JP4789991B2 - Exhaust gas sensor deterioration diagnosis device - Google Patents

Description

  The present invention relates to a diagnostic apparatus for detecting a deterioration failure of an exhaust gas sensor provided in an exhaust passage of an internal combustion engine.

  An exhaust gas sensor for measuring an exhaust gas component is generally attached to an exhaust passage of an internal combustion engine of a vehicle. The exhaust gas sensor outputs the air-fuel ratio in the exhaust gas, and the control device of the internal combustion engine controls the air-fuel ratio of the fuel supplied to the internal combustion engine based on this output value. Therefore, if the exhaust gas sensor is deteriorated and failed and cannot provide a sensor output that reflects the accurate air-fuel ratio, the control device cannot accurately control the air-fuel ratio for the internal combustion engine.

Several techniques have been disclosed as techniques for detecting such initial abnormality and deterioration failure of the exhaust gas sensor. For example, there is a technique for determining abnormality of the exhaust gas sensor by measuring the attenuation amount of the output waveform by utilizing the fact that the output waveform of the exhaust gas sensor at the time of failure is attenuated from the amplitude at the normal time. In Patent Document 1, the abnormality judgment based on the attenuation amount of the output waveform is processed in a stepwise manner using a plurality of filters, thereby suppressing deterioration of exhaust gas and deterioration of operability, and deterioration failure of the exhaust gas sensor. A method for detecting the above is disclosed.
JP 2007-270745 A

  The above-described known technique (Patent Document 1) can cope with a failure mode in which the amplitude of the output waveform of the exhaust gas sensor is attenuated. However, in this method, for example, when the air-fuel ratio shifts from the rich state (the fuel is high and the air is low) to the lean state (the fuel is low and the air is large), or when the air-fuel ratio shifts from the lean state to the rich state If any abnormality occurs in the exhaust gas sensor in either process, it cannot be detected.

  Further, abnormalities in the exhaust gas sensor include a failure mode in which the output waveform causes frequency distortion when a sine wave is used as the input waveform. Frequency distortion means that when a sine wave is used as an input waveform, it becomes a different output waveform.For example, a square wave or a triangular wave is mixed in part of the output waveform. This corresponds to the case where the falling is different. Although the input waveform and the output waveform are different, when the amplitude is not attenuated to the extent that it can be determined that the amplitude is abnormal, the above-described known technique for comparing the attenuation of the amplitude cannot determine the abnormality of the exhaust gas sensor.

  In view of the above problems, the present invention provides a diagnostic device that detects a failure mode in which a waveform different from an input waveform of a detection signal is output when diagnosing a deterioration failure of an exhaust gas sensor provided in an exhaust passage of an internal combustion engine. The purpose is to do.

  In order to solve the above problem, an embodiment of the present invention is an exhaust gas sensor deterioration failure diagnosis device that is provided in an exhaust passage of an internal combustion engine and generates an output corresponding to an exhaust gas component of the internal combustion engine. A detection signal generating means for generating a detection signal, and adding or multiplying the detection signal to the basic fuel injection amount to calculate a fuel injection amount including the detection signal, and an exhaust gas sensor evaluation for determining the state of the exhaust gas sensor Means.

  The exhaust gas sensor evaluation means includes a first bandpass filter that extracts a frequency component in a predetermined frequency band, and one or more other bands that extract a frequency component in a frequency band different from the first bandpass filter. A path filter is provided.

  Then, the exhaust gas sensor evaluation means calculates the ratio of the first frequency component extracted by the first band pass filter from the output of the exhaust gas sensor to the fuel injection amount and the other frequency component extracted by the other band pass filter. Based on this, it was configured to determine the state of the exhaust gas sensor.

  In the failure mode of the exhaust gas sensor in which a waveform different from the input waveform of the detection signal is output, the frequency component included in the output waveform is different from the frequency component included in the input waveform. Therefore, according to the above configuration, in evaluating the output waveform, a frequency component specific to the waveform is acquired through a plurality of band pass filters having different frequency bands. Then, by determining the frequency component ratio, a failure mode of the exhaust gas sensor that outputs a waveform different from the input waveform of the detection signal is detected. In this way, for example, a failure with frequency distortion that results in a different output waveform when a sine wave is used as an input waveform is normal by determining the ratio of the frequency component specific to the waveform through different bandpass filters in a plurality of frequency bands. Or failure.

  In the configuration of the above-described embodiment, the frequency band of the first bandpass filter can be configured to match the frequency band of the detection signal.

  In the above configuration, the detection signal can be configured to be a signal obtained by adding a sine wave or cosine wave to a predetermined offset value.

  In the above configuration, the frequency band of the other bandpass filter is preferably configured to be a frequency that is an integral multiple of the frequency band of the first bandpass filter.

  In the above configuration, the ratio of the frequency components is calculated based on the ratio between the first frequency component extracted by the first bandpass filter and the other frequency component extracted by the other bandpass filter, and the ratio is equal to or less than a predetermined value. It can be configured to determine that a failure has occurred.

  Furthermore, the exhaust gas sensor evaluation means may extract a frequency response corresponding to the detection signal from the output of the exhaust gas sensor and add a configuration for determining the state of the exhaust gas sensor based on this frequency response. By adding such a configuration, it is possible to cope with a failure mode in which the amplitude of the output waveform of the exhaust gas sensor is attenuated.

  Further, feedback representative value calculating means for calculating a feedback representative value from a feedback correction coefficient calculated to correct the fuel injection amount based on an output value from the exhaust gas sensor during normal operation, and detecting the feedback representative value And a fuel amount calculation means for calculating a final fuel injection amount for input to the internal combustion engine by multiplying a basic fuel injection amount including a signal for use, wherein the feedback representative value calculation means is for detecting deterioration failure. In the middle, a feedback representative value calculated from the feedback correction coefficient before failure detection is held, and the fuel amount calculation means is configured to calculate the final fuel injection amount using the held feedback representative value. You can also

  The present invention can provide a diagnostic device that detects a failure mode in which a waveform different from the input waveform of a detection signal is output when diagnosing a deterioration failure of an exhaust gas sensor provided in an exhaust passage of an internal combustion engine.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an overall configuration for explaining the concept according to the present embodiment.

[Description of functional block]
The detection signal generator 101 has a function of generating a predetermined detection signal KIDSIN obtained by adding a trigonometric function wave FDSIN or the like to the offset value IDOFT. The detection signal KIDSIN is added to the basic fuel injection amount to calculate the fuel injection amount INJ, and the fuel is injected into the internal combustion engine 102. In the present embodiment, an example in which the detection signal KIDSIN is added will be described, and an example in which the detection signal KIDSIN is multiplied will be described later.

  Exhaust gas having an output corresponding to the fuel injection amount is discharged from the exhaust system of the internal combustion engine 102. A wide-area air-fuel ratio sensor (exhaust gas sensor, hereinafter referred to as LAF sensor) 103 detects the exhaust gas that has been exhausted, and sends an equivalent ratio KACT that is an output thereof to the responsiveness evaluation unit 104. The responsiveness evaluation unit 104 performs bandpass filtering on the equivalence ratio KACT by two first bandpass filters BF1 and BF2 having different frequency bands, and performs absolute value conversion, integration, etc., and performs exhaust gas sensor evaluation. Send the result to the department. The exhaust gas sensor evaluation unit has a function of performing a deterioration failure diagnosis of the exhaust gas sensor based on these values.

  The internal combustion engine 102 is an internal combustion engine whose final fuel injection amount can be controlled by an injection controller. The LAF sensor 103 is a sensor that detects an air-fuel ratio in a wide range from lean to rich with respect to exhaust gas discharged from the internal combustion engine 102 and generates an equivalent ratio KACT.

  In the present embodiment, the detection signal KIDSIN is a sine wave having a frequency fid of about 4 Hz, the frequency band of the first bandpass filter BF1 is about 4 Hz, which is the same as the frequency fid, and the frequency band of the second bandpass filter BF2 is a frequency. It is set to about 8 Hz which is an integer multiple (twice) of fid. Note that this is an example, and it goes without saying that the detection signal is a sine wave and is not limited to a frequency of about 4 Hz.

  The functions of the detection signal generation unit 101, the response evaluation unit 104, and the exhaust gas sensor evaluation unit can be realized by an ECU (electronic control unit) shown in FIG. FIG. 2 is an overall block diagram of the ECU 200. The ECU 200 may be provided with an ECU dedicated to exhaust gas sensor failure diagnosis. In the present embodiment, the ECU 200 that controls the internal combustion engine system includes a detection signal generation unit 202, a response evaluation unit 204 (first bandpass filter). The functions of the fuel amount calculation unit 206 and the exhaust gas sensor evaluation unit 203 are incorporated.

  The ECU 200 includes a processor that executes calculations, a storage area that temporarily stores various data, a random access memory (RAM) that provides a work area for calculations performed by the processor, a program executed by the processor, and various data used for calculations. A read-only memory (ROM) stored in advance and a rewritable non-volatile memory for storing the results of computations by the processor and data to be saved from the parts of the engine system are provided. The nonvolatile memory can be realized by a RAM with a backup function that is always supplied with a voltage even after the system is stopped.

  The input interface 201 is an interface unit between the ECU 200 and each part of the engine system, receives information indicating the driving state of the vehicle sent from various parts of the engine system, performs signal processing, and analog information is converted into a digital signal. These are converted and passed to the exhaust gas sensor evaluation unit 203, the response evaluation unit 204, and the fuel amount calculation unit 206. In FIG. 2, the equivalent ratio KACT value, the vehicle speed V, the engine speed Ne, the engine load W, and the LAF sensor activation signal output from the LAF sensor 103 are shown, but not limited thereto. Various information is input.

  The detection signal generation unit 202 has a function of generating a predetermined detection signal KIDSIN obtained by adding a trigonometric wave FDSIN or the like to the offset value IDOFT based on a command from the exhaust gas sensor evaluation unit 203 (also FIG. 1). reference). The detection signal KIDSIN will be described in detail in the exhaust gas sensor failure diagnosis process.

  The exhaust gas sensor evaluation unit 203 performs calculation and condition determination to execute an exhaust gas sensor failure diagnosis process described later based on data passed from the input interface 201, and further includes a detection signal generation unit 202 and a responsiveness evaluation unit 204. And the fuel amount calculation unit 206 is controlled.

  In response to the command from the exhaust gas sensor evaluation unit 203, the responsiveness evaluation unit 204 converts the equivalent ratio KACT, which is the output from the LAF sensor 103, into a bandpass by using the two first bandpass filters BF1 and BF2. Filter. Thereafter, according to the evaluation of the exhaust gas sensor evaluation unit 203, this value is converted into an absolute value, and the converted value is integrated over a predetermined period. These functions will be described in detail in the exhaust gas sensor failure diagnosis process.

  The fuel amount calculation unit 206 has a function of receiving the detection signal KIDSIN calculated by the detection signal generation unit 202 and passing the fuel injection amount INJ generated by adding to the basic fuel injection amount to the output interface 205.

  The output interface 205 has a function of outputting the fuel injection charge INJ to the injection function of the internal combustion engine 102. The output interface 205 also receives a control signal from the exhaust gas sensor evaluation unit 203 and outputs it to the failure lamp. However, the present invention is not limited to this, and another controller or the like can be connected to the output interface 205.

[Explanation of exhaust gas sensor failure diagnosis process]
Next, an exhaust gas sensor failure diagnosis process for diagnosing a deterioration failure of the LAF sensor 103 will be described with reference to FIG. FIG. 3 is a flowchart showing the exhaust gas sensor failure diagnosis process of the present embodiment.

  When the exhaust gas sensor failure diagnosis process is called from the main program, the exhaust gas sensor evaluation unit 203 refers to the exhaust gas sensor evaluated flag and determines whether or not the exhaust gas sensor has already been evaluated for a deterioration failure (S301). . Here, since the exhaust gas sensor has not yet been evaluated and the exhaust gas sensor evaluated flag is set to 0, the process proceeds to S302 to determine whether or not the detection condition is satisfied. Here, the detection condition refers to a state where the vehicle speed, the engine speed, and the engine load are within a predetermined range. Therefore, the exhaust gas sensor evaluation unit 203 acquires the vehicle speed V, the engine speed Ne, and the engine load W via the input interface 201, and determines whether all of these are within a predetermined range. When this detection condition is not satisfied (S302: No), the exhaust gas sensor evaluation unit 203 advances the process to S315. In this case, the deterioration failure detection is not performed.

  Since the deterioration failure detection is not performed, the responsiveness evaluation unit 204 sends a command to the detection signal generation unit 202 to stop the detection signal, and sets KIDSIN to 0 by the changeover switch (step S315).

  Here, KIDSIN is a coefficient for outputting the fuel injection amount added to the basic fuel injection amount and added with the detection signal as shown in FIG. Therefore, when KIDSIN is 0, the fuel injection amount INJ, which is the basic fuel injection amount during normal operation, is injected from the injection.

  As disclosed in Japanese Patent No. 3957208, when a command is sent to the detection signal generation unit 202, the exhaust gas sensor evaluation unit 203 sets a predetermined time in the timer and starts counting down the timer. It can also be configured as follows. Here, the predetermined time set in the timer is the fuel injection in which the detection signal is reflected from the engine after the exhaust gas sensor evaluation condition is satisfied and the fuel injection in which the detection signal is reflected is performed. The time until the response to is stably output. In this way, by setting the timer to start the evaluation after the lapse of a predetermined time, it is possible to avoid the unstable output state immediately after the detection signal is reflected in the fuel and evaluate the response, so that the detection Accuracy can be improved.

  When KIDSIN is set to 0 (S315), the exhaust gas sensor evaluation unit 203 resets the exhaust gas sensor evaluated flag to 0 (S316) and ends this process.

  Next, when the exhaust gas sensor failure diagnosis process is called again by the main program, the process of S301 is executed. However, since the exhaust gas sensor has not yet been evaluated, the process proceeds to S302, and the detection condition is satisfied. It is determined whether or not there is. When the detection condition is satisfied in S302, the exhaust gas sensor evaluation unit 203 receives the LAF sensor activation signal via the input interface 201, and determines whether or not the LAF sensor 103 has been activated (S303). When the engine has started, the LAF sensor 103 has not been activated. Therefore, if the predetermined time has not elapsed since the engine was started, the exhaust gas sensor evaluation unit 203 advances the process to S315 (S303: No). The subsequent flow to S316 is the same as described above, and will be omitted.

  After the above process ends, the exhaust gas sensor failure diagnosis process is called again by the main program. The exhaust gas sensor evaluated flag is reset by the above-described process, and the LAF sensor 103 has been activated after a predetermined time has elapsed after the engine is started. Therefore, the exhaust gas sensor evaluation unit 203 moves the process from S301 to S302. In step S303, the process proceeds to step S304.

  When all the above-described detection conditions are satisfied, the exhaust gas sensor evaluation unit 203 transmits a KIDSIN calculation request to the detection signal generation unit 202. When a KIDSIN calculation request is transmitted, the detection signal generator 202 generates a sine wave IDSIN having a frequency fid (here, 4 Hz) and an amplitude aid. Then, KIDSIN is created by adding an offset amount IDOFT (here, 1.0) to the generated sine wave IDSIN (S304).

  The KIDSIN is continuously transmitted to the fuel amount calculation unit 206. When KIDSIN is transmitted, the fuel amount calculation unit 206 calculates the fuel injection amount INJ by adding KIDSIN to the basic fuel injection amount. This fuel injection amount INJ is input to the injection of the internal combustion engine 102 via the output interface 205.

  When the internal combustion engine 102 is operated at the fuel injection amount INJ, the exhaust gas that is an output corresponding to the fuel injection amount INJ that is an input is discharged from the exhaust system of the engine. The LAF sensor 103 detects the exhaust gas that has been discharged, and its output KACT is input to the responsiveness evaluation unit 204 via the input interface 201. For example, the responsiveness evaluation unit 204 calculates the output KACT_F after bandpass filtering by substituting KACT into the following equation (S305, S308).

KACT_F (k) = a1KACT_F (k-1) + a2KACT_F (k-2) + a3KACT_F (k-3) + b0KACT (k) + b1KACT (k-1) + b2KACT (k-2) + b3KACT (k-3)
a1, a2, a3, b0, b1, b2, b3: filter coefficients

  Here, the frequency characteristic of the first bandpass filter BF1 is a filter that passes the same 4 Hz as the detection signal frequency fid as shown in FIG. 4, and the output after bandpass filtering is KACT_F1. The frequency characteristic of the second bandpass filter BF2 is about 8 Hz which is an integral multiple (twice) of the frequency fid, and the output after bandpass filtering is KACT_F2.

[Evaluation of each criterion]
Next, the exhaust gas sensor evaluation unit 203 uses KACT_F1 and KACT_F2 to specifically compare with the criteria and determine the failure of the LAF sensor 103. There are three criteria, 1 to 3, which are standards for determining a normal mode, a failure mode in which the amplitude of the output waveform is attenuated, and a failure mode in which a waveform different from the input waveform of the detection signal is output.

  The criterion 1 obtains an attenuation rate of the amplitude of the output waveform with respect to the input waveform, and determines whether or not this attenuation rate exceeds a predetermined value. If the attenuation rate falls below a predetermined value, the LAF sensor 103 is determined to be out of order. Next, the criterion 2 determines whether or not the attenuation rate is smaller than a predetermined value. If the attenuation rate is larger than a predetermined value, it is determined that the LAF sensor 103 is normal.

  FIG. 5 is an explanatory diagram schematically showing the criteria. As described above, when the attenuation rate is smaller than the predetermined value by the criterion 1, it is a failure mode failure in which the amplitude of the output waveform is attenuated. When the attenuation rate is larger than the predetermined value by the criterion 2, it is determined as the normal mode. However, failures in the failure mode in which a waveform different from the input waveform of the detection signal is output are distributed between the criteria 1 and the criteria 2 in FIG.

  Therefore, in the present embodiment, a criterion 3 is newly provided between the criteria 1 and the criteria 2, and a failure mode in which a waveform different from the input waveform of the detection signal is output by the criterion 3 is determined.

[Criteria 1 and 2]
In the criterion 1, it is determined whether or not the output KACT_F1 subjected to the bandpass filtering at 4 Hz is attenuated as compared with the detection signal KIDSIN (S306). FIG. 6 shows an example of the output of the bandpass filter BF1. In (a), the amplitude is large and no attenuation is observed, but in (b), the amplitude is small and attenuated. If it attenuates as shown in (b) and the predetermined attenuation factor is small, it is determined that the LAF sensor 103 is malfunctioning (S306: No), and the malfunction lamp is turned on (S312). Then, the exhaust gas sensor evaluated flag is set to 1 (S313), and the process proceeds to S314. The exhaust gas sensor evaluation unit 203 instructs the detection signal generation unit 202 to set KIDSIN to 1.0 (S314), stops the detection signal, and ends this process.

  Next, in the case of FIG. 6A, the process proceeds to the determination of the criterion 2 that compares the amplitude attenuation rate with a predetermined value (S306: Yes).

  In the criterion 2 determination, if the attenuation rate of the amplitude is equal to or greater than the predetermined value, the LAF sensor 103 is normal (S307: No), and the exhaust gas sensor evaluation unit 203 determines that the exhaust gas sensor has not deteriorated. Then, the exhaust gas sensor evaluated flag is set to 1 (S311), and the command is transmitted to the fuel amount calculation unit 206. Then, the exhaust gas sensor evaluation unit 203 instructs the detection signal generation unit 202 to set KIDSIN to 0 (S314), stops the detection signal, and ends this process. Then, when it cannot be determined whether or not the LAF sensor 103 is faulty even in the determination of the criterion 2, the process proceeds to the determination of the criterion 3 (S307: Yes).

  As disclosed in Japanese Patent No. 3957208, the criteria 1 and 2 are determined by calculating the KACT_FA converted by the responsiveness evaluation unit 204 from KACT_F1 to the absolute value, and calculating the integrated value LAF_DLYP from the KACT_FA. The exhaust gas sensor evaluation unit 203 may be configured to determine whether or not the integral value LAF_DLYP is equal to or greater than a predetermined value LAF_DLYP_OK. Here, the LAF_DLYP_OK value is a threshold value for determining whether or not the exhaust gas sensor has deteriorated and failed based on the integral value LAF_DLYP.

[Criteria 3]
First, the method for determining the criterion 3 will be described, and then the description will be returned to the flow of FIG. FIG. 7 shows the result of fast Fourier transform (FFT) of (a) output signal and (b) output when the input signal is a sine wave of 4 Hz when the LAF sensor 103 is normal. FIG. 8 shows (a) an output signal and (b) an FFT of the output signal when the LAF sensor 103 has a failure in which a waveform different from the input waveform of the detection signal is output, and the input signal is a 4 Hz sine wave. Is the result of

  In FIG. 7, when the output waveform of the LAF sensor 103 is a normal sine wave as in the input signal as shown in (a), only the frequency component (4 Hz) of the input signal is increased as shown in (b). . On the other hand, in FIG. 8, when the output of the LAF sensor 103 transitions from the plus on the rich side to the minus on the lean side as shown in (a), the responsiveness deteriorates and a delay occurs. And, as shown in (b), the frequency component (4 Hz) of the input signal and the integral multiple frequency components (8 Hz, 12 Hz,...) Are large as the inherent frequency of this output waveform.

  This embodiment pays attention to this point, and calculates the ratio of (4 Hz frequency component) / (8 Hz frequency component). This ratio is smaller at the time of failure in which a waveform different from the input waveform of the detection signal in FIG. 8 is output as compared to the normal time in FIG. In the criterion 3, a failure is determined by comparing these values.

  As the failure pattern of the LAF sensor 103, six patterns are assumed as shown in FIG. In FIG. 9, (a) is a normal state, (b) is a failure state in which a symmetrical response delay occurs in the transition from lean to rich and rich to lean, and (c) transitions from lean to rich. (D) is a failure state in which the response delay becomes longer when transitioning from rich to lean as opposed to (c), and (e) is in a rich state. In contrast to (e), (f) is a failure state in which a delay occurs when leaning, and (g) is a failure state in which a delay occurs when rich and lean. The above-described failure state in FIG. 8 corresponds to a case where the response delay becomes long when transitioning from rich to lean in FIG. 9D.

  In the following description, the failure states (b) to (g) will be described as failure patterns 1 to 6 in this order. The failure pattern 1 can be determined by using the conventional technique for comparing the amplitude attenuation described above, and therefore, the failure patterns 2 to 6 will be described below.

  FIG. 10 shows the ratio of the frequency component of each frequency to the output of the frequency component of 4 Hz when the input signal is a sine wave of 4 Hz for typical examples of the failure patterns 2 to 6. The vertical axis in FIG. 10 is the ratio, and the horizontal axis is the frequency. Accordingly, the ratio of 4 Hz on the horizontal axis is 1 because the frequency components are the same.

  As can be seen from FIG. 10, the ratio of (4 Hz frequency component) / (8 Hz frequency component) is clearly lower in the failure patterns 2 and 3 and in the failure patterns 4 to 6 than in the normal state. Yes. In particular, the ratio of the failure patterns 2 and 3 is also apparent from the FFT results in FIGS. 7B and 8B. In such a failure mode in which frequency distortion occurs in the output with respect to the input, the frequency components of the input and output are different. Therefore, failure or abnormality is detected by performing bandpass filtering using a plurality of bandpass filters of different frequency bands. It becomes possible to do.

  As described above, according to the present embodiment, the failure pattern 1 “bilaterally symmetric response” can be detected by the above-described criteria 1 and 2, and the failure pattern 2 and 3 “one-side response delay” and the failure pattern 4 “both sides” can be detected by the criterion 3. It is possible to detect “time delay” and failure patterns 5 and 6 “one-side time delay”. With such a configuration, in addition to the failure in which the amplitude of the output signal of the prior art is attenuated, it is possible to diagnose the failure even for a waveform in which the output signal is not attenuated, which was not possible in the prior art.

  Returning to the exhaust gas sensor failure diagnosis process, when the exhaust gas sensor evaluation unit 203 cannot determine whether or not the LAF sensor 103 is failed even if the criterion 2 is determined (S307: Yes), the KACT_F1 and the KACT_F2 (S308) are used (4Hz). Frequency component) / (frequency component of 8 Hz) is calculated (S309). The ratio RF is such that the frequency component of 4 Hz and the frequency component of 8 Hz are compared with the predetermined value calculated from the relationship shown in FIGS. 7, 8, and 10 described above. (S310: No), the failure lamp is turned on (S312). If the ratio RF is greater than the predetermined value, it is determined to be normal (S310: Yes), the exhaust gas sensor evaluation unit 203 determines that the exhaust gas sensor has not deteriorated, and sets the exhaust gas sensor evaluated flag to 1 ( S311) A command is transmitted to the fuel amount calculation unit 206. Then, the exhaust gas sensor evaluation unit 203 instructs the detection signal generation unit 202 to set KIDSIN to 0 (S314), stops the detection signal, and ends this process.

  According to the present embodiment, noise components at the time of sensor measurement can be removed by removing frequency components other than the detection frequency using the output subjected to bandpass filtering, and in particular, air-fuel ratio fluctuation that occurs during transient operation, etc. The influence of other frequency components generated by the above can be removed, and the detection accuracy can be further improved.

  In the above description, the bandpass filters of 4 Hz and 8 Hz are described as examples as the plurality of bandpass filters having different frequency bands. However, as shown in the examples of FIGS. Needless to say, this is not limited to 4 Hz and 8 Hz band-pass filters.

  As described above, according to the present embodiment, in addition to the determination of the criterion 1 for evaluating the attenuation of the amplitude of the conventional frequency component, the criterion 3 diagnoses a failure in which the amplitude is not attenuated and a waveform different from the input waveform of the detection signal is output. Is possible.

  In the above description, a sine wave is used as a detection signal, but a cosine wave has the same effect.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to the drawings. Note that portions that are the same as those in the first embodiment will be omitted, and differences will be mainly described. FIG. 11 is a block diagram showing an overall configuration for explaining the second embodiment of the exhaust gas sensor degradation failure diagnosis apparatus. In addition, about the functional block common to 1st Embodiment, the same reference number is attached | subjected and description is abbreviate | omitted.

  In this embodiment, the fuel injection amount including the detection signal is calculated by multiplying the basic fuel injection amount by the detection signal. That is, the fuel amount calculation unit according to the present embodiment has a function of receiving the detection signal KIDSIN calculated by the detection signal generation unit 101 and passing the final fuel injection amount INJ generated by multiplying the basic fuel injection amount to the output interface. Have.

  When the deterioration failure detection is not performed, the responsiveness evaluation unit 104 sends a command to the detection signal generation unit 101 to stop the detection signal, and the detection signal generation unit 101 sets IDOFT to a constant 1.0 and FDSIN. The constant 0 is set, and KIDSIN which is a combined signal obtained by adding them is created (in this case, the combined signal KIDSIN is 1.0). When KIDSIN is 1.0, the basic fuel injection amount during normal operation is injected from the injection. Therefore, in the flow shown in FIG. 3, S314 and S315 both set KIDSIN to 1.0.

  As described above, the present embodiment has been described with reference to the drawings. However, the present embodiment differs from the first embodiment only in how the generated detection signal is used as an input, and is the same exhaust as in the first embodiment. It is possible to diagnose failure of the gas sensor.

  According to the present embodiment, the fuel injection amount multiplied by a detection signal such as a sine wave fluctuation for evaluating the exhaust gas sensor is given to the engine, and the response of the exhaust gas sensor is evaluated based on the subsequent exhaust gas sensor output. Therefore, it is possible to always obtain an output from the exhaust gas sensor including a frequency component of a certain ratio or more, and it is possible to improve detection accuracy when determining the state of the exhaust gas sensor using the frequency response characteristics. .

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to the drawings. Note that portions overlapping with the first embodiment or the second embodiment described above will be omitted, and description will be made with a focus on differences. FIG. 12 is a block diagram showing an overall configuration for explaining a third embodiment of the exhaust gas sensor degradation failure diagnosis apparatus. In addition, about the functional block common to 1st Embodiment or 2nd Embodiment, the same reference number is attached | subjected and description is abbreviate | omitted.

  In the third embodiment, as will be described later, by correcting the fuel injection amount during the deterioration failure detection using the feedback representative value, the increase in the exhaust gas component during the detection is further increased as compared with the case where the feedback is stopped. Can be small. In the following examples, description will be made assuming that feedback is performed for the second embodiment in which the detection signal KIDSIN is multiplied by the fuel injection amount. However, the detection signal KIDSIN is added to the fuel injection amount in the first embodiment. The same can be applied to this.

  In the present embodiment, after the second fuel injection amount INJ2 multiplied by KIDSIN generated by the detection signal generation unit 101 is calculated, feedback control is performed. Therefore, the present embodiment further includes an output of the LAF sensor 103 to the feedback compensator 404, and further includes a feedback representative value calculator 409 and switches 410 and 411 interlocking with each other.

  The feedback compensator 404 has a function of generating a feedback correction coefficient KAF for keeping the air-fuel ratio appropriate based on the output value from the LAF sensor 103. The calculation by the feedback compensator is a deterioration failure of the exhaust gas sensor. Stops during detection.

  The feedback representative value calculator 409 uses the feedback correction coefficient KAF calculated by the feedback compensator 404 to calculate a feedback representative value KAFCENTER that is a representative value thereof. Specifically, KAFCENTER is a value that mainly represents the steady-state deviation of the feedback correction coefficient, such as the average value, median value, and smoothed value of the feedback correction coefficient KAF. During the detection of the deterioration failure of the exhaust gas sensor, the feedback compensator 404 stops the feedback correction coefficient calculation.

  This representative feedback value is a coefficient that is multiplied by the basic fuel injection amount including the detection signal in place of the feedback correction coefficient in order to generate the final fuel injection amount. The feedback representative value calculator 409 also performs the feedback representative value calculation during the normal operation, but stops the calculation of the feedback representative value during the deterioration failure detection and holds the feedback representative value immediately before the stop of the calculation. Become.

  In the feedback compensation for the fuel injection amount, the feedback correction coefficient KAF is used except when the deterioration failure is being detected, and the feedback representative value KAFCENTER held in the feedback representative value calculator 409 is used during the detection. This switching is represented by switches 110 and 111 in the figure, and both switches operate simultaneously in conjunction with each other.

  The functions of the exhaust gas sensor evaluation unit, the detection signal generation unit 101, the feedback compensator 404, the response evaluation unit 105, and the feedback representative value calculator 409 can be realized in the ECU as in the first embodiment. it can.

  In this embodiment, the fuel amount calculation unit 206 in FIG. 2 receives the detection signal KIDSIN calculated by the detection signal generation unit 202 and adds it to the basic fuel injection amount (hereinafter referred to as the first basic fuel injection amount). Further, it has a function of passing the final fuel injection amount INJF generated by multiplying this by a feedback correction coefficient (or feedback representative value) to the output interface 205.

  In addition, the fuel amount calculation unit 206 uses a detection value from the exhaust gas sensor, a feedback compensation function for calculating the feedback correction coefficient for maintaining the air-fuel ratio in the vicinity of the theoretical air-fuel ratio, and a feedback representative value calculation described later. Built-in functionality.

  Next, an exhaust gas sensor failure diagnosis process for diagnosing a deterioration failure of the LAF sensor 103 will be described with reference to FIG. FIG. 13 is a flowchart showing the exhaust gas sensor failure diagnosis process of the present embodiment. The same steps as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted.

  In this embodiment, after the detection condition in the first embodiment shown in FIG. 3 is established (S302), the feedback representative value is calculated (S503, S504, S519, S520) and 1.0 is set in KIDSIN (S514). The calculation of the feedback representative value (S516, S517) is different from the first embodiment. Further, as described above, in the present embodiment, since the detection signal KIDSIN is multiplied by the fuel injection amount, the detection signal KIDSIN is set to 1.0 in S514 and S515.

  When the detection condition is not satisfied (S302: No), the exhaust gas sensor evaluation unit 203 advances the process to S519. In this case, since no deterioration failure is detected, a feedback correction coefficient that is an operation during normal operation is calculated, and a feedback representative value calculation is performed in S520.

  Specifically, the calculation of the feedback correction coefficient KAF is performed based on the output from the LAF sensor. The exhaust gas sensor evaluation unit 203 determines whether the final fuel injection amount discharged by the injection is lean or rich based on KACT that is an output value from the LAF sensor received via the input interface. When it is determined that the fuel is rich, the fuel amount calculation unit 206 decreases the previous calculation value of the feedback correction coefficient by a certain ratio, and increases the constant by a certain ratio when lean. In addition, in order to control the air-fuel ratio in the vicinity of the theoretical air-fuel ratio, when the signal changes from lean to rich or from rich to lean, the correction coefficient may be changed not in a constant ratio but in a discontinuous step shape. .

The feedback representative value is obtained by calculating the feedback correction coefficient KAF as follows, and the calculation result is stored and held.
KAFCENTER = (1−c1) · KAF _i−1 + c1 · KAF _i
Here, c1 is an annealing coefficient. Although the annealing calculation is used here, the feedback representative value KAFCENTER can be obtained by using an average value of a plurality of feedback correction coefficients.

For example, when using the average value:
KAFCENTER = (KAF _i + KAF _{i + 1} +... + KAF _i−j ) / (i−j + 1)
And can be calculated.

Further, the median value of the feedback correction coefficient can be obtained and used as the feedback representative value KAFCENTER. In this case, m central values KAF _M1 , KAF _M2 ,..., KAF _Mm are extracted from KAF ₁ to KAF _n in which the obtained feedback correction coefficient KAF values are rearranged in ascending order. It is good also as calculating | requiring a median value by calculating an average value like this.
KAFCENTER = (KAF _M1 +... + KAF _Mm ) / m

  When the deterioration failure detection is not performed, as described above, KIDSIN is 1.0, the basic fuel injection amount during normal operation is output, and the final fuel injection amount INJF obtained by multiplying this by the feedback correction coefficient KAF is It will be injected from the injection.

  Note that the feedback correction coefficient calculation in S519 and later-described S516 means a feedback correction coefficient calculation in a normal feedback calculation operation including stopping feedback during fuel cut, and continues to calculate the feedback correction coefficient under all conditions. It does not mean that.

  If the detection condition is satisfied in S302, the exhaust gas sensor evaluation unit 203 advances the process to S503 in order to prepare the process for deterioration detection, and sends a command to the fuel amount calculation unit 206 to calculate a feedback correction coefficient. In step S504, the feedback representative value calculation is also stopped. At the same time, the feedback representative value calculated at that time is held.

  When all the detection conditions are satisfied, the exhaust gas sensor evaluation unit 203 transmits a calculation request for KACT_F1, 2 to the detection signal generation unit 202. When the calculation request for KACT_F1, 2 is transmitted, the detection signal generator 202 creates KIDSIN (S306). The KIDSIN is continuously transmitted to the fuel amount calculation unit 206. When KIDSIN is transmitted, the fuel amount calculation unit 206 multiplies the first basic fuel injection amount by KIDSIN, and further multiplies the stored feedback representative value KAFCENTER to calculate the final fuel injection amount INJF. This final fuel injection amount INJF is input to the injection of the internal combustion engine 102 via the output interface 205.

  Thereafter, when the flow described in the first embodiment is continued and it is determined that the exhaust gas sensor has not deteriorated, the exhaust gas sensor evaluated flag is set to 1 (S313), and a feedback correction coefficient calculation (S516) is performed. ) And a feedback calculation value calculation (S517) are transmitted to the fuel amount calculation unit 206. The exhaust gas sensor evaluation unit 203 instructs the detection signal generation unit 202 to set KIDSIN to 1.0 (S514), stops the detection signal, and ends this process.

  By adopting such a configuration, even when feedback calculation is stopped to detect a deterioration failure, the fuel amount is controlled using the feedback representative value based on the feedback correction coefficient. It is possible to suppress an increase in exhaust gas components.

  The preferred embodiments of the present invention have been described above. The present invention is not limited to the one described in the drawings, and design changes can be made without departing from the spirit of the present invention.

1 is a block diagram showing an overall configuration for explaining a first embodiment of an exhaust gas sensor degradation failure diagnosis apparatus according to the present invention. FIG. It is a whole block diagram of ECU (electronic control unit) of a 1st embodiment. It is a flowchart showing the exhaust gas sensor failure diagnosis process of 1st Embodiment. It is an example of the frequency characteristic of the band pass filter used in 1st Embodiment. It is explanatory drawing which represented typically the criteria of the failure diagnosis in 1st Embodiment. An example of the output of a band pass filter is shown. It is the result of the fast Fourier transform (FFT) of the output signal and output when the input signal is a sine wave of 4 Hz when the LAF sensor is normal. FIG. 6 is a result of FFT of the output signal and the output signal when the input signal is a 4 Hz sine wave in a case where the LAF sensor outputs a waveform different from the input waveform of the detection signal. It is explanatory drawing of the failure pattern of a LAF sensor. It is the figure which showed the ratio of the frequency component about the typical example of a failure pattern. It is a block diagram which shows the whole structure for describing 2nd Embodiment of the deterioration failure diagnostic apparatus of the exhaust gas sensor concerning this invention. It is a block diagram which shows the whole structure for demonstrating 3rd Embodiment of the deterioration failure diagnostic apparatus of the exhaust gas sensor concerning this invention. It is a flowchart showing the exhaust gas sensor failure diagnosis process of 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Detection signal generation part 102 Internal combustion engine 103 LAF sensor 104 Responsiveness evaluation part 200 ECU
DESCRIPTION OF SYMBOLS 201 Input interface 202 Detection signal generation part 203 Exhaust gas sensor evaluation part 204 Responsiveness evaluation part 205 Output interface 206 Fuel amount calculation part

Claims (8)

An exhaust gas sensor deterioration failure diagnosis device that is provided in an exhaust passage of an internal combustion engine and generates an output corresponding to an exhaust gas component of the internal combustion engine,
A detection signal generating means for generating a detection signal;
Fuel amount calculation means for calculating a fuel injection amount in which the detection signal is reflected;
An exhaust gas sensor evaluation means for determining the state of the exhaust gas sensor,
The exhaust gas sensor evaluation means includes
A first band-pass filter that extracts a frequency component of a predetermined frequency band, and one or more other band-pass filters that extract a frequency component of a frequency band different from the first band-pass filter,
The relative magnitude relationship between the first frequency component extracted by the first band-pass filter from the output of the exhaust gas sensor and the other frequency component extracted by the other band-pass filter with respect to the fuel injection amount is An exhaust gas sensor deterioration failure diagnosis device configured to determine that the state of the exhaust gas sensor is a failure when in a predetermined relationship .   The deterioration failure diagnosis apparatus for an exhaust gas sensor according to claim 1, wherein a frequency band of the first bandpass filter matches a frequency band of the detection signal.   The exhaust gas sensor deterioration failure diagnosis apparatus according to claim 1, wherein the detection signal is a signal obtained by adding a sine wave or a cosine wave to a predetermined offset value.   4. The exhaust gas sensor degradation failure diagnosis apparatus according to claim 1, wherein the frequency band of the other bandpass filter is a frequency that is an integral multiple of the frequency band of the first bandpass filter. 5. The relative magnitude relation, calculated as the ratio of the other of said other of said first frequency component in which the first band-pass filter is extracted for the frequency component band pass filter is extracted, the ratio is a predetermined value The exhaust gas sensor deterioration failure diagnosis apparatus according to any one of claims 1 to 4, wherein a failure is determined in the following case.   The exhaust gas sensor evaluation unit according to claim 1, wherein the exhaust gas sensor evaluation unit extracts a frequency response corresponding to the detection signal from an output of the exhaust gas sensor, and determines a state of the exhaust gas sensor based on the frequency response. Degradation fault diagnosis device. Further comprising a feedback representative value calculation means to calculating the feedback representative value from the feedback correction coefficient calculated in order to correct the fuel injection amount based on an output value from the exhaust gas sensor during normal operation,
The During degradation fault diagnosis, to stop the feedback representative value calculation means, and hold the feedback representative value immediately before stopping, the fuel amount calculating means, final fuel injection using a feedback representative value the holding The exhaust gas sensor deterioration failure diagnosis device according to any one of claims 1 to 6 , wherein the amount of the exhaust gas sensor is calculated. The exhaust gas sensor is determined to be faulty when an attenuation rate of the amplitude of the first frequency component that is an output waveform with respect to the amplitude of the detection signal that is an input waveform is equal to or less than a first threshold value, and The exhaust gas is determined to be normal when it is greater than or equal to a second threshold value that is greater than the first threshold value, and when the decay rate is greater than the first threshold value and smaller than the second threshold value The exhaust gas sensor deterioration failure diagnosis apparatus according to any one of claims 1 to 7, wherein the deterioration failure diagnosis of the gas sensor is performed.

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