JPH07133738A - Air-fuel ratio estimating device per cylinder for internal combustion engine - Google Patents

Abstract

PURPOSE:To simplify an operation so as to improve estimating accuracy by making the weight coefficient of specified combustion hysteresis at the level of zero (0) when an air-fuel ratio is estimated by setting an observor for measuring inner condition while setting a model for recording behavior of an exhaust system on the basis of the output of an air-fuel ratio sensor. CONSTITUTION:In a multiple cylinder internal combustion engine 10, a single air-fuel ratio sensor 40 is arranged per manifold part in an exhaust system 22, the air-fuel ratio of air mixture in each cylinder is estimated on the basis of the output value thereof by a control unit 42. Namely, the output value is regarded as a value obtained from a weighted average value multiplied a weight coefficient by the combustion hysteresis of each cylinder, a condition equation in which the air-fuel ratio of each cylinder is set as a condition variable is set, and an observor for measuring inner condition thereof is set so as to find out an output. The air-fuel ratio of each cylinder is estimated from the output of the observor. In this case, when the number of the combustion hysteresis is set to three (3) or more, the weight coefficient of the weighted average is set to zero (0) in the prior combustion hysteresises except two combustion hysteresises just before that time.

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 more specifically, a single air-fuel ratio sensor is provided for each exhaust system collecting portion of a multi-cylinder internal combustion engine to determine the behavior of the exhaust system. In addition to inputting the sensor output by setting the model describing, the observer for observing the internal state is provided, and in the cylinder-by-cylinder air-fuel ratio estimation device of the internal combustion engine for estimating the air-fuel ratio of each cylinder from the output, The present invention relates to a device for improving the estimation accuracy of the air-fuel ratio of a cylinder.

[0002]

2. Description of the Related Art It is often practiced to provide an air-fuel ratio sensor in the exhaust system of an internal combustion engine to detect the air-fuel ratio, and one example thereof is the technique described in Japanese Patent Laid-Open No. 59-101562. The applicant of the present invention also previously filed Japanese Patent Application No. 3-3.
In JP 59339 (JP-A-5-180059),
We have proposed a technology that sets up a model that describes the behavior of the exhaust system, inputs the output of a single air-fuel ratio sensor provided in the exhaust system collecting part, and estimates the air-fuel ratio of each cylinder 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 an output characteristic proportional to the oxygen concentration in the exhaust gas before and after the stoichiometric air-fuel ratio. Are using.

[0003]

Although the air-fuel ratio of each cylinder can be accurately estimated by the above-mentioned configuration, the operating state changes frequently, and it is necessary to change the calculation parameters accordingly. In actual control, sufficient calculation time cannot always be obtained.

Therefore, the present invention is an improvement of the previously proposed technique, and provides a cylinder-by-cylinder air-fuel ratio estimating device for an internal combustion engine in which the calculation is simplified and the observer's air-fuel ratio estimation accuracy is further improved. The purpose is to

Further, in the above-mentioned observer, the coefficient used for the calculation of the matrix changes according to the operating state of the engine.

Therefore, a second object of the present invention is to optimize the observer matrix calculation in response to changes in the coefficient used for the observer matrix calculation depending on the operating state of the engine to improve the estimation accuracy of the observer. An object is to provide a cylinder-by-cylinder air-fuel ratio estimation device.

Further, recently, as disclosed in Japanese Patent Laid-Open No. 275043/1990, there has been proposed a so-called variable valve timing mechanism for switching the valve timing of an internal combustion engine according to the operating state of the engine. In such a variable valve timing mechanism, in particular, one in which the valve timing on the exhaust side is also changed, the exhaust timing changes, so that it is expected that the behavior of the air-fuel ratio of the collecting portion will be affected accordingly.

Therefore, a third object of the present invention is to optimize the observer matrix calculation even in an internal combustion engine equipped with a variable valve timing mechanism to improve the estimation accuracy of the observer. It is to provide an estimation device. Furthermore, it is also incidental to provide a cylinder-by-cylinder air-fuel ratio estimation device for an internal combustion engine having a variable valve timing mechanism, which improves sampling accuracy of an air-fuel ratio sensor output to improve observer estimation accuracy. It has a purpose. Further, it is an additional object to provide a cylinder-by-cylinder air-fuel ratio estimation device for performing feedback control for each cylinder of the air-fuel ratio based on the observer estimated value.

[0009]

In order to solve the above-mentioned problems, a cylinder-by-cylinder air-fuel ratio estimating apparatus for an internal combustion engine according to a first aspect of the present invention provides a single air-fuel ratio for each exhaust system collecting portion of a multi-cylinder internal combustion engine. A device for arranging a sensor and estimating the air-fuel ratio of the input air-fuel mixture of each cylinder from its output, comprising an output value of the sensor consisting of a weighted average value obtained by multiplying a combustion history of each cylinder by a weighting coefficient Cn. A first means for setting a model describing the behavior of the exhaust system and establishing a state equation with the air-fuel ratio of each cylinder as a state variable and setting an observer for observing the internal state and obtaining the output thereof. And a second means for estimating the air-fuel ratio of each cylinder from the observer output, in the cylinder-by-cylinder air-fuel ratio estimation device, when the number of combustion histories to be considered in the internal combustion engine is 3 or more, immediately before Of 2
The weighting coefficient Cn of the weighted averages of the previous combustion histories excluding the two combustion histories is set to zero.

According to a second aspect of the present invention, a single air-fuel ratio sensor is arranged for each exhaust system collecting portion of the multi-cylinder internal combustion engine, and the air-fuel ratio of the input air-fuel mixture of each cylinder is estimated from its output. The output value of the sensor is regarded as a weighted average value obtained by multiplying the combustion history of each cylinder by a predetermined coefficient, and a model describing the behavior of the exhaust system is set to set the air-fuel ratio of each cylinder as a state variable. And a second means for estimating the air-fuel ratio of each cylinder from the output by setting an observer matrix for observing the internal state of the cylinder
In the cylinder-by-cylinder air-fuel ratio estimation device for an internal combustion engine, the first means sets a plurality of observer matrices, obtains outputs thereof, and determines an operating state determined from the engine speed and the engine load. One of the outputs obtained according to the above is selected, and the air-fuel ratio of each cylinder is estimated from the selected output.

According to a third aspect of the present invention, a single air-fuel ratio sensor is arranged for each exhaust system collecting portion of the multi-cylinder internal combustion engine, and the air-fuel ratio of the input mixture of each cylinder is estimated from its output. The output value of the sensor is regarded as a weighted average value obtained by multiplying the combustion history of each cylinder by a predetermined coefficient, and a model describing the behavior of the exhaust system is set to set the air-fuel ratio of each cylinder as a state variable. And a second means for estimating the air-fuel ratio of each cylinder from the output by setting an observer matrix for observing the internal state of the cylinder
In the air-fuel ratio detecting device for an internal combustion engine,
A changing means for changing the valve timing of the internal combustion engine among a plurality of characteristics is provided, and the first means is configured to change the observer matrix according to the changed valve timing.

In the device of claim 4, the first means is
The observer matrix is separately set according to a plurality of characteristics of the valve timing, the output thereof is obtained, and one of the obtained outputs is selected according to the changed valve timing.

[0013]

According to the first aspect of the present invention, the weighting coefficient C of the weighted average is used.
Although n changes depending on the operating state, if the values of the combustion histories before the immediately preceding two combustion histories in the multi-cylinder internal combustion engine are set to zero, the total value of the weighting factors is 1, so that the two combustion histories Is determined, and the other is subtracted from 1. As a result, for example, in the case of four cylinders, it is sufficient to identify the coefficient for one cylinder, and the estimation accuracy of the observer matrix is improved as compared with that for identifying three cylinders, and the coefficient identification accuracy of the observer is improved. Because
The estimation accuracy of the air-fuel ratio of each cylinder is improved. In the above description, the air-fuel ratio sensor is arranged for each exhaust system collecting portion in order to include the case where the air-fuel ratio sensor is arranged for each bank in a V-type engine. The observer order itself is an integral multiple of the estimated cylinder number.

In the second aspect, the behavior of the air-fuel ratio of the collecting portion changes according to the operating conditions such as the engine speed and the engine load, so that there are a plurality of observer matrices. However, if the observer matrix is changed depending on the operating region, the air-fuel ratio estimation calculation for each cylinder cannot be completed. Therefore, the estimation of the air-fuel ratio of each cylinder is performed using a plurality of matrices that assume different operating conditions, and the estimation results are exchanged to reduce the number of convergences and improve the estimation accuracy of the air-fuel ratio of each cylinder.

According to the third aspect of the present invention, since a plurality of matrix operations are performed according to the valve timing, the estimation accuracy is improved regardless of the change of the valve timing.
The estimation accuracy of the air-fuel ratio of each cylinder is improved. Here, the valve timing includes either the intake side or the exhaust side, or both. Further, in an engine having a plurality of intake side and exhaust side valves, at least one valve timing is changed. This is because if the valve timing on the intake side and the valve timing on the exhaust side are changed even a little, the intake characteristic of the engine changes, and therefore the exhaust characteristic of the engine also changes. Further, the valve timing switching characteristic is two kinds in the embodiment described later, but may be three or more kinds. The same applies to claim 4.

According to the present invention, the air-fuel ratio of each cylinder cannot be estimated instantaneously, and several calculations are required to complete the observer calculation. Therefore, the calculation using the observer matrix before the valve timing change is performed. By simultaneously performing the operation using the changed observer matrix with
The estimation result can be easily changed, the number of convergences can be reduced, and the estimation accuracy of the air-fuel ratio of each cylinder can be further improved.

[0017]

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 according to the present invention. Reference numeral 1 in the figure
Reference numeral 0 indicates an internal combustion engine of four cylinders, and the intake air introduced from the air cleaner 14 arranged at the tip of the intake passage 12 is
The flow rate is adjusted by the throttle valve 16 and is introduced into the first to fourth cylinders via the intake manifold 18. An injector 20 is provided near the 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), passes through the exhaust pipe 24, is purified by the three-way catalytic converter 26, and is discharged to the outside of the engine. In addition, the intake passage 12 has a bypass passage 2 that bypasses the throttle valve arrangement position in the vicinity thereof.
8 are provided.

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 by absolute pressure are also provided. Further, in the exhaust system, a wide area 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. The outputs of these sensors 34 and the like are sent to the control unit 42.

FIG. 2 is a block diagram showing the details of the control unit 42. The output of the wide range air-fuel ratio sensor 40 is input to the 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 centering on the theoretical air-fuel ratio. The air-fuel ratio (A / F) consisting of is detected. For details, refer to another application previously proposed by the applicant (Japanese Patent Laid-Open No. 4-3694).
No. 71), so further explanation is omitted. In the following description, this sensor will be referred to as "LAF
Sensor ”(Linear AFB sensor).
The output of the detection circuit 46 is sent to the CP via the A / D conversion circuit 48.
It is loaded into a microcomputer including U50, ROM 52, RAM 54, etc., and stored in RAM 54.

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.
8 and the second A / D conversion circuit 60, and the output of the crank angle sensor 34 is waveform-shaped by the waveform shaping circuit 62, and then the output value is counted by the counter 64. The count value is stored in the microcomputer. Entered in. In the microcomputer, the CPU 50 calculates a control value from the detected value in accordance with the instruction stored in the ROM 52, drives the injector 20 of each cylinder via the drive circuit 66, and the solenoid valve 70 via the second drive circuit 68. Is driven 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 above will be briefly described for convenience of understanding.

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 modeled as a first-order delay system to create a model as shown in FIG. LA here
Assuming that F: LAF sensor output and A / F: input A / F, the state equation can be expressed by the following equation 1.

[0024]

[Equation 1]

When this is discretized with the period ΔT, it becomes as shown by the equation 2. FIG. 4 is a block diagram showing Equation 2.

[0026]

[Equation 2]

Therefore, by using the equation 2, the true air-fuel ratio can be obtained from the sensor output. That is, number 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.

[0028]

[Equation 3]

[0029]

[Equation 4]

Specifically, if the expression 2 is expressed by a transfer function using 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. 5 shows a block diagram of the real-time A / F estimator.

[0031]

[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 explained. 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. In addition, since F (fuel amount) is the control amount, “fuel air ratio F / A” is used here, but for convenience of understanding in the following description, “air fuel ratio” is used as long as there is no problem.
The air-fuel ratio (or the fuel-air ratio) means a true value obtained by correcting the response delay previously obtained by the equation (5).

[0033]

[Equation 6]

That is, the air-fuel ratio of the collecting portion is the sum of the past combustion history of each cylinder multiplied by the weighting coefficient Cn (for example, the most recently burned cylinder is 40%, the previous one is 30%, etc.). expressed. A block diagram of this model is shown in FIG.

The equation of state is as shown in equation 7.

[0036]

[Equation 7]

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

[0038]

[Equation 8]

In the above, since u (k) is unobservable, even if an observer is designed from this equation of state, x
(K) cannot be observed. Therefore, assuming 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 where it does not change abruptly, Equation 9 is obtained.

[0040]

[Equation 9]

Here, the simulation results of the model obtained as described above will be shown. FIG. 7 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 is set to 1
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.
In the figure, a step-like output is obtained, but if the response delay of the LAF sensor is further taken into consideration here, the sensor output has a waveform shown as "model output value" in FIG. In the figure, the "actual measurement value" is the actual measurement value of the LAF sensor output in the same case, but it is verified by comparison with this that the above model models the exhaust system of the multi-cylinder internal combustion engine well.

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

[0043]

[Equation 10]

[0044]

[Equation 11]

[0045]

[Equation 12]

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

[0047]

[Equation 13]

The general structure of the observer is as shown in FIG. 10. 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.

[0049]

[Equation 14]

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

[0051]

[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.

[0053]

[Equation 16]

FIG. 12 shows a combination of the above model and the observer. The simulation result is omitted because it is shown in the previous application, but this allows the air-fuel ratio of each cylinder to be accurately extracted from the air-fuel ratio of the collective portion.

Since the observer can estimate the air-fuel ratio of each cylinder from the air-fuel ratio of the collecting portion, it is possible to control the air-fuel ratio for each cylinder by using a control law such as PID. Specifically, as shown in FIG. 13, 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 #n for each cylinder KLAF is the feedback correction term #n for each cylinder of the collecting unit A / F.
The PID rule is used to eliminate the deviation between the target value obtained by dividing the average value of KLAF by the previous calculation value and the observer estimated value # nA / F.

As a result, the air-fuel ratio (A / F) of each cylinder converges to the assembly air-fuel ratio (A / F), and the assembly air-fuel ratio (A / F).
F) will converge to the target air-fuel ratio (A / F),
As a result, the air-fuel ratios (A / F) of all the cylinders converge to the target air-fuel ratio (A / F). Where the fuel injection amount of each cylinder #
nTout (specified by the injector valve opening time) is: #nTout = Tim x KCMD x KTOTAL x #nK
It is calculated by LAF × KLAF. In the above, Tim is a basic value, KCMD is a target air-fuel ratio, and KTOTAL is another correction term. Further, although there are additional terms such as battery correction, they are omitted. still,
Details of such control are described in Japanese Patent Application No.
No. 251138, so further explanation is omitted.

The present invention will be described based on the above.

FIG. 14 shows a first embodiment of the present invention. Weight coefficient C ₁ of the weighted average and the, C _2, C _3, the C _4, it C _n of this exhaust (combustion) cylinders, the last, second last and 3TDC before the exhaust (combustion) which each C _n cylinders _-1 , C _n-2 , C _n-3 , _two times before and 3
The weighting factors C _{n- 2} and C _n-3 for the exhaust (combustion) cylinder before TDC are set to zero, and as shown in the figure, for the two most recent (immediately before) cylinders, that is, the most recent (immediately before) two combustion histories. I asked for only about. For example, if the first cylinder is an exhaust (combustion) cylinder now, the third cylinder and the fourth cylinder
The weight coefficient for the cylinder is set to zero.

As described in the previous application, the weighting coefficient Cn indicating the behavior of the collective portion air-fuel ratio needs to be changed according to the operating state, but in any case, the value of the weighting coefficient Cn is accurately set. It is difficult to know. Therefore, in a four-cylinder internal combustion engine, the last two (just before) exhaust (combustion) sequence
Except for one combustion history, the weighting factors of other combustion history are set to zero. Since the weighting coefficient is 1 as a whole, one of the most recent (immediately before) combustion histories is obtained, and the other one is obtained by subtracting the obtained value from 1 (this is the weighting coefficient in the previous application. The same is true even if is obtained for all cylinders). That is, the configuration of FIG.
Modified like 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 originally, and there is a risk of using incorrect identification values. With the configuration as described above, one coefficient to be identified is sufficient, so that the calculation interval is shortened, and the estimation accuracy is rather improved in the verification by simulation. This problem is also related to the distance from the cylinder exhaust port to the position of the air-fuel ratio sensor of the collecting portion. When the distance is relatively short, the estimation accuracy can be improved by configuring as described above.

In the case of the embodiment, the four-cylinder internal combustion engine has been taken as an example, but it is expected that the weighting coefficient for the fifth to sixth cylinders may be similarly obtained for the two nearest cylinders. For an internal combustion engine having more cylinders than that, the number of cylinders for which the weighting coefficient should be obtained may be increased.

Further, since the V-type engine is provided with an air-fuel ratio sensor for each bank, a cylinder having a weighting coefficient of zero is selected in each bank according to the exhaust sequence. For example, V-type 6 cylinders (cylinders in the right bank are first, second, third, and cylinders in the left bank are fourth, fifth, and sixth), and the ignition order is 1 (right) -4 (left). ) -2 (right) -5 (left) -3
Assuming that (right) -6 (left), if the third cylinder now burns in the right bank, the weighting coefficient for the first cylinder is set to zero. If the fourth cylinder now burns in the left bank, the weighting factor for the fifth cylinder is set to zero. It should be noted here that the order of the observer is an integer multiple of the estimated number of cylinders, preferably one, and 4 in the embodiment.

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

The observer matrix is expressed by the equation (14).
Therefore, the value A-KC is represented by a 4 × 4 matrix, in which the weighting coefficient C changes according to the engine operating state as described above. Therefore, it is conceivable to obtain a solution for this matrix value in advance over a range of change expected for the engine speed and the engine load and map it. However, even in that case, when there is no value corresponding to the map value, it is not desirable to obtain the value by interpolation calculation because it is not compensated as a matrix value. Further, since the expression of the expression 14 is a recurrence expression, when the coefficient changes in the middle of the calculation, it is necessary to repeat the calculation.

Therefore, as shown in FIG. 15, a plurality of observer matrices 1 to n are prepared and operated in parallel, and one of the matrix values is selected according to the engine operating condition. This can shorten the calculation time and improve the estimation accuracy of the air-fuel ratio of each cylinder of the observer. The number of observer matrices is 2 here.
Any number is acceptable as long as it is more than one. Further, the calculation of the observer matrix does not always have to be performed all at the same time, and a change in the engine operating state may be predicted and only the observer matrix corresponding to the operating state may be calculated.

In the previous application, in designing the observer, the weighted distributions Q and R of the Riccati equation are Q / R = 1/1.
And This evaluation function is very important for the observer's performance, but after repeated verification through simulations, the convergence time shortens as the value of Q / R increases, but when it exceeds a certain level, It was confirmed that there was almost no change. Therefore, from that limit, Q / R ≧ 10
When set to 0, a good estimation result could be obtained. That is, since the evaluation function is a dimensionless number, it can take any value, which is rather difficult to determine.
As a result of repeated verification, it was confirmed that the estimation accuracy was improved by setting Q / R to 100 or more.

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

The variable valve timing mechanism will be briefly described with reference to FIGS. 17 and 18.

In the illustrated example, the variable valve timing mechanism 60 comprises three rocker arms 614, 616, 618 rotatably arranged on rocker shafts 612 provided near the intake valve 54 and the exhaust valve 56, respectively ( Since the intake side and the exhaust side have the same configuration, the suffix i (e) is added after the reference numeral in the drawings, and both will be commonly described below). The rocker arm includes two low speed cams each mounted on a cam shaft (not shown), and one high speed cam having a shape protruding in the radial direction as compared with the low speed cam (both shown in FIG. (Not shown).

The rocker arms 614, 616, 618 have oil passages 650, holes 632, holes 634, 636, and pins 6.
A hydraulic pressure switching mechanism 660 including a connecting mechanism 630 composed of 40, 642, 644, etc., interposed between an oil passage 650 and a hydraulic pressure source (not shown), pressurizes oil in the oil passage 650 via an electromagnetic valve 680. Supply / stop, which causes the pin to advance / retract and the rocker arm to engage / disengage. 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 the rocker arm is released. Since the details of the variable valve timing mechanism have been described in the above-mentioned prior art, the description will be omitted here.

This connection / disconnection is specifically determined from the engine speed Ne and the intake pressure Pb, as shown in FIG. Hereinafter, the case of using the high speed cam is referred to as “HiV / T”, and the case of using the low speed cam is referred to as “LoV / T”.
In comparison with LoV / T, the valve timing is advanced and the amount of overlap increases as a result, and the amount of lift also increases. The hydraulic pressure switching mechanism 660
Is provided with a V / T sensor 600 including a hydraulic switch, and the rocker arm is connected / released by the oil pressure of the oil passage 650, that is, the valve timing is LoV / T and HiV / T.
It is detected which of the two controls. As shown by an 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 collective air-fuel ratio (A / F), the sampling timing of the air-fuel ratio (A / F) should be optimized in each cylinder air-fuel ratio (A / F) estimation observer calculation. It is necessary to plan. That is, the output of the LAF sensor clearly shows a characteristic that is synchronized with the engine speed, but the control unit side is digital sampling, so the behavior may not be captured depending on the timing. The proper sample timing changes depending on the engine speed and engine load, but it seems that the valve timing has a particularly large effect. Therefore, in the internal combustion engine equipped with 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, the behavior of the collective air-fuel ratio (A / F) also changes depending on the valve timing, so it is necessary to change the observer matrix in synchronization with the switching of the valve timing. However, the air-fuel ratio (A / F) of each cylinder cannot be estimated instantaneously, and several calculations are required to converge the observer calculation. Therefore, the calculation using the observer matrix before the valve timing change and the observer matrix after the change The calculation using A is overlapped and performed simultaneously, and after it is determined that the observer calculation has converged, that is, after the valve timing changing operation is completed, the air-fuel ratio (A / F) estimation result for each cylinder is replaced.

Explaining with reference to the flow chart of FIG. 16, first, in S100, the engine speed Ne, the intake pressure Pb, and the valve timing V / T are read out, and the routine proceeds to S102, where the valve timing is HiV / T or LoV / T. Judgment, and proceed to S104 and 106 according to the judgment result
To retrieve the timing map for Lo valve timing. Its characteristics are shown in FIG.

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

Further, regarding the relation with the valve timing, an arbitrary value Ne1 of the engine speed is Ne1-Lo for the Lo side, Ne-HI for the Hi side, and an arbitrary value for the intake pressure is also for the Lo side. Pb1-
Assuming Pb1-Hi for the Lo and Hi sides, the characteristics of the map are Pb1-Lo> Pb1-Hi, Ne1-Lo>
Ne1-Hi. That is, in HiV / T, the opening time of the exhaust valve is earlier than that in LoV / T. Therefore, if the engine speed or the intake pressure value is the same, an early sampling value is selected. .

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

Since the third embodiment is constructed 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, so that the detection accuracy is improved and the valve timing is adjusted. Since the observer matrix is changed accordingly, the estimation accuracy of the air-fuel ratio of each cylinder is improved.

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

The fourth embodiment is a modification of the third embodiment,
Explaining below, after reading the engine speed Ne and the like in S200, the flow proceeds to S202 to search for the LoV / T timing map, the flow proceeds to S204 to select the sampling value of the sensor output for LoV / T, and to S206. Then, the observer matrix calculation is performed for LoV / T. Then S
From 208 to 212, the same process is performed on the HiV / T side.

Then, the process proceeds to S214, where the valve timing is judged, and according to the judgment result, the process proceeds to either S216 or 218 to select the calculation result. That is, Lo or Hi selected in the third embodiment in the observer matrix calculation.
While the calculation is performed using the sampling value of either V / T in common, in the fourth embodiment, Lo and Hi are used.
The difference is that calculation is performed using different sampling values for V / T. The rest of the configuration and effects are similar to those of the third embodiment.

In the third and fourth embodiments, the variable valve timing mechanism in which both the exhaust valve and the intake valve are changed has been taken as an example, but the present invention is not limited to this, and only one of them is as described above. It also applies to the changed mechanism.
It also applies to a mechanism that allows the intake valve to be stopped. Further, although the hydraulic switch has been taken as an example of the means for detecting the valve timing, the position is not limited to the hydraulic switch, and the positions of the pins 640, 642, 644 may be detected, or the control unit of the variable valve timing mechanism may be used. It may be detected by referring to the valve timing switching command signal.

The first to fourth embodiments described above are as follows.
The description has been given by taking the case where the model describing the behavior of the exhaust system is set and the air-fuel ratio control is performed using an observer that observes the internal state thereof, but the air-fuel ratio detection technology according to the present invention is limited to that. It is not applicable to all technologies, and is applicable to all technologies 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 the intake air amount, the throttle opening, or the like. It may also be corrected at atmospheric pressure.

Further, in the above embodiment, an example has been shown in which the response delay of the wide range air-fuel ratio sensor is analyzed to obtain the true air-fuel ratio, and the air-fuel ratio is detected from the output of the collective portion of one sensor based on it. However, the present invention is not limited to this, and is also applicable to a case where the same number of sensors as the number of cylinders are arranged in the exhaust system of a multi-cylinder internal combustion engine and the air-fuel ratio is detected from the output thereof.

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

[0087]

According to the first aspect of the present invention, the number of parameters to be identified is reduced, the estimation accuracy of the observer matrix is improved, and the coefficient identification accuracy of the observer is improved. It can be estimated well.

According to the second aspect, the number of times of convergence is reduced, so that the estimation accuracy of the observer is improved and the air-fuel ratio of each cylinder can be estimated more accurately.

According to the third aspect, the estimation accuracy is improved and the air-fuel ratio of each cylinder can be accurately estimated regardless of the change of the valve timing.

According to the fourth aspect of the present invention, it is easy to change over the estimation result, the number of times of convergence is reduced, and the air-fuel ratio of each cylinder can be estimated more accurately.

[Brief description of drawings]

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

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

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

FIG. 4 is a model in which the model shown in FIG. 3 is discretized with a period ΔT.

FIG. 5 is a block diagram showing 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 an internal combustion engine.

FIG. 7 is a diagram showing a model shown in FIG. 6 in which a 4-cylinder internal combustion engine has an air-fuel ratio of 3 cylinders of 14.7 and an air-fuel ratio of 1 cylinder of 1;
It is a data figure which shows the case where it makes 2.0 and supplies fuel.

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

FIG. 9 compares the data showing the air-fuel ratio of the collecting portion 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 with the actual measurement value of the LAF sensor output in the same case. It is a graph figure.

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 previous 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, which is 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 is provided according to the second embodiment of the present invention.

FIG. 16 is a flow chart showing a third embodiment of the present invention.

FIG. 17 is a partial cross-sectional view including a hydraulic circuit diagram for explaining a variable valve timing mechanism planned for the 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 sample timing of the air-fuel ratio sensor output used in the flow chart of FIG. 16;

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

[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 60 Variable Valve Timing Mechanism 600 V / T Sensor

Front page continuation (72) Inventor Shusuke Akasaki 1-4-1 Chuo, Wako-shi, Saitama Stock Research Institute Honda Technical Research Institute (72) Inventor Yoichi Nishimura 1-4-1 Chuo, Wako-shi, Saitama Stock Association Inside Honda Research Laboratory

Claims (4)

[Claims] 1. An apparatus for arranging a single air-fuel ratio sensor for each exhaust system collecting portion of a multi-cylinder internal combustion engine and estimating the air-fuel ratio of an input air-fuel mixture of each cylinder from the output thereof. A state in which the output value of the sensor is regarded as a weighted average value obtained by multiplying the combustion history of each cylinder by a weighting coefficient Cn, and a model describing the behavior of the exhaust system is set to use the air-fuel ratio of each cylinder as a state variable. First means for establishing an equation and setting an observer for observing its internal state to obtain its output; and b. In the cylinder-by-cylinder air-fuel ratio estimation device for an internal combustion engine, which comprises second means for estimating the air-fuel ratio of each cylinder from the observer output, the number of combustion histories to be considered in the internal combustion engine is 3
In the above case, the cylinder-by-cylinder air-fuel ratio estimation device for an internal combustion engine, wherein the weighted average weighting coefficient Cn for the previous combustion histories excluding the immediately preceding two combustion histories is set to zero. 2. A device for arranging a single air-fuel ratio sensor for each exhaust system collecting portion of a multi-cylinder internal combustion engine and estimating the air-fuel ratio of the input air-fuel mixture of each cylinder from the output thereof. A state where the output value of the sensor is regarded as a weighted average value obtained by multiplying the combustion history of each cylinder by a predetermined coefficient, and a model describing the behavior of the exhaust system is set to use the air-fuel ratio of each cylinder as a state variable. A first means for establishing an equation, setting an observer matrix for observing its internal state, and obtaining its output, and b. In a cylinder-by-cylinder air-fuel ratio estimation device for an internal combustion engine, which comprises second means for estimating the air-fuel ratio of each cylinder from the output, the first means sets a plurality of observer matrices and obtains their outputs, respectively. Cylinder air-fuel ratio of the internal combustion engine characterized by selecting one of the outputs obtained according to the operating state determined from the engine speed and the engine load, and estimating the air-fuel ratio of each cylinder from the selected output Estimator. 3. A device for arranging a single air-fuel ratio sensor for each exhaust system collecting portion of a multi-cylinder internal combustion engine and estimating the air-fuel ratio of the input air-fuel mixture of each cylinder from the output thereof. A state where the output value of the sensor is regarded as a weighted average value obtained by multiplying the combustion history of each cylinder by a predetermined coefficient, and a model describing the behavior of the exhaust system is set to use the air-fuel ratio of each cylinder as a state variable. A first means for establishing an equation, setting an observer matrix for observing its internal state, and obtaining its output, and b. An air-fuel ratio detecting device for an internal combustion engine, comprising: second means for estimating the air-fuel ratio of each cylinder from the output; c. An internal combustion engine, comprising: a changing unit that changes a valve timing of the internal combustion engine between a plurality of characteristics, and the first unit changes the observer matrix according to the changed valve timing. Cylinder air-fuel ratio estimation device. 4. The first means sets the observer matrix separately according to a plurality of characteristics of the valve timing, obtains its output, and outputs the output obtained according to the changed valve timing. 4. The cylinder-by-cylinder air-fuel ratio estimation device according to claim 3, wherein any one of them is selected.