JP4403156B2 - Oxygen sensor diagnostic device for internal combustion engine - Google Patents

Description

  The present invention relates to an oxygen sensor diagnostic apparatus for an onboard internal combustion engine, and more particularly to an oxygen sensor diagnostic apparatus for an internal combustion engine that can improve the diagnostic accuracy of an oxygen sensor disposed downstream of a catalyst in an exhaust passage.

  2. Description of the Related Art Conventionally, in an in-vehicle internal combustion engine, an exhaust purification catalyst is provided in an exhaust passage, and oxygen sensors (air-fuel ratios) are respectively provided upstream and downstream of the catalyst for air-fuel ratio control and determination of the state of the catalyst. Including a sensor) is known. It is also known to perform fuel cut and fuel cut recovery (return) as necessary to reduce fuel consumption.

  In such an in-vehicle internal combustion engine, in order to determine whether or not an abnormality has occurred in an oxygen sensor (hereinafter referred to as a catalyst downstream oxygen sensor) disposed on the downstream side of the catalyst, the following Patent Document 1 and the like are disclosed. As can be seen, in the situation where oxygen is suddenly given to the catalyst by the fuel cut, and the catalyst downstream oxygen sensor measures the response time of the catalyst downstream oxygen sensor, There has been proposed an oxygen sensor diagnostic apparatus that determines whether or not a sensor is abnormal.

Japanese Patent No. 2858406

However, in the conventional oxygen sensor diagnostic device, the catalyst O ₂ storage amount varies depending on the air-fuel ratio state before the fuel cut is performed and the air-fuel ratio state until the air resulting from the fuel cut reaches the catalyst. It is not considered that the downstream air-fuel ratio changes.

Therefore, for example, the air-fuel ratio before the fuel cut is leaner than the stoichiometric air-fuel ratio, and before the air by the fuel cut saturates the O ₂ in the catalyst, the O ₂ in the catalyst is saturated, and the air-fuel ratio on the downstream side of the catalyst Does not change stepwise but gradually changes to lean, the response time of the catalyst downstream oxygen sensor becomes longer, making a false determination that the catalyst downstream oxygen sensor is normal but abnormal There was a fear that the diagnostic accuracy was not good.

  The present invention has been made to solve the above-described conventional problems, and the object of the present invention is not to make a false determination that the catalyst downstream oxygen sensor is abnormal although it is normal. An object of the present invention is to provide an oxygen sensor diagnostic apparatus for an internal combustion engine with high diagnostic accuracy and reliability.

In order to achieve the above object, one of the oxygen sensor diagnosis apparatuses for an internal combustion engine according to the present invention is basically an air-fuel ratio sensor that is disposed upstream of a catalyst in an exhaust passage and detects an air-fuel ratio upstream of the catalyst. An oxygen sensor diagnosis device for an internal combustion engine, which is provided downstream of the catalyst and detects an air-fuel ratio on the downstream side of the catalyst , wherein the oxygen sensor in a period from fuel cut to fuel cut recovery An abnormality determining means for determining an abnormality of the oxygen sensor based on the output, and a predetermined time setting means for setting a predetermined time corresponding to a time required for air to be supplied to the catalyst when the fuel cut is started If, based on the catalyst upstream-side air-fuel ratio and the engine intake air quantity, means for calculating the desorbed amount of O ₂ from the feed or the catalyst to the catalyst, the catalyst O ₂ storage amount from the integrated value of the amount of O ₂ Calculation And means for, and a storage means for storing the catalyst O ₂ storage amount at a time when the predetermined time has elapsed from the fuel cut start.

Then, the abnormality determining means, when the catalyst O ₂ storage amount stored in the storage means is a predetermined value or more does not perform the abnormality determination of the oxygen sensor is characterized by.

Preferably, the abnormality determination means calculates a predetermined value for the catalyst O ₂ storage amount based on an actual measurement value or an estimated value of the catalyst temperature.

Another one of the oxygen sensor diagnostic apparatuses for an internal combustion engine according to the present invention is basically an air-fuel ratio sensor or oxygen sensor that is disposed upstream of the catalyst in the exhaust passage and detects the air-fuel ratio upstream of the catalyst, An oxygen sensor diagnostic apparatus for an internal combustion engine, which is provided downstream of the catalyst and detects an air-fuel ratio on the downstream side of the catalyst , and outputs the oxygen sensor during a period from fuel cut to fuel cut recovery An abnormality determining means for determining an abnormality of the oxygen sensor, a predetermined time setting means for setting a predetermined time corresponding to a time required for air to be supplied to the catalyst when the fuel cut is started, Storage means for storing the output value of the oxygen sensor at the time when the predetermined time has elapsed from the start of the fuel cut .

Then, the abnormality determining means, when the output value of the oxygen sensor, which is stored in the storage means is smaller than a predetermined value, does not perform the abnormality determination of the oxygen sensor is characterized by.

  The elapsed time measuring means preferably estimates the elapsed time from the start of the fuel cut based on the engine speed and / or load or at least one parameter related thereto.

According to the present invention, when the predetermined amount of time corresponding to the time required for air to be supplied to the catalyst when the fuel cut is started elapses, the catalyst O ₂ storage amount is greater than or equal to the predetermined value. In a situation where the diagnostic accuracy may be reduced, the determination of abnormality of the catalyst downstream oxygen sensor is not performed, so that an erroneous determination that the catalyst downstream oxygen sensor is normal is abnormal. Therefore, it is possible to improve diagnostic accuracy and reliability.

  Embodiments of an oxygen sensor diagnostic apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall configuration diagram showing an embodiment of an oxygen sensor diagnostic apparatus for an internal combustion engine according to the present invention, together with an example of an in-cylinder in-cylinder injection engine to which it is applied.

  The illustrated internal combustion engine 10 is an in-line four-cylinder engine having, for example, four cylinders, and includes a cylinder head 11, a cylinder block 12, and a piston 15 slidably inserted into the cylinder block 12. A combustion chamber 17 is defined above the piston 15. In the combustion chamber 17, an ignition plug 35 to which a high voltage is applied from the ignition coil 34 and a fuel injection valve 30 that injects fuel directly into the combustion chamber 17 are provided. In the drawing, the ignition plug 35 and the fuel injection valve 30 are provided side by side on the left and right of the ceiling portion of the combustion chamber 17 for convenience, but their arrangement positions can be set as appropriate.

  Air used for fuel combustion is taken in from an inlet 21a of an air cleaner 21 provided at the start end of an intake passage 20 (intake pipe, intake port), passes through an air flow sensor 24, and is accommodated in an electric throttle valve 25. The combustion chambers of the cylinders enter the collector 27 through the throttle body 26, and are connected to the downstream end of the intake passage 20 from the collector 27 and are opened and closed by an intake camshaft 29. 17 is inhaled.

  The air-fuel mixture of the air sucked into the combustion chamber 17 and the fuel injected from the fuel injection valve 30 is ignited by the spark plug 35 and explosively burned. The combustion waste gas (exhaust gas) is exhausted by the exhaust camshaft 49. It is discharged to an exhaust passage 40 (exhaust port, exhaust pipe) through an exhaust valve 48 that is driven to open and close, purified by a catalyst 46 disposed in the exhaust passage 40, and then discharged to the outside.

  Further, a catalyst upstream air-fuel ratio sensor 51 for detecting an air-fuel ratio upstream of the catalyst is disposed upstream of the catalyst 46 in the exhaust passage 40, and an air-fuel ratio downstream of the catalyst is detected downstream of the catalyst 46. A catalyst downstream oxygen sensor 52 is disposed.

  On the other hand, fuel such as gasoline injected from the fuel injection valve 30 is primarily pressurized from the fuel tank 50 by the low pressure fuel pump 61 and regulated to a constant pressure by the fuel pressure regulator 62, and the exhaust camshaft 49. In the high-pressure fuel pump 60 driven by the pump drive cam 47 provided in the cylinder, the secondary pressure is increased to a higher pressure and pumped to the pressure accumulating chamber (common rail) 53, and fuel is provided from the common rail 53 to each cylinder. Supplied to the fuel injection valve 30. The fuel pressure (fuel pressure) supplied to the fuel injection valve 30 is detected by a fuel pressure sensor 56.

  In the present embodiment, in order to perform various controls of the engine 10, a control unit 100 incorporating a microcomputer is provided.

  As shown in FIG. 2, the control unit 100 basically includes an MPU 101, an EP-ROM 102, a RAM 103, an I / O LSI 104 including an A / D converter, and the like, and an airflow sensor 24 as an input signal. A signal corresponding to the intake air amount detected by the fuel pressure sensor, a signal corresponding to the fuel pressure detected by the fuel pressure sensor 56, a signal corresponding to the opening of the throttle valve 25 detected by the throttle sensor 23, a cam angle sensor (phase sensor) ) A detection (angle) signal indicating the phase (rotation position) of the exhaust camshaft 49 from 36, a detection (angle) signal indicating the rotation angle / phase (rotation position) of the crankshaft 18 from the crank angle sensor 37, and upstream of the catalyst. A signal corresponding to the air-fuel ratio upstream of the catalyst detected by the side air-fuel ratio sensor 51, the catalyst downstream-side oxygen sensor 52 In addition to a signal corresponding to the air-fuel ratio downstream of the catalyst detected and a signal corresponding to the engine cooling water temperature detected by the water temperature sensor 19 disposed in the cylinder block 12, a starter switch not shown in FIG. A signal indicating the amount of depression of the accelerator pedal obtained from the accelerator sensor is also supplied.

  The control unit 100 fetches each signal with a predetermined period, executes a predetermined calculation process, and uses the control signal calculated as the calculation result as the fuel injection valve 30, the ignition coil 34, the electric throttle valve 25, and the like. To control the fuel injection (injection amount, injection timing) control, ignition timing control, throttle valve 25 opening control, etc., including fuel cut and fuel cut recovery control, as described below. Based on the output of the catalyst downstream oxygen sensor 52 during the period from the cut to the fuel cut recovery, the catalyst downstream oxygen sensor 52 is diagnosed (determining whether an abnormality has occurred). However, in this case, in a situation where there is a possibility that the diagnostic accuracy may be lowered, abnormality determination of the catalyst downstream oxygen sensor 52 is not performed.

Hereinafter, this will be described in detail with reference to FIGS.
In general, as shown in FIG. 3, when the air-fuel ratio upstream of the catalyst is leaner than the stoichiometric air-fuel ratio, the catalyst O ₂ storage capacity theoretically calculates the air-fuel ratio inside the catalyst by storing the O _2. On the other hand, when the air-fuel ratio upstream of the catalyst is richer than the stoichiometric air-fuel ratio as shown in FIG. 4, the catalyst releases O ₂ to bring the air-fuel ratio inside the catalyst to the stoichiometric air-fuel ratio. It is a function to keep.

  With this capability, even when the air-fuel ratio upstream of the catalyst deviates from the stoichiometric air-fuel ratio, the air-fuel ratio inside the catalyst is maintained at the stoichiometric air-fuel ratio, and the purification performance of the catalyst can be maintained.

Here, when the excess O ₂ to catalyst O ₂ storage capacity was fed to the catalyst, the catalyst is not completely storage of O _2, because the air-fuel ratio of the internal catalyst becomes lean, decrease purification performance of the catalyst To do. Conversely, when the excess O ₂ to catalyst O ₂ storage capacity has left the catalyst, O ₂ is depleted in the catalyst, since the air-fuel ratio of the internal catalyst becomes rich, the purification performance of the catalyst is reduced .

  Next, a conventional example (conventional technology) of the abnormality determination program (routine) for the catalyst downstream oxygen sensor executed by the control unit 100 will be described with reference to the flowchart of FIG.

  In this conventional example, it is first determined in step 501 whether or not the fuel is being cut. If the fuel is not being cut, this routine is terminated. If the fuel is being cut, the catalyst downstream side sensor 52 ( In step 503, the time measurement is started in step 503. In the case of No, step 503 is skipped and the process proceeds to step 504.

  In step 504, it is determined whether or not the catalyst downstream sensor 52 (the output thereof) has passed the lean threshold value from rich to lean. If yes, time measurement is terminated in step 505, and measurement is performed in step 506. It is determined whether or not the time is equal to or greater than a predetermined value. If No, this routine is terminated.

  If it is determined in step 506 that the measurement time is equal to or greater than the predetermined value, an abnormality determination process is executed in step 507 on the assumption that an abnormality has occurred in the catalyst downstream oxygen sensor 52. In step 506, the measurement time is less than the predetermined value. If it is determined that the catalyst downstream oxygen sensor 52 is normal in step 508, normality determination processing is performed.

6 and 7 show time charts when the abnormality determination routine shown in FIG. 5 is executed.
FIG. 6 shows the results when the catalyst downstream oxygen sensor 52 is normal, and FIG. 7 shows the results when the catalyst downstream oxygen sensor 52 is abnormal.

In FIG. 6, when the fuel cut is started, the air-fuel ratio on the upstream side of the catalyst changes to lean with a delay of t <b> 1 from the time when the fuel cut is started due to the exhaust transport delay from the combustion chamber 17 to the catalyst upstream-side air-fuel ratio sensor 51. . The air-fuel ratio downstream of the catalyst changes to lean after t2 after the air-fuel ratio upstream of the catalyst changes to lean. This t2 is mainly the time until the O ₂ in the catalyst 46 is saturated and oxygen is released to the downstream of the catalyst. The t ₂ is the O ₂ state in the catalyst at the time t1 after the fuel cut and the O ₂ storage capacity of the catalyst Dependent.

  When the air-fuel ratio downstream of the catalyst changes stepwise as shown in FIG. 6, the catalyst downstream oxygen sensor 52 responds and its output crosses the rich threshold. Then, the time measurement timer starts counting, and thereafter, when the output of the catalyst downstream oxygen sensor 52 crosses the lean side threshold, the measurement time timer stops counting. Thereby, the time T required from the time when the output of the catalyst downstream oxygen sensor 52 crosses the rich side threshold from rich to lean to the time when the lean side threshold crosses from rich to lean is measured.

  Here, since the time T measured by the time measurement timer is less than the predetermined value, the diagnosis downstream flag is set assuming that the catalyst downstream oxygen sensor 52 is normal (steps 506 and 508 in FIG. 5).

  On the other hand, as shown in FIG. 7, when an abnormality occurs in the catalyst downstream oxygen sensor 52, when the output change of the catalyst downstream oxygen sensor 52 is normal with respect to the step change in the catalyst downstream air-fuel ratio. Compared to the rich side threshold value, the time T from the rich side threshold value to the crossing of the lean side threshold value becomes longer.

  Therefore, in such a case, since the time T measured by the time measurement timer is equal to or greater than a predetermined value, it is determined that an abnormality has occurred in the catalyst downstream oxygen sensor 52, and a diagnosis completion flag is set and a catalyst downstream sensor abnormality has occurred. A determination flag is set (steps 506 and 507 in FIG. 5).

  The above is a description of a program example (prior art) when determining whether the catalyst downstream oxygen sensor is normal or abnormal. However, an erroneous determination may occur only with such a determination program. This will be described below.

  FIG. 8 shows a case where the catalyst downstream oxygen sensor is normal and a disturbance occurs in which the air-fuel ratio upstream of the catalyst becomes lean before the fuel cuts and before the air reaches the catalyst upstream after the fuel cut. It is a time chart.

When such an air-fuel ratio disturbance enters, before the air due to fuel cut reaches the catalyst, O ₂ in the catalyst is saturated by the disturbance and the downstream of the catalyst changes to a lean air-fuel ratio. Output gradually changes to lean, and the time T described above becomes longer.

  Therefore, in such a state, even if the catalyst downstream oxygen sensor is normal, there is no difference from the operation of the abnormal product. Therefore, in the prior art, it is determined that the normal product is abnormal or the diagnostic accuracy is reduced. Exists.

Therefore, in this embodiment, in order to prevent erroneous determination due to the air-fuel ratio state before the fuel cut or the air-fuel ratio state after the fuel cut until the air reaches the catalyst, the air due to the fuel cut reaches the catalyst. The O ₂ state in the catalyst immediately before the determination is grasped, and when the inside of the catalyst that lowers the diagnostic accuracy is in the O ₂ saturation state, abnormality determination of the catalyst downstream oxygen sensor 52 is not performed.

This will be described in detail below.
FIG. 9 is a functional block diagram of the oxygen sensor diagnostic apparatus 1 of the present embodiment. The apparatus 1 includes a catalyst O ₂ storage amount calculation unit 201, a catalyst temperature estimation unit 202, a catalyst O ₂ storage amount threshold value calculation unit 203, a predetermined time setting unit 204, and a catalyst downstream side sensor abnormality determination unit 200. Yes.

Catalyst O ₂ storage amount in the catalyst O ₂ storage amount calculation means 201 calculates by accumulating the value obtained by multiplying the catalyst upstream-side air-fuel ratio and the engine intake air amount, thereby O ₂ in the catalyst before the fuel cut It becomes possible to grasp the state.

The estimated catalyst temperature in the catalyst temperature estimating means 202 is calculated by calculating the amount of heat supplied to the catalyst 46 from a map of the engine speed and the load, calculating the amount of heat released by the traveling wind from a vehicle speed table, It can be calculated by calculating the balance. In the catalyst O ₂ storage amount threshold value calculation unit 203 calculates a catalyst O ₂ storage amount threshold value in the table from the estimated catalyst temperature. In this embodiment, as described above, it is necessary to grasp the O ₂ saturation state in the catalyst such that the amount of O ₂ in the catalyst exceeds the catalyst O ₂ storage capacity before the air reaches the catalyst at the time of fuel cut. Therefore, the catalyst O ₂ storage amount threshold value is preferably a value according to the catalyst O ₂ storage capacity.

Further, it has been found from the experimental data that the catalyst O ₂ storage capacity has the characteristics as shown in FIG. 13 with respect to the catalyst temperature. Therefore, the catalyst O ₂ storage amount threshold is based on the estimated catalyst temperature. By calculating, it is possible to accurately determine the O ₂ saturation state in the catalyst.

The predetermined time setting means 204 sets a predetermined time corresponding to the time required for air to be supplied to the catalyst 46 when the fuel cut is started, and the catalyst downstream oxygen sensor abnormality determination means starts from the fuel cut start. The catalyst O ₂ storage amount at the time when the predetermined time has elapsed is stored, and when the stored catalyst O ₂ storage amount is greater than or equal to a predetermined value, the abnormality determination of the catalyst downstream oxygen sensor 52 is not performed. The

Here, if the predetermined time is too long, the storage amount of the catalyst O ₂ in a state where the fuel cut air is supplied to the catalyst 46 is stored. If the predetermined time is too short, the fuel cut air reaches the catalyst. Therefore, it is necessary to set the catalyst O ₂ storage amount to about t1 shown in FIG.

  From the experimental results, this t1 has characteristics as shown in FIG. 12 with respect to the engine speed and the load, and t1 becomes shorter as the engine speed increases and the load increases. For this reason, in this embodiment, the accuracy of the storage timing is ensured by setting the predetermined time based on the engine speed and the load.

  Next, an example of a catalyst downstream oxygen sensor abnormality determination program (routine) executed by the control unit 100 having functional means as shown in FIG. 9 will be described with reference to the flowchart of FIG. The flowchart of this example is obtained by adding steps 1001, 1002, and 1003 to the flowchart of the conventional example shown in FIG. 5, and the same steps (501 to 508) as those shown in FIG. .

In FIG. 10, in step 1001, it is determined whether or not the elapsed time after the fuel cut has reached a predetermined time set by the predetermined time setting means in FIG. 9, and once reached, once per fuel cut. is stored in step 1002 the catalyst _{O 2} storage amount calculated in the catalyst _{O 2} storage amount calculation means 201 of FIG.

Step 1003 is performed at the timing when the catalyst downstream sensor 52 changes the lean threshold value from rich to lean, and the catalyst O ₂ storage amount is not stored, or the stored catalyst O ₂ storage amount is greater than or equal to a predetermined value. In this case, the abnormality determination of the catalyst downstream oxygen sensor 52 is not performed by terminating this routine.

  FIG. 11 shows the case shown in FIG. 8 (when the catalyst downstream oxygen sensor is normal and the air-fuel ratio upstream of the catalyst is lean between before the fuel cut and after the fuel cut until the air reaches the catalyst upstream. The operation when the embodiment of the present invention is applied is shown in the case of a disturbance that becomes

In the equilibrium state of the catalyst O ₂ storage amount, between before fuel cut to the air after the fuel cut to reach the catalyst upstream, when the air-fuel ratio upstream of the catalyst has entered disturbance to be lean, the catalyst O ₂ storage amount The catalyst O ₂ storage amount is stored at the timing when the predetermined time t1 ′ elapses after the fuel cut.

Here, even if the time T measured when the catalyst downstream oxygen sensor 52 crosses the lean side threshold value is equal to or greater than the predetermined value, the catalyst O ₂ storage amount storage value is equal to or greater than the predetermined value. Neither the flag nor the diagnosis completion flag is set, and abnormality determination is not performed.

As can be seen from the above description, in the present embodiment, when the catalyst O ₂ storage amount at the time when the predetermined time t1 ′ has elapsed from the start of the fuel cut is greater than or equal to the predetermined value, that is, there is a possibility that the diagnostic accuracy may decrease. Therefore, it is possible not to make an erroneous determination that the catalyst downstream oxygen sensor is abnormal even though the catalyst downstream oxygen sensor is normal. Diagnostic accuracy and reliability can be improved.

  In the above embodiment, the catalyst temperature is estimated based on the engine speed and the load. However, the catalyst temperature may be actually measured with a thermometer or the like.

  Next, another embodiment of the oxygen sensor diagnostic apparatus according to the present invention will be described with reference to FIGS.

FIG. 14 is a functional block diagram of an oxygen sensor diagnostic apparatus 1 ′ according to another embodiment. This apparatus 1 ′ includes a predetermined time setting unit 204 and a catalyst downstream side sensor abnormality determination unit 300, and the O ₂ state in the catalyst 46 immediately before the air at the start of the fuel cut reaches the catalyst 46 is determined by the catalyst downstream. Detection is based on the output value of the side oxygen sensor 52.

  Therefore, in the functional block diagram of this example, only the predetermined time setting means 204 and the catalyst downstream side sensor abnormality determination means 300 are configured compared to the functional block diagram of FIG.

  Next, an example of a catalyst downstream oxygen sensor abnormality determination program (routine) executed by the control unit 100 having functional means as shown in FIG. 14 will be described with reference to the flowchart of FIG. The flowchart of this example is different from the flowchart of the conventional example shown in FIG. 5 and the flowchart of the embodiment shown in FIG. 10 in steps 1501 (corresponding to step 1001) and 1502 Step 1002) and Step 1503 corresponding to Step 1003 are added.

  16 shows the case shown in FIG. 8 (when the catalyst downstream oxygen sensor 52 is normal and the air-fuel ratio upstream of the catalyst is from before the fuel cut until the air reaches the catalyst upstream after the fuel cut. The operation when the embodiment of the present invention is applied to a case where a disturbance that becomes lean) is shown.

If there is a disturbance in which the air-fuel ratio upstream of the catalyst becomes lean before the fuel reaches the upstream side of the catalyst after the fuel cut, the amount of O ₂ in the catalyst is saturated after a predetermined time from the fuel cut. Therefore, the catalyst downstream oxygen sensor output value shows a low value, and the catalyst downstream oxygen sensor output value is stored here.

  After that, even if the time T measured when the catalyst downstream oxygen sensor crosses the lean threshold value is equal to or greater than the predetermined value, the catalyst downstream oxygen sensor output stored value is equal to or less than the predetermined value. And the diagnosis completion flag are not set together, and abnormality determination of the catalyst downstream oxygen sensor 52 is not performed.

  Also by doing in this way, the effect substantially the same as the said embodiment is acquired.

In the above embodiment, since it is not necessary to calculate the catalyst O ₂ storage amount, substantially the same operation and effect can be obtained even in a system configuration using an oxygen sensor with low air-fuel ratio detection accuracy on the upstream side of the catalyst.

  In the present specification, the air-fuel ratio sensor and the oxygen sensor are distinguished from each other. However, since they differ only in detection accuracy, an air-fuel ratio sensor (which also has higher detection accuracy instead of the oxygen sensor) A kind of oxygen sensor) may be used. Therefore, in the above embodiment, the oxygen sensor 52 is disposed on the downstream side of the catalyst, but the principle is the same when an air-fuel ratio sensor with higher detection accuracy than the oxygen sensor 52 is disposed on the downstream side of the catalyst. Needless to say, the present invention can also be applied to this case.

1 is an overall configuration diagram showing an embodiment of an oxygen sensor diagnostic apparatus for an internal combustion engine according to the present invention together with an engine to which the oxygen sensor diagnostic apparatus is applied. The block diagram with which it uses for description of the internal structure of the control unit shown by FIG. FIG. 3 is a diagram used for explaining the principle of the present invention. FIG. 3 is a diagram used for explaining the principle of the present invention. The flowchart which shows the prior art example of the abnormality determination routine of the catalyst downstream oxygen sensor used as the foundation of this invention. 6 is a time chart for explaining the abnormality determination routine (when the catalyst downstream oxygen sensor is normal) shown in FIG. 5. 6 is a time chart for explaining the abnormality determination routine (when the catalyst downstream oxygen sensor is abnormal) shown in FIG. 5; FIG. 6 is a time chart for explaining the abnormality determination routine shown in FIG. 5 (when the catalyst downstream oxygen sensor is normal and there is a disturbance in the air-fuel ratio). The functional block diagram which shows an example of the processing content of a control unit. The flowchart which shows an example of the abnormality determination routine of the catalyst downstream oxygen sensor which a control unit performs. 11 is a time chart used for explaining the abnormality determination routine shown in FIG. The figure used for description of the predetermined time setting map. Catalyst O ₂ storage capacity characteristic diagram. The functional block diagram which shows other embodiment of the processing content of a control unit. The flowchart which shows the other example of the abnormality determination routine of the catalyst downstream oxygen sensor which a control unit performs. 16 is a time chart used for explaining the abnormality determination routine shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oxygen sensor diagnostic apparatus 10 of internal combustion engine In-cylinder injection type internal combustion engine 17 Combustion chamber 20 Intake passage 30 Fuel injection valve 40 Exhaust passage 46 Catalyst 51 Air-fuel ratio sensor 52 Oxygen sensor 100 Control unit

Claims (4)

Is disposed upstream of the catalyst in the exhaust passage, and the air-fuel ratio sensor for detecting the catalyst upstream-side air-fuel ratio, is disposed downstream of the catalyst, an internal combustion engine having an oxygen sensor for detecting a catalyst downstream air-fuel ratio, the The oxygen sensor diagnostic device of
An abnormality determining means for determining an abnormality of the oxygen sensor based on an output of the oxygen sensor during a period from a fuel cut to a fuel cut recovery;
And the predetermined time setting means for setting a predetermined time for air when the fuel cut is started corresponds to the time required to be supplied to the catalyst,
Based engine intake air amount and the catalyst upstream-side air-fuel ratio, means for calculating the desorbed amount of O ₂ from the feed or the catalyst to the catalyst, calculates a catalyst O ₂ storage amount from the integrated value of the amount of O ₂ Means,
And a storage means for storing the catalyst O ₂ storage amount at the time has elapsed the predetermined time from the start of the fuel cut,
The abnormality determining means, when the catalyst O ₂ storage amount stored in the storage means is a predetermined value or more does not perform the abnormality determination of the oxygen sensor, the oxygen sensor diagnostic apparatus for an internal combustion engine, characterized in that. _2. The oxygen sensor diagnosis for an internal combustion engine according to claim 1, wherein the abnormality determination unit calculates a predetermined value for the storage amount of the catalyst O ₂ based on a measured value or an estimated value of the temperature of the catalyst. apparatus. Is disposed upstream of the catalyst in the exhaust passage, comprising air-fuel ratio sensor or oxygen sensor for detecting a catalyst upstream-side air-fuel ratio, is disposed downstream of the catalyst, and an oxygen sensor for detecting the catalyst downstream air-fuel ratio, the An oxygen sensor diagnostic device for an internal combustion engine,
An abnormality determining means for determining an abnormality of the oxygen sensor based on an output of the oxygen sensor during a period from a fuel cut to a fuel cut recovery;
And the predetermined time setting means for setting a predetermined time for air when the fuel cut is started corresponds to the time required to be supplied to the catalyst,
And a storage means for storing an output value of the oxygen sensor at the time when the predetermined time has elapsed from the fuel cut start,
The abnormality determining means, when the output value of said oxygen sensor, which is stored in the storage means is less than the prescribed value, it does not perform an abnormality determination of the oxygen sensor, the oxygen sensor diagnostic apparatus for an internal combustion engine, characterized in that .   4. The elapsed time measuring means estimates an elapsed time from the start of the fuel cut based on an engine speed and / or load or at least one parameter related thereto. The oxygen sensor diagnostic apparatus for an internal combustion engine according to claim 1.

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