the fuel pump 62, and the PM regeneration control and sulfur poisoning (hereinafter referred to as “S poisoning”) recovery control, which will be described later. Execute the process.

  As the combustion mode control executed by the ECU 70, a combustion mode selected from two types of a normal combustion mode and a low temperature combustion mode is executed according to the operating state. Here, the low-temperature combustion mode is a combustion mode in which NOx and smoke are simultaneously reduced by slowing the increase in the combustion temperature by a large amount of exhaust gas recirculation using the EGR valve opening map for low-temperature combustion mode. In this embodiment, the low-temperature combustion mode is executed in the low-load low-medium rotation region, and air-fuel ratio feedback control is performed by adjusting the throttle opening degree TA based on the air-fuel ratio AF detected by the air-fuel ratio sensor 48. The combustion mode other than this is a normal combustion mode in which normal EGR control (including the case where EGR is not performed) is executed using the normal combustion mode EGR valve opening degree map.

  There are four types of catalyst control modes for executing control processing on the exhaust purification catalyst: a PM regeneration control mode, an S poison recovery control mode, a NOx reduction control mode, and a normal control mode. The PM regeneration control mode is a mode in which the PM accumulated on the filter 38a in the second catalytic converter 38 is burned as described above at a high temperature and discharged as CO2 and H2O. In this mode, fuel addition from the addition valve 68 is repeated in an air-fuel ratio state higher than stoichiometric (theoretical air-fuel ratio) to raise the catalyst bed temperature (for example, 600 to 700 ° C.). There is a case where after-injection that is fuel injection into the combustion chamber 4 in the stroke or exhaust stroke is added.

  In the S poison recovery control mode, when the NOx occlusion reduction catalyst 36a and the filter 38a are poisoned with S and the NOx occlusion capacity is reduced, a sulfur component (hereinafter referred to as "S component") is released to remove from the S poison. This is a recovery mode. In this mode, fuel addition from the addition valve 68 is repeated to increase the catalyst bed temperature (for example, 650 ° C.), and the air-fuel ratio is stoichiometrically increased by intermittent fuel addition from the addition valve 68. An air-fuel ratio reduction process is performed to make the air-fuel ratio slightly lower than stoichiometry. In this mode, after-injection by the fuel injection valve 58 may be added.

  The NOx reduction control mode is a mode in which the NOx occluded in the NOx occlusion reduction catalyst 36a and the filter 38a is reduced to N2, CO2 and H2O and released. In this mode, by intermittent fuel addition from the addition valve 68 with a relatively long time, the catalyst bed temperature is relatively low (for example, 250 to 500 ° C.), and the air-fuel ratio is reduced or lower than the stoichiometry. .

It should be noted that states other than these three catalyst control modes become the normal control mode, and in this normal control mode, fuel addition from the addition valve 68 and after-injection by the fuel injection valve 58 are not performed.
Next, the S poison recovery control process executed by the ECU 70 will be described. A flowchart of this process is shown in FIG. This process is a process executed by interruption every certain time. When this process is started, it is first determined whether or not an execution condition for the S poison recovery control process is satisfied (S102). For example, the S poisoning amount has reached the S release control determination amount, and the NOx occlusion reduction catalyst 36a and the filter 38a are both in the low temperature state, not in the PM regeneration control mode, but determined from the exhaust temperatures Texin and Texout. And whether it is in a temperature range excluding an overheated state. Here, if the execution condition of the S poison recovery control process is not satisfied (“NO” in S102), the process is temporarily terminated as it is.

  When the execution condition of the S poison recovery control process is satisfied (“YES” in S102), it is next determined whether or not the S release control process start condition is satisfied (S104). This S release control process start condition is determined by whether or not the catalyst bed temperatures of the NOx storage reduction catalyst 36a and the filter 38a have been raised to a target temperature increase (here, 650 ° C.). For example, it is determined whether or not the estimated catalyst bed temperature of the NOx storage reduction catalyst 36a ≧ 600 ° C. The estimated catalyst bed temperatures of the NOx storage reduction catalyst 36a and the filter 38a are calculated from the engine operating state (here, load and engine speed NE) and the amount of fuel added. Note that the value of the exhaust temperature Texin may be determined.

  If the S release control process start condition is not satisfied (“NO” in S104), the temperature increase control is executed (S106). In the temperature rise control, assuming that the NOx storage reduction catalyst 36a is a new catalyst that has not yet deteriorated, the estimated catalyst bed temperature of the NOx storage reduction catalyst 36a is 600 ° C. or higher within a range in which the NOx storage reduction catalyst 36a does not overheat. A predetermined amount of fuel is intermittently added from the addition valve 68. The filter 38a has a catalyst bed temperature close to that of the NOx occlusion reduction catalyst 36a, but the variation in the catalyst bed temperature is small. Therefore, the problem of overheating during the S release control process occurs in the NOx storage reduction catalyst 36a. Therefore, in the present embodiment, the NOx storage reduction catalyst 36a will be mainly described.

  When the S release control process start condition is satisfied by executing the temperature increase control (“YES” in S104), the deterioration degree determination process (S108) and the S release control process (S110) are executed. FIG. 3 shows the deterioration degree determination process, and FIG. 4 shows the S release control process.

  Deterioration degree determination processing (FIG. 3) will be described. In this process, it is first determined whether or not a deterioration degree determination stability condition is satisfied (S122). This deterioration degree determination stability condition is a condition for determining that the value of the exhaust gas temperature Texin detected by the first exhaust gas temperature sensor 44 is in a state of showing a stable periodic change. It is determined that the deterioration degree determination stability condition is satisfied when the load (for example, the load and the engine speed NE) is stable.

Here, if the deterioration degree determination stability condition is not satisfied (“NO” in S122), this process is temporarily terminated and the process proceeds to the next S release control process (FIG. 4).
On the other hand, if the deterioration degree determination stability condition is satisfied (“YES” in S122), then in the S poison recovery control executed by the arrival of the S poison amount to the current S release control determination amount, It is determined whether or not the amplitude Ampin has already been acquired (S123). If the amplitude Ampin has already been acquired (“NO” in S123), the process is temporarily terminated as it is, and the process proceeds to the next S release control process (FIG. 4).

  When the amplitude Ampin has not been acquired (“YES” in S123), next, acquisition processing of the maximum value Tinmax of the exhaust temperature Texin detected by the first exhaust temperature sensor 44 is executed (S124), and then the exhaust temperature. The process of acquiring the minimum value Tinmin of Texin is executed (S126).

  Here, the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 36a by the S release control process (FIG. 4), which will be described later, is repeated between a rich time Rt and a rich pause time Lt as shown in FIG. As a result, the actual catalyst bed temperature of the NOx occlusion reduction catalyst 36a rises by the rich time Rt and repeats the state of lowering by the rich rest time Lt.

  The exhaust temperature Texin detected by the first exhaust temperature sensor 44 corresponds to a physical quantity that reflects the actual catalyst bed temperature of the NOx storage reduction catalyst 36a. From this, the maximum value Tinmax appearing in the exhaust temperature Texin of the first exhaust temperature sensor 44 reflects the maximum value of the catalyst bed temperature generated by the rich time Rt. Further, the minimum value Tinmin appearing in the exhaust temperature Texin of the first exhaust temperature sensor 44 reflects the minimum value of the catalyst bed temperature generated by the rich downtime Lt.

  Therefore, when a detection value larger than the previous and subsequent detection values is found from the transition of the detection value of the first exhaust temperature sensor 44 during the execution of the S release control process (FIG. 4), this detection value is set as the maximum value Tinmax. When a detection value smaller than the previous and subsequent detection values is found, this detection value is acquired as a minimum value Tinmin.

  Next, it is determined whether or not both the maximum value Tinmax and the minimum value Tinmin are acquired (S128). While either or both of the maximum value Tinmax and the minimum value Tinmin are not obtained (“NO” in S128), this process is temporarily terminated and the process proceeds to the next S release control process (FIG. 4). .

  As shown in FIG. 6, when the maximum value Tinmax is first obtained with the rich time Rt (t0) and then the minimum value Tinmin is obtained with the rich rest time Lt (t1), "YES" is determined in step S128. Is determined. Next, the amplitude Ampin (corresponding to peak-to-peak here) is calculated as shown in Equation 1 (S130).

[Formula 1]
Ampin ← Tinmax − Tinmin
The amplitude Ampin is also set in a nonvolatile memory in the ECU 70, and the value is maintained even when the ECU 70 is powered off.

Thus, the present process is temporarily terminated, and the process proceeds to the S release control process (FIG. 4).
The S release control process (FIG. 4) will be described. When this processing is started, it is first determined whether or not the amplitude Ampin has already been acquired in the S poison recovery control executed by the arrival of the S poison amount to the current S release control determination amount ( S152).

  Here, if it is the first process after the S poisoning amount reaches the current S release control determination amount and the amplitude Ampin has not yet been acquired (“NO” in S152), the initial value Rtint is set at the rich time Rt. It is set (S154). This initial value Rtint is the catalyst bed temperature that causes thermal deterioration of the NOx storage reduction catalyst 36a even if the rich state is continued by adding fuel from the addition valve 68 to the NOx storage reduction catalyst 36a that has not deteriorated (FIG. 6). And a sufficiently long time is obtained and set in an experiment.

  Next, the rich pause time Lt is calculated from the map g (S158). This map g shows the initial value Rint of the rich time, the heat generation amount Hex due to the added fuel amount Qadd from the addition valve 68, the exhaust temperature Tex flowing into the NOx storage reduction catalyst 36a, the exhaust amount Vex, the heat capacity Cex of the exhaust system, and the target floor Based on the temperature Tcat, the rich pause time Lt is calculated. By this calculation, the rich downtime Lt for achieving the target bed temperature Tcat in the NOx storage reduction catalyst 36a is obtained.

  Here, the fuel amount Qadd added by the addition valve 68 is a fuel amount added from the addition valve 68 as the rich time Rt = initial value Rtint. The heat generation amount Hex is the amount of heat generated when the fuel amount Qadd is oxidized by a new (undegraded) NOx storage reduction catalyst 36a. The exhaust temperature Tex flowing into the NOx occlusion reduction catalyst 36a is estimated from the engine operating state (load and engine speed NE). The exhaust amount Vex is the exhaust amount in the total time of the rich time Rt and the rich rest time Lt, and is calculated from the intake air amount GA detected by the intake air amount sensor 24 and the total time. The heat capacity Cex of the exhaust system is a fixed value determined in advance by the type of engine obtained through experiments.

  Then, it is determined whether or not the rich time Rt has elapsed (S160). Here, since it is the first time, the rich time Rt has not yet elapsed (“NO” in S160), and fuel addition from the addition valve 68 is executed (S162). As a result, exhaust enrichment due to fuel addition is started, and the rich time elapsed counter is counted up (S164).

  Thereafter, the above-described processing is repeated unless the rich time Rt elapses. When the rich time Rt has elapsed (“YES” in S160), the fuel addition from the addition valve 68 is stopped (S166). Next, it is determined whether or not the rich pause time Lt has elapsed (S168). Since the rich pause has just started (“NO” in S168), the rich pause time elapsed counter is counted up (S170).

  Thereafter, as long as the rich rest time Lt has not elapsed, “NO” in step S152, “YES” in step S154, step S158, and step S160, “NO” in step S166 and step S168, and step S170 are repeated. When the rich pause time Lt has elapsed (“YES” in S168), the rich time elapsed counter is cleared (S172), and the rich pause time elapsed counter is cleared (S174).

  If the amplitude Ampin is not acquired in the next control cycle (“NO” in S152), “Rt ← Rtint” (S154), “Lt ← g (Rtint, Hex, Tex, Vex, Cex, Tcat) ”(S158), it is assumed that the rich time Rt has not elapsed (“ NO ”in S160), and riching is started again (S162).

  During the execution of the above-described processing, the maximum value Tinmax and the minimum value Tinmin are acquired (“YES” in S128) and the amplitude Ampin is calculated (S130) in the deterioration degree determination processing (FIG. 3). In step S152 of the S release control process (FIG. 4), “YES” is determined. Accordingly, the rich time Rt is set based on the map f (S156). The map f is shown in FIG. The map f sets the rich time Rt according to the amplitude Ampin reflecting the degree of deterioration of the NOx storage reduction catalyst 36a. Since the degree of deterioration is smaller as the amplitude Ampin is larger, the fuel oxidation efficiency (same as the purification rate) in the NOx storage reduction catalyst 36a is higher. For this reason, the rich time Rt is shortened because a sufficiently long time is set within a range in which overheating does not occur in accordance with the rapid rise of the catalyst bed temperature after the start of the enrichment. Further, the smaller the amplitude Ampin is, the greater the degree of deterioration is, so that the fuel oxidation efficiency in the NOx storage reduction catalyst 36a is low. For this reason, the rich time Rt is set to be long because a sufficiently long time is set within a range in which overheating does not occur in accordance with the slow rise of the catalyst bed temperature after the start of the enrichment.

  Next, as described above, the value of g (Rint, Hex, Tex, Vex, Cex, Tcat) is set as the rich pause time Lt (S158). If the rich time Rt has not elapsed ("NO" in S160), the fuel addition is executed (S162) and the rich time elapsed counter is incremented (S164).

  In the control period of the next deterioration degree determination process (FIG. 3), since the amplitude Ampin has already been acquired (“NO” in S123), the processes in steps S124 to S130 are not performed. Therefore, after that, in step S156 of the S release control process (FIG. 4), the rich time Rt is set by the amplitude Ampin acquired first in the current S poison recovery control.

  Then, after recovering from the S poisoning and determining “NO” in step S102, if the S poisoning amount reaches the S release control determination amount again (“YES” in S102), the processing described above is performed. Repeated. That is, again, the initial value Rtint is set for the rich time Rt (S154), and the amplitude Ampin is obtained (S124 to S130). Then, the rich time Rt in the S poison recovery control at this time is set by this amplitude Ampin (S156), and the process is repeated.

  As shown in FIG. 6, the rich time Rt is set according to the amplitude Ampin by the processing described above. In FIG. 6, since the new NOx storage reduction catalyst 36a and the filter 38a are used, the rich time Rt set in accordance with the amplitude Ampin is the same as the initial value Rint when the amplitude Ampin is obtained.

  In the case of FIG. 7, the deterioration degree of the NOx storage reduction catalyst 36a is high, and the rich time Rt set according to the amplitude Ampin is longer than the initial value Rint when the amplitude Ampin is obtained. . As a result, the target bed temperature is achieved, and the maximum value Tinmax is adapted to the upper limit temperature to the same extent as when it is new (FIG. 6).

  In the configuration described above, the first exhaust temperature sensor 44 corresponds to the catalyst bed temperature detecting means and the exhaust temperature sensor. The relation with the claim of the catalyst control device for the internal combustion engine is that the steps S152 and S154 of the deterioration degree determination process (FIG. 3) and the S release control process (FIG. 4) are the processes as the deterioration degree detection means. Step S156 of the processing (FIG. 4) corresponds to processing as sulfur poisoning recovery control correcting means. The relationship with the claim of the catalyst deterioration determination device for the internal combustion engine is that the S release control process (FIG. 4) is different from the process as the fuel supply means in the deterioration degree determination process (FIG. 3) and the S release control process (FIG. 4). Step S156 corresponds to processing as a deterioration degree determination means.

According to the first embodiment described above, the following effects can be obtained.
(I). By repeating the rich time Rt and the rich rest time Lt by intermittent supply of fuel, the catalyst bed temperature of the NOx storage reduction catalyst 36a is oscillated up and down to generate an amplitude. This amplitude is reflected in the amplitude Ampin of the exhaust temperature Texin in the first exhaust temperature sensor 44. Since the degree of amplitude Ampin, that is, the degree of fluctuation of the catalyst bed temperature becomes smaller as the NOx storage reduction catalyst 36a deteriorates, the degree of deterioration can be detected by the amplitude Ampin.

  Accordingly, when it is detected from the map f in FIG. 5 based on the amplitude Ampin that the amplitude Ampin is large and the deterioration is not progressing, the rich time Rt can be set short, so that the catalyst bed of the NOx storage reduction catalyst 36a accompanying the enrichment can be set. It is possible to prevent the maximum value of the temperature from becoming an overheated region.

  When it is detected that the amplitude Ampin is small and the deterioration is progressing, the rich time Rt can be lengthened so that the maximum value of the catalyst bed temperature does not enter the overheating region corresponding to the degree of deterioration appearing in the amplitude Ampin. . As a result, a decrease in the catalyst bed temperature can be prevented and the S component release efficiency can be maintained, so that the accuracy of the S poison recovery control is not lowered. Therefore, neither emission is deteriorated nor fuel consumption is deteriorated due to prolonged S poison recovery control.

Thus, even if the deterioration degree of the NOx storage reduction catalyst 36a changes, the catalyst bed temperature is not overheated, and highly accurate S poisoning recovery control is possible.
(B). The detection of the amplitude Ampin of the exhaust gas temperature Texin is performed by setting the rich time Rt to the initial value Rtint. That is, the amplitude Ampin is always detected in the intermittent fuel supply state with the rich time corresponding to the undegraded state, and the degree of deterioration is determined based on the amplitude Ampin.

As described above, since the degree of deterioration is detected in a certain rich time (initial value Rtint), the amplitude Ampin corresponding to the degree of deterioration can be obtained with higher accuracy.
Furthermore, since the rich time (initial value Rtint) corresponding to the undegraded state of the exhaust purification catalyst is used, the degree of deterioration can be detected with the amount of fuel added from the addition valve 68 being the minimum. For this reason, even when the degree of deterioration is detected, the NOx storage reduction catalyst 36a is not overheated.

[Embodiment 2]
The present embodiment differs from the first embodiment in that the degree of deterioration of the exhaust purification catalyst is detected by the rate of increase of the exhaust gas temperature Texin, and the correction target based on this degree of deterioration is the rich pause time Lt.

  Therefore, in the present embodiment, the deterioration degree determination process shown in FIG. 8 is executed instead of the deterioration degree determination process (FIG. 3), and the S release control process shown in FIG. 9 instead of the S release control process (FIG. 4). Is executed. Other processing and hardware configuration are the same as those in the first embodiment, and will be described with reference to FIGS.

  Deterioration degree determination processing (FIG. 8) will be described. When this process is started, it is first determined whether or not a deterioration degree determination stability condition is satisfied (S202). The deterioration degree determination stability condition is as described in step S122 of the deterioration degree determination process (FIG. 3).

Here, if the deterioration degree determination stability condition is not satisfied (“NO” in S202), the present process is temporarily terminated as it is, and the process proceeds to the next S release control process (FIG. 9).
On the other hand, if the deterioration degree determination stability condition is satisfied (“YES” in S202), then the detection timing tdt of the upstream side exhaust temperature Texin is calculated based on the intake air amount GA from the map h shown in FIG. (S204). This detection timing tdt is represented by an elapsed time from the timing at which fuel is added from the addition valve 68 in an S release control process (FIG. 9) described later. That is, the NOx occlusion reduction catalyst 36a generates heat due to the addition of fuel and the catalyst bed temperature rises. The rate of increase varies depending on the degree of deterioration of the NOx occlusion reduction catalyst 36a and the intake air amount GA. If the degree of deterioration is large, the increase rate is low, and if the intake air amount GA is large, the increase rate is high. The map h (FIG. 10) cancels the difference in the intake air amount GA, and sets the detection timing tdt at which the same increase rate can be obtained if the degree of deterioration is the same. That is, the detection timing tdt is set in order to detect the rate of increase in the standard exhaust flow rate state.

  Next, it is determined whether or not the elapsed time after the start of addition is being counted (S206). The counting of the elapsed time after the start of addition is started in step S212, which will be described later. If the elapsed time after the start of addition is not being counted ("NO" in S206), it is next determined whether or not it is the timing for starting the addition. (S208). That is, when the state is switched from the “YES” state to the “NO” state in step S240 of the S release control process (FIG. 9) described later in the immediately preceding cycle, it is determined that it is the addition start timing, and otherwise It is determined that it is not the addition start timing.

If it is not the addition start timing (“NO” in S208), the process is temporarily terminated and the process proceeds to the S release control process (FIG. 9).
If it is the addition start timing (“YES” in S208), then the exhaust temperature Texin at this timing is set to the addition start exhaust temperature Ta (S210). Then, the elapsed time counting after the start of addition is started (S212). Thus, the present process is temporarily terminated, and the process proceeds to the S release control process (FIG. 9).

  Since the elapsed time after the start of addition is being counted in the next control cycle (“YES” in S206), whether or not the elapsed time from the start of addition has reached the detection timing tdt based on the elapsed time count after the start of addition Is determined (S214). If it has not reached (“NO” in S214), the process is temporarily terminated and the process proceeds to the S release control process (FIG. 9).

If the detection timing tdt is reached (“YES” in S214), the exhaust gas temperature difference ΔTin between the start of addition and after the detection timing tdt is calculated by Equation 2 (S216).
[Formula 2]
ΔTin ← Texin − Ta
This exhaust gas temperature difference ΔTin corresponds to an increase rate of the exhaust gas temperature Texin in units of time from the start of addition in the standard exhaust gas flow rate state to the detection timing tdt.

Next, the elapsed time count after the start of addition is stopped (S218), and the present process is temporarily terminated and the process proceeds to the S release control process (FIG. 9).
If the exhaust gas temperature difference ΔTin has not been calculated in step S216, the exhaust gas temperature difference ΔTin is set to the exhaust gas temperature difference corresponding to the undegraded NOx storage reduction catalyst 36a as the initial value ΔTint.

  The S release control process (FIG. 9) will be described. First, based on the exhaust gas temperature difference ΔTin, the initial value ΔTint, the exhaust gas temperature difference ΔTine, and the exhaust gas temperature Tex, which will be described later, the fuel purification rate Kex is calculated by the arithmetic processing k (ΔTin, ΔTint, ΔTine, Tex). (S232).

  Here, the arithmetic processing k (ΔTin, ΔTint, ΔTine, Tex) is first determined from the fuel purification rate map of the undeteriorated fuel purification rate Kexs and the already deteriorated fuel purification rate Kexe shown in FIG. The fuel purification rate Kexs and the already deteriorated fuel purification rate Kexe are obtained. Then, the fuel purification rate Kex is obtained by proportional distribution based on the exhaust gas temperature differences ΔTin, ΔTine and the initial value ΔTint.

  The undegraded fuel purification rate Kexs is a fuel purification rate in the undegraded NOx storage reduction catalyst 36a obtained in advance by experiments using the exhaust temperature Tex flowing into the NOx storage reduction catalyst 36a as a parameter. The already deteriorated fuel purification rate Kexe is a fuel purification rate in the NOx occlusion reduction catalyst 36a that has been deteriorated to some extent, which is obtained in advance through experiments using the exhaust temperature Tex as a parameter. The exhaust gas temperature difference ΔTin obtained in an experiment corresponding to this certain degree of deterioration is the exhaust gas temperature difference ΔTine.

Here, the fuel purification rate Kex is calculated as shown in Equation 3.
[Formula 3]
Kex ← Kexs-{(Kexs-Kexe) × (ΔTinint-ΔTin) / (ΔTinint-ΔTine)}
Next, an initial value Rint is set to the rich time Rt (S234). This process is as described in step S154 of the S release control process (FIG. 4).

Based on the fuel purification rate Kex and the undegraded fuel purification rate Kexs as shown in Expression 4, the heat generation amount Hex by one fuel addition amount is calculated (S236).
[Formula 4]
Hex ← (Kex / Kexs) × Hexint
Here, the undegraded heat generation amount Hexint is a heat generation amount generated by one fuel addition amount when the NOx storage reduction catalyst 36a is in an undegraded state, and is a fixed value.

  Next, the rich pause time Lt is calculated from the map g (Rt, Hex, Tex, Vex, Cex, Tcat) (S238). This map g is as described in step S158 of the S release control process (FIG. 4).

Thereafter, steps S240 to S254 are performed. Steps S240 to S254 are the same as steps S160 to S174 of the S release control process (FIG. 4).
As described above, the degree of deterioration of the NOx storage reduction catalyst 36a is reflected in the exhaust gas temperature difference ΔTin, and it can be determined that the degree of deterioration of the NOx storage reduction catalyst 36a progresses as the exhaust gas temperature difference ΔTin decreases. The exhaust temperature difference ΔTin is reflected in the length of the rich stop time Lt via the fuel purification rate Kex and the heat generation amount Hex, so that the rich stop time Lt becomes shorter in order to achieve the target bed temperature as the degree of deterioration progresses. Will be adjusted.

  The timing chart of FIG. 12 shows the transition of the air-fuel ratio AF and the catalyst bed temperature when there is no deterioration, and the timing chart of FIG. 13 shows the transition of the air-fuel ratio AF and the catalyst bed temperature when the deterioration progresses. In the case of FIG. 12, since the exhaust gas temperature difference ΔTin after the detection timing tdt elapses (t21, t23) from the start of addition (t20, t22) is large, the rich pause time Lt is also set sufficiently long. In the case of FIG. 13, since the exhaust gas temperature difference ΔTin after the detection timing tdt elapses (t31, t33) from the start of addition (t30, t32) is small, the rich pause time Lt is correspondingly shortened. As a result, the target bed temperature is achieved.

  In the configuration described above, the first exhaust temperature sensor 44 corresponds to the catalyst bed temperature detecting means and the exhaust temperature sensor. The relationship with the claim of the catalyst control device for the internal combustion engine is that the deterioration degree determination process (FIG. 8) is a process as a deterioration degree detection means, and steps S232, S236, and S238 of the S release control process (FIG. 9) are sulfur. This corresponds to processing as poisoning recovery control correction means. The relation with the claim of the catalyst deterioration determination device for the internal combustion engine is that the S release control process (FIG. 9) is different from the process as the fuel supply means in the deterioration degree determination process (FIG. 8) and the S release control process (FIG. 9). Step S232 corresponds to processing as a deterioration degree determination means.

According to the second embodiment described above, the following effects can be obtained.
(I). By repeating the rich time Rt and the rich rest time Lt by intermittent fuel supply, the catalyst bed temperature of the NOx storage reduction catalyst 36a oscillates up and down. Among these, the exhaust gas temperature difference ΔTin corresponding to the rate of increase in the catalyst bed temperature accompanying the start of the rich time Rt becomes smaller as the deterioration degree of the NOx storage reduction catalyst 36a becomes higher. Therefore, the degree of deterioration of the NOx storage reduction catalyst 36a is reflected in the exhaust gas temperature difference ΔTin, and the degree of deterioration can be detected from the exhaust gas temperature difference ΔTin.

  When it is detected that the exhaust gas temperature difference ΔTin is large and the deterioration is not progressing, a high fuel purification rate Kex is set from the fuel purification rate map of FIG. 11, so that the rich downtime Lt is lengthened and the entire control becomes the target catalyst bed. Maintained at temperature. Therefore, it is possible to prevent the maximum value of the catalyst bed temperature of the NOx occlusion reduction catalyst 36a accompanying the enrichment from entering the overheating region.

  When it is detected that the exhaust gas temperature difference ΔTin has become smaller and the deterioration has progressed, the low fuel purification rate Kex is set from the fuel purification rate map of FIG. 11, so the rich rest time Lt is shortened. Since the target catalyst bed temperature is thereby maintained, the S component release efficiency can be maintained.

In this way, even if the deterioration degree of the NOx storage reduction catalyst 36a changes, the catalyst bed temperature is not overheated, and highly accurate S poisoning recovery control is possible.
[Embodiment 3]
In the present embodiment, the rich pause time Lt is adjusted as in the second embodiment using the amplitude Ampin calculated as in the deterioration degree determination process (FIG. 3) in the first embodiment. Therefore, the S release control process shown in FIG. 14 is executed instead of the S release control process (FIG. 4). Since other processes and hardware configuration are the same as those of the first embodiment, description will be made with reference to FIGS.

  The S release control process (FIG. 14) will be described. When this process is started, an initial value Rtint is first set to the rich time Rt (S302). This setting process is the same as that in step S154 (FIG. 4).

  Next, it is determined whether or not the amplitude Ampin has already been acquired in the S poison recovery control executed when the S poison control amount reaches the current S release control determination amount (S304). Here, if it is the first processing after reaching the S poisoning amount to the current S release control determination amount and the amplitude Ampin has not yet been acquired (“NO” in S304), the initial value Ltint is set at the rich pause time Lt. Is set (S306). This initial value Lint is obtained when the fuel is added from the addition valve 68 to the NOx storage reduction catalyst 36a that has not deteriorated during the rich time Rt (= Rtint). It is set to be.

  Next, the processes of steps S314 to S328 are executed. This process is the same as steps S160 to S174. In this process, the maximum value Tinmax and the minimum value Tinmin are acquired in the deterioration degree determination process (FIG. 3) by the combination of the rich time Rt (= Rtint) and the rich pause time Lt (= Ltint) (S128). "YES"), the amplitude Ampin is calculated (S130).

  When the amplitude Ampin is acquired in this way, “YES” is determined in step S304 of the S release control process (FIG. 14). Thus, the fuel purification rate Kex is calculated by the arithmetic processing m (Ampin, Amplint, Ampe, Tex) based on the amplitude Ampin, the initial value Amplint described later, the amplitude Ampe described later, and the exhaust gas temperature Tex (S308).

  Here, the arithmetic processing m (Ampin, Amplint, Ampe, Tex) is first determined based on the exhaust temperature Tex from the fuel purification rate map of the undegraded fuel purification rate Kexs and the already deteriorated fuel purification rate Kexe shown in FIG. A deteriorated fuel purification rate Kexs and an already deteriorated fuel purification rate Kexe are obtained. The fuel purification rate Kex is obtained by proportional distribution based on the amplitudes Ampin, Ampe and the initial value Amplint.

  The amplitude corresponding to the undegraded NOx storage reduction catalyst 36a is the initial value Aminint. The amplitude obtained by the NOx occlusion reduction catalyst 36a which has deteriorated to some extent corresponding to the already deteriorated fuel purification rate Kexe is the amplitude Ampe.

Here, the fuel purification rate Kex is calculated as shown in Equation 5.
[Formula 5]
Kex ← Kexs-{(Kexs-Kexe) × (Ampinint-Ampin) / (Ampinint-Ampe)}
Then, the calorific value Hex by one fuel addition amount is calculated based on the fuel purification rate Kex and the undegraded fuel purification rate Kexs as shown in the equation 4 (S310).

Next, the rich pause time Lt is calculated from the map g (S312). This process is as described in step S158 (FIG. 4).
Thereafter, steps S314 to S328 are performed.

  As described above, it can be seen that the deterioration degree of the NOx storage reduction catalyst 36a is reflected in the amplitude Ampin, and the deterioration degree of the NOx storage reduction catalyst 36a is advanced as the amplitude Ampin becomes smaller. The amplitude Ampin is reflected on the length of the rich pause time Lt via the fuel purification rate Kex and the heat generation amount Hex, and the rich pause time Lt is adjusted to be shorter as the degree of deterioration progresses.

  The timing chart of FIG. 15 shows changes in the air-fuel ratio AF and the catalyst bed temperature when the deterioration progresses. If the deterioration has not progressed, it is as described with reference to FIG. In the case of FIG. 15, the rich pause time Lt is shorter than the initial value Lint when the amplitude Ampin is obtained. As a result, the target bed temperature is achieved.

  In the configuration described above, the first exhaust temperature sensor 44 corresponds to the catalyst bed temperature detecting means and the exhaust temperature sensor. The relationship with the claims of the catalyst control device for the internal combustion engine is that the steps S304 and S306 of the deterioration degree determination process (FIG. 3) and the S release control process (FIG. 14) are the processes as the deterioration degree detection means. Steps S308 to S312 of the processing (FIG. 14) correspond to processing as sulfur poisoning recovery control correcting means. The relation with the claim of the catalyst deterioration determination device for the internal combustion engine is that the S release control process (FIG. 14) is different from the process as the fuel supply means in the deterioration degree determination process (FIG. 3) and the S release control process (FIG. 14). Step S308 corresponds to processing as a deterioration degree determination means.

According to the third embodiment described above, the following effects can be obtained.
(I). By repeating the rich time Rt and the rich rest time Lt by intermittent supply of fuel, the catalyst bed temperature of the NOx storage reduction catalyst 36a is oscillated up and down to generate an amplitude. This amplitude is reflected in the amplitude Ampin of the exhaust temperature Texin in the first exhaust temperature sensor 44. Since the degree of amplitude Ampin, that is, the degree of fluctuation of the catalyst bed temperature becomes smaller as the NOx storage reduction catalyst 36a deteriorates, the degree of deterioration can be detected by the amplitude Ampin.

  When it is detected that the amplitude Ampin is large and the deterioration is not progressing, the rich pause time Lt can be set longer by the processing in steps S308 to S312. Therefore, the target catalyst bed temperature can be set without shortening the rich time Rt. Can be achieved. Therefore, it is possible to prevent the maximum value of the catalyst bed temperature of the NOx occlusion reduction catalyst 36a from entering the overheated region during the rich time Rt. When the amplitude Ampin is small and it is detected that the deterioration is progressing, the rich pause time Lt can be set short, so that the target catalyst bed temperature can be achieved without increasing the rich time Rt. This can prevent the catalyst bed temperature from decreasing and maintain the S component release efficiency.

In this way, even if the deterioration degree of the NOx storage reduction catalyst 36a changes, the catalyst bed temperature is not overheated, and highly accurate S poisoning recovery control is possible.
(B). The detection of the amplitude Ampin of the exhaust gas temperature Texin is performed by setting the rich pause time Lt to the initial value Ltint. That is, the amplitude Ampin is always detected in the intermittent fuel supply state during the rich downtime corresponding to the undegraded state, and the degree of deterioration is determined based on the amplitude Ampin.

As described above, since the degree of deterioration is detected at a constant rich pause time (initial value Lint), the amplitude Ampin corresponding to the degree of deterioration can be obtained with higher accuracy.
[Embodiment 4]
In the present embodiment, the rich time Rt is adjusted as in the first embodiment using the exhaust gas temperature difference ΔTin calculated as in the deterioration degree determination process (FIG. 8) in the second embodiment. Therefore, the S release control process shown in FIG. 16 is executed instead of the S release control process (FIG. 9). The other processes are the same as those in the second embodiment, and will be described with reference to FIGS.

  The S release control process (FIG. 16) will be described. When this process is started, the rich time Rt is first calculated from the map p based on the exhaust gas temperature difference ΔTin (S402). The map p is shown in FIG. The map p sets the rich time Rt according to the exhaust gas temperature difference ΔTin reflecting the degree of deterioration of the NOx storage reduction catalyst 36a. As the exhaust gas temperature difference ΔTin is larger, the degree of deterioration is smaller, so the fuel oxidation efficiency (same as the purification rate) in the NOx storage reduction catalyst 36a is higher. For this reason, the rich time Rt is shortened because a sufficiently long time is set within a range in which overheating does not occur in accordance with the rapid rise of the catalyst bed temperature after the start of the enrichment. Further, the smaller the exhaust gas temperature difference ΔTin is, the greater the degree of deterioration is, so that the fuel oxidation efficiency in the NOx storage reduction catalyst 36a is low. For this reason, the rich time Rt is set to be long because a sufficiently long time is set within a range in which overheating does not occur in accordance with the slow rise of the catalyst bed temperature after the start of the enrichment.

Next, the rich pause time Lt is calculated from the map g (S404). This process is the same as step S158 of the S release control process (FIG. 4).
Thereafter, steps S406 to S420 are performed. This process is as described in steps S160 to S174.

  As described above, the degree of deterioration of the NOx storage reduction catalyst 36a is reflected in the exhaust gas temperature difference ΔTin, and the exhaust gas temperature difference ΔTin is reflected in the length of the rich time Rt by the map p. As a result, the rich time Rt is adjusted to become longer as the degree of deterioration progresses.

  The timing chart of FIG. 18 shows the transition of the air-fuel ratio AF and the catalyst bed temperature when the deterioration progresses. If the deterioration has not progressed, it is as described with reference to FIG. In the case of FIG. 18, the rich time Rt becomes longer than the initial value Rtint as the exhaust gas temperature difference ΔTin decreases. As a result, the NOx storage reduction catalyst 36a is not overheated and the target bed temperature is achieved.

  In the configuration described above, the first exhaust temperature sensor 44 corresponds to the catalyst bed temperature detecting means and the exhaust temperature sensor. The relationship with the claim of the catalyst control device for the internal combustion engine is that the deterioration degree determination process (FIG. 8) is the process as the deterioration degree detection means, and the steps S402 and S404 of the S release control process (FIG. 16) are sulfur poisoning. This corresponds to processing as a recovery control correction means. The relationship with the claim of the catalyst deterioration determination device for the internal combustion engine is that the S release control process (FIG. 16) is different from the process as the fuel supply means in the deterioration degree determination process (FIG. 8) and the S release control process (FIG. 16). Step S402 corresponds to processing as a deterioration degree determination means.

According to the fourth embodiment described above, the following effects can be obtained.
(I). By repeating the rich time Rt and the rich rest time Lt by intermittent fuel supply, the catalyst bed temperature of the NOx storage reduction catalyst 36a oscillates up and down. Among these, the exhaust gas temperature difference ΔTin corresponding to the increase rate of the exhaust gas temperature Texin accompanying the start of the rich time Rt becomes smaller as the deterioration degree of the NOx storage reduction catalyst 36a becomes higher. Therefore, the degree of deterioration of the NOx storage reduction catalyst 36a is reflected in the exhaust gas temperature difference ΔTin, and the degree of deterioration can be detected from the exhaust gas temperature difference ΔTin.

  When it is detected that the exhaust gas temperature difference ΔTin is large and the deterioration is not progressing, the short rich time Rt is set from the map p in FIG. 17, so the maximum of the catalyst bed temperature of the NOx storage reduction catalyst 36a accompanying the enrichment is set. The value can be prevented from becoming an overheated region. When it is detected that the exhaust gas temperature difference ΔTin is small and the deterioration is progressing, the rich time Rt is set so that the maximum value of the catalyst bed temperature does not enter the overheating region corresponding to the deterioration degree appearing in the exhaust gas temperature difference ΔTin. Can be long. This can prevent the catalyst bed temperature from decreasing and maintain the S component release efficiency.

In this way, even if the deterioration degree of the NOx storage reduction catalyst 36a changes, the catalyst bed temperature is not overheated, and highly accurate S poisoning recovery control is possible.
[Other embodiments]
(A). In the second and fourth embodiments, the exhaust gas temperature difference ΔTin is calculated by executing the S release control process with the values at that time without returning the rich pause time Lt and the rich time Rt to the initial values. Instead, as in the first and third embodiments, the rich pause time Lt and the rich time Rt are returned to their initial values at the start of the S poison recovery control, and the exhaust gas temperature difference ΔTin is calculated. Alternatively, the S release control process may be executed by adjusting the rich pause time Lt or the rich time Rt.

  In the second and fourth embodiments, the addition start exhaust gas temperature Ta is detected immediately at the start of the rich time Rt. However, the intake air amount GA is set to the intake air amount GA after the start of the rich time Rt in consideration of the rise in the exhaust gas temperature Texin. The addition start exhaust gas temperature Ta may be detected after the corresponding waiting time has elapsed.

  (B). In each of the embodiments described above, enrichment is performed by adding fuel from the addition valve 68, but exhaust is enriched by after-injection, which is fuel injection from the fuel injection valve 58 into the combustion chamber in the expansion stroke or exhaust stroke. Then, the S release control process may be executed.

  (C). In each of the above-described embodiments, the time adjustment according to the degree of deterioration is performed for either the rich pause time Lt or the rich time Rt, but is performed for both by reducing the adjustment range. May be.

1 is a block diagram showing a schematic configuration of a vehicle diesel engine as a first embodiment and a control system that functions as a catalyst control device and a catalyst deterioration determination device. The flowchart of the S poison recovery control process which ECU of Embodiment 1 performs. The flowchart of a degradation degree determination process similarly. The flowchart of S discharge | release control processing similarly. FIG. 6 is a configuration explanatory diagram of a map f for obtaining a rich time Rt from an exhaust gas amplitude Ampin. 4 is a timing chart illustrating an example of processing according to the first embodiment. 4 is a timing chart illustrating an example of processing according to the first embodiment. The flowchart of the deterioration degree determination process which ECU of Embodiment 2 performs. The flowchart of S discharge | release control processing similarly. FIG. 7 is a configuration explanatory diagram of a map h for obtaining a detection timing tdt from an intake air amount GA. FIG. 3 is a configuration explanatory diagram of a fuel purification rate map showing a relationship between an exhaust temperature Tex and a fuel purification rate depending on a degree of deterioration. 9 is a timing chart illustrating an example of processing according to the second embodiment. 9 is a timing chart illustrating an example of processing according to the second embodiment. 10 is a flowchart of S release control processing executed by the ECU according to the third embodiment. 10 is a timing chart illustrating an example of processing according to the third embodiment. The flowchart of the S discharge | release control processing which ECU of Embodiment 4 performs. The structure explanatory drawing of the map p for calculating | requiring the rich time Rt from exhaust temperature difference (DELTA) Tin. 9 is a timing chart illustrating an example of processing according to the fourth embodiment.

Explanation of symbols

  2 ... Diesel engine, 4 ... Combustion chamber, 6 ... Intake valve, 8 ... Intake port, 10 ... Intake manifold, 12 ... Surge tank, 13 ... Intake passage, 14 ... Intercooler, 16 ... Exhaust turbocharger, 16a ... Compressor, 16b ... exhaust turbine, 18 ... air cleaner, 20 ... EGR path, 20a ... EGR gas supply port, 20b ... EGR gas intake port, 22 ... throttle valve, 22a ... throttle opening sensor, 22b ... motor, 24 ... intake air amount sensor , 26 ... intake temperature sensor, 28 ... exhaust valve, 30 ... exhaust port, 32 ... exhaust manifold, 34 ... exhaust path, 36 ... first catalytic converter, 36a ... NOx occlusion reduction catalyst, 38 ... second catalytic converter, 38a ... Filter, 40 ... third catalytic converter, 40a ... oxidation catalyst, 44 ... first exhaust temperature sensor, 46 ... second Temperature sensor 48 ... Air-fuel ratio sensor 50 ... Differential pressure sensor 52 ... EGR catalyst 54 ... EGR cooler 56 ... EGR valve 58 ... Fuel injection valve 58a ... Fuel supply pipe 60 ... Common rail 62 ... Fuel pump , 64 ... Fuel pressure sensor, 66 ... Fuel supply pipe, 68 ... Addition valve, 70 ... ECU, 72 ... Accelerator pedal, 74 ... Accelerator opening sensor, 76 ... Cooling water temperature sensor, 78 ... Crankshaft, 80 ... Engine speed Sensor, 82 ... cylinder discrimination sensor.

Claims (13)

Rich time and fuel supply in which the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is reduced to less than the stoichiometric with the fuel supply by intermittently supplying fuel from the upstream of the exhaust purification catalyst arranged in the exhaust system of the internal combustion engine A catalyst control device for an internal combustion engine that executes sulfur poisoning recovery control for recovering the exhaust purification catalyst from a sulfur poisoning state by repeating a rich pause time that occurs with a stop,
A deterioration degree detecting means for detecting a deterioration degree of the exhaust purification catalyst;
Sulfur poisoning recovery control correcting means for correcting a relative length of the rich time with respect to the rich pause time according to the deterioration degree detected by the deterioration degree detecting means;
A catalyst control device for an internal combustion engine, comprising: 2. The sulfur poisoning recovery control correcting means according to claim 1, wherein the sulfur poisoning recovery control correcting means adds a correction to increase the relative length of the rich time as the deterioration degree detected by the deterioration degree detecting means is larger. A catalyst control device for an internal combustion engine. 3. The sulfur poisoning recovery control according to claim 1, wherein the sulfur poisoning recovery control is based on an exhaust temperature flowing into the exhaust purification catalyst and a heat generation amount obtained from a supply amount of the fuel and a fuel purification rate in the exhaust purification catalyst. By controlling the catalyst bed temperature of the exhaust purification catalyst by estimating the catalyst bed temperature of the exhaust purification catalyst and adjusting the relative length of the rich time,
The sulfur poisoning recovery control correcting means corrects the relative length of the rich time by correcting the fuel purification rate according to the deterioration degree detected by the deterioration degree detecting means. A catalyst control device for an internal combustion engine. In any one of Claims 1-3, The catalyst bed temperature detection means which detects the physical quantity reflecting the actual catalyst bed temperature of the said exhaust purification catalyst is provided,
The deterioration degree detecting means is configured such that the deterioration degree is larger as the fluctuation range of the actual catalyst bed temperature that appears in the physical quantity detected by the catalyst bed temperature detecting means with the intermittent supply of the fuel is smaller. An internal combustion engine catalyst control device. In any one of Claims 1-3, The catalyst bed temperature detection means which detects the physical quantity reflecting the actual catalyst bed temperature of the said exhaust purification catalyst is provided,
The internal combustion engine characterized in that the deterioration degree detecting means has a larger degree of deterioration as the rate of increase in the actual catalyst bed temperature that appears in the physical quantity detected by the catalyst bed temperature detecting means after the fuel is supplied is smaller. Engine catalyst control device. 6. The catalyst according to claim 4, wherein the deterioration degree detection unit performs the intermittent supply of the fuel based on a relative length of the rich time corresponding to an undegraded state of the exhaust purification catalyst. A catalyst control apparatus for an internal combustion engine, wherein the degree of deterioration is detected by a physical quantity detected by a bed temperature detecting means. 7. The catalyst bed temperature detecting means according to claim 4, wherein the catalyst bed temperature detecting means is an exhaust temperature sensor provided downstream of the exhaust purification catalyst, and the physical quantity detected by the catalyst bed temperature detecting means is the exhaust gas temperature sensor. A catalyst control apparatus for an internal combustion engine, characterized in that the exhaust gas temperature is detected by an air temperature sensor. 8. The catalyst control apparatus for an internal combustion engine according to claim 1, wherein the exhaust purification catalyst is a NOx storage reduction catalyst. 9. The catalyst control device for an internal combustion engine according to claim 1, wherein the internal combustion engine is a diesel engine. 10. The catalyst for an internal combustion engine according to claim 1, wherein the fuel is supplied by addition to an exhaust system by an addition valve, or by fuel injection into a combustion chamber in an expansion stroke or an exhaust stroke. Control device. A catalyst deterioration determination device for an internal combustion engine for detecting a deterioration degree of an exhaust purification catalyst disposed in an exhaust system of the internal combustion engine,
Fuel supply means for intermittently supplying fuel from upstream of an exhaust purification catalyst disposed in an exhaust system of the internal combustion engine;
Catalyst bed temperature detection means for detecting a physical quantity reflecting the actual catalyst bed temperature of the exhaust purification catalyst;
Deterioration degree for determining that the deterioration degree is larger as the fluctuation range of the actual catalyst bed temperature appearing in the physical quantity detected by the catalyst bed temperature detection means, which is caused by intermittent fuel supply by the fuel supply means, is smaller. A determination means;
An apparatus for determining catalyst deterioration of an internal combustion engine, comprising: 12. The catalyst bed temperature detecting means according to claim 11, wherein the catalyst bed temperature detecting means is an exhaust temperature sensor provided downstream of the exhaust purification catalyst, and the physical quantity detected by the catalyst bed temperature detecting means is detected by the exhaust temperature sensor. An apparatus for determining deterioration of a catalyst for an internal combustion engine, characterized in that the temperature is an exhaust temperature. 13. The catalyst deterioration determination device for an internal combustion engine according to claim 11, wherein the exhaust purification catalyst is a NOx storage reduction catalyst.

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