JP2000120428A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently raise a temperature of an NOx absorber, and effectively perform reduction/removal of NOx and regeneration from SOx poisoning by controlling a reducing means so as to be operated for time set according to a temperature of a nitrogen oxides cleaning means just before stopping fuel supply of an internal combustion engine. SOLUTION: An NOx absorber (an NOx absorbing catalyst) 24 having a three-way catalytic function is arranged in an exhaust pipe 22 so that a temperature sensor 48 is arranged downstream of it. When operating an engine, an ECU 60 discriminates whether or not an NOx absorber temperature is not less than a prescribed value (for example, 300 deg.C to 500 deg.C). When this judgment is YES, and when an engine speed is not less than a prescribed engine speed (for example, 1000 rpm), air-fuel ratio rich control is performed. While, when stopping of fuel supply is judged, a rich fuel control duration is searched from the engine speed by a table to then calculate a factor according to the NOx absorber temperature to correct the duration (the rich fuel control duration) by multiplying the duration by this factor group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, lean air-fuel ratios such as lean-burn engines have been developed. In such engines, when exhaust gas is in a lean atmosphere, nitrogen oxides in the exhaust gas are absorbed, A NOx absorbent (NOx absorption catalyst, nitrogen oxide purifying means) for reducing (purifying) nitrogen oxides absorbed when the exhaust gas is in a rich atmosphere below the stoichiometric air-fuel ratio.
Purification of NOx (nitrogen oxide) components in a lean atmosphere is performed by using such methods.

For example, Japanese Patent Application Laid-Open No. 6-129246 discloses an internal combustion engine provided with this type of NOx absorbent.
When the operating state of the engine shifts from the operating range where the lean mixture is burned to the operating range where the stoichiometric air-fuel mixture is to be burned, the air-fuel ratio of the air-fuel mixture is temporarily made rich and then made the stoichiometric air-fuel ratio Technology has been proposed.

[0004]

The fuel contains sulfur S. If the sulfur adheres (absorbs) as SOx (sulfur oxide) to the catalyst surface or micropores, the purification efficiency of the catalyst decreases. I do. In particular, the above-mentioned NO
The x-absorbing material easily absorbs sulfur, causing so-called sulfur poisoning, and lowering NOx absorption efficiency.

[0005] The temperature suitable for absorption (adsorption) or reduction (desorption) of the NOx absorbent is from 250 ° C to 550 ° C, but the temperature suitable for sulfur poisoning regeneration is higher than 600 ° C in a rich atmosphere. ℃, and 700 ℃
When the temperature is raised to the extent, the sulfur poisoning can be more effectively regenerated.

The regeneration from the sulfur poisoning is performed by supplying the rich air-fuel ratio while raising the temperature of the NOx absorbent in the same manner as the reduction and desorption of NOx. As shown in FIG. 7, after the fuel supply is stopped (fuel cut), the rich air-fuel ratio and then the stoichiometric air-fuel ratio are supplied.

[0007] As a result, the temperature of the NOx absorbent cannot be sufficiently raised, so that not only the reduction and desorption of NOx cannot be effectively performed, but also the regeneration of SOx poisoning is intended. Cannot be performed effectively.

Accordingly, an object of the present invention is to solve the above-mentioned disadvantages, and the NO
By supplying a rich air-fuel ratio for a time set according to the temperature of the x-absorber, the NOx-absorber is sufficiently heated,
Accordingly, it is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, which effectively performs reduction and desorption of NOx and regeneration from SOx poisoning.

[0009]

In order to achieve the above object, according to the present invention, an exhaust system of an internal combustion engine is provided, and when the air-fuel ratio of the exhaust gas is lean, the amount of the exhaust gas is reduced. Nitrogen oxide purifying means for absorbing nitrogen oxides and reducing the absorbed nitrogen oxides when the air-fuel ratio of the exhaust gas is stoichiometric or rich; and making the air-fuel ratio of the exhaust gas stoichiometric or rich In the exhaust gas purifying apparatus for an internal combustion engine having the reducing means, the reducing means is operated for a time set in accordance with the temperature of the nitrogen oxide purifying means immediately before stopping the fuel supply to the internal combustion engine.

[0010] Thus, the unburned components of HC and CO having a rich air-fuel ratio supplied immediately before the stop of the fuel supply can be supplied as a reducing agent, and the nitrogen oxides absorbed by the nitrogen oxide purifying means are reduced and purified. be able to.

Further, the temperature of the nitrogen oxide purifying means can be reliably raised to the regeneration temperature by burning the HC, CO, etc. by the oxygen in the exhaust gas while the fuel supply is stopped. Thus, the nitrogen oxide purifying means can be reliably regenerated from poisoning by sulfur.

[0012]

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 multi-cylinder internal combustion engine such as a four-cylinder engine (hereinafter referred to as "engine").
Indicates its body.

The intake air introduced from an air cleaner (not shown) disposed at the end of the intake pipe 12 is controlled in its flow rate by a throttle valve 16 housed in a throttle body 14 while a surge tank and an intake manifold (both in FIG. (Not shown), and flows into each cylinder.

An injector (fuel injection valve) 18 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 22 via an exhaust valve (not shown) and an exhaust manifold (not shown). A NOx absorbent (NOx absorption catalyst or nitrogen oxide purifying means) 24 having a three-way catalyst function is disposed in the exhaust pipe 22.

The NOx absorbent 24 is the same as that described in
-66129 or a catalyst of the same type as the NOx absorbent described in JP-A-7-217474,
NO in the exhaust gas when the exhaust gas is in a lean atmosphere
x (nitrogen oxide), and when the exhaust gas is in a rich atmosphere below the stoichiometric air-fuel ratio, in other words, when the oxygen concentration in the exhaust gas decreases, the absorbed NOx is converted into unburned HC, CO in the exhaust gas. And purify by reduction.

In the intake pipe 12, a bypass air passage 26 that connects the intake pipe 12 to the atmosphere is connected between the injector 18 and the throttle body 14. An air cleaner 28 is attached to the atmosphere opening end of the bypass air passage 26, and a bypass air control valve (EACV) 30 is arranged in the middle of the air cleaner 28.

The bypass air control valve 30 is a normally closed type, and has a valve body 30a for continuously changing the opening degree (opening area) of the bypass air passage 26;
a spring 30b for urging the valve body 30a in the closing direction, and an electromagnetic solenoid 30c for moving the valve body 30a in the opening direction against the spring force when energized.

In FIG. 1, a crank angle sensor (shown as "NE" in the figure) 34 is provided near a camshaft or a crankshaft (both not shown) of the engine body 10, and a cylinder is provided for each specific crank angle of a specific cylinder. It outputs a discrimination signal, a TDC signal at or near TDC (top dead center), and a CRK signal at every predetermined crank angle.

A throttle opening sensor (shown as "TH" in the figure) 36 is connected to the throttle valve 16, and outputs a signal proportional to the throttle opening TH. An absolute pressure sensor (indicated as “PBA” in the figure) 40 is provided at the end of the downstream branch path 38 and outputs a signal corresponding to the absolute pressure PBA in the intake pipe.

A water temperature sensor (shown as "TW" in the figure) 42 is provided at an appropriate position such as a cylinder block to output a signal corresponding to the engine cooling water temperature TW, and is provided upstream of the NOx absorbent 24 in the exhaust pipe 22. Is provided with an O ₂ sensor (shown as “O ₂ ”) 46 in the figure, and outputs a signal proportional to the oxygen concentration in the exhaust gas.

Further, NO
x Temperature sensor close to the absorber 24 (“TCAT” in the figure)
48), and the temperature TC of the NOx absorbent 24
A signal corresponding to AT (or exhaust temperature) is output.

Further, a vehicle speed sensor 50 is provided near a drive shaft (not shown) of a vehicle (not shown) on which the engine 10 is mounted, and a signal corresponding to a predetermined rotation of the drive shaft, that is, a signal corresponding to the vehicle speed V is provided. Is output.

An automatic transmission 52 (shown as "A / T" in the figure) 52 having four forward speeds is connected to the engine 10.
The output of the engine 10 is input. A shift controller 54 composed of a microcomputer is connected to the automatic transmission 52.

The shift controller 54 determines the gear ratio (gear position) from the vehicle speed V and the throttle opening according to a shift scheduling map (not shown), and changes the output of the engine 10.

An inclination sensor 56 is disposed at an appropriate position of the vehicle on which the engine 10 is mounted, and outputs a signal proportional to the inclination (gradient) of the traveling road on which the vehicle is located.

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 aforementioned CRK signal to detect the engine speed NE, calculates the basic fuel injection amount from the engine speed NE and the absolute pressure PBA in the intake pipe based on the valve opening time of the injector 18, and calculates the target idle speed. The basic ignition timing is calculated from the engine speed NE and the intake pipe absolute pressure PBA, and is corrected based on the water temperature and the like, in addition to the correction based on the fuel ratio.

Further, the CPU 60b controls the reduction and desorption of NOx and SOx as described subsequently. In addition, CPU
The shift controller 60b and the above-described shift controller 54 are communicably connected.

Next, the above-described operation of the apparatus according to the present application will be described with reference to the flowchart of FIG. The illustrated program is executed for each TDC, for example.

First, at S10, it is determined whether a fuel supply stop (fuel cut) condition is satisfied. The fuel supply stop (fuel cut) condition is satisfied in a deceleration operation state in an operation region determined by the engine speed NE and the intake pipe absolute pressure PBA (load).

When the result in S10 is negative, the subsequent processing is skipped. When the result is affirmative, the process proceeds to S12, in which it is determined whether or not the bit of the rich spike flag FRS (described later) is set to 1. Proceeds to S14, and determines whether or not the vehicle is in a lean operation.

Here, "lean operation" means an operation state in which the target air-fuel ratio is controlled to a lean air-fuel ratio of around 22: 1.

When the result in S14 is negative, the subsequent processing is skipped. When the result is affirmative, the process proceeds to S16, in which a rich control execution determination is made to determine whether or not the supply air-fuel ratio should be a rich air-fuel ratio.

FIG. 3 is a subroutine flowchart showing the operation.

First, in S100, the NOx absorbent temperature T
It is determined whether the CAT is equal to or greater than a predetermined value Tref1. The predetermined value Tref1 is set to a value suitable for determining whether or not the temperature of the NOx absorbent 24 has reached a reproducible temperature, for example, from 300 ° C. to 500 ° C. by supply of a rich air-fuel ratio to be performed later. I do.

When the result in S100 is NO, it is determined that the temperature of the NOx absorbent is relatively low and the desorption efficiency of NOx and SOx is low, and the program proceeds to S102, in which the rich control for setting the supply air-fuel ratio to the rich air-fuel ratio is performed. The flag FRS is reset to 0.

As described above, resetting the bit of the flag FRS to 0 means that the rich air-fuel ratio is not supplied, and setting the bit of the flag FRS to 1 as described later means that the rich air-fuel ratio is not changed. Means to supply.

On the other hand, if the result in S100 is affirmative, S10
4, the engine speed NE becomes the predetermined speed NEre
f, for example, it is determined whether it is 1000 rpm or more.

When the result in S104 is negative, the fuel supply suspension time is shortened, and it is considered that it is insufficient to raise the temperature to the above-mentioned regeneration temperature.

When the result in S104 is affirmative, the program proceeds to S106, in which it is determined from the output of the inclination sensor 56 whether or not the vehicle is currently climbing a hill. Since it is considered insufficient to raise the temperature to the regeneration temperature, the process proceeds to S102. still,
At this time, it may be determined whether the climbing angle is equal to or larger than a predetermined angle.

On the other hand, when the result in S106 is NO, S10
Proceeding to 8, the rich control for setting the supply air-fuel ratio to the rich air-fuel ratio is performed, and the bit of the flag FRS is set to 1.

Returning to the description of the flow chart of FIG.
If the result of the determination in step 12 is affirmative, and it is determined that the bit of the flag FRS is set to 1, the routine proceeds to step S18, where rich control is performed to set the supply air-fuel ratio to the rich air-fuel ratio.

FIG. 4 is a subroutine flowchart showing the operation.

First, in S200, it is determined whether or not the bit of the rich control flag FRT (described later) is set to 1. Since the initial value of this flag bit is set to 0, it is negated in the first program loop and S2
In step 02, the rich fuel control continuation time Tr is calculated from the engine speed NE when the fuel supply is determined to be stopped by searching a table (characteristics are not shown).

Then, the program proceeds to S204, in which a coefficient Kt is calculated according to the detected NOx absorbent temperature TCAT. This is performed by searching a table (not shown) from the detected temperature TCAT. When the detected temperature TCAT is high, the coefficient Kt is set to, for example, 0.9 to shorten the duration Tr, and when the detected temperature TCAT is low, For example, it is set to 1.1 to extend the duration Tr.

Next, proceeding to S206, when traveling on a downhill, searching a table (not shown) according to the downhill angle to calculate the coefficient Ka, and proceeding to S208, the gear ratio (gear position).
A coefficient (Km) is calculated by retrieving a table (not shown) according to. As for the coefficients Ka and Km, appropriate values obtained by experiments in advance are set to be freely searchable from the above parameters so that the duration Tr becomes the rich air-fuel ratio supply time without excess or deficiency.

Next, the program proceeds to S210, in which the calculated duration time Tr is multiplied by the retrieved coefficient group to correct the duration time (rich fuel control duration time) Tr. The duration after correction is T
ro. Next, the flow proceeds to S212, where the value of the timer T (up counter) is reset to zero, and the flow proceeds to S214, where the timer T is started to start time measurement.

Then, the program proceeds to S216, in which the current operation state is determined.
That is, the basic fuel injection quantity Tim calculated in accordance with the detected operating condition, multiplied by the air-fuel ratio correction coefficient KO ₂ and the target air-fuel ratio correction coefficient KCMD, calculated as follows fuel injection amount Tout. Tout (N) = Tim × KO ₂ × KCMD

As described above, the basic fuel injection amount Tim and the fuel injection amount Tout are specifically indicated by the valve opening time of the injector 18. Note that N indicates a discrete sample number, more specifically, the execution time of the flow chart of FIG.
Further, for simplification of the description, description of other correction items will be omitted.

In this step, as described above, the fuel injection amount (time) Tout is calculated, and the target air-fuel ratio correction coefficient KCMD is changed from a lean value (for example, 22: 1) to a rich value (for example, 12: 1). ).

Then, the program proceeds to S218, in which it is determined whether or not the value of the timer T has become equal to or greater than the corrected duration time Tro. If not, the program proceeds to S220 in which the bit of the rich control flag FRT is set to 1. At the same time, when the result is affirmative, the process proceeds to S222, and the bit of the rich control flag FRT is reset to 0.

Therefore, in the next and subsequent program loops, until the value of the timer T reaches the corrected duration time Tro, the result in S200 is affirmative, and the enrichment process is continued in S216.

After that, the fuel supply is stopped in a routine (not shown).

The above processing will be described with reference to FIG.
In the prior art shown in FIG. 7, after the fuel supply was stopped, the rich air-fuel ratio (rich spike) was supplied, whereas in the control of the present application shown in FIG. 5, the fuel supply was performed after the rich air-fuel ratio was supplied. Stopping, that is, supplying the rich air-fuel ratio immediately before stopping the fuel supply, in other words, operating the reducing means.

As a result, the unburned components of HC and CO having a rich air-fuel ratio supplied immediately before the stop of the fuel supply can be supplied as the reducing agent, and the NOx absorbed by the NOx absorbent 24 can be supplied.
Can be performed.

Further, NOx is combusted by the combustion of O _{2 in} the exhaust gas while the fuel supply is stopped, such as HC and CO.
The temperature of the absorbent 24 can be reliably raised to the regeneration temperature, and the NOx absorbent 24
(Sulfur oxide) can be effectively regenerated from poisoning.

As described above, the temperature suitable for the regeneration from SOx poisoning is the temperature (250
C. to 550 ° C.), and 6 for a rich atmosphere.
If the temperature can be raised to about 00 ° C. and further to about 700 ° C., the regeneration can be performed more effectively.

In the prior art shown in FIG. 7, since the rich air-fuel ratio is supplied after the fuel supply is stopped, no HC or CO reacts with O ₂ during the fuel supply stop period. The temperature of the absorber 24 cannot be raised sufficiently. The fuel supply stop period ends, even when supplying rich air-fuel ratio, can not be sufficiently raised in temperature NOx absorbent 24 for O ₂ is low.

FIG. 6 shows the fuel supply stop interruption control performed in parallel with the above-described rich control.

That is, if the exhaust gas temperature rises excessively when the fuel supply is stopped after the above-described rich control is performed, and the NOx absorbent temperature rises excessively, the NOx absorbent 2
4 is a control to avoid the possibility of deterioration.

In the following, it is determined whether or not fuel supply is stopped in S300. If the result is negative, the subsequent processing is skipped. If the result is affirmative, the process proceeds to S302, where the NOx absorbent temperature TCAT is reduced to a predetermined temperature Tref2. ,
For example, it is determined whether the temperature is from 900 ° C. to 950 ° C. or more.

When the result in S302 is negative, the subsequent processing is skipped. When the result is affirmative, S304 is executed.
Then, the fuel supply stop is stopped, and the fuel injection amount (time) with the target air-fuel ratio set to the rich air-fuel ratio or the stoichiometric air-fuel ratio is supplied.

As a result, the O ₂ concentration in the exhaust gas decreases, the oxidation reaction in the NOx absorbent 24 decreases, and an excessive rise in the temperature of the NOx absorbent 24 can be avoided. Can be prevented.

In this embodiment, as described above,
It is provided in an exhaust system (exhaust pipe 22) of an internal combustion engine (engine 10). When the air-fuel ratio of the exhaust gas is lean, it absorbs nitrogen oxides NOx in the exhaust gas, and the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or Nitrogen oxide purifying means (NOx absorbent 24) for reducing nitrogen oxides absorbed when rich, and reducing means (ECU 60, S10 to S18, S100 for reducing the air-fuel ratio of the exhaust gas to the stoichiometric air-fuel ratio or rich) In the exhaust gas purifying apparatus for an internal combustion engine having S108, S200 to S222), the reducing means is turned on immediately before the fuel supply of the internal combustion engine is stopped by a time Tr (Tro) set according to the temperature TCAT of the nitrogen oxide purifying means. (S200 to S222).

More specifically, an internal combustion engine (engine 1
0) is provided in the exhaust system (exhaust pipe 22) to absorb nitrogen oxides NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio or rich. Nitrogen oxide purifying means (NOx absorbent 24) for reducing the absorbed nitrogen oxides, and reducing means (ECU 6) for making the air-fuel ratio of the exhaust gas stoichiometric or rich.
0, S10 to S18, S100 to S110, S20
0 to S222), the rich air-fuel ratio should be supplied based on at least the parameters (engine speed NE, uphill) including the temperature TCAT of the nitrogen oxide purifying means (NOx absorbent 24). Rich air-fuel ratio supply determining means (ECU 6
0, S14, S100 to S106), and when the rich air-fuel ratio determining means determines that the rich air-fuel ratio should be supplied, the supply time for supplying the rich air-fuel ratio (rich fuel control continuation time Tr (Tro)) Supply time determining means (ECU 60, S16, S18, S200
To S222), and the reducing means is operated for the determined supply time immediately before the fuel supply of the internal combustion engine is stopped (S200 to S222).

More specifically, after supplying the rich air-fuel ratio, the nitrogen oxide purifying means (NOx absorbent 24)
A fuel supply suspension suspending means (ECU) for suspending the fuel supply suspension when the temperature TCAT is equal to or higher than a predetermined temperature Tref2.
60, S300 to S304).

In the above description, the rich air-fuel ratio is supplied as the reducing agent. Alternatively, an injector may be provided in the exhaust system to directly inject the reducing agent.

Although the temperature of the NOx absorbent is detected from the sensor, the temperature may be estimated using an appropriate logic.

Although a NOx absorbent having a three-way catalyst function is used, a three-way catalyst may be provided independently.

[0074]

According to the first aspect of the present invention, the unburned components of HC and CO having a rich air-fuel ratio supplied immediately before the stop of the fuel supply can be supplied as a reducing agent, and are absorbed by the nitrogen oxide purifying means. Nitrogen oxides can be reduced and purified.

Furthermore, by burning HC, CO, etc. with oxygen in the exhaust gas while the fuel supply is stopped, the temperature of the nitrogen oxide purifying means can be surely raised to the regeneration temperature. Thus, the nitrogen oxide purifying means can be reliably regenerated from poisoning by sulfur.

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

FIG. 3 is a subroutine flowchart showing a rich control execution determination process in the flowchart of FIG. 2;

FIG. 4 is a subroutine flowchart showing a rich control process in the flowchart of FIG. 2;

FIG. 5 is an explanatory time chart showing the control of FIG. 2;

FIG. 6 is a subroutine flowchart showing a fuel supply stop interruption determination process performed in parallel with the flowchart of FIG. 2;

FIG. 7 is a time chart similar to FIG.
It is a chart.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Internal combustion engine (engine) 12 Intake pipe 16 Throttle valve 18 Injector 22 Exhaust pipe 24 NOx absorbent (NOx absorption catalyst. Nitrogen oxide purifying means) 34 Crank angle sensor 40 Absolute pressure sensor 48 Temperature sensor 52 Automatic transmission (AT) 54 shift controller 60 ECU (electronic control unit)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/06 330 F02D 41/06 330J (72) Inventor Tokatsu Takabuki 1-4-4 Chuo, Wako-shi, Saitama 1 F-term in Honda R & D Co., Ltd. (Reference) 3G091 AA02 AA12 AA23 AA28 AB03 AB06 BA04 BA11 BA14 BA33 CA13 CA18 CB02 CB05 CB06 CB08 CB09 DA01 DA02 DA03 DA04 DA08 DB06 DB10 EA00 EA01 EA03 EA30 EA30 EA30 FA05 FA19 FB10 FB11 FB12 FC02 HA08 HA36 HB03

Claims (1)

[Claims] 1. An exhaust system for an internal combustion engine, which absorbs nitrogen oxides in an exhaust gas when the air-fuel ratio of the exhaust gas is lean, and absorbs the nitrogen oxides in the exhaust gas when the air-fuel ratio of the exhaust gas is a stoichiometric air-fuel ratio or rich. An exhaust gas purification device for an internal combustion engine, comprising: a nitrogen oxide purification device that reduces the nitrogen oxides that have been reduced; and a reduction device that makes the air-fuel ratio of the exhaust gas a stoichiometric air-fuel ratio or rich. An exhaust gas purifying apparatus for an internal combustion engine, wherein the reducing means is operated for a time set according to the temperature of the nitrogen oxide purifying means.