JP4101133B2 - Self-diagnosis device for air-fuel ratio control device of internal combustion engine - Google Patents

Description

  The present invention relates to a self-diagnosis device for an air-fuel ratio control device for an internal combustion engine that self-diagnose an abnormality in an air-fuel ratio control device that feedback-controls the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine (hereinafter referred to as “engine”). .

In an air-fuel ratio control apparatus that feedback-controls the air-fuel ratio of an air-fuel mixture supplied to an automobile engine, an oxygen sensor that detects the oxygen concentration in exhaust gas is attached to the exhaust pipe, and the output voltage of this oxygen sensor is adjusted to the stoichiometric air-fuel ratio. The air-fuel ratio is controlled in the vicinity of the theoretical 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, the controllability of the air-fuel ratio becomes worse. Therefore, in order to detect the failure of the oxygen sensor, there is one that diagnoses the presence or absence of the failure of the oxygen sensor by comparing the output current of the oxygen sensor with the failure determination level after a certain time has elapsed since the start of fuel cut. (See Patent Document 1).
JP-A-60-233343

  However, in the self-diagnosis method of Patent Document 1 described above, the sensor current after a certain time has elapsed from the start of fuel cut is compared with the failure determination level. However, depending on the air-fuel ratio state immediately before the fuel cut, the same oxygen sensor is 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 until the sensor current reaches the failure determination level is also different. Therefore, if a failure is diagnosed with a sensor current after a certain time has elapsed since the start of 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 of the present invention is to diagnose the presence or absence of an abnormality of the air-fuel ratio sensor without being affected by the state of the air-fuel ratio before the start of diagnosis, It is an object of the present invention to provide a self-diagnosis device for an air-fuel ratio control device for an internal combustion engine that can improve diagnosis accuracy.

In order to achieve the above object, the self-diagnosis device for an air-fuel ratio control device for an internal combustion engine according to claim 1 of the present invention continuously changes the output according to the air-fuel ratio (A / F) of the exhaust gas of the internal combustion engine. Detecting a change in the amount of fuel supplied to the internal combustion engine, wherein self-diagnosis of an abnormality of the 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 the air-fuel ratio sensor , the storing output of the air-fuel ratio sensor, the rate of change of the output of the air-fuel ratio sensor after the detection of a change in the fuel supply amount when the change in the fuel supply amount is detected by the detection means, said memory and air-fuel ratio sensor output that is, the change rate determining means for the sensor output from the air-fuel ratio sensor output which is the storage is determined based on the time required for the change to the predetermined value, determined by the rate of change judging means An abnormality determining means for determining whether the air-fuel ratio sensor is abnormal based on a rate of change in the output of the air-fuel ratio sensor, and the detecting means detects a fuel cut start or a fuel cut return as a change in fuel supply amount To do.

  According to a second aspect of the present invention, the change rate determination means may obtain a change amount per unit time as a change rate of the output of the air-fuel ratio sensor.

Alternatively, according to a third aspect of the present invention, the change rate determination means measures a time until the output of the sensor changes from the stored output of the air-fuel ratio sensor by a predetermined amount after the fuel supply amount changes. The rate of change in the output of the air-fuel ratio sensor may be determined based on the length of the measurement time.

Alternatively, according to a fourth aspect of the present invention, the rate-of-change determination means changes the output of the air-fuel ratio sensor from the stored output of the air-fuel ratio sensor that changes within a predetermined time after the fuel supply amount changes. The change rate of the air-fuel ratio sensor may be determined based on the amount of change.

Furthermore, as according to claim 5, in place of the change rate determining means described above, the change in the fuel supply amount is stored the output of the air-fuel ratio sensor when it is detected, the fuel supply amount is stored after the change in air Time measuring means for measuring a response delay time from the output of the fuel ratio sensor until the output of the air fuel ratio sensor starts to change is provided, and the presence / absence of abnormality of the air / fuel ratio sensor is determined based on the response delay time measured by the time measuring means. It is good also as a structure which provided the abnormality determination means.

  According to another aspect of the present invention, the air-fuel ratio feedback gain of the air-fuel ratio feedback control may be switched according to the normality / abnormality determination of the air-fuel ratio sensor by the abnormality determination means.

  Further, as described in claim 7, an output current may be used as an output of the air-fuel ratio sensor.

According to the first aspect of the present invention, when the change in the fuel supply amount to the internal combustion engine (hereinafter referred to as the “engine”) is detected by the detecting means, the diagnostic process is started and the change in the fuel supply amount is detected. The output of the air-fuel ratio sensor at this time is stored, and the rate of change of the air-fuel ratio sensor output from the stored output of the air-fuel ratio sensor after detecting the change in the fuel supply amount is obtained by the change rate determination means. Then, based on the change rate of the air-fuel ratio sensor output obtained by the change rate determination means, the abnormality determination means determines whether the air-fuel ratio sensor is abnormal. In this case, even if there is a situation in which the air-fuel ratio sensor output at the beginning of diagnosis (initial detection of fuel supply amount change) changes depending on the air-fuel ratio state before the diagnosis starts (before fuel supply amount change detection), The change rate of the sensor output is hardly affected by the air-fuel ratio before the diagnosis is started. Therefore, by diagnosing the presence / absence of abnormality of the air / fuel ratio sensor based on the rate of change of the air / fuel ratio sensor output, it is possible to diagnose the presence / absence of abnormality of the air / fuel ratio sensor without being affected by the state of the air / fuel ratio before the diagnosis is started. It becomes possible.

  By the way, the cause of the change in the fuel supply amount is, for example, fuel cut start / fuel cut return, fuel supply is stopped by fuel cut start, and fuel supply is restarted by fuel cut return. A major change in the fuel supply occurs due to the return.

  Accordingly, in the first aspect of the invention, the fuel cut start or the fuel cut return is further detected by the detecting means, thereby detecting the change in the fuel supply amount indirectly. The timing of the start of fuel cut and the return of fuel cut is controlled by the engine control device and can be accurately determined.

  According to a second aspect of the present invention, the change amount per unit time is obtained as the change rate of the air-fuel ratio sensor output by the change rate determination 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, or by dividing the predetermined amount of change by the time required for the change, or empty. You may make it provide the detection circuit which detects the change rate (inclination) of a fuel ratio sensor output by hardware.

According to a third aspect of the present invention, the rate-of-change determination means determines a time from when the fuel supply amount at the start of fuel cut or after fuel cut is changed to when the output of the air-fuel ratio sensor changes to a predetermined amount from the stored output of the air-fuel ratio sensor. Measurement is performed, and the rate of change of the air-fuel ratio sensor output is indirectly determined based on the length of the measurement time. In other words, the longer the measurement time, the smaller the change rate of the air-fuel ratio sensor output, and the shorter the measurement time, the larger the change rate of the air-fuel ratio sensor output. In this case, it is not necessary to divide the change amount of the air-fuel ratio sensor output by the measurement time.

On the other hand, in the fourth aspect, the change rate determination means changes the air-fuel ratio sensor output from the stored output of the air-fuel ratio sensor, which changes within a predetermined time after the fuel supply amount at the start or return of fuel cut changes. The change rate of the air-fuel ratio sensor is indirectly determined based on the magnitude of the change amount. In other words, the change rate of the air-fuel ratio sensor output increases as the change amount within the predetermined time increases, and the change rate of the air-fuel ratio sensor output decreases as the change amount 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 claim 3.

By the way, when the characteristics of the air-fuel ratio sensor deteriorate, the responsiveness of the air-fuel ratio sensor deteriorates, and the response delay time until the output of the air-fuel ratio sensor starts to change after the fuel supply amount changes tends to become longer. Therefore, in claim 5, instead of the rate of change of the air-fuel ratio sensor output described above, the output of the air-fuel ratio sensor is changed from the stored output of the air-fuel ratio sensor after the fuel supply amount at the start of fuel cut or the return of fuel cut changes. The response delay time until the change starts is measured by the time measuring means, and based on the response delay time measured by the time measuring means, the presence or absence of abnormality of the sensor is determined by the abnormality determining means. Thus, even if a diagnosis is made based on the response delay time, it is possible to diagnose the presence or absence of a sensor abnormality without being affected by the state of the air-fuel ratio before the diagnosis is started.

  According to a sixth aspect of the present invention, the air-fuel ratio feedback gain of the air-fuel ratio feedback control is switched according to the normality / abnormality determination of the air-fuel ratio sensor by the abnormality determination means. Thereby, divergence and hunting of the air-fuel ratio when the air-fuel ratio sensor is abnormal (deterioration) can be prevented.

  Further, as described in claim 7, an output current may be used as an output of the air-fuel ratio sensor.

    [Example 1]

  A first embodiment of the present invention will be described below 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 the intake pipe 12 connected to the 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 path 16 that bypasses the throttle valve 15. The opening degree of the throttle valve 15 is detected by a throttle opening degree sensor 18, and the intake pipe pressure downstream of the throttle valve 15 is detected by an intake pipe pressure sensor 19.

  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 the fuel pump 22 → the fuel filter 23 → the pressure regulator 24, and the fuel pressure is maintained at a constant pressure with respect to the intake pipe pressure by the pressure regulator 24. Excess fuel is returned to 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 in accordance with the air-fuel ratio (A / F) in the exhaust gas, and an exhaust gas purifying apparatus. A three-way catalyst (not shown) is provided. A water temperature sensor 30 for detecting the coolant temperature is attached to a water jacket 29 that cools the engine 10. A distributor 32 that distributes 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 provided. The distributor 32 is supplied with the high-voltage secondary current of the igniter 35.

  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 with the battery 37 as a power source, and starts the engine 10 by an ON signal of the ignition switch 38. During operation of the engine 10, the air-fuel ratio is shown in FIG. 5 based on the output signal of the air-fuel ratio sensor 28. By increasing or decreasing the feedback correction coefficient, the air-fuel ratio is feedback-controlled in the vicinity of the theoretical air-fuel ratio.

  Further, the ECU 36 diagnoses the presence or absence of abnormality of the air-fuel ratio sensor 28 by the sensor abnormality diagnosis routine shown in FIG. 2, and informs the driver by lighting a warning lamp 39 (warning means) at the time of abnormality. This sensor abnormality diagnosis routine is processed every time the main routine is executed (for example, every 8 ms) to obtain the change rate ΔI of the output current of the air-fuel ratio sensor 28 after the start of fuel cut at the time of deceleration, and the change rate ΔI is an abnormality determination value. When it is smaller than Ifc, it is determined that the sensor is abnormal. FIG. 3 shows 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 a fuel cut is started. Here, the fuel cut execution timing is controlled by the fuel cut determination routine shown in FIG. 6, and a time chart showing the flow of the processing is shown in FIG. This fuel cut determination routine is also processed 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 caused by the fuel cut during deceleration, the throttle is fully closed. It is determined whether or not a predetermined time To has elapsed (the throttle fully closed switch (not shown) is on). If the predetermined time To has elapsed, the routine proceeds to step 122 where the engine speed NE becomes the fuel cut start speed NFC. Determine if 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 rotational speed NFC is set higher as the cooling water temperature is lower so as not to enter the fuel cut in the idle state.

  On the other hand, when it is determined as “No” in any of steps 121 and 122, that is, when the throttle fully closed state has not passed the predetermined time To, or 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 process. If the fuel cut has been executed in the previous process, the routine proceeds to step 124 where the engine speed NE is set. It is determined whether or not the fuel cut return rotational speed NRT has fallen below. If it has fallen below the fuel cut return rotational speed NRT, the routine proceeds to step 125 and the fuel cut execution flag XFC is set to “0”. Then return from the fuel cut and restart fuel injection. If it is determined in step 124 that the engine speed NE has not decreased below the fuel cut return speed NRT, the process proceeds to step 126 and fuel cut is continued. If “No” in step 123, that is, if the fuel cut has not been executed in the previous process, the process is finished in step 125 and fuel injection is continued.

  As described above, in the sensor abnormality diagnosis routine shown in FIG. 2, first, at 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. The sensor abnormality diagnosis routine is terminated. The processing in step 101 corresponds to detection means for detecting a change in the amount of fuel supplied to the engine 10. When fuel cut is started by the process of the fuel cut determination routine, “Yes” is determined in step 101 and the process proceeds to step 102 to output the air-fuel ratio sensor 28 at the start of fuel cut (hereinafter referred to as “sensor output”). ) I1 is read and stored, and the timer is activated to count the elapsed time after the start of fuel cut. Next, in step 103, it is determined whether or not the sensor output has increased to I2, and the process waits until the sensor output has increased 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 until the sensor output rises to I2 from the count value of the timer, the process proceeds to step 105. The sensor output change rate ΔI is calculated by the following equation.

ΔI = (I2−I1) / T1
The processing in step 105 functions as a change rate determination means in the claims.

  In subsequent step 106, the sensor output change rate ΔI calculated by the above equation is compared with the abnormality determination value Ifc. If the sensor output change rate ΔI is equal to or greater than the abnormality determination value Ifc, the responsiveness of the air-fuel ratio sensor 28 is degraded. Since the sensor output is normal, this routine is terminated. However, since the rate of change ΔI of the sensor output decreases as the responsiveness 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 is detected. It is determined that there is (deterioration). 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 lit to notify the driver. The processing in step 106 functions as an abnormality determination means in the claims.

  Further, in this embodiment, in order to prevent the divergence and hunting of the air-fuel ratio at the time of sensor abnormality (deterioration), the air-fuel ratio feedback gain is switched according to the normality / abnormality of the sensor by the air-fuel ratio feedback gain switching routine in FIG. That is, at 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 routine proceeds to step 113 where the air-fuel ratio feedback gain (integral constant, skip value, etc.) is set to normal. However, 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 sensor output change rate ΔI after the start of the fuel cut (after the fuel supply amount change is detected) is obtained, and the sensor abnormality is determined depending on whether the change rate ΔI is smaller than the abnormality determination value Ifc. If the presence or absence is determined, the sensor output at the beginning of diagnosis (initially at the start of fuel cut) changes depending on the air-fuel ratio before the diagnosis is started (before the fuel cut is started). Since the change rate ΔI of the sensor output is hardly affected by the air-fuel ratio before the start of diagnosis, it can be diagnosed whether there is an abnormality in the sensor without being affected by the state of the air-fuel ratio before the start of diagnosis. Compared with the conventional diagnosis method that is easily affected by the air-fuel ratio, a slight sensor abnormality (characteristic deterioration) can be detected, and the diagnosis accuracy can be improved. Thereby, it is possible to prevent a decrease in dryness and a deterioration in emissions due to a sensor abnormality (characteristic deterioration).
[Example 2]

  In the first embodiment, the start of fuel cut is detected as a change in the fuel supply amount serving as a diagnosis start condition. On the contrary, diagnosis processing (determination of the rate of change in sensor output) is started on the condition that fuel cut is restored. You may make it do. A second embodiment of the present invention that embodies this will be described below 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 the abnormality determination value Ifr. Determine whether there is a sensor abnormality. FIG. 9 shows 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, at step 201, it is determined whether or not the fuel cut is restored (restarting fuel injection). If the fuel cut is not restored, the sensor abnormality diagnosis is performed without performing the subsequent processing. End the routine. Thereafter, when fuel cut return is performed, “Yes” is determined in step 101 and the process proceeds to step 202 where the sensor output I3 at the time of fuel cut return is read and stored, and a timer is activated to cut the fuel cut. The elapsed time after returning is counted. In subsequent step 203, it is determined whether or not the sensor output has decreased to I4, and the process waits until the sensor output decreases 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, the process proceeds to step 205. The sensor output change rate ΔI is calculated by the following equation.

ΔI = (I4−I3) / T2
In subsequent step 206, the sensor output change rate ΔI calculated by the above equation is compared with the abnormality determination value Ifr. If the sensor output change rate ΔI is equal to or less than the abnormality determination value Ifr (in the absolute value comparison, | ΔI | ≧ | In the case of Ifr |), the responsiveness of the air-fuel ratio sensor 28 has not deteriorated and the sensor output is normal, so this routine is terminated. However, since the absolute value of the sensor output change rate ΔI decreases as the responsiveness of the air-fuel ratio sensor 28 deteriorates, the sensor output change rate ΔI becomes greater than the abnormality determination value Ifc (absolute value comparison). 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 lit to notify the driver.

  In the first embodiment and the second embodiment described above, the fuel cut start or the fuel cut return is detected as a change in the fuel supply amount serving as a diagnosis start condition. However, a change in the target air-fuel ratio that causes a change in the fuel supply amount. 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 and T2 until the sensor output changes to the predetermined values I2 and I4 are measured, and the predetermined change amount of the sensor output is divided by the times T1 and T2 to output the sensor output. However, the change rate ΔI of the sensor output may be calculated by measuring the change amount within a predetermined time and dividing the change amount by the predetermined time. This is embodied in the third embodiment of the present invention shown in FIGS. 10 and 11 and the fourth embodiment of the present invention shown in FIGS.
[Example 3]

  The third embodiment of the present invention shown in FIGS. 10 and 11 is an embodiment corresponding to the first embodiment for obtaining the change rate ΔI of the sensor output after the start of the fuel cut, and the processing of steps 303 and 304 is the same as the first embodiment. Only the process is different, and the other processes are substantially the same as those in the first embodiment. In this third embodiment, the sensor output I5 at the start of fuel cut is read and stored (step 302), and then the sensor output I6 when the predetermined time T3 has elapsed 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, the fourth embodiment of the present invention shown in FIGS. 12 and 13 is an embodiment corresponding to the second embodiment for obtaining the change rate ΔI of the sensor output after returning from the fuel cut, and the processing of steps 403 and 404 is the embodiment. The other processes are substantially the same as those in the second embodiment. In the fourth embodiment, the sensor output I7 when the fuel cut is restored is read and stored (step 402), and then the sensor output I8 when the predetermined time T4 has elapsed is read and stored (steps 403 and 404). The change rate ΔI is calculated by the following equation (step 405).

ΔI = (I8−I7) / T4
[Example 5]

  Incidentally, as shown in FIG. 3, there is a response delay time T5 from the start of fuel cut until the sensor output starts to change. When the characteristics of the air-fuel ratio sensor 28 are deteriorated, the response is delayed and the response delay time T5 tends to become longer.

  Accordingly, in the fifth embodiment of the present invention shown in FIGS. 14 and 15, the response delay time T9 from the start of 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 if there is a sensor abnormality. Specifically, in steps 501 and 502, the sensor output I9 at the start of fuel cut is read and stored, and a timer is activated to count the elapsed time after the start of fuel cut.

Next, in step 503, the process waits until the sensor output rises to I9 + Δi (where Δi is a change width that is recognized as an increase in output). When the sensor output rises to I9 + Δi, the process proceeds to step 504 to start fuel cut. The response delay time T9 until the sensor output increases 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 responsiveness of the air-fuel ratio sensor 28 is 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 there is an abnormality (deterioration) of the air-fuel ratio sensor 28, and the routine proceeds to step 506 where the sensor abnormality is detected in the memory of the ECU 36. At the same time, the warning lamp 39 is lit to notify the driver. In this case, the processing of steps 503 and 504 functions as time measuring means 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. Is. The sixth embodiment corresponds to the third embodiment (FIGS. 10 and 11) in which the change rate ΔI is calculated by dividing the change amount of the sensor output within a predetermined time by the predetermined time. The flowchart of FIG. 16 will be described with reference to the reference numerals 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 the sensor output I10 at the start of fuel cut is obtained and stored, and from the start of fuel cut until the sensor output increases to I10 + Δi. The response delay time T10 is measured and stored. In the subsequent step 605, the process waits until the predetermined time Δt has elapsed since the sensor output increased to I10 + Δi, and after the predetermined time Δt has elapsed, the sensor output I11 is read and stored (step 606). In the subsequent step 607, the sensor output change rate ΔI is calculated by the following equation.

ΔI = {I11− (I10 + Δi)} / Δt
Thereafter, in step 608, the rate of change ΔI of the sensor output is compared with the abnormality determination value Icf2, and if ΔI <Icf2, it is determined that the air-fuel ratio sensor 28 is abnormal (deteriorated), the process proceeds to step 609, and the ECU 36 The sensor abnormality is stored in the memory and the warning lamp 39 is lit to notify the driver.

  In the first embodiment, measurement of the sensor output change rate ΔI may be started after the response delay time T10 has elapsed after the fuel cut is started. The concept of each of the fifth and sixth embodiments is not limited to when the fuel cut is started, but can also be applied when detecting other fuel supply amount changes such as when the fuel cut is restored.

  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 sensor output change rate 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 change rate of the sensor output is indirectly determined based on the length of the measurement time. That is, the relationship is such that the longer the measurement time, the smaller the change rate of the sensor output, and the shorter the measurement time, the greater the change rate of the sensor output. In this case, it is not necessary to divide the change amount of the sensor output by the measurement time.

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

  If the method (1) or (2) is used, there is no need to divide the change amount of the sensor output by time, and there is an advantage that the calculation load can be reduced. Further, a detection circuit that detects the change rate (slope) of the sensor output in hardware 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 examples. For example, sensor abnormality occurs both at the start of fuel cut and at the return of fuel cut. You may make it perform determination of.

  In the above 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 embodiment, the warning lamp 39 is used as a warning means for warning the driver when the sensor is abnormal. However, a warning such as a buzzer or the like is used, or the engine speed is changed by periodically changing the fuel supply or ignition timing. The driver may be warned of sensor abnormality by roughening.

1 is a schematic configuration diagram of an entire engine control system showing Embodiment 1 of the present invention. The flowchart which shows the flow of a process of the sensor abnormality diagnosis routine of Example 1. Time chart showing the flow of abnormality diagnosis processing of the first embodiment A flowchart showing the flow of the air-fuel ratio feedback gain switching routine A diagram showing the change over time of the air-fuel ratio feedback correction coefficient Flow chart showing the flow of processing of the fuel cut determination routine Flow chart showing fuel cut operation The flowchart which shows the flow of a process of the sensor abnormality diagnosis routine of Example 2 of this invention. Time chart showing the flow of abnormality diagnosis processing of the second embodiment The flowchart which shows the flow of a process of the sensor abnormality diagnosis routine of Example 3 of this invention. Time chart showing the flow of abnormality diagnosis processing of Example 3 The flowchart which shows the flow of a process of the sensor abnormality diagnosis routine of Example 4 of this invention. Time chart showing the flow of abnormality diagnosis processing of Example 4 The flowchart which shows the flow of a process of the sensor abnormality diagnosis routine of Example 5 of this invention. Time chart showing the flow of abnormality diagnosis processing of Example 5 The flowchart which shows the flow of a process of the sensor abnormality diagnosis routine of Example 6 of this invention. Time chart showing the flow of abnormality diagnosis processing of Example 5

Explanation of symbols

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)

In the self-diagnosis of the abnormality of the 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 the 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;
The output of the air-fuel ratio sensor when a change in the fuel supply amount is detected by the detection means is stored, and the change rate of the output of the air-fuel ratio sensor after the change in the fuel supply amount is detected is stored. A rate-of-change determination means that is determined based on the air-fuel ratio sensor output and the time required for the sensor output to change from the stored air-fuel ratio sensor output to a predetermined value ;
An abnormality determination unit that determines that the air-fuel ratio sensor is abnormal when the rate of change of the output of the sensor obtained by the change rate determination unit is smaller than a predetermined value;
The self-diagnosis device for an air-fuel ratio control apparatus for an internal combustion engine, wherein the detection means detects start of fuel cut or return of fuel cut as a change in fuel supply amount. In the self-diagnosis of the abnormality of the 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 the 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;
Storing the output of the air-fuel ratio sensor when the change in the fuel supply amount of more fuel cut start or fuel cut recovery is detected in this detection means, the air-fuel ratio sensor after the detection of a change in the fuel supply amount A rate-of-change determination means for obtaining a rate of change in output based on the stored air-fuel ratio sensor output and a time required for the sensor output to change from the stored air-fuel ratio sensor output to a predetermined value ;
An abnormality determination unit that determines that the air-fuel ratio sensor is abnormal when the rate of change of the output of the sensor obtained by the change rate determination unit is smaller than a predetermined value;
The self-diagnosis device for an air-fuel ratio control apparatus for an internal combustion engine, wherein the change rate determination means obtains a change amount per unit time as a change rate of the output of the sensor. In the self-diagnosis of the abnormality of the 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 the 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;
The output of the air-fuel ratio sensor when a change in the fuel supply amount at the start of fuel cut or the return of fuel cut is detected by this detecting means is stored, and the output of the air-fuel ratio sensor after detecting the change in the fuel supply amount A rate-of-change determination means for obtaining a rate of change of
An abnormality determination unit that determines that the air-fuel ratio sensor is abnormal when the rate of change of the output of the sensor obtained by the change rate determination unit is smaller than a predetermined value;
The rate-of-change determination means measures a time from when the fuel supply amount changes until the output of the sensor changes by a predetermined amount from the stored output of the air-fuel ratio sensor, and determines the sensor output according to the length of the measurement time. A self-diagnosis device for an air-fuel ratio control device for an internal combustion engine, characterized in that an output change rate is determined. In the self-diagnosis of the abnormality of the 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 the 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;
Storing the output of the air-fuel ratio sensor when the change in the fuel supply amount of more fuel cut start or fuel cut recovery is detected in this detection means, the air-fuel ratio sensor after the detection of a change in the fuel supply amount A rate-of-change determination means for obtaining a rate of change in output;
An abnormality determination unit that determines that the air-fuel ratio sensor is abnormal when the rate of change of the output of the sensor obtained by the change rate determination unit is smaller than a predetermined value;
The change rate determination means obtains a change amount of the sensor output from the stored output of the air-fuel ratio sensor , which changes within a predetermined time after the fuel supply amount changes, and depends on the magnitude of the change amount. A self-diagnosis device for an air-fuel ratio control device for an internal combustion engine, wherein a rate of change in output of the sensor is determined. In the self-diagnosis of the abnormality of the 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 the 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;
Air-fuel ratio sensor, wherein storing the output of the air-fuel ratio sensor, said stored after detecting a change in the fuel supply amount when the change in the fuel supply amount of the fuel cut start or fuel cut recovery is detected by the detection means A time delay means for measuring a response delay time from the output of the sensor until the output of the sensor starts to change as a time from the stored output of the stored air-fuel ratio sensor to a change corresponding to a change width recognized as an increase in output ,
A self-diagnosis device for an air-fuel ratio control apparatus for an internal combustion engine, comprising: an abnormality determination unit that determines whether the sensor is abnormal based on a response delay time measured by the time measuring unit. In the self-diagnosis of the abnormality of the 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 the 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;
Storing the output of the air-fuel ratio sensor when the change in the fuel supply amount of more fuel cut start or fuel cut recovery is detected in this detection means, the air-fuel ratio sensor after the detection of a change in the fuel supply amount A rate-of-change determination means for obtaining a rate of change in output based on the stored air-fuel ratio sensor output and a time required for the sensor output to change from the stored air-fuel ratio sensor output to a predetermined value ;
An abnormality determination unit that determines that the air-fuel ratio sensor is abnormal when the rate of change of the output of the sensor obtained by the change rate determination unit is smaller than a predetermined value;
A self-diagnosis device for an air-fuel ratio control apparatus for an internal combustion engine, wherein the air-fuel ratio feedback gain of the air-fuel ratio feedback control is switched in accordance with the normality / abnormality of the air-fuel ratio sensor by the abnormality determination means. Self-diagnosis of an abnormality in the 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 the air-fuel ratio sensor whose output current continuously changes according to the air-fuel ratio of the exhaust gas of the internal combustion engine In
Detecting means for detecting a change in the amount of fuel supplied to the internal combustion engine;
The air-fuel ratio sensor after the more change in the fuel supply amount of the fuel cut start or the fuel cut recovery is to store the output current of the air-fuel ratio sensor when it is detected, detects a change in the fuel supply quantity to the detection means The change rate of the output current is based on the stored air-fuel ratio sensor output current and the time required for the output current of the air-fuel ratio sensor to change from the stored air-fuel ratio sensor output current to a predetermined value. Change rate determination means to obtain,
An internal combustion engine characterized by comprising: an abnormality determination unit that determines that the air-fuel ratio sensor is abnormal when the change rate of the output current of the air-fuel ratio sensor obtained by the change rate determination unit is smaller than a predetermined value. Self-diagnosis device for engine air-fuel ratio control device.

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