JP3042638B2 - Engine exhaust purification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an engine, and more particularly, to a catalytic converter for reducing harmful components contained in exhaust gas by catalytic action in an exhaust passage downstream of a combustion chamber. an exhaust sensor for detecting the residual oxygen concentration in the exhaust gas on the upstream side installed, so control the air-fuel ratio of the mixture supplied to the combustion chamber in accordance with the detected value of the exhaust gas sensor to the target air-fuel ratio The present invention relates to an exhaust purification device for an engine.

[0002]

2. Description of the Related Art In engines for vehicles and the like, in order to reduce harmful components contained in exhaust gas after combustion,
Among the above harmful components, carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NO
_x ) A catalytic converter using a three-way catalyst exhibiting excellent purification characteristics of the three components is installed in the exhaust system, and is supplied to the combustion chamber so that the catalytic action of the three-way catalyst is efficiently exhibited. There is an air-fuel ratio control that maintains an air-fuel ratio of an air-fuel mixture at a predetermined target air-fuel ratio (for example, stoichiometric air-fuel ratio; air / fuel = 14.7). In this air-fuel ratio control, specifically, an exhaust sensor whose output state is reversed after the excess air ratio λ (actual air-fuel ratio / stoichiometric air-fuel ratio) is 1 is installed upstream of the catalytic converter. When the detected value of the exhaust sensor indicates an oxygen-deficient state (for example, a state in which fuel is rich in air; hereinafter, referred to as a rich state), the fuel supply amount is reduced, and the detected value is determined in an oxygen-excess state (for air). Therefore, for example, when the fuel indicates a lean state; hereinafter , referred to as a lean state, the fuel supply amount is increased so that the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber converges on the target air-fuel ratio.

[0003] Incidentally, the three-way catalyst used in the above-mentioned catalytic converter has impurities attached to the catalyst components, for example, by lubricating leaded gasoline, etc., so that even within a service period set in consideration of aging. There is a problem that performance is deteriorated.

In order to solve such a problem, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-97852, a second method for detecting an oxygen concentration downstream of a catalytic converter installed in an exhaust system of an engine is disclosed. There is an exhaust sensor in which the deterioration of the catalytic action is determined based on the number of output reversals during the air-fuel ratio feedback control of the exhaust sensor. This is to indirectly judge the deterioration of the catalyst by focusing on the fact that the oxygen concentration at the downstream side of the catalyst hardly differs from that at the upstream side due to the decrease in the oxygen storage capacity at the time of deterioration of the catalyst.

[0005]

The catalyst in the catalytic converter installed in the exhaust passage repeats the oxidation-reduction reaction for harmful components by adsorption and desorption of oxygen. There is a problem that the oxygen partial pressure on the side is hard to fluctuate, and depending on the operation state, the state of oxygen excess or the state of oxygen shortage is not constant. That is, since the air-fuel mixture supplied to the combustion chamber of the engine is controlled near the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas discharged from the combustion chamber also takes a value reflecting the stoichiometric air-fuel ratio. Therefore, when the amount of oxygen in the exhaust gas in the upstream example of the catalytic converter is large, the oxygen downstream of the catalytic converter becomes excessive due to the oxygen overflowing the oxygen storage capacity of the catalyst, and the amount of oxygen in the exhaust gas is small.
No Sometimes, the oxygen downstream from the fact that all the oxygen is adsorbed on the catalyst becomes insufficient state. For this reason, there is a problem that when the catalyst deterioration is determined based on the detection value of the exhaust sensor downstream of the catalytic converter, good determination accuracy cannot be obtained.

[0006] In order to solve such a problem, the oxygen partial pressure in the vicinity of the exhaust sensor downstream of the catalytic converter during the catalyst deterioration detection period may be in an oxygen excess state (lean state) or an oxygen shortage state (rich state). it is conceivable to change the control constant of the feedback control so biased to either the differences or the system configuration of the control constants engine briefly is Me determined by such variation or secular change of the output characteristics of the exhaust sensor A new problem will arise. That is, for example, even if the control constant is set so that the exhaust state when detecting deterioration of the catalyst is leaned to the lean side, if the lean state is too lean, the output of the exhaust sensor is inverted to the rich state. As a result, good detection sensitivity cannot be obtained, and the determination accuracy will not be improved unless biased.

According to the present invention, exhaust sensors for detecting oxygen concentration are installed upstream and downstream of a catalytic converter installed in an exhaust system of an engine, and feedback control of an air-fuel ratio is performed in accordance with a detection value of an exhaust sensor on the upstream side. At the same time, the present invention addresses the above-described problem in an engine in which the catalyst deterioration is determined based on the detection value of the downstream exhaust sensor, and improves the catalyst deterioration determination accuracy without impairing the air-fuel ratio control accuracy. The purpose is to:

[0008]

That is, an exhaust gas purifying apparatus for an engine according to the invention of claim 1 of the present application (hereinafter referred to as a first invention) is provided upstream of an exhaust gas purifying catalyst provided in an exhaust system of the engine. A first exhaust sensor disposed on the side of the catalyst to detect the concentration of residual oxygen contained in the exhaust gas, and a second exhaust sensor disposed downstream of the catalyst for detecting the concentration of residual oxygen contained in the exhaust gas. Feedback control means for performing feedback control of an air-fuel ratio to a target air-fuel ratio in accordance with a detection value of the first exhaust sensor, and an output state of a detection value of the second exhaust sensor during feedback control by the feedback control means. engine and is provided deterioration determining means for performing the deterioration determination of the catalyst
An exhaust emission control device, wherein the deterioration determining means includes:
Predetermined during feedback control by feedback control means.
Detection value of the second exhaust sensor is detected over a period of
The catalyst based on the output state of the detected value.
Is configured to judge the deterioration of
The control constant of the feedback control means during the fixed period
A second exhaust sensor during feedback control other than a predetermined period;
When the detected value indicates rich state and lean state
For the control constant when the ratio with the interval becomes a predetermined ratio,
Excessive or insufficient oxygen partial pressure near the second exhaust sensor
A control constant changing means for changing so as to bias to either
It is characterized in that

The invention of claim 2 of the present application (hereinafter referred to as the
The exhaust gas purifying apparatus for an engine according to the present invention
The second exhaust sensor may be a predetermined ratio in the first invention.
The optimum exhaust gas purification characteristics of the catalyst
It is characterized by using such a ratio as is possible.

The invention of claim 3 of the present application (hereinafter referred to as “third invention”)
An exhaust gas purifying apparatus for an engine according to the present invention includes a first exhaust sensor installed upstream of an exhaust gas purifying catalyst provided in an exhaust system of the engine to detect a concentration of residual oxygen contained in exhaust gas; A second sensor is installed downstream of the catalyst to detect the concentration of residual oxygen contained in the exhaust gas.
An exhaust sensor, feedback control means for feedback-controlling an air-fuel ratio to a target air-fuel ratio in accordance with a detection value of the first exhaust sensor, and an output state of a detection value of the second exhaust sensor during feedback control by the feedback control means An exhaust gas purification device for an engine , comprising:
The deterioration determining means may include the feedback control means.
Over a predetermined period during feedback control by
The detected value of the second exhaust sensor is detected, and the detected value is detected.
The deterioration of the catalyst is determined based on the output state of the value.
And feedback during the above-mentioned predetermined period.
The control constants of the
During the feedback control, the value detected by the second exhaust sensor is excessive.
Control constant when the condition and the oxygen-deficient condition are repeated evenly
On the other hand, the oxygen partial pressure near the second exhaust sensor
Is a control constant change that is biased toward one of the shortage side
Means are provided.

[0011]

On the other hand, the invention of claim 4 of the present application (hereinafter referred to as the fourth invention)
An exhaust gas purifying apparatus for an engine according to the present invention includes: an exhaust sensor installed downstream of an exhaust gas purifying catalyst provided in an exhaust system of the engine to detect a concentration of residual oxygen contained in exhaust gas; Air-fuel ratio control means for performing air-fuel ratio control so that the rich state and the lean state are alternately repeated, and during the air-fuel ratio control by the air-fuel ratio control means.
Deterioration determination means and is provided engine for deterioration determination of the catalyst based on the output state of the detection value of the exhaust sensor
Exhaust purification device, wherein the deterioration determination means is
Over a predetermined period during the air-fuel ratio control by the fuel-ratio control means.
To detect the detected value of the exhaust sensor, and
Based on the output state of the output value, it is necessary to determine the deterioration of the catalyst.
And the air-fuel ratio control during the predetermined period.
The control constant of the control means during the air-fuel ratio control other than the predetermined period.
Time when the exhaust gas sensor indicates a rich state and lean
Control setting when the ratio with the time indicating the status becomes a predetermined ratio
Excessive oxygen partial pressure near exhaust sensor
Is a control constant change that is biased toward one of the shortage side
Means are provided.

The invention of claim 5 of the present application (hereinafter referred to as the
5 exhaust purification over device for an engine according to the present invention hereinafter), the upper
In the first, third or fourth invention, the control constant changing means is provided.
Indicates that the oxygen partial pressure is biased to either the excess side or the underside
In this manner, the value is changed by a predetermined value.

[0014]

According to each invention of the present application, the following effects can be obtained.
You.

According to the first aspect of the present invention, during a predetermined period in which the deterioration determination means makes a determination of catalyst deterioration, the catalyst deterioration determination is performed.
Feedback control constant
However, the oxygen partial pressure near the second exhaust sensor is excessive or
It will be changed to be biased to one of the feet . Accordingly, the catalyst deterioration determination based on the output state of the detection value of the second exhaust sensor is performed in a state where the composition of the exhaust gas near the second exhaust sensor is biased toward either the oxygen excess side or the oxygen shortage side. As a result, the deterioration determination accuracy is improved .

The change of the control constant is
During the feedback control other than the predetermined period, the second exhaust sensor
The detected value of the sensor indicates the rich state and the lean state
For the control constant when the ratio with time becomes a predetermined ratio
Since performed, the difference or the system configuration of the engine, the second
The control constants are set appropriately without being affected by variations in the output characteristics of the exhaust sensor or changes over time.

According to the second aspect, the predetermined ratio
However, the exhaust condition near the second exhaust sensor is optimized for catalyst purification.
Is determined so that the rate characteristics can be obtained.
Feeds other than the above-mentioned predetermined period in which the stage determines catalyst deterioration
During the back control, the exhaust gas purification efficiency of the catalyst is favorably maintained.

[0018] Then, by the third invention, during a predetermined period for performing the deterioration determination of the deterioration determination means catalyst deterioration of the catalyst
Feedback control compared to the period during which no
The constant is that the oxygen partial pressure near the second exhaust sensor is on the excessive side or
Is changed so as to be biased toward one of the shortage sides, so that the same operation as the above first invention is obtained.

In particular, according to the third invention, such a
Changes in control constants may cause feedback outside the specified period.
During the control, the detection value of the second exhaust sensor indicates that the oxygen excess state and the oxygen
For the control constant when the shortage condition is repeated evenly
In this case, the engine system
Due to differences in the configuration and variations in the output characteristics of the second exhaust sensor
Or the above control values are not affected by aging.
The number is set appropriately, and the exhaust gas purification efficiency of the catalyst is favorably maintained.

[0020]

On the other hand, according to the fourth aspect , an exhaust sensor installed downstream of an exhaust gas purifying catalyst provided in an exhaust system of an engine for detecting the concentration of residual oxygen contained in exhaust gas, and an air-fuel ratio There the air-fuel ratio control means for executing Repetitive <br/> Rikae be by Uni fuel ratio control alternately the rich state and a lean state,
In the exhaust purification apparatus for an engine provided with a deterioration judging means for performing the deterioration determination of the catalyst based on the output state of the detection value of the exhaust gas sensor during the air-fuel ratio control by the air-fuel ratio control means, and said first invention A similar effect will be obtained.

Further, according to the fifth invention, the control constant is changed.
Since the control constant is changed by the predetermined value by the means, an appropriate control constant in which the oxygen partial pressure around the exhaust sensor on the downstream side of the catalyst is not excessively biased can be obtained. In each of the above inventions, the catalyst downstream
The composition of the exhaust gas near the exhaust sensor on the
When it is changed to the bias side,
As a result, the response delay of the sensor is avoided, and the detection accuracy is good.
Is obtained.

[0023]

Embodiments of the present invention will be described below.

First, the control system of the engine 1 will be described with reference to FIG .
An intake passage 5 and an exhaust passage 6 communicating with the combustion chamber 4 through the air passage are provided. In the intake passage 5, an air cleaner 7, an air flow meter 8, and a throttle valve 9 are provided upstream thereof.
Is installed, and a fuel injection valve 10 is installed downstream of the throttle valve 9.

On the other hand, in the exhaust passage 6 is installed catalytic converter 11 of the three-way catalytic purifying exhaust gas after combustion, detects the residual oxygen concentration in the exhaust gas upstream and downstream of the catalytic converter 11 First and second exhaust sensors 1
2 and 13 are respectively installed.

The control system controls the fuel injection amount from the fuel injection valve 10 and the catalytic converter 1
An electronic control type control unit (hereinafter, referred to as ECU) 14 for performing the deterioration determination of 1 is provided . The ECU 14 receives an intake air amount signal from the air flow meter 8, a throttle opening signal from a throttle sensor 15 for detecting the opening of the throttle valve 9, a vehicle speed signal from a vehicle speed sensor 16 for detecting the vehicle speed of the vehicle. An engine speed signal from a rotation sensor 17 for detecting the engine speed, a water temperature signal from a water temperature sensor 18 for detecting the temperature of the engine coolant, and the first and second exhaust sensors 1.
The oxygen concentration signals detected by the combustion chambers 2 and 13 are input, and the air-fuel ratio control of the air-fuel mixture supplied to the combustion chamber 4 and the deterioration judgment processing of the catalytic converter 11 are performed based on these signals. The ECU 14 also controls the lighting of a warning lamp 19 for warning the deterioration of the catalytic converter 11.

[0027] Here, an outline of air-fuel ratio control ECU 14 performs, ECU 14 is on the read various signals, based on the engine speed indicated by the intake air amount and the engine speed signal indicating the intake air amount signal Then, the amount of air taken into the combustion chamber 4 per cycle is calculated, and the corresponding basic injection amount is set. Next, the ECU 14 determines whether the air-fuel ratio feedback condition is satisfied. That is, the ECU 14 determines whether the operating state of the engine 1 using the throttle opening degree representing the engine load and the engine speed as parameters belongs to a predetermined feedback range, and the engine cooling water temperature indicated by the water temperature signal becomes equal to or higher than a predetermined value. For example, it is determined that the feedback condition is satisfied, and the air-fuel ratio feedback control is executed.

The air-fuel ratio feedback control is performed as follows. That is, the ECU 14
When the oxygen concentration signal from the exhaust sensor 12 indicates a lean state, the feedback correction amount C _FB is set so as to increase the fuel. On the other hand, when the oxygen concentration signal indicates a rich state, the feedback correction amount is set so that the fuel decreases. Set C _FB . Further, the feedback correction amount C
_The final injection amount is determined by correcting the basic injection amount using the _FB and the water temperature correction amount. Then, a fuel injection signal is output to the fuel injection valve 10 so as to obtain the final injection amount.

[0029] In addition, the feedback correction amount C _FB is,
Specifically, it is obtained as follows. That is, EC
U is the first exhaust sensor 1 as shown in FIG.
It is determined that the air-fuel ratio when the second output voltage V is greater than a predetermined reference voltage V _l is inverted from a lean state to a rich state, the feedback correction amount C at that time
The value of _FB is set to a lean delay constant D as shown in FIG.
_The update is continuously performed using the rich integration constant I _Rl only during _Ll , and after the delay constant D _Ll elapses, the lean skip value P _Ll is reduced at once, and then gradually reduced using the lean integration constant I _Ll . Then, the output voltage V of the first exhaust sensor 12 is determined to the air-fuel ratio is now at the time of lower than the reference voltage V _l inverted from the rich state to the lean state, the feedback correction amount at that time C _FB Is set to the above-mentioned lean integration constant I only during the rich delay constant _DR1.
The update is continued using _L1, and after the delay constant _DR1 has elapsed, the rich skip value _PRI is increased at once, and then gradually increased using the rich integration constant _IR1 .

Furthermore, ECU 14 is the constantly examines the output voltage V of the second exhaust gas sensor 13, as shown in FIG. 2 (c), the output voltage V is the reference voltage V ₂ or the duration of the oxygen-deficient state (hereinafter , and the rich time of) T _R, also the output voltage V is the reference voltage V ₂ is less than the oxygen-excess state of the duration (hereinafter, as and the lean time of) T _L a 1-to-1, the respective skip value P _L1 , P _R1 , integration constant I _L1 , I
_R1 and the delay constants D _L1 and D _R1 are each _subjected to learning correction.

On the other hand, ECU 14 when it is determined that it is not the feedback condition is satisfied, the throttle opening, engine speed, so that the fuel injection quantity read from the fuel injection map set water temperature and the like as parameters, Open loop control for outputting a fuel injection signal to the fuel injection valve 10 is executed.

[0032] Subsequently explained catalyst deterioration detection process is a feature of the present invention, it becomes in accordance with the flowchart of FIG.

[0033] That is, ECU 14 determines whether a predetermined catalyst deterioration detecting conditions are satisfied in step S1.
That is, the ECU 14 determines that the catalyst deterioration detection condition is satisfied when the air-fuel ratio feedback condition is satisfied and the throttle opening, the vehicle speed, and the like satisfy predetermined conditions.

[0034] Then, when ECU14 has been determined that the catalyst deterioration detecting conditions are satisfied, it is determined whether the rich period T _R and the lean time T _L advances to step S2 match, if it is determined that YES step S from the feedback constant at that time by 3 to calculate the number of catalyst deterioration detection Yojo.
That is, as shown in FIG. 2, when attention is focused on the skip value, the rich skip value P when to be changed is the integration constant and delay constant, for example, where the rich period T _R and the lean time T _L match Lean skip value P _L1 for _R1
Is slightly increased, the feedback correction amount C _FB surely changes in the fuel reduction direction. Of course, the rich skip value _PR1 may be made relatively smaller than the lean skip value _PL1 . A similar relationship holds for the integration constant and the delay constant. Therefore, the second exhaust sensor 1 downstream of the catalytic converter 11
3 catalyst deterioration detection Yojo number that does not unduly oxygen starved exhaust state of the vicinity will be sought.

After changing the feedback control constant to the catalyst deterioration detection constant, the ECU 14 sets the first output signal V per unit time indicated by the output voltage V of the first exhaust sensor 12.
A reversal number N _1, counts each second inversion number N ₂ and the per output unit indicated by the voltage V the time of the second exhaust gas sensor 13 (step S4 to S6). And step S
7 in a second proportion of the transition number N ₂ to the first inversion number N ₁ is determined whether it is greater than a predetermined deterioration determination reference value K, when it is determined that YES catalyst deterioration is determined in step S8 It is determined whether or not this is the case, and if it is determined as YES, step S9 is executed to turn on the warning lamp 19. Incidentally, ECU 14 first is for the first inversion number N ₁ example 2
Ratio of transition number N ₂ is adapted to determine the catalyst deterioration when generated three times in succession can be greater than the deterioration determination reference value K.

The ECU 14 determines in steps S7 and S7
If NO is determined in step S8, the process proceeds to step S10, and the catalyst deterioration detection changed in step S4 is performed .
To cancel a constant number.

Next, the operation of the embodiment.

[0038] That is, in the catalyst degradation determination in using an output value of the second exhaust sensor 13, for example, FIGS. 4 (a)
As shown in (b), the output voltage V of the first exhaust sensor 12
Change but from the lean state lean skip value P _L2 after reversed to the rich state, to a larger value only than the lean skip value P _L1 of normal time when not carried out the deterioration determination _{δ PL (δP L = P L2} -P L1) is also the voltage V is rich skip value P _R2 after inverted from the rich state to the lean state, [delta] P than the rich skip value P _R1 during the normal _{R (δP R = P R2 -} P
_R1 ) is changed to be smaller. Therefore, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 4 shifts to a lean state, and the fuel becomes slightly fuel shortage. As a result, the oxygen concentration in the exhaust gas discharged from the combustion chamber 4 increases, and oxygen near the second exhaust sensor 13 is surely in an oxygen excess state due to the oxygen that cannot be occluded by the catalytic converter 11.
As described above, when the oxygen excess state occurs, the attachment / detachment of oxygen in the second exhaust sensor 13 is smoothly performed, and the oxygen concentration is detected with high sensitivity.

At this time, when the catalytic converter 11 is activated, as shown in FIG. 4C, the output voltage V of the second exhaust sensor 13 changes while leaning to the lean side. without ratio of the second inversion number N ₂ for the number N ₁ is greater than the deterioration determination reference value K, the deterioration determination is not carried out.

[0040] In contrast, the output voltage V of the second exhaust sensor 13, the reference voltage V ₂ as shown by a broken line shown in FIG. 4 (c)
Becomes much degree of reversal to the rich side beyond, the ratio of the second inversion number N ₂ is often larger than the deterioration determination reference value K for the first inversion number N _1, the catalyst deterioration is deterministic When the determination is made, the warning lamp 19 is turned on to notify the driver of the abnormality. In that case
, As described above, and the rich time T _R, the lean time T _L
So that the above skip values P _L1 , P _R1 ,
The integration constants I _L1 and I _R1 and the delay constants D _L1 and D _R1 are each learned.
Oxygen partial pressure is not excessively biased because it is corrected
Appropriate control constants can be obtained, and catalyst deterioration detection
The output accuracy will be significantly improved.

In this embodiment, detection of catalyst deterioration is performed.
Although the skip value is changed with respect to the normal time during the period , the integration constant or the delay time may be changed, or all of them may be changed.

[0042]

According to the exhaust gas purifying apparatus of the first invention, an exhaust gas sensor for detecting the oxygen concentration is provided upstream and downstream of the exhaust gas purifying catalyst provided in the exhaust system. The feedback control of the air-fuel ratio to the target air-fuel ratio based on the detection value of the exhaust sensor of the first embodiment, and the determination of the deterioration of the catalyst based on the output state of the detection value of the downstream exhaust sensor. Means touch
During a predetermined period for determining the deterioration of the medium, the deterioration of the catalyst is determined.
The feedback control constant is
2 If the oxygen partial pressure near the exhaust sensor is
It will be changed so as to be biased to either . Accordingly, the catalyst deterioration determination based on the output state of the detection value of the second exhaust sensor is performed in a state where the composition of the exhaust gas near the second exhaust sensor is biased toward either the oxygen excess side or the oxygen shortage side. As a result, the deterioration determination accuracy is improved .

Then, such a change of the control constant is
During the feedback control other than the predetermined period, the second exhaust sensor
The detected value of the sensor indicates the rich state and the lean state
For the control constant when the ratio with time becomes a predetermined ratio
Since performed, the difference or the system configuration of the engine, the second
The control constants are set appropriately without being affected by variations in the output characteristics of the exhaust sensor or changes over time.

According to the second aspect, the predetermined ratio
However, the exhaust condition near the second exhaust sensor is optimized for catalyst purification.
Is determined so that the rate characteristics can be obtained.
Feeds other than the above-mentioned predetermined period in which the stage determines catalyst deterioration
During the back control, the exhaust gas purification efficiency of the catalyst is favorably maintained.

[0045] Then, by the third invention, during a predetermined period for performing the deterioration determination of the deterioration determination means catalyst deterioration of the catalyst
Feedback control compared to the period during which no
The constant is that the oxygen partial pressure near the second exhaust sensor is on the excessive side or
Is changed so as to be biased toward one of the shortage sides, so that the same operation as the above first invention is obtained.

In particular, according to the third invention, such a
Changes in control constants may cause feedback outside the specified period.
During the control, the detection value of the second exhaust sensor indicates that the oxygen excess state and the oxygen
For the control constant when the shortage condition is repeated evenly
In this case, the engine system
Due to differences in the configuration and variations in the output characteristics of the second exhaust sensor
Or the above control values are not affected by aging.
The number is set appropriately, and the exhaust gas purification efficiency of the catalyst is favorably maintained.

[0047]

On the other hand, according to the fourth invention, an exhaust sensor installed downstream of an exhaust gas purifying catalyst provided in an exhaust system of an engine for detecting the concentration of residual oxygen contained in exhaust gas, and an air-fuel ratio There the air-fuel ratio control means for executing Repetitive <br/> Rikae be by Uni fuel ratio control alternately the rich state and a lean state,
In the exhaust purification apparatus for an engine provided with a deterioration judging means for performing the deterioration determination of the catalyst based on the output state of the detection value of the exhaust gas sensor during the air-fuel ratio control by the air-fuel ratio control means, and said first invention A similar effect will be obtained.

Further, according to the fifth invention, the control constant is changed.
Since the control constant is changed by the predetermined value by the means, an appropriate control constant in which the oxygen partial pressure around the exhaust sensor on the downstream side of the catalyst is not excessively biased can be obtained. In each of the above inventions, the catalyst downstream
The composition of the exhaust gas near the exhaust sensor on the
When it is changed to the bias side,
As a result, the response delay of the sensor is avoided, and the detection accuracy is good.
Is obtained.

[Brief description of the drawings]

FIG. 1 is a control system diagram of an engine.

FIG. 2 is a time chart showing a change in a feedback correction amount in a normal state.

FIG. 3 is a flowchart illustrating a catalyst deterioration detection process.

FIG. 4 is a time chart showing a change in a feedback correction amount when catalyst deterioration is detected.

[Explanation of symbols]

 Reference Signs List 1 engine 6 exhaust passage 10 fuel injection valve 11 catalytic converter 12 first exhaust sensor 13 second exhaust sensor 14 ECU

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F02D 45/00 314 F02D 45/00 314T (72) Inventor Hirofumi Nishimura 3-1, Fuchu-cho, Shinchu, Aki-gun, Hiroshima Prefecture Mazda Motor Corporation (56) References JP-A-2-30915 (JP, A) JP-A-63-97845 (JP, A) JP-A-2-283834 (JP, A) JP-A-3-175129 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/14 F02D 41/22 F02D 45/00

Claims (5)

(57) [Claims] 1. A first exhaust sensor disposed upstream of an exhaust gas purifying catalyst provided in an exhaust system of an engine for detecting a concentration of residual oxygen contained in exhaust gas, and a first exhaust sensor disposed downstream of the catalyst. A second exhaust sensor for detecting the concentration of residual oxygen contained in the exhaust gas; feedback control means for feedback-controlling the air-fuel ratio to a target air-fuel ratio in accordance with the detection value of the first exhaust sensor; a exhaust gas purification device for an engine provided with a deterioration judging means for performing the deterioration determination of the upper Symbol catalyst based on the output state of the detection value of the second exhaust gas sensor during the feedback control by means, the said deterioration determination means ,
Predetermined during feedback control by feedback control means.
Detection value of the second exhaust sensor is detected over a period of
The catalyst based on the output state of the detected value.
Is configured to judge the deterioration of
The control constant of the feedback control means during the fixed period
A second exhaust sensor during feedback control other than a predetermined period;
When the detected value indicates rich state and lean state
For the control constant when the ratio with the interval becomes a predetermined ratio,
Excessive or insufficient oxygen partial pressure near the second exhaust sensor
An exhaust gas purifying apparatus for an engine, further comprising control constant changing means for changing the control constant so as to be biased toward one of the following . 2. The engine exhaust system according to claim 1, wherein the predetermined ratio is such that an exhaust state in the vicinity of the second exhaust sensor provides an optimum purification rate characteristic of the catalyst. Purification device. 3. A first exhaust sensor installed upstream of an exhaust gas purifying catalyst provided in an exhaust system of an engine to detect a concentration of residual oxygen contained in exhaust gas, and a first exhaust sensor installed downstream of the catalyst. A second exhaust sensor for detecting the concentration of residual oxygen contained in the exhaust gas; feedback control means for feedback-controlling the air-fuel ratio to a target air-fuel ratio in accordance with the detection value of the first exhaust sensor; An exhaust purification device for an engine, comprising: a deterioration determination unit configured to determine deterioration of the catalyst based on an output state of the detection value of the second exhaust sensor during feedback control by the unit. The above file
Predetermined during feedback control by feedback control means.
Over a period of time, a detected value of said second exhaust sensor
The catalyst based on the output state of the detected value.
Is configured to judge the deterioration of
The control constant of the feedback control means during the fixed period
A second exhaust sensor during feedback control other than a predetermined period;
The detected values of the oxygen-excess state and the oxygen-deficient state
For the control constant when returning, the acid near the second exhaust sensor
An exhaust gas purifying apparatus for an engine, further comprising control constant changing means for changing the elementary partial pressure so as to be biased toward either an excessive side or an insufficient side . 4. An exhaust gas provided in an exhaust system of an engine.
Installed downstream of purification catalyst and contained in exhaust gas
Exhaust sensor that detects residual oxygen concentration and rich air-fuel ratio
Air-fuel ratio control to alternate between alternate states and lean states
Air-fuel ratio control means for executing
Output state of the detection value of the above exhaust sensor during air-fuel ratio control
Degradation determination means for determining the degradation of the catalyst based on the state
An exhaust gas purification device for an engine, comprising:
During the air-fuel ratio control by the air-fuel ratio control means.
Detection value of the exhaust sensor over a predetermined period of time
The catalyst based on the output state of the detected value.
Is configured to judge the deterioration of
The control constant of the air-fuel ratio control means during the fixed period is
Exhaust sensor detection value rich during air-fuel ratio control other than
Is the predetermined ratio
Oxygen near the exhaust sensor for the control constant when
Change the partial pressure to bias either the excess side or the underside.
Characterized in that a control constant changing means for changing
Engine exhaust purification device. 5. The control constant changing means, wherein the oxygen partial pressure is on the excess side.
Or change by a predetermined value so that
5. The method as claimed in claim 1, wherein the number of the parts is changed.
An exhaust gas purifying apparatus for an engine according to Claim 1.