JP2017115798A - Air-fuel ratio sensor abnormal state detecting device and abnormal state detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio sensor abnormal state detecting device and abnormal state detecting method capable of detecting an abnormal state in responding characteristic in the air-fuel ratio sensor for both rich direction and lean direction.SOLUTION: Under a state in which an air-fuel ratio varies alternatively between a rich side and a lean side, a period Ta in which an output voltage V of an air-fuel ratio sensor is not varied when it is changed to the rich side and the number of occurrence Xa of the period Ta are calculated and when it is changed to the lean side, a period Tb showing no variation in the output voltage V of the air-fuel ratio sensor and the time of occurrence Xb of the period Tb are calculated. The calculated value of the period Ta is divided by the calculated value of the time of occurrence Xa to detect an average value Tax of the period Ta, and the calculated value of the period Tb is divided by the calculated value of the time of occurrence Xb to detect an average value Tbx of the period Tb. It is judged whether or not an abnormality in responding characteristic of the air-fuel ratio sensor occurs when the air-fuel ratio varies to the rich side and it is judged whether or not an abnormality in responding characteristic of the air-fuel ratio sensor varies to the lean side on the basis of the comparison between these average values Tax, Tbx.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an abnormality detection apparatus and an abnormality detection method for an air-fuel ratio sensor in an internal combustion engine that performs air-fuel ratio feedback control using the air-fuel ratio sensor.

  An internal combustion engine of an automobile includes an air-fuel ratio sensor (also referred to as a LAF sensor or an A / F sensor) whose output voltage changes according to the air-fuel ratio, and an air-fuel mixture of injected fuel and intake air is detected from the detection output of the air-fuel ratio sensor. The air-fuel ratio (ratio of air mass to fuel mass) is obtained, and the fuel injection amount is feedback-controlled (air-fuel ratio feedback control) so that the air-fuel ratio becomes an ideal air-fuel ratio, so-called theoretical air-fuel ratio.

  Specifically, in the air-fuel ratio sensor, the electromotive force changes according to the difference between the oxygen concentration in the atmosphere and the oxygen concentration in the exhaust gas. That is, when the ratio of fuel to intake air is large (the air-fuel ratio is rich), more oxygen is consumed in the intake air, so that the concentration of oxygen in the exhaust gas decreases, and the output of the air-fuel ratio sensor accordingly. The voltage rises. When the ratio of fuel to intake air is small (the air-fuel ratio is lean), the consumption of oxygen in the intake air is small, so the concentration of oxygen in the exhaust gas increases, and the output voltage of the air-fuel ratio sensor decreases accordingly. .

  If this air-fuel ratio sensor fails, it is of course difficult to perform proper air-fuel ratio feedback control.

  As a countermeasure against the failure of the air-fuel ratio sensor, for example, as in Patent Document 1, a device that monitors the change in the output voltage of the air-fuel ratio sensor and detects an abnormality of the air-fuel ratio sensor based on the monitoring result has been proposed.

JP 2005-307961 A

  As an abnormality related to the responsiveness of the air-fuel ratio sensor, there are a response delay when the air-fuel ratio is rich and the output voltage changes upward, and a response delay when the air-fuel ratio is rich and the output voltage changes downward.

  In the case of the above detection device, even if an abnormality related to the responsiveness of the air-fuel ratio sensor can be detected, it cannot be determined whether the responsiveness is abnormal in the rich direction or abnormal in the lean direction.

  An object of the present invention is to provide an abnormality detection device and an abnormality detection method for an air-fuel ratio sensor that can detect an abnormality in responsiveness of the air-fuel ratio sensor in both the rich direction and the lean direction.

  An abnormality detection apparatus for an air-fuel ratio sensor according to a first aspect of the invention detects an abnormality of the air-fuel ratio sensor in which the output voltage changes according to the air-fuel ratio, and includes an integrating means, a detecting means, and a determining means. . In the situation where the air-fuel ratio varies alternately between the rich side and the lean side, the integrating means includes a period Ta in which the output voltage V of the air-fuel ratio sensor does not change during the change to the rich side and the number of occurrences Xa of the period Ta And a period Tb in which the output voltage V of the air-fuel ratio sensor does not change during the fluctuation to the lean side and the number of occurrences Xb of the period Tb are accumulated. The detecting means detects the average value Tax of the period Ta by dividing the integrated value of the period Ta by the integrated value of the number of occurrences Xa, and detects the integrated value of the period Tb by the integrated value of the number of occurrences Xb. By dividing, the average value Tbx of the period Tb is detected. Based on the comparison between the average values Tax and Tbx, the determination means includes an abnormality in responsiveness of the air-fuel ratio sensor when the air-fuel ratio changes to the rich side, and the air-fuel ratio when the air-fuel ratio changes to the lean side. The air-fuel ratio sensor response abnormality is determined.

  The abnormality detection device for an air-fuel ratio sensor of the invention according to claim 2 limits the integrating means, detection means, and determination means of the invention according to claim 1. In a situation where the air-fuel ratio fluctuates alternately between the rich side and the lean side, the integrating means has a period Ta during which the output voltage V of the air-fuel ratio sensor does not change during the fluctuation to the rich side over a certain time t1, and the period The number of occurrences Xa of Ta is integrated, and the period Tb in which the output voltage V of the air-fuel ratio sensor does not change during the fluctuation to the lean side and the number of occurrences Xb of the period Tb are integrated, and the integration of this constant time t1 The process is repeated a predetermined number of times N. The detecting means detects the average value Tax of the period Ta by dividing the integrated value of the period Ta by the integrated value of the number of occurrences Xa every time the predetermined time t1 elapses, and the integrated value of the period Tb Is divided by the integrated value of the number of occurrences Xb to detect the average value Tbx of the period Tb, and after the integration process over the predetermined number N, the total values of the detected average values Tax, Tbx are By dividing by a predetermined number N, further average values Tax0, Tbx0 of the average values Tax, Tbx are calculated. Based on the comparison of the calculated average values Tax0 and Tbx0, the determination means determines whether the air / fuel ratio sensor is abnormal when the air / fuel ratio changes to the rich side, and when the air / fuel ratio changes to the lean side. The abnormality of the responsiveness of the air-fuel ratio sensor is determined.

  The abnormality detection device for an air-fuel ratio sensor of the invention according to claim 3 limits the determination means of the invention according to claim 2. The determination means determines that there is no abnormality in the air-fuel ratio sensor when both the average values Tax0 and Tbx0 are less than the set value Ts, and the average value Tax0 is equal to or greater than the set value Ts and the average value Tbx0 is less than the set value Ts. In the case where the air-fuel ratio sensor determines that there is “abnormal reaction start delay in the rich direction”, and the air-fuel ratio is determined when the average value Tax0 is less than the set value Ts and the average value Tbx0 is greater than or equal to the set value Ts. It is determined that the sensor has a “reaction start delay abnormality in the lean direction”.

  An abnormality detection method for an air-fuel ratio sensor according to a fourth aspect of the invention is a method for detecting an abnormality in the air-fuel ratio sensor in which the output voltage changes according to the air-fuel ratio, and the air-fuel ratio varies alternately between the rich side and the lean side. In this situation, the period Ta during which the output voltage V of the air-fuel ratio sensor does not change when the change to the rich side and the number of occurrences Xa of the period Ta are integrated, and the change of the air-fuel ratio sensor when the change to the lean side occurs. The period Tb in which the output voltage V does not change and the number of occurrences Xb of the period Tb are integrated. Further, the average value Tax of the period Ta is detected by dividing the integrated value of the period Ta by the integrated value of the generation number Xa, and the integrated value of the period Tb is divided by the integrated value of the generation number Xb. Thus, the average value Tbx of the period Tb is detected. Then, based on the comparison between the detected average values Tax and Tbx, an abnormality in the responsiveness of the air-fuel ratio sensor when the air-fuel ratio fluctuates to the rich side, and the air-fuel ratio when the air-fuel ratio fluctuates to the lean side. An abnormality in the response of the fuel ratio sensor is determined.

  According to the abnormality detection device and abnormality detection method for an air-fuel ratio sensor of the present invention, an abnormality in the responsiveness of the air-fuel ratio sensor can be detected in both the rich direction and the lean direction.

The figure which shows the structure of one Embodiment of this invention. The figure which shows the output voltage waveform of the air-fuel ratio sensor in case there is no abnormality in the air-fuel ratio sensor concerning the embodiment. The flowchart which shows the control of the same embodiment. The figure which shows the output voltage waveform of an air fuel ratio sensor in case the air fuel ratio sensor concerning the embodiment has "the reaction start delay abnormality of a rich direction." The figure which shows the output voltage waveform of an air fuel ratio sensor when the air fuel ratio sensor concerning the embodiment has "response delay abnormality of the lean direction".

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, an internal combustion engine (engine) 1 includes a cylinder 2, a piston 3, a spark plug 4, an intake valve 5, and an exhaust valve 6. When the piston 3 is lowered, the internal combustion engine (engine) 1 is moved to the combustion chamber 2 a in the cylinder 2. Then, air is sucked through the intake port 7 and the intake valve 5 (intake stroke).

  An air flow meter 11 that detects the intake air amount, a throttle valve 12 that determines the intake air amount, and an intake passage injector 13 that injects fuel toward the intake valve 5 are disposed in the intake port 7.

  The fuel injected by the intake passage injector 13 is mixed with the intake air, and the mixture is supplied to the combustion chamber 2 a via the intake valve 5. The air-fuel mixture supplied into the combustion chamber 2a is compressed by the rise of the piston 3 (compression stroke), and the compressed air-fuel mixture is ignited by the spark of the spark plug 4 to burn and explode (combustion stroke). The piston 3 descends again by this combustion / explosion, and the above operation is repeated. The gas generated by the combustion / explosion is discharged through the exhaust valve 6 and the exhaust port 8 (exhaust stroke).

  In the exhaust port 8, an air-fuel ratio sensor 14 and a catalyst 15 for purifying exhaust gas are arranged.

  The air-fuel ratio sensor 14 is also referred to as a LAF (Linear Air-Fuel ratio) sensor or an A / F (Air-Fuel ratio) sensor, and represents the concentration of oxygen in the exhaust gas that has passed through the exhaust valve 6 and the concentration of oxygen in the atmosphere. The electromotive force changes according to the difference. That is, when the ratio of fuel to intake air is large (the air-fuel ratio is rich), more oxygen is consumed in the intake air, so that the concentration of oxygen in the exhaust gas decreases, and accordingly, as shown in FIG. Thus, the output voltage V of the air-fuel ratio sensor 14 increases. When the ratio of fuel to intake air is small (the air-fuel ratio is lean), the consumption of oxygen in the intake air is low, so the concentration of oxygen in the exhaust gas rises. As a result, as shown in FIG. The output voltage V of the fuel ratio sensor 14 decreases. This voltage waveform is obtained when there is no abnormality in the air-fuel ratio sensor 14, and the slope when rising and the slope when falling are almost the same.

  On the other hand, the ECU 20 as a control unit is connected to the air flow meter 11, the throttle valve 12, the intake passage injector 13, the air-fuel ratio sensor 14, the ignition coil 21, the rotation speed sensor 22, the accelerator opening sensor 23, the abnormality notification lamp 24, A memory 25 or the like is connected.

  The ignition coil 21 supplies a driving voltage for ignition to the spark plug 4. The rotation speed sensor 22 detects the angle of the crank interlocked with the vertical movement of the piston 3 as the rotation speed. The accelerator opening sensor 23 detects the accelerator opening (the amount of depression of the accelerator pedal). The abnormality notification lamp 24 is used to notify the abnormality of the air-fuel ratio sensor 14 and is disposed near the driver's seat of the vehicle on which the internal combustion engine 1 is mounted. The memory 25 stores abnormal contents of the air-fuel ratio sensor 14.

The ECU 20 also functions as an abnormality detection device that detects an abnormality of the air-fuel ratio sensor 14 in addition to a function of controlling the operation of the internal combustion engine 1, and the following (1) relating to the abnormality detection of the air-fuel ratio sensor 14 It has means (4).
(1) The air-fuel ratio (average value) of the mixture of injected fuel and intake air is obtained from the output voltage V of the air-fuel ratio sensor 14, and the fuel injection of the intake passage injector 13 is performed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Air-fuel ratio feedback control means for feedback control of the amount. The air-fuel ratio feedback control means intentionally sets the air-fuel ratio to the rich side and the lean side so that an optimal combustion state is obtained in a so-called stoiciometry state where the air-fuel ratio (average value) is the stoichiometric air-fuel ratio. Control is performed to make slight fluctuations alternately.

  (2) In a situation where the stoichiometric state is set by the air-fuel ratio feedback control means and the air-fuel ratio changes alternately between the rich side and the lean side, the output voltage V of the air-fuel ratio sensor 14 changes upon the rich side change. A period Ta in which there is no period and the number of occurrences Xa of the period Ta are accumulated, and a period Tb in which there is no change in the output voltage V of the air-fuel ratio sensor 14 in response to the change to the lean side and the number of occurrences Xb in that period Tb are accumulated. means.

  (3) The average value Tax of the period Ta is detected by dividing the integrated value of the period Ta by the integrated value of the generation number Xa, and the integrated value of the period Tb is divided by the integrated value of the generation number Xb. Detecting means for detecting an average value Tbx of the period Tb.

  (4) Based on the comparison between the average values Tax and Tbx, the responsiveness abnormality of the air-fuel ratio sensor 14 when the air-fuel ratio changes to the rich side, and the air-fuel ratio sensor 14 when the air-fuel ratio changes to the lean side A determination means for determining an abnormality in the responsiveness.

  Note that the integration means of (2) is specifically set to a certain time (for example, in a situation in which the stoichiometric state is set by the air-fuel ratio feedback control means and the air-fuel ratio varies alternately between the rich side and the lean side. 10 sec) Over a period t1, the period Ta in which the output voltage V of the air-fuel ratio sensor 14 does not change during the fluctuation toward the rich side and the number of occurrences Xa of the period Ta are integrated, and the air-fuel ratio sensor 14 during the fluctuation toward the lean side The period Tb in which the output voltage V is not changed and the number of occurrences Xb of the period Tb are integrated, and the integration process for the predetermined time t1 is repeated N times for a predetermined number of times (for example, 5 times).

  Specifically, the detection means of (3) calculates the average value Tax of the period Ta by dividing the integrated value of the period Ta by the integrated value of the number of occurrences Xa every time the fixed time t1 elapses. And detecting the average value Tbx of the period Tb by dividing the integrated value of the period Tb by the integrated value of the number of occurrences Xb, and after the integration process over the predetermined number N, the detected average Further average values Tax0 and Tbx0 of the average values Tax and Tbx are calculated by dividing the total value of the values Tax and Tbx by the predetermined number N, respectively.

  Specifically, the determination means (4) determines that the air-fuel ratio sensor 14 is normal when both the average values Tax0 and Tbx0 are less than a set value (for example, 250 msec) Ts, and the average value Tax0 is When the average value Tbx0 is equal to or greater than the set value Ts and is less than the set value Ts, it is determined that the air-fuel ratio sensor 14 has “abnormal reaction start delay in the rich direction”, and the average value Tax0 is less than the set value Ts and the above value When the average value Tbx0 is equal to or greater than the set value Ts, it is determined that the air-fuel ratio sensor 14 has a “reaction start delay abnormality in the lean direction”, and when both the average values Tax0 and Tbx0 are equal to or greater than the set value Ts, It is determined that the air-fuel ratio sensor 14 has “abnormal reaction start delay in both rich and lean directions”.

Next, the abnormality detection process executed by the ECU 20 will be described with reference to the flowchart of FIG.
The ECU 20 sets the stoichiometric state by the air-fuel ratio feedback control and causes the air-fuel ratio to slightly vary alternately between the rich side and the lean side (step S1), provided that the abnormality detection flag f is “0”. (YES in step S2), the time count t is started (step S3).

  With the start of the time count t, the ECU 20 monitors whether the air-fuel ratio fluctuation by the air-fuel ratio feedback control is in the rich direction or the lean direction (steps S4, S5). Upon variation in the rich direction (YES in step S4), the ECU 20 detects and integrates a period (referred to as no change period) Ta in which the output voltage V does not change (increase change) (step S6), and the no change period. The number of occurrences Xa of Ta is integrated (step S7). Upon variation in the lean direction (NO in step S4, YES in step S5), the ECU 20 detects and integrates a period (referred to as no change period) Tb in which the output voltage V does not change (decrease in change) (step S8). The number of occurrences Xb of the no-change period Tb is integrated (step S9).

  With this integration process, the ECU 20 determines whether the time count t has reached a certain time t1 (step S10). When the time count t is less than the predetermined time t1 (NO in step S10), the ECU 20 returns to the monitoring in steps S4 and S5.

  When the time count t reaches the predetermined time t1 (YES in step S10), the ECU 20 clears the time count t to zero (step S11) and increases the number of times “1” (step S12). Then, the ECU 20 detects the average value Tax of the non-change period Ta at the fixed time t1 by dividing the integrated value of the non-change period Ta at the fixed time t1 by the integrated value of the number of occurrences Xa at the fixed time t1, and The average value Tbx of the non-change period Tb at the fixed time t1 is detected by dividing the integrated value of the non-change period Tb at the fixed time t1 by the integrated value of the number of occurrences Xb at the fixed time t1 (step S13).

  Following this detection, the ECU 20 determines whether the number n has reached the predetermined number N (step S14). When the number n is less than the predetermined number N (NO in step S14), the ECU 20 returns to step S3 and restarts the time count t. By repeating this time count t, a plurality of average values Tax and a plurality of average values Tbx can be detected.

  When the number n reaches the predetermined number N (YES in step S14), the ECU 20 clears the number n to zero (step S15). Accordingly, the ECU 20 calculates a further average value Tax0 (= “total value of Tax” / N) of the average value Tax by dividing the total value of the average values Tax detected so far by a predetermined number N. Then, a further average value Tbx0 (= “total value of Tbx” / N) of the average value Tbx is calculated by dividing the total value of the average values Tbx detected so far by the predetermined number N (step S16).

  When there is no abnormality in the responsiveness of the air-fuel ratio sensor 14, the output voltage V of the air-fuel ratio sensor 14 starts to rise without reaction delay with respect to the rich fluctuation of the air-fuel ratio, as shown in FIG. Start descent without delay in response to fluctuations. In this case, the calculated average values Tax0 and Tbx0 are both less than the set value Ts.

  When the average values Tax0 and Tbx0 are both less than the set value Ts (YES in step S17), the ECU 20 determines that the air-fuel ratio sensor 14 is normal (step S18).

  On the other hand, if the output voltage V of the air-fuel ratio sensor 14 does not rise immediately as shown in FIG. 4 despite the fact that the air-fuel ratio has been switched from decrease to increase, both the average values Tax0 and Tbx0 are less than the set value Ts. Is not satisfied (NO in step S17), and the condition that the average value Tax0 is equal to or greater than the set value Ts and the average value Tbx0 is less than the set value Ts is satisfied (YES in step S19). In this case, the ECU 20 determines that the air-fuel ratio sensor 14 has a “rich reaction start delay abnormality” (step S20). “Rich reaction start delay abnormality” refers to an abnormality in responsiveness when the air-fuel ratio fluctuates to the rich side.

  If the output voltage V of the air-fuel ratio sensor 14 does not drop immediately as shown in FIG. 5 even though the air-fuel ratio has been switched from increasing to decreasing, a condition that both the average values Tax0 and Tbx0 are less than the set value Ts. Is not satisfied (NO in step S17), and the condition that the average value Tax0 is equal to or greater than the set value Ts and the average value Tbx0 is less than the set value Ts is satisfied (NO in step S19, YES in step S21). In this case, the ECU 20 determines that the air-fuel ratio sensor 14 has a “reaction start delay abnormality in the lean direction” (step S22). “Lean direction reaction start delay abnormality” is an abnormality in responsiveness when the air-fuel ratio fluctuates to the lean side.

  The output voltage V of the air-fuel ratio sensor 14 does not increase immediately even though the air-fuel ratio has been switched from decrease to increase, and the output of the air-fuel ratio sensor 14 does not change even though the air-fuel ratio has been switched from increase to decrease. If the voltage V does not drop immediately, the condition that both the average values Tax0 and Tbx0 are less than the set value Ts is not satisfied (NO in step S17), and the condition that both the average values Tax0 and Tbx0 are equal to or greater than the set value Ts is satisfied ( NO in step S19, NO in step S21). In this case, the ECU 20 determines that the air-fuel ratio sensor 14 has “abnormal reaction start delay in both the rich and lean directions” (step S23).

  If any one of “rich response delay abnormality”, “lean response delay abnormality”, and “rich and lean response delay abnormality” is determined, the ECU 20 drives the abnormality notification lamp 24 to indicate the abnormality. In addition to notifying the person, data representing the abnormality is stored in the memory 25 (step S24). Accordingly, the ECU 20 sets the abnormality detection flag f to “1” (step S25), and repeats the processing from the first step S1. In this case, since the abnormality detection flag f is “1” (NO in step S2), the ECU 20 does not execute the processing from step S3.

  Data in the memory 25 can be read out by a worker who replaces or repairs the air-fuel ratio sensor 14 using a personal computer. The operator can accurately recognize what abnormality is occurring in the air-fuel ratio sensor 14 by this reading.

  As described above, an abnormality in the responsiveness of the air-fuel ratio sensor 14 can be accurately identified and detected in both the rich direction and the lean direction. As a result, it is possible to take an appropriate exhaust gas reduction measure according to the abnormality of the air-fuel ratio sensor 14.

  Since the abnormality notification lamp 24 notifies that the air-fuel ratio sensor 14 is abnormal, the air-fuel ratio sensor 14 can be replaced or repaired at an early stage. Since data representing the content of the abnormality is stored in the memory 25, the work for replacing or repairing the air-fuel ratio sensor 14 is facilitated.

  In the above embodiment, the fixed time t1 is 10 seconds and the predetermined number N is 5. However, the values of the fixed time t1 and the predetermined number N are not limited and can be set as appropriate.

  In the above embodiment, the case where an abnormality in the response delay of the air-fuel ratio sensor 14 is detected has been described as an example. However, an abnormality in which the air-fuel ratio sensor 14 reacts excessively compared to the change in the air-fuel ratio is also determined by the same determination process. It is possible to detect.

  In addition, the said embodiment and modification are shown as an example and are not intending limiting the range of invention. The novel embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the spirit of the invention. In these embodiments and modifications, the scope of the invention is included in the gist, and is included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Cylinder, 2a ... Combustion chamber, 3 ... Piston, 4 ... Spark plug, 5 ... Intake valve, 6 ... Exhaust valve, 7 ... Intake port, 8 ... Exhaust port, 11 ... Air flow meter, 12 DESCRIPTION OF SYMBOLS ... Throttle valve, 13 ... Intake path injector, 14 ... Air-fuel ratio sensor, 15 ... Catalyst, 20 ... ECU, 21 ... Ignition coil, 22 ... Revolution sensor, 23 ... Accelerator opening sensor, 24 ... Abnormality alarm lamp, 25 …memory

Claims (4)

An air-fuel ratio sensor abnormality detection device in which an output voltage changes according to an air-fuel ratio,
In a situation where the air-fuel ratio varies alternately between the rich side and the lean side, the period Ta in which the output voltage V of the air-fuel ratio sensor does not change during the change to the rich side and the number of occurrences Xa of the period Ta are integrated, And an integration means for integrating the period Tb in which the output voltage V of the air-fuel ratio sensor does not change during the change to the lean side and the number of occurrences Xb of the period Tb;
By dividing the integrated value of the period Ta by the integrated value of the number of occurrences Xa, the average value Tax of the period Ta is detected, and by dividing the integrated value of the period Tb by the integrated value of the number of occurrences Xb Detecting means for detecting an average value Tbx of the period Tb;
Based on the comparison between the average values Tax and Tbx, the responsiveness abnormality of the air-fuel ratio sensor when the air-fuel ratio varies to the rich side, and the air-fuel ratio sensor when the air-fuel ratio varies to the lean side Determination means for determining abnormality of responsiveness;
An abnormality detection device for an air-fuel ratio sensor comprising: In the situation where the air-fuel ratio fluctuates alternately between the rich side and the lean side, the integrating means has a period Ta during which the output voltage V of the air-fuel ratio sensor does not change during the fluctuation to the rich side over a certain time t1 and its The number of occurrences Xa of the period Ta is integrated, and the period Tb in which the output voltage V of the air-fuel ratio sensor does not change upon fluctuation to the lean side and the number of occurrences Xb of the period Tb are integrated, and the constant time t1 Repeat the integration process for a predetermined number N,
The detection means detects the average value Tax of the period Ta by dividing the integrated value of the period Ta by the integrated value of the number of occurrences Xa, and the integrated value of the period Tb every time the predetermined time t1 elapses. The average value Tbx of the period Tb is detected by dividing the value by the integrated value of the number of occurrences Xb. After the integration process over the predetermined number N, the total values of the detected average values Tax and Tbx are respectively calculated. By dividing by the predetermined number N, further average values Tax0, Tbx0 of the average values Tax, Tbx are calculated.
Based on the comparison between the calculated average values Tax0 and Tbx0, the determination means detects an abnormality in the responsiveness of the air-fuel ratio sensor when the air-fuel ratio changes to the rich side, and the air-fuel ratio changes to the lean side. Determining an abnormality in the responsiveness of the air-fuel ratio sensor at the time of
The abnormality detection apparatus for an air-fuel ratio sensor according to claim 1. The determination means includes
When the average values Tax0 and Tbx0 are both less than the set value Ts, it is determined that there is no abnormality in the air-fuel ratio sensor,
When the average value Tax0 is equal to or greater than the set value Ts and the average value Tbx0 is less than the set value Ts, it is determined that the air-fuel ratio sensor has a “reaction start delay abnormality in the rich direction”;
When the average value Tax0 is less than the set value Ts and the average value Tbx0 is greater than or equal to the set value Ts, it is determined that the air-fuel ratio sensor has “reaction start delay abnormality in the lean direction”.
The abnormality detection apparatus for an air-fuel ratio sensor according to claim 2. An air-fuel ratio sensor abnormality detection method in which an output voltage changes according to an air-fuel ratio,
In a situation where the air-fuel ratio varies alternately between the rich side and the lean side, the period Ta in which the output voltage V of the air-fuel ratio sensor does not change during the change to the rich side and the number of occurrences Xa of the period Ta are integrated, In addition, the period Tb in which the output voltage V of the air-fuel ratio sensor does not change during the change to the lean side and the number of occurrences Xb of the period Tb are integrated,
By dividing the integrated value of the period Ta by the integrated value of the number of occurrences Xa, the average value Tax of the period Ta is detected, and by dividing the integrated value of the period Tb by the integrated value of the number of occurrences Xb An average value Tbx of the period Tb is detected;
Based on the comparison between the average values Tax and Tbx, the responsiveness abnormality of the air-fuel ratio sensor when the air-fuel ratio varies to the rich side, and the air-fuel ratio sensor when the air-fuel ratio varies to the lean side Judgment of abnormal response
An abnormality detection method for an air-fuel ratio sensor.

Images