JPH09166569A - Air-fuel ratio sensor abnormality detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the abnormality of an air-fuel ratio sensor with good accuracy. SOLUTION: The air-fuel ratio sensors are installed on the upstream side and on the downstream side from a catalyst, respectively. An error between the central value (FA/F central value) of an air-fuel ratio on the upstream side from the catalyst detected by the upstream side air-fuel sensor and the central value (RA/F central value) of air-fuel ratio on the downstream side from the catalyst detected by the downstream side air-fuel ratio sensor is calculted (step 121), and the absolute value of the error is compared with a specified abnormality determination value (k) (step 122). If |Error|<=k, both the upstream side air-fuel ratio sensor 28 and the downstream side air-fuel ration sensor 29 are judged to be normal. On the other hand, if |Error|>k, either the upstream side air-fuel ratio sensor 28 or the downstream side air-fuel ratio sensor 29 is deteriorated or fails so that the sensor output does not show a correct sir-fuel ratio. Accordingly, in this case, it enters the step 123, and the air-fuel ratio sensor abnormality detecting processing is conducted (step 123).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio sensor abnormality detecting device for detecting abnormality of air-fuel ratio sensors installed upstream and downstream of an exhaust gas purifying catalyst.

[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) whose output changes linearly according to the residual oxygen concentration in the exhaust gas is used, and the air-fuel ratio detected by this air-fuel ratio sensor is loaded into the engine control computer to correct the air-fuel ratio. Is calculated, and the fuel injection amount is corrected based on this air-fuel ratio correction amount. As a result, optimal combustion in the engine is realized, and harmful components (CO, HC, NO in exhaust gas are
x, etc.) is reduced.

In such an 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. Therefore, it is demanded that the abnormality diagnosis of the air-fuel ratio sensor be carried out with high accuracy. ing. Therefore,
For example, Japanese Unexamined Patent Publication No. 62-225943, "Method for detecting abnormality in oxygen concentration sensor", proposes to detect an abnormality in a connection system of a limiting current type oxygen concentration sensor from the relationship between applied voltage and detected current. .

[0004]

However, in the above-mentioned prior art, although a failure 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 due to it can be detected. Unable to detect symptoms.
In other words, if the air-fuel ratio detected by the air-fuel ratio sensor is within the range of the normal control state, even if the air-fuel ratio sensor deteriorates and its output (air-fuel ratio detection value) significantly deviates, the engine Since the control computer determines that the output of the air-fuel ratio sensor is normal and feedback-controls the air-fuel ratio, the control accuracy is significantly deteriorated.

The present invention has been made in consideration of such circumstances, and therefore an object thereof is to be able to detect an abnormality of the air-fuel ratio sensor with high accuracy, and further to use the detection result of the air-fuel ratio sensor to control the air-fuel ratio. An object of the present invention is to provide an air-fuel ratio sensor abnormality detection device capable of improving the accuracy of the above.

[0006]

In order to achieve the above-mentioned object, an air-fuel ratio sensor abnormality detecting device according to claim 1 of the present invention comprises:
It is applied to an air-fuel ratio control system in which air-fuel ratio sensors are installed on the upstream side and the downstream side of an exhaust gas purifying catalyst provided in an exhaust gas passage of an internal combustion engine. Then, the air-fuel ratio center value of the catalyst upstream is obtained based on the output of the upstream side air-fuel ratio sensor, and the air-fuel ratio center value of the catalyst downstream is obtained based on the output of the downstream side air-fuel ratio sensor. Find the deviation between the center value and the center value of the air-fuel ratio downstream of the catalyst, and determine whether the deviation is within a predetermined range to determine whether the upstream-side air-fuel ratio sensor or the downstream-side air-fuel ratio sensor is abnormal. Judgment is made by the judgment means.

That is, if both upstream / downstream air-fuel ratio sensors are normal, the air-fuel ratio center value upstream of the catalyst and the air-fuel ratio center value downstream of the catalyst detected by both air-fuel ratio sensors substantially match. A large deviation between the air-fuel ratio central values of the two means that one of the upstream-side / downstream-side air-fuel ratio sensors has deteriorated or has failed. Therefore, in the present invention, the upstream side air-fuel ratio sensor or the downstream side air-fuel ratio sensor is determined depending on whether the deviation between the air-fuel ratio center value upstream of the catalyst and the air-fuel ratio center value downstream of the catalyst detected by both air-fuel ratio sensors is within a predetermined range. It is accurately determined whether or not the fuel ratio sensor is abnormal.

In this case, it is determined whether the deviation of the air-fuel ratio center value between the catalyst upstream side and the catalyst downstream side is due to an abnormality in the upstream side air-fuel ratio sensor or an abnormality in the downstream side air-fuel ratio sensor. Can not.

Therefore, in claim 3, the behavior of the air-fuel ratio detected by the upstream side air-fuel ratio sensor or a control parameter that changes depending on the behavior of the air-fuel ratio (for example, an air-fuel ratio correction amount described later, a target air-fuel ratio variation amount, etc.). ), The presence or absence of abnormality of the upstream air-fuel ratio sensor is determined by the upstream abnormality determining means. In other words, the behavior of the air-fuel ratio detected by the upstream side air-fuel ratio sensor or the control parameter that changes depending on the behavior of the air-fuel ratio should reflect the air-fuel ratio control state that is actually being performed. Is not reflected, the upstream air-fuel ratio sensor is determined to be abnormal.

Further, according to claim 4, the basic fuel injection amount is calculated by the basic fuel injection amount calculation means in accordance with the operating state of the internal combustion engine, and the deviation between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio is calculated. Accordingly, the air-fuel ratio correction amount is set by the air-fuel ratio correction amount setting means, and the fuel injection amount is controlled by the injection control means based on the basic fuel injection amount and the air-fuel ratio correction amount. Then, the upstream abnormality determination means is the behavior of the air-fuel ratio detected by the upstream air-fuel ratio sensor when the basic fuel injection amount changes suddenly or the behavior of the air-fuel ratio correction amount set by the air-fuel ratio correction amount setting means. The presence or absence of abnormality of the upstream side air-fuel ratio sensor is determined based on the above.

That is, the characteristic is that the air-fuel ratio shifts to the rich side when the basic fuel injection amount is increased and corrected with a change in the operating state of the internal combustion engine, and conversely when the basic fuel injection amount is corrected to decrease, the air-fuel ratio shifts to the lean side. Therefore, if the upstream air-fuel ratio sensor is normal, the behavior of the detected air-fuel ratio or the air-fuel ratio correction amount calculated from the air-fuel ratio reflects the correction of the basic fuel injection amount. Therefore, when the behavior of the detected air-fuel ratio or the behavior of the air-fuel ratio correction amount does not reflect the correction of the basic fuel injection amount, the upstream side air-fuel ratio sensor is determined to be abnormal.

Further, according to the present invention, the upstream side abnormality judging means is configured to change the air-fuel ratio correction amount set by the air-fuel ratio correction amount setting means and the target air-fuel ratio setting means when the target air-fuel ratio suddenly changes. Whether or not the upstream side air-fuel ratio sensor is abnormal is determined by comparing the set target air-fuel ratio change amount. That is, the air-fuel ratio correction amount is set to match the actual air-fuel ratio with the target air-fuel ratio,
If the upstream air-fuel ratio sensor is normal, an appropriate air-fuel ratio correction amount is set according to the deviation between the detected air-fuel ratio and the target air-fuel ratio, and the air-fuel ratio correction amount is set according to the amount of change in the target air-fuel ratio. It will change. However, if the upstream side air-fuel ratio sensor is abnormal, the detected air-fuel ratio is inaccurate, and therefore an appropriate air-fuel ratio correction amount corresponding to the amount of change in the target air-fuel ratio cannot be set. In this case, the upstream air-fuel ratio sensor is determined to be abnormal.

Further, according to claim 6, the fuel injection amount is increased or decreased by the injection amount correction means according to the operating state of the internal combustion engine, and at the time of this fuel correction, the basic fuel injection amount calculation means calculates it. All correction amounts for the basic fuel injection amount are calculated by the total correction amount calculation means, and the upstream side abnormality determination means determines the total amount when the fuel injection amount is increased or decreased by the injection amount correction means. The presence or absence of abnormality of the upstream side air-fuel ratio sensor is determined by comparing the total correction amount calculated by the correction amount calculation means with the amount of change in the air-fuel ratio detected by the upstream side air-fuel ratio sensor. That is, if the upstream air-fuel ratio sensor is normal, the output of the upstream air-fuel ratio sensor changes depending on whether the total correction amount for the base fuel injection amount is the increase side or the decrease side. On the other hand, if the upstream air-fuel ratio sensor is abnormal, the sensor output corresponding to all the correction amounts cannot be obtained, and the upstream air-fuel ratio sensor is determined to be abnormal.

For example, when the internal combustion engine is started or under high load operation, the water temperature increase correction and the high load increase correction are performed, the air-fuel ratio feedback is stopped, and the air-fuel ratio is open-loop controlled. In this case, the total correction amount for the basic fuel injection amount is set to the increase side, and the upstream side air-fuel ratio sensor is diagnosed as to whether or not the sensor output corresponding to this increase correction is obtained. 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 these correction amounts (increase correction amount + air-fuel ratio correction amount) Based on the comparison result with the sensor output, the upstream side air-fuel ratio sensor is diagnosed for abnormality.

Further, in claim 7, the amplitude of the air-fuel ratio detected by the air-fuel ratio sensor is detected by the amplitude detecting means, and the upstream side abnormality judging means is operable when the operating state of the internal combustion engine is in a transient state. Whether the upstream side air-fuel ratio sensor is abnormal is determined based on the amplitude of the air-fuel ratio detected by the amplitude detecting means. That is, when the operating state of the internal combustion engine changes to a transient state, the air-fuel ratio temporarily changes and the actual amplitude of the air-fuel ratio increases. Therefore, if the upstream air-fuel ratio sensor is normal, the amplitude of the sensor output becomes large in the transient state.
On the other hand, if the upstream air-fuel ratio sensor is abnormal, the amplitude of the sensor output does not increase even in the transient state. In this case, the upstream air-fuel ratio sensor is determined to be abnormal.

Further, in claim 8, which of the upstream / downstream side air-fuel ratio sensor is abnormal is determined based on the determination result of the sensor system abnormality determination means and the determination result of the upstream side abnormality determination means. Determine. That is, when the sensor system abnormality determination means determines that either the upstream side / downstream side air-fuel ratio sensor is abnormal, whether the upstream side abnormality determination means has detected an abnormality in the upstream side air-fuel ratio sensor. Is used to determine which of the upstream / downstream air-fuel ratio sensor is abnormal. As a result, the abnormal air-fuel ratio sensor is specified, and the repair becomes easy.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The first embodiment of the present invention will be described below.
An embodiment will be described based on FIGS. 1 to 13. First, the schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of an intake pipe 12 of an engine 11 which is an internal combustion engine, and an intake air temperature sensor 14 for detecting an intake air temperature Tam is provided downstream of the air cleaner 13, and the intake air temperature sensor 14 is provided. A throttle valve 15 and a throttle opening sensor 16 that detects the throttle opening TH are provided on the downstream side. Further, on the downstream side of the throttle valve 15, the intake pipe pressure P
An intake pipe pressure sensor 17 for detecting M is provided, and a surge tank 18 is provided downstream of the intake pipe pressure sensor 17. In this surge tank 18, the engine 11
An intake manifold 19 for introducing air is connected to each of the cylinders, and an injector 20 for injecting fuel is attached to a branch pipe portion of each cylinder of the intake manifold 19.

A spark plug 21 is attached to each engine 11 for each cylinder, and a high voltage current generated in an ignition circuit 22 is distributed to a distributor 23 in each spark plug 21.
Is supplied via The distributor 23 is provided with a crank angle sensor 24 that outputs, for example, 24 pulse signals at every 720 ° C. (two crankshaft revolutions), and the engine speed Ne is detected by the output pulse interval of the crank angle sensor 24. It is supposed to do. A water temperature sensor 38 that detects the engine cooling water temperature Thw is attached to the engine 11.

On the other hand, an exhaust port (not shown) of the engine 11 is connected to an exhaust pipe 26 via an exhaust manifold 25.
(Exhaust gas passage) is connected, and in the middle of this exhaust pipe 26,
A catalyst 27 such as a three-way catalyst that reduces harmful components (CO, HC, NOx, etc.) in the exhaust gas is provided. An upstream air-fuel ratio sensor 28 and a downstream air-fuel ratio sensor 29, which output a linear air-fuel ratio signal (limit current) according to the air-fuel ratio of exhaust gas, are provided on the upstream side and the downstream side of the catalyst 27.

These upstream / downstream air-fuel ratio sensors 2
Both 8 and 29 have the structure shown in FIG. 2, and the structure will be specifically described below. The air-fuel ratio sensors 28 and 29 are attached so as to project into the exhaust pipe 26. The air-fuel ratio sensors 28 and 29 include an oxygen concentration detection element 51 that generates a limiting current corresponding to the oxygen concentration in the lean air-fuel ratio region or the carbon monoxide (CO) concentration in the rich air-fuel ratio region, and the oxygen concentration detection device 51. A heater 52 that heats from the inside, and an oxygen concentration detection element 51
And a small number of small holes 54 through which exhaust gas flows in are formed in the peripheral wall of the cover 53.

The oxygen concentration detecting element 51 has a solid electrolyte layer 55 formed in a cylindrical shape with a bottom, and the solid electrolyte layer 55.
It is composed of an atmosphere side electrode layer 56 and an exhaust gas side electrode layer 57 fixed to the inner and outer peripheral surfaces thereof, and a diffusion resistance layer 58 formed on the outer peripheral surface of the exhaust gas side electrode layer 57 by a plasma spraying method or the like. The solid electrolyte layer 55 is made of ZrO ₂ , HfO ₂ ,
ThO ₂ , Bi ₂ O _3, etc., CaO, MgO, Y ₂ O ₃ ,
It is formed of an oxygen ion conductive oxide sintered body containing Yb ₂ O ₃ or the like as a stabilizer. The diffusion resistance layer 58 is made of alumina, magnesia, siliceous material, spinel,
It is made of a heat-resistant inorganic material such as mullite. The exhaust gas side electrode layer 57 and the atmosphere side electrode layer 56 are both formed 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. In this case, the area and the thickness of the exhaust gas side electrode layer 57 are, for example, 1
0 to 100 mM ^2, it has a approximately 0.5 to 2.0 [mu] m, the area and thickness of the atmosphere-side electrode layer 56, 10 mm ² or more, which is about 0.5 to 2.0 [mu] m.

On the other hand, the heater 52 is an oxygen concentration detecting element 51.
The oxygen concentration detecting element 51 (atmosphere side electrode layer 56, solid electrolyte layer 5)
5, the exhaust gas side electrode layer 57 and the diffusion resistance layer 58) are heated to activate the oxygen concentration detecting element 51.

Air-fuel ratio sensor 2 constructed as described above
The oxygen concentration detecting elements 51 of Nos. 8 and 29 generate a concentration electromotive force at the theoretical air-fuel ratio point and generate a limiting current corresponding to the oxygen concentration in the lean region 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 57, the thickness of the diffusion resistance layer 58, the porosity and the average pore diameter. Further, the oxygen concentration detecting element 51 can detect the oxygen concentration with a linear characteristic, but a high temperature of about 650 ° C. or higher is required to activate the oxygen concentration detecting element 51. Further, since the oxygen concentration detecting element 51 has a narrow activation temperature range, the activation temperature cannot be sufficiently secured by heating only the exhaust gas of the engine 11. Therefore, the oxygen concentration detecting element 51 is kept at the activation temperature by heating the heater 52. In the 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,
The oxygen concentration detection element 51 generates a limiting current according to the CO concentration.

Next, referring to FIG. 3, the air-fuel ratio sensors 28, 2
The voltage-current characteristics of No. 9 will be described. Air-fuel ratio sensor 2
The voltage-current characteristics of 8, 29 are the detected oxygen concentration (air-fuel ratio)
The relationship between the inflow current to the solid electrolyte layer 55 and the voltage applied to the solid electrolyte layer 55 is almost linear. Then, when the air-fuel ratio sensors 28 and 29 are in the active state at the temperature T = T1, the stable state is achieved by the characteristic line L1 shown by the solid line in FIG. In this case, the straight line portion of the characteristic line L1 parallel to the voltage axis V indicates the limiting current. The increase / decrease in the limit current corresponds to the increase / decrease in the air-fuel ratio (that is, lean or rich). The limit current increases as the air-fuel ratio becomes leaner and decreases as the air-fuel ratio becomes richer.

In this voltage-current characteristic, the voltage region smaller than the straight line portion parallel to the voltage axis V is the resistance dominated region, and the slope of the characteristic line L1 in the resistance dominated region is that of the solid electrolyte layer 55. Determined by internal resistance. Since the internal resistance of the solid electrolyte layer 34 changes with a change in temperature, when the temperature of the oxygen concentration detecting element 51 decreases, the inclination decreases due to an increase in resistance. That is, when the temperature T of the oxygen concentration detecting element 51 is at T2 lower than T1, the voltage-current characteristic has a characteristic line L2 shown by a dotted line in FIG.
It slips. In this case, the straight line portion parallel to the voltage axis V of the characteristic line L2 determines the limiting current at T = T2, and this limiting current is substantially equal to the limiting current according to the characteristic line L1.

In the characteristic line L, if a positive applied voltage Vpos is applied to the solid electrolyte layer 55, the current flowing through the oxygen concentration detecting element 51 becomes the limiting current Ipos. Further, if a negative applied voltage Vneg is applied to the solid electrolyte layer 55, the current flowing through the oxygen concentration detecting element 51 does not depend on the oxygen concentration, and a negative temperature current In proportional to only temperature is obtained.
eg is obtained (see point Pb in FIG. 3). In this embodiment, the circuit for monitoring the element temperatures of the air-fuel ratio sensors 28, 29 is omitted and the cost is low.

The outputs of the various sensors described above are read into the electronic control circuit 30 via the input port 31. The electronic control circuit 30 is mainly composed of a microcomputer, includes a CPU 32, a ROM 33, a RAM 34, and a backup RAM 35, and uses a fuel injection amount TAU by using engine operating state parameters obtained from various sensor outputs.
And the ignition timing Ig are calculated, and a signal corresponding to the calculation result is output from the output port 36 to the injector 20 and the ignition circuit 22.
To control the operation of the engine 11. Further, the electronic control circuit 30 executes a sensor abnormality detection process described later to diagnose whether the air-fuel ratio sensors 28 and 29 have abnormality,
When there is an abnormality, a lighting signal is output from the output port 36 to the warning lamp 37, and the warning lamp 37 is turned on to warn the driver of the occurrence of the abnormality.

Next, a method of air-fuel ratio control executed by the electronic control circuit 30 will be described. [1] Modeling of controlled object A system model in which an autoregressive moving average model of degree 1 having a dead time P = 3 is applied to a model of a system that controls the air-fuel ratio λ of the engine 11 is expressed by the following equation (1). Can be approximated by

Λ (k) = a · λ (k−1) + b · FAF (k−3) (1) where FAF is the air-fuel ratio correction coefficient, and a and b are the responsiveness of the model. Shows model constants for determination, k, k
−1 and k−3 respectively indicate the number of times from the start of the first sampling.

In consideration of the disturbance d in the above equation (1), the model of the control system can be approximated by the following equation (2). λ (k) = a · λ (k−1) + b · FAF (k−3) + d (k−1) (2) For the model approximated as described above, the rotation period ( It is easy to determine the model constants a and b by discretization by sampling at 360 ° C. A), that is, to obtain the transfer function G of the system that controls the air-fuel ratio λ.

[2] Method of displaying state variable amount X (where X is a vector amount) The above equation (2) is used as state variable amount X (k) = [X1 (k), X
Rewriting using 2 (k), X3 (k), X4 (k)] ^T (T represents a transposed matrix) gives a determinant represented by the following equation (3).

[0032]

[Equation 1]

From the above determinant, the following equation is obtained. X1 (k + 1) = a * X1 (k) + b * X2 (k) + d (k) = [lambda] (k + 1) ... (4) X2 (k + 1) = FAF (k-2) ... (5) X3 (k + 1) ) = FAF (k-1) ... (6) X4 (k + 1) = FAF (k) ... (7)

[3] Design of Regulator When the regulator is designed based on the above equations (3) to (7), the air-fuel ratio correction coefficient FAF shows the optimum feedback gain K = [Kl, K2, K3, K4] and the state. Variable amount X
^T (k) = [λ (k), FAF (k-3), FAF (k
-2), FAF (k-1)] and expressed as the following equation (8). FAF (k) = K · X T (k) = K1 · λ (k) + K2 · FAF (k-3) + K3 · FAF (k-2) + K4 · FAF (k-1) ...... (8)

Further, when the integral term ZI (k) for absorbing the error is added to the above equation (8), the air-fuel ratio correction coefficient FAF is given by the following equation (9). FAF (k) = K1 · λ (k) + K2 · FAF (k-3) + K3 · FAF (k-2) + K4 · FAF (k-1) + ZI (k) (9)

The integral term ZI (k) is defined by the deviation between the target air-fuel ratio λTG and the actual air-fuel ratio λ (k) and the integral constant K.
It is a value determined from a and is given by the following equation (10). ZI (k) = ZI (k-1) + {λTG−λ (k)} (10)

FIG. 4 shows a block diagram of a control system for the air-fuel ratio λ whose model is designed as described above. In FIG. 4, the air-fuel ratio correction coefficient FAF (k) is set to FAF (k-
Although it was written using the Z ⁻¹ transformation to derive from 1),
This is the past air-fuel ratio correction coefficient FAF (k-1)
It is stored in 34 and is read out and used at the next control timing. By the way, FAF (k-1) represents the previous air-fuel ratio correction coefficient, FAF (k-2) represents the air-fuel ratio correction coefficient in the previous-two times, and FAF (k-3) represents the air-fuel ratio correction coefficient in the previous-two times. Represents

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).
And the block P2 is an integral term ZI.
(K) is a part (cumulative part) to be obtained, and is a block P3.
Is a part for calculating the current air-fuel ratio correction coefficient FAF (k) from the state variable amount X (k) determined in the block P1 and the integral term ZI (k) obtained in the block P2.

[4] Determination of Optimal Feedback Gain K and Integral Constant Ka The optimal feedback gain K and integral constant Ka can be set, for example, by minimizing the evaluation function J shown in the following equation (11).

[0040]

(Equation 2)

In the above equation (11), the evaluation function J is
This is intended to minimize the deviation between the air-fuel ratio λ (k) and the target air-fuel ratio λTG while restricting the movement of the air-fuel ratio correction coefficient FAF (k). In addition, the air-fuel ratio correction coefficient FAF
The weighting of the constraint on (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 optimum control characteristics are obtained, and to determine the optimum feedpack 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, in order to guarantee the stability (robustness) of the system with respect to the fluctuation (parameter fluctuation) of the system that controls the actual air-fuel ratio λ, the fluctuation amount of each of these model constants a and b is taken into consideration, and the optimum feedback gain K and integration constant K
It is necessary to set a. Therefore, the simulation is performed in consideration of the fluctuations that may actually occur in the model constants a and b, and the optimum feedback gain K that satisfies the stability is obtained.
And an integration constant Ka.

[1] Modeling of controlled object,
[2] The display method of the state variable amount, [3] the design of the regulator, [4] the determination of the optimal feedback gain and the integration constant have been described, but in the air-fuel ratio control system of the present embodiment, all of them have already been set. It is assumed that the electronic control circuit 30 executes the air-fuel ratio control using only the equations (9) and (10).

Next, the operation of the air-fuel ratio control system configured as described above will be described. FIG. 5 is a flow chart showing a fuel injection amount calculation routine executed by the CPU 32 in the electronic control circuit 30. This routine is executed every 360 ° C. A in synchronization with the rotation of the engine 11. When the processing of this routine is started, first, at step 101, the basic fuel injection amount Tp is calculated based on the intake pressure PM, the engine speed Ne, and the like. The process of step 101 functions as a basic fuel injection amount calculation means in the claims. Then, in the next step 102, it is determined whether or not the feedback condition of the air-fuel ratio λ is satisfied. Here, the feedback condition is satisfied, for example, when the engine cooling water temperature Thw is equal to or higher than a predetermined water temperature and the rotation speed and load are not high.

If the feedback condition is satisfied at the present time, the routine proceeds to step 103, where the air-fuel ratio correction coefficient FAF for setting the air-fuel ratio λ to the target air-fuel ratio λTG is set. That is, in step 103, the air-fuel ratio correction coefficient FAF is calculated from the target air-fuel ratio λTG and the air-fuel ratio λ (k) detected by the upstream side air-fuel ratio sensor 28 based on the above equations (9) and (10). calculate. Here, the target air-fuel ratio λTG is
For example, it is obtained using the map shown in FIG. According to this map, the target air-fuel ratio λTG shows that the theoretical air-fuel ratio is 14.7 (λ = in the high load / high rotation range and the low load / low rotation range).
1.0), and the lean side air-fuel ratio (λ> 1.0) is set in the intermediate range. The process of step 103 functions as an air-fuel ratio correction amount setting unit in the claims.

On the other hand, if the feedback condition is not satisfied in step 102, the process proceeds to step 104,
The air-fuel ratio correction coefficient FAF is set to "1.0". Here, FAF = 1.0 means that the air-fuel ratio λ is not corrected, and so-called open loop control is performed.

After the air-fuel ratio correction coefficient FAF is set in step 103 or 104, the routine proceeds to step 105, where the basic fuel injection amount Tp, the air-fuel ratio correction coefficient FAF and other correction coefficients FALL are used according to the following equation (12). Then, the fuel injection amount TAU is calculated. TAU = Tp / FAF / FALL ...... (12)

Then, a control signal based on the fuel injection amount TAU is output to the injector 20. This allows
The valve opening time (fuel injection time) of the injector 20 is controlled, and the air-fuel ratio λ is adjusted to the target air-fuel ratio λTG. The process of step 105 functions as the injection control unit in the claims.

Next, a process for determining whether either the upstream side air-fuel ratio sensor 28 or the downstream side air-fuel ratio sensor 29 is abnormal will be described. In this abnormality determination processing, first, the air-fuel ratio center value calculation routine of FIG.
8 and 29, the center value of the air-fuel ratio upstream of the catalyst and the center value of the air-fuel ratio downstream of the catalyst are calculated, and the center value of the air-fuel ratio upstream of the catalyst and the center value of the air-fuel ratio downstream of the catalyst are determined by the sensor system abnormality determination routine of FIG. Is determined, and whether the upstream side air-fuel ratio sensor 28 or the downstream side air-fuel ratio sensor 29 is abnormal is determined depending on whether the deviation is within a predetermined range. Hereinafter, this process will be described in detail.

First, based on FIG. 7, the upstream side of the catalyst 27
The process flow of the air-fuel ratio central value calculation routine for calculating the downstream air-fuel ratio central value will be described. In this routine, first, in step 111, it is determined whether or not it is in steady operation, and if it is not in steady operation, the air-fuel ratio shifts and an accurate air-fuel ratio center value cannot be calculated, so the following processing is performed. Without this routine, it ends. On the other hand, if it is a steady operation, the routine proceeds to step 112, where the output RA of the downstream side air-fuel ratio sensor 29.
/ F is within the specified range (KRB <RA / F <KRU; KR
B and KRU are predetermined values), and if outside this range, the air-fuel ratio is deviated and the accurate air-fuel ratio center value cannot be calculated. Therefore, the subsequent processing is not performed. This routine ends.

On the other hand, when the output RA / F of the downstream side air-fuel ratio sensor 29 is within the predetermined range, the routine proceeds to step 113, and the step 114 continues until the first predetermined time elapses.
Then, the RA / F average value is calculated by the following equation. RA / F average value = {RA / F (current value) + RA / F average value (previous value)} / 2 After that, when the first predetermined time has elapsed, step 1
The routine proceeds to 15 and the RA / F average value obtained within the first predetermined time is set as the RA / F center value (air-fuel ratio center value downstream of the catalyst).

Next, in steps 116-119, the FA / F center value (catalyst upstream air-fuel ratio center value) is obtained based on the output FA / F of the upstream side air-fuel ratio sensor 28 by the same method as described above. That is, the output FA / F of the upstream air-fuel ratio sensor 28
Within a predetermined range (KFB <FA / F <KFU; KFB, K
FU is a predetermined value), the process of calculating the FA / F average value is repeated until the second predetermined time elapses, and the FA / F average value is set to the FA / F center when the second predetermined time elapses. The value.

On the other hand, the sensor system abnormality determination routine of FIG. 8 functions as the sensor system abnormality determination means in the claims. In this routine, first in step 121, F
Difference between A / F center value (catalyst upstream air-fuel ratio center value) and RA / F center value (catalyst downstream air-fuel ratio center value) Error
(= FA / F center value-RA / F center value) is calculated. Then, in the next step 122, the absolute value of the deviation Error of the air-fuel ratio center value is compared with a predetermined abnormality determination value k, and |
When Error | ≦ k, the deviation Error is small and the upstream side air-fuel ratio sensor 28 and the downstream side air-fuel ratio sensor 29
It is determined that both are normal, and this routine ends.

If | Error |> k, it means that either the upstream side air-fuel ratio sensor 28 or the downstream side air-fuel ratio sensor 29 has deteriorated or failed and the sensor output does not show the correct air-fuel ratio. . Therefore, in this case, the process proceeds to step 123 and the sensor abnormality detection process is performed.

On the other hand, FIGS. 9 and 10 show an upstream side air-fuel ratio sensor abnormality determining routine for determining whether or not there is an abnormality in the upstream side air-fuel ratio sensor 28, which functions as upstream side abnormality determining means in the claims. . First, a method of determining an abnormality of the upstream side air-fuel ratio sensor 28 performed by this routine will be described with reference to the time chart of FIG.

In the time chart of FIG. 11, for example, when the target air-fuel ratio λTG suddenly changes to the lean side at time t1, the air-fuel ratio correction coefficient FAF changes to the reducing side. When the fuel injection amount decreases as the air-fuel ratio correction coefficient FAF changes,
The air-fuel ratio λ detected by the upstream air-fuel ratio sensor 28 changes to the lean side. Further, when the target air-fuel ratio λTG changes suddenly, predetermined values KCT1 and KCT2 are set in the first counter CT1 and the second counter CT2. Then, the first counter CT1 is decremented with time after time t2, and the second counter CT2 is decremented after time t2 when the air-fuel ratio correction coefficient FAF converges to a predetermined value. After that, at time t3 when the value of the first counter CT1 becomes “0”, the change amount Δ of the target air-fuel ratio λTG.
The upstream side air-fuel ratio sensor 2 depends on whether the ratio of λTG and the amount of change ΔFAF of the air-fuel ratio correction coefficient FAF is within a predetermined range.
It is determined whether or not 8 is abnormal.

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, if the upstream air-fuel ratio sensor 28 is normal, it will be equal to the detected air-fuel ratio. An appropriate air-fuel ratio correction coefficient FAF is set according to the deviation from the target air-fuel ratio λTG, and the target air-fuel ratio λ
The air-fuel ratio correction coefficient FAF changes corresponding to the change amount ΔλTG of TG. However, if the upstream side air-fuel ratio sensor 28 is abnormal, the detected air-fuel ratio is inaccurate, and the appropriate air-fuel ratio correction coefficient FAF corresponding to the change amount ΔλTG of the target air-fuel ratio λTG cannot be set. In this case, the upstream air-fuel ratio sensor 28 is determined to be abnormal.

FIG. 12 is a diagram for explaining an example of the sensor output (limit current) when the upstream side air-fuel ratio sensor 28 is abnormal. In FIG. 12, the characteristic when the sensor is normal is indicated by “La”, and the characteristic when the sensor is abnormal due to element deterioration or heater abnormality is indicated by “Lb” and “Lc”. In this case, if the actual air-fuel ratio is set to "16", the limit current Ipa is obtained when the sensor is normal.
Becomes the sensor output, which 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. In such a state, the proper air-fuel ratio correction coefficient FAF corresponding to the change amount ΔλTG of the target air-fuel ratio λTG is not set,
The upstream side air-fuel ratio sensor 28 is determined to be abnormal.

The upstream side air-fuel ratio sensor abnormality determination routine shown in FIGS. 9 and 10 is executed in synchronization with the fuel injection operation of the injector 20. In this routine, first, at step 201, the current target air-fuel ratio λTG and the previous target air-fuel ratio λ
Whether the difference from T (i-1) is greater than or equal to a predetermined determination value KλTG,
That is, it is determined whether the target air-fuel ratio λTG has changed suddenly. If | λTG-λT (i-1) | <KλTG, it is determined that the target air-fuel ratio λTG has not changed suddenly, and the routine proceeds to step 205, where the value of the first counter CT1 exceeds "0". Or not. In this case, if the target air-fuel ratio λTG is maintained at the predetermined value as before time t1 in FIG. 11, the first counter CT1 is held at 0 (initial value), and this routine is performed without performing the subsequent processing. To finish.

Thereafter, when | λTG-λT (i-1) | ≧ KλTG (time t1 in FIG. 11), it is determined that the target air-fuel ratio λTG has changed suddenly, and the routine proceeds to step 202, where the first counter A predetermined value KCT1 is set in CT1. Where K
CT1 is a value corresponding to, for example, 15 injections. Then, in the next step 203, the target air-fuel ratio λTG (λ-1) is calculated by subtracting the target air-fuel ratio λT (i-1) one time before from the current target air-fuel ratio λTG (ΔλTG = λTG- λT (i-1)).
Then, in step 204, the air-fuel ratio correction coefficient F at that time is calculated.
The AF is stored in the RAM 34 as the pre-change correction coefficient FAFBF.

After that, the routine proceeds to step 211, where the first counter CT1 is decremented by "1", and the following step 2
At 12, it is determined whether the value of the first counter CT1 is "0". Initially, it is determined to be “No” in step 212, the routine is finished as it is, and thereafter, the first counter CT1 is decremented in step 211 at each processing until it is determined in step 212 that CT1 = 0. It

After the sudden change in the target air-fuel ratio λTG (see FIG. 11)
(After time t1), each time it is determined as “No” in step 201, the process proceeds to step 205, and if CT1> 0, the process proceeds to step 206. Then, in step 206, the difference between the current target air-fuel ratio λTG and the target air-fuel ratio λTG (i-1) one time before is added to ΔλTG up to then to update ΔλTG. Thereafter, at step 207, it is determined whether or not the absolute value of the difference between the current air-fuel ratio correction coefficient FAF and the air-fuel ratio correction coefficient FAF (i-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.

If | FAF-FAF (i-1) |> KFA
In the case of F, that is, before the air-fuel ratio correction coefficient FAF converges (time tl to t2 in FIG. 11), “N” is determined in step 207.
It is determined to be "o", the process proceeds to step 208, and a predetermined value KCT2 is set in the second counter CT2. Where KC
T2 is a value corresponding to, for example, 15 injections.

On the other hand, | FAF-FAF (i-1) | ≤KFA
In the case of F, that is, after the air-fuel ratio correction coefficient FAF has converged (after time t2 in FIG. 11), in step 207, “Yes
s ”, the process proceeds to step 209, the second counter CT2 is decremented by“ 1 ”, and the following step 21
At 0, it is determined whether or not the second counter CT2 is "0". If CT2 ≠ 0, the above step 21
Proceed to 1. After that, the second counter CT2 is decremented in step 209 for each processing until it is determined in step 210 that CT2 = 0.

After that, when either of the counters CT1 and CT2 becomes "0" (time t3 in FIG. 11), the process proceeds to step 213 in FIG. 10 and the change stored in step 204 from the current air-fuel ratio correction coefficient FAF. Pre-correction coefficient FAF
BF is subtracted to change the air-fuel ratio correction coefficient FAF ΔFA
Calculate F (ΔFAF = FAF−FAFBF). Then, in the next step 214, both counters CT1 and CT2 are cleared to "0".

Then, in step 215, the ratio of the absolute value of ΔFAF to the absolute value of ΔλTG is within a predetermined range (KCGL to K).
CGH) is determined (for example, KCGL =
0.9, KCGH = 1.1). At this time, if the air-fuel ratio correction coefficient FAF has changed corresponding to the change in the target air-fuel ratio λTG, it is determined as “Yes” in step 215. That is, if the upstream side air-fuel ratio sensor 28 outputs a normal signal along with the change in the target air-fuel ratio λTG, the air-fuel ratio correction coefficient FAF normally changes by reflecting the output result, and ΔFA
The ratio between the absolute value of F and the absolute value of ΔλTG becomes around 1. In this case, the upstream side air-fuel ratio sensor 28 is determined to be normal, and in step 216, the upstream side abnormality determination flag XE.
The RAF is cleared to "0" and this routine ends.

On the other hand, when the air-fuel ratio correction coefficient FAF excessively changes or excessively changes with respect to the change of the target air-fuel ratio λTG, the ratio between the absolute value of ΔFAF and the absolute value of ΔλTG is “1”. , And is determined to be “No” in step 215. In this case, the upstream air-fuel ratio sensor 28 is determined to be abnormal, and the routine proceeds to step 217, where it is determined whether or not the upstream abnormality determination flag XERAF has already been set to "1". If XERAF = 0, XERAF = 1 is set in step 218, and this routine is finished. If the upstream air-fuel ratio sensor 28 is again determined to be abnormal in the next abnormality determination, a predetermined diagnostic process is executed in step 219 (for example, the warning lamp 37 is turned on or air-fuel ratio feedback is stopped). ).

On the other hand, FIG. 13 shows an abnormal sensor selection routine for selecting which of the upstream / downstream air-fuel ratio sensors 28, 29 is abnormal. In this routine, first, at step 221, the upstream air-fuel ratio sensor 28
Is abnormal. This determination is made based on the abnormality determination result by the upstream side air-fuel ratio sensor abnormality determination routine shown in FIGS. 9 and 10 described above, that is, whether the upstream side abnormality determination flag XERAF is “1”.
When AF = 1, the routine proceeds to step 222, where it is determined that the upstream air-fuel ratio sensor 28 is abnormal.

On the other hand, when XERAF = 0,
Proceeding to step 223, it is determined whether either of the upstream or downstream air-fuel ratio sensors 28, 29 is abnormal. This determination is made based on the abnormality determination result by the above-described sensor system abnormality determination routine shown in FIG. 8. If either of the air-fuel ratio sensors 28, 29 is determined to be abnormal, the routine proceeds to step 224, and the downstream side air-fuel ratio sensor 29 determines that it is abnormal. That is, in the case of “No” in step 221 (when it is determined that the upstream air-fuel ratio sensor 28 is not abnormal)
Further, if it is determined in step 223 that either of the air-fuel ratio sensors 28, 29 is abnormal, the abnormal air-fuel ratio sensor can be determined to be the downstream side air-fuel ratio sensor 29. On the other hand, when it is determined to be "No" in step 223, neither of the air-fuel ratio sensors 28 and 29 is abnormal, and this routine is ended without doing anything.

In the first embodiment described above, if both the upstream / downstream side air-fuel ratio sensors 28, 29 are normal, the catalyst upstream air-fuel ratio center value detected by the both air-fuel ratio sensors 28, 29 and the catalyst Paying attention to the point that the downstream air-fuel ratio central value substantially matches, whether the deviation of the air-fuel ratio central values detected by the air-fuel ratio sensors 28 and 29 by the sensor system abnormality determination routine shown in FIG. 8 is within a predetermined range. Therefore, it is determined whether or not the upstream side air-fuel ratio sensor 28 or the downstream side air-fuel ratio sensor 29 is abnormal. Therefore, not only an abnormality in the circuit configuration such as disconnection or short circuit of the connection system, but also sensor deterioration Abnormalities can also be detected, and abnormalities in the sensor system can be accurately detected. As a result, the air-fuel ratio control using the detection results of the air-fuel ratio sensors 28, 29 and the deterioration detection of the catalyst 27 can be performed with good control.

In this case, it is not possible to determine whether the cause of the deviation of the air-fuel ratio center value between the catalyst upstream side and the catalyst downstream side is the abnormality of the upstream side air-fuel ratio sensor 28 or the abnormality of the downstream side air-fuel ratio sensor 29. .

Therefore, in the first embodiment, the change amount ΔλTG and the change amount Δ of the air-fuel ratio correction coefficient FAF when the target air-fuel ratio λTG changes suddenly by the upstream side air-fuel ratio sensor abnormality determination routine shown in FIGS. 9 and 10. Since the presence / absence of abnormality of the upstream air-fuel ratio sensor 28 is determined based on the result of comparison with the FAF, the abnormality of the upstream air-fuel ratio sensor 28 can be accurately determined. Thus, the abnormal sensor selection routine shown in FIG. 13 can identify the abnormal air-fuel ratio sensor, and the repair can be easily performed.

On the other hand, the second embodiment of the embodiment of the present invention shown in FIGS. 14 to 16 is to detect the presence or absence of abnormality of the upstream side air-fuel ratio sensor 28 by a method different from the first embodiment. In the second embodiment, the abnormality of the upstream side air-fuel ratio sensor 28 is detected from the behavior of the output signal of the upstream side air-fuel ratio sensor 28 when the water temperature of the fuel injection amount is increased or when the load is increased, and the detection thereof is performed. The principle will be described with reference to the time chart of FIG.

In FIG. 14, it is assumed that the ignition key is turned on and the engine 11 is started at time t10. At this time, since the engine 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 t1
At 1, the air-fuel ratio feedback is started, and the air-fuel ratio correction coefficient FAF is set to a small value (on the decrease side) against the water temperature increase at that time. As a result, 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 engine 11 is warmed up and the water temperature increase amount ends, the air-fuel ratio correction coefficient FAF converges to around “1.0”. To do.

At this time, from time t10 to t11, the air-fuel ratio λ (detection result by the upstream air-fuel ratio sensor 28) shifts to the rich side as the water temperature increases. Based on the behavior of the air-fuel ratio λ with respect to the water temperature increase correction, the upstream side air-fuel ratio sensor 2
8 abnormality diagnosis is performed. In addition, time t11 to t12
Then, although the water temperature increase is continued, the air-fuel ratio correction coefficient F
AF is set to the reduction side, and the air-fuel ratio λ is the target air-fuel ratio λTG
(ΛTG = 1.0 in FIG. 14). In this case, abnormality diagnosis of the upstream air-fuel ratio sensor 28 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, the high load increase correction by acceleration is executed. At this time,
The air-fuel ratio feedback temporarily becomes open loop 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,
The air-fuel ratio λ (the detection result of the upstream air-fuel ratio sensor 28) shifts to the rich side. During the period from t13 to t14, the abnormality diagnosis of the upstream air-fuel ratio sensor 28 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 decelerating, 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.

The processing described above is executed as follows by the fuel injection main routine shown in FIG. 15 and the upstream side air-fuel ratio sensor abnormality determination routine shown in FIG. The fuel injection main routine shown in FIG. 15 is executed in synchronization with the fuel injection operation of the injector 20. When the processing of this routine is started, first, at step 301, the fuel injection amount calculation routine of FIG. 5 is executed to calculate the fuel injection amount TAU. Thereafter, in step 302, the air-fuel ratio average value λAV is calculated by the following equation by 1/64 smoothing calculation. λAV = (63 · λAV (i-1) + λ) / 64

Then, in the next step 303, the fuel injection amount TAU is divided by the basic fuel injection amount Tp and the air-fuel ratio learning value FKG as in the following equation to obtain the fuel correction amount FOTHER for the fuel injection amount TAU. FOTHER = TAU / Tp / FKG

Here, the fuel correction amount FOTHER corresponds to the total correction amount excluding the air-fuel ratio learning 100 million FKG, and is obtained as a correction coefficient including, for example, the water temperature correction coefficient FWL, the load correction coefficient FOTP, and the air-fuel ratio correction coefficient FAF. That is, the operating state of the engine 11 (engine speed Ne, intake pressure P
The basic fuel injection amount Tp calculated according to M) is originally set so as to control the air-fuel ratio λ to the stoichiometric air-fuel ratio λ = 1, and the fuel injection due to individual difference of each engine 11 or change over time. The variation in the amount is corrected by the air-fuel ratio learning value FKG. Therefore, in step 303, “total correction amount” is obtained by dividing “TAU” by “Tp · FKG” on the assumption that the air-fuel ratio λ = 1 is realized. The process of step 303 functions as a total correction amount calculation unit in the claims.

Thereafter, in step 304, the correction coefficient average value FAV is calculated by the following equation. FAV = (63.FAV (i-1) + F0THER) / 64 Then, in the next step 305, the upstream side air-fuel ratio sensor abnormality determination routine shown in FIG. 16 is executed as follows.

First, at step 401, the water temperature correction coefficient FW
It is determined whether L exceeds a predetermined determination value KFWL.
For example, when the water temperature is increased at the time of starting (time t1 in FIG. 14).
In 0), FWL> KFWL, and it is determined “Yes” in step 401, and jumps to step 403. However, if FWL ≦ KFWL, the process proceeds to step 402, and the load correction coefficient FOTP sets a predetermined determination value KFOTP. It is determined whether or not to exceed. For example, during high load increase (Fig. 1
At time t13) of 4, FOTP> KFOTP,
When it is determined as “Yes” in step 402, step 4
In step 03, it is determined whether the air-fuel ratio learning process has been completed in the entire operating range of the engine 11. In this case, if there is no water temperature increase or high load increase (steps 401, 40)
2 is both “No”), or when the air-fuel ratio learning is not completed (when Step 403 is “No”),
In step 404, the counter CAFER is cleared to [0] and this routine ends. In other words, if the air-fuel ratio learning is not completed, the engine 11 is
It is not possible to correct variations in fuel injection amount due to individual differences and changes over time. Therefore, the abnormality diagnosis of the upstream air-fuel ratio sensor 28 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,
Any of 402 is "Yes", and step 403
Is "Yes"), the routine proceeds to step 405, where 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, it is determined to be “No” in step 405, the process proceeds to step 406, and the counter CAFER has a predetermined value KCAFER (for example, a value corresponding to 15 injections). Is set, and this routine ends.

In this way, when the counter CAFER is set in step 406, when this routine is subsequently executed, it is determined to be "Yes" in step 405, the process proceeds to step 407, and the counter CAFER is set to "1". Decrement. Then, the next step 408
Then, it is determined whether or not the counter CAFER has become "0", and if it has not become "0", this routine is terminated without performing the subsequent processing, and until CAFER = 0,
The above processing is repeated.

After that, when CAFER = 0, the routine proceeds from step 408 to step 409, and the target air-fuel ratio λTG of the air-fuel ratio average value λAV calculated at step 302 of FIG. 15 is obtained.
The deviation amount “λAV” with respect to (λTG = 1.0 in this embodiment)
1.0 "and the deviation amount" FAV-1.0 "with respect to the reference value (= 1.0) of the correction coefficient average value FAV calculated in step 304 of FIG. The ratio “(λAV-11.0) / (FAV-11.0)” is obtained, and it is determined whether the ratio is within a predetermined range (KFL to KFH) (for example, KFL = 1−0.8, KFH =-
1.2).

When it is judged "Yes" at this step 409, it is judged that the output of the upstream air-fuel ratio sensor 28 is normal, and the routine proceeds to step 410, where the upstream abnormality judgment flag XERAF is cleared to [0]. This routine ends.

On the other hand, if "No" is determined in the above step 409, it is determined that the upstream side air-fuel ratio sensor 28 is abnormal, and the routine proceeds to step 411, where "1" is already set in the upstream side abnormality determination flag XERAF. It is determined whether or not it is set. If XERAF = 0, step 4
In step 12, XERAF = 1 is set, and this routine is finished. Then, at the next abnormality determination, the upstream side air-fuel ratio sensor 2
If it is determined that 8 is abnormal, a predetermined diagnostic process is executed in step 413 (for example, the warning lamp 37 is turned on or the air-fuel ratio feedback is stopped).

According to the second embodiment described above, the total correction amount is calculated for the basic fuel injection amount Tp calculated based on the engine speed Ne and the engine load (intake pressure PM) (step of FIG. 15). 303, 304), the presence or absence of abnormality of the upstream side air-fuel ratio sensor 28 is determined from the comparison result of the total correction amount and the change amount of the air-fuel ratio λ detected by the upstream side air-fuel ratio sensor 28. Similar to the first embodiment, the abnormality of the upstream air-fuel ratio sensor 28 can be accurately and easily determined.

On the other hand, FIGS. 17 and 18 show a third embodiment in which the presence / absence of abnormality of the upstream side air-fuel ratio sensor 28 is detected by a method different from the above-mentioned embodiments. In the third embodiment, the presence or absence of abnormality of the upstream air-fuel ratio sensor 28 is determined from the behavior of the air-fuel ratio λ (detection result of the upstream air-fuel ratio sensor 28) during transient operation. The determination principle will be described with reference to the time chart of FIG.

In FIG. 17, the vehicle is rapidly accelerated at time t21, and the air-fuel ratio λ temporarily changes to the lean side and the rich side accordingly. Further, the air-fuel ratio λ also greatly changes during the rapid deceleration at time t22. In this case, the presence or absence of abnormality of the upstream side air-fuel ratio sensor 28 is determined based on the difference between the lean peak λL and the rich peak λR (amplitude of the air-fuel ratio λ) when the air-fuel ratio λ changes.

The processing described above is executed as follows by the upstream side air-fuel ratio sensor abnormality determination routine shown in FIG. First, in step 501, it is determined whether the operating state of the engine 11 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 a steady state, step 5
In step 02, it is determined whether or not the value of the counter CAFDT exceeds "0". At the beginning of the abnormality diagnosis, the counter CAFDT is not set and remains 0 (initial value). Therefore, it is determined as "No" in step 502, and this routine is terminated without performing the subsequent processing.

If, for example, the vehicle is suddenly accelerated and is in a transient state, it is determined as "No" in step 501 (see FIG. 1).
7 time t21), the process proceeds to step 503 and the counter C
A predetermined value KCAFDT is set in AFDT. After this,
In step 504, it is determined whether or not the current air-fuel ratio λ is larger than the lean peak λL stored so far (whether or not it is leaner than λL), and the process proceeds to step 505 only when λ> λL. To update the lean peak λL. Thereafter, the routine proceeds to step 506, where it is judged whether or not the current air-fuel ratio λ is smaller than the rich peak λR stored until then (whether it is on the rich side of λR or not), and only when λ <λR, the step 507 is carried out. And the rich peak λR is updated. 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 process proceeds in the order of steps 501 → 502 → 508, the counter CAFDT is decremented by "1", and at the subsequent step 509, whether the counter CAFDT is "0" or not. If CAFDT ≠ 0, the above-mentioned step 50 is performed.
Proceed to 4. That is, during the period in which the counter CAFDT is decremented (time t21 to t22 in FIG. 17), 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. 17).
At time t22), it is determined to be “Yes” in step 509, and in the following step 510, it is determined whether or not the difference between the lean peak λL and the rich peak λP is less than or equal to a predetermined determination value KAFWD. Here, if λL-λR> KAFWD, the process proceeds to step 511, and the upstream side abnormality determination flag XELER is cleared to "0". That is, λL-λR
If> KAFWD, it means that the fuel amount increase correction due to the sudden acceleration of the vehicle or the like is normally reflected in the output of the upstream side air-fuel ratio sensor 28, and the upstream side air-fuel ratio sensor 28 is determined to be normal. Then, in the next step 515, the lean peak λL and the rich peak λ are prepared to prepare for the next abnormality determination.
Both R are reset to "1.0" and this routine ends.

On the other hand, in step 510, λL-λR
If it is determined that ≦ KAFWD, the process proceeds to step 512,
It is determined whether or not the upstream abnormality determination flag XELER has already been set to "1". If the upstream abnormality determination flag XELER has not been set to "1" yet, the process proceeds to step 513 and XELER = 1. Then, the next abnormality determination (steps 501 to 510 described above)
Process), it is determined again that there is an abnormality, step 51
The diagnostic process is executed at 4. Incidentally, steps 504 to 5
The process of updating the lean peak λL and the rich peak λR at 07 and obtaining λL-λR at step 510 functions as an amplitude detecting means for detecting the amplitude of the air-fuel ratio in the claims.

According to the third embodiment described above, the amplitude of the air-fuel ratio λ detected by the upstream side air-fuel ratio sensor 28 is obtained when the operating state of the engine 11 is in the transient state,
An abnormality of the upstream air-fuel ratio sensor 28 is diagnosed based on the amplitude (step 510 in FIG. 18). This makes it possible to accurately and easily determine whether or not there is an abnormality in the upstream air-fuel ratio sensor 28, as in each of the above-described embodiments.

The present invention can be embodied as follows in addition to the above embodiments. (1) In each of the above embodiments, the present invention is embodied in an air-fuel ratio control system that realizes air-fuel ratio feedback control using modern control theory. However, other control (for example, P
The present invention may be embodied in a system based on ID control or the like).

(2) In the second embodiment, the engine 11 is used.
The increase correction at the time of the operation (Whether the upstream side air-fuel ratio sensor 28 is abnormal with respect to the water temperature increase or the high load increase is determined. For example, in an air-fuel ratio control system having an evaporative purge mechanism that discharges (purges) the fuel vapor (evaporative gas) generated in the fuel tank to the intake system of the engine 11, the injector 20 of the injector 20 is changed according to the amount of evaporative purge. When the amount of fuel injection is reduced and corrected, the presence or absence of abnormality of the upstream side air-fuel ratio sensor 28 is determined based on the amount of change in the air-fuel ratio λ (output of the upstream side air-fuel ratio sensor 28) during the reduction correction. To be judged.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an entire engine control system showing a first example of an embodiment of the present invention.

FIG. 2 is a sectional view showing a detailed configuration of an upstream air-fuel ratio sensor.

FIG. 3 is a diagram showing voltage-current characteristics of an upstream air-fuel ratio sensor.

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

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

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

FIG. 7 is a flowchart showing a processing flow of an air-fuel ratio center value calculation routine.

FIG. 8 is a flowchart showing a processing flow of a sensor system abnormality determination routine.

FIG. 9 is a flowchart showing a processing flow of an upstream air-fuel ratio sensor abnormality determination routine (No. 1).

FIG. 10 is a flowchart (No. 2) showing a processing flow of an upstream air-fuel ratio sensor abnormality determination routine.

FIG. 11 is a time chart for explaining an upstream side air-fuel ratio sensor abnormality determination operation according to the first embodiment.

FIG. 12 is a voltage-current characteristic diagram for explaining the sensor output when the upstream air-fuel ratio sensor is abnormal.

FIG. 13 is a flowchart showing a processing flow of an abnormality sensor selection routine.

FIG. 14 is a time chart for explaining an upstream side air-fuel ratio sensor abnormality determination operation of the second embodiment.

FIG. 15 is a flowchart showing the flow of processing of a fuel injection main routine.

FIG. 16 is a flowchart showing a processing flow of an upstream side air-fuel ratio sensor abnormality determination routine of the second embodiment.

FIG. 17 is a time chart for explaining an upstream air-fuel ratio sensor abnormality determination operation of the third embodiment.

FIG. 18 is a flowchart showing the processing flow of an upstream side air-fuel ratio sensor abnormality determination routine of the third embodiment.

[Explanation of symbols]

11 ... Engine (internal combustion engine), 17 ... Intake pipe pressure sensor, 24 ... Crank angle sensor, 26 ... Exhaust pipe (exhaust gas passage), 27 ... Catalyst, 28 ... Upstream air-fuel ratio sensor, 29 ...
Downstream air-fuel ratio sensor, 30 ... Electronic control circuit (sensor failure determination means, basic fuel injection amount calculation means, air-fuel ratio correction amount setting means, injection control means, target air-fuel ratio setting means, injection amount correction means, total correction amount calculation Means, amplitude detecting means), 37 ... Warning lamp.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G01N 27/27 G01N 27/46 A 27/41 325P

Claims (8)

[Claims] 1. The present invention is applied to an air-fuel ratio control system in which air-fuel ratio sensors are installed on an upstream side and a downstream side of a catalyst for purifying exhaust gas provided in an exhaust gas passage of an internal combustion engine, respectively. Means for obtaining the air-fuel ratio central value of the catalyst upstream based on the output of the fuel ratio sensor, means for obtaining the air-fuel ratio central value of the catalyst downstream based on the output of the downstream side air-fuel ratio sensor, and the air-fuel ratio central value of the catalyst upstream And means for obtaining a deviation between the air-fuel ratio central value of the catalyst downstream, and whether the upstream side air-fuel ratio sensor or the downstream side air-fuel ratio sensor is abnormal depending on whether the deviation is within a predetermined range. An air-fuel ratio sensor abnormality detection device, comprising: a sensor system abnormality determination means for determining. 2. The air-fuel ratio sensor abnormality detecting device according to claim 1, further comprising upstream abnormality determining means for determining whether or not there is abnormality in the upstream air-fuel ratio sensor. 3. The upstream-side abnormality determining means determines whether or not there is an abnormality in the upstream-side air-fuel ratio sensor based on the behavior of the air-fuel ratio detected by the upstream-side air-fuel ratio sensor or a control parameter that changes depending on the behavior of the air-fuel ratio. The air-fuel ratio sensor abnormality detection device according to claim 2, wherein 4. A basic fuel injection amount calculation means for calculating a basic fuel injection amount according to an operating state of an internal combustion engine, and an air-fuel ratio according to a deviation between an air-fuel ratio detected by the air-fuel ratio sensor and a target air-fuel ratio. The upstream-side abnormality determination includes: an air-fuel ratio correction amount setting means for setting a correction amount; and an injection control means for controlling a fuel injection amount to an internal combustion engine based on the basic fuel injection amount and the air-fuel ratio correction amount. The means, based on the behavior of the air-fuel ratio detected by the upstream side air-fuel ratio sensor or the behavior of the air-fuel ratio correction amount set by the air-fuel ratio correction amount setting means when the basic fuel injection amount suddenly changes 4. The presence or absence of abnormality of the side air-fuel ratio sensor is determined.
The air-fuel ratio sensor abnormality detection device described in. 5. A target air-fuel ratio setting means for setting a target air-fuel ratio according to the operating state of the internal combustion engine, wherein the upstream side abnormality judging means sets the air-fuel ratio correction amount when the target air-fuel ratio suddenly changes. Means for determining the presence or absence of abnormality of the upstream side air-fuel ratio sensor by comparing the change amount of the air-fuel ratio correction amount set by the means and the change amount of the target air-fuel ratio set by the target air-fuel ratio setting means. The air-fuel ratio sensor abnormality detection device according to claim 4, which has. 6. An injection amount correcting means for increasing or decreasing a fuel injection amount according to an operating state of an internal combustion engine, and the basic fuel injection amount calculating means for correcting the fuel by the injection amount correcting means. And a total correction amount calculation unit for calculating all correction amounts for the basic fuel injection amount, wherein the upstream-side abnormality determination unit is provided when the fuel injection amount is increased or decreased by the injection amount correction unit. A means for determining the presence or absence of abnormality of the upstream side air-fuel ratio sensor by comparing the total correction amount calculated by the total correction amount calculation means and the change amount of the air-fuel ratio detected by the upstream side air-fuel ratio sensor. It has, It has characterized by the above-mentioned.
The air-fuel ratio sensor abnormality detection device described in. 7. An amplitude detection means for detecting the amplitude of the air-fuel ratio detected by the air-fuel ratio sensor is provided, and the upstream-side abnormality determination means is the amplitude detection means when the operating state of the internal combustion engine is in a transient state. 5. A means for determining whether or not there is an abnormality in the upstream side air-fuel ratio sensor based on the amplitude of the air-fuel ratio detected by
The air-fuel ratio sensor abnormality detection device described in. 8. A means for determining which of the upstream / downstream side air-fuel ratio sensor is abnormal based on the determination result of the sensor system abnormality determination means and the determination result of the upstream side abnormality determination means. The air-fuel ratio sensor abnormality detection device according to any one of claims 2 to 7.