JP2000104533A - Internal combustion engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] Regarding an internal combustion engine, irrespective of a change in NOx release characteristics of a NOx catalyst, N is reliably reduced without deteriorating fuel consumption.
NOx stored in the Ox catalyst can be released and reduced. SOLUTION: The NOx stored in a NOx catalyst 6A provided in an exhaust passage of an internal combustion engine is released and reduced by setting an exhaust air-fuel ratio to an atmosphere having a low oxygen concentration.
If the NOx concentration released from the NOx catalyst 6A detected by the NOx sensor 10 provided downstream of the catalyst falls below a predetermined value, the atmosphere changing means 23 changes the exhaust air-fuel ratio from an atmosphere having a low oxygen concentration to an atmosphere having an excessive oxygen. Allow to do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an internal combustion engine provided with a NOx catalyst, and more particularly to an internal combustion engine capable of releasing or reducing NOx stored in the NOx catalyst.

[0002]

2. Description of the Related Art At present, a NOx catalyst capable of purifying NOx even in an oxygen-excess atmosphere in which oxygen in exhaust gas is excessive has been developed.
The provision of an Ox catalyst purifies NOx during lean combustion. As one of the NOx catalysts, NOx
Oxidation type NOx catalysts (hereinafter simply referred to as NOx catalysts) have been developed which purify NOx in exhaust gas by storing NOx on the catalyst. The NOx catalyst oxidizes NOx in the exhaust gas to generate nitrate in an oxygen-excess atmosphere, thereby storing NOx. On the other hand, in an oxygen-low concentration atmosphere, the NOx catalyst stores nitrate in the exhaust gas and C in the exhaust gas.
O has the function of reacting with O to form a carbonate, thereby releasing and decomposing NOx. Of course, the NOx storage amount of the NOx catalyst has a limit. Therefore, by making the exhaust air-fuel ratio rich before the NOx storage amount exceeds the limit,
The atmosphere surrounding the Ox catalyst is changed to an atmosphere having a reduced oxygen concentration, and NOx stored on the catalyst is released.

[0003] As such a technique, Japanese Patent Laid-Open No. 7-166 is disclosed.
There is one disclosed in Japanese Patent No. 851. With this technology,
A NOx sensor is provided downstream of the NOx catalyst, and a decrease in the purification efficiency of the NOx catalyst is detected based on the output of the NOx sensor in an oxygen-excess atmosphere. And NO
x When the purification efficiency of the catalyst is reduced, the NOx stored in the NOx catalyst is released by setting the atmosphere to a reduced oxygen concentration for a predetermined period of time, and the NOx storage performance of the NOx catalyst is secured again, and the exhaust gas during lean burn operation is reduced. NOx in
The purifying function is maintained.

[0004]

SUMMARY OF THE INVENTION However, NOx
The NOx emission characteristics of the catalyst change due to changes in operating conditions such as A / F (air-fuel ratio), exhaust temperature, S / V (ratio of the total surface area of the combustion chamber to the volume of the combustion chamber), and deterioration of the catalyst itself. Is what you do. Therefore, as in the above-described prior art, when the time for the oxygen-concentration-lowering atmosphere is fixed to a preset time, there is a problem that it is impossible to cope with a change in NOx emission characteristics.

[0005] In other words, if the time for setting the atmosphere to a low oxygen concentration atmosphere is insufficient because it does not correspond to the NOx release characteristics of the NOx catalyst, the purification efficiency of the NOx catalyst is reduced since NOx is not completely released, and The amount of NOx emission to the air will increase. Conversely, if the time for setting the atmosphere in which the oxygen concentration is low is too long, useless fuel injection is performed, which results in deterioration of fuel efficiency.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to reliably release and reduce NOx stored in a NOx catalyst without deteriorating fuel efficiency irrespective of a change in NOx release characteristics of the NOx catalyst. It is an object to provide an internal combustion engine as described above.

[0007]

For this reason, in the internal combustion engine of the present invention, the exhaust air-fuel ratio is set to an atmosphere having a low oxygen concentration to release NOx stored in the NOx catalyst provided in the exhaust passage of the internal combustion engine. Alternatively, reduction is performed, but NO detected by state detection means provided downstream of the NOx catalyst is
x Based on the result of comparing the release state and the predetermined state,
The atmosphere changing means changes the exhaust air-fuel ratio from the oxygen-concentrated atmosphere to the oxygen-excess atmosphere.

Accordingly, the NOx releasing operation can be performed without excess or shortage according to the change in the NOx releasing characteristics of the NOx catalyst, and the NOx stored in the NOx catalyst can be reliably released or reduced without deteriorating the fuel efficiency. It becomes possible.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. First, an outline of a configuration of an internal combustion engine according to an embodiment of the present invention will be described. As shown in FIG. 2A, the internal combustion engine is a four-cycle engine, a spark ignition type, and a combustion type. It is configured as a direct injection internal combustion engine (direct injection engine) that directly injects fuel into a room.

An intake passage 2 and an exhaust passage 3 are connected to the combustion chamber 1 so that they can communicate with each other. The communication between the intake passage 2 and the combustion chamber 1 is controlled by an intake valve 4.
The communication between the exhaust passage 3 and the combustion chamber 1 is controlled by an exhaust valve 5. The intake passage 2 is provided with an air cleaner and a throttle valve (not shown).
The exhaust passage 3 is provided with an exhaust purification device 6 and a muffler (muffler) not shown. 9 is a high-temperature sensor, and 10 is a NOx sensor.

An ignition plug 7 is provided at the upper center of the combustion chamber 1, and an injector 8 is provided at an upper side edge of the combustion chamber 1.
Is provided. This injector (fuel injection valve) 8
Are arranged so that the opening faces the combustion chamber 1. With such a configuration, the air drawn in according to the opening of the throttle valve (not shown) is drawn into the combustion chamber 1 by opening the intake valve 4, and the electronic control unit (ECU) 2
On the basis of the signal from 0, the fuel is mixed with the fuel directly injected from the injector 8. Then, the ignition plug 7 is ignited at an appropriate timing to generate combustion, and after generating an engine torque, is discharged from the combustion chamber 1 as exhaust gas to the exhaust passage 3.
O, HC, since the purifying three harmful components NO _x,
The sound is muted by the muffler and desorbed to the atmosphere.

The exhaust gas purifying device 6 includes a storage NO _x catalyst (hereinafter simply referred to as NO _x catalyst) 6A and two three-way catalysts 6A.
B, 6C. That is, since the air-fuel ratio is in the case of lean, the flue gas CO, HC can not be purified to NO _x in the three-way catalyst when the oxygen-excess atmosphere what concentration of NO _x is to be rapidly while hardly contained, the NO _x is occluded by the NO _x catalyst 6A that functions in an oxygen-excess atmosphere, and under a stoichiometric air-fuel ratio, the three-way catalyst 6B,
The three-way function of 6C is has become so purifies CO in the exhaust gas, HC, and NO _x.

Further, one of the three-way catalyst. 6C, than the NO _x catalyst 6A is disposed on the upstream side, so as to function as a front catalyst. The front catalyst receives a higher temperature exhaust gas at the time of cold start of the engine, and is activated immediately to purify HC and other exhaust gas components. In addition, the arrangement of the three-way catalyst 6C is as shown in FIG.
The NO _x catalyst 6A, may be arranged in proximity to separately engine body and the three-way catalyst 6B, as shown in FIG. 2 (b),
The NO _x catalyst 6A, may be arranged integrally with the three-way catalyst 6B.

The three-way catalyst 6B has NO_xCatalyst 6A and one
It may be embodied. That is, NO_xThree for catalyst 6A
The original function may be provided. In this case,
NO _xSensor 10 is located downstream of the integrated catalyst.
It is. By the way, NO_xThe catalyst 6A is NO_xContinue to occlude
Saturates soon after it is burnt
NO_xWill be released into the atmosphere. There
And NO_xWhen the catalyst 6A reaches the saturated state,
NO_xMust be released once, but this NO
_xRelease is NO_xThe atmosphere around the catalyst 6A has a low oxygen concentration.
N stored in the lower atmosphere (reducing atmosphere)
O_xNO_TwoAnd then HC, CO (return
NO by supply of base agent)_TwoTo reduce N _TwoDischarge as
By doing it.

Here, the NO _x catalyst 6 in the internal combustion engine
The release of NO _x from A will be described in more detail. In a direct injection engine such as the internal combustion engine, as a mode of fuel injection, a late injection mode (compression lean) in which fuel injection is performed during a compression stroke in order to realize lean operation by the above-described stratified super-lean combustion and improve fuel efficiency. Mode) and
Achieved lean operation by premixed combustion and fuel injection during the intake stroke in order to obtain output by slow acceleration (intake lean mode), and stoichiometric operation by premixed combustion to achieve lean operation. In order to improve the output, a stoichiometric mode in which fuel is injected during the intake stroke and an enrich mode in which rich operation by premixed combustion is realized and the output is improved more than in the stoichiometric operation mode are provided. It can be switched according to the operating state.

[0016] Then, under the lean operation as described above, since the periphery of the NO _x catalyst 6A is in the oxygen excessive atmosphere, the the NO _x catalyst 6A produced by lean combustion N
O _x is stored, and the NO _x thus stored is released and reduced in an atmosphere having a reduced oxygen concentration.
In order to release the NOx stored in the catalyst 6A, an atmosphere changing means 23 for changing the exhaust passage to an atmosphere having a reduced oxygen concentration is provided. This atmosphere changing means 23 is adapted to create an atmosphere having a reduced oxygen concentration by utilizing fuel injection control.

That is, as shown in the functional block diagram of FIG.
And fuel injection control means 25 are provided. The mode selecting means 24 selects one of the above modes according to the engine speed Ne and the average effective pressure Pe. The fuel injection control means 25 includes a normal fuel injection control means 26 for injecting fuel to perform normal combustion for obtaining an engine output, and an additional fuel injection control means 27 for creating an atmosphere having a reduced oxygen concentration. It is provided.

The normal fuel injection control means 26 selects a fuel injection control map corresponding to the mode set by the mode selection means 24, and uses the selected fuel injection control map to determine the engine speed Ne and the average effective speed. Fuel injection amount and injection timing for performing normal combustion according to the pressure Pe (that is, fuel injection end timing and fuel injection start timing)
Set.

The detection information (or calculation information) of the engine rotation speed sensor 13 is used for the engine rotation speed Ne, and the calculation information of the effective pressure calculation means 28 is used for the average effective pressure Pe. In the effective pressure calculating means 28, the engine speed Ne and the accelerator position sensor (AP
S) The average effective pressure Pe is calculated from each information of the accelerator opening θ detected in 14 (when the throttle opening always corresponds to the accelerator opening, the throttle opening may be used instead of the accelerator opening).

The additional fuel injection control means 27 controls an additional fuel injection (rich spike) for releasing and reducing NOx from the NOx catalyst 6A. This additional fuel injection is performed during the expansion stroke of each cylinder (preferably at a timing close to the end of the expansion stroke as well) in consideration of securing HC and CO in the exhaust gas and the effect on the output torque of the engine. Like that. Thus, the total air-fuel ratio (total A / F) of the normal fuel injection (main injection) and the additional fuel injection is made rich. As a method of changing the atmosphere around the NOx catalyst 6A to an atmosphere with a reduced oxygen concentration, a method of enriching the air-fuel ratio only by normal fuel injection without using additional fuel injection may be used. Since the engine output fluctuates, it is necessary to perform processing such as ignition timing control, intake air amount control, or the like to suppress fluctuations in the engine output.

The atmosphere changing means 23 has a function of making the surroundings of the NOx catalyst 6A into an atmosphere with a reduced oxygen concentration (reducing atmosphere) by such additional fuel injection. The additional fuel injection control means 27 and the additional fuel An injector (fuel injection valve) driven by an injector driver (not shown) under the control of the injection control means 27 to perform additional fuel injection
And 8.

The additional fuel injection is determined by the determination means 21.
The determination means 21 determines a start time and an end time of the additional fuel injection control. First, the start time is determined
The determination is performed by evaluating the NOx concentration β detected by the NOx sensor 10 corresponding to the state detection means provided on the downstream side of the NOx catalyst 6A, that is, the state of NOx release from the NOx catalyst 6A. That is, when an operation is performed in a lean mode such as the intake lean mode or the compression lean mode, the vicinity of the NOx catalyst 6A becomes an oxygen-excess atmosphere, and NOx is stored in the NOx catalyst 6A, and NOx purification by the NOx catalyst 6A is performed. Efficiency will gradually decrease. As a result, the NOx discharged downstream without being stored in the NOx catalyst 6A gradually increases, and the NOx concentration β detected by the NOx sensor 10 increases. Therefore, the NOx concentration β
Is evaluated, a decrease in the purification efficiency of the NOx catalyst 6A can be determined.

In evaluating the NOx concentration β, first,
The correction of the NOx concentration β is performed. That, NO _X sensor 10, sometimes not a little error in the detection accuracy or by aging the individual variations occur, also the NO _X concentration β of NO _X sensor 10 detects, NO _X concentration of the detection error of β ₀ is included. Therefore, it is necessary to grasp and correct the NO _X concentration β _{0 corresponding} to the detection error in advance, but in this case, the NO _X concentration β ₀ is used when the operating state is such that the NO _X release amount becomes almost _zero.
Seeking. For example, immediately after the additional fuel injection control for NO _X release, the mode is the stoichiometric feedback operation, and the NO _X concentration detected in the low-load low-speed operation state at the time of idling is determined by the detection error N
And O _X concentration (NO _X sensor correction amount) beta _0, judging means 2
1 is stored in the storage means.

That is, when the NO _X catalyst 6A is fully functioning during the stoichiometric feedback operation at a low load and a low speed, the NO _X concentration becomes substantially zero, so that the NO _X sensor 10 operates normally. (if there is an error in the output value) if any, NO _X concentration NO _X sensor 10 detects also should be zero. Therefore, at this time, if the NO _X sensor 10 detects a constant NO _X concentration β ₀ , this is the NO _X concentration corresponding to the detection error, that is, the NO _X sensor correction amount β ₀ . The NO _x sensor correction amount β ₀ is set each time the set conditions (ie, immediately after the additional fuel injection control, the stoichiometric feedback mode, the low-load low-speed state) are satisfied, and the storage means in the determination means 21 is set. Is updated.

Thus, NO_XSensor correction amount β₀By
NO_XNO detected by the sensor 10 _XCorrect the density β
NO_XIndividual variation of sensor 10 is compensated
And NO_XSensor correction amount β₀Is the setting condition
Is performed each time the condition is satisfied._XFrom concentration β
The effects of aging are also eliminated. this
NO set as above_XSensor correction amount β₀By
NO detected_XBy correcting (subtracting) the concentration β
, True NO_XDensity (corrected NO_XConcentration) γ (γ = β-
β₀) Is calculated.

The corrected NO _X concentration (hereinafter simply referred to as NO _X concentration) γ is the NO _X concentration detected downstream of the NO _X catalyst 6A during a lean operation such as an intake lean mode or a compression lean mode. Yes, as the purification efficiency of the NO _X catalyst 6A decreases, that is, as the NO _X storage amount approaches a saturated state, it increases. Therefore, this N
O _X concentration gamma compared with a predetermined start determining concentrations gamma ₁ corresponding to the NO _X concentration at which purification efficiency falls below the acceptable level of the NO _X catalyst 6A, purification of gamma ₁ ≦ gamma If NO _X catalyst 6A It can be determined that the efficiency has fallen below an acceptable level.

[0027] The determination means 21, NO _X catalyst 6A
If it is determined that the purification efficiency of
It is determined that additional fuel injection for releasing and reducing NOx from the NOx catalyst 6A needs to be performed, and a start signal of additional fuel injection is output to the additional fuel injection control means 27. The additional fuel injection control means 27 drives the injector 8 through an injector driver (not shown) in response to the input of the start signal, and performs additional fuel injection so that the air-fuel ratio becomes slightly smaller than the stoichiometric air-fuel ratio (for example, about 13). ing.

On the other hand, the end timing of the additional fuel injection control is determined based on the output of the NOx sensor 10 and the information from the engine speed sensor 13 and the effective pressure calculating means 28.
This is performed by evaluating the NOx concentration β obtained during the period of performing the additional fuel injection. That is, as shown in FIG. 3, the determination means 21 outputs the start signal of the additional fuel injection to the additional fuel injection control means 27, and at the same time, starts counting by the timer 12 (time point t ₀ ).
A predetermined time tt ₀₁ elapsed time (time t _1), to evaluate the NOx concentration β inputted from the NOx sensor 10.
However, the start time in the same manner as in the determination, the NO _X concentration beta N
The NO _X sensor 1 is corrected by the O _X sensor correction amount β ₀
True NO by eliminating the effects of individual variations of 0 and changes over time
_{The X} concentration γ (γ = β−β ₀ ) is calculated.

[0029] Here, NO _X concentration γ obtained, NO _X catalyst 6A during additional fuel injection control for of the NO _X release
A NO _X concentration detected downstream of, the NO _X concentration shows the NO _X emission state from NO _X catalyst 6A.
That, NO _X that was stored in the NO _X catalyst 6A As release of the NO _X from the NO _X catalyst 6A advances is reduced, NO _X concentration detected by the downstream of the NO _X catalyst 6A gradually decreases. Therefore, the NO _X concentration gamma NO _X
Compared to end judgment concentration corresponding to the NO _X concentration at the release completion (predetermined _{state) γ 2 (γ 2 ≦ γ} 1), NO X released from the gamma ≦ gamma ₂ If NO _X catalyst 6A is complete and Can be determined.

The end determination concentration γ ₂ is determined in consideration of a response delay due to an exhaust gas speed, a catalytic reaction speed, a sensor response delay, or the like. That is, due to the time lag due to these response delays, even if the NOx sensor 10 determines that the NOx release has been completed and terminates the additional fuel injection, the NOx catalyst 6A will remain in the rich atmosphere for a while even though the NOx release has been completed. The state is continued, and excess fuel injection leads to deterioration of fuel efficiency, and CO and HC are discharged, leading to deterioration of exhaust gas. Therefore, the end determination density γ ₂ is
The concentration is set slightly higher than the true termination determination concentration so that the additional fuel injection is terminated earlier by the response delay.

[0031] In addition, the NO _X concentration γ, NO _X catalyst 6A
In addition to the NO _X stored in the
Since the influence of NO _X flowing into the O _X catalyst 6A is also included, the end determination concentration γ ₂ is determined in consideration of the influence.
That is, the amount corresponding end determination concentration gamma ₂ inflow NO _X than setting slightly higher than the true end determination concentration. Also,
The effective pressure (load information) Pe input from the effective pressure calculation means 28 is not considered individually.
And the engine speed N input from the speed sensor 13
It may be set end determination concentration gamma ₂ on the basis of a map defined by as e.

[0032] Incidentally, the above-mentioned time tt ₀₁ is a margin time for preventing the erroneous determination immediately after the additional fuel injection control starts due to the vibration of the NO _X concentration beta. In other words, the exhaust gas velocity described above, catalytic rate, be started additional fuel injection by a signal from the ECU for the response delay due to the influence of the sensor response delay, etc., NO _X concentration detected by the NO _X sensor 10 is immediately are not changed, and the NO _X concentration β detected by the NO _X sensor 10 is accompanied by a slight vibration instead of smoothly changing, also, end determining concentration gamma ₂ and start determining the concentration gamma ₁ and the because differences in some cases depending on the operating region small, because there is a case where NO _X concentration gamma immediately after additional fuel injection control start (γ = β-β ₀₎ becomes the end determining concentration gamma ₂ or less.

[0033] Therefore, the time tt _01, must NO _X concentration to the extent that erroneous determination can be prevented β to secure the time until the rise, the exhaust gas velocity, catalytic rate, the response delay of the sensor response delay, etc. Decide in consideration. Alternatively, the determination may be made based on a map determined by the effective pressure (load information) Pe input from the effective pressure calculation means 28 and the engine speed Ne input from the speed sensor 13.

Thus, from the start of the additional fuel injection control,
Predetermined time (time tt₀₁NO) _XEvaluate concentration β as appropriate
By doing, NO_XNO from catalyst 6A_XRelease is complete
Can be determined. And NO_XTouch
NO from medium 6A_XWhen it is determined that the release has been completed,
That is, the corrected NO_XCatalyst γ is the end determination concentration γ_TwoLess than
When the determination has been made, the determination means 21
Outputs the end signal of additional fuel injection to 27
I have. The additional fuel injection control means 27 receives an end signal
To stop the driving of the injector 8
You.

[0035] Thus, the operating state of the engine becomes the normal intake lean mode or lean mode such as a compression lean mode, the exhaust air-fuel ratio is changed again to the oxygen-rich atmosphere, the occlusion of the NO _X in the NO _X catalyst 6A It is to be resumed. Since the internal combustion engine according to one embodiment of the present invention is configured as described above, additional fuel injection control for releasing NOx stored in the NOx catalyst 6A is performed, for example, as shown in the flowchart of FIG. It is.

First, in the judgment means 21, NO_XSensor 1
NO detected downstream of NOx catalyst 6A_XCheck concentration β
Out, NO_XSensor correction amount β₀Corrected by
NO _XDensity γ and predetermined start determination density γ₁Compare with
(Step S10). And NO_XDensity γ starts judgment
Concentration γ₁When it becomes above, NO_XPurification efficiency of catalyst 6A
From the NOx catalyst 6A
It is determined that the release of NOx is necessary. Additional fuel injection control means
At 27, the NOx catalyst 6A sends NOx
Additional fuel injection control to release
Is slightly smaller than the stoichiometric air-fuel ratio (for example, about 1
3) Inject additional fuel so that the NOx catalyst 6A
The surrounding atmosphere is set to an atmosphere having a reduced oxygen concentration. this
Accordingly, the NOx catalyst 6A controls the release of the stored NOx.
Start (step S20).

The predetermined time from the start of the additional fuel injection tt ₀₁ elapses after (step S30), the determination means 21, then, compares the corrected NO _X concentration gamma and end determination concentration gamma _2. However, termination determination concentration gamma ₂ is the exhaust gas velocity, catalytic rate, in consideration of the influence of the NO _X flowing to the NO _X catalyst 6A determines the response delay and in additional fuel injection control due to the effect of the sensor response delay and the like ( Step S40).

[0038] Then, NO _X concentration γ is the end determination concentration γ ₂
When equal to or less than, the determination unit 21 determines that NO _X release from NO _X catalyst 6A is completed. Adding fuel injection control means 27, based on this determination to end the additional fuel injection control, when the engine is in the compression lean mode or an intake lean mode, again oxygen-excess atmosphere surrounding atmosphere of the NO _X catalyst 6A Change to As a result, the NOx catalyst 6A starts storing NOx again (step S50).

As described above, according to the present internal combustion engine, the end timing of the additional fuel injection is determined based on the NOx concentration β detected by the NOx sensor 10.
It is possible to accurately determine whether or not the release of NOx from the Ox catalyst 6A has been completed. Thus, regardless of the change in the NOx release characteristics of the NOx catalyst 6A, the fuel consumption is not deteriorated due to unnecessary additional fuel injection. It is possible to reliably release and reduce the NOx stored in the NOx catalyst 6A.

In the present embodiment, the determination of the start time of the injection of the additional fuel is also made by the NOx concentration β detected by the NOx sensor 10.
, But in this case, NOx
It is possible to accurately determine the state of reduction in the purification efficiency of the catalyst, and it is possible to further reduce the amount of released NOx and prevent deterioration of fuel efficiency. By setting the additional fuel injection period to a necessary minimum as described above, excessive additional fuel injection is avoided, and the fuel efficiency can be improved. Further, since NOx can be reliably released and reduced, NO
x Emissions can be reduced, and consequently the lean operating range can be expanded, further improving fuel economy.

In the present embodiment, the end of the additional fuel injection
NO in the determination of the end time_XNO contained in concentration β
_XNO flowing into catalyst 6A_XCompletion judgment considering density
Degree γ _TwoIs determined, but NO_XConcentration β
When correcting, this inflow NO_XTo take into account the concentration
May be. That is, NO_XDetected by sensor 10
NO_XFrom the concentration β, the correction amount β for individual differences and changes over time
₀And inflow NO_XCorrection amount β₁And true N
O_XConcentration γ (γ = β−β₀−β₁)
Because

The correction amount β ₁ for the inflow NO _X is, for example, a map determined by the effective pressure (load information) Pe input from the effective pressure calculating means 28 and the engine speed Ne input from the speed sensor 13. May be determined based on Of course, N to immediately upstream of the NO _X catalyst 6A
The O _X sensor installed, it may be determined by detecting the NO _X concentration flowing into the NO _X sensor of the upstream side in the NO _X catalyst 6A, in this case, thereby enabling more accurate determination.

In this embodiment, the NOx sensor 10
The concentration of NOx in exhaust gas is detected by
End determination of additional fuel injection control based on the concentration, that is,
Although the completion of the NOx release from the NOx catalyst 6A is determined, some of the NOx released from the NOx catalyst in an atmosphere having a reduced oxygen concentration may become NH ₃ due to a reaction on the catalyst depending on the catalyst. Since this NH ₃ is a change of the NOx originally stored in the NOx catalyst,
The H ₃ concentration can also be detected and used to determine the completion of NOx release.

[0044] In this case, in general so that many NOx sensors can also detect NH ₃ concentration in addition to the NOx concentration, in the case of such a NOx sensor, the NOx sensor output value is output as the sum of both The determination of the completion of NOx release may be performed based on the determination. Conversely, if the NOx sensor is used to detect only the NOx concentration, newly provided NH ₃ sensor detects the NH ₃ concentration in exhaust gas, by both the NOx sensor output value and the NH ₃ sensor output value The determination may be made. Alternatively, the determination may be made only by the NH ₃ sensor.

Further, in this embodiment, when the lean operation is continued, if the NOx purification efficiency of the NOx catalyst is reduced due to the storage of NOx, the enrichment is performed (that is, an atmosphere having a reduced oxygen concentration) is performed to release NOx. Although the case of returning to the lean operation state after completion is described, the case of temporarily enriching and releasing NOx when switching from lean operation to stoichiometric operation due to acceleration by driver's accelerator operation etc. Alternatively, the completion of the NOx release may be determined by using this method, and the enrichment may be terminated to return to the stoichiometric operation.

In this embodiment, the case of the direct injection engine, which is one of the lean burn internal combustion engines, has been described. However, the internal combustion engine of the present invention is not limited to the direct injection engine. Any applicable internal combustion engine can be widely applied.

[0047]

As described in detail above, according to the internal combustion engine of the present invention, regardless of the change in the NOx release characteristics of the NOx catalyst, the NOx catalyst can be reliably stored in the NOx catalyst without causing fuel consumption deterioration due to useless fuel injection. The released NOx can be released or reduced. Further, by minimizing the oxygen concentration lowering atmosphere period to a necessary minimum, it is possible to further improve the fuel efficiency by expanding the lean operation region.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically illustrating a main configuration of a control system for additional fuel injection control of an internal combustion engine according to an embodiment of the present invention.

FIGS. 2A and 2B are schematic diagrams illustrating a configuration of an internal combustion engine according to an embodiment of the present invention, in which FIG. 2A is an overall configuration diagram, and FIG. FIG.

FIG. 3 is a diagram for explaining timings of start and end of injection of additional fuel for releasing NOx from a NOx catalyst.

FIG. 4 is a flowchart showing a flow of additional fuel injection control of the internal combustion engine according to one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 3 exhaust passage 6 exhaust purification device 6A NOx catalyst 6B three-way catalyst 6C three-way catalyst (front catalyst) 8 injection (fuel injection valve) 10 NOx sensor (state detection means) 20 ECU 21 determination means 23 atmosphere changing means 25 fuel injection control Means 27 Additional fuel injection control means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) F02D 45/00 314 F02D 45/00 314Z (72) Inventor Yuki Tamura 33-8-8 Shiba 5-chome, Minato-ku, Tokyo No. Mitsubishi Motors Corporation F-term (reference) 3G084 AA01 AA04 BA24 CA04 DA10 DA27 EA11 EB11 FA10 FA27 FA28 FA33 3G091 AA12 AA17 AA24 AB03 AB06 BA14 BA15 BA19 CB02 CB03 CB05 CB07 DA04 DB10 DC01 EA01 EA30 FA17 FB11 FB12 HA12 HA36 HA37 HA38 HA47 3G301 HA01 HA02 HA04 HA15 JA25 JA26 JB09 LB04 MA01 MA11 MA18 PA17A PD01A PD11A PE01A PF03A

Claims (1)

[Claims] 1. An NO provided in an exhaust passage of an internal combustion engine to store NOx in exhaust gas in an oxygen-excess atmosphere and to release or reduce the stored NOx in an oxygen-low atmosphere.
x catalyst, state detection means provided downstream of the NOx catalyst and detecting a NOx release state released from the NOx catalyst, and when releasing NOx from the NOx catalyst, setting the exhaust air-fuel ratio to an oxygen-concentrated atmosphere, And an atmosphere changing means for changing the exhaust air-fuel ratio to an oxygen-excess atmosphere based on a result of comparison between a NOx releasing state based on an output of the state detecting means and a predetermined state. organ.