JP2009203962A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of effectively combusting PM without causing unburnt residues of PM even when a material with low thermal conductivity is used for a DPF. <P>SOLUTION: The exhaust emission control device for an engine is provided to an exhaust pipe and includes the DPF for collecting PM in emissions and a filter regeneration means for performing a filter regeneration process for regenerating the DPF. The filter regeneration process includes a DPF elevated-temperature process S3 for elevating a DPF temperature and a normal regeneration combustion process S5 for combusting the PM deposited on the DPF. In this filter regeneration process, an oxygen concentration of the emissions is controlled to a concentration where PM combustion is suppressed when the DPF elevated-temperature treatment is performed and the oxygen concentration of the emissions is controlled to a concentration where the PM combustion is accelerated when the normal regeneration combustion treatment is performed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine, and more particularly, to an apparatus equipped with a DPF (diesel particulate filter) that collects PM (Particulate Matter) in exhaust gas of an internal combustion engine.

  A technique for reducing the amount of PM emission by providing a DPF for collecting PM in an exhaust system of an internal combustion engine is widely used. Since there is a limit to the amount of PM that can be collected by the DPF, a DPF regeneration process for burning the PM deposited on the DPF is appropriately executed. In this regeneration process, for example, fuel injection in the exhaust process (hereinafter referred to as “post injection”) is performed to raise the DPF to the self-ignition temperature of PM, and then PM is combusted (see Patent Document 1). ) Is executed.

  However, when such DPF regeneration processing is executed, if PM remains unburned in the DPF, the frequency of regeneration processing increases and fuel consumption deteriorates. In addition to this, there is a possibility that the fuel efficiency is further deteriorated due to an increase in pressure loss in the DPF, and the exhaust emission is also deteriorated. For this reason, it is preferable to execute the DPF regeneration process so that PM does not remain unburned.

Thus, for example, Patent Document 2 proposes an exhaust purification device that completely burns PM while preventing an excessive temperature rise of the DPF by controlling the oxygen concentration during execution of the DPF regeneration process. In this exhaust purification apparatus, the DPF regeneration process is divided into three periods of the first period, the middle period, and the second period, and after the DPF is rapidly heated in the first period, PM is burned while controlling the oxygen concentration in the middle and latter periods. More specifically, in the middle period, the PM combustion rate is reduced by lowering the oxygen concentration to prevent excessive temperature rise of the DPF, and in the latter period, the oxygen concentration is increased to prevent PM from remaining unburned.
JP-A-8-42326 JP 2004-28045 A

  By the way, as a material of DPF, for example, silicon carbide (SiC), aluminum titanate, cordierite, and the like are used. Aluminum titanate and cordierite are less expensive than silicon carbide, but have a low thermal conductivity.

  FIG. 10 is a diagram showing the relationship between the DPF regeneration time and the DPF temperature. In FIG. 10, the broken line indicates the case where silicon carbide is used as the material of the DPF, and the solid line indicates the case where aluminum titanate is used. In FIG. 10, a broken line 10a and a solid line 10b indicate a temperature change in the central portion of the DPF, and a broken line 10c and a solid line 10d indicate a temperature change in the outer peripheral portion of the DPF.

As shown in FIG. 10, the outer peripheral portion of the DPF tends to be harder to heat than the central portion. This is due to the following reasons.
That is, in the DPF disposed in the cylindrical exhaust passage, the exhaust gas tends to accumulate in the central portion of the DPF, so that a temperature difference occurs between the central portion of the DPF and the outer peripheral portion. Therefore, when the DPF regeneration process is performed, combustion starts from PM accumulated in the center of the DPF. Further, in the DPF, the portion where PM is deposited has a larger pressure loss than the portion where PM is not deposited. For this reason, the exhaust gas flows more concentrated on the central portion of the DPF, and the temperature difference between the central portion and the outer peripheral portion of the DPF is further increased.
When a material having a low thermal conductivity is used, the heat at the central portion of the DPF is not easily transmitted to the outer peripheral portion, so that the temperature difference between the central portion and the outer peripheral portion of the DPF is further increased.

  As a result, when a material with low thermal conductivity such as aluminum titanate is used, as shown in FIG. 10, even if the temperature of the central portion of the DPF reaches the combustible temperature of PM, the temperature of the outer peripheral portion is PM. The combustible temperature may not be reached.

  FIG. 11 is a diagram showing the relationship between the DPF regeneration time and the DPF regeneration efficiency. In FIG. 11, the broken line indicates the case where silicon carbide is used as the material of the DPF, and the solid line indicates the case where aluminum titanate is used. The regeneration efficiency indicates the ratio of the PM deposition weight after a predetermined time to the PM deposition weight at the start of DPF regeneration.

  As described above, when silicon carbide is used, the regeneration efficiency increases in proportion to the DPF regeneration time. However, when aluminum titanate is used, since the outer peripheral portion of the DPF has not reached the PM combustible temperature as described above, the increase in regeneration efficiency occurs after a predetermined time has elapsed since the start of DPF regeneration. It will slow down and PM will remain unburned.

  The exhaust emission control device of Patent Document 2 controls the oxygen concentration during PM combustion so that such unburned PM does not occur. However, when a material having a low thermal conductivity as described above is used for the DPF, the temperature of the outer peripheral portion of the DPF may not reach the PM combustible temperature when starting PM combustion. In such a case, even if the oxygen concentration is controlled, there is a risk that PM may remain unburned.

  The present invention has been made in consideration of the above-mentioned points. An internal combustion engine that can efficiently burn so that no PM remains unburned even when a material having low thermal conductivity is used for the DPF. An object is to provide an exhaust emission control device.

  In order to achieve the above object, a first aspect of the present invention provides a particulate filter (32) provided in an exhaust passage (4) of an internal combustion engine (1) for collecting particulates in the exhaust, and the particulates. An exhaust gas purification apparatus for an internal combustion engine, comprising: a filter regeneration unit that performs a filter regeneration process that regenerates a filter; and further comprising an oxygen concentration control unit that controls an oxygen concentration of exhaust gas when the filter regeneration process is performed, The process includes a filter temperature increasing process for increasing the temperature of the particulate filter, and a regeneration combustion process for burning the particulates deposited on the particulate filter, and the oxygen concentration control means executes the filter temperature increasing process. Sometimes, the oxygen concentration in the exhaust is controlled to a concentration that suppresses the combustion of particulates, and the regeneration combustion During physical execution, and controlling the oxygen concentration of the exhaust gas to a concentration that promotes burning of particulates.

The invention according to claim 2 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising target oxygen concentration setting means for setting a target oxygen concentration of the exhaust at the time of the filter temperature raising process, The concentration setting means sets the target oxygen concentration to a concentration that suppresses particulate combustion based on the temperature of the particulate filter and the space velocity of the exhaust gas in the particulate filter.
According to a third aspect of the present invention, the exhaust gas purification apparatus for an internal combustion engine according to the first aspect further comprises target oxygen concentration setting means for setting a target oxygen concentration of the exhaust gas during the filter temperature raising process, The concentration setting means is characterized in that the target oxygen concentration is reduced according to an increase in the temperature of the exhaust gas or the temperature of the particulate filter.

  The invention according to claim 4 is provided in the exhaust passage (4) of the internal combustion engine (1), the particulate filter (32) for collecting the particulates in the exhaust, and the filter regeneration for regenerating the particulate filter. An exhaust gas purification apparatus for an internal combustion engine, comprising: a filter regeneration unit that executes a process, further comprising an oxygen concentration control unit that controls an oxygen concentration of exhaust gas when the filter regeneration process is performed, wherein the filter regeneration process includes the particulate regeneration unit. A filter temperature raising process for raising the temperature of the filter, and a regeneration combustion process for burning the particulates deposited on the particulate filter, wherein the oxygen concentration control means sets the oxygen concentration of the exhaust during the filter temperature raising process. , Control the concentration so that the burning speed of the particulates is lower than the predetermined burning speed, and the regeneration During tempering process execution, the oxygen concentration of the exhaust, the combustion rate of particulate matter and controlling the concentration such that greater than a predetermined burn rate.

  According to a fifth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the fourth aspect, the exhaust gas temperature detecting means (22) for detecting the temperature (TE) of the exhaust gas upstream of the particulate filter, Target oxygen concentration setting means for setting a target oxygen concentration of exhaust at the time of the filter temperature raising process, and the target oxygen concentration setting means is based on the temperature of the exhaust detected by the exhaust temperature detecting means. The oxygen concentration is calculated such that the combustion rate of the curate is equal to or lower than a predetermined combustion rate, and the calculated oxygen concentration is set as a target oxygen concentration.

  According to a sixth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fifth aspects, an exhaust gas temperature detecting means for detecting a temperature (TE) of the exhaust gas upstream of the particulate filter. 22), wherein the filter regeneration means executes the filter temperature raising process, and the regeneration is performed when the temperature of the exhaust detected by the exhaust temperature detection means becomes equal to or higher than a predetermined judgment temperature (TTHA). A combustion process is performed.

  According to a seventh aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fifth aspects, wherein an exhaust gas temperature detecting means for detecting the temperature (TE) of the exhaust gas upstream of the particulate filter. 22), wherein the filter regeneration means executes the filter temperature raising process, and a predetermined time has elapsed after the temperature of the exhaust gas detected by the exhaust gas temperature detection means becomes equal to or higher than a predetermined judgment temperature (TTHB). After the elapse of time, the regeneration combustion process is performed.

  According to an eighth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fifth aspects, an outer peripheral temperature estimating means for estimating an outer peripheral temperature (TDPF) of the particulate filter. The filter regeneration means executes the filter temperature increasing process, and executes the regeneration combustion process when the temperature estimated by the outer peripheral temperature estimating means becomes equal to or higher than a predetermined determination temperature (TTHC). It is characterized by doing.

According to the first aspect of the present invention, the filter regeneration process for regenerating the particulate filter includes a filter temperature increase process for increasing the temperature of the filter and a regeneration combustion process for burning the accumulated particulates. Here, when the filter temperature raising process is executed, the oxygen concentration of the exhaust is controlled to a concentration that suppresses particulate combustion, and when the regeneration combustion process is executed, the oxygen concentration of the exhaust is controlled to a concentration that promotes particulate combustion.
As described above, the temperature of the outer peripheral portion of the filter is less likely to increase than that of the central portion. For this reason, when the particulates are burned while the temperature of the filter is raised, the particulates are regenerated from the central portion of the filter, and a pressure loss difference is generated between the central portion and the outer peripheral portion, resulting in unburned residue. According to this invention, first, the temperature of the entire filter can be raised while suppressing the combustion of the accumulated particulates by executing the filter temperature raising process. Next, the accumulated particulates can be burned by executing the regeneration combustion process. At this time, since the temperature of the filter is raised over the entire region, both the central portion and the outer peripheral portion of the filter can be regenerated uniformly. Therefore, even when a material having a low thermal conductivity is used for the filter, the particulates do not remain burned.
In addition, by completely regenerating the filter in this way, it is possible to shorten the time required for regeneration, reduce the frequency of regeneration, and improve fuel efficiency. In addition, exhaust emission can be improved.
Moreover, the temperature difference of a filter can be reduced by reproducing | regenerating uniformly in the center part and outer peripheral part of a filter. Thereby, the damage by the thermal shock of a filter base material can also be prevented.

  According to the second aspect of the invention, the target oxygen concentration is set to a concentration at which particulate combustion is suppressed based on the temperature of the particulate filter and the space velocity of the exhaust gas in the filter. As a result, it is possible to reduce the time required for the temperature rise while more reliably setting the oxygen concentration to a concentration that suppresses particulate combustion. As a result, the time required for reproduction can be shortened and fuel consumption can be improved.

  According to the third aspect of the present invention, the target oxygen concentration is reduced in accordance with an increase in the temperature of the exhaust gas or the temperature of the particulate filter. As a result, it is possible to reduce the time required for the temperature rise while more reliably setting the oxygen concentration to a concentration that suppresses particulate combustion. As a result, the time required for reproduction can be shortened and fuel consumption can be improved.

According to the fourth aspect of the present invention, the exhaust gas oxygen concentration is controlled to a concentration such that the particulate combustion rate is equal to or lower than a predetermined combustion rate when the filter temperature raising process is executed, and when the regeneration combustion process is executed, The oxygen concentration in the exhaust gas is controlled so that the burning rate of the particulates is greater than a predetermined burning rate.
Thus, by executing the filter temperature increasing process, it is possible to raise the temperature of the entire filter while suppressing the combustion of accumulated particulates. Next, the accumulated particulates can be burned by executing the regeneration combustion process. At this time, since the temperature of the filter is raised over the entire region, both the central portion and the outer peripheral portion of the filter can be regenerated uniformly. Therefore, the particulates will not remain unburned.
In addition, by completely regenerating the filter in this way, it is possible to shorten the time required for regeneration, reduce the frequency of regeneration, and improve fuel efficiency. In addition, exhaust emission can be improved.
Moreover, the temperature difference of a filter can be reduced by reproducing | regenerating uniformly in the center part and outer peripheral part of a filter. Thereby, the damage by the thermal shock of a filter base material can also be prevented.

  According to the fifth aspect of the present invention, the temperature of the exhaust gas upstream of the particulate filter is detected, and the oxygen concentration is calculated based on this temperature so that the particulate combustion rate is equal to or lower than the predetermined combustion rate. This oxygen concentration is set as the target oxygen concentration. As a result, it is possible to reduce the time required for the temperature rise while more reliably setting the oxygen concentration to a concentration that suppresses particulate combustion. As a result, the time required for reproduction can be shortened and fuel consumption can be improved.

  According to the sixth aspect of the present invention, the filter temperature increasing process is executed, and the regeneration combustion process is executed when the temperature of the exhaust gas upstream of the particulate filter becomes equal to or higher than a predetermined judgment temperature. Thereby, it is possible to raise the temperature of the filter more reliably over the entire region. Accordingly, the particulates can be burned evenly in the regeneration combustion process. Further, the time required for the filter temperature raising process can be minimized.

  According to the seventh aspect of the present invention, the filter temperature increasing process is executed, and after a predetermined time has elapsed since the temperature of the exhaust gas upstream of the particulate filter has become equal to or higher than the predetermined determination temperature, the regeneration combustion process is performed. Execute. Thereby, it is possible to raise the temperature of the filter more reliably over the entire region. Accordingly, the particulates can be burned evenly in the regeneration combustion process. Further, the time required for the filter temperature raising process can be minimized.

  According to the eighth aspect of the present invention, the filter temperature increasing process is executed, and the regeneration combustion process is executed when the temperature of the outer peripheral portion of the particulate filter becomes equal to or higher than a predetermined determination temperature. As a result, the regeneration combustion process can be executed after reliably raising the temperature of the outer peripheral portion of the filter that is most difficult to rise. Therefore, the particulates can be burned evenly. Further, the time required for the filter temperature raising process can be minimized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a diagram showing a configuration of an internal combustion engine and an exhaust purification device thereof according to a first embodiment of the present invention. An internal combustion engine (hereinafter referred to as “engine”) 1 is a diesel engine that directly injects fuel into the combustion chamber of each cylinder 7, and each cylinder 7 is provided with a fuel injection valve (not shown). These fuel injection valves are electrically connected by an electronic control unit (hereinafter referred to as “ECU”) 40, and the valve opening time and valve closing time of the fuel injection valve are controlled by the ECU 40.

  The engine 1 includes an intake pipe 2 through which intake air circulates, an exhaust pipe 4 through which exhaust gas circulates, an exhaust gas recirculation passage 6 that recirculates part of the exhaust gas in the exhaust pipe 4 to the intake pipe 2, and intake air into the intake pipe 2. And a supercharger 8 for pressure-feeding.

  The intake pipe 2 is connected to the intake port of each cylinder 7 of the engine 1 through a plurality of branch portions of the intake manifold 3. The exhaust pipe 4 is connected to the exhaust port of each cylinder 7 of the engine 1 through a plurality of branch portions of the exhaust manifold 5. The exhaust gas recirculation passage 6 branches from the exhaust manifold 5 and reaches the intake manifold 3.

  The supercharger 8 includes a turbine (not shown) provided in the exhaust pipe 4 and a compressor (not shown) provided in the intake pipe 2. The turbine is driven by the kinetic energy of the exhaust flowing through the exhaust pipe 4. The compressor is rotationally driven by the turbine, pressurizes the intake air, and pumps it into the intake pipe 2. The turbine includes a plurality of variable vanes (not shown), and is configured to change the turbine rotation speed (rotational speed) by changing the opening of the variable vanes. The vane opening degree of the turbine is electromagnetically controlled by the ECU 40.

  A throttle valve 9 for controlling the intake air amount GA of the engine 1 is provided upstream of the supercharger 8 in the intake pipe 2. The throttle valve 9 is connected to the ECU 40 via an actuator, and the opening degree is electromagnetically controlled by the ECU 40. In addition, an intercooler 11 for cooling the intake air pressurized by the supercharger 8 is provided on the downstream side of the supercharger 8 in the intake pipe 2.

  The exhaust gas recirculation passage 6 connects the exhaust manifold 5 and the intake manifold 3 and recirculates part of the exhaust discharged from the engine 1. The exhaust gas recirculation passage 6 is provided with an EGR cooler 12 that cools the exhaust gas that is recirculated, and an EGR valve 13 that controls the flow rate of the recirculated exhaust gas. The EGR valve 13 is connected to the ECU 40 via an actuator (not shown), and the valve opening degree is electromagnetically controlled by the ECU 40.

  A catalytic converter 31 and a DPF 32 as a particulate filter are provided in this order from the upstream side on the downstream side of the supercharger 8 in the exhaust pipe 4.

  The catalytic converter 31 includes, for example, an oxidation catalyst, purifies the exhaust gas by a reaction between the catalyst and the exhaust gas, and raises the temperature of the exhaust gas with heat generated by the reaction between the exhaust gas and the catalyst.

When the exhaust gas passes through fine holes in the filter wall, the DPF 32 collects PM mainly composed of carbon in the exhaust gas by depositing it on the surface of the filter wall and the holes in the filter wall. As a constituent material of the filter wall, for example, a porous body made of aluminum titanate, cordierite or the like is used.
When PM is collected to the limit of the collection capability of the DPF 32, that is, the accumulation limit, the pressure loss increases. Therefore, it is necessary to appropriately execute the DPF regeneration process for burning the collected PM and regenerating the DPF 32. In this DPF regeneration process, for example, fuel injection that does not contribute to torque (hereinafter referred to as “post-injection”), which is different from main injection, is performed, and the temperature of the exhaust gas flowing into the DPF 32 is changed to the PM collected in the DPF 32. This is done by raising the combustion temperature and burning PM. The procedure of this DPF regeneration process will be described in detail later with reference to FIG.

  The ECU 40 is connected to an exhaust gas temperature sensor 22 that detects the temperature TE of the exhaust gas upstream of the DPF 32 in the exhaust pipe 4, and the detection signal of this sensor is supplied to the ECU 40.

  The ECU 40 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter, “ CPU ”). In addition, the ECU 40 sends control signals to a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, a throttle valve 9, an EGR valve 13, a supercharger 8, and a fuel injection valve of the engine 1. An output circuit for outputting.

FIG. 2 is a flowchart showing a procedure of DPF regeneration processing by the ECU.
As shown in FIG. 2, the DPF regeneration process of the present embodiment includes a normal regeneration combustion process (step S5) in which PM accumulated in the DPF is combusted, and the DPF is increased before executing this ordinary regeneration combustion process. And a DPF temperature raising process (step S3) that suppresses PM combustion by lowering the target oxygen concentration of the exhaust gas while lowering the oxygen concentration in the normal regeneration combustion process.

  In step S1, it is determined whether or not a DPF regeneration request flag FDPFRR is “1”. If this determination is YES, the process proceeds to step S3, and if NO, the process proceeds to step S2, and the combustion that was scheduled according to the driver's request is performed. Here, the DPF regeneration request flag FDPFRR is a flag for requesting execution of the DPF regeneration process, and when the fuel consumption reaches a predetermined value, when the travel distance of the vehicle reaches a predetermined value, or PM Is set to “1”, for example, when the amount of the accumulated amount reaches a predetermined amount. Further, once this DPF regeneration request flag FDPFRR is set to “1”, it is returned to “0” by a process (not shown) after a predetermined regeneration time has elapsed.

  In step S3, a DPF temperature raising process is executed, and the process proceeds to step S4. In this DPF temperature raising process, for example, post injection is executed to raise the temperature of the DPF by raising the temperature of the exhaust gas flowing into the DPF.

  When executing the DPF temperature raising process, the temperature of the DPF is raised, and the oxygen concentration of the exhaust gas flowing into the DPF is controlled to be lower than the oxygen concentration when the normal regeneration combustion process described later is executed. . More specifically, the target oxygen concentration is set to an oxygen concentration (for example, 1% or less) that suppresses combustion of PM accumulated in the DPF, and the oxygen concentration of the exhaust gas is controlled so as to coincide with the target oxygen concentration. . Here, in order to reduce the oxygen concentration, for example, compared with the normal regeneration combustion processing, the fuel injection amount in the post injection is increased or the throttle valve is retarded while retarding the main injection from the normal combustion. Close to reduce intake.

  In step S4, it is determined whether or not a predetermined combustion start condition is satisfied. If this determination is YES, the process proceeds to step S5, and if this determination is NO, this process is immediately terminated.

The combustion start condition is a condition for ending the DPF temperature raising process and starting the normal regeneration combustion process. In the present embodiment, for example, the combustion start condition is that the exhaust gas temperature TE detected by the exhaust gas temperature sensor is equal to or higher than a predetermined determination temperature TTHA.
In addition, for example, the combustion start condition is that a predetermined time elapses after the exhaust gas temperature TE detected by the exhaust temperature sensor becomes equal to or higher than a predetermined determination temperature TTHB after the DPF temperature raising process is executed. It is good.
Further, for example, the temperature TDPF of the outer periphery of the DPF is estimated based on the exhaust temperature TE detected by the exhaust temperature sensor, and the combustion start condition is that the temperature TDPF of the DPF becomes equal to or higher than a predetermined determination temperature TTHC. Also good.

  In step S5, a normal regeneration combustion process is executed, and this process ends. In this normal regeneration combustion process, for example, PM accumulated in the DPF is burned by executing post injection. In the normal regeneration combustion process, the target oxygen concentration is set to an oxygen concentration (for example, 1% or more) that promotes the combustion of PM accumulated in the DPF, and the oxygen concentration of the exhaust gas is set to coincide with the target oxygen concentration. To control.

  The DPF regeneration process in the present embodiment as described above is compared with the DPF regeneration process in the comparative example. Here, the DPF regeneration process of the comparative example indicates a case where only the normal regeneration combustion process (step S5 in FIG. 2) in the present embodiment is executed. That is, it shows a case where the oxygen concentration of the exhaust gas flowing into the DPF is kept at a concentration that promotes PM combustion from the start to the end of the DPF regeneration process.

  FIG. 3 is a diagram showing the relationship between the DPF regeneration time, the temperature of the gas upstream of the DPF, and the temperature of the DPF. In FIG. 3, the left side shows the results of the comparative example, and the right side shows the results of the present embodiment. In addition, the alternate long and short dash line indicates the temperature at the center of the exhaust on the upstream side of the DPF, the alternate long and two short dashes line indicates the temperature at the outer periphery of the exhaust on the upstream side of the DPF, the broken line indicates the temperature at the center of the lower end of the DPF, and the solid line indicates The temperature of the outer peripheral part of the lower end of DPF is shown.

  4 to 6 are diagrams schematically illustrating the DPF during the DPF regeneration process. More specifically, FIG. 4 shows the DPF during the DPF regeneration process of the comparative example, FIG. 5 shows the DPF during the DPF temperature raising process, and FIG. 6 shows the DPF during the normal regeneration combustion process.

  As shown in FIG. 3, in the DPF regeneration process of the comparative example, the temperature of the exhaust gas upstream of the DPF suddenly rises to near the combustion temperature of PM immediately after the regeneration starts, and becomes substantially constant. Among the exhaust gases, the exhaust gas flowing into the outer peripheral portion of the DPF has a large amount of heat radiation to the outside, and the temperature is lower than that of the exhaust gas flowing into the central portion of the DPF. In addition to this, exhaust gas tends to accumulate in the central portion of the DPF, so that a temperature difference occurs between the central portion and the outer peripheral portion of the DPF.

  In the DPF regeneration process of the comparative example, PM is burned while the DPF is heated. For this reason, when the DPF regeneration process is performed, combustion starts from PM accumulated in the center of the DPF. Further, in the DPF, the portion where PM is deposited has a larger pressure loss than the portion where PM is not deposited. For this reason, the exhaust gas flows more concentrated in the central portion of the DPF (see FIG. 4), and the temperature difference between the central portion and the outer peripheral portion of the DPF becomes even larger. As a result, the outer periphery of the DPF does not reach the combustion temperature of PM, and PM may remain unburned on the outer periphery (see FIG. 4).

On the other hand, as shown in FIG. 3, in the DPF regeneration process of the present embodiment, the normal regeneration combustion process is performed after the DPF temperature increase process is performed.
In the DPF temperature increase processing period, the temperature of the central portion and the outer periphery of the DPF is increased over a predetermined time while controlling the oxygen concentration and suppressing the combustion of PM deposited on the DPF. Here, unlike the above-described comparative example, since PM combustion is suppressed, the pressure loss difference between the central portion and the outer peripheral portion of the DPF is small, and both the central portion and the outer peripheral portion of the DPF reach the combustion temperature of the PM. The temperature can be raised (see FIG. 5).

  In normal regeneration combustion processing, PM is burned by controlling the oxygen concentration of the exhaust to a concentration that promotes combustion of PM. In particular, at this time, the temperature of the central portion and the outer peripheral portion of the DPF has reached a temperature at which PM can be combusted. Therefore, as shown in FIG. 6, PM burns evenly in order from the upper end side of the DPF.

  FIG. 7 is a diagram showing the relationship between the DPF regeneration time and the regeneration efficiency. In FIG. 7, the solid line indicates the time change of the regeneration efficiency due to the DPF regeneration process of the present embodiment, and the broken line indicates the time change of the regeneration efficiency due to the DPF regeneration process of the comparative example.

As shown in FIG. 7, in the comparative example, the increase in the regeneration efficiency slows down with the lapse of the regeneration time, and after about 20 seconds from the start of the DPF regeneration process, the regeneration efficiency reaches about 64%. Converge. This is because, as described above, the outer periphery of the DPF does not reach the temperature at which PM can be combusted, and PM remains unburned.
On the other hand, in this embodiment, as in the case of using a material having high thermal conductivity such as silicon carbide (see FIG. 11 described above), the regeneration efficiency of the DPF increases in proportion to the regeneration time. As described above, this is because PM is burned after the DPF is heated at a low oxygen concentration, and thus it is possible to completely regenerate the DPF.

  In this embodiment, the fuel regeneration valve of the engine 1, the throttle valve 9, the catalytic converter 31, and the ECU 40 constitute a filter regeneration means, and the fuel injection valve, the throttle valve 9, and the ECU 40 of the engine 1 constitute an oxygen concentration control means. Then, the ECU 40 constitutes a target oxygen concentration setting means, and the exhaust gas temperature sensor 22 and the ECU 40 constitute an outer peripheral temperature estimation means. Specifically, the means related to the execution of the DPF regeneration process shown in FIG. 2 corresponds to a part of the filter regeneration means, the means related to the execution of steps S3 and S5 in FIG. 2 are the oxygen concentration control means, and the target oxygen concentration It corresponds to a part of the setting means, and the means relating to the execution of step S4 in FIG.

As described above in detail, according to the present embodiment, first, the DPF temperature raising process is executed, whereby the temperature of the entire DPF 32 can be raised while suppressing the combustion of the accumulated PM. Next, the accumulated PM can be burned by executing the normal regeneration combustion process. At this time, since the DPF 32 is heated over the entire region, both the central portion and the outer peripheral portion of the DPF 32 can be regenerated uniformly. Therefore, even when a material having a low thermal conductivity is used for the DPF 32, PM does not remain unburned.
In addition, by completely regenerating the DPF 32 in this way, it is possible to shorten the time required for regeneration, reduce the frequency of regeneration, and improve fuel efficiency. In addition, exhaust emission can be improved.
Further, the temperature difference of the DPF 32 can be reduced by regenerating both the central portion and the outer peripheral portion of the DPF 32 evenly. Thereby, the damage by the thermal shock of a DPF base material can also be prevented.

  Further, according to the present embodiment, the DPF temperature raising process is executed, and the normal regeneration combustion process is executed when the temperature TE of the exhaust gas upstream of the DPF becomes equal to or higher than a predetermined determination temperature. Thereby, it is possible to raise the temperature of the DPF 32 over the entire region more reliably. Therefore, PM can be burned uniformly in the normal regeneration combustion process. Further, the time required for the DPF temperature raising process can be minimized.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIGS.
This embodiment is different in how to set the target oxygen concentration in the DPF regeneration process according to the first embodiment (see step S2 and step S5 in FIG. 2). In the present embodiment, the target oxygen concentration is set based on the PM combustion rate.

FIG. 8 is a diagram showing the relationship between the temperature of the exhaust on the upstream side of the DPF and the combustion rate of PM, and shows the cases where the oxygen concentration of the exhaust is 10%, 5%, 3%, and 1%, respectively.
As shown in FIG. 8, the combustion speed of PM increases as the temperature of the exhaust gas increases, the combustion of PM is accelerated, the combustion speed of the PM decreases as the temperature of the exhaust gas decreases, and the combustion of PM is suppressed. The In particular, under the same exhaust temperature, the PM combustion rate increases as the oxygen concentration increases, and the PM combustion rate decreases as the oxygen concentration decreases.

FIG. 9 is a diagram showing the relationship between the exhaust gas temperature upstream of the DPF and the oxygen concentration when the PM combustion rate is set to a predetermined set combustion rate.
As shown in FIG. 9, as the exhaust gas temperature increases, the oxygen concentration in the exhaust gas required to keep the PM combustion rate constant decreases.

In the present embodiment, the target oxygen concentration is set based on the relationship between the PM combustion rate, the exhaust oxygen concentration, and the exhaust gas temperature.
More specifically, at the time of the DPF temperature raising process (see step S2 in FIG. 2), the PM combustion speed becomes equal to or lower than a predetermined set combustion speed based on the exhaust gas temperature TE detected by the exhaust gas temperature sensor. Such an oxygen concentration is calculated, and this oxygen concentration is set as a target oxygen concentration. Furthermore, PM combustion is suppressed by controlling the oxygen concentration of the exhaust gas so as to coincide with the target oxygen concentration.
Further, during the normal regeneration combustion process (see step S5 in FIG. 2), the oxygen concentration is such that the PM combustion rate is equal to or lower than a predetermined set combustion rate based on the exhaust gas temperature TE detected by the exhaust gas temperature sensor. And this oxygen concentration is set as the target oxygen concentration. Furthermore, PM combustion is promoted by controlling the oxygen concentration of the exhaust gas so as to coincide with the target oxygen concentration.

As described above in detail, according to the present embodiment, in addition to the effects of the first embodiment, the following effects can be obtained.
According to the present embodiment, the temperature TE of the exhaust gas upstream of the DPF 32 is detected, and based on this temperature TE, the oxygen concentration is calculated such that the PM combustion rate becomes a predetermined combustion rate or less, and this oxygen concentration is calculated. Set as the target oxygen concentration. As a result, it is possible to shorten the time required for temperature increase while more reliably setting the oxygen concentration to a concentration that suppresses the combustion of PM. As a result, the time required for reproduction can be shortened and fuel consumption can be improved.

  The present invention is not limited to the embodiment described above, and various modifications can be made.

In the first embodiment described above, the DPF temperature raising process is executed under a constant target oxygen concentration, but the present invention is not limited to this. For example, the target oxygen concentration may be set to a concentration that suppresses combustion of PM based on the temperature of the DPF and the space velocity of the exhaust gas in the DPF. Further, for example, the target oxygen concentration may be changed in accordance with a change in the exhaust gas temperature or the DPF temperature. More specifically, the target oxygen concentration may be reduced as the exhaust gas temperature or the DPF temperature increases.
As a result, it is possible to shorten the time required for temperature increase while more reliably setting the oxygen concentration to a concentration that suppresses the combustion of PM. As a result, the time required for reproduction can be shortened and fuel consumption can be improved.

  The present invention can also be applied to an exhaust emission control device such as a marine vessel propulsion engine such as an outboard motor having a vertical crankshaft.

1 is a diagram illustrating a configuration of an internal combustion engine and an exhaust purification device thereof according to a first embodiment of the present invention. It is a flowchart which shows the procedure of the DPF regeneration process by ECU which concerns on the said embodiment. It is a figure which shows the relationship between the time of the DPF regeneration which concerns on the said embodiment and a comparative example, the temperature of the gas of the upstream of DPF, and the temperature of DPF. It is a schematic diagram which shows DPF at the time of the DPF regeneration process which concerns on a comparative example. It is a schematic diagram which shows DPF at the time of DPF temperature rising process which concerns on the said embodiment. It is a schematic diagram which shows DPF at the time of the normal regeneration combustion process which concerns on the said embodiment. It is a figure which shows the relationship between the time of DPF reproduction | regeneration, and reproduction | regeneration efficiency which concern on the said embodiment and a comparative example. It is a figure which shows the relationship between the temperature of the exhaust_gas | exhaustion upstream of DPF which concerns on the 2nd Embodiment of this invention, and the combustion speed of PM. It is a figure which shows the relationship between the temperature of the exhaust_gas | exhaustion upstream of DPF which concerns on the said embodiment, and oxygen concentration. It is a figure which shows the relationship between the time of DPF regeneration, and the temperature of DPF. It is a figure which shows the relationship between the time of DPF regeneration, and the regeneration efficiency of DPF.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 9 ... Throttle valve (filter regeneration means, oxygen concentration control means)
22 ... Exhaust temperature sensor (exhaust temperature detection means, outer periphery temperature estimation means)
31 ... Catalytic converter (filter regeneration means)
32 ... DPF (Particulate Filter)
40. Electronic control unit (filter regeneration means, oxygen concentration control means, target oxygen concentration setting means, outer peripheral temperature estimation means)

Claims (8)

In an exhaust gas purification apparatus for an internal combustion engine, comprising: a particulate filter that is provided in an exhaust passage of the internal combustion engine and collects particulates in exhaust gas; and a filter regeneration unit that performs filter regeneration processing for regenerating the particulate filter. ,
Further comprising oxygen concentration control means for controlling the oxygen concentration of the exhaust when performing the filter regeneration processing;
The filter regeneration process includes a filter temperature raising process for raising the temperature of the particulate filter, and a regeneration combustion process for burning the particulate deposited on the particulate filter,
The oxygen concentration control means controls the oxygen concentration of the exhaust to a concentration that suppresses particulate combustion when the filter temperature raising process is executed, and promotes the combustion of the particulates when the regeneration combustion process is executed. An exhaust emission control device for an internal combustion engine, characterized in that the concentration is controlled. Further comprising target oxygen concentration setting means for setting a target oxygen concentration of exhaust during the filter temperature raising process,
The target oxygen concentration setting means sets the target oxygen concentration to a concentration that suppresses particulate combustion based on the temperature of the particulate filter and the space velocity of exhaust gas in the particulate filter. 2. An exhaust emission control device for an internal combustion engine according to 1. Further comprising target oxygen concentration setting means for setting a target oxygen concentration of exhaust during the filter temperature raising process,
2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the target oxygen concentration setting means reduces the target oxygen concentration in accordance with an increase in the temperature of the exhaust gas or the temperature of the particulate filter. In an exhaust gas purification apparatus for an internal combustion engine, comprising: a particulate filter that is provided in an exhaust passage of the internal combustion engine and collects particulates in exhaust gas; and a filter regeneration unit that performs filter regeneration processing for regenerating the particulate filter. ,
Further comprising oxygen concentration control means for controlling the oxygen concentration of the exhaust when performing the filter regeneration processing;
The filter regeneration process includes a filter temperature raising process for raising the temperature of the particulate filter, and a regeneration combustion process for burning the particulates deposited on the particulate filter,
The oxygen concentration control means controls the oxygen concentration of the exhaust when the filter temperature raising process is executed so that the combustion speed of the particulates is equal to or lower than a predetermined combustion speed, and when the regeneration combustion process is executed, An exhaust emission control device for an internal combustion engine, wherein the oxygen concentration is controlled to a concentration such that the combustion rate of particulates is greater than a predetermined combustion rate. Exhaust temperature detecting means for detecting the temperature of the exhaust gas upstream of the particulate filter;
A target oxygen concentration setting means for setting a target oxygen concentration of exhaust during the filter temperature raising process,
The target oxygen concentration setting means calculates an oxygen concentration such that the particulate combustion speed is equal to or lower than a predetermined combustion speed based on the exhaust gas temperature detected by the exhaust gas temperature detection means, and the calculated oxygen concentration The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the target oxygen concentration is set as the target oxygen concentration. Exhaust temperature detecting means for detecting the temperature of the exhaust gas upstream of the particulate filter,
The filter regeneration means executes the filter temperature increasing process, and executes the regeneration combustion process when the temperature of the exhaust gas detected by the exhaust gas temperature detection means becomes equal to or higher than a predetermined determination temperature. An exhaust emission control device for an internal combustion engine according to any one of claims 1 to 5. Exhaust temperature detecting means for detecting the temperature of the exhaust gas upstream of the particulate filter,
The filter regeneration means executes the filter temperature raising process, and after a predetermined time has elapsed since the temperature of the exhaust gas detected by the exhaust temperature detection means has exceeded a predetermined determination temperature, the regeneration combustion process is performed. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 5, wherein the exhaust gas purification device is executed. An outer peripheral temperature estimating means for estimating an outer peripheral temperature of the particulate filter;
The filter regeneration means executes the filter temperature increasing process, and executes the regeneration combustion process when the temperature estimated by the outer peripheral temperature estimation means becomes equal to or higher than a predetermined determination temperature. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 5.

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