JP4134480B2 - Air-fuel ratio sensor deterioration diagnosis device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a deterioration diagnosis device for an air-fuel ratio sensor of an internal combustion engine.
[0002]
[Prior art]
In order to accurately control the air-fuel ratio of the internal combustion engine to different target air-fuel ratios according to operating conditions, a wide-range air-fuel ratio sensor is provided in the exhaust system, and the fuel injection amount is feedback-controlled based on the output of the wide-area air-fuel ratio sensor The device is known.
[0003]
In this case, if the output characteristics fluctuate due to deterioration of the wide area air-fuel ratio sensor, the control accuracy of the air-fuel ratio decreases. Therefore, a function for self-diagnosis of deterioration or failure of the wide-range air-fuel ratio sensor is added, and when the fluctuation range of the sensor output exceeds a limit value, replacement or repair is promoted.
[0004]
Diagnosis of such deterioration is performed as follows, for example. Although the output of the wide area air-fuel ratio sensor changes in accordance with the (exhaust) air-fuel ratio, the response time for changes in the air-fuel ratio is generally different between a normal product and a deteriorated product, and the response time takes longer as the deterioration progresses. In other words, as the deterioration progresses, the change in output for the same reaction time becomes smaller.
[0005]
Therefore, the degree of deterioration can be determined by judging the change margin of the sensor output per unit time when the air-fuel ratio is changed by a certain value, and when this change margin becomes smaller than the specified value, the sensor due to deterioration An abnormality is judged.
[0006]
Meanwhile, commercially available fuels for internal combustion engines include standard fuels and heavy fuels. Heavy fuel has lower fuel volatility than standard fuel, and there is a time lag until the fuel injected into the intake pipe by the fuel injection valve actually reaches the combustion chamber and burns.
[0007]
For this reason, when diagnosing the wide-area air-fuel ratio sensor, deterioration may not be accurately determined depending on the fuel component.
[0008]
When the air-fuel ratio is changed, the delay time until the change of the air-fuel ratio is detected by the wide-area air-fuel ratio sensor installed in the exhaust pipe is different between the standard fuel and the heavy fuel. The output change margin of the air-fuel ratio sensor becomes smaller than that of the standard fuel. Therefore, when comparing the change amount of the air-fuel ratio sensor output with the reference value for the deterioration determination, the results differ between the standard fuel and the heavy fuel, and even if the air-fuel ratio sensor is normal, the deterioration may be erroneously determined. is there.
[0009]
It has been pointed out in Japanese Patent Application Laid-Open No. 11-241643 that the response of the air-fuel ratio detected by the air-fuel ratio sensor is delayed due to the difference in fuel components. In this publication, the air-fuel ratio sensor is switched when the air-fuel ratio is switched. It is proposed that the standard fuel and the heavy fuel are determined from the output change of the above, and that the fuel injection amount is corrected based on the determined fuel property.
[0010]
[Problems to be Solved by the Invention]
Conventionally, when diagnosing deterioration of an air-fuel ratio sensor, taking into account such differences in fuel properties, the diagnostic criteria that serve as a reference for comparison when diagnosing deterioration are taken into account, including the characteristics of fuel from standard (light fuel) to heavy fuel. In order to prevent misdiagnosis, the average criteria was used, or the operating range when making a diagnosis was limited.
[0011]
However, in this case, for example, there is a problem that the accuracy is lowered to give a margin for the diagnosis criteria, or the diagnosis area is limited, and the frequency of deterioration diagnosis of the air-fuel ratio sensor is lowered.
[0012]
An object of the present invention is to solve such a problem, and it is possible to accurately determine the deterioration of an air-fuel ratio sensor even if the fuel properties are different.
[0013]
[Means for Solving the Problems]
A first invention includes an air-fuel ratio sensor for detecting an exhaust air-fuel ratio installed in an exhaust system of an internal combustion engine, and a fuel injection valve provided in an intake system, and fuel injection from the fuel injection valve so as to achieve a target air-fuel ratio. In an internal combustion engine that controls the amount based on the output of the air-fuel ratio sensor, a means for determining the fuel property, and a diagnosis of the air-fuel ratio sensor when a diagnosis start delay time set according to the fuel property has elapsed after the fuel cut Means for determining that the air-fuel ratio is in the region, means for comparing the output change margin of the air-fuel ratio sensor with a predetermined reference value in this diagnostic region, and determining deterioration of the air-fuel ratio sensor, and depending on the fuel property Means for stopping the diagnosis.
[0014]
A second invention includes an air-fuel ratio sensor for detecting an exhaust air-fuel ratio installed in an exhaust system of an internal combustion engine, and a fuel injection valve provided in the intake system, and fuel injection from the fuel injection valve so as to achieve a target air-fuel ratio. In an internal combustion engine that controls the amount based on the output of the air-fuel ratio sensor,
Means for determining the fuel properties, means for determining the diagnostic region of the air-fuel ratio sensor according to the fuel properties, and comparing the output change margin of the air-fuel ratio sensor with a common reference value in each diagnostic region according to the fuel properties And means for judging deterioration of the air-fuel ratio sensor.
[0015]
A third invention includes an air-fuel ratio sensor for detecting an exhaust air-fuel ratio installed in an exhaust system of an internal combustion engine, and a fuel injection valve provided in the intake system, and fuel injection from the fuel injection valve so as to achieve a target air-fuel ratio. In an internal combustion engine that controls the amount based on the output of the air-fuel ratio sensor, a means for determining the fuel property, and a diagnosis of the air-fuel ratio sensor when a diagnosis start delay time set according to the fuel property has elapsed after the fuel cut Means for determining that there is a region, means for setting a different diagnostic reference value according to the fuel property, and comparing the change margin of the output of the air-fuel ratio sensor with the diagnostic reference value corresponding to the fuel property in the diagnostic region. Means for judging deterioration of the fuel ratio sensor.
[0016]
In a fourth aspect based on the second aspect, the means for determining the diagnosis area determines that the diagnosis area is in the diagnosis area when a diagnosis start delay time has elapsed after the fuel cut.
[0017]
In a fifth aspect based on the fourth aspect, the diagnosis start delay time is set to a different time according to the fuel property.
[0018]
[Action, effect]
In the first invention, when the determined fuel property coincides with the set fuel for performing the diagnosis of the air-fuel ratio sensor, the change amount of the output of the air-fuel ratio sensor is set as the diagnosis reference value when the diagnosis region is determined. In comparison, the determination of deterioration of the air-fuel ratio sensor is made, and when the fuel property is different from the set fuel, the determination of deterioration of the air-fuel ratio sensor is stopped. For this reason, the diagnostic region for performing the degradation diagnosis, the diagnostic reference value, and the like can be determined only in accordance with the characteristics of the set fuel, and the accuracy of the degradation diagnosis of the air-fuel ratio sensor is increased accordingly.
The diagnosis area is determined when the delay time has elapsed after the fuel cut, that is, when the air-fuel ratio has been switched in the intake system, and after the diagnosis start delay time set according to the fuel properties has elapsed, By determining the air-fuel ratio change allowance, the deterioration accuracy can be determined in a region where the air-fuel ratio sensor output change allowance is sufficiently large.
[0019]
In the second invention, the diagnosis region is changed according to the fuel property, and therefore, even if the diagnosis reference value is the same, it is possible to make an appropriate diagnosis according to each fuel characteristic, and the responsiveness due to the difference in fuel property The air-fuel ratio sensor can be diagnosed accurately without being affected by the change in the air-fuel ratio.
[0020]
In the third aspect of the invention, the diagnostic reference value is changed according to the fuel properties, and accordingly, in this case as well, the deterioration diagnosis of the appropriate air-fuel ratio sensor can be performed according to the respective fuel properties.
The diagnosis area is determined when the delay time has elapsed after the fuel cut, that is, when the air-fuel ratio has been switched in the intake system, and after the diagnosis start delay time set according to the fuel properties has elapsed, By determining the air-fuel ratio change allowance, the deterioration accuracy can be determined in a region where the air-fuel ratio sensor output change allowance is sufficiently large.
[0021]
In the fourth aspect of the invention, the diagnosis region is determined when the delay time elapses after the fuel cut, that is, when the air-fuel ratio is switched in the intake system and a predetermined time elapses. Therefore, the deterioration diagnosis is performed, so that the deterioration can be determined in a region where the change in the output of the air-fuel ratio sensor is sufficiently large, and the diagnosis accuracy is improved.
[0022]
In the fifth aspect of the invention, the delay time at which the change in the air-fuel ratio sensor output changes with respect to the change in the air-fuel ratio differs depending on the fuel properties. Therefore, by setting the delay time corresponding to each, the appropriate deterioration diagnosis can be performed for each. Yes.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0024]
In FIG. 1, 1 is an engine body, 2 is an intake pipe, 3 is an exhaust pipe, and the intake pipe 2 is provided with a fuel injection valve 4 for injecting necessary fuel. An intake throttle valve 5 controls the engine output by controlling the amount of intake air, and 6 is a catalyst (three-way catalyst) that purifies harmful components in the exhaust gas installed in the exhaust pipe.
[0025]
A controller 10 is provided to control the fuel injection amount injected from the fuel injection valve 4 so as to become a target air-fuel ratio set according to the operating conditions.
[0026]
The controller 10 includes an input circuit, a central processing circuit (microprocessor), a storage circuit, an output circuit, and the like. The controller 10 includes a crank angle sensor 12 that detects an engine speed and an air flow meter 13 that detects an intake air amount. The throttle valve opening sensor 14 for detecting the intake throttle valve opening, the water temperature sensor 15 for detecting the engine cooling water temperature, and the vehicle speed sensor 16 for detecting the vehicle speed are inputted, and the exhaust air-fuel ratio upstream of the catalyst is further detected. Signals from the wide area air-fuel ratio sensor 11 and the oxygen sensor 20 for detecting the downstream exhaust air-fuel ratio are also input, and based on these, the fuel injection amount is calculated so as to reach the target air-fuel ratio according to the operating conditions, and the engine rotation is performed. Synchronously, a fuel injection signal is output to the fuel injection valve 4.
[0027]
The controller 10 also has a diagnostic function for determining whether the output characteristics of the wide area air-fuel ratio sensor 11 are normal. This diagnosis is also shown in the flow chart described later, and the characteristics of the fuel supplied to the engine, that is, whether it is standard fuel or heavy fuel, is determined, and the diagnosis area is changed according to this determination result, or different diagnosis criteria are set. By using it, accurate determination can always be made regardless of the fuel properties.
[0028]
FIG. 2 is a flowchart showing the diagnostic contents of the first embodiment, which is repeatedly executed by the controller 10 at predetermined time intervals.
[0029]
First, in step S1, it is determined whether or not the fuel property is a standard fuel. In this determination, for example, when the air-fuel ratio is changed stepwise during idling after warm-up, the output waveform of the air-fuel ratio sensor 11 at this time is standard with respect to the step waveform A as shown in FIG. The fuel is B, and the heavy fuel with low volatility is C. The deviation from the step waveform A can determine whether the fuel is a standard fuel or a heavy fuel.
[0030]
In step S2, it is determined whether or not the operation state is such that the diagnosis can be transferred. For example, the vehicle speed VSP is between the predetermined lower limit value AFVSPL1 and the upper limit value AFVSPH1, the fuel injection pulse width TP is between the predetermined lower limit value AFTPL1 and the upper limit value AFTPH1, or the engine speed NE is It is determined by determining whether the value is between the predetermined lower limit value AFNEL1 and the upper limit value AFENEH1, and when it is within the upper and lower limit values, in other words, when the air-fuel ratio is stoichiometric or at a constant air-fuel ratio, diagnosis It is determined that the transfer is possible, and the process proceeds to step S3.
[0031]
Here, whether or not it is a diagnosis region is determined by whether or not the operating condition has passed a predetermined diagnosis start delay time AFFCD1 after the fuel cut. Due to the fuel cut, the output of the air-fuel ratio sensor 11 changes from the stoichiometry up to that point to lean (only air) containing no fuel.
[0032]
If the operating conditions before the fuel cut are different, the change characteristics of the air-fuel ratio are different and an accurate comparison cannot be made. Therefore, the determination in step S2 is performed to match the conditions.
[0033]
Further, the predetermined diagnosis start delay time AFFCD1 is given after the fuel cut, as shown in FIG. 4, there is a time delay from the fuel cut to the change of the air-fuel ratio of the exhaust system, and the initial change Since the absolute value of the margin is small and detection errors are likely to occur, a certain time is set until the diagnosis is started.
[0034]
When the delay time elapses, the change amount ΔA / F of the output of the wide area air-fuel ratio sensor 11 is calculated in step S4. This change amount ΔA / F of the sensor output is calculated as an output change width in a fixed calculation section DAFTM1.
[0035]
In step S5, the sensor output variation ΔA / F thus calculated is compared with the air-fuel ratio diagnosis criterion DAFNG1 to determine whether the response characteristic of the air-fuel ratio sensor 11 is in the normal range or abnormal. . The diagnostic criteria DAFNG1 is set according to the fuel properties. In this embodiment, the diagnosis criteria DAFNG1 is set as a comparison reference value for deterioration determination with respect to standard fuel instead of heavy fuel.
[0036]
As shown in FIG. 4, in the same fuel property, the output change margin in the unit response time of the air / fuel ratio sensor in the normal range is larger than the deteriorated one. Therefore, the diagnosis criteria set in advance according to the fuel property and By comparing, the characteristics of the air-fuel ratio sensor 11 can be diagnosed accurately.
[0037]
If the change amount ΔA / F of the air-fuel ratio is larger than the diagnosis criteria DAFNGI, the air-fuel ratio sensor 11 is normal and the diagnostic operation is terminated. If it is smaller, it is judged that the air-fuel ratio sensor 11 has been deteriorated. In step S6, abnormality is determined with the responsiveness of the air-fuel ratio sensor 11 being below the reference.
[0038]
In this way, the diagnosis as to whether or not the output characteristic of the wide area air-fuel ratio sensor 11 is normal first determines the current fuel property, and performs the deterioration diagnosis only when this is the standard fuel. Therefore, the diagnostic criteria at this time is set based on the sensor responsiveness at the time of the standard fuel. Therefore, the difference in responsiveness at the time of switching the air / fuel ratio due to the volatility of the fuel is excluded, and the air / fuel ratio is accurately determined. Only the deterioration of the output characteristics of the sensor 11 can be determined.
[0039]
Incidentally, since the volatility of heavy fuel is low, the delay until the air-fuel ratio change in the intake system reaches the exhaust system is large, the change allowance per unit time is also small, even if the output characteristics of the wide-area air-fuel ratio sensor 11 Even if is normal, the change amount ΔA / F of the sensor output becomes small.
[0040]
Therefore, if the change amount ΔA / F of the sensor output is compared with the standard criteria of the standard fuel, the abnormality is not judged despite the normality, but the fuel property is heavy as in the present invention. Such misdiagnosis can be prevented by stopping the diagnosis when fuel is used.
[0041]
FIG. 5 is a flowchart showing a second embodiment of the present invention, which will be described.
[0042]
In this embodiment, the diagnosis start delay time and the sensor output change amount ΔA / F are set differently based on the determination result of the fuel property, so that diagnosis for different fuel properties can be performed accurately. I was able to do it.
[0043]
Steps S11 to S16 are determinations of the deterioration of the air-fuel ratio sensor 11 for the standard fuel, and this is exactly the same as the operations from step S1 to step S6 in FIG.
[0044]
On the other hand, when it is determined in step S11 that the fuel is not the standard fuel, that is, when the fuel is heavy, the process proceeds to step S17 to determine whether or not the current operating state is in a state where the diagnosis can be transferred. The fuel injection pulse width and the engine speed are determined by comparing the upper limit value and the lower limit value AFVSPH2 and AFVSPL2, AFTPH2 and AFTPL2, and AFNEH2 and AFNEL2, respectively.
[0045]
These upper and lower limits are different from those of the standard fuel, and are set to optimum values corresponding to the heavy fuel.
[0046]
When any one of these values is within the upper and lower limits, it is determined that the diagnosis can be transferred, and the process proceeds to step S18. Here, the process waits until a predetermined diagnosis start delay time AFFCD2 elapses after the fuel cut, and when it elapses, the process proceeds to step S19 to calculate the change amount ΔA / F of the output of the wide area air-fuel ratio sensor 11 in the calculation section DAFTM2. In step S20, the calculated change amount ΔA / F is compared with the common diagnosis criterion DAFNG1, and if it is smaller than this, it is determined that the air-fuel ratio sensor 11 is normal, and the diagnosis operation is terminated.
[0047]
However, when the change amount ΔA / F of the air-fuel ratio is smaller than the diagnosis criteria DAFNG1 in step S20, it is determined in step S21 that the output responsiveness is lowered due to the deterioration of the wide area air-fuel ratio sensor 11.
[0048]
The diagnosis start delay time after fuel cut in the case of heavy fuel is longer than the delay time of the standard fuel, and the calculation interval of the change amount ΔA / F is also longer. This is because heavy fuel has lower fuel volatility, and the time delay until the wide-area air-fuel ratio sensor 11 in the exhaust system detects this change is larger than the change in the fuel supply amount in the intake system. . Therefore, comparing the same delay time and calculation interval, even if the wide area air-fuel ratio sensor 11 is normal, the change amount ΔA / F of the air-fuel ratio becomes small in the case of heavy fuel, and this is the same diagnosis. Judging by criteria as criteria, it may be judged that the product has deteriorated by mistake.
[0049]
However, in this embodiment, the diagnosis start delay time is varied depending on the fuel properties, and a sufficient delay time is taken for heavy fuel with a large time delay, so that even if comparison is performed using the same diagnosis criteria, it can be accurately determined. It is.
[0050]
As shown in FIG. 6, for heavy fuel, by increasing the diagnosis start delay time and lengthening the calculation section of the change amount ΔA / F, the change amount ΔA / F of the air-fuel ratio becomes the standard fuel. This makes it possible to accurately determine the deterioration of the air-fuel ratio sensor 11 with the common diagnostic criteria for any fuel.
[0051]
Next, a third embodiment of the present invention shown in the flowchart of FIG. 7 will be described.
[0052]
In this embodiment, the calculation start delay time and the sensor output variation ΔA / F are set to be the same for the standard fuel and the heavy fuel, but by making the diagnosis criteria different, both fuels can be accurately determined. The air-fuel ratio sensor 11 can be diagnosed.
[0053]
Steps S31 to S36, which are diagnostic operations for standard fuel, are substantially the same as steps S1 to S6 in FIG. 2, and step S40 to step S41 are also included in steps S37 to S41. Except for this, it is the same as steps S2 to S6.
[0054]
That is, the diagnostic criteria as a reference value for comparing the air-fuel ratio variation ΔA / F used in step S35 and step S40 is DAFNG1 when the standard fuel is used, but DAFNG2 when the heavy fuel is used. , Its size is different. In the same diagnosis delay time and calculation interval, the standard fuel DAFNG1 is set to be larger than the DAFNG2 because the standard fuel has a larger air-fuel ratio change amount ΔA / F than the heavy fuel.
[0055]
This makes it possible to appropriately determine the deterioration of the air-fuel ratio sensor 11 when using standard fuel and when using heavy fuel.
[0056]
The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of the present invention.
FIG. 2 is a flowchart showing a control operation of the first embodiment.
FIG. 3 is a comparative explanatory view of an air-fuel ratio sensor response waveform with respect to a change in air-fuel ratio between standard fuel and heavy fuel.
FIG. 4 is an explanatory diagram of a response waveform with respect to a change in air-fuel ratio when the air-fuel ratio sensor is normal and when it deteriorates.
FIG. 5 is a flowchart showing a control operation of the second embodiment.
FIG. 6 is an explanatory diagram of a response waveform with respect to a change in air-fuel ratio when the air-fuel ratio sensor is normal and when it deteriorates.
FIG. 7 is a flowchart showing a control operation of the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine main body 2 Intake pipe 3 Exhaust pipe 4 Fuel injection valve 6 Catalyst 10 Controller 11 Air fuel ratio sensor 12 Crank angle sensor 13 Air flow meter 16 Vehicle speed sensor

Claims (5)

An air-fuel ratio sensor for detecting an exhaust air-fuel ratio installed in the exhaust system of the internal combustion engine and a fuel injection valve provided in the intake system, and the amount of fuel injection from the fuel injection valve is adjusted by the air-fuel ratio sensor so as to achieve the target air-fuel ratio. In an internal combustion engine that controls based on output,
Means for determining fuel properties;
Means for determining that it is in the diagnosis region of the air-fuel ratio sensor when the diagnosis start delay time set according to the fuel property has elapsed after the fuel cut;
Means for determining the deterioration of the air-fuel ratio sensor by comparing the output change margin of the air-fuel ratio sensor with a predetermined reference value in this diagnostic region;
An apparatus for diagnosing deterioration of an air-fuel ratio sensor, comprising: means for stopping diagnosis of the air-fuel ratio sensor according to fuel properties. An air-fuel ratio sensor for detecting an exhaust air-fuel ratio installed in the exhaust system of the internal combustion engine and a fuel injection valve provided in the intake system, and the amount of fuel injection from the fuel injection valve is adjusted by the air-fuel ratio sensor so as to achieve the target air-fuel ratio. In an internal combustion engine that controls based on output,
Means for determining fuel properties;
Means for determining the diagnostic region of each air-fuel ratio sensor according to the fuel properties;
A deterioration diagnosis device for an air-fuel ratio sensor, comprising means for comparing the output change margin of the air-fuel ratio sensor with a common reference value in each diagnosis region in accordance with the fuel properties and determining deterioration of the air-fuel ratio sensor . An air-fuel ratio sensor for detecting an exhaust air-fuel ratio installed in the exhaust system of the internal combustion engine and a fuel injection valve provided in the intake system, and the amount of fuel injection from the fuel injection valve is adjusted by the air-fuel ratio sensor so as to achieve the target air-fuel ratio. In an internal combustion engine that controls based on output,
Means for determining fuel properties;
Means for determining that it is in the diagnosis region of the air-fuel ratio sensor when the diagnosis start delay time set according to the fuel property has elapsed after the fuel cut;
Means for setting different diagnostic reference values according to fuel properties;
A deterioration diagnosis device for an air-fuel ratio sensor, comprising: a means for comparing the change in the output of the air-fuel ratio sensor with a diagnostic reference value corresponding to the fuel property in the diagnosis region to determine deterioration of the air-fuel ratio sensor. The deterioration diagnosis device for an air-fuel ratio sensor according to claim 2, wherein the means for determining the diagnosis region determines that the diagnosis region is in the diagnosis region when a diagnosis start delay time has elapsed after the fuel cut.   The deterioration diagnosis apparatus for an air-fuel ratio sensor according to claim 4, wherein the diagnosis start delay time is set to a different time according to the fuel property.

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