JP2004003513A - Self-diagnosis device of air fuel ratio controller for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To diagnose abnormality without being affected by air-fuel ratio before diagnosis start. <P>SOLUTION: Diagnosis is started by starting cut of fuel (step 101), sensor output I1 when starting fuel cut is read and stored, and a timer is operated to count time elapsed after starting fuel cut (step 102). Next, time T1 from fuel cut start to rise of sensor output to I2 is read from count values of the timer (steps 103, 104), and change rate of sensor output, ΔI=(I2-I1)/T1, is calculated (step 105). Then, the calculated change rate ΔI of sensor output is compared with abnormality judging value Ifc (step 106). If ΔI≥Ifc, the response property of the sensor is normal, but if Δ<Ifc, abnormality (deterioration) is observed in the response property of the sensor. Therefore, sensor abnormality is stored in memory, and an alarm lamp 39 is lit to inform a driver of sensor abnormality (step 107). <P>COPYRIGHT: (C)2004,JPO

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-diagnosis device for an air-fuel ratio control device for an internal combustion engine that performs self-diagnosis of an abnormality of an air-fuel ratio control device that feedback-controls an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine (hereinafter referred to as an "engine"). .

In the air-fuel ratio control device that performs feedback control of the air-fuel ratio of the air-fuel mixture supplied to the automobile engine, an oxygen sensor that detects the oxygen concentration in the exhaust gas is attached to the exhaust pipe, and the output voltage of this oxygen sensor is set to the stoichiometric air-fuel ratio. The air-fuel ratio is controlled near the stoichiometric air-fuel ratio by increasing or decreasing the air-fuel ratio feedback correction coefficient as compared with the corresponding reference voltage. In such an air-fuel ratio feedback control system, if the output of the oxygen sensor deviates from a normal value due to characteristic deterioration or failure, controllability of the air-fuel ratio deteriorates. Therefore, in order to detect a failure of the oxygen sensor, there is a configuration in which the output current of the oxygen sensor is compared with a failure determination level after a lapse of a predetermined time from the start of the fuel cut to diagnose the presence or absence of the failure of the oxygen sensor. (See Patent Document 1).
JP-A-60-233343

However, in the self-diagnosis method of Patent Document 1, the sensor current after a lapse of a predetermined time from the start of the fuel cut is compared with the failure determination level. However, depending on the state of the air-fuel ratio immediately before the fuel cut, the same oxygen sensor may be used. However, the sensor current at the start of the fuel cut is different, and accordingly, the time from the start of the fuel cut to the time when the sensor current reaches the failure determination level is also different. Therefore, if the failure is diagnosed by the sensor current after a certain time has elapsed from the start of the fuel cut, the failure diagnosis is greatly affected by the state of the air-fuel ratio immediately before the fuel cut, and the failure or deterioration of the oxygen sensor cannot be accurately diagnosed. In some cases, the diagnostic accuracy is low.

The present invention has been made in view of such circumstances, and therefore, the object is to be able to diagnose the presence or absence of an abnormality in the air-fuel ratio sensor without being affected by the state of the air-fuel ratio before the start of diagnosis. An object of the present invention is to provide a self-diagnosis device for an air-fuel ratio control device for an internal combustion engine, which can improve diagnosis accuracy.

To achieve the above object, a self-diagnosis device for an air-fuel ratio control device for an internal combustion engine according to claim 1 of the present invention has an output that continuously changes according to an air-fuel ratio (A / F) of exhaust gas of the internal combustion engine. Detecting self-diagnosis of an abnormality of an air-fuel ratio control device that feedback-controls an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine by an output of an air-fuel ratio sensor, and detecting a change in a fuel supply amount to the internal combustion engine; A change rate determining means for determining a change rate of the output of the air-fuel ratio sensor after detecting a change in the fuel supply amount by the detecting means; and a change rate of the output of the air-fuel ratio sensor determined by the change rate determining means. Abnormality determination means for determining the presence or absence of an abnormality in the air-fuel ratio sensor on the basis of the above, and the detection means detects the start of fuel cut or the return from fuel cut as a change in the fuel supply amount.

Further, as in claim 2, the change rate determining means may determine a change amount per unit time as a change rate of the output of the air-fuel ratio sensor.

Alternatively, as in claim 3, the change rate determining means measures a time until the output of the sensor changes by a predetermined amount after the fuel supply amount changes, and determines the air-fuel ratio based on the length of the measurement time. The change rate of the sensor output may be determined.

Alternatively, as in claim 4, the change rate determining means obtains a change amount of the output of the air-fuel ratio sensor that changes within a predetermined time after the change of the fuel supply amount, and determines the change amount according to the magnitude of the change amount. The change rate of the output of the air-fuel ratio sensor may be determined.

According to a fifth aspect of the present invention, in place of the above-described change rate determining means, a time measuring means for measuring a response delay time until the output of the air-fuel ratio sensor starts to change after a change in the fuel supply amount is provided. An abnormality determining means may be provided for determining whether the air-fuel ratio sensor is abnormal based on the response delay time measured by the means.

The air-fuel ratio feedback gain of the air-fuel ratio feedback control may be switched according to the determination of whether the air-fuel ratio sensor is normal / abnormal by the abnormality determining means.

(5) The output current may be used as the output of the air-fuel ratio sensor.

According to the configuration of claim 1 of the present invention, at the time when the change in the fuel supply amount to the internal combustion engine (hereinafter referred to as “engine”) is detected by the detecting means, the diagnostic process is started and the change in the fuel supply amount is detected. The change rate of the output of the air-fuel ratio sensor after the calculation is obtained by the change rate determining means. Then, based on the change rate of the output of the air-fuel ratio sensor obtained by the change rate determining means, the presence or absence of an abnormality of the air-fuel ratio sensor is determined by the abnormality determining means. In this case, even if the output of the air-fuel ratio sensor at the beginning of the diagnosis (at the beginning of the detection of the change in the fuel supply amount) changes depending on the state of the air-fuel ratio before the start of the diagnosis (before the change in the fuel supply amount is detected), The rate of change of the sensor output is hardly affected by the air-fuel ratio before the start of diagnosis. Therefore, by diagnosing the presence or absence of an abnormality of the air-fuel ratio sensor based on the change rate of the output of the air-fuel ratio sensor, it is possible to diagnose the presence or absence of the abnormality of the air-fuel ratio sensor without being affected by the state of the air-fuel ratio before the start of the diagnosis. It becomes possible.

By the way, the cause of the change in the fuel supply amount is, for example, the start of fuel cut and the return of fuel cut. The fuel supply is stopped by the start of fuel cut, and the fuel supply is restarted by the return of fuel cut. The return causes a large change in fuel supply.

Therefore, in claim 1, the detection means detects the start of fuel cut or the return of fuel cut, thereby indirectly detecting a change in the fuel supply amount. The timing of the start of fuel cut and the return of fuel cut are controlled by the engine control device, and can be accurately determined.

According to the second aspect, the change rate per unit time is obtained as the change rate of the air-fuel ratio sensor output by the change rate determining means. Here, the amount of change per unit time is obtained by dividing the amount of change within a predetermined time by the predetermined time, by obtaining the predetermined amount of change by dividing the time required for the change, or A detection circuit for detecting the change rate (slope) of the fuel ratio sensor output in a hardware manner may be provided.

According to the third aspect, the change rate determination means measures a time until the output of the air-fuel ratio sensor changes by a predetermined amount after the fuel supply amount changes, and determines the change rate of the output of the air-fuel ratio sensor based on the length of the measurement time. Judge indirectly. In other words, the relationship that the change rate of the output of the air-fuel ratio sensor is small if the measurement time is long and the change rate of the output of the air-fuel ratio sensor is large as the measurement time is short is used. In this case, it is not necessary to divide the amount of change in the output of the air-fuel ratio sensor by the measurement time.

On the other hand, in claim 4, the change rate determining means obtains a change amount of the air-fuel ratio sensor output that changes within a predetermined time after the fuel supply amount changes, and determines a change in the output of the air-fuel ratio sensor according to the magnitude of the change amount. The rate is determined indirectly. In other words, it utilizes the relationship that the rate of change of the output of the air-fuel ratio sensor increases as the amount of change within the predetermined time increases, and the rate of change of the output of the air-fuel ratio sensor decreases as the amount of change within the predetermined time decreases. It is. Also in this case, it is not necessary to divide the amount of change by time, as in the case of the third aspect.

By the way, if the characteristics of the air-fuel ratio sensor deteriorate, the response of the air-fuel ratio sensor deteriorates, and the response delay time from when the fuel supply amount changes to when the output of the air-fuel ratio sensor starts to change tends to be long. Therefore, in claim 5, instead of the above-described rate of change of the output of the air-fuel ratio sensor, a response delay time until the output of the air-fuel ratio sensor starts to change after the fuel supply amount changes is measured by a timer. The presence / absence of an abnormality in the sensor is determined by the abnormality determination unit based on the response delay time measured by the unit. As described above, even if the diagnosis is performed based on the response delay time, it is possible to diagnose whether or not the sensor is abnormal without being affected by the state of the air-fuel ratio before the start of the diagnosis.

According to a sixth aspect of the present invention, the air-fuel ratio feedback gain of the air-fuel ratio feedback control is switched in accordance with the normal / abnormal judgment of the air-fuel ratio sensor by the abnormality judgment means. Thus, divergence and hunting of the air-fuel ratio when the air-fuel ratio sensor is abnormal (deteriorated) can be prevented.

(5) The output current may be used as the output of the air-fuel ratio sensor.

[Example 1]

Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of an intake pipe 12 connected to an intake port 11 of the engine 10 (internal combustion engine), and an intake air temperature sensor 14 is provided downstream of the air cleaner 13. A throttle valve 15 is provided in the middle of the intake pipe 12, and an idle speed control valve 17 is provided in a bypass 16 that bypasses the throttle valve 15. The opening of the throttle valve 15 is detected by a throttle opening sensor 18, and the intake pipe pressure downstream of the throttle valve 15 is detected by an intake pipe pressure sensor 19.

Further, a fuel injection valve 20 that injects fuel supplied from the fuel tank 21 is provided near the intake port 12. The fuel in the fuel tank 21 is supplied to the fuel injection valve 20 through a path of a fuel pump 22 → a fuel filter 23 → a pressure regulator 24, and the pressure regulator 24 keeps the fuel pressure constant with respect to the intake pipe pressure. Then, excess fuel is returned into the fuel tank 21 through the return pipe 25.

On the other hand, an exhaust pipe 27 connected to the exhaust port 26 of the engine 10 has an air-fuel ratio sensor 28 whose output current continuously changes according to the air-fuel ratio (A / F) in the exhaust gas, and an exhaust gas purifying device. A three-way catalyst (not shown) is provided. A water temperature sensor 30 for detecting a cooling water temperature is attached to a water jacket 29 for cooling the engine 10. A distributor 32 for supplying a high-voltage current to the ignition plug 31 of each cylinder of the engine 10 includes a cylinder discrimination sensor 33 for discriminating a crank angle reference position of a specific cylinder, and a pulse signal having a frequency corresponding to the engine speed. Is output. The high voltage secondary current of the igniter 35 is supplied to the distributor 32.

The output signals of the various sensors described above are input to an engine control circuit (hereinafter referred to as “ECU”) 36 and used as engine control data. The ECU 36 operates using the battery 37 as a power source, starts the engine 10 in response to an ON signal of an ignition switch 38, and operates the engine 10 based on the output signal of the air-fuel ratio sensor 28 as shown in FIG. The air-fuel ratio is feedback-controlled near the stoichiometric air-fuel ratio by increasing or decreasing the feedback correction coefficient.

The ECU 36 diagnoses whether the air-fuel ratio sensor 28 is abnormal by the sensor abnormality diagnosis routine shown in FIG. 2 and, when abnormal, turns on a warning lamp 39 (warning means) to notify the driver. This sensor abnormality diagnosis routine is executed every time the main routine is executed (for example, every 8 ms), and a change rate ΔI of the output current of the air-fuel ratio sensor 28 after the start of the fuel cut at the time of deceleration is obtained. When it is smaller than Ifc, it is determined that the sensor is abnormal. FIG. 3 is a time chart showing the flow of processing when this sensor abnormality diagnosis routine is executed.

In this sensor abnormality diagnosis routine, first, in step 101, it is determined whether or not the fuel cut has started. Here, the execution timing of the fuel cut is controlled by the fuel cut determination routine shown in FIG. 6, and a time chart showing the flow of the process is shown in FIG. This fuel cut determination routine is also executed every time the main routine is executed (for example, every 8 ms). When the process is started, first, in step 121, in order to reduce the shock due to the fuel cut during deceleration, the throttle fully closed state is set. It is determined whether or not (the ON state of the throttle fully closed switch, not shown) has passed a predetermined time ToＴ. If the predetermined time ToＴ has passed, the routine proceeds to step 122, where the engine speed NE is reduced to the fuel cut start speed NFC. It is determined whether it is higher. If NE> NFC, the routine proceeds to step 126, where the fuel cut execution flag XFC is set to "1" and the fuel cut is executed. The fuel cut start rotation speed NFC is set higher as the cooling water temperature is lower so that the fuel cut is not started in the idle state.

On the other hand, if “No” is determined in either of steps 121 and 122, that is, if the throttle fully closed state has not passed the predetermined time To, or if the engine speed NE is equal to or less than the fuel cut start speed NFC. In this case, the routine proceeds to step 123, where it is determined whether or not the fuel cut has been executed in the previous processing. If the fuel cut has been executed in the previous processing, the routine proceeds to step 124, where the engine speed NE is reduced. It is determined whether or not the fuel cut return rotation speed NRT has fallen below the NRT. If it has fallen below the fuel cut return rotation speed NRT, the routine proceeds to step 125, where the fuel cut execution flag XFC is set to "0". To return from fuel cut and restart fuel injection. If it is determined in step 124 that the engine speed NE has not fallen below the fuel cut return rotation speed NRT, the routine proceeds to step 126, where fuel cut is continued. If "No" in the step 123, that is, if the fuel cut has not been executed in the previous process, the process proceeds to the step 125, and the fuel injection is continuously executed.

As described above, in the sensor abnormality diagnosis routine shown in FIG. 2, first, in step 101, it is determined whether or not the fuel cut has been started. If the fuel cut has not been started, the subsequent processing is not performed, and The sensor abnormality diagnosis routine ends. The processing in step 101 corresponds to a detecting means for detecting a change in the amount of fuel supplied to the engine 10. When the fuel cut is started by the processing of the fuel cut determination routine, "Yes" is determined in step 101, and the process proceeds to step 102, where the output of the air-fuel ratio sensor 28 at the start of the fuel cut (hereinafter, referred to as "sensor output"). ) I1} is read and stored, and the timer is operated to count the elapsed time after the start of the fuel cut. Next, in step 103, it is determined whether or not the sensor output has risen to I2 、, and the process stands by until the sensor output rises to I2.

Thereafter, when the sensor output rises to I2, the process proceeds to step 104, and after reading and storing the time T1 from the start of fuel cut to the sensor output rising to I2 from the count value of the timer, the process proceeds to step 105. The change rate ΔI of the sensor output is calculated by the following equation.

ΔI = (I2−I1) / T1
The process of step 105 functions as a change rate determination unit described in the claims.

In the following step 106, the change rate ΔI of the sensor output calculated by the above equation is compared with the abnormality determination value Ifc, and if the change rate ΔI of the sensor output is equal to or more than the abnormality determination value Ifc, the responsiveness of the air-fuel ratio sensor 28 is deteriorated. Since this is not the case and the sensor output is normal, this routine ends. However, since the rate of change ΔI of the sensor output decreases as the response of the air-fuel ratio sensor 28 deteriorates, if the rate of change ΔI of the sensor output is less than the abnormality determination value Ifc, the abnormality of the air-fuel ratio sensor 28 (Deterioration) is determined to be present. In this case, the routine proceeds to step 107, where the sensor abnormality is stored in the memory of the ECU 36, and the warning lamp 39 is turned on to notify the driver. The processing in step 106 functions as an abnormality determination unit described in the claims.

Further, in this embodiment, in order to prevent divergence and hunting of the air-fuel ratio when the sensor is abnormal (deteriorated), the air-fuel ratio feedback gain is switched according to the sensor normal / abnormal by the air-fuel ratio feedback gain switching routine in FIG. That is, in step 111, it is determined whether or not the diagnosis result of the sensor abnormality diagnosis routine of FIG. 2 is a sensor abnormality. When the sensor is normal, the process proceeds to step 113, and the air-fuel ratio feedback gain (integration constant, skip value, etc.) is normally set. When the sensor is abnormal (deteriorated), the routine proceeds to step 112, where the air-fuel ratio feedback gain is made smaller than the normal value. As a result, as shown in FIG. 5, when the sensor is abnormal (deteriorated), the amplitude of the air-fuel ratio feedback correction coefficient becomes smaller than when the sensor is normal, and divergence and hunting of the air-fuel ratio are suppressed.

As in the first embodiment described above, the change rate ΔI of the sensor output after the start of the fuel cut (after the detection of the change in the fuel supply amount) is determined, and the sensor abnormality is determined based on whether the change rate ΔI is smaller than the abnormality determination value Ifc. If the presence / absence is determined, even if the sensor output at the beginning of the diagnosis start (the beginning of the fuel cut) changes depending on the air-fuel ratio state before the start of the diagnosis (before the start of the fuel cut), even after the start of the diagnosis, Since the rate of change ΔI of the sensor output is hardly affected by the air-fuel ratio before the start of the diagnosis, it is possible to diagnose whether or not the sensor is abnormal without being affected by the state of the air-fuel ratio before the start of the diagnosis. As compared with the conventional diagnosis method which is easily affected by the air-fuel ratio, a slight sensor abnormality (characteristic deterioration) can be detected, and the diagnosis accuracy can be improved. As a result, it is possible to prevent a decrease in drivability and a decrease in emission due to a sensor abnormality (characteristic deterioration).
[Example 2]

In the first embodiment, the fuel cut start is detected as a change in the fuel supply amount serving as the diagnosis start condition. On the contrary, the diagnosis process (judgment of the rate of change of the sensor output) is started on the condition of the fuel cut return. You may do it. Hereinafter, a second embodiment of the present invention that embodies this will be described with reference to FIGS. The sensor abnormality diagnosis routine shown in FIG. 8 is processed every time the main routine is executed (for example, every 8 ms), and a change rate ΔI of the sensor output after returning from the fuel cut is obtained, and the change rate ΔI is compared with an abnormality determination value Ifr. The presence or absence of a sensor abnormality is determined. FIG. 9 is a time chart showing the flow of processing when this sensor abnormality diagnosis routine is executed.

In the sensor abnormality diagnosis routine of the second embodiment, first, in step 201, it is determined whether or not fuel cut recovery (restart of fuel injection) has been performed. If not fuel cut recovery, the subsequent processing is not performed and the sensor abnormality diagnosis is performed. End the routine. Thereafter, when the fuel cut is restored, "Yes" is determined in step 101, and the routine proceeds to step 202, where the sensor output I3 # at the time of returning from the fuel cut is read and stored, and the timer is operated to operate the fuel cut. The elapsed time after return is counted. In the following step 203, it is determined whether or not the sensor output has dropped to I4 #, and the process waits until the sensor output drops to I4 #.

Thereafter, when the sensor output decreases to I4 #, the process proceeds to step 204. After reading and storing the time T2 # from the start of fuel cut to the sensor output decreasing to I4 # from the count value of the timer described above, the process proceeds to step 205. The change rate ΔI of the sensor output is calculated by the following equation.

ΔI = (I4-I3) / T2
In step 206, the sensor output change rate ΔI calculated by the above equation is compared with the abnormality determination value Ifr, and when the sensor output change rate ΔI is equal to or smaller than the abnormality determination value Ifr (| ΔI | ≧ | Ifr |), the responsiveness of the air-fuel ratio sensor 28 has not deteriorated and the sensor output is normal, so this routine ends. However, as the responsiveness of the air-fuel ratio sensor 28 deteriorates, the absolute value of the rate of change ΔI of the sensor output becomes smaller. Therefore, when the rate of change ΔI of the sensor output becomes larger than the abnormality determination value Ifc (comparison of the absolute values). If | ΔI | <| Ifr |), it is determined that the air-fuel ratio sensor 28 is abnormal (deteriorated). In this case, the routine proceeds to step 107, where the sensor abnormality is stored in the memory of the ECU 36, and the warning lamp 39 is turned on to notify the driver.

In the first and second embodiments described above, the start of fuel cut or the return of fuel cut is detected as the change of the fuel supply amount serving as the diagnosis start condition. However, the change of the target air-fuel ratio causing the change of the fuel supply amount is detected. Alternatively, a change in the fuel increase value / fuel decrease value may be used as the diagnosis start condition.

In the first and second embodiments, the time T1, T2 until the sensor output changes to the predetermined value I2, I4 is measured, and the predetermined change amount of the sensor output is divided by the time T1, T2 to obtain the sensor output. Although the change rate ΔI is determined, the change amount within a predetermined time may be measured, and the change amount divided by the predetermined time to obtain the sensor output change rate ΔI. This is embodied in a third embodiment of the present invention shown in FIGS. 10 and 11, and a fourth embodiment of the present invention shown in FIGS. 12 and 13.
[Example 3]

A third embodiment of the present invention shown in FIGS. 10 and 11 is an embodiment corresponding to the first embodiment for calculating the rate of change ΔI of the sensor output after the start of the fuel cut, and the processes of steps 303 and 304 are different from those of the first embodiment. The only difference is that the other processes are substantially the same as those of the first embodiment. In the third embodiment, the sensor output I5 at the start of the fuel cut is read and stored (step 302), and thereafter, the sensor output I6 at the time when a predetermined time T3 {elapses} is read and stored (steps 303 and 304). Is calculated by the following equation (step 305).

ΔI = (I6-I5) / T3
[Example 4]

On the other hand, a fourth embodiment of the present invention shown in FIGS. 12 and 13 is an embodiment corresponding to the second embodiment for calculating the rate of change ΔI of the sensor output after returning from the fuel cut. The second embodiment is different from the second embodiment only, and other processes are substantially the same as those of the second embodiment. In the fourth embodiment, the sensor output I7 at the time of returning from the fuel cut is read and stored (step 402), and then the sensor output I8 at the time when a predetermined time T4 has elapsed is read and stored (steps 403 and 404). Is calculated by the following equation (step 405).

ΔI = (I8−I7) / T4
[Example 5]

{By the way, as shown in FIG. 3, there is a response delay time T5} from the start of the fuel cut until the sensor output starts to change. If the characteristics of the air-fuel ratio sensor 28 deteriorate, the response tends to be slow and the response delay time T5 # tends to be long.

Therefore, in the fifth embodiment of the present invention shown in FIGS. 14 and 15, the response delay time T9 from the start of the fuel cut until the sensor output starts to change is measured, and this response delay time T9 is compared with the abnormality determination value Tfc. To determine whether there is a sensor abnormality. Specifically, in steps 501 and 502, the sensor output I9 # at the start of the fuel cut is read and stored, and the timer is operated to count the elapsed time after the start of the fuel cut.

Next, in step 503, the process waits until the sensor output rises to I9 + Δi (where Δi is a change width recognized as an increase in output). When the sensor output rises to I9 + Δi, the process proceeds to step 504, and The response delay time T5 from the start of cutting until the sensor output rises to I9 + Δi is read from the count value of the timer described above. Thereafter, in step 505, the response delay time T9 is compared with the abnormality determination value Tfc. If T9 ≦ Tfc, the response of the air-fuel ratio sensor 28 has not deteriorated and the sensor output is normal. End the routine.

However, if T9> Tfc, the responsiveness of the air-fuel ratio sensor 28 has deteriorated, so it is determined that the air-fuel ratio sensor 28 is abnormal (deteriorated), and the routine proceeds to step 506, where the sensor abnormality is stored in the memory of the ECU 36. At the same time, the warning lamp 39 is turned on to notify the driver. In this case, the processing of steps 503 and 504 functions as a time measuring means referred to in the claims.
[Example 6]

On the other hand, in the sixth embodiment of the present invention shown in FIGS. 16 and 17, the measurement accuracy of the change rate ΔI is improved by starting the measurement of the change rate ΔI of the sensor output after the response delay time T10 has elapsed after the start of the fuel cut. Things. The sixth embodiment corresponds to a third embodiment (FIGS. 10 and 11) in which a change amount of a sensor output within a predetermined time is divided by the predetermined time to obtain a change rate ΔI. The flowchart of FIG. 16 will be described with reference to the symbols in the time chart.

The processing in steps 601 to 604 is the same as the processing in steps 501 to 504 in FIG. 14, and calculates and stores the sensor output I10 at the start of the fuel cut, and the processing from the start of the fuel cut until the sensor output rises to I10 + Δi. The response delay time T10 is measured and stored. In the following step 605, the process waits until a predetermined time Δt elapses after the sensor output rises to I10 + Δi, and after the predetermined time Δt elapses, reads and stores the sensor output I11 (step 606). In the following step 607, the rate of change ΔI of the sensor output is calculated by the following equation.

ΔI = {I11− (I10 + Δi)} / Δt
Thereafter, at step 608, the sensor output change rate ΔI is compared with the abnormality determination value Icf2. If ΔI <Icf2, it is determined that the air-fuel ratio sensor 28 is abnormal (deteriorated). The sensor abnormality is stored in the memory and the warning lamp 39 is lit to notify the driver.

In the first embodiment, the measurement of the rate of change ΔI of the sensor output may be started after the response delay time T10 has elapsed after the start of the fuel cut. The concept of each of the fifth and sixth embodiments can be applied not only to the start of the fuel cut, but also to the detection of another change in the fuel supply amount, such as at the time of returning from the fuel cut.

In each of the embodiments except for the fifth embodiment, the change amount of the sensor output is divided by the time to obtain the change amount per unit time as the change rate ΔI of the sensor output. Instead of directly calculating ΔI, the change rate of the sensor output may be indirectly determined as follows.

(1) The time until the sensor output changes by a predetermined amount after the fuel supply amount changes is measured, and the rate of change of the sensor output is indirectly determined based on the length of the measurement time. In other words, the relationship that the change rate of the sensor output is small when the measurement time is long and the change rate of the sensor output is large when the measurement time is short is used. In this case, it is not necessary to divide the amount of change in the sensor output by the measurement time.

(2) A change in the sensor output that changes within a predetermined time after the change in the fuel supply amount is determined, and the rate of change in the sensor output is indirectly determined based on the magnitude of the change. In other words, the relationship that the change rate of the sensor output increases as the change amount within the predetermined time increases, and the change rate of the sensor output decreases as the change amount within the predetermined time decreases. Also in this case, it is not necessary to divide the amount of change by time, as in the case described above.

(4) When the method (1) or (2) is used, there is no need to divide the amount of change in sensor output by time, so that there is an advantage that the calculation load can be reduced. Further, a detection circuit for detecting the change rate (slope) of the sensor output in a hardware manner may be provided.

The determination of the change in the fuel supply amount and the determination of the rate of change in the sensor output may be performed by appropriately combining the above-described examples. For example, the sensor abnormality may be detected both at the start of the fuel cut and at the time of the return from the fuel cut. May be determined.

Further, in the above-described embodiment, the air-fuel ratio sensor 28 whose output continuously changes according to the air-fuel ratio in the exhaust gas is used. However, the oxygen sensor whose output changes stepwise according to the oxygen concentration in the exhaust gas. May be used.

Further, in the above-described embodiment, the warning lamp 39 is used as a warning unit for warning the driver when the sensor is abnormal. However, a warning is given by a sound such as a buzzer, or the engine speed is changed by periodically changing the fuel supply or the ignition timing. May be roughened to warn the driver of a sensor abnormality.

1 is a schematic configuration diagram of an entire engine control system according to a first embodiment of the present invention. 5 is a flowchart illustrating the flow of a sensor abnormality diagnosis routine according to the first embodiment. Time chart showing the flow of the abnormality diagnosis processing of the first embodiment Flow chart showing the flow of the air-fuel ratio feedback gain switching routine Diagram showing change over time of air-fuel ratio feedback correction coefficient Flow chart showing the flow of processing of a fuel cut determination routine Flow chart showing operation of fuel cut 9 is a flowchart illustrating a process flow of a sensor abnormality diagnosis routine according to a second embodiment of the present invention. Time chart showing the flow of the abnormality diagnosis processing of the second embodiment 11 is a flowchart showing the flow of processing of a sensor abnormality diagnosis routine according to a third embodiment of the present invention. Time chart showing the flow of the abnormality diagnosis processing of the third embodiment 4 is a flowchart illustrating a process flow of a sensor abnormality diagnosis routine according to a fourth embodiment of the present invention. 4 is a time chart illustrating a flow of an abnormality diagnosis process according to the fourth embodiment. 5 is a flowchart illustrating a process flow of a sensor abnormality diagnosis routine according to a fifth embodiment of the present invention. 5 is a time chart showing the flow of the abnormality diagnosis processing according to the fifth embodiment. 6 is a flowchart showing the flow of processing of a sensor abnormality diagnosis routine according to a sixth embodiment of the present invention. 5 is a time chart showing the flow of the abnormality diagnosis processing according to the fifth embodiment.

Explanation of reference numerals

10. Engine (internal combustion engine),
20: fuel injection valve,
27 ... exhaust pipe,
28 ... Air-fuel ratio sensor,
36 ... engine control circuit (detection means, change rate determination means, abnormality determination means),
39 warning lamp (warning means).

Claims (7)

The self-diagnosis of an air-fuel ratio control device that feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine by the output of an air-fuel ratio sensor whose output continuously changes according to the air-fuel ratio of the exhaust gas of the internal combustion engine ,
Detecting means for detecting a change in the amount of fuel supplied to the internal combustion engine,
Change rate determining means for determining a change rate of the output of the air-fuel ratio sensor after detecting a change in the fuel supply amount by the detecting means;
Abnormality determination means for determining the presence or absence of an abnormality in the air-fuel ratio sensor based on the change rate of the output of the sensor obtained by the change rate determination means,
A self-diagnosis device for an air-fuel ratio control device for an internal combustion engine, wherein the detection means detects a start of fuel cut or a return from fuel cut as a change in fuel supply amount. The self-diagnosis of an air-fuel ratio control device that feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine by the output of an air-fuel ratio sensor whose output continuously changes according to the air-fuel ratio of the exhaust gas of the internal combustion engine ,
Detecting means for detecting a change in the amount of fuel supplied to the internal combustion engine,
Change rate determining means for determining a change rate of the output of the air-fuel ratio sensor after detecting a change in the fuel supply amount by the detecting means;
Abnormality determination means for determining the presence or absence of an abnormality in the air-fuel ratio sensor based on the change rate of the output of the sensor obtained by the change rate determination means,
The self-diagnosis device for an air-fuel ratio control device for an internal combustion engine, wherein the change rate determining means obtains a change amount per unit time as a change rate of an output of the sensor. The self-diagnosis of an air-fuel ratio control device that feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine by the output of an air-fuel ratio sensor whose output continuously changes according to the air-fuel ratio of the exhaust gas of the internal combustion engine ,
Detecting means for detecting a change in the amount of fuel supplied to the internal combustion engine,
Change rate determining means for determining a change rate of the output of the air-fuel ratio sensor after detecting a change in the fuel supply amount by the detecting means;
Abnormality determination means for determining the presence or absence of an abnormality in the air-fuel ratio sensor based on the change rate of the output of the sensor obtained by the change rate determination means,
The change rate determining means measures a time until the output of the sensor changes by a predetermined amount after the fuel supply amount changes, and determines a change rate of the output of the sensor based on the length of the measurement time. A self-diagnosis device for an air-fuel ratio control device of an internal combustion engine. The self-diagnosis of an air-fuel ratio control device that feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine by the output of an air-fuel ratio sensor whose output continuously changes according to the air-fuel ratio of the exhaust gas of the internal combustion engine ,
Detecting means for detecting a change in the amount of fuel supplied to the internal combustion engine,
Change rate determining means for determining a change rate of the output of the air-fuel ratio sensor after detecting a change in the fuel supply amount by the detecting means;
Abnormality determination means for determining the presence or absence of an abnormality in the air-fuel ratio sensor based on the change rate of the output of the sensor obtained by the change rate determination means,
The change rate determination means obtains a change amount of the output of the sensor that changes within a predetermined time after the fuel supply amount changes, and determines a change rate of the output of the sensor based on the magnitude of the change amount. A self-diagnosis device for an air-fuel ratio control device of an internal combustion engine. In self-diagnosis of an abnormality of an air-fuel ratio control device that feedback-controls an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine by an output of a sensor that detects an air-fuel ratio or an oxygen concentration of an exhaust system of an internal combustion engine,
Detecting means for detecting a change in the amount of fuel supplied to the internal combustion engine,
A time measuring means for measuring a response delay time until the output of the sensor starts to change after detecting the change in the fuel supply amount by the detecting means;
A self-diagnosis device for an air-fuel ratio control device for an internal combustion engine, comprising: abnormality determination means for determining the presence or absence of an abnormality in the sensor based on the response delay time measured by the time measurement means. The self-diagnosis of an air-fuel ratio control device that feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine by the output of an air-fuel ratio sensor whose output continuously changes according to the air-fuel ratio of the exhaust gas of the internal combustion engine ,
Detecting means for detecting a change in the amount of fuel supplied to the internal combustion engine,
Change rate determining means for determining a change rate of the output of the air-fuel ratio sensor after detecting a change in the fuel supply amount by the detecting means;
Abnormality determination means for determining the presence or absence of an abnormality in the air-fuel ratio sensor based on the change rate of the output of the sensor obtained by the change rate determination means,
A self-diagnosis device for an air-fuel ratio control device for an internal combustion engine, wherein an air-fuel ratio feedback gain of the air-fuel ratio feedback control is switched according to a determination of normality / abnormality of the air-fuel ratio sensor by the abnormality determination means. Self-diagnosis of an air-fuel ratio control device that feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the output of an air-fuel ratio sensor whose output current continuously changes according to the air-fuel ratio of the exhaust gas of the internal combustion engine At
Detecting means for detecting a change in the amount of fuel supplied to the internal combustion engine,
Change rate determining means for determining a change rate of an output current of the air-fuel ratio sensor after detecting a change in the fuel supply amount by the detecting means;
Abnormality determination means for determining whether or not the air-fuel ratio sensor is abnormal based on the change rate of the output current of the sensor obtained by the change rate determination means. Self-diagnosis device.

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