JP4032774B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
Diesel engines are economical, but it is important to remove particulate matter (particulate matter: hereinafter referred to as “PM”) unless otherwise specified. It has become a challenge. For this reason, a technique is known in which a particulate filter (hereinafter simply referred to as “filter”) that collects PM is provided in the exhaust system of a diesel engine so that PM is not released into the atmosphere.
[0003]
This filter can prevent PM in the exhaust gas from being collected once and released into the atmosphere. However, when PM collected by the filter accumulates on the filter, the filter may be clogged. If this clogging occurs, the pressure of the exhaust gas upstream of the filter may increase, leading to a decrease in the output of the internal combustion engine and damage to the filter. In such a case, the PM accumulated on the filter can be removed by igniting and burning. The removal of PM deposited on the filter in this way is called filter regeneration.
[0004]
In such filter regeneration, for example, in Japanese Patent Laid-Open No. H5-288037, the average value of the degree of clogging after a plurality of filter regenerations is detected from the differential pressure across the filter, and the regeneration timing is corrected according to the detected value. ing. Here, if there is a difference between the filter clogging level at the time of a new product or the clogging level at the beginning of filter use after the filter regeneration multiple times, the change will be in the ash collected in the filter. It can be seen as the cause. Therefore, instead of inferring the clogging degree change that the ash contributes from the travel distance, the clogging degree change caused by the ash is detected directly by detecting the filter after multiple filter regenerations, that is, the degree average value. The filter regeneration time is corrected. In this way, the corrected filter regeneration time can be made appropriate, and the amount of PM trapped each time can be made constant and stable regeneration can be performed.
[0005]
[Problems to be solved by the invention]
However, in the method of detecting filter clogging using only the differential pressure before and after the filter, it is possible to make a determination only under specific operating conditions such as during deceleration, idling, steady operation, etc. It is difficult to make a clogging determination at. If a large amount of PM accumulates without the clogging determination being made for a long period of time, the filter may be overheated due to the burning of a large amount of PM during the next filter regeneration, which may cause thermal degradation of the filter.
[0006]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of detecting clogging of a filter in a wide range of operation in an exhaust purification device for an internal combustion engine. .
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine of the present invention employs the following means. That is, the first invention is
A filter that can temporarily capture particulate matter in the exhaust;
Pressure detecting means for detecting pressure at least upstream of the filter;
Intake air amount detection means for detecting the amount of fresh air sucked into the internal combustion engine;
Clogging determination means for determining the degree of clogging of the filter by a value obtained by dividing the pressure detected by the pressure detection means by the amount of fresh air detected by the intake air amount detection means;
It is characterized by comprising.
[0008]
The most significant feature of the present invention is that in an exhaust gas purification apparatus for an internal combustion engine, an operating state is obtained by using a value obtained by dividing the pressure detected by the pressure detecting means by the amount of fresh air detected by the intake air amount detecting means. This is to eliminate the fluctuation of the sensor output due to the occurrence of clogging and to accurately perform the clogging determination even during acceleration / deceleration.
[0009]
In the exhaust gas purification apparatus for an internal combustion engine thus configured, the pressure detection means detects the pressure before the filter or the differential pressure before and after the filter. Here, since the value detected by the pressure detecting means varies greatly during acceleration / deceleration, it is difficult to determine the clogging of the filter based only on this value. However, since the pressure detected by the pressure detection means has a correlation with the intake air amount, the detection value of the pressure detection means is divided by the detection value of the intake air amount detection means, resulting from a change in the operating state. It is possible to remove fluctuations. As a result, it is possible to obtain a value representing the degree of filter clogging even during acceleration / deceleration, and it is possible to determine clogging of the filter.
[0010]
In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine of the present invention employs the following means. That is, the second invention is
A filter that can temporarily capture particulate matter in the exhaust;
Pressure detecting means for detecting pressure at least upstream of the filter;
Intake air amount detection means for detecting the amount of fresh air sucked into the internal combustion engine;
Exhaust temperature detecting means for detecting the temperature of the exhaust gas flowing into the filter;
Pressure correcting means for correcting the pressure detected by the pressure detecting means to a pressure in a reference state based on the temperature of the exhaust detected by the exhaust temperature detecting means;
Clogging determination means for determining the degree of clogging of the filter by a value obtained by dividing the pressure corrected by the pressure correction means by the amount of fresh air detected by the intake air amount detection means;
It is characterized by comprising.
[0011]
The greatest feature of the present invention is that, in an exhaust gas purification apparatus for an internal combustion engine, a value obtained by adding a temperature correction to the pressure detected by the pressure detecting means is divided by the amount of fresh air detected by the intake air amount detecting means. By using the value, the fluctuation of the sensor output due to the operating state is removed, and the clogging determination is performed accurately even during acceleration / deceleration.
[0012]
In the exhaust gas purification apparatus for an internal combustion engine thus configured, the pressure detection means detects the pressure before the filter or the differential pressure before and after the filter. In addition, since the pressure detected by the pressure detection unit also varies when the exhaust temperature varies, the pressure correction unit converts the pressure detected based on the exhaust temperature to the pressure in the reference state.
[0013]
Here, since the pressure value detected by the pressure correction means varies greatly during acceleration / deceleration, it is difficult to determine clogging of the filter based only on this value. However, since the pressure value corrected by the pressure correction means has a correlation with the intake air amount, the operation is performed by dividing the pressure value corrected by the pressure correction means by the value detected by the intake air amount detection means. It is possible to remove the fluctuation due to the change of the state. As a result, it is possible to obtain a value representing the degree of filter clogging even during acceleration / deceleration, and it is possible to determine clogging of the filter.
[0014]
In the present invention, the clogging determination means can perform filter clogging determination by excluding a value obtained when the acceleration of the vehicle is outside a predetermined range. Here, at the time of sudden acceleration or sudden deceleration, the correlation between the intake air amount and the pre-filter pressure may not be established due to a pulsating wave or a response delay. Therefore, it is possible to prevent erroneous determination by excluding the value at this time.
[0015]
In the present invention, the clogging determination means can perform filter clogging determination by excluding a value obtained when the value detected by the intake air amount detection means is equal to or less than a predetermined value. Here, when the intake air amount is small, the influence of the pulsating wave propagating to the intake air is large, and thus there is a possibility of erroneously detecting the intake air amount. Therefore, it is possible to prevent erroneous determination by excluding the value at this time.
[0016]
In the present invention, the clogging determination means can perform clogging determination using a value obtained by performing the averaging process. In the exhaust gas purification apparatus for an internal combustion engine configured as described above, the remaining fluctuation can be reduced. The averaging process can be performed by, for example, annealing or averaging.
[0017]
In the present invention, the filter can carry a NOx catalyst that reduces nitrogen oxides to nitrogen. Here, by supporting the NOx catalyst, the particulate matter collected by the filter can be easily removed. Moreover, since it is not necessary to increase the amount of intake air when determining the clogging of the filter, it is possible to maintain the ability to continuously regenerate particulate matter.
[0018]
In the present invention, the clogging determination means obtains a change rate of the determination value, and when the change rate is equal to or greater than a predetermined value, the interval for removing the particulate matter collected by the filter may be shortened. it can. In the exhaust gas purification apparatus for an internal combustion engine configured as described above, it is possible to continuously determine the clogging of the filter, so by detecting the clogging of the filter at an early stage and removing the particulate matter collected in the filter, It is possible to suppress excessive accumulation of particulate matter on the filter.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing a schematic configuration of an engine and its intake / exhaust system according to the present embodiment.
[0020]
The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.
[0021]
An intake pipe 2 is connected to the internal combustion engine 1, and an air flow meter 3 that outputs an electrical signal corresponding to the mass of intake air flowing through the intake pipe 2 is attached to the intake pipe 2. Yes.
[0022]
On the other hand, an exhaust pipe 4 is connected to the internal combustion engine 1, and a particulate filter (hereinafter simply referred to as a filter) 5 carrying an NOx storage reduction catalyst is provided in the middle of the exhaust pipe 4. An exhaust gas temperature sensor 6 that outputs an electrical signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 4 is attached to the exhaust pipe 4 upstream of the filter 5. One end of an upstream introduction pipe 7a for introducing exhaust gas is connected upstream of the filter 5, and one end of a downstream introduction pipe 7b is connected downstream of the filter 5. The other end of the upstream introduction pipe 7 a and the other end of the downstream introduction pipe 7 b are connected to the differential pressure sensor 7. The differential pressure sensor 7 outputs an electrical signal corresponding to the differential pressure of the exhaust gas introduced from the upstream side introduction pipe 7a and the downstream side introduction pipe 7b.
[0023]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 11 for controlling the internal combustion engine 1. The ECU 11 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.
[0024]
Various sensors are connected to the ECU 11 via electric wiring, and output signals of the various sensors described above are input to the ECU 11. The ECU 11 stores various application programs and various control maps.
[0025]
By the way, when PM collected by the filter 5 accumulates on the filter 5, the filter 5 may be clogged. When this clogging occurs, the pressure of the exhaust gas upstream of the filter 5 may increase, leading to a reduction in the output of the internal combustion engine 1 and damage to the filter 5. In such a case, it is necessary to regenerate the filter 5 to remove PM accumulated on the filter 5.
[0026]
As a method of regenerating such a filter, after adding fuel to the exhaust gas or increasing the amount of recirculated EGR gas to increase the amount of soot generated to the maximum, further increase the amount of EGR gas. There are conceivable methods such as low-temperature combustion (Japanese Patent No. 3116876), sub-injection in which fuel is injected again during the expansion stroke after main injection in which fuel is injected for engine output.
[0027]
In the present embodiment, a reducing agent supply mechanism for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust pipe 4 upstream from the filter 5 is provided, and the fuel is supplied from the reducing agent supply mechanism into the exhaust gas. By adding, the oxygen concentration of the exhaust gas flowing into the filter 5 is lowered, and the filter 5 is regenerated.
[0028]
As shown in FIG. 1, the reducing agent supply mechanism is attached so that its injection hole faces the exhaust pipe 4, and the reducing agent injection valve 8 that opens by the signal from the ECU 11 to inject fuel, and the fuel And a reducing agent supply path 10 for guiding the fuel discharged from the pump 9 to the reducing agent injection valve 8.
[0029]
In such a reducing agent supply mechanism, high-pressure fuel discharged from the fuel pump 9 is applied to the reducing agent injection valve 8 through the reducing agent supply path 10. Then, the reducing agent injection valve 8 is opened by a signal from the ECU 11 and fuel as a reducing agent is injected into the exhaust pipe 4.
[0030]
Next, regeneration control of the filter 5 by adding fuel to the exhaust will be described.
[0031]
In the regeneration control, the ECU 11 executes fuel addition control for adding fuel to the exhaust gas flowing into the filter 5.
[0032]
The ECU 11 temporarily sets the air-fuel ratio of the exhaust gas flowing into the filter 5 to a predetermined target air-fuel ratio by controlling the reducing agent injection valve 8 to inject fuel as a reducing agent from the reducing agent injection valve 8.
[0033]
Specifically, the ECU 11 reads out the engine speed, the accelerator opening, the output signal value (intake air amount) of the air flow meter 3, the fuel injection amount, and the like. Further, the ECU 11 accesses the reducing agent addition amount control map using the engine speed, the accelerator opening, the intake air amount, and the fuel injection amount as parameters, and sets the air / fuel ratio of the exhaust to a preset target air / fuel ratio. The amount of addition of the reducing agent (target addition amount) required above is calculated.
[0034]
Subsequently, the ECU 11 accesses the flow rate adjustment valve control map using the target addition amount as a parameter, and opens the reducing agent injection valve 8 necessary for injecting the reducing agent injection valve 8 with the target addition amount. Calculate the time (target valve opening time).
[0035]
When the target valve opening time of the reducing agent injection valve 8 is calculated, the ECU 11 opens the reducing agent injection valve 8.
[0036]
The ECU 11 closes the reducing agent injection valve 8 when the target valve opening time elapses from the time when the reducing agent injection valve 8 is opened.
[0037]
Thus, when the reducing agent injection valve 8 is opened for the normal target valve opening time, the normal target addition amount of fuel is injected into the exhaust pipe 4 from the reducing agent injection valve 8. Then, the reducing agent injected from the reducing agent injection valve 8 is mixed with the exhaust gas flowing from the upstream side of the exhaust pipe 4 to form an air-fuel mixture having a target air-fuel ratio and flows into the filter 5.
[0038]
As a result, the exhaust gas flowing into the filter 5 changes its oxygen concentration in a relatively short cycle. Then, the active oxygen is released by the fuel flowing into the filter 5, so that the PM is easily oxidized and the amount capable of being removed by oxidation per unit time is improved. Further, the addition of fuel removes oxygen poisoning of the catalyst and increases the activity of the catalyst, so that active oxygen is easily released. Furthermore, the temperature of the filter 5 rises due to the oxidation reaction of the fuel. Then, PM is oxidized and burned by active oxygen and removed.
[0039]
By the way, the NOx storage reduction catalyst carried by the filter 5 stores nitrogen oxide (NOx) in the exhaust gas when the oxygen concentration of the exhaust gas flowing into the NOx catalyst is high, and flows into the NOx catalyst. When the oxygen concentration in the exhaust gas decreases, the stored NOx is released. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust, the NOx catalyst converts nitrogen oxide (NOx) released from the NOx catalyst to nitrogen (N ₂ ).
[0040]
Here, when the internal combustion engine 1 is in a lean combustion operation, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 becomes a lean atmosphere, and the oxygen concentration of the exhaust becomes high. Therefore, nitrogen oxides (NOx) contained in the exhaust ) Is stored in the NOx catalyst. However, if the lean combustion operation of the internal combustion engine 1 is continued for a long period of time, the NOx storage capacity of the NOx catalyst is saturated, and nitrogen oxides (NOx) in the exhaust gas become NOx catalyst. It will be released into the atmosphere without being removed at
[0041]
Therefore, when the internal combustion engine 1 is in lean burn operation, the reducing agent is supplied to the NOx catalyst before the NOx storage capacity of the NOx catalyst is saturated, and the nitrogen oxide (NOx) stored in the NOx catalyst is reduced. There is a need.
[0042]
As a method of supplying such a reducing agent, fuel addition to the exhaust can be performed. When a reducing agent is supplied to the filter 5 by such a method, NOx is reduced and PM is oxidized and removed as described above.
[0043]
By the way, if the filter regeneration process is performed after a predetermined amount or more of PM has been captured by the filter, the filter may be overheated by heat generated when the captured PM is burned, which may cause thermal degradation. Therefore, it is necessary to regenerate the filter before a predetermined amount or more of PM is captured, and it is important to accurately obtain the regeneration time of the filter.
[0044]
Here, in the conventional exhaust gas purification apparatus for an internal combustion engine, the timing for regenerating the filter is determined based on the differential pressure before and after the filter or the intake air amount. That is, when the differential pressure before and after the filter when the internal combustion engine is in a specific operation state such as an idle state, a deceleration state, or a steady state is greater than a predetermined value, or when the internal combustion engine is in a predetermined operation state When the amount of intake air becomes smaller than a predetermined value, it is determined that the filter is clogged.
[0045]
In such a determination method, during acceleration / deceleration, fluctuations of the sensor and the like increase, and it is difficult to determine clogging of the filter except in a predetermined operation state. Also, for example, when the determination is made using the differential pressure before and after the filter during deceleration, the EGR valve is closed and the intake throttle valve is opened to increase the intake air amount to improve the differential pressure detection accuracy. However, in such a state, the bed temperature of the filter is likely to be lowered, and there is a possibility that PM may be deposited on the filter due to a decrease in the ability of continuously regenerating PM.
[0046]
Therefore, in this embodiment, the filter clogging is determined based on the value obtained by dividing the differential pressure before and after the filter by the intake air amount. Here, the differential pressure before and after the filter is detected by the differential pressure sensor 7, and the intake air amount is detected by the air flow meter 3. Since both values fluctuate during acceleration / deceleration, either value is used alone. It is difficult to determine clogging. However, there is a correlation between the differential pressure before and after the filter and the intake air amount. Therefore, if the differential pressure before and after the filter is divided by the intake air amount, fluctuations in the sensor output due to acceleration / deceleration are eliminated, and Even so, a numerical value representing the degree of clogging of the filter can be obtained.
[0047]
In this embodiment, the output value of the differential pressure sensor 7 is not used as it is, but the value is converted into the pressure in the reference state according to the exhaust temperature. This is because when the temperature of the exhaust gas varies, the differential pressure before and after the filter varies even if the amount of exhaust gas does not vary. As a result, it is possible to perform clogging determination with high accuracy even in an operation state in which fluctuations in the exhaust temperature are large. Here, the exhaust temperature is obtained from the output signal of the exhaust temperature sensor 6. The differential pressure ΔP before and after the filter 5 is converted into the differential pressure ΔP ′ in the reference state from the exhaust temperature detected by the exhaust temperature sensor 6. The conversion formula at this time may be obtained in advance by experiments or the like.
[0048]
Further, in the present embodiment, sensor output values are excluded when sudden acceleration / deceleration that is outside the predetermined acceleration range is performed. This is because the path from the air flow meter 3 to the differential pressure sensor 7 is long, so that it takes time until the intake air amount detected by the air flow meter 3 is detected by the differential pressure sensor 7, and the correlation is not established. This is because it becomes difficult to eliminate fluctuations in sensor output. Further, since only the output of the differential pressure sensor 7 fluctuates due to pulsation generated in the exhaust pipe 4, it is difficult to determine clogging.
[0049]
Further, in the present embodiment, clogging is determined by excluding the sensor output value when the engine speed is low. This is because when the amount of intake air is small, the amplitude of the intake pulsation wave is large and the output signal of the air flow meter 3 fluctuates. In particular, in a diesel engine that does not include an intake throttle valve, the influence is increased because the pulsation wave is not blocked by the intake throttle valve.
[0050]
On the other hand, in the present embodiment, clogging is determined by adding an averaging process to a value obtained by correcting the differential pressure across the filter 5 by the exhaust temperature and further dividing by the intake air amount. As a result, sensor detection failure or output fluctuation due to noise or the like can be eliminated to some extent, and the accuracy of clogging determination can be improved. Here, in the present embodiment, for example, the corrected differential pressure ΔP ′ is calculated every 0.1 second, and annealing (exponential averaging) is performed with a weight of 200 to 300. Alternatively, the differential pressure ΔP ′ after correction is calculated every 0.1 second, and 200 to 300 data are averaged (addition average). Alternatively, the corrected differential pressure ΔP ′ may be calculated every second, and annealing may be performed by adding 19 / 20th of the existing data and 1/20 of the newly calculated data.
[0051]
In the present embodiment, PM regeneration is performed because there is a possibility that the filter 5 may be clogged when the value obtained by correcting the differential pressure across the filter 5 with the exhaust temperature and further dividing by the intake air amount exceeds a predetermined value. Do. The predetermined value as the determination condition can be obtained in advance by experiments or the like.
[0052]
Here, FIG. 2 shows the differential pressure ΔP before and after the filter, the intake air amount Ga, the corrected differential pressure ΔP ′ per intake air amount Ga, and the corrected differential pressure ΔP ′ per intake air amount Ga with respect to the transition of the vehicle speed. It is a figure which shows the value which made | formed the value and correction | amendment differential pressure | voltage (DELTA) P 'per intake air amount Ga, and excluded the value at the time of sudden acceleration / deceleration and idle.
[0053]
Region {circle around (1)} is a state where the vehicle is stopped and is in an idle state. At this time, fluctuations in the differential pressure ΔP and the intake air amount Ga are large. Further, since there is no correlation between the differential pressure ΔP and the intake air amount Ga, the variation of the value obtained by dividing the differential pressure ΔP ′ by the intake air amount Ga is also large. Therefore, since it is difficult to accurately determine clogging, the value at this time is excluded when clogging is determined.
[0054]
Region (2) is a state in which the vehicle is slowly accelerating. At this time, since there is a correlation between the differential pressure ΔP and the intake air amount Ga, the fluctuation of the value obtained by dividing the differential pressure ΔP ′ by the intake air amount Ga is small. Furthermore, by performing the annealing process, the fluctuation can be reduced, and the clogging determination can be performed.
[0055]
Region (3) is a steady state in which the vehicle is traveling at a constant speed. At this time, since there is a correlation between the differential pressure ΔP and the intake air amount Ga, the fluctuation of the value obtained by dividing the differential pressure ΔP ′ by the intake air amount Ga is small. Furthermore, by performing the annealing process, the fluctuation can be reduced, and the clogging determination can be performed.
[0056]
Region (4) is a state in which the vehicle is rapidly accelerating. At this time, since there is no correlation between the differential pressure ΔP and the intake air amount Ga, the fluctuation of the value obtained by dividing the differential pressure ΔP ′ by the intake air amount Ga is large. Therefore, since it is difficult to accurately determine clogging, the value at this time is excluded when clogging is determined.
[0057]
Region (5) is in a steady state and is similar to region (3).
[0058]
Region (6) is a state where the vehicle is slowly decelerating. At this time, since there is a correlation between the differential pressure ΔP and the intake air amount Ga, the fluctuation of the value obtained by dividing the differential pressure ΔP ′ by the intake air amount Ga is small. Furthermore, by performing the annealing process, the fluctuation can be reduced, and the clogging determination can be performed.
[0059]
Region (7) is in an idle state and is the same as region (1).
[0060]
Thus, in the present embodiment, it is possible to determine whether the filter is clogged in the areas (2), (3), (5), and (6) in the vehicle state of FIG.
[0061]
Next, the flow of the PM clogging determination method according to this embodiment will be described.
[0062]
FIG. 3 is a flowchart showing a flow of the PM clogging determination method according to the present embodiment.
[0063]
In step S101, the differential pressure ΔP across the filter 5, the engine intake air amount Ga, the exhaust temperature T upstream of the filter 5, and the vehicle speed V are detected.
[0064]
In step S102, the differential pressure ΔP before and after the filter is converted into the differential pressure in the standard state based on the exhaust temperature T, and the corrected differential pressure ΔP ′ is calculated.
[0065]
In step S103, a differential pressure across the filter (ΔP ′ / Ga) per intake air amount is calculated.
[0066]
In step S104, it is determined whether a differential pressure detection condition is satisfied. As a differential pressure detection condition, it is determined whether or not the intake air amount Ga is larger than a predetermined value. Here, the predetermined value is the intake air amount Ga at the time of idling and is obtained in advance by experiments or the like. Furthermore, it is also determined whether or not the vehicle acceleration is within a predetermined range as a differential pressure detection condition. The acceleration of the vehicle is obtained by calculating the rate of change of the vehicle speed obtained from a signal from a speed sensor (not shown). The acceleration within the predetermined range is obtained in advance through experiments or the like.
[0067]
If an affirmative determination is made in step S104, the process proceeds to step S105. On the other hand, if a negative determination is made, this routine ends.
[0068]
In step S105, a smoothing process (averaging process) is performed on the differential pressure before and after the filter (ΔP ′ / Ga) per intake air amount calculated in step S103. A differential pressure before and after the filter after the annealing process is set to (ΔP ′ / Ga) ave.
[0069]
In step S106, it is determined whether or not the filter front-rear differential pressure (ΔP ′ / Ga) ave per intake air amount subjected to the annealing process in step S105 is greater than a predetermined value. Here, a value when the filter 5 is clogged is obtained in advance by experiments or the like, and a numerical value smaller than that is stored in the ECU 11 as a predetermined value as a determination condition.
[0070]
If an affirmative determination is made in step S106, the process proceeds to step S107. On the other hand, if a negative determination is made, this routine is terminated.
[0071]
In step S107, PM regeneration control is performed. The ECU 11 supplies a reducing agent to the filter 5 and oxidizes and removes the accumulated PM.
[0072]
In this manner, the PM regeneration timing of the filter 5 can be obtained and PM regeneration control can be executed.
[0073]
Here, in the conventional exhaust gas purification apparatus for an internal combustion engine, the PM regeneration timing can be obtained in a limited operating state.
[0074]
However, clogging cannot be determined unless the operating state is suitable for determining the filter regeneration time, and a large amount of PM may accumulate on the filter.
[0075]
In that respect, the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment can accurately obtain the PM regeneration timing of the filter even during acceleration / deceleration.
[0076]
In the present embodiment, when the differential pressure ΔP before and after the filter is corrected by the exhaust gas temperature T and further divided by the intake air amount Ga is changed at a speed higher than a predetermined value, the PM regeneration interval is shortened. You may do it. Here, in a conventional internal combustion engine exhaust gas purification device, a filter clogging determination is made under predetermined operating conditions. Therefore, when operating outside the conditions, clogging of the filter proceeds rapidly due to the occurrence of smoke or the like. Even so, it could not be detected. Therefore, a large amount of PM may be accumulated on the filter.
[0077]
In that respect, the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment can continuously determine clogging even in an acceleration state or the like, and can determine the rate of change of the degree of clogging of the filter. When the degree of clogging changes at a predetermined speed or higher, the filter regeneration interval can be shortened to prevent a large amount of PM from accumulating on the filter 5. In this way, overheating of the filter during PM removal can be suppressed.
[0078]
Although the differential pressure before and after the filter is used in the present embodiment, the pressure upstream of the filter may be used instead.
[0079]
As described above, in the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, it is determined that the filter may be clogged when the differential pressure before and after the filter per intake air amount exceeds a predetermined value. can do.
[0080]
【The invention's effect】
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, it can be determined that the filter is clogged when the value obtained by dividing the pressure upstream of the filter or the differential pressure before and after the filter by the intake air amount is greater than a predetermined value. As a result, it is possible to accurately determine the timing for removing the particulate matter deposited on the filter. Therefore, it can be suppressed that a large amount of particulate matter accumulates on the filter and the filter is overheated by heat generated when the particulate matter is burned and removed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an engine to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied and an intake / exhaust system thereof.
FIG. 2 is a time chart showing the transition of vehicle speed, sensor output value, and judgment value.
FIG. 3 is a flowchart showing a flow of a PM clogging determination method.
[Explanation of symbols]
1 ... Internal combustion engine
2 ... Intake pipe
3. Air flow meter
4 ... Exhaust pipe
5 ... Particulate filter
6 ... Exhaust temperature sensor
7 ... Differential pressure sensor
8 ... Reducing agent injection valve
9. Fuel pump
10 ... Reducing agent supply path
11 ... ECU

Claims (6)

A filter that can temporarily capture particulate matter in the exhaust;
Pressure detecting means for detecting pressure at least upstream of the filter;
Intake air amount detection means for detecting the amount of fresh air sucked into the internal combustion engine;
Clogging determination means for determining the degree of clogging of the filter by a value obtained by dividing the pressure detected by the pressure detection means by the amount of fresh air detected by the intake air amount detection means;
Equipped with,
The exhaust gas purification apparatus for an internal combustion engine, wherein the clogging determination means performs filter clogging determination by excluding a value obtained when a vehicle acceleration is outside a predetermined range . A filter that can temporarily capture particulate matter in the exhaust;
Pressure detecting means for detecting pressure at least upstream of the filter;
Intake air amount detection means for detecting the amount of fresh air sucked into the internal combustion engine;
Clogging determination means for determining the degree of clogging of the filter by a value obtained by dividing the pressure detected by the pressure detection means by the amount of fresh air detected by the intake air amount detection means;
Comprising
The clogging determination means obtains a change ratio of the determination value, and shortens an interval for removing particulate matter collected by the filter when the change ratio is equal to or greater than a predetermined value. Exhaust purification equipment.   Exhaust temperature detecting means for detecting the temperature of the exhaust gas flowing into the filter;
  Pressure correcting means for correcting the pressure detected by the pressure detecting means to a pressure in a reference state based on the temperature of the exhaust detected by the exhaust temperature detecting means;
  Further comprising
  The clogging determining means determines the degree of clogging of the filter by a value obtained by dividing the pressure corrected by the pressure correcting means by the amount of fresh air detected by the intake air amount detecting means. 3. An exhaust emission control device for an internal combustion engine according to 1 or 2.   4. The clogging determination unit performs filter clogging determination by excluding a value obtained when a value detected by the intake air amount detection unit is equal to or less than a predetermined value. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1.   The exhaust purification device for an internal combustion engine according to any one of claims 1 to 4, wherein the clogging determination means performs clogging determination using a value obtained by performing an averaging process. 6. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the filter carries a NOx catalyst for reducing nitrogen oxides to nitrogen.

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