JP2001073844A - Air-fuel ratio presuming device for each cylinder of internal-combustion engine and control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the presumptive accuracy of the air-fuel ratio of each cylinder by an observer and implement the feedback control of the air-fuel ratio using the obtained estimate. SOLUTION: In case the number of combustion history to be taken into consideration with an internal-combustion engine is three or more, the weighting factor of the weighted mean for the prior combustion history excluding the combustion history more than two immediately before and less than the mentioned number of combustion history to be taken into consideration is made zero. Estimate is used for feedback control of the air-fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder-by-cylinder air-fuel ratio estimating apparatus and control apparatus for an internal combustion engine, and more specifically, an air-fuel ratio sensor is provided in an exhaust system assembly of a multi-cylinder internal combustion engine.
A model describing the behavior of the exhaust system is set, a sensor output is input, and an observer for observing the internal state is provided, and a cylinder-by-cylinder air-fuel ratio estimating apparatus for estimating the air-fuel ratio of each cylinder from the output is provided. In addition, the present invention relates to a method of improving the accuracy of estimating the air-fuel ratio of each cylinder by an observer and performing feedback control of the air-fuel ratio based on the estimated value.

[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-described configuration, the operating condition frequently changes, and it is necessary to change the calculation parameters accordingly. In actual control, a sufficient calculation time cannot always be obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the technique proposed above, and to provide a cylinder-by-cylinder air-fuel ratio estimating apparatus for an internal combustion engine, in which the calculation is simplified and the observer is further improved in estimating the air-fuel ratio of each cylinder. The purpose is to provide.

It is a further object of the present invention to provide a cylinder-by-cylinder air-fuel ratio feedback control device for performing air-fuel ratio feedback control based on the value estimated as described above.

[0006]

According to a first aspect of the present invention, an air-fuel ratio sensor is disposed in an exhaust system collecting portion of a multi-cylinder internal combustion engine, and an input of each cylinder is obtained from an output of the sensor. A device for estimating an air-fuel ratio of an air-fuel mixture, wherein a model describing an exhaust system behavior is set by regarding the output value of the sensor as a weighted average value obtained by multiplying a combustion history of each cylinder by a weight coefficient Cn. First means for setting the state equation using the air-fuel ratio of each cylinder as a state variable, setting an observer for observing the internal state thereof, and obtaining the output thereof, and estimating the air-fuel ratio of each cylinder from the output of the observer When the number of combustion histories to be considered in the internal combustion engine is three or more, in the cylinder-by-cylinder air-fuel ratio estimation device having the second means, From the number of combustion history Except no combustion history, and as configured to zero the weighting factors Cn weighted average of the previous combustion history.

According to a second aspect of the present invention, there is provided an air-fuel ratio feedback control device for each cylinder of an internal combustion engine, wherein an output value of an air-fuel ratio sensor arranged in an exhaust system collecting section of a multi-cylinder internal combustion engine is stored in a combustion history of each cylinder. When the number of combustion histories to be considered in the internal combustion engine is 3 or more and the number of combustion histories to be considered in the internal combustion engine is 3 or more, A state equation using the air-fuel ratio of each cylinder as a state variable by setting a model that describes the behavior of the exhaust system by setting the weighted average weight coefficient Cn of the previous combustion history to zero, excluding the combustion history less than A first means for setting an observer for observing the internal state thereof and obtaining its output; a second means for estimating an air-fuel ratio # nA / F of each cylinder from the observer output; Mind Air-fuel ratio # nA / F section each cylinder feedback correction performs feedback control to the target value #nK of
A third means for calculating the LAF and a feedback control means for feedback-controlling the air-fuel ratio of the internal combustion engine based on the cylinder-by-cylinder feedback correction term #nKLAF are provided.

According to a third aspect of the present invention, the air-fuel ratio of the exhaust system collecting section is detected from the output of the air-fuel ratio sensor, and the detected air-fuel ratio of the exhaust system collecting section is controlled to a target value. A fourth means for calculating a collective feedback correction term KLAF; wherein the feedback control means performs feedback control of the air-fuel ratio of the internal combustion engine based on the collective feedback correction term KLAF and a cylinder-by-cylinder feedback correction term #nKLAF; It was configured as follows.

[0009]

According to the first aspect, the weighting coefficient C of the weighted average
Although n changes according to the operating state, for example, in a multi-cylinder internal combustion engine, if the value of the combustion history before the two immediately preceding combustion histories is set to zero, the total value of the weighting coefficients is 1, so that the two combustion histories are 1. One of the histories is identified, and the other is obtained by subtracting 1 from the history. As a result, when the number of cylinders is four, it is sufficient to identify the coefficient for one cylinder, and when compared to identifying the coefficient for three cylinders, the estimation accuracy of the observer matrix is improved, and the coefficient identification accuracy of the observer is improved. So
The accuracy of estimating the air-fuel ratio of each cylinder is improved.

The weighting coefficient Cn of the weighted average of previous combustion histories, excluding combustion histories that are equal to or greater than the two immediately preceding combustion histories and less than the number of combustion histories to be considered, is set to zero. The reason is that, for an internal combustion engine having a large number of cylinders to be estimated,
This is because there is a possibility that the number of cylinders for which the weight coefficient is to be obtained will be increased, as will be described later. Note that the order of the observer itself is an integral multiple of the estimated number of cylinders.

In the second aspect, the air-fuel ratio # nA / F of each cylinder estimated by the same method as described in the first aspect.
Is calculated based on the cylinder-by-cylinder feedback correction term #nKLAF, which feedback-controls the air-fuel ratio of the internal combustion engine to the target value. The air-fuel ratio feedback control of each cylinder can be performed with high accuracy only by using the above sensor.

[0012] When the number of combustion histories to be considered in the internal combustion engine is three or more, the combustion histories excluding the combustion histories that are more than the two immediately preceding combustion histories and less than the number of combustion histories to be considered are excluded. The weighted average weight coefficient Cn of the previous combustion history is set to zero. "However, in the embodiment, when the number of combustion histories to be considered in the internal combustion engine is three or more, the two immediately preceding combustion The weight coefficient Cn of the weighted average for the previous combustion history excluding the history is set to zero.

According to a third aspect of the present invention, the air-fuel ratio of the exhaust system collecting section is detected from the output of the air-fuel ratio sensor, and the detected air-fuel ratio of the exhaust system collecting section is controlled to a target value. A fourth means for calculating a collective feedback correction term KLAF; wherein the feedback control means performs feedback control of the air-fuel ratio of the internal combustion engine based on the collective feedback correction term KLAF and a cylinder-by-cylinder feedback correction term #nKLAF; With such a configuration, in addition to the effect described in claim 2, the air-fuel ratio of each cylinder converges to the collecting air-fuel ratio, and the collecting air-fuel ratio converges to the target air-fuel ratio. The air-fuel ratios of all the cylinders converge to the target air-fuel ratio, and the convergence of the air-fuel ratio feedback control can be improved.

[0014]

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

FIG. 1 is a schematic diagram generally showing an air-fuel ratio feedback control device for realizing a cylinder-by-cylinder air-fuel ratio estimation device for an internal combustion engine according to the present invention. In the figure, reference numeral 1
0 indicates a four-cylinder internal combustion engine, and the intake air introduced from the air cleaner 14 disposed at the tip of the intake passage 12 is:
The gas flows into the first to fourth cylinders through the intake manifold 18 while the flow rate is adjusted by the throttle valve 16. 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 an ignition plug (not shown) in each cylinder and burns to drive 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, the intake passage 12 has a bypass passage 2 that bypasses the vicinity of the throttle valve arrangement position.
8 are provided.

In a distributor (not shown) of the internal combustion engine 10, a crank angle sensor 34 for detecting a crank angle position of a piston (not shown) is provided.
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, an analog output from the throttle opening sensor 36 and the like is supplied to a level conversion circuit 56 and a 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.

Before describing the present invention, a model for describing the behavior of the exhaust system proposed earlier will be briefly described for the sake of convenience.

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, this delay is tentatively modeled as a first-order delay system, and a model as shown in FIG. 3 is created. Here LA
When 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 by the period ΔT, it becomes as shown in Expression 2. FIG. 4 is a block diagram showing the equation (2).

[0023]

(Equation 2)

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

[0025]

(Equation 3)

[0026]

(Equation 4)

More specifically, if Equation 2 is expressed as a transfer function using Z-transformation, Equation 5 is obtained, and the inverse input transfer function is multiplied by the current sensor output LAF to determine the previous input air-fuel ratio in real time. Can be estimated. FIG. 5 shows a block diagram of the real-time A / F estimator.

[0028]

(Equation 5)

Next, a 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 described. The value at the time k was considered as a weighted average in consideration of the temporal contribution of the air-fuel ratio of the cylinder, and was represented as in Expression 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 the sum of the values obtained by multiplying the past combustion history of each cylinder by a weighting coefficient Cn (for example, 40% for the most recently burned cylinder, 30% before that, etc.). expressed. This model is represented by a block diagram as shown in FIG.

The state equation is as shown in the following equation (7).

[0033]

(Equation 7)

When the air-fuel ratio of the collecting portion is defined as 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
(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 are shown for the model obtained as described above. FIG. 7 shows that the air-fuel ratio of three cylinders is set to 14.7 for a four-cylinder internal combustion engine,
The case where the fuel is supplied at 2.0 is shown. FIG. 8 shows the air-fuel ratio of the collecting portion at that time obtained by the above model.
Although a step-like output is obtained in the same figure, if the response delay of the LAF sensor is further taken into consideration, the sensor output has a waveform smoothed as shown in FIG. 9 as “model output value”. 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.

Thus, the problem is reduced to the problem of the ordinary Kalman filter for observing x (k) in the state equation and the output equation shown in Expression 10. 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)

When A-KC is obtained from this, the following equation (13) is obtained.

[0044]

(Equation 13)

Although the general observer configuration is as shown in FIG. 10, there is no input u (k) in the present model, so that only y (k) is input as shown in FIG. When this is expressed by a mathematical formula, it becomes as shown in Expression 14.

[0046]

[Equation 14]

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

[0048]

(Equation 15)

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

[0050]

(Equation 16)

FIG. 12 shows a combination of the above-described model and 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.

Since the air-fuel ratio of each cylinder can be estimated from the air-fuel ratio of the collecting section by the observer, the air-fuel ratio can be controlled for each cylinder using a control law such as PID. More specifically, as shown in FIG. 13, an aggregate feedback correction term KLAF is obtained from the sensor output (aggregate A / F) and the target air-fuel ratio using a PID control law, and the observer estimated value # nA / F is used. A feedback correction term #nKLAF (n: cylinder) for each cylinder is obtained. More specifically, the feedback correction term #nKLAF for each cylinder is changed to the feedback correction term #n for each cylinder.
The target value obtained by dividing the average value of KLAF by the previous calculation value and the observer estimated value # nA / F are determined using the PID rule so as to eliminate the deviation.

As a result, the air-fuel ratio (A / F) of each cylinder converges to the air-fuel ratio (A / F) at the collecting portion, and the air-fuel ratio (A / F) at the collecting portion.
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 (defined by the injector valve open time) 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. Further, there are addition terms such as battery correction, but they are omitted. still,
The details of such control are described in Japanese Patent Application No. Hei.
No. 251138, further description is omitted.

The present invention will be described on the premise of the above.

FIG. 14 shows a first embodiment of the present invention.
You. Weighting coefficient C of the above-mentioned weighted average ₁ , C_Two , C_Three , C
_Four About this time, it is C of the exhaust (combustion) cylinder._n,Previous
Times, 2 times before and 3TDC before exhaust (combustion) cylinder
To C_n-1 , C_n-2 , C _n-3 And before and after
Weights for exhaust (combustion) cylinders before and 3TDC
Number C_n-2 , C_n-3 As zero, as shown in the figure, the most recent (immediately before)
Of the two cylinders, that is, the two most recent (immediately before)
Only the burning history was requested. For example, now the first
Assuming that the cylinder is an exhaust (combustion) cylinder, the third cylinder and the
The weight coefficient for the four cylinders was set to zero.

As described in the previous application, the weighting coefficient Cn indicating the behavior of the air-fuel ratio at the collecting section needs to be changed according to the operating state. In any case, the value of the weighting coefficient Cn is accurately determined. It is difficult to know. Therefore, in a four-cylinder internal combustion engine, the most recent (immediate) two in the exhaust (combustion) order
The weight coefficients of the other combustion histories except for one combustion history were set to zero. Since the weighting factor is 1 as a whole, it is obtained for one of the most recent (immediate) combustion histories, and the other is obtained by subtracting the obtained value from 1 (this is the weighting factor in the earlier application). Is the same for all cylinders). That is, the configuration of FIG.
Modified as in 4.

When this was verified by simulation, good results were obtained. That is, it is extremely difficult as a practical matter to identify three weighting factors Cn from the beginning, and there is a possibility that an incorrect identification value may be used. With the above configuration, the number of coefficients to be identified is sufficient, so that the calculation interval is shortened, and the verification accuracy in simulation has been improved. This problem is also related to the distance from the cylinder exhaust port to the arrangement of the air-fuel ratio sensor in the collecting section. When the distance is relatively short, the configuration as described above can improve the estimation accuracy.

In the present embodiment, a four-cylinder internal combustion engine is taken as an example. However, it is expected that the weight coefficient for five to six cylinders will be sufficient if it is similarly obtained for the two nearest cylinders. For an internal combustion engine having a larger number of cylinders, there is a possibility that the number of cylinders for which the weight coefficient is to be obtained will be increased.

In the V-type engine, since an air-fuel ratio sensor is provided for each bank, a cylinder having a weight coefficient of zero in each bank is selected in accordance with the exhaust order. For example, in a V-type 6 cylinder (the right bank cylinders are first, second, and third cylinders, and the left bank cylinders are fourth, fifth, and sixth cylinders), and the ignition order is 1 (right) -4 (left ) -2 (right) -5 (left) -3
Assuming that (right) -6 (left), assuming that the third cylinder has just burned for the right bank, the weight coefficient for the first cylinder is set to zero. Assuming that the fourth cylinder has just burned for the left bank, the weight coefficient for the fifth cylinder is set to zero. It should be noted that the order of the observer is an integer multiple of the estimated number of cylinders, preferably one, and is four in this embodiment.

FIG. 15 is an explanatory diagram showing a second embodiment of the present invention.

The observer matrix is represented by the equation (14).
Therefore, the value A-KC is represented by a 4 × 4 matrix, in which the weight coefficient C changes according to the engine operating state as described above. Therefore, it is conceivable that a solution is obtained in advance over the expected change range of the engine speed and the engine load, and the matrix values are mapped. However, even in that case, when there is no value corresponding to the map value, it is not desirable to obtain the value by the interpolation operation because the matrix value is not compensated. Furthermore, since the equation of Equation 14 is a recurrence equation, it is necessary to repeat the operation when the coefficient changes during the operation.

Therefore, as shown in FIG. 15, a plurality of observer matrices from 1 to n are prepared and operated in parallel, and one of the matrix values is selected according to the engine operating state. As a result, the calculation time can be shortened, and the accuracy of estimating the cylinder air-fuel ratio of the observer can be improved. Here, the number of observer matrices is 2
Any number is acceptable as long as it is equal to or more than the number. Also, it is not necessary to always perform all the operations of the observer matrix at the same time, and it is also possible to predict a change in the engine operating state and perform only the observer matrix corresponding to the operating state.

In the prior application, when designing the observer, the weighted distributions Q and R of the Riccati equation are calculated as follows: Q / R = 1/1
And This evaluation function is very important for the performance of the observer. After verification through simulations, the convergence time decreases as the value of Q / R increases. It was confirmed that it hardly changed. Therefore, from the limit, Q / R ≧ 10
When set to 0, good estimation results could be obtained. That is, since the evaluation function is a dimensionless number, it can take any value and is rather difficult to determine.
As a result of repeated verification, it was found that the estimation accuracy was improved by setting the Q / R to 100 or more.

FIG. 16 is a flow chart showing a third embodiment of the present invention. The third embodiment relates to a case where the air-fuel ratio is estimated for an internal combustion engine having a so-called variable valve timing mechanism.

The variable valve timing mechanism will be briefly described with reference to FIGS.

In the case of the illustrated example, the variable valve timing mechanism includes three rocker arms 614, 616, 618 rotatably disposed on rocker shafts 612 provided near the intake valve 54 and the exhaust valve 56, respectively. Since the configuration is the same on the exhaust side and the exhaust side, a suffix i (e) is added after the reference numeral in the drawings, and both will be described in common below). Each of the rocker arms has two low-speed cams attached to a camshaft (not shown) and one high-speed cam having a shape protruding in the radial direction as compared with the low-speed cam (both figures are shown). (Not shown).

The rocker arms 614, 616, and 618 have oil passages 650, holes 632, holes 634, 636, and pins 6.
40, 642, 644 and the like, and a hydraulic pressure switching mechanism 660 inserted between the oil passage 650 and a hydraulic source (not shown) is connected to the oil passage 650 via a solenoid valve 680. Is supplied / stopped, whereby the pin is advanced / retracted and the rocker arm is connected / released. The valve timing and the lift amount are determined based on the movement of the high-speed cam when the rocker arm is connected, and based on the movement of the low-speed cam when released. Since the details of the variable valve timing mechanism are described in the above-mentioned prior art, the description will be limited to this extent.

The connection / disconnection is specifically determined from the engine speed Ne and the intake pressure Pb, as shown in FIG. Hereinafter, the case using the high speed cam is referred to as “HiV / T”, and the case using the low speed cam is referred to as “LoV / T”.
In, the valve timing is advanced and the overlap amount is increased and the lift amount is increased as compared with LoV / T. The hydraulic pressure switching mechanism 660
Is provided with a V / T sensor 600 composed of a hydraulic switch, and the connection / release of the rocker arm through the hydraulic pressure of the oil passage 650, that is, the valve timing is LoV / T and HiV / T.
To which of the two is controlled. As indicated by the imaginary line in FIG. 2, the output of the V / T sensor 600 is input to the control unit 42.

In order to capture the temporal behavior of the air-fuel ratio (A / F) of the collecting section, the sampling timing of the air-fuel ratio (A / F) must be optimized in the calculation of the air-fuel ratio (A / F) estimation observer for each cylinder. It is necessary to plan. That is, although the output of the LAF sensor clearly shows a characteristic synchronized with the engine speed, since the control unit performs digital sampling, the behavior may not be able to be detected depending on the timing. Although the appropriate sample timing changes depending on the engine speed and the engine load, it is considered that the influence of the valve timing is particularly large. Therefore, in the internal combustion engine having the variable valve timing mechanism as described above, the sample timing is determined from the engine speed, the engine load, and the valve timing.

Similarly, since the behavior of the air-fuel ratio (A / F) changes depending on the valve timing, it is necessary to change the observer matrix in synchronization with the switching of the valve timing. However, the estimation of each cylinder air-fuel ratio (A / F) cannot be performed instantaneously, and the convergence of the observer operation requires several operations. Therefore, the operation using the observer matrix before the valve timing change and the observer matrix after the change are performed. Are performed at the same time in an overlapped manner, and after it is determined that the observer calculation has converged, that is, after the valve timing changing operation is completed, the estimation result of each cylinder air-fuel ratio (A / F) is changed.

Referring to the flow chart of FIG. 16, first, at S100, the engine speed Ne, the intake pressure Pb, and the valve timing V / T are read, and the program proceeds to S102, at which the valve timing is HiV / T or LoV / T. Judge and proceed to S104, S106 according to the judgment result to Hi
Or search a timing map for Lo valve timing. FIG. 19 shows the characteristics.

It is desirable that the LAF sensor output be sampled at a position close to the actual inflection point. However, if the inflection point (peak value) is constant for the sensor reaction time, the crank speed increases as the engine speed decreases. Occurs at an angle. Also, it is expected that the higher the engine load, the higher the exhaust gas pressure and volume, the higher the exhaust gas flow rate and the earlier the arrival time at the sensor. Therefore, the characteristics of the map are set such that the value sampled at a faster crank angle is selected as the engine speed Ne is lower or the intake pressure Pb is higher.
Here, “early” means a relatively old value sampled at a position closer to the previous TDC.

Further, regarding the relationship with the valve timing, an arbitrary value Ne1 of the engine speed is Ne1-Lo for the Lo side, Ne1-Hi for the Hi side, and the arbitrary value of the intake pressure is Lo for the Lo side. Pb1
Assuming that Pb1−Hi for −Lo and Hi sides, the characteristics of the map are Pb1−Lo> Pb1−Hi, Ne1−Lo.
> Ne1-Hi. That is, in the case of HiV / T, the opening point of the exhaust valve is earlier than that of LoV / T, so that if the values of the engine speed or the intake pressure are the same, an earlier sampling value is selected. .

Then, the process proceeds to S108, where the sensor output is sampled from the retrieved map value, and the process proceeds to S110, where the observer matrix shown in Equation 14 is calculated from the sampled value for HiV / T, and then the process proceeds to S112. Is performed for LoV / T. Then S114
Then, the valve timing is determined again, and according to the determination result, the process proceeds to S116, 118 to select the calculation result and finish. Based on the calculation result, the air-fuel ratio feedback control for each cylinder as described with reference to FIG. 13 is performed.

Since the third embodiment is configured as described above, the sampling value of the air-fuel ratio sensor output is selected in consideration of the engine speed, the intake pressure and the valve timing. Since the observer matrix is changed according to the timing, the estimation accuracy of the air-fuel ratio of each cylinder is improved.

FIG. 20 is a flow chart similar to FIG. 16, but showing a fourth embodiment of the present invention.

The fourth embodiment is a modified example of the third embodiment. To be described below, after reading the engine speed Ne and the like in S200, the process proceeds to S202 and proceeds to LoV /
A timing map for T is searched, and the process proceeds to S204, where L
Select the sampling value of the sensor output for oV / T,
Proceeding to 206, an observer matrix operation is performed for LoV / T. Subsequently, the process proceeds from S208 to 212 to perform the same processing on the HiV / T side.

Then, the program proceeds to S214, in which the valve timing is determined, and in accordance with the result of the determination, the program proceeds to one of S216, 218 to select a calculation result. That is, in the observer matrix operation, the operation is performed by using the selected sampling value of any of Lo or HiV / T in the third embodiment, whereas in the fourth embodiment, the operation is performed in the fourth embodiment.
The difference is that calculations are performed using different sampling values for o and HiV / T. The remaining configuration and effects are the same as in the third embodiment.

In the third and fourth embodiments, a variable valve timing mechanism in which both the exhaust valve and the intake valve are changed has been described as an example. However, the present invention is not limited to this. This also applies to the mechanism that is changed only for. Further, the present invention is also applicable to a mechanism capable of stopping the intake valve.
Further, although a hydraulic switch has been described as an example of a means for detecting the valve timing, the present invention is not limited to this, and the position of the pins 640, 642, 644 may be detected, or the control unit of the variable valve timing mechanism may be detected. The detection may be performed with reference to a valve timing switching command signal.

In the first to fourth embodiments, a case is described in which a model describing the behavior of the exhaust system is set, and the air-fuel ratio control is performed using an observer for observing the internal state of the model. As described above, the air-fuel ratio detection technology according to the present invention is not limited to this, and is applicable to any technology for controlling the air-fuel ratio based on the actual measurement value of the air-fuel ratio sensor.

Further, the operating state is detected from the engine speed and the intake pressure, but the present invention is not limited to this, and other parameters may be added. The parameter indicating the engine load is not limited to the intake pressure, but may be an intake air amount, a throttle opening, or the like. Alternatively, the correction may be made at atmospheric pressure.

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 the present invention is also applicable to the case where the air-fuel ratio is controlled using a so-called O ₂ sensor.

[0083]

According to the first aspect of the present invention, the estimation accuracy of the observer matrix is improved, and the identification accuracy of the observer coefficient is improved. Therefore, the estimation accuracy of each cylinder air-fuel ratio is improved.

According to the second aspect, in addition to the effects described in the first aspect, the air-fuel ratio feedback control of each cylinder can be accurately performed only by using a single sensor.

According to a third aspect of the present invention, in addition to the effects described in the second aspect, the air-fuel ratio of each cylinder converges to the collecting air-fuel ratio, and the collecting air-fuel ratio converges to the target air-fuel ratio. As a result, the air-fuel ratios of all the cylinders converge to the target air-fuel ratio, and the convergence of the air-fuel ratio feedback control can be improved.

[Brief description of the drawings]

FIG. 1 is an overall block diagram showing an air-fuel ratio feedback control device for an internal combustion engine that implements a cylinder-by-cylinder air-fuel ratio estimation device and control device according to the present invention.

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

FIG. 3 is a block diagram showing an example in which the detection operation of the air-fuel ratio sensor described in the earlier application is modeled.

FIG. 4 is a model obtained by discretizing the model shown in FIG. 3 with a period ΔT.

FIG. 5 is a block diagram illustrating a true air-fuel ratio estimator that models the detection behavior of an air-fuel ratio sensor.

FIG. 6 is a block diagram showing a model showing a behavior of an exhaust system of the internal combustion engine.

FIG. 7 shows a four-cylinder internal combustion engine having an air-fuel ratio of 14.7 and an air-fuel ratio of one cylinder of 1 using the model shown in FIG.
FIG. 4 is a data diagram showing a case where fuel is supplied at 2.0.

8 is a data diagram showing the air-fuel ratio of the gathering part of the model of FIG. 6 when the input shown in FIG. 7 is given.

9 compares data representing the air-fuel ratio of the collective part of the model of FIG. 6 when the input shown in FIG. 7 is given in consideration of the response delay of the LAF sensor, and the measured value of the LAF sensor output in the same case. FIG.

FIG. 10 is a block diagram showing a configuration of a general observer.

FIG. 11 is a block diagram showing a configuration of an observer used in the earlier application.

12 is an explanatory block diagram showing a configuration in which the model shown in FIG. 6 and the observer shown in FIG. 11 are combined.

FIG. 13 is a block diagram showing cylinder-by-cylinder feedback control of an air-fuel ratio planned in the present invention.

FIG. 14 is a block diagram of a model partially similar to FIG. 6 showing the first embodiment of the present invention;

FIG. 15 is an explanatory diagram showing a configuration in which a plurality of observer matrices are provided according to the second embodiment of the present invention.

FIG. 16 is a flowchart showing a third embodiment of the present invention;
It is a chart.

FIG. 17 is a partial cross-sectional view including a hydraulic circuit diagram for explaining a variable valve timing mechanism planned in a third embodiment.

FIG. 18 is an explanatory diagram showing switching characteristics of valve timing.

FIG. 19 is an explanatory diagram showing characteristics of a map for sampling timing of the output of the air-fuel ratio sensor used in the flow chart of FIG. 16;

FIG. 20 shows a fourth embodiment of the present invention,
It is a flow chart similar to.

[Explanation of symbols]

 Reference Signs List 10 internal combustion engine 18 intake manifold 20 injector 22 exhaust manifold 40 air-fuel ratio sensor (LAF sensor) 42 control unit 600 V / T sensor

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Eisuke Kimura 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Shusuke Akasaki 1-4-1 Chuo, Wako-shi, Saitama Inside Honda R & D Co., Ltd. (72) Inventor Yoichi Nishimura 1-4-1 Chuo, Wako-shi, Saitama Pref.

Claims (3)

[Claims] 1. An apparatus for arranging an air-fuel ratio sensor in an exhaust system collecting portion of a multi-cylinder internal combustion engine and estimating an air-fuel ratio of an input air-fuel mixture of each cylinder from an output of the sensor. Assuming that the output value of the sensor is constituted by a weighted average value obtained by multiplying the combustion history of each cylinder by a weight coefficient Cn, a model is set which describes the behavior of the exhaust system, and the air-fuel ratio of each cylinder is set as a state variable. First means for setting an equation, setting an observer for observing its internal state and determining its output, and b. A second means for estimating the air-fuel ratio of each cylinder from the observer output, wherein the number of combustion histories to be considered in the internal combustion engine is 3
When the above, excluding combustion histories that are equal to or greater than the two immediately preceding combustion histories and less than the number of combustion histories to be considered,
Weight coefficient Cn of the weighted average of the combustion history before that
A cylinder-by-cylinder air-fuel ratio estimating device for an internal combustion engine. 2. a. The output value of the air-fuel ratio sensor arranged in the exhaust system collecting part of the multi-cylinder internal combustion engine is regarded as consisting of a weighted average value obtained by multiplying the combustion history of each cylinder by a weight coefficient Cn, and the combustion to be considered in the internal combustion engine is considered. When the number of histories is three or more, the weighting coefficient Cn of the weighted average of the previous combustion histories excluding the combustion histories that are equal to or more than the two immediately preceding combustion histories and less than the number of the combustion histories to be considered is set to zero. A first means for setting a model describing the behavior of the exhaust system, setting a state equation using the air-fuel ratio of each cylinder as a state variable, setting an observer for observing the internal state thereof, and obtaining the output thereof, b. From the observer output, the air-fuel ratio of each cylinder # nA / F
A second means for estimating c. Third means for calculating a cylinder-by-cylinder feedback correction term #nKLAF for feedback-controlling the estimated air-fuel ratio # nA / F of each cylinder to a target value; and d. Feedback control means for performing feedback control of the air-fuel ratio of the internal combustion engine based on the cylinder-by-cylinder feedback correction term #nKLAF. 3. Further, e. An assembly feedback correction term KLAF for detecting the air-fuel ratio of the exhaust system assembly from the output of the air-fuel ratio sensor and controlling the detected air-fuel ratio of the exhaust system assembly to a target value.
The feedback control means is configured to feedback-control the air-fuel ratio of the internal combustion engine based on the collective feedback correction term KLAF and the cylinder-by-cylinder feedback correction term #nKLAF. The cylinder-by-cylinder air-fuel ratio feedback control device for an internal combustion engine according to claim 2, characterized in that: