JP3134698B2 - Air-fuel ratio sensor deterioration diagnosis device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for diagnosing deterioration of an air-fuel ratio sensor used in an exhaust gas purification system for an automobile engine or the like.

[0002]

2. Description of the Related Art In recent years, an exhaust system of an automobile gasoline engine is provided with an oxidation-reduction type exhaust purification catalyst (hereinafter, three-way catalyst) in order to reduce harmful exhaust gas components. The three-way catalyst is a device that purifies exhaust gas by oxidizing hydrocarbons (HC) and carbon monoxide (CO) while reducing nitrogen oxides (NO _x ). The redox reaction of the three-way catalyst is the theoretical air-fuel ratio (14.7)
Since the operation is performed only in a narrow area (window) in the vicinity, an O ₂ sensor is installed in an exhaust manifold or the like, and the air-fuel ratio is feedback-controlled based on the output signal.

[0003] A general O ₂ sensor has a structure in which a porous platinum electrode is coated on the inner and outer surfaces of a test tubular zirconia element and the atmosphere is introduced into the inside, while the outer surface is exposed to exhaust gas. I have. In such an O ₂ sensor, when the oxygen concentration in the exhaust gas decreases, oxygen in the atmosphere is ionized and moves toward the outer surface in the zirconia element, and an electromotive force is generated according to the principle of an oxygen concentration cell. At this time, even if a small amount of oxygen is present in the exhaust gas, if the mixture ratio is rich, it is reduced by the catalytic action of platinum, so that the electromotive force changes abruptly near the stoichiometric air-fuel ratio. I do. Therefore, by detecting the output voltage of the O ₂ sensor, it is possible to accurately determine whether the air-fuel ratio of the air-fuel mixture is richer or leaner than the stoichiometric air-fuel ratio. It is possible to maintain the fuel ratio within the window.

[0004]

Since the output characteristics of the O ₂ sensor greatly change at a low temperature, the O ₂ sensor is installed at a portion exposed to high-temperature exhaust gas such as a junction of an exhaust manifold. Therefore, when used for a long period of time, the O ₂ sensor gradually deteriorates due to elution of the platinum electrode, clogging of pores, and the like. When the O ₂ sensor deteriorates,
As shown in FIG. 9, as the number of inversions of the output voltage decreases, the amplitude also decreases, and the responsiveness to a change in the air-fuel ratio becomes extremely poor. As a result, the air-fuel ratio control in the window cannot be performed naturally, the harmful exhaust gas component increases due to the reduction of the oxidation-reduction reaction, and the drivability deteriorates due to the over-rich or over-lean air-fuel ratio. Had been done. However, such a problem can be confirmed only by a method such as using an exhaust gas tester at the time of a periodic inspection. There is a fear that the 続 け る will continue to be used.

Therefore, an apparatus for diagnosing deterioration of an O ₂ sensor based on an output signal of the O ₂ sensor during operation is disclosed in Japanese Unexamined Patent Publication No.
It has been proposed in, for example, JP-A-34597. In this type of deterioration diagnosis device, the air-fuel ratio of the air-fuel mixture is forcibly excited, and the output voltage at that time is used to diagnose the deterioration of the O ₂ sensor. That is, after the O ₂ sensor is initialized while keeping the air-fuel ratio of the mixture rich or lean for a certain period of time, the air-fuel ratio is periodically changed between rich and lean, and the output voltage of the O ₂ sensor becomes a threshold ( For example, the time required to cross 0.5 V) and the amplitude of the output voltage are measured. In this case, O ₂
If the sensor is deteriorated, the above-mentioned time becomes longer or the amplitude becomes smaller. Therefore, the deterioration can be diagnosed by comparing with a predetermined determination value. However, when the air-fuel ratio is forcibly excited, the range of the air-fuel ratio enrichment and leanness is reduced by one.
To take as large as 0-15%, of course,
The harmful exhaust gas component is greatly increased, and the output torque of the engine fluctuates and drivability is deteriorated.

[0006] The present invention has been made in view of the above situation,
An object of the present invention is to provide a deterioration diagnosis device for an air-fuel ratio sensor that performs a preliminary diagnosis during the air-fuel ratio feedback control and performs a deterioration diagnosis accompanied by a forced fluctuation according to the result.

[0007]

Therefore, according to the present invention, there is provided an air-fuel ratio sensor for detecting an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine for a vehicle, and a detection signal of the air-fuel ratio sensor. Air-fuel ratio control means for feedback-controlling the air-fuel ratio of the air-fuel mixture so as to approach a predetermined target air-fuel ratio,
When the air-fuel ratio control means is performing air-fuel ratio feedback control, based on the detection signal of the air-fuel ratio sensor,
Detecting ability determining means for determining the detecting ability of the air-fuel ratio sensor; and, when the detecting ability determining means determines that the detecting ability of the air-fuel ratio sensor has decreased, the detecting ability determining means has priority over the air-fuel ratio controlling means. Forcibly changing means for forcibly changing the air-fuel ratio of the air-fuel mixture, based on a detection signal of the air-fuel ratio sensor when the forcible change is performed by the forcible changing means,
The present invention proposes an air-fuel ratio sensor deterioration diagnosis device including a deterioration judgment unit for judging deterioration of the air-fuel ratio sensor.

According to a second aspect of the present invention, in the deterioration diagnosing apparatus according to the first aspect, the detection ability determination means detects the air-fuel ratio sensor when the air-fuel ratio feedback control is being performed by the air-fuel ratio control means. A first measuring means for measuring a first responsiveness information amount indicating a responsiveness of the air-fuel ratio sensor based on the signal, and the first responsiveness information amount measured by the first measuring means is determined by a predetermined first reference A value that determines whether the responsiveness of the air-fuel ratio sensor is lower than the responsiveness corresponding to the first reference value to thereby determine a decrease in the detection capability of the air-fuel ratio sensor. suggest.

According to a third aspect of the present invention, in the deterioration diagnosing apparatus according to the first or second aspect, the deterioration determining means detects the detection signal of the air-fuel ratio sensor when the air-fuel ratio is forcibly changed by the forcible changing means. A second responsiveness information indicating the responsiveness of the air-fuel ratio sensor based on the second responsiveness information, and the second responsiveness information measured by the second measurement means is used as a predetermined second reference value. By comparing with
It is proposed to determine whether the air-fuel ratio sensor has deteriorated by determining whether the responsiveness of the air-fuel ratio sensor has dropped below the responsiveness corresponding to the second reference value.

According to a fourth aspect of the present invention, in the deterioration diagnosis apparatus according to the third aspect, the second reference value is a value corresponding to a response worse than the response corresponding to the first reference value. suggest. In a preferred embodiment , claim 2
In the deterioration diagnosis device described above, the first responsiveness information amount may be a number of inversions of an output signal of the air-fuel ratio sensor per predetermined time.

Further, in the apparatus for diagnosing deterioration of 請 Motomeko 2, wherein the first response information amount is preferably a reversal frequency of the output signal of the air-fuel ratio sensor. In addition,請 Motomeko 2
In the deterioration diagnostic apparatus according, the first response information amount is preferred for the amplitude of the output signal of the air-fuel ratio sensor
New

[0012]

According to the first aspect of the present invention, when the detection capability determining means determines that the detection capability has not decreased based on the detection signal of the air-fuel ratio sensor when the air-fuel ratio feedback control is being performed, the present invention is applied to the deterioration diagnosis device. Without performing a diagnosis,
Diagnose the air-fuel ratio sensor as normal. Then, when the detection capability determining means determines that the detection capability has decreased, the main diagnosis with forced fluctuation is performed for the first time.

Further, in the deterioration diagnosis apparatus according to the second aspect, for example, the detection capability determination means monitors an output signal of the air-fuel ratio sensor during the air-fuel ratio feedback control, and the number of inversions and the amplitude thereof are set to the first reference value. If it is less than
It is determined that the detection ability has decreased. Further, in the deterioration diagnosis device according to claim 3, for example, after initialization holds air briefly to the lean, varied between the rich and lean at a predetermined cycle, O ₂ sensor when the The deterioration is diagnosed based on whether or not the output voltage has reached the diagnosis reference value within a predetermined time.

Further, in the deterioration diagnosis apparatus according to the fourth aspect, the preliminary diagnosis is performed based on the first reference value corresponding to relatively good responsiveness, so that when the deterioration of the air-fuel ratio sensor is suspected, the deterioration is relatively poor. This diagnosis is performed using the second reference value corresponding to the response. Further, the deterioration diagnosis apparatus of claim 2 is preferable.
In the aspect , for example, in the air-fuel ratio feedback control, the number of inversions of the output signal of the air-fuel ratio sensor within a predetermined time is measured, and if the value is equal to or less than the first reference value, the main diagnosis with forced fluctuation is performed.

Further, another preferred deterioration diagnostic apparatus according to claim 2
In a preferred embodiment , the amplitude of the output signal of the air-fuel ratio sensor in the air-fuel ratio feedback control is measured, and if the value is equal to or less than the first reference value, the main diagnosis with forced fluctuation is performed. In a further preferred aspect of the deterioration diagnosis apparatus according to claim 2 , in the air-fuel ratio feedback control, the inversion frequency of the output signal of the air-fuel ratio sensor is measured, and if the value is less than or equal to the first reference value. This diagnosis with forced fluctuation is performed.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an internal combustion engine provided with the deterioration diagnosis device according to the present invention. Referring to FIG. 1, an air cleaner 5, a Karman vortex air flow sensor 6, a throttle valve 7, an ISC (idle) is connected to an intake port 2 of an engine 1 via an intake manifold 4 in which a fuel injection valve 3 is attached to each cylinder. Speed controller) 8
Are connected. An exhaust pipe 12 is connected to the exhaust port 10 through an exhaust manifold 11, and a three-way catalyst 13 and a muffler (not shown) are attached to the exhaust pipe 12. An O ₂ sensor 14 is mounted in the exhaust pipe 12 on the upstream side of the three-way catalyst 13. The O ₂ sensor 14 reacts with oxygen in the exhaust gas before passing through the three-way catalyst 13 and generates a voltage according to the concentration.

The engine 1 has a crank angle sensor 20 for detecting the engine rotation speed Ne and the like, and a cooling water temperature TW.
A throttle sensor 22 for detecting the opening θTH of the throttle valve 7 and an atmospheric pressure sensor 2 for detecting the atmospheric pressure Ta are provided in the intake system.
3. Various sensors such as an intake air temperature sensor 24 for detecting the intake air temperature Ta are connected. In the figure, reference numeral 30 denotes a spark plug disposed above a combustion chamber 31;
This is an ignition coil that outputs a high voltage to the ignition coil.

On the other hand, in the cabin, an input / output device (not shown) and a storage device (RO) containing a large number of control programs are provided.
M, RAM, nonvolatile RAM, etc.), central processing unit (CP
U), an ECU (engine control unit) 40 including a timer counter and the like is provided. ECU40
On the input side, a large number of sensors and switches are connected in addition to the various sensors described above, and detection information from these is input. On the output side, the fuel injection valve 3 or I
The SC8, the ignition coil 32, and the like are connected, and an optimum value calculated based on input information from various sensors is output to these. The ECU 40 controls fuel injection, ignition timing, ISC, and the like, and also performs deterioration diagnosis of the O ₂ sensor 14. In the figure, 41 is a warning lamp installed in the vehicle interior, lights when the deterioration of the O ₂ sensor 14, attention to the driver.

First, the fuel injection control in this embodiment will be briefly described. Simultaneously with the start of the engine 1 by the driver, open loop control of fuel injection by the ECU 40 is executed. When this control is started, the ECU 40
Calculates the intake air amount information A / N per intake stroke based on the output signals of the air flow sensor 6 and the crank angle sensor 20, and calculates the basic fuel injection time from the value and the target air-fuel ratio (normally, the stoichiometric air-fuel ratio). Calculate TBASE. Next, the ECU 4
0 performs correction based on the output signals of the atmospheric pressure sensor 23 and the intake air temperature sensor 24 with respect to the basic fuel injection time TBASE, and further increases the warm-up amount based on the output signals of the water temperature sensor 21 and the throttle sensor 22. Then, the fuel injection time TINJ is calculated by correcting the fuel injection time or increasing the acceleration. And ECU
Numeral 40 denotes an invalid injection time T which complements the fuel injection time TINJ obtained in this manner to compensate for the delay in opening the fuel injection valve 3.
After adding D, the fuel injector 3 is driven via a fuel injector driver (not shown).

Now, the activation of the O ₂ sensor 14 is completed, the engine 1 is not in an acceleration state, a high load and a high rotation state, and the like.
When predetermined operating conditions are satisfied, the ECU 40 starts air-fuel ratio feedback control. When this control starts, EC
U40, the output voltage VO with a predetermined threshold value VTH of the O ₂ sensor 14 (e.g., 0.5V) to compare the magnitude of the performs feedback correction of the air-fuel ratio. That is, the O ₂ sensor 14
Indicates that the output voltage VO suddenly changes from the highest voltage (for example, 1.0 V) to the lowest voltage (for example, 0 V) before and after the air-fuel ratio of the air-fuel mixture reaches the stoichiometric air-fuel ratio (14.7).
When O falls below a threshold value VTH (for example, 0.5 V), the fuel injection time TINJ is gradually increased to shift to the rich side,
Conversely, when the output voltage VO exceeds the threshold value VTH, the fuel injection time TINJ is gradually shortened to shift to the lean side. As a result, the air-fuel ratio of the air-fuel mixture is always maintained near the stoichiometric air-fuel ratio, and the three-way catalyst 13 purifies the exhaust gas with high efficiency.

In the air-fuel ratio feedback control in this embodiment, learning correction is performed so that the central value of the feedback correction coefficient becomes 1.0, and the learning correction amount is stored in a nonvolatile RAM. Then, by using the learning correction amount, the accuracy of the above-described open loop control is improved, and the deviation amount at the start of the feedback control is reduced.

The flowcharts of FIGS. 2 to 7 and FIG.
The procedure of the O ₂ sensor deterioration diagnosis in this embodiment will be described with reference to the graph of FIG. When the driver engine 1 to the ignition switch is turned ON is started, O ₂ sensor deterioration diagnosis subroutine of FIG. 2 is executed. When this subroutine is started, the ECU 40 first determines in step S2 that O
₂ It is determined whether or not a normal flag FOK indicating that the sensor 14 is functioning normally is 1. The normal flag FOK is
It is reset to 0 each time the ignition switch is turned off, and is set to 1 when the O ₂ sensor 14 is diagnosed as normal. Therefore, immediately after the start of the engine 1, the normal flag FOK always becomes 0, and the ECU 40
Goes to step S4 because the determination in step S2 is No (No).

[0023] ECU40, after reading the input information from the sensors to the RAM in step S4, determines whether a condition for performing the deterioration diagnosis of the O ₂ sensor 14 in step S6 (diagnosis condition) is satisfied I do. Here, it is sequentially confirmed that the air-fuel ratio feedback control is being performed, and that the engine speed Ne and the volumetric efficiency ηv are within predetermined ranges, and the determination is Yes when all the conditions are satisfied.
(Yes). If the determination in step S6 is No, the ECU 40 returns to the start and waits until the diagnosis condition is satisfied. Here, the reason for confirming that the engine speed Ne and the volumetric efficiency ηv are within predetermined ranges is that when these are not stable, the O ₂ concentration of the exhaust gas is not stable, and normal feedback control is performed. Because it is not done.

When the result of the determination in step S6 is Yes,
ECU40 is then in step S8, based on the output voltage VO from the O ₂ sensor 14, the detection capability determination threshold NX (this example the average value of a predetermined number of reversals of NO _2, 15 times /
Min) or not. If the determination is Yes, it is determined that the O ₂ sensor 14 is normal, and the process returns to the start and repeats the processing from step S2. That is, the processing of step S8 is preliminary diagnosis in the present embodiment, the detection capability of the O ₂ sensor determines whether or not some degradation, the possibility of the O ₂ sensor is deteriorated is seen by this preliminary diagnosis If not, the subroutine is repeatedly executed without performing this diagnosis.
If the O ₂ sensor has not deteriorated at all, the number of reversals N
The average value of the O ₂ is about 60 to 120 times / min.

When the average value of the number of reversals NO ₂ is smaller than the detection capability determination threshold value NX and the determination in step S8 is No, the ECU 40 determines in step S10 the flowcharts of FIGS. 3 to 5 and the graphs of FIG. This diagnostic subroutine shown in FIG. When this diagnostic subroutine starts,
The ECU 40 first reads the input information from each sensor into the RAM again in step S32 in FIG.
At 34, it is determined whether or not the main diagnosis start flag Fchek is 1. Since the initial value of the diagnosis start flag Fchek is set to 0, this determination is No, and the ECU 40 determines whether or not the initialization start flag Finit is 1 in step S36 in FIG. Since the initial value of the initialization start flag Finit is also set to 0, this determination is No and E
The CU 40 starts the initialization of the air-fuel ratio A / F in step S38. The initialization of the air-fuel ratio A / F in the present embodiment is performed by setting the air-fuel ratio A / F to a predetermined ratio (in the present embodiment, 1 to the stoichiometric air-fuel ratio obtained by the air-fuel ratio feedback control).
(2.5%).

When the initialization of the air-fuel ratio A / F is started in step S38, the ECU 40 sets the initialization start flag Finit to 1 in step S40, and starts counting up the first timer T1 in step S42. , Return to start. After returning to the start, the ECU 40 proceeds to step S
Since the determination of 36 is Yes, it is determined in step S44 whether or not the value of the first timer T1 has exceeded a predetermined value T1A (1 second in the present embodiment). Then, the initialization of the air-fuel ratio A / F is continued. As a result, the output voltage VO of the O ₂ sensor drops sharply and becomes almost 0V. (Section a in FIG. 8) When the value of the first timer T1 reaches the predetermined value T1A, step S3
If the determination in step 6 is Yes, the ECU 40 proceeds to step S4
In 6, the diagnostic start flag Fchek is set to 1, and in step S48, the initialization start flag Finit is reset to 0, and the process returns to start.

After returning to the start, the ECU 40 returns to step S50 because the determination in step S34 is Yes.
It is determined whether or not the excitation start flag Fvib is 1.
Since the initial value of the vibration start flag Fvib is set to 0, this determination is No, and the ECU 40 determines in step S
At 52, the second timer T2 starts counting up. Thereafter, the ECU 40 sets the excitation start flag Fvib to 1 in step S54, and sets the air-fuel ratio A / A in step S56.
The forced vibration of F is started. Specifically, a predetermined cycle (1.2 seconds in the present embodiment) with respect to the stoichiometric air-fuel ratio described above.
The air-fuel ratio A / F is set to a predetermined ratio (in this embodiment,
± 10%) to fluctuate to rich and lean sides.

After starting the forced vibration in step S56,
The ECU 40 determines in step S58 in FIG. 5 that the second timer T2
Is determined to have exceeded a predetermined value T2A (5 seconds in this embodiment). And if this determination is No, (in this embodiment, 0.5V) output voltage VO is given diagnosis reference value VTH of the O ₂ sensor 14 in step S60 determines whether exceeded. At this time, if the O ₂ sensor 14 is normal, the output voltage VO becomes the highest value (for example, as shown by the solid line in FIG.
1V) to the lowest voltage (for example, 0 V), and this determination becomes Yes. However, when the O ₂ sensor 14 is deteriorated, the output voltage VO is inverted with a change in the air-fuel ratio, but as shown by a dashed line in FIG. The determination is No.

If the determination in step S60 is No, the ECU 40 determines that the determination in step S50 is Yes.
Therefore, the determinations in steps S58 and S60 are repeated, and while both of them are No, the forced vibration is continued.
If the determination in step S58 is No, step S6
0 of the determination is Yes, i.e., if the value of the second timer T2 is the output voltage VO of the O ₂ sensor 14 before exceeding a predetermined value T2A exceeds the criteria value VTH, ECU 40 is, O ₂ sensor 14 is normal It is diagnosed that there is, and a normal processing subroutine of FIG. 6 is executed in step S62.

[0030] In normal operation processing subroutine, first, in step S82, the turns off the warning lamp 41, O ₂ sensor 14 is shown to the driver that it is functioning properly. next,
In step S84, the the ECU 40 O ₂ sensor 14
The operation for deleting the fault code is performed so that the fault code corresponding to the deterioration of the RAM does not remain in the RAM. Then, step S8
In step 6, the normality flag FOK is set to 1 to store that the O ₂ sensor 14 is functioning normally.

[0031] Thus, when the normal flag FOK is once set to 1, when the O ₂ next run of the sensor degradation diagnosis subroutine, determination in step S2 is Yes. Therefore, in this case, set the ignition switch to OF
Until the state becomes F, the subroutine ends without performing the deterioration determination of the O ₂ sensor 14 again. On the other hand, when the determination in step S60 is Yes without the determination in step S60 being Yes, that is, when O ₂
If the value of the second timer T2 exceeds the predetermined value T2A without the output voltage VO of the sensor 14 exceeding the diagnostic reference value VTH,
The ECU 40 diagnoses that the O ₂ sensor 14 has deteriorated, and executes the deterioration processing subroutine of FIG. 7 in step S64.

[0032] In the deterioration during processing subroutine, first, in step S92, the warning lamp 41 is lit to urge the repair informs the deterioration of the O ₂ sensor 14 to the driver. And
In step S94, the ECU 40 O ₂ sensor 14
Is stored in the RAM. In this way, when repairing, it is possible to easily know the contents of the failure by reading out the failure code, and the O ₂ sensor 1
4 can be promptly dealt with.

When the normal processing subroutine or the deterioration processing subroutine is completed, the ECU 40 proceeds to step S.
At 66, the forced excitation of the air-fuel ratio A / F is stopped. Next, EC
U40 is a main diagnosis start flag Fchek and vibration start flag Fvib ends the diagnostic subroutine resets both to 0 in step S68, starts again the deterioration diagnosis back to the start of the O ₂ sensor deterioration diagnosis subroutine.

As described above, in the present embodiment, the preliminary diagnosis is performed during the air-fuel ratio feedback control prior to the main diagnosis involving the forced fluctuation of the air-fuel ratio. Therefore, when the O ₂ sensor has not deteriorated, The forced fluctuation is hardly performed, and it is possible to prevent an increase in harmful exhaust gas components and a deterioration in drivability. This concludes the description of specific embodiments, but embodiments of the present invention are not limited to these embodiments. That is, in the above embodiment, the number of inversions of the O ₂ sensor is measured in the preliminary diagnosis, but the inversion frequency and the amplitude may be measured. Further, in the above embodiment, whether or not the output voltage of the O ₂ sensor reaches the threshold value within a predetermined time in this diagnosis is determined. However, the amplitude of the output voltage may be compared with a predetermined threshold value. Good. In the above embodiment, the air-fuel ratio sensor is a voltage output type O _2.
Although the sensor is used, a current output type sensor such as a linear air-fuel ratio sensor may be used. In addition to the forced fluctuation of the air-fuel ratio, various methods can be employed, such as performing switching once between rich and lean only once, in addition to applying vibration as in the above embodiment. Further, starting with the specific procedure of the control, the specific value such as each threshold value can be changed without departing from the gist of the present invention.

[0035]

According to the first aspect of the present invention, there is provided an air-fuel ratio sensor for detecting an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine for a vehicle, and a detection signal from the air-fuel ratio sensor. Air-fuel ratio control means for feedback-controlling the air-fuel ratio of the air-fuel mixture so as to approach a predetermined target air-fuel ratio; and when the air-fuel ratio control means is performing air-fuel ratio feedback control, the detection signal of the air-fuel ratio sensor is Based on the detection capability of the air-fuel ratio sensor, and when the detection capability determination unit determines that the detection capability of the air-fuel ratio sensor is reduced, priority is given to the air-fuel ratio control unit. Means for forcibly varying the air-fuel ratio of the air-fuel mixture, and based on the detection signal of the air-fuel ratio sensor when the forced variation is performed by the forced-fluctuation means. When the detection capability determination unit determines that the detection capability is not reduced by the detection signal of the air-fuel ratio sensor when the air-fuel ratio feedback control is being performed, Without performing this diagnosis, the air-fuel ratio sensor is diagnosed as normal, so that an increase in harmful exhaust gas components and a deterioration in drivability due to forced fluctuation are prevented.

According to the deterioration diagnosis apparatus of the second aspect,
2. The deterioration diagnosis apparatus according to claim 1, wherein the detection capability determination unit is configured to respond to the air-fuel ratio sensor based on a detection signal of the air-fuel ratio sensor when the air-fuel ratio feedback control is being performed by the air-fuel ratio control unit. Measuring means for measuring a first responsiveness information amount indicating the responsiveness, the first responsiveness information amount measured by the first measuring means is determined by a predetermined first
By determining whether the responsiveness of the air-fuel ratio sensor is lower than the responsiveness corresponding to the first reference value by comparing with a reference value, it is determined whether the detection capability of the air-fuel ratio sensor is reduced. As a result, the detection capability of the air-fuel ratio sensor can be reduced quantitatively and accurately, and the frequency of performing this diagnosis is reduced.

According to the third aspect of the present invention, there is provided a deterioration diagnostic apparatus.
3. The deterioration diagnosis device according to claim 1, wherein the deterioration determination unit is responsive to the air-fuel ratio sensor based on a detection signal from the air-fuel ratio sensor when the air-fuel ratio is forcibly changed by the forcible fluctuation unit. 4. A second measuring unit for measuring a second responsiveness information amount indicating the second responsiveness information amount, and comparing the second responsiveness information amount measured by the second measuring unit with a predetermined second reference value to thereby provide the air-fuel ratio sensor. The deterioration of the air-fuel ratio sensor is determined by determining whether the response of the air-fuel ratio sensor is lower than the response corresponding to the second reference value. Becomes possible.

Further, according to the deterioration diagnosis apparatus of the fourth aspect,
4. The deterioration diagnostic apparatus according to claim 3, wherein the second reference value is a value corresponding to a response that is worse than the response corresponding to the first reference value. Is not determined to be normal by the preliminary diagnosis. Further, preferred embodiments of the deterioration diagnosis device 請 Motomeko 2 wherein
As the first response information amount, the air-fuel ratio is the better the reversal number of times per predetermined time of the output signal of the sensor,
As a result , the accuracy of determining the detection capability is increased, and the frequency of performing the main diagnosis is reduced.

[0039] In addition, another of the deterioration diagnosis apparatus of 請 Motomeko 2, wherein
As a preferred embodiment , the first responsiveness information amount is preferably an amplitude of an output signal of the air-fuel ratio sensor .
As a result , the detection accuracy of the detection capability is increased, and the frequency of performing the main diagnosis is reduced. Also, further deterioration diagnostic device 請 Motomeko 2 wherein
As a preferred embodiment , the first responsiveness information amount is preferably an inversion frequency of an output signal of the air-fuel ratio sensor ,
As a result , the accuracy of determining the detection capability is increased, and the frequency of performing the main diagnosis is reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine including a deterioration diagnosis device according to the present invention.

FIG. 2 is a flowchart showing a procedure of an O ₂ sensor deterioration diagnosis subroutine.

FIG. 3 is a flowchart showing a procedure of a diagnostic subroutine.

FIG. 4 is a flowchart showing a procedure of a diagnostic subroutine.

FIG. 5 is a flowchart showing a procedure of a diagnosis subroutine.

FIG. 6 is a flowchart illustrating a procedure of a normal processing subroutine.

FIG. 7 is a flowchart illustrating a procedure of a degradation processing subroutine.

FIG. 8 is a graph showing a relationship between an air-fuel ratio at the time of forced vibration and an output voltage of an O ₂ sensor.

FIG. 9 is a graph showing an output voltage of an O ₂ sensor during air-fuel ratio feedback control.

[Description of Signs] 1 engine 12 exhaust pipe 13 three-way catalyst 14 O ₂ sensor 40 ECU 41 warning light

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/22 305 F02D 41/22 305K G01N 27/409 G01N 27/58 B (72) Inventor Toshiro Nomura Shibago, Minato-ku, Tokyo No. 33-8, Mitsubishi Motors Corporation (72) Inventor Eiji Kanao 5-33-8, Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (56) References JP-A-6-34597 ( JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/26 391 F02B 77/08 F02D 35/00 368 F02D 41/14 310 F02D 41/22 305 G01N 27/409

Claims (4)

(57) [Claims] 1. An air-fuel ratio sensor for detecting an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine for a vehicle, and based on a detection signal from the air-fuel ratio sensor, the air-fuel ratio of the air-fuel mixture approaches a predetermined target air-fuel ratio. Air-fuel ratio control means for feedback-controlling the fuel ratio, and when the air-fuel ratio control means is performing air-fuel ratio feedback control, based on a detection signal of the air-fuel ratio sensor,
Detecting ability determining means for determining the detecting ability of the air-fuel ratio sensor; and if the detecting ability determining means determines that the detecting ability of the air-fuel ratio sensor has decreased, the detecting ability determining means has priority over the air-fuel ratio controlling means. A forced variation means for forcibly varying the air-fuel ratio of the air-fuel mixture, and a deterioration determination means for determining the degradation of the air-fuel ratio sensor based on a detection signal of the air-fuel ratio sensor when the forced variation is performed by the forced variation means. deterioration diagnosis device for an air-fuel ratio sensor, characterized in that example Bei a. 2. The detection ability determination means, based on a detection signal of the air-fuel ratio sensor when air-fuel ratio feedback control is being performed by the air-fuel ratio control means, a first signal indicating a response of the air-fuel ratio sensor. A first measuring unit for measuring the responsiveness information amount, and by comparing the first responsiveness information amount measured by the first measuring unit with a predetermined first reference value, the responsiveness of the air-fuel ratio sensor is improved. 2. The method according to claim 1, further comprising determining whether the air-fuel ratio sensor has a lower detection capability by determining whether the response is lower than the responsiveness corresponding to the first reference value. 3.
An apparatus for diagnosing deterioration of an air-fuel ratio sensor according to any one of the preceding claims. 3. The responsiveness information indicating the responsiveness of the air-fuel ratio sensor based on a detection signal of the air-fuel ratio sensor when the air-fuel ratio is forcibly varied by the forced variation unit. The second to measure the quantity
Measuring means for comparing the second responsiveness information amount measured by the second measuring means with a predetermined second reference value so that the responsiveness of the air-fuel ratio sensor corresponds to the second reference value; The deterioration diagnosis device for an air-fuel ratio sensor according to claim 1, wherein the deterioration of the air-fuel ratio sensor is determined by determining whether the air-fuel ratio sensor has deteriorated. 4. The deterioration diagnosis of the air-fuel ratio sensor according to claim 3, wherein the second reference value is a value corresponding to a response worse than the response corresponding to the first reference value. apparatus.