JPH07305623A - Catalyst deterioration diagnostic device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improved diagnostic precision of catalyst deterioration by restraining wrong diagnosis. CONSTITUTION:This device is provided with an upstream air-fuel ratio sensor 50 and a downstream air-fuel ratio sensor 51 respectively arranged upstream and downstream of catalyst interposed in an exhaust passage, and means 52 for judging operating conditions of engine. It is provided with frequency calculating means 56 for calculating each signal frequency of the upstream air-fuel ratio sensor 50 and the downstream air-fuel ratio sensor 51, a means 57 for conducting a filter process of the signal of the downstream air-fuel ratio sensor 51 based on the signal frequency of the upstream air-fuel ratio sensor 50 when a judging result of the engine operating conditions is within a specified catalyst deterioration diagnostic region, and an amplitude ratio calculating means 58 for calculating an amplitude ratio between the filter-processed signal of the downstream air-fuel ratio sensor 51 and the signal of the upstream air-fuel ratio sensor 50. It is also provided with a means 59 for calculating a threshold value of the amplitude ratio in accordance with a judging result of the engine operating conditions, and a deterioration judging means 60 for judging deterioration of the catalyst based on comparison result of the amplitude ratio and the threshold value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an apparatus for diagnosing a deteriorated state of a catalyst for purifying exhaust gas of an internal combustion engine.

[0002]

As a device for cleaning the exhaust gas of an internal combustion engine, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio on the basis of the output of an air-fuel ratio sensor such as an oxygen sensor, and HC and CO are oxidized in the exhaust passage. Those equipped with a three-way catalyst that simultaneously reduces NOx have been widely put into practical use.

When the performance of the three-way catalyst is deteriorated, the conversion efficiency is gradually reduced, and exhaust purification is hindered. It is desirable to take measures such as replacing the catalyst whose performance has deteriorated. Therefore, in order to determine such a deteriorated state of the catalyst, a device such as that proposed in Japanese Patent Laid-Open No. 3-57862 has heretofore been known. Has been.

This is because an oxygen sensor is provided on each of the upstream side and the downstream side of the catalyst interposed in the exhaust passage of the internal combustion engine,
The air-fuel ratio feedback control is executed mainly by using the output signal of the upstream oxygen sensor, and the deterioration of the catalyst is diagnosed by comparing the output signals of both sensors.

That is, during the execution of the air-fuel ratio feedback control, the fuel supply amount is controlled mainly by the pseudo proportional-plus-integral control based on the output signal of the upstream oxygen sensor, and the actual air-fuel ratio is the theoretical air-fuel ratio. The output signal of the upstream oxygen sensor is periodically rich and lean as shown in FIG. 21 (a), and the oxidation and reduction functions of the three-way catalyst are maximized. Maintained at.

On the other hand, in the air-fuel ratio of the exhaust gas that has passed through the catalyst, oxygen is stored by the action of the catalyst, so that the fluctuation of the residual oxygen concentration in the exhaust gas becomes very gentle.
As shown in FIG. 21B, the output signal of the downstream oxygen sensor has a smaller number of inversions and a longer cycle than the output signal of the upstream oxygen sensor.

When the oxygen storage capacity decreases due to the deterioration of the catalyst, the oxygen concentrations in the exhaust gas on the upstream side and the downstream side of the catalyst do not change so much, and the output signal of the downstream side oxygen sensor is shown in FIG. 21 (d). In this way, while repeating the inversion at a cycle close to the output signal of the upstream oxygen sensor,
The number of inversions also increases.

Therefore, the upstream oxygen sensor rich,
The ratio between the lean inversion number and the downstream oxygen sensor rich / lean inversion number is obtained, and when the inversion number ratio becomes equal to or more than a predetermined value, it is determined that the catalyst has deteriorated.

As a catalyst deterioration diagnosing device of this type, as disclosed in Japanese Patent Laid-Open No. 60-231155,
A device for determining deterioration of a catalyst when the amplitude of an output signal of a downstream oxygen sensor exceeds a predetermined value, and JP-A-3-286.
As disclosed in Japanese Unexamined Patent Publication No. 160-160, in an apparatus for diagnosing deterioration of a catalyst by comparing outputs of oxygen sensors arranged on the upstream side and the downstream side of the catalyst, the oxygen of the oxygen is monitored by monitoring the output of the upstream oxygen sensor. It is known that, when the responsiveness of the sensor decreases, the deterioration diagnosis of the catalyst is interrupted to prevent erroneous diagnosis.

[0010]

By the way, during execution of the air-fuel ratio feedback control, in addition to the air-fuel ratio fluctuating with a preset amplitude, the base air-fuel ratio, which is the median value of this amplitude, also drives the internal combustion engine. Since the output signal of the upstream oxygen sensor fluctuates according to the conditions, as shown in (a) of FIG. 21, the output signal of the upstream side oxygen sensor reverses between rich and lean at a predetermined cycle with the stoichiometric air-fuel ratio as a boundary, and by this air-fuel ratio feedback. The signal including the control frequency becomes a high frequency of 1 to 2 Hz (here, 1 Hz or higher is a high frequency and 1 Hz is a low frequency. The same applies below), and the base air-fuel ratio is shifted to the rich or lean side according to the operating conditions of the internal combustion engine. The frequency associated with the deviation from the stoichiometric air-fuel ratio appears as a low frequency of, for example, about 0.1 Hz. While the catalyst is normal, the control frequency is absorbed by the oxygen storage function of the catalyst, and as shown in FIG. 21 (b), only the frequency associated with the deviation from the stoichiometric air-fuel ratio is detected in the output signal of the downstream oxygen sensor. As the degree of deterioration of the catalyst increases, the control frequency is added to the output signal of the downstream oxygen sensor to increase the amplitude, as shown in (c) and (d) of FIG.

However, in the above-mentioned conventional apparatus, since the output signal of the downstream oxygen sensor includes the frequency associated with the deviation from the stoichiometric air-fuel ratio due to the shift of the base air-fuel ratio, the deterioration of the catalyst is judged. In addition to the control frequency of the air-fuel ratio feedback, the frequency associated with the shift of the base air-fuel ratio is added. In some cases, the reversal period or the number of times of reversal was calculated and the catalyst was erroneously diagnosed as deteriorated.

Therefore, the present invention has been made in view of the above problems, and suppresses the influence of the frequency due to the shift of the base air-fuel ratio included in the downstream oxygen sensor to accurately diagnose the deterioration of the catalyst. An object is to provide a catalyst deterioration diagnosis device for an engine.

[0013]

As shown in FIG. 1, a first aspect of the present invention is directed to a catalyst interposed in an exhaust passage, an upstream air-fuel ratio sensor 50 disposed upstream of the catalyst, and a catalyst. A downstream side air-fuel ratio sensor 51 arranged downstream, a means 52 for determining an engine operating condition, and a basic injection amount setting means 53 for setting a basic fuel injection amount according to the result of the engine operating condition determination.
And a correction coefficient calculation means 54 for calculating the feedback correction coefficient α based on the signal from the upstream air-fuel ratio sensor 50,
In an internal combustion engine including a fuel injection amount correction means 55 that corrects the basic fuel injection amount according to the feedback correction coefficient α, when the determination result of the engine operating condition is in a predetermined catalyst deterioration diagnosis region, Frequency calculating means 56 for calculating the frequencies of the signals from the upstream side air-fuel ratio sensor 50 and the downstream side air-fuel ratio sensor 51, respectively, and the signal from the downstream side air-fuel ratio sensor 51 to the upstream side air-fuel ratio sensor 50.
Means 57 for filtering based on the signal frequency of
Amplitude ratio calculation means 58 for calculating the ratio of the amplitudes of the filtered signals of the downstream side air-fuel ratio sensor 51 and the signals of the upstream side air-fuel ratio sensor 50, and the engine operating condition determination means 52.
Means 59 for calculating the threshold value of the amplitude ratio in accordance with the result of the judgment, and deterioration judging means 60 for judging the deterioration of the catalyst based on the result of the comparison between the amplitude ratio and the threshold value.

The second invention, as shown in FIG.
A catalyst installed in the exhaust passage, an upstream air-fuel ratio sensor 50 arranged upstream of the catalyst, a downstream air-fuel ratio sensor 51 arranged downstream of the catalyst, and means for determining the operating condition of the engine. 52, a basic injection amount setting means 53 for setting a basic fuel injection amount according to the determination result of the engine operating condition, and a correction coefficient calculating means for calculating a feedback correction coefficient α based on a signal from the upstream air-fuel ratio sensor 50. 54 and a fuel injection amount correction means 55 that corrects the basic fuel injection amount according to the feedback correction coefficient α, in the internal combustion engine, the determination result of the engine operating condition determination means 52 is a predetermined catalyst deterioration diagnosis. Frequency calculating means 56 for calculating the frequencies of the signals from the upstream side air-fuel ratio sensor 50 and the downstream side air-fuel ratio sensor 51, respectively, and the downstream side air-fuel ratio sensor 51. Signal of the upstream side air-fuel ratio sensor 5
Means 57 for filtering based on a signal frequency of zero
And means 61 for calculating the number of inversions by comparing the filtered signal of the downstream side air-fuel ratio sensor 51 and the filtered signal of the upstream side air-fuel ratio sensor 50 with a predetermined threshold value, respectively.
Inversion number ratio calculation means 62 for calculating the ratio of the number of inversions of the signal of the upstream side air-fuel ratio sensor 50 and the signal of the filtered downstream side air-fuel ratio sensor 51, and according to the determination result of the engine operating condition. Means 59 for calculating the threshold value of the inversion number ratio, and deterioration determination means 6 for determining deterioration of the catalyst based on the comparison result of the inversion number ratio and the threshold value.
With 0 and.

The third invention, as shown in FIG.
A catalyst installed in the exhaust passage, an upstream air-fuel ratio sensor 50 arranged upstream of the catalyst, a downstream air-fuel ratio sensor 51 arranged downstream of the catalyst, and means for determining the operating condition of the engine. 52, a means 57 for filtering the signal of the downstream side air-fuel ratio sensor 51 based on the signal of the upstream side air-fuel ratio sensor 50, the amplitude of the filtered signal of the downstream side air-fuel ratio sensor 51 and the upstream side air-fuel ratio. Amplitude ratio calculating means 58 for calculating a ratio with the amplitude of the signal of the fuel ratio sensor 50, and a comparison result of the amplitude ratio and a predetermined reference value when the engine operating condition determination result is a predetermined catalyst deterioration diagnosis region. Deterioration determination means 60 for determining the deterioration of the catalyst based on the above.

The fourth invention is, as shown in FIG.
A catalyst installed in the exhaust passage, an upstream air-fuel ratio sensor 50 arranged upstream of the catalyst, a downstream air-fuel ratio sensor 51 arranged downstream of the catalyst, and means for determining the operating condition of the engine. 52, a means 57 for filtering the signal of the downstream side air-fuel ratio sensor 51 based on the signal of the upstream side air-fuel ratio sensor 50, a signal of the filtered downstream side air-fuel ratio sensor 51 and an upstream side air-fuel ratio sensor Means 6 for calculating the number of inversions by comparing each of the 50 signals with a predetermined threshold value
1, a means 62 for calculating the ratio of the number of inversions of the signal of the upstream side air-fuel ratio sensor 51 and the filtered signal of the downstream side air-fuel ratio sensor 51, and the result of the determination of the engine operating condition is a predetermined catalyst deterioration. A deterioration determination unit 60 that determines the deterioration of the catalyst based on the result of comparison between the inversion frequency ratio and a predetermined reference value in the diagnostic region is provided.

A fifth aspect of the present invention is the first to fourth aspects of the invention.
In any one of the above inventions, the filter processing means 57 allows a signal having a frequency equal to or higher than the signal frequency of the upstream side air-fuel ratio sensor 50 among the signals of the downstream side air-fuel ratio sensor 51 to pass.

The sixth aspect of the invention is as shown in FIG.
A catalyst installed in the exhaust passage, an upstream air-fuel ratio sensor 50 arranged upstream of the catalyst, a downstream air-fuel ratio sensor 51 arranged downstream of the catalyst, and means for determining the operating condition of the engine. 52, a basic injection amount setting means 53 for setting a basic fuel injection amount based on the determination result of the engine operating condition, and a correction coefficient calculating means 54 for calculating a feedback correction coefficient based on a signal from the upstream air-fuel ratio sensor 50. And a fuel injection amount correction means 55 for correcting the basic fuel injection amount according to the feedback correction coefficient, in an internal combustion engine, means 63 for calculating the amplitude of the feedback correction coefficient, and the downstream side air-fuel ratio. Means 57 for filtering the signal of the sensor 51 based on the amplitude of the feedback correction coefficient, and the signal of the downstream side air-fuel ratio sensor 51 that has been filtered. Amplitude ratio calculating means 58 for calculating a ratio between the width and the amplitude of the signal of the upstream air-fuel ratio sensor 50 or the amplitude of the feedback correction coefficient, and the amplitude when the engine operating condition is in a predetermined catalyst deterioration diagnosis region. Deterioration determination means 60 for determining the deterioration of the catalyst based on the comparison result of the ratio and a predetermined reference value.

The seventh invention, as shown in FIG.
A catalyst installed in the exhaust passage, an upstream air-fuel ratio sensor 50 arranged upstream of the catalyst, a downstream air-fuel ratio sensor 51 arranged downstream of the catalyst, and means for determining the operating condition of the engine. 52, a basic injection amount setting means 53 for setting a basic fuel injection amount based on the determination result of the engine operating condition, and a correction coefficient calculating means 54 for calculating a feedback correction coefficient based on a signal from the upstream air-fuel ratio sensor. In an internal combustion engine including a fuel injection amount correction means 55 that corrects the basic fuel injection amount according to the feedback correction coefficient, a means 61 that calculates the number of times the feedback correction coefficient is inverted, and the downstream side air-fuel ratio. Means 57 for filtering the signal of the sensor 51 based on the number of times the feedback correction coefficient is inverted, and the signal of the downstream side air-fuel ratio sensor 51 that has been filtered. Inversion frequency ratio calculating means for calculating a ratio of the number of inversions inversion frequency or the feedback correction coefficient of inversion frequency signal of the upstream air-fuel ratio sensor 50 of 6
2 and deterioration determination means 60 for determining the deterioration of the catalyst based on the result of comparison between the inversion frequency ratio and a predetermined reference value when the engine operating condition is in a predetermined catalyst deterioration diagnosis region.

The eighth aspect of the invention, as shown in FIG.
A catalyst installed in the exhaust passage, an upstream air-fuel ratio sensor 50 arranged upstream of the catalyst, a downstream air-fuel ratio sensor 51 arranged downstream of the catalyst, and means for determining the operating condition of the engine. 52, a basic injection amount setting means 53 for setting a basic fuel injection amount based on the determination result of the engine operating condition, and a correction coefficient calculating means 54 for calculating a feedback correction coefficient based on a signal from the upstream air-fuel ratio sensor 50. And a fuel injection amount correction means 55 for correcting the basic fuel injection amount according to the feedback correction coefficient, an ordinary air-fuel ratio feedback control frequency f ₀ is calculated based on the engine operating condition. Control frequency calculation means 6
4 and FFT processing means 65 for filtering the signal of the downstream side air-fuel ratio sensor 51 by fast Fourier transform.
And an intensity calculation means 66 for calculating the intensity D of the air-fuel ratio feedback control frequency component at the normal air-fuel ratio feedback control frequency f ₀ of the signal of the downstream side air-fuel ratio sensor 50 subjected to the FFT process, and the engine operating condition is predetermined. In the catalyst deterioration diagnosis region, the deterioration determining means 60 is provided for comparing the intensity D with a preset intensity slice level to determine catalyst deterioration.

[0021]

According to the first aspect of the present invention, the frequencies of the output of the upstream side air-fuel ratio sensor and the frequency of the output of the downstream side air-fuel ratio sensor are respectively calculated in the catalyst deterioration diagnosis area where the operation condition determination result is predetermined.
The output of the downstream side air-fuel ratio sensor is filtered based on the frequency of the upstream side air-fuel ratio sensor, and the control frequency of the air-fuel ratio feedback included in the output of the downstream side air-fuel ratio sensor is extracted. The ratio of the amplitude of the output of the downstream side air-fuel ratio sensor and the amplitude of the control frequency included in the output of the upstream side air-fuel ratio sensor, where the frequency associated with the deviation from the theoretical air-fuel ratio is removed by filtering to extract only the control frequency. Since the deterioration of the catalyst is determined based on the result of comparison with the threshold value calculated according to the operating condition, the deterioration of the catalyst can be accurately diagnosed.

In the second aspect of the invention, the frequencies of the output of the upstream side air-fuel ratio sensor and the frequency of the output of the downstream side air-fuel ratio sensor are respectively calculated in the catalyst deterioration diagnosis region where the operation condition judgment result is a predetermined value, and the downstream side air-fuel ratio sensor is calculated. The output of the fuel ratio sensor is filtered based on the frequency of the upstream air-fuel ratio sensor, and the control frequency of the air-fuel ratio feedback included in the output of the downstream air-fuel ratio sensor is extracted. The number of reversals of the output of the downstream air-fuel ratio sensor and the number of reversals of the control frequency included in the output of the upstream side air-fuel ratio sensor, where the control process removes the frequency associated with the deviation from the theoretical air-fuel ratio and extracts only the control frequency. Since the deterioration of the catalyst is determined based on the result of comparing the ratio of 1 with the threshold value calculated according to the operating condition, the deterioration of the catalyst can be accurately diagnosed.

According to a third aspect of the invention, the output of the downstream side air-fuel ratio sensor is filtered based on the output of the upstream side air-fuel ratio sensor in the catalyst deterioration diagnosis region where the operating condition determination result is predetermined, and the downstream side The control frequency of the air-fuel ratio feedback included in the output of the air-fuel ratio sensor is extracted. The ratio of the amplitude of the output of the downstream side air-fuel ratio sensor and the amplitude of the control frequency included in the output of the upstream side air-fuel ratio sensor, where the frequency associated with the deviation from the theoretical air-fuel ratio is removed by filtering to extract only the control frequency. Since the deterioration of the catalyst is determined based on the result of comparison with the reference value set in advance according to the operating condition, the deterioration of the catalyst can be accurately diagnosed.

Further, in a fourth aspect of the present invention, in the catalyst deterioration diagnosis region where the operation condition determination result is predetermined, the output of the downstream side air-fuel ratio sensor is filtered based on the output of the upstream side air-fuel ratio sensor, and the downstream side The control frequency of the air-fuel ratio feedback included in the output of the air-fuel ratio sensor is extracted. The number of reversals of the output of the downstream air-fuel ratio sensor and the number of reversals of the control frequency included in the output of the upstream side air-fuel ratio sensor, where the control process removes the frequency associated with the deviation from the theoretical air-fuel ratio and extracts only the control frequency. Since the deterioration of the catalyst is determined based on the result of comparing the ratio of 1 with a reference value set in advance according to the operating condition, the deterioration of the catalyst can be accurately diagnosed.

According to a fifth aspect of the present invention, the filter processing means allows a component of the output of the downstream side air-fuel ratio sensor that is equal to or higher than the frequency of the upstream side air-fuel ratio sensor to pass therethrough and is included in the output of the downstream side air-fuel ratio sensor. The low frequency due to the deviation from the fuel ratio is removed because it is lower than the control frequency of the air-fuel ratio feedback of the output of the upstream side air-fuel ratio sensor, and the deterioration diagnosis of the catalyst is accurately diagnosed based on the control frequency of the air-fuel ratio feedback. be able to.

In a sixth aspect of the present invention, the output of the downstream side air-fuel ratio sensor is filtered on the basis of the amplitude of the feedback correction coefficient in the catalyst deterioration diagnosis region where the operation condition determination result is predetermined, and the downstream side air-fuel ratio is obtained. The control frequency of the air-fuel ratio feedback included in the output of the sensor is extracted. The amplitude of the output of the downstream side air-fuel ratio sensor, which has been filtered to remove the frequency associated with the deviation from the theoretical air-fuel ratio, and extracted only the control frequency, and the control frequency or feedback correction coefficient included in the output of the upstream side air-fuel ratio sensor. Since the deterioration of the catalyst is determined based on the result of comparing the amplitude ratio of the above with a reference value set in advance according to the operating conditions, the deterioration of the catalyst can be accurately diagnosed.

In a seventh aspect of the present invention, the output of the downstream side air-fuel ratio sensor is filtered based on the number of inversions of the feedback correction coefficient in the catalyst deterioration diagnosis region where the operation condition determination result is predetermined, and the downstream side air-fuel ratio sensor The control frequency of the air-fuel ratio feedback included in the output of the fuel ratio sensor is extracted.
The number of reversals of the output of the downstream side air-fuel ratio sensor in which only the control frequency is extracted by removing the frequency associated with the deviation from the theoretical air-fuel ratio by filtering and the control frequency or feedback correction included in the output of the upstream side air-fuel ratio sensor Since the deterioration of the catalyst is determined based on the result of comparing the ratio of the number of times of inversion of the coefficient with the threshold value calculated according to the operating condition, the deterioration of the catalyst can be accurately diagnosed.

Further, in the eighth aspect of the present invention, in the catalyst deterioration diagnosis region in which the operation condition determination result is predetermined, the output of the downstream side air-fuel ratio sensor is subjected to the air-fuel ratio feedback by the filter processing by the fast Fourier transform (hereinafter, FFT processing). While extracting the control frequency, the control frequency f ₀ of the normal air-fuel ratio feedback is calculated from the engine operating condition, and the strength of the air-fuel ratio feedback control frequency after the FFT processing at the normal air-fuel ratio feedback control frequency f ₀ is calculated. The low-frequency component due to the deviation from the theoretical air-fuel ratio and the air-fuel ratio feedback control frequency are reliably separated, and the strength of the calculated air-fuel ratio feedback control frequency component is compared with the preset intensity slice level to make a false diagnosis. The deterioration of the catalyst can be accurately diagnosed by suppressing the above.

[0029]

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

As shown in FIG. 8, a catalytic converter 13 composed of a three-way catalyst is provided in the exhaust passage 2 of the engine 1, and an upstream oxygen sensor as an air-fuel ratio sensor is provided upstream of the catalytic converter 13. 14 and a downstream oxygen sensor 15 are also provided downstream.

Both the upstream oxygen sensor 14 and the downstream oxygen sensor 15 generate an electromotive force according to the residual oxygen concentration in the exhaust gas. Especially, the electromotive force suddenly changes at the theoretical air-fuel ratio, The air-fuel ratio has a high level (about 1 V) on the rich side (hereinafter, rich) and a low level (about 100 mmV) on the lean side.

On the other hand, in the intake passage 3 of the engine 1, a fuel injection valve 17 for supplying fuel to each intake port is provided for each cylinder, and air passing through an air flow meter 18 for detecting an intake air amount Q is supplied. Is throttled by the throttle valve 19 and then flows into each intake port.

Reference numeral 4 denotes a control unit, which is composed of, for example, a microprocessor and the like, so that the fuel supply amount supplied to the intake passage 3 of the engine 1 through the fuel injection valve 17 is basically the theoretical air-fuel ratio. Feedback control.

Therefore, the control unit 4 includes
Signals from a crank angle sensor 19 that detects the engine speed Ne, a water temperature sensor 16 that detects the water temperature of the cooling water, an air flow meter 18, and a vehicle speed sensor 20 are respectively input, and an upstream oxygen sensor 14 and a downstream oxygen sensor. A signal from 15 is input, and the fuel supply amount set to have a predetermined ratio with respect to the intake air amount Q is feedback-controlled based on the output of the upstream oxygen sensor 14, and further the downstream oxygen sensor 15 The fuel injection amount is corrected so that the stoichiometric air-fuel ratio becomes correct based on the output.

The outline of the air-fuel ratio feedback control will be described. First, the basic injection from the fuel injection valve 17 is performed based on the intake air amount Q detected by the air flow meter 18 and the engine speed Ne detected by the crank angle sensor 19. The basic pulse width Tp that determines the amount is calculated by Tp = K × Q / Ne. This basic pulse width Tp is the fuel injection valve 17
The basic pulse width T
Let p be the basic fuel injection amount Tp.

The drive pulse width Ti of the fuel injection valve 17 is determined by adding a correction such as an increase correction or a feedback correction to the basic injection amount Tp, and the drive pulse width Ti is obtained by the following equation.

Ti = Tp × COEF × α + Ts (1) Here, COEF indicates various increase correction coefficients, and includes, for example, water temperature increase correction according to cooling water temperature, air-fuel ratio correction at high speed and high load, and the like. Further, Ts is a voltage correction coefficient added according to the battery voltage in order to correct the dead time of the fuel injection valve 17.

Further, α is a feedback correction coefficient mainly calculated based on the detection signal of the upstream oxygen sensor 14, and compares the output signal of the upstream oxygen sensor 14 with a predetermined slice level corresponding to the theoretical air-fuel ratio. However, this output signal is a value obtained by pseudo-proportional integration based on the inversion to the rich side or the lean side. If this α is 1 or more, to the rich side, if it is less than 1, to the lean side. Is corrected.

For example, from the upstream oxygen sensor 14 to FIG.
When an output signal as shown in (a) is detected, the corresponding feedback correction coefficient α changes as shown in FIG. 22 (b). As described above, the feedback correction coefficient α is obtained by pseudo proportional integration. When the feedback correction coefficient α is inverted from the rich side to the lean side across a predetermined slice level (S / L) of the upstream oxygen sensor 14, the feedback correction coefficient α is corrected. A predetermined proportional amount P _L is added to the coefficient α, and the integral amount is gradually added with a slope of a predetermined integration constant I _L. The feedback correction coefficient α is multiplied by the basic injection amount Tp as described above, and the actual air-fuel ratio gradually increases the concentration.

When the output signal of the upstream oxygen sensor 14 is inverted from the lean side to the rich side, a predetermined proportional amount P _R is subtracted from the feedback correction coefficient α and integration is performed with a slope of a predetermined integration constant I _R. Minutes are gradually subtracted. By repeating such control, the actual air-fuel ratio is maintained near the stoichiometric air-fuel ratio while changing at a high frequency of about 1 to 2 Hz.

When some kind of fuel increase / decrease is performed during the air-fuel ratio control by this feedback, for example, at the time of low water temperature, high speed / high load, or fuel cut during deceleration, the feedback correction coefficient α is fixed to 1. At the same time, it becomes substantially open loop control.

During such air-fuel ratio feedback control, the control unit 4 operates the upstream oxygen sensor 1
4 and a catalyst deterioration diagnosis for determining whether or not the catalytic converter 13 is functioning normally is performed based on the ratio of the output amplitudes of the downstream side oxygen sensor 15. That is, the deterioration of the catalyst is determined based on the ratio of the output amplitude of the upstream oxygen sensor 14 to the output amplitude of the filtered downstream oxygen sensor 15, and the warning lamp 3 connected to the control unit 4 is determined.
0 is turned on according to the determination result.

The catalyst deterioration diagnosis control operation by this filter processing will be described with reference to the flowcharts of FIGS. 9 and 10. This measurement control operation is performed, for example, at every predetermined time during the air-fuel ratio feedback control,
Specifically, it is executed by timer interrupt processing of the microprocessor.

First, in step S1, the upstream oxygen sensor 1
4 and the output of the downstream oxygen sensor 15 are read respectively, and in step S2, the control frequency associated with the air-fuel ratio feedback control included in the output of the upstream oxygen sensor 14 is calculated.

Next, in step S3, the output of the downstream oxygen sensor 15 is filtered at this control frequency,
The low-frequency component accompanying the shift of the base air-fuel ratio included in the output of the downstream oxygen sensor 15 is removed.

To remove low frequency components, the filtered signal is Z [K] and the downstream oxygen sensor 15 signal is X.
[K], the low frequency component removed by the filter processing is Y
[K] is set and processing is performed based on the following equation.

Z [K] = X [K] -Y [K] = X [K]-(X [K] + X [K-1] + X [K-
2]) / 3 = X [K] -X [K] * KY- [K-1] * (1-
The differentiation process represented by K) may be performed. Here, the number of moving average data and the weighted average coefficient K are appropriately set according to the frequency of the low frequency component to be removed.

After calculating the amplitude V ₁ of the output of the upstream oxygen sensor 14 and the amplitude V ₂ of the output of the downstream oxygen sensor 15 from which low frequency components have been removed, the ratio V ₂ / V of these amplitudes is calculated.
₁ is calculated (steps S4 and S5).

A bandpass filter that passes only a frequency higher than the control frequency constituting the signal of the upstream oxygen sensor 14 among the output signals of the downstream oxygen sensor 15 is interposed between the downstream oxygen sensor 15 and the control unit 4. Alternatively, if the catalytic converter 13 is in a normal state as a result of being filtered by software or hardware in this way, it is included in the output of the downstream oxygen sensor 15 as shown in FIG. The low frequency of about 0.1 Hz is filtered by the air-fuel ratio feedback control frequency including the high frequency of 1 to 2 Hz.
As shown in FIG. 11B, the low frequency components are cut off, and when the deterioration of the catalytic converter 13 progresses, FIG.
As shown in (c) and (d), only the amplitudes V ₂ and V ₂ ′ of the high frequency component of the output of the downstream side oxygen sensor 15 after the filter processing increase in accordance with the degree of deterioration. The amplitude ratio V ₂ / V ₁ increases.

In this way, the deterioration diagnosis process after step S6 shown in FIG. 10 is performed based on the amplitude ratio V ₂ / V ₁ calculated during the air-fuel ratio feedback control.

This deterioration diagnosis process is performed by the crank angle sensor 1
9. When the sensor output of the vehicle speed sensor 20 or the like is read and the operating condition of the internal combustion engine is within a predetermined catalyst deterioration diagnosis region, for example, 1. Vehicle speed V _SP is within the specified range 2. The engine speed Ne is within a predetermined range 3. The judgment is made based on a preset condition such as the engine load being below a predetermined value (step S
6, S7). The engine load is the control unit 4
It is possible to substitute the basic injection amount Tp calculated in.

If the above conditions are met, step S
8 Search map set in advance the slice level S / L to be compared with the amplitude ratio V ₂ / V ₁ obtained in step S5.

This slice level S / L is preset according to the intake air amount as shown in FIG. 12, and FIG. 12 shows the preset intake air amount categories for simplifying the calculation. Accordingly, the slice level S / L is set stepwise, and the slice level S / L corresponding to the intake air amount calculated from the output of the air flow meter 18 or the crank angle sensor 19 is read.

Thus, the read slice level S /
L is compared with the amplitude ratio V ₂ / V ₁ (step S
9) If the amplitude ratio V ₂ / V ₁ is less than the slice level S / L, the process proceeds to step S10 and the catalytic converter 13
On the other hand, when the amplitude ratio V ₂ / V ₁ is equal to or higher than the slice level S / L, it is determined that the catalytic converter 13 has deteriorated beyond the allowable range, and the warning lamp 30 To turn on and let the driver catalytic converter 1
The deterioration of 3 is displayed.

With the above construction, and the overall operation will be described below, by filtering the output of the downstream oxygen sensor 15 read during the air-fuel ratio feedback control with the output frequency of the upstream oxygen sensor 14, Since the low-frequency component accompanying the fluctuation of the base air-fuel ratio is removed from the output signal of the downstream oxygen sensor 15, the amplitude ratio V ₂ / V ₁ calculated in step S5 is included in the output signal of the downstream oxygen sensor 15. It is possible to accurately indicate the magnitude of the control frequency of the air-fuel ratio feedback, and it is possible to easily detect the degree of decrease in the oxygen storage capacity of the catalytic converter 13 from the increase in the amplitude ratio V ₂ / V ₁ .

Then, the degree of deterioration of the catalytic converter 13 is determined by comparing the intake air amount of the engine 1, that is, the slice level S / L preset according to the operating condition of the engine 1 and the amplitude ratio V ₂ / V _1. Since the determination is made, it becomes possible to perform the deterioration diagnosis of the catalytic converter 13 in a wide range of the operating condition of the engine 1, and suppress the erroneous diagnosis of the catalyst deterioration caused by the variation of the base air-fuel ratio as described above, and perform the diagnosis. The accuracy can be improved.

FIG. 13 and FIG. 14 show the second embodiment, in which the degree of deterioration of the catalytic converter 13 in the first embodiment is detected by the number of reversals of the outputs of the upstream oxygen sensor 14 and the downstream oxygen sensor 15. The process is performed from the ratio T ₂ / T ₁ , and the other structure is the same as that of the first embodiment.
The parts different from the first embodiment will be described in detail below.

In FIG. 13, steps A1 to A3 filter the output of the downstream oxygen sensor 15 with the output frequency of the upstream oxygen sensor 14, as in steps S1 to S3 shown in FIG. From the output of the oxygen sensor 15, the low frequency component associated with the variation of the base air-fuel ratio is removed.

In step A4, the number of inversions of the output of the upstream oxygen sensor 14 and the filtered output of the downstream oxygen sensor 15 is calculated. As shown in FIG. 11, the calculation of the number of times of inversion improves the calculation accuracy by counting the number of times the slice levels S / L-H and S / L-L provided with hysteresis are passed.

The upstream oxygen sensor 14 calculated in this way
The inversion number ratio T ₂ / T ₁ is calculated from the inversion number T ₁ of the output of ₁ and the inversion number T ₂ of the output of the downstream oxygen sensor 15 (step A5).

The deterioration diagnosing process of the catalytic converter 13 is performed when the operating condition of the engine 1 enters a predetermined diagnosing region as in steps S6 and S7, and the reversal number ratio T ₂ / T ₁ is set in the same manner as in step S8. The slice level S / L to be compared with is retrieved from a preset map.

This slice level S / L is the one in which the slice level S / L is set stepwise according to the preset classification of the intake air amount, as in FIG. 12 shown in the first embodiment. The slice level S / L of the reversal frequency ratio corresponding to the intake air amount calculated according to the operating conditions is read.

Thus, the read slice level S /
L is compared with the inversion number ratio T ₂ / T ₁ in step A9. If the inversion number ratio T ₂ / T ₁ is less than the slice level S / L, the process proceeds to step A10 to proceed to the catalytic converter 1
On the other hand, when the inversion number ratio T ₂ / T ₁ is equal to or higher than the slice level S / L, it is determined that the catalytic converter 13 has deteriorated beyond the allowable range and a warning is issued. The light 30 is turned on to call the driver's attention.

In this way, the inversion frequency ratio T calculated based on the output of the downstream oxygen sensor 15 which has been filtered.
_{Even with 2} / T ₁ , it is possible to suppress the influence of the low frequency component due to the fluctuation of the base air-fuel ratio and perform the deterioration diagnosis of the catalytic converter 13 with high accuracy and under a wide range of operating conditions, as in the first embodiment. Therefore, the reliability of deterioration diagnosis can be improved.

FIGS. 15 and 16 show the third embodiment, in which the deterioration of the catalytic converter 13 in the first embodiment is detected and the intensity of the air-fuel ratio feedback control frequency component included in the output of the downstream oxygen sensor 15. The other configuration is the same as that of the first embodiment. The parts different from the first embodiment will be described in detail below.

The flowcharts shown in FIGS. 15 and 16 are as follows.
Similar to the flowcharts shown in FIG. 9 and FIG. 10, it is executed every predetermined time during the air-fuel ratio feedback control.

First, in step B1, the engine speed Ne from the crank angle sensor 19 or the air flow meter 18
The operating condition of the engine 1 is read from the intake air amount Q from, and in step B2, the frequency f ₀ of the normal air-fuel ratio feedback control is calculated from the read current operating condition as a frequency band f ₀ having a predetermined range. .

Normal air-fuel ratio feedback control frequency band f
_{Since 0} is related to the intake air amount Q of the engine 1, as shown in FIG. 17, the normal air-fuel ratio feedback control frequency band f preset according to the range of the intake air amount Q is set.
It is calculated based on the ₀ map.

Next, in step B3, the output of the downstream oxygen sensor 15 is read, and in step B4, this output is subjected to filter processing (hereinafter referred to as FFT processing) by the fast Fourier transform to reduce the output due to fluctuations in the base air-fuel ratio. The high frequency component by air-fuel ratio feedback control is separated from the frequency component.

By this FFT processing, as shown in FIG.
The low-frequency component and the high-frequency air-fuel ratio feedback control frequency due to the fluctuation of the base air-fuel ratio as shown in (d) are separated, and the air-fuel ratio feedback control frequency component is separated as shown in FIGS. 11 (b) to (d). Only is extracted.

In step B5, the intensity in the normal air-fuel ratio feedback control frequency band f ₀ obtained in step B2 among the air-fuel ratio feedback control frequency components of the downstream oxygen sensor 15 extracted by the FFT processing is air-fuel ratio feedback control. It is calculated as the frequency component strength D.

Thus, in steps B1 to B5,
Based on the intensity D of the frequency component of the air-fuel ratio feedback control calculated during the air-fuel ratio feedback control, the catalyst deterioration diagnosis process after step B6 shown in FIG. 16 is performed as follows.

The deterioration diagnosis process of the catalytic converter 13 is performed in steps B6 and B7 in step S of the first embodiment.
6 and S7, the operation is performed when the operating condition of the engine 1 enters a predetermined diagnostic region, and if it is the diagnostic region in step B7, the intensity slice level S / L for determining the deterioration of the catalytic converter 13 is determined in step B8. Calculate

The calculation of the intensity slice level S / L is
As shown in FIG. 18, it is searched from the relationship between the performance of the catalytic converter 13 and the strength D which is preset based on the conversion efficiency and the like, and it is determined that the performance of the catalytic converter 13 has deteriorated (NG in the figure). The intensity of the air-fuel ratio feedback control frequency component is set to intensity slice level S / L.

In step B9, the intensity slice level S / L calculated in step B8 is the same as in step B5.
If the intensity D of the air-fuel ratio feedback control frequency component is less than the intensity slice level, the process proceeds to step B10 to determine that the catalytic converter 13 is normal, while the intensity D calculated in When D is equal to or higher than the slice level S / L, the routine proceeds to step B11, where it is determined that the catalytic converter 13 has deteriorated beyond the allowable range, and the warning light 30 is turned on to call the driver's attention.

Here, when the catalytic converter 13 deteriorates and the high frequency component of the air-fuel ratio feedback control becomes large as shown in FIGS. 11 (a) to 11 (d), the FF
The intensities D of the air-fuel ratio feedback control frequency components calculated by the T process are as shown in FIGS. 19 (a) to 19 (d), respectively.

FIG. 19 (a) shows the intensity D corresponding to the output of the upstream oxygen sensor 14 shown in FIG. 11 (a). The intensity at this time is the largest, while it is shown in FIG. 11 (b). When the catalytic converter 13 is normal, the air-fuel ratio feedback control frequency component does not appear in the downstream oxygen sensor 15, so the intensity D becomes almost 0 as shown in FIG. 19 (b). That is, the intensity D at this time is less than the intensity slice level S / L shown in FIG.

On the other hand, the catalytic converter 13 is deteriorated, and as shown in FIG.
1 (c) and (d), the downstream oxygen sensor 15
When the air-fuel ratio feedback control frequency component in the output of 1 increases, the intensity D in the normal air-fuel ratio feedback control frequency band f ₀ also increases as shown in FIGS. 19 (c) and (d). Therefore, by comparing the intensity D with the intensity slice level S / L, the air-fuel ratio feedback control frequency component can be separated from the low-frequency component due to the fluctuation of the base air-fuel ratio, and the deterioration of the catalytic converter 13 can be accurately determined. Of.

In general, the air-fuel ratio feedback control frequency tends to decrease due to deterioration of the upstream oxygen sensor 14 or fuel transportation delay due to a wall flow phenomenon in which fuel adheres to the intake system of the engine 1, and in this case, the catalytic converter 13
Although the deterioration of itself has not progressed, the downstream oxygen sensor 15
Output follows the air-fuel ratio feedback control frequency irrespective of the deterioration of the catalytic converter 13, as shown in FIGS.

The intensity D of the air-fuel ratio feedback control frequency contained in the output of the downstream oxygen sensor 15 corresponding to FIGS. 20 (a ') to 20 (d') is shown in FIGS.
As shown in (d '), the intensities are substantially equal in the region lower than the normal air-fuel ratio feedback control frequency band f ₀ .

Here, since the normal air-fuel ratio feedback control frequency band f ₀ is obtained from the operating conditions of the engine 1 in steps B1 and B2, the signal subjected to the FFT processing based on the output of the downstream oxygen sensor 15 is empty. Since the intensity D of the fuel ratio feedback control frequency component in the normal air-fuel ratio feedback control frequency band f ₀ is smaller than the intensity slice level S / L shown in FIG. 18, the deterioration of the catalytic converter 13 is not determined, and a false diagnosis is made. It is possible to improve the diagnostic accuracy by preventing the above.

In this way, the air-fuel ratio feedback control frequency extracted from the output of the downstream oxygen sensor 15 by the FFT process is grasped as the intensity D in the normal air-fuel ratio feedback control frequency band f ₀ calculated from the operating condition of the engine 1. In the same manner as in the above embodiment, it is possible to suppress the influence of the low frequency component due to the fluctuation of the base air-fuel ratio and perform the deterioration diagnosis of the catalytic converter 13 with high accuracy and a wide range of operating conditions. It is also possible to prevent erroneous diagnosis due to disturbances such as a failure or a wall flow phenomenon of the intake system, and improve the reliability of deterioration diagnosis.

In the above embodiment, the filtering process in step S4 or A4 is performed on the upstream oxygen sensor 15
Although the band-pass filter processing is performed based on the output frequency of, a high pass filter may be used.

Further, in the above embodiment, the filtering of the output of the downstream side air-fuel ratio sensor 15 may be performed based on the number of times of reversal or the amplitude of the theoretical air-fuel ratio of the feedback correction coefficient α as a threshold value, and the feedback correction Coefficient α
Alternatively, the deterioration of the catalytic converter 13 can be diagnosed based on the ratio between the output of the upstream side air-fuel ratio sensor 14 and the number of reversals or the amplitude of the filtered output of the downstream side air-fuel ratio sensor 15. It is possible to suppress the erroneous diagnosis of the catalyst deterioration due to the change of the air-fuel ratio and improve the diagnosis accuracy.

[0085]

As described above, according to the first aspect of the invention, the catalyst interposed in the exhaust passage, the upstream air-fuel ratio sensor arranged upstream of the catalyst, and the downstream arranged downstream of the catalyst. A side air-fuel ratio sensor, means for determining engine operating conditions, basic injection amount setting means for setting a basic fuel injection amount according to the determination result of the engine operating conditions, and based on a signal from the upstream air-fuel ratio sensor In an internal combustion engine including a correction coefficient calculation unit that calculates a feedback correction coefficient and a fuel injection amount correction unit that corrects the basic fuel injection amount in accordance with the feedback correction coefficient, the engine operating condition determination result is predetermined. Of the signal from the upstream side air-fuel ratio sensor and the frequency of the signal from the downstream side air-fuel ratio sensor, and the signal of the downstream side air-fuel ratio sensor Means for filtering based on the signal frequency of the flow side air-fuel ratio sensor, and an amplitude ratio calculating means for calculating the ratio of the amplitudes of the filtered signal of the downstream side air-fuel ratio sensor and the signal of the upstream side air-fuel ratio sensor, The means for calculating the threshold value of the amplitude ratio according to the determination result of the engine operating condition, and the deterioration determination means for determining the deterioration of the catalyst based on the comparison result of the amplitude ratio and the threshold value, the upstream The control frequency of the air-fuel ratio feedback included in the output of the side air-fuel ratio sensor can be extracted from the output of the downstream side air-fuel ratio sensor, and it becomes possible to accurately detect the degree of catalyst deterioration based on the control frequency. Therefore, it is possible to suppress the erroneous diagnosis and improve the diagnostic accuracy, and compare the ratio of the output of the upstream side air-fuel ratio sensor and the extracted output of the downstream side air-fuel ratio sensor with the threshold value according to the operating conditions. It is can also diagnose the deterioration of exactly catalyst in a wide range of operating conditions.

The second aspect of the present invention includes a catalyst interposed in the exhaust passage, an upstream air-fuel ratio sensor arranged upstream of the catalyst, and a downstream air-fuel ratio sensor arranged downstream of the catalyst. A means for determining the operating condition of the engine, a basic injection amount setting means for setting a basic fuel injection amount according to the determination result of the engine operating condition, and a feedback correction coefficient calculated based on the signal from the upstream air-fuel ratio sensor. In the internal combustion engine including the correction coefficient calculation means for performing the correction, and the fuel injection amount correction means for correcting the basic fuel injection amount in accordance with the feedback correction coefficient α, the engine operating condition determination result is a predetermined catalyst deterioration diagnosis. Frequency calculation means for calculating the frequency of the signal from each of the upstream side air-fuel ratio sensor and the downstream side air-fuel ratio sensor when in a region, and the signal from the downstream side air-fuel ratio sensor to the upstream side air-fuel ratio The means for filtering based on the signal frequency of the sensor and the filtered signal of the downstream side air-fuel ratio sensor and the signal of the upstream side air-fuel ratio sensor are respectively compared with predetermined threshold values to calculate the number of inversions. Means, a reversal number ratio calculating means for calculating a ratio of the number of reversals of the signal of the upstream side air-fuel ratio sensor and the signal of the filtered downstream side air-fuel ratio sensor, and depending on the determination result of the engine operating condition. Included in the output of the upstream side air-fuel ratio sensor is a means for calculating the threshold value of the reversal frequency ratio, and a deterioration determination means for determining deterioration of the catalyst based on the comparison result of the reversal frequency ratio and the threshold value. The control frequency of the air-fuel ratio feedback that is generated can be extracted from the output of the downstream side air-fuel ratio sensor, and it becomes possible to accurately determine the catalyst deterioration based on the control frequency. It is possible to suppress it and improve the diagnostic accuracy.By comparing the ratio of the number of reversals of the output of the upstream side air-fuel ratio sensor and the extracted output of the downstream side air-fuel ratio sensor with the threshold value according to the operating conditions, it is possible to widen the range. It is possible to accurately diagnose deterioration of the catalyst even under operating conditions.

The third aspect of the present invention includes a catalyst provided in the exhaust passage, an upstream air-fuel ratio sensor provided upstream of the catalyst, and a downstream air-fuel ratio sensor provided downstream of the catalyst. , Means for determining the operating condition of the engine, means for filtering the signal of the downstream side air-fuel ratio sensor based on the signal of the upstream side air-fuel ratio sensor, and the amplitude of the signal of the filtered downstream side air-fuel ratio sensor And an amplitude ratio calculating means for calculating a ratio between the amplitude of the signal of the upstream side air-fuel ratio sensor, and the determination result of the engine operating condition is a predetermined catalyst deterioration diagnosis region,
A deterioration determination means for determining deterioration of the catalyst based on a comparison result of the amplitude ratio and a predetermined reference value, and a control frequency of the air-fuel ratio feedback included in the output of the upstream side air-fuel ratio sensor is set to the downstream side air-fuel ratio sensor. Can be extracted from the output, and the deterioration of the catalyst can be accurately determined based on the amplitude ratio, so that erroneous diagnosis can be suppressed and diagnostic accuracy can be improved.

The fourth aspect of the present invention is directed to a catalyst installed in the exhaust passage, an upstream air-fuel ratio sensor arranged upstream of the catalyst, and a downstream air-fuel ratio sensor arranged downstream of the catalyst. , Means for determining the operating conditions of the engine, means for filtering the signal of the downstream side air-fuel ratio sensor based on the signal of the upstream side air-fuel ratio sensor, and the signal and upstream of the filtered downstream side air-fuel ratio sensor Means for calculating the number of times of reversal by comparing the signal of the side air-fuel ratio sensor with a predetermined threshold value, and the number of times of reversal of the signal of the upstream side air-fuel ratio sensor and the signal of the filtered downstream side air-fuel ratio sensor And a means for calculating the ratio of the engine operating condition, and when the determination result of the engine operating condition is in a predetermined catalyst deterioration diagnosis region, the deterioration of the catalyst is determined based on the comparison result of the inversion frequency ratio and a predetermined reference value. Deterioration determination means The control frequency of the air-fuel ratio feedback included in the output of the upstream side air-fuel ratio sensor can be extracted from the output of the downstream side air-fuel ratio sensor, and the deterioration of the catalyst can be accurately determined based on the inversion frequency ratio. Therefore, it is possible to suppress erroneous diagnosis and improve diagnosis accuracy.

The fifth aspect of the present invention is the above-mentioned first to fourth aspects.
In any one of the inventions, the filter processing means allows a signal having a frequency equal to or higher than the signal frequency of the upstream side air-fuel ratio sensor to pass among the signals of the downstream side air-fuel ratio sensor, and is included in the output of the downstream side air-fuel ratio sensor. Since the low frequency component due to the shift of the base air-fuel ratio is removed, it is possible to suppress the erroneous diagnosis and perform the catalyst deterioration diagnosis with high accuracy.

The sixth aspect of the present invention is directed to a catalyst provided in the exhaust passage, an upstream air-fuel ratio sensor provided upstream of the catalyst, and a downstream air-fuel ratio sensor provided downstream of the catalyst. A means for determining an engine operating condition, a basic injection amount setting means for setting a basic fuel injection amount based on a result of the engine operating condition determination, and a feedback correction coefficient calculated based on a signal from an upstream air-fuel ratio sensor. In the internal combustion engine, which comprises a correction coefficient calculating means for adjusting the basic fuel injection quantity according to the feedback correction coefficient, and means for calculating the amplitude of the feedback correction coefficient; Means for filtering the signal of the side air-fuel ratio sensor based on the amplitude of the feedback correction coefficient, and the amplitude of the signal of the downstream side air-fuel ratio sensor that has been filtered and the upstream side Amplitude ratio calculating means for calculating the ratio of the amplitude of the signal of the fuel ratio sensor or the amplitude of the feedback correction coefficient, and when the engine operating condition is in a predetermined catalyst deterioration diagnosis region, the amplitude ratio and a predetermined reference value Deterioration determination means for determining the deterioration of the catalyst based on the comparison result, and extracts the control frequency of the air-fuel ratio feedback included in the output of the downstream side air-fuel ratio sensor by the filter processing based on the amplitude of the feedback correction coefficient, Deterioration of the catalyst can be accurately determined based on the extracted amplitude ratio of the control frequency, and erroneous diagnosis can be suppressed and diagnostic accuracy can be improved.

The seventh aspect of the present invention is directed to a catalyst interposed in the exhaust passage, an upstream air-fuel ratio sensor disposed upstream of the catalyst, and a downstream air-fuel ratio sensor disposed downstream of the catalyst. A means for determining an engine operating condition, a basic injection amount setting means for setting a basic fuel injection amount based on a result of the engine operating condition determination, and a feedback correction coefficient calculated based on a signal from an upstream air-fuel ratio sensor. In the internal combustion engine, which comprises a correction coefficient calculation means for performing the correction, and a fuel injection amount correction means for correcting the basic fuel injection amount according to the feedback correction coefficient; Means for filtering the signal of the downstream side air-fuel ratio sensor based on the number of times of inversion of the feedback correction coefficient, and inversion of this filtered signal of the downstream side air-fuel ratio sensor Number and the number of times of reversal of the signal of the upstream air-fuel ratio sensor or the number of times of reversal of the feedback correction coefficient, a reversal number ratio calculating means, and when the engine operating condition is in a predetermined catalyst deterioration diagnosis region, The deterioration determination means for determining the deterioration of the catalyst based on the comparison result of the inversion frequency ratio and the predetermined reference value is provided, and is included in the output of the downstream side air-fuel ratio sensor by the filter processing based on the inversion frequency of the feedback correction coefficient. It is possible to extract the control frequency of the air-fuel ratio feedback and accurately determine the catalyst deterioration based on the amplitude ratio of the extracted control frequency, and it is possible to suppress erroneous diagnosis and improve the diagnostic accuracy.

The eighth aspect of the present invention includes a catalyst provided in the exhaust passage, an upstream air-fuel ratio sensor provided upstream of the catalyst, and a downstream air-fuel ratio sensor provided downstream of the catalyst. A means for determining an engine operating condition, a basic injection amount setting means for setting a basic fuel injection amount based on a result of the engine operating condition determination, and a feedback correction coefficient calculated based on a signal from an upstream air-fuel ratio sensor. In the internal combustion engine including the correction coefficient calculation means for controlling the basic fuel injection amount according to the feedback correction coefficient, the normal air-fuel ratio feedback control frequency is set based on the engine operating condition. Control frequency calculating means for calculating, FFT processing means for filtering the signal of the downstream side air-fuel ratio sensor by fast Fourier transform, and this FF
Intensity calculation means for calculating the intensity of the air-fuel ratio feedback control frequency component at the normal air-fuel ratio feedback control frequency of the signal of the downstream side air-fuel ratio sensor that has been T-processed;
When the engine operating condition is in a predetermined catalyst deterioration diagnosis region, the deterioration judgment means for judging the deterioration of the catalyst by comparing the strength with a preset strength slice level is provided, and the output of the downstream side air-fuel ratio sensor The fast-fuel Fourier transform is used to extract the air-fuel ratio feedback control frequency component, the intensity at the normal air-fuel ratio feedback control frequency f ₀ calculated from the engine operating conditions of the extracted frequency component is calculated, and this intensity is set as the predetermined intensity slice level. Since the deterioration of the catalyst is determined by comparison, it is possible to accurately separate the air-fuel ratio feedback control frequency component from the low-frequency component due to the deviation from the stoichiometric air-fuel ratio, and it is possible to perform the catalyst deterioration accurately. It is possible to prevent erroneous diagnosis due to disturbances such as a failure of the upstream air-fuel ratio sensor and the influence of wall flow, and to diagnose catalyst deterioration. It is possible to improve the accuracy.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram corresponding to a first invention.

FIG. 2 is a claim correspondence diagram corresponding to the second invention.

FIG. 3 is a claim correspondence diagram corresponding to a third invention.

FIG. 4 is a claim correspondence diagram corresponding to a fourth invention.

FIG. 5 is a claim correspondence diagram corresponding to the sixth invention.

FIG. 6 is a claim correspondence diagram corresponding to a seventh invention.

FIG. 7 is a claim correspondence diagram corresponding to an eighth invention.

FIG. 8 is a block diagram showing an embodiment of the present invention.

FIG. 9 is a flowchart showing an example of control for catalyst deterioration diagnosis.

FIG. 10 is a flow chart showing an example of control for catalyst deterioration diagnosis as well.

FIG. 11 is a graph showing the output of the upstream oxygen sensor and the output of the downstream oxygen sensor after filtering.

FIG. 12 is a graph showing a relationship between an intake air amount and a slice level of an amplitude ratio or an inversion frequency ratio.

FIG. 13 is a flowchart showing an example of control of catalyst deterioration diagnosis showing the second embodiment.

FIG. 14 is a flowchart of the same.

FIG. 15 is a flowchart showing an example of control of catalyst deterioration diagnosis showing a third embodiment.

FIG. 16 is a flowchart of the same.

FIG. 17 is a graph showing the relationship between the air-fuel ratio feedback control frequency band f ₀ and the intake air amount.

FIG. 18 is a graph showing the relationship between strength D and the degree of catalyst deterioration.

FIG. 19 is a graph showing the relationship between intensity D and frequency.

FIG. 20 is a graph showing the output of the upstream oxygen sensor and the output of the downstream oxygen sensor when the response delay becomes large.

FIG. 21 is a graph showing the output of the upstream oxygen sensor and the output of the downstream oxygen sensor.

FIG. 22 is a graph showing the relationship between the output of the upstream oxygen sensor and the correction coefficient α.

[Explanation of symbols]

 4 Control Unit 13 Catalytic Converter 14 Upstream Oxygen Sensor 15 Downstream Oxygen Sensor 50 Upstream Air-Fuel Ratio Sensor 51 Downstream Air-Fuel Ratio Sensor 52 Operating Condition Determining Means 53 Basic Injection Amount Setting Means 54 Correction Coefficient Calculating Means 55 Fuel Correction Amount Calculating Means 56 frequency calculation means 57 filter processing means 58 amplitude ratio calculation means 59 threshold value calculation means 60 deterioration determination means 61 inversion number calculation means 62 inversion number ratio calculation means 63 amplitude calculation means 64 control frequency calculation means 65 FFT processing means 66 strength calculation means

Claims (8)

[Claims] 1. A catalyst installed in an exhaust passage, an upstream air-fuel ratio sensor disposed upstream of the catalyst, a downstream air-fuel ratio sensor disposed downstream of the catalyst, and engine operating conditions Determining means, basic injection amount setting means for setting a basic fuel injection amount according to the determination result of the engine operating condition, and correction coefficient calculating means for calculating a feedback correction coefficient based on a signal from the upstream side air-fuel ratio sensor. In an internal combustion engine comprising a fuel injection amount correction means for correcting the basic fuel injection amount according to the feedback correction coefficient, the upstream side when the determination result of the engine operating condition is a predetermined catalyst deterioration diagnosis region. Frequency calculating means for calculating the frequency of the signal from each of the side air-fuel ratio sensor and the downstream side air-fuel ratio sensor,
Means for filtering the signal of the downstream side air-fuel ratio sensor based on the signal frequency of the upstream side air-fuel ratio sensor, and the signal of the filtered downstream side air-fuel ratio sensor and the upstream side air-fuel ratio sensor before filtering. Amplitude ratio calculating means for calculating a ratio of signal amplitudes, means for calculating a threshold value of the amplitude ratio according to a result of the determination of the engine operating condition, and the above-mentioned method based on a comparison result of the amplitude ratio and the threshold value. A catalyst deterioration diagnosing device for an internal combustion engine, comprising: deterioration judging means for judging deterioration of a catalyst. 2. A catalyst installed in the exhaust passage, an upstream air-fuel ratio sensor arranged upstream of the catalyst, a downstream air-fuel ratio sensor arranged downstream of the catalyst, and operating conditions of the engine. Determining means, basic injection amount setting means for setting a basic fuel injection amount according to the determination result of the engine operating condition, and correction coefficient calculating means for calculating a feedback correction coefficient based on a signal from the upstream side air-fuel ratio sensor. In an internal combustion engine comprising a fuel injection amount correction means for correcting the basic fuel injection amount according to the feedback correction coefficient, the upstream side when the determination result of the engine operating condition is a predetermined catalyst deterioration diagnosis region. Frequency calculating means for calculating the frequency of the signal from each of the side air-fuel ratio sensor and the downstream side air-fuel ratio sensor,
Means for filtering the signal of the downstream side air-fuel ratio sensor based on the signal frequency of the upstream side air-fuel ratio sensor, and the signal of the filtered downstream side air-fuel ratio sensor and the upstream side air-fuel ratio sensor before filtering. Means for calculating the number of inversions by comparing the signal with a predetermined threshold value,
Inversion number ratio calculation means for calculating a ratio of the number of inversions of the signal of the upstream side air-fuel ratio sensor and the signal of the filtered downstream side air-fuel ratio sensor, and the number of inversions according to the determination result of the engine operating condition. A catalyst deterioration diagnosing device for an internal combustion engine, comprising: a means for calculating a ratio threshold value; and a deterioration determining means for judging deterioration of the catalyst based on a comparison result of the inversion frequency ratio and the threshold value. . 3. A catalyst installed in an exhaust passage, an upstream air-fuel ratio sensor arranged upstream of the catalyst, a downstream air-fuel ratio sensor arranged downstream of the catalyst, and operating conditions of the engine. Determining means, means for filtering the signal of the downstream side air-fuel ratio sensor based on the signal of the upstream side air-fuel ratio sensor,
Amplitude ratio calculation means for calculating a ratio between the amplitude of the signal of the downstream side air-fuel ratio sensor and the signal amplitude of the upstream side air-fuel ratio sensor which have been subjected to the filter processing, and a catalyst deterioration diagnosis region in which the engine operating condition determination result is a predetermined value. And a deterioration determination unit for determining deterioration of the catalyst based on a comparison result between the amplitude ratio and a predetermined reference value. 4. A catalyst installed in the exhaust passage, an upstream air-fuel ratio sensor arranged upstream of the catalyst, a downstream air-fuel ratio sensor arranged downstream of the catalyst, and operating conditions of the engine. Determining means, means for filtering the signal of the downstream side air-fuel ratio sensor based on the signal of the upstream side air-fuel ratio sensor,
Means for calculating the number of reversals by comparing the signal of the downstream side air-fuel ratio sensor and the signal of the upstream side air-fuel ratio sensor which have been subjected to this filtering with a predetermined threshold value respectively, and the signal of the upstream side air-fuel ratio sensor and the above A means for calculating the ratio of the number of reversals of the signal of the downstream side air-fuel ratio sensor that has been filtered, and the reversal number ratio and a predetermined reference value when the engine operating condition determination result is in a predetermined catalyst deterioration diagnosis region. And a deterioration determination unit that determines deterioration of the catalyst based on a comparison result with the catalyst deterioration diagnosis apparatus for an internal combustion engine. 5. The filter processing means allows a signal having a frequency equal to or higher than a signal frequency of an upstream side air-fuel ratio sensor to pass among signals of the downstream side air-fuel ratio sensor to pass therethrough. 13. A catalyst deterioration diagnosing device for an internal combustion engine according to. 6. A catalyst installed in an exhaust passage, an upstream air-fuel ratio sensor arranged upstream of the catalyst, a downstream air-fuel ratio sensor arranged downstream of the catalyst, and operating conditions of the engine. Determining means, basic injection amount setting means for setting a basic fuel injection amount based on the determination result of the engine operating condition, and correction coefficient calculating means for calculating a feedback correction coefficient based on a signal from the upstream air-fuel ratio sensor. In the internal combustion engine having a fuel injection amount correction means for correcting the basic fuel injection amount according to the feedback correction coefficient, a means for calculating the amplitude of the feedback correction coefficient and a signal of the downstream side air-fuel ratio sensor Means for filtering based on the amplitude of the feedback correction coefficient, and the amplitude of the filtered signal of the downstream side air-fuel ratio sensor and the signal of the upstream side air-fuel ratio sensor Amplitude ratio calculation means for calculating the amplitude or the ratio of the amplitude of the feedback correction coefficient, and when the engine operating condition is a predetermined catalyst deterioration diagnosis region,
A catalyst deterioration diagnosing device for an internal combustion engine, comprising: deterioration judging means for judging deterioration of the catalyst based on a comparison result of the amplitude ratio and a predetermined reference value. 7. A catalyst installed in an exhaust passage, an upstream air-fuel ratio sensor arranged upstream of the catalyst, a downstream air-fuel ratio sensor arranged downstream of the catalyst, and operating conditions of the engine. Determining means, basic injection amount setting means for setting a basic fuel injection amount based on the determination result of the engine operating condition, and correction coefficient calculating means for calculating a feedback correction coefficient based on a signal from the upstream air-fuel ratio sensor. In an internal combustion engine comprising a fuel injection amount correction means for correcting the basic fuel injection amount according to the feedback correction coefficient, a means for calculating the number of times the feedback correction coefficient is inverted and a downstream side air-fuel ratio sensor Means for filtering the signal based on the number of times the feedback correction coefficient is inverted, and the number of times the signal of the filtered downstream side air-fuel ratio sensor is inverted and the upstream side air-fuel ratio sensor. Sensor reversal frequency or a ratio of the feedback correction coefficient to the reversal frequency, and a reversal frequency ratio calculating means for calculating a ratio between the reversal frequency of the feedback correction coefficient and the reversal frequency of the feedback correction coefficient. A catalyst deterioration diagnosing device for an internal combustion engine, comprising: deterioration judging means for judging deterioration of the catalyst based on a comparison result of reference values. 8. A catalyst installed in an exhaust passage, an upstream air-fuel ratio sensor arranged upstream of the catalyst, a downstream air-fuel ratio sensor arranged downstream of the catalyst, and operating conditions of the engine. Determining means, basic injection amount setting means for setting a basic fuel injection amount based on the determination result of the engine operating condition, and correction coefficient calculating means for calculating a feedback correction coefficient based on a signal from the upstream air-fuel ratio sensor. In an internal combustion engine including a fuel injection amount correction unit that corrects the basic fuel injection amount according to the feedback correction coefficient, a control frequency calculation unit that calculates a normal air-fuel ratio feedback control frequency based on the engine operating condition. And FFT processing means for filtering the signal of the downstream side air-fuel ratio sensor by fast Fourier transform, and the signal of the downstream side air-fuel ratio sensor subjected to this FFT processing. Strength calculation means for calculating the strength of the air-fuel ratio feedback control frequency component at the normal air-fuel ratio feedback control frequency, and the strength and preset strength slice level when the engine operating condition is in a predetermined catalyst deterioration diagnosis region. And a deterioration determination unit that determines deterioration of the catalyst by comparing the above.