JPH08232730A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To perform proper feedback control of an air-fuel ratio by cylinders even when the control processing time of an internal combustion engine by an ECU is brought into an insufficient state along with the increase of the number of revolutions of an engine. CONSTITUTION: An observer OBSV estimates an air-fuel ratio #nA/F from a detecting air-fuel ratio KACT of an exhaust system assembly. A PID block calculates an air-fuel ratio correction factor #nKLAF by cylinders by applying a PID control rule on an air-fuel ratio #nA/F by cylinders, and feedback correction is made on an output fuel injection amount #Tout by cylinders. A memory block REF has a function to hold and output a fixed value or an air-fuel ratio correction factor #nKLAF by cylinders determined right near the fixed value. A first control block DH1X effects control of switch connection between a demultiplexer DMPX and a multiplexer MPX according to the number of revolutions of an engine. A second control block CH2 indicates estimation processing of the observer OBSV and the stop thereof according to the number of revolutions. By thinning and stopping processing by a PID block, shortening of processing is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to estimating the air-fuel ratio of each cylinder based on the detection output of an air-fuel ratio sensor installed in the collecting part of the exhaust system. The present invention relates to a fuel injection control device for feedback controlling the fuel injection amount for each cylinder to be supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the air-fuel ratio of each cylinder.

[0002]

2. Description of the Related Art Conventionally, in a fuel injection control device for an internal combustion engine, attention has been paid to the fact that the purification rate of exhaust gas by a catalyst device provided in an exhaust system becomes maximum at a stoichiometric air-fuel ratio. The air-fuel ratio is detected by the fuel ratio sensor, and the fuel injection amount is feedback-controlled so that the detected value becomes the stoichiometric air-fuel ratio (Japanese Patent Laid-Open No. 59-101562).

Further, as shown in FIG. 30 showing the exhaust process, only one air-fuel ratio sensor is provided in the exhaust system collecting part of the multi-cylinder (the figure shows four cylinders as a typical example) internal combustion engine to detect the air-fuel ratio. However, since the air-fuel ratios of the cylinders # 1 to # 4 cannot be accurately detected, and only the mixed value of the air-fuel ratios of all the cylinders is detected, the air-fuel ratio can be determined based on this detected value. Even if the feedback control is performed, the exhaust gas purification efficiency cannot be improved. Therefore, in order to solve such a problem, a theoretical model of the exhaust system is constructed, and the detection output of one air-fuel ratio sensor is applied to this theoretical model to estimate the air-fuel ratio of each cylinder, There is a technique for performing feedback control of the air-fuel ratio of each cylinder to a target value based on the value (JP-A-5-180040). Furthermore, this technique solves the problem that the air-fuel ratio of the exhaust system collecting portion cannot be accurately determined by simply sampling the detection output of the air-fuel ratio sensor in synchronization with the system clock of the engine control unit (ECU). In order to do so, a sampling operation block (called sel-V) is provided.
That is, since the behavior of the exhaust gas in the exhaust system collecting portion varies depending on the engine speed and the like, the air-fuel ratio of the exhaust system collecting portion is obtained by setting the sampling timing that can follow the behavior of the exhaust gas. I am trying. Then, by applying the air-fuel ratio of the collecting portion thus obtained to the observer according to the modern control theory, the air-fuel ratio of each cylinder is estimated, and further, based on the air-fuel ratio of each cylinder,
The fuel injection amount of each cylinder is feedback-controlled so as to eliminate the variation in the air-fuel ratio of each cylinder.

According to this latter technique, the efficiency of exhaust gas purification can be improved by eliminating the variation in the air-fuel ratio among the cylinders, and a plurality of air-fuel ratio sensors are provided independently for each cylinder. A simple structure is realized because it is not necessary.

[0005]

By the way, in the latter technique, attention is paid to an exhaust system including an exhaust manifold, a state equation for the output with respect to the input to the exhaust system is established, and this state equation is gradually calculated. It uses the observer theory that the internal state variables of the exhaust system can be estimated by solving in the formula form. That is, in this technique, a theoretical model (observer) to which such an internal state variable is applied is constructed, and when the air-fuel ratio of the collecting portion obtained by the sampling operation block (sel-V) is input, the air-fuel ratio of each cylinder is changed. Estimate the fuel ratio as output. Then, the engine control unit (ECU) executes a predetermined application program to realize the estimation processing based on the observer theory.

However, since the time required for the processing for this feedback control is almost uniquely determined depending on the processing speed of the application program, the engine speed Ne is increased (increased) and the TDC of each engine is increased. If the cycle becomes short, it becomes difficult to execute such feedback control in synchronization with each TDC. That is, FIG.
As shown in (a), the processing time required for the feedback control is fixed for the above reason. On the other hand, if the TDC cycle becomes shorter as the engine speed Ne increases, the period required for each estimation process becomes apparent. , Becomes relatively shorter than the TDC cycle when the engine speed Ne decreases, and the original feedback control cannot be performed.

Further, in order to solve such a problem, FIG.
As shown in 0 (b), it is also considered to perform a so-called thinning-out process in which the cylinder-by-cylinder air-fuel ratio is not calculated for each TDC but the cylinder-by-cylinder air-fuel ratio is calculated once in a plurality of TDC cycles. However, the true air-fuel ratio cannot be estimated for each cylinder even if the thinning process is simply performed.
That is, as shown in FIG. 7B, when the thinning process is performed once, the air-fuel ratio of the first cylinder # 1 in the previous two times, the air-fuel ratio of the fourth cylinder # 4 in the previous time, and the first air-fuel ratio in the current time To detect the air-fuel ratio of the cylinder # 1 of the second cylinder # 2 and the third cylinder # 2.
However, there is a problem that the air-fuel ratio of each cylinder cannot be estimated from the air-fuel ratio of the exhaust system collecting part.

Further, if a simple intermittent process is performed in which the estimation process is stopped when the engine speed Ne increases and the estimation process is restarted when the engine speed Ne decreases again, the observer uses the above recurrence formula. Since the cylinder-by-cylinder air-fuel ratio is estimated by applying the format, when the estimation process is stopped, the estimated value for the cylinder-by-cylinder air-fuel ratio is not calculated. Differently, the estimated value naturally becomes discontinuous, the true cylinder-by-cylinder air-fuel ratio cannot be obtained, and the stability of the control deteriorates.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel injection amount control device for an internal combustion engine, which performs appropriate feedback control for each cylinder even if the engine speed increases. To aim.

[0010]

In order to achieve such an object, according to a first aspect of the present invention, the multi-cylinder internal combustion engine is arranged in an exhaust system collecting portion, and is discharged from each cylinder of the multi-cylinder internal combustion engine. Based on a model that defines the behavior of the air-fuel ratio in the exhaust system of the multi-cylinder internal combustion engine, and the internal state of the exhaust system while inputting the air-fuel ratio By setting an observer for observing, the air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder, and reducing the variation of the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder, In a fuel injection amount control device for an internal combustion engine, which comprises an air-fuel ratio correction coefficient calculation means for calculating a cylinder-by-cylinder air-fuel ratio correction coefficient for correcting the cylinder-by-cylinder fuel injection amount supplied to each cylinder of the cylinder internal combustion engine, the engine speed is Predetermined If it exceeds, while continuing the estimation processing of the air-fuel ratio of each cylinder by the air-fuel ratio estimation means, the calculation processing of the cylinder-by-cylinder air-fuel ratio correction coefficient by the air-fuel ratio correction coefficient calculation means is sequentially shifted and stopped in the order of the stroke of the cylinder. The control means is provided.

According to another aspect of the present invention, there is provided air-fuel ratio detecting means arranged in an exhaust system collecting portion of the multi-cylinder internal combustion engine for detecting an air-fuel ratio of the air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine. Based on a model that defines the behavior of the air-fuel ratio in the exhaust system of the multi-cylinder internal combustion engine, an observer that inputs the air-fuel ratio and observes the internal state of the exhaust system is set, and the air-fuel ratio of each cylinder is estimated. And a fuel injection amount for each cylinder to be supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder. In a fuel injection amount control device for an internal combustion engine, which comprises an air-fuel ratio correction coefficient calculation means for calculating a cylinder-by-cylinder air-fuel ratio correction coefficient, when the engine speed exceeds a predetermined value, each of the air-fuel ratio estimation means Cylinder sky While continuing the ratio estimation processing, the cylinder-by-cylinder air-fuel ratio correction coefficient by the air-fuel ratio correction coefficient calculation means is fixed to a predetermined value, or is held at the most recently obtained air-fuel ratio correction coefficient and is supplied to each cylinder. The control means for correcting the different fuel injection amount is provided.

According to another aspect of the present invention, there is provided air-fuel ratio detecting means arranged in the exhaust system collecting portion of the multi-cylinder internal combustion engine, for detecting the air-fuel ratio of the air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine. Based on a model that defines the behavior of the air-fuel ratio in the exhaust system of the multi-cylinder internal combustion engine, an observer that inputs the air-fuel ratio and observes the internal state of the exhaust system is set, and the air-fuel ratio of each cylinder is estimated. And a fuel injection amount for each cylinder to be supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder. In a fuel injection amount control device for an internal combustion engine, which comprises an air-fuel ratio correction coefficient calculating means for calculating an air-fuel ratio correction coefficient, when the engine speed exceeds a predetermined value, the cylinder-by-cylinder air-fuel ratio estimating means is used. Of each cylinder While continuing the estimation process fuel ratio, and a structure having a control means for stopping the calculation of cylinder air-fuel ratio correction coefficient according to the air-fuel ratio correction coefficient calculating means.

[0013]

In the fuel injection amount control apparatus for the internal combustion engine according to claim 1, when the cycle of TDC becomes shorter as the engine speed increases, the control means causes the air-fuel ratio correction coefficient calculation means to determine the cylinder-by-cylinder air space. A so-called thinning process is performed by sequentially shifting and stopping the calculation process of the fuel ratio correction coefficient in the order of the stroke of the cylinder. However, the air-fuel ratio estimating means continues to estimate the air-fuel ratio of each cylinder.

In the fuel injection amount control apparatus for the internal combustion engine according to the second aspect, when the cycle of TDC becomes shorter as the engine speed increases, the cylinder-by-cylinder air-fuel ratio correction coefficient is calculated by the air-fuel ratio correction coefficient calculating means. The cylinder-specific fuel injection amount supplied to each cylinder is corrected by fixing it to a predetermined value or holding the most recently obtained air-fuel ratio correction coefficient and holding the cylinder-specific fuel injection amount supplied to each cylinder. However, the air-fuel ratio estimating means continues to estimate the air-fuel ratio of each cylinder.

In the fuel injection amount control system for an internal combustion engine according to claim 3, when the cycle of TDC becomes shorter as the engine speed increases, the cylinder-by-cylinder air-fuel ratio correction coefficient of the air-fuel ratio correction coefficient calculation means is changed. Stop arithmetic processing. However, the air-fuel ratio estimating means continues to estimate the air-fuel ratio of each cylinder.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fuel injection control device for an internal combustion engine according to the present invention will be described with reference to the drawings. A typical example applied to a four-cylinder internal combustion engine will be described.

FIG. 1 is a schematic diagram showing the overall construction of this fuel injection control device. In the figure, the intake air introduced from the air cleaner 14 provided at the tip of the intake pipe 12 is
The surge tank 18 while the flow rate is adjusted by the throttle valve 16.
And through the intake manifold 20, and further through an intake valve (not shown) for each cylinder to flow into each cylinder of the four-cylinder internal combustion engine 10.

An injector 22 for fuel injection is provided near the intake valve of each cylinder, and a mixture of intake air and injected fuel is ignited by an ignition plug (not shown) provided for each cylinder. Then, they are burned and drive each piston (not shown).

The exhaust gas after combustion is exhausted to an exhaust manifold 24 via an exhaust valve (not shown) of each cylinder, and the exhaust pipe 2 connected to a collecting portion of the exhaust manifold 24.
After passing through 6, it is cleaned by the first three-way catalyst device 28 and the second three-way catalyst device 30 and discharged to the outside of the engine.

The throttle valve 16 is a pulse motor M that rotates according to operating conditions such as the amount of depression of the accelerator pedal.
A bypass passage 34 for controlling the secondary air amount according to the opening / closing amount of the solenoid valve 32 is provided in the vicinity of the throttle valve 16 of the intake pipe 12 in parallel. The throttle valve 16 may be mechanically interlocked with the accelerator pedal, similarly to a generally known mechanism.

Further, in the internal combustion engine 10, an exhaust gas recirculation mechanism (EGR mechanism) 100 that recirculates a part of the exhaust gas to the intake system by controlling the opening / closing amount of a solenoid valve (not shown).
And a canister purge mechanism 200 for supplying the evaporated fuel (purge gas) generated in the fuel tank 38 to the intake system according to the opening / closing amount of a solenoid valve (not shown).

Further, the internal combustion engine 10 is disclosed in Japanese Patent Laid-Open No. 2-27.
A so-called variable valve timing mechanism 300 disclosed in Japanese Patent Publication No. 5043 is provided, and the engine speed N
The valve timing V / T of the internal combustion engine 10 has two types of timing characteristics, LoV / T and HiV /, depending on parameters such as e and the intake pressure Pb in the intake system.
It is variably controlled between T.

Further, a crank angle detecting sensor 40 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 the throttle opening is provided near the throttle valve 16. Degree θ
A throttle opening detection sensor 42 for detecting _TH is provided, and an intake pipe 12 has an absolute pressure sensor 44 for detecting an intake pressure (absolute pressure) Pb downstream of the throttle valve 16 and an intake air temperature upstream of the throttle valve 16. And an intake air temperature sensor 46 for detecting At appropriate positions of the internal combustion engine 10, an atmospheric pressure sensor 48 for detecting the atmospheric pressure Pa and a water temperature sensor 50 for detecting the temperature Tw of the engine cooling water are provided. Although not shown in FIG. 1, the variable valve timing mechanism 300 is provided with a detection sensor 52 for detecting the selective valve timing characteristic. The detection signals of these sensors 40 to 52 are supplied to the control unit 36 one by one.

In the exhaust pipe 26, a wide area air-fuel ratio sensor 54 as a first air-fuel ratio detecting means is attached to a portion on the upstream side of the three-way catalyst devices 28, 30.
Between the O ₂ sensor 5 as the second air-fuel ratio detecting means.
6 is mounted.

As the wide-range air-fuel ratio sensor 54, the LAF sensor disclosed in, for example, Japanese Patent Application Laid-Open No. 2-11842 previously filed by the present applicant is applied.
Has a wide range characteristic capable of linearly detecting the oxygen concentration in exhaust gas over a wide range from lean to rich. Then, the respective detection signals of the LAF sensor 54 and the O ₂ sensor 56 are supplied to the control unit 36 via the low pass filters 58 and 60 set to the predetermined cutoff frequencies.

Next, based on the circuit block diagram of FIG.
The system configuration of the control unit 36 will be described. The control unit 36 includes a microprocessor 62 and various input / output ports, and a central control unit (hereinafter referred to as a CPU core) 6
4 executes various application programs firmwareized by the ROM 76 to perform feedforward control and feedback control described later.

The detection signal of the LAF sensor 54 is input to the first detection circuit 66 via the low-pass filter 58, and the detection circuit 66 performs a predetermined linearization process on this detection signal to obtain a wide range from lean to rich. A linear air-fuel ratio (A / F) proportional to the oxygen concentration in the exhaust gas at is obtained and output to the multiplexer 68. The detection signal from the O ₂ sensor 56 is input to the second detection circuit 70 through the low pass filter 60, and the detection circuit 70 applies the detection signal value to the characteristic curve as shown in FIG. A signal indicating whether the air-fuel ratio of the air-fuel mixture supplied to 10 is rich or lean with respect to the theoretical air-fuel ratio (λ = 1) is generated and output to the multiplexer 68. The detection signals from the sensors 42 to 52 are also supplied to the multiplexer 68. Then, each signal is time-divisionally transferred to the A / D converter 72 via the multiplexer 68 that performs channel switching in synchronization with a predetermined switching timing and converted into digital data, and stored in the random access memory (RAM) 74. It is stored in a predetermined buffer area and is used for the calculation of the CPU core 64. In this embodiment, the A / D converter 72 A / D converts the detection signal from the second detection circuit 70 for each predetermined crank angle (for example, 15 degrees).

Further, the detection signal from the crank angle sensor 40 is waveform-shaped by the waveform shaping circuit 78 into a binary logic rectangular signal, and then counted by the counter 80, and the counted value is also stored in a predetermined buffer area of the RAM 74. Or C
It is used for calculation of the PU core 64.

The read-only memory (ROM) 76 stores in advance the various application programs described above, the above-described timing characteristic LoV / T and HiV / T map data, and various search map data to be described later.
The core 64 determines the optimum fuel injection control condition according to the operating state by executing the above application program while applying various data of the RAM 74 and the ROM 76, and the injector 22 via each of the drive circuits 82 to 88.
The electromagnetic valve 32, the electromagnetic valve 102 of the exhaust gas recirculation mechanism (EGR mechanism) 100, and the electromagnetic valve 202 of the canister purge mechanism 200 are controlled.

FIG. 4 is a block diagram showing the function of the fuel injection control apparatus according to the present embodiment. It is a feedforward control system for compensating the characteristics of the intake system with respect to the internal combustion engine 10, and three feedback control systems. Is provided and the various application programs described above are executed, so that a control function equivalent to the block diagram is exerted.

That is, as in the main flowchart shown in FIG. 5, in step S400, the latest various sensor outputs such as the engine speed Ne, the intake pressure Pb, the throttle opening θ _TH , the cooling water temperature Tw, etc. are read into the RAM 74, and step S400 is executed. The basic fuel injection amount TiM-F is determined by performing the calculation processing of the feedforward control system in S500, and the target air-fuel ratio KCMD and the target air-fuel ratio correction are performed by performing the calculation processing of the first feedback system in step S600. The correction coefficient KSTR for the adaptive feedback control is obtained by obtaining the coefficient KCMDM and the like and performing the calculation processing of the second feedback system in step S700.
And KLAF, etc., and in step S800, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is obtained, and in step S900, the target air-fuel ratio correction coefficient KCMDM is added to the basic fuel injection amount TiM-F.
By multiplying each correction coefficient KSTR or KLAF with #nKLAF, the final output fuel injection amount for each cylinder #nTout
Is determined and the injector 22 is driven. The subscript #n indicates each cylinder, and the output fuel injection amount #n
Tout defines the valve opening time of the injector 22 of each cylinder. Further, the processing of this main flowchart is performed in synchronization with TDC.

Next, the function of each block will be described. First, a feedforward control system (shown as "FFC" in FIG. 4) is disclosed in Japanese Patent Application No. 6-1972 previously proposed by the applicant.
Since it is disclosed in No. 38, it will be briefly described about all effective volumes from the downstream of the throttle valve 16 in the intake system to the intake port of each cylinder (the chamber including the relevant portion of the intake pipe 12 and the surge tank 18). By constructing a fluid dynamics model (mathematical model) of the above, and applying the throttle opening θ _TH and the intake pressure Pb to this fluid dynamics model, all operating states including not only the steady operating state but also the transient operating state The optimum basic fuel injection amount TiM-F at is determined.

FIG. 6 is a flowchart showing a basic fuel injection amount TiM-F calculation routine (corresponding to step S500 in FIG. 5), and FIG. 7 is a block diagram explaining this calculation routine. Based on this, the function of the feedforward control system will be described.

In step S502, it is determined whether or not the engine is in the starting state. If the result is affirmative, step S50
Basic fuel injection amount TiM-F corresponding to the start mode in No. 4
Is set, and if the result is negative, it is determined in step S506 whether the fuel cut state is set. If the determination is affirmative, the basic fuel injection amount TiM-F (= 0) for fuel cut is set in step S508, and if the determination is negative, the basic fuel injection amount TiM-F for setting the basic fuel injection amount corresponding to the normal operating state is set. The process moves to S510 and thereafter.

In step S510, a predetermined map of the ROM 76 is searched using the engine speed Ne and the intake pressure Pb as parameters to obtain the fuel injection amount (reference value) TiM in the steady operation state. That is, the fuel injection amount TiM with the engine speed Ne and the intake pressure Pb as parameters is previously obtained based on the speed density method, and the fuel injection amount TiM is stored in the ROM 76 as map data.

In step S512, the throttle opening θ
_{By applying} the _TH value to the first-order lag transfer function (1-B) / (Z-B), the first-order lag value θ _TH-D of the throttle opening θ _TH is calculated. That is, in the transient operation state, since the change in the throttle opening θ _TH does not directly correspond to the intake air amount of the intake port, the first-order delay value θ _TH-D is used for approximation. Incidentally, B in the transfer function is a coefficient.

In step S514, as shown in FIG. 7, a map stored in advance in the ROM 76 is searched to obtain a throttle projected area (throttle projected area in the longitudinal direction of the intake pipe) corresponding to the throttle opening θ _TH. S
And a correction coefficient (product of the flow coefficient α and the gas expansion correction coefficient ε) C corresponding to the throttle opening θ _TH and the intake pressure Pb, and the throttle projected area S is multiplied by the correction coefficient C to obtain a steady operation. The throttle effective opening area A in the state is calculated.

In step S516, as shown in FIG. 7, a map stored in advance in the ROM 76 is searched to find the throttle projection area S corresponding to the first-order lag value θ _TH-D of the throttle opening and the first-order lag. By _obtaining the correction coefficient C corresponding to the value θ _TH-D and the intake pressure Pb, and multiplying this throttle projected area S by the correction coefficient C,
Calculate the throttle effective opening area A _DELAY during transient operation.

In step S518, the opening cross section A _BYPASS of the bypass passage 34 is also taken into consideration,

[0040]

[Equation 1]

As a result, the effective opening area A during steady operation is
Ratio of effective opening area A _DELAY during transient operation to RATIO-
Calculate A.

In step S520, the fuel injection amount TiM-F 'is adapted to the steady operation state and the transient operation state by multiplying the fuel injection amount TiM by the ratio RATIO-A.
Ask for. That is, the value of the ratio RATIO-A becomes 1 in the steady operation state and becomes a certain value except 1 in the transient operation state, which corresponds to both the steady operation state and the transient operation state. Therefore, by multiplying the fuel injection amount TiM by the ratio RATIO-A, the fuel injection amount TiM-F 'adapted to the steady operation state and the transient operation state can be obtained.

In step S522, a predetermined map in the ROM 76 is searched based on parameters such as the engine speed Ne, the intake pressure Pb, the intake temperature and the cooling water temperature Tw, the purge gas concentration PUG, and the exhaust gas recirculation rate. Obtain the correction coefficient KTOTAL, and further, fuel injection amount TiM-F '
EGR mechanism 1 by multiplying by the correction coefficient KTOTAL
00 and the canister purge mechanism 200 are compensated for the basic fuel injection amount TiM-F.

As described above, this feedforward control system is optimized for the cylinder inflow air amount from the throttle opening θ _TH and the intake pressure Pb, even if the cylinder inflow air amount fluctuates according to the change in the operating condition. Basic fuel injection amount T
Determine iM-F.

Next, the first feedback system will be described. This feedback system includes functional blocks indicated by "KCMD", "KCMD correction", and "KCMDM" in FIG. 4, and performs arithmetic processing according to the flowchart shown in FIG. 8 (corresponding to step S600 in FIG. 5).

First, in step S602 of FIG.
RO using the engine speed Ne and the intake pressure Pb as parameters
The basic value KBS of the air-fuel ratio is obtained by searching the predetermined map of M76. That is, this basic value KBS is data of the air-fuel ratio that can be obtained from the output of the O ₂ sensor 56 in the steady operation state using the engine speed Ne and the intake pressure Pb as parameters, and is stored in the ROM 76 in advance. Note that this map also stores basic values corresponding to the idle operation state. Further, in a so-called lean burn engine for improving the combustion characteristics by increasing the air-fuel ratio supplied to the engine at a low load of the engine (small in terms of equivalence ratio), the basic value for lean burn is also stored. Has been done.

In step S604, by referring to the value of the built-in timer circuit (not shown), it is determined whether or not lean burn control is being executed after the engine is started, and during the lean burn control period. If so, the lean correction coefficient is, for example, 0.89; otherwise, 1.0.
And

The reason for making this determination is as follows. The internal combustion engine 10 according to the present embodiment is provided with the variable valve timing mechanism 300, and during the cranking period (starting period) after the start, one of the intake valves of each cylinder is made to stop, so that the target empty space is reached. Lean burn control is performed in which the fuel ratio is set slightly leaner than the stoichiometric air-fuel ratio, and as a result, an increase in hydrocarbons (HC) can be suppressed even during the start-up period when the catalyst device is not yet activated. This is because the effect of still,
In a normal internal combustion engine (internal combustion engine not provided with a variable valve timing mechanism) having two intake valves for each cylinder, if the target air-fuel ratio is set to the lean side after engine start,
Combustion in the engine becomes unstable, leading to misfire. However, in the internal combustion engine of this embodiment equipped with such a variable valve timing mechanism 300, one of the intake valves is stopped. Since a so-called swirl flow is created in the combustion chamber, stable combustion can be obtained even if leaning is performed immediately after the engine is started. In step S606,
Determine whether the throttle opening is fully open (WOT),
A full-opening increase correction value is calculated according to this determination result, and it is further determined in step S608 whether the cooling water temperature Tw is high, and an increase correction coefficient KTWOT is calculated according to this determination result. The increase correction coefficient KTWOT also includes a correction coefficient value for engine protection at high water temperature.

In step S610, the basic value KBS is multiplied by the correction coefficient KTWOT to obtain the basic value KBS.
And the target air-fuel ratio by the calculation shown in Equation 2.
Determine KCMD. That is, as shown in FIG. 3, within a range where the output of the O ₂ sensor 56 near the stoichiometric air-fuel ratio has a linear characteristic (indicated by a broken line on the vertical axis), a window for finely controlling the air-fuel ratio (hereinafter referred to as DKCMD -OFFSET) and then add this window value DKCMD-OFFSET to the corrected basic value KBS to obtain the target air-fuel ratio KCMD
Ask for.

[0050]

[Equation 2]

Next, in step S612, after performing limit processing of the target air-fuel ratio KCMD (k) (where k is time), in step S614, the target air-fuel ratio KC
Judge whether MD (k) is 1 or a value near it,
When the determination is affirmative, activation of the O ₂ sensor 54 is determined in step S616. The activation determination is executed by another routine (not shown) and is performed by detecting the voltage change of the detection signal of the O ₂ sensor 56.

Next, in step S618, MID
The value DKCMD for O ₂ control is calculated. Where MIDO ₂
The control means the O ₂ sensor 56 on the downstream side of the three-way catalyst device 28.
Output of the target air-fuel ratio KC of the LAF sensor 54 on the upstream side.
It means the work that makes MD (k) variable. In detail, as shown in FIG. 3, the value DKCMD is calculated by using the PID control law for the deviation between the predetermined comparison voltage VrefM and the output voltage VO2M of the O ₂ sensor 56. The comparison voltage VrefM is the atmospheric pressure P.
a, the water temperature Tw, the exhaust volume (which can be obtained from the engine speed Ne and the intake pressure Pb), and the like.

Furthermore, the above window value DKCMD-OFFSET
Is an offset value added in order to maintain the purification rates of the three-way catalytic converters 28 and 30 in an optimum state, and is different due to the characteristics peculiar to the catalytic converter. Therefore, the characteristics of the three-way catalytic converter 28 are taken into consideration. Will be decided. Also, the window value DKCMD-
Since OFFSET changes due to deterioration over time of the catalyst devices 28 and 30, learning is performed by weighted averaging using the calculated value of the value DKCMD each time. In particular,

[0054]

(Equation 3)

It is obtained by the arithmetic expression of Here, W is a weighting factor, k is time, and more specifically, a control cycle. That is, the target air-fuel ratio KCMD is set to the window value DKCMD-
By performing the learning calculation with the previously calculated value of OFFSET, the feedback control is performed to the air-fuel ratio where the purification rates of the catalyst devices 28 and 30 are optimized without being affected by the deterioration over time.

Next, in step S620, the target air-fuel ratio KCMD (k) is added to the calculated value DKCMD (k) to set (update) a new target air-fuel ratio KCMD (k). In step S622, the correction coefficient KETC is obtained by searching a predetermined table in the ROM 76 based on the updated target air-fuel ratio KCMD (k). The correction coefficient KETC is provided to compensate for a difference in intake air filling efficiency due to heat of vaporization. Specifically, the calculated correction coefficient KETC is added to the target air-fuel ratio KCMD.
corrected (updated) by multiplying (k)
The target air-fuel ratio correction coefficient KCMDM (k) is calculated. That is, in this control, the target air-fuel ratio is indicated by the equivalence ratio, and the value obtained by performing the filling efficiency correction on the target air-fuel ratio correction coefficient KCMDM (k)
And

When the result of the step S614 is negative, it means that the target air-fuel ratio KCMD (k) to be controlled is largely deviated from the stoichiometric air-fuel ratio, for example, during lean burn operation. , Immediately jump to step S622.

Finally, in step S624, the target air-fuel ratio correction coefficient KCMD (k) is limited, and
As shown in FIG. 4, the required fuel injection amount Tcyl is calculated by multiplying the basic fuel injection amount TiM-F from the feedforward control system by the target air-fuel ratio correction coefficient KCMDM (k).

As described above, the function of the first feedback system is that the target air-fuel ratio KCMD and the target air-fuel ratio KCMD are obtained by performing the above-described predetermined correction processing on the basic value KBS of the air-fuel ratio in the steady operation state based on the output of the O ₂ sensor 56. The target air-fuel ratio correction coefficient KCMDM is calculated, and the required fuel injection amount Tcyl that can set the ideal air-fuel ratio for the catalyst device is calculated by multiplying the basic fuel injection amount TiM-F by the target air-fuel ratio correction coefficient KCMDM. .

Next, the second feedback system will be described. This feedback system is provided with an adaptive controller indicated by "STR" in FIG. 4, a PID controller indicated by "PIDC", and a switching mechanism indicated by "switch SW". It is realized by executing a predetermined application program by the core 64. Since this feedback system is disclosed in detail in Japanese Patent Application No. 6-340021, its outline will be described here.

In this feedback system, the response delay of the internal combustion engine 10 can be obtained only by obtaining the required fuel injection amount Tcyl by multiplying the basic fuel injection amount TiM calculated by the feedforward system by the target air-fuel ratio correction coefficient KCMDM. As the target air-fuel ratio KCMD becomes a blunted air-fuel ratio, the feedback correction coefficient KSTR is set using the adaptive controller STR for the purpose of dynamically compensating the response of the air-fuel ratio from the target air-fuel ratio KCMD. This feedback correction coefficient KSTR
Therefore, the required fuel injection amount Tcyl is further corrected. Further, since the adaptive controller STR has relatively high control responsiveness, if the target air-fuel ratio KCMD fluctuates greatly in accordance with the operating state, the control amount will rather oscillate and the control stability will deteriorate. If the control becomes unstable due to a problem, the required fuel injection amount Tcyl is corrected by the feedback correction coefficient KLAF obtained by the PID controller PIDC. A switching mechanism is provided to switch and apply these feedback correction coefficients KSTR and KLAF according to the operating state. Further, when switching the feedback correction coefficient determined based on a different control law, since the respective characteristics are different, a step is generated in the correction coefficient, the operation amount changes abruptly, and the control amount becomes unstable. Since there is a possibility that the stability may be reduced, the switching mechanism smoothly executes the switching so that the feedback correction coefficient does not become discontinuous.

First, the PID controller PIDC is based on the air-fuel ratio (hereinafter referred to as the detected air-fuel ratio KACT) of the exhaust system collecting portion estimated by the sampling operation block (shown as "sel-V" in the figure). The target air-fuel ratio KCMD is dynamically compensated. Here, the sampling operation block sel-V has a function of calculating the detected air-fuel ratio KACT from the detection signal of the LAF sensor 54, and this detected air-fuel ratio KACT is also used in the third feedback system described later. Then, predetermined feedback control is performed. The details of the sampling operation block sel-V will be described together with the third feedback system.

The process of the PID controller PIDC will be described below.
First, the control deviation DKAF between the target air-fuel ratio KCMD and the detected air-fuel ratio KACT
To

[0064]

[Equation 4]

Is calculated. In addition, d'represents a dead time until KCMD is reflected in KACT. Therefore, KCMD (k-d ') indicates the target air-fuel ratio before the dead time control cycle. KACT (k) indicates the detected air-fuel ratio of the control cycle this time. Further, the air-fuel ratio in this specification shows both the target value KCMD and the detected value KACT as an equivalent ratio, that is, Mst / M = 1 / λ (Mst is a theoretical air-fuel ratio, M is an air consumption amount). Ratio of A and fuel consumption F A / F, λ is excess air ratio).

Then, it is multiplied by a predetermined coefficient to obtain the P term KL.
AFP (k), I term KLAFI (k), and D term KLAFD (k),

[0067]

(Equation 5)

Is calculated.

As described above, the P term is obtained by multiplying the deviation DKAF (k) by the proportional gain KP, and the I term is the value obtained by multiplying the deviation by the integral gain KI as the previous value KLAF (k) of the feedback correction coefficient. Calculated by adding, D term is the current deviation value DKAF
Calculated by multiplying the difference between (k) and the previous value DKAF (k-1) by the derivative gain KD. Each gain KP, KI, KD is obtained by a predetermined map search using the engine speed Ne and the intake pressure Pb as parameters. Further, as shown in Expression 6, these values are added together and the offset amount of 1.0 is added to obtain the present value KLAF (k) of the feedback correction coefficient according to the PID control law of the PID controller PIDC.

[0070]

(Equation 6)

Next, the function of the adaptive controller STR will be described with reference to FIG. The adaptive controller STR has a STR controller and a parameter adjusting mechanism, and the STR controller is a target air-fuel ratio KCMD from the first feedback system.
(k) and the detected air-fuel ratio KACT (k) from the sampling operation block (sel-V) are input, and the coefficient vector identified by the parameter adjustment law (mechanism) proposed by Landau et al. The feedback correction coefficient KSTR (k) is calculated by performing signal processing. In other words, the feedback correction coefficient KSTR (k) is calculated using a recurrence formula.

According to this method, a so-called adaptive system is converted into an equivalent feedback system composed of a linear block and a non-linear block, Popov's integral inequality for input / output is established for the non-linear block, and the linear block is strongly positive real. The stability of the adaptive system is guaranteed by determining the adjustment rule so that still,
Such a method is described, for example, in “Compute Roll” (published by Corona) No. Pages 27.28 to 41 or "Automatic Control Handbook" (published by Ohmsha Co., Ltd.), pages 703 to 707.

The adaptive control technique using the adjustment law of Landau et al. Will be described below. According to the adjustment law of Landau et al., The denominator of the transfer function A (Z ^-1 ) / B (Z ^-1 ) of the controlled object of the discrete system. When the polynomial of the numerator is set as in Equation 7, the adaptive parameter θ hat (k) and the input ζ (k) to the adaptive parameter adjusting mechanism are determined as in Equation 7. Number 7
Then, the case where m = 1, n = 1, and d = 3, that is, a plant having a dead time of three control cycles in the primary system is taken as an example. Here, k indicates time, more specifically, a control cycle.

[0074]

(Equation 7)

Here, the adaptive parameter θ hat (k) is expressed by equation 8. Further, Γ (k) and e asterisk (K) in Equation 8 are a gain matrix and an identification error signal, respectively, and are represented by recurrence formulas such as Equation 9 and Equation 10.

[0076]

(Equation 8)

[0077]

[Equation 9]

[0078]

[Equation 10]

Various concrete algorithms are given depending on how to select λ1 (k) and λ2 (k) in the equation (9). λ1 (k)
= 1 and λ2 (k) = λ (0 <λ <2), the gradual gain algorithm (least squares method when λ = 1), λ1 (k) =
λ1 (0 <λ1 <1), λ2 (k) = λ2 (0 <λ2 <λ)
Then, the variable gain algorithm (weighted least squares method when λ2 = 1) is set as λ1 (k) / λ2 (k) = σ, and λ
When 3 is expressed as in Equation 11, if λ1 (k) = λ3 is set, a fixed trace algorithm is obtained. Also, λ1 (k) = 1,
When λ2 (k) = 0, the fixed gain algorithm is used. In this case, as is clear from Equation 9, Γ (k) = Γ (k-1), and therefore Γ (k) = Γ is a fixed value.

[0080]

[Equation 11]

Here, in FIG. 9, the above-mentioned STR
The controller (adaptive controller) and the adaptive parameter adjustment mechanism are placed outside the fuel injection amount calculation system, and the detected air-fuel ratio KACT
(K) is the target air-fuel ratio KCMD (k-d ') (where d'is as described above)
The feedback correction coefficient KSTR (k) operates by adaptively matching the dead time until KCMD is reflected in KACT.
Is calculated. That is, the STR controller receives the coefficient vector θ hat (k) adaptively identified by the adaptive parameter adjusting mechanism and forms a feedback compensator so as to match the target air-fuel ratio KCMD (k−d ′).

Thus, the feedback correction coefficient KSTR
(k) and the detected air-fuel ratio KACT (k) are obtained and input to the adaptive parameter adjusting mechanism, where the adaptive parameter θ hat (k) is calculated and input to the STR controller.
The target air-fuel ratio KCMD (k) is input to the STR controller.
And the detected air-fuel ratio KACT (k) is the target air-fuel ratio KCMD (k)
The feedback correction coefficient KSTR (k) shown in Expression 12 is calculated by using a recurrence formula so that

[0083]

(Equation 12)

Calculated feedback correction coefficient KSTR
(k) is multiplied by the required fuel injection amount Tcyl via the switching mechanism, and the corrected fuel injection amount Tcyl 'is further corrected by the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF of the third feedback control system described later. As a result, the cylinder-by-cylinder output fuel injection amount #nTout is obtained.

The switching mechanism uses a predetermined switching flag FKST.
In the operating state in which the switching process is performed in synchronization with R and the target air-fuel ratio KCMD fluctuates greatly, the feedback correction coefficient KLAF (k) is switched and selected, and the required fuel injection amount Tcyl is multiplied to obtain the target air-fuel ratio. In an operating state in which KCMD does not fluctuate significantly, the feedback correction coefficient KSTR (k) is switched and selected, and the required fuel injection amount Tcyl is multiplied. That is, the required fuel injection amount Tcyl is the feedback correction coefficient KSTR or
Corrected by KLAF.

Next, the third feedback system will be described. This feedback system is basically an observer (OB in FIG. 4) for the air-fuel ratio of the exhaust system collecting portion estimated by the sampling operation block “sel-V”, that is, the detected air-fuel ratio KACT.
(Denoted as SV), the cylinder-by-cylinder air-fuel ratio #n
KACT is obtained, and further, the air-fuel ratio correction coefficient #nKLAF for each cylinder is calculated from the cylinder-specific air-fuel ratio #nKACT according to the PID control law (shown as PID in FIG. 4). The subscript #n indicates each cylinder. Then, by multiplying the fuel injection amount Tcyl ′ by the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF, the output fuel injection amount #nTout capable of equalizing the air-fuel ratio of each cylinder is set, and by extension, the three-way catalyst 28, The exhaust gas cleaning efficiency of No. 30 is improved. That is, this third feedback system is to perform feedback correction of variations in the air-fuel ratio in each cylinder. First, before describing the operation of the feedback system, the sampling operation block “sel-V” and the observer will be described.

Since the exhaust gas is discharged in the exhaust stroke, the behavior of the air-fuel ratio in the exhaust system collecting portion of the multi-cylinder internal combustion engine 10 is apparently in synchronism with TDC.
Therefore, when a single LAF sensor 54 is provided at the collecting portion of the exhaust system and the air-fuel ratio is sampled, it is necessary to perform it in synchronization with TDC. However, the LAF sensor 54
Depending on the sampling timing of the control unit (ECU) 36 that processes the detection output of 1, the behavior of the air-fuel ratio may not be accurately captured.

That is, for example, when the air-fuel ratio of the exhaust system collecting portion with respect to TDC is as shown in FIG. 10, the control unit 3
The air-fuel ratio recognized in 6 has a completely different value depending on the sampling timing, as shown in FIG. Further, the change in the air-fuel ratio is due to the exhaust gas being detected by the LAF sensor 54
It also varies depending on the time required to reach the position and the reaction time of the LAF sensor 54. Among them, the arrival time to the LAF sensor 54 changes depending on the exhaust gas pressure, the exhaust gas volume, and the like. Furthermore, sampling in synchronization with TDC means sampling based on the crank angle, so that it is inevitably affected by the engine speed Ne. As described above, the detected value of the air-fuel ratio largely depends on the operating state of the engine. In order to solve such a problem, a sampling operation block sel-V and an observer OBSV are provided.

In order to accurately separate and extract the air-fuel ratio of each cylinder from the detection signal of the single LAF sensor 54 provided in the exhaust system collecting portion, it is necessary to accurately clarify the detection response delay of the LAF sensor 54. is there. Therefore, as shown in FIG. 12, if this delay is simulated by a pseudo first-order delay system,
The equation of state can be expressed by Equation 13.

[0090]

(Equation 13)

When this is discretized with the period ΔT, it becomes as shown in Expression 14. FIG. 13 is a block diagram of the equation (14).

[0092]

[Equation 14]

Therefore, by using Equation 14, LA
The true air-fuel ratio can be obtained from the detection output of the F sensor 54. That is, since the equation (15) is obtained by modifying the equation (14), the value at the time k-1 can be calculated backward from the value at the time k by the equation (16).

[0094]

(Equation 15)

[0095]

[Equation 16]

More specifically, if Expression 15 is expressed by a transfer function using Z conversion, Expression 17 is obtained. Therefore, by multiplying the inverse transfer function by the detection output LAF (k) of the LAF sensor 54 this time, The input air-fuel ratio can be estimated in real time. FIG. 14 shows a block diagram of the real-time A / F estimator.

[0097]

[Equation 17]

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 air-fuel ratio of the exhaust gas collecting portion is temporally calculated from the air-fuel ratio of each cylinder. Considering that it is a weighted average considering the contribution,
The value at the time of was expressed like Formula 18. 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 unless there is a 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 (17).

[0099]

(Equation 18)

That is, the air-fuel ratio of the collecting portion is determined by weighting the past combustion history for each cylinder by C (for example, the most recently burned cylinder is 40
%, Before that 30%. ． ． It was expressed as the sum of those multiplied by. A block diagram of this model is shown in FIG.
It becomes like 5.

The equation of state is as shown in equation (19).

[0102]

[Formula 19]

When the air-fuel ratio of the collecting portion is set to y (k), the output equation can be expressed as in equation (20).

[0104]

(Equation 20)

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. So 4TDC before (ie
If x (k + 1) = x (k-3), assuming that the air-fuel ratio of the same cylinder is in a steady operation state where it does not change rapidly,
become that way.

[0106]

[Equation 21]

When a simulation is performed on such a model, the result that the model output value follows the measured value of the LAF sensor 54 output satisfactorily is obtained. I was able to verify that

Therefore, the problem of an ordinary Kalman filter for observing x (k) in the state equation and the output equation (Equation 20) shown by the equation 22 is reduced. When the weight matrix Q and R are placed as in Equation 23 and the Riccati equation is solved, the gain matrix K becomes as in Equation 24.

[0109]

[Equation 22]

[0110]

(Equation 23)

[0111]

[Equation 24]

From this, A-KC is obtained as shown in Equation 25.

[0113]

(Equation 25)

By the way, the structure of a general observer is as shown in FIG. 16, but in this model, the input u
Since there is no (k), the configuration is such that only y (k) is input as shown in FIG. 17, and this can be expressed by Equation 26.

[0115]

(Equation 26)

When y (k) is input, the observer,
That is, the system matrix of the Kalman filter is expressed as in Equation 27.

[0117]

[Equation 27]

In the model this time, when the element of the weight distribution R of the Riccati equation: the element of Q = 1: 1, the system matrix S of the Kalman filter is given by equation 28.

[0119]

[Equation 28]

FIG. 18 shows a combination of the above model and the observer. According to the result of the simulation, it was verified that the air-fuel ratio of each cylinder can be accurately extracted from the air-fuel ratio of the collecting portion.

As described above, since the observer was able to estimate the air-fuel ratio # nA / F of each cylinder from the air-fuel ratio A / F of the collecting portion (that is, A / F is equivalent to KACT), It is possible to calculate the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF for controlling the air-fuel ratio for each cylinder using the PID control rule.

Specifically, as shown in FIG. 19, the air-fuel ratio (that is, KACT) of the exhaust system collecting part is set to the previous value of the average value of all cylinders of the air-fuel ratio correction coefficient #n for each cylinder. PI is set so as to eliminate the deviation between the target value obtained by dividing by the calculated value and the estimated value # nA / F for each cylinder of the observer.
It is calculated using the D control law. That is, as shown in Equation 29, P
The above target value KCMDOBSV applied to the ID control law is TD
Air-fuel ratio correction coefficient # 1KLAF for each cylinder estimated at C #
It can be obtained by dividing the detected air-fuel ratio KACT obtained this time by the average value of 4KLAF.

[0123]

[Equation 29]

On the other hand, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is
As shown in Expression 30, for each cylinder #n, the detected air-fuel ratio #n
The deviation #nDKACT (m) between the KACT (m) and the target value KCMDOBSV is calculated, and the deviation #nDKACT (m) calculated this time and the deviation #nDKACT (m-1) calculated last time #NDDKACT, and by applying these calculation results, the KP term, KI term, and KD term of the PID control law corresponding to each cylinder #n are determined, and finally, these KP terms And the KI and KD terms are applied to obtain the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF. In addition, #n is each cylinder # 1 to # 4
And m indicates the time point every 4TDC. That is, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is calculated once every 4TDC. In the following equation, the KPOBSV term, KIOBSV term, and KDOBSV term, which are the reference gains, are set to different values when the engine is idling and when the engine is not operating, and are stored in the ROM 76 as a data map in advance. Since it is stored, a map search is performed according to the driving state during such calculation.

[0125]

[Equation 30]

As a result, the air-fuel ratio of each cylinder converges to the collective air-fuel ratio, and the collective air-fuel ratio converges to the target air-fuel ratio. As a result, the air-fuel ratios of all the cylinders reach the target air-fuel ratio. Converge. Here, the output fuel injection amount #nTout of each cylinder
(Specified by the valve opening time of the injector)

[0127]

[Equation 31]

(N is a cylinder).

The basic principle of the sampling operation block sel-V, the observer and the third feedback system has been described above. Further, in the middle of the path of the third feedback system, as shown in FIG. 20, at the input / output terminal of the functional block (PID) for calculating the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF based on the PID control law. A demultiplexer DMPX and a multiplexer MPX are provided, and a memory block REF for storing data of a predetermined fixed value or re-storing new data is provided. The first control block CH1 instructs the demultiplexer DMPX and the multiplexer MPX to switch each channel according to the operation state described later, and the second control block CH2 operates the observer OBSV for the estimation process. It is configured to instruct and stop. It should be noted that such a function may be realized by program processing by the engine control unit 36 or may be realized by hardware.

Next, the specific operation of the sampling operation block sel-V and the third feedback system will be described with reference to the flowcharts of FIGS. 21 and 22.

First, the operation until the sampling operation block sel-V obtains the air-fuel ratio (that is, KACT) of the exhaust system collecting portion will be described based on the flow chart of FIG.
Note that this process is actually executed in advance in step S400 in the routine shown in FIG. 5, so that the detected air-fuel ratio KA in steps S700 and S800 is executed.
The CT and the estimated value # nA / F can be used.

In FIG. 21, in step S402,
Engine speed Ne, intake pressure Pb, valve timing V / T
By reading out the timing map for HiV / T and LoV / T and then sampling the output of the LAF sensor 54 for HiV / T and LoV / T in step S408. , HiV / T detected air-fuel ratio KACT and LoV / T detected air-fuel ratio KACT.

FIG. 23 is an explanatory diagram showing the characteristic of the timing map. As shown in the figure, the characteristic is that the value sampled at a faster crank angle is obtained as the engine speed Ne is lower or the intake pressure (negative pressure) Pb is higher. Set to select. Here, "early" means a value sampled at a position closer to the previous TDC position (in other words, an old value). On the contrary, the higher the engine speed Ne or the lower the intake pressure Pb is, the slower the crank angle is, that is, the later TDC.
A value sampled at a crank angle close to the position (in other words, a new value) is set to be selected. That is, L
It is best to sample the AF sensor output at a position as close as possible to the inflection point of the actual air-fuel ratio as shown in FIG. 11, but the inflection point, for example, the first peak value is
Assuming that the reaction time of the sensor is constant, as shown in FIG. 24, the lower the engine speed Ne, the faster the crank angle. Further, it is expected that as the load increases, the exhaust gas pressure and the exhaust gas volume increase, and therefore the flow velocity of the exhaust gas increases and the arrival time at the LAF sensor 54 is shortened. From that meaning, the sample timing is set as shown in FIG.

Further, regarding the valve timing, an arbitrary value Ne1 of the engine speed is set to Ne1-Lo, Hi on the Lo side.
Ne1-Hi for the side, and any value for the intake pressure is Pb1-Lo for the Lo side and Pb1-H for the Hi side.
When i is set, the map characteristic is 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 so that the map characteristic is selected. Is set.

The processes of steps S402 to S408 described above correspond to the sampling operation block sel-V. Therefore, as shown in the lower part of FIG. 25, the CPU core 64 can accurately recognize the maximum value and the minimum value of the sensor output.
Then, the feedback control shown in steps S700 and S800 in FIG. 5 is performed based on the accurate air-fuel ratio.

Next, the operation of the cylinder-by-cylinder feedback control in step S800 in FIG. 5 will be described with reference to the flowchart in FIG. Incidentally, the internal combustion engine 10 of the present embodiment
Since the valve timing mechanism 300 is provided in, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is calculated after estimating the cylinder-by-cylinder air-fuel ratio # nA / F according to the valve timings HiV / T and LoV / T. It has become.

In FIG. 22, in step S802,
The engine speed Ne is a predetermined value (in this embodiment, 3000 r
pm) or less. That is, when the engine speed Ne exceeds the predetermined value and the cycle of each TDC becomes short, it becomes impossible to perform a series of processes for feedback control at each TDC. If (determination is affirmative), the process proceeds to steps S804 to S814. And FIG.
The first control block CH1 shown in FIG. 2 controls the switching connection between the demultiplexer DMPX and the multiplexer MPX so that the output of the observer OBSV is connected to the PID block and normal cylinder-by-cylinder feedback control is performed as shown in FIG. Further, the second control block CH2 causes the observer OBSV to perform the cylinder-by-cylinder air-fuel ratio # A / F estimation process. On the other hand, when the result in step S802 is negative, the process proceeds to step S816.

Steps S804 to S812 are a routine for estimating the cylinder-by-cylinder air-fuel ratio # nA / F by the observer OBSV. First, in steps S804 and S806, the HiV / value obtained in step S408 is first determined.
The air-fuel ratio # nA / F of each cylinder for HiV / T is estimated from the detected air-fuel ratio KACT for T, and the air-fuel ratio # nA / of each cylinder for LoV / T is detected from the detected air-fuel ratio KACT for LoV / T. F
To estimate. Subsequently, in step S808, the current valve timing V / T is determined, and depending on the determination result, the process proceeds to step S810 or S812, and either the HiV / T or the LoV / T-specific air fuel # nA / Select F and output.

Next, in step S814, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF is obtained by using the PID control law for the selected cylinder-by-cylinder air-fuel # nA / F, and then step S900 in FIG. The output fuel injection amount #nTout for each cylinder shown in is calculated.

As described above, the engine speed Ne is set to the predetermined value (3
000 rpm) or less, both the cylinder-by-cylinder air-fuel ratio # nA / F estimation processing and the cylinder-by-cylinder feedback calculation processing by the observer OBSV are executed in synchronization with each TDC as shown in the determination condition table of FIG. It Further, as shown more specifically in the process diagram of FIG. 27, the period T for which TDC is sufficient
Since i is i, the estimation calculation process (process of period τ3) and the feedback calculation process for each cylinder (process of period τ4) by the observer OBSV are performed for each TDC, and at the same time, another process, that is, the feedforward system and the first, Processing of the second feedback system (processing of period τ1) and processing of inputting detection signals from various sensors that are basically necessary for performing engine control (processing of period τ2) are performed. That is, the normal feedback control for each cylinder is performed.

Returning to FIG. 22, the description will be continued. Step S
When the result in 802 is negative, in step S816, it is determined whether the engine speed Ne is within a predetermined range. In this embodiment, 3000 rpm <Ne ≦ 4500 rp
In the case of m, the processing shifts to steps S818 to S820, and as shown in the judgment condition table of FIG.
The cylinder-by-cylinder air-fuel ratio # nA / F estimation processing by SV is performed every TD.
Although it is executed in synchronization with C, the feedback calculation for each cylinder based on the PID control law is performed a predetermined number of times (one or more times) within a plurality of TDC cycles.
A so-called thinning process is performed, which is stopped. The thinning process is performed by the first control block CH1 in FIG.
Is synchronized with TDC, and is realized by sequentially controlling the on / off switching of the demultiplexer DMPX and the multiplexer MPX. For example, the jth cylinder #
When thinning out the feedback control for j,
The switching contact between the demultiplexer DMPX and the multiplexer MPX is turned off in order to interrupt the processing of the PID control law in the path related to the th cylinder #j, and the PID in the path related to the remaining cylinders is processed as usual. By turning on the multiplexer DMPX and the multiplexer MPX and sequentially performing such switching control for each of the cylinders # 1 to #n, the feedback control of each path is made uniform in time even if the thinning process is performed. ing.

First, in step S818, similarly to steps S804 to S812, the cylinder-by-cylinder air-fuel ratio #nA.
Estimate / F. Next, in step S820, the thinning process is performed. Since the processing routine shown in FIG. 22 is synchronized with TDC, the order in which thinning processing is performed is every time this processing routine is executed (each TDC).
Be changed.

In step S900, since the feedback correction coefficient #jKLAF for the route #j corresponding to the thinning-out process is not obtained, only the output fuel injection amount #jTout for the cylinder is not feedback-corrected and the remaining Output fuel injection amount for cylinder #n Tou
For t (excluding #jTout), the cylinder-by-cylinder feedback control by the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF (excluding #jKLAF) is performed as usual.

FIG. 28 is a process chart showing a first concrete example of the thinning-out process, and FIG. 29 is a process chart showing a second concrete example of the thinning-out process.

First, in the decimation process of FIG. 28, the cylinder-by-cylinder feedback calculation related to one cylinder is stopped once during 4TDC, and the process of shifting the order of the cylinders corresponding to the stop of the calculation is repeated. ing. In other words,
In the normal stroke of FIG. 27, the feedback calculation of each cylinder is 4
In the decimation process of FIG. 28, the feedback calculation of each cylinder is repeated every 8TDC, and the phase of the decimation process is 1T between the cylinders.
They are staggered by DC. When the thinning-out process is performed in this manner, the cycle of TDC becomes Tj as the engine speed Ne increases.
Even if shortened to (<Ti), the engine control unit 36
It is possible to execute the processing by the above in synchronization with TDC. For example, as shown in FIG. 28, when performing feedback control for each cylinder according to the PID control law (indicated by period τ4), processing for inputting the detection signal of each sensor (indicated by period τ2) is performed. When not performing the cylinder-by-cylinder feedback control according to the PID control rule, the processing time is distributed by performing processing so as to perform processing for inputting the detection signal of each sensor during the idle period. Since it can be substantially shortened, it is possible to perform cylinder-by-cylinder feedback control that copes with an increase in the engine speed Ne.

In the thinning process of FIG. 29, assuming that the exhaust stroke is repeated in the order of cylinders # 1 → # 3 → # 4 → # 2, the first TDC with 3TDC as one set.
Only in the case of the observer OBSV, the cylinder-by-cylinder air-fuel ratio # nA / F estimation processing and the cylinder-by-cylinder feedback calculation by the PID control law are performed. Then, the thinning process of stopping the feedback calculation for each cylinder based on the PID control law is repeated. According to this thinning-out process, feedback calculation of each cylinder is performed by 12T.
While repeating for each DC, the phase of the thinning process is shifted by 2TDC between the cylinders. Then, similarly to the case shown in FIG. 28, when performing the cylinder-by-cylinder feedback control according to the PID control law (indicated by period τ4), processing for inputting the detection signal of each sensor (in period τ2). Is not performed and the cylinder-by-cylinder feedback control based on the PID control rule is not performed, by decentralizing the processing so as to perform processing for inputting the detection signal of each sensor during the idle period, Since the processing time can be substantially shortened, it is possible to perform cylinder-by-cylinder feedback control that copes with an increase in the engine speed Ne.

The decimation processing shown in FIGS. 28 and 29 is an example, and if decimation processing is performed so that the feedback control according to the PID control rule of each path is temporally uniform, another method is used. May be taken.

Returning to FIG. 22 again, when the result in step S816 is negative and the process proceeds to step S822, it is determined in step S822 whether the engine speed Ne is within another predetermined range. In this embodiment, when 4500 rpm <Ne ≦ 6000 rpm,
The process proceeds to steps S824 to S826, and as shown in the determination condition table of FIG. 26, the process of estimating the cylinder-by-cylinder air-fuel ratio # nA / F by the observer OBSV is executed in synchronization with each TDC, but according to the PID control law. The process of feedback calculation for each cylinder is stopped.

That is, the first control block CH1 shown in FIG. 20 separates the demultiplexer DMPX and the multiplexer MPX from all PID blocks and switches and connects them to the memory block REF side. Here, a predetermined value (for example, 1.
0) is stored, and by performing such a switching connection, all cylinder-by-cylinder air-fuel ratio correction coefficients #nKLAF are fixed to their predetermined values, and substantial cylinder-by-cylinder feedback control is performed even if the calculation process of step S900 is performed. To stop. Alternatively, instead of applying such a predetermined value, the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF most recently obtained is held in the memory block REF, and feedback is performed by the held cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF. You may make it control. In any case, since the calculation process based on the PID control law can be omitted, it is possible to cope with the shortening of the TDC cycle accompanying the increase of the engine speed Ne. However, the second control block CH2 is an observer O
Continue the BSV estimation process.

First, in step S824, step S
Similar to 804 to S812, the cylinder-by-cylinder air-fuel ratio # nA / F is estimated. Next, in step S826, all of the cylinder-by-cylinder air-fuel ratio correction coefficients #nKLAF are fixed to the above predetermined values, or the cylinder-by-cylinder air-fuel ratio correction coefficients #nKLAF obtained most recently (before the processing is started). Hold on.

Then, in step S900, the feedback control for the output fuel injection amount #jTout is substantially stopped.

On the other hand, when the result in step S822 is NO, it means that the internal combustion engine 10 is rotating at an extremely high speed, and the flow proceeds to steps S828 to S830 to estimate the cylinder-by-cylinder air-fuel ratio # nA / F like the observer OBSV. Both the processing and the calculation processing of the cylinder-by-cylinder air-fuel ratio correction coefficient #nKLAF based on the PID control law are stopped. That is, the first in FIG.
Control block CH1 shuts off all feedback paths to the demultiplexer DMPX and the multiplexer MPX, and the second control block CH2
Causes the observer OBSV to stop the estimation process. Therefore, when the engine speed Ne decreases again, the recurrence-form observer OBSV restarts the estimation process from the initial state.

As described above, according to this embodiment, when the TDC cycle becomes shorter as the engine speed Ne increases, the cylinder-by-cylinder feedback control is thinned out or stopped according to the engine speed Ne. Since the spare time is secured by doing so, the processing of the engine control unit 36 can be distributed to the spare time, and as a result, the processing of the engine control unit 36 is substantially shortened and the engine speed N
Cylinder feedback control that copes with an increase in e can be performed. Furthermore, in the thinning process, the PID
Cylinder-specific air-fuel ratio correction coefficient #nKLAF based on the control law is thinned out, while observer OBSV cylinder-specific air-fuel ratio #
Since the nA / F estimation process is continued, the accuracy of the cylinder-by-cylinder air-fuel ratio # nA / F can be maintained without interrupting the estimation process of the recurrence-type observer OBSV, and the stability of the control can be improved. Can be secured.

[0154]

In the fuel injection amount control system for an internal combustion engine according to the first aspect of the present invention, so-called decimation processing is performed, and other processing can be dispersed and performed in the time vacated by the decimation, so that the engine can be operated. Cylinder feedback control that copes with an increase in the number of revolutions can be performed. Further, in the thinning-out process, the calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient is thinned out, whereas the estimation process of the air-fuel ratio estimating means is continued, so that the estimation process is not interrupted and the cylinder-by-cylinder air-conditioning is performed. It is possible to prevent the response delay of the air-fuel ratio control due to the delay of the calculation of the cylinder-by-cylinder air-fuel ratio estimated value at the time of restarting the cylinder-by-cylinder feedback control using the fuel ratio estimated value.

In the fuel injection amount control device for the internal combustion engine according to the second aspect, the cylinder-by-cylinder air-fuel ratio correction coefficient by the air-fuel ratio correction coefficient calculating means is fixed to a predetermined value or is set to the most recently obtained air-fuel ratio correction coefficient. The cylinder-by-cylinder fuel injection amount to be held and supplied to each cylinder is corrected to correct the cylinder-to-cylinder fuel injection amount to be supplied to each cylinder. Therefore, the cylinder-by-cylinder air-fuel ratio correction coefficient calculation processing by the air-fuel ratio correction coefficient calculation means is performed. It is not necessary to do so, and the processing time can be shortened. Therefore, other processes can be dispersed and performed in the idle time due to the shortening, and the feedback control for each cylinder that copes with the increase in the engine speed can be performed. Further, while the calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient is stopped, the estimation process of the air-fuel ratio estimating means is continued, and therefore the cylinder-by-cylinder air-fuel ratio estimated value is used without interruption of the estimation process. It is possible to prevent the response delay of the air-fuel ratio control due to the delay in the calculation of the estimated air-fuel ratio value for each cylinder when the feedback control for each cylinder is restarted.

In the fuel injection amount control device for the internal combustion engine according to the third aspect of the present invention, the calculation processing of the cylinder-by-cylinder air-fuel ratio correction coefficient by the air-fuel ratio correction coefficient calculation means is stopped. Processing can be performed in a distributed manner,
It is possible to cope with an increase in engine speed. Further, in the stop processing, the calculation of the cylinder-by-cylinder air-fuel ratio correction coefficient is stopped, whereas the estimation processing of the air-fuel ratio estimating means is continued, so that the estimation processing is not interrupted and the cylinder-by-cylinder It is possible to prevent the response delay of the air-fuel ratio control due to the delay in the calculation of the cylinder-specific air-fuel ratio estimated value at the time of restarting the cylinder-specific feedback control using the air-fuel ratio estimated value.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an overall configuration of a fuel injection device for an internal combustion engine according to an embodiment.

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

FIG. 3 is an explanatory diagram showing the output characteristics of the air-fuel ratio sensor in FIG.

FIG. 4 is a block diagram showing a function of a fuel injection device for an internal combustion engine according to an embodiment.

FIG. 5 is a flow chart for explaining the operation of the fuel injection device.

FIG. 6 is a flowchart for explaining the operation of the feedforward system.

FIG. 7 is a block diagram for explaining a function of a feedforward system.

FIG. 8 is a flowchart for explaining the operation of the first feedback system.

FIG. 9 is a block diagram for explaining a function of a second feedback system.

FIG. 10 is an explanatory diagram showing a relationship between TDC of a multi-cylinder internal combustion engine and an air-fuel ratio of an exhaust system collecting section.

FIG. 11 is an explanatory diagram showing quality of sampling timing with respect to an actual air-fuel ratio.

FIG. 12 is a block diagram showing a model of a LAF sensor.

FIG. 13 is a block diagram further showing a model of the LAF sensor.

FIG. 14 is a block diagram showing a Z conversion display model of a LAF sensor.

FIG. 15 is a block diagram showing an air-fuel ratio estimator.

FIG. 16 is a block diagram showing a general observer.

FIG. 17 is a block diagram showing a configuration of an observer according to the example.

FIG. 18 is a block diagram showing a configuration in which an air-fuel ratio estimator and an observer are combined.

FIG. 19 is a block diagram showing a function of a third feedback system.

FIG. 20 is a block diagram further showing the function of the third feedback system.

FIG. 21 is a flowchart showing the sampling operation of the detected air-fuel ratio in the sampling operation block (sel-V).

FIG. 22 is a flowchart illustrating the operation of a third feedback system (cylinder feedback system).

23 is an explanatory diagram showing characteristics of a timing map used in the flowchart of FIG. 21. FIG.

24 is an explanatory diagram further showing the characteristics of the timing map used in the flowchart of FIG.

FIG. 25 is a timing chart for explaining the sampling operation of the sampling operation block (sel-V).

FIG. 26 is an explanatory diagram showing conditions under which the operation of the third feedback system is switched according to the engine speed.

FIG. 27 is a process chart for explaining a normal operation of the third feedback system.

FIG. 28 is a process chart for explaining the operation of the thinning-out process of the third feedback system.

FIG. 29 is a process chart for explaining another operation of the thinning-out process of the third feedback system.

FIG. 30 is an explanatory diagram for explaining a problem of the conventional technique.

[Explanation of symbols]

10 ... Internal combustion engine, 12 ... Intake pipe, 14 ... Air cleaner,
16 ... Throttle valve, 18 ... Surge tank, 20 ... Intake manifold, 22 ... Injector, 24 ... Exhaust manifold, 26 ... Exhaust pipe, 28, 30 ... Catalytic device, 32 ...
Solenoid valve, 34 ... Bypass passage, 36 ... Engine control unit, 38 ... Fuel tank, 40 ... Crank angle detection sensor,
42 ... Throttle opening detection sensor, 44 ... Absolute pressure sensor, 46 ... Intake temperature sensor, 48 ... Atmospheric pressure sensor, 50
... water temperature sensor, 52 ... timing detecting sensor, 54 ... air-fuel ratio sensor (LAF sensor), 56 ... O ₂ sensor,
58, 60 ... Low-pass filter, 62 ... Microprocessor, 64 ... CPU core, 66 ... Detection circuit, 68 ... Multiplexer, 70 ... Detection circuit, 72 ... A / D converter, 7
4 ... RAM, 76 ... ROM, 78 ... Waveform shaping circuit, 80
... counter, 82-88 ... drive circuit, 100 ... EGR mechanism, 102 ... solenoid valve, 200 ... canister purge mechanism,
202 ... Solenoid valve, 300 ... Valve timing mechanism, RE
F ... Memory block, CH1 ... First control block, C
H2 ... 2nd control block, DMPX ... Demultiplexer, MPX ... Multiplexer.

Claims (3)

[Claims] 1. An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture exhausted from each cylinder of the multi-cylinder internal combustion engine, the air-fuel ratio detecting means being arranged in an exhaust system collecting portion of the multi-cylinder internal combustion engine. Based on a model that defines the behavior of the air-fuel ratio in the exhaust system, by setting an observer for observing the internal state of the exhaust system while inputting the air-fuel ratio, an air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder, and , A cylinder-by-cylinder air-fuel ratio correction for correcting the cylinder-by-cylinder fuel injection amount to be supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder In a fuel injection amount control device for an internal combustion engine equipped with an air-fuel ratio correction coefficient calculating means for calculating a coefficient, when the engine speed exceeds a predetermined value, the air-fuel ratio estimating means estimates the air-fuel ratio of each cylinder. Continue processing A fuel injection amount control device for an internal combustion engine, further comprising control means for sequentially shifting and stopping the calculation processing of the cylinder-by-cylinder air-fuel ratio correction coefficient by the air-fuel ratio correction coefficient calculation means. . 2. An air-fuel ratio detecting means arranged in an exhaust system collecting portion of the multi-cylinder internal combustion engine for detecting an air-fuel ratio of an air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine; Based on a model that defines the behavior of the air-fuel ratio in the exhaust system, by setting an observer for observing the internal state of the exhaust system while inputting the air-fuel ratio, an air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder, and , A cylinder-by-cylinder air-fuel ratio correction for correcting the cylinder-by-cylinder fuel injection amount to be supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder In a fuel injection amount control device for an internal combustion engine equipped with an air-fuel ratio correction coefficient calculating means for calculating a coefficient, when the engine speed exceeds a predetermined value, the air-fuel ratio estimating means estimates the air-fuel ratio of each cylinder. Continue processing While continuing, the cylinder-by-cylinder air-fuel ratio correction coefficient by the air-fuel ratio correction coefficient calculation means is fixed to a predetermined value, or the cylinder-by-cylinder fuel injection amount to be supplied to each of the cylinders is held at the most recently obtained air-fuel ratio correction coefficient. A fuel injection amount control device for an internal combustion engine, comprising a control means for making correction. 3. An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture discharged from each cylinder of the multi-cylinder internal combustion engine, the air-fuel ratio detecting means being arranged in an exhaust system collecting portion of the multi-cylinder internal combustion engine. Based on a model that defines the behavior of the air-fuel ratio in the exhaust system, by setting an observer for observing the internal state of the exhaust system while inputting the air-fuel ratio, an air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder, and , A cylinder-by-cylinder air-fuel ratio correction for correcting the cylinder-by-cylinder fuel injection amount to be supplied to each cylinder of the multi-cylinder internal combustion engine so as to reduce the variation in the air-fuel ratio of each cylinder based on the estimated air-fuel ratio of each cylinder In a fuel injection amount control device for an internal combustion engine equipped with an air-fuel ratio correction coefficient calculating means for calculating a coefficient, when the engine speed exceeds a predetermined value, the air-fuel ratio estimating means estimates the air-fuel ratio of each cylinder. Continue processing A fuel injection amount control device for an internal combustion engine, comprising: a control means for stopping the calculation processing of the cylinder-by-cylinder air-fuel ratio correction coefficient while continuing the operation.