JP2003020989A - Abnormality diagnosing device of air/fuel ratio sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abnormality diagnosing device of an air/fuel ratio sensor capable of diagnosing the abnormality precisely in a short period of time. SOLUTION: The abnormality diagnosis routine is executed during the fuel recovery operation after the fuel cut operation. The quantity ΔA/F of change of the air/fuel ratio during a prescribed change quantity calculation period ΔT is calculated one by one (S15) based on the output of the air/fuel ratio sensor (S11), and the maximum value ΔA/Fmax of a plurality of these quantities of change and a previously set criterion value ΔA/Fsaf are compared (S19). When the maximum value is smaller than the criterion value, it is determined that the air/fuel ratio sensor is abnormal (S24).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine equipped with an air-fuel ratio sensor for detecting the air-fuel ratio of exhaust gas, and more particularly to an abnormality diagnosis for diagnosing whether the air-fuel ratio sensor has abnormalities such as excessive deterioration or disconnection. Regarding the device.

[0002]

2. Description of the Related Art For example, in an internal combustion engine using a three-way catalyst, it is necessary to control the air-fuel ratio with high accuracy. Therefore, an air-fuel ratio sensor is provided in the exhaust passage of the engine so that the air-fuel ratio in the exhaust gas is reduced. The intake air amount and the fuel supply amount are feedback-controlled based on the output of the air-fuel ratio sensor according to the fuel ratio. here,
If the air-fuel ratio sensor is broken or excessively deteriorated,
As a matter of course, normal control of the fuel supply amount becomes impossible, which may lead to deterioration of exhaust components and deterioration of fuel consumption. And, this kind of abnormality is generally difficult for the driver to notice within a range in which drivability is not deteriorated. Therefore, various types of devices for detecting such abnormality of the air-fuel ratio sensor have been conventionally proposed.

For example, in Japanese Patent Laid-Open No. 60-233343, an abnormality of the oxygen sensor is obtained by comparing the output current value of the oxygen sensor (air-fuel ratio sensor) with a failure determination level after a certain time has elapsed from the start of fuel cut. A technique for diagnosing the presence or absence of is described.

Further, Japanese Unexamined Patent Publication No. 11-326137 discloses a technique for adjusting the target air-fuel ratio and the intake air amount to intentionally change the exhaust air-fuel ratio to the rich side or the lean side to determine an abnormality. Has been done.

Further, in Japanese Unexamined Patent Publication No. 8-177575, one change rate of the output of the air-fuel ratio sensor after fuel cut is obtained, and this change rate is compared with an abnormality determination value. A technique for determining an abnormality when the value exceeds the limit is described.

[0006]

However, in the diagnostic method disclosed in Japanese Patent Laid-Open No. 60-233343, the time until the sensor current reaches the failure determination level changes depending on the sensor current value at the start of fuel cut. In addition, there is a problem that the diagnosis cannot be performed accurately and the diagnostic accuracy is low. In addition, in the case of the type that self-diagnoses the response of the sensor by determining the sensor output current or the sensor output change rate after a lapse of a predetermined time from the fuel cut in this way, it is caused by the exhaust gas response delay due to operating conditions. , The diagnostic accuracy may decrease.

Further, in the technique disclosed in Japanese Unexamined Patent Publication No. 11-326137, since the fuel injection amount and the air-fuel ratio are intentionally changed in order to carry out the abnormality diagnosis, deterioration of exhaust emission and the like during the abnormality diagnosis is avoided. Absent.

Further, in the technique disclosed in Japanese Unexamined Patent Publication No. 8-177575, the state of the air-fuel ratio before the fuel cut, that is, the sensor output at the time of starting the fuel cut, is not so much influenced, and therefore the above-mentioned Japanese Unexamined Patent Publication No. 60-233343. Although it is possible to make a more accurate diagnosis than the one disclosed in the official gazette, since an abnormality is diagnosed from the only change rate of the air-fuel ratio, it may be more accurate depending on the period, timing, etc. at which this change rate is calculated. The diagnosis may not be possible or the diagnosis time may be long, and further improvement is desired.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a novel abnormality diagnosis device capable of accurately and quickly determining whether or not there is an abnormality in the air-fuel ratio sensor.

[0010]

As shown in FIG. 5, in the abnormal air-fuel ratio sensor, the change in the output voltage of the air-fuel ratio sensor during the fuel recovery operation after the fuel cut operation ( (Decrease) tends to be moderate. The present invention has been made in view of this point, and has a configuration in which the abnormality diagnosis of the sensor is performed based on the amount of change in the air-fuel ratio during the fuel recovery operation.

That is, the abnormality diagnosis device for an air-fuel ratio sensor according to the present invention is applied to an internal combustion engine equipped with an air-fuel ratio sensor for detecting the air-fuel ratio of exhaust gas, and the engine after the fuel cut operation is performed. Fuel recovery operation detection means for detecting that the fuel recovery operation is in progress, and a change for sequentially calculating the amount of change in the air-fuel ratio during a predetermined amount of change calculation period based on the output of the air-fuel ratio sensor during this fuel recovery operation. The amount calculation means, the maximum value of the plurality of change amounts calculated in this way, and a preset reference value is compared,
If the maximum value is smaller than the determination reference value, a determination unit that determines an abnormality is provided.

More specifically, when the fuel recovery operation is performed after the fuel cut operation is performed during engine deceleration,
The change amount of the air-fuel ratio during the change amount calculation period is repeatedly calculated. The maximum value of the plurality of change amounts thus calculated is compared with a preset reference value, and if the maximum value is smaller than the reference value, the air-fuel ratio sensor is abnormal. judge. During the fuel recovery operation, the air-fuel ratio decreases as shown in FIG. 5,
The change amount (absolute value) of the air-fuel ratio corresponds to the decrease amount of the air-fuel ratio.

Here, the difference between the average value of the normal product and the average value of the abnormal product in the maximum value of the change amount of the air-fuel ratio is D, the standard deviation of the normal product is σOK, and the standard deviation of the abnormal product is σNG,
When the predetermined constant is K, it is preferable that (D−KσN
The change amount calculation period is set so that the value of G) / σOK becomes large. In other words, the normal air-fuel ratio sensor (normal product) and the abnormal (deteriorated) air-fuel ratio sensor (abnormal product) are widely separated from each other in the distribution of the maximum value of the air-fuel ratio change amount, which is a diagnostic parameter, and the diagnostic accuracy is high. The change amount calculation period is set so that

[0014] Typically, the change amount calculation period is set to 200
˜300 ms, more preferably about 250 ms. When the change amount calculation period is set to 200 to 300 ms in this manner, variations in the movement delay of the exhaust gas, etc., which occur between the state in which some cylinders are in the fuel recovery operation and the time in which all the cylinders are in the fuel recovery operation, are appropriately adjusted. Can be absorbed into.

Further, in order to make an appropriate diagnosis according to the engine operating state, it is preferable to use an air conditioner as a diagnostic parameter based on the intake air amount, atmospheric pressure, engine speed, element temperature of the air-fuel ratio sensor, etc. Correct the fuel ratio change amount or its maximum value appropriately. For example, means for detecting or estimating the intake air amount,
And a means for correcting the variation of the air-fuel ratio or its maximum value in accordance with the intake air amount. In this case, it is possible to effectively suppress the deterioration of the diagnostic accuracy due to the delay in the movement of the exhaust gas due to the intake air amount.

More preferably, when the air-fuel ratio is equal to or more than a predetermined value (for example, 100 to 150), the accuracy of calculation of the amount of change in the air-fuel ratio may be deteriorated. Prohibit calculation.

[0017]

According to the first aspect of the present invention, during the fuel recovery operation, the change amount of the air-fuel ratio in the predetermined change amount calculation period is sequentially calculated, for example, every 10 ms or every predetermined crank angle. Since the maximum value is compared with the determination reference value, accurate abnormality diagnosis can be performed in a short time.

In particular, when the change amount calculation period is set as in the second aspect of the invention, the difference between the normal product and the abnormal product at the maximum displacement amount is sufficiently large, and almost no erroneous determination occurs. Therefore, the diagnostic accuracy is further improved.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows a schematic configuration of an abnormality diagnosis device for an air-fuel ratio sensor according to an embodiment of the present invention. A combustion chamber 2 is formed in each cylinder of the internal combustion engine 1, and fuel is directly supplied to each combustion chamber 2 from a fuel injection valve 3.
An intake passage 4 and an exhaust passage 5 are connected to each combustion chamber 2. The intake passage 4 has an intake passage 4 corresponding to atmospheric pressure.
An atmospheric pressure sensor 6 for detecting the internal pressure is provided.
A well-known three-way catalyst 7 is arranged in the exhaust passage 5, and an air-fuel ratio sensor 8 is arranged at a position closer to the combustion chamber 2 than the catalyst 7.

The air-fuel ratio sensor 8 is a wide area type air-fuel ratio sensor capable of continuously detecting the air-fuel ratio of the exhaust gas in the exhaust passage 5 in a wide range from rich to lean, and is also shown in FIG. As described above, the output power increases as the air-fuel ratio increases. This air-fuel ratio sensor 8
During operation, the sensor element section (not shown) is stably heated by the built-in heater so as to be always above a predetermined activation temperature. Further, as a means for detecting the engine speed (crank angle) of the internal combustion engine 1, an angle sensor 9 for detecting the angle of the camshaft that rotates in synchronization with the crankshaft is provided.

Detection signals from various sensors such as the atmospheric pressure sensor 6, the air-fuel ratio sensor 8 and the angle sensor 9 described above are input to an ECU as a control unit. This EC
U is a well-known microcomputer including a memory and a CPU, which performs fuel injection control of the fuel injection valve 3 based on a detection signal of the air-fuel ratio sensor 8, that is, air-fuel ratio control by a feedback control method, and the like described later. An abnormality diagnosis of the fuel ratio sensor 8 is performed, and when the abnormality is diagnosed, a warning lamp (not shown) is turned on and displayed, and the abnormality is stored in the memory as necessary.

1 and 2 are flow charts showing the control flow of abnormality diagnosis processing of the air-fuel ratio sensor 8 according to this embodiment. Referring to FIG. 2, in S (step) 1, it is determined whether the fuel cut operation has been performed for a predetermined period. This fuel cut operation is generally performed during deceleration based on the engine speed, vehicle speed, etc. detected by the angle sensor 9. In S2, it is determined whether the idle SW is ON. In S3, it is determined whether or not a diagnostic region condition such as engine temperature is satisfied. In S4, it is determined whether the fuel recovery operation state after the fuel cut operation is completed. If all of these conditions of S1 to S4 are satisfied, the routine proceeds to S5, where the abnormality diagnosis routine of the air-fuel ratio sensor 8 shown in FIG. 1 is executed.

Referring to FIG. 1, in S11, outputs of various sensors including the air-fuel ratio sensor 8 are read. In S12, it is determined whether the output voltage of the air-fuel ratio sensor 8 is less than a predetermined maximum value. That is, when the output voltage of the air-fuel ratio sensor 8 corresponding to the air-fuel ratio becomes excessively large, there is a concern that the calculation accuracy of the change amount ΔA / F of the air-fuel ratio, which will be described later, may decrease. 100 to 150) or more, the calculation of ΔA / F is prohibited.

In S13, the output voltage-air-fuel ratio table of the air-fuel ratio sensor 8 is corrected based on the atmospheric pressure detected by the atmospheric pressure sensor 6. The reason for this is that, as shown in FIG. 4, the atmospheric pressure and the O ₂ partial pressure are normal (at normal times) in highlands.
When the output voltage (b) of the air-fuel ratio sensor 8 is lower than the output voltage (a) at normal atmospheric pressure,
It tends to be low. Therefore, when the correction of S13 is not performed, the value of ΔA / F, which is the diagnostic parameter, is the normal atmospheric pressure, and the low atmospheric pressure due to high altitude.
Because it will be very different.

Table 1 shows an example of such an output voltage-air / fuel ratio table. The maximum value ABF15 of the actual air-fuel ratio in this table is set to the predetermined maximum value (for example, 100 to 150) as described above.

[0026]

[Table 1]

In S14, the air-fuel ratio A / F of the exhaust gas is calculated and stored based on the output voltage of the air-fuel ratio sensor 8 and the corrected output voltage-air-fuel ratio table. Then, in S15, the difference between the current air-fuel ratio A / F and the air-fuel ratio A / F before the predetermined change amount calculation period ΔT, that is, the change amount ΔA / F (absolute value) of the air-fuel ratio in the change amount calculation period ΔT. Is calculated and sequentially stored in the memory. Since the air-fuel ratio decreases during the fuel recovery operation, the change amount ΔA / F (absolute value) corresponds to the decrease amount of the air-fuel ratio.

At S16, it is determined whether the fuel recovery operation has been performed for a predetermined diagnosis period P. This diagnosis period P
As shown in FIG. 5, the output voltage of the air-fuel ratio sensor 8 changes (decreases) almost immediately after the start of the fuel recovery operation.
It is set to a range (for example, a few seconds) until it stops. In other words, S14 and S until the diagnosis period P elapses.
15, the air-fuel ratio A / F and the change amount ΔA / F of the air-fuel ratio
Is repeatedly calculated and stored every predetermined time (for example, every 10 ms or every predetermined crank angle). When the predetermined diagnosis period P has elapsed, the process proceeds from S16 to S17, and the maximum value ΔA / Fmax of the change amount is selected and read from the plurality of change amounts ΔA / F.

In the following S18, the maximum value ΔA / Fmax of the air-fuel ratio is corrected according to the engine operating condition. For example, as shown in FIG. 6, ΔA / Fmax is corrected based on the intake air amount Qa (engine rotation × fuel injection amount) in order to eliminate the deterioration of the diagnostic accuracy due to the movement delay (flow velocity) of the exhaust gas. . More specifically, the correction coefficient N corresponding to the intake air amount Qa is referred to by referring to a table of 16 grids as shown in Table 2.
TPHOS0, NTPHOS1, ..., NTPHOS15
Is selected, and ΔA / Fmax is corrected using this correction coefficient.

[0030]

[Table 2]

Further, preferably, the maximum variation amount ΔA / Fmax is corrected based on the element temperature of the air-fuel ratio sensor 8. It should be noted that these correction processes are performed by ΔA / F detected in S13.
May be sequentially performed for each.

Then, in step S19, the corrected maximum variation amount ΔA / Fmax is compared with the preset and stored determination reference value (diagnosis criteria) ΔA / Fsaf.
The maximum change amount ΔA / Fmax is the determination reference value ΔA / Fsa.
If it is f or more, it is diagnosed that the air-fuel ratio sensor 8 is normal (S21), the stored contents of the flag FNG and the like which will be described later are cleared (S20), and this diagnosis processing is ended. When it is diagnosed that the engine is normal, the execution of this diagnostic routine is preferably prohibited until the engine is stopped. However,
The diagnosis routine may be repeatedly performed even after it is determined to be normal.

On the other hand, in S19, the maximum change amount ΔA
If it is determined that / Fmax is smaller than the determination reference value ΔA / Fsaf, the air-fuel ratio sensor 8 may be abnormal, so the routine proceeds to step S22. In this embodiment, S22 is performed so that the driver is not given an unnecessary alarm by being erroneously determined to be abnormal due to variations in the measured values.
Only when it is determined that ΔA / Fmax is smaller than ΔA / Fsaf twice in succession using the flag FNG shown in S23 and S23, the process proceeds to S24, and the air-fuel ratio sensor 8 is diagnosed as abnormal, and is not shown. The warning light is turned on.

Next, the variation calculation period ΔT for calculating the diagnostic parameter ΔA / F will be described in detail with reference to FIGS. 7 and 8. 7 is a characteristic diagram showing the distribution (variation) of the maximum value ΔA / Fmax of the air-fuel ratio change amount ΔA / F, and the solid line m indicates the maximum value ΔA / Fmax of a normal air-fuel ratio sensor (normal product). The solid line n indicates the distribution of the maximum value ΔA / Fmax of the abnormal (deteriorated) air-fuel ratio sensor (abnormal product). As shown in FIG. 7, the maximum change amount Δ
In A / Fmax, the difference between the average value of the normal product and the average value of the abnormal product is D, the standard deviation of the normal product is σOK, the standard deviation of the abnormal product is σNG, and the determination reference value ΔA / Fsa.
When the diagnostic criterion corresponding to f is K · σNG (K is a predetermined constant), this diagnostic criterion K · σNG
Margin (S / N) of normal product (standard deviation σOK) of
Is expressed by the following equation.

[0035]

## EQU1 ## S / N = (D-K.sigma.NG) /. Sigma.OK Note that K = 3 in this embodiment, but this value can be set to an appropriate value according to the required accuracy for determining an abnormal product.

The larger the margin margin S / N, the higher the diagnostic accuracy. Therefore, in this embodiment, as shown in FIG. 8, the above period ΔT is set so that the margin margin S / N is sufficiently large. That is, the change amount calculation period ΔT
Is preferably 200 to which the margin S / N becomes about 5 or more.
300 ms, more preferably about 25 with maximum S / N
Set to 0 ms.

As described above, according to the present embodiment, during the extremely short diagnostic period P from the start of the fuel recovery operation, a predetermined shorter variation amount calculation period ΔT (for example, 200 to 300 m).
s), the change amount ΔA / F of the air-fuel ratio is, for example, 10 m
The maximum value ΔA of these changes ΔA / F is calculated sequentially for each s.
Since / Fmax is compared with the determination reference value ΔA / Fsaf, accurate abnormality diagnosis can be performed in a short time.

Particularly, the margin allowance S / from the diagnostic criteria
The change amount calculation period ΔT is optimized so that N becomes sufficiently large. Specifically, the calculation period ΔT is 200 to 3
Since it is set to 00 ms, and more preferably to about 250 ms, almost no erroneous determination occurs and the diagnostic accuracy is very excellent. In addition, the calculation period ΔT is 20
By setting a relatively large value such as 0 to 300 ms, variations in the movement delay of the exhaust gas, etc., which occur between the state in which some cylinders are in fuel recovery operation and the time in which all cylinders are in fuel recovery operation, are appropriately set. It also has the advantage that it can be absorbed.

Although the present invention has been described based on the specific embodiments as described above, the present invention is not limited to the above embodiments and includes various modifications and changes.
For example, in the above embodiment, the sensor output-air-fuel ratio table is corrected based on the atmospheric pressure (S13 in FIG. 1),
The output voltage of the air-fuel ratio sensor may be directly corrected. In addition to the intake air amount described above, the air-fuel ratio change amount ΔA / F or its maximum value ΔA / F is also determined according to the engine operating conditions such as the atmospheric pressure, the engine speed, the element temperature of the air-fuel ratio sensor 8.
By directly or indirectly correcting max, it is possible to further improve the diagnostic accuracy.

[Brief description of drawings]

FIG. 1 is an abnormality diagnosis routine of a flowchart showing a control flow of an abnormality diagnosis device for an air-fuel ratio sensor according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a control flow of the abnormality diagnosis device for the air-fuel ratio sensor.

FIG. 3 is a structural explanatory view showing a mechanical structure of the present embodiment.

FIG. 4 is a characteristic diagram showing changes in output characteristics of the air-fuel ratio sensor due to a decrease in atmospheric pressure and O ₂ partial pressure.

FIG. 5 is a characteristic diagram showing the output of the air-fuel ratio sensor and the amount of change in the air-fuel ratio near the fuel recovery operation.

FIG. 6 is a characteristic diagram showing a relationship between an intake air amount and an air-fuel ratio change amount in a fuel recovery operation state.

FIG. 7 is a characteristic diagram showing the distribution of the maximum value of the air-fuel ratio change amount of a normal product and an abnormal product.

FIG. 8 is a characteristic diagram showing the relationship between the change amount calculation period and the margin S / N from the diagnostic criteria.

[Explanation of symbols]

1 ... Internal combustion engine 3 ... Fuel injection valve 4 ... Intake passage 5 ... Exhaust passage 6 ... Atmospheric pressure sensor 7 ... Catalyst 8 ... Air-fuel ratio sensor

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Claims (6)

[Claims] 1. An abnormality diagnosis processing device for an air-fuel ratio sensor applied to an internal combustion engine equipped with an air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas, wherein the engine is in a fuel recovery operation state after a fuel cut operation. A fuel recovery operation detecting means for detecting, and a change amount calculating means for sequentially calculating the change amount of the air-fuel ratio in a predetermined change amount calculation period based on the output of the air-fuel ratio sensor during the fuel recovery operation, Comparing the maximum value of the plurality of calculated change amounts with a preset determination reference value, and when the maximum value is smaller than the determination reference value, determining means for determining an abnormality, A device for diagnosing air-fuel ratio sensor abnormality. 2. The change amount calculation period is 200 to 300.
The abnormality diagnosis device for an air-fuel ratio sensor according to claim 1, wherein the abnormality diagnosis device is set to ms. 3. The abnormality diagnosis device for an air-fuel ratio sensor according to claim 1, wherein the change amount calculation period is set to about 250 ms. 4. At the maximum value of the amount of change in the air-fuel ratio,
(D-KσNG) / σOK The abnormality diagnosis device for an air-fuel ratio sensor according to any one of claims 1 to 3, wherein the change amount calculation period is set so as to increase the value of. 5. A means for detecting or estimating the intake air amount,
An abnormality diagnosis device for an air-fuel ratio sensor according to any one of claims 1 to 4, further comprising: means for correcting the amount of change in the air-fuel ratio or its maximum value in accordance with the intake air amount. 6. The air-fuel ratio sensor according to claim 1, wherein when the air-fuel ratio is greater than or equal to a predetermined value, calculation of the change amount of the air-fuel ratio by the change amount calculating means is prohibited. Abnormality diagnosis device.