JP3630174B2 - Abnormality detection device for fuel supply system of internal combustion engine - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an abnormality detection device for a fuel supply system of an internal combustion engine, and more particularly, based on an average value of an air-fuel ratio correction coefficient set according to an output value of an exhaust gas concentration detector provided in an exhaust system of the internal combustion engine. The present invention relates to an abnormality detection device for a fuel supply system of an internal combustion engine that detects an abnormality that has occurred in a fuel supply system.
[0002]
[Prior art]
For example, the following is proposed by the applicant of the present invention as a method for detecting an abnormality in the fuel supply system of an internal combustion engine, that is, a clogged fuel injection valve, a foreign object biting, or a deviation from the controllable range of the fuel supply amount due to secular change. (Japanese Patent Application No. 4-218628).
[0003]
That is, the air-fuel ratio correction coefficient is calculated based on the detected value of the exhaust gas concentration sensor provided in the engine exhaust system, and it is determined that the fuel supply system is abnormal when the average value of the air-fuel ratio correction coefficient deviates from the predetermined range. To do.
[0004]
[Problems to be solved by the invention]
However, according to the above-described conventional method, after the average value of the air-fuel ratio correction coefficient deviates from the predetermined range and is determined to be abnormal, if the average value is further calculated, this value is further updated to determine abnormality. There may be a large difference from the reference value. In such a case, when the fuel supply system is normalized, it takes a long time for the average value to return to the predetermined range (normal range), and although the fuel supply system is normal, it is abnormal. There was a problem of continuing the determination that there was.
[0005]
The present invention has been made to solve this problem, and is able to quickly detect that the engine is normal when the fuel supply system returns to a normal state after determining that the fuel supply system is abnormal. An object of the present invention is to provide an abnormality detection device for a fuel supply system.
[0006]
[Means for Solving the Problems]
Abnormality detection apparatus for a fuel supply system of an internal combustion engine according to claim 1 of the present invention in order to achieve the above object, an exhaust gas concentration detector disposed in the exhaust system of an internal combustion engine, the output of the exhaust gas concentration-detecting means An air-fuel ratio correction coefficient calculating means for calculating an air-fuel ratio correction coefficient for correcting the amount of fuel supplied to the engine so as to achieve a predetermined air-fuel ratio, an operating state detecting means for calculating an operating state of the engine, An average value calculating means for calculating an average value of the air-fuel ratio correction coefficient when the operating state detecting means detects that the engine is in a predetermined operating state; and the average value is calculated from an upper limit value for deterioration determination and a lower limit for deterioration determination. An abnormality determination means for determining whether or not the engine fuel supply system is abnormal when deviating from a range indicating a normal determination region up to a value. In the apparatus, when the average value is larger than the upper limit value of the average value has said deterioration determination upper limit or a value at the time it is determined that the larger abnormally than the deterioration determination upper limit by the abnormality determining unit the said means for holding the average value to the upper limit value or the average value of the deterioration judgment lower limit of when the average value is determined to be smaller than the deterioration determination for the lower limit abnormality by the abnormality determining means, when it becomes smaller than the lower limit value with the following values values are those of the average value was provided at least one of the means for holding the lower limit value.
[0007]
[Action]
When the average value of the air-fuel ratio correction coefficient is greater than the upper limit value for deterioration determination and the fuel supply system is determined to be abnormal, and the average value is greater than the upper limit value having a value equal to or greater than the upper limit value for deterioration determination The average value is held at the upper limit value, or when the average value of the air-fuel ratio correction coefficient is smaller than the lower limit value for deterioration determination and the fuel supply system is determined to be abnormal, the average value is the lower limit for deterioration determination. When it becomes smaller than the lower limit value having a value less than or equal to the value, the average value is held at the lower limit value.
[0008]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0009]
FIG. 1 is an overall configuration diagram of a fuel supply control apparatus including an abnormality detection apparatus for a fuel supply system according to an embodiment of the present invention. Reference numeral 1 is divided into left and right groups, for example, 3 cylinders, and 6 cylinders are combined. A four-cycle internal combustion engine of the arranged type is shown. A throttle body 3 is provided in the middle of an intake pipe 2 of the engine 1, and a throttle valve 3 'is arranged therein. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3 ′ and outputs an electric signal corresponding to the opening of the throttle valve 3 ′ to an electronic control unit (hereinafter referred to as “ECU”) 5. Supply.
[0010]
A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 ′ and slightly upstream of an intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel tank via a fuel pump 7. 8 and electrically connected to the ECU 5, and the valve opening time of the fuel injection valve 6 is controlled by a signal from the ECU 5.
[0011]
On the other hand, an intake pipe absolute pressure (PBA) sensor 10 is provided immediately downstream of the throttle valve 3 'via a pipe 9, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 10 is sent to the ECU 5. Supplied. Further, an intake air temperature (TA) sensor 11 is attached downstream thereof, detects the intake air temperature TA, outputs a corresponding electrical signal, and supplies it to the ECU 5.
[0012]
An engine water temperature (TW) sensor 12 mounted on the main body of the engine 1 includes a thermistor and the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies the temperature signal to the ECU 5. The engine speed (NE) sensor 13 and the cylinder discrimination (CYL) sensor 14 are mounted around the cam shaft or crank shaft (not shown) of the engine 1. The engine speed sensor 13 outputs a signal pulse (hereinafter referred to as “TDC signal pulse”) at a predetermined crank angle position every 120 ° rotation of the crankshaft of the engine 1, and the cylinder discrimination sensor 14 is a predetermined crank of a specific cylinder. A signal pulse is output at the angular position, and each of these signal pulses is supplied to the ECU 5.
[0013]
The three-way catalyst 15 is disposed in the collective exhaust pipe 17 of the exhaust pipes 16L and 16R provided in the left and right cylinder groups of the engine 1, respectively, and purifies components such as HC, CO, and NOx in the exhaust gas. O ₂ sensors 18L and 18R as exhaust gas concentration detectors are mounted on the exhaust pipes 16L and 16R for the left and right cylinder groups, respectively, and detect the oxygen concentration in the exhaust gas for each of the left and right cylinder groups and detect the respective detected values. A signal corresponding to the above is output and supplied to the ECU 5.
[0014]
Further, a vehicle speed sensor 23 for detecting the vehicle speed V of the vehicle on which the engine 1 is mounted is connected, and the detection signal is input to the ECU 5. Further, the ECU 5 is connected with an LED (light emitting diode) 19 for issuing a warning when an abnormality of the fuel supply system is detected by the method shown in FIG.
[0015]
Between the upper part of the sealed fuel tank 8 and the intake pipe 2 immediately after the throttle valve 3 ', a 2-way valve 20, a canister 21, and a purge control valve 22 constituting a fuel evaporative emission control device are provided. The purge control valve 22 is connected to the ECU 5 and is controlled by a signal from the ECU 5. That is, when the evaporative gas generated in the fuel tank 8 reaches a predetermined set pressure, the positive pressure valve of the two-way valve 20 is pushed open and flows into the canister 21 for storage. When the purge control valve 22 is opened by a control signal from the ECU 5, the evaporated gas temporarily stored in the canister 21 is sucked from the outside air intake port provided in the canister 21 due to the negative pressure of the intake pipe 2. The air is sucked into the intake pipe 2 together with the outside air and sent to the cylinder. Further, when the fuel tank 8 is cooled due to the influence of outside air and the negative pressure in the fuel tank increases, the negative pressure valve of the 2-way valve 20 opens, and the evaporated gas temporarily stored in the canister 21 is removed from the fuel tank 8. Returned to In this way, the fuel evaporative gas generated in the fuel tank 8 is prevented from being released to the atmosphere.
[0016]
The ECU 5 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and the like, and a central processing circuit (hereinafter referred to as “CPU”). 5b, a storage means 5c for storing various calculation programs executed by the CPU 5b, calculation results, etc., the fuel injection valve 6, the purge control valve 22, an output circuit 5d for supplying a drive signal to the LED 19, and the like.
[0017]
The CPU 5b discriminates various engine operation states such as a feedback control operation region and an open loop control operation region according to the oxygen concentration in the exhaust gas based on the various engine parameter signals described above, and according to the engine operation state, Based on (1), the fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated.
[0018]
TOUT = Ti × K ₁ × KO ₂ + K ₂ ... (1)
Here, Ti is a reference value of the injection time TOUT of the fuel injection valve 6 and is read from a Ti map set in accordance with the engine speed Ne and the intake pipe absolute pressure PBA.
[0019]
KO ₂ is an air-fuel ratio feedback correction coefficient, which is set according to the oxygen concentration in the exhaust gas detected by the O ₂ sensors 18L and 18R at the time of feedback control, and a plurality of open loop control operation regions in which feedback control is not performed. Is a coefficient set according to each operation region. The correction coefficient KO ₂ is set for each left and right cylinder group. For example, the correction coefficient KO ₂ R for the right cylinder group is an addition of a well-known proportional term (P term) when the output level of the O ₂ sensor 18R for the right cylinder group is inverted. It is calculated by proportional control by processing. When the output level does not invert, it is calculated by integration control by addition processing of a well-known integral term (I term). The correction coefficient KO ₂ L for the left cylinder group is also calculated in the same manner as described above based on the output voltage of the O ₂ sensor 18L for the left cylinder group.
[0020]
K ₁ and K ₂ are other correction coefficients and correction variables calculated in accordance with various engine parameter signals, respectively, so that various characteristics such as fuel consumption characteristics and engine acceleration characteristics can be optimized according to engine operating conditions. The predetermined value is determined.
[0021]
The CPU 5b supplies a drive signal for opening the fuel injection valve 6 to the fuel injection valve 6 via the output circuit 5d based on the fuel injection time TOUT obtained as described above.
[0022]
FIG. 2 is a flowchart showing the overall configuration of a fuel supply system abnormality detection program to which the present invention is applied. This program is executed by the CPU 5b in synchronism with the occurrence of each TDC signal pulse.
[0023]
In step S1 of FIG. 2, it is determined whether or not the precondition is satisfied. Here, the precondition is a condition that is established when the abnormality determination of the fuel supply system can be executed. Specifically, the success or failure is determined by the procedure shown in FIG. When the precondition is not satisfied, the flag FFS45FIN set to “1” at the end of the abnormality determination by this process is set to “0” (step S2), and the integral value (smoothed average value) KAV of the air-fuel ratio correction coefficient KO2 is calculated. A KAV calculation timer tCHKAVE for setting the time interval is initialized to a predetermined value (for example, 2 seconds) and started (step S4), and this process is terminated.
[0024]
When the precondition is satisfied, it is determined in step S3 whether or not the abnormality determination end flag FFS45FIN is “1”. If FFS45FIN = 1, the process proceeds to step S4. When the flag FFS45FIN is “0”, the process proceeds to step S5, and the integral value KAV is calculated. Specifically, this calculation is performed according to the procedure shown in FIG. Next, it is determined whether or not the KAV calculation timer tCHKAVE is “0”. If tCHKAVE> 0, this processing is immediately terminated.
[0025]
After tCHKAVE = 0 and calculation of the KAV value over a predetermined time set in the timer tCHKAVE, comparison and update processing (step S7) of the parameter KO2AVE for abnormality (aging) determination, KO2AVE value level check Processing (step S8) and purge confirmation processing (step S9) are performed. Specific contents of these processes will be described later with reference to FIGS. 4, 6, and 7.
[0026]
FIG. 3 is a flowchart showing a processing procedure for determining the precondition in step S1 of FIG. 2, and this processing is executed in the background.
[0027]
In step S11, whether or not the fuel supply system abnormality determination execution permission flag FGO45 indicating "0" indicates that execution of fuel supply system abnormality determination is prohibited for reasons other than the conditions determined in this process is "1". If FGO45 = 0, the process proceeds to step S15, and a predetermined time (for example, 2 seconds) is set to a delay timer tCONT for which the passage of time is determined in step S16 to be described later, and this is started and purged. Confirmation processing is performed (step S17), a predetermined time (for example, 4 seconds) is set in the stabilization timer tFMPGS after purge cut for which the passage of time is determined in step S21 described later, and this is started (step S18). It is determined that the precondition is not satisfied (step S22).
[0028]
The purge confirmation process in step S17 is specifically executed according to the procedure shown in FIG.
[0029]
First, in step S71, it is determined whether or not forced purge cut (see FIG. 3, steps S19 and 20) is being executed. If not, the process is immediately terminated. On the other hand, when the forced purge cut is being performed, it is determined whether or not the purge has been performed before the forced purge cut is performed (step S72). If the purge is performed, the purge is performed (step S73). Continue purge cut.
[0030]
Returning to FIG. 3, when the fuel supply system abnormality determination execution permission flag FGO45 = 1 and the abnormality determination is permitted in step S11, the operation state of the engine 1 and the vehicle on which the engine 1 is mounted is in the specific operation region. It is determined whether or not there is (step S13). Specifically, whether or not the intake air temperature TA is within a range from a predetermined lower limit value FUELTAL (for example, 0 ° C.) to a predetermined upper limit value FUELTAH (for example, 90 ° C.), the engine water temperature TW is a predetermined lower limit value FULTWL (for example, 75 ° C.). Whether the engine speed NE is within a range from a predetermined lower limit value NEL (for example, 1000 rpm) to a predetermined upper limit value NEH (for example, 3400 rpm), Whether or not the intake pipe absolute pressure PBA is within the range of a predetermined lower limit value PBL (for example, 210 mmHg) to a predetermined upper limit value PBH (for example, 610 mmHg), the throttle valve opening θTH is determined from the predetermined lower limit value θTHAVEL (for example, 2 deg). Whether it is within the range of θTHAVEH (for example, 45 deg) and the vehicle speed V is a predetermined lower limit value VA. It is determined whether or not a predetermined upper limit value VAVEH (for example, 96 Km / h) is within a range from EL (for example, 24 Km / h). Proceed to S15.
[0031]
When all the operating parameters are within the predetermined upper and lower limit values, it is determined whether or not the air-fuel ratio feedback control is being performed based on the outputs of the O ₂ sensors 18R and 18L (step S14). In step S15, if feedback control is being performed, it is determined whether or not the value of the delay timer tCONT set in step S15 is "0" (step S16). Since tCONT> 0 at first, the process proceeds to step S17. When tCONT = 0 after a predetermined time has elapsed, it is determined whether or not the abnormality determination parameter KO2AVE is smaller than a predetermined purge lower limit value KO2AVEPGL (step S19). The predetermined purge lower limit value KO2AVEPGL is set to a value (for example, 0.84) that can ignore the influence of the purge if the KO2AVE value is larger than this.
[0032]
If KO2AVE ≧ KO2AVEPGL is satisfied in step S19, the process immediately proceeds to step S21. If KO2AVE <KO2AVEPGL is satisfied, a forced purge cut is performed to eliminate the influence of the purge, and a forced purge cut flag FPGSCNT is set to indicate that. Set to "1" and proceed to step S21.
[0033]
In step S21, it is determined whether or not the value of the post-purge cut stabilization timer tFMPGS set in step S18 is “0”. Since tFMPGS> 0 at first, it is determined that the precondition is not satisfied (step S22), and when tFMPGS = 0 after a predetermined time has elapsed, it is determined that the precondition is satisfied (step S23).
[0034]
Next, the calculation process of the integral value KAV (FIG. 2, step S5) will be described with reference to FIG.
[0035]
In step S31, it is determined whether or not the flag FAF2 to be inverted is inverted when the magnitude relationship between the output VO2 of the O ₂ sensors 18R and 18L and the reference value VREF is inverted. Calculate (step S32).
[0036]
KAV = KO2 × CO2AV / A + KAV × (A−CO2AV) / A (2)
Here, KAV on the right side is a KAV value calculated so far, A is a predetermined value set to, for example, 10,000, and CO2AV is an annealing coefficient set to a value between 1 and A.
[0037]
If the flag FAF2 is not inverted in step S31, it is determined whether or not the flag FAF2 is inverted once after the previous condition is satisfied in the current monitor (abnormality determination) (step S33). If it has been reversed once, this processing is immediately terminated. If it has never been reversed, the air-fuel ratio correction coefficient KO2 at that time is set as the integral value KAV, and the KAV value is initialized (step S34). finish.
[0038]
According to this processing, as shown in FIG. 8A, the integral value KAV is updated each time the proportional term control of the air-fuel ratio correction coefficient KO2 is performed, and changes as indicated by the broken line in FIG.
[0039]
FIG. 6 is a flowchart of the abnormality determination parameter KO2AVE comparison / update process in step S7 of FIG.
[0040]
In step S41, it is determined whether or not the integral value KAV is larger than a value obtained by adding an aging change determination deviation ΔKO2AVE (for example, 0.0078) to the abnormality determination parameter KO2AVE, and when KAV> KO2AVE + ΔKO2AVE is satisfied, the following equation is satisfied. The KO2AVE value is updated (step S43).
[0041]
KO2AVE = KO2AVE + ΔKO2AVE / 2 (3)
When KAV ≦ KO2AVE + ΔKO2AVE is established, it is determined whether or not the integral value KAV is smaller than the value obtained by subtracting the deviation ΔKO2AVE from the KO2AVE value (step S42). When KAV ≧ KO2AVE−ΔKO2AVE is established, this processing is immediately performed. finish. When KAV <KO2AVE−ΔKO2AVE is established, the KO2AVE value is updated by the following equation (step S44).
[0042]
KO2AVE = KO2AVE−ΔKO2AVE / 2 (4)
According to this process, if the KAV value is within the range of KO2AVE ± ΔKO2AVE, the previous value of the KO2AVE value is maintained as it is, and if it falls outside this range, the KO2AVE value is updated by the above formula (3) or (4). (See FIG. 8 (b)).
[0043]
FIG. 7 is a flowchart of the KO2AVE level check process in step S8 of FIG.
[0044]
In step S51, it is determined whether or not the abnormality determination parameter KO2AVE is larger than the deterioration determination upper limit value KO2AVEFSH (for example, 1.25). If KO2AVE> KO2AVESHSH is satisfied, the KO2AVE value is further increased to the upper limit value KO2AVEFSHLMT (for example, 1.254) It is determined whether it is larger (step S58).
[0045]
As a result, when KO2AVE ≦ KO2AVEFSHLMT is established, the process immediately proceeds to step S62, in which it is determined that there is an abnormality in the fuel supply system, the abnormality detection flag FFSD45 is set to “1” to indicate that abnormality, and the abnormality detection process ends. Is set to “1” (step S63), and the process is terminated.
[0046]
If KO2AVE> KO2AVEFSHLMT is established, the KO2AVE value is set to the limit value KO2AVEFSHLMT, and the process proceeds to step S62.
[0047]
If KO2AVE ≦ KO2AVEFSH is satisfied in step S51, the process proceeds to step S52, and it is determined whether or not the KO2AVE value is smaller than the predetermined purge lower limit value KO2AVEPGL (FIG. 3, step S19).
[0048]
As a result, when KO2AVE ≧ KO2AVEPGL is established, the routine proceeds to step S53, where it is determined whether or not the forced purge cut is performed at the time of the current monitoring (when the abnormality determination process is executed). The fuel supply system is determined to be normal, the abnormality determination flag FFSD45 is set to “0”, and the process proceeds to step S63. On the other hand, when the forced purge cut has been performed, the abnormality determination is stopped until the ignition switch is turned off (step S54), and the process proceeds to step S57.
[0049]
If KO2AVE <KO2AVEPGL is satisfied in step S52, the forced purge cut is performed at the next monitoring (step S55), and whether or not the KO2AVE value is smaller than the deterioration determination lower limit value KO2AVEFSL (for example, 0.83) is determined. A determination is made (step S56). As a result, when KO2AVE ≧ KO2AVEFSL is satisfied, it is determined that the fuel supply system is normal, and the process proceeds to step S57.
[0050]
When KO2AVE <KO2AVEFSL is satisfied in step S56, it is further determined whether or not the KO2AVE value is smaller than the lower limit KO2AVEFSLLMT (for example, 0.824) (step S60). As a result, when KO2AVE ≧ KO2AVEFSLLMT is established, the process immediately proceeds to step S62, whereas when KO2AVE <KO2AVEFSLLMT is established, the KO2AVE value is set to the limit value KO2AVEFSLLMT and the process proceeds to step S62.
[0051]
According to this process, if the abnormality determination parameter KO2AVE is outside the range of the deterioration determination upper and lower limit values KO2AVEFSH, KO2AVEFSL, it is determined that the fuel supply system is abnormal (steps S51, S56, S62). Further, at the time of the abnormality, the KO2AVE value is held within the range determined by the upper limit value KO2AVEFSHLMT and the lower limit value KO2AVEFSLLMT by steps S58, S59 or steps S60, S61. Immediately, it can be determined that the system is normal.
[0052]
That is, in the conventional determination method, for example, as shown in FIG. 9A, the abnormality determination parameter KO2AVE decreases after an abnormality determination (in the case of an abnormality that causes excessive fuel supply), and the system returns to a normal state. Even in this case, it took a long time to determine that it is normal. However, according to the present embodiment, as shown in FIG. 5B, after the abnormality determination, the KO2AVE value is held in the lower limit value KO2AVEFSLLMT. If the system returns to the normal state, it can be immediately determined that the system is normal.
[0053]
Note that the magnitude relationship among the upper and lower limit values KO2AVEFSH, KO2AVEFSL, the upper and lower limit values KO2AVEFSHLMT, KO2AVEFSLLMT, and the predetermined purge lower limit value KO2AVEPGL for deterioration determination is set as shown in FIG.
[0054]
Moreover, the purge confirmation process in step S9 of FIG. 2 is the process shown in FIG. 4 described above.
[0055]
【The invention's effect】
As described above in detail, according to the present invention, the average value of the air-fuel ratio correction coefficient is greater than the upper limit value for deterioration determination, and when the fuel supply system is determined to be abnormal, the average value is equal to or greater than the upper limit value for deterioration determination. When the value becomes larger than the upper limit value having the above value, the average value is held at the upper limit value, or the average value of the air-fuel ratio correction coefficient becomes smaller than the lower limit value for deterioration determination, and the fuel supply system is abnormal. When the average value becomes smaller than the lower limit value having a value equal to or lower than the lower limit value for deterioration determination when the determination is made, the average value is held at the lower limit value. When returning to, it is possible to quickly detect that it is normal.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an overall configuration of a fuel supply system abnormality determination process;
FIG. 3 is a flowchart of processing for performing precondition determination for abnormality determination processing;
FIG. 4 is a flowchart of a purge confirmation process.
FIG. 5 is a flowchart of processing for calculating an integral value KAV.
FIG. 6 is a flowchart of an abnormality determination parameter KO2AVE comparison / update process.
FIG. 7 is a flowchart of a level check process for an abnormality determination parameter KO2AVE.
FIG. 8 is a diagram for explaining the transition of the integral value KAV and the update of the abnormality determination parameter KO2AVE.
FIG. 9 is a diagram illustrating a transition of an abnormality determination parameter KO2AVE.
10 is a diagram showing the magnitude relationship of reference values used in the processing of FIG.
[Explanation of symbols]
1 Internal combustion engine 5 Electronic control unit (ECU)
6 Fuel injection valve 18L, 18R O ₂ sensor

Claims (1)

An exhaust gas concentration detection means provided in the exhaust system of the internal combustion engine and an air-fuel ratio correction coefficient for correcting the amount of fuel supplied to the engine based on the output of the exhaust gas concentration detection means so as to obtain a predetermined air-fuel ratio An air-fuel ratio correction coefficient calculating means, an operating state detecting means for calculating the operating state of the engine, and an average of the air-fuel ratio correction coefficient when the operating state detecting means detects that the engine is in a predetermined operating state. An average value calculating means for calculating a value;
An internal combustion engine having abnormality determination means for determining that the fuel supply system of the engine is abnormal when the average value deviates from a range indicating a normal determination region from an upper limit value for deterioration determination to a lower limit value for deterioration determination. In the fuel supply system abnormality detection device,
When the average value is larger than the upper limit value of the average value has said deterioration determination upper limit or a value at the time it is determined that the larger abnormally than the deterioration determination upper limit by the abnormality determining means, the means for holding the average value to the upper limit value, or the average value of the average value is less than the degradation determination lower limit value at the time it is determined that the abnormality becomes smaller than the deterioration determination for the lower limit value by the abnormality determining unit when it becomes smaller than the lower limit value having a value, the fuel supply system abnormality detecting device for an internal combustion engine, characterized in that the average value provided with at least one means for retaining the lower limit value .

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