JP2006307746A - Diagnostic device of air-fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more precisely diagnose whether an air-fuel sensor is abnormal or not. <P>SOLUTION: Since an output of a λ sensor at a time t1 is moved from a lean condition into a rich condition, after an air fuel ratio feedback correction efficient FAF is skip controlled by a skip amount Kp, a rich counter TimeLR is incremented followed by an integral control between times t1 and t2. After the output of the λ sensor 34 is moved into the lean condition at the time t2, and the air-fuel ratio feedback correction coefficient FAF is skip controlled by the skip amount Kp, the lean counter TimeRL is incremented accompanied by the integral control upto an time t3. When the ratio Rate of both the counters is approximated to 1, it is judged that the control of the air-fuel ratio is normal, and it is diagnosed whether the λ sensor is abnormal or not. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio sensor diagnostic apparatus for diagnosing the presence or absence of an abnormality in an air-fuel ratio sensor.

  As this type of diagnostic device, for example, as shown in Patent Document 1 below, a type of air conditioner whose output greatly changes depending on whether the actual air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio. A sensor that detects the presence or absence of a so-called oxygen sensor that is a fuel ratio sensor has also been proposed. In this diagnostic apparatus, it is determined that the oxygen sensor is abnormal when the accumulated value for a period when the output of the air-fuel ratio sensor shows lean or a period when the output shows rich is equal to or greater than a predetermined value.

  The detection of the presence or absence of abnormality of the oxygen sensor based on the cumulative value of the period indicating lean or the period indicating rich needs to be performed when the operating state of the internal combustion engine is steady. For this reason, the diagnostic device determines whether or not the operating state of the internal combustion engine is steady based on the rotational speed of the internal combustion engine, the pressure in the intake passage, the intake air amount, and the like.

By the way, it is the inventor that determining whether or not the operating state of the internal combustion engine is a steady state in the above-described aspect is insufficient for accurately diagnosing the presence or absence of abnormality of the air-fuel ratio sensor. Have been found. That is, for example, even when the operation state of the internal combustion engine is determined to be steady in the above-described mode, if the intake air amount increases very slowly, the lean air-fuel ratio is detected. It will continue to be done. For this reason, the cumulative value of the period indicating lean becomes equal to or greater than a predetermined value, and an erroneous determination is made that the air-fuel ratio sensor is abnormal although the air-fuel ratio sensor is normal.
JP 7-234199 A

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an air-fuel ratio sensor diagnostic apparatus capable of more accurately diagnosing the presence or absence of an abnormality of the air-fuel ratio sensor.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  Means 1 increases the fuel injection amount stepwise when the air-fuel ratio lean state is detected by the air-fuel ratio sensor for detecting the air-fuel ratio of the internal combustion engine, and when the rich state is detected, the fuel An air-fuel ratio control means for performing air-fuel ratio control for gradually reducing the injection amount, a lean period measuring means for measuring a period during which a lean state is detected by the air-fuel ratio sensor, and a rich state detected by the air-fuel ratio sensor The air-fuel ratio control is steady when the rich period measuring means for measuring the measured period, the period measured by the lean period measuring means, and the period measured by the rich period measuring means are approximate. Determining means for determining that there is a state; and diagnostic means for diagnosing the presence or absence of abnormality of the air-fuel ratio sensor when the determining means determines that it is in the steady state. Characterized in that it obtain.

  In the above configuration, when the period measured by the lean period measuring unit and the period measured by the rich period measuring unit are approximate, it can be determined that the control of the air-fuel ratio is steady. In particular, even if the rotational speed, load, etc. of the internal combustion engine are steady, this condition is not always satisfied. Therefore, according to the above aspect, it can be accurately determined that the control of the air-fuel ratio is steady. Then, since it is diagnosed whether or not the air-fuel ratio sensor is abnormal when it is determined that the control of the air-fuel ratio is steady in the above aspect, according to the above configuration, the presence or absence of the abnormality of the air-fuel ratio sensor can be more accurately determined. Can be diagnosed.

  The means 2 is the means 1, wherein the determining means is a ratio of a period measured by the lean period measuring means and a period measured by the rich period measuring means in one cycle of the lean state and the rich state. Is approximately "1", it is determined that the control of the air-fuel ratio is steady.

  In the above configuration, since the control of the air-fuel ratio is determined to be steady when the ratio of each period in one cycle between the lean state and the rich state approximates “1”, is the air-fuel ratio control steady? Whether or not can be determined accurately and quickly.

  In means 1 or 2, the air / fuel ratio control means performs skip control for greatly reducing the fuel injection amount when a shift from the lean state to the rich state is detected, and then the rich air is controlled. While the state is detected, integral control for gradually decreasing the fuel injection amount is performed, and when the transition from the rich state to the lean state is detected, skip control for greatly increasing the fuel injection amount is performed. After that, while the lean state is detected, integral control for increasing the fuel injection amount in stages is performed.

  In the above configuration, by performing skip control when shifting from lean to rich, it is possible to quickly shift from rich to lean as compared with the case where only integral control is used. Further, by performing skip control at the time of shifting from rich to lean, it is possible to quickly shift from lean to rich as compared to the case of using only integral control.

  Means 4 is characterized in that, in any one of means 1 to 3, the air-fuel ratio sensor is a sensor that linearly increases or decreases its output in accordance with the air-fuel ratio of the internal combustion engine.

  In the above configuration, a sensor that linearly increases or decreases the output according to the air-fuel ratio is used. In the diagnosis of the presence or absence of abnormality of this sensor, the waste time, which is the time from when the fuel injection amount changes suddenly until the air-fuel ratio starts to change, and the time constant indicating the degree of change of the air-fuel ratio are within an allowable range. Some of them require a very high diagnostic accuracy, such as those for diagnosing whether or not. In order to perform highly accurate diagnosis, it is required to determine with high accuracy that the control of the air-fuel ratio is steady. In this regard, according to the above configuration, the effects of the means 1 to 3 can be suitably achieved.

  In the above configuration, when diagnosing whether the waste time or the time constant is within an allowable range as a diagnosis of the presence / absence of an abnormality of the air-fuel ratio sensor, as in the case of the means 3, the skip control and the integral control are performed. Is particularly effective.

  The means 5 further comprises operating state judging means for judging whether or not at least one of the rotational speed and the load of the internal combustion engine is steady in the means 4, and the fuel injection amount is increased stepwise and stepwise. The reduction control is performed when the operation state determination means determines that the engine is steady. The operation state determination for determining whether at least one of the rotational speed and the load of the internal combustion engine is steady. And a stepwise increase and a stepwise decrease control of the fuel injection amount is performed when the operation state determination unit determines that the fuel injection amount is steady.

  Since the above configuration is based on the configuration of the means 4, the air-fuel ratio sensor linearly increases or decreases the output according to the actual air-fuel ratio. For this reason, when controlling the air-fuel ratio to the target air-fuel ratio, feedback control such as PID control based on the deviation between the detected air-fuel ratio and the target air-fuel ratio is performed, so that the actual air-fuel ratio becomes the target. The air / fuel ratio can be suitably followed.

  On the other hand, steady rotation speed and load of the internal combustion engine are necessary conditions for steady control of the air-fuel ratio. For this reason, in the above configuration, when the necessary condition for the air-fuel ratio control to be steady is satisfied, the step-by-step increase control and decrease control of the fuel injection amount are performed, so that the air-fuel ratio control is not steady. Also, it is possible to set to perform control by other methods. That is, when the air-fuel ratio control is not steady, feedback control for accurately following the actual air-fuel ratio, such as the PID control, can be performed as much as possible.

  The means 6 is any one of the means 1 to 5, wherein the diagnosis means determines whether the output of the air-fuel ratio sensor satisfies a predetermined standard when the determination means determines that the steady state is present. A diagnostic function for diagnosing the above, a counter function for counting the number determined as not satisfying the standard by the diagnostic function, and a function for diagnosing whether the air-fuel ratio sensor is abnormal based on a counter value by the counter function It is characterized by providing.

  In the above configuration, it is possible to appropriately diagnose the presence or absence of abnormality of the air-fuel ratio sensor based on the number determined that the output of the air-fuel ratio sensor does not satisfy a predetermined standard. In particular, when the above configuration includes the configuration of the means 2, it is determined whether the output of the air-fuel ratio sensor satisfies a predetermined criterion for each lean and rich cycle, and it is determined that the criterion is not satisfied. The presence / absence of an abnormality in the air-fuel ratio sensor is diagnosed on the basis of the number obtained. Therefore, in this case, the diagnosis can be performed particularly quickly and the accuracy of the diagnosis can be further improved.

  Hereinafter, an embodiment of a diagnostic apparatus for an air-fuel ratio sensor according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of an air-fuel ratio sensor diagnostic apparatus according to the present embodiment. As shown in the figure, an air flow meter 6 for detecting the intake air amount is provided in the intake passage 4 of the internal combustion engine 2. Further, an electronically controlled throttle valve 10 driven by a motor 8 is provided downstream thereof. A throttle sensor 12 for detecting the opening degree of the throttle valve 10 is provided in the vicinity of the throttle valve 10. Further, a fuel injection valve 14 is provided downstream of the throttle valve 10. The fuel injection valve 14 injects the fuel pumped up from the fuel tank 16 by the fuel pump 18 into the intake passage 4.

  The intake passage 4 and the combustion chamber 20 are communicated and blocked by the opening / closing operation of the intake valve 22. The air-fuel mixture introduced into the combustion chamber 20 with the opening operation of the intake valve 22 is ignited and burned by the spark discharge of the spark plug 24.

  The combustion chamber 20 and the exhaust passage 30 are communicated and blocked by the opening / closing operation of the exhaust valve 28. The air-fuel mixture subjected to combustion in the combustion chamber 20 is discharged as exhaust into the exhaust passage 30 as the exhaust valve 28 is opened.

  A catalyst 32 that purifies the exhaust gas is provided in the exhaust passage 30. Further, a so-called λ sensor 34 that is an air-fuel ratio sensor of a type that linearly increases or decreases the output in accordance with the air-fuel ratio of the internal combustion engine 2 is provided upstream of the catalyst 32 in the exhaust passage 30.

  The ECU (electronic control unit) 40 includes a central processing unit and an appropriate memory. The ECU 40 takes in the output of each of the above-described sensors as well as the output of the crank angle sensor 42 that detects the rotation angle of the output shaft of the internal combustion engine 2. The ECU 40 controls the output of the internal combustion engine 2 based on the output of each sensor.

  In particular, the ECU 40 controls the air-fuel ratio of the internal combustion engine 2 to a target air-fuel ratio (for example, the theoretical air-fuel ratio) based on the output of the λ sensor 34. That is, based on the output of the λ sensor 34, for example, PID control is performed so that the actual air-fuel ratio follows the target air-fuel ratio.

  Further, the ECU 40 diagnoses whether the λ sensor 34 is abnormal. When diagnosing the presence or absence of this abnormality, air-fuel ratio control is performed in the manner shown in FIG.

  FIG. 2 (a) shows the transition of the output of the λ sensor 34, and FIG. 2 (b) shows the transition of the air-fuel ratio feedback correction coefficient, which is a correction coefficient for the fuel injection amount related to the air-fuel ratio control. Incidentally, in FIG. 2A, the target air-fuel ratio is set to “1.0”, and a leaner state and a richer state are defined. The air-fuel ratio feedback correction coefficient is a coefficient that is multiplied by the basic fuel injection amount set based on the rotational speed of the internal combustion engine 2 and the intake air amount.

  As shown in the figure, in the present embodiment, after performing the skip control for greatly reducing the fuel injection amount when the transition from the lean state to the rich state is detected, the fuel injection amount is detected while the rich state is detected. Integral control is performed to gradually decrease. In addition, after performing the skip control that greatly increases the fuel injection amount when the transition from the rich state to the lean state is detected, the integral control that gradually increases the fuel injection amount is performed while the lean state is detected. Do.

  By performing the air-fuel ratio control in the above-described manner, it is possible to appropriately detect deterioration of the response of the λ sensor 34 or the like. That is, since the stepwise increase amount and decrease amount of the skip amount of the skip control and the fuel injection amount related to the integral control are set in advance, the period during which the lean state is detected by the λ sensor 34 and the λ sensor 34 The reference that can be taken when the λ sensor 34 is normal can be set for the period during which the rich state is detected. For this reason, when the output of the λ sensor 34 deviates from a preset reference, it can be determined that there is an abnormality such as a deterioration in the response of the λ sensor 34.

  2C and 2D show examples when the responsiveness of the λ sensor 34 is deteriorated. Specifically, FIG. 2C shows the transition of the output of the λ sensor 34, and FIG. 2D shows the transition of the air-fuel ratio feedback correction coefficient. In the example shown in FIGS. 2C and 2D, compared to the example shown in FIGS. 2A and 2B, the period during which the lean state is detected by the λ sensor 34 and the rich state are detected. The period during which is detected is longer. However, since the stepwise change amount of the fuel injection amount related to the integral control and the skip amount of the skip control are set in advance, if the λ sensor 34 is normal, its output should behave within a certain range. . For this reason, about the example shown in FIG.2 (c) and FIG.2 (d), this can be judged to be abnormal.

  However, such a comparison can be made only when the control of the air-fuel ratio is steady. That is, it is limited to the time when the lean state is detected (TimeRL1, TimeRL2) and the time period when the rich state is detected (TimeLR1, TimeLR2) by the skip control and the integration control.

  FIGS. 2E and 2F show an example in which the air-fuel ratio control is not in a steady state. Specifically, FIG. 2 (e) shows the transition of the output of the λ sensor 34, and FIG. 2 (f) shows the transition of the air-fuel ratio feedback correction coefficient. Here, an example is shown in which the air-fuel ratio biased toward the lean state is gradually controlled to a steady state by the skip control and the integration control. For this reason, the amplitude center of the output of the λ sensor 34 indicated by the broken line in the figure converges from the lean side to the target air-fuel ratio. In this case, in the initial stage of control, the period during which the lean state is detected by the λ sensor 34 (TimeRL3) is longer than the period during which the rich state is detected by the λ sensor 34 (TimeLR3). For this reason, for example, when the presence or absence of abnormality of the λ sensor 34 is diagnosed based on the period during which the lean state is detected by the λ sensor 34 (TimeRL3), it is erroneously determined that the λ sensor 34 is abnormal although it is normal. There is a risk.

  Therefore, in this embodiment, when the ratio of the period in which the lean state is detected and the period in which the rich state is detected approximates “1” in one cycle of the lean state and the rich state, the air-fuel ratio control is performed. It is determined that it is steady, and at this time, the presence or absence of abnormality of the λ sensor 34 is diagnosed. Here, first, a process for determining whether the air-fuel ratio control is steady will be described.

  FIG. 3 shows the procedure of the processing relating to the above determination. This process is repeatedly executed by the ECU 40 at a predetermined cycle, for example.

  In this series of processes, first, in step S10, it is determined whether or not an execution condition for the air-fuel ratio feedback control by the skip control and the integral control is satisfied. This condition is that the rotational speed of the internal combustion engine 2 and the intake air amount are in a steady state. In step S10, whether or not it is established is determined based on the execution condition of the diagnostic air-fuel ratio feedback control. That is, in the present embodiment, the air-fuel ratio feedback control using the skip control and the integral control is performed only when it is determined that the rotation speed and the intake air amount of the internal combustion engine 2 are steady, and at other times, for example, Based on the deviation between the air-fuel ratio detected by the λ sensor 34 and the target air-fuel ratio by PID or the like, control is performed to make this zero.

  If it is determined in step S10 that the execution condition is satisfied, it is determined in step S12 whether the air-fuel ratio is lean with respect to the target air-fuel ratio. Then, in step S12, depending on whether it is determined that the air-fuel ratio is lean or rich with respect to the target air-fuel ratio, the processing after step S14 or the processing after step S28 is performed. Will be performed.

  The processes in steps S14 to S26 are processes related to skip control and integration control and measurement of a period during which a lean state is detected. First, in step S14, a lean detection flag xLean, which is a flag indicating that a lean state is detected, is turned on, and a rich detection flag xRich, which is a flag indicating that a rich state is detected, is turned off.

  In a succeeding step S16, it is determined whether or not the previous detected value of the air-fuel ratio by the λ sensor 34 is rich. In other words, this time, it is determined whether or not the detection value of the λ sensor 34 has shifted from the rich state to the lean state. If it is determined in step S16 that the vehicle has shifted from the rich state to the lean state, a lean skip flag xSkipRL, which is a flag indicating that skip control is performed in the lean state, is turned on in step S18. In the subsequent step S20, the air-fuel ratio feedback correction coefficient FAF is increased by the skip amount Kp with respect to the previous value FAF [i−1].

  On the other hand, if it is determined in step S16 that the vehicle has not shifted from the rich state to the lean state, the lean skip flag xSkipRL is turned off in step S22. In subsequent step S24, the air-fuel ratio feedback correction coefficient FAF is increased by a predetermined amount Ki with respect to the previous value FAF [i-1]. This predetermined amount Ki is smaller than the skip amount Kp.

  In the subsequent step S26, a lean counter TimeRL that measures the period in which the lean state has been reached is incremented.

  The processes in steps S28 to S40 are processes related to skip control and integration control and measurement of a period during which the rich state is detected. First, in step S28, the lean detection flag xLean, which is a flag indicating that a lean state is detected, is turned off, and the rich detection flag xRich, which is a flag indicating that a rich state is detected, is turned on.

  In the subsequent step S30, it is determined whether or not the previous detected value of the air-fuel ratio by the λ sensor 34 was lean. In other words, this time, it is determined whether or not the detection value of the λ sensor 34 has shifted from the lean state to the rich state. When it is determined in step S30 that the vehicle has shifted from the lean state to the rich state, in step S32, the rich-time skip flag xSkipLR, which is a flag indicating that skip control is performed in the rich state, is turned on. In the subsequent step S34, the air-fuel ratio feedback correction coefficient FAF is decreased by the skip amount Kp with respect to the previous value FAF [i−1]. Incidentally, the skip amount Kp is set equal to the skip amount Kp in step S20.

  On the other hand, if it is determined in step S30 that the vehicle has not shifted from the rich state to the lean state, the rich-time skip flag xSkipLR is turned off in step S36. In the subsequent step S38, the air-fuel ratio feedback correction coefficient FAF is decreased by a predetermined amount Ki with respect to the previous value FAF [i−1]. Incidentally, the predetermined amount Ki is set equal to the predetermined amount Ki in step S24.

  In the subsequent step S40, the rich counter TimeLR that measures the period in which the rich state has been reached is incremented.

  When it is determined in step S16 that the state has shifted from the rich state to the lean state, or in step S30, it has been determined that the state has shifted from the lean state to the rich state. This is the timing for performing the process of calculating the ratio.

  That is, when the processing of step S20 is completed, it is determined whether the lean counter TimeRL is zero in step S42, and in step S44, it is determined whether the rich counter TimeLR is zero. If it is determined that both of them are not zero, in step S46, the ratio Rate of the period in which the lean state is set to the period in which the rich state is set is calculated. In the subsequent step S48, the rich counter TimeLR is initialized.

  When the process of step S34 is completed, it is determined in step S50 whether the rich counter TimeLR is zero, and in step S52, it is determined whether the lean counter TimeRL is zero. If it is determined that both of them are not zero, in step S54, the ratio Rate of the period in which the lean state is set to the period in which the rich state is set is calculated. In the subsequent step S26, the lean counter TimeRL is initialized.

  When the process of step S48 and the process of step S56 are completed, it is determined in step S58 whether or not the ratio Rate is close to “1”. If it is determined in step S58 that the ratio Rate is close to “1”, in step S60, the steady flag xTable, which is a flag indicating that the air-fuel ratio control is in a steady state, is turned on. On the other hand, when it is determined in step S58 that the ratio Rate is not close to “1”, the steady flag xStable is turned off in step S62.

  If it is determined in step S10 that the execution condition is not satisfied, a lean counter TimeRL, a rich counter TimeLR, and a steady flag xStable are initialized in step S64.

  When it is determined in steps S42 and S52 that the lean counter TimeRL is zero, or when the rich counter TimeLR is determined to be zero in steps S44 and S50, the processes in steps S26, S40, and S60 to S64 are performed. When is completed, this series of processing is once ended.

  Here, transition examples of various parameters by the process shown in FIG. 3 will be described with reference to FIG.

  FIG. 4A shows whether or not the execution condition of the feedback control at the time of diagnosis is satisfied. FIG. 4B shows the transition of the output of the λ sensor 34. FIG. 4C shows the transition of the lean detection flag, and FIG. 4D shows the transition of the rich detection flag. FIG. 4E shows the transition of the lean skip flag xSkipRL, and FIG. 4F shows the transition of the rich skip flag xSkipLR. FIG. 4G shows the transition of the air-fuel ratio feedback correction coefficient FAF. FIG. 4H shows the transition of the lean counter TimeRL, and FIG. 4I shows the transition of the rich counter TimeLR. FIG. 4 (j) shows the transition of the ratio Rate, and FIG. 4 (k) shows the transition of the steady flag xStable.

  In this example, the air-fuel ratio control is not steady before time t5, and the output of the λ sensor 34 is biased to a lean state. In other words, the amplitude center that is the center of the output of the λ sensor 34 shown by the broken line in FIG. 4B is leaner than the target air-fuel ratio.

  Now, assuming that the execution condition shown in step S10 of FIG. 3 is satisfied at time t1, the lean counter TimeRL and the rich counter TimeLR are both initialized at this time. Then, since the output of the λ sensor 34 shifts from lean to rich at time t1, skip control is performed to decrease the air-fuel ratio feedback correction coefficient FAF by the skip amount Kp, and then the previous diagram from time t1 to t2. The rich counter TimeLR is incremented with the integration control in step S38 of step 3. When the output of the λ sensor 34 shifts to lean at time t2, after performing skip control for increasing the air-fuel ratio feedback correction coefficient FAF by the skip amount Kp, the integration control in step S24 of FIG. 3 is performed until time t3. Accordingly, the lean counter TimeRL is incremented.

  At time t3, skip control is performed to decrease the air-fuel ratio feedback correction coefficient FAF by the skip amount Kp in order to shift the output of the λ sensor 34 from lean to rich again. Further, at this time, since both the rich counter TimeLR and the lean counter TimeRL are not zero, the ratio Rate is calculated in step S54 of FIG. Thereafter, in step S56, the lean counter RL is initialized. Further, thereafter, in step S58 of FIG. 3, it is determined whether or not the ratio Rate is close to “1”.

  As described above, the lean counter TimeRL and the rich counter TimeLR are initialized and incremented in accordance with the skip control and the integration control, and the steady state flag xStable is turned on at time t7 when it is determined that the ratio Rate of these counters approximates “1”. The

  Next, a process for diagnosing whether there is an abnormality in the λ sensor 34 performed when the steady flag xStable is turned on will be described.

  FIG. 5 shows a processing procedure for diagnosis of whether the λ sensor 34 is abnormal. This process is repeatedly executed by the ECU 40 at a predetermined cycle, for example.

  In this series of processing, first, in step S70, it is determined whether or not the steady flag xStable is turned on. If it is determined in step S70 that the steady flag xStable is on, it is determined in step S72 whether or not the output of the λ sensor 34 satisfies the standard. Here, the reference is an output of the λ sensor 34 assumed when the air-fuel ratio control is in a steady state and the output of the λ sensor 34 is normal. Of course, the above-mentioned standard has a predetermined range in order to allow variation among individuals of each λ sensor 34.

  Specifically, as shown in FIG. 6 (a), a waste time which is a time until a change starts to appear in the output of the λ sensor 34 due to a rapid increase (or decrease) in the air-fuel ratio feedback correction coefficient FAF, It is determined whether or not the time constant defined by the degree of change in output after the change appears is within an allowable range. Specifically, for example, as shown in FIG. 7A, the time T required for the output of the λ sensor 34 to return to the value when the skip control is performed (FIG. 7B). ) To measure the waste time. Further, the time constant may be measured based on the differential value of the output of the λ sensor 34 during this period.

  If it is determined in step S72 that the output of the λ sensor 34 does not satisfy the standard, the abnormal accumulation counter is incremented in step S74. This counter is a counter that counts the number of times it is determined in step S72 that the output of the λ sensor 34 does not satisfy the standard.

  In a succeeding step S76, it is determined whether or not the abnormality accumulation counter is equal to or larger than a predetermined value α. Here, the predetermined value α is for diagnosing whether the λ sensor 34 is abnormal. That is, the value is set to avoid the determination that the output of the λ sensor 34 does not satisfy the standard in step S72 due to the influence of noise or the like.

  If it is determined in step S76 that the abnormal accumulation counter is less than the predetermined value α, normality is determined in step S78. On the other hand, if it is determined in step S76 that the abnormality accumulation counter is greater than or equal to the predetermined value α, it is determined in step S80 that the responsiveness of the λ sensor 34 has deteriorated.

  When it is determined in step S70 that xStable is OFF, or when it is determined in step S72 that the output of the λ sensor 34 satisfies the standard, the processing in steps S78 and S80 is completed. Is temporarily terminated.

  Incidentally, the abnormality accumulation counter may be initialized under a predetermined condition, for example, the ignition switch is turned off, in order to avoid the abnormality accumulation counter from exceeding the predetermined value α due to the influence of noise or the like. .

  As described above, in the present embodiment, when the air-fuel ratio control is steady, the presence / absence of abnormality of the λ sensor 34 is diagnosed. On the other hand, if the diagnosis of the presence / absence of the abnormality of the λ sensor 34 is performed when it is determined that the rotation speed and the load are steady, the λ sensor 34 is within a range of variation allowed as an individual difference, and λ Even though the sensor 34 is normal, there is a risk of determining this as abnormal. In particular, when the allowable output characteristic for the λ sensor 34 includes setting the waste time and time constant within allowable ranges, the diagnosis requires extremely high accuracy. In this regard, in the present embodiment, the presence / absence of abnormality of the λ sensor 34 can be accurately determined by diagnosing the presence / absence of abnormality when it is determined that the control of the air-fuel ratio is steady.

  Further, in the present embodiment, it is determined that the air-fuel ratio control is steady when the ratio Rate in one cycle between the lean state and the rich state is close to “1”, and whether the output of the λ sensor 34 satisfies the standard. Judged whether or not. On the other hand, for example, when determining the steady state of the air-fuel ratio control based on the ratio between the lean state period and the rich state period in two cycles, for example, in the two cycles from time t4 to t7 in FIG. There is a possibility that it cannot be determined as steady. For this reason, the determination that the air-fuel ratio control is steady is delayed. Furthermore, when the period during which the air-fuel ratio control is steady is short, there is a possibility that the diagnosis cannot be performed within a period in which it is desired to diagnose whether the λ sensor 34 is abnormal.

  In particular, some diagnosis of whether or not the internal combustion engine 2 is abnormal may be performed on the condition that the λ sensor 34 is determined to be normal, such as a diagnosis of whether or not the catalyst 32 is abnormal. For this reason, in order to complete the diagnosis of the presence / absence of all these abnormalities within a predetermined period, the period during which the diagnosis of the presence / absence of the abnormality of the λ sensor 34 is desired is relatively short. In this regard, according to the present embodiment, an opportunity for diagnosing the presence or absence of abnormality of the λ sensor 34 in order to determine whether the air-fuel ratio control is steady in any one cycle of the lean state and the rich state. Can be increased.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) When it is determined that the control of the air-fuel ratio is in a steady state, the presence or absence of an abnormality in the λ sensor 34 is diagnosed. Thereby, the presence or absence of abnormality of the λ sensor 34 can be diagnosed more accurately.

  (2) It is determined that the control of the air-fuel ratio is steady when the ratio Rate of these periods approximates “1” in one cycle of the lean state and the rich state. As a result, it is possible to accurately and quickly determine whether the air-fuel ratio control is steady.

  (3) After performing the skip control for greatly reducing the fuel injection amount when the transition from the lean state to the rich state is detected, the integration control for decreasing the fuel injection amount in stages is performed, and the lean state to the lean state is performed. After performing the skip control that greatly increases the fuel injection amount when the shift to is detected, integral control that increases the fuel injection amount stepwise is performed. Thereby, compared with the case where only integral control is used, the shift from rich to lean and the shift from lean to rich can be performed quickly.

  (4) As the air-fuel ratio sensor, a λ sensor 34 that linearly increases or decreases the output according to the air-fuel ratio of the internal combustion engine 2 is used. The diagnosis of the presence / absence of the abnormality of the λ sensor 34 requires that the air-fuel ratio control is determined with high accuracy, so that the effects (1) to (3) are preferably achieved. be able to.

  (5) When it is determined that the rotational speed of the internal combustion engine 2 and the intake air amount, which are necessary conditions for the air-fuel ratio control being steady, are steady, the skip control and the integral control are performed. Thereby, when the control of the air-fuel ratio is not steady, feedback control based on the difference between the actual air-fuel ratio and the target air-fuel ratio can be performed as much as possible.

  (6) The λ sensor 34 determines that an abnormality has occurred when the abnormality accumulation counter becomes equal to or greater than the predetermined value α. Thereby, the accuracy of diagnosis can be further improved.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  The effects (1) to (5) of the previous embodiment can be obtained even if the determination whether or not the abnormal accumulation counter is equal to or greater than the predetermined value α is excluded.

  In the above embodiment, the skip control and the integral control are performed when the rotational speed and the intake air amount of the internal combustion engine 2 are steady. However, the present invention is not limited thereto, and at least one of the rotational speed and the load is steady. If it is.

  -Air-fuel ratio feedback control using skip control or integral control can be performed even when the rotational speed and load are not steady.

  Even if only integral control is performed instead of skip control and integral control, it is not possible to determine whether the air-fuel ratio control is steady based on the lean state period and the rich state period at this time. it can.

  The method for determining that the control of the air-fuel ratio is steady when the lean period and the rich engine are approximate is not limited to that exemplified in the above embodiment. For example, even if the ratio between the lean state period and the rich state period in two cycles is used, the effects (1) and (3) to (6) of the first embodiment can be obtained.

  The sensor for detecting the air-fuel ratio of the internal combustion engine is not limited to the λ sensor 34, and the output varies greatly depending on whether the actual air-fuel ratio is lean or rich with respect to a predetermined air-fuel ratio. It may be an oxygen sensor.

The figure which shows the structure of the internal combustion engine etc. in one Embodiment of the diagnostic apparatus of the air fuel ratio sensor concerning this invention. The time chart which shows transition of the output of a lambda sensor, and an air fuel ratio feedback correction coefficient. The flowchart which shows the process sequence which judges whether air-fuel ratio control is steady. The time chart which shows transition of the various parameters concerning the said process. The flowchart which shows the procedure of the process which diagnoses the presence or absence of abnormality of (lambda) sensor. The time chart which shows how to define the reference | standard of the output of (lambda) sensor. The time chart which shows an example of the diagnostic method of the presence or absence of abnormality of (lambda) sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Internal combustion engine, 6 ... Air flow meter, 32 ... Catalyst, 34 ... Lambda sensor, 40 ... ECU (electronic control unit), 42 ... Crank angle sensor.

Claims (6)

The fuel injection amount is increased stepwise when the air-fuel ratio lean state is detected by an air-fuel ratio sensor that detects the air-fuel ratio of the internal combustion engine, and the fuel injection amount is stepped when the rich state is detected An air-fuel ratio control means for performing air-fuel ratio control to reduce automatically,
Lean period measuring means for measuring a period during which a lean state is detected by the air-fuel ratio sensor;
Rich period measuring means for measuring a period during which a rich state is detected by the air-fuel ratio sensor;
Determining means for determining that the control of the air-fuel ratio is in a steady state when the period measured by the lean period measuring means approximates the period measured by the rich period measuring means;
A diagnostic device for an air-fuel ratio sensor, comprising: a diagnostic means for diagnosing whether or not the air-fuel ratio sensor is abnormal when it is judged by the judging means to be in the steady state.   When the ratio of the period measured by the lean period measuring unit and the period measured by the rich period measuring unit approximates “1” in one cycle of the lean state and the rich state 2. The diagnostic apparatus for an air-fuel ratio sensor according to claim 1, wherein the control of the air-fuel ratio is determined to be steady.   The air-fuel ratio control unit performs skip control for greatly reducing the fuel injection amount when the transition from the lean state to the rich state is detected, and then performs the fuel injection while the rich state is detected. Integral control that gradually decreases the amount is performed, and when the shift from the rich state to the lean state is detected, skip control that greatly increases the fuel injection amount is performed, and then the lean state is detected 3. The air-fuel ratio sensor diagnostic apparatus according to claim 1, wherein integral control for increasing the fuel injection amount in a stepwise manner is performed.   The air-fuel ratio sensor diagnosis apparatus according to any one of claims 1 to 3, wherein the air-fuel ratio sensor is a sensor that linearly increases or decreases its output in accordance with an air-fuel ratio of the internal combustion engine. An operating state determining means for determining whether at least one of the rotational speed and the load of the internal combustion engine is steady;
5. The air-fuel ratio sensor according to claim 4, wherein the stepwise increase and stepwise decrease control of the fuel injection amount is performed when the operation state determining means determines that the fuel injection amount is steady. Diagnostic equipment.   The diagnostic means diagnoses whether the output of the air-fuel ratio sensor satisfies a predetermined standard when the determination means determines that the steady state is present; and 6. A counter function for counting a number determined to not satisfy the condition, and a function for diagnosing whether the air-fuel ratio sensor is abnormal based on a counter value obtained by the counter function. A diagnostic apparatus for an air-fuel ratio sensor according to claim 1.

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