JP2684012B2 - Air-fuel ratio control device 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 provides an air- fuel ratio sensor at the exhaust system collecting portion of a multi-cylinder internal combustion engine, sets a model describing the behavior of the exhaust system, inputs the sensor output, and observes its internal state. In an air- fuel ratio control device for an internal combustion engine that provides an observer to estimate the air-fuel ratio of each cylinder from its output, it is possible to improve the estimation accuracy of the air-fuel ratio of each cylinder by the observer and to improve the feedback control accuracy of the air-fuel ratio. Regarding what you did.

[0002]

2. Description of the Related Art It is common practice to provide an air-fuel ratio sensor in an exhaust system of an internal combustion engine to detect an air-fuel ratio, and an example thereof is disclosed in Japanese Patent Application Laid-Open No. Sho 59-101562. In addition, the present applicant has also previously filed Japanese Patent Application No. Hei.
No. 59339 (JP-A-5-180059),
A technique has been proposed in which a model describing the behavior of the exhaust system is set, the output of a single air-fuel ratio sensor provided in the exhaust system assembly is input, and the air-fuel ratio of each cylinder is estimated via an observer. Here, the air-fuel ratio sensor is not a wide-range air-fuel ratio sensor, that is, an O ₂ sensor whose output is inverted at the stoichiometric air-fuel ratio, but has an output characteristic proportional to the oxygen concentration in the exhaust gas before and after the stoichiometric air-fuel ratio. You are using

[0003]

Although the air-fuel ratio of each cylinder can be accurately estimated by the above-mentioned configuration, it is difficult to secure the calculation time depending on the operating condition, or the air-fuel ratio sensor output There are cases where the responsiveness is not sufficient.

Therefore, an object of the present invention is to provide an air- fuel ratio control system for an internal combustion engine , which is adapted to cope with such an operating condition.

Further, a second object of the present invention is that it is difficult to secure the calculation time of the observer when the air-fuel ratio of each cylinder is feedback-controlled to the target value by using the estimated value of the air-fuel ratio of each cylinder by the observer. An object of the present invention is to provide an air- fuel ratio control device for an internal combustion engine , which copes with various operating conditions.

[0006]

In order to solve the above-mentioned problems, an air- fuel ratio control device for an internal combustion engine according to a first aspect of the present invention is an air-fuel ratio sensor arranged at an exhaust system collecting portion of a multi-cylinder internal combustion engine.
Out to detect the air-fuel ratio of the exhaust system collectively unit from power, detects the
For controlling the air-fuel ratio of the exhaust system collecting part to a target value
First step to calculate the unit feedback correction term KLAF
Stage, wherein the output value of the air-fuel ratio sensor to set the model describing the behavior of the exhaust system is regarded as consisting of a weighted average value obtained by multiplying a predetermined coefficient to the combustion history of each cylinder, a state the air-fuel ratio of each cylinder set the state equation for the variable, second means for determining the output by setting the observer for observing the internal state, the air-fuel ratio of each cylinder from the previous SL observer output # nA /
Third means for estimating F , air-fuel in each of the estimated cylinders
For each cylinder for which the ratio # nA / F is feedback-controlled to a target value
Fourth hand to calculate feedback correction term #nKLAF
Stage, a fifth means for detecting the operating state of the internal combustion engine,
And the collective feedback correction term KLAF and each cylinder
The internal combustion engine based on the feedback correction term #nKLAF
Feedback for feedback control of engine air-fuel ratio
In an air-fuel ratio control device for an internal combustion engine having a control means ,
The feedback control means controls the air-fuel ratio #nA of each cylinder by the third means from the detected operating condition.
/ Estimation of F is determined difficult Rutoki, said it will stop estimating the air-fuel ratio # nA / F of each cylinder, wherein each cylinder off
Feedback correction term #nKLAF based feedback
Control control is stopped, and the collective portion feedback correction term KL
Feedback of the air-fuel ratio of the internal combustion engine based on AF
It was configured to control .

The apparatus according to claim 2 is the feedback device.
The control means controls the feedback correction item #nKLAF for each cylinder.
If you decide to cancel the feedback control based on is, the gas
It was constructed as Ru to <br/> cylinder each feedback correction term #nKLAF to a predetermined value.

According to a third aspect of the present invention, the predetermined value is based on the feedback correction term #nKLAF for each cylinder.
The value immediately before the feedback control is stopped # nKLAFn-
It was configured as 1 .

The apparatus according to claim 4 is configured such that the predetermined value is a learned value in a predetermined operation region.

[0010]

According to the first and second aspects of the invention, in a device that estimates and controls the air-fuel ratio of each cylinder according to the combustion history, the estimation is stopped, in other words, in an operating state where it is difficult to estimate the air-fuel ratio. For example, instead of thinning out, the process is stopped completely, so there is no loss of consistency with the cylinders and there is no risk of misjudgment.

[0011] In the claims 1 and 2 wherein, without having to erroneously estimated the degree of variation in air-fuel ratio between the cylinders, even in a region which can not be estimated observer, a significant degree or it is possible to converge the current engagement portion air-fuel ratio to the target value. In the second aspect, the predetermined value is, for example, 1
And

According to the third aspect of the present invention, the degree of variation in the air-fuel ratio between the cylinders does not change abruptly. Therefore, even if it is impossible to estimate the air-fuel ratio among the cylinders, the variation among the cylinders is small. Can be absorbed to some extent, and the air-fuel ratio of the collecting portion can be converged to the target value .

According to the fourth aspect, since the learned value is used, the past combustion history can be reflected in the feedback correction term, and it is impossible to estimate the air-fuel ratio of each cylinder. Even if there is, it is possible to further absorb the degree of variation between the cylinders and converge the air-fuel ratio of the collective portion to the target value.

[0014]

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

FIG. 1 shows the air- fuel ratio control of an internal combustion engine according to the present invention.
It is an overall schematic view of an air-fuel ratio feedback control system for implementing the control device. In the figure, reference numeral 10 is 4
1 shows a cylinder internal combustion engine, in which intake air introduced from an air cleaner 14 arranged at the tip of an intake passage 12 flows into the first to fourth cylinders through an intake manifold 18 while its flow rate is adjusted by a throttle valve 16. To be done. An injector 20 is provided near an intake valve (not shown) of each cylinder to inject fuel. The air-fuel mixture injected and integrated with the intake air is ignited by a spark plug (not shown) in each cylinder and burned to drive a piston (not shown). The exhaust gas after combustion is discharged to the exhaust manifold 22 via an exhaust valve (not shown), and the exhaust pipe 24
After being purified by the three-way catalytic converter 26, it is discharged to the outside of the engine. Further, the intake passage 12 is provided with a bypass passage 28 near the position where the throttle valve is arranged to bypass the throttle valve.

A crank angle sensor 34 for detecting a 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 sensor 36 for detecting the opening of the throttle valve 16 and an absolute pressure sensor 38 for detecting the intake pressure downstream of the throttle valve 16 as an absolute pressure are also provided. Further, in the exhaust system, a wide-range air-fuel ratio sensor 40 including an oxygen concentration detecting element is provided between the exhaust manifold 22 and the three-way catalytic converter 26, and outputs a value proportional to the oxygen concentration in the 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 wide-range air-fuel ratio sensor 40 is input to a detection circuit 46, where appropriate linearization processing is performed, and a linear characteristic proportional to the oxygen concentration in the exhaust gas in a wide range from lean to rich around the stoichiometric air-fuel ratio. The air-fuel ratio (A / F) is detected. The details are described in another application previously proposed by the present applicant (Japanese Unexamined Patent Publication No.
No. 71), further description is omitted. In the following description, this sensor is referred to as “LAF
Sensor "(linear EV sensor).
The output of the detection circuit 46 is supplied to the CP via the A / D conversion circuit 48.
U50, ROM52, RAM54 and the like are taken into a microcomputer and stored in RAM54.

Similarly, the analog output of the throttle opening sensor 36 and the like is converted to the level conversion circuit 56 and the multiplexer 5.
After the output of the crank angle sensor 34 is shaped by the waveform shaping circuit 62, the output value is counted by the counter 64, and the count value is stored in the microcomputer. Is input to In the microcomputer, the CPU 50 calculates a control value from the detected value according to a command stored in the ROM 52, drives the injector 20 of each cylinder via the drive circuit 66, and controls the solenoid valve 70 via the second drive circuit 68. To control the amount of secondary air passing through the bypass 28 shown in FIG.

FIG. 3 shows the air- fuel ratio control of the internal combustion engine according to the present invention.
Although it is a flow chart for explaining the operation of the control device, before entering the description, for convenience of understanding, a model for describing the behavior of the exhaust system proposed above will be briefly described.

First, in order to accurately separate and extract the air-fuel ratio of each cylinder from the output of one LAF sensor, it is necessary to accurately clarify the detection response delay of the LAF sensor. Therefore, for the time being, this delay was pseudo-modeled as a first-order delay system to create 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.

[0021]

(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).

[0023]

(Equation 2)

Therefore, by using the equation 2, the true air-fuel ratio can be obtained from the sensor output. That is, Equation 2
When is modified, it becomes as shown in Formula 3, so that the value at time k−1 can be back-calculated as in Formula 4 from the value at time k.

[0025]

(Equation 3)

[0026]

(Equation 4)

Specifically, if the expression 2 is expressed by a transfer function using the Z conversion, it becomes as shown in the expression 5. Therefore, by multiplying the inverse transfer function by the sensor output LAF of this time, the previous input air-fuel ratio can be realized in real time. Can be estimated. FIG. 6 shows a block diagram of the real-time A / F estimator.

[0028]

(Equation 5)

Next, the method of separating and extracting the air-fuel ratio of each cylinder based on the true air-fuel ratio obtained as described above will be explained. As described in the previous application, The value at the time k was considered as the weighted average considering the temporal contribution of the air-fuel ratio of the cylinder, and the value at the time k was expressed as in Equation 6. Note that "F / A" is used here because F (fuel amount) is a control amount, but "Air / fuel ratio" will be used in the following description for convenience of understanding unless there is a problem.
Note that the air-fuel ratio (or the fuel-air ratio) means a true value obtained by correcting the response delay previously obtained by Expression 5.

[0030]

(Equation 6)

That is, the air-fuel ratio of the collecting portion is weighted by C in the past combustion history of each cylinder (for example, the most recently burned cylinder is 40
%, Before that 30%. . . , Etc.). A block diagram of this model is shown in FIG.
become that way.

The equation of state is as shown in equation 7.

[0033]

(Equation 7)

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

[0035]

(Equation 8)

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, if x (k + 1) = x (k-3) assuming that the air-fuel ratio before 4TDC (that is, the same cylinder) is in a steady operation state in which the air-fuel ratio does not suddenly change, Equation 9 is obtained.

[0037]

(Equation 9)

Here, simulation results of the model obtained as described above will be shown. FIG. 8 shows that for a 4-cylinder internal combustion engine, the air-fuel ratio of 3 cylinders is set to 14.7 and only 1 cylinder has 1
The case where the fuel is supplied at 2.0 is shown. FIG. 9 shows the air-fuel ratio of the collecting portion at that time obtained by the above model.
In the figure, a step-like output is obtained, but when the response delay of the LAF sensor is further taken into consideration here, the sensor output has a waveform as shown as "model output value" in FIG. In the figure, “actual measurement value” is an actual measurement value of the LAF sensor output in the same case, and it is verified by comparison with this that the above model models the exhaust system of the multi-cylinder internal combustion engine well.

Therefore, the problem of an ordinary Kalman filter for observing x (k) in the equation of state and the equation of output expressed by the equation 10 results. When the Riccati equation is solved by using the weight matrices Q and R as in Equation 11, the gain matrix K is as shown in Equation 12.

[0040]

(Equation 10)

[0041]

[Equation 11]

[0042]

(Equation 12)

From this, A-KC is obtained as shown in Equation 13.

[0044]

(Equation 13)

The general structure of the observer is as shown in FIG. 11. However, 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.

[0046]

[Equation 14]

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

[0048]

(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 equation 16.

[0050]

(Equation 16)

FIG. 13 shows a combination of the above model and the observer. The simulation result is omitted since it is shown in the earlier application, but the air-fuel ratio of each cylinder can be accurately extracted from the air-fuel ratio of the collecting portion.

To explain with reference to the flow chart of FIG. 3 based on the above, first, in S10, the output values of the crank angle sensor 34, the LAF sensor 40, etc. are read out.
The LAF sensor output is a value at the exhaust system collecting part.

Subsequently, the program proceeds to S12, where it is determined whether or not the LAF sensor 40 is activated by an appropriate method. When the determination is affirmative, the program proceeds to S14 where it is determined whether the engine speed exceeds the observer limit speed. To do. As mentioned earlier,
When the rotation speed is high, the TDC cycle becomes short and the observer calculation time may not be secured. Also, at such a high rotation speed, due to the detection response delay described in the equation 1, LA
The responsiveness of the F sensor 40 is also insufficient.

On the other hand, as described in the equations 6 and after, in the present invention, the air-fuel ratio of the collecting portion is regarded as the sum of the combustion history of each cylinder, and the state equation is expressed in the recurrence form, and
The observer is designed on the assumption that the air-fuel ratio before TDC, that is, the air-fuel ratio of the same cylinder from the previous air-fuel ratio to the current air-fuel ratio does not change rapidly, and the observer matrix is sequentially calculated according to the ignition order.

By the way, conventionally, in the calculation of the fuel injection amount, generally, the previous calculated value is used as it is, that is, the calculation is thinned out, at the time of high rotation where the calculation time cannot be secured. However, in the observer calculation, as described above, since the air-fuel ratio of the previous cylinder is sequentially input and performed in accordance with the ignition order, when the calculation is thinned, the calculation result and the cylinder number cannot be matched, and each cylinder cannot be matched. The air-fuel ratio estimation of

Therefore, the engine speed which is difficult to secure the calculation time or has insufficient sensor response is set as the observer limit speed in advance, and the detected engine speed is compared with that in S14, and the detected engine speed is When it is determined that the engine speed is not within the limit speed, the process proceeds to S16, the observer matrix calculation is performed to estimate the air-fuel ratio (A / F) of each cylinder, and when it is determined that the observer limit speed is reached, the process proceeds to S18. The observer (matrix operation) is stopped. If it is determined in S12 that the sensor has not been activated yet, the program is immediately terminated.

Since this embodiment is configured as described above, the observer calculation time cannot be secured in the high rotation range.
If the responsiveness of the sensor is not sufficient, the observer's calculation is stopped, in other words, the calculation is not thinned out but stopped completely, so that the estimated value does not correspond to the cylinder. There is no inconvenience. The operation state in which the observer calculation is stopped includes, in addition to high rotation, a low load in which exhaust gas takes a long time to reach, or a fuel cut in which exhaust gas does not occur.

FIG. 14 shows a second embodiment of the present invention.
It is a flow chart similar to FIG. In the case of the second embodiment, an example is shown in which the air-fuel ratio of each cylinder is feedback-controlled to the target value based on the estimated value.

That is, since the observer was able to estimate the air-fuel ratio of each cylinder from the air-fuel ratio of the collecting portion, PI
It is possible to control the air-fuel ratio for each cylinder using a control law such as D. Specifically, as shown in FIG. 15, the collective feedback correction term KLAF is obtained from the sensor output (collecting section A / F) and the target air-fuel ratio using the PID control law, and the observer estimated value # nA / F is calculated. The feedback correction term #nKLAF (n: cylinder) for each cylinder is obtained.
More specifically, the feedback correction term #nKLAF for each cylinder is obtained by dividing the aggregate A / F by the previous calculation value of the average value of the feedback correction term #nKLAF for each cylinder and the observer estimated value #nA. It is determined using the PID rule so as to eliminate the deviation from / F.

As a result, the air-fuel ratio (A / F) of each cylinder converges to the collecting part air-fuel ratio (A / F), and the collecting part air-fuel ratio (A / F).
F) converges to the target air-fuel ratio (A / F),
As a result, the air-fuel ratios (A / F) of all cylinders converge on the target air-fuel ratio (A / F). Here, the fuel injection amount of each cylinder #
nTout (specified by the valve opening time of the injector) is # nTout = Tim × KCMD × KTOTAL × # nK
It is determined by LAF × KLAF. In the above, Tim: basic value, KCMD: target air-fuel ratio, and KTOTAL: other correction terms. In addition to this, there are addition terms such as a battery correction term, but they are omitted. The details of such control are described in Japanese Patent Application No. 5-251138 previously proposed by the present applicant, and therefore further description will be omitted.

With this configuration, the cylinder-by-cylinder feedback correction term #nKLAF functions to converge each cylinder A / F (air-fuel ratio) to the collecting portion A / F (air-fuel ratio), and its average value converges to 1. Therefore, the correction term did not diverge, and as a result, only the variation between the cylinders could be absorbed. On the other hand, the collecting section A / F (air-fuel ratio) is the target A
Since it converges to / F (air-fuel ratio), as a result, the air-fuel ratios of all the cylinders can converge to the target A / F (air-fuel ratio).

That is, in the configuration of the feedback loop for each cylinder shown in FIG. 15, when the feedback correction term #nKLAF for each cylinder is set to 1, the feedback loop is until the deviation disappears, that is, the denominator (feedback correction term average for each cylinder is averaged). Value) becomes 1, which means that the operation is performed to eliminate the air-fuel ratio variation among the cylinders. It should be noted that although it is shown as A / F (air-fuel ratio) in FIG.
A (fuel air ratio) is used.

Based on the above, the second embodiment will be described with reference to the flow chart of FIG. Note that this program determines the fuel injection amount of each cylinder at a predetermined crank angle from TDC, that is, for each injection order (first cylinder, third cylinder, fourth cylinder, second cylinder).

First, in S100, the engine speed Ne,
Intake pressure Pb, detection A / F (air-fuel ratio), etc. are read,
If the determination is negative, the process proceeds to S102, and if negative, the process proceeds to S104 to determine whether the fuel is cut. If the result in S104 is negative, the program proceeds to S106, in which the basic value Tim is retrieved. This is done by searching a map (not shown) set from the engine speed and the intake pressure.

Subsequently, the flow proceeds to S108, where the LAF sensor 40 is
S is determined if the activation of the
In step 110, it is determined whether the detected engine speed is within the observer limit speed described above. When the result in S110 is negative, the program proceeds to S112 in which the observer matrix calculation is performed to estimate the air-fuel ratio (A / F) of each cylinder, and the process proceeds to S114 to calculate the feedback correction term #nKLAF for each cylinder.

That is, as described above with reference to FIG.
Eliminates the deviation between the target value obtained by dividing the collective air-fuel ratio (A / F) by the previous calculated value of the average value of the feedback correction term #nKLAF for each cylinder and the observer estimated air-fuel ratio (A / F) of each cylinder. To be set appropriately based on the PID rule.
Next, in S116, the collective feedback correction term KLAF is calculated using the PID control rule so as to eliminate the deviation between the collective air-fuel ratio detected from the output of the LAF sensor 40 and the target air-fuel ratio. Next, the routine proceeds to S118, where the fuel injection amount #nTout for each cylinder is determined as shown in the figure, and S12
The process proceeds to 0 and outputs to the drive circuit of the injector 20 of the cylinder.

If it is determined in S110 that the observer limit rotational speed is reached, the flow proceeds to S122 to stop the observer (matrix calculation), and proceeds to S124 where the feedback correction term #nKLAF for each cylinder is set to the previous value # nKLAFn-1. (For simplification of illustration, subscript n
Is omitted). That is, due to the consistency with the cylinder, the observer matrix calculation is not thinned out and is completely stopped, and while the observer is stopped, the fuel injection amount is determined based on the value immediately before the stop.

That is, the degree of variation in the air-fuel ratio among the cylinders does not originally change so much, and the value of the feedback correction term for each cylinder is a small value as compared with the value of the collective feedback correction term, which is around 1. Becomes the value of. Also,
The existence of unpredictable areas is unavoidable due to the capacity of the planned observer. Therefore, it is possible to reduce the degree of fluctuation of the air-fuel ratio by using the value before entering the disabled region in the relatively smaller feedback correction term for each cylinder.

If it is determined in S108 that the LAF sensor 40 has not been activated, the process proceeds to S126.
Therefore, the cylinder-by-cylinder feedback correction term #nKLAFidle calculated during idling before the engine is stopped is read from the backup section of the RAM 54, the process proceeds to S130, and the value of the collective feedback correction term KLAF is set to 1 (meaning that collective feedback control is stopped ), S1 from those values
In step 18, the fuel injection amount #nTout is calculated.

That is, since it is judged at S108 that the activation is not completed at the engine start (the state after the cranking at S102), at that time, at the idle time before the engine is stopped. This is because the correction using the calculated value can suppress the variation in the air-fuel ratio between the cylinders as much as possible. It should be noted that the reason why the value calculated at the time of idling is used is that the accuracy of observer estimation is high because the calculation time is long due to low rotation.

When it is judged to be cranking in S102, the routine proceeds to S132, where the fuel injection amount Ticr during cranking is calculated from the water temperature detected by the water temperature sensor (not shown in FIG. 1) according to a predetermined characteristic, and S134. Then, the fuel injection amount Tout is determined on the basis of the equation (the description is omitted) of the starting mode. Further, when it is determined in S104 that the fuel is cut, the routine proceeds to S136, where the fuel injection amount T
Out is set to zero, the observer (matrix calculation) is stopped in S138, and the feedback correction term for each cylinder is set to the value immediately before the stop, similarly to S124 in S140. S13
The reason why the observer (matrix calculation) is stopped in 8 is that combustion is not performed and the correct air-fuel ratio cannot be measured.

Since this embodiment is configured as described above, if the observer computation time cannot be secured, such as when the rotation speed is high, or if the response of the LAF sensor is not sufficient, the observer matrix computation is not canceled and the operation is completely stopped. As a result, there is no possibility that the consistency with the cylinder is lost and the estimation is erroneous.

Further, even during the observer stop period, it is considered that the variation between the cylinders of the fuel supply system does not change extremely depending on the region. Therefore, the value calculated immediately before the stop is used. It is possible to absorb the variation in the air-fuel ratio of (3) to a considerable extent and accurately converge the air-fuel ratio of each cylinder to the target value. Accordingly, when the target air-fuel ratio is set to the theoretical air-fuel ratio, the three-way catalyst 2
The purification rate of 6 can be improved. Further, if the target air-fuel ratio is set to the lean side, lean burn control can be realized with high accuracy.

FIG. 16 is a partial view of a flow chart showing the third embodiment of the present invention. Explaining with a focus on the points different from the second embodiment, in S1240 corresponding to S124 in FIG. 14, when the observer (matrix calculation) is stopped, the feedback correction term #nKLAF for each cylinder is given.
Was fixed at 1.0. That is, as described above, the degree of variation in the air-fuel ratio between the cylinders is originally small and is expected to be set to a value near 1. Therefore, when the observer (matrix calculation) is stopped, The value of the feedback correction term was immediately set to 1. This can simplify the configuration. The remaining structure and effects are
It is not different from the second embodiment.

FIG. 17 is a partial view of a flow chart showing the fourth embodiment of the present invention. Explaining with a focus on the points different from the second embodiment, in S1280 corresponding to S128 in FIG. 14, when the activation of the sensor is not completed, the feedback correction term #nKLA for each cylinder.
F was set to the value #nKLAFSTY obtained by learning.

That is, the value of the feedback correction term for each cylinder in the idle operation state is expressed by the following equation: # nKLAFsty = C × # nKLAF + (1-C) × #
Learning was always performed using nKLAFstyn-1, and the latest learning value was used when sensor activation was not completed. Here, #nKLAFsty: latest learning value, C: weighting coefficient, #n
KLAFsytn-1: Previous learning value. With this configuration, the past combustion history can be better reflected in the correction term as compared with the second embodiment. The remaining structure and effects are the same as those of the second embodiment.

Further, the case where the wide range air-fuel ratio sensor is used as the air-fuel ratio sensor has been described as an example, but it is also applicable to the case where the so-called O ₂ sensor is used to control the air-fuel ratio.

[0078]

According to the first and second aspects of the invention, in an apparatus that estimates and controls the air-fuel ratio of each cylinder according to the combustion history, the estimation is stopped in an operating state where it is difficult to estimate the air-fuel ratio, In other words, it is not the thinning-out but the complete stop, so that the estimation is not erroneous because the consistency with the cylinder is lost.

[0079] Also In the claims 1 and 2 wherein, without having to erroneously estimated the degree of variation in air-fuel ratio between the cylinders, even in a region which can not be estimated observer, a significant degree or it is possible to converge the current engagement portion air-fuel ratio to the target value.

According to the third aspect of the present invention, the degree of variation in the air-fuel ratio among the cylinders does not change abruptly, so even if it is impossible to estimate the air-fuel ratio among the cylinders, the variation among the cylinders can be varied. Can be absorbed to some extent, and the air-fuel ratio of the collecting portion can be converged to the target value .

According to the fourth aspect, since the learning value is used, the past combustion history can be reflected in the feedback correction term, and it is impossible to estimate the air-fuel ratio of each cylinder. Even if there is, it is possible to further absorb the degree of variation between the cylinders and converge the air-fuel ratio of the collective portion to the target value.

[Brief description of the drawings]

FIG. 1 is a block diagram generally showing an air-fuel ratio feedback control device for an internal combustion engine, which realizes an air- fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 2 is a block diagram showing details of a control unit in FIG. 1;

FIG. 3 is a flow chart showing the operation of the air- fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 4 is a block diagram showing an example of modeling the detection operation of the air-fuel ratio sensor described in the previous application.

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 an air-fuel ratio sensor.

FIG. 7 is a block diagram showing a model showing a behavior of an exhaust system of an internal combustion engine.

8 is a graph showing the four-cylinder internal combustion engine using the model shown in FIG. 7, where the air-fuel ratio of three cylinders is 14.7 and the air-fuel ratio of one cylinder is 1;
FIG. 4 is a data diagram showing a case where fuel is supplied at 2.0.

9 is a data diagram showing the air-fuel ratio of the collecting portion of the model of FIG. 7 when the input shown in FIG. 8 is given.

FIG. 10 compares the data showing the air-fuel ratio of the collecting portion of the model of FIG. 7 in consideration of the response delay of the LAF sensor with the input shown in FIG. 8, and the measured value of the LAF sensor output in the same case. It is a graph figure.

FIG. 11 is a block diagram showing a configuration of a general observer.

FIG. 12 is a block diagram showing a configuration of an observer used in the previous application.

13 is an explanatory block diagram showing a configuration in which the model shown in FIG. 7 and the observer shown in FIG. 12 are combined.

FIG. 14 is a flowchart similar to FIG. 3, showing a second embodiment of the present invention.

FIG. 15 is a block diagram showing cylinder-by-cylinder feedback control of the air-fuel ratio, which is planned in the present invention.

FIG. 16 is a flow chart of FIG. 14 showing the third embodiment of the present invention.
It is a partial view of a chart.

FIG. 17 is a flow chart of FIG. 14 showing the fourth embodiment of the present invention.
It is a partial view of a chart.

[Explanation of symbols]

 10 Internal Combustion Engine 18 Intake Manifold 20 Injector 22 Exhaust Manifold 40 Air-Fuel Ratio Sensor (LAF Sensor) 42 Control Unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-180040 (JP, A) JP-A-60-166734 (JP, A) Practical application Sho-59-165941 (JP, U)

Claims (4)

(57) [Claims] 1. A. Placed at the exhaust system collecting part of a multi-cylinder internal combustion engine
Air-fuel from the output of the air-fuel ratio sensor which is of the exhaust system set unit
Ratio, and set the detected air-fuel ratio of the exhaust system collecting part to the target value.
A set portion feedback correction term KLAF for control Gosuru
First means for computing, b . The output value of the air-fuel ratio sensor is set as a model that describes the behavior of the exhaust system by regarding the combustion history of each cylinder as a weighted average value obtained by multiplying a predetermined coefficient, and sets the air-fuel ratio of each cylinder as a state variable. Second means for setting the state equation to be set , setting the observer for observing the internal state, and obtaining the output thereof, c . From the observer output, the air-fuel ratio of each cylinder # nA / F
A third means for estimating d . The estimated air-fuel ratio # nA / F of each cylinder is set as a target value.
Each cylinder feedback correction term you feedback control
Fourth means for computing #nKLAF, e . Fifth means for detecting the operating state of the internal combustion engine, and f . For each cylinder, the collective feedback correction term KLAF
The internal combustion engine based on the feedback correction term #nKLAF
The feedback control of the air-fuel ratio of the engine feedback
Control means, air-fuel ratio control apparatus for an internal combustion engine wherein the Fi
The feedback control means is set in front of the detected operating condition.
Serial third said by means of the air-fuel ratio in each cylinder # nA / F estimated is determined difficult Rutoki is air #n of the respective cylinders
A / F estimation is stopped , and
Feedback control based on the clock correction term #nKLAF
Then, based on the collective section feedback correction term KLAF,
An air-fuel ratio control device for an internal combustion engine, wherein the air-fuel ratio of the internal combustion engine is feedback-controlled based on the above . 2. The feedback control means is provided for each cylinder.
Feedback bar based on feedback correction term #nKLAF
Tsu To cancel click control, the each cylinder feedback correction term #nKLAF air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein, wherein to Rukoto to a predetermined value. 3. The feed value for each cylinder is the predetermined value.
3. The air- fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the value is # nKLAFn-1 immediately before the feedback control based on the feedback correction term #nKLAF is stopped. 4. The air- fuel ratio control device for an internal combustion engine according to claim 3 , wherein the predetermined value is a learned value in a predetermined operating region.