JP2003293744A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine having technology for determining a regeneration timing for SOx poisoning. <P>SOLUTION: The exhaust emission control device comprises a NOx catalyst 5, a NOx reducing means 8 for supplying a reducer to the NOx catalyst 5 and reducing NOx, an oxygen concentration detecting means 7 for detecting oxygen concentration downstream from the NOx catalyst 5, an oxygen concentration storing means 11 for storing oxygen concentration when no SOx poisoning occurs and the reducer is supplied, and a SOx poisoning amount estimating means 11 for estimating a SOx poisoning amount of the NOx catalyst by comparing the oxygen concentration detected by the oxygen concentration detecting means 7 with the oxygen concentration stored by the oxygen concentration storing means 11 when the reducer is supplied to the NOx catalyst 5. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust emission control device for an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, internal combustion engines mounted in automobiles,
In particular, diesel engines and lean burn engines that can burn an air-fuel mixture that is in an oxygen excess state (so-called lean air-fuel mixture)
In a gasoline engine, a technique for purifying nitrogen oxides (NOx) contained in exhaust gas of the internal combustion engine is desired.

In response to such demands, a technique for arranging a NOx storage agent in the exhaust system of an internal combustion engine has been proposed. As one of the NOx storage agents, when the oxygen concentration of the inflowing exhaust gas is high, nitrogen oxides (NOx) in the exhaust gas are stored (absorbed, adsorbed), the oxygen concentration of the inflowing exhaust gas decreases, and the reducing agent becomes Nitrogen oxides (NO when stored)
An occlusion reduction type NOx catalyst that reduces x) to nitrogen (N ₂ ) is known.

When the NOx storage reduction catalyst is arranged in the exhaust system of the internal combustion engine, nitrogen oxide (NOx) in the exhaust gas is generated when the internal combustion engine is operated in lean combustion and the air-fuel ratio of the exhaust gas becomes high.
Is stored in the NOx storage reduction catalyst, and when the air-fuel ratio of the exhaust flowing into the NOx storage reduction catalyst becomes low, the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst are nitrogen (N ₂ ). Is reduced to.

By the way, the NOx storage reduction catalyst is a sulfur oxide (S) produced by combustion of sulfur contained in fuel.
Ox) is also stored by the same mechanism as NOx. SOx stored in this way is less likely to be released than NOx,
x Accumulates in the catalyst. This is called SOx poisoning, NOx
Since the purification rate decreases, it is necessary to perform poisoning recovery processing for recovering from SOx poisoning at an appropriate time. In this poisoning recovery process, the NOx catalyst is heated to a high temperature (eg 600 to 650 ° C).
The exhaust gas, whose oxygen concentration has been lowered, is passed through the NOx catalyst.

By the way, if the SOx poisoning recovery process cannot be performed at an appropriate time, the Nx of the NOx storage reduction catalyst will be reduced.
There is a risk that the Ox storage capacity will be reduced and the emission will deteriorate. Therefore, it is important to properly set the time for performing the SOx poisoning recovery process.

There is known a technique for determining when to perform the SOx poisoning recovery process. For example, Japanese Patent Laid-Open No. 2000-51
In the invention described in Japanese Patent No. 662, the degree to which SOx is stored in the NOx catalyst is calculated according to at least one of the air-fuel ratio, the sulfur component content in the fuel, and the catalyst temperature, and based on this value and the fuel injection amount The SOx storage amount can be calculated. Based on the SOx storage amount thus obtained, the SOx
Poisoning recovery control can be performed.

[0008]

However, in the invention described in the above publication, the degree of SOx occlusion is calculated by using the sulfur component content in the fuel that is determined in advance, so the fuel changes and the If the sulfur component content changes, accurate determination becomes difficult.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a technique for determining the SOx poisoning recovery timing in an exhaust purification system of an internal combustion engine.

[0010]

In order to achieve the above object, the exhaust gas purifying apparatus for an internal combustion engine of the present invention employs the following means. That is, when the air-fuel ratio of the exhaust gas is lean, the NOx catalyst stores NOx and reduces the stored NOx in the presence of the reducing agent, and the reducing agent is supplied to the NOx catalyst to supply NO.
NOx reducing means for reducing x and NOx in the NOx catalyst
Is stored, NOx storage determination means for determining whether or not is stored, SOx poisoning determination means for determining whether or not SOx poisoning has occurred in the NOx catalyst, and oxygen in exhaust gas flowing out from the NOx catalyst. Oxygen concentration detection means for detecting the concentration,
Exhaust gas detected by the oxygen concentration detection means when the NOx reduction means supplies a reducing agent to the NOx catalyst when the SOx poisoning determination means determines that SOx poisoning has not occurred. An oxygen concentration storage means for storing the oxygen concentration of the NOx storage means, and when the NOx reduction means supplies a reducing agent to the NOx catalyst and the NOx storage determination means determines that NOx is not stored. SO for estimating the SOx poisoning amount of the NOx catalyst by comparing the oxygen concentration detected by the oxygen concentration detection means with the oxygen concentration stored by the oxygen concentration storage means
x poisoning amount estimating means.

The greatest feature of the present invention is that in the exhaust gas purification apparatus for an internal combustion engine, there is a correlation between the oxygen concentration in the exhaust gas flowing out from the NOx catalyst when the reducing agent is supplied and the SOx poisoning amount. The oxygen concentration when supplying the reducing agent when no poison is generated, and the oxygen concentration when supplying the current reducing agent,
It is to estimate the SOx poisoning amount based on.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, SOx in the exhaust gas is stored in the NOx catalyst and SOx in the exhaust gas is stored.
x Poisoning occurs. Here, as the SOx poisoning amount of the NOx catalyst increases, the oxygen concentration in the exhaust gas flowing out from the NOx catalyst at the time of supplying the reducing agent for reducing the stored NOx increases. In order to estimate the SOx poisoning amount using the oxygen concentration in the exhaust gas, the oxygen concentration storage means stores the oxygen concentration in the exhaust gas flowing out from the NOx catalyst when the reducing agent is supplied when SOx poisoning is not occurring. To do. Then, the SOx poisoning amount estimation means detects the oxygen concentration of the exhaust gas flowing out from the NOx catalyst at the time of supplying the reducing agent after reducing all the NOx,
By comparing this detected value with the oxygen concentration stored in the oxygen concentration storage means, the SOx poisoning amount of the NOx catalyst can be estimated depending on how high the oxygen concentration is.
Here, the oxygen concentration after reducing all the NOx is detected because the reducing agent is supplied after reducing all the NOx stored in the NOx catalyst, rather than when the NOx is storing in the NOx catalyst. This is because the oxygen concentration in the exhaust gas flowing out from the NOx catalyst at that time becomes low.

In the present invention, there is further provided SOx poisoning recovery means for supplying a reducing agent to the NOx catalyst to recover SOx poisoning, and the SOx poisoning determination means is characterized in that the SOx poisoning recovery means is SOx poisoned. Immediately after the recovery of NOx
It can be determined that the catalyst is not SOx poisoned.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the SOx poisoning recovery means recovers SOx poisoning by, for example, decreasing the oxygen concentration in the exhaust gas while raising the temperature of the NOx catalyst. Immediately after the SOx poisoning is recovered, the SOx poisoning is almost recovered. Therefore, the SOx poisoning determination means can determine that the SOx poisoning has not occurred at this time.

In the present invention, the SOx poisoning judging means can judge that the NOx catalyst is not SOx poisoned when the NOx catalyst is in a new state.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, SOx poisoning does not occur when the NOx catalyst is in a new state. Therefore, the SOx poisoning determination means can determine that SOx poisoning has not occurred at this time.

In the present invention, immediately after the SOx poisoning recovery means recovers the SOx poisoning and when the reducing agent is being supplied to the NOx catalyst by the NOx reducing means, the NOx occlusion judgment is made. When NOx is determined not to be occluded by the means, the oxygen concentration detected by the oxygen concentration detecting means and the oxygen concentration stored in the oxygen concentration storage means are compared to perform a averaging process, It can be determined that the NOx catalyst is deteriorated when the value after the averaging process is equal to or more than a predetermined value.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the NOx storage capacity is lowered due to heat deterioration of the NOx catalyst, SOx poisoning which cannot be recovered, and the like. Along with this, S
Even immediately after the recovery of SOx poisoning by the Ox poisoning recovery means, there is a difference between the oxygen concentration detected by the oxygen concentration detection means and the oxygen concentration stored by the oxygen concentration storage means. Getting bigger. Therefore, SO
x Even immediately after the poisoning recovery, if the value obtained by comparing the oxygen concentration detected by the oxygen concentration detection means with the oxygen concentration stored by the oxygen concentration storage means is a predetermined value or more, NOx It is possible to determine that the catalyst has deteriorated. In addition, SOx poisoning recovery means S
Immediately after the recovery of Ox poisoning is performed, the oxygen concentration detected by the oxygen concentration detection means and the oxygen concentration stored by the oxygen concentration storage means are compared to perform a averaging process. The fluctuation of the detected value by the oxygen concentration detecting means can be removed, and accurate determination can be performed.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of an internal combustion engine according to the present invention will be described below with reference to the drawings. Here, a case where the internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.

FIG. 1 is a diagram showing a schematic structure of an engine and its intake / exhaust system according to the present embodiment.

The engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders.

An intake pipe 2 is connected to the engine 1, and an air flow meter 3 for outputting an electric signal corresponding to the mass of the intake air flowing through the intake pipe 2 is installed in the intake pipe 2 in the middle of the intake pipe 2. Has been.

On the other hand, an exhaust pipe 4 is connected to the engine 1, and the exhaust pipe 4 is connected downstream to a muffler (not shown).

In the middle of the exhaust pipe 4, a storage reduction type NO
A particulate filter (hereinafter, simply referred to as a filter) 20 supporting x catalyst is provided. An exhaust gas temperature sensor 6 that outputs an electric signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 4 is attached to the exhaust pipe 4 upstream of the filter 5. An air-fuel ratio sensor 7 that outputs an electric signal corresponding to the air-fuel ratio (oxygen concentration) of the exhaust gas flowing through the exhaust pipe 4 is attached to the exhaust pipe 4 downstream of the filter 5.

In the present embodiment, a reducing agent supply mechanism for adding fuel (light oil), which is a reducing agent, to the exhaust gas flowing through the exhaust pipe 4 upstream of the filter 5 is provided. By adding fuel to the filter 5, the oxygen concentration of the exhaust gas flowing into the filter 5 is reduced and the concentration of the reducing agent is increased.

As shown in FIG. 1, the reducing agent supply mechanism is attached so that its injection hole faces the exhaust pipe 4,
A reducing agent injection valve 8 that opens by a signal from the ECU 11 to inject fuel, a fuel pump 9 that discharges fuel, and a reducing agent supply path that guides the fuel discharged from the fuel pump 9 to the reducing agent injection valve 8. 10 is provided.

In such a reducing agent supply mechanism, the high-pressure fuel discharged from the fuel pump 9 is supplied to the reducing agent injection valve 8 via the reducing agent supply passage 10. Then, the ECU 11
The reducing agent injection valve 8 is opened by the signal from the exhaust pipe 4
Fuel as a reducing agent is injected into the inside. Reducing agent injection valve 8
The reducing agent injected from the inside of the exhaust pipe 4 reduces the oxygen concentration of the exhaust gas flowing from the upstream side of the exhaust pipe 4. afterwards,
The reducing agent injection valve 8 is closed by a signal from the ECU 11,
The addition of the reducing agent into the exhaust pipe 4 is stopped.

As a result of supplying the reducing agent to the filter 5 in this manner, the oxygen concentration of the exhaust gas flowing into the filter 5 changes in a relatively short cycle. Then, the exhaust gas having a low oxygen concentration flowing into the filter 5 is
The nitrogen oxides (NOx) stored in the storage-reduction type NOx catalyst carried by the catalyst are reduced to nitrogen (N ₂ ).

The engine 1 configured as described above is provided with an electronic control unit (ECU) 11 for controlling the engine 1. The ECU 11 is a unit that controls the operating state of the engine 1 according to the operating conditions of the engine 1 and the driver's request.

Various sensors are connected to the ECU 11 through electrical wiring, and the output signals of the various sensors described above are EC.
It is designed to be input to U11. On the other hand, the ECU 1
A reducing agent injection valve 8 and the like are connected to 1 via electric wiring and can be controlled. In addition, the EC
U11 stores various application programs and various control maps and performs various controls.

For example, in the NOx purification control, the ECU 11
Performs fuel addition control (so-called rich spike control) that reduces the oxygen concentration in the exhaust gas flowing into the filter 5 in a spike-like manner in a relatively short cycle.

In the fuel addition control, the ECU 11 determines whether or not the fuel addition control execution condition is satisfied every predetermined period. The fuel addition control execution condition is, for example, that the storage reduction NOx catalyst carried on the filter 5 is in an active state, the output signal value (exhaust temperature) of the exhaust temperature sensor 6 is equal to or less than a predetermined upper limit value, It is possible to exemplify the condition that the SOx poisoning recovery control is not executed.

When it is determined that the fuel addition control execution condition as described above is satisfied, the ECU 11 causes the reducing agent injection valve 8 to inject the reducing agent injection valve 8 with the spiked reducing agent fuel. The air-fuel ratio of the exhaust gas flowing into the filter 5 is temporarily set to a predetermined target rich air-fuel ratio by controlling

More specifically, the ECU 11 stores the stored engine speed, engine load (accelerator opening), output signal value of the air flow meter 3 (intake air amount), and air-fuel ratio sensor 7.
Output signal, fuel injection amount, etc. are read.

The ECU 11 accesses the reducing agent addition amount control map using the engine speed, engine load, intake air amount, and fuel injection amount as parameters, and sets the exhaust air-fuel ratio to a preset target air-fuel ratio. The addition amount of the reducing agent (target addition amount) required above is calculated.

Subsequently, the ECU 11 accesses the reducing agent injection valve control map using the target addition amount as a parameter, and the reducing agent injection valve necessary for injecting the target addition amount of the reducing agent from the reducing agent injection valve 8. The valve opening time of 8 (target valve opening time) is calculated.

When the target opening time of the reducing agent injection valve 8 is calculated, the ECU 11 opens the reducing agent injection valve 8.

The ECU 11 closes the reducing agent injection valve 8 when the target valve opening time elapses from the time when the reducing agent injection valve 8 is opened.

As described above, when the reducing agent injection valve 8 is opened for the target opening time, the target addition amount of fuel is reduced.
Is injected into the exhaust pipe 4. Then, the reducing agent injected from the reducing agent injection valve 8 mixes with the exhaust gas flowing from the upstream side of the exhaust pipe 4, forms a mixture of the target air-fuel ratio, and flows into the filter 5.

As a result, the air-fuel ratio of the exhaust gas flowing into the filter 5 is such that the oxygen concentration changes in a relatively short cycle, so that the storage reduction type NOx carried by the filter 5 is changed.
The catalyst alternately repeats storage and reduction of nitrogen oxides (NOx) in a short cycle.

In this way, it becomes possible to reduce the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst by making the air-fuel ratio of the exhaust gas flowing into the filter 5 a target rich air-fuel ratio in a spike manner.

Next, in the poisoning recovery control, the ECU 11
SOx poisoning recovery processing is carried out in order to recover the poisoning by the oxide of the NOx storage reduction catalyst carried by the filter 5.

Here, sulfur (S) is used as the fuel for the engine 1.
When such a fuel is burned in the engine 1, sulfur oxides (SOx) such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) are generated.

Sulfur oxide (SOx) flows into the filter 5 together with the exhaust gas, and is stored in the storage-reduction type NOx catalyst by a mechanism similar to that of nitrogen oxide (NOx).

Specifically, when the oxygen concentration of the exhaust gas flowing into the filter 5 is high, the sulfur oxide (SO ₂ ) such as sulfur dioxide (SO ₂ ) or sulfur trioxide (SO ₃ ) in the inflowing exhaust gas is used.
x) is oxidized on the surface of platinum (Pt) and stored in the filter 5 in the form of sulfate ions (SO ₄ ²⁻ ). Further, the sulfate ions (SO ₄ ²⁻ ) stored in the filter 5 combine with barium oxide (BaO) to form a sulfate salt (BaSO ₄ ).

By the way, sulfate (BaSO ₄ ) is more stable and less likely to be decomposed than barium nitrate (Ba (NO ₃ ) ₂ ), and is decomposed even when the oxygen concentration of the exhaust gas flowing into the filter 5 becomes low. Instead, they remain in the filter 5.

Sulfate (BaSO ₄ ) in the filter 5
As the amount of nitrogen increases, nitrogen oxides (NOx) correspondingly increase.
Oxide (BaO) that can be involved in the storage of
As a result, so-called SOx poisoning occurs, in which the NOx storage capacity of the NOx storage reduction catalyst decreases.

As a method for recovering SOx poisoning of the filter 5, the ambient temperature of the filter 5 is set to about 600 to 6.
By increasing the temperature to a high temperature range of 50 ° C. and reducing the oxygen concentration of the exhaust gas flowing into the filter 5, barium sulfate (BaSO ₄ ) stored in the filter 5 is reduced to S.
A method of thermally decomposing into O ₃ ⁻ or SO ₄ ⁻ and then reacting SO ₃ ⁻ or SO ₄ ⁻ with hydrocarbons (HC) or carbon monoxide (CO) in the exhaust gas to reduce to gaseous SO ₂ ^−. Can be illustrated.

Therefore, in the SOx poisoning recovery process according to the present embodiment, the ECU 11 first executes the catalyst temperature raising control for raising the bed temperature of the filter 5, and then lowers the oxygen concentration of the exhaust gas flowing into the filter 5. I decided to do it.

In the catalyst temperature raising control, the ECU 11 causes secondary injection of fuel from a fuel injection valve (not shown) and addition of fuel from the reducing agent injection valve 8 to the exhaust during the expansion stroke of each cylinder. By doing so, those unburned fuel components may be oxidized in the filter 5, and the bed temperature of the filter 5 may be raised by the heat generated during the oxidation.

When the bed temperature of the filter 5 rises to a high temperature range of about 600 ° C. to 650 ° C. due to the catalyst temperature raising process as described above, the ECU 11 causes the reducing agent injection to reduce the oxygen concentration of the exhaust gas flowing into the filter 5. Fuel is injected from the valve 8.

When the poisoning recovery process is executed in this way,
When the bed temperature of the filter 5 is high, the oxygen concentration of the exhaust gas flowing into the filter 5 becomes low, so that barium sulfate (BaSO ₄ ) stored in the filter 5 becomes SO ₃ ⁻ or SO ₄ ^−.
Is thermally decomposed into SO ₃ ⁻ and SO ₄ ^{−, which} are reduced by reacting with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas,
As a result, the SOx poisoning of the filter 5 is recovered.

By the way, as described above, the storage reduction type NO
When SOx is stored in the x-catalyst in a predetermined amount or more, the NOx storage capacity is lowered, which causes deterioration of emission. Also, SO
If the SOx poisoning recovery process is frequently performed even if the amount of poisoning x is small, fuel is required to raise the temperature of the NOx storage reduction catalyst, leading to deterioration of fuel efficiency. Therefore, it is important to properly set the execution timing of the SOx recovery process.

Here, in the conventional exhaust gas purification apparatus for an internal combustion engine, the degree of SOx poisoning is obtained from the air-fuel ratio, catalyst temperature, and fuel properties, and the SOx poisoning amount is determined based on the SOx poisoning degree and the fuel injection amount. Was estimated. However, since the amount of the sulfur component contained in the fuel varies depending on the fuel, it is difficult to accurately estimate the SOx poisoning amount when the fuels having different sulfur component amounts are used.

Therefore, in the present embodiment, it is possible to accurately determine how much SOx is actually stored based on the output signal of the air-fuel ratio sensor 7 provided downstream of the filter 5 when fuel is added for NOx reduction. Detect well.

FIG. 2 is a time chart showing the time transition of the output signal of the air-fuel ratio sensor 7 and the NOx amount when fuel is added a plurality of times. Area A in FIG. 2 is SOx.
The respective values are shown when the poisoning is not occurring, while the region B in FIG. 2 is the respective values when the SOx poisoning is occurring. Here, the air-fuel ratio of the exhaust gas when fuel is not added is equal in the region A and the region B.

As shown in FIG. 2, when fuel is added for NOx reduction, the air-fuel ratio downstream of the filter 5 decreases, and the minimum air-fuel ratio at this time becomes close to the theoretical air-fuel ratio. However, when SOx poisoning occurs in the NOx storage reduction catalyst, the minimum air-fuel ratio shifts to the lean side and becomes larger than when the SOx poisoning does not occur. Since there is a correlation between the value shifted to the lean air-fuel ratio side and the SOx poisoning amount, the SOx poisoning amount of the NOx storage reduction catalyst can be obtained by detecting how much the air-fuel ratio shifts to the lean side. be able to. At this time, the amount of SOx poisoning is calculated based on how much the air-fuel ratio deviates with reference to the air-fuel ratio when the catalyst is new or when fuel is added immediately after SOx poisoning is recovered.

On the other hand, the larger the amount of NOx stored in the NOx storage reduction catalyst, the larger the minimum air-fuel ratio downstream of the catalyst when fuel is added. Therefore, in the present embodiment, the SOx poisoning amount is estimated based on the minimum air-fuel ratio detected at the time of fuel addition after reducing all stored NOx in order to make the conditions for determination uniform. Here, even after all of the NOx has been reduced, if operating at a lean air-fuel ratio, NOx is newly stored, so fuel addition is also performed thereafter.

Further, in this embodiment, in order to eliminate the fluctuation of the air-fuel ratio of the exhaust gas at the time of fuel addition, an averaging process is added to the minimum air-fuel ratio downstream of the filter 5 detected at a plurality of times of fuel addition. The amount of SOx poisoning is estimated and the estimation accuracy is improved.

Next, the flow of the method for estimating the SOx poisoning amount will be described.

FIG. 3 is a flow chart showing the determination flow of the SOx poisoning recovery control execution condition.

In step S101, fuel addition control (rich spike control) is performed for NOx reduction.

In step S102, it is determined whether all the NOx stored in the NOx storage reduction catalyst has been reduced by the fuel addition control. In this determination, the reduction of NOx may be completed when fuel addition is performed for a predetermined time, and the minimum air-fuel ratio detected by the air-fuel ratio sensor 7 at the time of fuel addition is a substantially constant value. When it becomes, it may be determined that the reduction of NOx is completed.

If a positive determination is made in step S102, the process proceeds to step S103, while if a negative determination is made, the process returns to step S101.

In step S103, the minimum air-fuel ratio detected during the fuel addition control immediately after the completion of the previous SOx poisoning recovery control is read.

Since SOx is released after release of NOx during execution of SOx poisoning recovery control, immediately after completion of SOx poisoning recovery control, NOx and SOx are not stored in the NOx storage reduction catalyst.

Here, the minimum air-fuel ratio detected by the air-fuel ratio sensor 7 during the fuel addition control immediately after the completion of the SOx poisoning recovery control is stored in the ECU 11.

Since the SOx poisoning recovery control is not performed when the filter 5 is new, in this case, the minimum air-fuel ratio when new is stored in the ECU 11 and read in step S103.

In step S104, step S101
The minimum air-fuel ratio of the exhaust gas flowing out from the filter 5 is detected by the addition of the fuel performed in the above. The ECU 11 obtains and stores the minimum air-fuel ratio from the output signal of the air-fuel ratio sensor 7.

In step S105, the lean deviation ratio is calculated. Here, the lean deviation ratio is step S1.
It is a value obtained by dividing the minimum air-fuel ratio detected in 04 by the minimum air-fuel ratio read in step S103. The actual minimum air-fuel ratio deviates from the minimum air-fuel ratio when SOx poisoning does not occur by any proportion. It is a value indicating whether or not there is.

In step S106, the storage reduction type NOx
It is determined whether the temperature of the catalyst is equal to or higher than a predetermined temperature. Since the storage reduction type NOx catalyst has a temperature range (hereinafter referred to as an active range) where the purification capacity is high, the storage reduction type NOx catalyst is reduced.
If the temperature of the catalyst is outside the range of this active region, the purification rate of exhaust gas will decrease. Therefore, even if the SOx storage amount is the same, if the temperature of the NOx storage reduction catalyst is outside the active region, the output signal of the air-fuel ratio sensor 7 changes, making it difficult to determine the SOx poisoning amount. turn into.
Therefore, the SOx poisoning determination is performed only when the temperature is a temperature at which the NOx storage reduction catalyst is activated (for example, 250 ° C.) or higher. The temperature of the NOx storage reduction catalyst is obtained from the output signal of the exhaust temperature sensor 6.

If an affirmative decision is made in step S106, the routine proceeds to step S107, while if a negative decision is made, this routine is ended.

In step S107, the lean deviation ratio is averaged. This is because the minimum air-fuel ratio detected in step S104 may fluctuate, and an accurate value cannot be obtained even if the SOx storage amount is calculated based on the fluctuated value. The averaging process is performed by, for example, an averaging process by weighting several tens to several thousands, and can be expressed by the following equation.

Lean deviation ratio after averaging processing = {(n-
1) / n} · (lean deviation ratio after previous averaging processing) +
(1 / n) · (lean deviation ratio calculated this time) Here, n is a value of several tens to several thousands.

In step S108, step S107
It is determined whether or not the lean deviation ratio averaged in is larger than the determination value. The judgment value is a value obtained in advance by experiments or the like.

Here, FIG. 4 is a graph showing the relationship between the SOx poisoning amount of the NOx storage reduction catalyst and the lean deviation ratio. For example, when the poisoning amount of SOx is 1 g, that is, when the lean deviation ratio is 1.1, SOx poisoning recovery is necessary, and this value can be used as a determination value.

If an affirmative decision is made in step S108, the routine proceeds to step S109, while if a negative decision is made, this routine is ended.

In step S109, SOx poisoning recovery control is performed. The minimum air-fuel ratio detected at the time of fuel addition after completion of the SOx poisoning recovery control is newly stored in the ECU 11.

In this way, it is possible to determine the time when SOx poisoning recovery is to be performed, and it is possible to suppress excessive SOx occlusion or to suppress deterioration of fuel consumption due to unnecessary SOx poisoning recovery. .

Here, in the conventional exhaust gas purification apparatus for an internal combustion engine, the SOx poisoning amount of the NOx storage reduction catalyst is estimated from the fuel consumption amount and the like. However, since the amount of the sulfur component contained in the fuel varies depending on the fuel, it is difficult to accurately estimate the SOx storage amount when the fuel is changed. Therefore, SOx poisoning recovery may not be performed at the optimum time, and there is a possibility that the catalyst capacity may decrease. Moreover, even if the poisoning recovery was carried out, it was not possible to confirm whether the SOx poisoning was actually recovered.

On the other hand, a NOx sensor may be provided downstream of the filter 5 to determine the SOx poisoning regeneration timing from the NOx purification rate.

FIG. 5 is a diagram showing the relationship between the SOx poisoning amount and the NOx purification rate for a new and deteriorated NOx storage reduction catalyst.

For example, when the SOx poisoning amount is 1 g, 90% or more of NOx can be purified with a new product, but only about 75% of NOx can be purified with a deteriorated product. In this way, the NOx purification rate is different when the storage reduction type NOx catalyst is new and when it is deteriorated, and the smaller the degree of deterioration, the smaller the SOx poisoning amount is detected. Therefore, as the degree of deterioration is smaller, the SOx poisoning recovery interval becomes longer, and the SOx poisoning amount may be excessive.

If a NOx sensor is provided, the cost will increase.

In this respect, in the present embodiment, how much SOx is actually stored based on the output signal of the air-fuel ratio sensor 7 provided downstream of the filter 5 at the time of adding fuel for NOx reduction. It can be detected accurately.
Therefore, the SOx poisoning recovery execution timing can be accurately obtained.

In the present embodiment, the SOx poisoning amount is calculated with reference to the air-fuel ratio at the time of fuel addition immediately after SOx poisoning recovery, but instead of this, the fuel when the filter 5 is in a new state is used. The SOx poisoning amount may be calculated based on the air-fuel ratio at the time of addition.

Further, the reference air-fuel ratio may be calculated based on the engine speed and the engine load.

Here, FIG. 6 is a map showing the relationship among engine speed, engine load and minimum air-fuel ratio. This map is obtained by experiments or the like and stored in the ECU 11.
Then, the ECU 11 can detect the engine speed and the engine load and substitute them into this map to calculate the reference minimum air-fuel ratio.

In this case, in step S103 in FIG.
The predicted value of the minimum air-fuel ratio of the exhaust gas flowing out from the filter 5 when the fuel is added in step S101 is read.

Further, in the present embodiment, the SO 5 is based on the air-fuel ratio at the time of fuel addition when the filter 5 is in a new state.
x Deterioration of the NOx storage reduction catalyst can be determined by obtaining the lean deviation ratio of the minimum air-fuel ratio at the time of fuel addition immediately after execution of the x poisoning recovery process.

FIG. 7 is a diagram showing the relationship between the vehicle travel distance and the value obtained by averaging the lean deviation ratio immediately after recovery from SOx poisoning. Here, the solid line shows the increase in the lean deviation ratio that usually occurs, while the broken line shows the rapid increase in the lean deviation ratio due to thermal deterioration or the like. Also,
The lean deviation ratio at this time is a value obtained by dividing the minimum air-fuel ratio actually detected at the time of fuel addition by the minimum air-fuel ratio at the time of fuel addition when the filter 5 is new. It is a value indicating whether the minimum air-fuel ratio has shifted.

With the NOx storage reduction catalyst, it is difficult to completely recover the SOx poisoning even if the SOx poisoning recovery control is performed, and some sulfur component remains in the NOx storage reduction catalyst. Further, the NOx storage reduction catalyst may undergo thermal deterioration at high temperatures. In such a state, the storage capacity of NOx is reduced due to the residual sulfur components and thermal deterioration, and there is a possibility that NOx may be released into the atmosphere. Therefore, it is important to detect catalyst deterioration. Here, as shown in FIG. 7, when the NOx storage reduction catalyst deteriorates, the lean shift ratio increases even immediately after the SOx poisoning recovery. Therefore, the amount of SOx poisoning detected when fuel is added for NOx reduction immediately after SOx poisoning recovery is
It can be detected as catalyst deterioration that is difficult to recover. In the present embodiment, fuel is added immediately after the completion of SOx poisoning recovery processing, and the catalyst is deteriorated when the SOx poisoning amount detected at this time is larger than a predetermined value obtained in advance by experiments or the like. judge.

Further, in the present embodiment, the sulfur component content in the fuel is determined by the deviation between the SOx poisoning amount calculated from the air-fuel ratio detected during NOx reduction and the SOx poisoning amount estimated from the fuel consumption amount. The amount may be estimated, and if the content exceeds the allowable range, the driver may be warned by lighting a warning light (not shown).

Here, the amount of sulfur component contained in the fuel is
Although this may vary depending on the supplied fuel, as the amount of this sulfur component increases, the amount of SOx in the exhaust increases, so the speed at which SOx poisoning of the NOx storage reduction catalyst advances. Therefore, the amount of fuel required for SOx poisoning recovery increases and the fuel economy deteriorates, and the amount of unrecovered SOx poisoning increases and the filter life is shortened. Therefore,
In the present embodiment, the allowable sulfur component amount is set, and a warning is given when the amount of the sulfur component of the supplied fuel is larger than the allowable amount.

The SOx poisoning amount when the fuel containing the allowable sulfur component amount is supplied can be obtained from the consumption amount of the fuel supplied for operating the engine. When the SOx poisoning amount obtained from the minimum air-fuel ratio at the time of adding the fuel is larger than the SOx poisoning amount obtained from the fuel consumption amount, it is considered that the sulfur content in the fuel is larger than the allowable value.

In this way, when it is determined that the fuel containing the sulfur component in a larger amount than the allowable value is supplied, the driver is warned and the life of the NOx storage reduction catalyst is shortened. Can be suppressed.

[0097]

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the S-fuel ratio is detected by detecting the air-fuel ratio downstream of the NOx catalyst when adding fuel.
The amount of Ox poisoning can be estimated. Therefore, the recovery timing of SOx poisoning can be accurately obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an engine to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied and an intake / exhaust system thereof.

FIG. 2 is an output signal of the air-fuel ratio sensor and N when fuel is added.
It is a time chart figure which shows the time transition of the amount of Ox.

FIG. 3 is a flowchart showing a determination flow of SOx poisoning recovery control execution conditions.

FIG. 4 is a diagram showing the relationship between the SOx poisoning amount (storage amount) of the NOx catalyst and the lean deviation ratio.

FIG. 5 is a diagram showing the relationship between the SOx poisoning amount and the NOx purification rate for new and deteriorated NOx catalysts.

FIG. 6 is a map showing the relationship between engine speed, engine load, and minimum air-fuel ratio.

FIG. 7 is a diagram showing a relationship between a vehicle travel distance and a lean deviation ratio immediately after SOx poisoning recovery.

[Explanation of symbols]

1 ... Engine 2 ... Intake pipe 3 ... Air flow meter 4 ... Exhaust pipe 5 ... Particulate filter 6 ... Exhaust temperature sensor 7 ... Air-fuel ratio sensor 8 ... Reducing agent injection valve 9 ... Fuel pump 10 ... Reductant supply path 11 ... ECU

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 45/00 312 F02D 45/00 314Z 314 B01D 53/36 101B (72) Inventor Hisashi Oki 1 Toyota Town, Toyota City, Aichi Prefecture Address Toyota Motor Vehicle Co., Ltd. F-term (reference) 3G084 AA01 BA15 BA24 DA10 DA22 DA27 EB25 FA07 FA10 FA17 FA18 FA26 FA27 FA29 3G091 AA18 AB06 AB09 AB13 BA11 BA14 BA33 CA01 CA18 CB03 DB01 EA01 EA0 A0 A02 EA08 A02 EA08 A02 EA08 A02 EA08 A02 EA08 EA08 A02 EA08 EA08 A02 EA08 A02 EA08 A02 EA08 A02 EA08 A02 EA08 A02 EA08 AA EA08 AA EA08 AA EA08 AA EA08 AA EA08 AA EA08 AA EA08 AA EA08 AA EA08 AA EA0 AA 4 AA EA08 AA EA08 AA EA0 AA EA0 AA 4 AA EA0 AA EA0 AA 0 AA A of EA08 of A of our of our of all kinds. AB02 AB07 BA15X BA30X BC01 BD03 CC61 CD05 CD06 DA01 DA02 DA03 DA08 DA10 DA20 EA04

Claims (4)

[Claims] 1. A NOx catalyst that stores NOx when the air-fuel ratio of the exhaust gas is lean and reduces the stored NOx in the presence of a reducing agent; and a reducing agent that is supplied to the NOx catalyst to reduce the NOx. Let N
Ox reduction means, NOx storage determination means for determining whether or not NOx is stored in the NOx catalyst, SOx poisoning determination means for determining whether or not SOx poisoning has occurred in the NOx catalyst, The oxygen concentration detecting means for detecting the oxygen concentration in the exhaust gas flowing out from the NOx catalyst, and the case where it is determined by the SOx poisoning determining means that SOx poisoning has not occurred, and the NOx reducing means is the NOx reducing means. When the reducing agent is supplied to the NOx catalyst by the NOx reducing means, an oxygen concentration storing means for storing the oxygen concentration in the exhaust gas detected by the oxygen concentration detecting means when the reducing agent is supplied to the catalyst. Therefore, when the NOx occlusion determination means determines that NOx is not stored, the oxygen concentration detected by the oxygen concentration detection means and the oxygen concentration storage means are stored. By comparing the oxygen concentration are N
An exhaust emission control device for an internal combustion engine, comprising: SOx poisoning amount estimation means for estimating the SOx poisoning amount of an Ox catalyst. 2. The SOx poisoning recovery means for supplying a reducing agent to the NOx catalyst to recover the SOx poisoning, the SOx
The internal combustion engine according to claim 1, wherein the poisoning determination means determines that the NOx catalyst is not SOx poisoned immediately after the SOx poisoning recovery means recovers the SOx poisoning. Exhaust purification device. 3. The internal combustion engine according to claim 1, wherein the SOx poisoning determination means determines that the NOx catalyst is not SOx poisoned when the NOx catalyst is in a new state. Exhaust gas purification device for engines. 4. Immediately after SOx poisoning is recovered by the SOx poisoning recovery means, and the Nx is reduced by the NOx reduction means.
When the reducing agent is being supplied to the Ox catalyst, and the NOx occlusion determining means determines that NOx is not stored, the oxygen concentration detected by the oxygen concentration detecting means and the oxygen concentration storing means The average value is compared with the stored oxygen concentration, and it is determined that the NOx catalyst is deteriorated when the averaged value is equal to or more than a predetermined value. An exhaust emission control device for an internal combustion engine according to claim 3.