JP3468144B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to a NOx purification countermeasure technique at the time of starting.

[0002]

2. Description of the Related Art Conventionally, when the exhaust air-fuel ratio is lean above a predetermined temperature, NOx in the exhaust gas is absorbed, and when the exhaust air-fuel ratio is stoichiometric or rich, the absorbed NOx is absorbed. An engine provided with an exhaust gas purification catalyst that releases and reduces the gas is known (Patent No. 260049).
(See No. 2).

[0003]

In the exhaust purification catalyst, it has been known that the NOx absorption / release action is influenced by the temperature, but the NOx once absorbed by the exhaust purification catalyst.
It wasn't known until it was released due to a rise in temperature.

However, the exhaust purification catalyst is NOx.
When the engine operation is stopped while absorbing NOx and the temperature drops to a level that does not have NOx absorbing / releasing action, the already absorbed NOx continues to be absorbed and held until the next operation, and the temperature after the next start It was clarified that the phenomenon of release occurs with the rise.

That is, conventionally, there has been a problem that residual NOx is discharged after starting. The present invention has been made in view of such a conventional problem, and an internal combustion engine capable of suppressing the emission of residual NOx after a start by appropriately combining an exhaust gas purification catalyst having an HC adsorbing / releasing action. An object is to provide an exhaust emission control device for an engine.

[0006]

Therefore, the invention according to claim 1 is arranged in an exhaust passage of an engine, and a NOx emission start temperature is set.
When it reaches the limit, it releases the retained NOx and
In a completely activated state, the first exhaust purification catalyst having a function of absorbing and releasing NOx in accordance with the air-fuel ratio of the exhaust, and the first exhaust purification catalyst arranged in the exhaust passage upstream of the Of an internal combustion engine configured to include a second exhaust gas purification catalyst having an action of absorbing and releasing HC according to
In the exhaust gas purification device, the first exhaust gas purification after the engine is started.
Time for the oxidization catalyst to reach the NOx emission start temperature
Then, after the engine is started, the second exhaust gas purification catalyst releases HC.
At the related position where the time to reach the initial temperature is almost the same
The first exhaust purification catalyst and the second exhaust purification catalyst
It is characterized by being arranged .

According to the first aspect of the present invention, after the engine is stopped, the engine is restarted when the temperature of the second exhaust purification catalyst is lower than the temperature at which HC can be released. HC is absorbed, but the temperature rises and H
When the release start temperature of C is reached, the absorbed HC is released.

On the other hand, after the engine is started, when the temperature of the first exhaust purification catalyst also rises to reach the NOx emission start temperature,
NOx absorbed by the catalyst is released. And
HC released from the second exhaust purification catalyst on the upstream side and NOx released from the first exhaust purification catalyst on the downstream side react with each other, and NOx is reduced by the HC and purified, and at the same time, HC is also removed. Both NOx and HC are purified by being oxidized by NOx which is an oxidant.

Although the HC emission start temperature of the second exhaust purification catalyst is higher than the NOx emission start temperature of the first exhaust purification catalyst, the second exhaust purification catalyst is higher than the NOx emission start temperature of the first exhaust purification catalyst. by arranging the upstream side, relative temperature rise is earlier, it is possible that a is closer Rukoto reaches to the NOx release start temperature reaches HC emission initiation temperature, exhaust
Based on the heat capacity of the air passage, etc.
The HC release start temperature is reached by setting it precisely.
And the time to reach the NOx emission start temperature
Can be made to substantially coincide with each other, whereby NOx and HC
The purification function by interaction with can be further promoted.

[0010]

[0011]

The invention according to claim 2 is the exhaust gas of an engine.
It is placed in the passage and holds when the NOx emission start temperature is reached.
Released NOx and fully activated
Then, NOx is absorbed and released according to the air-fuel ratio of the exhaust gas.
First exhaust gas purifying catalyst having an effect, the first exhaust purification
It is arranged in the exhaust passage on the upstream side of the oxidation catalyst,
Second exhaust purification catalyst having an action of absorbing and releasing
And heating means arranged upstream of the first exhaust purification catalyst
And, after starting the engine, operate the heating means for a predetermined time.
As a result, the first exhaust purification catalyst releases the NOx.
Time to reach start temperature and second exhaust purification catalyst
The time to reach the HC release start temperature
That a heating control unit, characterized in that it is configured to include to
It

According to the second aspect of the present invention, the first exhaust gas purification catalyst and the second exhaust gas are so arranged that the time required to reach the HC release start temperature and the time required to reach the NOx release start temperature are substantially the same. In the case where it is difficult to arrange the purification catalyst, the heating control means operates the heating means for a predetermined time after the engine is started, so that the both times can be substantially matched and the exhaust gas purification function can be promoted. .

The invention according to claim 3 is the exhaust gas of an engine.
It is placed in the passage and holds when the NOx emission start temperature is reached.
Released NOx and fully activated
Then, NOx is absorbed and released according to the air-fuel ratio of the exhaust gas.
First exhaust gas purifying catalyst having an effect, the first exhaust purification
It is arranged in the exhaust passage on the upstream side of the oxidation catalyst,
Second exhaust purification catalyst having an action of absorbing and releasing
And heating means arranged upstream of the first exhaust purification catalyst
And the first exhaust purification catalyst has the NOx emission start temperature
And the time when the second exhaust purification catalyst becomes HC
Emission start to estimate the time to reach the emission start temperature and
Time estimation means and estimation by the emission start time estimation means
Based on the result, the first exhaust purification catalyst is changed to the NOx.
The time until the emission start temperature is reached is the second exhaust gas cleaning
Longer than the time it takes for the catalyst to reach the HC release start temperature
If it is determined that the heating means is operated,
And the first exhaust gas purification catalyst has the NOx emission start temperature
And the second exhaust purification catalyst releases HC.
Heating control that makes the time to reach the discharge start temperature approximately match
It is characterized in that it is configured to include a control means.

According to the third aspect of the present invention, even when the arrangement of the both catalysts is appropriately set so that the start of HC release and the start of NOx release are substantially the same, the outside air temperature is considerably lower than room temperature. In this situation, the temperature rise delay of the first exhaust purification catalyst on the downstream side becomes large, and the NOx release start is delayed as compared with the HC release start. Therefore, the time until reaching the HC release start temperature and the time until reaching the NOx release start temperature are estimated, and when it is determined that the NOx release start is delayed, the heating means is operated to activate the first exhaust purification catalyst. HC release start and NOx
The emission purification function can be promoted by making the emission start substantially coincide with the emission start.

Further, in the invention according to claim 4 , the emission start temperature estimating means detects the temperature of each of the first exhaust purification catalyst and the second exhaust purification catalyst at the time of engine start, and the means for detecting the temperature. The time until the first exhaust purification catalyst reaches the temperature at which NOx is released based on the respective catalyst temperatures and the second
And means for estimating the time until the exhaust purification catalyst reaches the temperature at which HC is released.

According to the fourth aspect of the present invention, by detecting the catalyst temperatures of the first exhaust purification catalyst and the second exhaust purification catalyst, the time until the NOx emission start temperature is reached and the HC emission start temperature are determined. It is possible to highly accurately estimate the time required to reach the destination.

The invention according to claim 5 is characterized in that a three-way catalyst is arranged in the exhaust passage downstream of the first exhaust purification catalyst.

According to the fifth aspect of the present invention, HC released from the first exhaust purification catalyst and NOx released from the second exhaust purification catalyst do not completely reduce or oxidize each other, or the reduction or oxidation does not occur. Even if the amount of NOx or HC is large even if the oxidation is carried out, and the surplus is generated, the surplus can be converted by the three-way catalyst to ensure the exhaust purification performance.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 2 is a diagram showing a system configuration of the internal combustion engine according to the first embodiment. In the intake passage 2 connected to the engine 1, an air cleaner 3 for purifying intake air from an upstream side,
An air flow meter 4 for measuring the intake air amount, a throttle valve 5 for controlling the intake air amount, and a fuel injection valve 6 for injecting and supplying fuel are provided, and a detection signal of the air flow meter 2 is output to a control module 7. It

Further, the engine 1 is provided with a water temperature sensor 8 for detecting a warm-up state and a crank angle sensor 9 for detecting an engine rotation speed. The detection of the water temperature sensor 8 and the crank angle sensor 9 is carried out. The signal is output to the control module 7. Control module 7
Then, the basic fuel injection amount Tp is calculated based on the intake air amount detected by the air flow meter 2 and the engine rotation speed detected by the crank angle sensor 9, and based on the water temperature detected by the water temperature sensor 8. Then, the fuel increase correction amount is added to the basic fuel injection amount Tp, and the fuel corresponding to the calculated fuel injection amount is injected from the fuel injection valve 6. The fuel injection valve may directly inject into the combustion chamber of the engine 1.

On the other hand, the exhaust passage 10 connected to the engine 1 is equipped with an air-fuel ratio sensor 11 for detecting the air-fuel ratio of the exhaust gas, and the detection signal of the air-fuel ratio sensor 11 is output to the control module 7. Control module 7
Detects the deviation from the target air-fuel ratio from the exhaust air-fuel ratio, and reflects it as a correction term or as a learning value after memory-learning the correction term in the calculation of the fuel injection amount of the next injection. Further, a first exhaust purification catalyst 12 having a NOx absorption / release function at a predetermined temperature or higher is mounted downstream of the exhaust passage 10. The first
Specifically, the exhaust purification catalyst 12 absorbs NOx when the air-fuel ratio of the exhaust gas is lean at a predetermined temperature or higher, and releases NOx when the air-fuel ratio is stoichiometric or rich. A second exhaust purification catalyst having an action of absorbing and releasing HC according to temperature in the exhaust passage 10 upstream of the first exhaust purification catalyst 11.
13 is installed.

The operation of the first embodiment will be described. In the state where the first exhaust purification catalyst 11 is fully activated by the temperature rise and is capable of absorbing and releasing NOx, FIG.
As shown in a), for example, when the catalyst temperature is 350 ° C, a large amount of NOx can be absorbed. After that, when the operation of the engine 1 is stopped, NOx is still absorbed by the first exhaust purification catalyst 12 unless the air-fuel ratio is set to the stoichiometric air-fuel ratio or rich before the operation is stopped. Generally, in this state, the catalyst temperature then decreases, and when restarting, the first exhaust gas purification catalyst 12 becomes N
In many cases, the temperature is a temperature at which Ox is not absorbed or released. In this case, since the first exhaust purification catalyst 12 absorbs and holds the NOx before the operation stop, it is restarted in this state and the catalyst temperature rises to a temperature (for example, 200 ° C) at which NOx starts to be released. When reached, the retained NOx
Are released (see FIG. 3).

On the other hand, in the second exhaust purification catalyst 13 arranged on the upstream side of the first exhaust purification catalyst 12, HC in the exhaust is absorbed in the low temperature state after the engine is started, but the temperature rises. When the temperature at which HC is released is reached, the absorbed H
C is released.

Then, the HC released from the second exhaust purification catalyst 13 and the NOx released from the first exhaust purification catalyst 11 react with each other, and the NOx is reduced by the HC and purified. . On the other hand, HC is also purified by being oxidized by NOx which is an oxidant. That is, both NOx and HC will be purified.

Since the second exhaust purification catalyst 13 is provided on the upstream side of the exhaust passage 10 as compared with the first exhaust purification catalyst 12, the temperature rises faster (see FIG. 4). Then, the HC emission start temperature of the second exhaust purification catalyst 13 (for example, 300 °
C) is higher than the NOx release start temperature (for example, 200 ° C.) of the first exhaust purification catalyst 12, the second exhaust purification catalyst 13 is on the upstream side and the first exhaust purification catalyst is on the downstream side as described above. By arranging 12, it is possible to purify NOx and HC at the same time, but at this time, if either NOx or HC is released earlier, the emission of either of them will be emitted. Is not desirable. Therefore, when the second exhaust purification catalyst 13 on the upstream side and the first exhaust purification catalyst 12 on the downstream side reach the NOx release start temperature of the first exhaust purification catalyst 12 and the second exhaust purification catalyst
By arranging 13 so that it reaches the HC release start temperature at substantially the same time, the emission of either emission is suppressed as much as possible. The positional relationship is determined by experiments or the like according to the amount of heat discharged after the engine is started, the heat capacity of the exhaust passage, and the like.

However, in some cases, it may be difficult to arrange the above-mentioned positional relationship due to the relationship with the vehicle body, suspension device, silencer, and the like. In such a case, in consideration of the fact that the temperature rise on the downstream side of the exhaust passage is slower, the first passage arranged on the downstream side is considered.
It is necessary to raise the temperature of the exhaust purification catalyst 12 in the early stage.

FIG. 5 shows the system configuration of the internal combustion engine in the second embodiment for performing the temperature rise control. In addition to the configuration of FIG. 1, the exhaust passage downstream of the second exhaust purification catalyst 13 is added. An electric heater (EHC) 14 is attached to 10 as a heating means, and the electric heater 20 is energized for a predetermined time after the engine is started to heat the second exhaust purification catalyst 13 to accelerate the temperature rise.

With this configuration, even when the positional relationship between the catalysts cannot be optimally set, the time required to reach the HC release start temperature and the time required to reach the NOx release start temperature are made substantially equal to each other, The purification function due to the interaction between NOx and HC can be further promoted.

Even when the positional relationship between the catalysts is optimally set, the normal outside air temperature (for example, 20 ° C. to 40 ° C.).
In the starting at 0 ° C), the second exhaust purification catalyst 13 reaches the HC release start temperature, and the first exhaust purification catalyst 12 becomes NOx.
Even if the release start temperature can be reached at approximately the same time, the release start temperatures are not necessarily reached at the same time, for example, when the outside air temperature is 10 ° C. In such a case, a time T1 until the second exhaust purification catalyst 13 on the upstream side reaches the HC release start temperature and a time T2 until the first exhaust purification catalyst 12 on the downstream side reaches the NOx release start temperature. When it is determined that the time to reach the NOx emission start temperature is longer than the first exhaust purification catalyst 12 on the downstream side,
Control for accelerating the temperature rise of
T2 is made to substantially match so that NOx and HC are purified at the same time.

FIG. 6 shows the system configuration of the internal combustion engine in the third embodiment for performing the above control. In addition to the configuration of FIG. 1, the time required for the first exhaust purification catalyst 12 to reach the HC release start temperature. To detect the catalyst temperature, the first temperature sensor 21 for detecting the catalyst temperature, and the second temperature sensor 22 for detecting the catalyst temperature to predict the time until the second exhaust purification catalyst 13 reaches the NOx release start temperature. While wearing each,
An electric heater (EHC) 14, for example, is mounted as a heating means in the exhaust passage 10 on the downstream side of the second exhaust purification catalyst 13.

FIG. 7 shows a flowchart of the control routine in the above embodiment. In Step 1, the first
The catalyst temperature NTEMP of the exhaust purification catalyst 12 and the catalyst temperature HTEMP of the second exhaust purification catalyst 13 are detected.

In step 2, the first exhaust purification catalyst
It is determined whether or not the catalyst temperature NTEMP of 12 is equal to or higher than the NOx release completion temperature (for example, 300 ° C). In step 3, the catalyst temperature HTEMP of the second exhaust purification catalyst 13 is set to the HC release completion temperature (for example, 400 ° C). ) Is less than or equal to.

If both NTEMP and HTEMP are below the release completion temperature, NOx and HC have not started to be released or are being released, so the routine proceeds to step 4 to shift to the control according to the present invention, and , NTEMP, HTE
If either MP is equal to or higher than the set temperature, it is determined that the release of NOx or HC is completed, and this routine is ended.

Next, at step 4, NTEMP is NO.
It is determined whether or not the temperature is equal to or higher than the x emission start determination temperature (eg, 150 ° C.). This should be judged based on the temperature at which NOx release starts (for example, 200 ° C), but it may be too late if the control described below is performed after the actual NOx release start temperature is judged. Therefore, the determination is made at a temperature lower than the actual NOx release start temperature.

When it is determined in step 4 that NTEMP is equal to or higher than the NOx release start determination temperature, the process proceeds to step 5, where the difference between NTEMP and HTEMP (= HTEMP-N
TEMP) is calculated and the difference (HTEMP-NTEM) is calculated.
P) as the HC release start temperature (for example, 300 ° C) and NOx
Difference from emission start temperature (eg 200 ° C) DT (100
° C).

When HTEMP-NTEMP> DT, it is judged that the second exhaust purification catalyst 13 reaches the HC release start temperature later than the NOx release start temperature of the first exhaust purification catalyst 12. However, in this case, the process proceeds to step 6 in order to raise the catalyst temperature of the first exhaust purification catalyst 12.

When HTEMP-NTEMP≤DT, the first exhaust purification catalyst 12 reaches the NOx release start temperature and the second exhaust purification catalyst 13 reaches the HC release start temperature at the same time. If so, this is a desirable state, and this routine is terminated.

In step 6, in order to heat the first exhaust purification catalyst 12 on the downstream side, the electric heater 23 is energized to start heating control. According to the above, as shown in FIG. 8, the time T1 to reach the NOx release start temperature and the time T2 to reach the HC release start temperature depending on the arrangement of the first and second exhaust purification catalysts and the outside air temperature. Even when it is difficult to make the two coincide with each other, it is possible to make the two times T1 and T2 coincide with each other by forcibly controlling the heating by a heating means such as an electric heater.

FIG. 9 shows the system configuration of the internal combustion engine in the fourth embodiment, and in addition to the configuration of FIG.
HC and NOx in the exhaust passage 10 downstream of the exhaust purification catalyst 12
The three-way catalyst 15 having the oxidation / reduction function of is interposed.

As described above, by providing the three-way catalyst 15, the H released from the second exhaust purification catalyst 13 on the upstream side.
C, when NOx released from the first exhaust purification catalyst 12 is not completely reduced / oxidized with each other, or even if reduction / oxidation is performed, the amount of either NOx or HC is large, Even if a surplus is generated in either one, the surplus can be converted by the three-way catalyst 15, so that perfect exhaust gas purification performance can be secured.

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration of an internal combustion engine according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a characteristic of a NOx absorption amount with respect to a temperature of a first exhaust purification catalyst.

FIG. 3 is a diagram showing a characteristic of NOx emission due to a temperature rise of a first exhaust purification catalyst.

[FIG. 4] NOx, H with respect to temperature changes of the first exhaust purification catalyst and the second exhaust purification catalyst in the first embodiment.
The figure which shows the release characteristic of C.

FIG. 5 is a diagram showing a system configuration of an internal combustion engine according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a system configuration of an internal combustion engine according to a third embodiment of the present invention.

FIG. 7 is a flowchart showing a control routine of a third embodiment.

FIG. 8 shows NOx and H with respect to temperature changes of the first exhaust purification catalyst and the second exhaust purification catalyst according to the third embodiment.
The figure which shows the release characteristic of C.

FIG. 9 is a diagram showing a system configuration of an internal combustion engine according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 Internal combustion engine 2 Intake passage 7 Control module 10 exhaust passage 12 First exhaust purification catalyst 13 Second exhaust purification catalyst 14 Electric heater 15 three-way catalyst 21 First temperature sensor 22 Second temperature sensor

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kaname Naganuma 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Pref. Nissan Motor Co., Ltd. (56) References JP-A-8-284646 (JP, A) JP-A-7- 238826 (JP, A) JP 2000-145439 (JP, A) JP 9-100716 (JP, A) Patent 2600492 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/08-3/24

Claims (5)

(57) [Claims] 1. A NOx emission opening device arranged in an exhaust passage of an engine.
When the initial temperature is reached, the retained NOx is released
In addition, in the fully activated state, NO depending on the air-fuel ratio of the exhaust gas.
a first exhaust purification catalyst having a function of absorbing and releasing x, and arranged in the exhaust passage on the upstream side of the first exhaust purification catalyst,
In an exhaust gas purification device for an internal combustion engine , which includes a second exhaust gas purification catalyst that has the function of absorbing and releasing HC according to temperature, in the exhaust gas purification device for an internal combustion engine, the first exhaust gas purification catalyst causes the NOx release
The time required to reach the starting temperature and the second time after the engine is started
Time to reach the HC emission start temperature of the exhaust purification catalyst
And the first exhaust gas purification catalyst at a relational position where
An exhaust emission control device for an internal combustion engine, comprising: the second exhaust emission control catalyst . 2. An NOx emission opening device arranged in an exhaust passage of an engine.
When the initial temperature is reached, the retained NOx is released
In addition, in the fully activated state, NO depending on the air-fuel ratio of the exhaust gas.
First exhaust gas purification catalyst having a function of absorbing and releasing x
A medium and is arranged in the exhaust passage on the upstream side of the first exhaust purification catalyst,
First, which has the function of absorbing and releasing HC according to temperature
No. 2 exhaust purification catalyst, heating means arranged on the upstream side of the first exhaust purification catalyst, and operating the heating means for a predetermined time after the engine is started.
Causes the first exhaust purification catalyst to start releasing the NOx.
The time until the temperature is reached and the second exhaust purification catalyst is H
The time required to reach the C emission start temperature is made approximately equal.
Exhaust gas purification of an internal combustion engine characterized by including a heat control means
apparatus. 3. An NOx emission opening device arranged in the exhaust passage of the engine.
When the initial temperature is reached, the retained NOx is released
In addition, in the fully activated state, NO depending on the air-fuel ratio of the exhaust gas.
First exhaust gas purification catalyst having a function of absorbing and releasing x
A medium and is arranged in the exhaust passage on the upstream side of the first exhaust purification catalyst,
The had an effect of performing the emission and absorption of HC in response to the temperature
The second exhaust purification catalyst, the heating means arranged on the upstream side of the first exhaust purification catalyst, and the first exhaust purification catalyst reach the NOx emission start temperature.
And the second exhaust purification catalyst releases HC.
Emission start time to estimate the time to reach the start temperature and
Based on the estimation means and the estimation result by the release start time estimation means,
The first exhaust purification catalyst reaches the NOx emission start temperature.
Until the second exhaust purification catalyst releases HC
When it is judged that it is longer than the time to reach the start temperature
And by activating the heating means, the first
Until the exhaust purification catalyst reaches the NOx emission start temperature
Time and the second exhaust purification catalyst reaches the HC release start temperature
Exhaust control of an internal combustion engine, characterized in that it comprises a heating control means for substantially matching the time until
apparatus. Wherein said discharge initiation temperature estimating means includes means for detecting a first exhaust gas purifying catalyst and second temperature of the exhaust gas purifying catalyst at the time of engine start, respectively, first on the basis of the catalyst temperature issued該検And a means for estimating the time until the exhaust purification catalyst of No. 1 reaches the temperature for releasing NOx and the time until the second exhaust purification catalyst reaches the temperature for releasing HC of the second exhaust purification catalyst. An exhaust emission control device for an internal combustion engine according to claim 3 . 5. A method according to claim 1 to claim 4, characterized in that a three-way catalyst in an exhaust passage of the first exhaust gas purifying catalyst downstream
2. An exhaust gas purification device for an internal combustion engine according to any one of 1.