JP3564064B2 - Diagnosis device for engine exhaust gas purification device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a diagnostic device for an engine exhaust gas purification device using an air-fuel ratio sensor or an oxygen concentration sensor (hereinafter, referred to as an air-fuel ratio sensor) or a catalytic converter.
[0002]
[Prior art]
The device for purifying the exhaust of the engine mainly comprises a catalytic converter and an air-fuel ratio feedback control device. The catalytic converter is installed in an exhaust pipe to remove HC, NOx, and CO contained in exhaust gas. Also, the air-fuel ratio feedback control device needs to keep the air-fuel ratio constant in order to fully exert the function of the catalyst converter. Therefore, an oxygen sensor is installed upstream of the catalyst converter to supply the fuel at the air-fuel ratio. It is for controlling.
[0003]
[Problems to be solved by the invention]
In a conventional three-way catalyst system such as the above-mentioned conventional technology, if the performance of the oxygen sensor provided upstream of the catalytic converter is deteriorated, the air-fuel ratio deviates from a certain narrow range centered on the stoichiometric ratio, thereby causing harmful components. Conversion efficiency decreases. Further, when the performance of the catalytic converter itself deteriorates, there is a problem that the conversion efficiency of harmful components is reduced even if the air-fuel ratio is accurately controlled.
[0004]
In order to solve this problem, it is necessary to determine the state of deterioration of the catalyst. However, a diagnostic device that diagnoses these performance deteriorations during operation and enables quick response has not been established yet.
[0005]
As a technique for such catalyst deterioration determination, for example, there is a "catalyst deterioration determination apparatus for an internal combustion engine" described in JP-A-2-3091. This is because an oxygen sensor is provided before and after the catalyst (note: the oxygen sensor in this case is a binary sensor), the output value of the front oxygen sensor is inverted, and then the output value of the rear sensor is inverted. It measures the time lag until you do it. Then, the deterioration state of the catalyst is determined based on the magnitude of the time difference. Specifically, if the time difference is small, it is determined that the catalyst is in a deteriorated state.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in order to solve such a conventional problem, and is directed to a diagnosis of an engine exhaust gas purifying apparatus capable of diagnosing whether performance has deteriorated in an air-fuel ratio sensor, an oxygen sensor, or a catalytic converter during operation. It is intended to provide an apparatus and a diagnostic method.
[0007]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and in one aspect, an air-fuel ratio in an engine exhaust gas is detected, and a fuel injection amount is adjusted so as to maintain the air-fuel ratio in the exhaust gas at a predetermined value. A diagnostic device for an engine exhaust gas purifying device for purifying exhaust gas with a catalyst, which is intended for an engine having an air-fuel ratio control device to perform, comprising: a front air-fuel ratio sensor for detecting an air-fuel ratio on an exhaust gas upstream side of the catalyst; From the output signals of the rear air-fuel ratio sensor that detects the air-fuel ratio on the exhaust gas downstream side of the catalyst and the front air-fuel ratio sensor and the rear air-fuel ratio sensor, the air-fuel ratio control frequency band of the air-fuel ratio control device is A characteristic waveform extracting means for attenuating a signal in a low frequency band, a correlation function calculating means for calculating a correlation function of the signal having passed through the characteristic waveform extracting means, and Diagnostic apparatus for an engine exhaust gas purifying apparatus; and a catalyst state judging means for judging the deterioration state of the medium is provided.
[0008]
Another aspect of the present invention is directed to an engine having an air-fuel ratio control device that detects an air-fuel ratio in engine exhaust gas and adjusts a fuel injection amount so as to maintain the air-fuel ratio in the exhaust gas at a predetermined value. A diagnostic device for an engine exhaust gas purifying device for purifying exhaust gas with a catalyst, comprising: a front air-fuel ratio sensor for detecting an air-fuel ratio on an exhaust gas upstream side of the catalyst; and an air-fuel ratio on an exhaust gas downstream side of the catalyst. The auto-correlation function φ of the output signal of the front air-fuel ratio sensor and the rear air-fuel ratio sensor to be detected_xxAuto-correlation function calculating means for calculating and outputting a cross-correlation function φ between an output signal of the front air-fuel ratio sensor and an output signal of the rear air-fuel ratio sensor._xyCross-correlation function calculating means for calculating and outputting_xyAnd the autocorrelation function φ_xxAnd the ratio of the value to_iDegradation index calculating means for outputting as_iAnd a reference value set in advance to provide a diagnostic device for an engine exhaust gas purifying device, characterized by having a catalyst state determining means for determining the deterioration state of the catalyst.
[0009]
In this case, the deterioration index calculating means performs the cross-correlation function φ_xyMaximum value (φ_xy)_maxAnd the autocorrelation function φ within the period_xxMaximum value (φ_xx)_maxWith the above sequential deterioration index Φ_iMay be output.
[0010]
Further, the deterioration index calculating means has a function of calculating an average value of the sequential deterioration indexes for a predetermined number of times in the past, and outputting the average value as a final deterioration index. Φ_iAlternatively, the deterioration state of the catalyst may be determined by comparing the final deterioration index with a preset reference value.
[0011]
Further, there is provided an operating state detecting means for detecting an engine speed and / or a temperature of the catalyst, and the deterioration index calculating means calculates the final deterioration index using the detection result of the operating state detecting means as a coefficient. It may be something.
[0012]
Further, a characteristic waveform extracting means for attenuating a signal in a frequency band lower than an air-fuel ratio control frequency band of the air-fuel ratio control device from output signals of the front air-fuel ratio sensor and the rear air-fuel ratio sensor, The autocorrelation function calculation means and the cross-correlation function means use an autocorrelation function φ based on the signal after passing through the characteristic waveform extraction means._xx, The cross-correlation function φ_xyIs preferably calculated. Note that the characteristic waveform extracting means may be a high-pass filter or a band-pass filter.
[0013]
Further, it is preferable that the vehicle has a crank angle detecting means for detecting a crank angle of the engine, and the front air-fuel ratio sensor executes data sampling corresponding to the crank angle detected by the crank angle detecting means.
[0014]
Another aspect of the present invention is directed to an engine having an air-fuel ratio control device that detects an air-fuel ratio in engine exhaust gas and adjusts a fuel injection amount so as to maintain the air-fuel ratio in the exhaust gas at a predetermined value. A diagnostic device for an engine exhaust gas purifying device for purifying exhaust gas with a catalyst, comprising: an air-fuel ratio sensor for detecting an air-fuel ratio on an exhaust gas upstream side of the catalyst; and an autocorrelation function φ of an output signal of the air-fuel ratio sensor._xxAutocorrelation function calculating means for calculating and outputting_xxAnd a sensor state judging means for judging the deterioration state of the air-fuel ratio sensor by comparing the value of the air-fuel ratio sensor with a preset reference value.
[0015]
In this case, the autocorrelation function φ_xxMaximum value (φ_xx)_maxIs calculated, and (φ_xx)_maxA sensor deterioration index calculating means for calculating an average value of the sensor deterioration index and outputting the sensor deterioration index as a sensor deterioration index. The sensor state determining means compares the sensor deterioration index with a preset reference value to obtain the air-fuel ratio. It is preferable to determine the deterioration state of the sensor.
[0016]
The apparatus further includes a characteristic waveform extracting unit configured to attenuate a signal in a frequency band lower than an air-fuel ratio control frequency band of the air-fuel ratio control device from the output signal of the air-fuel ratio sensor. Based on the signal after passing through the waveform extracting means, the autocorrelation function φ_xxIs preferably calculated. Note that the characteristic waveform extracting means may be a high-pass filter or a band-pass filter.
[0017]
Another aspect of the present invention is directed to an engine having an air-fuel ratio control device that detects an air-fuel ratio in engine exhaust gas and adjusts a fuel injection amount so as to maintain the air-fuel ratio in the exhaust gas at a predetermined value. A diagnostic device for an engine exhaust gas purifying device for purifying exhaust gas with a catalyst, comprising: a front air-fuel ratio sensor for detecting an air-fuel ratio on an exhaust gas upstream side of the catalyst; and an air-fuel ratio on an exhaust gas downstream side of the catalyst. The auto-correlation function φ of the output signal of the front air-fuel ratio sensor and the rear air-fuel ratio sensor to be detected_xxAuto-correlation function calculating means for calculating and outputting a cross-correlation function φ between an output signal of the front air-fuel ratio sensor and an output signal of the rear air-fuel ratio sensor._xyCross-correlation function calculating means for calculating and outputting_xyAnd the autocorrelation function φ_xxAnd the ratio of the value to_iDegradation index calculating means for outputting as_iAnd a reference value set in advance to compare the autocorrelation function φ with the catalyst state determination means for determining the deterioration state of the catalyst._xxAnd a sensor state judging means for judging the deterioration state of the front air-fuel ratio sensor by comparing the value of the pre-air-fuel ratio sensor with a preset reference value. .
[0018]
Another aspect of the present invention is directed to an engine having an air-fuel ratio control device that detects an air-fuel ratio in engine exhaust gas and adjusts a fuel injection amount so as to maintain the air-fuel ratio in the exhaust gas at a predetermined value. A method for diagnosing an engine exhaust gas purifying apparatus for purifying exhaust gas with a catalyst, wherein an autocorrelation function φ of measurement data of an air-fuel ratio on an upstream side of the catalyst is provided at predetermined time intervals._xxMaximum value (φ_xx)_maxCross-correlation function between the measured data of the air-fuel ratio on the upstream side of the catalyst and the measured data of the air-fuel ratio on the downstream side of the catalyst_xyMaximum value (φ_xy)_maxAnd calculating a ratio of the catalyst ratio and comparing the ratio value with a predetermined reference value to determine a catalyst deterioration state.
[0019]
According to another aspect of the present invention, an engine having an air-fuel ratio control device that detects an air-fuel ratio in engine exhaust gas with an air-fuel ratio sensor and adjusts a fuel injection amount so as to maintain the air-fuel ratio in exhaust gas at a predetermined value. A method for diagnosing an engine exhaust gas purifying apparatus for purifying exhaust gas with a catalyst, wherein the autocorrelation function φ of measurement data of the air-fuel ratio on the upstream side of the catalyst is provided at predetermined intervals._xxMaximum value (φ_xx)_maxIs calculated, and the maximum value (φ_xx)_maxIs compared with a predetermined reference value to determine the state of deterioration of the air-fuel ratio sensor.
[0020]
[Action]
The front air-fuel ratio sensor and the rear air-fuel ratio sensor detect and output the air-fuel ratio between the upstream side and the downstream side of the catalyst in accordance with the crank angle detected by the crank angle detecting means. The characteristic waveform extracting means attenuates a signal in a frequency band lower than the air-fuel ratio control frequency band of the air-fuel ratio control device from the output signal.
[0021]
The autocorrelation function calculating means calculates the autocorrelation function φ of the signal passing through the characteristic waveform extracting means._xxIs calculated and output. On the other hand, the cross-correlation function means is a cross-correlation function φ between the output signal of the front air-fuel ratio sensor and the output signal of the rear air-fuel ratio sensor that has passed through the characteristic waveform extraction means._xyIs calculated and output.
[0022]
The deterioration index calculating means calculates the cross-correlation function φ for each predetermined period._xyMaximum value (φ_xy)_maxAnd the autocorrelation function φ within the period_xxMaximum value (φ_xx)_max, And the sequential deterioration index Φ_iAnd Further, the sequential deterioration index Φ for a predetermined number of times in the past_iIs calculated, and this is output as the final deterioration index. In this case, the deterioration index calculating means may calculate the final deterioration index using the detection result of the operating state detecting means as a coefficient.
[0023]
The catalyst state determination means determines the sequential deterioration index Φ_iAlternatively, the final deterioration index is compared with a preset reference value to determine the deterioration state of the catalyst.
[0024]
Another embodiment will be described.
[0025]
The air-fuel ratio sensor detects an air-fuel ratio on the exhaust gas upstream side of the catalyst.
[0026]
The characteristic waveform extracting means attenuates a signal in a frequency band lower than the air-fuel ratio control frequency band of the air-fuel ratio control device from the output signal of the air-fuel ratio sensor.
[0027]
The autocorrelation function calculation means calculates the autocorrelation function φ of the signal after passing through the characteristic waveform extraction means._xxIs calculated, and for each predetermined period, the autocorrelation function φ within the period_xxMaximum value (φ_xx)_maxIs output.
[0028]
The sensor deterioration index calculating means calculates the above (φ_xx)_maxIs calculated and output as a sensor deterioration index.
[0029]
The sensor state determination means performs the above (φ_xx)_maxAlternatively, the deterioration state of the air-fuel ratio sensor is determined by comparing the sensor deterioration index with a preset reference value.
[0030]
【Example】
An embodiment of the present invention will be described with reference to the drawings.
[0031]
First, the concept of the present embodiment will be described with reference to FIG.
[0032]
The diagnostic apparatus according to the present embodiment includes a catalyst converter 2 and an air-fuel ratio sensor O disposed before and after the catalyst converter 2.₂Sensors 3 and 4 and the O₂The present invention is directed to a system having a fuel injection control means 7 for performing air-fuel ratio feedback based on the outputs of the sensors 3 and 4.
[0033]
As the air-fuel ratio sensor, in this embodiment, O₂Sensors 3 and 4 are used. In this specification, “oxygen sensor”, “O₂The term “sensor” refers to a so-called lambda sensor capable of detecting the oxygen concentration linearly without detecting the oxygen concentration in a binary manner. Specifically, it is a sensor such as zirconia and titania.
[0034]
First, control in the premise system will be described.
[0035]
The fuel injection control means 7 includes a fuel injection calculation means 9, an output means 10, and an air-fuel ratio feedback calculation means. The fuel injection amount calculation means 9 is based on the following equation 1 based on the detection value of the sensor 5 for detecting the load (for example, the intake air amount Qa) of the engine 1 and the detection value of the sensor 6 for detecting the rotation speed Ne. Injection amount F₀Ask for.
[0036]
(Equation 1)
F₀= K₀Qa / Ne
F₀： Basic injection amount
Qa: Intake air volume
Ne: rotation speed
On the other hand, the air-fuel ratio feedback calculation means 8 is provided with an air-fuel ratio sensor (hereinafter referred to as "front O") provided upstream of the catalytic converter 2.₂3) is sampled at a predetermined timing, and a correction signal α is generated in accordance with the detected value.
[0037]
The fuel injection amount calculating means 9 calculates the basic injection amount F₀The injection amount F is obtained by taking into account the correction signal α (see Expression 2). Then, this is converted into a voltage duty signal by the output means 10 and applied to the fuel injection valve.
[0038]
(Equation 2)
F = k₀Qa / Ne (1 + α)
F: injection amount
F₀： Basic injection amount
Qa: Intake air volume
Ne: rotation speed
α: correction signal
Due to such control, the air-fuel ratio is constantly perturbed upstream and downstream of the catalytic converter 2 at values before and after stoichiometry.
[0039]
The diagnostic device of this embodiment uses the perturbation of the air-fuel ratio by the air-fuel ratio feedback control as a test signal for diagnosing deterioration of the catalytic converter. That is, if the catalytic converter 2 is not deteriorated, the perturbation of the air-fuel ratio is reduced in the downstream of the catalytic converter 2 due to the oxidation / reduction action of the catalyst. On the other hand, when the catalytic converter 2 deteriorates, the downstream air-fuel ratio perturbation approaches the upstream one. Thus, the deterioration is diagnosed by focusing on the similarity of the air-fuel ratio perturbation before and after the catalytic converter.
[0040]
The greatest feature is that the degradation diagnostic means 11 for evaluating this similarity using a correlation function is provided.
[0041]
First, the deterioration diagnosis means 11₂Sensor 3 and rear O₂From the output of the sensor 4, components such as DC components that are not directly related to the deterioration of the catalytic converter 2, that is, components that may cause an error when performing an operation using the correlation function, are removed by the characteristic waveform extracting unit 12. Here, a differential filter, a high-frequency band-pass filter or a band-pass filter is appropriate as the characteristic waveform extracting means 12. In addition, after this,₂The signal originating from the sensor 3 is denoted by the symbol x and₂The signal resulting from the sensor 4 is indicated by the symbol y.
[0042]
Next, the auto-correlation function calculating means 13 calculates O₂Autocorrelation function φ of output signal x of sensor 3_xxIs calculated. Further, the cross-correlation function calculating means 14 calculates the value of O₂Output signal x of sensor 3 and rear O₂Cross-correlation function φ between output signal y of sensor 4_xyIs calculated.
[0043]
(Equation 3)
φ_xx(Τ) = ∫x (t) x (t−τ) dt
[0044]
(Equation 4)
φ_xy(Τ) = ∫x (t) y (t−τ) dt
Further, by changing the phase τ in the integration interval (0 to T) of the correlation function, φ_xyMaximum value (φ_xy)_maxAnd φ_xxMaximum value (φ_xx)_maxAnd ask. Then, using these values, the catalyst converter 2 and the O₂The deterioration of the sensor 3 is determined.
[0045]
The deterioration judgment of the catalyst converter 2 is made by the catalyst converter judgment means 16. The catalytic converter deterioration determining means 16 calculates the deterioration index Φ_iIs calculated, and this is compared with a predetermined reference value to determine the deterioration of the catalytic converter.
[0046]
(Equation 5)
Φ_i= (Φ_xy)_max/ (Φ_xx)_max
That is, when the catalyst deteriorates, the similarity of the air-fuel ratio perturbation before and after the catalytic converter 2 increases, so that the sequential deterioration index Φ_iIncreases (approaches 1).
[0047]
On the other hand, before O₂The deterioration determination of the sensor 3 is made by the air-fuel ratio sensor deterioration determination means 15. The air-fuel ratio sensor deterioration determination means 15 determines (φ_xx)_maxIs used as the deterioration index to determine the deterioration of the air-fuel ratio sensor. That is, before O₂When the sensor 3 deteriorates, the response of the air-fuel ratio sensor is delayed, so that the maximum value (φ_xx)_maxBecomes smaller, the deterioration is detected by monitoring the value and comparing it with a predetermined reference value. FIG. 4 shows the state before and after the air-fuel ratio sensor has not deteriorated and the air-fuel ratio sensor has deteriorated.₂The power spectrum of the output of the sensor 3 for each frequency is shown. In the deteriorated state, the peak is shifted to the low frequency side, and it can be seen that the response speed is low.
[0048]
The diagnostic device according to the present embodiment will be described more specifically.
[0049]
The diagnostic device itself mainly includes a single-chip microcomputer having an A / D converter and a high-frequency bandpass filter.
[0050]
The high-frequency region pass filter corresponds to the characteristic waveform extracting means 12A and 12B.
[0051]
The microcomputer realizes the functions of the above-described units, the autocorrelation function calculating unit 13, the catalyst converter deterioration determining unit 16 and the like by operating according to the built-in software.
[0052]
However, the hardware configuration is not limited to this.
[0053]
The operation of the diagnostic device will be described with reference to FIG. In the figure, each block is assigned the same number as each unit in FIG. 1 corresponding to the processing performed in the block.
[0054]
First, the operation for determining the deterioration of the catalyst converter 2 will be described.
[0055]
Previous O₂The output signal of the sensor 3 (hereinafter referred to as “previous O₂Sensor signal) 114 and after O₂The output signal of the sensor 4 (hereinafter referred to as “the rear O₂A / D converter 18 synchronously converts digital data into digital data.
[0056]
Next, a DC component which is a disturbance for diagnosis is removed from each signal by a high-frequency band-pass filter (blocks 12A and 12B). Here, it is assumed that both filters have the same characteristics. FIG. 3 shows an actual example of feature waveform extraction. O₂The DC component included in the voltage signal of the sensor has been removed, but the control cycle is preserved. FIG. 4 shows the power spectrum of these signals for each frequency. In each signal, a frequency component lower than the air-fuel ratio feedback control frequency which is a disturbance in diagnosis is removed.
[0057]
In this embodiment, only low-frequency components are cut. However, as described above, band-pass filters may be used to cut higher-frequency components than the air-fuel ratio feedback control frequency band. In this case, the frequency band used for calculating the correlation function is only a frequency band having a certain width including the air-fuel ratio feedback control frequency, so that more accurate determination can be made.
[0058]
Then, before O₂Autocorrelation function φ at time t = 0 of signal x (t) 105 obtained from sensor signal 114_xxFind (0) (block 13). Here, φ_xx(0) is determined by the autocorrelation function φ_xxIs the maximum value (φ at t = 0)_xx)_maxBecause it takes
[0059]
Also, before O₂The signal x (t) obtained from the sensor signal 114 and the subsequent O₂From the signal y (t) obtained from the sensor signal 102 and the cross-correlation function φ_xy(Τ) is determined in a fixed integration interval T (block 14). Here, the integration section T is set in advance so that the fluctuation of the engine speed does not exceed a predetermined range in that section.
[0060]
Then, φ in the integration section T_xy(Τ) maximum value (φ_xy)_maxAnd find the (φ_xy)_max, The sequential deterioration index Φ_i(= (Φ_xy)_max/ Φ_xx(0), see Equation 5) (block 16A, see FIG. 5). Note that the sequential deterioration index Φ_iPhase τ, in other words (φ_xy) / Φ_xxSince the phase τ at which (0) takes the maximum value varies depending on operating conditions and machine differences, Φ_iIs obtained by actually searching for data.
[0061]
And Φ_iIs stored in a memory (RAM), and in the next integration period T, Φ_{i + 1}Ask for.
[0062]
By repeating the above operation n times, Φ_iFind the average value of Then, the average value is used as the final deterioration index I of the catalytic converter 2. When calculating the final deterioration index I, a correction coefficient k based on various operating conditions is used.₁, K₂(Blocks 16B, 16C, 16D, see Equation 6 below)
[0063]
(Equation 6)
I = (Σk₁k₂Φ_i) / N
I: Final deterioration index
k₁: Correction factor depending on engine load
k₂： Correction coefficient by catalyst temperature
Φ_i: Sequential deterioration index
n: Number of measurements
Note that k₁, K₂Are previously stored in a memory (ROM) as map data.
[0064]
Subsequently, the deterioration index I is set to a predetermined deterioration determination level I._DThe deterioration state is determined by comparing with. The deterioration index I is equal to the deterioration determination level I_DIf it is larger than this, it is determined that the image has deteriorated (block 16E).
[0065]
Where the sequential deterioration index Φ_iIs not used as it is, but the average value, that is, the final deterioration index I is used when the engine speed and the load fluctuate during normal running, as shown in FIG._iIs also affected and fluctuates. That is, the sequential deterioration index Φ for a certain time, a certain number of rotations, or a certain load zone._iAre obtained and accumulated, and the average value is used as the final deterioration index I, thereby making it possible to determine the deterioration in the entire operation range. However, when the operation state is limited to some extent, the sequential deterioration index Φ_iMay be used as it is to make the determination.
[0066]
Next, before O₂The operation of determining the deterioration of the sensor 3 will be described.
[0067]
The determination operation is based on the previous O₂Autocorrelation function φ of sensor signal_xxPerform using only As described above, the autocorrelation function has a maximum value (φ_xx)_max, But the maximum value (φ_xx)_maxIs O₂As the sensor 3 deteriorates, its value decreases.
Therefore, the (φ_xx)_maxIs detected and compared with a predetermined reference value to obtain₂The deterioration of the sensor 3 can be detected.
[0068]
Note that the autocorrelation function φ_xxAs in the case of the catalyst converter deterioration determination, a frequency component lower than the air-fuel ratio feedback control frequency band is removed from the data used when determining the value. FIG. 4 shows power spectra before and after removing the low frequency component.
[0069]
Here, the maximum value (φ_xx)_maxIs used as it is, but as in the case of determining the deterioration of the catalyst converter 2, the maximum value (φ_xx)_maxThe determination may be made using the average value of.
[0070]
In this case, the O₂The sensor 3 has been described.₂The same can be applied to the sensor 4.
[0071]
In addition, before O₂Sensor 3 or rear O₂The sampling from the sensor 4 may be performed at regular intervals. Further, a sensor for detecting the crank angle of the engine may be provided, and the detection may be performed according to the crank angle. When determining the deterioration of the catalyst converter 2, it is more preferable to perform sampling corresponding to the crank angle. This is because when the deterioration determination of the catalyst converter 2 is performed, the components lower in frequency than the air-fuel ratio feedback control frequency are cut as described above, but this air-fuel ratio feedback control frequency is This is because it is changed according to the engine speed. In other words, when sampling is performed in accordance with the crank angle, there is no need to make any correction because it is not affected by the change in the number of revolutions, but when sampling is performed at regular intervals, correction is required. Because. On the other hand, before O₂The deterioration characteristic of the sensor 3 depends only on the state of the sensor itself and is not affected by the engine speed.₂The same applies to any method for determining the deterioration of the sensor 3.
[0072]
In the above-described embodiment, deterioration of the catalytic converter, the air-fuel ratio sensor, and the oxygen sensor, which are the exhaust gas purification control devices of the engine, can be diagnosed during the normal running of the vehicle. In addition, since the correlation function is used in the signal similarity determination, it is more resistant to noise than when the determination is made using the frequency, amplitude, and the like.
[0073]
【The invention's effect】
As described above, according to the present invention, it is possible to diagnose the deterioration of the catalytic converter, the air-fuel ratio sensor, and the oxygen sensor, which are the exhaust gas purification control devices of the engine, during normal running of the vehicle.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is an explanatory diagram illustrating the operation of the present embodiment.
FIG. 3 is an explanatory diagram illustrating extraction of a characteristic waveform according to the present embodiment.
FIG. 4 is a power spectrum diagram for each frequency for explaining the operation of feature waveform extraction.
FIG. 5 is a characteristic diagram for explaining the function of determining catalytic converter deterioration.
FIG. 6 is a characteristic diagram for explaining an operation of determining catalytic converter deterioration.
[Explanation of symbols]
2: Catalytic converter, 3: Front O₂Sensor, 4: rear O₂Sensor, 12: characteristic waveform extracting means, 13: autocorrelation function calculating means, 14: cross-correlation function calculating means, 15: O₂Sensor deterioration determining means, 16: catalytic converter deterioration determining means,
17: judgment result output means, Φ_i: Sequential deterioration index, I: final deterioration index, I_D: Deterioration judgment level
x: air-fuel ratio sensor provided upstream of the catalytic converter (before O₂Sensor) output
y: air-fuel ratio sensor (rear O) provided downstream of the catalytic converter₂Sensor) output
φ_xx: Autocorrelation function of signal x
φ_xy: Cross-correlation function between signal x and signal y

Claims (2)

An engine for purifying exhaust gas with a catalyst for an engine having an air-fuel ratio control device that detects an air-fuel ratio in the engine exhaust gas and adjusts a fuel injection amount to maintain the air-fuel ratio in the exhaust gas at a predetermined value. A diagnostic device for an exhaust gas purification device,
A front air-fuel ratio sensor that detects an air-fuel ratio on the exhaust gas upstream side of the catalyst,
A rear air-fuel ratio sensor that detects an air-fuel ratio on the exhaust gas downstream side of the catalyst,
A correlation function for obtaining a correlation function that is a function of the phase (τ) of the output signal of the front air-fuel ratio sensor and the rear air-fuel ratio sensor during feedback control so as to maintain the air-fuel ratio in the exhaust gas at a predetermined value. Calculating means;
Catalyst state determination means for determining the deterioration state of the catalyst based on the value of the correlation function,
A diagnostic device for an engine exhaust gas purifying device, comprising:   The diagnostic device for an engine exhaust gas purifying device according to claim 1,
  An engine exhaust system further comprising: a catalyst deterioration determining unit that determines an index value based on the correlation function, and compares the index value with a predetermined degradation determination reference value to determine a catalyst degradation state. Diagnosis device for gas purification equipment.

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