JP2005240618A - Engine control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device having high robustness against noises for diagnosing an air-fuel ratio detecting means with high accuracy even when the air-fuel ratio detecting means is arranged on either the upstream or downstream side of a catalyst in an exhaust passage. <P>SOLUTION: The engine control device having the air-fuel ratio detecting means 51 arranged in the exhaust passage 40 comprises a predetermined frequency band component extracting means 220 such as a band filter for extracting signal components in a predetermined frequency band out of output signals from the air-fuel ratio detecting means 51, an amplitude/power computing means 231 for computing the amplitude or power of the signal components in the predetermined frequency band, and a diagnosing means 230 for diagnosing the air-fuel ratio detecting means in accordance with the amplitude or power. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an engine control device, and more particularly, to a control device capable of diagnosing air-fuel ratio detection means disposed upstream or downstream of a catalyst in an exhaust passage with high accuracy.

In recent years, exhaust regulations have been strengthened. A three-way catalyst is attached to the exhaust passage to purify HC, CO, and NOx discharged from the engine, and an A / F sensor (or O ₂ sensor) upstream of the catalyst in the exhaust passage is used for high efficiency use of the catalyst. In addition to this, it is becoming common to use an air-fuel ratio F / B control with high robustness using an O ₂ sensor downstream. On the other hand, in North America, Europe, Japan, etc., the accuracy of diagnosis of the A / F sensor and the O ₂ sensor is also demanded to be improved. Against this background, the responsiveness of the A / F sensor and the O ₂ sensor deteriorates (decreases). Several methods have been proposed in the past for detecting).

  For example, in Patent Document 1 below, a time differential value (output change speed) of a sensor output is obtained, and responsiveness deterioration of the air-fuel ratio sensor is detected based on an average value, standard deviation value, or maximum value of the time differential value. It has been proposed to do. That is, the sensor response is obtained from the sensor output change speed.

  Further, Patent Document 2 below proposes a method based on the frequency at which the time differential value of the sensor output becomes equal to or greater than a predetermined value in order to detect responsiveness deterioration of the air-fuel ratio sensor downstream of the catalyst. However, since the gain of the differentiator becomes higher as the frequency becomes higher, the characteristic of the differentiator is likely to be affected by noise and may deteriorate the detection accuracy.

On the other hand, in Patent Document 3 below, for the purpose of increasing the accuracy of air-fuel ratio F / B control, in order to reduce the influence of noise, when the amount of change per predetermined time of the air-fuel ratio sensor output is larger than a predetermined amount, It has been proposed to determine that the air-fuel ratio sensor output is not valid, correct the output value, and use it as a control signal.
JP 61-31640 (pages 1-6, FIGS. 1-17) Japanese Patent Laid-Open No. 9-4496 (pages 1-5, FIGS. 1-7) JP-A-6-229295 (pages 1 to 11 and FIGS. 1 to 8)

  However, as described above, when diagnosing responsiveness deterioration of the sensor, it is reasonable to perform based on the change rate of the output signal. However, since a differentiator is used, it is affected by noise and causes misdiagnosis. there is a possibility.

  The present invention has been made in view of the above circumstances, and an object thereof is a case where the robustness against noise is high and the air-fuel ratio detection means is arranged either upstream or downstream of the catalyst in the exhaust passage. Even if it exists, it is providing the control apparatus which can diagnose this air-fuel-ratio detection means with high precision.

  In order to achieve the above object, a first aspect of an engine control apparatus according to the present invention is applied to an engine equipped with an air-fuel ratio detection means, and a signal in a predetermined frequency band from an output signal of the air-fuel ratio detection means. Predetermined frequency band component extracting means for extracting components, amplitude / power calculating means for calculating the amplitude or power of the signal component in the predetermined frequency band, and diagnosis for diagnosing the air-fuel ratio detecting means based on the amplitude or power And means (see FIG. 1).

That is, as shown in FIG. 17, the output of the air-fuel ratio detection means such as an O ₂ sensor is normal (when responsiveness is normal) and when it is deteriorated (when responsiveness is deteriorated). And different. FIG. 18 shows the result of frequency analysis of the output signal when the response is normal and when the response is deteriorated, and it can be seen that the power (response index) of the frequency in the specific band is different. Accordingly, it is possible to extract only the band related to the responsiveness of the air-fuel ratio detecting means and diagnose the air-fuel ratio detecting means (responsiveness deterioration determination) based on the amplitude (or power) of the signal component in the band. .

  In a second aspect of the control device according to the present invention, the predetermined frequency band component extracting means is constituted by a band-pass filter that passes only a predetermined frequency band of the output signal of the air-fuel ratio detecting means (see FIG. 2). .

  That is, a band-pass filter (hereinafter referred to as a band-pass filter) is used to extract only the band related to the responsiveness of the air-fuel ratio detection means, and the air-fuel ratio detection is performed based on the amplitude (or power) of the signal component in the band. Diagnose means (determination of responsiveness deterioration). Specifically, as shown in FIG. 16, in the frequency characteristics of the air-fuel ratio detection means, the pass band of the band-pass filter is set to a region where the gain characteristics are different when the response is normal and when the response is degraded. By setting the passband in this way, it is possible to detect a gain decrease due to response deterioration without being affected by high-frequency noise.

  In a third aspect of the control device according to the present invention, the predetermined frequency band component extracting means extracts a signal component of the predetermined frequency band from the output signal of the air-fuel ratio detecting means by Fourier transform (FIG. 3).

  That is, as shown in FIG. 18, the band of only the portion related to the responsiveness of the air-fuel ratio detecting means is extracted using Fourier transform, and the responsiveness deterioration is based on the amplitude (or power) of the signal component in the band. Determine. By setting the passband in this way, it is possible to detect a gain decrease due to response deterioration without being affected by high-frequency noise.

  In a fourth aspect of the control device according to the present invention, the air-fuel ratio detection means is disposed downstream of the catalyst in the exhaust passage (see FIG. 4).

  In a fifth aspect of the control apparatus according to the present invention, the air-fuel ratio detecting means is an A / F sensor capable of detecting a wide range of air-fuel ratio (see FIG. 5).

According to a sixth aspect of the control apparatus of the present invention, the air-fuel ratio detecting means is an O ₂ sensor that can detect whether the air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio (see FIG. 6). .

  According to a seventh aspect of the control device of the present invention, the diagnosis means determines that the air-fuel ratio detection means has deteriorated when the amplitude or power is equal to or less than a predetermined value A (see FIG. 7).

  That is, when the responsiveness deteriorates, the amplitude (power) of the signal after passing through the bandpass filter decreases as shown in FIG. Therefore, when the amplitude or power of the signal is equal to or less than the predetermined value A, it is determined that the responsiveness of the air-fuel ratio detecting means has deteriorated.

  In an eighth aspect of the control device according to the present invention, the diagnosis means determines that the air-fuel ratio detection means has deteriorated when the amplitude or power is not more than a predetermined value A and not less than a predetermined value B. (See FIG. 8).

That is, the oxygen concentration in the exhaust gas corresponding to the input of the air-fuel ratio detection means does not necessarily have a vibration waveform having an amplitude. In particular, in the case of downstream of the catalyst, the influence of O ₂ storage and desorption functions in the catalyst. For this reason, the oxygen concentration in the exhaust gas is stable. In this case, even if the responsiveness of the air-fuel ratio detecting means is normal, the amplitude (power) of the signal after passing through the band-pass filter is small, and there is a possibility of erroneously diagnosing responsiveness degradation. From this, by adding a condition in which the power is equal to or greater than the predetermined value B, it is possible to prevent erroneous diagnosis when the oxygen concentration in the exhaust gas is stable.

  According to a ninth aspect of the control apparatus of the present invention, in the configuration of the seventh aspect, the diagnostic means includes means for calculating a number n1 of times that the amplitude or power in a predetermined period is equal to or less than a predetermined value A, and the number n1 Is equal to or greater than a predetermined value K1, it is determined that the responsiveness of the air-fuel ratio detecting means has deteriorated (see FIG. 9).

  That is, in the configuration of the ninth aspect, when the responsiveness of the air-fuel ratio detecting means deteriorates, the amplitude or power becomes not more than the predetermined value A, but when the diagnosis is performed while the vehicle is running, the input signal of the air-fuel ratio detecting means May not be able to achieve a desired specification with high diagnostic accuracy. In view of this, in this aspect, a sufficient diagnosis period or diagnosis opportunity is ensured and the diagnosis is performed probabilistically.

  According to a tenth aspect of the control device of the present invention, in the configuration according to the eighth aspect, the diagnosis unit calculates the number n2 of times that the amplitude or power in the predetermined period is equal to or less than the predetermined value A and equal to or greater than the predetermined value B. When the number n2 is equal to or greater than a predetermined value K2, it is determined that the responsiveness of the air-fuel ratio detecting means has deteriorated (see FIG. 10).

  That is, in view of the same situation as the ninth aspect, in the configuration of the eighth aspect, a sufficient diagnosis period or a diagnosis opportunity is ensured, and the diagnosis is performed probabilistically.

  An eleventh aspect of the control device according to the present invention is an operation state detection means for detecting an operation state of the engine, and a diagnosis permission determination for determining whether to permit detection of the amplitude or power based on the operation state. Means (see FIG. 11).

  That is, it is accurate to perform diagnosis in a region where the frequency component of the oxygen concentration in the exhaust gas, which is the output signal of the air-fuel ratio detection means, is large in the band corresponding to the pass band of the band-pass filter as shown in FIG. From the viewpoint of. In general, the vibration frequency of the oxygen concentration (air-fuel ratio) in the exhaust gas changes according to the operating state of the engine. From this, for example, engine operating conditions such as engine speed and intake air amount are detected, and diagnosis is performed in a region where the S / N ratio of diagnosis is high.

  A twelfth aspect of the control device according to the present invention comprises air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied for combustion based on the output signal of the air-fuel ratio detection means, The air-fuel ratio control parameter is changed based on the amplitude or power (see FIG. 12).

  That is, when the air-fuel ratio F / B control is performed based on the output of the air-fuel ratio detection means, the optimum value of the F / B control parameter depends on the responsiveness of the air-fuel ratio detection means. Therefore, by detecting the responsiveness of the air-fuel ratio detection means from the amplitude (power) of the signal after passing through the band-pass filter and adapting the F / B control parameters, the stability of the F / B control is always improved. Responsiveness can be ensured while maintaining.

  According to a thirteenth aspect of the control device of the present invention, in the configuration of the fourth aspect, the air-fuel ratio of the air-fuel mixture provided for combustion is controlled based on the output signal of the air-fuel ratio detecting means disposed downstream of the catalyst. The air-fuel ratio control means is configured to change the air-fuel ratio control parameter based on the amplitude or power (see FIG. 13).

  That is, similarly to the twelfth aspect, the parameters of the air-fuel ratio F / B control performed using the air-fuel ratio detecting means downstream of the catalyst are adapted according to the responsiveness of the air-fuel ratio detecting means downstream of the catalyst.

  According to a fourteenth aspect of the control device of the present invention, in the configuration of the twelfth aspect, the control device includes means for calculating a control period of the air-fuel ratio control means, and the diagnosis means has the control period equal to or greater than a predetermined value C. It is determined that the air-fuel ratio detection means has deteriorated (see FIG. 14).

  That is, if the parameters of the air-fuel ratio F / B control performed using the air-fuel ratio detection means are adapted according to the responsiveness of the air-fuel ratio detection means, the F / B control cycle becomes longer. Therefore, by measuring the F / B control cycle, it becomes possible to indirectly detect the deterioration of the responsiveness of the air-fuel ratio detection means.

  According to a fifteenth aspect of the control device of the present invention, in the configuration of the thirteenth aspect, the control device includes means for calculating a control period of the air-fuel ratio control means, and the diagnosis means has the control period equal to or greater than a predetermined value D. It is determined that the air-fuel ratio detecting means has deteriorated (see FIG. 15).

  That is, as in the fourteenth aspect, if the parameters of the air-fuel ratio F / B control performed using the air-fuel ratio detecting means downstream of the catalyst are adapted according to the responsiveness of the air-fuel ratio detecting means downstream of the catalyst, The B control cycle becomes longer. Therefore, by measuring the F / B control cycle, it becomes possible to indirectly detect the deterioration of the responsiveness of the air-fuel ratio detection means.

  On the other hand, an automobile according to the present invention is characterized in that an engine to which the control device is applied is mounted.

  The control apparatus according to the present invention extracts a band of only a portion related to the responsiveness of the air-fuel ratio detection unit using a predetermined frequency band extraction unit such as a bandpass filter, and the amplitude (or power) of the signal component in the band. ), The air-fuel ratio detection means is diagnosed (responsiveness deterioration judgment). At this time, in the frequency characteristics of the air-fuel ratio detection means, the pass band of the band-pass filter is changed to the normal response and the response characteristics. By setting the gain characteristics in different areas at the time of deterioration, it is possible to detect gain reduction due to responsiveness deterioration without being affected by high-frequency noise. The air-fuel ratio detection means is highly robust and the air-fuel ratio detection means can be used regardless of whether the air-fuel ratio detection means is located upstream or downstream of the catalyst in the exhaust passage. It can be diagnosed in accuracy.

Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
FIG. 19 is a schematic configuration diagram illustrating a first embodiment of the control device according to the present invention together with an example of an in-vehicle engine to which the control device is applied.

  The illustrated engine 10 is a multi-cylinder engine having four cylinders # 1, # 2, # 3, and # 4, for example, and includes a cylinder 12 and each cylinder # 1, # 2, # 3, # of the cylinder 12. 4, and a piston 15 slidably inserted into the piston 4. A combustion chamber 17 is defined above the piston 15. A spark plug 35 is provided in the combustion chamber 17.

  Air used for combustion of fuel is taken in from an air cleaner 21 provided at the start end of the intake passage 20, passes through an air flow sensor 24, passes through an electric throttle valve 25, enters a collector 27, and passes through the collector 27. The air is sucked into the combustion chambers 17 of the cylinders # 1, # 2, # 3, and # 4 via the intake valve 28 disposed at the downstream end (intake port) of the intake passage 20. A fuel injection valve 30 is provided in the downstream portion (branch passage portion) of the intake passage 20.

  The mixture of the air sucked into the combustion chamber 17 and the fuel injected from the fuel injection valve 30 is ignited by the spark plug 35 and explosively burned, and the combustion waste gas (exhaust gas) is exhausted from the combustion chamber 17. The exhaust gas is discharged to the individual passage portion forming the upstream portion of the exhaust passage 40 through the valve 48, and flows into the three-way catalyst 50 disposed in the exhaust passage 40 through the exhaust collecting portion and purified. After that, it is discharged outside.

Further, an O ₂ sensor 52 is disposed downstream of the three-way catalyst 50 in the exhaust passage 40, and an A / F sensor 51 is disposed in an exhaust collecting portion upstream of the catalyst 50 in the exhaust passage 40. .

The A / F sensor 51 has a linear output characteristic with respect to the concentration of oxygen contained in the exhaust gas. The relationship between the oxygen concentration in the exhaust gas and the air-fuel ratio is almost linear. Therefore, the A / F sensor 51 that detects the oxygen concentration can determine the air-fuel ratio in the exhaust gas collecting portion. Further, from the signal from the O ₂ sensor 52, it can be determined whether the oxygen concentration downstream of the three-way catalyst 50 or the stoichiometric value is rich or lean.

  Further, a part of the exhaust gas discharged from the combustion chamber 17 to the exhaust passage 40 is introduced into the intake passage 20 through the EGR passage 41 as necessary, and is supplied to each cylinder through the branch passage portion of the intake passage 20. It returns to the combustion chamber 17. The EGR passage 41 is provided with an EGR valve 42 for adjusting the EGR rate.

  And in the control apparatus 1 of this embodiment, in order to perform various control of the engine 10, the control unit 100 incorporating a microcomputer is provided.

  As shown in FIG. 20, the control unit 100 basically includes a CPU 101, an input circuit 102, an input / output port 103, a RAM 104, a ROM 105, and the like.

In the control unit 100, as an input signal, a signal corresponding to the intake air amount detected by the air flow sensor 24, a signal corresponding to the opening of the throttle valve 25 detected by the throttle sensor 28, a crank angle sensor (engine speed) Sensor) a signal representing rotation (engine speed) and phase of the crankshaft 18 obtained from the sensor 37, oxygen in the exhaust gas detected by an O ₂ sensor 52 disposed downstream of the three-way catalyst 50 in the exhaust passage 40 A signal corresponding to the concentration, a signal corresponding to the oxygen concentration (air-fuel ratio) detected by the A / F sensor 51 disposed in the exhaust collecting portion upstream of the catalyst 50 in the exhaust passage 40, and disposed in the cylinder 12. A signal corresponding to the engine cooling water temperature detected by the water temperature sensor 19, an accelerator pedal obtained from the accelerator sensor 36. Signal or the like corresponding to the amount of depression of the Le 39 (indicating the requested torque of the driver) is supplied.

In the control unit 100, outputs of sensors such as an A / F sensor 51, an O ₂ sensor 52, a throttle sensor 28, an air flow sensor 24, a crank angle sensor 37, a water temperature sensor 16, and an accelerator sensor 36 are input. After signal processing such as noise removal is performed in the circuit 102, the signal is sent to the input / output port 103. The value of the input port is stored in the RAM 104 and processed in the CPU 101. A control program describing the contents of the arithmetic processing is written in the ROM 105 in advance. A value representing each actuator operation amount calculated according to the control program is stored in the RAM 104 and then sent to the output port 103.

  The operation signal for the spark plug 35 is set to an ON / OFF signal that is ON when the primary coil in the ignition output circuit 116 is energized and is OFF when the primary coil is not energized. The ignition timing is the time when the ignition timing changes from ON to OFF. The signal for the spark plug 35 set in the output port 103 is amplified to a sufficient energy necessary for ignition by the ignition output circuit 116 and supplied to the spark plug 35. The drive signal for the fuel injection valve 30 is set to an ON / OFF signal that is ON when the valve is opened and OFF when the valve is closed. The fuel injection valve drive circuit 117 has sufficient energy to open the fuel injection valve 30. Amplified and supplied to the fuel injection valve 30. A drive signal for realizing the target opening degree of the electric throttle valve 25 is sent to the electric throttle valve 30 through the electric throttle valve drive circuit 118.

In the control unit 100, the air-fuel ratio upstream of the three-way catalyst 50 is calculated from the output signal of the A / F sensor 51, and the oxygen concentration or stoichiometry downstream of the three-way catalyst 50 is rich from the output signal of the O ₂ sensor 52. Calculate which is lean. Further, feedback control for sequentially correcting the fuel injection amount or the intake air amount is performed using the outputs of the sensors 51 and 52 so that the purification efficiency of the three-way catalyst 50 is optimized.

  FIG. 21 is a functional block diagram showing the processing contents (means) of the control unit 100. The diagnosis permission judging means 210, the bandpass filter 220 which is means for extracting signal components in a predetermined frequency band, and the A / F sensor. The sensor diagnostic means 230 for determining whether the response of 51 has deteriorated is provided.

Hereinafter, each processing means will be described in detail.
<Diagnosis permission determination means 210>
FIG. 22 is a diagram illustrating the processing contents of the diagnosis permission determination unit 210. The cooling water temperature Twn detected by the water temperature sensor 19 is greater than or equal to a predetermined value Twndag, the engine speed Ne detected by the engine speed sensor 37 is less than or equal to a predetermined value NedagH and greater than or equal to a predetermined value NedagL, and is detected by the airflow sensor 24 When the intake air amount Qa is equal to or smaller than the predetermined value QadagH and equal to or larger than the predetermined value QadagL, the deterioration diagnosis permission flag Fpdag is set to 1, and the A / F sensor 51 is diagnosed. Twndag, NedagH, NedagL, QadagH, and QadagL improve the diagnostic accuracy by setting a driving state in which the amplitude (power) of the input signal becomes large in the passband of the bandpass filter 220 by performing a vehicle (engine) running test or the like. (See FIG. 16).

  That is, the diagnosis is performed in a region where the frequency component of the oxygen concentration in the exhaust gas, which is the output signal of the A / F sensor 51, increases in a band corresponding to the pass band of the band pass filter as shown in FIG. Desirable in terms of accuracy. In general, the vibration frequency of the oxygen concentration (air-fuel ratio) in the exhaust gas changes according to the operating state of the engine. From this, for example, the operating state of the engine, such as the cooling water temperature, the engine speed, the intake air amount, is detected, and the diagnosis is performed in a region where the S / N ratio of the diagnosis is high.

<Band pass filter 220>
As shown in FIG. 23, the bandpass filter 220 performs a bandpass filter process including an FIR or IIR filter on the output RABF of the A / F sensor 51, and sets the filter output to RABF_FIL. As is well known, both FIR and IIR filter configurations have their merits and demerits, so it is better to decide according to actual use conditions. The pass band and stop band of the band pass filter 220 are preferably determined according to the responsiveness of the A / F sensor 51, as shown in FIG. That is, it is desirable to set a band where the difference between the normal response time and the response deterioration time is the largest as the pass band. Since there are many documents and books about the design method of the filter, it will not be described in detail here.

<Sensor diagnostic means 230>
FIG. 24 is a diagram illustrating the processing contents of the sensor diagnosis unit 230. When the deterioration diagnosis permission flag Fpdag calculated by the diagnosis permission determination unit 210 is 1, the difference between the RABF_FIL calculated (currently) by the bandpass filter 220 and the RABF_FIL calculated last time is taken, and the absolute value of the difference is calculated. Let it be FIL_ABS. The difference is taken in order to eliminate the direct current component and extract only the amplitude component. Since a difference is taken with respect to the signal after passing through the band pass filter 220, the high frequency component is not amplified. When the value obtained by integrating FIL_ABS for a predetermined period is ABS_SUM, the deterioration diagnosis permission flag is 1, and when ABS_SUM is not less than ABS_SUM_L and not more than ABS_SUM_H, it is determined that the responsiveness of the A / F sensor 51 has deteriorated. It lights up. ABS_SUM_L and ABS_SUM_H are preferably determined according to the characteristics of the vehicle (engine) and the target diagnostic accuracy.

  In addition, the number of times n2 at which ABS_SUM is equal to or higher than ABS_SUM_L and equal to or lower than ABS_SUM_H is calculated during a predetermined period, and when n2 is equal to or lower than a predetermined value K2, it is determined that the responsiveness of the A / F sensor 51 has deteriorated. (See FIG. 10). K2 is also preferably determined according to the characteristics of the vehicle (engine) and the target diagnostic accuracy.

  As described above, the control device 1 according to the present embodiment uses the band-pass filter 220 to extract only the band related to the responsiveness of the A / F sensor 51, and the amplitude (or power) of the signal component in the band. The diagnosis of the A / F sensor 51 (determination of responsiveness deterioration) is performed based on the frequency characteristics of the A / F sensor 51. At this time, in the frequency characteristics of the A / F sensor 51, the passband of the bandpass filter 220 is set to Since the gain characteristics are set in different areas when the response is deteriorated, it is possible to detect a gain decrease due to the response deterioration without being affected by the high frequency noise. This can be avoided, has high robustness against noise, and the sensor can be used regardless of whether the sensor is disposed upstream or downstream of the catalyst 50 in the exhaust passage 40. It can be diagnosed in accuracy.

[Second Embodiment]
In the second embodiment, the O ₂ sensor 52 downstream of the catalyst 50 is diagnosed. Specifically, the same processing is performed using the output signal of the O ₂ sensor 52 instead of the A / F sensor 51 in the first embodiment. The configuration of each part of the second embodiment is basically the same as that of the first embodiment (FIGS. 19 to 24) described above, but the input signal of the bandpass filter 220 is the same as that of the first embodiment. In this case, the output signal of the A / F sensor 51 is an output signal of the O ₂ sensor 52 in the present embodiment. Details of each processing means will be described below.

<Diagnosis permission determination means 210>
The diagnosis permission determination unit 210 of the second embodiment is the same as that of the first embodiment (see FIG. 22), and thus will not be described in detail. Twndag, NedagH, NedagL, QadagH, and QadagL are the same as those of the first embodiment. Not a value.

<Band pass filter 220>
In the first embodiment, the output of the A / F sensor 51 becomes a filter input, but in the second embodiment, the output of the O ₂ sensor 52 is used (see FIG. 23). The output VRO2 of the O ₂ sensor 52 is subjected to bandpass filter processing constituted by an FIR or IIR filter, and the filter output is set to VRO2_FIL. As is well known, both FIR and IIR filter configurations have their merits and demerits, so it is better to decide according to actual use conditions. The passband and stopband of the bandpass filter are preferably determined according to the responsiveness of the A / F sensor 51, as shown in FIG. That is, it is desirable to set a band where the difference between the normal response time and the response deterioration time is the largest as the pass band. Since there are many documents and books about the design method of the filter, it will not be described in detail here.

<Sensor diagnostic means 230>
Similar to the first embodiment (see FIG. 24), in this sensor diagnosis means 230, when the deterioration diagnosis permission flag Fpdag calculated by the diagnosis permission determination means 210 is 1, it is calculated by the bandpass filter 220 (this time). The difference between VRO2_FIL and the previously calculated VRO2_FIL is taken, and the absolute value of the difference is taken as FIL_ABS2. The difference is taken in order to eliminate the direct current component and extract only the amplitude component. Since a difference is taken with respect to the signal after passing through the band pass filter 220, the high frequency component is not amplified. When the value obtained by integrating FIL_ABS2 for a predetermined period is ABS_SUM2, the deterioration diagnosis permission flag is 1, and when ABS_SUM2 is equal to or higher than ABS_SUM_L and equal to or lower than ABS_SUM_H, it is determined that the responsiveness has deteriorated. ABS_SUM_L and ABS_SUM_H should be determined according to the characteristics of the vehicle (engine) and the target diagnostic accuracy, and do not necessarily match those of the first embodiment.

  In addition, as shown in FIG. 10, the number of times n2 at which ABS_SUM2 is equal to or higher than ABS_SUM_L and equal to or lower than ABS_SUM_H is calculated during a predetermined traveling period, and when n2 becomes equal to or lower than a predetermined value K2, the responsiveness is deteriorated. It is good to judge. K2 is also preferably determined according to the characteristics of the vehicle (engine) and the target diagnostic accuracy.

[Third Embodiment]
As described above, in addition to performing diagnosis (determination of response deterioration) of the A / F sensor 51 or the O ₂ sensor 52, in the third embodiment, the response of the A / F sensor 51 upstream of the catalyst 50 is used. Based on the diagnosis result, air-fuel ratio F / B (feedback) control parameter tuning using the A / F sensor 51 is performed.

  FIG. 25 is a diagram showing the processing contents of the F / B control means 250 that performs the air-fuel ratio F / B control based on the output of the A / F sensor 51. Based on the deviation DRABF between the target air-fuel ratio TRABF and the output RABF of the A / F sensor 51, the air-fuel ratio correction term LAMBDA is obtained by PI control. Although not shown in the figure, the air-fuel ratio correction term LAMBDA is multiplied by the fuel injection amount, and the air-fuel ratio of the air-fuel mixture used for combustion is corrected as appropriate. Further, the P gain and the I gain are adjusted based on ABS_SUM calculated by the sensor diagnosis unit 230 of FIG. That is, ABS_SUM is an index representing the responsiveness of the A / F sensor 51.

  The optimum value of the F / B gain of the F / B control by the A / F sensor 51 depends on the responsiveness of the system, but when the responsiveness of the A / F sensor 51 changes, the responsiveness of the system also changes accordingly. The optimum value of the F / B gain also changes. The F / B gain is tuned online to an optimum value based on ABS_SUM representing at least the responsiveness of the A / F sensor 51. The optimum values of ABS_SUM, P gain, and I gain can be determined theoretically, but may be determined from experimental results.

That is, when the air-fuel ratio F / B control is performed based on the output of the A / F sensor 51 (or the O ₂ sensor 52), the optimum value of the F / B control parameter depends on the response of the sensor. Therefore, by detecting the responsiveness of the sensor from the amplitude (power) of the signal after passing through the bandpass filter and adapting the F / B control parameters, the stability of the F / B control is always maintained. Responsiveness can be ensured.

[Fourth Embodiment]
In the fourth embodiment, parameter tuning of air-fuel ratio F / B (feedback) control using the O ₂ sensor 52 is performed based on the diagnostic result of the responsiveness of the O ₂ sensor 52 downstream of the catalyst 50.

FIG. 26 is a diagram showing the processing contents of the F / B control means 260 that performs air-fuel ratio F / B control based on the output of the O ₂ sensor 52. In addition to the F / B control based on the output of the A / F sensor 51 in the third embodiment, the target air-fuel ratio air-fuel ratio TRABF is obtained by PI control based on the O ₂ sensor 52 output VRO2 and the target VRO2 TVRO2. Although not shown in the figure, TRABF is calculated by specific PI control using the O ₂ sensor 52 which is a binary sensor. Details of the PI control using the O ₂ sensor 52 are not described here because there are many documents. Further, the P gain and the I gain are adjusted based on ABS_SUM2 calculated by the sensor diagnosis unit 230 of the second embodiment (FIG. 24). That is, ABS_SUM2 is an index representing the responsiveness of the O ₂ sensor 52. O ₂ optimum value of F / B gain of F / B control by the sensor 52 is dependent on the response of the system, O ₂ vary accordingly the response of the sensor 52 changes the response of the system, F / The optimum value of B gain also changes. The F / B gain is on-line tuned to an optimum value based on at least ABS_SUM2 representing the response of the O ₂ sensor 52.

The ABS_SUM2, the optimum values of the P gain and the I gain can be theoretically determined, but may be determined from the experimental results. By combining the third and fourth embodiments, the P gain and I gain of both the F / B control based on the output of the A / F sensor 51 and the F / B control based on the O ₂ sensor 52 are tuned online. Also good.

[Fifth Embodiment]
In the fifth embodiment, diagnosis (responsiveness deterioration determination) of the A / F sensor 51 based on the air-fuel ratio F / B control cycle using the A / F sensor 51 is performed.

  In the third embodiment, when the P gain and I gain of the F / B control using the A / F sensor 51 are tuned online based on the responsiveness of the A / F sensor 51, the A / F sensor 51 As the responsiveness deteriorates (decreases), the P gain and the I gain become smaller and the F / B control cycle becomes longer. This F / B control cycle is detected as shown in FIG. 14, and when the control cycle becomes equal to or greater than a predetermined value C, it is determined that the responsiveness of the A / F sensor 51 has deteriorated. As a method for detecting the F / B control cycle, there is a method of obtaining the correction value of the F / B control by the time in the rich side correction and the cycle of the time in the lean side correction.

[Sixth Embodiment]
In the sixth embodiment, it is to perform diagnosis of the O ₂ sensor 52 based on the air-fuel ratio F / B control period using the O ₂ sensor 52 (response deterioration determination).

In the fourth embodiment, based on the response of the O ₂ sensor 52, the P gain and I gain of F / B control using an O ₂ sensor 52 is online tuning, the response of the O ₂ sensor 52 As it deteriorates, the P gain and the I gain become smaller and the F / B control cycle becomes longer. This F / B control cycle is detected as shown in FIG. 15, and when this control cycle is equal to or greater than a predetermined value D, it is determined that the responsiveness of the O ₂ sensor 52 has deteriorated. In addition, as a method for detecting the F / B control cycle, there is a method of obtaining the correction value of the F / B control by the time in the rich side correction and the cycle of the time in the lean side correction.

[Seventh Embodiment]
FIG. 27 is a functional block diagram showing the processing contents (means) of the control unit 100 according to the seventh embodiment. The diagnosis permission judging means 310 and FFT means for extracting (detecting) signal components in a predetermined frequency band. (DFT) the response of the computing unit 320, a / F sensor 51 (or O ₂ sensor 52) is provided with a sensor diagnostic means 330 for determining whether the deteriorated.

  Since the diagnosis permission determination unit 310 is the same as that of the first embodiment (see FIG. 21), detailed description thereof is omitted, and the FFT (DFT) calculation unit 320 and the sensor diagnosis unit 330 will be described in detail below. To do.

<FFT (DFT) Operation Unit 320>
As shown in FIG. 28, the FFT (DFT) calculation unit 320 obtains power in a predetermined frequency band using an FFT (Fast Fourier Transform) 322. Based on the output signal RABF of the A / F sensor 51 or the output signal VRO2 of the O ₂ sensor 52, the difference unit 321 obtains the difference between the current calculated value and the previous calculated value, and performs FFT or DFT (Discrete Fourier) on this difference. Transform) processing (Fourier transform) is performed to obtain power in a predetermined frequency band, and set as RABF_FIL (VRO2_FIL). The frequency band extracted by the FFT (DFT) 322 is preferably determined according to the responsiveness of the A / F sensor 51 (or the O ₂ sensor 52) as shown in FIG. In other words, it is desirable to set a band where the difference between the normal response time and the response deterioration time is the largest as the extraction band.

<Sensor diagnosing means 330>
FIG. 29 is a diagram showing the processing contents of the sensor diagnosis means 330. When the deterioration diagnosis permission flag Fpdag calculated by the diagnosis permission determination unit 310 is 1, the value obtained by integrating the RABF_FIL (VRO2_FIL) calculated by the FFT (DFT) calculation unit 320 for a predetermined period is defined as ABS_SUM (ABS_SUM2), and the deterioration diagnosis is permitted. When the flag is 1 and ABS_SUM (ABS_SUM2) is not less than ABS_SUM_L and not more than ABS_SUM_H, it is determined that the responsiveness of the A / F sensor 51 (or O ₂ sensor 52) has deteriorated, for example, a warning light is turned on. . ABS_SUM_L and ABS_SUM_H should be determined according to the characteristics of the vehicle (engine) and the target diagnostic accuracy, and do not necessarily match when the A / F sensor 51 is used and when the O ₂ sensor 52 is used.

  It is also possible to calculate the number n2 of establishments during which the ABS_SUM (ABS_SUM2) is greater than or equal to ABS_SUM_L and less than or equal to ABS_SUM_H during a predetermined period, and when n2 is less than or equal to the predetermined value K2, it may be determined that the responsiveness is deteriorated ( (See FIG. 10). K2 is also preferably determined according to the characteristics of the vehicle (engine) and the target diagnostic accuracy.

The figure which is provided for description of the 1st aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 2nd aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 3rd aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 4th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 5th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 6th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 7th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 8th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 9th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 10th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 11th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 12th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 13th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 14th aspect of the control apparatus which concerns on this invention. The figure which is provided for description of the 15th aspect of the control apparatus which concerns on this invention. The figure which shows the frequency characteristic at the time of the normal response of an air fuel ratio detection means, and the response deterioration, and the pass band of a band pass filter. Shows the time response normal and the output signal at the time of response deterioration of the air-fuel ratio detecting means (O ₂ sensor). Air-fuel ratio shows the time response normal and the frequency analysis results of the response time of the degradation of the detection means (O ₂ sensor). BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows 1st Embodiment of the control apparatus which concerns on this invention with the engine to which it is applied. The internal block diagram of the control unit in 1st Embodiment. The functional block diagram with which it uses for description of the processing content of the control unit in 1st Embodiment. The figure which is provided to description of the diagnosis permission determination means in 1st Embodiment. The figure which is provided for description of the band pass filter in 1st Embodiment. The figure which is provided for description of the sensor diagnostic means in the first embodiment. The figure which is provided to description of the F / B control means based on the A / F sensor output in 3rd Embodiment. Is a diagram illustrating the F / B control means based on the O ₂ sensor output in the fourth embodiment. . The functional block diagram with which it uses for description of the processing content of the control unit in 7th Embodiment. The figure which is provided for description of the FFT (DFT) calculating part in 7th Embodiment. The figure which is provided for description of the sensor diagnostic means in the seventh embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control apparatus 10 Engine 17 Combustion chamber 19 Water temperature sensor 20 Intake passage 21 Air cleaner 24 Air flow sensor 25 Electric throttle valve 28 Throttle opening sensor 30 Fuel injection valve 35 Spark plug 37 Crank angle (engine speed) sensor 39 Accelerator opening sensor 40 Exhaust passage 50 Three-way catalyst 51 A / F sensor 52 Oxygen sensor 100 Control unit 210 Diagnosis permission determination means 220 Band pass filter (predetermined frequency band component extraction means)
230 Sensor diagnosis means 250 Air-fuel ratio F / B control means 310 Diagnosis permission determination means 320 FFT (DFT) calculation unit 330 Sensor diagnosis means

Claims (16)

  An engine control apparatus including an air-fuel ratio detection unit, wherein the predetermined frequency band component extraction unit extracts a signal component of a predetermined frequency band from an output signal of the air-fuel ratio detection unit, and the amplitude of the signal component of the predetermined frequency band Alternatively, a control apparatus comprising: amplitude / power calculation means for calculating power; and diagnosis means for diagnosing the air-fuel ratio detection means based on the amplitude or power.   2. The control apparatus according to claim 1, wherein the predetermined frequency band component extracting unit is composed of a band-pass filter that allows passage of only a predetermined frequency band of an output signal of the air-fuel ratio detecting unit.   2. The control device according to claim 1, wherein the predetermined frequency band component extracting unit extracts a signal component of the predetermined frequency band from an output signal of the air-fuel ratio detecting unit by Fourier transform. .   The control device according to any one of claims 1 to 3, wherein the air-fuel ratio detection means is arranged downstream of the catalyst in the exhaust passage.   5. The control device according to claim 1, wherein the air-fuel ratio detecting means is an A / F sensor capable of detecting a wide range of air-fuel ratio. 5. The control device according to claim 1, wherein the air-fuel ratio detection means is an O ₂ sensor capable of detecting whether the air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio. .   The control device according to any one of claims 1 to 6, wherein the diagnosis unit determines that the air-fuel ratio detection unit has deteriorated when the amplitude or power is equal to or less than a predetermined value A.   The diagnostic means determines that the air-fuel ratio detecting means has deteriorated when the amplitude or power is not more than a predetermined value A and not less than a predetermined value B. The control device described.   The diagnostic means includes means for calculating the number of times n1 when the amplitude or power in a predetermined period is equal to or less than a predetermined value A. When the number of times n1 is equal to or greater than the predetermined value K1, the responsiveness of the air-fuel ratio detecting means is degraded. The control device according to claim 7, wherein the control device is determined.   The diagnostic means includes means for calculating the number of times n2 at which the amplitude or power in a predetermined period is not more than a predetermined value A and not less than the predetermined value B, and when the number of times n2 is not less than the predetermined value K2, the air-fuel ratio 9. The control device according to claim 8, wherein it is determined that the responsiveness of the detection means has deteriorated.   An operation state detection unit that detects an operation state of the engine, and a diagnosis permission determination unit that determines whether or not to detect the amplitude or power based on the operation state are provided. The control device according to claim 1.   Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture to be used for combustion based on the output signal of the air-fuel ratio detection means, and the air-fuel ratio control means controls the air-fuel ratio based on the amplitude or power The control device according to claim 1, wherein the parameter is changed.   Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied for combustion based on the output signal of the air-fuel ratio detection means disposed downstream of the catalyst, the air-fuel ratio control means comprising the amplitude or power 5. The control apparatus according to claim 4, wherein the air-fuel ratio control parameter is changed based on the control.   13. The apparatus according to claim 12, further comprising means for calculating a control period of the air-fuel ratio control means, wherein the diagnosis means determines that the air-fuel ratio detection means has deteriorated when the control period is equal to or greater than a predetermined value C. The control device described in 1.   14. The apparatus according to claim 13, further comprising means for calculating a control period of the air-fuel ratio control means, wherein the diagnosis means determines that the air-fuel ratio detection means has deteriorated when the control period is equal to or greater than a predetermined value D. The control device described in 1.   An automobile equipped with an engine to which the control device according to any one of claims 1 to 15 is applied.

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