JP3122856B2 - Air-fuel ratio detection device failure detection device and engine control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fault detection of an air-fuel ratio detecting device for feedback-controlling an air-fuel ratio of an engine to a target air-fuel ratio.

[0002]

2. Description of the Related Art In air-fuel ratio control of an engine, for example, in the case of air-fuel ratio control based on a fuel injection amount, a basic injection amount according to an intake air amount of an engine and an engine speed is calculated, and the basic injection amount is calculated based on an engine water temperature and the like. Correction according to
Feedback correction is performed based on a detection signal from an O ₂ sensor or the like for detecting the oxygen concentration in the exhaust gas, and the final injection amount is set. Then, the injector is driven by the injection pulse corresponding to the final injection amount to make the air-fuel ratio converge to the target air-fuel ratio. According to such air-fuel ratio feedback control, the air-fuel ratio of the engine can be controlled to, for example, a stoichiometric air-fuel ratio, so that a three-way catalyst or the like can be disposed in the exhaust passage to efficiently purify the exhaust gas. Becomes Here, the air-fuel ratio sensor is generally provided on the upstream side of the catalyst.

As described above, when a catalyst is disposed in an exhaust passage of an engine and a feedback control system is configured to control an air-fuel ratio to, for example, a stoichiometric air-fuel ratio, a variation in output characteristics of an air-fuel ratio sensor or a lapse of time. A second air-fuel ratio sensor is provided downstream of the catalyst to compensate for deterioration, and a delay process is performed when the output of the upstream air-fuel ratio sensor changes from a rich signal to a lean signal and from a lean signal to a lean signal. It has been conventionally proposed to provide a double O ₂ sensor system that corrects the set time of the sensor according to the output of the downstream air-fuel ratio sensor. Further, for example, in Japanese Patent Application Laid-Open No. 61-234241, in such a double O ₂ sensor system, a decrease in responsiveness (a decrease in control frequency) due to deterioration of the upstream air-fuel ratio sensor is minimized. In order to limit the skip value, a so-called P value feedback control is performed in which a skip value (P value) of the air-fuel ratio control by the upstream air-fuel ratio sensor is feedback-corrected by the output of the downstream air-fuel ratio sensor. In this case, the change in the output characteristics of the downstream air-fuel ratio sensor reflects the degree of deterioration of the upstream air-fuel ratio sensor. Therefore, the failure (deterioration) of the upstream air-fuel ratio sensor is detected based on the output of the downstream air-fuel ratio sensor. Can be performed.

By the way, O ₂ disposed upstream of the catalyst is
The deterioration of the air-fuel ratio sensor such as a sensor includes a lean shift deterioration in which the control center shifts to the lean side, a rich shift deterioration in which the control center shifts to the rich side, and an inversion frequency of the output waveform, that is, It is known that there are three types of frequency degradation in which is small. Among them, lean shift deterioration and rich shift deterioration are detected based on whether or not the skip value (P value) of the air-fuel ratio feedback control set by the P value feedback control has reached an abnormal level (threshold). On the other hand, the frequency deterioration is detected by increasing the ratio between the frequency of the upstream air-fuel ratio sensor and the frequency of the downstream air-fuel ratio sensor.

In the double O ₂ sensor system, P
The value feedback control is also used for detecting deterioration of the catalyst. In this case, using the frequency ratios of the upstream and downstream air-fuel ratio sensors as detection values, a deterioration state (purification rate) is determined based on the detection characteristics, and an abnormal state is determined based on a predetermined MF (malfunction) level. Is determined.

[0006]

To detect a INVENTION Problems to be Solved] frequency deterioration of the O ₂ sensor or the like the air-fuel ratio sensors disposed upstream of the catalyst for the air-fuel ratio feedback control, both in the double O ₂ sensor system, as described above When looking at the ratio of the sensor frequencies, when the response of the air-fuel ratio sensor deteriorates and the determination time of rich and lean becomes longer, finally the swing of the air-fuel ratio becomes large and the window of the catalyst deviates greatly, The O ₂ storage effect of the catalyst can no longer be obtained,
The output of the downstream sensor has a waveform similar to that when the catalyst is deteriorated. Therefore, in the above-described conventional method, there is a problem that when the catalyst is deteriorated, the air-fuel ratio sensor is determined to have failed even though the air-fuel ratio sensor is normal.

In the double O ₂ sensor system which performs the P value feedback control as described above,
When the air-fuel ratio deviates from the catalyst window due to deterioration of the upstream air-fuel ratio sensor, the direction of the deviation is detected by the output signal of the downstream sensor to correct the P value. Since it takes some time to converge and absorb the deterioration of the air-fuel ratio sensor, if the deterioration of the catalyst is detected during this time, the deterioration is detected in a state where the deterioration of the air-fuel ratio sensor is not absorbed, and an erroneous determination is made. There was also a problem that occurred.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a deterioration detection of a first air-fuel ratio sensor disposed upstream of a catalyst for air-fuel ratio feedback control of an engine is disposed downstream of the catalyst. An object of the present invention is to use the output of the second air-fuel ratio sensor to prevent the deterioration of the catalyst and the air-fuel ratio sensor from being confused and to accurately detect the deterioration of the first air-fuel ratio sensor. .

[0009]

Means for Solving the Problems According to claim 1 of the present application.
The present invention relates to a failure detection device for an air-fuel ratio detection device for achieving the above object, and FIG. 1 is an overall configuration diagram thereof. According to the present invention, the air-fuel ratio sensor (first air-fuel ratio sensor) on the upstream side of the catalyst deteriorates and the responsiveness deteriorates, and the fluctuation of the air-fuel ratio increases. Although the frequency of the output waveform of the fuel ratio sensor becomes small, such a phenomenon is particularly remarkable during off-idling (with a load). The effect of deterioration of the response of the first air-fuel ratio sensor is small because the cycle of the fluctuation is long. On the other hand, when the catalyst deteriorates, the O ₂ storage effect cannot be obtained regardless of idle or off-idle. The fact that the phenomenon that the frequency of the second air-fuel ratio sensor decreases becomes apparent even at the time of idling, and this configuration is used for purifying exhaust gas in the exhaust passage of the engine. Is disposed upstream of the catalyst,
A first air-fuel ratio sensor that outputs an air-fuel ratio signal to air-fuel ratio control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to a target air-fuel ratio; and a second air-fuel ratio sensor disposed downstream of the catalyst. Fuel ratio sensor and these first air-fuel ratio sensors
And the output of the second air-fuel ratio sensor,
An air-fuel ratio detection device having sensor failure detection means for detecting a failure of the first air-fuel ratio sensor based on an output frequency ratio.
Oite receives the output of the intake air amount detecting means for detecting a parameter related to the intake air amount of the engine, the frequency of the output of the second air-fuel ratio sensor when the intake air amount <br/> is equal to or greater than the set value
When the ratio of the frequency of the output of the first air-fuel ratio sensor to that of the first air-fuel ratio sensor becomes substantially 1 and the intake air amount is equal to or less than the set value, the second air-fuel ratio sensor
Of the output of the first air-fuel ratio sensor to the frequency of the sensor output
The sensor failure detecting means is configured to determine that the first air-fuel ratio sensor has failed when the frequency ratio becomes equal to or greater than a predetermined value. As the intake air amount detecting means, for example, an idle switch for detecting that the throttle valve is fully closed can be used.

[0010] The invention according to claim 2 of the present application is:
Catalyst for purifying exhaust gas in the engine exhaust passage
Of the mixture supplied to the engine
Air-fuel ratio for feedback control of fuel ratio to target air-fuel ratio
A first air-fuel ratio sensor that outputs an air-fuel ratio signal to the control unit;
A second air-fuel ratio sensor disposed downstream of the catalyst;
Receiving outputs of the first air-fuel ratio sensor and the second air-fuel ratio sensor,
The first air-fuel ratio based on the frequency ratio of the outputs of the two air-fuel ratio sensors
Sensor failure detecting means for detecting a sensor failure;
Receiving outputs of the first air-fuel ratio sensor and the second air-fuel ratio sensor,
Deterioration of catalyst based on frequency ratio of output of both air-fuel ratio sensors
Control device equipped with catalyst deterioration detecting means for detecting
In this case, the sensor failure detection means
Intake air amount detection method for detecting parameters related to air volume
Receiving the output of the stage, When the value is below the fixed value, the second
First air-fuel ratio sensor for output frequency of air-fuel ratio sensor
If the ratio of the output frequencies is equal to or greater than a predetermined value,
It is determined that the fuel ratio sensor has failed.
The stage detects parameters related to the engine intake air volume.
Receiving the output of the intake air amount detection means
When the frequency is equal to or less than the set value, the output frequency of the second air-fuel ratio sensor
The ratio of the frequency of the output of the first air-fuel ratio sensor to the
In the above case, detection of catalyst deterioration was not performed.
It is characterized by the following.

[0011]

According to the first aspect of the present invention, the air-fuel ratio of the engine is feedback-controlled to the target air-fuel ratio based on the output of the first air-fuel ratio sensor disposed upstream of the catalyst. Further, in an area where the intake air amount of the engine at the time of idling or the like is equal to or less than the set value, the sensor failure detecting means operates, and the frequency ratio between the output of the first air-fuel ratio sensor and the output of the second air-fuel sensor downstream of the catalytic converter is reduced. The deterioration of the first air-fuel ratio sensor is detected based on the detection.

FIGS. 2A and 2B are time charts for explaining the operation of the present invention. FIG . 2A shows a vehicle speed mode including idle and off-idle, and FIG. 2B shows an output waveform of the first air-fuel ratio sensor in a normal state. (C) shows the output waveform of the first air-fuel ratio sensor when it deteriorates, (d) shows the output waveform of the second air-fuel ratio sensor when the first air-fuel ratio sensor deteriorates, and (e) shows when the first air-fuel ratio sensor is normal. And (f) schematically shows the output waveform of the second air-fuel ratio sensor when the catalyst is deteriorated. As shown in this figure, when the first air-fuel ratio sensor deteriorates, its waveform decreases in off-idle with a large intake air amount. On the other hand, in the case of the second air-fuel ratio sensor, the frequency at the time of off-idle becomes large due to the deterioration of the first air-fuel ratio sensor, and the frequency ratio with the first air-fuel ratio sensor approaches 1, but the intake air amount is small. At idle, the waveform is not much different from the normal waveform. The frequency of the waveform of the second air-fuel ratio sensor also increases when the catalyst has deteriorated. In this case, the frequency also increases in an idle region where the amount of intake air is small. Therefore, by performing sensor deterioration detection during idling or the like as described above, confusion between catalyst deterioration and air-fuel ratio sensor deterioration is prevented, and deterioration of the first air-fuel ratio sensor is accurately detected.

[0013] Further, according to the invention of claim 2 of the present application.
If the intake air amount is equal to or less than the set value, the second air-fuel ratio
Of the output of the first air-fuel ratio sensor with respect to the frequency of the
If the wave number ratio is equal to or higher than a predetermined value, detection of catalyst deterioration is
Line.

[0014]

FIG. 3 is an overall system diagram showing an embodiment of the invention according to this application. In the drawing, reference numeral 1 denotes an engine body. An independent intake passage 2a for each cylinder is provided on the intake side of the engine body 1, and these independent intake passages 2a are connected to an upstream intake passage 2c via a surge tank 2b.
The upstream side intake passage 2c is connected to the air cleaner 3 at the tip, and the air flow meter 4 is located at an upstream position near the connection with the air cleaner 3, and the surge tank 2b
A throttle valve 5 is provided at a downstream position near the entrance of the throttle valve. An exhaust passage 6 is connected to the exhaust side of the engine body 1, and a catalyst 7 is disposed in the exhaust passage 6.

[0015] and the injector 8 for fuel injection is disposed on the independent intake passages 2a of each cylinder. These injectors 8 are controlled by a control unit 9 composed of a microcomputer or the like. The air-fuel ratio of the engine is controlled by controlling the fuel injection amount by the injector 9. Therefore, the control unit 9
, An intake air amount signal is input from the air flow meter 4, and a crank angle signal is output from the crank angle sensor 10.
An engine water temperature signal is input from the water temperature sensor 11, and an idle switch signal is input from an idle switch attached to the throttle valve 5. In the exhaust passage 6, a first air-fuel ratio sensor (O ₂ sensor) 12 is provided upstream of the catalyst 7.
A second air-fuel ratio sensor (O ₂ sensor) 13 is disposed on the downstream side, and the first and second air-fuel ratio sensors 1
The detection signals 2 and 13 are input to the control unit 9.

As is well known, the control unit 9 calculates an intake air amount Qa detected by the air flow meter 4 from an engine rotation speed Ne calculated from a crank angle signal.
Is multiplied by a constant K to set a basic fuel injection amount T ₀ , which is corrected by the engine coolant temperature or the like. Further, a feedback correction amount CFB based on the difference between the air-fuel ratio detected by the first air-fuel ratio sensor 12 upstream of the catalyst 7 and the target air-fuel ratio is added to set a final injection amount T. An injection pulse having a corresponding pulse width is output to the injector 8. As a result, the air-fuel ratio of the engine is controlled to, for example, the stoichiometric air-fuel ratio (14.7).

[0017] The feedback correction amount CFB is, the second
The correction is made by P value feedback control based on the output of the air-fuel ratio sensor 13. FIG. 4 is a time chart for explaining the P value feedback control, and FIG.
The signal waveform of the air-fuel ratio sensor, (b) is the signal waveform of the second air-fuel ratio sensor, and (c) is the P value (skip value) of CFB when the air-fuel ratio shifts from rich side to lean side.
(D) shows CGPFLR, which is the P value of CFB when the air-fuel ratio shifts from the lean side to rich side, and (e) shows the corrected CFB.

The output of the second air-fuel ratio sensor 13 is substantially adhered shape to the rich side or the lean side to be the P value feedback. Further, when the P-value feedback is performed, the fluctuation of the air-fuel ratio becomes large, and the air-fuel ratio easily deviates from the purification window of the catalyst.
3 shows a fluctuation waveform. The waveform of the second air-fuel ratio sensor 13 has a long fluctuation cycle when the first air-fuel ratio sensor 12 is normal, and the cycle becomes short when the first air-fuel ratio sensor 12 is deteriorated. The P value feedback control detects the deterioration of the first air-fuel ratio sensor and detects the PB of the CFB.
The value is corrected, and while the output of the second air-fuel ratio sensor 13 is stuck on the rich side, the minute ratio ΔSKIP (for example, 0.2%) every unit time (for example, 8.2 ms)
The output of the second air-fuel ratio sensor 13 is attached to the lean side, and the CGPPFRL is also increased by ΔSKIP to decrease the CGPFLR. Thereby, the CGPF
The centers (average values) of LR and CGP FRL converge to a value corresponding to the degree of deterioration of the first air-fuel ratio center 12, and the deterioration is absorbed.

The control unit 9 determines whether the first air-fuel ratio sensor 12 has deteriorated in frequency and outputs a deterioration determination signal. When the frequency of the first air-fuel ratio sensor 12 deteriorates,
Frequency of the output waveform is reduced Oite during off idle, whereas, the frequency ratio of the frequency of the second air-fuel ratio sensor 13 and the first air-fuel ratio sensor 12 is larger at the time of off idle approaches one. However, the phenomenon that the frequency of the second air-fuel ratio sensor 13 increases also appears when the catalyst 7 is deteriorated. Further, the frequency of the second air-fuel ratio sensor 13 is not significantly affected by the deterioration of the first air-fuel ratio sensor 12 during idling. Therefore, first, both sensors 12, 1 at the time of off-idling are used.
Looking at the frequency ratio of 3, if the frequency ratio becomes almost 1,
Next, the frequency ratio during idling is checked, and if this exceeds a threshold value, it is determined that the first air-fuel ratio sensor 12 has deteriorated in frequency. Here, the determination at the time of idling and at the time of off-idling are performed by an idle switch signal.

FIG . 5 is a flow chart for executing the control of the frequency deterioration detection of the above embodiment, and
04 shows each step. In this flow, when started, it is checked in S101 whether the ratio of the frequency of the first air-fuel ratio sensor (front O ₂ ) and the frequency of the second air-fuel ratio sensor (rear O ₂ ) at the time of off-idle is 1 or not. If the frequency ratio is 1 (YES), S10
2 and this time the frequency ratio at idle is
If it is determined that the frequency ratio exceeds K (YES), it is determined in S103 that the frequency of the first air-fuel ratio sensor has deteriorated, and the routine returns.

Further, if that the frequency ratio of the off idle is not 1 (NO in S101), or off-frequency ratio at the time is also idle frequency ratio is 1 at the time of idling the following K as (NO in S102) In this case, the flow goes to S104 to determine the deterioration of the catalyst (catalyst), and then returns.

FIG . 6 is a flowchart for executing control related to the invention of this application. In this control , the deterioration of the catalyst disposed in the exhaust passage is detected after the deterioration of the lean shift and the rich shift of the air-fuel ratio sensor is detected and corrected. This is the same as FIG. 3 according to the embodiment. Again,
Again, air-fuel ratio feedback control is performed, and P-value feedback control is performed. Hereinafter, this control will be described with reference to the flow of FIG. In addition, S201 to S222 show each step of this flow.

In the flow of FIG . 6, when starting,
First, in S201, it is determined whether the first air-fuel ratio sensor (front O ₂ ) is active. And active (YES)
If so, the process proceeds to S202 to execute the air-fuel ratio feedback control, and then determines in S203 whether the second air-fuel ratio sensor (rear O ₂ ) is active.

If the determination in S203 is YES and both the first air-fuel ratio sensor and the second air-fuel ratio sensor are active, S
At step 204, the execution flag of the P value feedback control is set. Then, it is determined whether or not the output of the second air-fuel ratio sensor is equal to or higher than the slice level (set value) in S205. If the output is equal to or higher than the slice level (YES), a rich flag is set in S206, and CGPFLR is set to ΔS in S207.
KIP is increased and CGPFRL is increased by ΔSKIP
Just make it smaller.

If the output of the second air-fuel ratio sensor is lower than the slice level (NO in S205), the flow goes to S20.
8, a lean flag is set, and in S209, CGPFLR is reduced by ΔSKIP, and CGPFLL is reduced by ΔSK.
Increase only IP.

Further, the second air-fuel ratio sensor is not active (S
If (NO in 203), the execution flag of the P value feedback control is lowered in S210. Then, the process goes to S211 to update both CGPFLR and CGPFLL with the previous values.

In step S207 or S208, the CGPFLR
Alternatively, when CGPFRL is increased or decreased, then S
At 212, it is determined whether the average value of CGP (CGPFLR and CGPFLL) does not exceed the fail determination threshold. If it does not exceed the threshold (YES), the process proceeds to S213, and the difference B between the current fail determination threshold and the CGP average value and the difference B between the previous fail determination threshold and the CGP average value B (i-1), that is, B-
The value ΔA of B (i−1) is obtained, and it is determined whether the P-value control has converged based on whether this ΔA has become equal to or less than the convergence determination threshold value of CGP. And ΔA is CGP
If the value is equal to or less than the convergence determination threshold value (YES), a CGP convergence determination flag is set in S214,
At S215, a determination is made as to whether the system is normal, and at S216, a feedback correction amount (CFB) is calculated.
At S217, catalyst deterioration detection is executed.

If ΔA is not equal to or smaller than the convergence judgment threshold value of CGP in the judgment of S213 (NO), S
Go to 218, lower the CGP convergence determination flag, and go to S2
After executing the CFB operation in step 19, the process returns.

If the determination in S212 is NO, that is, CG
If the P average value has exceeded the threshold value, the flow goes to S220 to determine a system abnormality, and the lamp is turned on in S221.

Further , the first air-fuel ratio sensor is not active (S
If NO in step 201), the air-fuel ratio feedback is not executed, so that the CFB is fixed in step S222.

[0031]

Since the invention of this application is constructed as described above, it can be used to detect the deterioration of the upstream first air-fuel ratio sensor based on the output of the second air-fuel ratio sensor disposed downstream of the catalyst. Thus, the deterioration of the first air-fuel ratio sensor can be accurately detected without being confused with the deterioration of the catalyst. Also, misjudgment of catalyst deterioration
Can be prevented.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of the invention of this application.

FIG. 2 is a time chart illustrating the operation of the invention of this application.

FIG. 3 is an overall system diagram of an embodiment of the invention of this application.

FIG. 4 is a time chart for explaining P value feedback control in one embodiment of the present invention;

FIG. 5 is a flowchart illustrating control for detecting frequency deterioration of an air-fuel ratio sensor according to an embodiment of the present invention;

FIG. 6 is a flowchart for executing control relating to the invention of this application;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 6 Exhaust passage 7 Catalyst 8 Injector 9 Control unit 12 First air-fuel ratio sensor 13 Second air-fuel ratio sensor

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F02D 45/00 368 F02D 45/00 368G 368H (56) References JP-A-2-204648 (JP, A) JP-A-4- 116239 (JP, A) JP-A-3-286160 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/00-41/40 F02D 43/00-45/00

Claims (2)

(57) [Claims] 1. An air-fuel ratio control means disposed in an exhaust passage of an engine on an upstream side of a catalyst for purifying exhaust gas and for feedback-controlling an air-fuel ratio of an air-fuel mixture supplied to the engine to a target air-fuel ratio. 1st output of air-fuel ratio signal
An air-fuel ratio sensor, a second air-fuel ratio sensor disposed downstream of the catalyst, a first air-fuel ratio sensor and a second air-fuel ratio sensor.
And a sensor failure detecting means for detecting a failure of the first air-fuel ratio sensor based on the frequency ratio of the outputs of the two air-fuel ratio sensors. Receiving the output of the intake air amount detecting means for detecting a parameter related to the intake air amount of the second air-fuel ratio sensor when the intake air amount is equal to or more than a set value.
The ratio of the output frequency of the first air-fuel ratio sensor to
And when the intake air amount is equal to or less than the set value, the second
The first air-fuel ratio sensor with respect to the frequency of the output of the air-fuel ratio sensor
When the ratio of the frequency of the sensor output exceeds a predetermined value,
A failure detection device for an air-fuel ratio detection device, wherein the sensor failure detection means is configured to determine that the first air-fuel ratio sensor has failed. 2. An exhaust gas purifier in an exhaust passage of an engine.
Installed upstream of the catalyst for
Feedback control of the air-fuel ratio of the air-fuel mixture
Output the air-fuel ratio signal to the air-fuel ratio control means in order to control
An air-fuel ratio sensor, and a second air disposed downstream of the catalyst.
A fuel ratio sensor, the first air-fuel ratio sensor and the second air-fuel ratio sensor.
The frequency ratio of the output of both air-fuel ratio sensors
For detecting a failure of the first air-fuel ratio sensor based on
The first air-fuel ratio sensor and the second air-fuel
Receives the output from the ratio sensor and outputs the frequency of the output from both air-fuel ratio sensors.
Catalyst deterioration detection for detecting deterioration of the catalyst based on a numerical ratio
An engine control device comprising the means, The sensor failure detecting means is configured to detect an intake air amount of the engine.
Of the intake air amount detecting means for detecting the parameter related to
When the output is received and the intake air amount is below the set value, The second
The first air-fuel ratio sensor with respect to the frequency of the output of the air-fuel ratio sensor
If the ratio of the output frequencies of the sensors is equal to or greater than a predetermined value,
(1) It is determined that the air-fuel ratio sensor has failed, The catalyst deterioration detecting means detects the amount of intake air of the engine.
The output of the intake air amount detection means for detecting related parameters
When the intake air amount is equal to or less than the set value, the second air
The first air-fuel ratio sensor with respect to the frequency of the output of the fuel ratio sensor
If the ratio of the output frequency of the
Characterized in that the deterioration detection is not executed
Engine control device.