JPH08232724A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To perform dynamic compensation for a delay of fuel transport and to conduct coincidence of an air-fuel ratio to a value demanded by a catalyst by a method wherein a fuel transport delay correction fuel injection amount is calculated based on a transport delay of injection fuel and from a detecting air-fuel ratio of exhaust gas situated downstream from a catalyst device, a target air-fuel ratio is corrected. CONSTITUTION: A wide area air-fuel ratio sensor 54 is arranged upper spream from a catalyst device 28 and an O2 sensor 56 situated downstream therefrom. Output signals therefrom are inputted to a control unit 34 togetherwith sensor signals from a crank angle sensor 40 and a throttle opening sensor 42. An air-fuel ratio correction factor by means of which a fuel injection amount is corrected is calculated so that an air-fuel ratio is converged to a target air-fuel ratio from a detecting air-fuel ratio by the wide area air-fuel ratio sensor 54, and a fuel injection amount is corrected. Further, based on a transport delay of injecting fuel, a fuel transport delay correction fuel injection amount is calculated, and based on the value, a fuel injection amount is decided. Further, a target air-fuel ratio is corrected from a detecting air-fuel ratio detected by the O2 sensor 56.

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 specifically, it dynamically compensates a fuel transportation delay with respect to a corrected fuel injection amount corrected by a feedback correction, and a catalyst window. The air-fuel ratio is controlled minutely to further improve the purification rate of the catalyst.

[0002]

2. Description of the Related Art In a fuel injection control system for an internal combustion engine, a catalytic converter provided in an exhaust system has a maximum purification rate at a theoretical air-fuel ratio. Therefore, an oxygen concentration sensor is provided in the exhaust system so that the air-fuel ratio becomes theoretical. It is known to feedback control the fuel injection amount so that the fuel ratio is obtained.

Further, recently, as in the technique described in Japanese Patent Laid-Open No. 3-185,244, a first oxygen concentration sensor (wide-range air-fuel ratio sensor) is arranged upstream of the catalyst and a second oxygen concentration sensor is arranged downstream thereof. An oxygen concentration sensor (O ₂ sensor) is arranged, a target air-fuel ratio is set so as to obtain an optimum purification rate in the catalyst window according to the output of the second sensor, and the target air-fuel ratio and the first air-fuel ratio are set.
There is also proposed a technique of controlling the fuel injection amount according to the sensor output of. In this conventional technique, the controlled object is modeled, and an optimum regulator is designed to control the fuel injection amount.

[0004]

However, in the above-mentioned conventional technique, the behavior of the air-fuel ratio is dynamically compensated by feedback control with respect to the controlled object, but since the adhesion correction is not performed. , The desired control accuracy of the air-fuel ratio before the catalyst cannot be obtained because the action of accurately injecting the corrected fuel injection amount into the cylinder is insufficient, and the air-fuel ratio required by the catalyst changes. However, there was an inconvenience that could not be dealt with. This is because the fuel adhesion correction is not performed in the above-mentioned related art.

Therefore, the object of the present invention is to solve the above-mentioned drawbacks of the prior art, to dynamically compensate for the fuel transportation delay, and to correct the target value of the air-fuel ratio feedback according to the behavior of the air-fuel ratio downstream of the catalyst. Accordingly, it is an object of the present invention to provide a fuel injection control device for an internal combustion engine, which controls fuel injection to match the air-fuel ratio required by the catalyst with high accuracy.

[0006]

In order to achieve the above object, in the present invention, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine, which is provided in the exhaust system of the internal combustion engine, is detected. Air-fuel ratio detection means and an air-fuel ratio correction coefficient for correcting the fuel injection amount supplied to the internal combustion engine so that the air-fuel ratio of the internal combustion engine converges to the target air-fuel ratio from the detected air-fuel ratio detected by the air-fuel ratio detection means. An air-fuel ratio correction coefficient calculation means, a fuel injection amount correction means for correcting the fuel injection amount supplied to the internal combustion engine by the air-fuel ratio correction coefficient, and the fuel injection amount corrected. Fuel transportation delay correction fuel injection amount calculation means for calculating a fuel transportation delay correction fuel injection amount based on the fuel transportation delay, and supply to the internal combustion engine based on the calculated fuel transportation delay correction fuel injection amount. A fuel injection amount determining means for determining a fuel injection amount, and a catalyst device provided downstream of the air-fuel ratio detecting means in the exhaust system of the internal combustion engine; and a catalyst device of the catalyst device in the exhaust system of the internal combustion engine. Second air-fuel ratio detection means, which is provided downstream and detects the air-fuel ratio of the exhaust gas discharged from the internal combustion engine, and the target air-fuel ratio is corrected from the detected air-fuel ratio detected by the second air-fuel ratio detection means. And a target air-fuel ratio correction means for performing the above.

According to a second aspect of the present invention, the catalyst device has a multi-stage catalyst bed, and the second air-fuel ratio detecting means is arranged between the multi-stage catalyst beds.

According to another aspect of the present invention, the fuel injection amount correcting means includes means for correcting the intake air amount based on the effective opening area of the throttle valve provided in the intake pipe.

[0009]

According to the present invention, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is detected, and the internal combustion engine is controlled so that the detected air-fuel ratio converges the air-fuel ratio of the internal combustion engine to the target air-fuel ratio. An air-fuel ratio correction coefficient for correcting the supplied fuel injection amount is calculated, the fuel injection amount supplied to the internal combustion engine is corrected by the air-fuel ratio correction coefficient, and the injected fuel is injected with respect to the corrected fuel injection amount. Of the fuel transport delay correction fuel injection amount based on the transport delay of the internal combustion engine, and the fuel injection amount to be supplied to the internal combustion engine based on the calculated fuel transport delay correction fuel injection amount. Second air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas discharged from the internal combustion engine, and correcting the target air-fuel ratio from the detected air-fuel ratio detected by the second air-fuel ratio detection means. Like As a result, the fuel transportation delay is dynamically compensated, and the target value of the air-fuel ratio feedback is corrected according to the behavior of the air-fuel ratio downstream of the catalyst, so that the air-fuel ratio required by the catalyst can be matched with high accuracy. be able to.

According to the present invention, the catalyst device has a multi-stage catalyst bed, and the second air-fuel ratio detecting means is arranged between the multi-stage catalyst beds. When a large-capacity catalyst device having a multi-stage catalyst bed is used, the second air-fuel ratio detecting means is installed at a position where the detection accuracy of the second air-fuel ratio detecting means is optimum, so that the target can be achieved with higher accuracy. The air-fuel ratio can be corrected, the air-fuel ratio before the catalyst device can be controlled more accurately, and the purification rate of the catalyst device can be further improved.

According to the third aspect of the invention, the fuel injection amount correcting means includes means for correcting the intake air amount based on the effective opening area of the throttle valve provided in the intake pipe. The calculation accuracy of the basic fuel injection amount corrected by the feedback correction coefficient can be further improved, the load on the feedback system is reduced, and the stability is improved without impairing the responsiveness.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fuel injection control device for an internal combustion engine according to this application will be described below with reference to the accompanying drawings.

FIG. 1 is an overall view schematically showing the apparatus.

In the figure, reference numeral 10 indicates an OHC in-line 4-cylinder internal combustion engine, and intake air introduced from an air cleaner 14 arranged at the tip of an intake pipe 12 is surged while its flow rate is adjusted by a throttle valve 16. After passing through the tank 18 and the intake manifold 20, they are introduced into the first to fourth cylinders via two intake valves (not shown). An injector 22 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 an exhaust manifold 24 via two exhaust valves (not shown), and passes through an exhaust pipe 26 to a first catalyst device (three-way catalyst) 28 and a second catalyst device. It is purified by the catalyst device (three-way catalyst) 30 and discharged to the outside of the engine. In the above, the throttle valve 16 is mechanically disconnected from the accelerator pedal (not shown), and is controlled through the pulse motor M to an opening degree according to the depression amount of the accelerator pedal and the operating state. Further, the intake pipe 12 is provided with a bypass passage 32 that bypasses the throttle valve 16 in the vicinity thereof.

The internal combustion engine 10 is provided with an exhaust gas recirculation mechanism 100 that recirculates exhaust gas to the intake side.

Referring to FIG. 2, the exhaust gas recirculation path 121 of the exhaust gas recirculation mechanism 100 has one end 121a at the exhaust pipe 2.
6, the other end 121b communicates with the upstream side of the first catalyst device 28 (not shown in FIG. 2) and the downstream side of the throttle valve 16 (not shown in FIG. 2) of the intake pipe 12. This exhaust gas recirculation path 1
An exhaust gas recirculation valve (recirculation gas control valve) 122 for adjusting the exhaust gas recirculation amount and a volume chamber 121c are provided in the middle of 21. The exhaust gas recirculation valve 122 is a solenoid valve having a solenoid 122a, and the solenoid 122a is connected to a control unit (ECU) 34 described later, and the control unit 34
The valve opening is linearly changed by the output from the.
The exhaust gas recirculation valve 122 is provided with a lift sensor 123 that detects the valve opening degree, and the output thereof is sent to the control unit 34.

Further, the intake system of the internal combustion engine 10 and the fuel tank 36 are also connected to each other, and the canister purge mechanism 200 is provided.
Is provided.

As shown in FIG. 3, the canister / purge mechanism 200 includes a closed upper portion of the fuel tank 36 and the intake pipe 12.
The canister 2 having a steam supply passage 221 and an adsorbent 231 built in between the throttle valve 16 and the downstream side of the throttle valve 16.
23 and a purge passage 224. Steam supply passage 2
A two-way valve 222 is installed in the middle of 21, a purge control valve 225 is installed in the middle of the purge passage 224, a flow meter 226 for detecting the flow rate of a mixture containing fuel vapor flowing in the purge passage 224, and the inside of the mixture. An HC concentration sensor 227 for detecting the HC concentration of The purge control valve (solenoid valve) 225 is connected to the control unit 34 as described later, and is controlled in accordance with a signal from the control unit 34 to linearly change the valve opening amount.

According to this canister purge mechanism, the fuel vapor (fuel vapor) generated in the fuel tank 36 is
When the predetermined set amount is reached, the positive pressure valve of the 2-way valve 222 is pushed open and flows into the canister 223, and the adsorbent 2
It is adsorbed and stored by 31. When the purge control valve 225 is opened by the valve opening amount according to the duty ratio of the on / off control signal from the control unit 34, the canister 22 is opened.
Due to the negative pressure in the suction pipe 12, the vaporized fuel temporarily stored in No. 3 is sucked into the intake pipe 12 through the purge control valve 225 together with the outside air sucked from the outside air intake port 232, and is sent to each cylinder. Further, when the fuel tank 36 is cooled by the outside air and the negative pressure in the fuel tank increases, the two-way valve 22
The negative pressure valve 2 is opened, and the evaporated fuel temporarily stored in the canister 223 is returned to the fuel tank 36.

Further, the internal combustion engine 10 is provided with a so-called variable valve timing mechanism 300 (shown as V / T in FIG. 1). The variable valve timing mechanism 300 is described in, for example, Japanese Patent Application Laid-Open No. 2-275043, and there are two types of valve timing V / T of the engine shown in FIG. 4 according to operating conditions such as the engine speed Ne and the intake pressure Pb. The timing characteristic of is switched between LoV / T and HiV / T. However, since it is a known mechanism per se, description thereof will be omitted. It should be noted that the switching of the valve timing characteristics includes the operation of suspending one of the two intake valves.

As shown in FIG. 1, a crank angle 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 an opening degree of the throttle valve 16 is provided. There is also provided a throttle opening sensor 42 for detecting the above, and an absolute pressure sensor 44 for detecting the intake pressure Pb downstream of the throttle valve 16 by the absolute pressure. At the appropriate position of the internal combustion engine 10, the atmospheric pressure Pa
An atmospheric pressure sensor 46 for detecting the temperature is provided, an intake air temperature sensor 48 for detecting the temperature of intake air is provided upstream of the throttle valve 16, and a water temperature sensor 50 for detecting the engine cooling water temperature is provided at an appropriate position of the engine. Is provided. Also,
A valve timing (V / T) for detecting the selected valve timing characteristic of the variable valve timing mechanism 300 via hydraulic pressure.
) A sensor 52 (not shown in FIG. 1) is also provided.

Further, in the exhaust system, the exhaust manifold 2
4, a wide-range air-fuel ratio sensor 54 is provided as a first air-fuel ratio detecting means at the exhaust system collecting portion on the upstream side of the first catalyst device 28, and the second air-fuel ratio is provided downstream thereof. An O ₂ sensor 56 is provided as a detection means. here,
The capacity of the first catalytic device 28 is about 1 liter, and the capacity of the second catalytic device 30 is about 1.7 liter. The capacities of the catalyst devices 28 and 30 are set to the optimum capacities in consideration of the purification performance and the temperature rising characteristics of the catalyst devices.

Here, as shown in FIG. 5, the first catalyst device 28 has a multi-stage, in the illustrated example, two-stage catalyst bed (CAT).
Floor) (carrier), and the O ₂ sensor 56 has first and second
It may be arranged between the CAT floors. In that case, the capacity of the first CAT floor is about 1 liter, the capacity of the second CAT
The capacity of the AT floor will be about 1 liter. As a result,
The first of the entire catalyst unit 28 has a capacity of about 2 liters of O ₂ sensor that is provided at the position of the, the O ₂ sensor is substantially downstream of the catalytic converter of approximately 1 liter shown in Is provided, and the time for which the output is inverted becomes shorter than that provided in the downstream of the catalyst device having a capacity of 2 liters. Therefore, the O ₂ sensor 5
Based on the output of No. ₆ , the control accuracy at the time of performing minute control of the air-fuel ratio in the catalyst window (this is referred to as "MIDO ₂ control" in this specification) is improved as described later.

A filter 58 is connected to the next stage of the wide area air-fuel ratio sensor 54. The second filter 60 is also connected to the next stage of the O ₂ sensor 56. These sensor output and filter output are sent to the control unit 34.

FIG. 6 is a block diagram showing the details of the control unit 34. The output of the wide-range air-fuel ratio sensor 54 is input to the first detection circuit 62, where appropriate linearization processing is performed and detection having a linear characteristic proportional to the oxygen concentration in the exhaust gas in a wide range from lean to rich is performed. Outputs a signal (hereinafter, this wide-range air-fuel ratio sensor is called "LAF
"Sensor"). The output of the O ₂ sensor 56 is the second
As shown in FIG. 7, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 10 is the theoretical air-fuel ratio (λ =
The detection signal indicating rich or lean is output with respect to 1).

The output of the first detection circuit 62 is input into the CPU via the multiplexer 66 and the A / D conversion circuit 68. CPU is a CPU core 70, ROM 72, R
More specifically, the output of the first detection circuit 62 includes an AM 74, and more specifically, the output of the first detection circuit 62 is A /
It is D-converted and sequentially stored in one of the buffers in the RAM 74. As shown in FIG. 47, the No. 0 to No. 11 buffers are stored in the 12 buffers. Is attached. Further, the output of the second detection circuit 64 and the output of the analog sensor such as the throttle opening sensor 42 are also taken into the CPU via the multiplexer 66 and the A / D conversion circuit 68 and stored in the RAM 74.

The output of the crank angle sensor 40 is waveform-shaped by the waveform shaping circuit 76, the output value is counted by the counter 78, and the count value is input into the CPU.
In the CPU, the CPU core 70 calculates a control value as described later according to the instruction stored in the ROM 72, and drives the injector 22 of each cylinder via the drive circuit 82. Further, the CPU core 70 controls the electromagnetic valve 90 (the bypass passage 32 for adjusting the amount of secondary air) via the drive circuits 84, 86, 88.
Opening / closing), and the exhaust recirculation control solenoid valve 122 described above.
Also, the canister purge control solenoid valve 225 is driven. The lift sensor 123, the flow meter 226, and the HC concentration sensor 227 are not shown in FIG.

FIG. 8 is a functional block diagram for explaining the operation of the fuel injection control device according to the embodiment.

As shown in the figure, in the fuel injection control device according to the embodiment, an observer (shown as OBSV in the figure) for estimating the air-fuel ratio of each cylinder from the output of the single LAF sensor 54 is provided, and the LAF sensor is also provided. The adaptive controller (Self Tuning Regu
lator type adaptive controller. (Indicated as STR in the figure).

The output VO ₂ M of the O ₂ sensor 56 is passed through a filter 60 to a target air-fuel ratio correction block (KCM in the figure).
Is input to indicate a D correction), O ₂ target value of the sensor (Vre
The target air-fuel ratio correction coefficient KCMDM is calculated according to the difference with fM). On the other hand, as will be described later, the basic fuel injection amount TiM-F is calculated based on the change in the effective opening area of the throttle valve, and the target air-fuel ratio correction coefficient KCMDM is various corrections including the EGR or canister purge correction coefficient described later. Coefficient KTOTAL
At the same time, the required fuel injection amount Tcyl is obtained by multiplying the basic fuel injection amount TiM-F (the multiplication symbol used in place of the addition point in the figure indicates this) to correct it.

The corrected target air-fuel ratio KCMD is input to the adaptive controller STR and the PID controller (shown as PID in the figure), and the feedback correction coefficient KSTR or KLAF according to the difference with the LAF sensor output as described later. Is required,
Either one is multiplied by the required fuel injection amount Tcyl according to the operating state via a changeover switch (shown as changeover SW in the figure),
The output fuel injection amount Tout is determined. Output fuel injection amount T
The out is subjected to adhesion correction as described below and is supplied to the internal combustion engine 10.

That is, the air-fuel ratio is controlled to the target air-fuel ratio on the basis of the output of the LAF sensor 54, and at the vicinity of the target value, that is, in the vicinity of the so-called catalyst window, the MI is set as described above.
That is, DO ₂ control is performed. When this is further described, it is the O ₂ storage effect of the storage of O ₂ slightly lean during the exhaust gas passage as the action of the catalyst device, for O ₂ in the catalytic converter is lowered purification rate when saturated, at that time It is necessary to supply a slightly rich exhaust gas to release O ₂ . When the release of O ₂ is completed, a slightly lean exhaust gas is sent again, and this operation is repeated, whereby the purification rate of the catalyst device can be maximized.
MIDO ₂ control intends this.

In order to further improve the purification rate in the MIDO ₂ control, it is necessary to match the air-fuel ratio before the catalyst device to the target air-fuel ratio in the shortest possible time after the output of the O ₂ sensor 56 after the catalyst device is reversed. , It is necessary that the detected air-fuel ratio KACT becomes the target air-fuel ratio KCMD, but the target air-fuel ratio correction coefficient is added to the fuel injection amount calculated by the feedforward system.
The target air-fuel ratio KCMD becomes the blunted detected air-fuel ratio KACT because there is a response delay of the engine only by multiplying KCMDM.

In order to improve it, the response of the detected air-fuel ratio KACT is dynamically compensated from the target air-fuel ratio KCMD, specifically, the correction coefficient KSTR (the output of the adaptive controller STR output) which dynamically compensates the target air-fuel ratio KCMD. ). By doing so, the detected air-fuel ratio KACT quickly converges to the target air-fuel ratio KCMD, and the catalyst purification rate can be improved. In this specification, the target value KCMD and the actual value (detection value) KACT of the air-fuel ratio are both actually represented by the equivalence ratio, that is, Mst / M = 1 / λ (M
st: theoretical air-fuel ratio, M = A / F (A: air consumption, F: fuel consumption), λ: excess air ratio).

Here, the description of the filter will be supplemented.

In the case of the apparatus shown in the figure, a multiple feedback configuration is provided in which a plurality of control methods are provided in parallel using a single sensor output. More specifically, since the configuration is such that multiple feedback and a plurality of control methods are switched, the cutoff frequency characteristic of the filter is set according to the control method.

Specifically, the output of the LAF sensor 54 is
It takes about 400 ms for 100% response. However, if it is left as it is, there is a lot of noise of high frequency components, and the controllability deteriorates. So, if you pass a 500Hz low-pass filter, you can remove harmful high frequency component noise,
It was found that the deterioration of the response characteristics was hardly seen.
Therefore, when the filter frequency was lowered to 4 Hz, the high frequency noise was further reduced. The time required for 100% response was also stable. However, the response characteristic in that case is slightly slower than that in the case where no filter is passed or when a 500 Hz low-pass filter is passed.
It took about 400 ms or more for 0% response.

From the above, in the case of the embodiment, the filter 5
8 is a low-pass filter with a cutoff frequency characteristic of 500 Hz, and the input to the observer is 500 Hz.
The output of the low pass filter 58 is used as it is. This is because the observer itself does not control so that the detected air-fuel ratio KACT converges to the target air-fuel ratio KCMD, and the air-fuel ratio of each cylinder is estimated from the air-fuel ratio estimated by the observer by the PID controller. Since it is configured to absorb, even if the response time of the sensor is not very stable, it does not significantly affect the estimation result, rather the faster response time improves the controllability. is there.

On the other hand, the filter 92 (only shown in FIG. 8) connected before the input of the adaptive controller STR is a low-pass filter having a cutoff frequency characteristic of 4 Hz. That is, since a device such as STR that performs dead beat control operates so as to faithfully compensate for the delay with respect to the detected air-fuel ratio, if the noise or response time of the detected air-fuel ratio changes, the control performance itself Affect. Therefore, the filter 92 is 4H
The low-pass filter has a cutoff frequency characteristic of z.
The filter 93 connected before the input of the PID controller attaches importance to response time, and the filter 9 has a cutoff frequency characteristic.
2 or more, or 200 Hz in the case of the embodiment
And In addition, the filter 6 connected to the O ₂ sensor 56
In the case of 0, the response time of the O ₂ sensor is originally much higher than that of the LAF sensor due to the characteristics of the O ₂ sensor.
A low-pass filter having a cutoff frequency characteristic of about 0 Hz is used.

The operation of the apparatus according to the application will be described below with reference to the block diagram of FIG.

First, the basic fuel injection amount TiM-F is calculated.

As described above, this makes it possible to optimally determine the basic (required) fuel injection amount based on the change in the effective opening area of the throttle valve over all operating conditions including the transient operating condition.

FIG. 9 is a flow chart showing the work of calculating the basic fuel injection amount TiM-F, and FIG. 10 is a block diagram for explaining the calculation of the flow chart of FIG. 9, which will be described with reference to FIG. Before doing so, a method of approximating the model by using the idea of the fluid dynamics model, which is the premise of this method, will be described. The details are described in Japanese Patent Application No. 6-197,238 previously proposed by the present applicant, and will be briefly described below.

That is, as shown in FIG. 11, the throttle projected area S (throttle projected area in the longitudinal direction of the intake pipe) S is obtained from the throttle opening θTH according to a preset characteristic. On the other hand, as shown in FIG. 12, the throttle opening θTH
And a coefficient C (product of a flow coefficient α and a gas expansion correction coefficient ε) according to another preset characteristic of the intake pressure Pb, and they are multiplied to obtain an effective opening area A of the throttle. Since the throttle is not the throttle in the so-called throttle fully open region, the throttle fully open region is obtained as a critical value for each engine speed, and when the detected throttle opening exceeds it, the critical value is set as the throttle opening. To do. Further, regarding this, the atmospheric pressure is corrected, but the description thereof will be omitted.

Next, the amount of air in the chamber Gb is obtained from the equation shown in equation 1 based on the equation of state of gas, and the amount of air ΔGb filled in the chamber this time is obtained from the change in chamber pressure ΔP according to the equation of equation 2. Assuming that the air amount filled in the chamber this time is not sucked into the cylinder combustion chamber, the cylinder intake air amount Gc per unit time ΔT is given by
It can be expressed as the formula shown in. The "chamber" here is not only the so-called surge tank equivalent part,
It means all parts from the throttle downstream to the intake port. Further, the “chamber” means an effective volume actually acting as a chamber. In this specification, k indicates sampling time.

[0047]

[Equation 1]

[0048]

[Equation 2]

[0049]

(Equation 3)

On the other hand, as shown in the characteristic of FIG. 13, the ROM 72 has the fuel injection amount Tim in the steady operation state.
ap is preset and mapped and stored so that it can be retrieved from the engine speed Ne and the intake pressure Pb based on the so-called speed density method. Further, the fuel injection amount Timap is corrected according to the target air-fuel ratio KCMD determined according to the engine speed Ne and the intake pressure Pb.
As shown in Fig. 4, the target air-fuel ratio KCMD, more specifically, the basic value KBS, is also determined by the engine speed Ne and the intake pressure Pb.
It is stored as a map in advance so that it can be searched freely. However, the correction of the fuel injection amount Timap by the target air-fuel ratio is MID
No correction is made here as it relates to O ₂ control. M
The correction based on the target air-fuel ratio including the IDO ₂ control will be described later. Note that the fuel injection amount Timap is directly set with the valve opening time of the injector 22 as a unit.

Here, focusing on the relationship between the fuel injection amount Timap obtained by retrieving the map and the above-mentioned throttle passing air amount Gth, under certain conditions (engine speed Ne1 and intake pressure Pb1) in the steady operation state. ), The fuel injection amount Timap1 determined by the map search is as shown in Formula 4.

[0052]

[Equation 4]

Here, the throttle passing air amount in the transient operating state can be expressed from the throttle passing air amount in the steady state according to the change in the effective opening area of the throttle.
Specifically, it can be expressed by using the ratio of the effective opening area of the throttle valve in the steady state and the effective opening area of the throttle valve in the transient state. This is described in detail in Japanese Patent Application No. 6-197,238 mentioned above.

That is, assuming that the effective opening area of the current throttle valve is A and the effective opening area of the throttle valve in the steady operation state is A1, the effective opening area A1 of the throttle valve in the steady operation state is the same as that of the current throttle valve. It was presumed that it could be grasped as the first-order lag of the effective opening area A, and when verified through simulation, it was confirmed as shown in FIG. That is, when the first-order lag of A is called "ADELAY", it can be seen that A1 and ADELAY have almost the same value. Therefore, if the model is approximated using the idea of the fluid dynamics model, A / “first-order delay” may be used. As shown in FIG. 16, in the transient operation state, at the moment when the throttle is opened, the differential pressure before and after the throttle is large, so the amount of air passing through the throttle flows at once, and then gradually falls to a steady state. We thought that Gth could be expressed by this ratio A / A DELAY. As shown in the lower part of FIG. 17, this ratio is consistently 1 in the steady operation state. Hereinafter, this ratio is referred to as "RATIO-A".

Further, focusing on the relationship between the effective opening area of the throttle and the throttle opening θTH, since the effective opening area greatly depends on the throttle opening, the effective opening area is the throttle opening as shown in FIG. It is supposed to change almost following the changes. If so, the above-mentioned first-order lag value of the throttle opening is theoretically one of the effective opening areas.
It should correspond to the next delay almost equivalently. Therefore, in FIG.
As shown in 0, the effective opening area (first-order lag value) ADELAY is calculated from the first-order lag value of the throttle opening (note that (1-B) / (z-B) in FIG. 10 is discrete. It means the first-order lag in the transfer function of the system).

That is, the throttle projection area S is obtained from the throttle opening θTH according to a preset characteristic, and
From the throttle opening first-order lag value θTH-D and the intake pressure Pb, the coefficient C is calculated according to the characteristic shown in FIG. 12, and then the product of the two is calculated to determine the effective opening area (first-order lag value) ADELAY.
Was calculated. Furthermore, the chamber filling air amount ΔG
In order to eliminate the delay in reflecting b to the intake air amount, the value ΔG
The first-order delay of b is also used.

Further, as a result of examination, it is not necessary to individually obtain the throttle passing air amount Gth and the chamber filling air amount ΔGb, and the chamber intake air amount ΔGb is calculated from the throttle passing air amount Gth to obtain the cylinder intake air amount. Gc
However, it could be calculated only from the throttle passing air amount Gth. This simplifies the configuration and reduces the amount of calculation. That is, in the equation 1, the cylinder intake air amount Gc per unit time ΔT can be expressed by the equation 5, which is equivalent to the equations 6 and 7. When Expression 6 and Expression 7 are expressed in transfer function form, Expression 8 is derived. That is, as shown in Equation 8, the intake air amount Gc can be obtained from the first-order lag value of the throttle passing air amount Gth. This is shown in a block diagram in FIG. Since the transfer function in FIG. 18 is different from that in FIG. 10, (1-B ′) / (z−B ′) is added to indicate that.

[0058]

(Equation 5)

[0059]

(Equation 6)

[0060]

(Equation 7)

[0061]

(Equation 8)

Therefore, the basic fuel injection amount TiM-F is expressed as follows: TiM-F = Map search fuel injection amount TiM × actual throttle effective opening area / intake pressure Pb and throttle effective opening obtained by the primary delay value θTH-D Area = Map search Fuel injection amount TiM × RATIO-A

Based on the above, the operation of this control device will be described with reference to the flow chart of FIG.

First, the engine speed N detected in S10
e, intake pressure Pb, throttle opening θTH, atmospheric pressure Pa, engine cooling water temperature Tw, etc. are read. The throttle opening θ
TH learns the throttle fully closed opening in idle operation,
The value detected based on that value is used.

Subsequently, the program proceeds to S12, where it is determined whether the engine is cranking (starting), and when the result is negative, the process proceeds to S14 where it is determined whether the fuel cut is performed. Engine speed Ne and intake pressure Pb
From this, a map showing the characteristics thereof is stored in the ROM 72 and the fuel injection amount TiM (fuel injection amount Timap in the steady operation state) is obtained by searching a map showing the characteristics. It should be noted that the calculated fuel injection amount TiM is then appropriately corrected by atmospheric pressure and the like, but since the correction itself is not the gist of the present invention, detailed description thereof will be omitted. Next, in S18, the detected primary delay value θTH-D of the throttle opening is calculated.

Then, the program proceeds to S22, in which the throttle opening θTH
And the intake pressure Pb, the current effective opening area A of the throttle
To calculate. Next, in S24, the first-order delay value ADELAY of the effective opening area of the throttle is calculated from the throttle opening first-order delay value θTH-D and the intake pressure Pb.

Next, in S26, RATIO-A is calculated from the equation RATIO-A = (A + ABYPASS) / (A + ABYPASS) DELAY. The value ABYPASS is the bypass 3
2 means the amount of air taken into the combustion chamber without passing through the throttle valve 16 (shown as “lift amount” in FIG. 10), and this amount of air is also taken into consideration in order to accurately determine the fuel injection amount. Since it is necessary to convert the corresponding value into a throttle opening ABYPASS according to a predetermined characteristic and add it to the effective opening area A, the sum (A +
ABYPASS) and its first approximation (“(A + ABYPASS) DELA
Y)), and call it RATIO-A.

As described above, as a result of adding to both the numerator and the denominator, even if there is an error in the measurement of the amount of air taken into the combustion chamber without passing through the throttle valve, the degree of influence on the determined fuel injection amount. Becomes smaller. Next, in S28, the fuel injection amount TiM is multiplied by RATIO-A to calculate the basic fuel injection amount TiM-F corresponding to the throttle passing air amount. Incidentally, S12
When it is determined that cranking is in progress, the process proceeds to S30, a predetermined table (not shown) is searched from the water temperature Tw to calculate the fuel injection amount Ticr at the time of cranking, and in S32, a formula for the start mode (not explained). The fuel injection amount TiM-F is determined on the basis of the fuel injection amount TiM-F, and if it is determined in S14 that the fuel is cut, the process proceeds to S34 to make the fuel injection amount TiM-F zero.

The above-described calculation method of the basic fuel injection amount TiM-F can express from the steady operation state to the transient operation state by a simple algorithm, and the fuel injection amount in the steady operation state is guaranteed to some extent by the map search. At the same time, it is possible to optimally determine the fuel injection amount without requiring complicated calculation. Moreover, there is no need to change the model formula between the steady operation state and the transient operation state.
Since all driving states can be expressed by one equation,
In general, the control discontinuity as seen near the switching point does not occur. Further, since the behavior of air can be well expressed, controllability and control accuracy can be improved.

Returning to the block diagram of FIG. 8, various correction coefficients KTOTAL including the EGR correction coefficient KEGR and the canister purge correction coefficient KPUG are calculated next.

First, the EGR correction coefficient will be described.

Since the exhaust gas recirculation amount becomes a disturbance when controlling the fuel injection amount of the internal combustion engine, it is necessary to accurately estimate the exhaust gas recirculation rate or the exhaust gas recirculation amount. Here, the “exhaust gas recirculation ratio” means the volume ratio or the weight ratio of exhaust gas / intake air.

FIG. 19 is a flow chart for explaining the operation of estimating the exhaust gas recirculation rate.

Before starting the description of FIG. 20, an algorithm for estimating the exhaust gas recirculation rate according to the embodiment will be described with reference to FIG.

The amount of gas passing through the exhaust gas recirculation valve is determined by the valve opening area and the pressure ratio before and after the valve, that is, the flow rate characteristics (design specifications), when viewed as a single valve. That is, it is considered that the valve opening area, that is, the ratio of the lift amount to the upstream / downstream pressure of the valve is obtained. Also in the actual machine, as shown in FIG. 20, the recirculation gas amount can be estimated to some extent by obtaining the ratio between the valve lift amount and the atmospheric pressure Pa and the intake pressure Pb of the intake pipe 12 (actually, to some extent. The flow rate characteristic changes slightly depending on the exhaust pressure and the exhaust temperature, but it is considered that the change in the characteristic can be absorbed to a considerable extent by using the gas amount ratio as described later).

Therefore, first, paying attention to this point, the reflux rate is determined based on the flow rate characteristic. The opening area is obtained from the lift amount because the valve having a structure in which the lift amount corresponds to the opening area is used. Therefore, when using another structure such as a linear solenoid, the opening area is obtained from another parameter.

By the way, the reflux rate includes a steady-state reflux rate and a transient reflux rate. Among them, the steady-state reflux rate is a value in a state where the lift command value is equal to the actual lift, The recirculation rate is a value in a state where the lift command value is not equal to the actual lift, as shown in FIG. Then, in the algorithm according to the present invention, the difference at the time of transition is, as shown in FIG. 20, only the gas flow rate corresponding to the reflux rate,
I thought that it was caused by deviation from the regular reflux rate.

Specifically, in the steady state, the lift command value = actual lift, the gas amount ratio = 1, that is, the recirculation rate = the recirculation rate in the steady state. In the transient state, the lift command value ≠ actual lift, the gas amount ratio ≠ 1 Reflux rate = steady-state reflux rate (map search value) x gas amount ratio.

Thus, it was considered that the net recirculation rate flowing into the combustion chamber can be obtained by multiplying the recirculation rate in the steady state by the ratio of both gas amounts. The formula is as follows. Net recirculation rate = (recirculation rate in steady state) x (gas amount QACT obtained from actual lift and pressure ratio before and after valve) / (gas amount QCMD obtained from lift command value and pressure ratio before and after valve)

Here, the return rate in the steady state is obtained by obtaining a return rate correction coefficient and subtracting it from 1. That is,
If the constant return rate correction coefficient is called KEGRMAP, the constant return rate = (1-KEGRMAP). In this specification, the steady-state recirculation rate or the steady-state recirculation rate correction coefficient is also referred to as a basic exhaust gas recirculation rate or a basic exhaust gas recirculation rate correction coefficient. Further, the steady-state recirculation rate correction coefficient KEGRMAP is experimentally obtained from the engine speed Ne and the intake pressure Pb in advance and set as a map as shown in FIG. 22, and is searched and obtained.

By the way, in the exhaust gas recirculation control, the lift command value of the exhaust gas recirculation valve is determined from the engine speed, the engine load, etc., but as shown in FIG. Value) has a delay. Furthermore, there is a delay in the flow of the reflux gas into the combustion chamber in response to the valve opening operation.

Therefore, the present applicant previously filed Japanese Patent Application No. 6-10.
In No. 0,557, the above equation, net recirculation rate = (recirculation rate in steady state) × (gas amount QACT obtained from actual lift and pressure ratio before and after valve) / (obtained from lift command value and pressure ratio before and after valve) The amount of gas QCMD) was used to find the net reflux rate, but the inflow delay of the reflux gas was based on the concept of first-order delay. Here, using the idea of dead time,
The recirculation gas that has passed through the exhaust gas recirculation valve can be regarded as flowing into the combustion chamber at once after a certain dead time has elapsed. Therefore, the above-mentioned net recirculation rate is calculated for each predetermined cycle and stored in the storage means, and the recirculation rate of the exhaust gas that has truly flown into the combustion chamber is calculated with the calculated value of the past cycle corresponding to the dead time. I tried to regard it.

The operation of the apparatus according to the embodiment will be described below with reference to FIG.
It will be described according to the 9 flow chart. It should be noted that this program is started at each TDC position.

First, in S200, the engine speed Ne, the intake pressure Pb, the atmospheric pressure Pa, the actual lift LACT (lift sensor 1
(Output of 23) is read, and the routine proceeds to S202, where the lift command value LCMD is retrieved from the engine speed Ne and the intake pressure Pb. Here, the lift command value LCMD is as shown in FIG.
The map is obtained by searching for a map whose characteristics are set in advance.

Next, in S204, the map shown in FIG. 22 is retrieved from the engine speed Ne and the intake pressure Pb to obtain the basic exhaust gas recirculation ratio correction coefficient KEGRMAP. Next, the routine proceeds to S206, where it is confirmed that the detected actual lift LACT is not zero, that is, after confirming that the exhaust gas recirculation valve 122 is open, the routine proceeds to S208, where the retrieved lift command value LC
MD is compared with a predetermined lower limit value LCMDLL (small value).

When it is determined in S208 that the search value is not less than the lower limit value, the routine proceeds to S210, where the intake pressure Pb is set.
A ratio (Pb / Pa) between the air pressure Pa and the atmospheric pressure Pa is obtained, and a gas amount QCMD is obtained by searching a map (not shown) of the characteristics shown in FIG. 20 from the obtained lift command value LCMD.
This is the “gas amount obtained from the lift command value and the pressure ratio before and after the valve” in the above formula.

Next, in S212, the detected actual lift is detected.
Similarly, a map (not shown) of the characteristics shown in FIG. 20 is searched from the ratio Pb / Pa similar to LACT to find the gas amount QA.
Ask for CT. This corresponds to the “gas amount obtained from the actual lift and the pressure ratio before and after the valve” in the above formula.

Then, the routine proceeds to S214 where the value obtained by subtracting the retrieved basic exhaust gas recirculation ratio correction coefficient KEGRMAP from 1 is defined as the steady exhaust gas recirculation ratio (basic exhaust gas recirculation ratio or steady recirculation ratio). Here, the steady-state recirculation rate is, as described above, the recirculation rate when the exhaust gas recirculation operation is stable, that is, the exhaust gas recirculation operation is not in a transient state such as when the exhaust gas recirculation operation is started or stopped. Means the reflux rate at that time.

Next, in S216, the steady return rate is multiplied by the ratio QACT / QCMD of the values QACT and QCMD to obtain the net return rate, as shown in the figure. Next, in S218, the fuel injection correction coefficient KEGRN for the exhaust gas recirculation rate is calculated. FIG. 24 is a subroutine flow chart showing the work.

Explaining in accordance with the figure, in S300, the net recirculation rate (obtained in S216 of FIG. 19) is subtracted from 1, and the value is used as the fuel injection correction coefficient KEGRN for the exhaust recirculation rate. Subsequently, the process proceeds to S302, and the fuel injection correction coefficient KEGRN for the calculated exhaust gas recirculation rate is stored (stored) in the ring buffer. FIG. 25 is an explanatory diagram showing the configuration of the ring buffer, and the RAM 7 of the control unit 34.
It is provided in 4. The ring buffer has n addresses as shown, and each address is numbered from 0 to n. Then, every time the flow chart of FIG. 19 (and FIG. 24) is started by TDC and the fuel injection correction coefficient KEGRN is calculated, the flow chart is sequentially stored (updated) from the upper side in the figure.

Subsequently, in S304, the dead time τ is searched by searching the map from the detected engine speed Ne and the engine load, for example, the intake pressure Pb. FIG. 26 is an explanatory diagram showing the characteristics. That is, the dead time described above represents a delay time until the recirculation gas that has passed through the exhaust gas recirculation valve flows into the combustion chamber, but it varies depending on the engine speed and the engine load, such as the intake pressure. Here, the dead time τ is more specifically indicated by the above-mentioned buffer number.

Next, in S306, the calculated value (fuel injection correction coefficient KEGRN for the exhaust gas recirculation rate) stored in the corresponding address is read out based on the retrieved dead time τ (more specifically, the buffer number). That is, as shown in FIG. 27, when the current time point is A, for example, the calculated value 12 times before is selected and used as the fuel injection correction coefficient KEGRN for the exhaust gas recirculation rate at this time.

Seeing this from the operation of the exhaust gas recirculation valve, 12
The fuel injection correction coefficient KEGRN with respect to the exhaust gas recirculation rate before the time was 1.0, which means that the exhaust gas recirculation valve was closed. After that, the fuel injection correction coefficient KEGRN with respect to the exhaust gas recirculation rate gradually decreases to, for example, 0.99, 0.98, etc. In other words, the exhaust gas recirculation valve is opened up to the present time point A, but in the case of the illustrated example, Currently,
It is determined that the recirculation gas has not yet flowed into the combustion chamber, and therefore the correction for reducing the fuel injection is not performed.

At the same time, the fuel injection amount is corrected based on the fuel injection correction coefficient KEGRN for the determined exhaust gas recirculation rate.
The correction of the fuel injection amount is performed by multiplying the basic fuel injection amount TiM-F obtained from the engine speed and the engine load by a fuel injection correction coefficient KEGRN for the exhaust gas recirculation rate, which will be described later.
This is done by finding l.

In the flow chart of FIG. 19, S
When the actual lift LACT is judged to be zero in 206, the exhaust gas recirculation is not being performed, but the fuel injection correction coefficient KEGRN for the exhaust gas recirculation rate is determined from the value after the dead time τ has passed, and therefore, through S220. After S214, the fuel injection correction coefficient KEGRN for the net recirculation rate and the exhaust recirculation rate is calculated. In this case, in S216, the net return rate is set to 0, as shown in FIG.
In S300 of the flow chart, the fuel injection correction coefficient KEGRN for the exhaust gas recirculation rate is set to 1.0.

When it is determined in S208 that the lift command value LCMD is less than or equal to the lower limit value LCMDLL, the process proceeds to S222, and the lift command value LCMD holds the previous value LCMDk-1 as it is (for simplification, in this specification, This time, adding k to the value was omitted.)

This is because even if the lift command value LCMD becomes zero when the region where the exhaust gas recirculation is executed is changed to the region where the exhaust gas recirculation is not executed, the dynamic characteristic of the exhaust gas recirculation valve 122 is delayed. Since it does not become zero, if the lift command value LCMD is below the lower limit value (threshold) LCMDLL, the lift command value LCMD should be held at the previous value LCMDk-1 (value at the time of the previous control cycle k-1). did. This previous value hold is performed until it is confirmed in S206 that the actual lift LACT has become zero.

When the lift command value LCMD is less than or equal to the lower limit value LCMDLL, the lift command value LCMD may be zero. In that case, the QCMD search value in S210 is also zero and S216.
In the calculation of 0, the division becomes zero and the calculation becomes impossible. However, by holding the previous value as described above, there is no risk of inoperability. Although the lower limit value LCMDLL is set to a small value, it may be zero.

Next, in S224, the map search value of the basic exhaust gas recirculation rate correction coefficient KEGRMAP (search in S204) is replaced with the previous search value KEGRMAPk-1. This is because the basic exhaust gas recirculation ratio correction coefficient KEGRMAP retrieved in S204 is set to 1 in the characteristic planned in this embodiment in an operating state in which the lift command value LCMD retrieved in S202 is determined to be less than or equal to the lower limit value. This is because the steady recirculation rate may become 0 in the calculation of S214 because it is set.

As described above, the net recirculation rate of the exhaust gas flowing through the exhaust gas recirculation valve into the combustion chamber is calculated from the detected engine speed and engine load, for example, the intake pressure and the operating state of the exhaust gas recirculation valve. Calculated for each cycle, based on which the fuel injection correction coefficient for the exhaust gas recirculation rate is sequentially calculated and stored for each operation cycle, and waste until exhaust gas passes through the exhaust gas recirculation valve and flows into the combustion chamber. Seek time,
Since the calculated value of the calculation cycle corresponding to the dead time is selected and regarded as the fuel injection correction coefficient for the exhaust gas recirculation rate in the current calculation cycle, complicated calculation and uncertain calculation elements are reduced as much as possible. Therefore, it is possible to accurately obtain the recirculation rate of the exhaust gas flowing into the combustion chamber and accurately correct the fuel injection amount with a simple configuration. In the above, the net reflux rate may be stored in the ring buffer instead of KEGRN, and the dead time τ may be a fixed value. The details thereof are described in Japanese Patent Application No. 6-294,014 previously proposed by the present applicant, and a further description will be omitted.

Next, the canister purge correction coefficient KPUG
(Depending on the purge mass) will be described.

When purging the canister, the canister 2
Since the gas containing the fuel component from 23 is sucked into the intake system, the air-fuel ratio shifts to the rich side. This deviation is later corrected by the feedback system. However, since it is expected that the air-fuel ratio will shift to the rich side in advance during canister purge, if the reduction correction amount according to the purge mass is previously corrected as KPUG, the correction amount of the feedback system decreases, that is, Since the load on the feedback system is reduced,
Stability and followability to disturbance are improved.

As a correction method, an inflowing canister
A method of calculating the fuel amount during canister purging from the purge flow rate and concentration, or a method of obtaining the correction coefficient KPUG according to the purge mass from the deviation of the air-fuel ratio sensor from the target air-fuel ratio can be considered. An example of calculating the canister purge correction coefficient KPUG based on the former method will be described below.

FIG. 28 is a flow chart showing the calculation method.

First, in step S400, the flow rate of the canister purge is detected via the flow meter 226, and in step S402, the concentration thereof is detected via the HC concentration sensor 227. Next, the inflowing fuel amount (mass) by the canister purge is calculated from the flow rate and the concentration detected in S404. Next, in S406, the calculated inflow fuel amount is converted into a gasoline fuel amount. That is, most of the fuel component in the canister purge is butane, which is a light component of gasoline.
Since butane and gasoline have different theoretical air-fuel ratios, they are converted to gasoline equivalent here. Then proceed to S408,
The map retrieval fuel injection amount TiM is multiplied by the target air-fuel ratio to obtain the cylinder intake air amount Gc, and from this and the converted gasoline amount, the correction coefficient KPUG according to the purge mass is calculated.

The purge control valve 225 is controlled by a program (not shown) so as to satisfy the target canister purge amount in accordance with predetermined engine speed and engine load and other operating conditions. Needless to say, when the canister purge is not executed, the correction coefficient KPUG corresponding to the purge mass becomes 1.

In the above, the correction coefficient KPUG corresponding to the target purge mass, for example, 0.95 may be set first, and the purge control valve may be controlled so as to match the value. Further, as described above, the correction coefficient KPUG according to the purge mass may be obtained from the deviation of the air-fuel ratio sensor from the target air-fuel ratio. Further, the cylinder intake air amount Gc may be set as a map value from the engine speed and the engine load. Furthermore, S40
The gasoline fuel amount obtained in 6 may be subtracted from the required fuel injection amount Tcyl.

In addition, the correction coefficient KTOTAL includes a correction coefficient based on the water temperature and a correction coefficient based on the intake air temperature, but since these are publicly known, the description thereof will be omitted. Fuel injection correction coefficient KEGRN for the thus obtained exhaust gas recirculation rate, KP according to the purge mass
The basic fuel injection amount TiM-F is multiplied as KTOTAL by adding UG and the like to correct it.

Next, the target air-fuel ratio KCMD and the target air-fuel ratio correction coefficient KCMDM are calculated.

FIG. 29 is a flow chart showing the calculation work.

First, the basic value KB described above in S500.
Search for S. This is obtained by searching the map shown in FIG. 14 from the engine speed Ne and the intake pressure Pb. The map also includes the basic values at idle. Further, in a so-called lean-burn engine in which the air-fuel ratio supplied to the engine at a low load of the engine is increased (or reduced in terms of an equivalence ratio) to improve fuel consumption characteristics, a basic value for lean-burn is also included.

Next, in S502, it is determined whether or not lean burn control is being performed after the engine is started by referring to the value of an appropriate timer. Since the internal combustion engine 10 according to the embodiment is provided with the variable valve timing mechanism, the target air-fuel ratio is slightly leaner than the stoichiometric air-fuel ratio for the predetermined period after the start by suspending the operation of one of the intake valves. The lean burn control is set on the side. That is, the inconvenience of increasing HC is avoided by enriching the air-fuel ratio while the catalyst device after starting has not been activated yet.

In an ordinary engine having two intake valves, if the target air-fuel ratio is set to the lean side after the engine is started in this way, combustion of the engine may become unstable and misfiring may occur. However, in the engine provided with the variable valve timing mechanism according to the embodiment, when one of the intake valves is deactivated, a swirl called a swirl is created in the intake air in the combustion chamber, which is immediately after the engine is started. However, because stable combustion is obtained, it becomes possible to make lean even immediately after starting. Therefore, it is judged from the timer value whether it is in that period,
The lean correction coefficient is calculated accordingly. This value is calculated as, for example, 0.89 in the lean burn control period, and 1.0 when there is no lean burn control period.

Next, in S504, it is determined whether or not the throttle opening is fully open (WOT), and the fully open increase correction value is calculated according to the result of the determination. Next, in S506, it is determined whether the water temperature Tw is high, and the increase correction coefficient KTWOT is calculated according to the determination result. This value also includes a correction factor for engine protection at high water temperatures.

Next, in S508, the basic value KBS is multiplied by the correction coefficient obtained to correct the basic value KBS, and the target air-fuel ratio KCMD is determined. This is the corrected basic value KBS
Based on the above, as shown in FIG. 7, in the range where the output of the O ₂ sensor 56 near the stoichiometric air-fuel ratio has a linear characteristic (shown by the broken line on the vertical axis), the minute control of the air-fuel ratio (the above-mentioned MIDO ₂
This is done by setting a window (hereinafter referred to as DKCMD-OFFSET) for control) and adding the window value DKCMD-OFFSET to the corrected basic value KBS. That is, the target air-fuel ratio
Determine KCMD as follows. KCMD = KBS + DKCMD-OFFSET

Next, in S510, the target air-fuel ratio obtained is obtained.
Performs limit processing for KCMD (k) (k: time). Then S
In step 512, it is determined whether the calculated target air-fuel ratio KCMD (k) is 1 or a value in the vicinity thereof.
In step 514, the activation of the O ₂ sensor 56 is determined. This is executed by another routine not shown, and the O ₂ sensor 56
This is done by detecting the change in the output voltage of. Then S51
Proceed to step 6 to calculate DKCMD for MIDO ₂ control. This is the downstream of the first catalyst device 28 (the catalyst device 28 shown in FIG.
In the case of, the target air-fuel ratio KCMD (k) of the LAF sensor 54 on the upstream side of the output of the O ₂ sensor 56 (downstream of the first CAT bed)
Means work that can be changed. In detail, as shown in FIG. 7, the value DKCMD is calculated by using the PID control law for the deviation between the predetermined comparison voltage VrefM and the output voltage VO ₂ M of the O ₂ sensor 56. The comparison voltage VrefM is obtained according to the atmospheric pressure Pa, the water temperature Tw, the exhaust volume (which can be obtained from the engine speed Ne and the intake pressure Pb), and the like.

The window value DKCMD-OFFSET described above is used.
Is an offset value added by the first and second catalytic converters 28 and 30 to maintain the optimum purification rate. Since this differs depending on the characteristics of the catalyst device, it is determined in consideration of the characteristics of the first catalyst device 28 in the illustrated example. In addition, since it also changes due to deterioration over time, learning is performed by a weighted average using the calculated value of the value DKCMD each time. Specifically, DKCMD-OFFSET (k) = W x DKCMD + (1-W) x DKCMD-OF
Calculate with FSET (k-1). Here, W: weighting factor, k: time. That is, by performing the learning calculation of the target air-fuel ratio KCMD with the previously calculated value of the value DKCMD-OFFSET, it is possible to perform feedback control to the air-fuel ratio with which the purification rate becomes optimum without being affected by deterioration over time. It should be noted that this learning may be performed by dividing the operating state into each region based on the engine speed Ne and the intake pressure Pb.

Next, in S518, the calculated value DKCMD
(k) is added to update the target air-fuel ratio KCMD (k), and S520
Proceed to the table shown in FIG. 30 for the target air-fuel ratio.
Search with KCMD (k) to find the correction coefficient KETC. This is to compensate for the difference in the charging efficiency of the intake air due to the heat of vaporization. Specifically, KCMD is calculated using the calculated correction coefficient KETC.
(k) is corrected as shown, and the target air-fuel ratio correction coefficient KCMDM (k)
To calculate. That is, in this control, the target air-fuel ratio is indicated by the equivalence ratio and the value KCMD obtained by performing the filling efficiency correction
Let M be the target air-fuel ratio correction coefficient. When the result in S512 is negative, it means that the target air-fuel ratio KCMD to be controlled deviates greatly from the stoichiometric air-fuel ratio, for example, during lean burn operation, and there is no need to perform MIDO ₂ control. , Immediately jump to S520. Finally S522
Then, the target air-fuel ratio correction coefficient KCMDM (k) is limited, and the process ends.

As shown in the block diagram of FIG. 8, the target air-fuel ratio correction coefficient KCMDM and various correction coefficient summation values KTOTAL thus obtained are multiplied by the basic fuel injection amount TiM-F to obtain the required fuel injection amount Tcy.
l is calculated.

Next, a feedback correction coefficient such as KSTR is calculated. Before entering the description, sampling of the LAF sensor output and an observer will be described here. The sampling operation block is shown in FIG.
lV ".

Since the exhaust gas is discharged in the exhaust stroke in the internal combustion engine, the behavior of the air-fuel ratio in the exhaust system collecting portion of the multi-cylinder internal combustion engine is clearly synchronized with TDC. Therefore, when the LAF sensor 54 is provided in the exhaust system of the internal combustion engine to sample the air-fuel ratio, it must be performed in synchronization with TDC. However, depending on the sample timing of the control unit (ECU) 34 that processes the detection output, the air-fuel ratio There are cases where the behavior of can 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. 31, the air-fuel ratio recognized by the control unit is as shown in FIG.
As shown in, the values are completely different depending on the sample timing. In this case, it is desirable to sample at a position where the actual output change of the air-fuel ratio sensor can be grasped as accurately as possible.

Further, the change in the air-fuel ratio also differs depending on the arrival time of the exhaust gas to the sensor and the reaction time of the sensor.
Among them, the arrival time to the sensor 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. As described above, the detection of the air-fuel ratio largely depends on the operating state of the engine. Therefore, in the prior art, for example, the technique disclosed in Japanese Patent Laid-Open No. 1-313,644, whether or not the detection is appropriate is determined for each predetermined crank angle. However, since the configuration is complicated and the calculation time is long, the high rotation speed range is high. Then, there is a possibility that it may not be possible to cope with it, and there is also a problem that the inflection point of the output of the air-fuel ratio sensor is missed when the detection is decided.

FIG. 33 is a flow chart showing the sampling operation of the LAF sensor. However, since the detection accuracy of the air-fuel ratio is closely related to the estimation accuracy of the observer described above, before entering the explanation of FIG. Here, the air-fuel ratio estimation by the observer will be briefly described.

First, in order to accurately separate and extract the air-fuel ratio of each cylinder from the output of one LAF sensor, it is necessary to accurately clarify the detection response delay of the LAF sensor. Therefore, this delay is artificially modeled as a first-order delay system, and
A model as shown in 4 was created. LAF here: LAF
Assuming that the sensor output is A / F and the input is A / F, the equation of state can be expressed by the following equation 9.

[0125]

[Equation 9]

When this is discretized with the period ΔT, it becomes as shown in equation 10. FIG. 35 is a block diagram showing Equation 10.

[0127]

[Equation 10]

Therefore, by using the equation 10, the true air-fuel ratio can be obtained from the sensor output. That is, if the equation 10 is transformed into the equation 11, the time k
The value at the time of k−1 can be calculated backward from the value at the time of

[0129]

[Equation 11]

[0130]

(Equation 12)

Specifically, if the equation 10 is expressed by a transfer function using the Z-transform, the equation 13 is obtained. Therefore, the previous input air-fuel ratio is calculated in real time by multiplying the inverse transfer function by the LAF sensor output LAF of this time. Can be estimated. FIG. 36 shows a block diagram of the real-time A / F estimator.

[0132]

(Equation 13)

Next, a method for separating and extracting the air-fuel ratio of each cylinder based on the true air-fuel ratio obtained as described above will be explained. As described in the previous application, the air-fuel ratio of the collecting portion of the exhaust system is The value at time k was considered as a weighted average considering the temporal contribution of the air-fuel ratio of the cylinder, and the value at time k was expressed as in Eq. 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 (13).

[0134]

[Equation 14]

That is, the air-fuel ratio of the collecting portion is such that the past combustion history of each cylinder is weighted by Cn (for example, the cylinder that has recently burned has a weight of 4).
0%, 30% before that. ． ． It was expressed as the sum of those multiplied by. A block diagram of this model is shown in FIG.

The equation of state is as shown in equation 15.

[0137]

(Equation 15)

When the air-fuel ratio of the collecting portion is set to y (k), the output equation can be expressed as in equation (16).

[0139]

[Equation 16]

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

[0141]

[Equation 17]

Here, the simulation results of the model obtained as described above will be shown. FIG. 38 shows that for a four-cylinder internal combustion engine, the air-fuel ratio of three cylinders is set to 14.7 and only one cylinder is
The case where the fuel is supplied at 2.0 is shown. FIG. 39 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. Here, further considering the response delay of the LAF sensor,
The sensor output has a blunted waveform as shown in FIG. 40 as "model output value". In the figure, "measured value" is the same LA
The measured value of the F sensor output is compared with this value, and it is verified that the above model well models the exhaust system of the multi-cylinder internal combustion engine.

Therefore, the problem of an ordinary Kalman filter for observing x (k) in the state equation and the output equation shown in the equation 18 results. When the Riccati equation is solved using the weighting matrices Q and R as shown in Expression 19, the gain matrix K becomes as shown in Expression 20.

[0144]

(Equation 18)

[0145]

[Formula 19]

[0146]

(Equation 20)

When A-KC is obtained from this, the following equation 21 is obtained.

[0148]

[Equation 21]

The general structure of the observer is as shown in FIG. 41. 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 22.

[0150]

[Equation 22]

Here, the observer to which y (k) is input, that is, the system matrix of the Kalman filter is expressed as in Eq.

[0152]

(Equation 23)

In the present model, when the elements of the weight distribution R of the Riccati equation R: the elements of Q = 1: 1, the system matrix S of the Kalman filter is given by Equation 24.

[0154]

[Equation 24]

FIG. 43 shows a combination of the above model and 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 collective air-fuel ratio, 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. 44, the PID control law is used to combine the sensor output (collection unit A / F, that is, the detected air-fuel ratio KACT) and the past value of the cylinder-specific feedback correction coefficient of each cylinder. Estimated # nA / F for each cylinder estimated by the observer while obtaining the feedback correction coefficient KLAF
From this, a feedback correction coefficient #nKLAF (n: cylinder) for each cylinder is obtained. Feedback correction coefficient #nKL for each cylinder
More specifically, AF is the aggregation unit A / F, that is, KACT is divided by the previous calculation value of the average value of all cylinders of the feedback correction coefficient #nKLAF for each cylinder (use the division symbol instead of the addition point). It is shown here) PI should be set so as to eliminate the deviation between the target value obtained from the above and the observer estimated value # nA / F.
It is calculated using the D rule.

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 fuel injection amount #nTout of each cylinder (defined by the valve opening time of the injector) is obtained by # nTout = Tcyl × # nKLAF × KLAF (n: cylinder). The details of such control are described in Japanese Patent Application No. 5-251138 previously proposed by the present applicant, and therefore further description will be omitted.

Now, returning to the flow chart of FIG. 33, sampling of the LAF sensor output will be described. It should be noted that this program is started at the TDC position.

A description will be given below with reference to the flow chart of FIG. First, in S600, the engine speed Ne, the intake pressure Pb, and the valve timing V / T are read out, and S604,
In step S606, a timing map (described later) for HiV / T or LoV / T is searched, and in step S608, HiV / T.
And the sensor output used for the observer calculation for LoV / T is sampled. Specifically, the timing map is searched from the engine speed Ne and the intake pressure Pb, and any one of the 12 buffers described above is selected as the No. Select with, and select the sampling value stored there.

FIG. 45 is an explanatory view showing the characteristic of the timing map. As shown in the figure, the characteristic is selected such that the lower the engine speed Ne or the higher the intake pressure (load) Pb, the faster the crank angle is sampled. Is set to do. 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, as shown in FIG. 32, the LAF sensor output is best sampled at a position as close as possible to the inflection point of the actual air-fuel ratio, but at that inflection point, for example, the first peak. Assuming that the reaction time of the sensor is constant, the value occurs at a faster crank angle as the engine speed becomes lower, as shown in FIG. 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 sensor is shortened. From that meaning, the sample timing is shown in FIG.
It was set as shown in.

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.
If i, the map characteristics 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, so if the engine speed or intake pressure is the same, the sampling value is selected early so that the map characteristics Is set.

Next, in S610, the observer matrix is calculated for HiV / T, and then in S612, the same calculation is performed for LoV / T. Then, the process proceeds to S614, the valve timing is determined again, and the process proceeds to S616 and S618 in accordance with the determination result to select and end the calculation result.

That is, since the behavior of the air-fuel ratio collecting portion changes with the switching of the valve timing, it becomes necessary to change the observer matrix. However, the estimation of the air-fuel ratio of each cylinder cannot be performed instantaneously, and several calculations are required until the air-fuel ratio estimation calculation for each cylinder finishes converging.Therefore, it is not possible to calculate using the observer matrix before the valve timing change. The calculation using the changed observer matrix is overlapped, and even if the valve timing is changed, the valve timing can be selected in S614 according to the changed valve timing. After each cylinder is estimated, as described above, the feedback correction coefficient is calculated so as to eliminate the deviation from the target value, and the injection amount is determined.

With this structure, the accuracy of detecting the air-fuel ratio can be improved. That is, as shown in FIG. 47, since the sampling is performed at a relatively short interval, the sampling value almost faithfully reflects the sensor output, and the values sampled at the relatively short interval are sequentially stored in the buffer group. The inflection point of the sensor output is predicted according to the engine speed and the intake pressure (load), and the corresponding value is selected from the buffer group at the predetermined crank angle. After this, an observer calculation is performed to estimate the air-fuel ratio of each cylinder, and feedback control for each cylinder of the air-fuel ratio is performed as described with reference to FIG.

Therefore, as shown in the lower part of FIG. 47, the CPU
The core 70 can accurately recognize the maximum value and the minimum value of the sensor output. Therefore, even when estimating the air-fuel ratio of each cylinder by using the above-mentioned observer with this configuration, it is possible to use a value that approximates the behavior of the actual air-fuel ratio, and the estimation accuracy of the observer is improved. The accuracy at the time of performing the cylinder-by-cylinder air-fuel ratio feedback control described with reference to 44 is also improved.

Regarding sensor output sampling,
It is also possible to determine the characteristics of both Lo and Hi without actually determining which characteristic the valve timing is, and then determine the characteristics for the first time. Also, LAF
When the air-fuel ratio of the mixture to be detected by the sensor is lean, the reaction time becomes shorter than when it is rich, so when the air-fuel ratio to be detected is lean, an earlier crank angle It is desirable to select the sampling value detected in. Further, when a vehicle equipped with an internal combustion engine travels in a highland, the atmospheric pressure decreases and the exhaust pressure decreases, so that the arrival time of the exhaust gas to the sensor becomes shorter than that in the lowland, It is desirable to select sampled values detected at earlier crank angles as altitude increases. Further, when the LAF sensor deteriorates, the responsiveness deteriorates and the reaction time becomes longer. Therefore, it is desirable to select the sampling value detected at the crank angle in the later period as the degree of deterioration advances. However, the details are
It is described in detail in Japanese Patent Application No. 6-243,277 previously proposed by the present applicant, and a further description will be omitted.

Next, the calculation of the feedback correction coefficient such as KSTR will be described.

In the air-fuel ratio control of the internal combustion engine, FIG.
Generally, a PID controller is used as shown in
The feedback correction coefficient is calculated by multiplying the deviation between the target value and the manipulated variable (output of the controlled object) by the proportional term, the integral term, and the differential term. Recently, however, the feedback correction coefficient can be calculated using modern control theory. Proposed.

As described above, also in this application, in the MIDO ₂ control, there is a response delay of the engine just by multiplying the fuel injection amount calculated in the feedforward system by the target air-fuel ratio correction coefficient KCMDM. Therefore, the target air-fuel ratio KCMD becomes the blunted detected air-fuel ratio KACT. Therefore, with the intention of dynamically compensating the response of the detected air-fuel ratio KACT from the target air-fuel ratio KCMD, the collective feedback correction shown in FIG. Instead of the coefficient KLAF, the adaptive controller STR is used to obtain the feedback correction coefficient KSTR, which is multiplied by the fuel injection amount calculated in the feedforward system.

By the way, when the feedback correction coefficient is determined using the modern control theory like the adaptive controller, the control response is comparatively high. Therefore, the controlled variable oscillates depending on the operating condition, and the control stability is increased. May decrease. Further, the fuel supply is stopped (fuel cut) in a predetermined operating state such as during cruise of the vehicle traveling, and as shown in FIG. 48, the air-fuel ratio is open loop (O / L) controlled during the fuel cut.

Then, when the fuel supply is restarted to reach the stoichiometric air-fuel ratio, for example, the fuel supply amount is determined and supplied by the feedforward system according to the characteristics obtained in advance by experiments. As a result, the true air-fuel ratio suddenly changes from the lean side to 14.7. However, it takes some time for the supplied fuel to burn and reach the air-fuel ratio sensor arrangement position, and the air-fuel ratio sensor itself has a detection delay. for that reason,
The detected air-fuel ratio does not match the actual air-fuel ratio, but takes the value shown by the broken line in the figure, which causes a relatively large difference.

At this time, when the feedback correction coefficient is determined based on the adaptive control law, the adaptive controller STR determines the gain KSTR to eliminate the deviation between the target value and the detected value all at once. However, this difference is caused by the detection delay of the sensor and the like, and the detected value does not indicate the true air-fuel ratio. Nevertheless, since the adaptive controller tries to absorb this relatively large difference all at once, as shown in FIG. 48, KSTR oscillates greatly, and as a result, the control amount also oscillates and the control stability deteriorates. To do.

Such inconvenience does not stop only when returning from the fuel cut. The same is true when returning from full throttle increase control to feedback control or when returning from lean burn control to stoichiometric air-fuel ratio control. Furthermore, the same is true when switching from perturbation control for intentionally oscillating the target air-fuel ratio to control to a constant target air-fuel ratio. In other words, this is a common problem when the target air-fuel ratio fluctuates greatly.

Therefore, it is desirable to determine the feedback correction coefficient by using the adaptive control law and the PID control law, etc., and switch it appropriately according to the operating condition. However, 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 suddenly changes, and the control amount becomes unstable and the control amount becomes unstable. Stability may be reduced.

Therefore, in the embodiment, the feedback correction coefficient is determined by using the adaptive control law and the PID control law, and the feedback correction coefficient is appropriately switched according to the operating state, and the switching is smoothly performed so that the correction coefficient has a step. This prevents the control amount from becoming unstable due to a sudden change in the manipulated variable, thereby preventing the control stability from deteriorating.

FIG. 49 is a flow chart showing a calculation work such as KSTR. For convenience of understanding, the adaptive controller STR will be described with reference to FIG. More specifically, the adaptive controller includes an STR controller (STR CONTROLLER) and an adaptive parameter adjusting mechanism (also referred to as "parameter adjusting mechanism") as shown in the figure.

As described above, the feedforward system first calculates the required fuel injection amount Tcyl, and based on the calculated required fuel injection amount Tcyl, the output fuel injection amount Tout is determined as described later, and the control plant (internal combustion It is sent to the engine 10) via a fuel injection valve 22. Target air-fuel ratio KCMD (k) and control amount (detected air-fuel ratio) KACT (k) of feedback system
(Control plant output y (k)) is input to the STR controller, and the STR controller calculates the feedback correction coefficient KSTR (k) using the recurrence formula. That is, the STR controller receives the coefficient vector θ hat (k) identified by the parameter adjustment mechanism to form a feedback compensator.

One of the adjustment rules (mechanisms) for adaptive control is I.
D. There is a parameter adjustment rule proposed by Landau et al. This method transforms an adaptive control system into an equivalent feedback system consisting of a linear block and a non-linear block, and for the non-linear block, Popov's integral inequality for input and output is established, and the linear block is adjusted to be strongly positive real. This is a method that guarantees the stability of the adaptive control system by determining the law. That is, in the parameter adjustment law proposed by Landau et al., The adjustment law expressed in the recurrence form (adaptive law) is stable by using at least one of the above Popov's superstability theory or Lyapunov's direct method. Guarantees sex.

This method is described, for example, in "Compute Roll" (published by Corona Publishing Co.). Pages 27, 28 to 41, or "Automatic Control Handbook" (Ohm Publishing) pages 703 to 707, "A Survey of Model Reference Adaptive"
Techniques-Theory and Ap-plication "ID LANDAU
"Automatica" Vol. 10, pp. 353-379, 1974, "Unifi-c
ation of Discrete Time Explicit Model Reference A
daptive ControlDesigns "IDLANDAU and others" Automatic
a ”Vol. 17, No. 4, pp. 593-611, 1981, and" Comb
ining Model Reference Adaptive Controllers and Sto
chasticSelf-tuning Regulators "ID LANDAU" Autom
Atica ”Vol. 18, No. 1, pp. 77-84, 1982, it is a known technique.

The adaptive control technique of the illustrated example uses the adjustment law of Landau et al. Explaining below, according to the adjustment law of Landau et al., The transfer function B (Z ^-1 ) / A of the controlled object of the discrete system
When the polynomial of the denominator numerator of (Z ^-1 ) is set as in Equations 25 and 26, the adaptive parameter θ hat (k) identified by the parameter adjusting mechanism is represented by a vector (transposition vector) as in Equation 27. . Further, the input ζ (k) to the parameter adjusting mechanism is determined as shown in Expression 28. Where m
= 1, n = 1, d = 3, that is, a plant having a dead time of 3 control cycles in the primary system is taken as an example.

[0182]

(Equation 25)

[0183]

(Equation 26)

[0184]

[Equation 27]

[0185]

[Equation 28]

Here, the adaptive parameter θ hat shown in Expression 27 is a scalar quantity b 0 hat that determines the gain.
^-1 (k), control element BR hat expressed using manipulated variable
Control element S expressed using (Z ^-1 , k) and the controlled variable
It is ^{composed of} (Z ⁻¹ , k) and is expressed as in Expressions 29 to 31, respectively.

[0187]

[Equation 29]

[0188]

[Equation 30]

[0189]

[Equation 31]

The parameter adjusting mechanism identifies and estimates the coefficients of these scalar quantities and control elements, and sends them to the STR controller as the adaptive parameter θ hat shown in the above-mentioned Expression 26. The parameter adjustment mechanism is the operation amount u of the plant.
(I) and control amount y (j) (i and j include past values)
Is used to calculate the adaptive parameter θ hat so that the deviation between the target value and the control amount becomes zero. The adaptive parameter θ hat is specifically calculated as in Expression 32. Number 32
, Γ (k) is a gain matrix (m + n + d-th order) that determines the identification / estimation speed of the adaptive parameter, and e asterisk (k) is a signal indicating the identification / estimation error, which is a recurrence such as Equation 33 and Equation 34, respectively It is represented by a formula.

[0191]

[Equation 32]

[0192]

[Expression 33]

[0193]

(Equation 34)

Various concrete algorithms are given depending on how to select λ1 (k) and λ2 (k) in the equation 33.
For example, if λ1 (k) = 1 and λ2 (k) = λ (0 <λ <2), the gradual gain algorithm (least square method when λ = 1), λ1 (k) = λ1 (0 <λ1 <1), λ2 (k)
= Λ2 (0 <λ2 <λ), the variable gain algorithm (weighted least squares method when λ2 = 1), λ1
When (k) / λ2 (k) = σ is set and λ3 is expressed as in Expression 35, when λ1 (k) = λ3 is set, a fixed trace algorithm is obtained. Further, when λ1 (k) = 1 and λ2 (k) = 0, the fixed gain algorithm is used. In this case, as is clear from Equation 33, Γ (k) = Γ (k-1), and therefore Γ
(k) = fixed value of Γ. For time-varying plants such as fuel injection or air-fuel ratio, any of the decreasing gain algorithm, the variable gain algorithm, the fixed gain algorithm, and the fixed trace algorithm are suitable.

[0195]

[Equation 35]

As is apparent from the above, this adaptive controller is a recurrence type controller that takes into account the dynamic behavior of the controlled object (internal combustion engine) and compensates for the dynamic behavior of the controlled object. In order to do so, it is a controller described in the recurrence form. More specifically, since it is of the STR type, it can be defined as an adaptive controller having an adaptive parameter adjusting mechanism at the input of the controller, more specifically, an adaptive controller having an adaptive parameter adjusting mechanism of a recurrence type.

Here, the feedback correction coefficient KSTR (k)
Is specifically calculated as shown in Expression 36.

[0198]

[Equation 36]

The feedback correction coefficient KSTR based on the obtained adaptive control law is multiplied as the feedback correction coefficient KFB by the required fuel injection amount Tcyl, and the output fuel injection amount Tout (operation amount) is determined and input to the control plant. That is,
The output fuel injection amount Tout is determined by Tout = Tcyl * KTOTAL * KCMDM * KFB + TTOTAL as shown in the block diagram of FIG. 8 (and partly shown in the block diagram of FIG. 50). The output fuel injection amount Tout is a feedback correction coefficient #nKLAF for each cylinder according to the PID control law.
Is also multiplied, which was described above with reference to FIG. Further, in the above, TTOTAL indicates the total value of various correction values performed by the addition term such as atmospheric pressure correction (however, since the invalid time of the injector is added separately when the output fuel injection amount Tout is output, it is included in this. Not).

What is characteristic of FIG. 50 (and FIG. 8) is that
First, the STR controller is placed outside the fuel injection amount calculation system, and the target value is not the fuel injection amount but the air-fuel ratio. That is, the manipulated variable is indicated by the fuel injection amount. Therefore, the parameter adjustment mechanism operates so that the detected air-fuel ratio generated in the exhaust system matches the target air-fuel ratio, and the feedback correction coefficient
The point is that KSTR is determined and robustness against disturbance is improved. However, since this point is described in the application previously proposed by the applicant (Japanese Patent Application No. 6-66,594), detailed description will be omitted.

The second characteristic is that the feedback correction coefficient is multiplied by the basic value to determine the manipulated variable.
As a result, the control convergence is significantly improved. On the other hand, due to the configuration, if the manipulated variable is not appropriate, the controlled variable tends to oscillate. A third feature is that a conventional PID controller (shown as a PID controller) is provided together with the STR controller, the feedback correction coefficient KLAF is determined by the PID control law, and the final value of the feedback correction coefficient is set via the switching mechanism. That is, either KSTR or KLAF is selected as KFB.

By the PID controller, that is, P
The feedback correction coefficient KLAF based on the ID control law is calculated as follows. First, the control deviation DKAF between the target air-fuel ratio correction coefficient KCMD and the detected air-fuel ratio KACT is calculated as DKAF (k) = KCMD (kd) -KACT (k) (where d is the actual injected fuel detected by the LAF sensor). Equivalent to the dead time to be). In this specification, (k) indicates the time (calculation or control cycle), and more specifically, the program start time.
(kd): Target air-fuel ratio (in the control cycle before dead time), KACT
(k): Indicates the detected air-fuel ratio (current control cycle).

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) are P term: KLAFP (k) = DKAF (k) × KP I term: KLAFI (k) = KLAFI (k-1) + DKAF ( k) × KI D term: KLAFD (k) = (DKAF (k) −DKAF (k-1)) × KD. Thus, the P term is obtained by multiplying the deviation by the proportional gain KP, and the I term is obtained by adding the value obtained by multiplying the deviation by the integral gain KI to the previous value KLAFI (k-1) of the feedback correction coefficient, and D The term is the current deviation DKAF (k) and the previous deviation DKAF (k-1)
The difference is multiplied by the differential gain KD to obtain. Each gain KP, K
I and KD are obtained according to the engine speed and the engine load, and more specifically, using a map, the engine speed Ne and the intake pressure P
It is set so that it can be searched from b.

Finally, the value thus obtained is added as KLAF (k) = KLAFP (k) + KLAFI (k) + KLAFD (k) to obtain the current value KLAF (k) of the feedback correction coefficient according to the PID control law. In this case, since it is a feedback correction coefficient by multiplication correction, it is assumed that the offset 1.0 is included in the I term KLAFI (k) (that is, the initial value of the I term KLAFI is 1.0). ). When the feedback correction coefficient by the PID controller is selected, the STR controller holds the adaptive parameter so that the feedback correction coefficient KSTR stops at 1 (initial state).

Based on the above, the calculation of the feedback correction coefficient will be described with reference to the flow chart of FIG. The program of FIG. 49 is started at a predetermined crank angle.

First, the engine speed Ne, the intake pressure Pb, etc. detected in S700 are read out, and the routine proceeds to S704, where it is judged whether or not the fuel is cut. The fuel cut is performed in a predetermined operating state, for example, when the throttle opening is in the fully closed position and the engine speed is equal to or higher than a predetermined value, the fuel supply is stopped, and the air-fuel ratio is also controlled in open loop. To be done.

If it is determined in S704 that the fuel cut is not effected, the flow proceeds to S706, the above-mentioned required fuel injection amount Tcyl is read, and the flow proceeds to S708 where the LAF sensor 5 is operated.
It is determined whether the activation of 4 has been completed. This is for example
This is performed by determining that the activation is completed when the sensor cell voltage (reference voltage) of the LAF sensor 54 is smaller than a predetermined value (1.0 V, for example).

When it is determined in S708 that the activation is completed, the process proceeds to S710, and it is determined whether or not it is in the feedback control area. This is performed by another routine not disclosed, and is controlled by an open loop, for example, when the amount of full throttle is increased, when the engine speed is high, or when the operating state changes suddenly due to the influence of EGR or the like.

When the result in S710 is affirmative, the process proceeds to S71.
2, the detected exhaust air-fuel ratio is read, the process proceeds to step S714, the detected air-fuel ratio KACT (k) is obtained from the detected exhaust air-fuel ratio, and the process proceeds to step S716 to determine the final value of the feedback correction coefficient.
Find the KFB.

FIG. 51 is a subroutine flow chart showing the work.

Explaining according to the figure, in S800, it is determined whether or not the open loop control was performed last time (previous control or calculation cycle, that is, last program start time). When the open loop control such as the fuel cut was performed last time, the determination is affirmative and the process proceeds to S802 where the counter value C is reset to 0 and the process proceeds to S804 where the flag FKST is set.
The bit of R is reset to 0, and the process proceeds to S806 to calculate the final value KFB of the feedback correction coefficient. Incidentally, S80
Resetting the bit of flag FKSTR to 0 in 4
This means that the feedback correction coefficient should be determined by the PID control law. Further, as will be described later, when the bit of the flag FKSTR is set to 1, it means that the feedback correction coefficient should be determined by the adaptive control law.

FIG. 52 is a subroutine flow chart showing a concrete work of the feedback correction term KFB calculation. Explaining below, in S900, it is determined whether or not the bit of the flag FKSTR is set to 1, that is, whether it is in the STR (controller) operating region. Since this flag has been reset to 0 in S804 of the flow chart of FIG. 51, the determination in this step is negative and the flow proceeds to S902 where the bit of the previous flag FKSTR has been set to 1, that is, the previous STR ( Controller) Judge whether it is in the operating range.

The judgment here is of course also denied, and the program proceeds to S904 where the feedback correction coefficient KLAF (k) is calculated as described above based on the PID control law by the PID controller. More precisely, the feedback correction calculated by the PID controller is calculated. Select the coefficient KLAF (k). Next, returning to the flow chart of FIG. 51, the flow proceeds to S808, where KLF (k) is KF.
Let's call it B.

Continuing with the explanation of the flow chart of FIG. 51, if it is determined in S800 that the previous open-loop control was not performed, that is, if the open-loop control has returned to the feedback control, the process proceeds to S810 and the target air-fuel ratio is reached. Difference D between the previous value KCMD (kd) and the current value KCMD (k)
Calculate KCMD and compare with the reference value DKCMDref. And the difference D
When it is determined that KCMD exceeds the reference value DKCMDref, S
After 802, the feedback correction coefficient is calculated according to the PID control law. This is because when the change in the target air-fuel ratio is large, it is hard to say that the detected value always indicates a true value due to the detection delay of the air-fuel ratio sensor, etc., as in the case of the return of the fuel cut. This is because it may become unstable. As an example of a case where the target air-fuel ratio changes greatly, for example, when returning from the full opening increase amount, when returning from the lean burn control (for example, when the air-fuel ratio is 20: 1 or leaner) to the theoretical air-fuel ratio control, When returning from the perturbation control in which the target air-fuel ratio is changed to the theoretical air-fuel ratio control in which the target air-fuel ratio is constant, there can be mentioned.

On the other hand, in step S810, the difference DKCMD is the reference value DKCMDr.
When it is determined that the temperature is equal to or lower than ef, the process proceeds to S812, the counter value C is incremented, and the process proceeds to S814, where the detected water temperature Tw
Is compared with a predetermined value TWSTR.ON, and when it is determined that the value is less than the predetermined value, the process proceeds to S804 and thereafter to calculate the feedback correction coefficient according to the PID control law. This is because the combustion is not stable when the water temperature is low, there is a risk of misfire, and the stable detection value KACT cannot be obtained. Even when the water temperature is abnormally high, the feedback correction coefficient is calculated according to the PID control law for the same reason.

When it is determined in S814 that the detected water temperature is equal to or higher than the predetermined value, the process proceeds to S816, the detected engine speed Ne is compared with the predetermined value NESTRLMT, and when it is determined that the temperature is equal to or higher than the predetermined value, S is determined.
After 804, the feedback correction coefficient is calculated according to the PID control law. This is because the calculation time tends to be short when the engine speed is high, and the combustion is not stable.

If it is determined in S816 that the detected engine speed is less than the predetermined value, the flow proceeds to S818, it is determined which valve timing characteristic is selected, and it is determined that the HiV / T side characteristic is selected. When it is determined, the process proceeds to S804 and thereafter to calculate the feedback correction coefficient according to the PID control law. This is because when the HiV / T side characteristic is selected, the amount of overlap in valve timing is large, so there is a risk of intake air passing through the exhaust valve and escaping, a so-called intake blow-by phenomenon, and stable. This is because the detected value KACT cannot be expected.

[0218] If it is determined in S818 that it is on the LoV / T side (including the rest state of one of the two valves), S820
If it is affirmed, the process proceeds to S804 and thereafter to calculate the feedback correction coefficient according to the PID control law. This is because the operating condition is almost stable at the time of idling and a high gain like the STR control law is not required. Further, since the intake air amount is controlled by using an electric air control valve, so-called EACV, so that the engine speed is kept constant during idling, there is a possibility that the intake air amount control and the air-fuel ratio feedback control may interfere with each other. In that sense, the gain is set to be relatively low based on the PID control law.

If it is determined in S820 that the detected intake pressure Pb is not on the low load side, the routine proceeds to S822, where it is determined whether the detected intake pressure Pb is on the low load side or not.
After 804, the feedback correction coefficient is calculated according to the PID control law. This is also because the combustion is not stable.

If it is determined in S822 that the load is not low, the flow advances to S824 to set the counter value C to a predetermined value, for example, 5
Compare with As long as it is determined that the counter value C is less than or equal to the predetermined value, S804, S806, S900, S902
In steps S916, S904 and S808, the feedback correction coefficient KLAF (k) calculated by the PID controller is selected in the same manner as above.

That is, in FIG. 48, the time T1 when the fuel cut ends and the open loop control returns to the feedback control (counter value C = 1 touched in FIG. 51).
During the period from to T2 (counter value C = 5), the feedback correction coefficient is the value KLAF according to the PID control law determined by the PID controller. This PID
The feedback correction coefficient KLAF based on the control law is different from the feedback correction coefficient KSTR based on the STR controller in that it does not try to absorb the control deviation DKAF between the target value and the detected value all at once, but has a characteristic of absorbing it relatively slowly.

Therefore, even if the difference between the delay until the combustion of the fuel whose supply has been resumed and the detection delay of the air-fuel ratio sensor as shown in FIG. 48 is relatively large, the correction coefficient is S.
It does not become unstable as in the case of using the TR controller, so that the controlled variable (plant output) does not become unstable. Here, the predetermined value is 5, in other words, 5
The control period is set because it is considered that the combustion delay and the detection delay described above can be absorbed during this period. Note that this period (predetermined value) may be determined from the engine speed, engine load, etc., which are exhaust gas transportation delay parameters. For example, when the exhaust gas transportation delay parameter is small depending on the engine speed and intake pressure, The predetermined value may be set small and set large when the exhaust gas transportation delay parameter is large.

Returning to the explanation of the flow chart of FIG. 51,
If it is determined in S824 that the counter value C exceeds the predetermined value, that is, 6 or more, the process proceeds to S826 and the flag FKST is set.
The bit of R is set to 1, the process proceeds to S828, and FIG.
2 Calculate the final value KFB of the feedback correction coefficient according to the flow chart. In this case, in the flow chart of FIG. 52, the determination in S900 is affirmative and the routine proceeds to S906, where it is determined whether or not the bit of the previous flag FKSTR was reset to 0, that is, the previous PID operation area.

This determination is affirmative when it is the first time that the counter value has exceeded the predetermined value, and the flow advances to S908 to detect the detected air-fuel ratio.
Compare KACT (k) to a lower limit a, eg 0.8. When it is determined that the detected air-fuel ratio is equal to or higher than the lower limit value, the process proceeds to S910, and the detected air-fuel ratio is compared with the upper limit value b, for example, 1.2. Is used to calculate the feedback correction coefficient KSTR (k), more precisely, the feedback correction coefficient KSTR (k) calculated by the STR controller is selected.

In other words, if it is determined in S908 that the detected air-fuel ratio falls below the lower limit value a, or in S910 that the detected air-fuel ratio exceeds the upper limit value b, the routine proceeds to S904, where PI
The feedback correction coefficient is calculated based on the D control.
That is, switching from PID control to STR (adaptive) control is performed in the operating range of the STR controller and at the detected air-fuel ratio.
It was done when KACT became a value near 1. Accordingly, the PID control can be smoothly switched to the STR (adaptive) control, and the oscillation of the control amount can be prevented.

If it is determined in S910 that the detected air-fuel ratio KACT (k) is less than or equal to the upper limit value b, the process proceeds to S912 and ST
The scalar amount b ₀ that determines the gain in the R controller is divided by the previous value KLAF (k-1) of the feedback correction coefficient by PID control as shown in the figure, and S91
Proceed to step 4 to obtain the feedback correction coefficient KSTR (k) by the STR controller.

That is, the feedback correction coefficient KSTR (k) by the STR controller is originally obtained as shown in the equation 36, as described above, but is affirmative in S906 and S908.
When proceeding to the subsequent steps, the feedback correction coefficient is determined based on the PID control in the previous control cycle. And
In the configuration of FIG. 50, when the feedback correction coefficient is determined by the PID control, the STR controller sets the feedback correction coefficient KSTR to 1 and stops as described above. In other words, the adaptive parameter (vector) θ hat (k) used in the STR controller is KSTR
= 1.0. Therefore, when the feedback correction coefficient KSTR is determined again by the STR controller, if the value of KSTR deviates greatly from 1, the control amount becomes unstable. Therefore, the scalar amount b ₀ that determines the gain in the adaptive parameter θ hat (k) held so that KSTR becomes 1.0 (initial value) or near 1.0 is set as the feedback correction coefficient by the PID control. If it is divided by the previous value, for example, if the combination of adaptive parameters is set to KSTR = 1.0,
As shown in, since the first term is 1, the second term
The value of the term KLAF (k-1) becomes the correction coefficient KSTR (k) this time. As a result, in addition to setting the detection value KACT to 1 or a value in the vicinity thereof in S908 and S910, the PID control to ST
Switching to R control can be performed more smoothly.

[0228]

(37)

Incidentally, supplementing the explanation of the flow chart of FIG. 52, when it is determined in S902 that the STR (controller) operating region is the last time, the process proceeds to S916, and the previous value KSTR (k-1) of the feedback correction coefficient by the STR controller is set.
Is the previous value KLAFI (k-1) of the I term. As a result, S90
When KLAF (k) is calculated in 4, the I term KLAFI
Becomes KLAFI (k) = KSTR (k-1) + DKAF (k) × KI, and the obtained I term is added to the P and D terms to obtain KLAF (k).

That is, when the feedback correction coefficient is calculated by switching from the adaptive control to the PID control, the integral term may change abruptly. Thus, the value of KSTR is used to calculate the PID control correction coefficient. By determining the initial value, the difference between the correction coefficient KSTR (k-1) and the correction coefficient KLAF (k) can be kept small, and the value of the feedback correction coefficient is also changed when switching from STR control to PID control. It is possible to reduce the difference between the two and make them continuous smoothly, and it is possible to prevent a sudden change in the control amount.

In the flow chart of FIG. 52, S
In 900, it is judged to be in the STR (controller) operating range,
If it is also determined in S906 that it is not in the PID operation region last time, the process proceeds to S914, in which the feedback correction coefficient KSTR (k) is calculated based on the STR controller. As stated.

Returning to the flow chart of FIG. 51, the flow proceeds to S830, where it is confirmed whether the correction coefficient obtained in the flow chart of FIG. 52 is KSTR, and if affirmative, the flow proceeds to S832 where the adaptive correction coefficient KSTR and 1. Difference from 0 (1-KSTR (k))
And calculate the absolute value as the predetermined threshold value KSTR
Compare with ref.

That is, when the feedback correction coefficient fluctuates drastically, the control amount also changes abruptly, and the control stability deteriorates. Therefore, the absolute value of the difference between the calculated feedback correction coefficient and 1.0 is compared with the threshold value, and if it exceeds the threshold value, the process proceeds to S804, and the feedback correction coefficient is determined again based on the PID control. . This makes it possible to realize stable control without causing a sudden change in the control amount. In this case, the absolute value of the difference between the feedback correction coefficient and 1.0 was compared, but the threshold value KSTRref is set separately on the large and small sides of the feedback correction coefficient of 1.0 as shown in FIG. Is also good. When the absolute value of the feedback correction coefficient KSTR (k) obtained in S832 does not exceed the threshold value, the process proceeds to S834 and the value by the STR controller is set as the feedback correction coefficient KFB. Also, S
When the result in 830 is negative, the program proceeds to S836 and the flag FKST
Reset the R bit to 0, proceed to S838, and PID
The value from the controller is used as the final value of the feedback correction coefficient KFB.

Returning to the flow chart of FIG. 49, the program proceeds to S718, in which the final value KFB of the feedback correction coefficient obtained is multiplied by the required fuel injection amount Tcyl, and
The output fuel injection amount Tout is determined by adding the addition value TTOTAL. Next, in S720, the intake pipe wall surface adhesion correction is performed (described later), and in S722, the output fuel injection amount Tout (n) is output to the injector 22 as an operation amount. Here, n means a cylinder, and thus the output fuel injection amount Tout is finally determined for each cylinder.

When it is determined in S704 that the fuel cut is performed, the process proceeds to S728, and the output fuel injection amount Tout is set to zero. When the result in S708 to S710 is negative, the air-fuel ratio is open loop control.
In step S718, the final value KFB of the feedback correction coefficient is set to 1.0, and the output fuel injection amount Tout is obtained in step S718. Even when the result in S704 is affirmative, the open-loop control is performed and the output fuel injection amount Tout is set to a predetermined value (S7).
28).

In the above, when the open-loop control of the air-fuel ratio such as when returning from the fuel cut is completed and the feedback control is restarted, PI is maintained for a predetermined period.
Since the feedback correction coefficient is determined based on the D control law, it takes time for the supplied fuel to burn, or because the sensor itself has a detection delay, the detected air-fuel ratio and actual When there is a relatively large difference with the air-fuel ratio of, the feedback correction coefficient by the STR controller is not used, and as a result, the control amount (air-fuel ratio) becomes unstable and the control stability can be reduced. Absent.

On the other hand, since the period is set to a predetermined value, when the detected value becomes stable, the feedback correction coefficient by the STR controller is used to operate to absorb the control deviation between the target air-fuel ratio and the detected air-fuel ratio at once. The control convergence can be improved. In particular, in the embodiment, the control convergence is improved so that the feedback correction coefficient is multiplied by the basic value to determine the operation amount, so that the stability and convergence of the control are more preferably balanced. Can be made. Since the detected air-fuel ratio is not stable immediately after the LAF sensor 54 is activated, the LAF sensor 54
The feedback correction coefficient may be determined based on the PID control law for a predetermined period after the sensor 54 is activated.

Furthermore, when the fluctuation of the target air-fuel ratio is large,
Since the feedback correction coefficient is determined based on the PID control even after the lapse of a predetermined period of time, the stability and convergence of the control can be achieved even when returning from the open loop control such as the full opening increase, not limited to the fuel cut. And can be optimally balanced. Further, when the feedback correction coefficient by the STR controller becomes unstable, the feedback correction coefficient is determined based on the PID control law, so that the stability and the convergence of the control can be more optimally balanced. .

Particularly, at the time of shifting from the STR control to the PID control, at least a part of the elements, that is, the I term is calculated by using the feedback correction coefficient by the STR controller, so that the switching becomes smooth, It is possible to effectively prevent the control amount from oscillating due to a step difference in the correction coefficient and a sudden change in the operation amount. Therefore, it is possible to effectively prevent the stability of control from decreasing.

Further, when returning from PID control to STR control, a case where the detected value KACT is 1 or in the vicinity thereof is selected, and the first value of the feedback correction coefficient by the adaptive control law (STR controller) is determined by the PID control law. Since the feedback correction coefficient and the feedback correction coefficient are substantially the same, the switching can be smoothly performed even when the PID control is switched to the STR control. Thereby,
It is possible to effectively prevent the control amount from becoming unstable due to the step difference in the correction coefficient and the operation amount to change suddenly, and thus to effectively prevent the control stability from deteriorating.

Here, the correction of the adhering amount of the output fuel injection amount Tout to the wall surface of the intake pipe will be described. As described above, the intake pipe wall surface adhesion correction is performed for each cylinder, and the cylinder number n (n = 1, 2,
3, 4) are attached and specified.

In order to immediately respond to changes in adhesion parameters,
In front of the wall adhesion plant, a wall adhesion correction compensator having an inverse transfer function is inserted in series. The adhesion parameter of this wall surface adhesion correction compensator is searched by a map determined in advance based on the correspondence relationship with the engine operating state.

If the adhesion parameter of the wall adhesion correction compensator and the true adhesion parameter of the actual machine are equal,
Both of them have a transfer function of 1 when viewed from the outside, that is, the product of the transfer functions of the plant and the compensator becomes 1, and the target cylinder intake fuel amount = actual cylinder intake fuel amount, so perfect correction should be performed. .

On the premise of the above, regarding the wall surface adhesion correction work of the output fuel injection amount Tout in S720 of the flow chart of FIG. 49, its subroutine flow shown in FIG.
This will be described with reference to the chart. This routine is TDC
The output fuel injection amount Tou for all cylinders is performed in synchronization with the signal.
Only the number of cylinders is executed until t (n) is obtained. Also,
Although (k-1) in the figure indicates the previous calculation value for the cylinder n as described above, the addition of (k) for the current calculation value is omitted.

First, various parameters are read in S1000, and the flow proceeds to S1002, where the direct rate A and the take-away rate B are set.
Ask for. This is performed by searching the map showing the characteristic in FIG. 55 from the engine speed Ne and the intake pressure Pb. This map is set separately according to the valve timing characteristic of the variable valve timing mechanism, and the map corresponding to the currently selected valve timing characteristic is searched for. At the same time, the table showing the characteristics in FIG. 56 is searched from the detected water temperature Tw to obtain the correction coefficients KATW and KBTW, and the map search value is multiplied to correct. Although not shown, other similar correction coefficients KA and KB are calculated according to the presence or absence of execution of EGR or canister purge, and the magnitude of the target air-fuel ratio KCMD. Specifically, it is as follows. Ae = A × KATW × KA Be = B × KBTW × KB The corrected direct rate A is Ae and the carry-out rate B is Be.

Subsequently, the routine proceeds to S1004, where it is judged if the fuel cut is present or not. If the result is NO, the routine proceeds to S1006, where the output fuel injection amount Tout is corrected as shown in the figure, and the output fuel injection amount Tout (n)-for each cylinder. When F is obtained and affirmative, the routine proceeds to S1008, where the output fuel injection amount Tout for each cylinder
(n) -F is set to zero. Here, the value TWP (n) is the intake pipe adhering fuel amount.

FIG. 57 is a flow chart for calculating the intake pipe adhering fuel amount TWP (n), which is started at a predetermined crank angle.

First, in S1100, the current program start is the period from the start of calculation of the fuel injection amount Tout to the end of fuel injection in any cylinder (hereinafter referred to as "injection control period").
If it is affirmative, the routine proceeds to S1102, where the bit of the first flag FCTWP (n) indicating the end of the calculation of the adhered fuel amount of the cylinder is set to 0, and the adhered fuel amount of Allow the operation and terminate the program. When the result in S1100 is NO, the program proceeds to S1104, in which the first flag FCTW is entered.
It is determined whether or not the bit of P (n) is 1, and when the result is affirmative, the calculation of the amount of fuel adhering to the cylinder concerned has already been completed. Therefore, the process proceeds to S1106, and when it is negative, S1.
The routine proceeds to 108, where it is determined whether or not the fuel cut is performed.

When the result in S1108 is NO, S1110
Then, the routine proceeds to the step of calculating the intake pipe adhering fuel amount TWP (n) as shown in the figure. Where TWP (k-1) is the previous value of TWP (k). In addition, the first term on the right side means the amount of fuel that has remained without being taken away this time among the fuel that was previously attached, and the second term on the right side
The term means the amount of fuel newly attached to the intake pipe among the fuel injected this time. Subsequently, the flow proceeds to S1112, the bit of the second flag FTWPR (n) indicating that the amount of adhered fuel is zero is set to 0, and the flow proceeds to S1106.
Set the bit of TWP (n) to 1 and terminate the program.

If it is determined in S1108 that the fuel is cut, the routine proceeds to S1114, where it is determined whether or not the bit of the second flag FTWPR (n) indicating that the remaining adhered fuel amount is 0 is 1, and affirmative. If the amount of fuel adhered is zero (TWP (n) = 0), the process proceeds to S1106 and
When the determination is negative, the routine proceeds to S1116, and the adhered fuel amount TWP (n) is calculated from the equation shown. Here, the formula shown is S1
This is equivalent to the expression of 110 from which the second term on the right side is deleted.
This is because the fuel is being cut and there is no new fuel to be attached.

Subsequently, the flow proceeds to S1118, where it is determined whether or not the TWP (n) value is larger than the minute predetermined value TWPLG. When the result is affirmative, the process proceeds to S1112, and when it is negative, the remaining amount of adhered fuel can be ignored. Since the number is small, the program proceeds to S1120 to set TWP (n) = 0, proceeds to S1122 to set the bit of the second flag FTWPR (n) to 1, and proceeds to S1106.

In this way, the intake pipe adhering fuel amount TWP (n) for each cylinder can be accurately calculated, and is calculated.
By using the TWP (n) value to calculate the fuel injection amount Tout in FIG. 54, an appropriate amount of fuel considering the amount of fuel adhering to the intake pipe and the amount of fuel carried away from the adhering fuel is burned in each cylinder. Can be supplied to the chamber. Even in the engine start mode (including simultaneous injection and sequential injection) described above, the direct ratio A and the take-away ratio B are also included.
Also, start the calculation of the intake pipe adhering fuel amount TWP and execute the adhering correction.

As described above, this embodiment is provided in the exhaust system of the internal combustion engine, and the air-fuel ratio detecting means (LAF sensor 54) for detecting the air-fuel ratio of the exhaust gas discharged by the internal combustion engine.
And, so as to converge the air-fuel ratio KACT of the internal combustion engine to the target air-fuel ratio KCMD from the detected air-fuel ratio detected by the air-fuel ratio detecting means, an air-fuel ratio correction coefficient KSTR for correcting the fuel injection amount supplied to the internal combustion engine. Air-fuel ratio correction coefficient calculation means for calculating, fuel injection amount correction means for correcting the fuel injection amount supplied to the internal combustion engine by the air-fuel ratio correction coefficient, and fuel injected with respect to the corrected fuel injection amount Fuel delivery delay correction fuel injection amount calculation means for calculating a fuel transport delay correction fuel injection amount based on the above-mentioned transport delay, and fuel injection to be supplied to the internal combustion engine based on the calculated fuel transport delay correction fuel injection amount. A fuel injection amount determining means for determining the amount, and a catalyst device (2) provided downstream of the air-fuel ratio detecting means in the exhaust system of the internal combustion engine.
8) and second air-fuel ratio detecting means (O ₂ sensor 5) which is provided in the exhaust system of the internal combustion engine downstream of the catalyst device and detects the air-fuel ratio of the exhaust gas discharged by the internal combustion engine.
6) and the target air-fuel ratio correction means for correcting the target air-fuel ratio KCMD from the detected air-fuel ratio detected by the second air-fuel ratio detection means, the dynamic compensation for the fuel transportation delay is performed. At the same time, the target value of the air-fuel ratio feedback is corrected according to the behavior of the air-fuel ratio downstream of the catalyst, so that the air-fuel ratio required by the catalyst can be matched with high accuracy.

Further, in this embodiment, the adaptive control for calculating the correction coefficient KSTR of the fuel injection amount so that the air-fuel ratio detected by the first air-fuel ratio detecting means (LAF sensor 54) matches the target air-fuel ratio KCMD. Device (STR controller) and STR
A correction means for adjusting the target air-fuel ratio KCMD in accordance with the air-fuel ratio detected by the second air-fuel ratio detection means (O ₂ sensor 56) is provided. Since it is configured to be equipped with, it is possible to dynamically compensate the behavior of the air-fuel ratio,
The air-fuel ratio can be instantly matched with the target air-fuel ratio.

In FIG. 8, the third catalyst device 94 may be arranged upstream of the LAF sensor 54 in a block 400 indicated by an imaginary line. The third catalyst device 94 is preferably a so-called light-off catalyzer (early activation catalyzer). In addition, the third catalyst device 9
The capacity of 4 may be sufficiently smaller than that of the downstream catalyst device. Further, it may be of the same three-way catalyst type as the downstream catalyst device, or may be of the type called EHC (electrically heated catalyzer) that is electrically heated and activated early. The third catalyst device 94 may be provided as necessary. Particularly, when the system as described above is configured for each bank of the V-type engine, the exhaust volume is relatively reduced. It is effective when the temperature rise is slow. Needless to say, when the third catalyst device 94 is arranged, the dead time and the like are different, so that the control amount and the like are different.

A filter 96 may be arranged in front of the observer in FIG. 8 as shown by an imaginary line. Since the LAF sensor 54 has a response delay, the observer handles the internal calculation as described above.
A filter that compensates for the second delay characteristic (that is, a lead filter)
96 may be arranged and dealt with by hardware.

It should be noted that not all of the configurations shown in the block diagram of FIG. 8 are indispensable for the invention described in the claims. For example, the adaptive controller is not always an essential component for the invention of claim 1, and the basic fuel injection amount may be obtained by a method other than the disclosed method. The same applies to other constituent requirements.

FIG. 58 is a block diagram similar to FIG. 8 showing a second embodiment of the device according to the present application.

In the second embodiment, as shown in the figure,
A second O ₂ sensor 98 is arranged downstream of the second catalyst device 30. The detection output of the second O ₂ sensor 98 is used to correct the target air-fuel ratio KCMD, as shown in the figure. As a result, the target air-fuel ratio KCMD can be set even more optimally,
Controllability is improved. Further, by detecting the air-fuel ratio in the exhaust gas finally discharged to the atmosphere, the emission performance is improved and the deterioration state of the catalyst device on the upstream side of the second O ₂ sensor can be monitored. . The second O
_{The 2} sensor 98 may be a substitute for the first O ₂ sensor 56. Further, the second O ₂ sensor 98 may be mounted in the second catalyst device having a multi-stage structure as shown in FIG. 5, like the first O ₂ sensor 56.

In this case, a low pass filter 500 having a frequency characteristic of about 1000 Hz is connected to the next stage of the second O ₂ sensor 98. The filter 60 of the first O ₂ sensor 56 and the filter 50 of the second O ₂ sensor 98
For 0, a filter such as a linearizer may be used to compensate for the non-linear characteristic.

In the above-described first and second embodiments, the mechanism for driving the throttle valve 16 via the pulse motor M is used, but like the generally known mechanism,
It may be mechanically interlocked with the accelerator pedal.

Further, as for the exhaust gas recirculation mechanism, a responsive electric type exhaust gas recirculation valve is used, but an exhaust gas recirculation valve using a diaphragm operated by the negative pressure of the engine may be used.

The second catalyst device 30 may be omitted depending on the purification performance of the first catalyst device 28.

Further, although the low pass filter is used, a band pass filter which can obtain equivalent performance may be used.

Furthermore, in the above-mentioned configuration, an example in which one air-fuel ratio sensor is used to estimate the air-fuel ratio of each cylinder and control is performed to the target value has been shown. A fuel ratio sensor may be provided to directly detect the air-fuel ratio of each cylinder.

In the above, the air-fuel ratio is actually obtained by the equivalence ratio, but this is exactly the same as using the air-fuel ratio itself.

Further, although the feedback correction coefficients KSTR or KLAF are obtained as the multiplication value in the above, they may be obtained as the addition value.

Also, in the above, ST is used as an adaptive controller.
Although R has been described as an example, MRACS (model reference adaptive control) may be used.

[0269]

According to the first aspect of the present invention, the target value of the air-fuel ratio feedback is corrected according to the behavior of the air-fuel ratio downstream of the catalyst while dynamically compensating for the fuel transportation delay. The air-fuel ratio required by can be matched with high accuracy.

According to the second aspect of the present invention, when a large-capacity catalyst device having multiple catalyst beds is used, the second air-fuel ratio detection is performed at a position where the detection accuracy of the second air-fuel ratio detection means becomes optimum. By installing the means, the target air-fuel ratio can be corrected with higher accuracy, the air-fuel ratio before the catalyst device can be controlled with higher accuracy, and the purification rate of the catalyst device can be further improved.

According to the third aspect, the calculation accuracy of the basic fuel injection amount corrected by the feedback correction coefficient can be further improved, the load of the feedback system is reduced, and the responsiveness is not impaired. Improves stability.

[Brief description of drawings]

FIG. 1 is a schematic diagram generally showing a fuel injection control device for an internal combustion engine according to the present application.

FIG. 2 is an explanatory diagram showing details of an exhaust gas recirculation mechanism in FIG.

FIG. 3 is an explanatory diagram showing details of a canister purging mechanism in FIG.

FIG. 4 is an explanatory diagram showing valve timing characteristics of the variable valve timing mechanism in FIG.

5 is an explanatory diagram showing an arrangement configuration of a first catalyst device and an O ₂ sensor in FIG. 1. FIG.

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

FIG. 7 is an explanatory diagram showing an output of the O ₂ sensor in FIG.

FIG. 8 is a functional block diagram showing an operation of a fuel injection control device for an internal combustion engine according to the present application.

9 is a flow chart showing a work of calculating a basic fuel injection amount TiM-F in the block diagram of FIG.

FIG. 10 is a basic fuel injection amount TiM in the flow chart of FIG.
It is a block diagram explaining the calculation work of -F.

FIG. 11 is a block diagram showing a method of calculating an effective opening area of a throttle valve by using a flow coefficient and the like.

12 is an explanatory diagram showing map characteristics of coefficients used in the calculation of FIG.

13 is an explanatory diagram showing map characteristics of a fuel injection amount Timap in a steady operation state used in the flow chart of FIG. 9 and the block diagram of FIG. 10.

14 is an explanatory diagram showing a map characteristic of a target air-fuel ratio used in the flow chart of FIG. 9 and the block diagram of FIG. 10, more specifically, a basic value thereof.

FIG. 15 is a data diagram showing a simulation result of the effective opening area of the throttle in the calculation work of the basic fuel injection amount TiM-F in the flow chart of FIG. 9 and the block diagram of FIG. 10.

16 is an explanatory diagram showing a steady operating state and a transient operating state in the work of calculating the basic fuel injection amount TiM-F in the flow chart of FIG. 9 and the block diagram of FIG. 10.

17 is an explanatory diagram showing the relationship between the throttle opening and the effective opening area of the throttle in the work of calculating the basic fuel injection amount TiM-F in the flow chart of FIG. 9 and the block diagram of FIG. 10.

FIG. 18 is a basic fuel injection amount TiM in the flowchart of FIG.
It is a block diagram explaining the example of correction of the calculation work of -F.

19 is a flow chart showing an exhaust recirculation rate estimation operation in calculating an EGR correction coefficient in the block diagram of FIG.

20 is an explanatory diagram showing a basic algorithm for estimating the exhaust gas recirculation rate, and is an explanatory diagram showing characteristics of the gas amount with respect to the lift amount of the exhaust gas recirculation rate used in the calculation of the flow chart of FIG.

FIG. 21 is an explanatory diagram showing a delay of an actual lift and a recirculation gas with respect to a lift command value of an exhaust gas recirculation valve.

22 is an explanatory diagram showing a map characteristic of an exhaust gas recirculation ratio correction coefficient (basic exhaust gas recirculation ratio correction coefficient) in a steady state used in the calculation of the flow chart of FIG.

23 is an explanatory diagram showing a map characteristic of a lift command value used in the calculation of the flow chart of FIG.

24 is a subroutine flow chart showing the operation of calculating the fuel injection correction coefficient in the flow chart of FIG.

25 is an explanatory diagram showing a configuration of a ring buffer used in the work of the flow chart of FIG. 24. FIG.

FIG. 26 is an explanatory diagram showing map characteristics of dead time τ used in the work of the flow chart of FIG.

FIG. 27 is a timing chart illustrating the operation of the flow chart of FIG. 24.

FIG. 28 is a flow chart showing the operation of calculating the canister purge correction coefficient in the block diagram of FIG.

FIG. 29 is a flow chart showing the operation of calculating the target air-fuel ratio and the air-fuel ratio correction coefficient in the block diagram of FIG.

FIG. 30 is a correction coefficient KE in the flow chart of FIG. 29.
It is explanatory drawing which shows the characteristic of TC.

FIG. 31 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 part.

FIG. 32 is an explanatory diagram showing quality of sample timing with respect to an actual air-fuel ratio.

FIG. 33 is a flow chart showing the sampling operation of the detected air-fuel ratio in the Sel-V block of the block diagram of FIG. 8.

34 is a block diagram showing one example of the observer of the block diagram of FIG. 8 and modeling the detection operation of the LAF sensor described in the previous application. FIG.

35 is a model in which the model shown in FIG. 34 is discretized with a period ΔT.

FIG. 36 is a block diagram showing a true air-fuel ratio estimator that models the detection behavior of the air-fuel ratio sensor.

FIG. 37 is a block diagram showing a model showing the behavior of the exhaust system of the internal combustion engine.

FIG. 38 is a data diagram showing a case where fuel is supplied using the model shown in FIG. 37 with an air-fuel ratio of 3 cylinders of 14.7 and an air-fuel ratio of 1 cylinder of 12.0 in a 4-cylinder internal combustion engine. .

39 is a data diagram showing the air-fuel ratio of the collecting portion of the model of FIG. 37 when the input shown in FIG. 38 is given.

FIG. 40 compares the data showing the air-fuel ratio of the collecting portion of the model of FIG. 37 in consideration of the response delay of the LAF sensor with the input shown in FIG. 38 with the measured value of the LAF sensor output in the same case. It is a data diagram.

FIG. 41 is a block diagram showing a configuration of a general observer.

42 is a block diagram showing a configuration of an observer used in the previous application, which is the observer shown in the block diagram of FIG. 8. FIG.

43 is an explanatory block diagram showing a configuration in which the model shown in FIG. 37 and the observer shown in FIG. 42 are combined.

44 is a block diagram showing feedback control of the air-fuel ratio in the block diagram of FIG. 8.

45 is an explanatory diagram showing characteristics of a timing map used in the flow chart of FIG. 33.

FIG. 46 is an explanatory diagram showing sensor output characteristics with respect to engine speed and engine load, for explaining the characteristics of FIG. 45.

FIG. 47 is a timing chart explaining the sampling operation in the flow chart of FIG. 33.

FIG. 48 is a timing chart showing an air-fuel ratio detection delay when fuel supply is restarted from fuel cut.

49 is a flow chart showing the operation of calculating the feedback correction coefficient in the block diagram of FIG.

50 is a block diagram functionally showing the operation of the flow chart of FIG. 49. FIG.

FIG. 51 is a subroutine flow chart showing a more specific calculation operation of the feedback correction coefficient in the flow chart of FIG. 49.

52 is a similar subroutine flow chart showing a more specific calculation operation of the feedback correction coefficient in the flow chart of FIG. 51. FIG.

FIG. 53 is a timing chart explaining a part of the operation of the flow chart of FIG. 51.

FIG. 54 is a subroutine flow chart of the correction of the adhering amount of the output fuel injection amount on the wall surface of the intake pipe in the flow chart of FIG. 49.

FIG. 55 is an explanatory diagram showing map characteristics such as a direct rate used for the calculation of the flow chart of FIG. 54;

FIG. 56 is an explanatory diagram showing table characteristics of correction coefficients used in the calculation of the flow chart of FIG. 54.

FIG. 57 is a subroutine flow chart showing the calculation work of TWP (n) in the flow chart of FIG. 54.

FIG. 58 is a block diagram showing the configuration of another embodiment of a fuel injection control device for an internal combustion engine according to the present invention.

[Explanation of symbols]

10 Internal Combustion Engine 12 Intake Pipe 20 Intake Manifold 22 Injector 24 Exhaust Manifold 26 Exhaust Pipe 28 First Catalyst Device 30 Second Catalyst Device 34 Control Unit 54 Wide Range Air-Fuel Ratio Sensor (LAF Sensor) 56 O ₂ Sensor 92 Filter 93 Filter 94 Third catalyst device 96 Filter 98 Second O ₂ sensor 100 Exhaust gas recirculation mechanism 200 Canister purge mechanism 300 Variable valve timing mechanism 500 Filter

Front page continuation (72) Inventor Isao Komoritani 4-1-1 Chuo, Wako-shi, Saitama Stock Research Institute Honda Technical Research Institute (72) Inventor Yoichi Nishimura 1-1-4 Chuo, Wako-shi, Saitama Stock Association Incorporated Honda Research Laboratory (72) Inventor Toshiaki Hirota 1-4-1 Chuo, Wako City, Saitama Stock Company Incorporated Honda Research Laboratory

Claims (3)

[Claims] 1. A. Air-fuel ratio detection means, which is provided in an exhaust system of the internal combustion engine and detects an air-fuel ratio of exhaust gas discharged from the internal combustion engine; b. Air-fuel ratio correction that calculates an air-fuel ratio correction coefficient that corrects the fuel injection amount supplied to the internal combustion engine so that the air-fuel ratio of the internal combustion engine converges to the target air-fuel ratio from the detected air-fuel ratio detected by the air-fuel ratio detection means. Coefficient calculating means, c. Fuel injection amount correction means for correcting the fuel injection amount supplied to the internal combustion engine by the air-fuel ratio correction coefficient; d. Fuel transportation delay correction fuel injection amount calculation means for calculating a fuel transportation delay correction fuel injection amount based on the transportation delay of the injected fuel with respect to the corrected fuel injection amount, and e. Fuel injection amount determination means for determining a fuel injection amount to be supplied to the internal combustion engine based on the calculated fuel transportation delay correction fuel injection amount, and f. A catalyst device provided downstream of the air-fuel ratio detecting means in the exhaust system of the internal combustion engine; g. Second air-fuel ratio detection means, which is provided downstream of the catalyst device in the exhaust system of the internal combustion engine, for detecting the air-fuel ratio of the exhaust gas discharged by the internal combustion engine; and h. A fuel injection control device for an internal combustion engine, comprising: a target air-fuel ratio correction unit that corrects the target air-fuel ratio from the detected air-fuel ratio detected by the second air-fuel ratio detection unit. 2. The catalyst device has a multi-stage catalyst bed, and the second air-fuel ratio detecting means is arranged between the multi-stage catalyst beds.
A fuel injection control device for an internal combustion engine according to the above item. 3. The fuel injection amount correcting means includes means for correcting the intake air amount based on the effective opening area of a throttle valve provided in the intake pipe. A fuel injection control device for an internal combustion engine according to the above item.