JPH08220051A - Device for diagnosing deterioration of air-fuel ratio sensor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a deterioration diagnosis device for an air-fuel ratio sensor, which executes a preliminary diagnosis during air-fuel ratio feedback control, and performs deterioration diagnosis accompanied by forced fluctuation according to the result. [Configuration] The ECU 40 determines whether or not the number of inversions NO ₂ is a predetermined value NOX or more based on the output voltage VO of the O ₂ sensor 14 during the air-fuel ratio feedback control, and when this determination is Yes First, it is determined that the O ₂ sensor 14 is normal, and subsequent deterioration diagnosis is not performed. If this determination is No, after the air-fuel ratio is initialized, the air-fuel ratio is forcibly excited between rich and lean, and the output voltage VO changes to the diagnostic reference value VTH within the predetermined time T2. Or not is determined. Then, if this determination is Yes, it is diagnosed that the O ₂ sensor 14 is normal, and if No, it is diagnosed that the O ₂ sensor 14 is deteriorated, the warning lamp 41 is turned on, and the driver is prompted to replace it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deterioration diagnosis device for 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. A three-way catalyst is a device that purifies exhaust gas by oxidizing hydrocarbons (HC) and carbon monoxide (CO) while reducing nitrogen oxides (NO _x ). Redox reaction of three-way catalyst is theoretical air-fuel ratio (14.7)
Since it is performed only in a narrow area (window) in the vicinity, an O ₂ sensor is installed in the exhaust manifold or the like, and the air-fuel ratio is feedback-controlled based on the output signal thereof.

In a general O ₂ sensor, the inner and outer surfaces of a test tubular zirconia element are coated with a porous platinum electrode to introduce the atmosphere into the interior, while the outer surface is exposed to exhaust gas. There is. In such an O ₂ sensor, when the oxygen concentration in the exhaust gas becomes low, oxygen in the atmosphere is ionized and moves in the zirconia element toward the outer surface, and electromotive force is generated by the principle of the oxygen concentration battery. At this time, even if a slight 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 the electromotive force changes rapidly near the stoichiometric air-fuel ratio. To 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, and feedback control of the fuel injection amount etc. It is possible to maintain the fuel ratio within the unwind.

[0004]

By the way, since the output characteristics of the O ₂ sensor change greatly at low temperatures, the O ₂ sensor is installed at a portion exposed to high temperature exhaust gas, such as a confluent portion of an exhaust manifold. Therefore, if used for a long period of time, the O ₂ sensor will gradually deteriorate due to elution of the platinum electrode, clogging of pores, and the like. When the O ₂ sensor deteriorates,
As shown in FIG. 9, the number of times the output voltage is inverted decreases and the amplitude also decreases, resulting in extremely poor responsiveness to changes in the air-fuel ratio. As a result, the air-fuel ratio cannot be controlled within the window, the harmful exhaust gas components increase due to the reduction of the redox reaction, and the drivability deteriorates due to the air-fuel ratio overrich or over lean. I was taken down. However, since such a defect can be confirmed only by a method such as using an exhaust gas tester at the time of regular inspection, a large amount of harmful exhaust gas components are emitted or drivability is gradually deteriorated, but Could continue to be used.

Therefore, an apparatus for diagnosing the deterioration based on the output signal of the O ₂ sensor during operation is disclosed in Japanese Unexamined Patent Publication No. Hei 6 (1999) -96.
It is proposed in Japanese Patent Publication No. 34597. In this type of deterioration diagnosis device, the air-fuel ratio of the air-fuel mixture is forcibly excited and the deterioration of the O ₂ sensor is diagnosed from the output voltage at that time. That is, after the air-fuel ratio of the air-fuel mixture is kept rich or lean for a certain period of time to initialize the O ₂ sensor, the air-fuel ratio is periodically changed between rich and lean, and the output voltage of the O ₂ sensor becomes a threshold value ( 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 long and the amplitude becomes small. Therefore, the deterioration can be diagnosed by comparing with the predetermined judgment value. However, when the air-fuel ratio is forcibly excited, the range of enrichment or leaning of the air-fuel ratio is set to 1
Since it is as large as 0 to 15%, of course,
There was a problem that the harmful exhaust gas component increased significantly and the output torque of the engine fluctuated to deteriorate drivability.

The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a deterioration diagnosis device for an air-fuel ratio sensor, which executes 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 claim 1 of the present invention, 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 are used. 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 this air-fuel ratio control means is performing air-fuel ratio feedback control, based on the detection signal of the air-fuel ratio sensor,
When it is determined by the detection capability determination means that determines the detection capability of the air-fuel ratio sensor and the detection capability determination means determines that the detection capability of the air-fuel ratio sensor has decreased, the air-fuel ratio control means is given priority and the Based on the detection signal of the air-fuel ratio sensor when the forced change means for forcibly changing the air-fuel ratio of the air-fuel mixture and the forced change is performed by the forced change means,
A deterioration diagnosis device for an air-fuel ratio sensor is proposed, which is provided with a deterioration judgment means for judging deterioration of the air-fuel ratio sensor.

According to a second aspect of the present invention, in the deterioration diagnosis apparatus according to the first aspect, the detection capability 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 the responsiveness of the air-fuel ratio sensor based on the signal is provided, and the first responsiveness information amount measured by the first measuring means is a predetermined first reference. By comparing with the value, it is determined whether or not the responsiveness of the air-fuel ratio sensor is lower than the responsiveness corresponding to the first reference value. suggest.

According to a third aspect of the present invention, in the deterioration diagnosing device 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 forcing change means. On the basis of the second responsiveness information amount indicating the responsiveness of the air-fuel ratio sensor, the second responsiveness information amount measured by the second measuring means is provided as a predetermined second reference value. By comparing with
It is proposed that the deterioration of the air-fuel ratio sensor is judged by judging whether the responsiveness of the air-fuel ratio sensor is lower than 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 that is worse than the response corresponding to the first reference value. suggest. A fifth aspect of the present invention proposes the deterioration diagnosing device according to the second aspect, wherein the first responsiveness information amount is the number of times the output signal of the air-fuel ratio sensor is inverted per predetermined time.

In a sixth aspect of the present invention, it is proposed that in the deterioration diagnosis apparatus according to the second aspect, the first responsiveness information amount is an inversion frequency of an output signal of the air-fuel ratio sensor. A seventh aspect of the present invention proposes the deterioration diagnosis device according to the second aspect, wherein the first responsiveness information amount is an amplitude of an output signal of the air-fuel ratio sensor.

[0012]

According to the deterioration diagnosing device of the present invention, when the detection capability determining means determines that the detection capability is not deteriorated by the detection signal of the air-fuel ratio sensor when the air-fuel ratio feedback control is being executed, Without making a diagnosis
The air-fuel ratio sensor is diagnosed as normal. Then, when the detection capability determination means determines that the detection capability has deteriorated, the main diagnosis accompanied by the forced fluctuation is performed for the first time.

Further, in the deterioration diagnosing device according to claim 2, for example, the detecting ability judging means monitors the 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 the first reference value. Is less than
It is determined that the detection capability has deteriorated. Further, in the deterioration diagnosis device according to claim 3, for example, after the air-fuel ratio is held lean for a short time for initialization, the air-fuel ratio is changed between rich and lean at a predetermined cycle, and at that time, an O ₂ sensor is used. Deterioration is diagnosed based on whether or not the output voltage of has reached a diagnostic reference value within a predetermined time.

Further, in the deterioration diagnosis device according to the fourth aspect, the preliminary diagnosis is performed with the first reference value corresponding to the relatively good responsiveness, and when the deterioration of the air-fuel ratio sensor is suspected by this, it is relatively bad. This diagnosis is performed with the second reference value corresponding to the responsiveness. Further, in the deterioration diagnosis device according to claim 5, 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 less than or equal to the first reference value, the forced variation is performed. Perform this diagnosis with.

Further, in the deterioration diagnosing device of claim 6, 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 accompanied by forced fluctuation is performed. I do. Further, in the deterioration diagnosis device according to claim 7, 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, the main 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 equipped with a deterioration diagnosis device according to the present invention. In the figure, an intake port 2 of an engine 1 is provided with an air cleaner 5, a Karman vortex type air flow sensor 6, a throttle valve 7, an ISC (idle valve) via an intake manifold 4 to which a fuel injection valve 3 is attached for each cylinder. Speed controller) 8
An intake pipe 9 equipped with etc. is connected. An exhaust pipe 12 is connected to the exhaust port 10 via 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 upstream of the three-way catalyst 13 in the conduit of the exhaust pipe 12. 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 thereof.

The engine 1 is provided with a crank angle sensor 20 for detecting the engine rotation speed Ne and the cooling water temperature TW.
A water temperature sensor 21 for detecting the temperature is attached, and the intake system has 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.
3, various sensors such as the intake air temperature sensor 24 for detecting the intake air temperature Ta are connected. In the figure, 30 is a spark plug disposed above the combustion chamber 31, and 32 is a spark plug 30.
It is an ignition coil that outputs a high voltage to.

On the other hand, in the passenger compartment, an input / output device (not shown) and a storage device (RO
M, RAM, nonvolatile RAM, etc., central processing unit (CP)
U), an ECU (engine control unit) 40 including a timer counter and the like are installed. ECU40
In addition to the above-mentioned various sensors, a large number of sensors and switches are connected to the input side of, and detection information from these is input. On the output side, the fuel injection valve 3 and I
The SC8, the ignition coil 32, etc. are connected, and the optimum value calculated based on the input information from various sensors is output to them. Then, the ECU 40 controls fuel injection, ignition timing, ISC, etc., and also executes deterioration diagnosis of the O ₂ sensor 14. In the figure, reference numeral 41 denotes a warning light installed in the vehicle compartment, which lights up when the O ₂ sensor 14 is deteriorated and calls the driver's attention.

First, the fuel injection control in this embodiment will be briefly described. At the same time when the driver starts the engine 1, the ECU 40 executes open loop control of fuel injection. When this control is started, the ECU 40
Is 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 the basic fuel injection time is calculated from the value and the target air-fuel ratio (usually the theoretical air-fuel ratio). Calculate TBASE. Next, the ECU 4
A value of 0 corrects the basic fuel injection time TBASE based on the output signals of the atmospheric pressure sensor 23 and the intake air temperature sensor 24, 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 performing the acceleration increase correction and the like. And the ECU
40 is an invalid injection time T that complements the valve opening delay of the fuel injection valve 3 with respect to the fuel injection time TINJ obtained in this way.
After adding D, the fuel injection valve 3 is driven via a fuel injection valve driver (not shown).

By the way, when the activation of the O ₂ sensor 14 is completed, the engine 1 is not in an accelerating state, a high load and a high rotation state, etc.
When the predetermined operating condition is satisfied, the ECU 40 starts the air-fuel ratio feedback control. When this control starts, EC
U40 compares the output voltage VO of the O ₂ sensor 14 with a predetermined threshold value VTH (for example, 0.5 V) to perform a feedback correction of the air-fuel ratio. That is, the O ₂ sensor 14
The output voltage V0 suddenly changes from the highest voltage (eg, 1.0V) to the lowest voltage (eg, 0V) before and after the air-fuel ratio of the air-fuel mixture becomes the stoichiometric air-fuel ratio (14.7).
When O falls below a threshold value VTH (for example, 0.5V), the fuel injection time TINJ is gradually lengthened 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 exhaust gas is purified by the three-way catalyst 13 with high efficiency.

In the air-fuel ratio feedback control of this embodiment, the 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 the nonvolatile RAM. Then, by using the learning correction amount, the accuracy of the open loop control described above is improved, and the deviation amount at the time of rising 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. When the driver turns on the ignition switch to start the engine 1, the O ₂ sensor deterioration diagnosis subroutine of FIG. 2 is executed. When this sub-routine is started, the ECU 40 first determines in step S2
₂ It is determined whether or not the normality flag FOK indicating that the sensor 14 is functioning normally is 1. Normal flag FOK is
It is reset to 0 each time the ignition switch is turned off, and set to 1 when the O ₂ sensor 14 is diagnosed as normal. Therefore, immediately after the engine 1 is started, the normality flag FOK is always 0, and the ECU 40
Becomes No in step S2, the process proceeds to step S4.

The ECU 40 reads the input information from each sensor into the RAM in step S4, and then determines in step S6 whether a condition (diagnosis condition) for diagnosing the deterioration of the O ₂ sensor 14 is satisfied. To do. Here, it is sequentially confirmed that the air-fuel ratio feedback control is being performed, that the engine speed Ne and the volumetric efficiency ηv are within a predetermined range, etc., and if all the conditions are satisfied, the determination is Yes.
(Affirmation). Then, if the determination in step S6 is No, the ECU 40 returns to the start and waits until the diagnostic condition is satisfied. The reason for confirming that the engine rotation speed Ne and the volumetric efficiency ηv are within the predetermined ranges is that the O ₂ concentration of the exhaust gas is not stable when these are not stable and the normal feedback control is performed. This is because it is not done.

When the determination result of step S6 is Yes,
Next, in step S8, the ECU 40 determines, based on the output voltage VO from the O ₂ sensor 14, that the average value of the number of inversions NO ₂ is a predetermined detection capability determination threshold value NX (in this embodiment, 15 times /
Min) or more is determined. Then, if this determination is Yes, it is determined that the O ₂ sensor 14 is normal, and the process returns to the start and the processes in and after step S2 are repeated. 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 inversions N
The average value of O ₂ is about 60 to 120 times / minute.

Now, when the average value of the number of inversions NO ₂ falls below the detection capability determination threshold value NX and the determination in step S8 becomes No, the ECU 40 proceeds to step S10 and shows the flowcharts of FIGS. 3 to 5 and the graph of FIG. This diagnostic subroutine shown in is executed. When this diagnosis subroutine is started,
The ECU 40 first reads the input information from each sensor into the RAM again in step S32 of FIG.
At 34, it is determined whether 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 the initialization start flag Finit is 1 in step S36 of 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 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 at a predetermined ratio (in this embodiment, 1 to the theoretical air-fuel ratio obtained by the air-fuel ratio feedback control).
2.5%) and fixed on the lean side.

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 then starts counting up the first timer T1 in step S42. , Go back to the start. After returning to the start, the ECU 40 executes 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 exceeds the predetermined value T1A (1 second in this embodiment), and while this determination is No, the start is performed. Returning to this, 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 to almost 0V. (Section a in FIG. 8) When the value of the first timer T1 reaches the predetermined value T1A, step S3
When the determination of 6 is Yes, the ECU 40 determines in step S4
The diagnosis start flag Fchek is set to 1 in 6 and the initialization start flag Finit is reset to 0 in step S48, and then the process returns to the start.

The ECU 40 that has returned to the start step determines that the result of the determination in step S34 is Yes, and therefore, the step S50 is performed.
Then, it is determined whether the vibration 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 proceeds to step S
At 52, the second timer T2 starts counting up. After that, the ECU 40 sets the vibration start flag Fvib to 1 in step S54, and in step S56, the air-fuel ratio A /
Forced vibration of F is started. Specifically, with respect to the stoichiometric air-fuel ratio described above, a predetermined cycle (1.2 seconds in this embodiment).
Therefore, the air-fuel ratio A / F is set to a predetermined ratio (in the present embodiment,
± 10%) to change to rich and lean side.

After the forced vibration is started in step S56,
The ECU 40 executes the second timer T2 in step S58 of FIG.
It is determined whether or not the value of exceeds a predetermined value T2A (5 seconds in this embodiment). Then, if this determination is No, it is determined in step S60 whether or not the output voltage VO of the O ₂ sensor 14 exceeds a predetermined diagnostic reference value VTH (0.5 V in this embodiment). At this time, if the O ₂ sensor 14 is normal, the output voltage VO reaches the maximum value (for example, as shown by the solid line in FIG. 8 by performing forced excitation of the air-fuel ratio A / F).
This judgment is Yes after changing from 1 V) to the lowest voltage (for example, 0 V). However, when the O ₂ sensor 14 is deteriorated, the output voltage VO is reversed with the change of the air-fuel ratio, but as shown by the alternate long and short dash 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 are No, the forced vibration is continued.
Then, the determination in step S58 is No, and step S6
When the determination of 0 is Yes, that is, when the output voltage VO of the O ₂ sensor 14 exceeds the diagnostic reference value VTH before the value of the second timer T2 exceeds the predetermined value T2A, the ECU 40 determines that the O ₂ sensor 14 is normal. It is diagnosed that there is, and the normal process subroutine of FIG. 6 is executed in step S62.

In the normal processing subroutine, first, in step S82, the warning lamp 41 is turned off to show the driver that the O ₂ sensor 14 is functioning normally. next,
In step S84, the ECU 40 causes the O ₂ sensor 14 to
The failure code erasing operation is performed so that the failure code corresponding to the deterioration of No. remains in the RAM. Then, step S8
In step 6, the normality flag FOK is set to 1, and it is stored that the O ₂ sensor 14 is functioning normally.

In this way, once the normal flag FOK is set to 1, the determination at step S2 becomes Yes at the next execution of the O ₂ sensor deterioration diagnosis subroutine. Therefore, in this case, turn off the ignition switch.
Until F is set, the subroutine is ended without performing the deterioration determination of the O ₂ sensor 14 again. On the other hand, if the determination in step S58 is Yes without the determination in step S60 is Yes, that is, O ₂
When the value of the second timer T2 exceeds the predetermined value T2A while the output voltage VO of the sensor 14 does not exceed the diagnostic reference value VTH,
The ECU 40 diagnoses that the O ₂ sensor 14 is deteriorated, and executes the deterioration time processing subroutine of FIG. 7 in step S64.

In the deterioration time processing subroutine, first, in step S92, the warning light 41 is turned on to notify the driver of the deterioration of the O ₂ sensor 14 and prompt the repair. And
In step S94, the ECU 40 causes the O ₂ sensor 14 to
The failure code corresponding to the deterioration of is stored in the RAM. Thus, when repairing, the failure content can be easily known by reading this failure code, and the O ₂ sensor 1
It is possible to swiftly deal with the replacement of item 4 and the like.

Upon completion of the normal processing subroutine or the deterioration processing subroutine, the ECU 40 executes step S
At 66, the forced vibration of the air-fuel ratio A / F is stopped. Next, EC
In step S68, the U 40 resets both the main diagnosis start flag Fchek and the vibration start flag Fvib to 0, ends the main diagnosis subroutine, returns to the start of the O ₂ sensor deterioration diagnosis subroutine, and restarts the deterioration diagnosis.

As described above, in this 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 is not deteriorated, Almost no forced fluctuations occurred, and it became possible to prevent an increase in harmful exhaust gas components and deterioration of drivability. Although the description of the specific embodiment has been completed, the embodiment of the present invention is not limited to this embodiment. That is, in the above embodiment, the number of times of reversal of the O ₂ sensor was measured in the preliminary diagnosis, but the reversal frequency and amplitude may be measured. In the above embodiment, it is determined in this diagnosis whether or not the output voltage of the O ₂ sensor reaches the threshold value within a predetermined time. However, the amplitude of the output voltage may be compared with the 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. Further, as the forced change of the air-fuel ratio, various methods such as switching between rich and lean only once can be adopted in addition to the vibration as in the above embodiment. Furthermore, it is possible to change the specific procedure such as the control and the specific values such as the threshold values within a range not departing from the gist of the present invention.

[0035]

According to the deterioration diagnosing device of the first aspect of the present invention, based on the air-fuel ratio sensor for detecting the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine for a vehicle, and the 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, and when this air-fuel ratio control means is performing air-fuel ratio feedback control, the detection signal of the air-fuel ratio sensor Based on the detection capability determination means for determining the detection capability of the air-fuel ratio sensor, and if the detection capability determination means determines that the detection capability of the air-fuel ratio sensor has decreased, priority is given to the air-fuel ratio control means. Of the air-fuel ratio sensor based on the detection signal of the air-fuel ratio sensor when the air-fuel ratio of the air-fuel mixture is forcibly changed and the forced change is performed by the forced change means. Since it is provided with the deterioration determination means for determining, by the detection signal of the air-fuel ratio sensor when the air-fuel ratio feedback control is being executed, when the detection performance determination means determines that the detection performance is not reduced, Without performing this diagnosis, the air-fuel ratio sensor is diagnosed as normal, and an increase in harmful exhaust gas components and deterioration of drivability due to forced fluctuation are prevented.

According to the deterioration diagnosis device of claim 2,
The deterioration diagnosis device according to claim 1, wherein the detection capability determination means is 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 means, and a response of the air-fuel ratio sensor. A first measuring means for measuring a first responsiveness information amount indicating the property, and the first responsiveness information amount measured by the first measuring means is a first predetermined value.
By comparing with a reference value, it is determined whether or not the response of the air-fuel ratio sensor is lower than the response corresponding to the first reference value, thereby determining a decrease in the detection capability of the air-fuel ratio sensor. As a result, the detection capability of the air-fuel ratio sensor can be quantitatively and accurately reduced, and the frequency of this diagnosis is reduced.

According to the deterioration diagnosis device of claim 3,
3. The deterioration diagnosing device according to claim 1, wherein the deterioration determining means is responsive to the air-fuel ratio sensor based on a detection signal of the air-fuel ratio sensor when the air-fuel ratio is forcibly changed by the forced changing means. Is provided, and a second measuring means for measuring a second responsiveness information amount is provided. By comparing the second responsiveness information amount measured by the second measuring means with a predetermined second reference value, the air-fuel ratio sensor Since the deterioration of the air-fuel ratio sensor is judged by judging whether or not the responsiveness of is lower than the responsiveness corresponding to the second reference value, it is possible to judge the deterioration of the air-fuel ratio sensor with high accuracy. Is possible.

According to the deterioration diagnosis device of claim 4,
The deterioration diagnosis device 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, and therefore the air-fuel ratio sensor that is actually deteriorated. Will not be determined to be normal by preliminary diagnosis. Further, according to the deterioration diagnosis device of claim 5,
In the deterioration diagnosis device described above, since the first responsiveness information amount is the number of times of reversal of the output signal of the air-fuel ratio sensor per predetermined time, the determination accuracy of the detection capability is increased, and the frequency of performing this diagnosis is low. Become.

According to the deterioration diagnosis device of claim 6,
In the deterioration diagnosing device according to claim 2, since the first responsiveness information amount is the amplitude of the output signal of the air-fuel ratio sensor, the accuracy of determination of the detection capability is improved, and the frequency of the main diagnosis is reduced. According to the deterioration diagnosis device of claim 7,
In the deterioration diagnosing device according to claim 2, since the first responsiveness information amount is the inversion frequency of the output signal of the air-fuel ratio sensor, the accuracy of determination of the detection capability is improved, and the frequency of performing the main diagnosis is reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine equipped with 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 the procedure of this diagnosis subroutine.

FIG. 4 is a flowchart showing the procedure of this diagnosis subroutine.

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

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

FIG. 7 is a flowchart showing a procedure of a deterioration time processing subroutine.

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

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

[Explanation of symbols]

1 Engine 12 Exhaust Pipe 13 Three-Way Catalyst 14 O ₂ Sensor 40 ECU 41 Warning Light

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location F02D 41/22 305 F02D 41/22 305K G01N 27/409 G01N 27/58 B (72) Inventor Nomura Toshiro Mitsubishi Motors Co., Ltd. 3-5-3, Shiba, Minato-ku, Tokyo (72) Inventor Hidetsugu Kaneo 5-33-8, Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation

Claims (7)

[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 an air-fuel ratio air-fuel ratio of the air-fuel mixture so as to approach a predetermined target air-fuel ratio based on a detection signal of the air-fuel ratio sensor. Air-fuel ratio control means for feedback-controlling the fuel ratio, and when this air-fuel ratio control means is performing air-fuel ratio feedback control, based on the detection signal of the air-fuel ratio sensor,
When the detection capability determination unit that determines the detection capability of the air-fuel ratio sensor and the detection capability determination unit determines that the detection capability of the air-fuel ratio sensor is reduced, the detection unit has priority over the air-fuel ratio control unit. A forced change means for forcibly changing the air-fuel ratio of the air-fuel mixture; and a deterioration determination means for judging deterioration of the air-fuel ratio sensor based on a detection signal of the air-fuel ratio sensor when the forced change is performed by the forced change means. A deterioration diagnosis device for an air-fuel ratio sensor, comprising: 2. The detection capability determination means indicates a response of 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 means. By providing a first measuring means for measuring the responsiveness information amount, and comparing the first responsiveness information amount measured by the first measuring means with a predetermined first reference value, the responsiveness of the air-fuel ratio sensor can be improved. 2. The deterioration of the detection capability of the air-fuel ratio sensor is judged by judging whether the responsiveness corresponding to the first reference value has decreased.
A deterioration diagnosis device for the air-fuel ratio sensor described. 3. The second 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 changed by the forced change means. Second to measure quantity
A response is provided in which the responsiveness of the air-fuel ratio sensor corresponds to the second reference value by providing a measuring means and comparing the second responsiveness information amount measured by the second measuring means with a predetermined second reference value. Deterioration diagnosis device for an air-fuel ratio sensor according to claim 1 or 2, characterized in that the deterioration of the air-fuel ratio sensor is judged by judging whether or not the deterioration 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 that is worse than the response corresponding to the first reference value. apparatus. 5. The deterioration diagnosis device for an air-fuel ratio sensor according to claim 2, wherein the first responsiveness information amount is the number of times the output signal of the air-fuel ratio sensor is inverted per predetermined time. 6. The first responsiveness information amount is an inversion frequency of an output signal of the air-fuel ratio sensor,
The deterioration diagnosis device for an air-fuel ratio sensor according to claim 2. 7. The deterioration diagnosis device for an air-fuel ratio sensor according to claim 2, wherein the first responsiveness information amount is an amplitude of an output signal of the air-fuel ratio sensor.