JP2689362B2 - Air-fuel ratio detection method for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting an air-fuel ratio of an internal combustion engine, and more specifically, to an air-fuel ratio of an internal combustion engine capable of obtaining a real-time air-fuel ratio by estimating a response delay of an air-fuel ratio sensor. The present invention relates to a fuel ratio detection method.

[0002]

2. Description of the Related Art It is often practiced to provide an air-fuel ratio sensor consisting of an oxygen concentration detecting element in the exhaust system of an internal combustion engine to detect the air-fuel ratio of the input fuel, and one example thereof is JP-A-59-101562. The technology described in the publication can be mentioned. In this technique, in order to improve the detection accuracy, a delay time from the reference timing (first cylinder TDC) until the exhaust gas of each cylinder reaches the air-fuel ratio sensor is obtained in advance according to the operating state, and the cylinder is based on that. The air-fuel ratio is detected every time and feedback control is performed to the target value.

[0003]

By the way, in the air-fuel ratio sensor comprising the oxygen concentration detecting element described above, the chemical change occurring in the element contacting the exhaust gas is converted into an electromotive force to be detected, so that the exhaust gas acts as a sensor. There is a delay in appearing as a detected value even after reaching. Therefore, unless the delay is clarified, the air-fuel ratio of the burned air-fuel mixture cannot be accurately obtained, and therefore, it is possible to realize highly accurate and highly convergent air-fuel ratio control even when performing feedback control to the target value. I can't.

Therefore, the object of the present invention is to solve the above-mentioned drawbacks and to accurately estimate the detection response delay of the air-fuel ratio sensor to obtain the latest value of the burned air-fuel mixture. It is another object of the present invention to provide an air-fuel ratio detection method for an internal combustion engine, which can realize air-fuel ratio control with excellent accuracy and convergence.

[0005]

Means for Solving the Problems] air-fuel ratio detection method for an internal combustion engine according to the present invention in order to solve the above object, as shown in item 1 example claims, the air-fuel ratio is disposed in an exhaust system of an internal combustion engine also detects the air-fuel ratio of each cylinder from the detected values of the sensors meet the <br/>, and pseudo-model the response delay of the sensor in first-order system, setting a state equation describing the behavior
Then , the above equation of state is discretized with a period ΔT to obtain a transfer function.
(1−α hat) / (Z−α hat) is obtained, and the coefficient α hat of the transfer function is varied for each predetermined engine speed.
One inverse transfer function (Z-alpha hat) of the transfer function / (l-
α hat) , the obtained inverse transfer function is multiplied by the output of the air-fuel ratio sensor to obtain an estimated value of the air-fuel ratio of the air-fuel mixture input to the internal combustion engine, and the obtained estimated value of the air-fuel ratio is obtained . Within the above
It is common to set up a model that describes the behavior of the exhaust system of a combustion engine.
, Set an observer to observe its internal state, and
And the air-fuel ratio of each cylinder is detected from the output of the observer.
如 rather it was constructed.

[0006]

[Action] estimates the detection response delay of the sensor air-fuel ratio of the mixture burned could determined Mel be in real time and accurate to each cylinder, the response of the well control, such as when performing feedback control for each cylinder Therefore, it becomes possible to realize the air-fuel ratio control with improved accuracy and convergence. Also damn
There is no need to arrange an air-fuel ratio sensor for each cylinder,
The air-fuel ratio of each cylinder is detected based on the output of the fuel ratio sensor.
It can be estimated.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall schematic view of an air-fuel ratio detection / control apparatus for an internal combustion engine for implementing the method according to the present invention. In the figure, reference numeral 10 denotes a four-cylinder internal combustion engine, and intake air introduced from an air cleaner 14 disposed at the tip of an intake passage 12 passes through an intake manifold 18 while its flow rate is adjusted by a throttle valve 16. The fuel flows into the first to fourth cylinders. An injector 20 is provided near an intake valve (not shown) of each cylinder to inject fuel. The air-fuel mixture that has been injected and integrated with the intake air is ignited by a spark plug (not shown) in each cylinder, burns, and drives a piston (not shown). The exhaust gas after the combustion is discharged to an exhaust manifold 22 through an exhaust valve (not shown), and is discharged outside the engine through an exhaust pipe 24 while being purified by a three-way catalytic converter 26. In addition, a bypass passage 28 is provided in the intake passage 12 near the position where the throttle valve 16 is disposed to bypass the throttle valve 16.

A crank angle sensor 34 for detecting the crank angle position of a piston (not shown) is provided in a distributor (not shown) of the internal combustion engine 10, and a throttle opening for detecting the opening of the throttle valve 16 is provided. A degree sensor 36 and an absolute pressure sensor 38 for detecting the intake pressure downstream of the throttle valve 16 by absolute pressure are also provided. Furthermore,
In the exhaust system, an air-fuel ratio sensor 40 composed of an oxygen concentration detecting element is provided downstream of the exhaust manifold 22 and upstream of the three-way catalytic converter 26, and detects an air-fuel ratio of exhaust gas. Outputs of these sensors 34 and the like are sent to the control unit 42.

FIG. 2 is a block diagram showing details of the control unit 42. The output of the air-fuel ratio sensor 40 is
The air-fuel ratio (A / F) having a linear characteristic proportional to the oxygen concentration in the exhaust gas in a wide range from lean to rich, where appropriate linearization processing is performed.
Is detected. The details are described in the application proposed by the present applicant (Japanese Patent Application No. 3-169456).
Further description is omitted. In the following description, this sensor is referred to as a “LAF sensor” (Linear AV
Sensor). The output of the detection circuit 46 is taken into a microcomputer composed of a CPU 50, a ROM 52, and a RAM 54 via an A / D conversion circuit 48, and is stored in a RAM.
54. Analog output level conversion circuit 56, such as well the throttle opening sensor 36, via the multiplexer 58 and the second A / D converter circuit 60, also the output of the crank angle sensor 34 is shaped by a waveform shaper 62 After that, the counter 64 counts the output value, and the count value is input into the microcomputer. In the microcomputer, the CPU 50 is a ROM 52
Calculates the feedback control value of the air-fuel ratio from the detected value in accordance with the command stored in the second driving circuit 6 and drives the injector 20 of each cylinder via the driving circuit 66.
8 by driving the solenoid valve 70 via, for controlling the amount of secondary air passing through the by-path passage 28 shown in FIG.

Next, the operation of this control device will be described.
After all, the operation is to detect the air-fuel ratio, find the deviation from the target value, and control the fuel supply amount (injection amount) so as to eliminate the deviation. This is because the air-fuel ratio is to be estimated in real time by obtaining the response delay of the sensor, so the following description focuses on that point. An example of controlling the air-fuel ratio based on the detected air-fuel ratio will also be described.

FIG. 3 shows an example of a single-cylinder internal combustion engine, and shows measured data of the response of the air-fuel ratio sensor when the supplied fuel amount is changed stepwise while the intake amount is constant ("measured value" in the figure). . As shown in the figure, when the air-fuel ratio is changed stepwise, the measured value of the LAF sensor output has a delay with respect to the input value, but this delay is caused by a chemical reaction of the sensor, so that accurate analysis cannot be performed. Have difficulty. Therefore, the present inventors have tentatively modeled this delay as a first-order delay system and created a model as shown in FIG. Here LA
Assuming that F: LAF sensor output and A / F: input A / F, the state equation can be expressed by the following equation 1.

[0013]

(Equation 1)

When this is discretized with the period ΔT, it becomes as shown by the equation 2. FIG. 5 is a block diagram of Equation (2).

[0015]

(Equation 2)

Therefore, by using the equation 2, the true air-fuel ratio can be obtained from the sensor output. That is, Equation 2
Is modified as shown in equation (3), the value at time k-1 can be inversely calculated from the value at time k as in equation (4).

[0017]

(Equation 3)

[0018]

(Equation 4)

Specifically, if the expression 2 is expressed by a transfer function using the Z-transform, it becomes as shown in the expression 5. Therefore, the previous air-fuel ratio is estimated in real time by multiplying the inverse transfer function by the sensor output LAF of this time. can do. FIG. 6 shows a block diagram of the real-time A / F estimator. still,
As described above, the response delay of the LAF sensor is caused by a chemical reaction and is difficult to analyze accurately, but it was confirmed that there is a correlation with the engine speed. Therefore, the coefficient of the transfer function is set to be different for each predetermined engine speed set as appropriate. Therefore, by changing the A / F estimator, that is, the coefficient of the inverse transfer function for each predetermined engine speed, the accuracy of the estimated A / F value can be further improved.

[0020]

(Equation 5)

Simulation results for the above are shown in FIG. 3 (“simulation” in the figure) and FIG. 7. As described above, “actual measurement value” in FIG. 3 is an actual measurement value of the sensor output when a step-like air-fuel ratio input is given.
Here, it can be seen that the measured values and the simulation results (outputs obtained by inputting the step-like air-fuel ratio to the model in FIG. 5) substantially correspond to each other. From the above, it can be said that the correctness of pseudo modeling of the sensor response delay as the first-order delay has been verified. FIG. 7 shows a case where a true air-fuel ratio is estimated by multiplying an actually measured value of the sensor output by an inverse transfer function. In the figure, for example, the true air-fuel ratio at time Ta is 1
It can be estimated to be 13.2 instead of 2.5. The reason why the estimated value of the true air-fuel ratio slightly fluctuates is that there is a small variation in the actually measured value of the sensor output.

Next, the case where the air-fuel ratio is controlled based on the true air-fuel ratio obtained as described above will be described.

As described above, when one air-fuel ratio sensor is arranged in the multi-cylinder internal combustion engine, the output thereof shows a value obtained by mixing the detection values of the respective cylinders at the collecting portion of the exhaust system,
It is difficult to obtain a true detection value for each cylinder. Therefore, the A / F of each cylinder cannot be individually controlled to the target value, and a certain cylinder may be lean or another cylinder may be rich, which may cause deterioration of emission. In order to solve this, a sensor may be arranged for each cylinder, but this causes an increase in cost. Therefore, the inventors of the present invention have been able to model the sensor response delay as a first-order delay. Therefore, one air-fuel ratio sensor arranged in the collecting part of the exhaust system is used for multiple cylinders in the following method, and in the case of the embodiment, 4
The air-fuel ratio of the cylinder internal combustion engine can be detected accurately for each cylinder. This will be described below.

First, an exhaust system of an internal combustion engine was modeled as shown in FIG. 8 (hereinafter, this model is referred to as an "exhaust manifold model").
Called)). In this exhaust manifold model, the sampling time of the discrete system is set to the TDC cycle (when the engine speed is 1500 rpm).
0.02 sec). In this exhaust manifold model, since F (fuel) is a controlled variable, the air-fuel ratio is
/ A.

The inventors have considered that the air-fuel ratio (A / F) of the collecting portion of the exhaust system is a weighted average value in consideration of the temporal contribution of the air-fuel ratio of each cylinder. If so, the air-fuel ratio of the collecting part at the time k can be expressed as in Equation 6.

[0026]

(Equation 6)

That is, the air-fuel ratio of the collecting portion is weighted by C in the past combustion history for each cylinder (for example, the most recently burned cylinder is 40
%, Before that 30%. . . , Etc.) can be expressed as the sum of the products. Here, the mixed state of the exhaust gas of each cylinder in the collecting part differs depending on the operating state of the engine. That is, for example, the TDC cycle is long in a low engine speed range,
The degree of mixing of the exhaust from each cylinder is lower than in the high rotation range. Also, when the load is high, the back pressure is basically large,
Since the exhaust pressure of the exhaust gas increases, the degree of mixing of the exhaust gas from each cylinder is lower than when the load is low. In the case where the degree of mixing of the exhaust gases of the cylinders is low, it is necessary to increase the weight of the cylinder that has burned most recently. Therefore, the weight C is changed depending on the operating state of the engine. Specifically, the weight C is set by appropriately setting the engine speed and the load as parameters, prepared in a map, and searched for. In the above, #n indicates the cylinder number, and the combustion (ignition) order of the cylinders is 1, 3, 4, 2
And Here, the air-fuel ratio [F / A] means a true value obtained by correcting the response delay previously obtained by Expression 5.

Based on the above, the equation of state of the exhaust manifold model is as shown in equation 7.

[0029]

(Equation 7)

If the air-fuel ratio of the collecting portion is y (k),
The output equation can be expressed as in Equation 8.

[0031]

(Equation 8) Here, c ₁ : 0.25379, c ₂ : 0.101021, c ₃ :
_0.46111, c 4: to 0.18389.

In the above, since u (k) cannot be observed, even if an observer is designed from this equation of state, x (x)
(K) cannot be observed. Therefore, assuming that the air-fuel ratio F / A before 4TDC (that is, the same cylinder) is in a steady operation state in which it does not suddenly change, x (k + 1) = x (k−
If it is 3), it becomes like Equation 9.

[0033]

(Equation 9)

Here, simulation results of the exhaust manifold model obtained as described above will be shown. FIG. 9 shows a case where the air-fuel ratio of three cylinders is set to 14.7 and the fuel is supplied to one cylinder at 12.0 for a four-cylinder internal combustion engine. FIG.
Shows the air-fuel ratio (A / F) of the collecting portion (that is, the position where the air-fuel ratio sensor 40 is disposed on the exhaust manifold pipe 24 in FIG. 1) obtained by the above-mentioned exhaust manifold model. Although a step-like output is obtained in FIG. 10, if the response delay of the LAF sensor is further considered, the sensor output has a waveform simulated as “simulation” in FIG. In the figure, “actual measurement value” is an actual measurement value of the output of the LAF sensor in the same case.
It can be verified that the exhaust manifold model described above models the exhaust system of the multi-cylinder internal combustion engine well.

Therefore, the problem of a stationary Kalman filter for observing x (k) in the state equation and the output equation shown in the equation 10 is reduced. When the Riccati equation is solved by using the weighting matrices Q and R as shown in the equation 11, the gain matrix K becomes as shown in the equation 12.

[0036]

(Equation 10)

[0037]

[Equation 11]

[0038]

(Equation 12)

When A-KC is calculated from this, the result is as shown in the equation 13.

[0040]

(Equation 13)

The structure of a general observer is as shown in FIG. 12, but since there is no input u (k) in this model, the structure is such that only y (k) is input as shown in FIG. When this is expressed by a mathematical expression, it becomes as shown in Expression 14.

[0042]

[Equation 14]

Here, an observer whose input is y (k),
That is, the system matrix of the Kalman filter is expressed as in Equation 15.

[0044]

(Equation 15)

In the model this time, when the element of the weight distribution R of the Riccati equation: the element of Q = 1: 1, the system matrix S of the Kalman filter is given by the equation 16.

[0046]

(Equation 16)

Then, the waveform of the cylinder-by-cylinder air-fuel ratio is accurately created on the simulation, and the waveform is input to the exhaust manifold model to obtain the collective portion air-fuel ratio. This is input to the observer, and it is verified that the cylinder-by-cylinder air-fuel ratio is estimated. We also consider the tendency of the weight matrix and the estimated value.

In the model this time, as shown in Equation 17, the weight matrix Q is a diagonal matrix in which all the elements are the same.

[0049]

[Equation 17]

Therefore, what is to be considered is the ratio of the elements of Q and R. Table 1 shows the gains obtained by changing the ratio of the Q and R elements. Fig. 1 shows a simulation model combining an observer and an exhaust manifold model constructed using the model.
It is shown in FIG. Furthermore, using this model, the air-fuel ratio for each cylinder is set to 1
FIG. 15 shows the results calculated as ideal inputs of 2.0, 14.7, 14.7, and 14.7, and Table 2 shows observer estimation errors at that time. Further, the air-fuel ratio is set to 12.0 ±
0.2, 14.7 ± 0.2, 14.7 ± 0.2, 14.
FIG. 16 shows the results of calculation (virtual noise) independently varied as 7 ± 0.2, and Table 3 shows the estimated error of the observer at that time. In FIGS. 15 and 16, (a) to (e) show (a) each cylinder A / F (exhaust model input), (b) collecting section A / F (exit model output), and (c) Q Element: observer output when R element = 1: 10 (input is shown in (b)), (d) Observer output when Q element: R element = 1: 1 (input is (b) (E) Elements of Q: Elements of R = 10:
1 is the observer output (input is shown in (b)).

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

As shown in FIG. 15, when the air-fuel ratio of each cylinder is made constant, the larger the weight of Q, the faster the convergence. However, even when Q / R was 10 or more, the convergence was hardly changed. In FIG. 16, the estimated deviation (each cylinder air-fuel ratio−estimated air-fuel ratio) is illustrated in time series as shown in FIG. 17, and after the convergence of the observer, the Q element: the R element = 10: 1 and 1: 1.
Since there is not much difference between and, considering the disturbance resistance,
It can be said that the factor of Q: the factor of R = 1: 1 is better. As described above, the observer using the Kalman filter theory with respect to the input of the air-fuel ratio of the collecting portion enables the air-fuel ratio of each cylinder in the collecting portion to be accurately estimated. Although the weight matrix was best when Q / R = 1 to 10, it seems necessary to determine it from the response situation using actual data.

Subsequently, the actual assembly air-fuel ratio data obtained by inputting the actually measured data to the inverse transfer function of the LAF sensor shown above is input to the observer, and the result of estimating the cylinder-by-cylinder air-fuel ratio is shown in FIG. Show. In the figure, (a) LAF sensor output, (b) LAF sensor inverse transfer function output (input is shown in (a)), (c) element of Q: element of R = 1: 10
Observer output at the time of (input is shown in (b)),
(D) Observer output when Q element: R element = 1: 1: 1 (input is shown in (b)), (e) Observer output when Q element: R element = 10: 1 (input (Shown in (b)). Here, the measurement conditions of the LAF sensor output are as follows:
Engine speed = 1500 rpm, intake pressure = -281.9
mmHg, A / F = 12.0 (# 2), 14.7 (#
1, # 3, # 4). Also, since the true value of the actual input A / F is not known, the approximate value is [12.0 / 14.7 / 14.7 / 14.7] in the simulation.
Was used. As is clear from the figure, the observer output is 4
It changes in the TDC cycle, and the input A / F is almost estimated. It was also confirmed that the use of the Kalman filter enabled convergence in 2 to 8 periods by setting the weight matrix.

Next, the air-fuel ratio is controlled to a target value by using the cylinder-by-cylinder air-fuel ratio estimated as described above. FIG.
FIG. 6 is a block diagram showing a known control example using the PID method. Although the feedback is performed through the multiplication term, which is different from the normal PID control, this method is well known in the art, and as shown in the figure, the deviation of the actual air-fuel ratio caused by the input Ti (injection time) from the target value ( 1-1 /
It is sufficient to obtain λ) for each cylinder, multiply the gain KLAF accordingly, and perform feedback control to the target value. However,
Although the control method itself is publicly known, the air-fuel ratio of each cylinder can be accurately separated and extracted as described above, so that the air-fuel ratio of each cylinder can be accurately controlled to the target value.

In the above-described embodiment, the detection response delay of the air-fuel ratio sensor can be modeled as a primary delay, so that the input air-fuel ratio of the air-fuel ratio sensor can be accurately obtained. Further, it is possible to extract the air-fuel ratio of each cylinder from the output of the collecting portion of the air-fuel ratio sensor provided only in the exhaust system, so that the air-fuel ratio of each cylinder is accurately controlled to the target value. I was able to.

In the above embodiment, an example in which the detection response delay of the air-fuel ratio sensor is analyzed to find the true air-fuel ratio, and the air-fuel ratio is controlled from the output of one sensor based on the true air-fuel ratio has been shown. However, the number of cylinders in the exhaust system is not limited to that, and the true output of each sensor is calculated from the output of each sensor in consideration of the detection response delay, and the air-fuel ratio of each cylinder is calculated based on that. You may control to a target value.

[0059]

[Effect of the Invention] In the air-fuel ratio detection method for an internal combustion engine according to claim 1 wherein, der detects the air-fuel ratio in each cylinder from the detected value of the air-fuel ratio sensor disposed in an exhaust system of an internal combustion engine
And Tsu, artificially modeled response delay of the sensor in first-order system, set the state equation describing the behavior, the transfer function by discretizing the state equation in the period [Delta] T (l-alpha
Hat) / seeking (Z-alpha hat), engagement of the transfer function
The number α hat is changed for each predetermined engine speed and
Inverse transfer function of the reaching function (Z-α hat) / (l-α hat
Seeking g) to obtain the estimated value of the air-fuel ratio of the mixture supplied to the internal combustion engine by multiplying the inverse transfer function obtained in output <br/> force of the air-fuel ratio sensor, the estimated value of the air-fuel ratio determined Using the internal combustion engine
A model describing the behavior of the exhaust system of
Set an observer to observe the internal state of
Having 如 rather configured to detect the air-fuel ratio of each cylinder from the output of the observer, the true air-fuel ratio of the mixture burned in each cylinder
Real-time and accurate determination is possible, so cylinder
Control response even when performing feedback control for each
As a result, it is possible to realize air-fuel ratio control with improved accuracy and excellent accuracy and convergence . Also, the air-fuel ratio for each cylinder
There is no need to place a sensor, and a single air-fuel ratio sensor
The air-fuel ratio of each cylinder can be detected or estimated based on the force.
Can be.

In the method for detecting the air-fuel ratio of the internal combustion engine according to the second aspect of the present invention, since the cycle ΔT is made different for each predetermined engine speed, the control cycle is set to the engine when feedback control is performed. The air-fuel ratio can be accurately converged to the target value even when synchronized with the rotation speed.

[0061]

[Brief description of the drawings]

FIG. 1 is a schematic diagram generally showing an air-fuel ratio detection / control device for an internal combustion engine that implements a method according to the present invention.

FIG. 2 is a block diagram showing a configuration of a control unit in FIG.

FIG. 3 is a simulation result showing a response delay of an air-fuel ratio sensor when a supply amount of fuel is changed stepwise with a constant intake air amount in a single-cylinder internal combustion engine, and data representing an actual measurement value of an LAF sensor output in the same case; It is.

FIG. 4 is a block diagram showing an example in which a detection operation of an air-fuel ratio sensor is modeled.

FIG. 5 is a model obtained by discretizing the model shown in FIG. 4 with a period ΔT.

FIG. 6 is a block diagram showing a true air-fuel ratio estimator that models the detection behavior of the air-fuel ratio sensor according to the present invention.

FIG. 7 is a graph showing the measured value of the LAF sensor output and the estimated value of the true air-fuel ratio obtained by multiplying the measured value by the inverse transfer function.

FIG. 8 is a block diagram showing a model showing a behavior of an exhaust system of an internal combustion engine used in the present invention.

FIG. 9 shows an example in which the air-fuel ratio of three cylinders is set to 14.7 and the air-fuel ratio of one cylinder is set to 1 using a model shown in FIG.
It is data showing the case where the fuel is supplied at 2.0.

FIG. 10 shows data representing the air-fuel ratio of the aggregate of the model of FIG. 8 when the input shown in FIG. 9 is given.

FIG. 11 is a comparison of the data showing the air-fuel ratio of the collecting portion of the model of FIG. 8 when the input shown in FIG. 9 is given without correcting the response delay of the LAF sensor and the actual measurement value of the LAF sensor output at the same time. It is a graph to do.

FIG. 12 is a block diagram showing a configuration of a general observer.

FIG. 13 is a block diagram showing a configuration of an observer used in the present invention.

FIG. 14 is a block diagram showing a simulation model in which the model shown in FIG. 8 and the observer shown in FIG. 13 are combined.

15 shows a four-cylinder internal combustion engine with an air-fuel ratio of 14.7 and an air-fuel ratio of one cylinder of 1 using the model of FIG.
It is data which shows the simulation result at the time of supplying fuel to 2.0.

FIG. 16 is data showing a simulation result when fuel is supplied including virtual noise in the example of FIG. 15;

FIG. 17 is an explanatory diagram showing estimated deviations in a time series in the case shown in FIG. 16;

FIG. 18 is an explanatory view showing an observer output when an actual assembly air-fuel ratio obtained by inputting an actual measurement value of an air-fuel ratio sensor output to the air-fuel ratio estimator shown in FIG. 6 is input;

FIG. 19 is a block diagram showing an example of performing PID control for each cylinder to set an air-fuel ratio to a target value based on a value obtained from the observer output shown in FIG.

[Explanation of symbols]

 Reference Signs List 10 internal combustion engine 18 intake manifold 20 injector 22 exhaust pipe 40 air-fuel ratio sensor 42 control unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Komoritani 4-1-1 Chuo, Wako-shi, Saitama Inside Honda R & D Co., Ltd. (56) Reference JP-A-2-238150 (JP, A) JP-A 1-211648 (JP, A) JP-A 2-301805 (JP, A) JP-A 1-280647 (JP, A) JP-A 59-120726 (JP, A) JP-A 59-101562 (JP, A) A) Japanese Unexamined Patent Publication No. 2-173334 (JP, A) Actual Development No. 3-54260 (JP, U)

Claims (2)

(57) [Claims] 1. A meet those for detecting the air-fuel ratio of each cylinder from the detected value of the air-fuel ratio sensor disposed in an exhaust system of an internal combustion engine Te <br/>, a. A response delay of the sensor is simulated by a first-order delay system and a state equation describing the behavior thereof is set ; b. The above equation of state is discretized with a period ΔT to transfer function
Calculate (1−α hat) / (Z− α hat) , c. The coefficient α hat of the transfer function is set for each predetermined engine speed.
Inverse transfer function of the transfer function while differences (Z-alpha Hatton
G)) / (l-α hat) , and d . The inverse transfer function obtained by multiplying the output of the air-fuel ratio sensor obtains an estimate of the air-fuel ratio of the mixture supplied to the internal combustion engine, e. Exhaust gas of the internal combustion engine using the obtained estimated value of the air-fuel ratio
It sets a model describing the behavior of the system, its interior
Set observers to observe states, and f . The air-fuel ratio of each cylinder is detected from the output of the observer.
That, the air-fuel ratio detection method for an internal combustion engine, characterized in that it consists. 2. The method of detecting an air-fuel ratio of an internal combustion engine according to claim 1, wherein the cycle ΔT is made different for each predetermined engine speed.