JPH11294141A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device which can keep absorbing performance of NOx absorbing agent for a long time and keep satisfactory characteristics of exhaust gas. SOLUTION: In an exhaust emission control device for an internal combustion engine, an SOx reduction part housing an SOx reduction agent is arranged between an NOx absorbing part 17 housing NOx absorbing agent for absorbing NOx in the exhaust gas and an SOx absorbing part 15 arranged on an upstream side of the NOx absorbing part 17 for absorbing SOx in the exhaust gas. SO2 discharged from the SOx absorbing agent when SOx reduction is carried out for bringing about a rich state, is reduced to HS by the SOx reduction agent, and flowed into the NOx absorbing agent. It is thus discharged without being absorbed by the NOx absorbing agent. It is thus possible to prevent the NOx absorbing agent from being deteriorated by poisoning of sulfer.

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 exhaust system having NOx (nitrogen oxide).
The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine including an absorbent and an SOx absorbent that absorbs SOx (sulfur oxide).

[0002]

2. Description of the Related Art When a lean operation is performed in which the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine is set leaner than the stoichiometric air-fuel ratio, the amount of NOx emission tends to increase. A NOx absorbent that absorbs
A technique for purifying exhaust gas has been conventionally known. In this NOx absorbent, the air-fuel ratio is set leaner than the stoichiometric air-fuel ratio, and the oxygen concentration in the exhaust gas is relatively high (NOx
(Hereinafter referred to as “exhaust gas lean state”), while absorbing NOx, the air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is low, and the HC and CO components are low. In a state with a large amount of NOx (hereinafter, referred to as an "exhaust gas rich state"), it has a characteristic of releasing the absorbed NOx. In an exhaust gas purifying apparatus incorporating this NOx absorbent, in an exhaust gas rich state, NOx released from the NOx absorbent is reduced by HC and CO and discharged as nitrogen gas, and HC and CO are oxidized. It is configured to be discharged as water vapor and carbon dioxide.

[0003] Further, since the fuel supplied to the internal combustion engine and the lubricating oil in the cylinder contain sulfur (S), the exhaust gas contains SOx. This SOx is absorbed by the NOx absorbent together with NOx, becomes a compound that is difficult to remove, and is accumulated in the NOx absorbent, so that the absorption capacity of the NOx absorbent is reduced. To solve this problem, N
2. Description of the Related Art An exhaust gas purifying apparatus in which an SOx absorbent is disposed on the upstream side of an Ox absorbent is conventionally known (JP-A-6-2292).
No. 30).

According to this device, the amount of NOx that can be absorbed by the NOx absorbent and the amount of SOx that can be absorbed by the SOx absorbent are of course limited, so that the NOx absorbed by the NOx absorbent is released and reduced. (Hereinafter, referred to as “NOx reduction enrichment”) and SO
The air-fuel ratio for releasing and reducing the SOx absorbed by the x absorbent is temporarily enriched (hereinafter referred to as “SOx reduction enrichment”).

[0005]

However, SOx
When executing the reduction enrichment, is the SOx is absorbed into the SOx absorbent is released as SO ₂ (sulfur dioxide), it flows into the downstream side of the NOx absorbent. At this time, since the exhaust gas is in a rich state, it is not so much absorbed by the SO ₂ and NOx absorbents, but is absorbed and accumulated little by little. As a result, even if the SOx absorbent is provided, the NOx
There has been a problem that the absorbent is poisoned by sulfur and the ability to absorb NOx is reduced.

The present invention has been made in view of this point, and an exhaust gas purifying apparatus capable of maintaining the absorption capacity of the NOx absorbent and maintaining good exhaust gas characteristics for a longer period of time. The purpose is to provide.

[0007]

In order to achieve the above object, the present invention provides a NOx absorbent provided in an exhaust system of an internal combustion engine, which absorbs NOx in exhaust gas in an exhaust gas lean state. In an exhaust gas purifying apparatus for an internal combustion engine, which is provided on the upstream side and includes an SOx absorbent for absorbing SOx in exhaust gas, the NOx absorbent and the SOx
An SOx reducing agent for reducing SOx is provided between the SOx reducing agent and the x absorbent.

According to this configuration, when the SOx reduction enrichment is performed, the SO ₂ released from the SOx absorbent becomes S ₂
It is reduced to H ₂ S (hydrogen sulfide) by the Ox reducing agent, and NO
Since it flows into the x absorbent, it is released without being absorbed by the NOx absorbent. Therefore, it is possible to prevent the NOx absorbent from being deteriorated due to sulfur poisoning, and it is possible to maintain excellent exhaust gas characteristics over a long period of time.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of a control device for an internal combustion engine (hereinafter referred to as an “engine”) including an exhaust gas purifying device according to an embodiment of the present invention. A throttle valve 3 is disposed in the middle of the pipe 2. The throttle valve 3 has a throttle valve opening (θT
H) The sensor 4 is connected, and outputs an electric signal corresponding to the opening degree of the throttle valve 3 and supplies it to an engine control electronic control unit (hereinafter referred to as “ECU”) 5.

A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of an intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). The ECU 5 is electrically connected to the ECU 5 and controls a valve opening time of the fuel injection valve 6 based on a signal from the ECU 5.

On the other hand, an intake pipe absolute pressure (PBA) sensor 7 is provided immediately downstream of the throttle valve 3, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 7 is supplied to the ECU 5. . Further, an intake air temperature (TA) sensor 8 is mounted downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies the electric signal to the ECU 5.

The engine water temperature (TW) sensor 9 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 5.

An engine speed (NE) sensor 10 is provided around a camshaft or a crankshaft (not shown) of the engine 1.
And a cylinder discrimination (CYL) sensor 11. The engine speed sensor 10 outputs a TDC signal pulse at a crank angle position before a predetermined crank angle with respect to the top dead center (TDC) at the start of the intake stroke of each cylinder of the engine 1 (every 180 ° crank angle in a four-cylinder engine). The cylinder discriminating sensor 11 outputs a cylinder discriminating signal pulse at a predetermined crank angle position of a specific cylinder. These signal pulses are supplied to the ECU 5.

The exhaust pipe 12 is provided with an SOx absorbing section 15, a SOx reducing section 16 and a NOx absorbing section 17 which constitute an exhaust gas purifying apparatus. The SOx absorbing unit 15
The SOx reduction unit 15 is disposed on the upstream side of the absorption unit 17,
It is arranged between the SOx absorption section 15 and the NOx absorption section 17.

The NOx absorbing unit 17 is a unit for absorbing N
Built-in Ox absorbent and catalyst for promoting oxidation and reduction. The NOx absorbent is set such that the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set leaner than the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is relatively high (NOx is large) (exhaust gas lean state). On the other hand, the air-fuel ratio supplied to the engine 1 is set to a richer side than the stoichiometric air-fuel ratio while the NOx is absorbed, and the oxygen concentration in the exhaust gas is low.
In a state where the HC and CO components are large (exhaust gas rich state), the fuel cell has a characteristic of releasing the absorbed NOx. NO
In the exhaust gas lean state, the x absorbing section 17
While the x-absorbent absorbs NOx, in the exhaust gas rich state, the NOx released from the NOx absorbent becomes H
Reduced by C and CO and discharged as nitrogen gas,
HC and CO are oxidized and discharged as water vapor and carbon dioxide. As the NOx absorbent, for example, barium oxide (Ba0) is used, and as the catalyst, for example, platinum (Pt) is used. This NOx
In general, the higher the temperature, the higher the absorbed N
It has the property of easily releasing Ox.

The SOx absorber 15 absorbs SOx.
Built-in Ox absorbent and catalyst for promoting oxidation and reduction. SOx absorbent in the exhaust Gasurin state while absorbing the SOx in the reverse exhaust gas rich state, has the property of releasing the absorbed SOx as SO _2. As the SOx absorbent, for example, a carrier obtained by adding silver (Ag) or the like to an alumina-based carrier is used, and as the catalyst, for example, platinum (Pt) is used.
Generally, the higher the temperature, the more the SOx absorbent
It has the property of easily releasing absorbed SOx.

The SOx reducing section 16 reduces S
The SOx reducing agent is built in, for example, by adding platinum (Pt), rhodium (Rh), or the like having strong reducibility to an alumina-based carrier. With the SOx reducing agent, SOx flowing into the SOx reducing unit 16 is reduced to H ₂ S and released.

If NOx is absorbed to the limit of the NOx absorption capacity of the NOx absorbent, that is, to the maximum NOx absorption amount, NOx can no longer be absorbed, so that the air-fuel ratio is reduced and enriched to release and reduce NOx in a timely manner. That is, the NOx reduction enrichment is executed. Similarly, if SOx is absorbed up to the limit of the SOx absorption capacity of the SOx absorbent, that is, up to the maximum SOx absorption amount, the SOx cannot be absorbed any more. Therefore, the air-fuel ratio is reduced and enriched to release and reduce SOx in a timely manner. In other words, the SOx absorbent 15 that performs the SOx reduction enrichment has the SOx absorbent temperature T
A temperature sensor 18 for detecting ABS is provided, and a detection signal thereof is supplied to the ECU 5.

A proportional air-fuel ratio sensor 14 (hereinafter referred to as "LAF sensor 14") is located upstream of the SOx absorbing section 15.
The LAF sensor 14 outputs an electric signal substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas and supplies the electric signal to the ECU 5.

In the engine 1, the valve timing of the intake valve and the exhaust valve can be switched between two stages: a high-speed valve timing suitable for a high-speed rotation region of the engine and a low-speed valve timing suitable for a low-speed rotation region. It has a mechanism 30. The switching of the valve timing includes the switching of the valve lift amount. Further, when the low-speed valve timing is selected, one of the two intake valves is stopped to stabilize the air-fuel ratio even when the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio. We have tried to ensure the combustion that we did.

The valve timing switching mechanism 30 switches the valve timing via a hydraulic pressure, and an electromagnetic valve and a hydraulic sensor for switching the hydraulic pressure are connected to the ECU 5. The detection signal of the oil pressure sensor is supplied to the ECU 5, and the ECU 5 controls the solenoid valve to control the switching of the valve timing according to the operating state of the engine 1.

The ECU 5 shapes input signal waveforms from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value into a digital signal value. The CPU 5b includes a storage unit 5c for storing various calculation programs executed by the CPU 5b, calculation results, and the like, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like.

The CPU 5b determines various engine operating states based on the various engine parameter signals described above, and according to the determined engine operating states,
Based on the following equation (1), a fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated.

TOUT = TI × KCMD × KLAF × K1 + K2 (1) Here, TI is the basic fuel injection time of the fuel injection valve 6, and is determined according to the engine speed NE and the intake pipe absolute pressure PBA.

KCMD is a target air-fuel ratio coefficient. The engine speed NE, the intake pipe absolute pressure PBA, and the engine coolant temperature T
It is set according to the engine operating parameters such as W. The target air-fuel ratio coefficient KCMD is proportional to the reciprocal of the air-fuel ratio A / F, that is, the fuel-air ratio F / A, and takes a value of 1.0 at the stoichiometric air-fuel ratio.

The detected equivalent ratio KACT calculated from the detected value of the LAF sensor 14 is equal to the target equivalent ratio KCMD.
Is an air-fuel ratio correction coefficient calculated by PID control so as to coincide with

K1 and K2 are other correction coefficients and correction variables calculated in accordance with various engine parameter signals, respectively, so that various characteristics such as fuel consumption characteristics and engine acceleration characteristics can be optimized according to the engine operating condition. Is determined to be a predetermined value.

The CPU 5b supplies a drive signal for opening the fuel injection valve 6 to the fuel injection valve 6 via the output circuit 5d based on the fuel injection time TOUT obtained as described above.

FIG. 2 is a flowchart of a process for calculating the fuel injection time TOUT and controlling the fuel supply of the engine 1. This process is executed at regular intervals.

In step S11, it is determined whether lean operation is being performed, that is, step S24 to be described later during normal control in which SOx reduction enrichment or NOx reduction enrichment is not executed.
Stored value KCM of target air-fuel ratio coefficient KCMD stored in
It is determined whether the DB is smaller than “1.0” and the KCMD
If B ≧ 1.0 and the engine is not performing the lean operation, the process immediately proceeds to step S23, where the target air-fuel ratio coefficient KCMD and the like are set according to the engine operating state, and the normal fuel supply using the above equation (1) is performed. Perform control. Next, the target air-fuel ratio coefficient KCMD is stored as the storage value KCMDB (step S24), and the process ends. In the present embodiment, the target air-fuel ratio coefficient KCMD is almost set to a value smaller than 1.0 in an operation state other than the warm-up operation, the acceleration operation, and the full load operation, and the lean operation is performed.

If KCMDB <1.0 in step S11 and the engine is operating lean, the next step S13 is performed according to the engine speed NE and the intake pipe absolute pressure PBA.
The increment values ADDNOx and ADDSOx to be used are determined (step S12). Increment values ADDNOx and AD
DSOx is a parameter corresponding to the NOx amount and SOx amount discharged per unit time during lean operation,
It is set to increase as the engine speed NE increases and as the intake pipe absolute pressure PBA increases. Since SOx emission per unit time is much smaller than NOx emission, ADDSOx <ADDNO
x.

In step S13, step S
The increment values ADDNOx and ADDSOx determined in 12 are applied, and the NOx amount counter CNOx and the SOx amount counter CSOx are incremented. As a result, count values corresponding to the NOx emission amount and the SOx emission amount are obtained.

CNOx = CNOx + ADDNOx CSOx = CSOx + ADDSOx In the following step S14, it is determined whether or not the value of the SOx amount counter CSOx has exceeded the allowable value CSOxREF.
If CSOx ≦ CSOxREF, it is determined whether or not the value of the NOx amount counter CNOx has exceeded an allowable value CNOxREF (step S19). If the answers in steps S14 and S19 are both negative (NO), the process proceeds to step S23, where normal fuel supply control is performed.

In step S14, CSOx> CSOxRE
F, the temperature TABS of the SOx absorbent becomes the predetermined temperature T
It is determined whether the temperature is higher than ABSH (for example, 600 ° C.) (step S15). When TABS ≦ TABSH, SOx is not sufficiently released from the SOx absorbent even if the SOx reduction enrichment is performed. Therefore, the process proceeds to Step S19 without performing the SOx reduction enrichment.

If TABS> TABSH in step S15, the target air-fuel ratio coefficient KCMD is set to 11.0.
The SOx reduction enrichment is set to a value of a considerable degree (step S16). This SOx reduction enrichment is performed for a relatively long time, for example, about 8 minutes. Step S17
Then, it is determined whether or not the SOx reduction enrichment has been completed,
When the SOx reduction enrichment has not been completed, the present process is immediately terminated, and when the SOx reduction enrichment has been completed, the count value of the SOx amount counter CSOx is reset to “0” (step S18). Therefore, until the SOx reduction enrichment ends, steps S14 to S15, S1
6, the processing of S17 is repeatedly executed, and when it is completed, the process proceeds from step S14 to S19.

When the SOx reduction enrichment is performed, SO
The SOx absorbed by the x absorbent is released as SO ₂ , but as described above, the SO ₂ is reduced by the SOx reducing agent to H ₂ S. Therefore, NOx on the downstream side
The absorbent is not poisoned by sulfur and can maintain a good NOx absorption capacity for a long period of time.

On the other hand, in step S19, CNOx> CNO
xREF, the target air-fuel ratio coefficient KCMD is set to 1
The NOx reduction enrichment is set to a value equivalent to about 4.0 (step S20). This NOx reduction enrichment is performed for a relatively short time, for example, about 1 or 2 seconds. In step S21, it is determined whether or not the NOx reduction enrichment has been completed. If the NOx reduction enrichment has not been completed, the present process is immediately terminated. If the NOx reduction enrichment has been completed, the count value of the NOx amount counter CNOx is determined. Is reset to "0" (step S22). Therefore, NOx
Until the reduction enrichment is completed, steps S19 to S19
Steps S20 and S21 are repeatedly executed, and upon completion, the process proceeds from step S19 to S23.

As described above, in the present embodiment, since the SOx reducing section 16 containing a SOx reducing agent is provided between the SOx absorbing section 15 and the NOx absorbing section 17, SO ₂ is reduced by the SOx reducing agent. , H ₂ S and N on the downstream side
The Ox absorbent is not poisoned by sulfur and can maintain a good NOx absorption capacity for a long period of time. As a result, good exhaust gas characteristics can be maintained over a long period of time.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the fuel injection valve 6 may be provided in each cylinder so as to inject fuel directly into the combustion chamber of the engine 1 instead of the intake pipe 2.

[0041]

As described in detail above, according to the present invention, S
The SO ₂ released from the SOx absorbent when performing the Ox reduction enrichment is converted into H ₂ S (hydrogen sulfide) by the SOx reducing agent.
And flows into the NOx absorbent, and is released without being absorbed by the NOx absorbent. Therefore, NO
The x absorbent is prevented from being deteriorated due to sulfur poisoning, and excellent exhaust gas characteristics can be maintained over a long period of time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine including an exhaust gas purification device according to an embodiment of the present invention and a control device thereof.

FIG. 2 is a flowchart of a process for performing fuel supply control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 12 Exhaust pipe 15 SOx absorption part 16 SOx reduction part 17 NOx absorption part

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/28 301 F01N 3/28 301G

Claims (1)

[Claims] 1. An NO provided in an exhaust system of an internal combustion engine to absorb NOx in exhaust gas in an exhaust gas lean state.
An x-absorber and an SOx absorber provided upstream of the NOx absorber and absorbing SOx in the exhaust gas, wherein the NOx absorber and the SOx absorber An exhaust gas purifying apparatus for an internal combustion engine, further comprising an SOx reducing agent for reducing SOx.