JPH0625554B2 - Abnormality diagnosis device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality diagnosis device for an internal combustion engine, and more particularly, to a fuel provided in each cylinder by feedback-controlling an air-fuel ratio by an air-fuel ratio sensor provided in an exhaust passage. The present invention relates to an abnormality diagnosis device for an internal combustion engine that injects fuel with an injection valve.

2. Description of the Related Art A multi-cylinder internal combustion engine equipped with an air-fuel ratio feedback type electronically controlled fuel injection device calculates the basic injection amount of a fuel injection valve according to the intake air amount and the number of revolutions to calculate the oxygen concentration in the exhaust gas of the engine. The basic injection amount is corrected according to the air-fuel ratio correction amount calculated on the basis of the detection signal. In such a fuel injection device, the injection amount is controlled by the valve opening time of the fuel injection valve, and the valve opening time is determined by the energization time to the fuel injection valve.

In the fuel injection device as described above, mainly at least one fuel injection valve is collectively arranged in the intake passage portion before the gathering portion of the intake manifold to reduce the cost, and the fuel injection valve is commonly used for all the cylinders. So-called single point injection (SPI)
There is a system or a cylinder-by-cylinder injection system in which one fuel injection valve is provided for each cylinder and fuel injection is performed simultaneously or independently for each cylinder.

In the fuel injection device of the cylinder-by-cylinder injection system, if any one of the plurality of fuel injection valves has an abnormality such as disconnection or clogging, or a short circuit of the output circuit of the fuel injection valve drive circuit, the injection amount is changed. There has been a problem that the air-fuel ratio deviates from an appropriate amount and the air-fuel ratio changes greatly, the output of the engine greatly decreases and the drivability deteriorates even if the engine does not stop.

Therefore, the applicant of the present invention has proposed an abnormality diagnosing device which detects an abnormality of a fuel injection valve based on an inverted state of feedback of an air-fuel ratio (Japanese Patent Application No. 61-14038).
No. 4).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the conventional abnormality diagnosis device for the internal combustion engine, when the failure of the fuel injection valve is detected by the number of air-fuel ratio feedback reversals within a unit time during idling, the normal idling operation is performed. Since the number of air-fuel ratio feedback inversions differs between the time of idling and the idle-up operation, for example, if the diagnosis is made with the same reference determination value of the number of air-fuel ratio feedback inversions when the air conditioner is on and when it is off, there is a risk of erroneous determination.

That is, when the air conditioner is turned on, the load on the engine increases, and the exhaust gas flow rate increases due to idle-up, and the inversion cycle of air-fuel ratio feedback becomes faster.
When the engine is diagnosed in the same air-fuel ratio feedback inversion cycle when the air conditioner is turned on and off as in the conventional case, it is determined that an abnormality occurs even though no abnormality actually occurs.
A so-called erroneous determination may be made.

The present invention has been made to solve such a problem, and an object thereof is to appropriately diagnose a fuel injection valve regardless of whether an external load is applied to the engine during idle operation.

Means for Solving the Problems In order to achieve the above object, an abnormality diagnosis device for an internal combustion engine according to the present invention includes an air-fuel ratio detection means installed in an exhaust passage of the internal combustion engine including a fuel injection valve for each cylinder. , An air-fuel ratio feedback means for performing feedback control of the air-fuel ratio by the output of the air-fuel ratio detection means, an idle detection means for detecting an idle operation state of the internal combustion engine, and a frequency detection means for detecting an air-fuel ratio feedback frequency in the idle operation state A comparing means for comparing the detected frequency with a reference setting value and outputting an abnormal signal when the frequency is larger than the reference setting value; and a reference value setting means for switching the reference setting value to a large value when the load on the engine increases. It is characterized in that the occurrence of the abnormality signal is judged as an abnormality of the engine fuel injection valve.

Effect According to the present invention, when the load applied to the engine is increased, the reference set value of the number of reversals of the air-fuel ratio detection means for detecting the failure of the fuel injection valve is switched to a value larger than the normal time, The failure of the fuel injection valve can be accurately detected according to the load applied to the engine.

Embodiment An embodiment of the present invention will be described with reference to the drawings.

FIG. 2 shows an embodiment of an internal combustion engine to which the present invention is applied. In FIG. 2, an air flow meter 3, a throttle valve 12, and a fuel injection valve 7 are provided in the intake passage 2 of the engine body 1 in this order from the upstream side of the intake passage 2.

The air flow meter 3 directly measures the intake air amount Q, and a built-in potentiometer generates an output signal of an analog voltage proportional to the intake air amount. This output signal is the A / D with built-in multiplexer of the control circuit 10.
It is supplied to the converter 101.

The throttle valve 12 is closed during idle operation, and the opening degree increases as the engine load increases. The throttle valve 12 has a built-in potentiometer 13,
A voltage proportional to the opening degree of the throttle valve 12 is output, and an idle switch 14 for detecting the full closing of the throttle valve 12 is provided. The potentiometer 13 is connected to the A / D converter 101, and the idle switch 14 is connected to the input / output interface 102. The fuel injection valve 7 is provided for each cylinder and opens when energized to supply pressurized fuel to the intake port.

Further, an analog voltage proportional to the engine water temperature THW is generated by the water temperature sensor 11 attached to the cylinder block of the engine and is supplied to the A / D converter 101. The distributor 4 includes, for example, a crank angle sensor 5 whose axis is converted into a crank angle and which generates a reference position detection pulse signal every 720 °, and a crank angle sensor 5 which is converted into a crank angle of 30.
A crank angle sensor 6 that generates a pulse signal for detecting an angular position is provided for each °. The pulse signals of these crack angle sensors 5 and 6 are supplied to the input / output interface 102 of the control circuit 10, of which the crank angle sensor 6
Is supplied to the interrupt terminal of the CPU 103.

The exhaust passage 8 of the engine is provided with an O ₂ sensor 9 for generating an electric signal according to the oxygen component concentration in the exhaust gas.
The output of the O ₂ sensor 9 is supplied to the input / output interface 102 via the buffer circuit 109 and the comparison circuit 110 of the control circuit 10.

Further, 112 is an engine check lamp provided on an instrument panel or the like of a driver's seat for displaying an abnormality of the fuel injection valve 7 to an occupant of the vehicle. When the fuel injection valve 7 has an abnormality, an abnormality signal is output from the input / output interface 102. When it is output, it is turned on by the drive circuit 111.

The control circuit 10 is configured as, for example, a microcomputer, and includes an A / D converter 101 and an input / output interface 10
2, CPU 103, buffer circuit 109, comparison circuit 11
0, drive circuit 111, ROM 104, RAM 105
Etc. are provided. Further, in the control circuit 10, the down counter 106, the flip-flop 107, and the drive circuit 108 are for controlling the fuel injection valve 7. That is, when the fuel injection amount TAU is calculated, the fuel injection amount TAU is preset in the down counter 106 and also set in the flip-flop 107. As a result, the drive circuit 108 starts energizing the fuel injection valve 7. On the other hand, when the down counter 106 counts a clock signal (not shown) and finally reaches the carry-out terminal “1” level, the flip-flop 107 is reset and the drive circuit 108 energizes the fuel injection valve 7. To stop. That is, the fuel injection valve 7 is the same as the fuel injection amount TAU described above.
Is energized, so that an amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

The CPU 103 generates an interrupt when the A / D conversion of the A / D converter 101 is completed, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6, or the like. Further, the intake air amount data Q and the cooling water temperature data THW of the air flow meter 3 are executed A every predetermined time.
It is fetched by the / D conversion routine and updated and stored in a predetermined area of the RAM 105.

FIG. 3 is a partial circuit diagram of FIG. In FIG.
The buffer circuit 109 includes a capacitor 1091 and a resistor 10.
The comparison circuit 110 includes an operational amplifier 1101 and resistors 1102 and 1103 that generate a comparison voltage VR (= 0.45V). The resistor 1192 is for limiting the maximum level of the output voltage when the element temperature of the O ₂ sensor 9 becomes excessive. As a result, the output of the O ₂ sensor 9 is output to the buffer circuit 1
It is temporarily stored in 09 and is converted into a digital signal by the comparison circuit 110. This digital signal is sent to the input / output interface 102 for air-fuel ratio feedback control. In addition, Vcc is a power supply voltage of the control circuit 10, which is, for example, 5V.

Next, an example of the control procedure of the control circuit 10 of the present invention in FIG. 2 will be described. Before that, the reason why the present invention uses FIGS. 6 and 7 to diagnose the abnormality of the fuel injection valve 7 at idle time. Explain what to do.

6 and 7 show changes in the output waveform of the O ₂ sensor 9 and the air-fuel ratio correction when the fuel injection valve 7 of the first cylinder # 1 of the multi-cylinder engine causes a flow rate decrease of, for example, −20% or more. FIG. 6 is a change waveform of the coefficient FAF, and FIG. 6 shows the idle operation state, and FIG. 7 shows the case of no load and 2000 rpm. When the fuel injection valve of the # 1 cylinder causes a decrease in the flow rate, only the air-fuel mixture of the # 1 cylinder becomes lean, so that the exhaust gas discharged from the # 1 cylinder is always lean.
Since the exhaust gas discharged from the other cylinders is normal, the air-fuel ratio data detected by the air-fuel ratio sensor pulsates according to the lean signal of the # 1 cylinder.

As can be seen from the comparison between FIG. 6 and FIG. 7, this pulsation significantly appears in the output waveform of the O ₂ sensor at the time of idling, but at the time of higher rotation than at idling (2000 rpm in the example).
The pulsation is dampened and does not appear prominently. For the above reason, in the present invention, the abnormality diagnosis of the fuel injection valve is performed during the idle operation.

FIG. 5 shows the output waveform of the O ₂ sensor and the change waveform of the air-fuel ratio correction coefficient FAF when the four-cylinder engine is in normal idle operation when the air conditioner is off.
From this figure, when the engine is not loaded with a load for driving the air conditioner and the normal idle operation is being performed, when the rich / lean determination level is 0.45 V, for example, F
AF feeds back as shown.

However, when the fuel injection valve of the # 1 cylinder causes a flow rate decrease of, for example, −20% or more, the O ₂ sensor outputs a lean signal (a direction in which the voltage decreases) every time the lean exhaust gas from the # 1 cylinder hits. The output waveform of the O ₂ sensor 9 becomes as shown in FIG. 6 because the output waveform becomes a “comb” shape and the number of times of exceeding the judgment level of 0.45 V increases. The number of reversals of the O ₂ sensor in this figure is extremely greater than when the fuel injection valve is operating normally.

Therefore, in the present invention, the number of reversals of the output of the O ₂ sensor at the time of idling, that is, the feedback frequency is measured, and the abnormality of the fuel injection valve is diagnosed when the measured frequency exceeds a predetermined value.

Since the number of air-fuel ratio feedback reversals differs depending on the magnitude of the load on the engine, in the embodiments described below of the present invention, according to the magnitude of the load on the engine, for determining the abnormality of the fuel injection valve. The standard setting value is changed.

FIG. 4 shows the first embodiment of the present invention, and is a flow chart showing a fuel injection valve failure determination routine for determining a failure of the fuel injection valve. This routine is 0.47.
It is executed every 1 second.

In the first step 401, it is determined whether or not the engine is in the idle operation state. If it is not in the idle operation state, the process proceeds to step 418, where the failure determination count value CFAIL for determining the failure of the fuel injection valve is set to 0, and A skip count value CSKIP representing the number of skips of air-fuel ratio feedback is set to 0.

If it is determined in step 401 that the engine is in the idle operation state, the process proceeds to step 402 and the failure determination count value CF
It is determined whether the AIL is 5 / 0.471 or more, and C
If FAIL <5 / 0.471, the routine proceeds to step 403, where the failure determination count value CFAIL is incremented by 1, and this routine is ended.

If CFAIL ≧ 5 / 0.471, step 402
To 404, it is determined whether the air conditioner is off.

If the air conditioner is off, the routine proceeds from step 404 to step 405, and it is determined whether or not CSKIP is 10 or more. If CSKIP ≧ 10, the routine proceeds to step 406, where it is determined that the fuel injection valve has failed, and then step In step 407, the fail flag 1 is set. In step 405,
If CSKIP <10 is determined, the process proceeds to step 408, it is determined whether CSKIP is 3 or less, and CSKIP is determined.
If IP ≦ 3, the process proceeds to step 409, the fuel injection valve is considered to be normal, and then the process proceeds to step 410.
Set the normal flag 2. In step 408, CS
If it is determined that KIP> 3, the process proceeds from step 408 to step 413, and the determination suspension flag 3 is set.

If it is determined that the air conditioner is on, step 404
To step 411, skip count value CSK
It is determined whether the IP is 20 or more. CSK here
IP is a CS executed in the main routine shown in FIG.
With the KIP count-up routine, the air-fuel ratio is reversed from lean to rich or from rich to lean.
It is counted up by one. That is, if the air-fuel ratio was lean last time and is judged to be rich this time,
The process proceeds from step 801 to steps 802 and 804, and C
If SKIP is incremented by 1, and the air-fuel ratio is rich at the previous time and it is determined to be lean this time, the process proceeds from step 801 to steps 803 and 804, and CSKIP is incremented by 1.

If CSKIP ≧ 20, the process proceeds from step 411 to step 406, and it is considered that the fuel injection valve is defective. C
If SKIP <20, the process proceeds from step 411 to step 412 to determine whether or not CSKIP is 6 or less. If CSKIP ≦ 6, the process proceeds to step 409.
It is determined that the fuel injection valve is normal. If CSKIP> 6, the process proceeds from step 412 to step 413, and the judgment suspension flag 3 is set.

Next, at step 414, it is determined whether or not the judgment pending flag 3 is set. If the judgment pending flag 3 is not set, that is, if the fail flag 1 or the normal flag 2 is set, then the routine proceeds to step 415, where The judgment is replaced with the judgment of this time, and conversely, if the judgment suspension flag 3 is set, the process proceeds from step 414 to step 416 and the previous judgment is maintained. Next, at step 417, an injection valve determination signal is generated, and when proceeding to step 418, both CFAIL and CSKIP are set to 0, and this routine is ended.

In the flowchart shown in FIG. 4, when the air conditioner is off, it is determined that the fuel injection valve has failed when the feedback reversal number of the air-fuel ratio, that is, the skip count value CSKIP is 10 times or more, and is normal when the skip count value CSKIP is 3 times or less. This is because the number of air-fuel ratio feedback inversions when the air conditioner is off is almost 3 or less. When the air conditioner is turned on, the number of reversals of the air-fuel ratio feedback increases to 6 to 7, but in this case, there is no difference between the judgment reference value and 10 times when the fuel injection valve fails, and there is a risk of erroneous judgment. When the air conditioner is turned on, it is decided that the number of reversals of the air-fuel ratio feedback is 20 times or more and the fuel injection valve is defective, and 6 times or less that the fuel injection valve is normal. This eliminates erroneous determination when diagnosing a failure of the fuel injection valve regardless of whether the air conditioner is on or off, and ensures a normal operating state of the engine.

In the first embodiment, the failure determination level of the fuel injection valve is switched between when the air conditioner is on and when it is off. However, the present invention may prohibit the determination when the air conditioner is on. Further, the failure diagnosis of the fuel injection valve can be performed by utilizing the air-fuel ratio feedback inversion time itself in addition to the number of times the air-fuel ratio feedback is inverted in 5 seconds.

FIG. 9 shows a second embodiment of the present invention. In this case, the reference value for judging the abnormality of the fuel injection valve is switched depending on whether the shift position of the transmission is in the N range or another range. There is. That is, in FIG. 9, step 500 is step 404 of the flowchart shown in FIG.
Since the other processing routines are the same as those in FIG. 4, the same reference numerals as those shown in FIG. 4 are used.

In the second embodiment, when the transmission shift position is in the N range, that is, when the load on the engine is relatively low, the reference of the air-fuel ratio feedback reversal number, which is the fuel injection valve failure determination reference value, is set to a small value. In the D range, L range, R range, etc. other than the N range, the reference value of the air-fuel ratio feedback inversion number is set to a large value. This is to prevent the erroneous detection of the fuel injection valve fail by setting the determination reference value of the air-fuel ratio feedback corresponding to the load applied to the engine.

In the present invention, when the load applied to the engine is increased, the case where the air conditioner is on and the shift position of the transmission is outside the N range has been described in the first and second embodiments. The present invention can also be applied to the case where the load on the engine is increased by driving the machinery.

EFFECTS OF THE INVENTION As described above, according to the present invention, the determination reference value of the number of times the air-fuel ratio feedback is inverted is switched according to the value of the load applied to the engine. False detection can be reliably prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention, FIG. 2 is a schematic configuration diagram showing an embodiment of an internal combustion engine abnormality diagnosis apparatus to which the present invention is applied, and FIG. 3 is a partial circuit diagram of FIG. FIG. 4 is a flow chart showing a first embodiment of the control procedure of the control circuit of FIG. 2, and FIG. 5 is an output waveform of the O ₂ sensor when the engine is in normal idle operation when the air conditioner is off. And a waveform diagram showing a change waveform of the air-fuel ratio feedback correction coefficient FAF at that time, FIG. 6 is a waveform diagram corresponding to FIG. 5 when one fuel injection valve causes a decrease in flow rate, and FIG. 2000r without load
FIG. 8 is a part of the main routine of the control circuit shown in FIG. 2, showing the output waveform of the oxygen sensor during pm operation and the change waveform of the air-fuel ratio feedback correction coefficient FAF at that time. FIG. 9 is a flowchart showing a skip count value count-up routine at the time of air-fuel ratio feedback performed, and FIG. 9 is a flowchart corresponding to FIG. 4 in the second embodiment of the present invention. 1 ... Engine body, 2 ... Intake passage, 3 ... Air flow meter, 4 ... Distributor, 7 ... Fuel injection valve,
8 ... Exhaust passage, 9 ... O ₂ sensor (air-fuel ratio detecting means), 10 ... Control circuit, 12 ... Throttle valve, 13
...... Potentiometer, 14 ...... Circuit switch, 112
…… Engine check clamp.

Claims (1)

[Claims] 1. An air-fuel ratio detecting means installed in an exhaust passage of an internal combustion engine equipped with a fuel injection valve for each cylinder, and an air-fuel ratio feedback means performing feedback control of an air-fuel ratio by the output of this air-fuel ratio detecting means. Idle detection means for detecting the idle operation state of the internal combustion engine, frequency detection means for detecting the air-fuel ratio feedback frequency in the idle operation state, and comparing the detected frequency with the reference set value, and when it is higher than the reference set value, an abnormal signal And a reference set value switching means for switching the reference set value to a large value when the load applied to the engine is increased. Engine abnormality diagnosis device.