JP2006070778A - Deterioration detecting device for linear air-fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a deterioration detecting device for a linear air-fuel ratio sensor, capable of accurately detecting time constant deterioration of the linear air-fuel ratio sensor, without being affected by air-fuel ratio fluctuation (steady fluctuation) such as swell having a relatively large period, by providing an air-fuel ratio with disturbance, differentiating an output value of the linear air-fuel ratio sensor after forced change in the air-fuel ratio and determining time constant deterioration based on the differential value, at the time of deterioration detection of the linear air-fuel ratio sensor. <P>SOLUTION: The deterioration detecting device for the linear air-fuel ratio sensor is equipped with the linear air-fuel ratio sensor provided in an exhaust system of an engine and outputting a value proportional to oxygen concentration in exhaust gas and with an air-fuel ratio control means for performing feedback of the air-fuel ratio of air-fuel mixture supplied to the engine to a target air-fuel ratio based on the detected value by the linear air-fuel ratio sensor. The deterioration detecting device for the linear air-fuel ratio sensor is further provided with air-fuel ratio changing means Q3, Q4 for forcibly changing an air-fuel ratio, a differential means Q6 for differentiating the output value of the linear air-fuel ratio sensor after the change in the air-fuel ratio and a deterioration determination means R1 for determining time constant deterioration of the linear air-fuel ratio sensor based on the value obtained by the differential means Q6. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a deterioration detection apparatus for a linear air-fuel ratio sensor that detects deterioration of a linear air-fuel ratio sensor that is provided in an exhaust system of an engine and outputs a value proportional to the oxygen concentration in exhaust gas.

  Conventionally, a linear air-fuel ratio sensor that outputs a value proportional to the oxygen concentration in the exhaust gas is provided in the exhaust system of the engine, and the actual air-fuel ratio (actual air-fuel ratio) detected by this linear air-fuel ratio sensor is the target air-fuel ratio ( For example, the difference between the two air-fuel ratios is determined so that A / F = 14.7 or a predetermined value on the lean side in the case of a lean burn engine), the fuel injection amount is controlled, and the target air-fuel ratio is Air-fuel ratio feedback control that performs feedback control so as to be obtained is known.

  By the way, when the above-mentioned linear air-fuel ratio sensor changes with time and deteriorates, the responsiveness of the linear air-fuel ratio sensor deteriorates. Therefore, the air-fuel ratio control shifts, and the exhaust purification performance by the catalytic converter interposed in the engine exhaust system. Gets worse. For this reason, it is necessary to detect deterioration of the linear air-fuel ratio sensor described above.

As an apparatus for detecting deterioration of a linear air-fuel ratio sensor, there is an apparatus described in Patent Document 1, for example.
That is, the whole response cycle of the linear air-fuel ratio sensor provided in the engine exhaust system is detected. In order to detect the response deterioration in an enlarged manner, two outputs are detected with respect to the output of the linear air-fuel ratio sensor. A threshold value is provided, and the output of the linear air-fuel ratio sensor is converted into an “H” symbol (H is an abbreviation for high) and an “L” symbol (L is an abbreviation for low) using this threshold value, and the sensor output The response deterioration of the linear air-fuel ratio sensor is detected based on the fact that the response cycle becomes longer as the degree of sensor deterioration increases.

Although this conventional device has the advantage of being able to detect the deterioration of the linear air-fuel ratio sensor, the deterioration factor is detected because it is not separately detected as dead time deterioration and first-order lag deterioration (time constant deterioration). There was a problem that could not be done.
Japanese Patent No. 3377336

  Therefore, according to the present invention, when the deterioration of the linear air-fuel ratio sensor is detected, a disturbance is given to the air-fuel ratio, the output value of the linear air-fuel ratio sensor is differentiated after the forced change of the air-fuel ratio, and the time constant deterioration is based on this differential value. By determining, linearity can accurately detect time constant deterioration (first-order lag deterioration) of the linear air-fuel ratio sensor without being affected by air-fuel ratio fluctuations (steady fluctuations) such as swells with relatively large cycles. An object of the present invention is to provide a deterioration detection device for an air-fuel ratio sensor.

  A linear air-fuel ratio sensor deterioration detection apparatus according to the present invention is based on a linear air-fuel ratio sensor provided in an engine exhaust system that outputs a value proportional to the oxygen concentration in exhaust gas, and a detection value of the linear air-fuel ratio sensor. Air-fuel ratio control means for feeding back the air-fuel ratio of the air-fuel mixture supplied to the engine to the target air-fuel ratio, air-fuel ratio changing means for forcibly changing the air-fuel ratio, and linear after the air-fuel ratio change Differentiating means for differentiating the output value of the air-fuel ratio sensor, and deterioration determining means for determining time constant deterioration of the linear air-fuel ratio sensor based on the value obtained by the differentiating means.

  According to the above configuration, the air-fuel ratio changing means forcibly changes the air-fuel ratio of the air-fuel mixture supplied to the engine when the deterioration of the linear air-fuel ratio sensor is detected. The output value of the air-fuel ratio sensor is differentiated, and the deterioration determining means determines the time constant deterioration of the linear air-fuel ratio sensor based on the value (differential value) obtained by the differentiating means.

  In this way, when the deterioration of the linear air-fuel ratio sensor is detected, disturbance is given to the air-fuel ratio, and after the forced change of the air-fuel ratio, the output value of the linear air-fuel ratio sensor is differentiated to obtain a differential value, and based on this differential value Since the time constant deterioration is determined, it is not affected by air-fuel ratio fluctuations (steady fluctuations) such as swells having a relatively large period, and an appropriate differential value can be obtained when a disturbance is applied. For this reason, the time constant deterioration of the linear air-fuel ratio sensor can be accurately detected. In short, by differentiating the linear air-fuel ratio sensor output, it is possible to eliminate the influence of air-fuel ratio fluctuations such as the above-mentioned swell, and to obtain differential values corresponding to disturbances (rapid fluctuations). Can be detected appropriately, and the deterioration factor can be determined.

In one embodiment of the present invention, the deterioration determining means detects time constant deterioration based on the peak value of the output (differential value) obtained by the differentiating means.
The peak value of the differential value of the output of the linear air-fuel ratio sensor becomes smaller as the sensor deteriorates.

  According to the above configuration, since the time constant deterioration is determined based on the above-described peak value, it is not affected by the steady fluctuation of the air-fuel ratio, and when a disturbance is given, a peak value corresponding to the degree of deterioration is obtained. It is done. For this reason, the time constant deterioration of the linear air-fuel ratio sensor can be accurately detected.

In one embodiment of the present invention, the deterioration determining means has a time constant based on a time from when the output (differential value) obtained by the differentiating means starts to change and then reaches a peak value until it becomes zero. Detects deterioration
The time from when the differential value of the output of the linear air-fuel ratio sensor starts to change and reaches the peak value becomes longer as the sensor deteriorates.

  According to the above configuration, since the time constant deterioration is determined based on the time until the above-mentioned zero, it is not affected by the steady fluctuation of the air-fuel ratio, and corresponds to the degree of deterioration when a disturbance is given. Time to zero is appropriately obtained. For this reason, the time constant deterioration of the linear air-fuel ratio sensor can be accurately detected.

In one embodiment of the present invention, the deterioration judging means starts to change the output (differential value) obtained by the differentiating means and exceeds a predetermined threshold value, and then the output is lowered and predetermined. The time constant deterioration is detected based on the time from when the threshold is reached.
The time between the time when the differential value of the output of the linear air-fuel ratio sensor begins to change and exceeds a predetermined threshold and the time after which the output decreases and reaches the predetermined threshold is deteriorated. The shorter it is, the shorter it will be.

  According to the above configuration, since the time constant deterioration is determined based on the above-described time, it is not affected by the steady fluctuation of the air-fuel ratio, and when a disturbance is applied, the time corresponding to the degree of deterioration (the differential output is At the beginning of the change, the time between the time when the predetermined threshold is exceeded and the time when the output decreases and reaches the predetermined threshold is obtained. For this reason, the time constant deterioration of the linear air-fuel ratio sensor can be accurately detected.

In one embodiment of the present invention, the deterioration determining means determines the time based on the time from when the disturbance starts forcibly changing the air-fuel ratio until the output (differential value) obtained by the differentiating means reaches the peak value. It detects constant deterioration.
The time from when the disturbance is forcibly changed to when the differential value reaches the peak value becomes longer as the linear air-fuel ratio sensor deteriorates.

  According to the above configuration, since the time constant deterioration is determined based on the above-described time, it is not affected by the steady fluctuation of the air-fuel ratio, and when a disturbance is applied, the time corresponding to the degree of deterioration (disturbance start time point) The output obtained by the differentiating means, that is, the time until the differential value reaches the peak value) is obtained. For this reason, the time constant deterioration of the linear air-fuel ratio sensor can be accurately detected.

In one embodiment of the present invention, the deterioration determining means detects time constant deterioration based on the area of the output (differential value) obtained by the differentiating means.
The area of the differential value of the linear air-fuel ratio sensor becomes smaller as the sensor deteriorates.

  According to the above configuration, since the time constant deterioration is determined based on the area of the differential value described above, it is not affected by the steady fluctuation of the air-fuel ratio. can get. For this reason, the time constant deterioration of the linear air-fuel ratio sensor can be accurately detected.

In one embodiment of the present invention, the air-fuel ratio changing means is configured to switch the change of the air-fuel ratio from rich to lean and from lean to rich, and the deterioration determining means is the output obtained by the differentiating means. One-sided time constant deterioration of the linear air-fuel ratio sensor is detected based on (differential value).
The above-mentioned one side means the rich side or the lean side.
According to the above configuration, it is possible to detect one-side time constant deterioration of the linear air-fuel ratio sensor.

  In one embodiment of the present invention, the air-fuel ratio changing means is configured to alternately change the air-fuel ratio between rich and lean when detecting deterioration.

  According to the above configuration, since the air-fuel ratio is alternately changed between rich and lean, the air-fuel ratio in the catalytic converter (so-called catalyst) may be shifted to either the rich side or the lean side, leading to deterioration of emissions. Thus, it is possible to determine the time constant deterioration under the condition that the exhaust gas purification performance by the catalytic converter is maintained.

  According to the present invention, when the deterioration of the linear air-fuel ratio sensor is detected, a disturbance is given to the air-fuel ratio, the output value of the linear air-fuel ratio sensor is differentiated after the forced change of the air-fuel ratio, and the time constant deterioration is performed based on this differential value. Therefore, it is possible to accurately detect time constant deterioration (first-order lag deterioration) of the linear air-fuel ratio sensor without being affected by air-fuel ratio fluctuation (steady fluctuation) such as swell with a relatively long period. is there.

  For the purpose of accurately detecting the time constant degradation (first-order lag degradation) of linear air-fuel ratio sensors without being affected by air-fuel ratio fluctuations (steady fluctuations) such as swells with relatively large cycles, the air-fuel ratio is forced The air-fuel ratio changing means for changing the output value, the differentiating means for differentiating the output value of the linear air-fuel ratio sensor after the air-fuel ratio change, and the time constant of the linear air-fuel ratio sensor based on the value (differential value) obtained by the differentiating means The present invention is realized by a configuration including a deterioration determination unit that determines deterioration.

An embodiment of the present invention will be described in detail below with reference to the drawings.
The drawing shows a deterioration detection device for a linear air-fuel ratio sensor. First, an intake / exhaust system of an engine will be described with reference to FIG.

  FIG. 1 is a system diagram of an engine having a linear air-fuel ratio sensor. An airflow sensor 3 is connected to the rear of an element 2 of an air cleaner 1 for purifying intake air, and the intake air amount Qa is detected by the airflow sensor 3. It is configured accordingly.

  A throttle body 4 is connected to the rear of the air flow sensor 3 described above, and a throttle valve 6 for controlling the intake air amount is disposed in a throttle chamber 5 in the throttle body 4. A surge tank 7 as an expansion chamber having a predetermined capacity is connected to the intake passage downstream of the throttle valve 6, and an intake manifold 9 communicating with the intake port 8 is connected downstream of the surge tank 7. The intake manifold 9 is provided with an injector 10 (fuel injection valve).

  On the other hand, an intake valve 14 and an exhaust valve 15 that are opened and closed by a valve operating mechanism (not shown) are respectively attached to the intake port 8 and the exhaust port 13 that are in appropriate communication with the combustion chamber 12 of the engine 11. A spark plug (not shown) with a spark gap facing the combustion chamber 12 is attached to the cylinder head 16.

A linear air-fuel ratio sensor 18 (hereinafter simply referred to as a linear O ₂ sensor) that outputs a value proportional to the oxygen concentration in the exhaust gas is disposed in the exhaust passage 17 that communicates with the exhaust port 13 described above. A catalytic converter 19 for purifying exhaust gas, a so-called catalyst, is connected to the rear of the exhaust passage 17.

The catalytic converter 19 described above, for example, can be used HC, CO, three-way catalyst capable of simultaneously purifying the three components of the NO _X (the so-called TWC).
The throttle body 4 is provided with a throttle sensor 20 for detecting the throttle opening TVO.

FIG. 2 is a control circuit block diagram showing a deterioration detection device for the linear O ₂ sensor 18. The CPU 30 as the control means includes an intake air amount Qa from the air flow sensor 3, a throttle opening TVO from the throttle sensor 20, and the like. Based on various necessary inputs such as an engine speed Ne from the rotation sensor 21 for detecting the engine speed and a value proportional to the oxygen concentration from the linear O ₂ sensor 18, the fuel is determined according to a program stored in the ROM 22. The injector 10 as the injection unit is driven, and the RAM 23 as the storage unit stores data corresponding to a predetermined value of the number of samples, data corresponding to a predetermined value for determining time constant deterioration, and the like.

Here, the CPU 30 described above includes air-fuel ratio feedback control means (refer to the CPU 30 itself) that feeds back the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to the target air-fuel ratio based on the detection value of the linear O ₂ sensor 18. Only when the deterioration of the linear O ₂ sensor 18 is detected, means for forcibly changing the air-fuel ratio supplied to the engine 11, that is, by adding or subtracting the fuel injection amount a shown in FIG. Forcibly changing the air-fuel ratio (see steps Q3 and Q4 in the flowchart shown in FIG. 3) and the output b (see FIG. 4) of the linear O ₂ sensor 18 after the air-fuel ratio forcibly changed to differentiate the differential value c Differentiating means (see step Q6 in the flowchart shown in FIG. 3) for obtaining (see FIG. 4) and the value obtained by the above-mentioned differentiating means (see step Q6). Based doubles as a degradation determiner means constant degradation time of the linear _{O 2} sensor 18 (see routine R1 consisting of the steps Q9~Q17 in FIG. 3), the by.

  In the embodiment shown in FIGS. 3 and 4, the deterioration determining means (see routine R1) performs time constant deterioration based on the peak value P of the output (differential value c) obtained by the differentiating means (see step Q6). It is configured to detect.

The air-fuel ratio forcibly changing means (see steps Q3 and Q4) is configured to change the air-fuel ratio from rich to lean and from lean to rich, and the deterioration determining means (see routine R1) The one side (rich side or lean side) time constant deterioration of the linear O ₂ sensor 18 is detected based on the output (differential value c) obtained by the differentiating means (see step Q6).

Further, the above-described forced air-fuel ratio changing means (see steps Q3 and Q4) adds and subtracts the fuel injection amount injected from the injector 10 when the deterioration is detected (when the diagnosis execution condition is satisfied), as shown in FIG. The change of the air-fuel ratio is alternately switched between rich and lean. This is to prevent the air-fuel ratio in the catalytic converter 19 from deviating to one of the rich side or the lean side, leading to deterioration of emissions. When the deterioration of the linear O ₂ sensor 18 is detected, the forced change of the air-fuel ratio is rich. By alternately switching to and lean, the time constant deterioration determination is performed while the exhaust gas purification performance by the catalytic converter 19 is maintained.

The operation of the deterioration detection device for the linear O ₂ sensor 18 configured as described above will be described in detail below with reference to the flowchart shown in FIG. 3 and the time chart shown in FIG.

In step Q1 of the flowchart shown in FIG. 3, the CPU 30 determines whether or not a diagnosis execution condition for detecting deterioration of the linear O ₂ sensor 18 is satisfied. That is, the change amount of the throttle opening TVO detected by the throttle sensor 20 is not more than a predetermined change amount, the change amount of the engine speed Ne detected by the rotation sensor 21 is not more than the predetermined change amount, and CE = Qa / Ne. The process proceeds to the next step Q2 only when the change amount of the required charging efficiency CE is equal to or less than a predetermined change amount, including the so-called steady state (when YES is determined), and is unsteady (such as when NO is determined) such as acceleration / deceleration. To return.

  Here, for the purpose of preventing a decrease in the detection frequency of diagnosis, the above-described diagnosis execution condition has a certain tolerance, and for example, the diagnosis execution condition is established in the case of slow acceleration or the like. .

  In step Q2, the CPU 30 determines whether or not the previous disturbance was lean based on the fuel injection amount addition / subtraction (disturbance) at the time of the previous forced change of the air-fuel ratio. At the time of determination, the process proceeds to another step Q4.

In step Q3 described above, the CPU 30 adds a lean disturbance to the fuel injection amount via the injector 10 at the air-fuel ratio forced change start time t ₀ (see FIG. 4).

On the other hand, in step Q4 described above, the CPU 30 adds a rich disturbance to the fuel injection amount via the injector 10 at the air-fuel ratio forced change start time t ₀ (see FIG. 6).

  That is, if the previous disturbance is rich due to the processing of each of the above steps Q2, Q3, and Q4, the lean disturbance is added to the fuel injection amount a this time (the fuel injection amount is subtracted), while the previous disturbance is If it is lean, a rich disturbance is added to the fuel injection amount a this time (the fuel injection amount is added), so that the forced change of the air-fuel ratio is alternately switched between rich and lean as shown in FIG.

Next, in step Q5, the CPU 30 reads the output b of the linear O ₂ sensor 18 that outputs a value proportional to the oxygen concentration in the exhaust gas. When the linear O ₂ sensor 18 is normal or substantially normal and the wiggling disturbance is added, the output b becomes as shown by the solid line in FIG. 4, and the output of the linear O ₂ sensor 18 increases as the degree of deterioration increases. b shifts in the direction indicated by the phantom line in FIG.

Next, in step Q6, the CPU 30 obtains a value obtained by differentiating the output b of the linear O ₂ sensor 18, that is, a differential value c (see FIG. 4) by calculation.

Next, in step Q7, the CPU 30 obtains the peak value P of the differential value c by calculation. As shown in FIG. 4, when the linear O ₂ sensor 18 is normal or substantially normal, the above-described peak value P becomes large, and the peak value P decreases as the degree of deterioration of the linear O ₂ sensor 18 increases.

  Next, in step Q8, for the purpose of improving the reliability of the determination, the CPU 30 determines that the number of samples of the peak value P when the rich disturbance is given and the number of samples of the peak value P when the lean disturbance is given are predetermined values ( For example, when the determination is NO, the process returns to step Q1 and repeats the flowchart. On the other hand, when the determination is YES, the process proceeds to the next step Q9.

  The time chart shown in FIG. 4 shows the positive peak value P of the differential value c when a lean disturbance (subtraction of fuel injection amount) is given, but a rich disturbance (addition of fuel injection amount) is given. In such a case, the time constant deterioration can be detected or determined using the negative peak value of the differential value c (see FIG. 6). Here, instead of the configuration using the positive and negative peak values, the absolute value of the peak value may be used.

  In step Q9 described above, the CPU 30 calculates the average value (average peak value) of the plurality of rich-side peak values P that have reached the predetermined number of samples, and also calculates the plurality of lean-side peak values P that have reached the predetermined number of samples. The average value (average peak value) is calculated.

  Next, in step Q10, the CPU 30 determines that the absolute value of the value obtained by subtracting the lean side peak value PL (specifically, the lean side average peak value) from the rich side peak value PR (specifically, the rich side average peak value) is a predetermined value. When it is determined NO, the process proceeds to step Q11. When it is determined YES, the process proceeds to another step Q12.

  In this step Q12, the CPU 30 determines whether or not the rich-side peak value PR is smaller than a predetermined value. When YES is determined, the process proceeds to step Q13, and when NO is determined, the process proceeds to another step Q14.

In step Q13 described above, the CPU 30 determines that the rich-side peak value PR is degraded, that is, rich-side time constant degradation, corresponding to PR <predetermined value.
On the other hand, in step Q14, the CPU 30 determines whether or not the lean-side peak value PL is smaller than a predetermined value. When YES is determined, the process proceeds to step Q15, and when NO is determined, the process proceeds to another step Q16.

In step Q15 described above, the CPU 30 determines that the lean-side peak value PL is degraded (lean-side time constant degradation) corresponding to PL <predetermined value.
In step Q16 described above, the CPU 30 determines that both the rich-side peak value and the lean-side peak value are normal.

  On the other hand, in step Q11 described above, the CPU 30 adds the rich peak value PR (specifically, the rich average peak value) and the lean peak value PL (specifically, the lean average peak value) to a predetermined value. When the determination is NO, the process proceeds to step Q16. When the determination is YES, the process proceeds to another step Q17.

  In step Q16, the CPU 30 determines that both the rich-side peak value PR and the lean-side peak value PL are normal. In step Q17, the CPU 30 determines that the rich value corresponds to PR + PL <predetermined value. It is determined that both the side peak value PR and the lean side peak value PL (in other words, the time constants on both sides) are deteriorated.

FIG. 7 shows a measurement result of an actual vehicle test to support the above-described embodiment for detecting the time constant deterioration of the linear O ₂ sensor 18 based on the differential value c. The engine speed Ne = 1200 rpm, the charging efficiency CE = An actual measurement value is shown when a lean disturbance is applied to reduce the fuel injection amount a by 6% under the condition of 0.2.

As apparent from FIG. 7, the waveform of the differential value c of the output b of the linear O ₂ sensor 18 shows a high value when the peak value P is normal, and shows a low value when the peak value P is deteriorated. .

Thus the deterioration detector of the linear O ₂ sensor 18 of the above embodiment, the linear O ₂ sensor 18 which outputs a value proportional to the oxygen concentration in the exhaust gas provided in an exhaust system of the engine 11, the linear O ₂ Air-fuel ratio feedback control means (see CPU 30) for feeding back the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to the target air-fuel ratio based on the detection value of the sensor 18 is provided, and the air-fuel ratio is forcibly set. Air-fuel ratio forcibly changing means for changing (see steps Q3 and Q4), differentiating means for differentiating the output b of the linear O ₂ sensor 18 after the air-fuel ratio forcibly changing (see step Q6), and the differentiating means (see step Q6) and a degradation determiner means constant degradation time of the linear O ₂ sensor 18 (see routine R1) based on the obtained value (see differential value c) by Than it is.

According to this configuration, the air-fuel ratio forcibly changing means (see steps Q3 and Q4) forcibly changes the air-fuel ratio supplied to the engine 11 when the deterioration of the linear O ₂ sensor 18 is detected. Step Q6) differentiates the output b of the linear O ₂ sensor 18 after the forced change of the air-fuel ratio, and the deterioration determining means (see routine R1) is a value (differentiated value) obtained by the differentiating means (see Step Q6). The time constant deterioration of the linear O ₂ sensor 18 is determined based on c).

As described above, when the deterioration of the linear O ₂ sensor 18 is detected, a disturbance is given to the air-fuel ratio, and after the forced change of the air-fuel ratio, the output b of the linear O ₂ sensor 18 is differentiated to obtain a differential value c. Since the time constant deterioration is determined based on c, it is not affected by air-fuel ratio fluctuations (steady fluctuations) such as swells with relatively large cycles, and an appropriate differential value c is obtained when a disturbance is applied. It is done. For this reason, the time constant deterioration of the linear O ₂ sensor 18 can be accurately detected.

  Moreover, the deterioration determining means (see routine R1) detects time constant deterioration based on the peak value P of the output (differential value c) obtained by the differentiating means (see step Q6).

According to this configuration, since the time constant deterioration is determined based on the above-described peak value P, the degree of deterioration of the linear O ₂ sensor 18 is not affected by a steady fluctuation of the air-fuel ratio, and when a disturbance is applied. A peak value P corresponding to is obtained. For this reason, the time constant deterioration of the linear O ₂ sensor 18 can be accurately detected.

Further, the air-fuel ratio forcibly changing means (see steps Q3 and Q4) is configured to change the air-fuel ratio from rich to lean and from lean to rich, and the deterioration determining means (see routine R1) is a differentiating means. One-side time constant deterioration of the linear O ₂ sensor 18 is detected based on the output (see the differential value c) obtained by (see step Q6).

According to this configuration, it is possible to detect the time constant deterioration on one side (in this embodiment, the rich side or / and / or the lean side) of the linear O ₂ sensor 18.
Further, the air-fuel ratio forcibly changing means (see steps Q3 and Q4) is configured to alternately change the air-fuel ratio between rich and lean when detecting deterioration.

According to this configuration, since the air-fuel ratio is alternately changed between rich and lean, the air-fuel ratio in the contact converter 19 (so-called catalyst) is shifted to either the rich side or the lean side, leading to deterioration of emissions. Thus, the time constant deterioration of the linear O ₂ sensor 18 can be determined under the condition that the exhaust gas purification performance by the catalytic converter 19 is maintained.

8 and 9 are a flowchart and a time chart showing another embodiment of the deterioration detection device for the linear O ₂ sensor 18. Also in this embodiment, the circuit device shown in FIGS. 1 and 2 is used.

Also in this embodiment, the CPU 30 is an air-fuel ratio feedback control means for feeding back the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to the target air-fuel ratio based on the detection value of the linear O ₂ sensor 18 (refer to the CPU itself). And means for forcibly changing the air-fuel ratio supplied to the engine 11 only when the deterioration of the linear O ₂ sensor 18 is detected, that is, by adding or subtracting the fuel injection amount a shown in FIG. A differential value c is obtained by differentiating the air-fuel ratio forcibly changing means (see steps U3 and U4 in FIG. 8) that gives a disturbance on the lean side and the output b (see FIG. 9) of the linear O ₂ sensor 18 after the air-fuel ratio is forcibly changed. Based on the value obtained by the differentiating means to be obtained (see step U6 in FIG. 8) and the above-mentioned differentiating means (see step U6), the time constant deterioration of the linear O ₂ sensor 18 is determined. It also serves as a deterioration determining means (see routine R2 in FIG. 8).

  In the embodiments shown in FIGS. 8 and 9, the deterioration determining means (see routine R2) shows a peak value, with the output (see the differential value c) obtained by the differentiating means (see step U6) starting to change. The time constant deterioration is detected on the basis of a time TA (see FIG. 9) from the time point until it becomes zero thereafter.

The time TA until the above zero is short when the linear O ₂ sensor 18 is normal or substantially normal, and the time TA until it becomes zero becomes longer as the degree of deterioration increases.

The operation of this embodiment will be described in detail below with reference to the flowchart shown in FIG. 8 and the time chart shown in FIG.
In step U1 of the flowchart shown in FIG. 8, the CPU 30 determines whether or not a diagnosis execution condition for detecting deterioration of the linear O ₂ sensor 18 is satisfied. That is, the change amount of the throttle opening TVO detected by the throttle sensor 20 is not more than a predetermined change amount, the change amount of the engine speed Ne detected by the rotation sensor 21 is not more than the predetermined change amount, and CE = Qa / Ne. The process proceeds to the next step U2 only when the change amount of the required charging efficiency CE is equal to or less than a predetermined change amount, including the so-called steady state (YES determination), and is unsteady (according to NO determination) such as acceleration / deceleration. To return.

  Here, in order to prevent a decrease in the detection frequency of diagnosis, the above-described diagnosis execution condition has a certain tolerance, and for example, the diagnosis execution condition is established at the time of slow acceleration. .

  In step U2, the CPU 30 determines whether or not the previous disturbance was lean based on the fuel injection amount addition / subtraction (disturbance) at the time of the previous forced change of the air-fuel ratio. At the time of determination, the process proceeds to another step U4.

In step U3 described above, the CPU 30 adds a lean disturbance to the fuel injection amount via the injector 10 at the air-fuel ratio forced change start time t ₀ (see FIG. 9).
On the other hand, in step U4 above, CPU 30 in the air-fuel ratio forcibly change start time t _0, adds the rich disturbance to the fuel injection amount through the injector 10.

  That is, if the previous disturbance is rich due to the processing of each of the above steps U2, U3, U4, the lean disturbance is added to the fuel injection amount a this time (the fuel injection amount is subtracted), while the previous disturbance is If it is lean, a rich disturbance is added to the fuel injection amount a this time (fuel injection amount is added), so that the forced change of the air-fuel ratio is switched alternately between rich and lean as already shown in FIG. .

Next, in step U5, the CPU 30 reads the output b of the linear O ₂ sensor 18 that outputs a value proportional to the oxygen concentration in the exhaust gas. When the linear O ₂ sensor 18 is normal or substantially normal and the wiggane disturbance is added, the output b becomes as shown by the solid line in FIG. 9, and the output of the linear O ₂ sensor 18 increases as the degree of deterioration of the linear O ₂ sensor 18 increases. b will shift in the direction indicated by the phantom line in FIG.

Next, in step U6, the CPU 30 obtains a value obtained by differentiating the output b of the linear O ₂ sensor 18, that is, a differential value c (see FIG. 9) by calculation.

Next, in step U7, the CPU 30 obtains the time TA from the time when the differential value c starts to change and shows a peak value until it becomes zero by calculation. As shown in FIG. 9, when the linear O ₂ sensor 18 is normal or substantially normal, the time TA is small, and the time TA increases as the degree of deterioration of the linear O ₂ sensor 18 increases.

  Next, in step U8, for the purpose of improving the reliability of the determination, the CPU 30 sets a predetermined number (for example, 5) of the number of samples of the time TA when the rich disturbance is given and the number of samples of the time TA when the lean disturbance is given. 10 times), when the determination is NO, the process returns to step U1 and repeats the flowchart, and when the determination is YES, the process proceeds to the next step U9.

  In the time chart shown in FIG. 9, the time TA from the positive peak value P of the differential value c when the lean disturbance (subtraction of the fuel injection amount) is given to the subsequent zero is shown. When (addition of fuel injection amount) is given, time constant deterioration can be detected or determined using the time from the negative peak value of the differential value c to zero thereafter.

  In step U9 described above, the CPU 30 calculates the average value of the plurality of rich-side times TA that have reached the predetermined number of samples, and calculates the average value of the plurality of lean-side times TA that have reached the predetermined number of samples.

  Next, in step U10, the CPU 30 has the absolute value of the value obtained by subtracting the lean side time TAL (specifically, the average value of the lean side time) from the rich side time TAR (specifically, the average value of the rich side time) greater than a predetermined value. If NO is determined, the process proceeds to step U11. If YES is determined, the process proceeds to another step U12.

  In this step U12, the CPU 30 determines whether or not the rich side time TAR is larger than a predetermined value. When YES is determined, the process proceeds to step U13, and when NO is determined, the process proceeds to another step U14.

In step U13 described above, the CPU 30 determines that the rich side time TAR is degraded, that is, the rich side time constant is degraded, corresponding to TAR> predetermined value.
On the other hand, in step U14, the CPU 30 determines whether or not the lean side time TAL is larger than a predetermined value. When YES is determined, the process proceeds to step U15, and when NO is determined, the process proceeds to another step U16.

In step U15 described above, the CPU 30 determines that the lean side time TAL is deteriorated (lean side time constant deterioration) corresponding to TAL> predetermined value.
In Step U16 described above, the CPU 30 determines that both the rich side time TAR and the lean side time TAL are normal.

  On the other hand, in step U11 described above, the CPU 30 adds a value obtained by adding the rich side time TAR (specifically, the average value of the rich side time) and the lean side time TAL (specifically, the average value of the lean side time) to be greater than the predetermined value. If NO is determined, the process proceeds to step U16. If YES is determined, the process proceeds to another step U17.

  In step U16, the CPU 30 determines that both the rich side time TAR and the lean side time TAL are normal, and in step U17, the CPU 30 determines that the rich side time TAR + TAL> predetermined value. It is determined that both the TAR and the lean side time TAL (in other words, the time constants on both sides) are deteriorated.

  Thus, in the embodiments shown in FIGS. 8 and 9, the deterioration determining means (see routine R2) is such that the output (see the differential value c) obtained by the differentiating means (see step U6) begins to change. The time constant deterioration is detected on the basis of the time TA from the time when the peak value is shown until it reaches zero thereafter.

According to this configuration, since the time constant deterioration is determined based on the above-described time TA until zero, it is not affected by the steady fluctuation of the air-fuel ratio, and corresponds to the degree of deterioration when a disturbance is given. Thus, the time TA until it becomes zero can be appropriately obtained. For this reason, the time constant deterioration of the linear O ₂ sensor 18 can be accurately detected.
In the embodiment shown in FIGS. 8 and 9, the other operations and effects are substantially the same as those in the previous embodiment.

10 and 11 are a flowchart and a time chart showing still another embodiment of the deterioration detection apparatus for the linear O ₂ sensor 18. Also in this embodiment, the circuit device shown in FIGS. 1 and 2 is used.

Also in this embodiment, the CPU 30 is an air-fuel ratio feedback control means for feeding back the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to the target air-fuel ratio based on the detection value of the linear O ₂ sensor 18 (refer to the CPU itself). And means for forcibly changing the air-fuel ratio supplied to the engine 11 only when the deterioration of the linear O ₂ sensor 18 is detected, that is, by adding or subtracting the fuel injection amount a shown in FIG. The differential value c is obtained by differentiating the air-fuel ratio forcibly changing means (see steps X3 and X4 in FIG. 10) that gives a disturbance on the lean side and the output b (see FIG. 11) of the linear O ₂ sensor 18 after the forced change of the air-fuel ratio. The time constant of the linear O ₂ sensor 18 based on the value obtained by the differentiating means to be obtained (see step X6 in FIG. 10) and the above-mentioned differentiating means (see step X6). It also serves as deterioration determination means (see routine R3 in FIG. 10) for determining deterioration.

  In this embodiment shown in FIGS. 10 and 11, the above-described deterioration determination means (see routine R3) is such that the output (see differential value c) obtained by the differentiation means (see step X6) is as shown in FIG. The time constant deterioration is detected based on the time TB between the time when the predetermined threshold value th is exceeded and the time when the output decreases and reaches the predetermined threshold value th. ing.

  In other words, the time constant deterioration is detected based on the time TB between points at which the differential value c crosses a predetermined value (see threshold value th) after a disturbance is applied.

The operation of this embodiment will be described in detail below with reference to the flowchart shown in FIG. 10 and the time chart shown in FIG.
In step X1 of the flowchart shown in FIG. 10, the CPU 30 determines whether or not a diagnosis execution condition for detecting deterioration of the linear O ₂ sensor 18 is satisfied. That is, the change amount of the throttle opening TVO detected by the throttle sensor 20 is not more than a predetermined change amount, the change amount of the engine speed Ne detected by the rotation sensor 21 is not more than the predetermined change amount, and CE = Qa / Ne. The process proceeds to the next step X2 only when the change amount of the required charging efficiency CE is equal to or less than a predetermined change amount, including the so-called steady state (when YES is determined), and is unsteady (when NO is determined) such as acceleration / deceleration. To return.

  Here, in order to prevent a decrease in the detection frequency of diagnosis, the above-described diagnosis execution condition has a certain tolerance, and for example, the diagnosis execution condition is established at the time of slow acceleration. .

  In step X2 described above, the CPU 30 determines whether or not the previous disturbance was lean based on the fuel injection amount addition / subtraction (disturbance) at the time of the previous forced change of the air-fuel ratio. At the time of determination, the process proceeds to another step X4.

In step X3 described above, the CPU 30 adds a lean disturbance to the fuel injection amount via the injector 10 at the air-fuel ratio forced change start time t ₀ (see FIG. 11).

On the other hand, in the aforementioned step X4, CPU 30 in the air-fuel ratio forcibly change start time t _0, adds the rich disturbance to the fuel injection amount through the injector 10.

  That is, if the previous disturbance is rich due to the processing of each of the above steps X2, X3, and X4, the lean disturbance is added to the fuel injection amount a this time (the fuel injection amount is subtracted), while the previous disturbance is If it is lean, a rich disturbance is added to the fuel injection amount a this time (the fuel injection amount is added), so that the forced change of the air-fuel ratio is alternately switched between rich and lean as already shown in FIG. .

Next, in Step X5, the CPU 30 executes reading of the output b of the linear O ₂ sensor 18 that outputs a value proportional to the oxygen concentration in the exhaust gas. When the linear O ₂ sensor 18 is normal or substantially normal and the wiggling disturbance is added, the output b is as shown by the solid line in FIG. 11, and the output of the linear O ₂ sensor 18 increases as the degree of deterioration increases. b will shift in the direction indicated by the phantom line in FIG.

Next, in step X6, the CPU 30 obtains a value obtained by differentiating the output b of the linear O ₂ sensor 18, that is, a differential value c (see FIG. 11) by calculation.

Next, at step X7, the CPU 30 determines the time TB when the above-mentioned differential value c exceeds the predetermined threshold value th as a predetermined value, more specifically, when the threshold value th is exceeded and thereafter the output decreases. A time TB between the time when the value falls below the predetermined threshold th is obtained by calculation. As shown in FIG. 11, when the linear O ₂ sensor 18 is normal or substantially normal, the above-described time TB becomes large, and the time TB decreases as the degree of deterioration of the linear O ₂ sensor 18 increases.

  Next, in step X8, for the purpose of improving the reliability of the determination, the CPU 30 sets a predetermined number (for example, 5) of the number of samples at the time TB when the rich disturbance is given and the number of samples at the time TB when the lean disturbance is given. 10 times), if NO, the process returns to step X1 and repeats the flowchart. On the other hand, if YES, the process proceeds to the next step X9.

  Note that the time chart shown in FIG. 11 shows the time TB between points crossing the threshold value th on the plus side of the differential value c when lean disturbance (subtraction of fuel injection amount) is given. When (addition of fuel injection amount) is given, the time constant deterioration can be detected or determined using the time TB between points crossing the threshold value th on the minus side of the differential value c.

  In step X9, the CPU 30 calculates the average value of the plurality of rich-side times TB that have reached the predetermined number of samples and calculates the average value of the plurality of lean-side times TB that have reached the predetermined number of samples.

  Next, in step X10, the CPU 30 has an absolute value of a value obtained by subtracting the lean side time TBL (specifically, the average value of the lean side time) from the rich side time TBR (specifically, the average value of the rich side time) greater than a predetermined value. If NO is determined, the process proceeds to step X11. If YES is determined, the process proceeds to another step X12.

  In this step X12, the CPU 30 determines whether or not the rich side time TBR is smaller than a predetermined value. When YES is determined, the process proceeds to step X13, and when NO is determined, the process proceeds to another step X14.

In step X13 described above, the CPU 30 determines that the rich side time TBR is degraded, that is, the rich side time constant is degraded, corresponding to TBR <predetermined value.
On the other hand, in step X14, the CPU 30 determines whether or not the lean side time TBL is smaller than a predetermined value. When YES is determined, the process proceeds to step X15. When NO is determined, the process proceeds to another step X16.

In step X15 described above, the CPU 30 determines that the lean side time TBL is degraded (lean side time constant degradation) corresponding to TBL <predetermined value.
In Step X16 described above, the CPU 30 determines that both the rich side time TBR and the lean side time TBL are normal.

  On the other hand, in step X11 described above, the CPU 30 adds a value obtained by adding the rich side time TBR (specifically, the average value of the rich side time) and the lean side time TBL (specifically, the average value of the lean side time) to be greater than the predetermined value. When the determination is NO, the process proceeds to step X16. When the determination is YES, the process proceeds to another step X17.

  In step X16, the CPU 30 determines that both the rich side time TBR and the lean side time TBL are normal, and in step X17, the CPU 30 determines that the rich side time TBR + TBL <predetermined value. It is determined that both TBR and lean side time TBL (in other words, time constants on both sides) are deteriorated.

  Thus, in the embodiments shown in FIGS. 10 and 11, the deterioration determining means (see routine R3) is such that the output (see the differential value c) obtained by the differentiating means (see step X6) begins to change. The time constant deterioration is detected based on the time TB between the time point when the predetermined threshold value th is exceeded and the time point when the output decreases and reaches the predetermined threshold value.

The time TB between the time when the differential value c of the output of the linear O ₂ sensor 18 starts to change and exceeds a predetermined threshold and the time when the output decreases and reaches the predetermined threshold is expressed as follows: The shorter the sensor is, the shorter it is.

According to this configuration, since the time constant deterioration is determined based on the above-described time TB, it is not affected by the steady fluctuation of the air-fuel ratio, and when a disturbance is given, the time TB (differential) corresponding to the degree of deterioration is given. A time TB) between the time when the output starts to change and exceeds the predetermined threshold and the time when the output decreases and reaches the predetermined threshold is obtained. For this reason, the time constant deterioration of the linear O ₂ sensor 18 can be accurately detected.
In the embodiment shown in FIGS. 10 and 11, the other operations and effects are substantially the same as those in the previous embodiment.

FIGS. 12 and 13 are a flowchart and a time chart showing still another embodiment of the deterioration detection apparatus for the linear O ₂ sensor 18. Also in this embodiment, the circuit device shown in FIGS. 1 and 2 is used.

Also in this embodiment, the CPU 30 is an air-fuel ratio feedback control means for feeding back the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to the target air-fuel ratio based on the detection value of the linear O ₂ sensor 18 (refer to the CPU itself). And means for forcibly changing the air-fuel ratio supplied to the engine 11 only when the deterioration of the linear O ₂ sensor 18 is detected, that is, by adding or subtracting the fuel injection amount a shown in FIG. The differential value c is obtained by differentiating the air-fuel ratio forcibly changing means (see steps Y3 and Y4 in FIG. 12) that gives a disturbance on the lean side and the output b (see FIG. 13) of the linear O ₂ sensor 18 after the forced change of the air-fuel ratio. The time constant of the linear O ₂ sensor 18 based on the value obtained by the differentiating means to be obtained (see step Y6 in FIG. 12) and the above-mentioned differentiating means (see step Y6). It also serves as deterioration determination means (see routine R4 in FIG. 12) for determining deterioration.

12, in the embodiment shown in FIG. 13, the above-mentioned deterioration determination means (see Routine R4) were obtained by the differentiating means from a disturbance start time t ₀ which forcibly change the air-fuel ratio (refer to step Y6) output The time constant deterioration is detected based on the time TC until the (differential value c) reaches the peak value.

The effect | action of this Example is explained in full detail below with reference to the flowchart shown in FIG. 12, and the time chart shown in FIG.
In step Y1 of the flowchart shown in FIG. 12, the CPU 30 determines whether or not a diagnosis execution condition for detecting deterioration of the linear O ₂ sensor 18 is satisfied. That is, the change amount of the throttle opening TVO detected by the throttle sensor 20 is not more than a predetermined change amount, the change amount of the engine speed Ne detected by the rotation sensor 21 is not more than the predetermined change amount, and CE = Qa / Ne. The next step Y2 is shifted to the next step Y2 almost only during steady state (when YES determination) including the so-called steady state when the required change amount of the charging efficiency CE is equal to or less than the predetermined change amount, and during non-steady time such as acceleration / deceleration (NO determination time) To return.

  Here, in order to prevent a decrease in the detection frequency of diagnosis, the above-described diagnosis execution condition has a certain tolerance, and for example, the diagnosis execution condition is established at the time of slow acceleration. .

  In step Y2, the CPU 30 determines whether or not the previous disturbance was lean based on the fuel injection amount addition / subtraction (disturbance) at the time of the previous forced change of the air-fuel ratio. At the time of determination, the process proceeds to another step Y4.

In step Y3 described above, the CPU 30 adds the lean disturbance to the fuel injection amount via the injector 10 at the disturbance start time t ₀ (see FIG. 13).
On the other hand, in step Y4 above, CPU 30 in the disturbance beginning _{t 0,} adds the rich disturbance to the fuel injection amount through the injector 10.

  In other words, if the previous disturbance is rich by the processing of each of the above-described steps Y2, Y3, and Y4, the lean disturbance is added to the fuel injection amount a this time (the fuel injection amount is subtracted), while the previous disturbance is If it is lean, a rich disturbance is added to the fuel injection amount a this time (fuel injection amount is added), so that the forced change of the air-fuel ratio is alternately switched between rich and lean as already described in FIG. .

Next, in step Y5, the CPU 30 reads the output b of the linear O ₂ sensor 18 that outputs a value proportional to the oxygen concentration in the exhaust gas. When the linear O ₂ sensor 18 is normal or substantially normal and the wiggling disturbance is added, the output b is as shown by the solid line in FIG. 13, and the output of the linear O ₂ sensor 18 increases as the degree of deterioration increases. b will shift in the direction indicated by the phantom line in FIG.

Next, in step Y6, the CPU 30 obtains a value obtained by differentiating the output b of the linear O ₂ sensor 18, that is, a differential value c (see FIG. 13) by calculation.

In step Y7, CPU 30 is obtained by calculation time TC from disturbance disclosure time _{t 0} to the differential value c reaches the peak value. As shown in FIG. 13, when the linear O ₂ sensor 18 is normal or substantially normal, the above-described time TC is shortened, and the time TC is increased as the degree of deterioration of the linear O ₂ sensor 18 is increased.

  Next, in step Y8, for the purpose of improving the reliability of the determination, the CPU 30 determines whether the number of samples at the time TC when a rich disturbance is applied and the number of samples at the time TC when a lean disturbance is applied (for example, 5). 10 times), when the determination is NO, the process returns to step Y1 and repeats the flowchart, and when the determination is YES, the process proceeds to the next step Y9.

Incidentally, although the time TC until the differential value c when in disturbance disclosed time t ₀ gave lean disturbance (subtraction of the fuel injection amount) reaches a peak value on the positive side in the time chart shown in FIG. 13 When rich disturbance (addition of fuel injection amount) is given, time constant deterioration can be detected or determined using the time TC until the differential value c reaches the negative peak value.

  In step Y9, the CPU 30 calculates the average value of the plurality of rich-side times TC that have reached the predetermined number of samples, and calculates the average value of the plurality of lean-side times TC that have reached the predetermined number of samples.

  Next, in step Y10, the CPU 30 has the absolute value of the value obtained by subtracting the lean side time TCL (specifically, the average value of the lean side time) subtracted from the rich side time TCR (specifically, the average value of the rich side time) is greater than a predetermined value. If NO is determined, the process proceeds to step Y11. If YES is determined, the process proceeds to another step Y12.

  In this step Y12, the CPU 30 determines whether or not the rich side time TCR is greater than a predetermined value. When YES is determined, the process proceeds to step Y13, and when NO is determined, the process proceeds to another step Y14.

In step Y13 described above, the CPU 30 determines that the rich side time TCR is degraded, that is, the rich side time constant is degraded, corresponding to TCR> predetermined value.
On the other hand, in step Y14, the CPU 30 determines whether or not the lean side time TCL is larger than a predetermined value. When YES is determined, the process proceeds to step Y15, and when NO is determined, the process proceeds to another step Y16.

In step Y15 described above, the CPU 30 determines that the lean side time TCL is deteriorated (lean side time constant deterioration) in response to TCL> predetermined value.
In step Y16 described above, the CPU 30 determines that both the rich side time TCR and the lean side time TCL are normal.

  On the other hand, in step Y11 described above, the CPU 30 adds a value obtained by adding the rich side time TCR (specifically, the average value of the rich side time) and the lean side time TCL (specifically, the average value of the lean side time) to be greater than the predetermined value. When the determination is NO, the process proceeds to step Y16. When the determination is YES, the process proceeds to another step Y17.

  In step Y16, the CPU 30 determines that both the rich side time TCR and the lean side time TCL are normal. In step Y17, the CPU 30 determines that the rich side time TCR + TCL> predetermined value. It is determined that both the TCR and the lean time TCL (in other words, the time constants on both sides) are deteriorated.

Thus, in the embodiment shown in FIG. 12, FIG. 13, (see Routine R4) said deterioration determination means, by the differentiation means from the disturbance start time t ₀ which forcibly change the air-fuel ratio (refer to step Y6) The time constant deterioration is detected based on the time TC until the obtained output (refer to the differential value c) reaches the peak value.

Here, the time TC from the disturbance start time t ₀ which forcibly changes the air-fuel ratio of the above to the differential value c reaches a peak value, the linear O ₂ sensor 18 is higher deteriorates, becomes longer.

According to this configuration, since the time constant deterioration is determined based on the time TC described above, the time TC (disturbance corresponding to the degree of deterioration is not affected by the disturbance of the air-fuel ratio without being affected by the steady fluctuation of the air-fuel ratio. time from the start time point t ₀ until the output c obtained by differentiating means reaches a peak value TC) is obtained. For this reason, the time constant deterioration of the linear O ₂ sensor 18 can be accurately detected.
In the embodiment shown in FIG. 12 and FIG. 13, the other actions and effects are substantially the same as those in the previous embodiment.

14 and 15 are a flowchart and a time chart showing still another embodiment of the deterioration detection apparatus for the linear O ₂ sensor 18. Also in this embodiment, the circuit device shown in FIGS. 1 and 2 is used.

Also in this embodiment, the CPU 30 is an air-fuel ratio feedback control means for feeding back the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to the target air-fuel ratio based on the detection value of the linear O ₂ sensor 18 (refer to the CPU itself). And means for forcibly changing the air-fuel ratio supplied to the engine 11 only when the deterioration of the linear O ₂ sensor 18 is detected, that is, by adding or subtracting the fuel injection amount a shown in FIG. A differential value c is obtained by differentiating the air-fuel ratio forcibly changing means (see steps Z3 and Z4 in FIG. 14) for giving a disturbance on the lean side and the output b (see FIG. 15) of the linear O ₂ sensor 18 after the forced change of the air-fuel ratio. The time constant of the linear O ₂ sensor 18 based on the value obtained by the differentiating means to be obtained (see step Z6 in FIG. 14) and the above-mentioned differentiating means (see step Z6). It also serves as deterioration determination means (see routine R5 in FIG. 14) for determining deterioration.

  In the embodiments shown in FIGS. 14 and 15, the above-described deterioration determining means (see routine R5) is based on the area of the output (see differential value c) obtained by the differentiating means (see step Z6). Is configured to detect.

More specifically, the above-described deterioration determination means should detect time constant deterioration based on an area S (see FIG. 15) where the differential value c of the output of the linear O ₂ sensor 18 is equal to or greater than a threshold value th. By configuring this threshold value th, the detection accuracy of the time constant deterioration due to the area S between the normal product and the deteriorated product is improved.
As the degree of deterioration of the time constant of the linear O ₂ sensor 18 increases, the area S described above decreases.

The operation of this embodiment will be described in detail below with reference to the flowchart shown in FIG. 14 and the time chart shown in FIG.
In step Z1 of the flowchart shown in FIG. 14, the CPU 30 determines whether or not a diagnosis execution condition for detecting deterioration of the linear O ₂ sensor 18 is satisfied. That is, the change amount of the throttle opening TVO detected by the throttle sensor 20 is not more than a predetermined change amount, the change amount of the engine speed Ne detected by the rotation sensor 21 is not more than the predetermined change amount, and CE = Qa / Ne. The process proceeds to the next step Z2 only when the change amount of the required charging efficiency CE is less than a predetermined change amount, ie, the so-called steady state (when YES is determined), and is not steady (when NO is determined) such as acceleration / deceleration. To return.

  Here, in order to prevent a decrease in the detection frequency of diagnosis, the above-described diagnosis execution condition has a certain tolerance, and for example, the diagnosis execution condition is established at the time of slow acceleration. .

  In step Z2, the CPU 30 determines whether or not the previous disturbance was lean based on the fuel injection amount addition / subtraction (disturbance) at the time of the previous forced change of the air-fuel ratio. At the time of determination, the process proceeds to another step Z4.

In step Z3 described above, the CPU 30 adds a lean disturbance to the fuel injection amount via the injector 10 at the air-fuel ratio forced change start time t ₀ (see FIG. 15).

On the other hand, in the aforementioned step Z4, CPU 30 in the air-fuel ratio forcibly change start time t _0, adds the rich disturbance to the fuel injection amount through the injector 10.

  That is, if the previous disturbance is rich due to the processing of each of the above steps Z2, Z3, Z4, the lean disturbance is added to the fuel injection amount a this time (the fuel injection amount is subtracted), while the previous disturbance is If it is lean, a rich disturbance is added to the fuel injection amount a this time (the fuel injection amount is added), so that the forced change of the air-fuel ratio is alternately switched between rich and lean as already described in FIG. .

Next, in step Z5, the CPU 30 reads the output b of the linear O ₂ sensor 18 that outputs a value proportional to the oxygen concentration in the exhaust gas. When the linear O ₂ sensor 18 is normal or substantially normal and the wiggling disturbance is added, the output b is as shown by the solid line in FIG. 15, and the output of the linear O ₂ sensor 18 increases as the degree of deterioration increases. b is shifted in the direction indicated by the phantom line in FIG.

Next, in step Z6, the CPU 30 obtains a value obtained by differentiating the output b of the linear O ₂ sensor 18, that is, a differential value c (see FIG. 15) by calculation.

Next, in step Z7, the CPU 30 obtains an area S that is equal to or greater than a predetermined threshold th in the above-described differential value c by calculation. As shown in FIG. 15, when the linear O ₂ sensor 18 is normal or substantially normal, the area S described above becomes large, and the area S decreases as the degree of deterioration of the linear O ₂ sensor 18 increases.

  Next, in step Z8, for the purpose of improving the reliability of the determination, the CPU 30 determines whether the number of samples of the area S when the rich disturbance is given and the number of samples of the area S when the lean disturbance is given (for example, 5). 10 times), when the determination is NO, the process returns to step Z1 and repeats the flowchart, while when the determination is YES, the process proceeds to the next step Z9.

  The time chart shown in FIG. 15 shows the area S where the differential value c is equal to or greater than the threshold value th on the plus side when lean disturbance (subtraction of fuel injection amount) is given. (Addition of amount) is given, the time constant deterioration can be detected or determined using the area S where the differential value c is equal to or less than the negative threshold value th.

  In step Z9, the CPU 30 calculates the average value of the plurality of rich-side areas S that have reached the predetermined number of samples, and calculates the average value of the plurality of lean-side areas S that have reached the predetermined number of samples.

  Next, in step Z10, the CPU 30 has an absolute value greater than a predetermined value obtained by subtracting the lean side area SL (more specifically, the average value of the lean side area) from the rich side area SR (more specifically, the average value of the rich side area). If NO is determined, the process proceeds to step Z11. If YES is determined, the process proceeds to another step Z12.

  In this step Z12, the CPU 30 determines whether or not the rich side area SR is smaller than a predetermined value. When YES is determined, the process proceeds to step Z13, and when NO is determined, the process proceeds to another step Z14.

In step Z13 described above, the CPU 30 determines that the rich side area SR is degraded, that is, the rich side time constant is degraded, corresponding to SR <predetermined value.
On the other hand, in step Z14, the CPU 30 determines whether or not the lean side area SL is smaller than a predetermined value. When YES is determined, the process proceeds to step Z15, and when NO is determined, the process proceeds to another step Z16.

In step Z15 described above, the CPU 30 determines that the lean area SL is deteriorated (lean time constant deterioration) corresponding to SL <predetermined value.
In step Z16 described above, the CPU 30 determines that both the rich side area SR and the lean side area SL are normal.

  On the other hand, in step Z11 described above, the CPU 30 adds a value obtained by adding the rich side area SR (specifically, the average value of the rich side area) and the lean side area SL (specifically, the average value of the lean side area) to be greater than a predetermined value. When the determination is NO, the process proceeds to step Z16. When the determination is YES, the process proceeds to another step Z17.

  In step Z16, the CPU 30 determines that both the rich side area SR and the lean side area SL are normal. In step Z17, the CPU 30 determines that the rich side area corresponds to SR + SL <predetermined value. It is determined that both the SR and the lean area SL (in other words, the time constants on both sides) are deteriorated.

  As described above, in the embodiments shown in FIGS. 14 and 15, the deterioration determining means (see routine R5) is set to the area S of the output (see the differential value c) obtained by the differentiating means (see step Z6). Based on this, the time constant deterioration is detected.

Here, the area S of the differential value c of the linear O ₂ sensor 18 becomes smaller as the sensor 18 deteriorates.

According to this configuration, since the time constant deterioration is determined based on the area S of the differential value c described above, it is not affected by the steady fluctuation of the air-fuel ratio, and corresponds to the degree of deterioration when a disturbance is given. Area S is obtained. For this reason, the time constant deterioration of the linear O ₂ sensor 18 can be accurately detected.
In the embodiment shown in FIGS. 14 and 15, the other operations and effects are almost the same as those in the previous embodiment.

In the correspondence between the configuration of the present invention and the above-described embodiment,
The linear air-fuel ratio sensor of the present invention corresponds to the linear O ₂ sensor 18 of the embodiment,
Similarly,
The air-fuel ratio control means corresponds to the air-fuel ratio feedback control means (see CPU 30),
The air-fuel ratio changing means corresponds to the air-fuel ratio forcibly changing means (see steps Q3, Q4, U3, U4, X3, X4, Y3, Y4, Z3, Z4),
The differentiating means corresponds to each step Q6, U6, X6, Y6, Z6 under the control of the CPU 30,
The deterioration determination means corresponds to each routine R1, R2, R3, R4, R5,
The present invention is not limited to the configuration of the above-described embodiment.

The system diagram of the engine provided with the linear air fuel ratio sensor. The control circuit block diagram which shows the deterioration detection apparatus of a linear air fuel ratio sensor. The flowchart which shows a deterioration detection process. The time chart which shows a deterioration detection process. Explanatory drawing which shows the addition state of a disturbance. Time chart when rich disturbance is added. Explanatory drawing showing the measurement results of the linear air-fuel ratio sensor output and its differential value when lean disturbance is added by an actual vehicle Flowchart showing another embodiment of deterioration detection processing Time chart showing another embodiment of deterioration detection processing Flowchart showing still another embodiment of deterioration detection processing Time chart showing still another embodiment of deterioration detection processing Flowchart showing still another embodiment of deterioration detection processing Time chart showing still another embodiment of deterioration detection processing Flowchart showing still another embodiment of deterioration detection processing Time chart showing still another embodiment of deterioration detection processing

Explanation of symbols

11 ... engine 18 ... linear _{O 2} sensor (linear air-fuel ratio sensor)
30: Air-fuel ratio feedback control means (air-fuel ratio control means)
Q3, Q4 ... Air-fuel ratio forced change means (air-fuel ratio change means)
U3, U4 ... Air-fuel ratio forced change means (air-fuel ratio change means)
X3, X4 ... Air-fuel ratio forced change means (air-fuel ratio change means)
Y3, Y4 ... Air-fuel ratio forced change means (air-fuel ratio change means)
Z3, Z4: Air-fuel ratio forced change means (air-fuel ratio change means)
Q6, U6, X6, Y6, Z6 ... Differentiation means R1, R2, R3, R4, R5 ... Degradation judgment means

Claims (8)

A linear air-fuel ratio sensor that is provided in the exhaust system of the engine and outputs a value proportional to the oxygen concentration in the exhaust gas;
Air-fuel ratio control means for feeding back the air-fuel ratio of the air-fuel mixture supplied to the engine to the target air-fuel ratio based on the detection value of the linear air-fuel ratio sensor,
An air-fuel ratio changing means for forcibly changing the air-fuel ratio;
Differentiating means for differentiating the output value of the linear air-fuel ratio sensor after the air-fuel ratio change,
A deterioration detection device for a linear air-fuel ratio sensor, comprising: deterioration determination means for determining time constant deterioration of the linear air-fuel ratio sensor based on a value obtained by the differentiating means. The linear air-fuel ratio sensor deterioration detecting apparatus according to claim 1, wherein the deterioration determining means detects time constant deterioration based on the peak value of the output obtained by the differentiating means. 2. The linear air-fuel ratio sensor according to claim 1, wherein the deterioration determining means detects time constant deterioration based on a time from when the output obtained by the differentiating means starts to change and reaches a peak value until it becomes zero thereafter. Deterioration detection device. The deterioration determining means is based on the time between the time when the output obtained by the differentiating means starts to change and exceeds a predetermined threshold, and then the time when the output decreases and reaches the predetermined threshold. The deterioration detection device for a linear air-fuel ratio sensor according to claim 1, wherein the deterioration of the time constant is detected. 2. The linear air-fuel ratio according to claim 1, wherein the deterioration determining means detects time constant deterioration based on a time from when the disturbance is forcibly changed to when the output obtained by the differentiating means reaches a peak value. Sensor deterioration detection device. 2. The deterioration detection device for a linear air-fuel ratio sensor according to claim 1, wherein the deterioration determining means detects time constant deterioration based on an output area obtained by the differentiating means. The deterioration determination means is configured to switch the change of the air-fuel ratio from rich to lean and from lean to rich,
The linear air-fuel ratio sensor deterioration detection device according to any one of claims 1 to 6, wherein the deterioration determination means detects one-side time constant deterioration of the linear air-fuel ratio sensor based on an output obtained by the differentiation means. 8. The deterioration detection device for a linear air-fuel ratio sensor according to claim 1, wherein the air-fuel ratio changing means is configured to alternately change the air-fuel ratio between rich and lean when detecting deterioration.

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