JP2002332822A - Exhaust emission control device, and exhaust emission control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To burn soot without causing a catalyst to deteriorate, even when much soot is accumulated on the catalyst. SOLUTION: The soot, contained in exhaust gas in an internal combustion engine, is collected by a filter, and burned by oxidation catalyst carried on the filter. When a large amount of soot is accumulated on the filter, depending on an operation condition, the filter temperature is raised, then the air-fuel ratio of the exhaust gas is controlled stoichometrically or richly and is set at the lean air-fuel ratio intermittently for a short time. Thus, oxygen is supplied to the catalyst only little by little, so that soot can be burned in small steps, even when a large amount of soot is accumulated. If the combustion of the soot can be kept in a controllable state, the catalyst temperature will not rise abnormally, and there is no risk of speed up of the deterioration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a technique for purifying carbon-containing suspended particulates contained in exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art The exhaust gas of an internal combustion engine, particularly a diesel engine, contains carbon-containing suspended particulates such as black smoke (soot). From the viewpoint of preventing air pollution, the total amount of particulates discharged is reduced. There is a strong demand for a reduction.
In addition, a so-called in-cylinder injection gasoline engine, which injects gasoline directly into the combustion chamber, has a similar demand because carbon-containing suspended particulates may be discharged together with exhaust gas depending on operating conditions.

As a technique capable of greatly reducing the suspended carbon-containing particles discharged from the internal combustion engine, a heat-resistant filter is provided in the exhaust passage of the engine, and the suspended carbon-containing particles discharged together with the exhaust gas are filtered. A technique has been proposed in which the collected fine particles are burned using an oxidation catalyst supported on a filter while the collected fine particles are collected (Japanese Patent Publication No. Hei 7-1995).
No. 106290).

[0004] In such a technique, an oxidation catalyst is supported on a filter, so that even at relatively low temperature exhaust gas,
The trapped carbon-containing suspended particulates can be burned on a filter. On the other hand, in such a technique, if the internal combustion engine is operated for a long period of time under operating conditions in which the exhaust gas temperature is too low, the filter temperature gradually decreases, and it becomes impossible to burn the trapped particulates. Clogging may occur. Therefore, when the filter is operated continuously for a long time under low load operating conditions and there is a concern that the filter may be clogged, or when the differential pressure across the filter is increasing, the temperature of the exhaust gas is intentionally set. By raising, the carbon-containing suspended particulates on the filter are forcibly burned. In this way, by forcibly burning the collected suspended carbon-containing particles as necessary, the suspended carbon-containing particles discharged from the internal combustion engine can be significantly and stably reduced. It is possible.

[0005]

However, if the carbon-containing suspended particulates deposited on the filter become too large,
When the fuel is forcibly burned, there is a problem that the deposited fine particles burn at a stretch and the filter temperature is greatly increased, which may deteriorate the catalyst. This is because when the combustion of the deposited carbon-containing suspended particulates starts, the filter temperature rises due to the combustion heat, and the combustion is further promoted. As a result, the deposited particulates burn at once.

Of course, frequent forced combustion is performed,
If a large amount of carbon-containing suspended particulates is prevented from accumulating on the filter, it is possible to avoid deterioration of the catalyst due to a significant rise in the filter temperature, but if the frequency of forced combustion increases, This causes new problems such as an increase in fuel consumption and a hindrance to comfortable driving.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and is intended to deteriorate a catalyst on a filter even when a large amount of suspended carbon-containing particles is deposited on the filter. It is intended to provide a technology that can be appropriately burned.

[0008]

Means for Solving the Problems and Their Functions and Effects In order to solve at least part of the above-mentioned problems, the exhaust gas purifying apparatus of the present invention has the following configuration. That is, an exhaust gas purifying apparatus for purifying carbon-containing suspended particulates contained in exhaust gas of an internal combustion engine, wherein the apparatus is provided in an exhaust passage of the internal combustion engine and collects the carbon-containing suspended particulates. An exhaust gas purifying catalyst for purifying exhaust gas by burning the carbon-containing suspended particulates, and whether or not to start combustion promotion control for promoting combustion of the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst. An accelerating control start judging means for judging based on the accumulation state of the carbon-containing suspended particulates, and, when judging to start the combustion accelerating control, while limiting the amount of oxygen supplied to the exhaust gas purifying catalyst, The gist of the present invention is to include a combustion promoting means for promoting the combustion of the carbon-containing suspended fine particles.

Further, an exhaust gas purifying method of the present invention corresponding to the above exhaust gas purifying apparatus is an exhaust gas purifying method for purifying carbon-containing suspended particulates contained in exhaust gas of an internal combustion engine. By providing an exhaust gas purification catalyst in the exhaust passage of the above, while collecting the carbon-containing suspended particulates, burning the collected carbon-containing suspended particulates,
Whether or not to start combustion promotion control for promoting the combustion of the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst is determined based on the accumulation state of the carbon-containing suspended particulates,
When it is determined that the combustion promotion control is started, the gist of the invention is to promote the combustion of the carbon-containing suspended particulates while limiting the amount of oxygen supplied to the exhaust gas purification catalyst.

In the exhaust gas purifying apparatus and the exhaust gas purifying method of the present invention, when the carbon-containing suspended particulates are deposited on the exhaust gas-purifying catalyst, the carbon-containing suspended particulates are deposited by supplying oxygen to the catalyst. Promotes combustion. At this time, combustion is promoted while limiting the amount of oxygen supplied to the catalyst. In this way, if the supply amount of oxygen is limited, even if a large amount of carbon-containing suspended particulates are deposited on the catalyst, the particulates can be burned little by little, which causes deterioration of the catalyst. Thus, the deposited carbon-containing suspended particulates can be appropriately burned. Here, “based on the deposition status of the carbon-containing suspended particulates” is not limited to the detection of the deposition amount of the particulates directly or indirectly. May be empirically estimated.

In this exhaust gas purifying apparatus, the temperature of the exhaust gas purifying catalyst is raised to a predetermined temperature or higher, and the combustion of the carbon-containing suspended particulates is promoted while limiting the amount of oxygen supplied to the catalyst. It is good.

In general, the combustion reaction of a catalyst becomes active when the temperature of the catalyst rises. Therefore, if the temperature of the exhaust gas purification catalyst is raised to a predetermined temperature or more and oxygen is supplied while the supply amount is limited, the supply It is preferable because the carbon-containing suspended fine particles can be burned in accordance with the oxygen amount.
Here, the term “catalyst temperature” or “catalyst temperature” is not limited to a strict catalyst temperature, but refers to a temperature of a portion that fluctuates with the catalyst temperature, such as the temperature of exhaust gas passing through the catalyst. Needless to say, it can be substituted.

In such an exhaust gas purifying apparatus, a judgment as to whether or not to start the combustion promotion control is made by estimating the amount of the carbon-containing suspended particulates deposited on the exhaust gas purifying catalyst. It is good to do.

It is preferable to estimate the amount of the carbon-containing suspended particulates deposited on the catalyst, since it is possible to appropriately determine the start of the combustion promotion control. The term “estimation of the amount of suspended carbon-containing particles” used herein is not limited to explicitly calculating the amount of suspended carbon-containing particles itself, but indirectly refers to the amount of accumulated carbon-containing suspended particles. The amount of deposition may be implicitly estimated by detecting the corresponding numerical value or parameter.

In the exhaust gas purifying apparatus for estimating the deposition amount of the carbon-containing suspended fine particles, a pressure difference between the exhaust gas before and after the exhaust gas purifying catalyst is detected, and the detected pressure difference is detected. Based on this, the deposition amount of the suspended carbon-containing particles may be estimated.

If the deposition amount of the carbon-containing suspended fine particles increases,
Accordingly, the pressure difference before and after the exhaust gas purifying catalyst also increases. Therefore, if the deposition amount is estimated based on the pressure difference, the deposition amount can be relatively easily and accurately estimated. preferable.

Alternatively, in the above-mentioned exhaust gas purifying apparatus for estimating the deposited amount of the carbon-containing suspended particulates, the deposited amount may be calculated as follows. That is, the operating condition of the internal combustion engine is detected, and the accumulated amount per unit time according to the operating condition is accumulated to calculate the accumulated amount of the carbon-containing suspended particulates accumulated on the exhaust gas purification catalyst. I do. Next, it may be determined whether or not to start the combustion promotion control based on the magnitude relationship between the obtained accumulation amount and a predetermined threshold.

If the operating conditions of the internal combustion engine are determined, the amount of the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst per unit time when the internal combustion engine is operated under the operating conditions is determined experimentally. You can ask for it. From this, the accumulation amount of the carbon-containing suspended particulates is determined in advance according to the operating conditions of the internal combustion engine, and by accumulating the accumulation amount, the accumulation amount of the carbon-containing suspended particulates deposited on the catalyst can be compared. It can be estimated with high target accuracy. It is preferable to determine whether or not to start the combustion promotion control based on the amount of accumulation obtained in this way, since it is possible to make an appropriate determination.

Alternatively, according to the operating conditions of the internal combustion engine,
The amount of particulates emitted per unit time during the period and the amount of particulates burned per unit time on the exhaust gas purification catalyst under the operating conditions are experimentally obtained, and the difference between them is taken to obtain the exhaust gas purification. The accumulated amount of the carbon-containing suspended particulates deposited on the catalyst per unit time may be obtained, and the obtained accumulated amount may be accumulated.

Further, when accumulating the accumulation amount of fine particles per unit time obtained according to the operating conditions of the internal combustion engine,
The correction coefficient may be multiplied and then accumulated. If accumulation is performed after multiplying the correction coefficient in this way, it is possible to improve the estimation accuracy of the amount of fine particles deposited on the catalyst by appropriately correcting a factor caused by a difference from an experimental condition or the like. preferable.

Further, in the exhaust gas purifying apparatus or the exhaust gas purifying method of the present invention described above, when promoting the combustion of the carbon-containing suspended particulates, the exhaust gas having the stoichiometric air-fuel ratio or the rich air-fuel ratio is subjected to the exhaust gas purifying. The amount of oxygen supplied to the exhaust gas purification catalyst may be limited by intermittently setting the air-fuel ratio of the exhaust gas to a lean air-fuel ratio while supplying the exhaust gas.

In this way, it is preferable to intermittently supply the exhaust gas having the lean air-fuel ratio because the amount of oxygen supplied to the catalyst can be easily limited. In this method, if the air-fuel ratio of the exhaust gas is maintained at the stoichiometric air-fuel ratio or the rich air-fuel ratio, and the exhaust gas having the lean air-fuel ratio is intermittently supplied for a short time, Even if the concentration of oxygen contained in the exhaust gas at the lean air-fuel ratio becomes somewhat high, it is preferable because a large amount of oxygen is not supplied to the catalyst.

The method of switching the air-fuel ratio of the exhaust gas is not limited to the method of switching the operating air-fuel ratio of the internal combustion engine. For example, by introducing air into the exhaust gas, the exhaust gas can be converted to the lean air-fuel ratio. Alternatively, the exhaust gas may be set to the stoichiometric air-fuel ratio or the rich air-fuel ratio by injecting additional fuel into the exhaust gas. Further, needless to say, the exhaust gas may be set to the stoichiometric air-fuel ratio or the rich air-fuel ratio by injecting additional fuel during the expansion stroke or the exhaust stroke of the internal combustion engine.

Alternatively, in the exhaust gas purifying apparatus of the present invention described above, by supplying the exhaust gas slightly leaner than the stoichiometric air-fuel ratio to the exhaust gas purifying catalyst, the exhaust gas is supplied to the exhaust gas purifying catalyst. The combustion may be promoted while limiting the amount of oxygen.

This is preferable because the amount of oxygen supplied to the exhaust gas purification catalyst can be limited without intermittently switching the air-fuel ratio. The lean exhaust gas near the stoichiometric air-fuel ratio means that the air-fuel ratio is "0.
Exhaust gas having a value larger by 2 "to" 4 ", more preferably a value having an air-fuel ratio larger by" 0.5 "to" 2 "can be obtained. If the value is too small, control for keeping the exhaust gas at a lean air-fuel ratio becomes complicated, and if the value is too large, the amount of oxygen supplied to the exhaust gas purification catalyst cannot be limited. If the value of the air-fuel ratio is set in such a range, it is preferable because the exhaust gas can be easily kept on the lean side near the stoichiometric air-fuel ratio.

In the exhaust gas purifying apparatus described above, the amount of temperature rise of the exhaust gas purifying catalyst by supplying the exhaust gas having the lean air-fuel ratio is detected, and the detected amount of temperature rise is set to a predetermined threshold value or less. When this happens, it may be determined that the combustion of the carbon-containing suspended particulates deposited on the catalyst has been completed, and the combustion promotion control may be terminated.

When the carbon-containing suspended particulates burn, the temperature of the catalyst rises due to the heat of combustion. When the amount of temperature rise of the exhaust gas purifying catalyst falls below a predetermined threshold, the carbon-containing suspended particulates deposited on the catalyst are removed. It can be determined that all the fine particles have burned. Therefore, it is preferable to determine the completion of combustion of the fine particles deposited by such a method, since the combustion promotion control can be appropriately terminated.

In addition, in the exhaust gas purifying apparatus, when the detected temperature rise amount falls from a value equal to or higher than the predetermined threshold to a value equal to or lower than the threshold, the combustion promotion control is terminated and the carbon-containing gas is removed. The value of the amount of the suspended fine particles may be initialized.

In this way, even if the estimated amount of fine particles deposited on the catalyst includes an error, the error is reset every time all the fine particles deposited on the exhaust gas purifying catalyst are burned. As a result, it is possible to improve the accuracy of estimating the accumulation amount, which is preferable.

Alternatively, in the exhaust gas purifying apparatus, the estimated accumulation amount is corrected according to the detected temperature increase amount, and whether the combustion promotion control is started based on the corrected accumulation amount is determined. May be determined.

That is, if the amount of carbon-containing suspended particulates deposited on the exhaust gas purifying catalyst is small, the amount of temperature rise when the exhaust gas having the lean air-fuel ratio is supplied is small.
If the amount of the deposited fine particles is large, the amount of temperature rise becomes large. From this, it is preferable to detect the amount of temperature rise of the catalyst and correct the estimated value of the accumulation amount according to the detected value, since it becomes possible to estimate more appropriately.

In such an exhaust gas purifying apparatus, the exhaust gas having a stoichiometric air-fuel ratio or an rich air-fuel ratio is supplied to the exhaust gas purifying catalyst, and the air-fuel ratio of the exhaust gas is intermittently switched to a lean air-fuel ratio. The estimated amount of accumulated fine particles may be corrected by detecting the amount of temperature rise of the exhaust gas purification catalyst in synchronization with the switching.

When exhaust gas having a lean air-fuel ratio is intermittently supplied, fine particles deposited on the catalyst also intermittently burn.
The catalyst temperature shows a peak-like change, that is, a decrease in temperature immediately after the temperature is once increased. If a peak appears in the catalyst temperature in this way, it is possible to easily detect the amount of temperature rise due to the supply of the exhaust gas having the lean air-fuel ratio. It is preferable that the detection of the amount of temperature rise is facilitated because the amount of accumulated fine particles can be easily corrected.

In the exhaust gas purifying apparatus of the present invention described above, the following catalyst may be used as the exhaust gas purifying catalyst. That is, in the exhaust gas with a lean air-fuel ratio, oxygen in the exhaust gas is stored together with nitrogen oxides, and in the exhaust gas with a rich air-fuel ratio or a stoichiometric air-fuel ratio, the stored oxygen is released as active oxygen. Accordingly, a catalyst for burning the collected carbon-containing suspended fine particles may be used.

Such exhaust gas purifying catalysts include, in addition to the noble metals belonging to the platinum group, alkali metals, alkaline earth metals,
The catalyst can support at least one of a rare earth element and a transition metal.

Such an exhaust gas purifying catalyst purifies nitrogen oxides in the exhaust gas and emits active oxygen, so that the carbon-containing suspended fine particles trapped on the catalyst can be burned. As a result, the carbon-containing suspended fine particles and the nitrogen oxides can be simultaneously purified, which is preferable.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to more clearly explain the operation and effect of the present invention, embodiments of the present invention will be described in the following order. A. First embodiment: A-1. Device configuration: A-2. Overview of engine control: A-3. Catalyst regeneration treatment: B. Second embodiment: B-1. Device configuration: B-2. Catalyst regeneration treatment: B-3. Modification:

A. First Embodiment An embodiment in which the exhaust gas purifying device of the present invention is applied to a diesel engine will be described below. Of course, the present invention is not limited to the diesel engine, and can be applied to other internal combustion engines such as a gasoline engine in which fuel is directly injected into a cylinder. In addition, the present invention can be applied to all types of internal combustion engines such as those mounted on a vehicle or a ship, or those for stationary installation.

A-1. Apparatus Configuration: FIG. 1 is an explanatory diagram showing a schematic configuration of a diesel engine 10 equipped with the exhaust gas purifying apparatus of the first embodiment. Diesel engine 1
0 is a so-called four-cylinder engine, # 1 to # 4
Has four combustion chambers. Each combustion chamber has an intake pipe 12
When the fuel is injected from the fuel injection valve 14 provided in each combustion chamber, the air and the fuel burn in the combustion chamber, and the exhaust gas is discharged from the exhaust pipe 16.

A supercharger 20 is provided in the exhaust pipe 16. The supercharger 20 includes a turbine 21 provided in the exhaust pipe 16, a compressor 22 provided in the intake pipe 12, and a shaft 23 connecting the turbine 21 and the compressor 22. When the exhaust gas discharged from the combustion chamber rotates the turbine 21 of the supercharger 20, the compressor 22 rotates via the shaft 23, compresses the air, and supplies the air to each combustion chamber. The supercharger 20 of the present embodiment
Is provided with an actuator 70, and the turbine 2
It is possible to change the opening area (hereinafter, referred to as turbine opening area) of a portion where the exhaust gas flows into the exhaust gas inlet 1. By appropriately controlling the turbine opening area according to the exhaust gas flow rate, the efficiency of the supercharger 20 can be improved.

An air cleaner 26 is provided upstream of the compressor 22. The compressor 22 compresses air taken from the air cleaner 26 and supplies the compressed air to the combustion chamber. Since the temperature of the air rises when compressed by the compressor 22, an intercooler 24 for cooling the air is provided downstream of the compressor 22, and the compressed air is cooled by the intercooler 24 before being supplied to the combustion chamber. It is also possible.

The exhaust pipe 16 has an electric throttle valve 2.
8 are provided. The electric throttle valve 28 is normally in a fully open state. However, when it is necessary to increase the temperature of the exhaust gas or to control the air-fuel ratio of the exhaust gas, the electric throttle valve 28 is controlled under the control of the engine control ECU 30. The opening is controlled.

The exhaust pipe 16 and the intake pipe 12 are connected to the EGR passage 6
0, and a part of the exhaust gas can be introduced into the intake pipe 12. The flow rate of the exhaust gas (EGR gas) introduced into the intake pipe 12 can be controlled by adjusting the opening of an EGR valve 62 provided in the EGR passage 60. High-temperature EGR gas is introduced into the intake pipe 12,
In order to prevent the temperature of the air supplied into the combustion chamber from rising, the EGR cooler 64 provided in the EGR passage 60
After the GR gas is cooled, it can be supplied into the intake pipe 12.

Fuel supply pump 18 and fuel injection valve 14
Injects an appropriate amount of fuel into the combustion chamber at an appropriate timing under the control of the engine control ECU 30.

The engine control ECU 30 includes a CPU,
A RAM, a ROM, an A / D converter, a D / A converter, a timer, and the like are connected to each other via a bus so that data can be exchanged therebetween. Such an engine control E
The CU 30 determines the engine speed Ne and the accelerator opening θ
The engine operating conditions such as ac are detected, and the fuel supply pump 18, the fuel injection valve 14, the EGR
The valve 62, the throttle valve 28, the actuator 70 of the supercharger 20, and the like are appropriately controlled.

In the diesel engine 10 of the present embodiment, an exhaust gas purifying catalyst 100 described later is provided in the exhaust pipe 16 and can purify carbon-containing suspended particulates and the like contained in the exhaust gas. Exhaust gas purification catalyst 100
A pressure sensor 82 and an exhaust temperature sensor 86 are provided in the exhaust pipe 16 on the upstream side, and a pressure sensor 84 and an exhaust temperature sensor 88 are provided on the downstream side. Further, an air-fuel ratio sensor 80 is provided in the exhaust pipe 16 so that the air-fuel ratio of the exhaust gas can be detected.
Although FIG. 1 shows the case where the exhaust gas purifying catalyst 100 is provided on the downstream side of the supercharger 20, it is not always necessary to provide the exhaust gas purification catalyst 100 on the downstream side of the supercharger. I do not care.

FIG. 2 is an explanatory diagram showing the structure of the exhaust gas purifying catalyst 100. As shown in FIG. FIG. 2A is a front view of the exhaust gas purifying catalyst 100 viewed from the side where the exhaust gas flows.
FIG. 2B is a side sectional view. As shown in the figure, the exhaust gas purifying catalyst 100 is a cordierite ceramic filter having a so-called honeycomb structure, and a platinum-based noble metal catalyst (for example, platinum Pt, palladium (A catalyst containing Pd, rhodium Rh, or the like as an active element). Inside the honeycomb structure, there are a number of passages 102 through which exhaust gas passes.
Are formed at the upstream or downstream ends of these passages, as shown in the figure. In FIG. 2, the seal 104 is shown with hatching.

When the exhaust gas flows from the left side in FIG. 2B, the exhaust gas flows into the exhaust gas purifying catalyst 100 from the passage 102 where the seal 104 is not provided on the upstream side. However, since the downstream side of the passage is closed by the stopper 104, as shown by an arrow in FIG. Go to 102. Cordierite has a porous structure formed inside when fired, and the exhaust gas
When passing through the porous structure in 06, carbon-containing suspended particulates and the like in the exhaust gas are collected. If the exhaust gas temperature reaches a certain temperature, the captured fine particles can be burned by the action of the supported noble metal catalyst.

A-2. Overview of Engine Control: FIG. 3 is a flowchart showing an overview of an engine control routine performed by the engine control ECU 30. In this control routine, the power is turned “ON” when a start key is inserted into the engine.
It starts when the state is reached.

When it is detected that the key inserted into the engine has been turned to the starting position, the engine control ECU 30
Starts the engine start control (step S10). In this process, the engine is started by injecting fuel at appropriate timing while cranking the engine with the starter motor. When starting the engine, the intake air temperature and the engine water temperature are detected, and if the temperature is so low that it is difficult to start the engine, the intake air and the combustion chamber are appropriately heated by a heater. When the injected fuel burns in the combustion chamber, a large torque is generated and the engine rotation speed increases. The engine control ECU 30 detects that the engine rotation speed has reached a predetermined rotation speed and performs engine start control. To end. In this embodiment, the engine rotation speed is detected from the output of a crank angle sensor 32 provided at the tip of the crankshaft.

When the engine start control is completed, an engine operating condition is detected (step S20). The main parameters that define the operating conditions of the engine are the engine rotation speed Ne and the accelerator opening θac, and other auxiliary parameters such as intake air temperature, engine cooling water temperature, fuel temperature, intake pressure, etc. In step S20, these parameters are detected. The engine rotation speed Ne is detected by a crank angle sensor 32, and the accelerator opening θac is detected by an accelerator opening sensor 34 mounted on an accelerator pedal.

When the operating condition of the engine is detected, a process for setting the control mode of the engine is performed according to the detected operating condition (step S30). As will be described in detail later,
In the diesel engine 10 of the present embodiment, when the clogging of the exhaust gas purification catalyst 100 is detected during operation, the control state of the engine is switched according to a predetermined procedure.
It is possible to burn the carbon-containing suspended particulates deposited on the catalyst. Such an operation is performed by performing various controls such as a fuel injection control and an EGR control described later in accordance with the control mode set in step S30.

The control mode is set by the engine control EC
This is performed by setting data indicating the control state at a predetermined address of the RAM incorporated in U30. FIG. 4 is an explanatory diagram conceptually showing address data indicating such a control state. As shown in FIG. 4A, one byte (8 bits) of memory is allocated to an address, and each bit indicates a control mode.

FIG. 4B is an explanatory diagram showing the correspondence between each bit and the control mode. The first bit (the most significant bit) is a bit corresponding to the flag Fn. The fact that the flag Fn is “ON”, that is, in a high voltage state, indicates that the engine is under normal operation control. The next bit is a bit corresponding to the flag Fa,
The fact that this flag Fa is “ON” indicates that the catalyst regeneration control is being performed. In other words, this indicates that the operation is performed while switching the control state according to a predetermined procedure in order to burn the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst 100. Normally, the flag Fa is "O
When "N", the flag Fn is switched to "OFF", that is, the low voltage state.

The three bits following the flag Fa are bits for a spare flag. The three bits remaining on the lower side are flags F1, F2, F3 indicating the control state during the catalyst regeneration control.
Is the bit corresponding to The fact that the flag F1 is in the “ON” state indicates that the catalyst temperature is being raised in order to burn the carbon-containing suspended fine particles deposited on the exhaust gas purification catalyst 100, and the flag F2 is “ON”. The state indicates that the carbon-containing suspended particulates are being combusted after the temperature rise of the catalyst. The flag F3 is a flag for controlling the amount of oxygen that can be supplied to the catalyst during the combustion of the carbon-containing suspended particulates. The meaning of the flag F3 and the process for setting each flag will be described later.

When the control mode is set in this way, fuel injection control is performed based on the control mode (step S).
40). The fuel injection control is a control for injecting an appropriate amount of fuel at an appropriate timing according to the operating conditions of the engine. The outline of the control is as follows. First,
The basic fuel injection amount and fuel injection timing are calculated based on the engine rotation speed Ne and the accelerator opening θac. Next, this value is corrected taking into account the effects of the intake air temperature, engine cooling water temperature, fuel temperature, etc.
An optimum injection amount and an optimum injection timing according to the engine operating conditions are calculated. In order to inject fuel at the injection amount and timing calculated in this way, the fuel supply pump 18
And the fuel injection valve 14 are controlled.

More specifically, the basic fuel injection amount and the basic fuel injection timing are used as a map for the engine speed Ne and the accelerator opening θac as the map for engine control.
It is stored in a ROM built in the CU 30. Also,
Various correction coefficients such as the intake air temperature and the engine cooling water temperature are also stored as a map in the ROM in the engine control ECU 30. These maps are provided in two sets: a map for normal operation control of the engine and a map for catalyst regeneration control. The engine control ECU 30 acquires the basic fuel injection amount, injection timing, and various correction coefficients by referring to an appropriate map according to the control mode. The optimum fuel injection amount and fuel injection timing are calculated based on the obtained fuel injection amount, injection timing, and various correction coefficients, and the fuel supply pump 18 and the fuel injection valve 14 are controlled.

When the fuel injection control is completed, the EGR
The control is started (step S50). EGR is Ex
Abbreviation for "haus Gas Recirculation", which refers to intentionally returning a part of the exhaust gas into the intake pipe. Under normal operating conditions, if a part of the exhaust gas is recirculated to the intake air, the combustion speed in the combustion chamber will decrease, so the maximum combustion temperature will decrease and the concentration of nitrogen oxides in the exhaust gas will decrease. it can. On the other hand, since combustion tends to be unstable when the amount of exhaust gas recirculation increases, it is necessary to control the amount of exhaust gas recirculation to be optimal according to the operating conditions of the engine. Such control is performed in the EGR control.

When the fuel injection control is completed, subsequently, a supercharging pressure control is performed (step S60). As described above with reference to FIG. 1, the supercharger 20 is provided in the diesel engine 10, and a large amount of air is supplied to the combustion chamber by increasing the pressure in the intake pipe 12 above the atmospheric pressure. be able to. As described above, increasing the pressure in the intake pipe higher than the atmospheric pressure is referred to as “supercharging”, and a pressure increase from the intake pipe before the supercharging is referred to as “supercharging pressure”. Increasing the boost pressure will increase the amount of oxygen available for combustion,
The effect of improving the maximum output of the engine or reducing the amount of emission of carbon-containing suspended particulates such as soot even under a constant output condition can be obtained. In the diesel engine 10 of the present embodiment, the opening area of the portion where the exhaust gas flows into the turbine 21 of the supercharger is controlled so that an appropriate supercharging pressure according to the operating conditions of the engine can be obtained. .

After the completion of the supercharging pressure control, a process for estimating the amount of accumulated fine particles is performed (step S70). As described above with reference to FIG. 2, the exhaust gas purifying catalyst 100 of this embodiment is
Can collect the carbon-containing suspended particulates in the exhaust gas and, if a certain catalyst temperature is maintained, continuously burn the collected particulates by the action of the noble metal catalyst. However, when the diesel engine 10 is operated for a long time under extremely low load conditions, the temperature of the catalyst decreases, and the carbon-containing suspended particulates collected cannot be burned. Gradually accumulates. When the amount of accumulated fine particles increases, the function of the catalyst may be reduced, or the passage resistance of the exhaust gas purification catalyst 100 may be increased, which may result in a decrease in engine performance. Therefore, in the diesel engine 10 of the present embodiment, the amount of accumulated particulates is estimated, and when the accumulated amount exceeds a predetermined amount, a catalyst regeneration process described later is performed. The deposition amount of the fine particles can be estimated by applying various methods. In the first embodiment, however, the output amount of the pressure sensor 82 provided on the upstream side of the exhaust gas purification catalyst 100 and the output of the pressure sensor 84 provided on the downstream side are determined. In addition, the amount of deposition is estimated by detecting the pressure difference before and after the catalyst.

Incidentally, instead of estimating the amount of fine particles deposited on the catalyst from the pressure difference between before and after the catalyst by the pressure sensors 82 and 84, the following method may be used. For example, a pressure switch that closes the contact due to the pressure difference before and after the catalyst is provided,
By detecting the opening and closing of the contact, it may be detected that the accumulation amount of the fine particles is equal to or larger than a predetermined value or equal to or smaller than the predetermined value. Alternatively, a pressure sensor may be provided only upstream of the catalyst, and the pressure upstream of the catalyst when the engine is operated under predetermined conditions may be detected to estimate the deposition amount of the carbon-containing suspended particulates.

After the end of the particulate matter amount estimating process as described above, it is detected whether or not the starting key inserted into the engine has been returned to the "off" position (step S80). If not returned to step S20, a series of subsequent processing is repeated.
The engine control ECU 30 repeats the above-described processing until the start key is returned to the “off” position. As a result, the engine is always optimally controlled according to changes in the operating conditions.

The diesel engine 1 of the first embodiment
In the case of 0, when it is estimated that a large amount of carbon-containing suspended particulates are deposited on the exhaust gas purification catalyst 100, a catalyst regeneration process described later is performed to forcibly burn the deposited particulates. By doing so, the exhaust gas purification catalyst 1
No. 00 function, and it is possible to appropriately purify the carbon-containing suspended particulates in the exhaust gas.

A-3. Catalyst regeneration treatment: As described above,
The diesel engine 10 according to the present embodiment is controlled in accordance with the settings of the data indicating the control mode (see FIG. 4), and even when the amount of accumulated fine particles on the exhaust gas purification catalyst 100 increases, the control mode is not changed. A catalyst regeneration process is performed according to the settings. Therefore, first, a process of setting each bit indicating the control mode will be described.

FIG. 6 is a flowchart showing the flow of processing for setting the control mode in this embodiment. Such processing is performed by the engine control EC of the diesel engine 10.
It is executed by the CPU built in U30. Less than,
This will be described with reference to FIG.

When the control mode setting process is started, first, it is determined whether or not the operating condition of the engine is in a catalyst regeneration controllable region (step S100). As described below,
Since the catalyst regeneration control is performed by raising the temperature of the exhaust gas purification catalyst 100 to a predetermined temperature or higher, the catalyst regeneration control is not performed under conditions where the engine load is low and it is difficult to raise the temperature. FIG.
The horizontal axis represents the engine speed Ne, and the vertical axis represents the accelerator opening θac.
FIG. 5 is an explanatory diagram conceptually showing a region where catalyst regeneration control is not performed. A portion indicated by a broken line in the drawing indicates an operation region (regeneration prohibition region) Linh in which the catalyst regeneration control is not performed because it is difficult to raise the temperature of the catalyst. In step S100, it is confirmed that the operating conditions of the engine are not in the regeneration prohibited area Linh.

If it is determined that the operating condition of the engine is in the regeneration prohibited area (step S100: no),
The flag Fn indicating that the normal operation control is to be performed is set to “ON” (step S102), the control mode setting process ends, and the process returns to the above-described engine control routine. When the flag Fn is set to “ON” in this manner, various controls such as fuel injection or EGR control and supercharging pressure control are performed in accordance with the normal operation control.

When it is determined that the operating condition of the engine is in the reproducible region (step S100: yes), the estimated amount of the fine particles deposited on the exhaust gas purifying catalyst 100 becomes
It is determined whether or not the value is greater than a first threshold value th1 (step S104). As the estimated amount of fine particles, the value most recently estimated in the fine particle accumulation amount estimation process (step S70 in FIG. 3) in the engine control routine is used. If it is determined that fine particles having the first threshold value th1 or more are deposited on the catalyst (step S104: yes),
The flag Fa indicating that the catalyst regeneration control is to be performed is set to “ON”.

Subsequently, it is determined whether or not the flag Fa indicating that the catalyst regeneration control is being performed is "ON" (step S108). If the flag Fa is "ON", the flag Fn is set to "OFF". (Step S110).
For reasons described later, when both the flag Fn and the flag Fa are “ON”, the setting of the flag Fn has priority. Therefore, the flag F is set to perform the catalyst regeneration control.
When a is set to “ON”, the flag Fn is set to “OFF”
It is set to.

As will be described in detail later, when it is determined that the regeneration of the catalyst is completed and the amount of accumulated fine particles is sufficiently reduced, the flag Fa is set to "OFF". Therefore, in step S108, the flag Fa is set to “OF”.
F ”(step S108: no),
Since it is considered that the accumulated amount of the fine particles has not yet reached the predetermined threshold since the catalyst regeneration process was completed first, the flag Fn indicating that the normal operation control is to be performed is set to "ON" (step S102). Then, the control mode setting process ends.

When the flag Fn is set to "OFF" while the flag Fa is "ON", it is determined whether the catalyst temperature is equal to or higher than the threshold temperature (step S112). That is, in order to burn the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst 100, it is necessary that the catalyst temperature is at least a certain level or higher, and the higher the catalyst temperature, the more quickly the deposited particulates are burned. First, it is determined whether or not the temperature of the exhaust gas purification catalyst 100 is at a predetermined threshold temperature. In this embodiment, the catalyst temperature is estimated from the exhaust gas temperature detected by the temperature sensor 88 provided downstream of the exhaust gas purification catalyst 100. Of course, a temperature sensor can be attached to the catalyst, or the catalyst temperature can be directly measured using an optical method based on blackbody radiation, or a so-called metal having a honeycomb structure formed using a metal plate. In the case of a catalyst, the catalyst temperature can be measured from the electrical resistance value of the honeycomb.

If it is determined that the catalyst temperature is equal to or lower than the predetermined threshold temperature (step S112: no), a flag F1 indicating that control for raising the temperature of the exhaust gas purifying catalyst 100 is performed.
Is set to "ON", and the control mode setting process ends.
When the flag F1 is set to “ON”, the corresponding maps are read out and controlled in each of the combustion injection control, the EGR control, and the supercharging pressure control in the engine control routine. The temperature of 100 gradually rises.

Various methods are known as a method for raising the temperature of the exhaust gas purification catalyst 100, and any of these methods can be applied.
The exhaust gas temperature is raised by increasing the R gas amount from the normal operation state, thereby raising the catalyst temperature. Normally, in a diesel engine, when the amount of EGR gas is increased, the exhaust gas temperature increases accordingly. This is for the following reason. When the fuel supplied to the combustion chamber is burned with air, part of the heat of combustion is converted into mechanical work to run the engine, and the remaining heat of combustion is used to raise the temperature of cooling water and exhaust gas . Here, if high-temperature exhaust gas is recirculated to the intake air, the temperature of the intake air supplied to the combustion chamber rises, and accordingly, the temperature of the exhaust gas also increases accordingly. If the high-temperature exhaust gas is recirculated to the intake air, the exhaust gas temperature further rises. That is, EGR
To return a part of the exhaust gas to the intake air, so that a part of the combustion heat that is discarded together with the exhaust gas if the EGR is not performed is gradually accumulated in a loop that returns from the exhaust gas to the intake gas and is exhausted again. As a result, the exhaust gas temperature rises. For this reason, when the amount of EGR gas is increased, the temperature of the exhaust gas increases accordingly.

In this embodiment, the exhaust gas temperature is raised by increasing the amount of EGR gas. However, the present invention is not limited to this, and another method may be used. For example, the electric throttle valve 28 may be closed, and the exhaust gas temperature may be increased by reducing the amount of air taken into the combustion chamber, or the fuel injection timing may be delayed, or the piston may be lowered. The exhaust gas temperature may be increased by injecting additional fuel throughout the expansion stroke. Of course, it is also possible to increase the catalyst temperature more quickly by appropriately combining these various methods.

The catalyst temperature raising control is performed in this way, and when it is determined that the catalyst temperature has reached the predetermined threshold temperature (step S
112: yes), and after returning the flag F1 indicating that the catalyst temperature increase control is being performed to “OFF”, sets the flag F2 to “O”.
N "(step S116). As described above, the flag F2 is a flag indicating that control for burning the carbon-containing suspended particulates deposited on the catalyst (hereinafter, referred to as deposited particulate combustion control) is performed. When both the flag F1 and the flag F2 are set to “ON”, the setting of the flag F1 has priority. From this, when the catalyst temperature reaches the threshold temperature, the flag F1 is once returned to "OFF", and then the flag F2 is set to "ON" to perform the deposited particulate combustion control.

After the flag F2 is set to "ON", the flag F3 is set (step S11).
8). The flag F3 is a flag for performing control by limiting the amount of oxygen supplied to the catalyst during the combustion control of accumulated particulates. When the flag F3 is "OFF", the catalyst is in an oxygen-deficient state. When the flag F3 is "ON", control is performed so that excessive oxygen is supplied to the catalyst. In the present embodiment, the initial state of the flag F3 is set to “OFF”, and the timer periodically sets “O” for a predetermined period.
N ". Thus, the exhaust gas purifying catalyst 100
After the temperature is increased to a predetermined temperature or more, the supply state of oxygen to the catalyst is controllably limited according to the setting of the flag F3, so that the carbon-containing suspended particulates deposited on the catalyst can be appropriately burned. It becomes possible. The control for burning the accumulated fine particles (the accumulation fine particle combustion control) will be described later with a specific example.

Next, it is determined whether or not the combustion of the carbon-containing suspended particulates deposited on the exhaust gas purifying catalyst 100 has been completed (step S120). This determination is made based on the temperature difference between the temperature sensors 86 and 88 provided before and after the exhaust gas purification catalyst 100. That is, while the carbon-containing suspended particulates are burning on the catalyst, the exhaust gas temperature rises due to the heat of combustion, so that the exhaust gas temperature downstream of the catalyst becomes higher than the exhaust gas temperature upstream of the catalyst. From this, it is determined that the temperature difference between before and after the catalyst has become equal to or less than the predetermined temperature, and it is determined that the combustion of the accumulated suspended particulates has been completed.

In this embodiment, the completion of the combustion of the accumulated suspended particulates is determined based on the difference between the temperatures of the exhaust gas before and after the exhaust gas purifying catalyst 100. However, the determination may be made using other methods. For example, the pressure difference between before and after the catalyst may be detected, and when the pressure difference becomes smaller than the second threshold th2, it may be determined that the combustion of the accumulated suspended particulates has been completed.

If it is determined in step S120 that the combustion of the accumulated suspended particulates has not been completed, (n
o), the control mode setting process is terminated, and the process returns to the engine control routine shown in FIG. If it is determined that the combustion of the suspended particulates has been completed (Step S120: y
es), the flag Fn is set to “O” to return to the normal operation control.
N "and various flags Fa,
F1, F2 and F3 are set to "OFF" (step S
122), and ends the control mode setting process.

In the engine control routine shown in FIG.
Based on the control mode set as described above, various controls such as fuel injection control, EGR control, and supercharging pressure control are performed. As a result, the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst 100 are removed. The catalyst can be appropriately burned during the operation of the engine, and the catalyst regeneration processing can be performed.

FIG. 8 is an explanatory diagram collectively showing the correspondence between the state of each flag set in the control mode setting process and the control state of the engine. As illustrated, when the flag Fn is set to “ON”, the engine is controlled to the normal operation state regardless of the setting states of the other flags. In the figure, "-" indicates "ON",
"OFF" indicates that any state is acceptable.

When the flag Fa is "ON", it indicates that the engine control is under the catalyst regeneration control. This corresponds to a state where it is determined that carbon-containing suspended particulates equal to or greater than the first threshold are deposited on the catalyst. When both the flag Fa and the flag Fn are “ON”, the engine operating condition has entered the regeneration prohibition region Linh, so that it is determined to be “no” in step S100 in FIG. 6 and the catalyst regeneration control is interrupted. Is shown. As described above, when both the flag Fn and the flag Fa are turned “ON”, the setting of the flag Fn is prioritized. Therefore, when the engine operating condition enters the regeneration inhibition area Linh during the catalyst regeneration control,
The control state of the engine is immediately switched to the normal operation state, and the catalyst regeneration control can be restarted immediately after the engine departs from the regeneration inhibition area Linh.

When the flag Fn is set to "OFF" and the flags Fa and F1 are all set to "ON", it indicates that the engine control is under the catalyst temperature increase control. Further, the flag Fn and the flag F1 are “OFF”
And both the flag Fa and the flag F2 are "O
N "indicates that the catalyst temperature has risen to a predetermined temperature during the catalyst regeneration control, and the deposited particulate combustion control is being performed. The setting state of the flag F3 has a meaning for the first time during the combustion control of accumulated particulates.
The flag F3 indicates that the engine is controlled so that the exhaust gas air-fuel ratio supplied to the catalyst becomes the stoichiometric air-fuel ratio.
"N" indicates that the engine is controlled so that the exhaust gas air-fuel ratio becomes lean.

The air-fuel ratio of the exhaust gas is an index indicating the balance between unburned fuel HC, carbon monoxide CO, and oxygen contained in the exhaust gas. H contained in exhaust gas
When the gas composition is such that oxygen remains when C and CO are reacted with oxygen, the exhaust gas air-fuel ratio is said to be lean. Conversely, lack of oxygen and H
If the gas composition has excess C or CO, it is said that "the exhaust gas composition is rich." Further, when the gas composition contains oxygen just enough to burn HC and CO, it is said that "the exhaust gas air-fuel ratio is at the stoichiometric air-fuel ratio." The stoichiometric air-fuel ratio is sometimes called stoichio. The exhaust gas air-fuel ratio is
Strictly, it depends on the properties of the fuel, but takes a value near "14.6 to 14.9" when the composition of the exhaust gas is stoichiometric. Further, the value of the exhaust gas air-fuel ratio increases as the composition of the exhaust gas becomes leaner, and the value of the exhaust gas air-fuel ratio decreases as the composition of the exhaust gas becomes richer.

FIG. 9 shows a diesel engine 1 of this embodiment.
Numeral 0 is an explanatory diagram showing a state in which the catalyst regeneration control of the exhaust gas purification catalyst 100, in particular, the control of combustion of deposited particulates is performed from the catalyst temperature increase control. The vertical axis in the figure shows the flags F1, F
2, the setting state of F3, the air-fuel ratio of the exhaust gas flowing into the exhaust gas purification catalyst 100, and the exhaust gas temperature before and after the exhaust gas purification catalyst 100 are shown.

As shown in FIG. 9, when the flag F1 is set to "ON" and the catalyst temperature increase control is performed, the temperature of the exhaust gas flowing into the exhaust gas purification catalyst 100 (shown by a broken line in the figure) Gradually rises, and accordingly, the temperature of the exhaust gas flowing out of the catalyst (indicated by a solid line in the figure) also rises. Next, at time t1, the exhaust gas temperature on the downstream side of the catalyst reaches the threshold temperature Tth, and the flag F1 indicating the catalyst temperature increase control is switched from "ON" to "OFF".
The flag F2 is switched from “OFF” to “ON”, and the control of burning deposited particulates is started. In this embodiment, the value of the threshold temperature Tth is set in a range from 400 ° C. to 500 ° C. Of course, the threshold temperature Tth is not limited to this range. For example, if you set a higher temperature,
The combustion on the catalyst is promoted, and the deposited carbon-containing particles can be burned more quickly. If the temperature is set to a lower temperature, the time required for the catalyst temperature rise control is shortened, and the combustion control of deposited particulates can be started more quickly. Needless to say, the threshold temperature is set to an appropriate value in accordance with the oxidation activity of the supported catalyst.

When the deposited particulate combustion control is started in this way, the exhaust gas air-fuel ratio is controlled according to the setting of the flag F3 so as to be stoichiometric. As described above, the flag F3 is "OFF" meaning stoichiometric in the initial state.
Is set to In this embodiment, the exhaust gas air-fuel ratio is controlled to be stoichiometric by increasing the EGR gas amount further than during the catalyst temperature increase control and increasing the fuel injection amount. The injection timing is also changed so that the engine output does not fluctuate due to an increase in the fuel injection amount. Of course, only one of the EGR gas amount and the fuel injection amount may be increased to set the exhaust gas air-fuel ratio to stoichiometric. As a result of controlling the engine in this way, the exhaust gas air-fuel ratio flowing into the exhaust gas purifying catalyst 100 quickly switches from the lean state during the catalyst temperature increase control to the stoichiometric state.

During the catalyst temperature increase control, the exhaust gas purifying catalyst 10
Although the temperature at the catalyst outlet side is slightly higher than the temperature of the exhaust gas flowing into 0, when the exhaust gas air-fuel ratio is switched to stoichiometric, the exhaust gas temperature at the inlet side of the catalyst and the exhaust gas temperature at the outlet side Is smaller. This is because the exhaust gas air-fuel ratio is lean during the catalyst temperature increase control, that is, because excess oxygen is present in the exhaust gas, the carbon-containing suspended particulates deposited on the catalyst partially burn, but the accumulated particulate combustion This is because, when the control is started and the exhaust gas air-fuel ratio is switched to stoichiometric, the amount of oxygen becomes insufficient, and the combustion of fine particles deposited on the catalyst is suppressed.

Flag F indicating start of deposited particulate combustion control
2 is turned “ON” and the engine control ECU 3
A built-in timer is set to 0, and an interrupt is periodically generated twice after the time ts elapses and further after the time tL elapses. Each time an interrupt from the timer is received, the CPU of the engine control ECU 30 alternately switches the setting of the flag F3 from “OFF” to “ON” or from “ON” to “OFF”. In step S118 of FIG. 6 described above, the process of periodically switching the setting of the flag F3 is performed. In the example shown in FIG.
At time t2, the flag F3 is switched from "OFF" to "ON" for the first time, and after maintaining the "ON" state for the time tL, returns to the "OFF" state again. Hereinafter, the flag F
3 is the period of time ts and time tL,
“OFF” and “ON” are repeated. In this embodiment, the time ts is 15 seconds and the time tl is 3 seconds.
These times may be set to appropriate values experimentally obtained.

According to the movement of the flag F3, the air-fuel ratio of the exhaust gas flowing into the exhaust gas purifying catalyst 100 is periodically switched between stoichiometric and lean. If the exhaust gas air-fuel ratio is made lean while the temperature of the exhaust gas purification catalyst 100 is high, the carbon-containing suspended particulates deposited on the catalyst and excess oxygen in the exhaust gas are burned by the action of the noble metal catalyst. To rapidly raise the catalyst temperature. Corresponding to this, the exhaust gas temperature at the catalyst outlet rises sharply. However, after the elapse of the time tL, the air-fuel ratio of the exhaust gas is returned to the stoichiometric ratio again, and the supply of excess oxygen to the catalyst is interrupted, so that the combustion of the accumulated carbon-containing suspended particulates cannot be continued. Correspondingly, the exhaust gas temperature at the catalyst outlet gradually decreases to the exhaust gas temperature at the inlet. Thereafter, at time t3, when the exhaust gas air-fuel ratio becomes lean again, the combustion of the carbon-containing suspended particulates deposited on the catalyst is started. When the exhaust gas air-fuel ratio switches to stoichiometry after the lapse of time tL, oxygen is removed. Combustion ends promptly due to lack.

As described above, during the accumulated particulate combustion control, the air-fuel ratio of the exhaust gas periodically repeats stoichiometric and lean according to the setting of the flag F3, and the carbon-containing suspended particulate deposited on the catalyst is slightly reduced. Burn each time. As the carbon-containing suspended particulates burn in this way and the amount of deposited particulates decreases, the temperature difference between the exhaust gas temperature before the catalyst and the exhaust gas temperature after the catalyst gradually decreases accordingly. . Alternatively, the exhaust gas pressure difference before and after the catalyst gradually decreases. When the temperature difference or the pressure difference becomes equal to or less than the predetermined threshold value, it is determined that all the carbon-containing suspended particulates deposited on the catalyst have burned, and various flags Fa, F1, F2, and F3 relating to the catalyst regeneration control are set to "OFF" And set the flag Fn indicating the normal operation control to “O
N ". Thus, the catalyst regeneration control is terminated, and the control returns to the normal operation control.

As described above, in the diesel engine 10 of this embodiment, when it is determined that a predetermined amount or more of the carbon-containing suspended particulates is deposited on the exhaust gas purification catalyst 100, the exhaust gas air-fuel ratio flowing into the catalyst is determined. Is controlled so that the exhaust gas air-fuel ratio becomes lean for a short time. With this configuration, the carbon-containing suspended particulates deposited on the catalyst can be burned only during the period in which the exhaust gas air-fuel ratio is lean and excess oxygen is supplied. Therefore, even if a large amount of carbon-containing suspended particulates are deposited on the catalyst, the particulates do not burn at once, and the catalyst temperature does not rise abnormally, and the catalyst does not deteriorate.

In the catalyst regeneration control described above,
The description has been made assuming that the exhaust gas air-fuel ratio is controlled to be stoichiometric while the flag F3 is “OFF”. Of course, the control may be performed so as to be slightly rich instead of stoichiometric. If the exhaust gas air-fuel ratio is controlled to be slightly rich during the period in which the flag F3 is “OFF”, even if the control air-fuel ratio slightly shifts to the lean side for some reason, the accumulation and floating on the catalyst may occur. The combustion of the fine particles can be reliably terminated. On the other hand, stoichiometric control is preferable because the amount of fuel injection that increases to make the air-fuel ratio stoichiometric can be minimized.

In the above description, the flag F3 repeats "ON" and "OFF" with the passage of time. However, the present invention is not limited to this, and the number of engine cycles is counted and the flag F3 is switched. No problem. For example, if the cycle is performed a predetermined number of M times while the flag F3 is "OFF", the flag F3 is turned "ON" for the next N times, and the flag F3 is returned to "OFF" again and the cycle is repeated M times. It may be.

In the above description, the flag F3 is set to "O
It has been described that the engine is operated at the stoichiometric or rich air-fuel ratio when "FF" and the operating air-fuel ratio of the engine is changed to lean when the flag F3 is turned "ON". On the other hand, an air pump may be provided, and air may be supplied to the catalyst from the exhaust pipe 16 upstream of the exhaust gas purification catalyst 100 by the air pump only while the flag F3 is turned “ON”. That is, the flag F
2 becomes “ON” and the deposited catalyst combustion control starts,
The engine is operated at the stoichiometric or rich air-fuel ratio, and air is supplied by the air pump only while the flag F3 is "ON". In this case, there is no need to change the operating air-fuel ratio of the engine with the change of the flag F3. Therefore, there is no possibility that the output will fluctuate due to the control air-fuel ratio, and the control of the engine can be simplified. It is preferable because it is possible.

In the above description, during the catalyst regeneration control, the exhaust gas air-fuel ratio is intermittently kept lean for a short period of time and oxygen is supplied to the exhaust gas purification catalyst 100 little by little to deposit. The carbon-containing fine particles were burned little by little. On the other hand, instead of changing the exhaust gas air-fuel ratio, the air-fuel ratio may be maintained at a slightly lean air-fuel ratio. That is, when the catalyst temperature is raised and the deposited particulate combustion control is started, the exhaust gas air-fuel ratio is controlled to be slightly lean. In this case, although the oxygen is continuously supplied to the exhaust gas purification catalyst, the supply amount per hour is small, and the carbon-containing suspended particulates deposited on the catalyst do not burn rapidly. Therefore, the deposited fine particles can be reliably burned without abnormally increasing the catalyst temperature. In addition, this is preferable because the operating air-fuel ratio of the engine is not changed during the combustion control of deposited particulates, so that the engine output does not change with the change of the air-fuel ratio. On the other hand, in the above-described method in which the exhaust gas air-fuel ratio is periodically set to lean, since the time during which the catalyst becomes lean and oxygen is supplied to the catalyst is short, for example, the lean air-fuel ratio is assumed. Even if the air-fuel ratio slightly deviates from the set air-fuel ratio (for example, about 20), the catalyst temperature is not significantly increased, which is preferable.

B. SECOND EXAMPLE In the first example described above, the deposition amount of the carbon-containing suspended particulates was estimated based on the exhaust pressure difference before and after the exhaust gas purification catalyst. On the other hand, the accumulation amount of the carbon-containing suspended particulates may be estimated from the operation history of the diesel engine 10. Hereinafter, such an exhaust gas purifying apparatus of the second embodiment will be described.

B-1. Apparatus configuration: In the exhaust gas purifying apparatus of the second embodiment, as described below, by periodically changing the air-fuel ratio of the exhaust gas, nitrogen oxides (hereinafter referred to as carbon oxide suspended particles in the exhaust gas) are added. Here, an exhaust gas purification catalyst capable of purifying NOx at the same time is used. Of course, a catalyst that does not purify NOx as used in the first embodiment may be used.

The exhaust gas purifying catalyst 20 used in the second embodiment
0 is different from the catalyst of the first embodiment in that a NOx accumulating agent is further supported. As the NOx accumulating agent, an alkali metal such as potassium K, an alkaline earth metal such as barium Ba, or the like can be used. The exhaust gas purifying catalyst 200 of the second embodiment takes in NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and reduces the taken-in NOx to nitrogen when the air-fuel ratio becomes stoichiometric or rich. Release. Further, by burning the carbon-containing suspended particulates using the active oxygen generated in this process, it is possible to purify the NOx and the carbon-containing suspended particulates in the exhaust gas. Hereinafter, this will be described in detail with reference to FIG.

FIG. 10 is a conceptual diagram showing an enlarged surface of the exhaust gas purifying catalyst 200 of the second embodiment. On the surface of the exhaust gas purification catalyst 200 of the second embodiment, a NOx storage agent 203 such as potassium K or barium Ba and a platinum-based noble metal catalyst 204 such as platinum Pt or palladium Pd are supported. The noble metal catalyst 204 is supported in the form of fine particles having a particle size of 1 μm or less on the NOx accumulating agent 203 in a state of being uniformly distributed.

FIG. 10A shows a case where the exhaust gas air-fuel ratio is lean. The exhaust gas contains NOx generated by combustion. Since NOx is mostly contained in the state of nitric oxide NO, in FIG.
Ox is indicated as nitric oxide NO. Since nitric oxide NO is a polar molecule, NO in exhaust gas is quickly adsorbed on a noble metal catalyst such as platinum Pt. Since the platinum-based noble metal catalyst has a strong oxidation activity, nitric NO nitrate ions NO3 via nitrogen dioxide NO2 ^- it is oxidized to. Nitrate ions NO3 thus generated over a noble metal catalyst ^- is by a phenomenon so-called "spillover", moves to the NOx storage agent 203. The "spillover phenomenon" is a phenomenon in which adsorbed molecules actively move around on a metal catalyst. On the catalyst, noble metal particles such as Pt are dispersed as uniformly as possible. To obtain, it is believed that the entire surface functions as a catalyst. As described above, under the condition where oxygen is excessively present in the exhaust gas, nitric oxide NO is oxidized on the noble metal catalyst, and the NOx accumulating agent 203 is caused by a spillover phenomenon.
Transported and stored in the form of nitrates. It should be noted that all of the nitrogen monoxide NO adsorbed on the noble metal catalyst is necessarily nitrate ions NO3 ^- not necessarily be oxidized to, some of nitrite ion NO2 ^- sometimes stored in the NOx storage agent 203 in the state It is thought to get.

Thus, when nitric oxide NO in the exhaust gas is taken in as nitrate, the NOx accumulating agent 203
Activated oxygen is generated. Since active oxygen has a very high reactivity, the carbon-containing suspended fine particles trapped on the exhaust gas purifying catalyst 200 can be oxidized and converted into carbon dioxide and water.

The mechanism by which active oxygen is released from the NOx accumulating agent 203 when nitric oxide NO is taken in the form of nitrate is considered to be as follows. N
Since the Ox storage agent 203 is heated to a high temperature by the exhaust gas, it is generally considered that the Ox storage agent 203 is combined with carbon dioxide to be in a carbonate state. Nitric oxide NO is NOx storage agent 2
When accumulated in 03 carbonate ions CO3 ^- nitrate ions NO3 ^- replaced by, evicted carbonate ions CO
It is considered that 3 ^- is decomposed into carbon dioxide and active oxygen, and as a result, active oxygen is released.

FIG. 10B shows a case where the exhaust gas air-fuel ratio is rich or stoichiometric. When the exhaust gas air-fuel ratio is stoichiometric or rich, the exhaust gas contains a reducing compound such as a hydrocarbon compound or carbon monoxide CO. Carbon-containing suspended particulates such as soot also act as reducing substances. In FIG. 10B, the hydrocarbon-based compound is represented as HC, and the carbon-containing suspended fine particles such as soot are schematically represented by C representing carbon. As described above, the platinum-based noble metal catalyst has a strong oxidizing activity. Therefore, if oxygen is present in the exhaust gas, these reduced substances can be oxidized and converted into carbon dioxide CO2 or water.

However, when there is not enough oxygen in the exhaust gas to match the reducing substance, as shown in FIG. 10B, the noble metal catalyst 204 removes the nitrate ions stored in the NOx storage agent 203. NO3 ^- decompose, oxidize the reducing substance by using the generated active oxygen. This phenomenon will be described with reference to FIG. NOx storage agent 203 The stored have nitrate ions NO3 ^- moves over a noble metal catalyst 204 by the spillover phenomenon. On noble metal catalyst 204, the nitrate ions NO3 ^- Results electron cloud of localized been attracted by the precious metal catalyst side, nitrate ions N
O3 ^- chemical bond between the nitrogen atom and the oxygen atom is in the state easy cut of. In FIG. 10 (b), the nitrate ion is indicated as “N + 3 · O”, which schematically shows that the bond between the nitrogen atom and the oxygen atom is easily broken. When a reducing substance acts on such a state, the bond between the nitrogen atom and the oxygen atom is broken, and active oxygen is generated. Active oxygen is an extremely reactive substance that reacts quickly with carbon-containing suspended particulates in addition to hydrocarbon compounds and carbon monoxide in exhaust gas, converting them to carbon dioxide, CO2, water, etc. I do. Moreover, nitrate ions NO3 ^- NOx storage agent 203 was discharged as a result of exposure to a high temperature by the exhaust gases to return to the state of the carbonate bonded to the carbon dioxide in the exhaust gas.

As described above, the exhaust gas purifying catalyst 200 of the second embodiment takes in oxygen and NOx as nitrate when the exhaust gas air-fuel ratio is lean, and converts nitrate when the exhaust gas air-fuel ratio is stoichiometric or rich. Decomposes into nitrogen. Further, it is possible to purify the carbon-containing suspended particulates by utilizing the active oxygen generated when purifying NOx.

In the diesel engine 10 according to the second embodiment, the air-fuel ratio of the exhaust gas flowing into the exhaust gas purifying catalyst 200 is controlled periodically or at a predetermined timing even during the normal operation control which is not the above-described catalyst regeneration control. , So that it becomes stoichio (or rich) for a predetermined time,
By controlling the engine, carbon-containing suspended particulates and NOx contained in the exhaust gas are purified.

Various methods can be applied as a method for making the exhaust gas air-fuel ratio stoichiometric or rich. However, during the catalyst regeneration control of the first embodiment, the exhaust gas air-fuel ratio is made stoichiometric or rich. The same method as that used for the above was used. That is, the exhaust gas air-fuel ratio is controlled to be stoichiometric by recirculating a large amount of the EGR gas and increasing the fuel injection amount.

In the exhaust gas purifying apparatus of the second embodiment, the exhaust gas air-fuel ratio is switched during the catalyst regeneration control as in the case of the above-described first embodiment. It is preferable to switch the exhaust gas air-fuel ratio because it becomes possible to purify NOx and carbon-containing suspended particulates in the exhaust gas without complicating the entire configuration.

B-2. Particle Estimation Amount Estimation Process: In the exhaust gas purifying apparatus of the second embodiment, the accumulation amount of the carbon-containing suspended particles accumulated on the exhaust gas purification catalyst 200 is estimated based on the operating conditions of the engine during the engine control routine. (Step S70 in FIG. 3). This makes it possible to appropriately start the catalyst regeneration control.
Hereinafter, the particulate matter accumulation amount estimation processing performed in the engine control routine of the second embodiment will be described.

FIG. 11 is a flowchart showing the flow of the particulate matter accumulation amount estimation processing performed in the engine control routine of the second embodiment. Such processing is performed by the engine control EC.
It is executed by the CPU built in U30.

In the particle accumulation amount estimation processing, first,
Based on the operating conditions of the engine, the amount of suspended carbon-containing particles (the amount of discharged particles Peout) discharged from the diesel engine 10 per unit time is acquired (step S20).
0). Normally, once the operating conditions of the engine are determined, the amount of carbon-containing suspended particulates discharged under those conditions is naturally determined, so that this value can be obtained experimentally. Therefore, under various operating conditions, the emission amount of the carbon-containing fine particles per unit time is experimentally obtained and stored in advance, and in the process of step S200, the engine operating conditions detected in step S20 of the engine control routine are determined. Is read out. E for engine control
The amount of carbon-containing suspended particulates discharged under each operating condition is stored in the ROM incorporated in the CU 30 by the engine speed Ne.
And a map for the accelerator opening θac.

Next, the amount of carbon-containing suspended particulates oxidized per unit time on the exhaust gas purifying catalyst 200 during the steady operation is obtained (step S202). That is, once one operating condition (in this case, a combination of the engine rotation speed Ne and the accelerator opening θac) is determined, the gas composition of the exhaust gas when the diesel engine is operated while repeating the lean and stoichiometric under these conditions. Since various conditions such as the catalyst temperature of the exhaust gas purification catalyst 200 are determined, the amount of carbon-containing suspended particulates per unit time that can be burned on the exhaust gas purification catalyst 200 (particle oxidation amount Pburn) can be experimentally obtained. . In the ROM incorporated in the engine control ECU 30, the particulate oxidation amount Pburn determined for each operating condition is stored in advance in the form of a map. In step S202, the particulate oxidation amount Pburn is referred to by referring to the map. To get.

Thus, if the amount Peout of particulates discharged from the engine per unit time and the amount of particulates burned on the catalyst per unit time (particulate oxidation amount Pburn) are known, the difference between the two will result in a difference in the amount of particulate on the catalyst. It can be inferred whether the accumulated fine particles gradually increase or decrease. However, such an estimated value becomes a reasonable value when the diesel engine 10 is operated in a steady state for a long time, and in practice, it is rarely operated in the steady state for a long time. The value is different from the actual increase / decrease value of the fine particles. In particular, the catalyst temperature fluctuates greatly under actual operating conditions, unlike the case where steady operation is continued for a long period of time. The amount will be different.

In order to correct such an influence, first, the actual catalyst temperature TcatR of the exhaust gas purifying catalyst 200 is detected (step S204). The actual catalyst temperature TcatR can be estimated from the exhaust gas temperature detected by the temperature sensor 88 provided on the downstream side of the exhaust gas purification catalyst 200. Next, a catalyst temperature when the engine is operated for a long time under the detected operating conditions, that is, a steady catalyst temperature TcatC under the condition where the particulate oxidation amount Pburn is experimentally obtained is acquired (step S206). The steady catalyst temperature TcatC is also stored in advance in the ROM incorporated in the engine control ECU 30 as a map for the engine operating conditions, and is obtained by referring to the map.

Next, a temperature difference between the actual catalyst temperature TcatR detected in step S204 and the steady catalyst temperature TcatC obtained in step S206 is calculated, and a temperature correction coefficient Ktmp corresponding to the obtained temperature difference is obtained ( Step S20
8). As shown in FIG. 12, the temperature correction coefficient Ktmp is stored in advance as a map for the value of the temperature difference.

The temperature correction coefficient Ktmp thus obtained is
By multiplying by the particulate oxidation amount Pburn obtained in step S202, the oxidation amount of the carbon-containing suspended particulates (corrected oxidation amount Pcbrn) in which the influence of the catalyst temperature is corrected is calculated (step S210). Next, the increase / decrease dP of the carbon-containing suspended particulates deposited on the exhaust gas purifying catalyst 200 is calculated by the following equation (1) (step S212). Fine particle increase / decrease amount dP = discharged fine particle amount Peout−corrected oxidation amount Pcbrn (1)

Next, by accumulating the obtained increase / decrease amount of fine particles dP, the amount of carbon-containing suspended fine particles deposited on the catalyst (the amount of accumulated fine particles Pacc) is calculated (step S214). In other words, a new particle accumulation amount Pacc is obtained by adding the particle increase / decrease amount dP obtained this time to the particle accumulation amount Pacc obtained in the previous particle accumulation amount estimation process. When the estimated value of the amount of accumulated particulates is obtained as described above, the process of estimating the amount of accumulated particles in FIG. 11 is terminated, and the process returns to the engine control routine shown in FIG.

In the control mode setting process in the engine control routine of the second embodiment, the control mode (see FIG. 4) is set based on the particulate matter amount estimated as described above, and the engine is set in accordance with the control mode. Control. When the catalyst regeneration control is performed and it is determined that the combustion of the fine particles deposited on the catalyst is completed (see step S120 in FIG. 6), each flag indicating the control mode is initialized, and the fine particle accumulation amount is reset. Is also initialized to "0".

By estimating the amount of the suspended carbon-containing particles deposited on the exhaust gas purifying catalyst 200 in this manner, it is possible to appropriately start the catalyst regeneration control. Further, if it is determined that the combustion of the fine particles deposited on the catalyst is completed by performing the catalyst regeneration control, the amount of the fine particle deposition is initialized, and the error accompanying the estimation is reset each time. . As a result, it is possible to accurately estimate the amount of accumulated fine particles without accumulating errors.

B-3. Variant: As explained above,
In the second embodiment, the amount of carbon-containing suspended particulates deposited on the exhaust gas purification catalyst 200 was estimated, and the catalyst regeneration process was started based on the estimated value. In addition to this,
Using the data during the catalyst regeneration processing, it is also possible to improve the accuracy of estimating the amount of accumulated fine particles. Hereinafter, such a modification of the second embodiment will be described.

In the exhaust gas purifying apparatus of this embodiment,
When the catalyst regeneration control is started, the deposited carbon-containing suspended particulates are burned while supplying oxygen little by little. When the deposited particulates are burned in this way, it is considered that a larger amount of the deposited particulates requires a larger amount of oxygen to be supplied to regenerate the catalyst. In other words,
If the amount of suspended carbon-containing particles actually deposited on the catalyst is almost equal to the estimated value of the amount of accumulated particles, the regeneration of the catalyst should be completed when the expected amount of oxygen is supplied. If the actual amount of accumulated fine particles is larger than the estimated amount of accumulated fine particles, the amount of oxygen required to complete the regeneration of the catalyst is considered to be larger than the expected amount of oxygen. Based on such a principle, the accuracy of estimating the amount of accumulated fine particles can be improved.

Hereinafter, a specific example will be described. First, after the start of the catalyst regeneration control, the amount of oxygen supplied to the exhaust gas purifying catalyst 200 is calculated during the accumulated particulate combustion control. The supplied oxygen amount can be represented by the number of times the air-fuel ratio of the exhaust gas is made lean or the cumulative time when the air-fuel ratio is made lean.
Next, a reference oxygen amount that must be supplied to burn the amount of fine particles at which catalyst regeneration is to be started is determined, and a ratio or deviation of the actually supplied oxygen amount to the reference oxygen amount is calculated.

From the ratio or deviation thus obtained,
From the following equation (2), the amount of increase / decrease in fine particles per unit time d
Calculate P. Fine particle increase / decrease amount dP = (discharged fine particle amount Peout−corrected oxidation amount Pcbrn) * correction coefficient K (2) Here, the value of correction coefficient K is the ratio or deviation between the actually supplied oxygen amount and the reference oxygen amount. Is set in advance in association with. For example, if the actual oxygen supply amount is larger than the reference oxygen amount (the ratio is larger than 1), it indicates that the actual deposition amount is larger than the estimated fine particle deposition amount, The value of the coefficient K is set to a value larger than “1”. Conversely, when the actual oxygen supply amount is smaller than the reference oxygen amount (the ratio is smaller than 1), the value of the correction coefficient K is set to a value smaller than “1”. By doing so, it is possible to improve the estimation accuracy by making the estimated value of the suspended carbon-containing particles deposited on the catalyst closer to the actual estimated value.

Although various embodiments have been described above, the present invention is not limited to all the embodiments described above, and can be implemented in various modes without departing from the gist of the invention.

For example, in the above-described modified example, the description has been given assuming that the estimated value of the carbon-containing suspended particulates deposited on the catalyst is corrected based on the oxygen supply amount. On the contrary,
During the volume particulate combustion control, the correction may be made based on the catalyst temperature increase when the exhaust gas air-fuel ratio is made lean. That is, as the amount of carbon-containing suspended particulates deposited on the exhaust gas purifying catalyst decreases, the amount of temperature rise of the catalyst also decreases, and conversely, as the amount of accumulation increases, the amount of temperature increase also increases. From this, for example, the catalyst temperature increase amount when the exhaust gas air-fuel ratio is made lean is detected, and if the detected temperature increase amount is larger than a predetermined threshold, more fine particles are accumulated than the estimated accumulation amount. Shows that Conversely, if the detected amount of temperature rise is small, it indicates that the amount of particulates actually deposited is smaller than the estimated amount of deposition. Therefore, it is preferable that the estimated value of the fine particles deposited on the catalyst is corrected in accordance with the detected temperature increase amount, because the estimated value can be made closer to the actual estimated value.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a diesel engine to which an exhaust gas purification device of the present embodiment is applied.

FIG. 2 is an explanatory diagram showing a structure of an exhaust gas purifying catalyst mounted on the diesel engine of the present embodiment.

FIG. 3 is a flowchart showing a flow of an engine control routine of the diesel engine of the embodiment.

FIG. 4 is an explanatory diagram showing a structure of data for displaying a control mode.

FIG. 5 is an explanatory diagram conceptually showing how various control amounts are stored as a map for operating conditions of an engine.

FIG. 6 is a flowchart showing a flow of a process for setting a control mode for defining control contents of an engine.

FIG. 7 is an explanatory view conceptually showing a prohibited area of a catalyst regeneration process.

FIG. 8 is an explanatory diagram collectively showing a correspondence relationship between setting contents of a control mode and contents of a catalyst regeneration control.

FIG. 9 is an explanatory diagram showing a state in which the catalyst regeneration control is performed while switching the control mode in accordance with the setting content of the control mode.

FIG. 10 is an explanatory view showing a principle of purifying trapped carbon-containing suspended fine particles by discharging active oxygen by an exhaust gas purifying catalyst in a second embodiment.

FIG. 11 is a flowchart illustrating a flow of a process of estimating a deposition amount of fine particles in the exhaust gas purifying apparatus of the present embodiment of the second embodiment.

FIG. 12 is an explanatory diagram conceptually showing a state in which a temperature correction coefficient is stored in association with a deviation between an actual catalyst temperature and a catalyst temperature in a steady state.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Diesel engine 12 ... Intake pipe 14 ... Fuel injection valve 16 ... Exhaust pipe 18 ... Fuel supply pump 20 ... Supercharger 21 ... Turbine 22 ... Compressor 23 ... Shaft 24 ... Intercooler 26 ... Air cleaner 28 ... Throttle valve 30 ... Engine Control ECU 32 ... Crank angle sensor 34 ... Accelerator opening sensor 60 ... EGR passage 62 ... EGR valve 64 ... EGR cooler 70 ... Actuator 80 ... Air-fuel ratio sensor 82,84 ... Pressure sensor 86,88 ... Temperature sensor 100 ... Exhaust gas Purification catalyst 102 Passage 106 Partition wall 200 Exhaust gas purification catalyst 203 NOx storage agent 204 Precious metal catalyst

Continued on the front page F term (reference) 3G090 AA03 BA01 CA01 CA02 DA04 DA13 DA18 DA20 EA04 EA05 EA06 4D019 AA01 BA05 BB06 BC07 CA01 4D048 AA14 AB01 AB07 AC06 BA01Y BA02Y BA14X BA15X BA18X BA30X BA31X BA32 DABA03 DA02 DA03 DA03 DA08 DA10 DA13 DA20 EA04 4D058 JA32 MA44 MA51 MA52 MA54 PA01 PA04 PA08 SA08

Claims (15)

[Claims] An exhaust gas purifying apparatus for purifying carbon-containing suspended particulates contained in exhaust gas of an internal combustion engine, wherein the apparatus is provided in an exhaust passage of the internal combustion engine and collects the carbon-containing suspended particulates. An exhaust gas purifying catalyst for purifying exhaust gas by burning the collected carbon-containing suspended particulates, and whether to start combustion promotion control for promoting combustion of the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst. An acceleration control start judging means for judging whether or not the combustion promotion control is to be started, and restricting an amount of oxygen supplied to the exhaust gas purification catalyst when it is judged that the combustion acceleration control is to be started. And a combustion promoting means for promoting the combustion of the carbon-containing suspended particulates. 2. The exhaust gas purifying apparatus according to claim 1, wherein the combustion promoting unit raises the temperature of the exhaust gas purifying catalyst to a predetermined temperature or more to promote the combustion of the carbon-containing suspended particulates. An exhaust gas purifying device that is means for performing 3. The exhaust gas purifying apparatus according to claim 1, wherein the promotion control start determining unit estimates a deposition amount of the carbon-containing suspended fine particles deposited on the exhaust gas purification catalyst. , An exhaust gas purifying device that is a means for making the determination. 4. The exhaust gas purifying apparatus according to claim 3, wherein the promotion control start determining unit includes a pressure difference detecting unit that detects a pressure difference of the exhaust gas before and after the exhaust gas purifying catalyst, An exhaust gas purifying device, which is a means for making the determination by estimating the deposition amount of the carbon-containing suspended particulates from the detected pressure difference. 5. The exhaust gas purifying apparatus according to claim 3, wherein the promotion control start determining means detects an operating condition of the internal combustion engine, and accumulates a deposition amount per unit time according to the operating condition. Thereby providing a deposition amount calculation means for calculating the deposition amount of the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst, and based on a magnitude relationship between the calculated deposition amount and a predetermined threshold value, An exhaust gas purifying device, which is a means for making the determination. 6. The exhaust gas purifying apparatus according to claim 1, wherein the combustion promoting unit supplies the exhaust gas having a stoichiometric air-fuel ratio or an rich air-fuel ratio to the exhaust gas purifying catalyst, and An exhaust gas purifying device which is means for intermittently setting the air-fuel ratio to a lean air-fuel ratio to thereby limit the amount of oxygen supplied to the exhaust gas purifying catalyst. 7. The exhaust gas purifying apparatus according to claim 1, wherein the combustion promoting means supplies the exhaust gas on the lean side near the stoichiometric air-fuel ratio to the exhaust gas purifying catalyst to thereby perform the exhaust gas purifying. An exhaust gas purifying device which is a means for limiting the amount of oxygen supplied to the catalyst. 8. The exhaust gas purifying apparatus according to claim 6, wherein a temperature rising amount detecting unit detects a temperature rising amount of the exhaust gas purifying catalyst by supplying the exhaust gas having the lean air-fuel ratio. When the detected temperature rise amount is equal to or less than a predetermined threshold,
An exhaust gas purifying apparatus comprising: a promotion control termination unit that determines that combustion of the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst has been completed, and terminates the combustion promotion control. 9. The exhaust gas purifying apparatus according to claim 8, further comprising: a deposit amount estimating means for estimating a deposit amount of the carbon-containing suspended fine particles deposited on the exhaust gas purifying catalyst, and wherein the promotion control is started. The judging means is means for judging whether or not to start the combustion promotion control based on the estimated accumulation amount, and the promotion control ending means is such that the detected temperature rise amount is equal to or more than a predetermined threshold value The exhaust gas purifying device is a means for terminating the combustion promotion control and initializing the value of the amount of the carbon-containing suspended particulates when the value becomes equal to or less than the threshold from the value of (i). 10. The exhaust gas purifying apparatus according to claim 6, wherein the lean air-fuel ratio includes a deposition amount estimating unit configured to estimate a deposition amount of the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst. A heating amount detecting means for detecting a heating amount of the exhaust gas purifying catalyst by supplying the exhaust gas, and a deposition amount correcting means for correcting the estimated deposition amount based on the detected temperature rising amount. And an acceleration control start determining unit that determines whether or not to start the combustion acceleration control based on the corrected accumulation amount. 11. The exhaust gas purifying apparatus according to claim 10, wherein the temperature increase amount detecting means supplies the exhaust gas having a stoichiometric air-fuel ratio or an rich air-fuel ratio to the exhaust gas purifying catalyst while supplying the exhaust gas. An exhaust gas purifying device which is means for detecting a temperature rise amount of the exhaust gas purifying catalyst in synchronization with the switching when the air-fuel ratio of the gas is intermittently switched to the lean air-fuel ratio. 12. The exhaust gas purifying apparatus according to claim 1, wherein the exhaust gas purifying catalyst accumulates oxygen in the exhaust gas together with nitrogen oxides in the exhaust gas having a lean air-fuel ratio, and In exhaust gas with rich air-fuel ratio or stoichiometric air-fuel ratio,
By releasing the accumulated oxygen as active oxygen,
An exhaust gas purifying device, which is a catalyst for burning the collected carbon-containing suspended particulates. 13. The exhaust gas purifying apparatus according to claim 12, wherein the exhaust gas purifying catalyst has at least one of an alkali metal, an alkaline earth metal, a rare earth, and a transition metal in addition to a noble metal belonging to the platinum group. An exhaust gas purification device that is a supported catalyst. 14. An exhaust gas purifying method for purifying carbon-containing suspended particulates contained in exhaust gas of an internal combustion engine, the method comprising: providing an exhaust gas purification catalyst in an exhaust passage of the internal combustion engine; And collecting the carbon-containing suspended particulates, and determining whether or not to start the combustion promotion control for promoting the combustion of the carbon-containing suspended particulates deposited on the exhaust gas purification catalyst. Judgment is made based on the accumulation state of the suspended carbon particles, and when it is determined that the combustion promotion control is started, the combustion of the suspended carbon particles is promoted while limiting the amount of oxygen supplied to the exhaust gas purification catalyst. Exhaust gas purification method. 15. The exhaust gas purifying method according to claim 14, wherein in promoting the combustion of the carbon-containing suspended particulates, exhaust gas having a stoichiometric air-fuel ratio or an rich air-fuel ratio is supplied to the exhaust gas purifying catalyst. An exhaust gas purifying method that promotes combustion while limiting the amount of oxygen supplied to the exhaust gas purifying catalyst by intermittently setting the air-fuel ratio of the exhaust gas to a lean air-fuel ratio.