JP4158459B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that performs rich spike control when the NOx storage amount approaches a limit in an internal combustion engine equipped with an NOx storage reduction catalyst in an exhaust system.
[0002]
[Prior art]
As an exhaust gas purification system for an internal combustion engine, NOx in the exhaust gas is occluded during the execution of stratified combustion or lean combustion, and when the stoichiometric air-fuel ratio or higher fuel concentration (rich) combustion is started and the oxygen concentration in the exhaust gas is reduced, occlusion is performed. A technique using a NOx occlusion reduction catalyst that releases and reduces NOx is known (Japanese Patent Laid-Open No. 7-166851). In this system, when the NOx concentration sensor detects that the NOx concentration downstream of the NOx storage reduction catalyst has increased, the exhaust air-fuel ratio is temporarily made rich by rich spike control to reduce the NOx stored in the NOx storage reduction catalyst. The NOx occlusion reduction catalyst is regenerated.
[0003]
However, in such a system, since the NOx storage reduction catalyst is regenerated by executing the rich spike control after the NOx concentration in the exhaust gas exhausted from the NOx storage reduction catalyst increases, the start of the rich spike control is not performed. Slow, it is still insufficient as a system for suppressing NOx emissions.
[0004]
Therefore, a system has been proposed in which the amount of NOx discharged from the internal combustion engine is estimated based on the operating state of the internal combustion engine, and the NOx storage amount of the NOx storage reduction catalyst is estimated by adding up the estimated NOx amount (Japanese Patent Application Laid-Open (JP-A)). 2001-271697). In this system, the NOx occlusion reduction catalyst is regenerated by rich spike control when the estimated NOx occlusion amount exceeds a predetermined value. As a result, the NOx storage reduction catalyst can be regenerated before the NOx concentration downstream of the NOx storage reduction catalyst increases.
[0005]
This predetermined value is a value that is determined in advance by experiment or the like to obtain the NOx occlusion amount until the NOx concentration downstream of the NOx occlusion reduction catalyst begins to increase, and with a certain amount of margin.
[0006]
[Problems to be solved by the invention]
However, the NOx storage reduction catalyst deteriorates with use. For example, the NOx occlusion capacity of the NOx occlusion reduction catalyst decreases due to deterioration due to heat or sulfur poisoning. If such deterioration occurs, the predetermined value set in advance may delay the start timing of the rich spike control and increase the NOx emission amount.
[0007]
In JP-A-2001-271697, the deterioration of the NOx storage reduction catalyst is determined by a NOx sensor provided on the downstream side of the NOx storage reduction catalyst. That is, when the operation of the internal combustion engine is continued in a state where the rich spike control is prohibited and the NOx concentration detected by the NOx sensor exceeds the increase determination value, the presence or absence of deterioration is determined based on the NOx occlusion amount level estimated at this time Is judged.
[0008]
However, in this disclosed technique, when deterioration is determined, only alarms and deterioration diagnosis information are stored in the memory, and no countermeasure is taken against the rich spike control. For this reason, even if it becomes clear that the start timing of the rich spike control is not appropriate, if it is left as it is, there is a possibility that the NOx emission amount increases.
[0009]
Further, the NOx occlusion reduction catalyst is not only deteriorated, but, for example, when it has deteriorated due to sulfur poisoning, the NOx occlusion ability may be restored by recovering from the deteriorated state depending on the operating state of the internal combustion engine. Even when the NOx occlusion capacity increases in this way, the Japanese Patent Application Laid-Open No. 2001-271697 does not take any measures.
[0010]
The present invention detects NOx in exhaust gas that has temporarily passed through the NOx storage reduction catalyst, and reflects this detection result in rich spike control, thereby increasing the amount of NOx emitted from the NOx storage reduction catalyst for a long period of time. It is an object of the present invention to enable continuous use of the NOx storage reduction catalyst.
[0011]
[Means for Solving the Problems]
  In the following, means for achieving the above object and its effects are described.
  (1) The invention described in claim 1 detects a NOx occlusion reduction catalyst that performs occlusion of NOx contained in exhaust gas and reduction of the occluded NOx, and detects NOx concentration in the exhaust gas that has passed through the NOx occlusion reduction catalyst. NOx detection means, and based on the determination that the estimated value of the NOx occlusion amount of the NOx occlusion reduction catalyst is greater than or equal to the rich spike execution judgment value, the fuel component in the exhaust gas is temporarily increased to In an exhaust gas purification apparatus for an internal combustion engine that performs rich spike control for reducing NOx of a NOx occlusion reduction catalyst, it is determined that NOx in the exhaust begins to pass through the NOx occlusion reduction catalyst based on a detection result of the NOx detection means. Sometimes, the rich spike execution determination value is updated based on the engine operation history at this time, and the execution of the rich spike control is performed. It is determined that the increase update condition including that of the engine is satisfied and that the state in which NOx in the exhaust begins to pass through the NOx storage reduction catalyst has not been reached based on the detection result of the NOx detection means. The gist of the present invention is that it includes an execution determination value updating means for updating the rich spike execution determination value in a manner that gradually increases during a certain period.
[0012]
When NOx flows into the NOx storage reduction catalyst from the internal combustion engine, the NOx storage amount of the NOx storage reduction catalyst increases. When the NOx occlusion amount approaches the limit and the NOx occlusion reduction catalyst cannot fully occlude flowing NOx, the NOx concentration in the exhaust gas exhausted by the NOx occlusion reduction catalyst begins to increase. Therefore, the timing at which the NOx concentration increasing state is detected by the NOx detecting means is immediately after the NOx storage reduction catalyst has exceeded the storage capacity, and therefore the NOx detecting means detects the increase in NOx concentration. The history of operation of the internal combustion engine at that time reflects the storage capacity of the NOx storage reduction catalyst.
[0013]
For this reason, the rich spike execution determination value update means updates the rich spike execution determination value based on the history of operation of the internal combustion engine. As a result, even if the storage capacity of the NOx storage reduction catalyst is changed due to deterioration or the like, it can be updated to the rich spike execution determination value suitable for the actual storage capacity of the NOx storage reduction catalyst. Thus, the start timing of the rich spike control becomes appropriate, and the increase in the NOx concentration discharged from the NOx storage reduction catalyst described above becomes temporary. Therefore, even if the NOx storage reduction catalyst is continuously used, the NOx emission amount is not increased, and the NOx storage reduction catalyst can be continuously used over a long period of time.
[0014]
  On the other hand, when the increase in NOx concentration is not detected by the NOx detection means between rich spike control and rich spike control, the rich spike execution determination value may be appropriate or the rich spike execution determination value is appropriate. May be smaller than range. If the rich spike execution determination value is too small, the execution frequency of the rich spike control may increase as a whole and the fuel consumption may deteriorate.
[0015]
  For this reason, the rich spike execution determination value updating means updates the rich spike execution determination value to increase when the NOx concentration increase is not detected by the NOx detection means under the increase update condition. If the rich spike execution determination value increases beyond the appropriate value due to the increase in the rich spike execution determination value, the rich spike control and the rich spike control are executed despite the rich spike control being repeatedly executed. The increase in the NOx concentration is detected by the NOx detecting means during the control. When the increase in the NOx concentration is detected in this way, the rich spike execution determination value update means appropriately updates the rich spike execution determination value based on the aforementioned history of internal combustion engine operation.
[0016]
  This makes it possible to maintain the rich spike execution determination value within an appropriate range, so that the NOx concentration in the exhaust gas discharged from the NOx storage reduction catalyst becomes temporary and the rich spike control execution is performed at a more suitable frequency. can do. For this reason, even if the NOx storage reduction catalyst is continuously used, it is possible to reliably prevent an increase in the NOx emission amount and to suppress an increase in fuel consumption.
[0017]
  (2) The invention according to claim 2 detects a NOx occlusion reduction catalyst that performs occlusion of NOx contained in exhaust gas and reduction of the occluded NOx, and detects NOx concentration in the exhaust gas that has passed through the NOx occlusion reduction catalyst. NOx detection means, and based on the determination that the estimated value of the NOx occlusion amount of the NOx occlusion reduction catalyst is greater than or equal to the rich spike execution judgment value, the fuel component in the exhaust gas is temporarily increased to In an exhaust purification device for an internal combustion engine that performs rich spike control for reducing NOx of a NOx storage reduction catalyst, the rich spike execution determination value is updated, and as an aspect thereof, based on a detection result of the NOx detection means When it is determined that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst, the rich gas is determined based on the engine operation history at this time. A first mode in which the Iku execution determination value is updated and the rich spike execution determination value is maintained at the updated value until it is determined that at least next NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst. When the rich spike execution determination value after updating in this mode is smaller than the limit value of the NOx storage amount of the NOx storage reduction catalyst at that time, the updated rich spike execution determination value is gradually increased. The execution determination value is continuously updated in such a manner that the rich spike execution determination value is set to a value larger than the limit value of the NOx storage amount through this, whereby the actual NOx storage amount of the NOx storage reduction catalyst becomes the value. Even if the limit value of the NOx occlusion amount is reached, a state in which the rich spike control is not executed is generated, and thereafter, based on the detection result of the NOx detecting means. When it is determined that NOx in the exhaust gas has started to pass through the NOx occlusion reduction catalyst, the execution determination value update has a second mode in which the rich spike execution determination value is updated based on the engine operation history at this time. The gist is to provide means.
[0018]
  (3) The invention according to claim 3 is the exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the execution determination value update means includes an execution update value condition that the rich spike control can be executed. Is gradually increased on the condition that it is determined that NOx in the exhaust gas has not started to pass through the NOx storage reduction catalyst based on the detection result of the NOx detection means. The gist is to update the rich spike execution determination value in the aspect.
[0019]
  (4) The invention according to claim 4 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the rich spike execution determination value update means is a detection result of the NOx detection means. The determination that the NOx concentration in the exhaust gas has passed from the state in which the NOx in the exhaust gas has not passed through the NOx occlusion reduction catalyst has shifted from the state in which the NOx concentration is less than the concentration increase determination value to the state in which it has exceeded this The gist is to do.
[0020]
  (5) The invention according to claim 5 is the exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the rich spike execution determination value update means uses the NOx in the exhaust as the NOx as the concentration increase determination value. The use of a value that can be reliably detected by the NOx detection means and that is set in advance as a value larger than “0” and in the vicinity of “0” using the NOx detection means. It is said.
[0021]
  (6) The invention according to claim 6 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein the execution determination value update means is configured so that an engine operation state is set under the increase update condition. The gist is to include being in an idling state.
[0022]
  As a result, the rich spike execution determination value is increased when the internal combustion engine is idle, so that the detection of the NOx concentration is executed in a state where the exhaust flow rate of the internal combustion engine is small. For this reason, in order to detect the NOx concentration increase by the NOx detection means, even if NOx is temporarily discharged from the NOx occlusion reduction catalyst, the absolute emission amount itself can be reduced, so the influence on the environment is less. Become.
[0023]
  (7) The invention according to claim 7 detects a NOx occlusion / reduction catalyst that performs occlusion of NOx contained in exhaust gas and reduction of the occluded NOx, and detects NOx concentration in the exhaust gas that has passed through the NOx occlusion reduction catalyst. NOx detection means, and based on the determination that the estimated value of the NOx occlusion amount of the NOx occlusion reduction catalyst is greater than or equal to the rich spike execution judgment value, the fuel component in the exhaust gas is temporarily increased to In an exhaust gas purification apparatus for an internal combustion engine that performs rich spike control for reducing NOx of a NOx occlusion reduction catalyst, it is determined that NOx in the exhaust begins to pass through the NOx occlusion reduction catalyst based on a detection result of the NOx detection means. Sometimes, the rich spike execution determination value is updated based on the engine operation history at this time, and the NOx occlusion is performed during the update. On the side smaller than the storage capacity of the original catalyst, a margin is set which is the difference between the storage capacity and the rich spike execution determination value, and the exhaust space velocity with respect to the NOx storage reduction catalyst is lower. A margin is set to be larger than the margin on the side where the exhaust space velocity with respect to the NOx storage reduction catalyst is high, whereby the rich spike execution determination value on the side where the exhaust space velocity is low is set as the exhaust space velocity. The gist of the invention is that it includes an execution determination value updating means for setting a value smaller than the rich spike execution determination value on the higher side.
[0024]
  The rich spike execution determination value updating means updates the rich spike execution determination value based on the history of operation of the internal combustion engine. As a result, even if the storage capacity of the NOx storage reduction catalyst is changed due to deterioration or the like, it can be updated to the rich spike execution determination value suitable for the actual storage capacity of the NOx storage reduction catalyst. Thus, the start timing of the rich spike control becomes appropriate, and the increase in the NOx concentration discharged from the NOx storage reduction catalyst described above becomes temporary. Therefore, even if the NOx storage reduction catalyst is continuously used, the NOx emission amount is not increased, and the NOx storage reduction catalyst can be continuously used over a long period of time.
Here, the space velocity represents the exhaust volume supplied per unit catalyst surface area per unit time. For example, if the load on the internal combustion engine increases or the engine speed increases, the exhaust flow rate from the internal combustion engine increases, so the space velocity increases, and if the load on the internal combustion engine decreases or the engine speed decreases. Since the exhaust flow rate is reduced, the space velocity is lowered.
[0025]
  The rich spike execution determination value updating means decreases the margin for the storage capacity of the NOx storage reduction catalyst on the side where the space velocity is high and increases on the side where the space velocity is low. For this reason, since the rich spike execution determination value is reduced on the side where the exhaust flow rate is low, rich spike control is executed more frequently than on the side where the exhaust flow rate is high. That is, the execution frequency of the rich spike control is biased toward a side where the exhaust flow rate is high rather than a side where the exhaust flow rate is high.
On the high space velocity side, there is a possibility that a part of the reducing agent as unburned gas supplied by the rich spike control may pass through the NOx storage reduction catalyst without being sufficiently used for NOx reduction, resulting in fuel consumption loss. Becomes larger. However, the probability that the rich spike control can be executed on the side where the fuel consumption is less likely to deteriorate than the side where the fuel consumption tends to deteriorate by biasing the execution frequency of the rich spike control to the lower side than the side where the space velocity is high as described above. As a result, fuel consumption can be prevented from deteriorating.
[0026]
  (8) According to an eighth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the seventh aspect, the execution determination value update means executes the rich spike control based on establishment of a rich spike prohibition execution condition. The gist is to cancel the prohibition of execution based on updating the rich spike execution determination value.
[0027]
  When the rich spike prohibition execution condition is satisfied, the regeneration of the NOx storage reduction catalyst is forcibly prohibited by prohibiting the execution of the rich spike control. For this reason, the NOx occlusion amount of the NOx occlusion reduction catalyst can be reliably brought close to the limit, and the NOx concentration downstream of the NOx occlusion reduction catalyst can be increased. For this reason, since an increase in the NOx concentration is reliably detected by the NOx detection means, the frequency of updating the rich spike execution determination value to an appropriate value can be increased.
When the rich spike execution determination value is updated, the execution of the rich spike control is permitted, and thereafter, the start timing of the rich spike control becomes suitable, and the NOx concentration increase discharged from the NOx storage reduction catalyst is temporary. It becomes. Therefore, even if the NOx storage reduction catalyst is continuously used, an increase in the NOx emission amount can be reliably prevented.
[0028]
  (9) The invention according to claim 9 is the exhaust gas purification apparatus for an internal combustion engine according to claim 8, wherein the execution determination value update means has an engine operation state in an idle operation state in the rich spike prohibition execution condition. The gist is to include.
[0029]
  As a result, execution of rich spike control is prohibited when the internal combustion engine is idle, so that the detection of the NOx concentration is executed in a state where the exhaust flow rate of the internal combustion engine is small. For this reason, in order to detect the NOx concentration increase by the NOx detection means, even if NOx is temporarily discharged from the NOx occlusion reduction catalyst, the absolute emission amount itself can be reduced, so the influence on the environment is less. Become.
[0030]
  (10) The invention according to claim 10 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 9, wherein the execution determination value updating means is configured such that NOx in the exhaust gas is reduced to NOx in the exhaust gas. Based on the engine operation history at the time when it is determined that it has started to pass through the catalyst, an estimated value of the NOx occlusion amount by the NOx occlusion reduction catalyst at that time is calculated, and the rich spike is calculated based on the calculated estimated value. The gist is to update the execution determination value.
[0031]
  The NOx occlusion amount at the time when the NOx concentration in the exhaust gas discharged from the NOx occlusion reduction catalyst begins to increase is a NOx occlusion amount that directly reflects the actual storage capacity of the NOx occlusion reduction catalyst. Therefore, the rich spike execution determination value updating means increases the NOx concentration in the exhaust discharged from the NOx storage reduction catalyst based on the history of operation of the internal combustion engine at the time when the increase in NOx concentration is detected by the NOx detection means. The NOx occlusion amount at the time of starting to do is estimated. The rich spike execution determination value is updated based on the estimated NOx occlusion amount.
This makes it possible to update the rich spike execution determination value suitable for the actual storage capacity of the NOx storage reduction catalyst, so that the start timing of the rich spike control becomes appropriate, and the NOx concentration increase that the NOx storage reduction catalyst exhausts increases. Will be temporary. For this reason, even if the NOx occlusion reduction catalyst is continuously used, the NOx emission amount is not increased, and the NOx occlusion reduction catalyst can be continuously used over a long period of time.
[0032]
  (11) According to an eleventh aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to tenth aspects, the execution determination value update means has a small fluctuation in the NOx flow rate in the exhaust gas. Under the engine operating state, the elapsed time from the time when the rich spike control is completed to the time when it is determined that NOx in the exhaust begins to pass through the NOx occlusion reduction catalyst is measured, and this measured elapsed time is measured as the exhaust. The gist is that it is used as the engine operation history at the time when it is determined that the NOx therein has started to pass through the NOx occlusion reduction catalyst.
[0033]
  In an internal combustion engine operation state in which the fluctuation of the NOx flow rate in the exhaust gas of the internal combustion engine is small, for example, at an idle time or other stable internal combustion engine operation state, it is not necessary to directly obtain the NOx amount as an internal combustion engine operation history. The duration in this operating state reflects the amount of NOx. Therefore, the rich spike execution determination value update means measures the elapsed time from the completion time of rich spike control to the time point when the increase in NOx concentration is detected by the NOx detection means. The elapsed time is used as a history of the operation of the internal combustion engine at the time when the increase in the NOx concentration is detected by the NOx detecting means, and the rich spike execution determination value can be appropriately updated based on the elapsed time.
[0034]
  For this reason, since the start timing of the rich spike control can be made appropriate by a relatively simple process of measuring the elapsed time, the load on the exhaust purification device can be reduced.
[0035]
  (12) The invention according to claim 12 is the exhaust gas purification apparatus for an internal combustion engine according to claim 11, wherein the execution determination value update means subtracts a detection delay time from the measured elapsed time, and is obtained thereby. The gist of the invention is to update the rich spike execution determination value based on the NOx occlusion limit time.
[0036]
  In particular, the elapsed time from when the rich spike control is completed to when the increase in the NOx concentration is detected by the NOx detection means coincides with the time when the NOx occlusion / reduction catalyst cannot actually occlude NOx. Not exclusively. For this reason, the rich spike execution determination value updating means subtracts the detection delay time from the measured elapsed time in order to obtain the elapsed time at which the NOx storage reduction catalyst cannot actually store NOx. By using the NOx occlusion limit time obtained in this way, the start timing of the rich spike control becomes more appropriate with a relatively simple process, so the load on the exhaust purification device can be reduced.
[0037]
  (13) The invention according to claim 13 is the exhaust gas purification apparatus for an internal combustion engine according to claim 12, wherein the execution determination value update means sets the detection delay time based on an engine operating state. It is said.
[0038]
  Since the NOx flow rate discharged from the internal combustion engine varies depending on the operating state of the internal combustion engine, the detection delay time also varies depending on the operating state of the internal combustion engine. Therefore, by setting the detection delay time according to the operating state of the internal combustion engine, an appropriate NOx storage limit time corresponding to the operating state of the internal combustion engine can be obtained.
[0039]
  (14) The invention according to claim 14 is the exhaust gas purification apparatus for an internal combustion engine according to claim 12 or 13, wherein the execution determination value update means is based on the NOx occlusion limit time and the NOx flow rate in the exhaust gas. The gist is to calculate the amount of NOx stored in the NOx storage reduction catalyst within the NOx storage limit time and update the rich spike execution determination value based on the calculated amount of NOx.
[0040]
  Since the NOx flow rate is the NOx amount per hour, the NOx occlusion amount within the NOx occlusion limit time can be obtained with high accuracy based on the NOx occlusion limit time and the NOx flow rate in the exhaust gas of the internal combustion engine. . The rich spike execution determination value can be appropriately updated based on this NOx occlusion amount.
[0041]
  (15) The invention according to claim 15 is the exhaust gas purification apparatus for an internal combustion engine according to claim 10, wherein the execution determination value updating means determines that the NOx in the exhaust gas is NOx from the time when the rich spike control is completed. Regarding the NOx flow rate state in the exhaust gas up to the time when it is determined that it has started to pass through the storage reduction catalyst, this is the engine operation history at the time when it is determined that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst. The gist is to use.
[0042]
  Even in an internal combustion engine operation state in which the fluctuation of the NOx flow rate in the exhaust gas of the internal combustion engine is large, the exhaust gas in the internal combustion engine from the time point when the rich spike control is completed to the time point when the increase in NOx concentration is detected by the NOx detection means By making the NOx flow rate state a history, the total amount of NOx discharged by the internal combustion engine in the corresponding period can be obtained. Therefore, the rich spike execution determination value updating means uses the NOx flow rate state in which the total NOx amount is known as a history to increase the chances of appropriately updating the rich spike execution determination value, so that the rich spike execution determination can be performed early. The value can be updated to an appropriate state.
[0043]
  (16) The invention according to claim 16 is the exhaust gas purification apparatus for an internal combustion engine according to claim 15, wherein the execution determination value update means determines that the NOx in the exhaust gas is NOx from the time when the rich spike control is completed. Based on the NOx flow rate state in the exhaust gas until it is determined that it has started to pass through the storage reduction catalyst, the total exhaust amount of NOx from the internal combustion engine in the period from the completed time to the determined time is calculated, The gist is to update the rich spike execution determination value using the calculated total emission amount as an estimated value of the NOx occlusion amount.
[0044]
  The total amount of NOx from the time when the rich spike control is completed to the time when the NOx concentration in the exhaust gas discharged from the NOx storage and reduction catalyst starts to increase corresponds to the storage capacity of the NOx storage and reduction catalyst. Therefore, by determining the total NOx amount based on the NOx flow rate state and setting it as the NOx occlusion amount, the rich spike execution determination value can be appropriately updated based on the NOx occlusion amount.
[0045]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
FIG. 1 shows a schematic configuration of a direct injection gasoline engine (hereinafter abbreviated as “engine”) 2 and an electronic control unit (hereinafter referred to as “ECU”) 4 mounted on a vehicle. The engine 2 is provided with a fuel injection valve 6 that directly injects fuel into the combustion chamber of each cylinder, and an ignition plug 8 that ignites the injected fuel. A throttle valve 12 whose opening degree is adjusted by a motor is provided in the middle of an intake passage 10 connected to the combustion chamber via an intake valve (not shown). The intake air amount GA (mg / sec) supplied to each cylinder is adjusted by the opening of the throttle valve 12 (throttle opening TA). The throttle opening degree TA is detected by the throttle opening degree sensor 14, and the intake air amount GA is detected by the intake air amount sensor 16 and read into the ECU 4.
[0046]
A three-way catalyst having an oxygen storage function for removing HC and CO components that are released in large quantities at the upstream side in the middle of an exhaust passage 18 connected to a combustion chamber via an exhaust valve (not shown). A certain start catalyst 20 is provided, and a NOx occlusion reduction catalyst 22 is provided downstream. An air-fuel ratio sensor 24 that detects the air-fuel ratio AF from the exhaust component is provided upstream of the start catalyst 20, and an O2 sensor 26 that detects oxygen in the exhaust component is provided downstream. A NOx sensor 28 that detects the NOx concentration Dnox in the exhaust gas is provided on the downstream side of the NOx storage reduction catalyst 22.
[0047]
The ECU 4 is an engine control circuit configured mainly with a digital computer. In addition to the throttle opening sensor 14, the intake air amount sensor 16, the air-fuel ratio sensor 24, the O2 sensor 26, and the NOx sensor 28, the ECU 4 receives signals from the following sensors. That is, the ECU 4 receives signals from an accelerator opening sensor 32 that detects the amount of depression of the accelerator pedal 30 (accelerator opening ACCP) and an engine speed sensor 34 that detects the engine speed NE from the rotation of the crankshaft (not shown). Is entered. The ECU 4 also receives a signal from a coolant temperature sensor 36 that detects the coolant temperature THW of the engine 2. Although not shown in the figure, sensors necessary for engine control such as a vehicle speed sensor are provided.
[0048]
The ECU 4 appropriately controls the fuel injection timing, the fuel injection amount, the ignition timing, and the throttle opening TA of the engine 2 based on the detection contents from the various sensors described above. Thus, for example, the combustion mode is switched between stratified combustion and homogeneous combustion. In the first embodiment, during the normal operation excluding the cold state, the combustion mode is determined based on the map of the engine speed NE and the load factor eklq. Here, the load factor eklq is a value obtained from a map using, for example, the accelerator opening ACCP and the engine speed NE as parameters, indicating the ratio of the current load to the maximum engine load.
[0049]
Next, in the present embodiment, a process related to exhaust purification for the NOx storage reduction catalyst 22 in the control executed by the ECU 4 will be described.
2 and 3 show rich spike setting processing, which is repeatedly executed at regular time intervals. When this process is started, it is first determined whether or not rich spike control is currently being performed (S102). If the rich spike control is being performed (“NO” in S102), this process is temporarily terminated and no substantial process is performed.
[0050]
If the rich spike control is not being executed (“YES” in S102), it is next determined whether or not it is immediately after the return from the rich spike control (S104). If it is immediately after the return from the rich spike control (“YES” in S104), NOx occluded in the NOx occlusion reduction catalyst 22 is all reduced, so the NOx occlusion amount enoxcnt (mg) is set to “0”. It sets (S106).
[0051]
On the other hand, if not immediately after the return from the rich spike control (“NO” in S104), the process of step S106 is not performed.
If “NO” is determined after step S106 or in step S104, the NOx emission amount enoxextrate (mg / sec) per unit time from the engine 2 is based on the load factor eklq and the engine speed NE. Is calculated from the map Menoxextrate (eklq, NE) (S108).
[0052]
Here, the map Menoxextrate (eklq, NE) is a map showing the NOx emission amount per unit time (mg / sec) obtained in advance by experiments using the load factor eklq and the engine speed NE as parameters. The map Menoxextrate (eklq, NE) is switched between stratified combustion and homogeneous combustion. Note that when the homogeneous combustion has a stoichiometric air fuel ratio or a fuel concentration higher than the stoichiometric air fuel ratio, there is almost no NOx emission amount. Therefore, NOx emission amount enoxextrate = 0 (mg / sec) is always used without using a map. good.
[0053]
The NOx emission amount enoxex (mg) discharged in the current control cycle is calculated by the product of the NOx emission amount enoxrate per unit time and the control cycle (sec) of this processing (S110). That is, the amount of NOx stored in the NOx storage reduction catalyst 22 in the current control cycle is calculated.
[0054]
Next, the NOx reduction amount enoxredrate (mg / sec) per unit time in the NOx storage reduction catalyst 22 is read (S112). The NOx reduction amount enoxredrate per unit time is a value obtained in the NOx reduction amount detection processing per unit time that is separately executed. This NOx reduction amount detection processing per unit time basically obtains the NOx reduction amount enoxredate per unit time from the air-fuel ratio AF and the intake air amount GA. Further, the NOx reduction amount obtained from the air-fuel ratio AF and the intake air amount GA is corrected based on the catalyst permeability of the reducing agent obtained from the temperature, the degree of deterioration, etc. of the NOx storage reduction catalyst 22, and the NOx reduction amount enoxredrate. You may ask for.
[0055]
Then, the NOx reduction amount enoxred in the current control cycle is calculated (mg) by the product of the NOx reduction amount enoxredrate per unit time and the control cycle of this process (S114). That is, the reduction purification amount of NOx stored in the NOx storage reduction catalyst 22 is calculated.
[0056]
Next, the NOx occlusion amount enoxcnt (mg) is updated by the following equation 1 (S116).
[0057]
[Expression 1]
enoxcnt ←
enoxcnt + enoxext-enoxred ... [Formula 1]
Here, enoxcnt on the right side is the NOx occlusion amount in the previous control cycle, and enoxcnt on the left side is the updated NOx occlusion amount.
[0058]
Next, the NOx storage capacity noxmax (mg) is calculated (S118). This NOx storage capacity noxmax is calculated based on the catalyst temperature etempave from a map Mnoxmax (map of Δ mark) showing the relationship between the catalyst temperature and the NOx storage capacity shown in FIG.
[0059]
Here, the NOx storage capacity noxmax represents the amount of NOx that can be stored to the maximum extent by the current NOx storage reduction catalyst 22, and represents the current NOx storage capacity of the NOx storage reduction catalyst 22. The NOx amount noxmaxinit that can be stored to the maximum extent by the NOx storage reduction catalyst 22 when the NOx storage reduction catalyst 22 is unused (undegraded) is indicated by a circle. Thus, the illustrated map Mnoxmax shows a state in which the storage capacity is lower than when not in use due to deterioration caused by the use of the NOx storage reduction catalyst 22. The map Mnoxmax is repeatedly updated by the storage capacity update process (FIGS. 5 and 6) described later so as to appropriately reflect the degree of deterioration of the NOx storage capacity.
[0060]
In the NOx occlusion reduction catalyst 22, the NOx occlusion capacity noxmax varies depending on the catalyst temperature etempave. For this reason, in the map Mnoxmax, the catalyst temperature etempave is divided into a plurality of regions, in FIG. 4, seven temperature regions tmp (1) to tmp (7), and the representative temperatures (indicated by Δ marks) provided for each temperature region are divided. The NOx occlusion capacity noxmax is maintained with respect to the temperature at the position shown in FIG.
[0061]
Therefore, in step S118, the catalyst temperature emptive is determined, and the NOx storage capacity (Δ mark) of the two temperature regions tmp (3) and tmp (4) is used, for example, as shown in FIG. 4 depending on the position of the catalyst temperature emptive. Interpolation calculation is performed to obtain the NOx storage capacity noxmax used in this process.
[0062]
The catalyst temperature etempave is estimated from the engine speed NE and the intake air amount GA by a temperature estimation process separately performed by the ECU 4. As this temperature estimation process, for example, the catalyst temperature can be estimated as the exhaust temperature obtained from the engine speed NE and the intake air amount GA during stable operation of the engine 2. Then, when the engine 2 is in transition, the catalyst temperature etempave is obtained by repeatedly calculating the catalyst temperature so as to follow the exhaust temperature based on the time constant based on the intake air amount GA. Instead of this estimation, a temperature sensor may be provided in the NOx occlusion reduction catalyst 22 and the catalyst temperature may be directly measured and used.
[0063]
Next, a rich spike execution determination value rspnoxmax is calculated based on the NOx storage capacity noxmax and margin allowance formation coefficient delta calculated as described above (S120).
[0064]
[Expression 2]
rspnoxmax <-noxmax x delta ... [Formula 2]
Here, the margin allowance formation coefficient delta is a coefficient for setting the rich spike execution determination value rspnoxmax to be smaller than the NOx storage capacity noxmax representing the current NOx storage capacity of the NOx storage reduction catalyst 22. Therefore, the margin allowance forming coefficient delta is set in a range of 0 <delta <1.0. The value of the margin allowance formation coefficient delta is set as a constant value here. As a result, a margin for the rich spike execution determination value rspnoxmax with respect to the NOx storage capacity noxmax can be set, and the NOx in the exhaust can be stored in the NOx storage reduction catalyst 22 with certainty.
[0065]
Next, it is determined whether or not the NOx occlusion amount enoxcnt determined by the equation 1 is equal to or greater than the rich spike execution determination value rspnoxmax determined by the equation 2 (S122).
[0066]
If enoxcnt <rspnoxmax (“NO” in S122), it is then determined whether or not the NOx occlusion amount enoxcnt is “0” or more (S124). If enoxcnt ≧ 0 (“YES” in S124), this process is temporarily terminated as it is.
[0067]
If enoxcnt <0 (“NO” in S124), “0” is set to the NOx occlusion amount enoxcnt (S126), and this process is temporarily terminated.
On the other hand, if enoxcnt ≧ rspnoxmax (“YES” in S122), it is determined whether rich spike control prohibition, which will be described later, is in a released state (S128). If it is not released, that is, in the rich spike control prohibited state (“NO” in S128), this processing is temporarily terminated as it is. That is, rich spike control is not executed.
[0068]
If the prohibition of rich spike control is cancelled (“YES” in S128), then the rich spike parameter is set to execute the rich spike control (S130). For example, the rich spike air-fuel ratio AFr and the rich spike period Rspt are set according to the value of the NOx storage capacity noxmax. In this way, this process is once completed.
[0069]
When the rich spike parameter is set in this way, the rich spike is started by the fuel injection amount control by the ECU 4, and the fuel concentration of the air-fuel mixture in the combustion chamber is temporarily sufficiently higher than the stoichiometric air-fuel ratio. A large amount of unburned gas such as HC and CO is discharged from the engine 2 to the exhaust path 18. As a result, the NOx occluded in the NOx occlusion reduction catalyst 22 is reduced, and finally all the NOx occluded is purified.
[0070]
5 and 6 show the storage capacity update process. This process is executed immediately after the rich spike setting process (FIGS. 2 and 3) at the same cycle as the rich spike setting process (FIGS. 2 and 3). When this process is started, it is first determined whether or not the engine is idling (S202). If it is not currently idle ("NO" in S202), the rich spike control prohibition is canceled (S222). The release of the rich spike control prohibition is canceled when a rich spike control prohibition setting (S210), which will be described later, has been made to enable execution of the rich spike control. If it is already in the release state, this release state is maintained. And this process is once complete | finished as it is.
[0071]
If it is currently idling (“YES” in S202), it is determined whether or not stratified combustion is in progress (S204). This determination may determine whether or not lean combustion is performed when the engine 2 performs lean combustion. In any case, it is determined whether or not the combustion state is such that the exhaust air-fuel ratio becomes lean.
[0072]
If stratified charge combustion is not being performed (“NO” in S204), the rich spike control inhibition is canceled as described above (S222), and the present process is temporarily terminated as it is. If it is during stratified combustion (“YES” in S204), the NOx storage capacity noxmax is still updated in the temperature range to which the current catalyst temperature etempave belongs in the next trip (period in which the engine is continuously operated). It is determined whether or not the process has been performed (S206). This is determined so that the rich spike control prohibition is not repeated in the same temperature region if the temperature region is already updated in the map Mnoxmax shown in FIG. 4 within one trip.
[0073]
If the update has already been completed in the same temperature range (“NO” in S206), the prohibition of rich spike control is canceled as described above (S222), and this process is temporarily terminated as it is.
[0074]
If the update has not yet been executed in the same temperature region (“YES” in S206), then the rich spike control was executed in the current operating state (here, the idle stratified combustion state in the same temperature region). It is determined whether or not (S207). If rich spike control has not yet been executed ("NO" in S207), the prohibition of rich spike control is canceled as described above (S222), and this process is temporarily terminated as it is.
[0075]
Then, in the rich spike setting process (FIGS. 2 and 3), “YES” is determined in step S122 and step S128, and step S130 is executed to execute rich spike control (“YES” in S207). Next, it is determined whether or not it is immediately after the return from the rich spike control (S208). Since it is immediately after the return from the rich spike control (“YES” in S208), the rich spike control prohibition setting is made (S210). As a result, “NO” is determined in step S128 of the rich spike setting process (FIGS. 2 and 3), and the rich spike control is not performed even if the NOx occlusion amount enoxcnt exceeds the rich spike execution determination value rspnoxmax. Never executed.
[0076]
Then, the timer count is started (S212). This timer is counted up at the same cycle as this processing, and the count value is started from “0” in order to measure the elapsed time in the stratified combustion from the completion of the rich spike control.
[0077]
Then, after this step S212, it is determined whether or not the NOx concentration Dnox detected by the NOx sensor 28 is equal to or greater than the NOx concentration increase determination value D2 (S214). The NOx concentration increase determination value D2 is set to a concentration value that can reliably determine that the NOx concentration has increased, mainly due to the detection accuracy of the NOx sensor 28. Therefore, if the NOx concentration Dnox detected by the NOx sensor 28 is equal to or higher than the NOx concentration increase determination value D2, the NOx storage reduction catalyst 22 cannot store NOx, and NOx is discharged downstream from the NOx storage reduction catalyst 22. It can be reliably detected that the timing is after the start.
[0078]
Here, even if NOx produced by stratified combustion is supplied from upstream of the NOx storage reduction catalyst 22 in a state where the execution of rich spike control is prohibited, the NOx storage reduction catalyst 22 can sufficiently store NOx in the initial stage. Dnox <D2 (“NO” in S214). Therefore, this process is temporarily terminated as it is.
[0079]
In the next control cycle, if the same operation state continues, it is determined as “YES” in steps S202, S204, S206, and S207, and in step S208, it is not immediately after the return from the rich spike control (in S208). “NO”), it is determined whether Dnox ≧ D2 (S214). As long as Dnox <D2 (“NO” in S214), this state continues. During this time, NOx is supplied to the NOx occlusion reduction catalyst 22 by stratified combustion, and the actual NOx occlusion amount of the NOx occlusion reduction catalyst 22 increases.
[0080]
When the actual NOx storage amount exceeds the storage capacity of the NOx storage reduction catalyst 22, the NOx concentration starts to increase on the downstream side of the NOx storage reduction catalyst 22. If the NOx concentration that can be detected with high accuracy by the NOx sensor 28 is determined by this increase and it is determined that Dnox ≧ D2 (“YES” in S214), the count value of the timer at the timing when Dnox ≧ D2 is thus obtained. T is set to the NOx increase period Tnox (S216).
[0081]
Then, as shown in the following expression 3, the NOx storage capacity noxmax is calculated (S218).
[0082]
[Equation 3]
noxmax ← enox × (Tnox−Ta) [Equation 3]
Here, the NOx emission amount enoxext is the value obtained in step S110 of the rich spike setting process (FIGS. 2 and 3) described above. The detection delay time Ta is Dnox ≧ D2 (“YES” in S214) from the timing when the NOx occlusion amount of the NOx occlusion reduction catalyst 22 coincides with the occlusion capacity (timing at which NOx begins to be exhausted from the NOx occlusion reduction catalyst 22) during idling. This is a timer count value indicating a time interval until. This detection delay time Ta is a value obtained in advance through experiments or the like.
[0083]
An example of a process from when the rich spike control is completed until the NOx concentration downstream of the NOx storage reduction catalyst 22 increases is shown in the timing chart of FIG. Here, since the engine 2 is idling, the NOx emission amount enoxrate per unit time is substantially constant, and the NOx emission amount enoxext is also substantially constant.
[0084]
For this reason, the NOx occlusion amount enoxcnt increases in proportion to the timer count value T representing the elapsed time from the completion of the rich spike control as shown by hatching in the figure. The NOx flow rate discharged from the NOx storage reduction catalyst 22 begins to increase immediately before or almost at the time ts when the NOx storage amount enoxcnt reaches the storage capacity of the NOx storage reduction catalyst 22.
[0085]
At time tnox, the NOx sensor 28 detects that Dnox ≧ D2. There is a time ts when the NOx occlusion amount enoxcnt reaches the occlusion capacity of the NOx occlusion reduction catalyst 22 before the detection delay time Ta before this time tnox. Therefore, in Equation 3, the NOx occlusion limit time Ts from the completion of the rich spike control to the time point ts is obtained by calculating “Tnox−Ta”. Then, the product of the NOx storage limit time Ts and the NOx emission amount enoxext determines the NOx amount corresponding to the entire area shown by hatching, that is, the actual NOx storage capacity noxmax of the NOx storage reduction catalyst 22.
[0086]
Next, the map Mnoxmax shown in FIG. 4 is updated based on the NOx storage capacity noxmax thus obtained (S220). Specifically, as shown in the example of FIG. 8, the NOx storage capacity noxmaxold (◯ mark) before the update is obtained by interpolation calculation according to the current catalyst temperature etempave. Then, a difference Δnoxmax (= noxmaxold−noxmax) between this value and the NOx storage capacity noxmax (ｍａｘ mark) obtained in step S218 is calculated. Then, by subtracting this difference Δnoxmax from the NOx storage capacity (the temperature of the upper Δ mark) at the representative temperature in the temperature region tmp (4) to which the catalyst temperature etempave belongs, a new value at the representative temperature in the temperature region tmp (4) is obtained. It is set as the NOx storage capacity (the temperature of the Δ mark on the lower side). As a result, the map Mnoxmax is updated.
[0087]
When the update of the map Mnoxmax is completed in this way, the prohibition of rich spike control is then released (S222), and this process is temporarily terminated.
As the map Mnoxmax is updated in this way, the NOx storage capacity noxmax calculated in step S118 of the rich spike setting process (FIGS. 2 and 3) is also changed correspondingly, and is calculated by the equation 2 in step S120. The rich spike execution determination value rspnoxmax is also updated.
[0088]
Since the prohibition of rich spike control has been canceled, in the rich spike setting process (FIGS. 2 and 3), it is determined as “YES” in both step S122 and step S128, and step S130 is executed. Therefore, the rich spike control is immediately executed to purify the NOx stored in the NOx storage reduction catalyst 22. For this reason, as shown in FIG. 7, the NOx concentration on the downstream side of the NOx storage reduction catalyst 22 that has started to rise rapidly decreases to “0”.
[0089]
In the next control cycle of the storage capacity update process (FIGS. 5 and 6), it is determined as “YES” in steps S202 and S204 when idling and stratified combustion continues. For example, since the update of the NOx storage capacity noxmax is completed within the same trip, it is determined as “NO” in step S206. As a result, the rich spike control prohibition cancellation in step S222 is continued, and thereafter, the rich spike control in the same temperature region can be executed.
[0090]
If the catalyst temperature etempave shifts to another temperature range within the same trip, it is determined again as “YES” in step S206, and the NOx storage capacity noxmax in the corresponding temperature range is updated as described above. Is done.
[0091]
Since the update of the map Mnoxmax (FIG. 4) is repeated in this way, the rich spike execution determination value rspnoxmax used in step S122 of the rich spike setting process is also updated to an appropriate value, and the rich spike is performed at a highly accurate timing. Control can be performed.
[0092]
In the configuration described above, the NOx sensor 28 corresponds to the NOx detection means, and the storage capacity update process (FIGS. 5 and 6) and the processes in steps S118 and S120 in FIG. 3 correspond to the process as the rich spike execution determination value update means. Steps S202 to S208 correspond to rich spike prohibition execution conditions.
[0093]
According to the first embodiment described above, the following effects can be obtained.
(I). When the NOx occlusion reduction catalyst 22 cannot fully occlude NOx in the exhaust from the engine 2, the NOx concentration downstream of the NOx occlusion reduction catalyst 22 starts to increase. From this, the engine operation history up to the time point when the increase in NOx concentration is detected by the NOx sensor 28, in this embodiment, from the time when the rich spike control is completed until the time point when the increase in NOx concentration is detected by the NOx sensor 28. The elapsed time (NOx increase period Tnox) reflects the storage capacity of the NOx storage reduction catalyst 22.
[0094]
Since the NOx increase period Tnox is measured during idling, there is little fluctuation in the NOx flow rate in the engine exhaust, and the NOx storage capacity noxmax can be obtained without obtaining the history of the NOx flow rate itself. That is, with respect to the NOx increase period Tnox, the calculation of Equation 3 is performed using the NOx emission amount enoxext during idling and the detection delay time Ta during idling set by experiment or the like. This makes it possible to estimate the NOx storage capacity noxmax when the NOx concentration downstream of the NOx storage reduction catalyst 22 actually starts to increase, and the storage capacity of the NOx storage reduction catalyst 22 is determined by the value of the NOx storage capacity noxmax. The represented map Mnoxmax can be updated appropriately.
[0095]
Then, by setting the rich spike execution determination value rspnoxmax using the map Mnoxmax updated in this way, even if the storage capacity of the NOx storage reduction catalyst 22 is changed due to deterioration or the like, the rich that matches the actual storage capacity The spike execution determination value rspnoxmax can be appropriately updated.
[0096]
Thus, the start timing of the rich spike control becomes appropriate, and the increase in the concentration of NOx discharged from the NOx storage reduction catalyst 22 is temporary. Therefore, even if the NOx occlusion reduction catalyst 22 is continuously used, the NOx occlusion reduction amount from the NOx occlusion reduction catalyst 22 is not increased, and the NOx occlusion reduction catalyst 22 can be continuously used over a long period of time.
[0097]
Moreover, the start timing of the rich spike control can be made appropriate by a relatively simple process of measuring the elapsed time from when the rich spike control is completed to when the increase in the NOx concentration is detected by the NOx sensor 28. The load on the ECU 4 can be reduced.
[0098]
(B). The measurement of the NOx increase period Tnox is performed in a state where the execution of the rich spike control is prohibited in advance and the regeneration of the NOx storage reduction catalyst 22 is not performed. For this reason, the NOx occlusion amount of the NOx occlusion reduction catalyst 22 can be reliably brought close to the limit, and the NOx concentration downstream of the NOx occlusion reduction catalyst 22 can be temporarily increased. Therefore, since the increase in the NOx concentration can be reliably detected by the NOx sensor 28, the frequency of updating the rich spike execution determination value rspnoxmax can be increased.
[0099]
When the rich spike execution determination value rspnoxmax is updated, the execution of the rich spike control is permitted (S222). Henceforth, the start timing of the rich spike control becomes suitable, and the NOx discharged from the NOx storage reduction catalyst 22 is improved. The increase in concentration is temporary. Therefore, even if the NOx storage reduction catalyst 22 is continuously used, an increase in the NOx emission amount from the NOx storage reduction catalyst 22 can be reliably prevented.
[0100]
(C). Since the rich spike prohibition execution condition includes the idle state (S202), the rich spike processing is prohibited during idling. For this reason, since the NOx concentration is detected with the exhaust flow rate of the engine 2 being small, even if the NOx storage / reduction catalyst 22 is temporarily exhausted, the absolute exhaust amount itself remains. Less is enough. The impact on the environment is therefore less.
[0101]
[Embodiment 2]
In the present embodiment, the setting of the margin allowance formation coefficient delta used for calculating the rich spike execution determination value rspnoxmax is performed in step S120 of the rich spike setting process (FIGS. 2 and 3) of the first embodiment. It is set as shown in 9 map Mdelta. Other configurations are the same as those in the first embodiment.
[0102]
The map Mdelta is a map using the load factor eklq and the engine speed NE as parameters, and is set in a range as indicated by a solid line, and this range corresponds to a region where stratified combustion is executed. That is, the margin allowance formation coefficient delta is set except for the limited regions on the high load factor side and the high rotation speed side. Then, as shown by the contour lines of the broken lines in the figure, the higher the load factor eklq or the higher the engine speed NE, the larger the margin allowance formation coefficient delta, and the lower the load factor eklq or the lower the engine speed NE. The margin allowance formation coefficient delta is set to be smaller. However, the margin allowance formation coefficient delta is limited to a range of 0 <delta <1.0 (for example, 0.5 at the minimum and 0.9 at the maximum).
[0103]
For this reason, the rich spike execution determination value rspnoxmax decreases as the load factor eklq increases or the engine speed NE increases, that is, as the space velocity increases as described above, the margin for the NOx storage capacity noxmax is reduced. As the load factor eklq decreases or the engine speed NE decreases, that is, the space velocity decreases, the allowance for the NOx storage capacity noxmax increases.
[0104]
According to the second embodiment described above, the following effects can be obtained.
(I). The effects (a) to (c) of the first embodiment can be obtained.
(B). As described above, according to the map Mdelta (FIG. 9), the margin allowance formation coefficient delta is increased on the high space velocity side and decreased on the low space velocity side. Therefore, the difference between the rich spike execution determination value rspnoxmax and the NOx storage capacity noxmax is increased on the side where the space velocity is low. Therefore, rich spike control is executed more frequently on the low space velocity side than on the high side, and the execution frequency of the rich spike control is biased to the lower side than the high space velocity side.
[0105]
On the high space velocity side, there is a possibility that a part of the reducing agent supplied as the unburned gas supplied by the rich spike control may pass through the NOx storage reduction catalyst 22 without being sufficiently used for NOx reduction. Loss increases.
[0106]
However, the probability that the rich spike control can be executed on the side where the fuel consumption is less likely to deteriorate than the side where the fuel consumption tends to deteriorate by biasing the execution frequency of the rich spike control to the lower side than the side where the space velocity is high as described above. As a result, fuel consumption can be prevented from deteriorating.
[0107]
[Embodiment 3]
The present embodiment is different from the first embodiment in that the storage capacity update process shown in FIGS. 10 and 11 is executed instead of the storage capacity update process (FIGS. 5 and 6). Other configurations are the same as those of the first embodiment. As in the second embodiment, the margin allowance formation coefficient delta may be set according to the map Mdelta shown in FIG.
[0108]
The storage capacity update process (FIGS. 10 and 11) will be described. This process is executed at the same cycle as the storage capacity update process (FIGS. 5 and 6) of the first embodiment. An example of the control of the present embodiment is shown in the timing chart of FIG.
[0109]
When this process is started, it is first determined whether or not stratified combustion is currently being performed (S302). This determination is as described in step S204 of FIG. 5. If the engine 2 performs lean combustion, it may be determined whether or not lean combustion is performed.
[0110]
Here, if it is not stratified combustion (“NO” in S302), the rich spike control prohibition is canceled (S332). The cancellation of the rich spike control prohibition is as described in step S222 of FIG. And this process is once complete | finished as it is.
[0111]
If it is during stratified combustion (“YES” in S302), it is next determined whether or not the NOx occlusion capacity noxmax has not yet been updated in the temperature range to which the current catalyst temperature etempave belongs in the current trip (S302). S304). This determination process is as described in step S206 of FIG.
[0112]
If the update has already been executed in the same temperature range (“NO” in S304), the rich spike control prohibition is canceled as described above (S332), and this process is temporarily terminated as it is.
[0113]
If the update has not yet been executed in the same temperature range (“YES” in S304), then whether or not the rich spike control has been executed in the current operating state (here, the stratified combustion state in the same temperature range) Is determined (S306). If rich spike control has not yet been executed (“NO” in S306), the prohibition of rich spike control is canceled as described above (S332), and this process is temporarily terminated as it is.
[0114]
Thereafter, when rich spike control is executed (“YES” in S306), it is next determined whether or not it is immediately after returning from rich spike control (S308). Since it is immediately after the return from the rich spike control (“YES” in S308), “0 (g)” is set as a value of an accumulated NOx amount Anox described later (S310). Then, rich spike control prohibition setting is made (S312). As a result, “NO” is determined in step S128 of the rich spike setting process (FIGS. 2 and 3), and rich spike control is prohibited.
[0115]
Then, the timer starts counting (S314). This timer is as described in step S212 in FIG.
Next, the detection delay time Tb is obtained from the detection delay time map MTb based on the load factor eklq and the engine speed NE (S316). The detection delay time Tb is Dnox in step S326 from the timing when the NOx occlusion amount of the NOx occlusion reduction catalyst 22 coincides with the occlusion capacity of the NOx occlusion reduction catalyst 22 (timing at which NOx begins to be discharged from the NOx occlusion reduction catalyst 22). It is a timer count value representing a time interval until it is determined that ≧ D2 (“YES”). This detection delay time map MTb is obtained in advance through experiments or the like. The detection delay time Ta in the first embodiment is a constant value because it is limited during stratified combustion during idling, but in this embodiment it is not limited to idling, so the detection delay time Tb depends on the operating state of the engine 2. Change.
[0116]
Next, the NOx emission amount enoxex determined in the rich spike setting process (FIGS. 2 and 3) is accumulated in the accumulation memory enoxext (Tr to T) (S318). Here, the storage memory enext (Tr to T) is a memory for storing the NOx emission amount enextend for each timer count value from the past timer count value Tr to the current timer count value T, and is stored in the RAM of the ECU 4. Is set. The capacity of the storage memory enext (Tr to T) is large enough to store the number of NOx emission amounts enext corresponding to the maximum value of the detection delay time Tb set in the detection delay time map MTb (eklq, NE). Is set. Accordingly, the NOx emission amount enextent obtained in the rich spike setting process (FIGS. 2 and 3) can be stored in the storage memory enextex (Tr to T) during the detection delay time Tb.
[0117]
Since the storage memory enext (Tr to T) is cyclically updated by writing the latest value with respect to the past value, the latest NOx emission amount enoxext is always stored in the storage memory enext (Tr to T). T).
[0118]
Next, it is determined whether or not the current timer count value T has exceeded the detection delay time Tb obtained in step S316 (S320). While T ≦ Tb (“NO” in S320), the detection delay time Tb is set to the previous detection delay time Tx (S324). Then, it is determined whether or not the NOx concentration Dnox detected by the NOx sensor 28 is equal to or greater than the NOx concentration increase determination value D2 (S326). This determination is as described in step S214 in FIG.
[0119]
Here, even if NOx generated by stratified combustion is supplied from upstream of the NOx storage reduction catalyst 22 in a state where the rich spike control is prohibited, in the initial stage, the NOx storage reduction catalyst 22 can sufficiently store NOx. Dnox <D2 (“NO” in S326). Therefore, this process is temporarily terminated as it is.
[0120]
In the next control cycle, since it is not immediately after the return from the rich spike control (“NO” in S308), a new detection delay time Tb is immediately calculated (S316), and a new NOx is stored in the storage memory enext (Tr to T). The discharge amount enoxext is accumulated (S318).
[0121]
As long as T ≦ Tb (“NO” in S320), the detection delay time Tb calculated in step S316 this time is set as the previous detection delay time Tx (S324). If Dnox <D2 (“NO” in S326), the process is temporarily terminated.
[0122]
When T> Tb is satisfied (“YES” in S320, time t0 in FIG. 12), an integrated NOx amount Anox is calculated as shown in the following equation 4 (S322).
[0123]
[Expression 4]
Anox ← Anox
+ Σenoxext (T−Tx˜T−Tb) [Formula 4]
Here, “T-Tx” represents a point in time that is back by the previous detection delay time Tx from the timer count value T corresponding to the current control cycle, and “T-Tb” is from the timer count value T corresponding to the current control cycle. This represents a point in time that is back by the detection delay time Tb. Accordingly, “Σenext (T−Tx to T−Tb)” is determined in each control cycle from the control cycle at the time “T-Tx” to the control cycle at the time “T-Tb” in step S110 of FIG. It represents that the calculated NOx emission amount enoxext is integrated.
[0124]
Therefore, when the detection delay time Tb is not changed, since “T−Tx = T−Tb”, “Σenext (T−Tx to T−Tb)” = “enoxext (T−Tb)”. That is, when the detection delay time Tb does not change, the calculation is the same as the calculation shown in the following equation 5.
[0125]
[Equation 5]
Anox <-Anox + enoxext (T-Tb) ... [Formula 5]
Equation 5 indicates that the NOx emission amount enoxext before the detection delay time Tb is sequentially accumulated in the integrated NOx amount Anox.
[0126]
Further, when the operation state changes from the previous control cycle and the detection delay time Tb becomes longer, “T−Tx> T−Tb” is satisfied, so “Σenext (T−Tx to T−Tb)” = It is set to “0”. That is, when the detection delay time Tb changes to become longer than the previous control cycle, the value of the integrated NOx amount Anox is maintained.
[0127]
Further, when the operating state changes from the previous control cycle and the detection delay time Tb becomes shorter, “T−Tx <T−Tb”, and therefore “Σenext (T−Tx to T−Tb)” = “Enoxext (T−Tx) +... + Enoxext (T−Tb)”. That is, when the detection delay time Tb is changed to be shorter than the previous control cycle, the value of the integrated NOx amount Anox is shortened by the detection delay time Tb from the current timer count value T by “T”. Since “−Tb” moves later in time, the corresponding NOx emission amount enoxext is accumulated.
[0128]
Actually, since the control cycle of the present embodiment is sufficiently short, the change of the detection delay time Tb for each cycle is within “± 1”.
By repeating the calculation of Equation 4, the accumulated NOx amount Anox is accumulated with the NOx emission amount enoxext from the time when the rich spike control is completed until the detection delay time Tb before the present time. This state continues as long as Dnox <D2 (“NO” in S326).
[0129]
When Dnox ≧ D2 is satisfied (“YES” in S326, FIG. 12: t1), the integrated NOx amount Anox obtained during this control cycle is set to the NOx occlusion capacity noxmax (S328).
[0130]
Next, the map Mnoxmax (FIG. 4) is updated based on the NOx storage capacity noxmax thus determined (S330). This update is as described in step S220 of FIG.
[0131]
That is, after the rich spike control is completed, the NOx occlusion amount (hatched portion) occluded in the NOx occlusion reduction catalyst 22 by time tb before detection delay time Tb from time t1 shown in FIG. 12 is obtained as the integrated NOx amount Anox. It is done. Then, the map Mnoxmax (FIG. 4) is updated on the assumption that the accumulated NOx amount Anox represents the current storage capacity of the NOx storage reduction catalyst 22.
[0132]
As the map Mnoxmax is updated in this way, the NOx storage capacity noxmax calculated in step S118 of the rich spike setting process (FIGS. 2 and 3) is also changed correspondingly, and is calculated by the equation 2 in step S120. The rich spike execution determination value rspnoxmax is also updated.
[0133]
When the update of the map Mnoxmax is completed in this way, the rich spike control prohibition is then released (S332), and this process is temporarily terminated.
Since the prohibition of rich spike control has been canceled, in the rich spike setting process (FIGS. 2 and 3), it is determined as “YES” in both step S122 and step S128, and step S130 is executed. Therefore, the rich spike control is immediately executed to purify the NOx stored in the NOx storage reduction catalyst 22. Therefore, as shown in FIG. 12, the NOx concentration on the downstream side of the NOx occlusion reduction catalyst 22 that has started to rise rapidly decreases to “0”.
[0134]
In the next control cycle of the storage capacity update process (FIGS. 10 and 11), even if it is determined “YES” in step S302 because stratified combustion continues, the NOx storage capacity noxmax is maintained in the same temperature range. Since the update has already been completed within the same trip, “NO” is determined in step S304. As a result, the rich spike control prohibition cancellation in step S332 continues, so that the rich spike control in the same temperature region can be executed thereafter.
[0135]
If the catalyst temperature etempave shifts to another temperature range within the same trip, it is determined again as “YES” in step S304, so that the rich spike control is still executed in the changed operating state in step S306. If not, “YES” is determined. Therefore, the NOx storage capacity noxmax in the corresponding temperature region is updated as described above.
[0136]
Since the update of the map Mnoxmax (FIG. 4) is repeated in this way, the rich spike execution determination value rspnoxmax used in step S122 of the rich spike setting process is also appropriately updated, and rich spike control is performed at a highly accurate timing. Can be executed.
[0137]
In the configuration described above, the NOx sensor 28 corresponds to the NOx detection means, and the storage capacity update processing (FIGS. 10 and 11) and the processing in steps S118 and S120 in FIG. 3 correspond to processing as the rich spike execution determination value update means. Steps S302 to S308 correspond to rich spike prohibition execution conditions.
[0138]
According to the third embodiment described above, the following effects can be obtained.
(I). When the NOx occlusion reduction catalyst 22 cannot fully occlude NOx in the exhaust of the engine 2, the NOx concentration in the exhaust exhausted by the NOx occlusion reduction catalyst 22 starts to increase. From this, the engine operation history until the NOx concentration increase is detected by the NOx sensor 28 (FIG. 12: t1), here, the NOx concentration increase is detected by the NOx sensor 28 after the rich spike control is completed. The state of the NOx emission amount enoxext until time reflects the storage capacity of the NOx storage reduction catalyst 22.
[0139]
That is, the NOx emission amount enoxext is integrated with the NOx emission amount enoxext from the completion of the rich spike control until the detection delay time Tb before the current time point, so that the NOx concentration downstream of the NOx storage reduction catalyst 22 actually increases. The NOx storage capacity noxmax at the time of starting is obtained. As a result, the map Mnoxmax representing the storage capacity of the NOx storage reduction catalyst 22 can be updated appropriately.
[0140]
Then, by setting the rich spike execution determination value rspnoxmax using the map Mnoxmax updated in this way, even if the storage capacity of the NOx storage reduction catalyst 22 is changed due to deterioration or the like, it is adapted to the actual storage capacity. The rich spike execution determination value rspnoxmax can be appropriately updated.
[0141]
Thus, the start timing of the rich spike control becomes appropriate, and the increase in the concentration of NOx discharged from the NOx storage reduction catalyst 22 is temporary. Therefore, even if the NOx occlusion reduction catalyst 22 is continuously used, the NOx occlusion reduction amount from the NOx occlusion reduction catalyst 22 is not increased, and the NOx occlusion reduction catalyst 22 can be continuously used over a long period of time.
[0142]
Moreover, even if the operating state of the engine 2 changes greatly, the rich spike execution determination value rspnoxmax can be appropriately updated. Therefore, the opportunity for updating is increased, and the rich spike execution determination value rspnoxmax is set early. It can be updated to an appropriate state.
[0143]
(B). The effect (b) of the first embodiment is produced.
(C). When the margin allowance formation coefficient delta is set using the map Mdelta (FIG. 9), the effect (b) of the second embodiment is produced.
[0144]
[Embodiment 4]
In the present embodiment, in the rich spike setting process (FIGS. 2 and 3), the process shown in FIG. 13 is executed instead of the process shown in FIG. Then, the storage capacity update process shown in FIGS. 14 and 15 is executed instead of the storage capacity update process (FIGS. 5 and 6), which is different from the first embodiment. Other configurations are the same as those of the first embodiment. As in the second embodiment, the margin allowance formation coefficient delta may be set according to the map Mdelta shown in FIG.
[0145]
The rich spike setting process (FIGS. 2 and 13) will be described. Since the processing of FIG. 2 is as described in the first embodiment, detailed description thereof is omitted. In FIG. 13, the same processing as that in FIG. 3 is assigned the same step number.
[0146]
After the NOx occlusion amount enoxcnt is calculated in step S116 (FIG. 2), it is determined whether or not the determination value increase flag Frinc for permitting the increase processing of the rich spike execution determination value rspnoxmax is “OFF” (S117a). . If Frsinc = “OFF” (“YES” in S117a), then the NOx storage capacity noxmax is calculated (S118). Then, the rich spike execution determination value rspnoxmax is calculated as shown in Equation 2 (S120).
[0147]
On the other hand, if Frsinc = “ON” (“NO” in S117a), the rich spike execution determination value rspnoxmax is gradually increased as shown in the following equation 6 (S117b).
[0148]
[Formula 6]
rspnoxmax <-rspnoxmax + dx ... [Formula 6]
Next to step S120 or step S117b, it is determined whether or not enoxcnt ≧ rspnoxmax (S122). If enoxcnt <rspnoxmax (“NO” in S122), it is determined whether or not enoxcnt ≧ 0 (S124). If enoxcnt ≧ 0 (“YES” in S124), this process is temporarily terminated as it is. If enoxcnt <0 (“NO” in S124), “0” is set to the NOx occlusion amount enoxcnt.
[0149]
On the other hand, if enoxcnt ≧ rspnoxmax (“YES” in S122), unlike the case of FIG. 3, the parameter for rich spike is immediately set (S130). As a result, rich spike control is executed.
[0150]
The storage capacity update process (FIGS. 14 and 15) will be described. This process is periodically executed in the same manner as the storage capacity update process (FIGS. 5 and 6) of the first embodiment. An example of the control of the present embodiment is shown in the timing chart of FIG.
[0151]
When this process is started, it is first determined whether or not the engine is idling (S402). If it is not currently idling (“NO” in S402), “OFF” is set to the determination value increase flag Frsinc (S422), and this process is temporarily terminated.
[0152]
Thus, “YES” is determined in step S117a of FIG. 13, and steps S118 and S120 are executed. Therefore, the NOx storage capacity noxmax is calculated from the map Mnoxmax shown in FIG. 4, and the rich spike execution determination value rspnoxmax is calculated from the equation 2 based on the NOx storage capacity noxmax. Based on the rich spike execution determination value rspnoxmax, it is determined in step S122 whether or not rich spike control is to be executed.
[0153]
If it is currently idling (“YES” in S402), it is determined whether or not stratified combustion is in progress (S404). This determination may be made as to whether or not lean combustion is performed when the engine 2 performs lean combustion as described in step S204 of FIG. If it is not stratified combustion (“NO” in S404), “OFF” is set to the determination value increase flag Frsinc as described above (S422), and this process is temporarily terminated.
[0154]
If it is during stratified combustion (“YES” in S404), whether or not the NOx occlusion capacity noxmax has not yet been updated in the temperature range to which the current catalyst temperature etempave belongs in the previous trip of the reference number. It is determined (S406). This is because the NOx discharge due to the gradual increase of the rich spike execution determination value rspnoxmax is not repeated in the same temperature region even if it is once updated in the map Mnoxmax (FIG. 4) within the reference number of trips. To be judged. The reference number is set to 1 to several times, for example.
[0155]
If the update has already been executed in the same temperature range within the reference number of trips (“NO” in S406), as described above, the determination value increase flag Frsinc is set to “OFF” (S422), and this processing is performed. Is temporarily terminated.
[0156]
If the update has not yet been executed in the same temperature range within the reference number of trips (“YES” in S406), then in the current operation state (here, the idle time stratified combustion state in the same temperature range) It is determined whether or not rich spike control has been executed (S407). If rich spike control has not yet been executed (“NO” in S407), the determination value increase flag Frsinc is set to “OFF” as described above (S422), and this process is temporarily terminated.
[0157]
When the rich spike control is executed (“YES” in S407), it is next determined whether or not it is immediately after the return from the rich spike control (S408). Since it is immediately after the return from the rich spike control (“YES” in S408), “ON” is set to the determination value increase flag Frsinc (S410). As a result, “NO” is determined in step S117a of FIG. 13, and step S117b described above is executed. As a result, the gradual increase of the rich spike execution determination value rspnoxmax is executed.
[0158]
Then, the timer starts counting (S412). This processing is as described in step S212 in FIG.
After step S412, it is determined whether or not the NOx concentration Dnox detected by the NOx sensor 28 is equal to or greater than the NOx concentration increase determination value D2 (S414). This determination is as described in step S214 in FIG.
[0159]
Here, if the rich spike execution determination value rspnoxmax is smaller than the actual NOx storage capacity of the NOx storage reduction catalyst 22, before NOx is discharged from the NOx storage reduction catalyst 22, enoxcnt ≧ rspnoxmax (FIG. 13: in S122) “YES”). As a result, rich spike control is executed before NOx is discharged from the NOx occlusion reduction catalyst 22, so that Dnox ≧ D2 is not determined in step S414 (“NO” in S414). The process ends. Therefore, the map Mnoxmax is not updated in steps S416 to S420.
[0160]
By repeating step S117b of FIG. 13 for each control cycle, the rich spike execution determination value rspnoxmax gradually increases. As a result, NOx is discharged from the NOx occlusion reduction catalyst 22 before enoxcnt ≧ rspnoxmax, and it is determined that Dnox ≧ D2 (“YES” in S414).
[0161]
For this reason, the timer count value T at the timing when Dnox ≧ D2 is set as the NOx increase period Tnox (S416). Then, as shown in the equation 3, the NOx storage capacity noxmax is calculated (S418). The map Mnoxmax (FIG. 4) is updated with the NOx storage capacity noxmax (S420).
[0162]
Then, the determination value increase flag Frsinc = “OFF” is set (S422), and this process is temporarily terminated.
Here, the timing chart of FIG. 16 shows an example of a course from the first rich spike control (time t10 to t11) after steps S402 to S406 are satisfied. Here, since it is idling, when rich spike control (time t10 to t11) is completed, NOx flows from the upstream side of the NOx occlusion reduction catalyst 22 at a substantially constant NOx emission amount enoxext. Therefore, the NOx occlusion amount enoxcnt increases in proportion to the timer count value T as shown by the solid line (t11 to t). Since the determination value increase flag Frsinc = “ON” (“NO” in S117a) after the completion of the rich spike control (t11-), the rich spike execution determination value rspnoxmax is gradually increased as indicated by the one-dot chain line in the process of step S117b. Will increase.
[0163]
When the NOx occlusion amount enoxcnt of the NOx occlusion reduction catalyst 22 becomes equal to or larger than the rich spike execution determination value rspnoxmax (“YES” in S122, t12), rich spike control (time t12 to t13) is executed. Thereafter, the rich spike execution determination value rspnoxmax (one-dot chain line) exceeds the actual NOx storage capacity (broken line) of the NOx storage reduction catalyst 22. For this reason, the NOx occlusion reduction catalyst 22 starts to discharge NOx downstream before enoxcnt ≧ rspnoxmax (t14). Thereafter, the NOx concentration Dnox becomes equal to or higher than the NOx concentration increase determination value D2 (t15). For this reason, it determines with "YES" in step S414, step S416-S420 is performed and map Mnoxmax (FIG. 4) is updated. Then, the determination value increase flag Frsinc = “OFF” is returned (S422).
[0164]
When Frsinc = “OFF”, “YES” is determined in step S117a of FIG. 13, and the rich spike execution determination value rspnoxmax is an appropriate value based on the map Mnoxmax (FIG. 4) in steps S118 and S120. Updated to Then, it is determined as “YES” in Step S122, and Step S130 is executed, whereby the rich spike control (t15 to t16) is immediately started.
[0165]
In the next control cycle of the storage capacity update process (FIGS. 14 and 15), the NOx storage capacity is updated in the same temperature range, so that “NO” is determined in step S406, and Frsinc = “OFF”. Is maintained (S422). Therefore, after that (t16-), it is determined as “YES” in step S117a of FIG. 13, and the rich spike execution determination value rspnoxmax is set based on the updated map Mnoxmax (FIG. 4) (S118, S120). . If enoxcnt ≧ rspnoxmax (“YES” in S122), rich spike control (t17 to t18) is executed according to the setting in step S130.
[0166]
If the catalyst temperature etempave shifts to another temperature region where the map Mnoxmax (FIG. 4) has not been updated in the trip within the reference number of times, “YES” is determined in step S406. Therefore, the rich spike execution determination value rspnoxmax is gradually increased, and the NOx storage capacity noxmax in the corresponding temperature region is updated as described above.
[0167]
Since the update of the map Mnoxmax (FIG. 4) is repeated in this way, the rich spike execution determination value rspnoxmax used in step S122 of the rich spike setting process is also updated to an appropriate value, and the rich spike is performed at a highly accurate timing. Control can be performed.
[0168]
In the configuration described above, the NOx sensor 28 serves as the NOx detection means, the storage capacity update process (FIGS. 14 and 15) and the processes of steps S117a, S117b, S118, and S120 of FIG. Equivalent to. Steps S402 to S408 correspond to an increase update condition.
[0169]
According to the fourth embodiment described above, the following effects can be obtained.
(I). The effect (a) of the first embodiment is produced.
(B). When the margin allowance formation coefficient delta is set using the map Mdelta (FIG. 9), the effect (b) of the second embodiment is produced.
[0170]
(C). The measurement of the NOx increase period Tnox is performed by gradually increasing the rich spike execution determination value rspnoxmax while repeating the reduction of the NOx storage reduction catalyst 22 without prohibiting the execution of the rich spike control in advance.
[0171]
Even in such an operation state in which rich spike control is possible, the start timing of rich spike control can be updated to an appropriate value. Therefore, the increase in the NOx concentration discharged from the NOx storage reduction catalyst 22 becomes temporary, and NOx emission The NOx storage reduction catalyst 22 can be continuously used over a long period of time without increasing the amount.
[0172]
(D). The increase update condition of the rich spike execution determination value rspnoxmax includes an idle state. As a result, the NOx concentration is detected in a state where the exhaust flow rate of the engine is small. Therefore, even if the NOx sensor 28 temporarily discharges NOx from the NOx occlusion reduction catalyst 22 in order to detect an increase in the NOx concentration, the absolute emission amount itself can be reduced, so that it has an impact on the environment. Will be less.
[0173]
[Embodiment 5]
In the present embodiment, in the rich spike setting process (FIGS. 2 and 3), the process shown in FIG. 17 is executed instead of the process shown in FIG. The storage capacity update process shown in FIGS. 18 and 19 is executed instead of the storage capacity update process (FIGS. 5 and 6), which is different from the first embodiment. Other configurations are the same as those of the first embodiment. As in the second embodiment, the margin allowance formation coefficient delta may be set according to the map Mdelta shown in FIG.
[0174]
The rich spike setting process (FIGS. 2 and 17) will be described. Since the processing of FIG. 2 is as described in the first embodiment, detailed description thereof is omitted. In FIG. 17, there is no determination (S128) of whether or not the rich spike control prohibition cancellation exists in FIG. Therefore, if NOx occlusion amount enoxcnt ≧ rich spike execution determination value rspnoxmax, rich spike control is always executed (S130). The other processes in FIG. 17 are the same as those in FIG. 3, and the same processes as those in FIG. 3 are given the same step numbers.
[0175]
Regarding the storage capacity update process (FIGS. 18 and 19), the determination of the non-update condition of the storage capacity update process (FIGS. 5 and 6) (FIG. 5: S206), the prohibition of rich spike control (FIG. 5: S210), and the rich spike control The other configuration is the same as the storage capacity updating process (FIGS. 5 and 6) except that the prohibition cancellation (FIG. 6: S222) does not exist. The same processes as those in FIGS. 5 and 6 are given the same step numbers.
[0176]
An example of control by this configuration is shown in the timing chart of FIG. This timing chart shows that the actual NOx storage capacity has deteriorated from the state in which the rich spike execution determination value rspnoxmax is set to an appropriate value with respect to the actual NOx storage capacity of the NOx storage reduction catalyst 22 (˜t21). An example of a gradual decrease is shown. Here, until the time t23, the actual NOx storage capacity does not fall below the rich spike execution determination value rspnoxmax. Therefore, the rich spike control is executed when NOx occlusion amount enoxcnt ≧ rspnoxmax (“YES” in step S122 of FIG. 17) (S130: t20 to t21, t22 to t23).
[0177]
However, after time t23, the actual NOx storage capacity becomes smaller than the rich spike execution determination value rspnoxmax. Therefore, the NOx occlusion reduction catalyst 22 starts to discharge NOx before the NOx occlusion amount enoxcnt ≧ rspnoxmax is satisfied (t24). Thereafter, when NOx concentration Dnox ≧ D2 (“YES” in S214), steps S216 to S220 are executed, and the map Mnoxmax (FIG. 4) is updated (t25). As a result, the rich spike execution determination value rspnoxmax becomes an appropriate value for the actual NOx storage capacity (FIG. 17: S118, S120). Then, it is determined that enoxcnt ≧ rspnoxmax (“YES” in S122), and rich spike control is immediately executed (S130).
[0178]
In the configuration described above, the NOx sensor 28 corresponds to the NOx detection means, and the storage capacity update process (FIGS. 18 and 19) and the processes of steps S118 and S120 of FIG. 17 correspond to the process as the rich spike execution determination value update means.
[0179]
According to the fifth embodiment described above, the following effects can be obtained.
(I). The effect (a) of the first embodiment is produced.
(B). Even if the rich spike control is executed as usual as in the present embodiment, the map Mnoxmax (FIG. 4) can be updated with respect to the deterioration degree of the NOx storage reduction catalyst 22, and the rich spike execution determination value rspnoxmax is an appropriate value. Can be updated.
[0180]
(C). When the margin allowance formation coefficient delta is set using the map Mdelta (FIG. 9), the effect (b) of the second embodiment is produced.
[Embodiment 6]
The present embodiment is different from the fifth embodiment in that the storage capacity update process shown in FIGS. 21 and 22 is executed instead of the storage capacity update process (FIGS. 18 and 19) of the fifth embodiment. . Other configurations are the same as those of the fifth embodiment. As in the second embodiment, the margin allowance formation coefficient delta may be set according to the map Mdelta shown in FIG.
[0181]
Regarding the storage capacity update process (FIGS. 21 and 22), the determination of the non-update condition of the storage capacity update process (FIGS. 10 and 11) of the third embodiment (S304), the prohibition of rich spike control (S312), and the rich spike control The other configuration is the same as the storage capacity update process (FIGS. 10 and 11) except that there is no prohibition cancellation (S332). The same processes as those in FIGS. 10 and 11 are given the same step numbers.
[0182]
An example of control by this configuration is shown in the timing chart of FIG. This timing chart shows that the actual NOx storage capacity gradually decreased from the state (˜t31) where the rich spike execution determination value rspnoxmax is set to an appropriate value with respect to the actual NOx storage capacity of the NOx storage reduction catalyst 22. An example is shown. Here, until the time t33, the actual NOx storage capacity (broken line) does not fall below the rich spike execution determination value rspnoxmax (dashed line). Therefore, the rich spike control is executed when NOx occlusion amount enoxcnt ≧ rspnoxmax (“YES” in step S122 of FIG. 17) (S130: t30 to t31, t32 to t33).
[0183]
However, after time t33, the actual NOx storage capacity becomes smaller than the rich spike execution determination value rspnoxmax. Therefore, the NOx occlusion reduction catalyst 22 starts to discharge NOx before the NOx occlusion amount enoxcnt ≧ rspnoxmax (t34). Thereafter, when NOx concentration Dnox ≧ D2 (“YES” in S326), steps S328 and S330 are executed, and the map Mnoxmax (FIG. 4) is updated (t35). As a result, the rich spike execution determination value rspnoxmax becomes an appropriate value for the actual NOx storage capacity (FIG. 17: S118, S120). Then, it is determined that enoxcnt ≧ rspnoxmax (“YES” in S122), and rich spike control is immediately executed (S130).
[0184]
In the configuration described above, the NOx sensor 28 corresponds to the NOx detection means, and the storage capacity update processing (FIGS. 21 and 22) and the processing in steps S118 and S120 in FIG. 17 correspond to processing as the rich spike execution determination value update means.
[0185]
According to the sixth embodiment described above, the following effects can be obtained.
(I). The effects (a) and (c) of the third embodiment and the effect (b) of the fifth embodiment are produced.
[0186]
[Other embodiments]
(A). In each of the embodiments described above, the map Mnoxmax (FIG. 4) is updated by the newly obtained NOx storage capacity noxmax by updating the NOx storage capacity at the representative temperature in the corresponding temperature region as described with reference to FIG. It was broken. In addition to this, the NOx storage capacities at two representative temperatures adjacent to the high temperature side and the low temperature side of the catalyst temperature etempave may be updated by Δnoxmax as shown in FIG. That is, the NOx storage capacity noxmaxold (◯ mark) before the update is obtained by interpolation calculation according to the catalyst temperature etempave, and this value and the NOx storage capacity noxmax (◎ mark) obtained in steps S218, S328, and S418. The difference Δnoxmax (= noxmaxold−noxmax) is calculated. Then, by subtracting this difference Δnoxmax from the NOx occlusion capacity (the temperature of the upper Δ mark) at the representative temperatures of the two temperature regions tmp (3), tmp (4), the temperature regions tmp (3), tmp (4) The new NOx storage capacity at the representative temperature (the temperature of the Δ mark on the lower side) is obtained.
[0187]
It should be noted that the NOx occlusion capacity at the representative temperatures in the two temperature regions tmp (3) and tmp (4) is not changed in the same way, but the nearer one is weighted according to the position of the catalyst temperature etempave. The NOx occlusion capacity at each representative temperature may be changed by reducing the weight.
[0188]
(B). In the first, second, and third embodiments, the NOx concentration Dnox downstream of the NOx storage reduction catalyst 22 is monitored by the NOx sensor 28 when the rich spike control is prohibited. In addition to this, even when the rich spike control is not prohibited, the same processing as in the fifth and sixth embodiments is executed to monitor the NOx concentration Dnox, and when Dnox ≧ D2, the map Mnoxmax (FIG. 4) May be updated.
[0189]
In the fourth embodiment, the NOx concentration Dnox in the exhaust gas is monitored by the NOx sensor 28 when the rich spike execution determination value rspnoxmax is gradually increased. In addition to this, even when the rich spike execution determination value rspnoxmax is set based on the map Mnoxmax (FIG. 4), the same processing as in the fifth embodiment is executed to monitor the NOx concentration Dnox, and Dnox ≧ D2. In this case, the map Mnoxmax (FIG. 4) may be updated.
[0190]
(C). In each of the above embodiments, the NOx sensor 28 is provided with the detection delay times Ta and Tb described above because the NOx concentration rise cannot be measured accurately at the timing when NOx starts to be discharged from the NOx storage reduction catalyst 22 with accuracy. It was. However, the detection delay times Ta and Tb may not be used as long as the NOx concentration increase can be determined at the timing when NOx starts to be discharged from the NOx storage reduction catalyst 22 using a highly accurate sensor for the NOx sensor 28. For example, instead of the equation 3 described in step S218 of FIG. 6, it can be calculated more simply as the following equation 7.
[0191]
[Expression 7]
noxmax <-enext x Tnox [Formula 7]
Further, steps S316 to S324 shown in FIG. 11 are simplified to the accumulation process of the NOx emission amount enoxex to the integrated NOx amount Anox as shown in the following equation 8.
[0192]
[Equation 8]
Anox ← Anox + enoxext [Formula 8]
(D). The map Mdelta illustrated in FIG. 9 described in the second embodiment is constant regardless of the degree of deterioration of the NOx storage reduction catalyst 22. Instead, as the NOx occlusion reduction catalyst 22 deteriorates, that is, as the value of the NOx occlusion capacity noxmax in the map Mnoxmax (FIG. 4) becomes lower, the overall value of the margin allowance formation coefficient delta is lowered and the margin allowance formation coefficient delta is reduced. The difference between the maximum value and the minimum value may be increased. That is, when the NOx occlusion reduction catalyst 22 deteriorates, the catalyst permeability of the unburned gas increases in the entire space velocity, and the catalyst permeability of the unburned gas particularly increases on the high space velocity side.
[0193]
(E). In each of the first to third embodiments, the rich spike control execution condition (FIG. 5: S207, FIG. 10: S306) is included as the rich spike prohibition execution condition, so that the rich spike control is executed. I was waiting. Instead, when step S202 to S206 (FIG. 5) or steps S302 and S304 (FIG. 10) are satisfied, rich spike control is forcibly executed, and step S208 (FIG. 5) or step S308 (FIG. 5) is executed. 10) The following processing may be executed. In this case, since it is possible to shift to a state where the NOx concentration downstream of the NOx storage reduction catalyst 22 increases early, the map Mnoxmax (FIG. 4) is quickly updated, and the rich spike execution determination value rspnoxmax is rich at an early stage. Spike control can be executed.
[0194]
(F). In each of the above embodiments, a cylinder injection engine is used, but the present invention can also be applied to a port injection engine that injects fuel into an intake port. In this configuration, lean combustion is performed instead of stratified combustion, and NOx is stored in the NOx storage reduction catalyst during the lean combustion.
[Brief description of the drawings]
FIG. 1 is a schematic configuration explanatory diagram of an engine and an ECU according to a first embodiment.
FIG. 2 is a flowchart of a rich spike setting process.
FIG. 3 is a flowchart of a rich spike setting process.
FIG. 4 is a configuration explanatory view of a map Mnoxmax that similarly shows the relationship between the catalyst temperature and the NOx storage capacity.
FIG. 5 is a flowchart of storage capacity update processing in the same manner.
FIG. 6 is a flowchart of storage capacity update processing in the same manner.
FIG. 7 is a timing chart that similarly shows an example of control.
FIG. 8 is a graph showing an example of updating the map Mnoxmax.
FIG. 9 is a configuration explanatory diagram of a map Mdelta according to the second embodiment.
10 is a flowchart of storage capacity update processing according to Embodiment 3. FIG.
FIG. 11 is a flowchart of storage capacity update processing in the same manner.
FIG. 12 is a timing chart that similarly shows an example of control.
FIG. 13 is a flowchart of rich spike setting processing according to the fourth embodiment;
FIG. 14 is a flowchart of the storage capacity update process.
FIG. 15 is a flowchart of storage capacity update processing in the same manner.
FIG. 16 is a timing chart that similarly shows an example of control.
FIG. 17 is a flowchart of rich spike setting processing according to the fifth embodiment;
FIG. 18 is a flowchart of storage capacity update processing in the same manner.
FIG. 19 is a flowchart of storage capacity update processing in the same manner.
FIG. 20 is a timing chart that similarly shows an example of control.
FIG. 21 is a flowchart of storage capacity update processing according to the sixth embodiment;
FIG. 22 is a flowchart of storage capacity update processing in the same manner.
FIG. 23 is a timing chart that similarly shows an example of control.
FIG. 24 is a graph showing another example of updating the map Mnoxmax.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 2 ... Engine, 4 ... ECU, 6 ... Fuel injection valve, 8 ... Spark plug, 10 ... Intake path, 12 ... Throttle valve, 14 ... Throttle opening sensor, 16 ... Intake air amount sensor, 18 ... Exhaust path, 20 ... Start catalyst, 22 ... NOx occlusion reduction catalyst, 24 ... Air-fuel ratio sensor, 26 ... O2 sensor, 28 ... NOx sensor, 30 ... Accelerator pedal, 32 ... Accelerator opening sensor, 34 ... Engine speed sensor, 36 ... Cooling water temperature Sensor.

Claims (16)

A NOx occlusion reduction catalyst that occludes NOx contained in the exhaust gas and reduces the occluded NOx; and NOx detection means that detects NOx concentration in the exhaust gas that has passed through the NOx occlusion reduction catalyst. Rich spike control for reducing the NOx of the NOx occlusion reduction catalyst by temporarily increasing the fuel component in the exhaust based on determining that the estimated value of the NOx occlusion amount of the catalyst is equal to or greater than the rich spike execution determination value In an exhaust gas purification apparatus for an internal combustion engine that performs
  When it is determined that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst based on the detection result of the NOx detection means, the rich spike execution determination value is updated based on the engine operation history at this time. NOx in the exhaust gas causes the NOx occlusion reduction catalyst based on the fact that the increase update condition including the execution of the rich spike control is satisfied and the detection result of the NOx detection means. Rich spike execution determination value updating means for updating the rich spike execution determination value in a manner that gradually increases the rich spike execution determination value in a period in which it is determined that the state has not started passing.
  An exhaust emission control device for an internal combustion engine. A NOx occlusion reduction catalyst that occludes NOx contained in the exhaust gas and reduces the occluded NOx; and NOx detection means that detects NOx concentration in the exhaust gas that has passed through the NOx occlusion reduction catalyst. Rich spike control for reducing the NOx of the NOx occlusion reduction catalyst by temporarily increasing the fuel component in the exhaust based on determining that the estimated value of the NOx occlusion amount of the catalyst is equal to or greater than the rich spike execution determination value In an exhaust gas purification apparatus for an internal combustion engine that performs
  The rich spike execution determination value is updated, and as a mode thereof, when it is determined based on the detection result of the NOx detection means that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst, The rich spike execution determination value is updated based on the engine operation history at this time, and the rich spike execution determination value is determined at least until it is determined that NOx in the exhaust gas next passes through the NOx storage reduction catalyst. When the rich spike execution determination value after being updated in this mode and the updated value in this mode is smaller than the limit value of the NOx occlusion amount of the NOx occlusion reduction catalyst at that time, The rich spike execution determination value is continuously updated in such a manner that the rich spike execution determination value after the update is gradually increased. By making the value larger than the limit value of the NOx occlusion amount, even if the actual NOx occlusion amount of the NOx occlusion reduction catalyst reaches the limit value of the NOx occlusion amount, the rich spike control is not executed, and thereafter When it is determined that the NOx in the exhaust gas has started to pass through the NOx occlusion reduction catalyst based on the detection result of the NOx detection means, the rich spike execution determination value is updated based on the engine operation history at this time. Rich spike execution determination value updating means having the second aspect
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 2,
  The rich spike execution determination value update means determines that an increase update condition including that the rich spike control can be executed is satisfied, and that NOx in the exhaust is based on the detection result of the NOx detection means. The rich spike execution determination value is updated in the mode of gradually increasing on the condition that it is determined that the state of starting to pass through the NOx storage reduction catalyst has not been reached.
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3,
  The rich spike execution determination value updating means is configured to change the NOx concentration in the exhaust gas from the state in which the NOx concentration, which is the detection result of the NOx detection means, is less than the concentration increase determination value and to the state in which the NOx concentration is higher than this. It is judged that it has reached the state that passes this from the state that has not passed
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 4,
  The rich spike execution determination value update means is a value that can reliably detect, as the concentration increase determination value, the timing at which NOx in the exhaust gas begins to pass through the NOx storage reduction catalyst by the NOx detection means. Use a value larger than “0” and set in advance as a value near “0”
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 5,
  The rich spike execution determination value update means includes that the engine update state is in an idle operation state in the increase update condition.
  An exhaust emission control device for an internal combustion engine. A NOx occlusion reduction catalyst that occludes NOx contained in the exhaust gas and reduces the occluded NOx; and NOx detection means that detects NOx concentration in the exhaust gas that has passed through the NOx occlusion reduction catalyst. Rich spike control for reducing the NOx of the NOx occlusion reduction catalyst by temporarily increasing the fuel component in the exhaust based on the determination that the estimated value of the NOx occlusion amount of the catalyst is greater than or equal to the rich spike execution determination value In an exhaust gas purification apparatus for an internal combustion engine that performs
  When it is determined that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst based on the detection result of the NOx detection means, the rich spike execution determination value is updated based on the engine operation history at this time. In this renewal, the storage capacity of the NOx storage reduction catalyst is set on the side smaller than this, and a margin margin that is the difference between the storage capacity and the rich spike execution determination value is set, and the NOx storage reduction The margin on the side where the space velocity of the exhaust with respect to the catalyst is low is set larger than the margin on the side where the space velocity of the exhaust with respect to the NOx storage reduction catalyst is high, thereby the rich on the side where the space velocity of the exhaust is low. A rich spike execution determination value that sets a spike execution determination value smaller than the rich spike execution determination value on the higher exhaust space velocity side. Equipped with a new means
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 7,
  The rich spike execution determination value updating means prohibits the execution of the rich spike control based on establishment of a rich spike prohibition execution condition, and cancels the execution prohibition based on updating the rich spike execution determination value.
  An exhaust emission control device for an internal combustion engine. The exhaust emission control device for an internal combustion engine according to claim 8,
  The rich spike execution determination value update means includes an engine operation state in an idle operation state in the rich spike prohibition execution condition.
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 9,
  The rich spike execution determination value update means is configured to store NOx by the NOx storage reduction catalyst at that time based on the engine operation history at the time when it is determined that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst. An estimated value of the amount is calculated, and the rich spike execution determination value is updated based on the calculated estimated value.
  An exhaust emission control device for an internal combustion engine. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 10,
  The rich spike execution determination value update means starts to pass NOx in the exhaust through the NOx occlusion reduction catalyst from the time when the rich spike control is completed under an engine operation state in which the fluctuation of the NOx flow rate in the exhaust is small. The elapsed time up to the time when the determination is made is measured, and this measured elapsed time is used as the engine operation history at the time when it is determined that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst.
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 11,
  The rich spike execution determination value updating means subtracts a detection delay time from the measured elapsed time, and updates the rich spike execution determination value based on the NOx storage limit time obtained thereby.
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 12,
  The rich spike execution determination value updating means sets the detection delay time based on the engine operating state.
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 12 or 13,
  The rich spike execution determination value updating means calculates the amount of NOx occluded in the NOx occlusion reduction catalyst within the NOx occlusion limit time based on the NOx occlusion limit time and the NOx flow rate in the exhaust gas, and this calculation The rich spike execution determination value is updated based on the amount of NOx that has been made
  An exhaust emission control device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 10,
  The rich spike execution determination value updating means updates the NOx flow rate state in the exhaust gas from when the rich spike control is completed until it is determined that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst. Used as the engine operation history when it is determined that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst.
  An exhaust emission control device for an internal combustion engine. The exhaust emission control device for an internal combustion engine according to claim 15,
  The rich spike execution determination value update means is based on the NOx flow rate state in the exhaust gas from when the rich spike control is completed until it is determined that NOx in the exhaust gas has started to pass through the NOx storage reduction catalyst. The total exhaust amount of NOx from the internal combustion engine in the period from the completion time point to the determined time point is calculated, and the calculated total exhaust amount is used as the estimated value of the NOx occlusion amount to determine the rich spike execution determination value. Update
  An exhaust emission control device for an internal combustion engine.

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