JPH06280662A - Trouble detection device of air-fuel ratio controller - Google Patents

Abstract

PURPOSE:To accurately judge deterioration/trouble even if output characteristic of a second air-fuel ratio sensor has dispersion by comparing the output characteristic of the measured second air-fuel ratio sensor with the output characteristic of a standard sensor, and correcting the output characteristics based on the result of comparison. CONSTITUTION:A detection means for detecting deterioration/trouble of a first sensor/catalyst converter(converter) 14 based on difference between output OF of the first air-fuel ratio sensor (first sensor) 13 and output OR of a second air-fuel ratio sensor (second sensor) 15 is provided. A measuring means for measuring output characteristic of the second sensor 15 and output characteristic of the measured second sensor 15 are compared with the output characteristic of the standard sensor, and then a corrective means for correcting the output characteristic of the second sensor is provided based on a comparion result. Accuracy of the judgement is highly maintained since the output OR of the second sensor 15 corrected by the corrective means is utilized by the judgement of the trouble/deterioration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure detection device for detecting a failure of an air-fuel ratio control device that performs air-fuel ratio feedback control based on an output signal of an air-fuel ratio sensor provided upstream of a catalytic converter.

[0002]

2. Description of the Related Art In air-fuel ratio control of an engine, for example, in the case of air-fuel ratio control based on a fuel injection amount, a basic injection amount is calculated according to an intake air amount of the engine and an engine speed, and this basic injection amount is used for engine water temperature and the like. According to
Feedback correction is performed based on a detection signal from an O2 sensor or the like that detects the oxygen concentration in the exhaust gas to set the final injection amount. Then, the injector is driven by the injection pulse corresponding to the final injection amount to converge the air-fuel ratio to the target air-fuel ratio. According to such air-fuel ratio feedback control, the air-fuel ratio of the engine can be controlled to, for example, the theoretical air-fuel ratio, so that a three-way catalyst or the like can be arranged in the exhaust passage to efficiently perform exhaust gas purification. Becomes Here, the air-fuel ratio sensor is generally provided on the upstream side of the catalyst.

When the catalyst is arranged in the exhaust passage of the engine as described above and the feedback control system is configured to control the air-fuel ratio to, for example, the stoichiometric air-fuel ratio, there are variations in the output characteristics of the air-fuel ratio sensor and time-dependent changes. In order to compensate for deterioration, a second air-fuel ratio sensor is provided on the downstream side of the catalyst, and delay processing is performed when the output of the upstream air-fuel ratio sensor changes from a rich signal to a lean signal or from a lean signal to a lean signal. It has been proposed in the past to use a double O2 sensor system that corrects the set time according to the output of the downstream side air-fuel ratio sensor. Further, for example, in the one disclosed in Japanese Patent Laid-Open No. 61-234241, in such a double O2 sensor system, deterioration of responsiveness (reduction of control frequency) due to deterioration of the upstream air-fuel ratio sensor is minimized. Therefore, so-called P-value feedback control is performed in which the skip value (P value) of the air-fuel ratio control by the upstream air-fuel ratio sensor is feedback-corrected by the output of the downstream air-fuel ratio sensor. In this case, the change in the output characteristic of the downstream side air-fuel ratio sensor reflects the degree of deterioration of the upstream side air-fuel ratio sensor, and therefore, the failure (deterioration) of the upstream side air-fuel ratio sensor is detected by the output of the downstream side air-fuel ratio sensor. Can be done.

That is, the deterioration of the air-fuel ratio sensor is corrected by monitoring the deviation of the air-fuel ratio in the exhaust gas from the target value due to the deterioration while monitoring the air-fuel ratio sensor provided downstream (so-called P value feedback control). ), The degree of deterioration / failure of the upstream air-fuel ratio sensor is determined based on the average value of the proportional control coefficient (so-called P value) used for the P value feedback control.

Further, the higher the purification capacity of the catalytic converter, the higher the oxygen consumption amount (so-called "oxygen storage effect"), so that the downstream air-fuel ratio tends to be richer. Therefore, if the voltage values on the rich side of the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor are integrated, and the downstream air-fuel ratio sensor output integrated value / upstream air-fuel ratio output sensor integrated value shows a relatively large value, the purification capacity is relatively high. It can be judged to be high.

[0006]

As described above, in the prior art, the proportional control coefficient obtained by the P value feedback control in the air-fuel ratio feedback control is used to detect the failure / deterioration of the air-fuel ratio sensor or the catalytic converter, and further, Since it is used for the data to compensate for the deterioration of the air-fuel ratio sensor,
Highly reliable data is required.

However, the air-fuel ratio sensor inevitably has production variations in its output characteristics. As the upstream air-fuel ratio sensor used for the air-fuel ratio feedback control, it is unavoidable to use a sensor having a proper output characteristic, but even if a downstream air-fuel ratio sensor is provided with a characteristic, it will cause a cost increase. However, it is meaningless to use a highly accurate upstream air-fuel ratio sensor by using one having different characteristics.

For example, the following specific problems occur. When the characteristics of the downstream air-fuel ratio sensor have a tendency of rich output variation or lean output variation: When the upstream air-fuel ratio sensor failure detection operation is performed, the downstream air-fuel ratio sensor output is When the output tends to be low (high), the downstream air-fuel ratio sensor makes a lean (rich) determination, and as the P value feedback control,
In order to perform the rich control, the deterioration of the upstream air-fuel ratio sensor is erroneously judged to be rich. The integrated value of the output of the downstream air-fuel ratio sensor becomes small if the downstream air-fuel ratio sensor has a characteristic of lean output when performing the catalytic converter failure detection operation. The ratio to the output integrated value becomes small, and the catalytic converter is erroneously determined to be in a deterioration tendency.

Therefore, the present invention has been proposed in order to solve the above-mentioned drawbacks of the prior art, and its object is to provide a catalytic converter in an air-fuel ratio control device having air-fuel ratio sensors upstream and downstream of the catalytic converter. In a failure detection device that detects deterioration or failure of the upstream air-fuel ratio sensor, even if there is variation in the output characteristics of the downstream air-fuel ratio sensor, it is possible to accurately determine the deterioration / failure of the catalytic converter or the upstream air-fuel ratio sensor. It proposes a possible failure detection device.

[0010]

As shown in FIG. 1, the present invention for achieving the above object comprises a first and a second air-fuel ratio sensor provided before and after a catalytic catalytic converter, and a first air-fuel ratio sensor. A failure detection device for detecting a failure of an air-fuel ratio control device having a feedback control means for feedback-controlling an air-fuel ratio of an air-fuel mixture supplied to an engine to a target air-fuel ratio based on an air-fuel ratio sensor output, Detection means for detecting deterioration and / or failure of the first air-fuel ratio sensor and / or the catalytic converter based on the difference between the output of the first air-fuel ratio sensor and the output of the second air-fuel ratio sensor; ,
The measuring means for measuring the output characteristic of the second air-fuel ratio sensor and the measured output characteristic of the second air-fuel ratio sensor are compared with the output characteristic of the reference sensor, and the output characteristic of the second air-fuel ratio sensor is compared based on the comparison result. And a correction means for correcting the output characteristic.

Since the output of the second air-fuel ratio sensor corrected by the correction means is used for the failure / deterioration determination, the accuracy of the determination is maintained high.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. <System Configuration> FIG. 2 shows an air-fuel ratio control system having a function of detecting a failure of the air-fuel ratio sensor. In FIG. 2, 1 is an air filter, 10 is an engine body, and 1 is
4 is a catalytic converter, 13 is a first air-fuel ratio sensor,
20 is an engine controller (EC
U).

The sucked air is cleaned by the air filter 1, its temperature T _A is detected by the sensor 3, and its flow rate Q A is detected by the sensor 4. Reference numeral 7 denotes a throttle valve, the opening of which is detected by the sensor 6. An unillustrated idle switch is incorporated in the sensor 6, and the idle state IDLE is detected by this switch. On the other hand, a bypass passage is formed between the upstream side and the downstream side of the throttle valve 7, the so-called ISC controller 5 is provided in the middle of this passage, and a signal ISC from the ECU 20 is provided.
Thus, the controller 5 controls the opening / closing amount of the bypass passage to control the supply air amount during idling.

The change in the flow rate of the air whose flow rate is controlled by the throttle valve 7 is absorbed by the surge tank 8, and the air is further sent into the combustion chamber through the intake manifold.
Reference numeral 9 is a fuel injection valve, and the fuel injection amount is controlled by a signal τ from the ECU 20. The engine speed N is detected by a sensor 11 provided on the crankshaft. Also,
The temperature T _W of the engine cooling water is detected by the sensor 12. Exhaust gas from the engine 10 is guided to the converter 14 through the exhaust passage and is purified there.

The oxygen concentration O _A in the exhaust gas is detected by the air-fuel ratio sensor 13. On the other hand, the oxygen concentration OR in the exhaust gas purified by the catalytic converter 14 is detected by the air-fuel ratio sensor 15. Signal O from the air-fuel ratio sensor 13
F is used for so-called air-fuel ratio feedback control. The oxygen concentration OR detected by the air-fuel ratio sensor 15 is used by the ECU 20 to detect a failure / deterioration of the air-fuel ratio sensor 13 and the catalytic converter 14.

In FIG. 2, the secondary air supply system comprises a control valve 2 and an air passage 16. A control valve (hereinafter abbreviated as ACV) 2 controls the amount of secondary air sent to the exhaust gas passage, and passes through the bypass passage 16 and the air-fuel ratio sensor 1
Secondary air is supplied upstream of the catalytic converter 14 on the downstream side of 3. Thus, the secondary air supplied via the ACV2 is converted by the air-fuel ratio sensor 13 into the converter 14
It does not affect the measurement of oxygen concentration in the upstream exhaust gas, but helps to activate the catalyst. While the secondary air is being supplied to the exhaust gas passage, the catalytic converter 14
Judgment is made by the signal OR from the air-fuel ratio sensor 15 provided downstream of the. <Outline of Control Function> Here, an outline of the air-fuel ratio control system of the embodiment will be described with reference to FIG. This system has: an air-fuel ratio sensor 13 upstream of the catalytic converter 14 and an air-fuel ratio sensor 15 downstream thereof, and the upstream air-fuel ratio sensor 1
The air-fuel ratio feedback control is performed based on the output OF of 3. This feedback control is performed only in a predetermined "feedback control execution region", and based on the output of the upstream air-fuel ratio sensor 13, the so-called P.
I (proportional integration) control is performed, and the coefficients for proportional control at that time are ΔPRL and ΔPLR. Where ΔP
RL acts in the enrichment direction, and ΔPLR acts in the lean direction. In the present embodiment, as an example, the feedback control execution region is in the non-idle operation state excluding the sudden acceleration / deceleration operation. In the feedback control execution region, the above-mentioned ΔPRL and ΔPLR are corrected based on the output OR of the downstream sensor 15 so that the air-fuel ratio feedback control converges quickly even if the upstream sensor 13 is deteriorated (hereinafter, “ Called "deterioration correction"). This deterioration correction is called P
It is control (proportional control). The proportional constant for this proportional control is δ. The reason why the deterioration correction compensates for the deterioration of the upstream air-fuel ratio sensor 13 will be described later. : In order to accurately determine the failure / deterioration of the upstream air-fuel ratio sensor 13 and the catalytic converter 14, in order to compensate the variation in the characteristics of the downstream air-fuel ratio sensor 15, a correction function is obtained in advance, and the sensor is used by this correction function. Output OF,
The OR is corrected and the corrected value is used for actual control. <Control Procedure> FIGS. 3 to 8 are control procedures executed by the ECU 20 for realizing the functions of the air-fuel ratio control system described above. In particular, FIG. 3 shows the main routine, and FIG. 4 shows step S30 in the main routine.
FIG. 5 is an interrupt routine for determining the maximum value Vmax and the minimum value Vmin of the output voltage of the downstream air-fuel ratio sensor, which is periodically activated by a time interrupt, and FIG. 6 is a main routine. Step S40
0 is a flowchart showing a "CFB calculation" subroutine of 0, FIG. 7 is a flowchart showing a "ΔPRL, ΔPLR update" subroutine of step S600 in the main routine, and FIG. 8 is a step S70 in the main routine.
It is a flowchart which shows the "fault / deterioration determination" subroutine of 0.

The main routine of FIG. 3 will be described.
In step S100, it is determined whether the current operating state is the "P value feedback execution region". The "P-value feedback execution region" is a non-idle operation region excluding abrupt acceleration / deceleration operation (this region is judged from the output of the above-mentioned idle switch) and a steady operation region. In the air-fuel ratio feedback control step S300, the output correction routine of the downstream air-fuel ratio sensor of FIG. 4 is executed.

As described above, the characteristics of the downstream air-fuel ratio sensor vary, and if the output signal is used for P-value feedback control, there is a risk that the upstream air-fuel ratio sensor or the catalytic converter may be erroneously determined to be deteriorated or malfunction. is there. This output correction routine corrects the output of the downstream air-fuel ratio sensor. FIG. 9 illustrates the principle of the correction. Sensor Output Correction Generally, the output characteristic of the air-fuel ratio sensor has a characteristic of excessively rich output or excessively lean output. In the example of FIG. 9, a sensor having a tendency to output excessively on the rich side is shown. A sensor that has a tendency to output excessively on the rich side (lean side) is a lean side (rich side).
It has the characteristic that the output is too small. The sensor output when the maximum swing to the rich side is Vmax, and the sensor output when the maximum swing to the lean side is -Vmin. Even with a sensor that tends to have such a "habit", the amplitude of the sensor output from Vmax to -Vmin is the same as that of other sensors with the same degree of deterioration. However, the amplitude tends to decrease over time.

FIG. 10 shows the output characteristic of the reference air-fuel ratio sensor. The output of this reference sensor does not have a "habit" such that it is biased toward the rich side or the lean side. The amplitude of this reference sensor is VRmax + VRmin, while the output amplitude of the downstream air-fuel ratio sensor having the "habit" actually used is Vmax + Vmin. Therefore, γ = (VRmax + VRmin) / (Vmax + Vmin) represents the amplitude characteristic of the downstream air-fuel ratio sensor 15 with respect to the reference sensor. Further, although VRmax-VRmin = 0, κ = (Vmax-Vmin) / 2 indicates a deviation of the output of the downstream air-fuel ratio sensor from the reference (0 volt). Therefore, if the downstream air-fuel ratio sensor 15 outputs the output OR (= Vx) at some point, the corrected output at that time becomes OR = γ · (Vx−κ). There are various other corrections such as this. For example, it is possible to store correction values in the memory as a map. Therefore, generally, the correction function is represented by f, and if the downstream air-fuel ratio sensor 15 outputs the output OR (= Vx) at a certain time point, the corrected output at that time is OR ', OR' = It is represented by f (Vx).

Returning to the flowchart of FIG. 4, in step S302, it is checked whether or not it is time to change the correction function. In this embodiment, the control procedure of FIG.
If it is executed 0 times, step S304 is executed. This is because the sensor itself does not deteriorate rapidly. If it is time to update the correction function f, in step S304 the correction function f
To correct. Correcting the correction function f means that the values of γ and κ change with the deterioration of the sensor in the above description.

In step S306, the output of the downstream air-fuel ratio sensor is corrected according to the correction function. FIG. 5 is a routine that is periodically activated by a time interrupt, and stores the maximum value Vmax and the minimum value Vmin of the output of the downstream air-fuel ratio sensor 15. The maximum value Vmax and the minimum value Vmin are used to correct the correction function f in step S304.

That is, in step S1002, step S
The downstream air-fuel ratio sensor output OR measured at 200 is stored. In steps S1004 and S1006, the maximum sensor output value among the sensor output values at a plurality of sampling points within a predetermined period is Vmax, and the minimum sensor output value is Vmin. In this way, if the output of the downstream air-fuel ratio sensor is corrected, step S400 of FIG. 3 is executed. Details of step S400 are shown in FIG. The calculation of CFB will be described with reference to FIG. Output O of the upstream air-fuel ratio sensor 13
When F is inverted from lean to rich, CFB = CFB-ΔPLR: proportional control (step S408) is performed, and CFB = CFB-ΔI: integral control (step S406) is performed in the rich region except immediately after inversion. . On the other hand, when the output OF of the air-fuel ratio sensor 13 reverses from rich to lean, CFB = CFB + ΔPLR: proportional control (step S414) is performed, and CFB = CFB + ΔI: integral control (step S420 is performed, and according to the P / I control of CFB,
FB will change as shown in FIG. Here, the proportional control constants ΔPRL and ΔPLR are defined as “ΔPRL and ΔPLR”, which will be described later.
Since it is updated by "update", the air-fuel ratio feedback control can be properly converged even if the metaphorical upstream sensor 13 is deteriorated.

Step S500 of the main routine of FIG.
Then, it is determined whether or not the current operating state is in the "fault / deterioration detection region". If this determination is NO, failure / deterioration determination is not performed, and the process directly proceeds to step S800 and feedback is performed.
On the other hand, if YES is determined in the step S500, a "ΔPRL, ΔPLR update" subroutine (details are shown in FIG. 7) is executed in a step S600. This “ΔPRL, ΔP
LR update "subroutine is ΔPRL, ΔPLR (that is, P value)
Since the updated ΔPRL and ΔPLR are fed back to the air-fuel ratio feedback control, the ΔPRL and ΔPLR update is called P value feedback control. Deterioration Compensation In FIG. 7, the output OR of the downstream sensor 15 is compared with a predetermined threshold value β0 in step S602. OR ≧ β0 (that is,
Rich), the proportional control constants ΔPRL, Δ
In steps S604 and S606, PLR is updated as ΔPLR = ΔPLR + δ ΔPRL = ΔPRL−δ. On the contrary, when it is determined in step S602 that OR <β0 (that is, lean), the proportional control constant ΔPR
L and ΔPLR are updated to ΔPLR = ΔPLR−δ ΔPRL = ΔPRL + δ in steps S608 and S610. Here, by P value feedback control,
The reason why the air-fuel ratio feedback control is compensated even when the air-fuel ratio sensor 13 is deteriorated will be described.

Deterioration of the upstream sensor 13 changes the purification performance of the converter 15. The degree of this purification performance is reflected in the consumption amount of oxygen flowing into the converter. That is, by detecting the oxygen concentration on the downstream side of the converter 15, the deviation from the optimum point (λ = 1) of the purification performance of the converter 15 can be known. Considering this characteristic, the downstream sensor 15
Proportional control coefficients ΔPRL and ΔP obtained by monitoring the output of
The “deviation” from the optimum point of LR is a material for determining the deterioration of the downstream sensor 15.

The reason is as follows. As described above, as described in FIG. 5, ΔPRL is a proportional control constant for correcting the air-fuel ratio of the air-fuel mixture to the rich side when the output of the upstream air-fuel ratio sensor 13 reverses from rich to lean. , ΔPLR are proportional control constants for correcting the air-fuel ratio of the air-fuel mixture to the lean side when the output of the upstream air-fuel ratio sensor 13 is inverted from lean to rich. Therefore,
ΔPRL can be called a “rich enrichment proportional control coefficient”, and ΔPLR can be called a “lean enrichment proportional control coefficient”. Then, in the "P value feedback control" of FIG. 7, when the output OR of the downstream air-fuel ratio sensor 15 indicates rich, the enriched proportional control coefficient ΔPRL is reduced (step S606), and the lean proportional control coefficient is obtained. Correction is made so that ΔPLR becomes large (step S604). When the output OR of the downstream air-fuel ratio sensor 15 indicates lean, the lean proportional control coefficient ΔPLR is reduced (step S608) and the rich proportional control coefficient ΔPRL is increased (step S610). To do. If the upstream sensor 13 deteriorates and tends to detect the air-fuel ratio of the exhaust gas leaner than it actually is, the air-fuel ratio of the air-fuel mixture becomes richer, and as a result, the downstream sensor 15 becomes rich for a longer time. Detect the condition. Therefore, the lean proportional control coefficient ΔPLR has a larger value, and the rich proportional control coefficient ΔPRL has a smaller value. That is, when the upstream sensor 13 deteriorates and tends to detect the air-fuel ratio of the exhaust gas leaner than it actually is, the lean proportional control coefficient ΔPLR becomes a larger value. In other words, since the correction of CFB in the air-fuel ratio feedback control becomes more lean, the deterioration of the upstream sensor is compensated. When the upstream sensor 13 deteriorates and tends to detect the air-fuel ratio of the exhaust gas richer than it actually is, the air-fuel ratio of the air-fuel mixture becomes leaner, and as a result, the downstream sensor 15
Detects a lean condition for a longer time. Therefore, the lean proportional control coefficient ΔPLR has a smaller value, and the rich proportional control coefficient ΔPRL has a larger value. That is, when the upstream sensor 13 deteriorates and tends to detect the air-fuel ratio of the exhaust gas richer than it actually is, the enrichment proportional control coefficient ΔPRL becomes a larger value. In other words, since the correction of CFB in the air-fuel ratio feedback control becomes more lean, the deterioration of the upstream sensor is compensated.

FIG. 12 shows the operation of the system in the air-fuel ratio feedback execution region in the form of a timing chart. When the P value is corrected in step S600, failure detection in step S6700 is performed. Failure Detection In the failure detection routine of FIG. 8, in step S602, average values of ΔPRL and ΔPLR are calculated. As shown in FIG. 13, this average value is calculated as an integrated value of each cycle of ΔPRL and ΔPLR. Therefore, ΔPRL, Δ
By comparing the respective average values of PLR with the threshold values (ε1, ε2), and as shown in FIGS. 14 and 15, if the respective average values exceed ε1, ε2, the upstream sensor 13 is not deteriorated. Judge as a failure.

Further, in step S612, it is determined whether or not it is in the operating region in which the failure of the catalytic converter is detected.
If this determination is YES, in step S614, the downstream air-fuel ratio sensor output integrated value / upstream air-fuel ratio output sensor integrated value is calculated. As indicated by OF and OR in FIG. 12, the upstream air-fuel ratio sensor output integrated value is the integrated value of the output voltage of the sensor 13 indicating rich in a predetermined integration section, and is the downstream air-fuel ratio output sensor integrated value. Is the integrated value of the output voltage of the sensor 15 indicating rich in the same integration section. As described above, the higher the purifying capacity of the catalytic converter, the more oxygen is consumed, and therefore the gas to be discharged tends to be rich. That is, the higher the purification capacity, the larger the value of the numerator in the above ratio equation, and the larger the ratio. Therefore, in step S614, that value is compared with a predetermined determination value to determine whether the catalytic converter is normal or abnormal. <Effects of Embodiment> According to the embodiments described above, i: in the feedback control execution region, the upstream sensor 13
"Deterioration correction" is performed so that the air-fuel ratio feedback control converges quickly even if there is deterioration of
The characteristics are improved. ii: deterioration / failure of the upstream air-fuel ratio sensor 13, and further,
The variation in the characteristics of the downstream air-fuel ratio sensor 15, which greatly affects the deterioration / failure determination of the catalytic converter 14, is shown in FIG.
The accuracy of the deterioration / fault determination is improved even if the characteristics of the downstream air-fuel ratio sensor 15 are not uniform.

[0028]

As described above, according to the failure detecting device for the air-fuel ratio control device of the present invention, the variation in the output characteristic of the second air-fuel ratio sensor (downstream air-fuel ratio sensor 15 in the embodiment) is eliminated. As a result, the failure and / or deterioration of the first air-fuel ratio sensor and / or the catalytic converter can be accurately determined.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration of the invention.

FIG. 2 is a block diagram showing a configuration of an air-fuel ratio control system of an embodiment to which the present invention is applied.

FIG. 3 is a flowchart illustrating a control procedure of the embodiment.

FIG. 4 is a flowchart illustrating a control procedure of the embodiment.

FIG. 5 is a flowchart illustrating a control procedure of the embodiment.

FIG. 6 is a flowchart illustrating a control procedure of the embodiment.

FIG. 7 is a flowchart illustrating a control procedure of the embodiment.

FIG. 8 is a flowchart illustrating a control procedure of the embodiment.

FIG. 9 is a diagram illustrating the principle of compensating for variations in sensor characteristics.

FIG. 10 is a diagram for explaining the principle of compensating for variations in sensor characteristics.

FIG. 11 is a diagram illustrating a CFB correction operation of air-fuel ratio feedback control according to the embodiment.

FIG. 12 is a timing chart illustrating the operation of the system in the “feedback control execution” area of the embodiment.

FIG. 13 is a diagram illustrating the principle of failure detection of the air-fuel ratio sensor in the embodiment.

FIG. 14 is a diagram illustrating the principle of failure detection of the air-fuel ratio sensor in the embodiment.

FIG. 15 is a diagram illustrating the principle of failure detection of the air-fuel ratio sensor in the embodiment.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G01M 15/00 Z 7324-2G

Claims (2)

[Claims] 1. A first and a second air-fuel ratio sensor provided before and after the catalytic converter, and an air-fuel ratio of an air-fuel mixture supplied to an engine is fed back to a target air-fuel ratio based on the output of the first air-fuel ratio sensor. A failure detection device for detecting a failure of an air-fuel ratio control device having feedback control means for controlling, which is based on a difference between an output of the first air-fuel ratio sensor and an output of the second air-fuel ratio sensor. Detecting means for detecting deterioration and / or failure of the first air-fuel ratio sensor and / or catalytic converter, measuring means for measuring the output characteristic of the second air-fuel ratio sensor, and the measured second An air-fuel ratio control apparatus comprising: a correction unit that compares the output characteristic of the air-fuel ratio sensor with the output characteristic of the reference sensor and corrects the output characteristic of the second air-fuel ratio sensor based on the comparison result. Obstacle detection device. 2. A failure detection device for an air-fuel ratio control device according to claim 1, wherein the output characteristic of the second air-fuel ratio sensor is represented by an average maximum value and an average minimum value of the output voltage of the sensor. A failure detection device for an air-fuel ratio control device.