JP2000045753A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately determine the deterioration of a NOx absorption catalyst (NOx absorbent) due to sulfur poisoning, to remove adhered sulfur and to regenerate the sulfur. SOLUTION: An SOx sensor is disposed in an exhaust system. Then, the sulfur concentration in the exhaust gas is detected (S102), and the integrated amount of SOx is calculated based on the detected value (S104). When the integrated amount exceeds the predetermined value A, the heating is performed (S106, S108),
When the exhaust temperature Tcat exceeds the predetermined temperature B (S11
0), enrich the air-fuel ratio (S112).

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 gas purifying apparatus for preventing poisoning such as sulfur.
NOx absorbent (NOx absorption catalyst) by removing poison easily
To play.

[0002]

2. Description of the Related Art As an exhaust gas purifying catalyst for an internal combustion engine,
Various oxidation catalysts, three-way catalysts, NOx selective reduction catalysts, NOx absorption catalysts (NOx absorbents), HC absorption catalysts, and the like have been proposed. In recent years, lean air-fuel ratios such as lean burn engines have been progressing. In such engines, purification of NOx (nitrogen oxide) components in a lean atmosphere using a NOx absorption catalyst (NOx absorbent) or the like has been carried out. I'm trying.

[0003] By the way, the fuel contains sulfur S, and the sulfur is deposited on the catalyst surface or on the micropores by SOx.
When attached (absorbed) as (sulfur oxide), the purification efficiency of the catalyst is reduced. In particular, the NOx absorption catalyst (N
Ox absorbent), that is, absorb NOx in a lean atmosphere,
In a catalyst for reducing and purifying NOx absorbed by supplying unburned HC (reducing agent), sulfur is easily absorbed,
The so-called sulfur poisoning is caused to lower the NOx absorption efficiency.

Therefore, Japanese Patent Application Laid-Open No. 6-66129 discloses that
The sulfur poisoning amount is estimated from the vehicle traveling distance, the NOx absorption amount or the exhaust gas temperature. When the estimated value exceeds a predetermined value, the electric heater is energized and heated for a certain period of time, and the air-fuel ratio of the supplied air-fuel mixture is changed to the stoichiometric air-fuel ratio And a technique for regenerating the catalyst by removing SOx is proposed.

[0005] Japanese Patent Application Laid-Open No. 7-217474 also discloses that
The sulfur poisoning amount is estimated from the engine speed, etc., and when the estimated value exceeds the allowable value and the exhaust gas temperature exceeds a predetermined value, the air-fuel ratio of the supplied mixture is enriched, SOx is removed, and the catalyst is removed. We propose a technology to regenerate.

[0006]

By the way, sulfur in fuel sold in Japan is regulated to 30 ppm, but in the United States, the average value is 400 ppm and the regulated value is 1000 ppm.
The sulfur content is as high as ppm, and although it varies from country to country in Europe, the majority is in a few hundred ppm or more.

Since the sulfur poisoning increases as the sulfur content in the fuel increases, it is necessary to accurately determine the sulfur poisoning and accurately regenerate the catalyst (NOx absorbent). In this method, the amount of sulfur poisoning is estimated from the distance traveled by the vehicle and the like, but the sulfur concentration in the exhaust gas is detected, and the amount of sulfur poisoning is estimated based on the detected amount, and the catalyst regeneration process is not performed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to eliminate the above-mentioned disadvantages, and to detect the sulfur concentration in exhaust gas and to directly determine the deterioration of the NOx absorbent due to sulfur poisoning based on the detected sulfur concentration. An object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine, which performs a proper regeneration process.

[0009]

In order to achieve the above object, according to the present invention, NOx in an exhaust gas of an exhaust gas is provided in an exhaust system of an internal combustion engine when the exhaust gas is in a lean atmosphere. A NOx absorbent to be absorbed, a heating means for heating the NOx absorbent, a sulfur concentration detecting means provided upstream of an arrangement position of the NOx absorbent and detecting a sulfur concentration in exhaust gas; Deterioration determination means for determining deterioration of the NOx absorbent due to sulfur poisoning based on the output of the detection means, temperature estimation means for estimating the temperature of the NOx absorbent, and the deterioration determination means for determining the deterioration, Further, when the temperature estimated by the temperature estimating means is higher than the sulfur poisoning regeneration temperature, a sulfur removal control means for supplying a rich air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio is provided.

[0010] Accordingly, the sulfur concentration in the exhaust gas is detected, and the deterioration due to sulfur poisoning is more directly determined based on the detected sulfur concentration, so that the deterioration determination accuracy can be improved. Therefore, even when a fuel having a high sulfur content is used, N
The regeneration treatment of the Ox absorbent can be accurately performed.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention.

FIG. 1 is an overall view schematically showing the exhaust gas purifying apparatus.

In FIG. 1, reference numeral 10 denotes a main body of a multi-cylinder internal combustion engine (hereinafter referred to as an "engine") such as a four-cylinder engine.
The intake air introduced from an air cleaner (not shown) disposed at the end of the intake pipe 12 flows into each cylinder via a surge tank and an intake manifold (both not shown) while the flow rate is adjusted by a throttle valve 14. Is done.

An injector (fuel injection valve) 16 is provided near an intake valve (not shown) of each cylinder to inject fuel. The air-fuel mixture injected and integrated with the intake air is ignited by an ignition plug (not shown) in each cylinder and burns to drive a piston (not shown).

The exhaust gas after combustion is sent to an exhaust pipe 18 via an exhaust valve (not shown) and an exhaust manifold (not shown). In the exhaust pipe 18, a three-way catalyst 22 is arranged on the upstream side to purify HC, CO, NOx components and the like in the exhaust gas, and a NOx absorption catalyst (the above-mentioned NOx absorbent) 24 is arranged downstream thereof. .

The NOx absorption catalyst 24 is disclosed in Japanese Patent Laid-Open No. 6-66129 or Japanese Patent Laid-Open No. 7-217474.
Of the same kind of catalyst as the NOx absorbent described in Japanese Patent Application
When the oxygen concentration in the exhaust gas is reduced, that is, in the rich atmosphere, it reacts with unburned HC and CO to reduce and purify NOx.

Here, the carrier for carrying the NOx absorption catalyst 24 is manufactured by extruding a material, firing it to form a ceramic, and then cutting it to an appropriate length. A current path is formed in the carrier, and the NOx absorption catalyst 24 itself is configured as an electrically heated catalyst having an electric heater structure.
The current path is connected to the positive and negative terminals 24a, 24b.

The apparatus shown in FIG. 1 has a changeover switch 26. When the terminal 26a of the changeover switch 26 is switched to 26b, the positive terminal 24a is connected to the alternator 28 and receives a current from the alternator 28 to supply the NOx absorption catalyst 24. Raise the temperature of.

When the terminal 26a of the changeover switch 26 is switched to the terminal 26c, the output of the alternator 28 is connected to the positive electrode of the battery 30, and charges the battery 30. The positive electrode of the battery 30 is connected via a line 32 to an electric load including the motor (not shown) of the air pump 34 described above.

The air pump 34 is connected to the other end of a branch passage 36 branched upstream of the exhaust pipe 18 at the position where the NOx absorption catalyst 24 is disposed, supplies oxygen to promote the combustion of unburned components, and improves the purification efficiency. Improve.

In FIG. 1, a crank angle sensor 38 is provided near a camshaft or a crankshaft (both not shown) of the engine body 10, and a signal CR is provided at every predetermined crank angle.
In addition to outputting K, a cylinder discrimination signal is output at a specific crank angle of a specific cylinder.

The throttle valve 14 is provided with a throttle opening sensor 40 for outputting a signal proportional to the throttle opening θTH. An absolute pressure sensor 44 is provided at the end of the downstream branch passage 42 and outputs a signal corresponding to the intake pipe absolute pressure PBA.

Further, an intake air temperature sensor 46 is provided downstream of the branch position to output a signal proportional to the intake air temperature TA, and a water temperature sensor 48 is provided at an appropriate position such as a cylinder block so that the engine cooling water temperature is provided. A signal corresponding to TW is output.

Further, an O ₂ sensor 50 is provided in the exhaust pipe 18 and outputs a signal proportional to the oxygen concentration in the exhaust gas.

Further, the three-way catalyst 22 and the NOx absorption catalyst 2
An exhaust temperature sensor 52 is provided between the exhaust gas sensors 4 and 4 and outputs a signal corresponding to the exhaust gas temperature Tcat near the position where the NOx absorption catalyst 24 is disposed.

Further, at the downstream of the NOx absorption catalyst 24, S
An Ox sensor (sulfur concentration detecting means) 54 is provided, and outputs a signal proportional to the concentration Sc of sulfur in the exhaust gas.

FIG. 2 is an explanatory sectional view showing the configuration of the SOx sensor 54 in detail.

The SOx sensor 54 has the shape of a plate formed by laminating solid electrolyte layers of oxygen ion conductivity such as zirconia porcelain, and has a first measuring chamber (internal space) 54a and a second measuring chamber (internal space). 54b and third measurement chamber (internal space)
54c is formed, and a reference chamber 54 communicating with the atmosphere is formed.
d is formed.

The exhaust gas flows to the first measurement chamber 54a through the gas diffusion control layer 54m. A pump cell is formed in the first measurement chamber 54a by electrodes 54e and 54f, pumps oxygen in the measurement chamber, and controls the oxygen partial pressure to a value at which NOx cannot be reduced. The oxygen concentration in the exhaust gas is detected by detecting the oxygen partial pressure as a potential difference between the electrodes 54g and 54h.

Similarly, the second measurement chamber 54b is provided with electrodes 54i and 54j made of a NOx reduction catalyst such as Rh. Oxygen partial pressure is detected by detecting a potential difference, that is, NOx is generated by reduction or decomposition. The oxygen partial pressure is detected to detect the NOx concentration.

Similarly, the third measurement chamber 54c is provided with electrodes 54k and 54l made of a SOx reduction catalyst such as Pt, and detects the SOx concentration from the potential difference between them. As described above, the SOx sensor 54 can detect not only the SOx concentration but also the oxygen concentration and the NOx concentration.

The outputs of these sensor groups are sent to an electronic control unit (hereinafter referred to as “ECU”) 60.

The ECU 60 includes an input circuit 60a, a CPU 6
0b, storage means 60c, and output circuit 60d. The input circuit 60a performs processes such as shaping input signal waveforms from various sensors, converting a signal level to a predetermined level, and converting an analog signal value to a digital signal value. The storage unit 60c stores various calculation programs executed by the CPU 60b, calculation results, and the like.

The CPU 60b counts the CRK signal to detect the engine speed NE, calculates the fuel injection amount (injector opening time) from the detected engine speed NE and the absolute pressure PBA in the intake pipe, and calculates the target idle speed. Correct with fuel ratio.

The target air-fuel ratio is set to a value in a lean direction (for example, 30: 1) exceeding the stoichiometric air-fuel ratio during low load operation.
During high load operation, the value is set to a value in a rich direction (for example, 12: 1) lower than the stoichiometric air-fuel ratio.

Further, the CPU 60b determines deterioration of the NOx absorption catalyst 24 due to sulfur poisoning, and removes (regenerates) the deterioration.
Do the work. That is, the sulfur component in the exhaust gas adheres to the catalyst surface or the micropores as SOx (sulfur oxide), which lowers the purification efficiency of the catalyst. If so-called sulfur poisoning becomes severe, the NOx absorption efficiency decreases.
The NOx absorption catalyst 24 is regenerated by removing the absorbed SOx.

Next, the operation of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described.

FIG. 3 is a flow chart showing the operation. The illustrated program is executed at appropriate time intervals (for example, 80 msec).

In the following, it is determined in S100 whether or not the control conditions, more specifically, the conditions for performing the sulfur poisoning deterioration determination and the catalyst regeneration processing are satisfied. Specifically, the NOx absorption catalyst 24 is, for example, 300 ° C. to 400 ° C.
And the engine 10 is in a steady operation state, it is determined that this condition is satisfied.

When the result in S100 is negative, the subsequent processing is skipped. When the result is affirmative, the process proceeds to S102, where the output Sc (the concentration of sulfur in the exhaust gas) of the SOx sensor 54 is sampled.

Next, the program proceeds to S104, in which an integrated SOx amount (that is, a sulfur poisoning amount) St estimated to be absorbed (adsorbed) by the NOx absorption catalyst 24 is calculated based on the detected sulfur concentration Sc and the coefficient a.

More specifically, the SOx integrated amount St is obtained by obtaining the exhaust gas volume Vg flowing through the exhaust pipe 18, multiplying the obtained value by the detected sulfur concentration, and integrating the product over the above-mentioned predetermined time. Ask for.

The exhaust gas volume Vg is mapped in a searchable manner from the engine speed NE and the intake pipe absolute pressure PBA. Note that the coefficient a is a coefficient indicating a ratio of the integrated value of SOx supplied to the arrangement position of the NOx absorption catalyst 24, which is estimated to be absorbed (adsorbed) by the NOx absorption catalyst 24.

Then, the program proceeds to S106, in which it is determined whether the calculated SOx integrated amount St exceeds a predetermined value A. Here, the predetermined value A is a threshold enough to determine the deterioration of the NOx absorption catalyst 24, and is set by obtaining an appropriate value through an experiment.

When the result in S106 is negative, it is determined that the NOx absorption catalyst 24 has not deteriorated, and the subsequent processing is skipped. When the result is affirmative, it is determined that the NOx absorption catalyst 24 has deteriorated, and the routine proceeds to S108. Then, the poisoning removal operation is started, and the NOx absorption catalyst 24 is electrically heated.

More specifically, the changeover switch 2
6. Alternator 28 (or battery 30) via 6
To the heater terminal 24a of the NOx absorption catalyst 24,
The temperature of the NOx absorption catalyst 24 is increased by energizing and heating. That is,
The absorbed SOx is desorbed when the catalyst temperature reaches around 700 ° C., so the temperature is increased by heating.

Then, the program proceeds to S110, in which it is determined whether the detected exhaust gas temperature Tcat exceeds a predetermined temperature B. The predetermined temperature B is set to about 700 ° C. When the result in S110 is negative, the subsequent processing is skipped. When the result is affirmative, the process proceeds to S112 to enrich the air-fuel ratio for a predetermined time (short time).

As a result, the exhaust gas becomes a rich atmosphere, and the SOx released from the NOx absorption catalyst 24 becomes unburned H
It is reduced with C and CO. Thus, the NOx absorption catalyst 24 can be regenerated.

It is to be noted that the NOx absorption catalyst 24
Of the NOx absorption catalyst 24
Although it is not the temperature itself, it can be regarded as the catalyst temperature by appropriately correcting the detected value.

In this embodiment, as described above, the sulfur concentration Sc in the exhaust gas is detected, and the catalyst deterioration due to sulfur poisoning is more directly determined based on the detected Sc concentration. Since the deterioration is performed, the deterioration of the NOx absorption catalyst due to sulfur poisoning can be accurately determined, and the regeneration process can be performed. Therefore, even if the sulfur content of the fuel increases, the NOx absorption catalyst 24 can be properly regenerated.

FIG. 4 is a flowchart showing the operation of the exhaust gas purifying apparatus for an internal combustion engine according to the second embodiment of the present invention.

A description will be given focusing on differences from the first or second embodiment. The processing from S200 to S208 is performed, and the process proceeds to S210, where the NOx absorption catalyst 24
It is determined whether or not the energization time TON to the power supply exceeds a predetermined time C.

The predetermined time C is set by appropriately obtaining a value sufficient to determine that the temperature of the NOx absorption catalyst 24 has reached 700 ° C.

When the result in S210 is negative, the subsequent processing is skipped. When the result is affirmative, the process proceeds to S212, where the air-fuel ratio is enriched for a short time as in the first or second embodiment.

In the second embodiment, as described above,
Since the energization heating is performed to promote the temperature rise of the NOx absorption catalyst 24, the poisoning removal operation can be performed accurately as in the first embodiment.

Since the exhaust gas temperature (in other words, the catalyst temperature) Tcat is estimated from the energizing time TON,
The installation of the exhaust temperature sensor 52 can be omitted.
The remaining configuration and effects are the same as in the first embodiment.

FIG. 5 is a flow chart showing the operation of the exhaust gas purifying apparatus for an internal combustion engine according to the third embodiment of the present invention.

The following description focuses on the differences from the previous embodiment. The processing from S300 to S308 is performed, and the process proceeds to S310, where the amount of power E supplied to the NOx absorption catalyst 24 exceeds the predetermined amount of power D. Is determined.

The supplied electric energy E is calculated by appropriately installing a voltage sensor and a current sensor (both not shown) and detecting the applied voltage V and the applied current I. The predetermined power amount D is set by appropriately obtaining a value sufficient to determine that the temperature of the NOx absorption catalyst 24 has reached 700 ° C.

When the result in S310 is negative, the subsequent processing is skipped. When the result is affirmative, the process proceeds to S312 to enrich the air-fuel ratio for a short time as in the first or second embodiment.

Also in the third embodiment, the heating is carried out by energizing to promote the temperature rise of the NOx absorption catalyst 24.
Poisoning removal work can be performed accurately as in the previous embodiment. The remaining configuration is the same as in the previous embodiment.

As described above, the first to third embodiments of the present invention provide an exhaust system (exhaust pipe 1) for an internal combustion engine (engine).
8) a NOx absorbent (NOx absorption catalyst 24) for absorbing NOx in the exhaust gas when the exhaust gas is in a lean atmosphere; heating means (NOx absorption catalyst heater) for heating the NOx absorbent; A sulfur concentration detecting means (SOx sensor 54) which is provided on the upstream side of the arrangement position of the NOx absorbent and detects the sulfur concentration Sc in the exhaust gas, and detects the sulfur concentration of the NOx absorbent based on the output of the sulfur concentration detecting means. Deterioration determination means (ECU for determining deterioration due to sulfur poisoning)
60, S106, S206, S306) and the NOx
Temperature estimating means for estimating the temperature Tcat of the absorbent (exhaust temperature sensor 52, ECU 60, S110, S210, S3
10) When the deterioration is determined by the deterioration determining means and the temperature estimated by the temperature estimating means is higher than the sulfur poisoning regeneration temperature (700 ° C.), the stoichiometric air-fuel ratio or a rich air-fuel ratio lower than the stoichiometric air-fuel ratio is determined. It is configured to include the sulfur removal control means (ECU 60, S110 to S112, S210 to S212, S310 to S312) to be supplied.

In the above description, the SOx sensor 54 is
JP-A-6-174892 or JP-A-9-18
It may have a structure described in Japanese Patent No. 9678. Further, the SOx sensor 54 detects the concentration of sulfur in the exhaust gas, but may detect the absolute amount.

In the above description, the upstream catalyst 22 is a three-way catalyst, but may be a NOx absorption catalyst.

[0065]

According to the present invention, the accuracy of the deterioration determination can be improved by detecting the concentration of sulfur in the exhaust gas and directly determining the deterioration due to sulfur poisoning based on the detected concentration. . Therefore, even when a fuel having a high sulfur content is used, the regeneration treatment of the NOx absorbent can be accurately performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an entire control device of an internal combustion engine including an exhaust gas purification device for an internal combustion engine according to the present invention.

FIG. 2 is an explanatory sectional view showing a configuration of an SOx sensor of the apparatus in FIG. 1 in detail.

FIG. 3 is a flowchart showing the operation of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention.

FIG. 4 is a flowchart showing an operation of the exhaust gas purification device for an internal combustion engine according to the second embodiment of the present invention.

FIG. 5 is a flowchart showing the operation of the exhaust gas purifying apparatus for an internal combustion engine according to the third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 internal combustion engine (engine) body 18 exhaust pipe (exhaust system) 22 three-way catalyst 24 electrically heated NOx absorption catalyst (NOx absorbent) 38 crank angle sensor 44 absolute pressure sensor 52 exhaust temperature sensor (temperature detecting means) 54 SOx Sensor (Sulfur concentration detection means) 60 ECU (Electronic control unit)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F01N 3/24 F01N 3/24 L F02D 41/04 305 F02D 41/04 305A F-term (reference) 3G091 AA12 AA17 AA23 AA28 AB03 AB06 BA11 BA14 BA15 BA19 BA32. JB09 KA21 KB02 LB02 MA13 NA08 NA09 NE01 NE13 NE14 NE15 PA07A PA10A PA11A PD01A PD02A PD11A PE01A PE03A PE05A PG01A PG02A

Claims (1)

[Claims] 1. A NOx absorbent provided in an exhaust system of an internal combustion engine for absorbing NOx in exhaust gas when the exhaust gas is in a lean atmosphere, heating means for heating the NOx absorbent, and the NOx absorbent And a sulfur concentration detecting means for detecting the sulfur concentration in the exhaust gas, and the NOx based on the output of the sulfur concentration detecting means.
A deterioration determining means for determining deterioration of the absorbent due to sulfur poisoning; a temperature estimating means for estimating the temperature of the NOx absorbent; and the deterioration being determined by the deterioration determining means, and being estimated by the temperature estimating means. An exhaust gas purifying apparatus for an internal combustion engine, comprising: sulfur removal control means for supplying a rich air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio when the temperature is higher than the sulfur poisoning regeneration temperature.