JP2005240682A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology for optimizing a starting time for SOx releasing treatment. <P>SOLUTION: This exhaust emission control device comprises a storage and reduction NOx catalyst, a temperature seizing means S102 for seizing the temperature of the NOx catalyst, an accumulated SOx amount estimating means S101 for estimating the amount of SOx accumulated on the NOx catalyst, a SOx releasing treatment means for SOx releasing treatment of releasing SOx accumulated on the NOx catalyst, and a treatment starting time determining means S103 or S106 for determining the starting time for the SOx releasing treatment by the SOx releasing treatment means. The treatment starting time determining means determines the starting time to be earlier as there is a larger amount of SOx accumulated on the NOx catalyst whose temperature is low. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device for an internal combustion engine that retains sulfur oxide (SOx) in exhaust gas and periodically releases the retained and accumulated SOx. Is.

  As an exhaust gas purification technique for an internal combustion engine, an NOx storage reduction catalyst (hereinafter sometimes simply referred to as “NOx catalyst”) is disposed in the exhaust system of an internal combustion engine (particularly a lean combustion engine or a diesel engine) to obtain a lean air-fuel ratio. A technique is known in which nitrogen oxides in exhaust gas (hereinafter sometimes simply referred to as “NOx”) are temporarily retained on the NOx catalyst before being released into the atmosphere during operation at the same time.

  By the way, sulfur (S) component is contained in fuel or oil, and this S component reacts with oxygen to become SOx. The NOx catalyst retains SOx as well as NOx in the exhaust gas. Therefore, when the amount of retained and accumulated SOx increases, the purification rate of NOx in the exhaust gas decreases, so-called SOx poisoning occurs.

  Therefore, the NOx catalyst on which a predetermined amount of SOx is deposited is set to a high temperature of, for example, 500 ° C. to 700 ° C., and the air fuel ratio of the exhaust gas flowing into the NOx catalyst is made rich by supplying fuel as a reducing agent to the NOx catalyst. Therefore, it is necessary to perform SOx release processing for releasing and reducing SOx deposited on the NOx catalyst by making the NOx catalyst high temperature and reducing atmosphere, thereby eliminating SOx poisoning of the NOx catalyst. .

  Then, as the timing for starting this SOx release process, the amount of SOx deposited on the NOx catalyst (hereinafter sometimes simply referred to as “deposited SOx amount”) is estimated based on, for example, the fuel injection time and the engine speed. It is known that the estimated accumulated SOx amount is equal to or greater than a predetermined amount.

  Further, the amount of SOx generated by combustion greatly depends on the air-fuel ratio, the S component content in the fuel, etc., and the amount of SOx deposited on the NOx catalyst among the generated SOx amount depends on the temperature of the NOx catalyst. Therefore, it has been proposed to estimate the amount of deposited SOx based on the air-fuel ratio of the exhaust, the fuel properties, and the temperature of the NOx catalyst (see, for example, Patent Document 1).

The amount of SOx deposited differs depending on the temperature of the NOx catalyst. The SOx is easily deposited when the temperature of the NOx catalyst is medium (for example, 300 to 500 ° C.), but the degree of activity is low when the temperature is low. Since SOx is emitted when the temperature is high, it is based on the property that it is difficult to deposit SOx at a temperature other than the medium temperature. Therefore, in the technique described in Patent Document 1, the amount of accumulated SOx estimated from the fuel injection integrated amount is corrected so that the amount deposited in the low temperature region is smaller than the amount deposited at the intermediate temperature. doing.
JP 2000-51662 A JP 9-317447 A JP-A-8-158857 Japanese Patent Laid-Open No. 11-350946 Japanese Patent Laid-Open No. 11-6422

  However, the SOx retained and deposited when the NOx catalyst is at a relatively high temperature (for example, 300 ° C. or higher) diffuses quickly into the catalyst because the temperature is high, whereas the NOx catalyst has a low temperature ( For example, the SOx deposited when the temperature is less than 300 ° C. is deposited on the surface of the NOx catalyst. The SOx deposited on the surface of the NOx catalyst reduces the chance of contact between the NOx in the exhaust and the NOx catalyst. Therefore, even if the same amount of SOx is deposited on the NOx catalyst, the deposition state differs depending on the temperature at the time of deposition, and the ability to purify NOx in the exhaust also varies. That is, even when the same amount of SOx is deposited on the NOx catalyst, the NOx purification rate decreases as the amount of deposited SOx increases when the NOx catalyst is at a low temperature.

  Therefore, when it is determined that the amount of accumulated SOx has reached the predetermined amount, the NOx purification performance is already lowered depending on the SOx accumulation state, and the NOx is purified by the NOx catalyst. There is a risk of being discharged as is. On the other hand, as described above, the SOx release process requires the NOx catalyst to have a high temperature and a reducing atmosphere.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can optimize the start timing of the SOx release process.

  In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine, and the temperature grasping means for grasping the temperature of the NOx catalyst. Estimated by the accumulated SOx amount estimating means for estimating the amount of SOx deposited on the NOx catalyst, SOx release processing means for performing SOx release processing for releasing the SOx deposited on the NOx catalyst, and the accumulated SOx amount estimating means. And a processing start timing determining means for determining the start timing of the SOx release processing by the SOx release processing means based on the amount of deposited SOx and the temperature at the time of SOx deposition grasped by the temperature grasping means. It is characterized by.

  As the temperature grasping means, the temperature is estimated based on the detection value of the temperature sensor provided upstream or downstream of the NOx catalyst, and the exhaust temperature changes based on the operating state of the internal combustion engine. Examples thereof include those detected based on the detection value of a temperature sensor provided directly on the NOx catalyst.

  As the accumulated SOx amount estimating means, one that estimates based on the operating state of the internal combustion engine is suitable. Specifically, there is a correlation between the operating state of the internal combustion engine and the fuel injection amount and the oil consumption amount, and the NOx catalyst is generated from the operating state and the injected fuel and consumed oil. There is also a correlation with the amount of SOx deposited. Therefore, if the correlation established among the fuel injection amount, the oil consumption amount, the operating state, and the accumulated SOx amount is derived in advance, the accumulated SOx amount can be estimated.

  By the way, if the start timing of the SOx release processing by the SOx release processing means is late, NOx may be discharged without being purified by the NOx catalyst, and conversely, if the timing is early, this may cause a deterioration in fuel consumption. Become.

  On the other hand, even if the same amount of SOx is deposited on the NOx catalyst, the deposition state differs depending on the temperature at the time of deposition, and the ability to purify NOx in the exhaust also varies. Specifically, even when the same amount of SOx is deposited on the NOx catalyst, the decrease in the NOx purification rate increases as the amount of SOx deposited when the NOx catalyst is at a low temperature increases.

  On the other hand, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the accumulated SOx amount estimated by the accumulated SOx amount estimating means and the temperature at which SOx grasped by the temperature grasping means are accumulated. Since the processing start timing determination means for determining the start timing of the SOx release processing based on the SOx release processing means is provided, the processing start timing determination means, for example, has a large amount of SOx deposited when the temperature of the NOx catalyst is low. Since the start time of the SOx release process is determined in consideration of the temperature at the time when the SOx is deposited, for example, the start time of the SOx release process is determined, the start time of the SOx release process is optimized. be able to. Therefore, exhaust purification can be improved, and fuel consumption deterioration associated with SOx release processing can be suppressed.

  Further, the processing start time determining means is configured to purify NOx of the NOx catalyst based on the accumulated SOx amount estimated by the accumulated SOx amount estimating means and the temperature at the time when SOx grasped by the temperature grasping means is deposited. It is preferable to have NOx purification rate estimation means for estimating the rate, and to determine when the NOx purification rate estimated by the NOx purification rate estimation means is equal to or less than a threshold as the start time.

  The NOx purification rate estimation means preferably estimates that the lower the NOx purification rate, the larger the amount of SOx deposited when the temperature of the NOx catalyst is low. As a result, as the amount of SOx deposited when the temperature of the NOx catalyst is low, the NOx purification rate becomes lower than the threshold earlier and the NOx release process is started earlier. Therefore, exhaust purification can be improved.

  On the other hand, the NOx purification rate estimation means does not estimate that the decrease in the NOx purification rate is large unless the amount of SOx deposited when the temperature of the NOx catalyst is low, and therefore the amount of SOx deposited when the temperature of the NOx catalyst is low. The NOx purification rate is slower than the case where the amount is larger, and is below the threshold value. Therefore, since the NOx releasing process is started later than when the amount of accumulated SOx is large when the temperature of the NOx catalyst is low, it is possible to suppress the deterioration of fuel consumption accompanying the SOx releasing process.

  Further, the processing start time determining means has NOx purification rate estimating means for estimating a NOx purification rate of the NOx catalyst based on the accumulated SOx amount estimated by the accumulated SOx amount estimating means, and the NOx purification rate The time when the NOx purification rate estimated by the estimation means falls below a threshold is determined as the start time, and further, the accumulated SOx amount estimated by the accumulated SOx amount estimation means and the temperature grasping means are grasped. There may be provided a threshold value changing means for changing the threshold value based on the temperature at the time when the SOx is deposited.

  In such a case, the NOx purification rate estimating means estimates the NOx purification rate based on the accumulated SOx amount estimated by the accumulated SOx amount estimating means, and the threshold value changing means is used when the temperature of the NOx catalyst is low. By changing the threshold based on the amount of deposited SOx and the temperature at which SOx was deposited, such as changing the threshold to increase as the amount of deposited SOx increases, eventually SOx was deposited. The start time of the SOx release process is determined in consideration of the temperature at the time. Therefore, the start timing of the SOx release process can be optimized, exhaust purification can be improved, and deterioration in fuel consumption associated with the SOx release process can be suppressed.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the start timing of the SOx release process can be optimized. Thereby, exhaust gas purification can be improved and fuel consumption deterioration associated with SOx release processing can be suppressed.

  The best mode for carrying out the present invention will be exemplarily described in detail below based on the following embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention only to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus according to an embodiment of the present invention is applied and its intake and exhaust system.

  An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2 and includes a fuel injection valve 3 that directly injects fuel into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4, and the common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5.

  An intake passage 7 is connected to the internal combustion engine 1, and the intake passage 7 is connected to an air cleaner box 8. An air flow meter 9 that outputs an electrical signal corresponding to the mass of the intake air flowing through the intake passage 7 is attached to the intake passage 7 downstream of the air cleaner box 8.

  A compressor housing 10 a for the supercharger 10 is provided in a portion of the intake passage 7 downstream of the air flow meter 9. An intercooler 11 is attached to the intake passage 7 downstream from the compressor housing 10a. Further, an intake throttle valve 12 for adjusting the flow rate of the intake air flowing through the intake passage 7 is provided in the intake passage 7 downstream of the intercooler 11. An intake throttle actuator 13 is attached to the intake throttle valve 12. It has been.

  Further, an exhaust passage 14 is connected to the internal combustion engine 1, and the exhaust passage 14 is connected downstream with a muffler (not shown). Further, a turbine housing 10b of the supercharger 10 is disposed in the middle of the exhaust passage 14, and an NOx storage reduction catalyst 15 is provided in a portion of the exhaust passage 14 downstream from the turbine housing 10b. The exhaust passage 14 upstream of the NOx catalyst 15 has an air-fuel ratio sensor 16 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust flowing in the exhaust passage 14 and the temperature of the exhaust flowing in the exhaust passage 14. And an exhaust gas temperature sensor 17 for outputting an electrical signal corresponding to the above.

  A fuel addition valve 18 for adding fuel as a reducing agent to exhaust gas flowing in the exhaust port is attached to the exhaust port of the first cylinder (# 1) of the internal combustion engine 1. Is connected to the fuel pump 6 through a fuel passage 19.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20 for controlling the internal combustion engine 1. The ECU 20 is an arithmetic logic operation circuit including a CPU, ROM, RAM, backup RAM, and the like.

  In addition to the air flow meter 9, the air-fuel ratio sensor 16, and the exhaust gas temperature sensor 17 described above, the ECU 20 is attached to a crank position sensor 21 and a water temperature sensor 22 that are attached to the internal combustion engine 1, and a vehicle in which the internal combustion engine 1 is mounted. Various sensors such as an accelerator position sensor (not shown) are connected via electric wiring, and output signals from the various sensors described above are input to the ECU 20.

  On the other hand, the fuel injection valve 3, the intake throttle actuator 13, the fuel addition valve 18 and the like are connected to the ECU 20 via electric wiring, and the ECU 20 controls the fuel injection valve 3, the intake throttle actuator 13 and the fuel addition valve 18. It is possible to do.

  For example, the ECU 20 executes input of output signals of various sensors, calculation of engine speed, calculation of fuel injection amount, calculation of fuel injection timing, and the like in a basic routine to be executed at regular intervals. Various signals input by the ECU 20 and various control values obtained by the ECU 20 in the basic routine are temporarily stored in the RAM of the ECU 20.

  Further, the ECU 20 reads various control values from the RAM in an interrupt process triggered by the input of signals from various sensors and switches, the elapse of a predetermined time, or the input of a pulse signal from the crank position sensor 21. The fuel injection valve 3 and the like are controlled according to the control value.

Next, the NOx catalyst 15 according to this embodiment will be described.
When the air-fuel ratio of the exhaust gas flowing into the catalyst is a lean air-fuel ratio (greater than the stoichiometric air-fuel ratio), the NOx catalyst 15 holds NOx in the exhaust gas so as not to be released into the atmosphere, and the exhaust gas flowing into the catalyst When the air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio (below the stoichiometric air-fuel ratio), the retained NOx is released and reduced.

  Further, the fuel or oil contains a sulfur (S) component, and this S component reacts with oxygen to become SOx. The NOx catalyst retains SOx in the exhaust gas by the same mechanism as NOx. Therefore, when the amount of retained and accumulated SOx increases, the NOx purification capacity of the NOx catalyst 15 decreases accordingly, so-called SOx poisoning occurs. Occur.

  If SOx poisoning occurs in the NOx catalyst 15 in this way, the NOx purification capacity is reduced, and NOx in the exhaust gas may be exhausted to the atmosphere without being purified by the NOx catalyst 15. Therefore, in the present embodiment, when the NOx purification capability is reduced to a certain level, the SOx release process is executed in which the SOx deposited on the NOx catalyst 15 is released and reduced to be removed.

  In this SOx release process, the ECU 20 that also functions as a SOx release process means performs a catalyst temperature raising process for raising the bed temperature of the NOx catalyst 15 to 500 to 700 ° C. An air-fuel ratio process is performed to make the fuel ratio.

  Specifically, in the catalyst temperature raising process, as means for increasing the temperature of the NOx catalyst 15 at an early stage, in addition to the normal main fuel injection in the vicinity of the compression top dead center of the internal combustion engine 1, during the exhaust stroke or the expansion stroke. In addition, secondary injection such as post injection for injecting fuel into the cylinder as a secondary means or bi-rubber injection for injecting fuel into the cylinder in the vicinity of the top dead center of the intake stroke or exhaust stroke is performed.

  Further, by adding fuel as a reducing agent from the fuel addition valve 18 into the exhaust gas instead of the above-described sub-injection or together with the sub-injection, those unburned fuel components are oxidized in the NOx catalyst 15 and are oxidized. The bed temperature of the NOx catalyst may be increased by the generated heat.

  When the bed temperature of the NOx catalyst 15 becomes high due to the catalyst temperature raising process as described above, the ECU 20 executes the reducing agent addition control for adding the fuel as the reducing agent from the fuel addition valve 18 to the NOx catalyst 15. Air-fuel ratio processing is performed in which the air-fuel ratio of the inflowing exhaust gas is made rich.

By the way, when the timing for executing this SOx release processing is late, NOx is converted into NOx catalyst 1.
5 is discharged without being purified. On the other hand, if the timing is early, the SOx release process includes the air-fuel ratio process in which the air-fuel ratio of the exhaust gas is set to a rich air-fuel ratio as described above.

  Therefore, in this embodiment, the timing for executing the SOx release process is determined as follows.

  FIG. 2 shows the correlation between the temperature of the NOx catalyst (SOx poisoning temperature), the temperature of the NOx catalyst, and the NOx purification rate when SOx is deposited. Specifically, the NOx catalyst (A) at the beginning of use which is not poisoned with SOx, the NOx catalyst (B) in which 2.5 g of SOx is deposited at 500 ° C., and the NOx in which 2.5 g of SOx is deposited at 250 ° C. The NOx purification rate is compared by changing the temperature of the catalyst (C).

  As shown in the figure, for example, when the temperature of the NOx catalyst is 300 ° C., the purification rate of the catalyst A is 100%, whereas the purification rate of the catalyst B is about 90%, and the purification rate of the catalyst C is About 75%. When the temperature of the NOx catalyst is 400 ° C., the purification rate of the catalyst A is 100%, whereas the purification rate of the catalyst B is about 97% and the purification rate of the catalyst C is about 80%.

  As a result, even if the accumulated SOx amount is the same, the NOx purification rate differs depending on the temperature of the NOx catalyst (SOx poisoning temperature) at the time when the SOx is deposited, and the lower the SOx poisoning temperature, the greater the decrease in the NOx purification rate. I understand.

  This is because SOx retained and deposited when the NOx catalyst is at a high temperature diffuses quickly into the catalyst because the temperature is high, whereas SOx deposited when the NOx catalyst is at a low temperature is NOx. This is thought to be because it accumulates on the surface of the catalyst and reduces the chance of contact between NOx in the exhaust and the NOx catalyst.

  Therefore, in this embodiment, the SOx release process start timing is determined in consideration of the accumulated SOx amount and the SOx poisoning temperature, and the SOx release process control for starting execution of the SOx release process is executed at this timing.

[First SOx release processing control]
As an outline of this control, the SOx poisoning state amount is obtained based on the accumulated SOx amount and the SOx poisoning temperature, the NOx purification rate is estimated from the SOx poisoning state amount, and the NOx purification rate falls below the threshold value. In this case, the execution of the SOx release process is started. Specifically, the SOx release process control will be described with reference to the flowchart shown in FIG.

  This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.

In this routine, the ECU 20 first estimates the amount of SOx (Qs) accumulated on the NOx catalyst 15 during the current flow from the previous flow in step (hereinafter simply referred to as “S”) 101. This is estimated based on the driving | running state in the meantime. There is a correlation between the operating state of the internal combustion engine 1 ascertained from at least one of the output values of the water temperature sensor 22, the crank position sensor 21 or the accelerator position sensor, and the fuel injection amount and the oil consumption amount. There is also a correlation between the operating state and the amount of SOx generated from the injected fuel and consumed oil. Therefore, a map indicating the correlation established between the operating state and the amount of SOx flowing into the NOx catalyst 15 is created in advance and stored in the ROM, and in this step, the map and the current operating state are used. NOx catalyst 15
The amount of SOx flowing into the NOx catalyst 15 is estimated, and the accumulated SOx amount Qs is estimated assuming that all of the inflowed SOx amount has accumulated on the NOx catalyst 15. In this way, this step functions as a deposited SOx amount estimating means.

  Thereafter, the process proceeds to S102, and the temperature of the NOx catalyst 15 at the time when the SOx estimated in S101 is deposited on the NOx catalyst 15, that is, the SOx poisoning temperature (T) of Qs is estimated. The temperature is estimated to be the same as the temperature of the exhaust gas flowing into the NOx catalyst 15, and is estimated based on the detected value of the exhaust temperature sensor 17. Alternatively, since the exhaust temperature changes according to the operating state of the internal combustion engine 1, a map showing the correlation between the operating state and the SOx poisoning temperature T is created in advance and stored in the ROM, and the map and the current The temperature T may be estimated based on the operating state. Further, the temperature of the NOx catalyst 15 may be detected by a temperature sensor provided directly on the NOx catalyst 15. In this way, this step functions as temperature grasping means.

  Thereafter, the process proceeds to S103, and the performance degradation coefficient Kt is determined. As described above, since the effect of the SOx deposited at that temperature on the NOx purification capacity varies depending on the SOx poisoning temperature, the performance degradation coefficient Kt is corrected by correcting the amount of SOx deposited at that temperature, and the SOx poisoning state. It is used to calculate the quantity. Therefore, as shown in FIG. 4, it changes according to the SOx poisoning temperature T. For example, when the SOx poisoning temperature T is 250 ° C., Kt is 1.25, and the SOx poisoning temperature T is 500 ° C. The time Kt is set to be 1. Then, the correlation between the SOx poisoning temperature T and the performance degradation coefficient Kt as shown in FIG. 4 is obtained in advance and stored in the ROM, and in this step, it is determined based on the map and the SOx poisoning temperature T estimated in S102. To do.

  Thereafter, the process proceeds to S104, and the SOx poisoning state quantity Qsr is calculated. This is obtained by adding a value obtained by multiplying the SOx poisoning state quantity Qsr calculated in the previous flow by the Qs calculated in S101 and the performance degradation coefficient Kt determined in S103, that is, “Qsr = Qsr + Qs × Kt”. The current SOx poisoning state quantity Qsr is calculated based on the equation.

  Thereafter, the process proceeds to S105, and the NOx purification rate is estimated from Qsr calculated in S104. The SOx poisoning state quantity Qsr calculated in S104 and the NOx purification rate are inversely proportional, that is, the NOx purification rate is low when the SOx poisoning state quantity Qsr is large, and the NOx purification rate is high when the SOx poisoning state quantity Qsr is small. . Therefore, the correlation between the SOx poisoning state quantity Qsr and the NOx purification rate is obtained in advance and stored in the ROM, and in this step, estimation is performed based on the map and the SOx poisoning state quantity Qsr calculated in S104. .

  Thus, the NOx purification rate is estimated from the SOx poisoning state quantity Qsr in S105, and this SOx poisoning state quantity Qsr is based on the Qs calculated in S101 and the SOx poisoning temperature of the Qs. Since it is calculated based on the performance degradation coefficient Kt calculated in S103, the processes from S103 to S105 function as NOx purification rate estimation means. Therefore, the NOx purification rate estimation means estimates the NOx purification rate based on the accumulated SOx amount and the temperature of the NOx catalyst when SOx is deposited.

  In S106, the ECU 20 determines whether or not the NOx purification rate estimated in S105 is equal to or less than a threshold value. The threshold value is a value set slightly higher than the limit NOx purification rate determined in consideration of the influence of the exhaust amount of the internal combustion engine and the NOx discharged into the atmosphere on the global environment. If an affirmative determination is made in this step, the process proceeds to S107 to start executing the SOx release process. On the other hand, if a negative determination is made, the execution of this routine is terminated. In other words, the time when the estimated NOx purification rate becomes equal to or less than the threshold is determined as the start time of the SOx release process from the process of S106. Therefore, the NOx purification rate estimating means and the process of S106 function as a process start time determining means for determining the start time of the SOx release process.

  After starting execution of the SOx release process in S107, the process proceeds to S108, and the ECU 20 determines whether or not the SOx release process end condition is satisfied. For example, when the pressure difference between the upstream side and the downstream side of the NOx catalyst 15 is equal to or less than a predetermined value, the elapsed time from the start of execution of the SOx release process is equal to or longer than a predetermined time. Some conditions can be exemplified.

  If it is determined in S108 that the SOx release process end condition is not satisfied, the SOx release process is continued until the SOx release process end condition is satisfied. On the other hand, after it is determined in S108 that the SOx release process termination condition is satisfied, the process proceeds to S109, where the SOx release process is terminated and the execution of this routine is terminated.

  According to this SOx release processing control, even if the accumulated SOx amount is the same, the NOx purification rate is estimated to be different depending on the temperature of the NOx catalyst 15 at the time when SOx is deposited, and the estimated NOx purification rate. Accordingly, the start time of the SOx release process is determined. Specifically, as the SOx poisoning temperature is lower, the value of the performance degradation coefficient Kt is larger and the SOx poisoning state quantity Qsr is larger, so the NOx purification rate is also lowered by that amount, and the start timing of the SOx release process is advanced. . Therefore, even if the same amount of SOx is deposited on the NOx catalyst 15, it is estimated that the greater the amount of SOx deposited when the temperature of the NOx catalyst 15 is lower, the greater the decrease in the NOx purification rate. Processing will start early.

  On the other hand, the higher the SOx poisoning temperature, the smaller the value of the performance deterioration coefficient Kt and the SOx poisoning state quantity Qsr does not rise so much. Therefore, the NOx purification rate does not fall as compared with the case where the SOx poisoning temperature is low. Therefore, since the NOx release process is started later than when the amount of accumulated SOx is large when the temperature of the NOx catalyst 15 is low, it is possible to suppress deterioration in fuel consumption associated with the SOx release process.

  Therefore, by determining the start time of the SOx release process in this way and starting the execution of the SOx release process at this timing, it is possible to improve exhaust gas purification and suppress deterioration in fuel consumption associated with the SOx release process. be able to.

[Second SOx Release Processing Control]
In the first SOx release processing control described above, the SOx poisoning state quantity Qsr is calculated in S104, and then the NOx purification rate is estimated from the SOx poisoning state quantity Qsr in S105, and then the NOx purification rate is determined in S106. When it is determined that the SOx release process is not more than a predetermined threshold value, the execution of the SOx release process is started. In this control, the SOx poisoning state quantity Qsr is a predetermined SOx poisoning state quantity threshold value. It is determined whether or not it is equal to or greater than Qst. When Qsr is equal to or greater than Qst, execution of SOx release processing is started.

  Specifically, the present SOx release process control will be described with reference to the flowchart of the present control routine of FIG. This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.

  In addition, since this control routine only replaces S205 in S105 and S106 of the control routine in the first SOx release processing control shown in FIG. 3, only this part will be described, and detailed description of other steps will be omitted. To do.

In S204, after calculating the SOx poisoning state quantity Qsr, the process proceeds to S205, and in this step, whether or not the SOx poisoning state quantity Qsr calculated in S204 is greater than or equal to a predetermined SOx poisoning state quantity threshold value Qst. Determine. If a negative determination is made, the execution of this routine is terminated. If an affirmative determination is made, the process proceeds to S207, and execution of the SOx release process is started. The threshold value Qst is a value set slightly lower than the limit SOx poisoning state amount determined in consideration of the influence of the exhaust amount of the internal combustion engine and NOx discharged to the atmosphere on the global environment. .

  As described above, even when the start timing of the SOx release process is determined based on the SOx poisoning state quantity, exhaust purification can be improved and SOx can be improved as in the case of using the first SOx release process control. Deterioration of fuel consumption associated with the release process can be suppressed.

[Third SOx release processing control]
In the first SOx release processing control described above, the amount of accumulated SOx is corrected by the SOx poisoning temperature to obtain the SOx poisoning state quantity Qsr, the NOx purification rate is estimated based on the Qsr, and the NOx purification rate is calculated. In this control, the NOx purification rate threshold value α is changed in consideration of the SOx poisoning temperature, and the accumulated SOx amount is calculated. When the estimated NOx purification rate becomes equal to or less than the threshold value α, the SOx release process is executed.

  Specifically, the present SOx release processing control will be described with reference to the flowchart shown in FIG. This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.

  The processes in S301 and S302 are the same as those in S101 and S102, respectively, and the processes after S307 are the same as the processes in S107 and after, so detailed description thereof will be omitted.

  In S303, a threshold change coefficient Kr, which is a coefficient for changing the predetermined threshold α based on the SOx poisoning temperature, is determined. Thereafter, the process proceeds to S304, and the threshold value α is changed. This is obtained by adding a value obtained by multiplying the threshold value α determined until the previous flow by Qs calculated in S301 and the threshold value change coefficient Kr determined in S303, that is, “α = α + Qs × Kr”. The current threshold value α is calculated based on the following formula. Therefore, the processing of S303 and S304 functions as a threshold value changing unit.

  As described above, as the SOx poisoning temperature decreases, the SOx deposited at that temperature decreases the NOx purification rate, so the threshold change coefficient Kr determined in S303 is low in the SOx poisoning temperature estimated in S302. In some cases, the threshold value is changed to be higher. That is, the threshold value change coefficient Kr changes according to the SOx poisoning temperature T as shown in FIG. 4. For example, when the SOx poisoning temperature T is 250 ° C., Kr is 1, and the SOx poisoning temperature T When K is 500 ° C., Kr is set to be zero.

  Then, the correlation between the SOx poisoning temperature T and the threshold change coefficient Kr as shown in FIG. 4 is obtained in advance and stored in the ROM, and in S303, the threshold is changed based on the map and the SOx poisoning temperature T estimated in S302. The coefficient Kr is determined.

In S305, the NOx purification rate is estimated from the SOx amount deposited from the end of the previous SOx release process to the current flow (hereinafter referred to as “total deposited SOx amount”). The total accumulated SOx amount can be estimated by integrating the accumulated SOx amount Qs estimated in S301 of each flow, and the total accumulated SOx amount and the NOx purification rate are inversely proportional, that is, the total accumulated SOx amount. If the amount is large, the NOx purification rate is low, and if the total amount of accumulated SOx is small, the NOx purification rate is high. Therefore, the correlation between the total accumulated SOx amount and the NOx purification rate is obtained in advance and stored in the ROM, and in this step, the NOx purification rate is estimated based on the map and the total accumulated SOx amount. Thus, the process of this step functions as a NOx purification rate estimation means.

  Thereafter, the process proceeds to S306, and it is determined whether or not the NOx purification rate estimated in S305 is equal to or less than the threshold value α calculated in S304. If an affirmative determination is made in this step, the process proceeds to S307, and SOx release processing is executed. On the other hand, if a negative determination is made, the execution of this routine is terminated. That is, the time when the estimated NOx purification rate becomes equal to or less than the threshold value α is determined as the start time of the SOx release process from the process of S306. Therefore, the threshold value changing means and the process of S306 function as a process start time determining means for determining the start time of the SOx release process.

  By determining the timing for starting the SOx release process in this way and starting the execution of the SOx release process at the timing, exhaust purification can be improved as in the case of using the first SOx release process control. At the same time, it is possible to suppress deterioration in fuel consumption associated with the SOx release process.

[Fourth SOx release processing control]
In the third SOx release processing control, the threshold value α is calculated in S304, and then the NOx purification rate is estimated from the total accumulated SOx amount in S305. Then, in S306, the NOx purification rate is equal to or less than the threshold value α calculated in S304. If it is determined that there is, the execution of the SOx release process is started. In this control, it is determined whether or not the total deposition SOx amount is equal to or greater than the total deposition SOx amount threshold Qst, and the total deposition SOx amount is determined. When the amount is equal to or greater than the threshold value Qst, execution of the SOx release process is started. Then, the threshold value Qst is changed based on the SOx poisoning temperature.

  Specifically, the present SOx release process control will be described with reference to the flowchart of the present control routine of FIG. This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.

  The processes in S401 and S402 are the same as those in S301 and S302, respectively, and the processes in and after S407 are the same as the processes in and after S107.

  In S403, a threshold change coefficient Kr2 for changing the threshold Qst of the total accumulated SOx amount is determined. As described above, the lower the SOx poisoning temperature, the more the SOx deposited at that temperature increases the decrease in the NOx purification rate. Therefore, the threshold change coefficient Kr2 determined in S403 is lower when the SOx poisoning temperature estimated in S402 is lower. Accordingly, the threshold value is changed to be lowered. That is, the threshold value change coefficient Kr2 changes according to the SOx poisoning temperature T as shown in FIG. 4. For example, when the SOx poisoning temperature T is 250 ° C., Kr2 is 1, and the SOx poisoning temperature T When Kr2 is 500 ° C., Kr2 is set to be zero. Then, the correlation between the SOx poisoning temperature T and the threshold value change coefficient Kr2 as shown in FIG. 4 is obtained in advance and stored in the ROM, and in S403, the threshold value is changed based on the map and the SOx poisoning temperature T estimated in S402. The coefficient Kr2 is determined.

  In S404, the threshold value Qst is calculated by subtracting the value obtained by multiplying Qs estimated in S401 by the threshold change coefficient Kr2 determined in S403 from the threshold value Qst calculated in the previous flow. That is, “Qst = Qst−Qs × Kr2” is calculated.

In S405, it is determined whether or not the total accumulated SOx amount is equal to or larger than the threshold value Qst calculated in S404. If it is determined that the total accumulated SOx amount is equal to or greater than Qst, S4
The process proceeds to 07 to start executing the SOx release process. On the other hand, if the total accumulated SOx amount is smaller than the threshold value Qst in S405, the execution of this routine is terminated.

  As described above, even when the start timing of the SOx release process is determined based on the SOx poisoning state quantity, exhaust purification can be improved and SOx can be improved as in the case of using the third SOx release process control. Deterioration of fuel consumption associated with the release process can be suppressed.

[Fifth SOx release processing control]
FIG. 8 shows the SOx poisoning temperature, the NOx catalyst temperature, and the desorption SOx concentration (when a certain amount of exhaust gas passes through the NOx catalyst, the desorbed SOx amount contained in the exhaust amount). This shows the correlation. Specifically, the temperature of the NOx catalyst (B) in which 2.5 g of SOx was deposited at 500 ° C. and the temperature of the NOx catalyst (C) in which 2.5 g of SOx was deposited at 250 ° C. were changed, and the desorbed SOx concentration was changed. Is a comparison.

  As shown in this figure, catalyst B has the highest desorbed SOx concentration at about 670 ° C., whereas catalyst C has the highest desorbed SOx concentration at about 600 ° C. That is, it is understood that when the temperature of the NOx catalyst is raised to about 600 ° C., more SOx deposited on the catalyst C is desorbed than SOx deposited on the catalyst B. In other words, in order to desorb a certain amount of SOx, the catalyst B has to be raised to, for example, about 670 ° C., whereas the catalyst C has only to be raised to about 600 ° C. That is, the SOx deposited on the catalyst C is more easily desorbed than the SOx deposited on the catalyst B, which means that the SOx is more easily desorbed as it is deposited at a lower temperature. This is because, as described above, the SOx retained and deposited when the NOx catalyst is at a high temperature diffuses quickly into the catalyst because the temperature is high, whereas the SOx catalyst is at a low temperature. It is thought that the SOx deposited is deposited on the surface of the NOx catalyst.

  From this, it can be seen that when the amount of deposited SOx is the same, the time required to desorb all of the deposited SOx, that is, the time required for the SOx release process, differs depending on the SOx poisoning temperature. On the other hand, as described above, the SOx release process includes the air-fuel ratio process in which the air-fuel ratio of the exhaust is made rich, so that if the time required for the SOx release process becomes longer, the fuel consumption deteriorates.

  Therefore, in the fifth SOx release process control, the start time of the SOx release process is determined so that the NOx purification rate does not become lower than the threshold and the time required for the SOx release process does not become long.

  Specifically, the present SOx release processing control will be described using the flowchart shown in FIG. This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.

  This control routine is different from the control routine in the second SOx release processing control shown in FIG. 5 only in S503 and S504. Therefore, only this part will be described, and detailed description of other steps will be omitted.

In S503, the above-described performance degradation coefficient Kt and performance degradation coefficient Ku are determined. As described above, since the ease of detachment of SOx deposited at that temperature differs depending on the SOx poisoning temperature, the performance degradation coefficient Ku is corrected by correcting the amount of SOx deposited at that temperature to obtain the SOx poisoning state quantity. It is used for calculation. Therefore, as shown in FIG. 10, it changes according to the SOx poisoning temperature T. For example, when the SOx poisoning temperature T is 250 ° C., Ku is zero, and when the SOx poisoning temperature T is 500 ° C., Ku. Is set to be 0.2. Then, the correlation between the SOx poisoning temperature T and the performance degradation coefficient Ku as shown in FIG. 10 is obtained in advance and stored in the ROM, and in this step, the performance degradation coefficient Kt is determined as described above, and the map Ku is also determined based on the SOx poisoning temperature T estimated in S502. Even in this step, the performance degradation coefficient Kt is determined as described in the first SOx release process control.

  In S504, the SOx poisoning state quantity Qsr is calculated. This is obtained by adding a value obtained by multiplying the SOx poisoning state quantity Qsr calculated in the previous flow by Qs calculated in S501 and the value obtained by adding the performance degradation coefficients Kt and Ku determined in S503. The current SOx poisoning state quantity Qsr is calculated on the basis of an expression of “Qsr = Qsr + Qs × (Kt + Ku)”.

  The processing after S505 is the same as the processing after S205. In S505, it is determined whether or not the SOx poisoning state quantity Qsr calculated in S504 is equal to or larger than a predetermined SOx poisoning state quantity threshold Qst. . If a negative determination is made, the execution of this routine is terminated. If an affirmative determination is made, the process proceeds to S507, and execution of the SOx release process is started. The threshold value Qst is slightly lower than the limit SOx poisoning state amount determined in consideration of the exhaust amount of the internal combustion engine, the influence of NOx discharged to the atmosphere on the global environment, the time required for the SOx release process, and the like. It is a value set to.

  By determining the timing for starting the SOx release processing in this way and starting the execution of the SOx release processing at this timing, the exhaust gas can be purified with higher accuracy, and the fuel consumption associated with the SOx release processing can be further reduced. It can be surely suppressed.

[Sixth SOx release processing control]
In the fifth SOx release process control described above, the SOx poisoning state quantity Qsr is obtained by correcting the accumulated SOx quantity based on the SOx poisoning temperature, and the SOx release process is performed when the Qsr exceeds a predetermined threshold value. In this control, the SOx poisoning temperature is set in the same manner as in the fourth SOx release processing control in consideration of the ease of desorption of the deposited SOx based on the SOx poisoning temperature. Based on this, the threshold value Qst of the total deposited SOx amount is changed, and the SOx release process is started when the total deposited SOx amount becomes equal to or greater than the threshold value Qst.

  Specifically, the present SOx release processing control will be described using the flowchart shown in FIG. This control routine is a routine that is stored in advance in the ROM of the ECU 20 and is a routine that is executed by the ECU 20 as an interrupt process triggered by elapse of a fixed time or input of a pulse signal from the crank position sensor 21.

  This control routine is different from the control routine in the fourth SOx release process control shown in FIG. 7 only in S603 and S604, so only this part will be described and detailed description of other steps will be omitted.

  In S603, a threshold change coefficient Kr2 and a threshold change coefficient Kv, which are coefficients for changing a predetermined threshold Qst based on the SOx poisoning temperature, are determined. As described above, the easiness of desorption of SOx deposited at that temperature differs depending on the SOx poisoning temperature. Therefore, the threshold value change coefficient Kv determined in S603 decreases as the SOx poisoning temperature estimated in S602 decreases. It is changed so that That is, the threshold value change coefficient Kv changes according to the SOx poisoning temperature T as shown in FIG. 10, for example, when the SOx poisoning temperature T is 250 ° C., the Kv is zero, and the SOx poisoning temperature T When K is 500 ° C., Kv is set to be 0.2.

  Then, the correlation between the SOx poisoning temperature T and the threshold value change coefficient Kv as shown in FIG. 10 is obtained in advance and stored in the ROM, and in S603, the threshold value is changed based on the map and the SOx poisoning temperature T estimated in S602. A coefficient Kv is determined. Also in this step, the threshold value change coefficient Kr2 is determined as described in the fourth SOx release process control.

  In S604, a value obtained by multiplying Qs estimated in S601 by the value obtained by adding the threshold change coefficients Kr2 and Kv determined in S603 is subtracted from the threshold Qst calculated in the previous flow, that is, , The current threshold value Qst is calculated based on the equation “Qst = Qst−Qs × (Kr2 + Kv)”.

  In S605, it is determined whether or not the total accumulated SOx amount is equal to or larger than the threshold value Qst calculated in S604. If it is determined that the total accumulated SOx amount is equal to or greater than Qst, the process proceeds to S407, and execution of the SOx release process is started. On the other hand, if the total accumulated SOx amount is smaller than the threshold value Qst in S605, the execution of this routine is terminated.

  By determining the timing for starting the SOx release processing in this way and starting the execution of the SOx release processing at this timing, the exhaust gas can be purified with higher accuracy and the fuel consumption associated with the SOx release processing can be more reliably reduced. Can be suppressed.

1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment is applied and an intake / exhaust system thereof. It is a figure which shows the correlation of the catalyst temperature of a NOx catalyst, a NOx purification rate, and SOx poisoning temperature. It is a flowchart figure of 1st SOx discharge | release process control. It is a figure which shows the correlation of performance degradation coefficient Kt or Kr, and SOx poisoning temperature. It is a flowchart figure of 2nd SOx discharge | release process control. It is a flowchart figure of 3rd SOx discharge | release process control. It is a flowchart figure of 4th SOx discharge | release process control. It is a figure which shows the correlation of the catalyst temperature of NOx catalyst, desorption | desorption SOx density | concentration, and SOx poisoning temperature. It is a flowchart figure of 5th SOx discharge | release process control. It is a figure which shows the correlation of threshold value change coefficient Ku or Kv, and SOx poisoning temperature. It is a flowchart figure of 6th SOx discharge | release process control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Common rail 5 Fuel supply pipe 6 Fuel pump 7 Intake passage 8 Air cleaner box 9 Air flow meter 10 Supercharger 11 Intercooler 12 Intake throttle valve 13 Intake throttle actuator 14 Exhaust passage 15 Exhaust purification device 16 Air-fuel ratio sensor 17 Exhaust temperature sensor 18 Fuel addition valve 19 Fuel passage 20 ECU
21 Crank position sensor 22 Water temperature sensor

Claims (6)

An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
Temperature grasping means for grasping the temperature of the NOx catalyst;
Deposited SOx amount estimating means for estimating the amount of SOx deposited on the NOx catalyst;
SOx release processing means for performing SOx release processing for releasing SOx deposited on the NOx catalyst;
A process of determining the start time of the SOx release process by the SOx release processing means based on the accumulated SOx quantity estimated by the deposited SOx quantity estimation means and the temperature at which the SOx grasped by the temperature grasping means is deposited. Start time determination means,
An exhaust emission control device for an internal combustion engine, comprising:   2. The exhaust gas purification of an internal combustion engine according to claim 1, wherein the processing start timing determining means determines that the start timing is earlier as the amount of SOx accumulated when the temperature of the NOx catalyst is lower is larger. apparatus.   The processing start timing determining means determines the NOx purification rate of the NOx catalyst based on the accumulated SOx amount estimated by the accumulated SOx amount estimating means and the temperature at the time when SOx is grasped by the temperature grasping means. 2. The method according to claim 1, further comprising a NOx purification rate estimation means for estimating, wherein the start time is determined when the NOx purification rate estimated by the NOx purification rate estimation means is equal to or less than a threshold value. Exhaust gas purification device for internal combustion engine.   4. The exhaust gas purification of an internal combustion engine according to claim 3, wherein the NOx purification rate estimating means estimates that the amount of decrease in the NOx purification rate increases as the amount of SOx accumulated when the temperature of the NOx catalyst is low increases. apparatus.   The processing start timing determining means includes NOx purification rate estimating means for estimating a NOx purification rate of the NOx catalyst based on the accumulated SOx amount estimated by the accumulated SOx amount estimating means, and the NOx purification rate estimating means Is determined as the start time, and is further grasped by the accumulated SOx amount estimated by the accumulated SOx amount estimating means and the temperature grasping means. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising threshold value changing means for changing the threshold value based on a temperature at the time when SOx is deposited.   6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5, wherein the threshold value changing means changes the threshold value to increase as the amount of SOx accumulated when the temperature of the NOx catalyst is low increases. .

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