JP2001271697A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas emission control device for an internal combustion engine, capable of reducing NOx discharge into the atmosphere left unpurified by release of NOx, at the of regeneration of an NOx adsorption reduction type catalyst and deciding deterioration of the NOx adsorption reduction type catalyst. SOLUTION: This device is provided with a NOx sensor 3 disposed on the downstream side the NOx adsorption reduction catalyst 2 for detecting NOx concentration; an air-fuel control means 7 for reducing NOx adsorbed in the NOx adsorption reduction type catalyst 2 by transferring to a rich air-fuel ratio before NOx concentration on the downstream side of the NOx adsorption reduction type catalyst 2; a deterioration decision means 5 for deciding deterioration of the NOx adsorption reduction type catalyst 2 at a point of time, when NOx concentration detected by the NOx sensor 3 increases; and an inhibiting means for inhibiting the transfer to the rich air-fuel ratio by the air-fuel control means 7, based on deterioration decision timing of the preliminarily set NPx adsorption reduction type catalyst 2. The device determines deterioration of the NOx adsorption reduction type catalyst 2, by inhibiting the transfer to the rich air-fuel ratio when timing reaches deterioration decision time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an apparatus for judging deterioration of the NOx adsorbing and reducing catalyst in an exhaust gas purifying apparatus provided with a NOx adsorbing and reducing catalyst.

[0002]

2. Description of the Related Art As an exhaust gas purifying apparatus for an internal combustion engine,
N generated during operation at a lean air-fuel ratio that is a lean burn state
Ox is adsorbed by the NOx adsorption reduction catalyst disposed in the exhaust passage, and the adsorbed NOx is released by operation at a rich air-fuel ratio in which the oxygen concentration is temporarily reduced,
There is one that purifies the exhausted NOx by reducing it with components such as unburned HC and CO in the exhaust gas. Hereinafter, in this specification, NOx adsorbed by the operation at the rich air-fuel ratio is released, and the released NOx is released.
The operation of purifying x by reducing x with components such as unburned HC and CO in the exhaust gas is referred to as “regeneration of the NOx adsorption reduction catalyst”. By the way, in the NOx adsorption reduction catalyst, deterioration occurs due to long-term use, and the adsorption amount of NOx decreases.
If the deteriorated catalyst continues to be used as it is, it will have an adverse effect on the purification performance and the like, so that replacement or repair is required.

[0003] As such an exhaust gas purifying apparatus, Japanese Patent Publication No. 2985638 discloses an apparatus that detects an increase in the NOx concentration downstream of a NOx adsorption reduction catalyst and regenerates the NOx adsorption reduction catalyst. I have. Further, Japanese Patent Application Laid-Open No. 7-208151 discloses a method of judging deterioration of a NOx adsorption reduction catalyst due to thermal deterioration, sulfur poisoning, or the like.
When the increase in NOx concentration downstream of the catalyst is detected, the NOx adsorption amount reaches saturation after the NOx adsorption at the lean air-fuel ratio is restarted, and the time until the downstream NOx concentration increases decreases below the set value. An exhaust gas purifying device that is judged to be deteriorated is disclosed.

[0004]

When the amount of adsorbed NOx approaches saturation, the NOx adsorbing capacity of the NOx adsorbing reduction catalyst decreases, and the NOx concentration downstream of the catalyst increases. The conventional exhaust gas purifying apparatus as described above uses NOx downstream of the catalyst.
The increase in the x concentration is detected, the NOx adsorption-reduction catalyst is regenerated, and the deterioration is determined. However,
When the NOx adsorption amount of the NOx adsorption reduction catalyst approaches saturation, N
When the regeneration of the NOx adsorption-reduction catalyst is performed when the Ox adsorption capacity is reduced, the amount of NOx that cannot be reduced and is released to the downstream of the catalyst increases (hereinafter, “NO
x), which increases the amount of NOx released to the atmosphere without purification.

FIG. 4 is a view for explaining the release of NOx of the NOx adsorption reduction catalyst. When the regeneration A1 of the NOx adsorption-reduction catalyst is performed at time t1 when the NOx concentration downstream of the NOx adsorption-reduction catalyst increases to reach the NOx concentration C1,
NOx release a1 occurs, and the NOx concentration temporarily increases. When the regeneration A2 of the NOx adsorption-reduction catalyst is performed at time t2 when the NOx concentration becomes C2 larger than C1, the release a2 of NOx further increases. In contrast, if the regeneration A3 of the NOx adsorption-reduction catalyst is performed at time t3 before the NOx concentration downstream of the NOx adsorption-reduction catalyst increases, the downstream NOx concentration hardly increases (a3) and the NOx concentration increases. The adsorptive reduction catalyst is regenerated.

[0006] This release of NOx is caused by the fact that the time required for enriching the air-fuel ratio is longer in a diesel engine that enriches the air-fuel ratio by controlling the fuel injection control and the exhaust gas recirculation purification device (EGR) than in a gasoline engine. , Which is particularly noticeable.

Therefore, in order to reduce the release of NOx and to further reduce the NOx released to the atmosphere without being purified, the NOx adsorption-reduction type is required before the NOx concentration downstream of the NOx adsorption-reduction catalyst increases (t3). It is necessary to regenerate the catalyst (A3).

However, if the regeneration of the NOx adsorption-reduction type catalyst is performed before the downstream NOx concentration increases, the downstream Nx concentration decreases.
There is a problem that it is not possible to judge the deterioration of the NOx adsorption-reduction catalyst for detecting the increase in the Ox concentration. As described in the above-mentioned Japanese Patent Application Laid-Open No. 7-208151, the deterioration is determined when the downstream NOx concentration increases, that is, when the NOx concentration increases.
Because it is performed using the saturation phenomenon of the adsorption reduction catalyst,
Unless this occurs, it is impossible to judge deterioration.

The present invention pays attention to the above problems, and
By performing regeneration before the NOx concentration downstream of the Ox adsorption reduction catalyst increases, and by judging the deterioration of the NOx adsorption reduction catalyst based on a preset deterioration judgment timing of the NOx adsorption reduction catalyst, NO during normal playback
N released to the atmosphere without purification by x release
It is an object of the present invention to provide an exhaust gas purification apparatus that can further reduce Ox and determine deterioration of a NOx adsorption reduction catalyst.

[0010]

According to the first aspect of the present invention, there is provided an exhaust passage of an internal combustion engine, which adsorbs NOx during operation at a lean air-fuel ratio and provides a rich air-fuel ratio. A NOx adsorption-reduction catalyst that reduces NOx adsorbed during operation, a NOx sensor that is disposed downstream of the NOx adsorption-reduction catalyst, and detects a NOx concentration;
air-fuel ratio control means for shifting to a rich air-fuel ratio before the NOx concentration downstream of the x-adsorption reduction catalyst increases to reduce NOx adsorbed on the NOx adsorption-reduction catalyst, and a NOx concentration detected by the NOx sensor At the time of increase in the NOx adsorption reduction catalyst, and a transition to a rich air-fuel ratio by the air-fuel ratio control means based on a preset deterioration judgment timing of the NOx adsorption reduction catalyst. Prohibiting means for prohibiting the exhaust gas purifying apparatus, wherein when the deterioration determination time is reached, the shift to the rich air-fuel ratio is prohibited to determine the deterioration of the NOx adsorption-reduction type catalyst. Provided.

In the invention according to claim 2, the deterioration determination time is determined by the number of repetitions of the lean air-fuel ratio and the rich air-fuel ratio of the NOx adsorption reduction catalyst, or the cumulative operation time of the internal combustion engine.
Alternatively, there is provided an exhaust gas purification device for an internal combustion engine in which the deterioration is determined based on the accumulated traveling distance of the vehicle.

According to a third aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine, wherein the internal combustion engine is a diesel engine.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall view of an internal combustion engine to which the exhaust gas purifying apparatus of the present invention is applied. In FIG. 1, 1 is an internal combustion engine such as a diesel engine, 2 is a NOx adsorption reduction catalyst, 3 is a NOx sensor, 6 is an exhaust passage, and 8 is a controller. In the exhaust passage 6 of the internal combustion engine 1, the NOx adsorption-reduction catalyst 2
The NOx sensor 3 is provided downstream of the NOx adsorption-reduction type catalyst 2. The controller 8 determines the operating state of the internal combustion engine 4, the deterioration determining means 5 of the NOx adsorption-reduction catalyst 2, and the air-fuel ratio control for regenerating the NOx adsorption-reduction catalyst 2 based on the information of the operating state determining means 4. Means 7.

The internal combustion engine 1 has an engine speed sensor for detecting the engine speed, a water temperature sensor for detecting the engine coolant temperature,
An engine provided with an EGR is provided with an EGR sensor for detecting the condition of the EGR, and an engine provided with a supercharger is provided with a supercharging pressure sensor for detecting a supercharging pressure.
Further, the internal combustion engine 1 is provided with a fuel injection device capable of controlling a fuel injection amount and a fuel injection timing, and a throttle valve capable of controlling an intake air amount.

The operating state judging means 4 detects the operating state of the internal combustion engine 1 by means of the above-mentioned sensors attached to the internal combustion engine 1 and an accelerator sensor attached to a vehicle (not shown). The NOx emission amount is calculated based on the map stored in (2). The accelerator sensor is a throttle sensor in a gasoline engine,
The engine generator may be a power generation instruction signal or a power generation load sensor, and may be one that indicates or detects the load of the internal combustion engine.

The air-fuel ratio control means 7 calculates and integrates the NOx emission amount S of the internal combustion engine 1 by the above-mentioned operating state determination means 4, and a predetermined value before the NOx adsorption amount of the NOx adsorption reduction catalyst 2 reaches saturation. When the value becomes equal to or more than the value, the NOx adsorption reduction type catalyst 2 is regenerated. That is, in the present invention,
By setting the rich air-fuel ratio before the concentration detected by the NOx sensor 3 increases, an increase in NOx emission due to release is prevented. The regeneration of the NOx adsorption reduction catalyst 2 is performed by controlling the fuel injection amount, the fuel injection timing, or the throttle valve of the fuel injection device of the internal combustion engine 1 to obtain a rich air-fuel ratio. It should be noted that the predetermined value of the NOx adsorption amount of the NOx adsorption-reduction type catalyst 2 is N until the NOx concentration downstream of the NOx adsorption-reduction type catalyst 2 starts to increase.
The Ox adsorption amount is obtained in advance by an experiment or the like, and is determined in consideration of a certain amount of margin.

FIG. 2 shows an actual measurement of the NOx emission amount for the operating state of the internal combustion engine 1 and a ROM (Read Only Memory).
Shows the map stored in the. Engine speed N and engine load L
(The accelerator sensor value, the throttle sensor value, etc.) are stored in the ROM of the operating state determining means 4 in the form of a numerical table in the form of a numerical value table. Further, the NOx emission amount is appropriately corrected based on values detected by the water temperature sensor, the EGR sensor, the supercharging pressure sensor, and the like. The correction is performed using a correction coefficient or a correction map obtained based on actual measurement.

The deterioration judging means 5 judges whether or not it is a deterioration judging time based on a preset deterioration judging time X0, and makes a judgment of deterioration when it is judged that it is the deterioration judging time. During this deterioration determination time, the shift to the rich air-fuel ratio by the air-fuel ratio control means 7 is temporarily prohibited, the adsorption amount of the NOx adsorption-reduction catalyst 2 is saturated, and the NOx sensor 3
To increase the NOx concentration detected. And NOx
When the concentration detected by the sensor 3 becomes equal to or greater than the NOx concentration increase determination value C0 set in advance by an experiment or the like, the operating state determination means 4 determines the amount of NOx emission S discharged from the internal combustion engine 1 until then. The calculated and integrated value, that is, the NOx adsorption amount ΣS, and the NOx, which is a deterioration determination value of the NOx adsorption-reduction catalyst 2 set in advance through experiments or the like,
The adsorption amount S0 is compared with the NOx adsorption amount ０S which is an integrated value.
If the number is small, it is determined that there is deterioration. Alternatively, the deterioration may be determined when the temporal change amount of the NOx concentration detected by the NOx sensor exceeds a certain value.

The deterioration determination time X0 is one of the number of repetitions of the lean air-fuel ratio and the rich air-fuel ratio of the NOx adsorption reduction catalyst 2, the cumulative operation time of the internal combustion engine 1, or the cumulative travel distance of the vehicle, or These may be set in combination. In the internal combustion engine 1 that does not run, such as an engine generator, the number of repetitions of the lean air-fuel ratio and the rich air-fuel ratio of the NOx adsorption reduction catalyst 2 or the cumulative operation time of the internal combustion engine 1 is set. Note that the deterioration determination timing X0
Since the deterioration time of the NOx adsorption-reduction type catalyst 2 varies depending on the type and size of the NOx adsorption-reduction type catalyst 2, the sulfur content in the fuel, and the like, it is preferable to determine the value by an experiment or the like.

FIG. 3 shows an example of a flowchart of a deterioration determination routine executed by the controller 8 at regular intervals (for example, several hundred μs). In step 101, it is determined whether or not the repetition number X of the lean air-fuel ratio and the rich air-fuel ratio of the NOx adsorption reduction catalyst 2 is equal to or greater than the deterioration determination time X0.
In the case of X0, it is determined that it is not yet the deterioration determination time, and the process proceeds to step 102. In the case of X ≧ X0, it is determined that the deterioration determination time has come, and the process proceeds to step 105.

In step 102, it is determined whether or not the NOx adsorption reduction catalyst 2 is being regenerated. If it is determined that regeneration is being performed, in step 103, the regeneration flag R during regeneration is set to 1 and the routine is terminated. If it is determined that the reproduction is not being performed, the reproduction flag is set to R = 0 in step 104, and the routine ends.

In steps 105 and 106, the end of the regeneration of the NOx adsorption-reduction catalyst 2 is waited in order to determine the subsequent deterioration. In step 105, the reproduction flag R determines whether or not the reproduction up to the previous time is being reproduced.
If = 0, the process proceeds to step 102 and thereafter, and waits until the reproduction is started and the reproduction flag R = 1. Step 105
If it is determined in the previous step that the reproduction flag R = 1 that the reproduction is being performed, the process proceeds to step 106.

In step 106, it is determined whether or not the reproduction is continuing. If the reproduction is continuing, the routine is terminated and the reproduction is terminated. If the reproduction is not being continued, that is, if the reproduction has been completed, the process proceeds to step 107 to start the deterioration determination.

In step 107, reproduction is prohibited until the deterioration judgment is completed.

In step 108, the operating state of the internal combustion engine 1 is read by the operating state determining means 4, and in step 10
In step 9, the NOx emission amount S of the internal combustion engine 1 that is appropriately corrected is calculated with reference to the map stored in the ROM. In the following step 110, the NOx emission amount S is integrated, and the NOx adsorption amount ΣS is calculated.

In step 111, the NOx concentration C downstream of the NOx adsorption-reduction type catalyst 2 is calculated from the value obtained by the NOx sensor. In the subsequent step 112, the NOx concentration C is determined in advance by an experiment or the like.
It is determined whether or not this is the case. If C <C0, the routine is terminated as it is, and the process waits until the NOx concentration C increases.
If C ≧ C0, the process proceeds to step 113 to make a deterioration determination.

In step 113, it is determined whether or not the NOx adsorption amount ΣS calculated in step 110 is equal to or larger than a deterioration determination value S0 of the NOx adsorption-reduction catalyst 2 set in advance through experiments or the like. It is determined that the NOx adsorption reduction catalyst 2 has not deteriorated, and the routine proceeds to step 115 and performs regeneration. If ΣS <S0, it is determined that the NOx adsorption-reduction catalyst 2 has deteriorated, and the routine proceeds to step 114, where processing for dealing with deterioration is performed.

In step 114, NO in step 113
Since it was determined that the x adsorption-reduction catalyst 2 was deteriorated,
Deterioration response processing is performed, and then the routine proceeds to step 114. Deterioration response processing is performed by, for example, the NOx adsorption reduction catalyst 2
An alarm indicating deterioration of the vehicle is activated to notify the driver. Also,
Even when the power is turned off, the information is retained as deterioration diagnosis information in a backup memory that can be retained.

In step 115, NO in step 113
Since the determination of deterioration of the x-adsorption-reduction catalyst 2 has been completed, the prohibition of regeneration in step 107 is released, and regeneration is performed.

In step 116, since a series of determinations of the deterioration determination time and the deterioration determination of the NOx adsorption reduction catalyst 2 have been completed, the repetition number X of the lean air-fuel ratio and the rich air-fuel ratio for determining the deterioration determination time is cleared. To end the routine.

In this embodiment, the case where the deterioration determination time is determined by the repetition number X of the lean air-fuel ratio and the rich air-fuel ratio has been described. However, in the case of a vehicular internal combustion engine, the cumulative travel distance of the vehicle may be used. . In this case, step 1 in FIG.
In step 01, the cumulative traveling distance X is determined based on the accumulated traveling distance X0 and a deterioration determination cumulative traveling distance X0 determined in advance by an experiment or the like. In step 116, the accumulated traveling distance X for determining the deterioration determination timing is cleared, and the routine ends. .

In the case of a non-running internal combustion engine such as an engine generator, the cumulative operation time of the internal combustion engine may be used.
In this case, in step 101 of FIG. 3, the cumulative operation time X is determined based on the cumulative operation time X0 and the cumulative deterioration operation time X0 determined in advance by experiments or the like. In step 116, the cumulative operation time X for determining the deterioration determination time is determined. Clear and end the routine.

[0034]

According to the present invention, the regeneration is performed before the NOx concentration downstream of the NOx adsorption-reduction catalyst increases, and the NOx adsorption-reduction catalyst is set based on a preset deterioration judgment timing of the NOx adsorption-reduction catalyst. By determining the deterioration of the reduction catalyst, NOx can be reduced during regeneration of the NOx adsorption reduction catalyst.
Released into the atmosphere without purification by the release of N
Ox can be reduced, and deterioration of the NOx adsorption reduction catalyst can be determined. In particular, when the present invention is applied to a diesel engine having a remarkable NOx release,
The effect in reducing NOx emission is very large.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an embodiment of an internal combustion engine to which an exhaust gas purification device of the present invention is applied.

FIG. 2 shows the NO stored in the operating state determining means of the present invention.
It is a figure which shows the map of x discharge amount.

FIG. 3 is a flowchart of a deterioration determination routine according to the present invention.

FIG. 4 is a diagram illustrating release of a NOx adsorption reduction catalyst.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... NOx adsorption-reduction type catalyst 3 ... NOx sensor 4 ... Operating state determination means 5 ... Deterioration determination means 6 ... Exhaust passage 7 ... Air-fuel ratio control means 8 ... Controller

Continued on the front page F term (reference) 3G084 AA01 BA09 BA24 DA10 DA27 EB22 FA10 FA12 FA20 FA28 FA33 FA37 3G091 AA02 AA10 AA11 AA12 AA18 AA28 AB06 AB09 BA14 BA33 CB02 CB03 CB07 DA01 DA02 DA08 DB06 DB10 EA01 EA06 EA06 EA06 EA06 FB11 FB12 FC02 HA18 HA37 HB05 HB06 3G301 HA02 HA15 JA25 JB09 MA01 PA06Z PD01Z PD15Z PE01Z PE08Z PF03Z

Claims (3)

[Claims] 1. A NOx adsorption reduction catalyst 2 disposed in an exhaust passage 6 of an internal combustion engine 1 for adsorbing NOx during operation at a lean air-fuel ratio and reducing NOx adsorbed during operation at a rich air-fuel ratio. A NOx sensor 3 disposed downstream of the NOx adsorption reduction catalyst 2 for detecting NOx concentration;
an air-fuel ratio control means 7 for shifting to a rich air-fuel ratio before the NOx concentration downstream of the x-adsorption-reduction catalyst 2 increases to reduce NOx adsorbed on the NOx adsorption-reduction catalyst 2;
At the time when the NOx concentration detected by the Ox sensor 3 increases, the deterioration determining means 5 for determining the deterioration of the NOx adsorption-reduction type catalyst 2 and the deterioration judgment timing of the NOx adsorption-reduction type catalyst 2 set in advance are set. Prohibiting means for prohibiting a transition to the rich air-fuel ratio by the air-fuel ratio control means 7, and prohibiting the transition to the rich air-fuel ratio when the deterioration determination time is reached to determine the deterioration of the NOx adsorption reduction catalyst 2. An exhaust gas purifying apparatus for an internal combustion engine, comprising: 2. The deterioration determination time is determined by the number of repetitions of a lean air-fuel ratio and a rich air-fuel ratio of the NOx adsorption reduction catalyst 2,
The exhaust gas purifying device according to claim 1, wherein the deterioration determination time is based on an accumulated operation time of the internal combustion engine or an accumulated traveling distance of the vehicle. 3. The exhaust gas purifying apparatus according to claim 1, wherein the internal combustion engine 1 is a diesel engine.