JP3446380B2 - Air-fuel ratio sensor abnormality diagnosis device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality diagnosis device for an air-fuel ratio sensor that linearly increases or decreases the output with respect to the air-fuel ratio of an internal combustion engine.

[0002]

2. Description of the Related Art In recent air-fuel ratio control systems,
An air-fuel ratio sensor (for example, a limiting current type oxygen sensor) that linearly detects the air-fuel ratio according to the oxygen concentration in the exhaust gas is used, and the microcomputer takes in the air-fuel ratio detection result by the sensor and sends it to the internal combustion engine. Control the fuel injection amount. In this case, the microcomputer calculates the air-fuel ratio correction amount based on the air-fuel ratio detection result by the air-fuel ratio sensor, and corrects the fuel injection amount by the air-fuel ratio correction amount. As a result, optimum combustion in the internal combustion engine is realized,
Harmful components (CO, HC, NOx, etc.) in the exhaust gas are reduced.

On the other hand, in the above-mentioned air-fuel ratio control system, if the reliability of the air-fuel ratio detected by the air-fuel ratio sensor is lowered, the control accuracy is significantly deteriorated. There is a demand for technology for this. Therefore, as a conventional technique, for example, Japanese Patent Laid-Open No.
In "Abnormality detection method for oxygen concentration sensor" of Japanese Patent No. 225943, an abnormality diagnosis procedure for detecting an abnormality in a connection system according to an applied voltage and a detected current is disclosed with respect to a limiting current type oxygen concentration sensor.

[0004]

However, in the above-mentioned prior art, although an abnormality in the circuit configuration such as a disconnection or a short circuit of the connection system can be detected, when the air-fuel ratio sensor is deteriorated, the abnormality is caused. Unable to detect the symptoms of.
That is, it was not possible to judge the authenticity of the air-fuel ratio detected by the air-fuel ratio sensor (whether the sensor output is normal or not), that is, the reliability of the sensor output.

The present invention has been made by paying attention to the above-mentioned conventional problems, and an object thereof is to accurately diagnose an abnormality of an air-fuel ratio sensor, and by extension use an air-fuel ratio using a detection result of the air-fuel ratio sensor. An object of the present invention is to provide an abnormality diagnosis device for an air-fuel ratio sensor that can contribute to improvement of control accuracy of a control system.

[0006]

In order to achieve the above object, the invention described in claim 1 is, as shown in FIG.
An air-fuel ratio sensor M2 that linearly increases or decreases the output with respect to the air-fuel ratio of the internal combustion engine M1, fuel supply means M3 for supplying fuel to the internal combustion engine M1, and basic fuel supply according to the engine speed and engine load. A basic fuel amount calculating means M4 for calculating an amount, an air-fuel ratio correction amount setting means M5 for setting an air-fuel ratio correction amount according to a deviation between an air-fuel ratio detected by the air-fuel ratio sensor M2 and a target air-fuel ratio, and Air-fuel ratio control for controlling the fuel supply amount by the fuel supply means M3 based on the basic fuel supply amount calculated by the basic fuel amount calculation means M4 and the air-fuel ratio correction amount set by the air-fuel ratio correction amount setting means M5 Which is applied to an air-fuel ratio control system including a means M6 and the basic fuel amount calculation means M4.
Fuel correction determination means M7 for determining that there is a correction command for the basic fuel supply amount calculated by the above, which exceeds a predetermined amount due to a change in engine operating conditions, and the effect of fuel correction by the fuel correction determination means M7. If is determined,
Sensor abnormality diagnosis means M8 for diagnosing an abnormality of the air-fuel ratio sensor M2 according to the behavior of the air-fuel ratio detected by the air-fuel ratio sensor M2 or the air-fuel ratio correction amount set by the air-fuel ratio correction amount setting means M5. The main point is to provide.

Further, a air-fuel ratio control system having a target air-fuel ratio setting means for setting a target air-fuel ratio according to the engine operating condition, the fuel correction determining means M7 is set by the target air-fuel ratio setting means The sensor abnormality diagnosing means M8 has means for determining the presence or absence of a correction command from the target air-fuel ratio change quantity, and the sensor abnormality diagnosis means M8 changes the air-fuel ratio correction quantity set by the air-fuel ratio correction quantity setting means M5 and the target. It has means for diagnosing an abnormality of the air-fuel ratio sensor M2 based on the result of comparison with the amount of change in the target air-fuel ratio set by the air-fuel ratio setting means.

In the invention described in claim 2 , the internal combustion engine M1
Air-fuel ratio sensor that increases or decreases the output linearly with respect to the air-fuel ratio of
Fuel for supplying fuel to the internal combustion engine M1.
Charge supply means M3 and a base according to the engine speed and engine load
A basic fuel amount calculating means M4 for calculating the main fuel supply amount;
The air-fuel ratio detected by the air-fuel ratio sensor M2 and the target air-fuel ratio
Air-fuel ratio correction that sets the air-fuel ratio correction amount according to the deviation from the ratio
The amount setting means M5 and the basic fuel amount calculating means M4
Calculated basic fuel supply amount and the air-fuel ratio correction amount setting means
Based on the air-fuel ratio correction amount set by M5,
Air-fuel ratio control for controlling the amount of fuel supplied by the fuel supply means M3
Applied to an air-fuel ratio control system including means M6
Therefore, it is calculated by the basic fuel amount calculation means M4.
The basic fuel supply amount
Fuel that determines that there is a correction command that exceeds a predetermined amount
The correction determination means M7 and the fuel correction determination means M7
If fuel correction is determined, the air-fuel ratio
Air-fuel ratio detected by the sensor M2, or the air-fuel ratio correction
The behavior of the air-fuel ratio correction amount set by the amount setting means M5
According to the sensor difference for diagnosing the abnormality of the air-fuel ratio sensor M2,
A fuel amount correction unit that includes a normal diagnosis unit M8 and executes an increase or decrease correction according to the operating condition of the internal combustion engine M1, and the basic fuel amount calculation unit M4 calculates the fuel amount when the fuel amount correction unit corrects the fuel. An air-fuel ratio control system for calculating all correction amounts for the supplied basic fuel supply amount, wherein the fuel correction determination means M7 executes the increase or decrease correction by the fuel amount correction means. If there is a correction command, the sensor abnormality diagnosing means M8 changes the total correction amount calculated by the total correction amount calculating means and the air-fuel ratio detected by the air-fuel ratio sensor M2. The abnormality of the air-fuel ratio sensor M2 is diagnosed based on the result of comparison with the amount.

[0009]

[0010]

According to the invention described in claim 1, in the air-fuel ratio control system shown in FIG. 16, the basic fuel amount calculation means M4 is used.
Calculates the basic fuel supply amount according to the engine speed and the engine load. The air-fuel ratio correction amount setting means M5 sets the air-fuel ratio correction amount according to the deviation between the air-fuel ratio detected by the air-fuel ratio sensor M2 and the target air-fuel ratio. The air-fuel ratio control means M6 is
The fuel supply amount by the fuel supply unit M3 is controlled based on the basic fuel supply amount calculated by the basic fuel amount calculation unit M4 and the air-fuel ratio correction amount set by the air-fuel ratio correction amount setting unit M5.

Further, the fuel correction determination means M7 determines that there is a correction command for the basic fuel supply amount calculated by the basic fuel amount calculation means M4 that exceeds a predetermined amount due to a change in engine operating conditions. . The sensor abnormality diagnosis means M8 is
When the fuel correction determination unit M7 determines that the fuel correction is to be performed, the air-fuel ratio detected by the air-fuel ratio sensor M2 or the air-fuel ratio correction amount set by the air-fuel ratio correction amount setting unit M5 The abnormality of the fuel ratio sensor M2 is diagnosed.

In short, if the basic fuel supply amount is increased and corrected in accordance with changes in engine operating conditions, the air-fuel ratio shifts to the rich side, and if the basic fuel supply amount is corrected to decrease, the air-fuel ratio shifts to the lean side. In this case, if the air-fuel ratio sensor M2 is normal, the behavior of the output signal or the air-fuel ratio correction amount calculated from the output signal should properly reflect the fuel correction, but if this is not done, the sensor malfunctions. It is determined that As a result, according to the above configuration, highly accurate and easy sensor abnormality diagnosis is realized.

Further, the target air-fuel ratio setting means sets the target air-fuel ratio according to the engine operating condition. Fuel correction determination means M7
Determines the presence or absence of a correction command from the amount of change in the target air-fuel ratio set by the target air-fuel ratio setting means. Further, the sensor abnormality diagnosing means M8 determines whether the change amount of the air-fuel ratio correction amount set by the air-fuel ratio correction amount setting means M5 is equal to the change amount of the target air-fuel ratio set by the target air-fuel ratio setting means. The abnormality of the fuel ratio sensor M2 is diagnosed.

That is, since the air-fuel ratio correction amount is set so that the actual air-fuel ratio matches the target air-fuel ratio, it changes corresponding to the amount of change in the target air-fuel ratio. In this case, if the air-fuel ratio sensor M2 is normal, a sensor output corresponding to a change in the target air-fuel ratio (an output that matches the actual air-fuel ratio) is obtained, and an appropriate air-fuel ratio correction for realizing the target air-fuel ratio is obtained. The amount is set. On the other hand, the air-fuel ratio sensor M
If 2 is abnormal, the sensor output corresponding to the change in the target air-fuel ratio cannot be obtained, and an appropriate amount of air-fuel ratio correction amount cannot be obtained. In this case, it is determined that the sensor is abnormal. As described above, according to the above configuration, the sensor abnormality is accurately and easily diagnosed.

According to the second aspect of the present invention, the fuel amount correction means executes the increase or decrease correction according to the operating conditions of the internal combustion engine M1. The total correction amount calculation means calculates all correction amounts (total correction amounts) with respect to the basic fuel supply amount calculated by the basic fuel amount calculation means M4 when the fuel correction is performed by the fuel amount correction means. The fuel correction determination means M7 determines that there is a correction command when the fuel amount correction means has performed the increase or decrease correction. Sensor abnormality diagnosis means M
Reference numeral 8 diagnoses an abnormality of the air-fuel ratio sensor M2 based on the result of comparison between the total correction amount calculated by the total correction amount calculation means and the change amount of the air-fuel ratio detected by the air-fuel ratio sensor M2.

That is, if the air-fuel ratio sensor M2 is normal, the sensor output fluctuates depending on whether the total correction amount with respect to the basic fuel supply amount is the increase side or the decrease side. On the other hand, if the air-fuel ratio sensor M2 is abnormal, the sensor output corresponding to all the correction amounts cannot be obtained, and it is determined that the sensor is abnormal. As described above, according to the above configuration, the sensor abnormality is accurately and easily diagnosed. More specifically, the water temperature increase correction and the high load increase correction are performed at the time of engine startup or high load operation. Further, generally, the air-fuel ratio feedback is stopped and the air-fuel ratio is open-controlled. In this case, all correction amounts with respect to the basic fuel supply amount are set on the increasing side, and abnormality diagnosis is performed depending on whether a sensor output corresponding to this increasing correction is obtained. Note that, for example, when the air-fuel ratio feedback is continued during the increase correction, the air-fuel ratio correction amount is set to the decrease side in opposition to the increase correction, and all these correction amounts (increase correction amount + air-fuel ratio correction amount) The abnormality is diagnosed based on the comparison result between the sensor output and the sensor output.

[0017]

[0018]

【Example】

(First Embodiment) A first embodiment in which the present invention is embodied in an air-fuel ratio control system for an internal combustion engine will be described below.

FIG. 1 is a schematic configuration diagram of an internal combustion engine provided with an air-fuel ratio control device for the internal combustion engine and peripheral equipment thereof according to the present embodiment. As shown in FIG. 1, the internal combustion engine 1 has four cylinders 4
It is configured as a cycle spark ignition type. The intake air passes through the air cleaner 2, the intake pipe 3, the throttle valve 4, the surge tank 5 and the intake manifold 6 from the upstream side, and is mixed with the fuel injected from each fuel injection valve 7 in the intake manifold 6 to a predetermined empty space. It is supplied to each cylinder as a fuel-air mixture. In this example,
The fuel injection valve 7 corresponds to the fuel supply means.

Further, the high voltage supplied from the ignition circuit 9 is distributed and supplied by the distributor 10 to the spark plug 8 provided in each cylinder of the internal combustion engine 1, and the spark plug 8
Ignites the air-fuel mixture in each cylinder at a predetermined timing. The exhaust gas after combustion is exhaust manifold 1
1 and the exhaust pipe 12, the three-way catalyst 13 provided in the exhaust pipe 12 purifies harmful components (CO, HC, NOx, etc.) and discharges them to the atmosphere.

The intake pipe 3 is provided with an intake temperature sensor 21 and an intake pressure sensor 22. The intake temperature sensor 21 indicates the temperature of intake air (intake temperature Tam), and the intake pressure sensor 22 is on the downstream side of the throttle valve 4. Intake air pressure (intake pressure PM)
Respectively detected. Further, the throttle valve 4 is provided with a throttle sensor 23 for detecting the opening of the valve 4 (throttle opening TH). The throttle sensor 23 outputs an analog signal corresponding to the throttle opening TH. , And outputs a detection signal indicating that the throttle valve 4 is substantially fully closed. A water temperature sensor 24 is provided in the cylinder block of the internal combustion engine 1, and the water temperature sensor 24 measures the temperature of the cooling water in the internal combustion engine 1 (cooling water temperature Th.
w) is detected. The distributor 10 is provided with a rotation speed sensor 25 for detecting the rotation speed of the internal combustion engine 1 (engine rotation speed Ne), and this rotation speed sensor 25 is for every two rotations of the internal combustion engine 1, that is, for every 720 ° CA. 24 at intervals
Output pulse signals.

Further, on the upstream side of the three-way catalyst 13 of the exhaust pipe 12, a wide range and linear air-fuel ratio signal is output in proportion to the oxygen concentration of the exhaust gas discharged from the internal combustion engine 1. Type A / F sensor 26 consisting of oxygen sensor
(Air-fuel ratio sensor) is provided. Also, three-way catalyst 1
A downstream O ₂ sensor 27 that outputs a voltage VOX2 depending on whether the air-fuel ratio λ is rich or lean with respect to the stoichiometric air-fuel ratio (λ = 1) is provided on the downstream side of 3. In this embodiment, the air-fuel ratio is represented by “λ” indicating the excess air ratio, and the theoretical air-fuel ratio (= 14.7) is described as the air-fuel ratio λ = 1.

FIG. 2 is a sectional view showing the outline of the A / F sensor 26. In FIG. 2, the A / F sensor 26 is provided so as to project toward the inside of the exhaust pipe 12, and the sensor 26 is roughly divided into a cover 31, a sensor body 32, and a heater 33. The cover 31 has a U-shaped cross section, and a large number of small holes 31 a that communicate the inside and outside of the cover are formed on the peripheral wall of the cover 31.
The sensor body 32 is configured such that the oxygen concentration in the lean air-fuel ratio region or the carbon monoxide (C
O) Generate a limiting current corresponding to the concentration.

The structure of the sensor body 32 will be described in detail.
In the sensor body 32, an exhaust gas side electrode layer 36 is fixed to the outer surface of a solid electrolyte layer 34 formed in a cup-shaped cross section, and an atmosphere side electrode layer 37 is fixed to the inner surface. A diffusion resistance layer 35 is formed on the outside of the exhaust gas side electrode layer 36 by a plasma spraying method or the like. The solid electrolyte layer 34 is made of ZrO ₂ , HfO ₂ , ThO ₂ , Bi.
CaO in ₂ O ₃ and the like, made of MgO, Y ₂ O _3, Yb ₂ O ₃ oxygen ion conductive oxide is dissolved as a stabilizer and the like sintered body, the diffusion resistance layer 35 is alumina, magnesia,
Consists of heat-resistant inorganic substances such as silica stone, spinel, and mullite. Both the exhaust gas side electrode layer 36 and the atmosphere side electrode layer 37 are made of a noble metal having a high catalytic activity such as platinum, and the surfaces thereof are subjected to porous chemical plating or the like. The area and thickness of the exhaust gas side electrode layer 36 are 10 to 100 mm ²
And 0.5 to 2.0 μm, while the area and thickness of the atmosphere-side electrode layer 37 are 10 mm ² or more and 0.5 to 2.0 μm.

The heater 33 is housed in the atmosphere-side electrode layer 37, and the heat generated by the heater 33 causes the sensor body 32 to be heated.
(Atmosphere side electrode layer 37, solid electrode material layer 34, exhaust gas side electrode layer 36, and diffusion resistance layer 35) are heated. Heater 33
Has a sufficient heat generation capacity to activate the sensor body 32.

In the A / F sensor 26 having the above structure, the sensor main body 32 generates a concentration electromotive force at the stoichiometric air-fuel ratio point,
A limiting current corresponding to the oxygen concentration in the lean region is generated from the theoretical air-fuel ratio point. In this case, the limiting current corresponding to the oxygen concentration is determined by the area of the exhaust gas side electrode layer 36, the thickness of the diffusion resistance layer 35, the porosity and the average pore diameter. Further, the sensor body 32 can detect the oxygen concentration with a linear characteristic, but about 65% is required to activate the sensor body 32.
A high temperature of 0 ° C or higher is required, and the sensor body 3
Since the active temperature range of 2 is narrow, the active region cannot be controlled by heating only the exhaust gas of the engine 1. for that reason,
In this embodiment, the heater 33 is controlled by the ECU 41, which will be described later, to keep the sensor body 32 at a predetermined temperature. In a region richer than the stoichiometric air-fuel ratio, the concentration of carbon monoxide (CO), which is unburned gas, changes almost linearly with respect to the air-fuel ratio, and the sensor body 32 changes the limiting current according to the CO concentration. Occur.

The voltage-current characteristics of the sensor body 32 will be described with reference to FIG. As shown in FIG. 3, the current-voltage characteristics are the inflow current to the solid electrolyte layer 34 of the sensor main body 32 that is proportional to the detected oxygen concentration (air-fuel ratio) of the A / F sensor 26, and the application to the solid electrolyte layer 34. It shows that the relationship with the voltage is linear. The temperature of the sensor body 32 is T =
When it is in the active state at T1, it shows a stable state with the characteristic line L1 as shown by the solid line in FIG. In such cases,
The straight line portion of the characteristic line L1 parallel to the voltage axis V is the sensor body 3
A limiting current of 2 is specified. The increase / decrease in the limit current corresponds to the increase / decrease in the air-fuel ratio (that is, lean / rich). The limit current increases as the air-fuel ratio becomes leaner, and the limit current decreases as the air-fuel ratio becomes richer.

In this voltage-current characteristic, a voltage region smaller than a straight line portion parallel to the voltage axis V is a resistance governing region, and the slope of the characteristic line L1 in the resistance governing region is the solid state in the sensor body 32. It is specified by the internal resistance of the electrolyte layer 34. Since the internal resistance of the solid electrolyte layer 34 changes with a change in temperature, when the temperature of the sensor body 32 is lowered, the inclination is reduced due to an increase in resistance. That is, when the temperature T of the sensor body 32 is at T2 lower than T1, the current-voltage characteristic is specified by the characteristic line L2 as shown by the broken line in FIG. In such a case, the straight line portion of the characteristic line L2 parallel to the voltage axis V specifies the limiting current of the sensor body 32 at T = T2, and this limiting current substantially matches the limiting current according to the characteristic line L1.

When a positive applied voltage Vpos is applied to the solid electrolyte layer 34 of the sensor body 32 on the characteristic line L1, the current flowing through the sensor body 32 becomes the limiting current Ipos (see point Pa in FIG. 3). Further, if a negative applied voltage Vneg is applied to the solid electrolyte layer 34 of the sensor body 32, the current flowing through the sensor body 32 does not depend on the oxygen concentration and becomes a negative temperature current Ineg proportional to only the temperature (FIG. 3). Point P
b)).

An electronic control unit (hereinafter referred to as ECU) 41 for controlling the operation of the internal combustion engine 1 shown in FIG.
(Central processing unit) 42, ROM (Read only memory)
43, a RAM (random access memory) 44, a backup RAM 45, and the like, which is configured as a logical operation circuit and which inputs a detection signal of each sensor.
Also, it is connected via a bus 48 to an output port 47 or the like that outputs a control signal to each actuator. Then, the ECU 41 receives the intake air temperature Tam, the intake pressure PM, the throttle opening TH from the respective sensors via the input port 46,
The cooling water temperature Thw, the engine speed Ne, the air-fuel ratio signal, etc. are input, the control signals such as the fuel injection amount TAU, the ignition timing Ig, etc. are calculated based on the respective values, and the control signals are output port 47. Via fuel injection valve 7 and ignition circuit 9
Etc. are output respectively. Further, the ECU 41 executes a sensor abnormality diagnosis process described later to diagnose the presence / absence of abnormality of the A / F sensor 26, and when there is an abnormality, the warning lamp 49 is turned on to warn the driver of the occurrence of abnormality. In the present embodiment, the ECU 4
The CPU 42 in 1 constitutes a basic fuel amount calculation means, an air-fuel ratio correction amount setting means, an air-fuel ratio control means, a fuel correction determination means, a sensor abnormality diagnosis means, and a target air-fuel ratio setting means.

Next, in the above-mentioned fuel injection control system, a method designed in advance for controlling the air-fuel ratio will be sequentially described. The following design method is disclosed in Japanese Patent Laid-Open No. 1-110853.

(1) Modeling of Controlled Object In this embodiment, an autoregressive moving average model of order 1 having a dead time P = 3 is used as a model of a system for controlling the air-fuel ratio λ of the internal combustion engine 1, and further disturbance is performed. It is approximated considering d.

First, the model of the system for controlling the air-fuel ratio λ using the autoregressive moving average model can be approximated by the following formula 1.

[0034]

[Equation 1]

However, in this equation 1, the code FAF
Represents an air-fuel ratio correction coefficient. The symbols a and b represent model constants for determining the responsiveness of the model. The symbol k represents a variable indicating the number of times of control from the start of the first sampling.

Further, considering the disturbance d, the model of the control system can be approximated by the following equation 2.

[0037]

[Equation 2]

For the model approximated as above, the model constants a and b are determined by discretizing the rotation period (360 ° CA) sampling using the step response, that is, the transmission of the system that controls the air-fuel ratio λ. It is easy to find the function G.

(2) Display method of state variable quantity X (however,
X is a vector quantity) The above-mentioned formula 2 is changed into the state variable quantity X (k) = [X1 (k), X
When rewritten using 2 (k), X3 (k), X4 (k)] ^T , the determinant as Equation 3 is obtained, and further Equation 4 is obtained. Here, the symbol T indicates a transposed matrix.

[0040]

[Equation 3]

[0041]

[Equation 4]

(3) Design of Regulator When the regulator is designed based on the above equations 3 and 4, the air-fuel ratio correction coefficient FAF has the optimum feedback gain K = [K1, K2, K3, K4] and the state variable amount X. ^T
(K) = [λ (k), FAF (k−3), FAF (k−)
2), FAF (k-1)], and can be expressed as Equation 5.

[0043]

[Equation 5]

Further, in the equation 5, when the integral term ZI (k) for absorbing the error is added, the air-fuel ratio correction coefficient FAF is given by the following equation 6.

[0045]

[Equation 6]

The integral term ZI (k) is a value determined by the deviation between the target air-fuel ratio λTG and the actual air-fuel ratio λ (k) and the integration constant Ka, and is given by the following equation 7. .

[0047]

[Equation 7]

FIG. 4 shows a block diagram of the air-fuel ratio λ control system for which the model is designed as described above. In FIG. 4, the air-fuel ratio correction coefficient FAF (k) is FA
It is described by using the Z ⁻¹ transformation to derive it from F (k−1), which is the past air-fuel ratio correction coefficient FAF (k−1).
Is stored in the RAM 44, and is read and used at the next control timing. Incidentally, "FAF (k-1)" represents the air-fuel ratio correction coefficient of one time before, and "FAF (k-2)"
Represents the air-fuel ratio correction coefficient two times before, and "FAF (k-
3) ”represents the air-fuel ratio correction coefficient three times before.

Further, in FIG. 4, the block P1 surrounded by the chain double-dashed line is in a state where the air-fuel ratio λ (k) is feedback-controlled to the target air-fuel ratio λTG, and the state variable amount X
(K) is a part that determines, and the block P2 is an integral term Z.
I (k) is a part (accumulation part) to be obtained, and the block P3 is the state variable quantity X determined by the block P1.
This is a part for calculating the current air-fuel ratio correction coefficient FAF (k) from (k) and the integral term ZI (k) obtained in the block P2.

(4) Determination of the optimum feedback gain K and the integration constant Ka The optimum feedback gain K and the integration constant Ka can be set, for example, by minimizing the evaluation function J shown in the following formula 8.

[0051]

[Equation 8]

However, in this equation 8, the evaluation function J
Restricts the movement of the air-fuel ratio correction coefficient FAF (k),
This is intended to minimize the deviation between the air-fuel ratio λ (k) and the target air-fuel ratio λTG. Also, the air-fuel ratio correction factor FA
The weighting of the constraint on F (k) can be changed by the values of the weighting parameters Q and R. Therefore, it is only necessary to change the values of the weighting parameters Q and R and repeat the simulation until the optimum control characteristics are obtained to determine the optimum feedback gain K and the integration constant Ka.

Further, the optimum feedback gain K and the integration constant Ka depend on the above model constants a and b. Therefore, system stability (robustness) against fluctuations (parameter fluctuations) of the system that controls the actual air-fuel ratio λ
In order to guarantee the above, it is necessary to set the optimum feedback gain K and the integration constant Ka in consideration of the variation of these model constants a and b. Therefore, the simulation is performed in consideration of the variations that may actually occur in the model constants a and b, and the optimum feedback gain K and the integration constant Ka that satisfy the stability are determined.

Above, (1) modeling of the controlled object,
Although (2) the display method of the state variable amount, (3) the design of the regulator, and (4) the determination of the optimum feedback gain and the integration constant have been described, all of them have already been set in the apparatus of the embodiment. And And the ECU
In 41, it is assumed that the air-fuel ratio control in the fuel injection control system is executed using only the equations 6 and 7.

Next, the operation of the air-fuel ratio control device of the present embodiment having the above-mentioned structure will be described. FIG. 5 shows an ECU
3 is a flowchart showing a fuel injection amount calculation routine executed by a CPU 42 in 41, which is executed every 360 ° CA in synchronization with the rotation of the internal combustion engine 1.

Now, the CPU 42 first executes step 101.
At step 102, the basic fuel injection amount Tp is calculated based on the intake pressure PM, the engine speed Ne, etc., and at the next step 102, it is judged if the feedback condition of the air-fuel ratio λ is satisfied. Here, as is well known, the feedback condition is satisfied when the cooling water temperature Thw is equal to or higher than a predetermined water temperature and the rotation speed is not high and the load is low. If the feedback condition is satisfied at the present moment, the CPU 42 proceeds to step 103, where the air-fuel ratio λ
Is set to the target air-fuel ratio λTG, the air-fuel ratio correction coefficient FAF is set, and then the routine proceeds to step 104. That is, in step 103, the target air-fuel ratio λ TG and the air-fuel ratio λ detected by the A / F sensor 26 are calculated based on the above-described formulas 6 and 7.
The air-fuel ratio correction coefficient FAF is calculated from (k). Here, the target air-fuel ratio λTG is obtained by the map shown in FIG. 6, for example. This map shows that the theoretical air-fuel ratio is 14.7 (λ =
1.0) is set, and the lean side air-fuel ratio (λ> 1.0) is set in the intermediate range.

If the feedback condition is not satisfied in step 102, the CPU 42 proceeds to step 1
In step 05, the air-fuel ratio correction coefficient FAF is set to "1.0", and then in step 104. In this case, FAF =
1.0 means that the air-fuel ratio λ is not corrected, and so-called open control is performed.

In step 104, the CPU 42 calculates the basic fuel injection amount Tp and the air-fuel ratio correction coefficient F according to the following equation (9).
Fuel injection amount TA from AF and other correction factors FALL
Set U.

[0059]

[Formula 9] TAU = Tp · FAF · FALL After that, a control signal based on the fuel injection amount TAU is output to the fuel injection valve 7, and the valve opening time of the valve 7, that is, the actual fuel injection time is controlled. As a result, the air-fuel ratio λ is adjusted to the target air-fuel ratio λTG.

Next, the sensor abnormality diagnosis process executed by the CPU 42 will be described with reference to the time chart of FIG. 7 and the flowcharts of FIGS. 8 and 9. First, Fig. 7
The sensor abnormality diagnosis processing in this embodiment will be briefly described using the time chart of FIG. In FIG. 7, when the target air-fuel ratio λTG suddenly changes to the lean side at time t1, the air-fuel ratio correction coefficient FA
F changes to the weight loss side. Then, the air-fuel ratio correction coefficient FAF
When the fuel injection amount decreases in accordance with the fluctuation of, the air-fuel ratio λ detected by the A / F sensor 26 fluctuates to the lean side.
When the target air-fuel ratio λTG changes suddenly, the counters CT1 and CT2 are set to predetermined values KCT1 and KCT2. Then, the counter CT1 is counted down with the lapse of time after the time t1, and the counter CT2
Is the time t2 when the air-fuel ratio correction coefficient FAF converges to a predetermined value.
After that, it is counted down. At time t3 when the value of the counter CT1 becomes “0”, the change amount Δ of the target air-fuel ratio λTG.
The abnormality diagnosis is performed depending on whether or not the ratio of λTG and the change amount ΔFAF of the air-fuel ratio correction coefficient FAF is within a predetermined range.

That is, since the air-fuel ratio correction coefficient FAF is set so that the actual air-fuel ratio matches the target air-fuel ratio λTG, it changes corresponding to the change amount ΔλTG of the target air-fuel ratio λTG. In this case, if the A / F sensor 26 is normal, a sensor output corresponding to a change in the target air-fuel ratio λTG (an output that matches the actual air-fuel ratio) is obtained, which is appropriate for realizing the target air-fuel ratio λTG. The air-fuel ratio correction coefficient FAF is set. On the other hand, if the A / F sensor 26 is abnormal,
A sensor output corresponding to a change in the target air-fuel ratio λTG cannot be obtained, and an appropriate amount of air-fuel ratio correction coefficient FAF cannot be obtained.
In this case, it is determined that the sensor is abnormal.

FIG. 10 is a diagram for explaining an example of the sensor output (limit current) when the sensor is abnormal. Figure 10
In the above, the characteristics when the sensor is normal are indicated by "La", and the characteristics when the sensor is abnormal due to element deterioration or heater abnormality are indicated by "Lb" and "Lc". In this case, if the actual air-fuel ratio is "16", the limit current Ipa becomes the sensor output when the sensor is normal, and this is the actual air-fuel ratio (A / F = 1).
Matches 6). On the other hand, the limiting currents Ipb and Ipc when the sensor is abnormal do not match the limiting current Ipa during normal operation, and the actual air-fuel ratio cannot be detected.

8 and 9 show a sensor abnormality diagnosing routine which is executed by the CPU 42 in synchronization with the fuel injection by the fuel injection valve 7. In FIG. 8, first, in step 201, the CPU 42 determines whether or not the difference between the current target air-fuel ratio λTG and the target air-fuel ratio λTi-1 one time before is a predetermined judgment value KλTG or more, that is, the target air-fuel ratio λTG. It is determined whether or not has changed suddenly. If | λTG-λTi-1 | <KλTG, step 201
Is determined negatively, the CPU 42 proceeds to step 205 and determines whether or not the value of the counter CT1 exceeds “0”. In this case, if the target air-fuel ratio λTG is maintained at the predetermined value as before the time t1 in FIG. 7, the counter CT1 = 0
The value is held at (initial value), and the CPU 42 ends this routine as it is.

On the other hand, if | λTG-λTi-1 | ≧ KλTG and step 201 is positively determined (time t in FIG. 7).
1), the CPU 42 proceeds to step 202 and the counter C
A predetermined value KCT1 is set to T1 (KCT1 is a value corresponding to, for example, 15 injections). Further, in step 203, the CPU 42 subtracts the target air-fuel ratio λTi-1 of the previous time from the current target air-fuel ratio λTG to obtain the change amount Δ of the target air-fuel ratio λTG.
Calculate λTG (ΔλTG = λTG−λTi-1). Furthermore, C
In the following step 204, the PU 42 stores the air-fuel ratio correction coefficient FAF at that time as the pre-change correction coefficient FAFBF.

Thereafter, the CPU 42 proceeds to step 211 to decrement the counter CT1 by "1", and at step 212 determines whether or not the value of the counter CT1 is "0". Initially, a negative determination is made in step 212, and the CPU 42 ends this routine as it is. After that, the counter CT1 is CT1 at step 212.
Each time it is processed, it is decremented in step 211 until = 0 is determined.

If a negative decision is made in step 201 after the target air-fuel ratio λTG has changed suddenly (after time t1 in FIG. 7), the CPU 42 proceeds to step 205 and further CT
If 1> 0, the process proceeds to the following step 206. CPU 42
In step 206, the difference between the present target air-fuel ratio λTG and the target air-fuel ratio λTGi-1 one time before is added to the previous “ΔλTG” to update “ΔλTG”.

Further, the CPU 42 determines in step 207 whether or not the difference between the current air-fuel ratio correction coefficient FAF and the air-fuel ratio correction coefficient FAFi-1 one time before has become equal to or less than a predetermined value KFAF, that is, the air-fuel ratio correction. It is determined whether or not the coefficient FAF has converged to a predetermined value. In this case, | FAF-FAFi-1 |
> KFAF, that is, before FAF convergence (time t in FIG. 7).
1 to t2), the CPU 42 makes a negative determination in step 207 and proceeds to step 208 to set the counter CT2 to the predetermined value KC.
T2 is set (KCT2 is a value corresponding to, for example, 15 injections). Also, | FAF-FAFi-1 | ≦ KFA
If F, that is, FAF has converged (after time t2 in FIG. 7), the CPU 42 makes an affirmative decision in step 207 to proceed to step 209, in which the counter CT2 is decremented by “1”, and in the subsequent step 210, the counter CT2 is set to “ It is determined whether it is "0". In this case, CT2 ≠ 0
If so, the process proceeds to step 211 described above. After that, the counter CT2 is decremented in step 209 for each processing until CT2 = 0 is determined in step 210.

After that, when one of the counters CT1 and CT2 becomes "0" (time t3 in FIG. 7), the CPU 42
Proceeds to step 213 in FIG. And the CPU 42
Is the correction coefficient FAF before change stored in step 204 from the current air-fuel ratio correction coefficient FAF in step 213.
BF is subtracted to change the amount of air-fuel ratio correction coefficient FAF ΔFAF
Is calculated (ΔFAF = FAF−FAFBF). further,
In step 214, the CPU 42 counters CT1, CT
Clear both 2 to "0".

Thereafter, the CPU 42 determines in step 215 whether or not the ratio between the absolute value of "ΔFAF" and the absolute value of "ΔλTG" is within a predetermined range (KCGL to KCGH) (for example, KCGL = 0.9, KCGH = 1.
1). In this case, if the air-fuel ratio correction coefficient FAF has changed corresponding to the change in the target air-fuel ratio λTG, step 21
5 is affirmatively determined. That is, if the A / F sensor 26 outputs a normal signal with the change of the target air-fuel ratio λTG,
The air-fuel ratio correction coefficient FAF changes by reflecting the output result. Therefore, the CPU 42 determines that the A / F sensor 26 is normal, and in step 216, the abnormality determination flag XERA.
F is cleared to "0" and this routine ends.

On the other hand, if the air-fuel ratio correction coefficient FAF changes too much or too little with respect to the change in the target air-fuel ratio λTG,
A negative decision is made in step 215. That is, the CPU 42
Considers that the output of the A / F sensor 26 is abnormal and proceeds to step 217 to determine whether or not the abnormality determination flag XERAF has already been set to "1". In this case, if XERAF = 0, the CPU 42 proceeds to step 2
If XERAF = 1 is set in 18 and it is determined that an abnormality has occurred again in the next abnormality diagnosis, a predetermined diagnostic process is executed in step 219 (for example, the warning lamp 49 is turned on or air-fuel ratio feedback is stopped). To).

As described above in detail, in this embodiment, the presence or absence of the correction command is judged from the change amount of the target air-fuel ratio λTG (step 201 in FIG. 8), and if the target air-fuel ratio λTG is suddenly changed, the change amount thereof is determined. ΔλTG and the amount of change ΔF in the air-fuel ratio correction coefficient FAF
An abnormality of the A / F sensor 26 is diagnosed from the result of comparison with AF (step 215 in FIG. 9). Thus, according to the above-mentioned diagnosis processing, it is possible to accurately and easily diagnose the sensor abnormality. As a result, in the air-fuel ratio control system using the linear A / F sensor (oxygen concentration sensor) 26 as in the above-described embodiment, the sensor output with low accuracy (for example,
The output when the sensor deteriorates) is not used for air-fuel ratio control, and highly accurate and highly reliable air-fuel ratio control can be realized. In this embodiment, the invention described in claims 1 and 2 is realized.

(Second Embodiment) Next, a second embodiment embodying the invention described in claim 3 will be described focusing on the difference from the first embodiment. In the second embodiment, an abnormality of the sensor 26 is diagnosed from the behavior of the output signal of the A / F sensor 26 when the water temperature of the fuel injection amount is increased or when the load is increased. In the present embodiment, the CPU 42 constitutes the fuel amount correction means and the total correction amount calculation means. FIG. 11 is a time chart showing the operation of the sensor abnormality diagnosis processing in the second embodiment. First, the time chart will be briefly described. In FIG. 11, time t10
Then, the internal combustion engine 1 is started according to the ON operation of the ignition key. At this time, since the cooling water is at a low temperature, the water temperature correction coefficient FWL is set to a value larger than “1.0” in order to perform the water temperature increase correction. After that, when the cooling water temperature gradually rises and reaches a predetermined value (for example, 40 ° C.), time t11
At this time, the air-fuel ratio feedback is started, and the air-fuel ratio correction coefficient F
AF is set to a small value (toward the weight reduction side) against the water temperature increase at that time. The air-fuel ratio correction coefficient FAF increases with a decrease in the water temperature correction coefficient FWL, and at the time t12 when the internal combustion engine 1 is warmed up and the water temperature increase amount ends, the air-fuel ratio correction coefficient FAF.
F converges near “1.0”.

In this case, from time t10 to t11, the air-fuel ratio λ (detection result by the A / F sensor 26) shifts to the rich side as the water temperature increases. Therefore, the abnormality diagnosis of the A / F sensor 26 is performed based on the behavior of the air-fuel ratio λ with respect to the water temperature increase correction. Further, at times t11 to t12, the water temperature increase is continued, but the air-fuel ratio correction coefficient FAF is set to the decrease side, and the air-fuel ratio λ is equal to the target air-fuel ratio λTG (in the figure, λ
It is held near TG = 1.0). In this case, abnormality diagnosis of the A / F sensor 26 is performed based on the behavior of the air-fuel ratio λ with respect to the water temperature increase correction and the FAF correction.

On the other hand, while the vehicle is traveling, at time t13, high load increase correction due to acceleration is executed. At this time, the air-fuel ratio feedback temporarily becomes open control, and the air-fuel ratio correction coefficient FAF is held at "1.0".
Further, the load correction coefficient FOTP is set to the increase side, and the air-fuel ratio λ (detection result of the A / F sensor 26) shifts to the rich side. During this time t13 to t14, the abnormality diagnosis of the A / F sensor 26 is performed based on the behavior of the air-fuel ratio λ with respect to the high load increase correction.

After that, at time t14 when the vehicle starts to decelerate, the high load increase correction is finished and the load correction coefficient FOTP
Is returned to "1.0". At this time, the fuel cut is executed, the air-fuel ratio λ temporarily shifts greatly to the lean side, and the air-fuel ratio feedback is restarted after the fuel cut.

Next, the arithmetic processing executed by the CPU 42 to realize the above operation will be described with reference to the flowcharts of FIGS. 12 and 13. Note that FIG. 12 shows a fuel injection main routine executed in synchronization with the injection, and FIG.
Shows a sensor abnormality diagnosis routine.

In FIG. 12, the CPU 42 executes the routine of FIG. 5 described above in step 301 to calculate the fuel injection amount TAU. The CPU 42 also executes step 30.
In step 2, the average value λAV of the air-fuel ratio is calculated by 1/64 smoothing calculation {λAV = (63 · λAVi-1 + λ) / 64}.

Further, in step 303, the CPU 42 divides the fuel injection amount TAU by the basic fuel injection amount Tp and the air-fuel ratio learning value FKG to obtain the fuel correction amount FOTHER for the fuel injection amount TAU (excluding the air-fuel ratio learning value FKG. Correction amount)
Is calculated {FOTHER = TAU / (Tp · FKG)}.
In this case, the fuel correction coefficient FOTHER corresponds to “total correction amount”, and for example, the water temperature correction coefficient FWL and the load correction coefficient FOT.
It is calculated as a correction coefficient including P and the air-fuel ratio correction coefficient FAF. That is, the basic fuel injection amount Tp calculated according to the engine operating state (engine speed Ne, intake pressure PM) is originally set to control the air-fuel ratio λ to the theoretical air-fuel ratio λ = 1. Variations in the fuel injection amount due to individual differences and changes with time between engines are corrected by the air-fuel ratio learning value FKG. Therefore, according to step 303, “TAU” is divided by “Tp × FKG” to obtain the “total correction amount” on the assumption that the air-fuel ratio λ = 1 is realized.

Thereafter, the CPU 42 calculates the correction coefficient average value FAV in step 304 {FAV = (63 · FAVi-1)
+ FOTHER) / 64}, and in the following step 305, the sensor abnormality diagnosis routine shown in FIG. 13 is executed.

Next, the sensor abnormality diagnosis routine of FIG. 13 will be described. In FIG. 13, the CPU 42 first determines in step 401 that the water temperature correction coefficient FWL is a predetermined determination value K.
It is determined whether or not FWL is exceeded. For example, when the water temperature is increased at the time of starting (time t10 in FIG. 11), FWL> KF
It becomes WL and step 401 is affirmatively determined. Also, C
The PU 42 determines in step 402 whether the load correction coefficient FOTP exceeds a predetermined determination value KFOTP. For example, when the high load is increased (time t13 in FIG. 11), the FOT
Since P> KFOTP, step 402 is positively determined.

Further, the CPU 42 determines in step 403 whether or not the air-fuel ratio learning process has been completed in all operating regions of the internal combustion engine 1. In this case, when there is no water temperature increase or high load increase (when both steps 401 and 402 are NO), or when the air-fuel ratio learning is not completed (step 4)
If NO in 03), the CPU 42 proceeds to step 404.
Then, the counter CAFER is cleared to "0" and the present routine ends. That is, if the air-fuel ratio learning is not completed, it is not possible to correct variations in the fuel injection amount due to individual differences between engines or changes over time in the unlearned region. Therefore, the abnormality diagnosis of this embodiment is performed only when the air-fuel ratio learning is completed.

On the other hand, the water temperature is increased or the high load is increased,
And when the air-fuel ratio learning is completed (step 401,
YES in step 402 and YE in step 403
In the case of S), the CPU 42 proceeds to step 405,
It is determined whether or not the value of the counter CAFER exceeds "0". Since CAFER = 0 (initial value) at the beginning of the abnormality diagnosis, a negative determination is made in step 405, and the CPU
42 proceeds to step 406 to set a predetermined value KCAFER (for example, a value corresponding to 15 injections) in the counter CAFER.

Then, in step 406, the counter C
When AFER is set, the affirmative determination is made in step 405 thereafter, and the CPU 42 determines the counter C in step 407.
Decrement the AFER by "1". In addition, the CPU 42
Determines whether or not the counter CAFER has become “0” in step 408, and when CAFER = 0, affirmatively determines step 408 and proceeds to step 409. In step 409, the CPU 42 determines the step 3 in FIG.
The deviation amount “λAV-1.Avg. Of the air-fuel ratio average value λAV calculated in step 02 from the target air-fuel ratio λTG (λTG = 1.0 in this embodiment).
0 ”and the deviation amount“ F ”with respect to the reference value (= 1.0) of the correction coefficient average value FAV calculated in step 304 of FIG.
AV-1.0 "is calculated and the ratio of both deviation amounts is" (λ
AV-1.0) / (FAV-1.0) ", and it is determined whether the ratio is within a predetermined range (KFL to KFH) (for example, KFL = -0.8, KFH =-). 1.2).

If the determination in step 409 is affirmative, the CPU 42 determines in step 410 the abnormality determination flag XE.
The RAF is cleared to "0" and this routine ends. On the other hand, if the determination in step 409 is negative, the CPU 42 determines that an abnormality has occurred, proceeds to step 411, and determines whether or not the abnormality determination flag XERAF has already been set to "1". In this case, if XERAF = 0, the CPU 42 sets XERAF = 1 in step 412, and if it is determined again in the next abnormality diagnosis that an abnormality has occurred, a predetermined diagnostic process is executed in step 413 (for example, a warning). The lamp 49 is turned on or the air-fuel ratio feedback is stopped).

According to the second embodiment described above, the engine speed Ne
And a total correction amount for the basic fuel injection amount Tp calculated based on the engine load (intake pressure PM) (steps 303 and 304 in FIG. 12), and the total correction amount and the A / F sensor 26.
From the comparison result with the change amount of the air-fuel ratio λ detected by
An abnormality of the / F sensor 26 is diagnosed (step 4 in FIG. 13).
09). As a result, similarly to the first embodiment, the sensor abnormality can be accurately and easily diagnosed, and the object of the present invention can be achieved.

(Third Embodiment) Next, a third embodiment which embodies the invention described in claim 4 will be described. In the third embodiment, the air-fuel ratio λ (A / F sensor 26
The abnormality of the sensor 26 is diagnosed based on the behavior of (detection result of 1). In the present embodiment, the CPU 42 constitutes an amplitude detecting means.

FIG. 14 is a time chart showing the operation of the sensor abnormality diagnosis processing in the third embodiment. First, the time chart will be briefly described. In FIG. 14, the vehicle is rapidly accelerated at time t21, and accordingly, the air-fuel ratio λ temporarily changes to the lean side and the rich side. Further, the air-fuel ratio λ also greatly changes during the rapid deceleration at time t22. In this case, the sensor abnormality diagnosis is performed based on the difference between the lean peak λL and the rich peak λR (the amplitude of the air-fuel ratio λ) when the air-fuel ratio λ changes.

FIG. 15 shows a sensor abnormality diagnosis routine in the third embodiment. In FIG. 15, the CPU 42
First, at step 501, it is judged if the operating state of the internal combustion engine 1 is a steady state. Here, the determination as to whether or not the vehicle is in a steady state is made based on, for example, during acceleration / deceleration, a sudden change in the target air-fuel ratio λTG, or a sudden change in the air-fuel ratio correction coefficient FAF. If it is in the steady state, the CPU 42 proceeds to step 502 and determines whether or not the value of the counter CAFDT exceeds "0". Counter C at the beginning of abnormality diagnosis
AFDT is not set (initial value CAFDT =
0), the CPU 42 makes a negative determination in step 502, and ends the present routine.

Further, for example, if the vehicle is suddenly accelerated to be in a transient state, a negative determination is made in step 501 (time t21 in FIG. 14), and the CPU 42 determines in step 503 the counter CA.
A predetermined value KCAFDT is set in FDT. Also, CP
The U42 proceeds to step 504 to determine whether or not the current air-fuel ratio λ is larger than the lean peak λL stored so far (whether or not it is on the lean side of λL), and λ>
Only in the case of λL, the lean peak λL is updated in step 505. Further, the CPU 42 proceeds to step 506 to determine whether or not the current air-fuel ratio λ is smaller than the rich peak λR stored so far (whether or not it is on the rich side of λR), and λ <λR Only if step 507
To update the rich peak λR. In this way, the lean peak λL and the rich peak λR in the transition period are updated.

After that, when the operating state returns to the steady state, the CPU 42 proceeds in the order of steps 501 → 502 → 508, and at step 508, the counter CAFDT is set to "1".
Decrement. The CPU 42 also executes step 50.
In 9 it is judged whether or not the counter CAFDT is "0". If CAFDT ≠ 0, the routine proceeds to step 504 described above. That is, during the period in which the counter CAFDT is decremented (time t21 to t22 in FIG. 14), the lean peak λL and the rich peak λR are updated in steps 504 to 507 described above.

After that, when CAFDT becomes 0 (see FIG. 14).
At time t22), the CPU 42 makes an affirmative decision in step 509, and in step 510, decides whether the difference between the lean peak λL and the rich peak λR is less than or equal to a predetermined determination value KAFWD. In this case, if λL−λR> KAFWD and step 510 is negatively determined, the CPU 42 proceeds to step 511 and clears the abnormality determination flag XELER to “0”. That is, it is determined that the fuel amount increase correction due to the sudden acceleration of the vehicle or the like is normally reflected in the output result of the A / F sensor 26, and the normal determination is made. Furthermore, the CPU 42
Proceeds to step 515, and both the lean peak λL and the rich peak λR are “1.0” in preparation for the next abnormality diagnosis.
Then, this routine is finished.

If .lambda.L-.lambda.R.ltoreq.KAFWD and step 510 is affirmatively determined, the CPU 42 proceeds to step 512, and the abnormality determination flag XELER is already "1".
It is determined whether or not it is set to. In this case, if the abnormality determination flag XELER has not been set,
The CPU 42 sets XELER = 1 in step 513.
Then, the next abnormality diagnosis (steps 501 to 51 described above)
If it is determined again that an abnormality has occurred in step 0), the CPU
42 executes the diagnosis process in step 514.

According to the third embodiment described above, the A / F sensor 26 is operated when the operating condition of the internal combustion engine 1 is in the transient state.
The amplitude of the air-fuel ratio λ detected by is calculated, and the abnormality of the A / F sensor 26 is diagnosed based on the amplitude (step 510 in FIG. 15). As a result, the sensor abnormality can be diagnosed accurately and easily as in each of the above embodiments.

The present invention can be embodied as follows in addition to the above embodiments. (1) In the above embodiment, the sensor abnormality diagnosis processing of the present invention is embodied in the air-fuel ratio control system that realizes the air-fuel ratio feedback control using the modern control theory, but it goes without saying that other control (for example, PID control, etc.) is performed. The present invention may be embodied in a system according to (1).

(2) In the above-described second embodiment, a specific example of increasing correction during engine operation (water temperature increase and high load increase is shown, but the abnormality diagnosis processing of the present invention can be realized even during decrease correction. For example, in an air-fuel ratio control system having an evaporative purge mechanism that releases (purges) fuel vapor (evaporative gas) generated in the fuel tank to the intake system of the internal combustion engine 1, the fuel injection valve 7 is used according to the evaporative purge amount. The fuel injection amount is reduced and corrected, and in this case, a sensor abnormality is diagnosed based on the amount of change in the air-fuel ratio λ (sensor output) during the reduction correction.

[0096]

According to the invention described in claim 1, the abnormality of the air-fuel ratio sensor can be diagnosed with high accuracy, and further, the control accuracy of the air-fuel ratio control system using the detection result of the air-fuel ratio sensor can be improved. It has the excellent effect of being able to

[0097] Further, from the comparison result between the air-fuel ratio correction amount of the change amount and the target air-fuel ratio change amount, the abnormality of the air-fuel ratio sensor can be accurately and easily diagnosed.

According to the second aspect of the invention, the abnormality of the air-fuel ratio sensor can be accurately determined based on the comparison result of all the correction amounts for the basic fuel supply amount and the change amount of the air-fuel ratio detected by the air-fuel ratio sensor. And it can be easily diagnosed.

[0099]

[0100]

[0101]

[0102]

[0103]

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an air-fuel ratio control device for an internal combustion engine in an embodiment.

FIG. 2 is a sectional view showing a detailed configuration of an A / F sensor.

FIG. 3 is a diagram showing a voltage-current characteristic of an A / F sensor.

FIG. 4 is a block diagram for explaining the principle of the air-fuel ratio control system.

FIG. 5 is a flowchart showing a fuel injection amount calculation routine.

FIG. 6 is a map for setting a target air-fuel ratio.

FIG. 7 is a time chart for explaining an abnormality diagnosis operation of the first embodiment.

FIG. 8 is a flowchart showing a sensor abnormality diagnosis routine of the first embodiment.

FIG. 9 is a flowchart showing a sensor abnormality diagnosis routine following FIG. 8.

FIG. 10 is a voltage-current characteristic diagram for explaining a sensor output when the sensor is abnormal.

FIG. 11 is a time chart for explaining an abnormality diagnosis operation of the second embodiment.

FIG. 12 is a flowchart showing a fuel injection main routine.

FIG. 13 is a flowchart showing a sensor abnormality diagnosis routine of the second embodiment.

FIG. 14 is a time chart for explaining an abnormality diagnosis operation of the third embodiment.

FIG. 15 is a flowchart showing a sensor abnormality diagnosis routine of the third embodiment.

FIG. 16 is a block diagram corresponding to a claim.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 26 ... A / F sensor as an air-fuel ratio sensor, 42 ... Basic fuel amount calculation means, air-fuel ratio correction amount setting means, air-fuel ratio control means, fuel correction determination means, sensor abnormality diagnosis means, target air-fuel ratio CPU as setting means, fuel amount correcting means, total correction amount calculating means, amplitude detecting means.

Continuation of the front page (56) Reference JP-A-6-74074 (JP, A) JP-A-62-174547 (JP, A) JP-A-5-5447 (JP, A) JP-A-62-247148 (JP , A) JP 62-247147 (JP, A) JP 62-32238 (JP, A) JP 3-23332 (JP, A) JP 6-34597 (JP, A) Special table flat 4-505793 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 41/14 310 F02D 41/22 305 F02D 45/00 368

Claims (2)

(57) [Claims] 1. An air-fuel ratio sensor for linearly increasing or decreasing an output with respect to an air-fuel ratio of an internal combustion engine, fuel supply means for supplying fuel to the internal combustion engine, and basic fuel according to engine speed and engine load. A basic fuel amount calculation means for calculating a supply amount, an air-fuel ratio correction amount setting means for setting an air-fuel ratio correction amount according to a deviation between an air-fuel ratio detected by the air-fuel ratio sensor and a target air-fuel ratio, and the basic fuel An air-fuel ratio control means for controlling the fuel supply quantity by the fuel supply means based on the basic fuel supply quantity calculated by the quantity calculation means and the air-fuel ratio correction quantity set by the air-fuel ratio correction quantity setting means. It is applied to an air-fuel ratio control system, and there is a correction command for the basic fuel supply amount calculated by the basic fuel amount calculation means that exceeds a predetermined amount due to a change in engine operating conditions. A fuel correction determination means for determining, and an air-fuel ratio detected by the air-fuel ratio sensor, or an air-fuel ratio set by the air-fuel ratio correction amount setting means when fuel correction is determined by the fuel correction determination means. depending on the behavior of the correction amount and a sensor abnormality diagnosis means for diagnosing abnormality of the air-fuel ratio sensor, the target air-fuel ratio to set the target air-fuel ratio in accordance with the engine operating state
An air-fuel ratio control system including a setting means, wherein the fuel correction determination means is a target air-fuel ratio setting means.
Whether or not there is a correction command based on the preset amount of change in the target air-fuel ratio
A determination means, and the sensor abnormality diagnosis means is the air-fuel ratio correction amount setting means.
Change amount of the air-fuel ratio correction amount set by
With the change amount of the target air-fuel ratio set by the fuel ratio setting means
A means for diagnosing abnormality of the air-fuel ratio sensor from the comparison result
An abnormality diagnosis device for an air-fuel ratio sensor characterized by having . 2. A linear output with respect to the air-fuel ratio of the internal combustion engine
An air-fuel ratio sensor for increasing / decreasing the fuel consumption , a fuel supply means for supplying fuel to the internal combustion engine, and a basic fuel supply amount according to the engine speed and the engine load.
The basic fuel amount calculating means, the air-fuel ratio detected by the air-fuel ratio sensor, and the target air-fuel ratio
Air-fuel ratio correction amount that sets the air-fuel ratio correction amount according to the deviation from
Setting means and basic fuel supply calculated by the basic fuel amount calculating means
Amount and the air-fuel ratio set by the air-fuel ratio correction amount setting means
Amount of fuel supplied by the fuel supply means based on the correction amount
And an air-fuel ratio control means for controlling the air-fuel ratio
And the basic fuel supply calculated by the basic fuel amount calculation means.
Exceeds the specified amount due to changes in engine operating conditions
The fuel correction determination means for determining that a correction command has been issued and the fuel correction determination means have determined that fuel correction has been performed.
In this case, the air-fuel ratio detected by the air-fuel ratio sensor
Ratio or the air set by the air-fuel ratio correction amount setting means
Diagnose abnormality of the air-fuel ratio sensor according to the behavior of the fuel ratio correction amount.
A sensor abnormality diagnosing means for disconnecting, and increasing or decreasing correction according to the operating conditions of the internal combustion engine
To perform the fuel amount correcting means, when the fuel correction by the fuel amount correcting means, the basic fuel
The total amount for the basic fuel supply amount calculated by the amount calculation means
Air-fuel equipped with all correction amount calculation means for calculating all correction amounts
In the ratio control system, the fuel correction determination means increases the fuel amount correction means.
If there is a correction command when the amount or weight reduction correction is executed
The sensor abnormality diagnosing means includes a determining means,
Calculated by the air-fuel ratio sensor
From the result of comparison with the amount of change in the air-fuel ratio
Abnormality-diagnosis device for air-fuel ratio sensor having means for diagnosing abnormality of the above