JPH0711994A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To suppress over-correction or under-correction respectively by means of feedback so as to prevent hunting, etc., by lowering converging speed of feedback for controlling an air-fuel ratio when a detection value of the air-fuel ratio is out of a specified range being capable of maintaining a specified control model. CONSTITUTION:Fuel is supplied to air which is supplied to an internal combustion engine M1 by a means M2 so as to generate air-fuel mixture supplied to the internal combustion engine M1. On the other hand, an air-fuel ratio of the air-fuel mixture is detected by a means M3 based on exhaust gas of the internal combustion engine M1. An air-fuel ratio corrective coefficient for each case is calculated by a means M4 while executing feedback for controlling the detected air-fuel ratio to a target air-fuel ratio. Further more, a supplied fuel quantity is controlled by a means M5 according to the air-fuel ratio corrective coefficient. By this constitution, it is judged by a means M6 whether a detection value of the air-fuel ratio is in a specified range in which maintainauce of the specified control model is practicable. The feedback is gradually converged when the detection value is out of the specified range.

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 control device for an internal combustion engine, which controls the amount of fuel supplied to the internal combustion engine to control the air-fuel ratio of the air-fuel mixture to a target air-fuel ratio. The present invention relates to implementation of an apparatus that guarantees a more stable control operation of a feedback system that controls an air-fuel ratio.

[0002]

2. Description of the Related Art Conventionally, as this type of air-fuel ratio control device, for example, there is a device described in Japanese Patent Laid-Open No. 1-110853. That is, this device is also basically
Considering a dynamic model of the system that controls the air-fuel ratio of the internal combustion engine,
The so-called modern control theory, in which the amount of fuel to be supplied each time is feedback-controlled under the optimum gain estimated by estimating the internal state of the model, is utilized. In view of the fact that it is necessary to construct a so-called state observing device and the control amount and control scale thereof become enormous, in this device, in particular, (1) air-fuel ratio detection means for detecting the air-fuel ratio of the internal combustion engine ( 2) Fuel supply amount control means for controlling the fuel supply amount to the internal combustion engine (3) Determine the control amount of the fuel supply amount control means based on the detected air-fuel ratio and control the air-fuel ratio of the internal combustion engine to the target air-fuel ratio (4) The air-fuel ratio control means approximates a dynamic model of the internal combustion engine that determines the air-fuel ratio to a dead time by an autoregressive model of degree 1, and further Building with consideration, (5) State variable amount output unit that outputs the air-fuel ratio of the internal combustion engine and the control amount of the fuel supply amount control means as a state variable amount that represents the internal state of the dynamic model of the internal combustion engine (6) Detected as the target air-fuel ratio Accumulation unit for accumulating the deviation from the air-fuel ratio (7) The control amount of the fuel supply amount control means is determined from the optimum feedback gain and the state variable amount and the accumulated value by the accumulation unit which are predetermined based on the dynamic model. By further comprising a control amount calculation unit for calculating, it is not necessary to construct such an observer.

[0003]

By the way, in such a structure, the above-mentioned model is a dynamic model that is properly established between the fuel supply amount to the internal combustion engine and the air-fuel ratio of the air-fuel mixture. Must always be structured with relationships.

However, the air-fuel ratio sensor constituting the air-fuel ratio detecting means generally has a tendency that the output on the rich side is less likely to be output than the output on the lean side, and in those areas, specifically, those sensors. In a region where the output cannot take a linear value, the dynamic model relationship may be broken. If the dynamic model relationship is broken in this way, over-correction or under-correction may occur due to the deviation between the actual air-fuel ratio and the detected air-fuel ratio, and even hunting may occur.

It should be noted that the output of such an air-fuel ratio sensor gradually changes in correlation with the oxygen concentration in the exhaust gas.
In view of the fact that the output suddenly changes at a predetermined oxygen concentration, the current air-fuel ratio and the target air-fuel ratio can be changed to the current air-fuel ratio and the target air-fuel ratio as seen in, for example, the air-fuel ratio control device disclosed in JP-A-62-248848. The difference between the output values of the corresponding air-fuel ratio sensors is compared with a predetermined value to switch the output state of the air-fuel ratio sensor, and the correlation output state of the same sensor (voltage is applied between the electrodes is applied until the detection result becomes almost stable. The feedback control of the air-fuel ratio is performed based on the output of the sensor), and after the detection result becomes stable, the feedback control of the air-fuel ratio is performed based on the output of the sudden change output state (the state where no voltage is applied between the electrodes) of the sensor. There are also some. However, even in this case, there is no change in the fact that the output on the rich side of the air-fuel ratio sensor is less likely to be output than the output on the lean side, and particularly on the rich side, the output itself in the above correlation output state However, it is also questionable whether or not the value is accurately correlated with the oxygen concentration in the exhaust gas. If such a correlation breaks down, the control performed based on the air-fuel ratio detection output will naturally be unreliable, and in this extreme case,
It may cause hunting.

The present invention has been made in view of such circumstances, and it is feared that the dynamic model relationship between the fuel supply amount to the internal combustion engine and the air-fuel ratio of the air-fuel mixture is maintained normally. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can maintain stable feedback control without causing hunting or the like.

[0007]

In order to achieve such an object, according to the present invention, as shown in FIG. 7, the fuel to the air sucked into the internal combustion engine M1 to form the air-fuel mixture is supplied to the internal combustion engine M1. Fuel supply means M2 for injecting and supplying the air-fuel ratio, air-fuel ratio detection means M3 for detecting the air-fuel ratio of the air-fuel mixture based on the exhaust gas of the internal combustion engine M1, and these fuel supply means M
2 to the air-fuel ratio detecting means M3 based on a control model set close to the controlled object and performing feedback for controlling the detected air-fuel ratio to the target air-fuel ratio, and adjusting the air-fuel ratio correction coefficient at each time. Required air-fuel ratio control means M4
And a fuel supply amount control means M5 for controlling the amount of fuel supplied by the fuel supply means M2 based on the obtained air-fuel ratio correction coefficient, the air-fuel ratio detection means M3. The detection value determination means M6 for monitoring the detection value of the air-fuel ratio detected by, and determining whether this detection value is within a predetermined range capable of maintaining the set control model is provided with the air-fuel ratio. Control means M4
When the detection value determination means M6 determines that the detection value is out of the predetermined range, the feedback control is performed with a low gain that gently converges the feedback to obtain the air-fuel ratio correction coefficient. To do so.

[0008]

When the dynamic model relationship between the fuel supply amount to the internal combustion engine M1 and the air-fuel ratio of the air-fuel mixture is properly established, the air-fuel ratio is detected by the detection value determination means M6 as described above. By monitoring whether or not the detected value of the air-fuel ratio by the means M3 is within the predetermined range, it can be determined whether or not the established dynamic model relationship is normally maintained. That is, as long as the air-fuel ratio detection value by the air-fuel ratio detecting means M3 is within a predetermined range in which the set control model can be maintained, such a dynamic model relationship is normally maintained at least at that time. It can be determined that On the contrary, when the detected value of the air-fuel ratio is out of this predetermined range, such dynamic model relationship is not always normally maintained. Therefore, as described above, if the convergence speed of the feedback system is positively slowed down based on the determination that the air-fuel ratio detection value by the air-fuel ratio detection means M3 is out of this predetermined range, Over-correction and under-correction due to feedback are naturally suppressed, and even when maintaining the dynamic model relationship is at risk, hunting and the like due to it can be prevented satisfactorily. Moreover, since the feedback by slowing down the convergence speed is performed only when the detected value of the air-fuel ratio deviates from the predetermined range, the responsiveness of the control device as a whole is thereby lowered. Absent.

The predetermined range monitored by the detection value determination means M6 can be set, for example, as a range in which the detection value of the air-fuel ratio detection means M3 can take a linear value. The range in which the detection value of the air-fuel ratio detecting means M3 can take a linear value is empirically determined in advance based on the voltage-current characteristics of the air-fuel ratio detecting means used with respect to the air-fuel ratio. In the detection value determination means M
6 may simply monitor whether or not the detected value of the air-fuel ratio detected by the air-fuel ratio detecting means M3 is within the range.

Further, in the case of this device, the air-fuel ratio control means M4
The feedback method executed through, that is, the method of calculating the air-fuel ratio correction coefficient is arbitrary. For example, (a) In a normal state where the detected value of the air-fuel ratio is within the above-mentioned predetermined range, a target set according to the state of the internal combustion engine while performing high-speed state feedback based on modern control theory. The air-fuel ratio correction coefficient corresponding to the air-fuel ratio is obtained, and when the detected value of the air-fuel ratio deviates from the predetermined range, the feedback gain of this state feedback is reduced. (b) In a normal state in which the detected value of the air-fuel ratio is within the above-mentioned predetermined range, similarly, it is set according to the state of the internal combustion engine while performing high-speed state feedback according to the modern control theory. An air-fuel ratio correction coefficient corresponding to the target air-fuel ratio is obtained, and when the detected value of the air-fuel ratio deviates from the above-mentioned predetermined range, the target air-fuel ratio is set to a specific value and the proportional / integral control is performed. And so on.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention, in which a four-cylinder, four-cycle spark ignition type internal combustion engine E and its fuel injection control system are applied with an air-fuel ratio control device for an internal combustion engine. Here is an example:

Under the operation of the internal combustion engine E shown in FIG. 1, (1) the airflow flowing through the air cleaner 10 into the intake pipe 20 is supplied to the throttle valve 20a and the surge tank 30 inside the intake pipe 20. Through intake manifold 40
Let it flow in. (2) The fuel injection valve 4 is fed by pressure from a fuel tank (not shown).
The fuel injected through 1 to 44 and the inflowing air flow are mixed in the intake manifold 40 to form an air-fuel mixture. (3) The formed air-fuel mixture is supplied to the combustion chamber of each cylinder of the engine body 50 and burned under the ignition of the spark plugs 51-54. (4) Exhaust manifold 6 with this burned gas
The exhaust gas is discharged into the exhaust pipe 80 as exhaust gas through the zero and three-way catalyst 70. Such an operation is repeated.

Here, each of the above-mentioned spark plugs 51-54
Is ignited by receiving a high voltage distributed from the distributor 90 in cooperation with the ignition circuit 100. The three-way catalyst 70 also serves to reduce harmful components (CO, HC, NOx, etc.) in the exhaust gas from the exhaust manifold 60.

Further, the fuel injection control system includes a rotation speed sensor 110, a throttle sensor 120, and a negative pressure sensor 13.
0, a water temperature sensor 140, an air temperature sensor 150, an air-fuel ratio sensor 160, and an oxygen concentration sensor 170, respectively. The function of each of these sensors will be briefly described below.

The rotation speed sensor 110 is provided in the distributor 90, detects the actual rotation speed of the output shaft of the engine body 50 (corresponding to the actual rotation speed of the internal combustion engine E), and is proportional to the detection result. Pulse signals are sequentially generated at the frequency. However, the number of pulse signals generated from the rotation speed sensor 110 is two rotations of the internal combustion engine E (that is, 720 times).
There are 24 per degree crank angle).

The throttle sensor 120 detects the actual opening of the throttle valve 20a and generates this as an opening detection signal. In addition, the throttle sensor 120 is assumed to have a built-in idle switch as well. This idle switch detects this when the throttle valve 20a is fully closed and generates a fully closed detection new word.

The negative pressure sensor 130 detects an actual negative pressure generated downstream of the throttle valve 20a in the intake pipe 20 and generates this as a negative pressure detection signal. Water temperature sensor 1
The reference numeral 40 detects the actual cooling water temperature in the cooling system of the engine body 50, and generates this as a water temperature detection signal.

The air temperature sensor 150 generates the actual temperature of the airflow flowing upstream of the throttle valve 20a in the intake pipe 20 as an air temperature detection signal. Further, the air-fuel ratio sensor 160 detects the actual unburned oxygen concentration in the exhaust gas upstream of the three-way catalyst 70 in the exhaust pipe 80, and generates this as an air-fuel ratio detection signal. In this case, the same air-fuel ratio detection signal takes a linear value with respect to the actual air-fuel ratio λ of the air-fuel mixture supplied to the engine body 50.

The oxygen concentration sensor 170 detects the actual unburned oxygen concentration in the exhaust gas downstream of the three-way catalyst 70 in the exhaust pipe 80, and generates this as an oxygen concentration detection signal. However, the oxygen concentration detection signal from the oxygen concentration sensor 170 indicates whether the air-fuel ratio λ is rich or lean with respect to the theoretical air-fuel ratio λ0.

All the sensors described above are well known,
A detailed description of the structure etc. will be omitted. The microcomputer 180 includes a CPU 181, a ROM 182,
The RAM 183, the backup RAM 184, the input port 185, the output port 186, the bus line 187 and the like are included.

The CPU 181 is the rotation speed sensor 1 described above.
10, a pulse signal from the throttle sensor 120, an opening detection signal from the throttle sensor 120 and a fully closed detection signal, a negative pressure detection signal from the negative pressure sensor 130, a water temperature detection signal from the water temperature sensor 140, and an air temperature detection from the air temperature sensor 150. The signal, the air-fuel ratio detection signal from the air-fuel ratio sensor 160, and the oxygen concentration detection signal from the oxygen concentration sensor 170 are received via the input port 185 and the bus line 187, and stored in the ROM 182, the RAM 183, and the backup RAM 184. The stored data is also received via the bus line 187 to execute a predetermined computer program as the fuel injection control system, and during this execution, the fuel is supplied via the bus line 187 and the output port 186. Drive control of the injection valves 41 to 44 and the ignition circuit 100 Performs arithmetic processing necessary for that.

However, the above computer program is stored in the ROM 182 in advance. Also, this RO
The state feedback described later is the earliest in M182 depending on whether the detected value of the air-fuel ratio output from the air-fuel ratio sensor 160 is within a predetermined range in which the control model described below can be maintained. The optimum feedback gain for convergence and a lower feedback gain for slowing down the convergence speed of the same-state feedback are also set and stored.

Next, in the above-mentioned fuel injection control system, a method designed in advance for controlling the air-fuel ratio will be sequentially described. (1) Modeling of controlled object In this embodiment, an autoregressive moving average model of degree 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 E, and the disturbance d is further considered. And are approximate.

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 equation (1). [lambda] (K) = a * [lambda] (K-1) + b * FAF (K-3) (1) However, in this equation (1), the symbol FAF represents an air-fuel ratio correction coefficient. The symbols a and b each represent a constant. Further, 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). [lambda] (K) = a * [lambda] (K-1) + b * FAF (K-3) + d (K-1) (2) The rotation period (360 It is easy to determine the above constants a and b by discretization by (degree crank angle) sampling, 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 IX (where IX is a vector amount) When the above equation (2) is rewritten using the state variable amount IX (K) represented by the following equation (3), It becomes a determinant like the equation (4), and further like the equation (5). However,
In Expression (3), the symbol T indicates a transposed matrix. Also,
The symbol "^" in the equation indicates exponentiation. IX (K) = [X1 (K), X2 (K), X3 (K), X4 (K)] ^ T (3) | X1 (K + 1) | | ab00 || X1 (K) | | 0 | | X2 (K + 1) | | 0010 || X2 (K) | | 0 | | X3 (K + 1) | = | 0001 || X3 (K) | + | 0 | FAF (K) | X4 (K + 1) | | 0000 || X4 (K) | | 1 | | 1 | | 0 | + | 0 | d (K) (4) | 0 | X1 (K + 1) = aX1 (K) + bX2 (K) + d (K) = λ (K + 1) X2 (K + 1) = FAF (K-2) X3 (K + 1) = FAF (K-1) X4 (K + 1) = FAF (K) (5) (3) Design of regulator Expression (3) above When the regulator is designed based on the equation (5), the air-fuel ratio correction coefficient FAF has an optimum feedback gain IK (having a vector amount). Relating to the following (6)
By using the equation and the equation (7) regarding the state variable amount IX (K), the equation (8) can be expressed. Here again, the symbol "^" in the formula indicates exponentiation. IK = [K1, K2, K3, K4] (6) IX ^ T (K) = [λ (K), FAF (K-3), FAF (K-2), FAF (K-1)] ... (7) FAF (K) = IK · IX ^ T (K) = K1 · λ (K) + K2 · FAF (K-3) + K3 · FAF (K-2) + K4 · (K-1) (8) Further, in the equation (8), when the integral term ZI (K) for absorbing the error is added, the air-fuel ratio correction coefficient FAF becomes
It 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 a value determined from 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 (10). ZI (K) = ZI (K−1) + Ka · (λTG−λ (K)) (10) FIG. 2 shows a block diagram of the air-fuel ratio λ control system model-designed as described above.

In FIG. 2, the air-fuel ratio correction coefficient FAF (K) is expressed by using (1 / Z) conversion in order to derive it from FAF (K-1), but this is actually shown.
The past air-fuel ratio correction coefficient FAF (K-1) is stored in the RAM 183.
Is stored in the memory and is read and used at the next control timing. Incidentally, "FAF (K-1)" represents the air-fuel ratio correction coefficient one time before, "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. 2, the block P1 surrounded by the one-dot chain 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 IX is set.
(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 IX determined by the block P1.
(K) and the integral term ZI (K) obtained in block P2 are the parts for calculating the current air-fuel ratio correction coefficient FAF (K). (4) Optimal feedback gain IK and integration constant Ka
The optimum feedback gain IK and the integration constant Ka can be set by, for example, minimizing the evaluation function J represented by the following equation (11). The fact that the symbol "^" in the formula indicates exponentiation is the same as before. J = Σ [Q {λ (K) -λTG} ^ 2 (K = 0 to ∞) + R {FAF (K) -FAF (K-1)} ^ 2] (11) However, in this equation (11) , The evaluation function J restricts the movement of the air-fuel ratio correction coefficient FAF (K), and the air-fuel ratio λ
It is intended to minimize the deviation between (K) and the target air-fuel ratio λTG. In addition, the air-fuel ratio correction coefficient FAF (K)
The weighting of the constraint on can be changed by the values of the weighting parameters Q and R. Therefore, the optimum feedback gain IK and the integration constant Ka may be determined by repeatedly changing the values of the weighting parameters Q and R until the optimum control characteristics are obtained.

Further, the optimum feedback gain IK and the integration constant Ka depend on the above model constants a and b (see the above equation (2) or equation (4)). Therefore, in order to guarantee the stability (robustness) of the system with respect to the fluctuation (parameter fluctuation) of the system that controls the current air-fuel ratio λ, the fluctuation amount of each of these model constants a and b is taken into consideration and the optimum feedback is considered. It is necessary to set the gain IK and the integration constant Ka.

Therefore, the simulation is carried out in consideration of the variations that can actually occur in the model constants a and b, and the optimum field back gain IK and integration constant Ka that satisfy the stability are determined.

Although the modeling of the controlled object, the display method of the state variable amount, the design of the regulator, and the determination of the optimum field back gain and the integration constant have been described above, all of them have already been set in the apparatus of this embodiment. It is assumed that Then, hereinafter, it is assumed that the air-fuel ratio control in the fuel injection control system is executed by using only the equations (9) and (10).

In the apparatus of this embodiment constructed as described above, when the fuel injection control system is in the operating state, the microcomputer 180 (to be exact, its CPU)
181) starts execution of the computer program according to the flowcharts of FIGS.

That is, the CPU 181 executes the step 200.
After starting the execution of the program in step 300
At, the basic injection amount Tp of the fuel injected and supplied into the intake manifold 40 is calculated. This basic injection amount Tp is calculated by calculating the frequency of the pulse signal output from the rotation speed sensor 110 for each 360-degree crank angle of the internal combustion engine E (correspondingly, the rotation speed Ne of the internal combustion engine E is naturally obtained),
This is performed based on the value of the negative pressure detection signal output from the negative pressure sensor 130 (hereinafter referred to as negative pressure PM) and the like. The CPU 181 which has thus calculated the basic fuel injection amount Tp then proceeds to the air-fuel ratio calculation processing routine 400 (see FIGS. 4 and 5), and starts the calculation and setting of the air-fuel ratio correction coefficient FAF described above.

The processing procedure of the CPU 181 in the air-fuel ratio calculation processing routine 400 will be described below with reference to FIG. The CPU 181 which has started this air-fuel ratio calculation processing routine 400 as step 400a determines whether or not the feedback condition of the air-fuel ratio λ is satisfied in the next step 410. However, it is assumed that the feedback condition is satisfied because the cooling water temperature in the cooling system of the engine body 50 is equal to or higher than a predetermined water temperature, the rotational speed and load of the internal combustion engine E are not high, and the like.

If the feedback condition is not satisfied at this stage, the CPU 181 determines "NO" in this step 410 and sets the air-fuel ratio correction coefficient FAF to "FAF = 1.0" in step 480. To do. That is, this means that the air-fuel ratio λ is not corrected,
In this case, so-called open control is performed.

In this way, the air-fuel ratio calculation processing routine 4
When the arithmetic processing of 00 ends at step 400b, C
In step 500 (see FIG. 3), the PU 181 calculates and sets the fuel injection amount TAU to be controlled at that time based on the following equation (12). TAU = FAF · Tp · FALL (12) By the way, in this formula (12), FAF is the air-fuel ratio correction coefficient obtained by this air-fuel ratio calculation processing routine 400,
Tp is the basic fuel injection amount obtained in step 300, and FALL is a correction coefficient for correcting the fuel injection amount by an element other than the air-fuel ratio control executed by the fuel injection control system. . The correction based on the correction coefficient FALL includes, for example, correction by EGR (exhaust gas recirculation system), correction by voltage at that time, correction by water temperature at that time, and the like.

On the other hand, when the computer program proceeds to step 410 (FIG. 4) as described above, the air-fuel ratio λ
If the feedback condition of is satisfied, the CPU 181
Determines “YES” in step 410.

When the CPU 181 determines that the feedback condition is satisfied in this way, the CPU 181 determines in step 420 that the target air-fuel ratio is set according to the operating state of the internal combustion engine E at that time.
After setting TG, in step 430, it is determined whether the detection value of the air-fuel ratio sensor 160 is within a predetermined range in which the set control model can be maintained.

Here, an example of this detection value determination method will be described with reference to FIG. FIG. 5 shows the air-fuel ratio sensor 1
It is the graph which showed the voltage (V) -current (I) characteristic with respect to each air fuel ratio of 60, and the curve shown by each solid line in the figure is,
Air-fuel ratio A / F = 12, air-fuel ratio A / F = 13, air-fuel ratio A /
F = 14, air-fuel ratio A / F = 15, air-fuel ratio A / F = 16,
The voltage (V) -current (I) characteristic curves of the air-fuel ratio sensor 160 correspond to the air-fuel ratio A / F = 17 and the air-fuel ratio A / F = 18, respectively. Further, in FIG. 5, a straight line E indicated by a one-dot chain line indicates the value of the voltage applied between the electrodes (not shown) of the air-fuel ratio sensor 160, and a point a at which the straight line E and each curve intersect. , B, c, d, e, and f, it is shown that the air-fuel ratio A / F can be detected linearly. Therefore, in the apparatus of this embodiment, the range of 13 ≦ A / F ≦ 18 (in the case of the example of FIG. 5) in which these linear detections are possible is defined as a predetermined range in which the set control model can be maintained. The detection value of the air-fuel ratio A / F output from the air-fuel ratio sensor 160 is set in this range “13 ≦ A /
If it is within F ≦ 18, it is determined as “YES”, and if it is out of the same range “13 ≦ A / F ≦ 18”, it is “N”.
It is determined to be “O”.

If it is determined to be "YES" in such determination in step 430, that is, if it is determined that the value detected by the air-fuel ratio sensor 160 is within the above range, the CPU 181 sets and stores in the ROM 182. The step 440 of selectively reading the optimum feedback gain IKn (n = 1, 2, 3, 4, A) of the state feedback system which has been performed is executed. On the other hand, in such a determination in step 430, if it is determined to be “NO”, that is, if it is determined that the value detected by the air-fuel ratio sensor 160 is outside the above range, the CPU 181
Is the lower feedback gain IK of the feedback gains set and stored in the ROM 182.
The step 450 of selectively reading n '(n = 1, 2, 3, 4, A) is executed. These feedback gains IKn (n = 1, 2, 3, 4, A) or IKn ′
(N = 1, 2, 3, 4, A) specifies the feedback constants “K1” to “K4” in the above expression (9) and the feedback constant “Ka” in the above expression (10), respectively. It is a value.

The CPU 181 then executes the next step 4
At 60, the selectively read feedback gain IKn (n = A) or IKn ′ (n = A) is substituted into the above equation (10) to calculate the integral term ZI (K), and then step 470. , The feedback gain IKn (n = 1, 2, 3, 4) or IK read selectively
The air-fuel ratio correction coefficient FAF is calculated by substituting n ′ (n = 1, 2, 3, 4) into the above equation (9).

When the calculation of the air-fuel ratio correction coefficient FAF in step 470 is completed in this way, the CPU 181
Is the same as the previous step (12) in step 500 (FIG. 3).
Based on the formula, the fuel injection amount TAU to be controlled at that time
Is calculated and set.

Then, the CPU 181 then uses the set fuel injection amount TAU as a fuel injection output signal to output the fuel injection valve 4 via the bus line 187 and the output port 186.
1 to 44 will be given. As a result, the fuel injection valves 41 to 44 inject fuel injected from the fuel tank into the intake manifold 40 in an amount corresponding to the value of the fuel injection output signal.

As described above, in executing the air-fuel ratio control based on the modern control theory, the apparatus of this embodiment: -The air-fuel ratio correction coefficient is set by the optimum feedback gain preset to converge the state feedback at high speed. A calculation unit for calculating FAF; and a calculation unit for calculating the same air-fuel ratio correction coefficient FAF with a low feedback gain set in advance so as to gently converge the same-state feedback. When it is determined that the detected value of the air-fuel ratio sensor is within the predetermined range that can maintain the set control model, the state feedback is converged at high speed by the optimum feedback gain, and the detected value is If it is determined that the value is out of the predetermined range, the same state feedback is performed with a lower feedback gain. Ya have so as to converge to one. Therefore, particularly when the detected value of the air-fuel ratio sensor is out of the predetermined range in which the set control model can be maintained, overcorrection or undercorrection due to the state feedback is naturally suppressed, even if the control model is the same. Even if it is feared that the maintenance of the device will be compromised, the occurrence of hunting or the like due to it is prevented effectively. Moreover, since the feedback by slowing down the convergence speed is performed only when the detection value of the air-fuel ratio sensor deviates from the predetermined range, the responsiveness of the entire control device is deteriorated. There is no.

FIG. 6 shows, as another embodiment of the air-fuel ratio control apparatus according to the present invention, the procedure for setting the air-fuel ratio correction coefficient of the air-fuel ratio control means, which is the essential part thereof. That is, also in this embodiment, the basic configuration, the modeling method, and the like are as described above, and only the procedure for setting the air-fuel ratio correction coefficient FAF as step 400 in FIG. 3 is shown in FIGS. It differs from the device of the embodiment shown. Therefore, in the following, duplicated description will be omitted, and only parts different from the apparatus of the embodiment shown in FIGS. 1 to 4 will be described.

Now, the device of the embodiment shown in FIG. 6 as an essential part is, as the air-fuel ratio control means: -while executing state feedback for controlling the detected air-fuel ratio to the target air-fuel ratio, A calculation unit that obtains an air-fuel ratio correction coefficient FAF corresponding to the target air-fuel ratio λTG set according to each state, and a normal proportional-integral that sets the target air-fuel ratio λTG to a specific value, for example, "1". The corresponding air-fuel ratio correction coefficient F in processing
In the case where it is determined in advance that the air-fuel ratio correction coefficient calculation means for calculating the AF and the air-fuel ratio correction coefficient calculation means are within a predetermined range in which the set control model can be maintained, If it is determined that the detected value is outside the above specified range by executing state feedback based on modern control theory to converge the system at high speed, the feedback is gently performed based on normal proportional / integral control. The system is made to converge.

That is, in step 4010 of FIG. 6, when the CPU 181 determines that the feedback condition is satisfied, in the next step 4020, the CPU 181 is the same as the above with respect to the detected value of the air-fuel ratio sensor 160, that is, step 430 of FIG. The same judgment is made. Then, when it is determined that the detection value of the air-fuel ratio sensor 160 is within the above range (that is, “YES”), the CPU 1
81 calculates and sets the air-fuel ratio correction coefficient FAF based on the modern control theory in accordance with the procedures listed below. (1) The target air-fuel ratio input TG corresponding to the operating state of the internal combustion engine E at that time is set (step 4030 in FIG. 6), and then the optimum feedback gain IKn (n = 1, 2) set and stored in the ROM 182 is set. , 3, 4, A) is read (step 4040 in FIG. 6). (2) The read optimum feedback gain IKn
Substituting (n = A) into the above equation (10), the integral term ZI
(K) is calculated (step 4050 in FIG. 6), and the optimum feedback gain IKn (n = 1, 2,
Substituting 3, 4) into the above equation (9), the air-fuel ratio correction factor FA
F is calculated (step 4060 in FIG. 6).

When the calculation of the air-fuel ratio correction coefficient FAF in step 4060 is completed in this way, the CPU 18
1 in step 500 (FIG. 3) is the same as (1
Based on equation (2), the fuel injection amount T to be controlled at that time
Calculate and set AU.

On the other hand, if it is determined in step 4020 that the value detected by the air-fuel ratio sensor 160 is outside the above range (that is, "NO"), the CPU 1
81 sets the target air-fuel ratio λTG to approximately “1” in step 4070. Incidentally, this means that the sensor current i of the air-fuel ratio sensor 160 is set to i = 0. Then, in this case, the CPU 181 executes the step 4
At 080, the air-fuel ratio correction coefficient FAF is calculated based on the proportional / integral calculation by the following equation (13). FAF (K) = 1 + Kx ([lambda] TG- [lambda] (K)) (13) In this equation (13), Kx is an integration constant for correcting the deviation of the air-fuel ratio. In such a case, since the detected value of the air-fuel ratio sensor 160 is in an unstable state outside the linear region, the integration constant Kx is made relatively small, and the air-fuel ratio correction coefficient FAF that avoids rapid correction is set. .

After the air-fuel ratio correction coefficient FAF is calculated and set in this way, the processing after step 500 (FIG. 3) is the same as the above. Also in this embodiment, if it is determined in step 4010 that the feedback condition is not satisfied, the air-fuel ratio correction coefficient FAF is set to "FAF = 1.0" in step 4090. , Shift to open control.

As described above, even in the apparatus of the embodiment whose main part is shown in FIG. 6, when the detected value of the air-fuel ratio sensor is out of the predetermined range in which the set control model can be maintained, Since the gradual feedback is performed based on the proportional / integral control, overcorrection and undercorrection are suppressed as in the above. Therefore, in this case as well, the occurrence of hunting or the like is satisfactorily prevented.

In the case of the device of the embodiment shown in FIG. 6, the optimum feedback gain IKn (n =
1, 2, 3, 4, A) and the integration constant Kx are R
It will be stored in advance in the OM 182.

By the way, in any of the above embodiments, the internal combustion engine to which it is applied and the fuel injection control system thereof have the configuration shown in FIG. 1, but the air-fuel ratio control of the internal combustion engine according to the present invention is performed. It is needless to say that the device is not limited to the application to the internal combustion engine and its fuel injection control system shown in FIG.
The present invention can be applied to any other internal combustion engine and its fuel injection control system as long as the controlled object can be modeled in the mode shown in FIG.

Further, the procedure shown in FIG. 4 or 6 as the processing for obtaining the air-fuel ratio correction coefficient is only an example. In short, when it is determined that the detected value of the air-fuel ratio is outside the predetermined range, the air-fuel ratio correction coefficient may be set in such a manner that the feedback system gradually converges.

[0054]

As described above, according to the present invention, based on the determination that the detected value of the air-fuel ratio is out of the predetermined range in which the preset control model can be maintained,
By slowing down the convergence speed of the feedback system, over-correction and under-correction due to the feedback are naturally suppressed, and even if the maintenance of the above control model is compromised, hunting etc. due to it is well generated. Will be prevented.

Further, the feedback by slowing down the convergence speed is carried out only when the detected value of the air-fuel ratio deviates from the above-mentioned predetermined range, so that the responsiveness of the entire control device is deteriorated. There is nothing to do.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an internal combustion engine and a fuel injection control system thereof to which an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention is applied.

FIG. 2 is a block diagram showing a configuration of a state feedback system modeled as a control target in the air-fuel ratio control device of the embodiment.

FIG. 3 is a flowchart showing a main processing routine for setting a fuel injection amount of the air-fuel ratio control system of the embodiment.

FIG. 4 is a flowchart showing a specific processing procedure of an air-fuel ratio correction coefficient setting procedure of the procedures shown in FIG. 3.

FIG. 5 is a graph showing a voltage-current characteristic with respect to each air-fuel ratio of the air-fuel ratio sensor used in the air-fuel ratio control device of the embodiment.

FIG. 6 is a flowchart showing another processing example of the procedure for setting the air-fuel ratio correction coefficient.

FIG. 7 is a claim correspondence diagram showing a configuration concept of an air-fuel ratio control device for an internal combustion engine according to the present invention.

[Explanation of symbols]

10 ... Air cleaner, 20 ... Intake pipe, 20a ... Throttle valve, 30 ... Surge tank, 40 ... Intake manifold, 41, 42, 43, 44 ... Fuel injection valve, 50
… Engine body, 60… Exhaust manifold, 70…
Three-way catalyst, 80 ... Exhaust pipe, 90 ... Distributor,
100 ... Ignition circuit, 110 ... Rotation speed sensor, 120 ... Throttle sensor, 130 ... Negative pressure sensor, 140 ... Water temperature sensor, 150 ... Air temperature sensor, 160 ... Air-fuel ratio sensor,
170 ... Oxygen concentration sensor, 180 ... Microcomputer, 181, CPU, 182 ... ROM, 183 ... RA
M, 184 ... Backup RAM, 185 ... Input port, 186 ... Output port, 187 ... Bus line.

Claims (4)

[Claims] 1. A fuel supply means for injecting and supplying fuel to air sucked into an internal combustion engine to form an air-fuel mixture to be supplied to the internal combustion engine, and an air-fuel ratio of the air-fuel mixture based on exhaust gas of the internal combustion engine. Executes feedback for controlling the detected air-fuel ratio to the target air-fuel ratio based on the air-fuel ratio detecting means for detecting and the control model set to approximate the controlled object from these fuel supply means to the air-fuel ratio detecting means. At the same time, the internal combustion engine is provided with air-fuel ratio control means for obtaining an air-fuel ratio correction coefficient for each case, and fuel supply amount control means for controlling the fuel amount supplied by the fuel supply means based on the obtained air-fuel ratio correction coefficient. In the air-fuel ratio control device, the detected value of the air-fuel ratio detected by the air-fuel ratio detection means is monitored, and the detected value is within a predetermined range in which the set control model can be maintained. Comprising a detection value determination means for determining whether or not, the air-fuel ratio control means, when it is determined that the detection value is outside the predetermined range by this detection value determination means,
An air-fuel ratio control apparatus for an internal combustion engine, wherein the air-fuel ratio correction coefficient is obtained while performing the feedback with a low gain that gently converges the feedback. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the detection value determination means sets a range in which the detection value of the air-fuel ratio detection means takes a linear value as the predetermined range. 3. The air-fuel ratio control means executes a state feedback for controlling the detected air-fuel ratio to a target air-fuel ratio, and a target air-fuel ratio set according to the state of the internal combustion engine at each time. For calculating the air-fuel ratio correction coefficient corresponding to the above-mentioned state feedback at a high speed, and calculating means for calculating the air-fuel ratio correction coefficient with an optimum feedback gain set in advance to converge the state feedback gently. Calculating means for obtaining the air-fuel ratio correction coefficient with a low feedback gain set in advance so as to selectively calculate the air-fuel ratio correction coefficient by these calculating means according to the judgment result of the detection value judging means. The air-fuel ratio control device for an internal combustion engine according to claim 1, which is executed in step 1. 4. The air-fuel ratio control means executes a state feedback for controlling the detected air-fuel ratio to a target air-fuel ratio, and sets a target air-fuel ratio set according to the state of the internal combustion engine at each time. And a calculating means for obtaining an air-fuel ratio correction coefficient corresponding to the target air-fuel ratio by a proportional / integral process in which the target air-fuel ratio is set to a specific value. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the calculation of the air-fuel ratio correction coefficient by these calculating means is selectively executed according to the determination result of the means.