JPH0783098A - Abnormality diagnostic device for air-fuel ratio detection device - Google Patents

Abstract

PURPOSE:To provide an abnormality diagnostic device for an air-fuel ratio detection device for accurately detecting any abnormal condition of an air-fuel ratio sensor. CONSTITUTION:Establishment of a previous condition is judged by an ECU 5 before an abnormal diagnosis of a downstream side oxygen sensor 15B. In the previous condition it is judged whether an engine cooling water temperature sensor 10, a fuel injection valve 6, an electric heater of the downstream side oxygen sensor 15B, and the electric heater of an upstream side oxygen sensor 15A have any trouble or not, and the execution of abnormal diagnosis process is inhibited by setting zero to a condition establishment flag for showing whether the previous condition is established or not when even one of these devices has trouble.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality diagnosis device for an air-fuel ratio detecting device for detecting the air-fuel ratio in the exhaust gas of an internal combustion engine as a parameter for controlling the air-fuel ratio of an air-fuel mixture.

[0002]

2. Description of the Related Art Generally, in order to control the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine to fall within a certain range around a desired value, the concentration of a specific component contained in exhaust gas, For example, the oxygen concentration is detected, an air-fuel ratio correction coefficient value is set according to the detected oxygen concentration, and the air-fuel ratio is corrected using this correction coefficient value. Exhaust gas concentration sensor (air-fuel ratio sensor) for detecting oxygen concentration from exhaust gas of internal combustion engine
The oxygen concentration sensor (O2 sensor) is a type including, for example, a zirconia solid electrolyte (ZrO2), and has a characteristic that its electromotive force rapidly changes before and after the stoichiometric air-fuel ratio of the air-fuel mixture. The output signal of becomes high level on the rich side and becomes low level on the lean side of the theoretical air-fuel ratio of the exhaust gas. Abnormalities such as disconnection, short circuit and deterioration of the O2 sensor for detecting the oxygen concentration have a great influence on the air-fuel ratio control. Therefore, O2
It is necessary to constantly monitor an exhaust gas concentration detection system including an exhaust concentration sensor such as a sensor and to make the air-fuel ratio control system function normally by a normal sensor signal.

As a method for detecting an abnormality in the exhaust gas concentration sensor for that purpose, as shown in Japanese Patent Laid-Open No. 1-272956, the output of the exhaust gas concentration sensor when a predetermined voltage is applied to the exhaust gas concentration sensor as an air-fuel ratio sensor. In some cases, it is determined that the exhaust gas concentration sensor is out of order when the amount of change in voltage is less than or equal to a predetermined value. In addition, JP-A-4-233
As disclosed in Japanese Patent No. 447, the internal impedance of the exhaust gas concentration sensor is calculated based on the fluctuation amount of the output voltage of the exhaust gas concentration sensor when a predetermined voltage is applied to the exhaust gas concentration sensor, and based on this internal impedance. It is also known to detect deterioration of the exhaust gas concentration sensor.

[0004]

By the way, an air-fuel ratio sensor such as an exhaust gas concentration sensor generally has an electric heater in order to accelerate its activation, and the heater is energized by failure or control. If not, it may be inactive. As described above, when the air-fuel ratio sensor is in the inactive state, the internal impedance of the air-fuel ratio sensor becomes high, and when the deterioration detection is performed based on the internal impedance as described above, the air-fuel ratio sensor is actually deteriorated. Although it is not present, it is erroneously detected as being deteriorated.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an abnormality diagnosis device for an air-fuel ratio detecting device capable of accurately detecting an abnormal state of the air-fuel ratio sensor.

[0006]

In order to achieve the above object, the first invention is an air-fuel ratio detecting means for detecting an air-fuel ratio in exhaust gas for feedback-controlling the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine. A heating means for heating the air-fuel ratio detecting means, and an abnormality detecting means for detecting an abnormality of the air-fuel ratio detecting means based on an output value of the air-fuel ratio detecting means when a predetermined voltage is applied to the air-fuel ratio detecting means In an abnormality diagnosis device for an air-fuel ratio detecting device comprising: a heating state detecting means for detecting a heating state of the air-fuel ratio detecting means by the heating means;
Prohibition means is provided for prohibiting the abnormality detection of the air-fuel ratio detection means by the abnormality detection means when the non-heated state of the air-fuel ratio detection means is detected by the heating state detection means.

In order to achieve the above object, a second aspect of the present invention is arranged such that an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine is fed back, the upstream side and the downstream side of a catalyst provided in an exhaust system of the internal combustion engine. Upstream side air-fuel ratio detecting means for controlling, and downstream side air-fuel ratio detecting means, heating means for heating the downstream side air-fuel ratio detecting means, and when a predetermined voltage is applied to the upstream side air-fuel ratio detecting means An upstream abnormality detecting means for detecting an abnormality of the upstream air-fuel ratio detecting means based on an output value of the upstream air-fuel ratio detecting means, and the downstream air when a predetermined voltage is applied to the downstream air-fuel ratio detecting means. In an abnormality diagnosis device for an air-fuel ratio detection device, which comprises a downstream-side abnormality detection means for detecting an abnormality in the downstream-side air-fuel ratio detection means based on an output value of the fuel-ratio detection means, the upstream side is detected by the upstream-side abnormality detection means. Sky Prohibition of heating of the downstream side air-fuel ratio detecting means by the heating means and prohibition of abnormality detection of the downstream side air-fuel ratio detecting means by the downstream side abnormality detecting means when an abnormality of the ratio detecting means is detected Means are provided.

[0008]

In the first aspect of the invention, the air-fuel ratio detecting means detects the air-fuel ratio in the exhaust gas in order to perform feedback control of the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine, and the abnormality detecting means functions as the air-fuel ratio detecting means. The abnormality of the air-fuel ratio detecting means is detected based on the output value of the air-fuel ratio detecting means when the predetermined voltage is applied.
Further, the heating means heats the air-fuel ratio detecting means, and this heating state is detected by the heating state detecting means.

When the heating state detecting means detects a non-heating state of the air-fuel ratio detecting means, the prohibiting means is
By prohibiting the abnormality detection of the air-fuel ratio detection means by the abnormality detection means, the abnormality detection is performed only when the air-fuel ratio detection means is in the active state, and the false detection of the abnormality is prevented.

In the second aspect of the invention, the upstream side air-fuel ratio detecting means and the downstream side air-fuel ratio detecting means, which are respectively arranged on the upstream side and the downstream side of the catalyst provided in the exhaust system of the internal combustion engine, are supplied to the internal combustion engine. In order to perform feedback control of the air-fuel ratio of the air-fuel mixture, the air-fuel ratio in the exhaust gas on the upstream side and upstream side is detected. Further, the heating means heats the downstream side air-fuel ratio detecting means. The upstream side abnormality detecting means detects an abnormality of the upstream side air-fuel ratio detecting means based on the output value of the upstream side air-fuel ratio detecting means when a predetermined voltage is applied to the upstream side air-fuel ratio detecting means, and the downstream side The side abnormality detecting means detects an abnormality of the downstream side air-fuel ratio detecting means based on an output value of the downstream side air-fuel ratio detecting means when a predetermined voltage is applied to the downstream side air-fuel ratio detecting means.

The prohibiting means is provided when the upstream abnormality detecting means detects an abnormality in the upstream air-fuel ratio detecting means.
By prohibiting the heating of the downstream side air-fuel ratio detecting means by the heating means and prohibiting the abnormality detection of the downstream side air-fuel ratio detecting means by the downstream side abnormality detecting means, the upstream side air-fuel ratio detecting means functions normally and mixes. Only when the air-fuel ratio of air is normally feedback-controlled, heating of the downstream side air-fuel ratio detecting means by the heating means and abnormality detection of the downstream side air-fuel ratio detecting means by the downstream side abnormality detecting means are performed. Accurately detect an abnormal state of the air-fuel ratio sensor.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a fuel supply control device for an internal combustion engine to which an abnormality diagnosis device for an air-fuel ratio detecting device according to an embodiment of the present invention is applied. In the figure, reference numeral 1 indicates, for example, a four-cylinder internal combustion engine,
An intake pipe 2 is connected to the engine 1, and a throttle valve 3 is provided in the intake pipe 2. A throttle valve opening sensor 4 for detecting the valve opening θTH is connected to the throttle valve 3 and outputs an electrical signal corresponding to the detected θTH value as a throttle valve opening signal. The throttle valve opening signal is sent to an electronic control unit (hereinafter referred to as “ECU”) 5.

A fuel injection valve 6 is provided between the engine 1 and the throttle valve 3. The fuel injection valve 6 is provided for each cylinder of the engine 1, is connected to a fuel pump (not shown), and a valve opening time for injecting fuel is controlled by a drive signal supplied from the ECU 5.

On the other hand, an intake pipe absolute pressure sensor 8 for detecting an absolute pressure PBA in the intake pipe 2 is connected to the intake pipe 2 downstream of the throttle valve 3 via a pipe 7, and a detection signal thereof is detected. Is sent to the ECU 5. Further, an intake air temperature sensor 9 for detecting the intake air temperature TA is attached to the intake pipe 2 downstream of the pipe 7, and a detection signal thereof is sent to the ECU 5.

An engine cooling water temperature sensor 10 for detecting the temperature TW of the cooling water is provided on the cylinder peripheral wall of the engine 1 which is filled with the cooling water, and the engine cooling water temperature sensor 10 detects the temperature TW of the cooling water. To be An engine speed sensor (hereinafter referred to as an NE sensor) 11 and a cylinder discrimination (CYL) sensor 12 are mounted around a cam shaft or a crank shaft (not shown) of the engine 1, and the former NE sensor 11 is a predetermined one for each cylinder. One pulse signal (TD per 180 degree rotation of the crankshaft at the crank angle position)
C signal pulse) to output the latter cylinder discrimination sensor 12
Outputs one pulse of a signal for identifying a specific cylinder at a predetermined crank angle position of the specific cylinder, and these pulse signals are sent to the ECU 5.

A three-way catalyst 14 is provided in the exhaust pipe 13 of the engine 1 to purify HC, CO and NOx components in the exhaust gas. An upstream O2 sensor 15A and a downstream O2 sensor 15B, which are exhaust gas concentration sensors, are attached to the upstream and upstream exhaust pipes 13 of the three-way catalyst 14, respectively, and these upstream O2 sensor 15A and downstream O2 are installed. Sensor 1
5B detects the oxygen gas concentration in the exhaust gas and supplies the detection signal to the ECU 5.

Further, another engine operating parameter sensor, for example, an atmospheric pressure sensor 16 is connected to the ECU 5, and the atmospheric pressure sensor 16 outputs a detection signal thereof.
Is being supplied to. Further, the ECU 5 is connected with a fail-safe processing unit, for example, an alarm means 17, when the upstream O2 sensor 15A and the downstream O2 sensor 15B are broken or deteriorated. In the alarm means 17, an abnormality such as a failure or deterioration occurs in the upstream O2 sensor 15A and the downstream O2 sensor 15B,
When this is diagnosed (checked), an alarm sound is generated, an LED is displayed, etc. based on a control signal sent from the ECU 5.

The ECU 5 shapes the input signal (analog) waveforms from the above various sensors, corrects the voltage level to a predetermined level, converts the analog signal value into a digital signal value, and the CPU 5b which controls various controls. , This CP
The storage unit 5c stores various calculation programs executed by U5b and calculation results, and an output circuit 5d that supplies a drive signal to the fuel injection valve 6.

FIG. 2 shows O2 in the input circuit 5a of the ECU 5 including a checker circuit for detecting deterioration of the upstream O2 sensor 15A and the downstream O2 sensor 15B.
It is a circuit diagram which shows the circuit block diagram of a sensor input circuit part.
Although FIG. 2 shows only the input circuit portion of the downstream O2 sensor 15B, the input circuit portion of the upstream O2 sensor 15A has the same structure.

As shown in FIG. 2, one end of the O 2 sensor 15B represented by the internal impedance r of the element and the battery 15a is grounded to the exhaust pipe wall, and the other end is EC through the signal line l.
It is connected to U5. Inside the input circuit 5a of the ECU 5, a low-pass filter composed of two capacitors C1 and C2 and a resistor R1 and an operational amplifier 520 are provided, and the output voltage VO2 of the O2 sensor 15 is supplied to the non-operational amplifier 520 through the low-pass filter. Applied to the inverting input terminal, the operational amplifier 52
Amplified by 0, the multiplexer inside the ECU 5, A / D
It is supplied to a converter (not shown).

Between the connection point between the capacitor C1 and the resistor R1 and the terminal to which the predetermined power supply voltage Vcc is supplied,
A series circuit of a switchable switch 530 as a checker circuit switch (SW) and a resistor R2 is connected, and the switch 530 is on / off controlled by a control signal from the output circuit 5d. Switch 530
May be an appropriate switch element.

In addition, the upstream O2 sensor 15A and the downstream O2
The sensor 15B has an electric heater H, and by being heated by the electric heater H, the sensor 15B is quickly activated. The electric power supply to the electric heater H is controlled by EC
This is performed by controlling the switch 540 to be turned on / off by U5.

In the above checker circuit, the current flowing into the downstream O2 sensor 15B is increased by turning on the switch 530, and the output voltage of the downstream O2 sensor 15B at the time of the increase in current is checked to check the output of the downstream O2 sensor 15B. Anomaly detection is performed. That is, an abnormality such as a failure or deterioration of the downstream O2 sensor 15B is diagnosed based on the difference between the output voltage of the downstream O2 sensor 15B before and when the current increases. However, this diagnosis is not executed when the engine cooling water temperature sensor 10 and the electric heater H are out of order.

Next, the heater H of the downstream O2 sensor 15B
The energization control for will be described with reference to the flowchart of FIG.

The ECU 5 firstly detects the upstream O2 sensor 15
It is determined whether or not the heater H of A has a failure (step S1). As a result, if the heater H of the upstream O2 sensor 15A has failed, the estimated CAT temperature flag is set to "0" so that the estimated temperature of the three-way catalyst 14 is lower than the predetermined value (step S11). Further, after the energization flag is set to "0" to indicate that energization of the heater H of the downstream O2 sensor 15B is prohibited (step S12), if the switch 540 is currently on, it is turned off. As a result, the heating of the downstream O2 sensor 15B is stopped (step S13), and this processing ends. In step S13, if the switch 540 is currently off, the present processing is ended as it is, and the non-heating state of the downstream O2 sensor 15B is continued.

In step S1, the upstream O2 sensor 15
When it is determined that the heater H of A has not failed, it is determined whether the engine cooling water temperature sensor (TW sensor) 10 has failed (step S2). As a result, T
If the W sensor 10 has failed, the heating of the downstream O2 sensor 15B is stopped by performing the processing of steps S11 to S13 as in the case of the failure of the heater H, and this processing ends. To do.

On the other hand, if the TW sensor 10 has not failed, it is judged whether or not the engine is stalled (step S3). If the engine is stalled, the upstream side O
As in the case where the heater H of the 2 sensor 15A or the TW sensor 10 fails, the heating of the downstream O2 sensor 15B is stopped and stopped by performing the processing of the above steps S11 to S13, and this processing is ended. .

On the other hand, if the engine is not stalled,
It is determined whether or not the estimated CAT temperature flag is "1" (step S4). If the estimated CAT temperature flag is "1", the process immediately proceeds to step S8 described later. The estimated CAT temperature flag is set to "1" when the estimated temperature of the three-way catalyst 14 is equal to or higher than a predetermined value, and is set to "0" when the estimated temperature of the three-way catalyst 14 is lower than the predetermined value. Is.

When it is determined in step S4 that the estimated CAT temperature flag is "0", it is determined whether the engine cooling water temperature at the engine starting time set in the register Twst is equal to or higher than a predetermined value. Determine (Step S
5). As a result, if the engine cooling water temperature at the time of starting the engine is a high temperature equal to or higher than the predetermined value, the process immediately proceeds to step S8 described below, as in the case where the estimated CAT temperature flag is "1".

On the other hand, if the engine cooling water temperature at the time of engine start is lower than the predetermined value, it is determined whether the estimated CAT temperature is higher than the predetermined value (step S6). as a result,
If the estimated CAT temperature is lower than the predetermined value, that is, if the estimated temperature of the three-way catalyst 14 is lower than the predetermined temperature, the process proceeds to steps S11 to S13 to set "0" to the estimated CAT temperature flag and the energization flag. Then, the heating of the downstream O2 sensor 15B is stopped, and the present processing is terminated.

On the other hand, if the estimated temperature of the three-way catalyst 14 is higher than the predetermined temperature, the estimated CAT temperature flag is set to "1" (step S7). Then, it is determined whether or not the battery voltage is equal to or higher than a predetermined value (step S8). as a result,
If the battery voltage is equal to or higher than the predetermined value, the above step S1
After proceeding to 1 to S13, the estimated CAT temperature flag and the energization flag are set to "0", the heating of the downstream O2 sensor 15B is stopped, and the like, and then this processing is ended.

Here, the temperature of the three-way catalyst is estimated based on the engine operating state, for example, the engine speed and the engine load, but the temperature of the three-way catalyst may be directly detected instead of being estimated. . When the temperature of the three-way catalyst is low, the heater is not energized because the element of the O2 sensor may be rapidly heated and damaged if the heater is energized when the temperature of the O2 sensor is low. .

On the other hand, if the battery voltage is lower than the predetermined value, the energization flag is set to "1" (step 9).
If the switch 540 is currently off, it is turned on to start heating the downstream O2 sensor 15B (step S10), and the process returns. In step S10, if the switch 540 is currently on,
By leaning as it is, the downstream O2 sensor 15
Continue heating B.

As described above, by preventing the downstream O2 sensor 15B from being heated when the battery voltage is equal to or higher than a predetermined value, it is possible to prevent the downstream O2 sensor 15B from being rapidly heated and destroyed by a large current. It becomes possible to prevent it. Further, when the downstream O2 sensor 15B or the TW sensor 10 is out of order, when the engine is stalled, that is, when the environment for detecting the air-fuel ratio (oxygen concentration) in the exhaust gas is not ready, the downstream O2 sensor By not heating 15B, it is possible to prevent waste of electric power.

Next, the success / failure determination process of the precondition for monitoring the abnormal state of the downstream O2 sensor 15B will be described with reference to the flowchart of FIG.

The ECU 5 first determines whether or not the Tw sensor 10, the fuel injection valve 6, the electric heater H of the downstream O2 sensor 15B, and the electric heater H of the upstream O2 sensor 15A are defective, and the downstream O2 sensor. 15B heater H
It is sequentially determined whether or not the power is being supplied to (steps S21 to S2.
4). As a result, if any one of them fails,
If the heater H of the downstream O2 sensor 15B is not energized, "0" is set to the monitored flag and the condition satisfaction flag (steps S32 and S33), and this processing ends.

The monitored flag is "0" to indicate that monitoring has not been completed, and "1" indicates that monitoring has been completed. The condition satisfaction flag indicates that the precondition for monitoring the abnormal condition of the downstream O2 sensor 15B is not satisfied when "0" and the precondition is satisfied when "1". Therefore, as described above, the monitored flag and the condition satisfaction flag are set to “0”.
By setting and returning to the main flow,
Tw sensor 10, fuel injection valve 6, downstream O2 sensor 15B
If at least one of the electric heaters H has a failure, and if the heater H of the downstream O2 sensor 15B is not energized, the deterioration detection process of the downstream O2 sensor 15B is not performed.

On the other hand, when all of the electric heaters HH of the Tw sensor 10, the fuel injection valve 6, and the downstream O2 sensor 15B are not in failure, and when the heater H of the downstream O2 sensor 15B is energized, the downstream It is determined whether or not the side O2 sensor 15B is activated (step S25). As a result, if the downstream O2 sensor 15B is not activated, the process proceeds to steps S32 and S33 described above, the monitored flag and the condition satisfaction flag are set to "0", and the process returns to the main flow, thereby The abnormality detection process for the side O2 sensor 15B is not performed. As described above, when the downstream O2 sensor 15B is not activated, that is, when the internal impedance is high, the abnormality detection process should not be performed because the downstream O2 sensor 15B is actually deteriorated. This is to prevent erroneous diagnosis that the product is deteriorated even though it is not present.

On the other hand, if the downstream O2 sensor 15B is activated, it is judged whether or not the three-way catalyst 14 is being monitored (CAT monitor) (step S26). As a result, if the CAT monitor is being performed, it is necessary to prevent the abnormality detection processing of the downstream O2 sensor 15B from being performed, the process proceeds to the above steps S32 and S33, and the monitored flag,
Then, "0" is set to the condition satisfaction flag, and this processing is ended. This is to prevent noise from other monitors from being mixed and to reduce the accuracy of abnormality detection.

On the other hand, if the CAT monitor is not being executed,
It is determined whether or not the checker circuit is on (step S27). As a result, if the checker circuit is on, the condition satisfaction flag is set to "1" (step S31), and the process returns to the main flow. In this process, as can be inferred from the description below, a voltage change (voltage drop) due to the checker circuit being turned on erroneously determines that the precondition for monitoring the abnormal state of the downstream O2 sensor 15B is not satisfied. Is done to prevent

On the other hand, if the checker circuit is not on, it is determined whether the output voltage SVO2 of the downstream O2 sensor 15B is equal to or higher than a predetermined upper limit value VO2FSH (step S28). As a result, if the output voltage of the downstream O2 sensor 15B is equal to or higher than the predetermined upper limit value VO2FSH, the condition satisfaction flag is set to "1" (step S31), and this processing ends.

On the other hand, if the output voltage SVO2 of the downstream O2 sensor 15B is smaller than the predetermined upper limit value VO2FSH, it is judged whether or not fuel cut, that is, fuel supply is stopped (step S29), and if fuel supply is not stopped. That is, the downstream O2 sensor 15B while fuel is being supplied.
If the output voltage SVO2 is smaller than the predetermined upper limit value VO2FSH, it is clear that the internal impedance of the downstream O2 sensor 15B is not high and the downstream O2 sensor 15B is not deteriorated. In order to do so, proceed to steps S32 and S33 above,
"0" is set to the monitored flag and the condition satisfaction flag, and this processing ends.

On the other hand, during the fuel cut, the output voltage SVO2 of the downstream O2 sensor 15B is set to the predetermined lower limit value VO.
It is determined whether or not it is 2FSL or less (step S30).
As a result, if the output voltage SVO2 of the downstream O2 sensor 15B is larger than the predetermined lower limit value VO2FSL, that is, the output voltage S of the downstream O2 sensor 15B in the fuel cut state.
If VO2 is larger than the predetermined lower limit value VO2FSL, downstream O2
The internal impedance of the sensor 15B is within the appropriate range,
Since it is clear that the downstream O2 sensor 15B has not deteriorated, in order to avoid unnecessary abnormality detection processing, the process proceeds to the above steps S32 and S33, and the monitored flag and the condition satisfaction flag are set to "0". "" Is set, and this processing ends.

On the other hand, in the fuel cut state, the downstream side O2
The output voltage SVO2 of the sensor 15B is the predetermined lower limit value VO2FSL.
If the following is true, the downstream O2 sensor 15B may be short-circuited. Therefore, in order to perform the abnormality detection processing of the downstream O2 sensor 15B, the condition satisfaction flag is set to "1" (step S31), This process ends.

As described above, the downstream O 2 sensor 1
In the heater energization control of FIG. 3, the abnormality detection process of 5B is not performed when the Tw sensor 10 is out of order.
Heater energization (heating) when engine water temperature (TW) is low
Since it is not performed, the downstream O2 sensor 15
This is because it is unknown whether B is active. Further, the reason why the abnormality detection process is not performed when the fuel injection valve 6 fails is that the variation in the output between the cylinders becomes large and noise is generated in the output voltage SVO2 of the downstream O2 sensor 15B, so that the abnormality detection is performed. This is because the accuracy decreases. Further, when the heater H of the downstream O2 sensor 15B is out of order and when the heater is not energized, the abnormality detection processing is not performed because the downstream O2 sensor
This is because if the sensor 15B is not heated and an abnormality is detected in an inactive state, the sensor 15B makes an erroneous detection as described above.

Next, an abnormality monitor of the downstream O2 sensor 15B will be described with reference to the flowchart of FIG.

First, the ECU 5 first detects the downstream O2 sensor 15
Based on the condition satisfaction flag, it is determined whether or not the precondition for performing the abnormality detection processing of B is satisfied (step S).
41). As a result, if the condition satisfaction flag is set to "1" and the previous condition is satisfied, it is determined whether or not the condition has been monitored by referring to the monitored flag (step S4).
2). As a result, if the monitored flag is set to "0" to indicate that it has not been monitored, the fluctuation value ΔSVO2 of the output voltage of the downstream O2 sensor 15B is calculated (step S43). Calculation of this fluctuation value ΔSVO2
From the output voltage value SVO2 of this time of the downstream O2 sensor 15B, the downstream O2 set in the previous SVO2 register described later.
This is performed by subtracting the previous output voltage value of the sensor 15B and obtaining the absolute value.

Next, it is judged whether or not the calculated fluctuation value ΔSVO2 is smaller than a predetermined value (step S44). As a result, if the fluctuation value ΔSVO2 is greater than or equal to the predetermined value, S
It is determined whether or not the checker circuit was turned on when the previous output voltage value was set in the VO2 register (step S45). As a result, when the checker circuit is turned on, that is, the switch 530 shown in FIG.
If the fluctuation value ΔSVO2 of the output voltage of the previous time and the current time when it is supplied to the sensor 15B is equal to or more than a predetermined value, it means that the downstream O2 sensor 15B is normal, and therefore the downstream O2 sensor normal flag is set. Is set to "1" (step S46). Then, the monitored flag is set to "1" to indicate that it has been monitored (step S4).
7), the current output voltage value SV of the downstream O2 sensor 15B
O2 was previously set in the SVO2 register (step S4
8), turn off the checker circuit (switch 5 in Figure 2
30 is turned off) (step S49), and this processing ends.

When it is determined in step S41 that the previous condition is not satisfied, it is determined in step S42 that the monitoring has been completed, and that it is determined in step S45 that the checker circuit was turned off last time. If so, the process proceeds to step S48, and the downstream O2 sensor 15
The current output voltage value SVO2 of B is set in the SVO2 register last time, and the process proceeds to step S49 where the checker circuit is turned off and this process is completed.

In step S44, the downstream O2 sensor 1
When it is determined that the fluctuation value ΔSVO2 of the output voltage of 5B is smaller than the predetermined value, it is judged whether or not a predetermined time has elapsed while the fluctuation value ΔSVO2 is smaller than the predetermined value (step S50). As a result, if the predetermined time has not elapsed, the process proceeds to step S49, the checker circuit is turned off, and the present process ends.

On the other hand, when the predetermined time has passed, the checker circuit is turned on by turning on the switch 530 (step S51). Then, after turning on the checker circuit, it is determined whether or not a predetermined time has passed (step S52). As a result, if the predetermined time has not elapsed, this processing ends. On the other hand, if the predetermined time has elapsed, that is, if the fluctuation value ΔSVO2 of the output voltage of the downstream O2 sensor 15B is smaller than the predetermined value for a predetermined time, the downstream O2 sensor 15B is abnormal. Since it means that there is, the downstream O2 sensor abnormality flag is set to "1" (step S53). Then, the checker circuit is turned off, and this processing ends.

As described above, when the precondition described in the flowchart of FIG. 4 is not established, particularly when the heater H of the downstream O2 sensor 15B fails, the abnormality detection processing of the downstream O2 sensor 15B is prohibited. Therefore, erroneous detection is prevented.

The present invention is not limited to the above embodiment, but can be applied to, for example, an air-fuel ratio detecting device having only an upstream O2 sensor. Further, even when the abnormality of the upstream O2 sensor is detected in the air-fuel ratio detecting device having the upstream and downstream O2 sensors, when the heater of the upstream O2 sensor fails, etc. By prohibiting the abnormality detection processing of the sensor,
It is also possible to prevent erroneous detection.

[0055]

As described above, according to the first aspect of the invention, when the heating means of the air-fuel ratio detecting means (air-fuel ratio sensor) is in a non-heating state due to a failure or the like, and the air-fuel ratio detecting means is in the inactive state. Since the prohibition means prohibits the abnormality detection of the air-fuel ratio detection means, it is possible to prevent erroneous detection as abnormal even though it is actually normal. The condition can be detected accurately.

According to the second aspect of the invention, when the upstream side air-fuel ratio detecting means is in an abnormal state and the air-fuel ratio of the air-fuel mixture is not normally feedback-controlled, the downstream side air-fuel ratio detecting means is heated, Since the abnormality detection of the upstream side air-fuel ratio detecting means is prohibited, the abnormal state of the air-fuel ratio detecting means (air-fuel ratio sensor) can be accurately detected.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a fuel supply control device for an internal combustion engine to which an abnormality detection device for an air-fuel ratio detection device according to an embodiment of the present invention is applied.

FIG. 2 O2 including a checker circuit inside the ECU
It is a circuit diagram which shows the structure of a sensor input circuit part.

FIG. 3 is a flowchart showing an energization control process for a heater of a downstream O 2 sensor.

FIG. 4 is a flowchart showing a detection process for detecting whether or not a precondition for performing an abnormality detection process for a downstream O 2 sensor is satisfied.

FIG. 5 is a flowchart showing an abnormality detection process of a downstream O2 sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Electronic control unit (ECU) 5a ... Input circuit 5b ... CPU 5c ... Storage means 5d ... Output circuit 6 ... Fuel injection valve 10 ... Engine cooling water temperature sensor 14 ... Three-way catalyst 15A ... Upstream side O2 sensor 15B … Downstream O2 sensor H… Electric heater

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Maeda 1-4-1 Chuo, Wako City, Saitama Prefecture Honda R & D Co., Ltd.

Claims (2)

[Claims] 1. An air-fuel ratio detecting means for detecting an air-fuel ratio in exhaust gas for feedback control of an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine, a heating means for heating the air-fuel ratio detecting means, and the air-fuel ratio. In the abnormality diagnosis device of the air-fuel ratio detection device, which includes an abnormality detection unit that detects an abnormality of the air-fuel ratio detection unit based on the output value of the air-fuel ratio detection unit when a predetermined voltage is applied to the detection unit, the heating Means for detecting the heating state of the air-fuel ratio detecting means by means, and the air-fuel ratio detecting means by the abnormality detecting means when the heating state detecting means detects a non-heating state of the air-fuel ratio detecting means. An abnormality diagnosis device for an air-fuel ratio detection device, comprising: prohibition means for prohibiting the abnormality detection of. 2. An upstream side air-fuel ratio detecting means, which is arranged upstream and downstream of a catalyst provided in an exhaust system of an internal combustion engine, for feedback-controlling an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine. , And a downstream side air-fuel ratio detecting means, a heating means for heating the downstream side air-fuel ratio detecting means, and an output value of the upstream side air-fuel ratio detecting means when a predetermined voltage is applied to the upstream side air-fuel ratio detecting means. Based on the output value of the upstream side air-fuel ratio detecting means for detecting an abnormality of the upstream side air-fuel ratio detecting means based on the output value of the downstream side air-fuel ratio detecting means when a predetermined voltage is applied to the downstream side air-fuel ratio detecting means. In the abnormality diagnosis device of the air-fuel ratio detection device including the downstream-side abnormality detection means for detecting the abnormality of the downstream-side air-fuel ratio detection means, the abnormality of the upstream-side air-fuel ratio detection means is detected by the upstream-side abnormality detection means. When The heating means prohibits heating of the downstream side air-fuel ratio detecting means and prohibits the downstream side abnormality detecting means from detecting an abnormality of the downstream side air-fuel ratio detecting means. Abnormality diagnosis device for fuel ratio detection device.