JP2005098184A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of securely regenerating a particulate filter by efficiently promoting the oxidation reaction of an oxidation catalyst irrespective of the oxidation capacity of the oxidation catalyst in the exhaust emission control device formed such that particulate matters arrested by the particulate filter are incinerated by using the oxidation reaction heat of the oxidation catalyst installed on the exhaust gas upstream side of the particulate filter. <P>SOLUTION: When the deposited amount of the particulate matters arrested by the particulate filter reaches a specified amount, hydrocarbon HC is fed to the oxidation catalyst installed on the exhaust gas upstream side of the particulate filter to incinerate and remove the particulate matters arrested by the particulate filter by the oxidation reaction heat of the HC in the oxidation catalyst. In this case, the HC is periodically fed to the oxidation catalyst (S16 to S22). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine, and more particularly to a regeneration technique for a particulate filter disposed in an exhaust passage of a diesel engine.

  Exhaust gas discharged from diesel engines mounted on buses, trucks, and the like contains a lot of particulate matter (abbreviated as PM) in addition to HC, CO, NOx, and the like. Therefore, diesel particulate filters (abbreviated as DPF) that capture PM and incinerate and remove it with an external heat source and oxidation catalysts that treat HC and CO have been put to practical use as aftertreatment devices for diesel engines. Recently, a continuous regenerative DPF has been developed in which an oxidation catalyst capable of generating an oxidizing agent for oxidizing and removing PM is provided upstream of the DPF instead of an external heat source, and the PM on the DPF is continuously processed. ing.

  By the way, even in a continuously regenerating DPF, PM may not be sufficiently processed and the amount of deposition may increase under an inert condition where the temperature of the oxidation catalyst or DPF is low, and thus the amount of PM deposition increases. Then, the exhaust pressure increases due to an increase in the filter pressure loss of the DPF, causing a pumping loss and the like. Further, in a state where PM is excessively accumulated on the filter, the filter may be damaged if the PM self-ignites during high load operation or the like.

Therefore, in such a case, when the PM trapped in the DPF reaches a predetermined amount, forced regeneration is performed to forcibly burn and remove the PM.
As a method of forced regeneration of the continuous regeneration type DPF, for example, fuel, that is, hydrocarbon (HC) is injected and supplied to the upstream side of the oxidation catalyst in the exhaust passage, and the HC is oxidized by the oxidation catalyst. There is one that incinerates and removes PM trapped in the DPF by using reaction heat.

In this case, it is necessary to maintain the DPF temperature at a predetermined high temperature during forced regeneration so that the DPF temperature is not too low or too high to melt the DPF. A technique of performing feedback control as much as possible is also known (see Patent Document 1).
JP-A-9-13945

By the way, the oxidation catalyst has the ability to take in and store oxygen (O ₂ ) in the exhaust gas. In the forced regeneration method, the supplied HC is oxidized by oxygen on the catalyst to generate heat.
However, if the oxidation catalyst deteriorates and oxygen uptake into the catalyst does not proceed sufficiently under the supply of high-concentration HC, the oxidation reaction will not progress even if HC is continuously supplied, so heat is generated. There is a problem that the amount is insufficient, the temperature of the DPF does not rise to the predetermined high temperature, and the PM trapped in the DPF cannot be sufficiently removed by incineration.

This problem is particularly noticeable in the case where an oxidation catalyst that has sufficiently taken up oxygen in a new state deteriorates its oxygen transfer function as it deteriorates over time.
The present invention has been made to solve such problems, and the object of the present invention is to capture the particulate filter using the oxidation reaction heat of the oxidation catalyst provided upstream of the exhaust of the particulate filter. Exhaust gas purification device for internal combustion engine capable of efficiently regenerating particulate filter by efficiently promoting oxidation reaction of oxidation catalyst regardless of oxidation capability of oxidation catalyst, in exhaust gas purification device configured to incinerate the generated particulate matter Is to provide.

  In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to claim 1, a particulate filter that is interposed in an exhaust passage of the internal combustion engine and captures particulate matter, and the particulate filter in the exhaust passage. An oxidation catalyst disposed in an upstream portion, a deposition amount detection means for detecting a deposition amount of the particulate matter captured by the particulate filter, and a particulate matter detected by the deposition amount detection means. When the deposition amount reaches a predetermined amount, hydrocarbon is supplied to the oxidation catalyst to oxidize, and the particulate matter captured by the particulate filter is forcibly burned and removed by the oxidation reaction heat of the hydrocarbon. Forcibly regenerating the particulate filter, and the forced regeneration means It is characterized by periodically supplying hydrocarbon to the oxidation catalyst.

  That is, when the accumulated amount of particulate matter captured by the particulate filter reaches a predetermined amount, hydrocarbon (HC) is supplied to the oxidation catalyst provided on the exhaust gas upstream side of the particulate filter, and the HC of the oxidation catalyst is reduced. The particulate matter trapped in the particulate filter by the heat of oxidation reaction is incinerated and removed. At this time, HC is periodically supplied to the oxidation catalyst.

Therefore, when the oxidation capability of the oxidation catalyst is low, for example, even when the oxidation catalyst cannot sufficiently store O ₂ necessary for HC oxidation due to deterioration over time, the HC is periodically cycled during forced regeneration. By supplying to the oxidation catalyst by increasing / decreasing to 0, the O ₂ in the exhaust is replenished to the oxidation catalyst as appropriate, and the oxidation reaction of the oxidation catalyst progresses efficiently regardless of the oxidation ability of the oxidation catalyst. Thus, the temperature of the particulate filter is reliably increased, and the particulate matter captured by the particulate filter is surely incinerated and removed.

In addition, the wasteful supply of HC that does not contribute to oxidation is reduced, and HC is prevented from being discharged into the atmosphere.
The exhaust gas purification apparatus for an internal combustion engine according to claim 2 further comprises oxygen concentration correlation value detection means for detecting an oxygen concentration or oxygen concentration correlation value in the oxidation catalyst according to claim 1, wherein the forced regeneration means comprises: Based on the oxygen concentration or the oxygen concentration correlation value detected by the oxygen concentration correlation value detecting means, the hydrocarbon supply period and non-supply period are set, and the hydrocarbon is supplied in pulses over the supply period. It is characterized by that.

That is, the oxygen concentration in the oxidation catalyst, or the oxygen concentration correlation value correlated with the O ₂ concentration (for example, the degree of change in the concentration of the oxidation catalyst outlet O ₂ during forced regeneration, or generated and discharged by an oxidation reaction during forced regeneration) The HC supply period and the non-supply period are appropriately set according to the CO ₂ concentration change degree), and HC is supplied in pulses only during the supply period.
Therefore, during forced regeneration, the amount of O ₂ that contributes to oxidation and the amount of HC can be substantially matched on the oxidation catalyst when supplying HC, and when the HC is not supplied, O ₂ in the exhaust is sufficient for the oxidation catalyst. As a result, the oxidation reaction of the oxidation catalyst progresses more efficiently, the temperature of the particulate filter is reliably increased, and the particulate matter trapped in the particulate filter is more reliably incinerated and removed. .

  Further, the exhaust gas purification apparatus for an internal combustion engine according to claim 3 relates to claim 1, further comprising catalyst temperature detection means for detecting the temperature of the oxidation catalyst, wherein the forced regeneration means is detected by the catalyst temperature detection means. The hydrocarbon supply period and non-supply period are set based on the degree of change in temperature of the oxidation catalyst, and the hydrocarbon is supplied in a pulsed manner over the supply period.

In other words, when an oxidation reaction occurs in the oxidation catalyst, the temperature of the oxidation catalyst rises due to the heat of the oxidation reaction, but the state of generation of the oxidation reaction heat, that is, the degree of change in the temperature of the oxidation catalyst, depends on the oxidation catalyst. The oxygen concentration that contributes, that is, the concentration of O ₂ stored on the oxidation catalyst, is extremely correlated, and accordingly, the HC supply period and non-supply period are appropriately set according to the degree of change in the temperature of the oxidation catalyst. Is supplied in pulses only during the supply period.

Therefore, during forced regeneration, the amount of O ₂ that contributes to oxidation and the amount of HC can be substantially matched on the oxidation catalyst when supplying HC, and when the HC is not supplied, O ₂ in the exhaust is sufficient for the oxidation catalyst. As a result, the oxidation reaction of the oxidation catalyst progresses more efficiently, the temperature of the particulate filter is reliably increased, and the particulate matter trapped in the particulate filter is more reliably incinerated and removed. .

According to the exhaust gas purification apparatus for an internal combustion engine of the first aspect of the present invention, when the accumulated amount of particulate matter captured by the particulate filter reaches a predetermined amount, the oxidation catalyst provided on the exhaust upstream side of the particulate filter. Hydrocarbon (HC) is supplied to the catalyst, and particulate matter trapped in the particulate filter is burned and removed by the oxidation reaction heat of the HC in the oxidation catalyst. At this time, HC is periodically used as an oxidation catalyst. Therefore, even if the oxidation ability of the oxidation catalyst is low, O ₂ in the exhaust gas can be appropriately replenished to the oxidation catalyst, and the oxidation catalyst can be supplied regardless of the oxidation ability of the oxidation catalyst. The particulate filter trapped by the particulate filter is heated efficiently by accelerating the oxidation reaction. It can be reliably burned and removed the matter.

Furthermore, the wasteful supply of HC that does not contribute to oxidation is reduced, and the discharge of HC into the atmosphere can be satisfactorily prevented.
Further, according to the exhaust gas purification apparatus for an internal combustion engine of claim 2, in claim 1, the oxygen concentration contributing to oxidation by the oxidation catalyst, that is, the O ₂ concentration on the oxidation catalyst, or the O ₂ concentration is correlated. The supply period and non-supply period of HC are appropriately set according to the oxygen concentration correlation value (for example, the degree of change in the concentration of O ₂ discharged during forced regeneration), and HC is supplied in pulses only during the supply period. As a result, during forced regeneration, the amount of O ₂ that contributes to oxidation and the amount of HC are substantially matched on the oxidation catalyst when HC is supplied, and O ₂ in the exhaust is used as the oxidation catalyst when HC is not supplied. Can be replenished enough. As a result, the oxidation reaction of the oxidation catalyst can be promoted more efficiently, the temperature of the particulate filter can be reliably increased, and the particulate matter trapped by the particulate filter can be incinerated and removed more reliably.

According to an exhaust gas purification apparatus for an internal combustion engine according to claim 3, the oxidation catalyst according to claim 1 having an extremely high correlation with the oxygen concentration contributing to oxidation by the oxidation catalyst, that is, the concentration of O ₂ stored on the oxidation catalyst. The HC supply period and the non-supply period are set appropriately according to the degree of temperature change, and HC is supplied in pulses only during the supply period, contributing to oxidation during forced regeneration and during HC supply. The amount of O _{2 and the} amount of HC to be substantially matched on the oxidation catalyst without excess or deficiency, and when HC is not supplied, O ₂ in the exhaust gas can be sufficiently supplemented to the oxidation catalyst. As a result, the oxidation reaction of the oxidation catalyst can be promoted more efficiently, the temperature of the particulate filter can be reliably increased, and the particulate matter trapped by the particulate filter can be incinerated and removed more reliably.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention. Hereinafter, the configuration of the exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to FIG.
As shown in FIG. 1, an engine 1 that is an internal combustion engine is, for example, a common rail in-line four-cylinder diesel engine. In the common rail engine 1, an electromagnetic fuel injection nozzle 4 is provided for each cylinder facing the combustion chamber 2, and each fuel injection nozzle 4 is connected to a common rail 6 by a high-pressure pipe 5. The common rail 6 is connected to a fuel tank 9 via a high-pressure pipe 7 in which a high-pressure pump 8 is interposed. Since engine 1 is a diesel engine, light oil is used as the fuel.

An intake passage 10 is connected to the combustion chamber 2 through an intake port, and an exhaust passage 20 is connected through an exhaust port. The intake passage 10 is provided with an air flow sensor 14 for detecting an intake flow rate, and the exhaust passage 20 is provided with an exhaust pressure sensor 21 for detecting an exhaust pressure.
Since the configuration of the valve operating mechanism of the engine 1 such as an intake valve and an exhaust valve is well known, the description thereof is omitted here.

A post-processing device is interposed in the exhaust passage 20. The post-processing apparatus is configured by providing an oxidation catalyst 24 upstream of a diesel particulate filter (DPF) 26. Note that the post-treatment device of this type in which the oxidation catalyst 24 is provided upstream of the DPF 26 is called a continuous regeneration type DPF 22 as a whole.
The continuous regeneration type DPF 22 oxidizes the nitrogen (N) component in the exhaust gas in the oxidation catalyst 24 to generate an oxidizing agent (NO ₂ ) that still has an oxidizing ability, and is deposited on the downstream DPF 26 by the generated oxidizing agent. Particulate matter (PM) is continuously and continuously oxidized and removed.

The oxidation catalyst 24 can oxidize unburned hydrocarbons (HC) and carbon monoxide (CO) in the presence of sufficient oxygen (O ₂ ) when the exhaust air-fuel ratio is a lean air-fuel ratio. Even when CO is in an excess atmosphere, HC and CO can be oxidized by O ₂ stored on the catalyst.
An HC addition injector 28 is disposed upstream of the oxidation catalyst 24 in the exhaust passage 20, and the HC addition injector 28 is connected to the fuel tank 9 via an HC supply passage 29. As a result, it is possible to inject and supply light oil, that is, HC component, which is fuel toward the oxidation catalyst 24. In addition, although light oil is injected from the HC addition injector 28 here, if it is HC component, it will not be restricted to light oil.

The oxidation catalyst 24 is provided with a temperature sensor 25 that detects the temperature Tcat of the oxidation catalyst 24, and the DPF 26 is provided with a temperature sensor 27 that detects the temperature Tdpf of the DPF 26.
Furthermore, between the oxidation catalyst 24 DPF 26, that is, downstream of the oxidation catalyst 24, O ₂ sensor 23 for detecting the concentration of oxygen (O ₂₎ is also provided, the oxidation catalyst 24 by the O ₂ sensor 23 The concentration of O ₂ flowing out is detected.

An EGR passage 30 extends from the exhaust passage 20, and the end of the EGR passage 30 is connected to the intake passage 10. An electromagnetic EGR valve 32 is interposed in the EGR passage 30.
Various sensors such as the air flow sensor 14, exhaust pressure sensor 21, O ₂ sensor 23, temperature sensor 25, temperature sensor 27 and the like are connected to the input side of the electronic controller (ECU) 40, and the fuel is connected to the output side. Various devices such as the injection nozzle 4, the HC addition injector 28, and the EGR valve 32 are connected.

As a result, various devices are controlled based on various input information, the engine 1 is appropriately controlled, and the HC addition injector 28 is appropriately controlled.
Hereinafter, the content of the forced regeneration control according to the present invention of the exhaust gas purification apparatus for an internal combustion engine configured as described above will be described.
As described above, in the continuous regeneration type DPF 22, NO ₂ is generated by the upstream side oxidation catalyst 24, and usually, PM deposited on the downstream DPF 26 is continuously oxidized and removed by the generated NO ₂ . . However, continuous regeneration is not sufficiently performed under inactive conditions where the temperature of the oxidation catalyst 24 and the DPF 26 is low, and depending on the operating state of the engine 1, the exhaust temperature does not rise and the oxidation catalyst 24 and the DPF 26 remain inactive. In some cases, a large amount of PM accumulates on the DPF 26 without continuous regeneration.

Therefore, in the exhaust purification apparatus, the PM thus deposited is forcibly and efficiently removed by incineration.
[First embodiment]
Referring to FIG. 2, a control routine of forced regeneration control (forced regeneration means) according to the first embodiment of the present invention of the continuous regeneration type DPF 22 executed by the ECU 40 is shown in a flowchart, and will be described along the flowchart. To do.

In forced regeneration control, first, in step S10, it is determined whether or not forced regeneration is necessary. Specifically, the amount of PM deposited on the DPF 26 is detected (deposition amount detection means), and it is determined whether or not the amount of accumulation has reached a predetermined amount that requires forced regeneration.
Specifically, there is a proportional relationship between the exhaust flow rate and the filter pressure loss due to the DPF 26, that is, the exhaust pressure, and the proportionality coefficient changes according to the amount of PM accumulated, that is, the degree of clogging of the DPF 26. Therefore, the PM accumulation amount can be easily estimated based on the exhaust flow rate information from the air flow sensor 14 and the exhaust pressure information from the exhaust pressure sensor 21, and the estimated PM accumulation amount becomes a predetermined amount. It is determined whether or not it has been reached. Here, the PM accumulation amount is obtained from the relationship between the exhaust gas flow rate and the filter pressure loss, but the method for detecting the PM accumulation amount is not limited to this.

In step S12, it is determined whether or not the temperature of the oxidation catalyst 24, that is, the catalyst temperature Tcat is equal to or higher than the activation temperature T0 (for example, 200 to 300 ° C.). If the determination result is false (No) and it is determined that the catalyst temperature Tcat is less than the activation temperature T0, the process proceeds to step S14, and the oxidation catalyst 24 is heated.
In order to raise the temperature of the oxidation catalyst 24, it is only necessary to raise the exhaust gas temperature. For example, the opening amount of the EGR valve 32 is increased to increase the EGR amount. As a result, the exhaust air-fuel ratio becomes closer to the rich air-fuel ratio, the combustion of unburned HC and CO is promoted in the exhaust passage 20, the exhaust temperature rises, and the oxidation catalyst 24 rises in temperature.

Although the EGR amount is increased here, the present invention is not limited to this, and the exhaust air-fuel ratio is made closer to the rich air-fuel ratio by injecting fuel (post-injection) from the fuel injection nozzle 4 after the expansion stroke. Alternatively, the oxidation catalyst 24 may be directly heated by an external heat source or the like.
On the other hand, when the determination result of step S12 is true (Yes) and the catalyst temperature Tcat is determined to be equal to or higher than the activation temperature T0, the process proceeds to step S16. When the temperature of the oxidation catalyst 24 is being increased, the temperature increase is terminated.

In step S16, fuel is injected into the exhaust gas from the HC addition injector 28, and HC is supplied to the oxidation catalyst 24. At this time, the amount of fuel injected from the HC addition injector 28 may be appropriately set according to the size, capacity, and the like of the oxidation catalyst 24.
When HC is supplied to the oxidation catalyst 24 in this way, the HC is oxidized in the oxidation catalyst 24. At this time, a large amount of oxidation reaction heat is generated, and the downstream DPF 26 is heated by the oxidation reaction heat, and the PM deposited on the DPF 26 is well removed by incineration.

In step S18, based on the information from the O ₂ sensor 23, the concentration of O ₂ discharged from the oxidation catalyst 24, that is, the change amount dDO2 / dt (oxygen concentration correlation value) of the O ₂ concentration DO2 is calculated (oxygen concentration correlation value). Value detecting means), it is determined whether or not the amount of change dDO2 / dt is equal to or greater than a predetermined value D1 ′, for example.
That, HC is consumed O ₂ on the oxidized catalyst in the oxidation catalyst 24, a decrease of the O ₂ is detected in the O ₂ sensor 23, the consumption of the O ₂ becomes a downward trend, the HC It is determined whether or not the oxidation reaction is attenuated.

If the determination result in step S18 is false (No) and the change amount dDO2 / dt is smaller than the predetermined value D1 ′, it can be determined that the oxidation reaction of HC is sufficiently carried out in the oxidation catalyst 24. In this case, in step S16 In HC, the supply of HC is continued.
On the other hand, if the determination result in step S18 is true (Yes) and the change amount dDO2 / dt is determined to be equal to or greater than the predetermined value D1 ′, that is, the consumption amount of O ₂ tends to decrease, and the HC oxidation reaction attenuates. If it is determined that there is, the process proceeds to step S20, where the supply of HC from the HC addition injector 28 is stopped and HC is not supplied.

In other words, the amount of change in O ₂ concentration DO2 dDO2 / dt has a high correlation with the concentration of O ₂ to be accumulated in the oxidation catalyst 24, therefore, when the consumption of O ₂ is determined to be decreasing, the oxidation catalyst 24 on O ₂ is depleted of, be continued supply of HC, longer be determined that the situation in which oxidation reaction heat is not generated, in this case so as to stop the supply of HC.
When the supply of HC is stopped in this way, O _{2 in} the exhaust is stored in the oxidation catalyst 24 again.

In step S22, it is determined whether or not the HC non-supply period has passed a predetermined period t1. Here, the predetermined period t1 may be set according to the time until O _{2 in} the exhaust gas is stored in the oxidation catalyst 24 to the maximum extent. Specifically, for example, the HC supply period of the oxidation catalyst 24, that is, the time when O ₂ on the catalyst is exhausted and the non-supply period, that is, the time until O ₂ is again stored in the oxidation catalyst 24 to the maximum extent. The predetermined period t1 is obtained from the product of the actual HC supply period and the period ratio.

Since the temperatures of the oxidation catalyst 24 and the DPF 26 tend to decrease during the non-supply period of HC, it is preferable to set the predetermined period t1 to such an extent that the temperatures of the oxidation catalyst 24 and the DPF 26 do not decrease so much.
If it is determined that the determination result in step S22 is false (No) and the predetermined period t1 has not yet elapsed, non-HC supply is continued in step S20, while the determination result is true (Yes) and the predetermined period t1 has elapsed. If it is determined that the process has been performed, the process proceeds to step S24.

  In step S24, whether or not the temperature of the DPF 26 based on the information from the temperature sensor 27, that is, the DPF temperature Tdpf has maintained a predetermined temperature T10 (for example, 400 to 600 ° C.) necessary for PM incineration and a predetermined period t2 has elapsed. That is, it is determined whether or not the forced regeneration may be terminated. Here, the predetermined period t2 is a time (for example, 5 to 30 min) until the predetermined amount of accumulated PM is completely incinerated and removed from the DPF 26 under the DPF temperature Tdpf at the predetermined temperature T10 by, for example, experiments in advance. Set to As described above, the amount of accumulated PM and hence the amount of incinerated PM removed are obtained from the relationship between the exhaust gas flow rate and the filter pressure loss, etc., thereby determining the regeneration status of the oxidation catalyst 24 and setting the predetermined period t2, or directly Alternatively, the end of forced regeneration may be determined.

If the determination result in step S24 is false (No) and it is determined that the predetermined period t2 has not yet elapsed, the process returns to step S16 and HC is supplied again. That is, the execution of steps S16 to S22 is repeated until the predetermined period t2 elapses, and the supply and non-supply of HC are repeated periodically.
As described above, when the supply and non-supply of HC are periodically performed, that is, the supply of HC is repeatedly performed in a pulsed manner, the HC is oxidized by replenishing the oxidation catalyst 24 with O ₂ consumed by combustion. 24 can be supplied without excessive supply, and when supplying HC, the amount of O ₂ and HC contributing to oxidation can be substantially matched on the oxidation catalyst without excess or deficiency, and the oxidation reaction of the oxidation catalyst 24 can be promoted efficiently. Thus, the heat of reaction can be secured, and the DPF 26 can be well maintained at a predetermined temperature T10 or higher required for PM incineration.

That is, referring to FIG. 3, the DPF temperature Tdpf (solid line), the HC supply amount (solid line), the HC concentration downstream of the oxidation catalyst (broken line), and O when the forced regeneration control according to the first embodiment of the present invention is performed. ₂ shows changes over time in the concentration DO2 (solid line). In the figure, the DPF temperature Tdpf (one-dot chain line), HC supply amount (one-dot chain line), and HC downstream of the oxidation catalyst when HC is continuously supplied are shown. the time variation of the concentration (two-dot chain line) and the O ₂ concentration DO2 (dashed line) are shown together, respectively, regardless of the oxidative capacity of the oxidation catalyst 24, thus, the O ₂ concentration DO2 (solid line ) Is the HC supply period, and the predetermined period t1 required for the replenishment of O ₂ is the HC supply period. These HC supply period and HC non-supply period Is repeated periodically to supply HC. By carrying out in a pulse form, the DPF temperature Tdpf can be maintained well above the predetermined temperature T10 compared to the case where HC is continuously supplied, and the HC concentration downstream of the oxidation catalyst is kept low overall, reducing the HC atmosphere. The discharge into the inside can be prevented satisfactorily.

Thereby, PM accumulated on the DPF 26 can be sufficiently incinerated and removed, and the DPF 26 can be reliably regenerated.
Therefore, even when the oxidation catalyst 24 has a weak O ₂ transfer function and the oxidation catalyst 24 cannot store enough O ₂ necessary for the oxidation of HC, it matches the oxidation capability of the oxidation catalyst 24. For example, an oxidation catalyst that has sufficient oxidation ability even when HC is continuously supplied when it is new, by repeatedly supplying HC periodically under an appropriate HC supply period and HC non-supply period Even when 24 deteriorates with time and the O ₂ transfer capacity decreases, the inconvenience that the regeneration capacity of the DPF 26 decreases or the discharge amount of HC into the atmosphere increases without knowledge. Avoided.

[Second Embodiment]
Referring to FIG. 4, a control routine of forced regeneration control (forced regeneration means) according to the second embodiment of the present invention of the continuous regeneration type DPF 22 executed by the ECU 40 is shown in a flowchart, and will be described along the flowchart. To do. In the second embodiment, since only the step S18 is different from the case of the first embodiment, the description of the same parts as the first embodiment is omitted, and the parts different from the first embodiment are described. Only explained.

In step S18 ′ after step S10 to step S16, based on the temperature information from the temperature sensor (catalyst temperature detection means) 25, the temperature of the oxidation catalyst 24, that is, the change amount dTcat / dt (degree of change) of the catalyst temperature Tcat is predetermined. It is determined whether or not the value is equal to or less than a value T1 ′ (for example, value 0).
That is, when HC undergoes an oxidation reaction in the oxidation catalyst 24, the oxidation catalyst 24 itself also rises in temperature due to reaction heat. However, the catalyst temperature Tcat of the oxidation catalyst 24 tends to decrease, and the oxidation reaction of HC attenuates. It is determined whether or not.

If the determination result in step S18 ′ is false (No) and the change amount dTcat / dt is larger than the predetermined value T1 ′, it can be determined that the oxidation catalyst 24 has sufficiently performed the oxidation reaction of HC. In S16, the supply of HC is continued.
On the other hand, when the determination result in step S18 ′ is true (Yes) and the change amount dTcat / dt is determined to be equal to or less than the predetermined value T1 ′, that is, the catalyst temperature Tcat tends to decrease, and the HC oxidation reaction is attenuated. If it is determined, the process proceeds to step S20, the supply of HC from the HC addition injector 28 is stopped, and the HC is not supplied.

That is, the change amount dTcat / dt of the catalyst temperature Tcat has a very high correlation with the O ₂ concentration on the oxidation catalyst 24. Therefore, if it is determined that the catalyst temperature Tcat is decreasing, the case of the first embodiment described above. Similarly, it can be determined that the O ₂ on the oxidation catalyst 24 is used up and the heat of oxidation reaction is no longer generated even if the supply of HC is continued. In this case, the supply of HC is stopped. To do.

That is, similarly to the above, the HC supply period is naturally set according to the O ₂ concentration on the oxidation catalyst 24, and HC is supplied over the HC supply period. After a lapse of time, the supply of HC is stopped.
Thereafter, the supply of HC (step S16) and the non-supply (step S20) are repeated periodically until the predetermined period t1 elapses in step S22.

Thus, similarly to the above, irrespective of the oxidative capacity of the oxidation catalyst 24, the HC while replenishing repeatedly spent O ₂ and oversupply supplied without the oxidation catalyst 24, contributes O ₂ amount to oxidation during the supply of HC And the amount of HC can be made to substantially coincide with each other on the oxidation catalyst without excess or deficiency, the oxidation reaction of the oxidation catalyst 24 is efficiently promoted to secure reaction heat, and the DPF 26 exceeds the predetermined temperature T10 required for incineration of PM. Can be maintained well.

That is, referring to FIG. 5, the time changes of the DPF temperature Tdpf (solid line), the HC supply amount (solid line), and the oxidation catalyst temperature Tcat (solid line) when the forced regeneration control according to the second embodiment of the present invention is performed. In the figure, the time changes of the DPF temperature Tdpf (one-dot chain line), the HC supply amount (one-dot chain line), and the oxidation catalyst temperature Tcat (one-dot chain line) when HC is continuously supplied are also shown. Although shown, the change amount dTcat / dt of the oxidation catalyst temperature Tcat (solid line) has become equal to or less than a predetermined value T1 ′ (for example, value 0) regardless of the oxidation ability of the oxidation catalyst 24. By setting the HC supply period to the point in time, the predetermined period t1 required for O ₂ replenishment as the HC supply period, and periodically repeating the HC supply period and the HC non-supply period, and performing the HC supply in a pulsed manner. , A place to supply HC continuously Compared to the above, the DPF temperature Tdpf can be maintained well above the predetermined temperature T10, and although not shown, the HC concentration downstream of the oxidation catalyst can be kept low overall to prevent the discharge of HC into the atmosphere. it can.
As a result, as in the case of the first embodiment, the PM deposited on the DPF 26 can be sufficiently incinerated and removed, and the DPF 26 can be reliably regenerated, regardless of the deterioration of the oxidation catalyst 24 over time.

[Third embodiment]
Referring to FIG. 6, a control routine of forced regeneration control (forced regeneration means) according to the third embodiment of the present invention of the continuous regeneration type DPF 22 executed by the ECU 40 is shown in a flowchart, and will be described along the flowchart. To do. In the third embodiment, only the steps S16 to S22 are different from those in the first and second embodiments. Therefore, the description of the same parts as those in the first and second embodiments is omitted. Only differences from the first and second embodiments will be described.

After performing Steps S10 to S14, in Step S15, the supply waveform of HC supplied from the HC addition injector 28 is changed to a waveform in which the HC supply amount periodically increases and decreases as shown in an example in FIG. Set.
That is, in the first and second embodiments, the HC supply period and the non-supply period are defined as the change amount dDO2 / dt of the O ₂ concentration DO2 or the change amount dTcat / dt of the catalyst temperature Tcat, that is, the oxidation on the oxidation catalyst 24. set in accordance with the concentration of contributing O ₂ to, but so as to implement the supply of HC to the pulsed, the in the third embodiment, the supply amount of HC so as to cyclically increase and decrease variations in the wave .

Actually, even in this case, it is preferable to set the fluctuation period and waveform in accordance with the O ₂ concentration on the oxidation catalyst 24. For example, the change amount DDO2 / dt of the O ₂ concentration DO2 and the change in the catalyst temperature Tcat are preferable. It is preferable to appropriately change and set the inversion period according to the amount dTcat / dt.
In step S17, HC is periodically injected from the HC addition injector 28 based on the HC supply waveform set as described above.

Even in this case, regardless of the oxidation ability of the oxidation catalyst 24, HC is supplied to the oxidation catalyst 24 without excessive supply while replenishing the consumed O _2, and the oxidation reaction of the oxidation catalyst 24 is efficiently performed. The heat of reaction can be ensured and the DPF 26 can be satisfactorily maintained at a predetermined temperature T10 or higher required for PM incineration.
As a result, in substantially the same manner as in the first and second embodiments, PM deposited on the DPF 26 can be sufficiently incinerated and removed, and the DPF 26 can be regenerated satisfactorily regardless of the deterioration of the oxidation catalyst 24 over time.

1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention. It is a flowchart which shows the control routine of the forced regeneration control which concerns on 1st Example of this invention. DPF temperature Tdpf when the forced regeneration control according to the first embodiment of the present invention was performed, HC supply amount is a time chart showing temporal changes of the HC concentration and the O ₂ concentration DO2 in the oxidation catalyst downstream. It is a flowchart which shows the control routine of the forced regeneration control which concerns on 2nd Example of this invention. It is a time chart which shows the time change of DPF temperature Tdpf, HC supply amount, and oxidation catalyst temperature Tcat at the time of performing forced regeneration control concerning the 2nd example of the present invention. It is a flowchart which shows the control routine of the forced regeneration control which concerns on 3rd Example of this invention. It is a figure which shows an example of the supply waveform of HC which concerns on 3rd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 4 Fuel injection nozzle 10 Intake passage 14 Air flow sensor 20 Exhaust passage 21 Exhaust pressure sensor 22 Continuous regeneration type DPF
23 O ₂ sensor 24 Oxidation catalyst 25 Temperature sensor 26 Diesel particulate filter (DPF)
27 Temperature sensor 28 HC addition injector 30 EGR passage 40 Electronic controller (ECU)

Claims (3)

A particulate filter interposed in the exhaust passage of the internal combustion engine and capturing particulate matter;
An oxidation catalyst disposed in a portion of the exhaust passage upstream of the particulate filter;
A deposition amount detecting means for detecting a deposition amount of the particulate matter captured by the particulate filter;
When the accumulated amount of particulate matter detected by the accumulated amount detection means reaches a predetermined amount, hydrocarbons are supplied to the oxidation catalyst for oxidation, and captured by the particulate filter by the oxidation reaction heat of the hydrocarbons. Forcibly regenerating the particulate filter by forcibly burning and removing the particulate matter,
The exhaust purification device of an internal combustion engine, wherein the forced regeneration means periodically supplies hydrocarbons to the oxidation catalyst. And oxygen concentration correlation value detecting means for detecting oxygen concentration or oxygen concentration correlation value in the oxidation catalyst,
The forced regeneration means sets a supply period and a non-supply period of the hydrocarbon based on an oxygen concentration or an oxygen concentration correlation value detected by the oxygen concentration correlation value detection means, and the hydrocarbon is supplied to the supply period. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas is supplied in a pulse form. Furthermore, a catalyst temperature detecting means for detecting the temperature of the oxidation catalyst is provided,
The forced regeneration means sets a supply period and a non-supply period of the hydrocarbon based on a degree of change in the temperature of the oxidation catalyst detected by the catalyst temperature detection means, and the hydrocarbon is supplied over the supply period. 2. An exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is supplied in a pulse form.

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