JPH10159640A - Diagnostic device for abnormality of air-fuel ratio sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately diagnose abnormality of a wide range air-fuel ratio sensor by diagnosing abnormality of the air-fuel ratio sensor based on the current value flowing between the electrodes of the air-fuel ratio sensor, when an abnormality diagnosis beginning condition including that an engine is operated at a fixed air-fuel ratio after starting the engine is judged to be realized. SOLUTION: For diagnosing abnormality of a wide range air-fuel ratio sensor 1, when an abnormality diagnosis beginning condition in which a fixed time lapses after starting, activity of the air-fuel ratio sensor is judged, an air-fuel ratio feedback control condition is materialized, and the like, is realized, monitoring of the current value between oxygen pump electrode parts 8A, 8B is begun. Next it is judged whether the current value is within a fixed range or not, and in the case of YES, the air-fuel ratio sensor 1 is judged to be normal. Meanwhile, in case of 'NO', it is judged that some abnormality exists so as to pass NG judgement. When such NG judgements are continuously generated for example two times, a warning lamp is lighted so as to let a driver and the like recognize existence of some abnormality and urge him dealing such as repair.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for diagnosing abnormality of a so-called wide-range air-fuel ratio sensor.

2. Description of the Related Art Conventionally, as a so-called wide-range air-fuel ratio sensor, for example, there is one as shown in FIG. As shown in FIG. 2, this material is placed in a body (formed of, for example, a heat-resistant porous insulating material such as zirconia Zr ₂ O ₃ having oxygen ion conductivity) provided with a heater portion 2, (Atmosphere introduction hole 3) communicating with (standard gas)
A gas diffusion layer (or gas diffusion gap) 6 that communicates with a gas to be detected (for example, exhaust gas from an internal combustion engine) via a gas introduction hole 4 to be detected, a protective layer 5, and the like is provided. The sensing portion electrodes 7A and 7B are composed of the air introduction hole 3 and the gas diffusion layer 6.
And oxygen pump electrodes 8A, 8B
Are provided on the gas diffusion layer 6 and the periphery of the main body 1 corresponding thereto. The sensing unit electrodes 7A and 7B (sensor units) detect a voltage generated according to the oxygen partial pressure ratio between the sensing unit electrodes which is affected by the oxygen ion concentration (oxygen partial pressure) in the gas diffusion layer 6. It has become. On the other hand, a predetermined voltage is applied to the oxygen pump electrodes 8A and 8B (specific component pump sections). That is, the sensing portion electrodes 7A and 7B detect the voltage generated by the oxygen partial pressure ratio between the sensing portion electrodes and change the air-fuel ratio to the stoichiometric air-fuel ratio (in other words, the excess air ratio λ).
= 1), it is possible to detect whether it is rich or lean. On the other hand, the oxygen pump electrode portions 8A, 8
In B, when a predetermined voltage is applied, oxygen ions in the gas diffusion layer 6 are moved in response to this, and a current flows between the oxygen pump electrode portions 8A and 8B.
The current value (limit current) Ip flowing between the oxygen pump electrode portions 8A and 8B when a predetermined voltage is applied between the electrodes is applied.
Is affected by the oxygen ion concentration in the gas diffusion layer 6, and therefore, if the current value (limit current) Ip is detected, the air-fuel ratio of the detection target gas (in other words, the excess air ratio λ) can be detected. . Therefore, for example, a correlation between the current / voltage between the oxygen pump electrodes and the air-fuel ratio of the detection target gas (in other words, the excess air ratio λ) as shown in Table A of FIG. 3 is obtained. . In addition, the sensing unit electrode 7A,
By inverting the application direction of the voltage to the oxygen pump electrode units 8A and 8B based on the rich / lean output of 7B, the oxygen pump electrode units 8A and 8B can be connected in both the lean and rich air-fuel ratio regions. This enables detection of a wide range of air-fuel ratios based on the current value (limit current) Ip flowing through. By detecting the current value Ip between the oxygen pump electrode portions according to the above-described air-fuel ratio detection principle, and referring to, for example, Table B in FIG. 3, the actual air-fuel ratio (excess air Rate λ) can be detected. The sensor detection value Ip is
For example, it can be obtained by the following equation. Ip = Do2 · PS · / (T · L) · ln （1 / (1-P
o2 / P)｝ Do2: diffusion coefficient of the porous layer of oxygen gas S: electrode area of the cathode L: thickness of the porous layer P: total pressure Po2: oxygen partial pressure T: temperature

However, no technology has been established for diagnosing whether the so-called wide-range air-fuel ratio sensor is normally operating or whether its performance is degraded. Therefore, it is not known whether or not the wide-range air-fuel ratio sensor can correctly detect the air-fuel ratio, which may hinder, for example, the air-fuel ratio control of the internal combustion engine, thereby improving the driving performance, exhaust performance, fuel consumption performance, and the like. May not be maintained. SUMMARY OF THE INVENTION The present invention has been made in view of such conventional circumstances, and has a relatively simple configuration, and is capable of highly accurately diagnosing whether or not a wide-range air-fuel ratio sensor can normally operate. It is intended to provide a device.

According to the first aspect of the present invention, there is provided an abnormality diagnosis apparatus for an air-fuel ratio sensor according to the present invention, as shown in FIG. An abnormality diagnosis device for an air-fuel ratio sensor configured to detect an air-fuel ratio of engine exhaust based on a current value flowing between the electrodes when a predetermined voltage is applied between the electrodes. Determining means for determining whether an abnormality diagnosis start condition including that the engine is operating at a fuel ratio is satisfied; and determining whether the abnormality diagnosis start condition is satisfied, based on the air-fuel ratio based on the current value. Abnormality diagnosis means for performing abnormality diagnosis of the sensor. According to such a configuration, for example, when the abnormality diagnosis start condition is satisfied after the engine is started (for example, when the engine is operated at a predetermined air-fuel ratio), the current value that can be obtained and the actual current value are determined. It is possible to diagnose the abnormality of the air-fuel ratio sensor based on the comparison of the current value with the current value, etc. Becomes In the invention described in claim 2, the abnormality diagnosis start condition includes that a predetermined time has elapsed after the engine is started. According to this configuration, the abnormality diagnosis of the air-fuel ratio sensor can be performed while avoiding the unstable state of the current value immediately after the engine is started, so that the accuracy of the abnormality diagnosis can be improved. In the invention described in claim 3, the abnormality diagnosis start condition includes that the air-fuel ratio sensor is activated. According to such a configuration,
Since the abnormality diagnosis of the air-fuel ratio sensor can be performed while avoiding the unstable state of the current value in the inactive state of the air-fuel ratio sensor, the accuracy of the abnormality diagnosis can be improved.
In the invention according to claim 4, the abnormality diagnosis start condition is:
This includes the fact that the air-fuel ratio feedback control is being performed based on the detection value of the air-fuel ratio sensor. During the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor, the exhaust air-fuel ratio is relatively stable in an attempt to maintain the exhaust air-fuel ratio at a predetermined value, so the current value is also relatively stable. Should be. Therefore, in such a situation, the current value that would be originally obtained, the actually detected current value,
By comparison, the presence or absence of an abnormality in the air-fuel ratio sensor can be diagnosed with high accuracy. In the invention described in claim 5, the abnormality diagnosis start condition includes that the voltage of the power supply source for engine operation control is equal to or higher than a predetermined value. According to such a configuration, when the power supply of the engine operation control power supply source is reduced, the air-fuel ratio of the engine exhaust is not normally controlled or the current value becomes unstable, so that abnormality diagnosis based on the current value is performed. In the above, there is a high possibility that a misdiagnosis is caused, but such a fear can be reliably eliminated. In the invention described in claim 6, the abnormality diagnosis means is configured to perform abnormality diagnosis of the air-fuel ratio sensor based on whether the current value is within a predetermined range. With this configuration, it is possible to diagnose the abnormality of the air-fuel ratio sensor with high accuracy with a relatively simple configuration. In the invention described in claim 7, the predetermined range is configured to be changed according to the target air-fuel ratio. According to this configuration, even if the target air-fuel ratio of the engine changes due to a change in the operating state or the like (regardless of feedback control or feedforward control), the predetermined range, which is the determination level of the abnormality diagnosis, is changed accordingly. Therefore, abnormality diagnosis of the air-fuel ratio sensor can be performed with higher accuracy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.
Description will be given based on the attached drawings. In the present embodiment, a method for diagnosing an abnormality of a wide-range air-fuel ratio sensor when a wide-range air-fuel ratio sensor is applied when detecting an exhaust air-fuel ratio of an internal combustion engine will be described as a representative. In FIG. 4 showing the overall configuration of one embodiment of the present invention, an air flow meter 13 for detecting an intake air flow rate Qa and a throttle valve 14 for controlling the intake air flow rate Qa in conjunction with an accelerator pedal are provided in an intake passage 12 of an engine 11. Is provided, and an electromagnetic fuel injection valve 15 is provided for each cylinder in a downstream manifold portion. Fuel injection valve 15
The valve is driven to open by a drive pulse signal set in the control unit 50 as described later, and is supplied by pressure from a fuel pump (not shown) to inject and supply fuel controlled to a predetermined pressure by a pressure regulator (not shown). . Further, a water temperature sensor 16 for detecting a cooling water temperature Tw in the cooling jacket of the engine 11 is provided. On the other hand, a wide area air-fuel ratio sensor 18 (corresponding to a wide-area air-fuel ratio sensor of the present invention, which detects the air-fuel ratio of the intake air-fuel mixture based on the oxygen concentration in the exhaust gas) is provided in the exhaust passage 17 near the manifold assembly. An air-fuel ratio sensor is also provided. On the downstream side, for example, CO, which is in the exhaust gas near the stoichiometric air-fuel ratio (λ = 1, A / F (air weight / fuel weight) ≒ 14.7),
A three-way catalyst 19 is disposed as an exhaust gas purifying catalyst for purifying exhaust gas by oxidizing HC and reducing NO _X satisfactorily.
As the exhaust purification catalyst, for example, a so-called lean NOx catalyst that reduces NOx in a lean (lean air-fuel ratio) region may be employed, or a general oxidation catalyst may be employed. Incidentally, the air-fuel ratio sensor 18 used in the present embodiment may be of any type as long as it uses the same detection principle as the conventional one shown in FIG. The distributor (not shown in FIG. 4) has a built-in crank angle sensor 20. The control unit 50 counts a crank unit angle signal output from the crank angle sensor 20 in synchronization with the engine rotation for a certain period of time. Alternatively, the engine rotation speed Ne is detected by measuring the cycle of the crank reference angle signal. Incidentally, the control unit 50 according to the present invention includes a CPU, a ROM,
The microcomputer comprises a microcomputer including a RAM, an A / D converter, an input / output interface, etc., receives input signals from various sensors, and receives an injection amount of the fuel injection valve 15 (that is, an idle amount) as follows. (Fuel ratio control amount). Examples of the various sensors include the air-fuel ratio sensor 18, the air flow meter 13, the water temperature sensor 16, the crank angle sensor 20, and the like. That is, the basic fuel injection pulse width (corresponding to the fuel injection amount) Tp = c × from the intake air flow rate Qa obtained from the voltage signal from the air flow meter 13 and the engine rotation speed Ne obtained from the signal from the crank angle sensor 20. Qa /
Ne (c is a constant) is calculated, and the final temperature is calculated by a water temperature correction coefficient Kw for forcibly correcting to a rich side at a low water temperature, a start and post-start increase correction coefficient Kas, an air-fuel ratio feedback correction coefficient α, and the like. Effective fuel injection pulse width Te = T
Calculate p × (1 + Kw + Kas +...) × α + Ts. Ts is a voltage correction amount. Then, the effective fuel injection pulse width Te is sent to the fuel injection valve 15 as a drive pulse signal, and the fuel adjusted to a predetermined amount is injected and supplied. The air-fuel ratio feedback correction coefficient α
Is a coefficient for correcting the deviation of the actual air-fuel ratio detected by the air-fuel ratio sensor 18 from the target air-fuel ratio. Based on this, the control unit 50 corrects the basic fuel pulse width Tp, and The air-fuel ratio is feedback-controlled to a target air-fuel ratio (for example, a stoichiometric air-fuel ratio). Here, the abnormality diagnosis control of the air-fuel ratio sensor executed by the control unit 50 in the present embodiment will be described with reference to the flowchart shown in FIG. This flow is performed, for example, once every startup. Note that the functions of the determination unit and the abnormality diagnosis unit according to the present invention are provided in the control unit 50 of the present embodiment as software as described below. In step (denoted by S in the figure, the same applies hereinafter), it is determined (determined) whether or not an abnormality diagnosis start condition is satisfied. That is, for example, the start of abnormality diagnosis is delayed until the following conditions are satisfied. For example, engine start key on → off (Key on → o
ff) It is determined whether or not a predetermined time has elapsed since the start (in other words, whether or not a predetermined time has elapsed after the start), and if it has not elapsed, the start of diagnosis is not permitted. For example, this is for preventing an erroneous diagnosis due to the influence of the increase in the starting amount and the formation of the wall flow, and an erroneous diagnosis due to the diagnosis being performed in the inactive state of the air-fuel ratio sensor 18. It is determined whether or not the air-fuel ratio sensor (A / F sensor) activity determination has been completed. If the determination has not been completed, the start of diagnosis is not permitted. This is for preventing erroneous diagnosis due to the diagnosis being performed in the inactive state of the air-fuel ratio sensor 18, and the like. It is determined whether or not the air-fuel ratio feedback control (A / F control) condition is satisfied. If the condition is not satisfied, the start of diagnosis is not permitted. This is to prevent a decrease in diagnostic accuracy when the air-fuel ratio is not controlled to the predetermined target value by the air-fuel ratio feedback control. It is determined whether or not the battery voltage is equal to or higher than a predetermined value. If the battery voltage is not equal to or higher than the predetermined value, the start of diagnosis is not permitted. This is to prevent erroneous diagnosis due to a decrease in battery voltage. In this way, as shown in the time chart of FIG. 6, in the unstable state of the air-fuel ratio sensor 18 after the start, the abnormality diagnosis is prohibited from being performed. Can be prevented as much as possible. In the following step 2, monitoring of the current value Ip between the oxygen pump electrode units 8A and 8B is started. In step 3, it is determined whether or not the current value Ip is within a predetermined range as shown in FIG. If YES, proceed to Step 4; if NO, proceed to Step 5. That is, if the air-fuel ratio sensor 18 is in the active state and the air-fuel ratio feedback control is being performed, the actual air-fuel ratio should be controlled so as to obtain a predetermined target air-fuel ratio. If normal, oxygen pump electrode 8A,
The current value Ip between 8B should converge within a predetermined range corresponding to the air-fuel ratio. Therefore, if the current value Ip between the oxygen pump electrode portions 8A and 8B does not converge within a predetermined range, it can be determined that there is a high possibility that the air-fuel ratio sensor 18 has some sort of failure, deterioration, or the like. Become.
In the present embodiment, the diagnosis of the air-fuel ratio sensor 18 is performed based on such a concept. In step 4, the current value Ip is within a predetermined range set according to the target air-fuel ratio, the air-fuel ratio sensor 18 is determined to be normal, an OK determination is made, and the present flow ends. On the other hand, in step 5, the current value Ip is not within the predetermined range set according to the target air-fuel ratio, and some abnormality {for example, a circuit failure of the oxygen pump unit or the sensing unit, a disconnection / short-circuit of the harness, or a deterioration ( The gas diffusion layer 6 and the protection layer 5 are clogged, etc.), and NG is determined. And such NG
If the determination is made, for example, twice (two trips) consecutively, the process proceeds to step 6, where a warning lamp (MIL) is turned on or the like to recognize that the driver or the like has some abnormality in the air-fuel ratio sensor 18. And encourage them to take measures such as repairs. Also, in order to minimize the deterioration of driving performance and exhaust performance, etc., the air-fuel ratio sensor
The air-fuel ratio feedback control based on the detection result of 18 may be prohibited, and in particular, lean combustion control or the like may be forcibly prohibited. If the process proceeds to step 6 when two consecutive trips (two trips) occur, the first NG decision is made when the NG decision is made for the first trip and the OK decision is made at the next trip. May be an erroneous determination, but such erroneous determination can be omitted, so that the abnormality diagnosis accuracy of the air-fuel ratio sensor 18 can be further improved. When starting is performed a predetermined number of times, if an NG determination is made at a predetermined rate, a warning light (MIL) is turned on to make a driver or the like recognize that the air-fuel ratio sensor 18 has some abnormality. You can also do so. Also, of course, a warning light (MIL) may be turned on every time NG is determined. As described above, according to the present embodiment, when the predetermined time has elapsed after the engine is started, the engine is rotating (operating), and the air-fuel ratio feedback control (closed-loop control) by the air-fuel ratio sensor 18 is being performed, the oxygen pump Since the abnormality diagnosis of the air-fuel ratio sensor is performed based on whether the current value Ip between the electrode portions 8A and 8B converges within a predetermined range, the air-fuel ratio can be quickly and accurately determined with a simple configuration. It is possible to diagnose whether or not the sensor is abnormal. Therefore,
Since the air-fuel ratio feedback control by the abnormal air-fuel ratio sensor is eliminated at an early stage, it is possible to prevent the deterioration of the driving performance, the exhaust performance, the fuel consumption performance, etc. before or promptly. In the above embodiment, the monitoring time for determining whether or not the current value Ip between the oxygen pump electrode units 8A and 8B converges within a predetermined range is not limited, but the monitoring time is limited to the predetermined time. It is good.
Further, when the target air-fuel ratio has been switched or when acceleration / deceleration operation has been detected, the diagnosis may be prohibited. The predetermined range for the OK / NG determination may be changed. By the way, in the present embodiment, it has been described that the abnormality diagnosis is performed in a state where the air-fuel ratio feedback control has been started.However, the present invention is not limited to this. Oxygen pump electrode 8
If the current value Ip between A and 8B is large or small, there is a possibility that an abnormality has occurred in the air-fuel ratio sensor. The abnormality diagnosis of the air-fuel ratio sensor can be performed using the concept of the abnormality diagnosis according to the present invention. That is, it is merely an example that the diagnosis start condition is satisfied when all of the above-described diagnosis start conditions are satisfied, and when any of these or any combination thereof is satisfied, the diagnosis start condition is satisfied. It can be established. Since the heater unit 2 and the sensing unit electrodes 7A and 7B are provided for improving the detection accuracy of the air-fuel ratio and expanding the air-fuel ratio detection range, the present invention is also applied to an air-fuel ratio sensor not provided with them. You can do it.

As described above, according to the first aspect of the present invention, for example, the gas diffusion layer which is obtained when the abnormality diagnosis start condition is satisfied after the engine is started is provided. Based on a comparison between the current value between the electrodes and the actual current value, etc., it is possible to diagnose an abnormality of the air-fuel ratio sensor. Diagnosis can be made with a simple configuration. According to the second aspect of the present invention, the abnormality diagnosis of the air-fuel ratio sensor can be performed while avoiding the unstable state of the current value immediately after the engine is started, so that the accuracy of the abnormality diagnosis can be improved. According to the third aspect of the present invention, it is possible to perform the abnormality diagnosis of the air-fuel ratio sensor while avoiding the unstable state of the current value in the inactive state of the air-fuel ratio sensor, thereby improving the abnormality diagnosis accuracy. be able to. According to the fourth aspect of the invention, during the air-fuel ratio feedback control based on the detection value of the air-fuel ratio sensor, the exhaust air-fuel ratio is relatively stable in an attempt to maintain the exhaust air-fuel ratio at a predetermined value. Using the fact that the current value is also relatively stable, an abnormality diagnosis is performed based on the current value that would be originally obtained under such circumstances and the actually detected current value. Therefore, it is possible to diagnose with high accuracy whether or not the air-fuel ratio sensor is abnormal. According to the invention as set forth in claim 5, when the supply power of the engine operation control power supply source is reduced, the air-fuel ratio of the engine exhaust is not normally controlled or the current value becomes unstable. In the abnormality diagnosis based on the value, there is a high possibility of causing an erroneous diagnosis, but such a fear can be reliably eliminated. According to the sixth aspect of the present invention, it is possible to diagnose the abnormality of the air-fuel ratio sensor with high accuracy by a relatively simple configuration. According to the invention described in claim 7, even if the target air-fuel ratio of the engine changes due to a change in the operating state or the like (regardless of the air-fuel ratio feedback control or the air-fuel ratio feedforward control), the abnormality diagnosis is determined accordingly. Since the predetermined range, which is the level, can be changed, abnormality diagnosis of the air-fuel ratio sensor can be performed with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is a structural diagram of a wide area air-fuel ratio sensor.

FIG. 3 is a diagram for explaining an air-fuel ratio detection principle of a wide-area air-fuel ratio sensor;

FIG. 4 is an overall configuration diagram of an embodiment of the present invention.

FIG. 5 is a flowchart illustrating abnormality diagnosis control of the air-fuel ratio sensor according to the embodiment.

FIG. 6 shows how the current value Ip changes between the oxygen pump electrode portions and a predetermined range (HGOPL, HGOP) which is a determination level.
H) Time chart showing

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Air-fuel ratio sensor main body 2 Heater part 3 Air introduction hole 4 Gas introduction hole to be detected 5 Protective layer 6 Gas diffusion layer (or gas diffusion gap) 7A, 7B Sensing part electrode 8A, 8B Oxygen pump electrode 11 Internal combustion engine 13 Air flow meter 17 Exhaust passage 18 Air-fuel ratio sensor 20 Crank angle sensor 50 Control unit

Claims (7)

[Claims] An air-fuel ratio of an engine exhaust is detected based on a value of a current flowing between the electrodes when a predetermined voltage is applied between electrodes provided with a gas diffusion layer provided facing the engine exhaust. An abnormality diagnosis device for an air-fuel ratio sensor configured as described above, comprising: a determination unit configured to determine whether an abnormality diagnosis start condition including that the engine is operating at a predetermined air-fuel ratio after the engine is started is satisfied; An abnormality diagnosis device for an air-fuel ratio sensor, comprising: abnormality diagnosis means for performing an abnormality diagnosis of the air-fuel ratio sensor based on the current value when it is determined that the condition is satisfied. 2. The abnormality diagnosis device for an air-fuel ratio sensor according to claim 1, wherein the abnormality diagnosis start condition includes a condition that a predetermined time has elapsed after the engine is started. 3. The abnormality diagnosis apparatus for an air-fuel ratio sensor according to claim 1, wherein the abnormality diagnosis start condition includes that the air-fuel ratio sensor is activated. 4. The apparatus according to claim 1, wherein the abnormality diagnosis start condition includes that air-fuel ratio feedback control is being performed based on a value detected by the air-fuel ratio sensor. Diagnostic device for air-fuel ratio sensor. 5. An air conditioner according to claim 1, wherein the abnormality diagnosis start condition includes that a voltage of a power supply source for engine operation control is equal to or higher than a predetermined voltage. Abnormality diagnostic device for fuel ratio sensor. 6. The air-fuel ratio sensor according to claim 1, wherein said abnormality diagnosis means performs an air-fuel ratio sensor abnormality diagnosis based on whether said current value is within a predetermined range. 1
An abnormality diagnosis device for an air-fuel ratio sensor according to any one of the first to third aspects. 7. The apparatus according to claim 6, wherein the predetermined range is changed according to a target air-fuel ratio.