JPH08232728A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To prevent worsening of controllability of an air-fuel ratio even when the characteristics of the air-fuel ratio sensor of an air-fuel ratio feedback device by cylinders are deteriorated, by a method wherein an air-fuel ratio for each cylinder is estimated based on the air-fuel ratio of an exhaust system assembly. CONSTITUTION: Deterioration of the characteristics of an LAF sensor 17 is decided at S401. When deterioration of response characteristics is detected, the selection timing of the output of the LAF sensor is varied at S404. When lean deterioration through which displacement of an output on the lean side is increased to a value higher than a theoretical air-fuel ratio by a given value is detected, air-fuel ratio feedback control by cylinders through which other air-fuel ratio than the theoretical air-fuel ratio is set to a target air-fuel ratio is stopped at S407. Further, when stoichiometric deterioration due to which output displacement in the vicinity of the theoretical air-fuel ratio is increased to a value higher than a given value is detected, air-fuel ratio control by cylinders is stopped at S406.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly to an air-fuel ratio feedback control for each cylinder by feedback control applying an observer based on modern control theory. The present invention relates to a fuel ratio control device.

[0002]

2. Description of the Related Art An observer for estimating the air-fuel ratio of each cylinder based on the output of an air-fuel ratio sensor provided in the exhaust system collecting portion of an internal combustion engine and generating an output proportional to the air-fuel ratio is introduced and the estimated cylinder BACKGROUND ART An air-fuel ratio control device that performs feedback control of an air-fuel ratio so as to eliminate variations in air-fuel ratio among cylinders according to another air-fuel ratio has been conventionally known (Japanese Patent Laid-Open No. 5-180040).

[0003]

However, the above-mentioned conventional control device does not take into consideration the deterioration of the characteristics of the air-fuel ratio sensor due to aging or the like. In some cases, the deviation between the estimated value of the cylinder-by-cylinder air-fuel ratio by the observer and the actual air-fuel ratio becomes large, and the feedback control using the estimated value may rather deteriorate the exhaust gas characteristics.

The present invention has been made in order to solve this problem, and provides an air-fuel ratio control device capable of preventing the controllability of the air-fuel ratio from deteriorating even when the characteristics of the air-fuel ratio sensor deteriorate. The purpose is to

[0005]

To achieve the above object, the present invention is based on an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine and an internal state thereof based on a model describing the behavior of the exhaust system of the engine. An observer for observing the air-fuel ratio, and an air-fuel ratio estimating means for each cylinder for estimating the air-fuel ratio of each cylinder by using the output of the air-fuel ratio sensor as an input, and for making the estimated air-fuel ratio of each cylinder converge to a target value. In an air-fuel ratio control device for an internal combustion engine, comprising: a cylinder-by-cylinder feedback control means for feedback-controlling an air-fuel ratio of an air-fuel mixture supplied to each of the cylinders; an engine operating state detecting means for detecting an operating state of the engine; Sampling means for sampling the output of the air-fuel ratio sensor for each predetermined crank angle rotation, and storing the sampled values in sequence, and the operating state of the engine. Then, selecting means for selecting one of the stored sample values, response deterioration detecting means for detecting deterioration of response characteristics of the air-fuel ratio sensor, and deterioration of response characteristics of the air-fuel ratio sensor are detected, Sample value changing means for changing the sample value selected by the selecting means to one sampled at a later timing, and the cylinder-by-cylinder feedback control means uses the changed sample value for the feedback control. It was done.

The present invention further sets an air-fuel ratio sensor provided in the exhaust system of an internal combustion engine and an observer for observing the internal state of the engine based on a model describing the behavior of the exhaust system of the engine. Cylinder air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder by using the output of the fuel ratio sensor as input, and the air-fuel ratio of the air-fuel mixture supplied to each cylinder so that the estimated air-fuel ratio of each cylinder converges to a target value. In an air-fuel ratio control device for an internal combustion engine, comprising: a cylinder-by-cylinder feedback control means for feedback controlling A detecting means and a prohibiting means for prohibiting the operation of the cylinder-by-cylinder feedback control means when the stoichiometric deterioration is detected are provided.

Furthermore, the present invention is based on an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine and capable of detecting at least an air-fuel ratio leaner than a stoichiometric air-fuel ratio, and a model describing the behavior of the exhaust system of the engine. An observer for observing the internal state is set, and the cylinder-by-cylinder air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder by using the output of the air-fuel ratio sensor as an input, and the estimated air-fuel ratio of each cylinder are converged to a target value. In the air-fuel ratio control device for an internal combustion engine, which comprises a cylinder-by-cylinder feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to each of the cylinders, in the lean-side air-fuel ratio from the theoretical air-fuel ratio of the air-fuel ratio sensor Lean deterioration detection means for detecting lean deterioration in which the corresponding output deviation is greater than or equal to a predetermined value is provided, and the cylinder-by-cylinder feedback control means detects the lean deterioration. It is obtained by the air-fuel ratio of the near stoichiometric air-fuel ratio to execute the feedback control of the target air-fuel ratio.

Further, the present invention sets an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine and an observer for observing an internal state of the engine based on a model describing the behavior of the exhaust system of the engine. A cylinder-by-cylinder air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder by using the output of the fuel ratio sensor as input, and at least one of a proportional term, an integral term and a differential term calculated according to the estimated air-fuel ratio of each cylinder. An air-fuel ratio control apparatus for an internal combustion engine, comprising: feedback control means for each cylinder for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to each cylinder so that the estimated air-fuel ratio of each cylinder converges to a target value. In the above, the response deterioration detecting means for detecting the deterioration of the response characteristic of the air-fuel ratio sensor is provided, and when the cylinder-by-cylinder feedback control means detects the response deterioration, the proportional term, the integral term, and the integral term. And changing at least one of the differential term to a smaller value is obtained so as to perform a feedback control.

[0009]

According to the air-fuel ratio control device of the first aspect, when the deterioration of the response characteristic of the air-fuel ratio sensor is detected, the cylinder-by-cylinder air-fuel ratio feedback control is performed using the output of the air-fuel ratio sensor sampled at a later timing. Is executed.

According to the air-fuel ratio control device of claim 2,
When the stoichiometric deterioration of the air-fuel ratio sensor is detected, the cylinder-by-cylinder air-fuel ratio feedback control is prohibited.

According to the air-fuel ratio control device of the third aspect,
When lean deterioration of the air-fuel ratio sensor is detected, feedback control is executed in which the target air-fuel ratio is an air-fuel ratio near the stoichiometric air-fuel ratio.

According to the air-fuel ratio control device of the fourth aspect,
When the cylinder-by-cylinder air-fuel ratio feedback control is performed using at least one of the proportional term, the integral term, and the derivative term, and when deterioration of the response characteristic of the air-fuel ratio sensor is detected, at least one of the proportional term, the integral term, and the derivative term is performed. Feedback control is performed by changing one to a smaller value.

[0013]

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

FIG. 1 is a diagram showing a configuration of an internal combustion engine (hereinafter referred to as "engine") and a control system therefor according to one embodiment of the present invention. In the figure, reference numeral 1 is a DOHC in-line 4-cylinder engine in which each cylinder is provided with a pair of intake valves and exhaust valves (not shown).

The intake pipe 2 of the engine 1 communicates with a combustion chamber of each cylinder of the engine 1 through a branch portion (intake manifold) 11. A throttle valve 3 is arranged in the middle of the intake pipe 2. Throttle valve opening (θTH) for throttle valve 3
The sensor 4 is connected, and outputs an electric signal according to the throttle valve opening θTH to supply it to an electronic control unit (hereinafter referred to as “ECU”) 5. The intake pipe 2 is provided with an auxiliary air passage 6 that bypasses the throttle valve 3, and an auxiliary air amount control valve 7 is provided in the middle of the passage 6.
Is arranged. The auxiliary air amount control valve 7 is connected to the ECU 5, and the ECU 5 controls the valve opening amount.

An intake air temperature (TA) sensor 8 is mounted on the upstream side of the throttle valve 3 of the intake pipe 2, and its detection signal is supplied to the ECU 5. A chamber 9 is provided between the throttle valve 3 of the intake pipe 2 and the intake manifold 11, and an absolute intake pipe absolute pressure (PBA) sensor 10 is attached to the chamber 9. The detection signal of the PBA sensor 10 is supplied to the ECU 5.

The engine water temperature (T
W) The sensor 13 is attached and its detection signal is EC
Supplied to U5. A crank angle position sensor 14 that detects a rotation angle of a crank shaft (not shown) of the engine 1 is connected to the ECU 5, and a signal corresponding to the rotation angle of the crank shaft is supplied to the ECU 5. The crank angle position sensor 14 is a cylinder discrimination sensor that outputs a signal pulse (hereinafter referred to as “CYL signal pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1, a top dead center (TDC) at the start of the intake stroke of each cylinder. ) At a crank angle position before a predetermined crank angle (in a 4-cylinder engine, the crank angle is 18
One pulse (hereinafter "CRK signal pulse") at a constant crank angle cycle (for example, 30 degree cycle) shorter than the TDC sensor and TDC signal pulse that outputs a TDC signal pulse (every 0 degrees)
CRYSENSOR, which generates a CYL signal pulse, a TDC signal pulse and a CRK signal pulse.
Supplied to U5. These signal pulses are used for various timing controls such as fuel injection timing and ignition timing, and for detecting the engine speed NE.

A fuel injection valve 12 is provided for each cylinder slightly upstream of the intake valve of the intake manifold 11, and each injection valve is connected to a fuel pump (not shown) and electrically connected to the ECU 5. Then, the fuel injection timing and the fuel injection time (valve opening time) are controlled by the signal from the ECU 5. The spark plug (not shown) of the engine 1 is also EC
It is electrically connected to U5, and the ignition timing θIG is controlled by the ECU 5.

The exhaust pipe 16 is a branch portion (exhaust manifold) 1
It is connected to the combustion chamber of the engine 1 via 5. In the exhaust pipe 16, immediately downstream of the portion where the branch portions 15 gather,
Wide-range air-fuel ratio sensor (hereinafter referred to as "LAF sensor") 17
Is provided. Further, an immediately below three-way catalyst 19 and an underfloor three-way catalyst 20 are arranged on the downstream side of the LAF sensor 17, and an oxygen concentration sensor (hereinafter referred to as "O2 sensor") is provided between these three-way catalysts 19 and 20. 18 is attached. The three-way catalysts 19 and 20 are HC and C in the exhaust gas.
Purifies O, NOx, etc.

The LAF sensor 17 includes a low pass filter 2
It is connected to the ECU 5 via 2 and outputs an electric signal substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas and supplies the electric signal to the ECU 5. The O2 sensor 18 has a characteristic that its output changes rapidly before and after the stoichiometric air-fuel ratio, and its output has a high level on the rich side and a low level on the lean side of the stoichiometric air-fuel ratio. O2 sensor 18
Is connected to the ECU 5 via the low-pass filter 23, and the detection signal thereof is supplied to the ECU 5.

The exhaust gas recirculation mechanism 30 is provided in the exhaust gas recirculation passage 31 that connects the chamber 9 of the intake pipe 2 and the exhaust gas pipe 16, and an exhaust gas recirculation valve 31 that controls the amount of exhaust gas recirculation (EGR). Valve 32 and a lift sensor 33 that detects the valve opening of the EGR valve 32 and supplies a detection signal to the ECU 5. The EGR valve 32 is a solenoid valve having a solenoid, and the solenoid is connected to the ECU 5, and the valve opening degree thereof can be linearly changed by a control signal from the ECU 5.

Next, the evaporative fuel treatment device 40 will be described with reference to FIG. The fuel tank 41 is the passage 4
2 to the canister 45, and the canister 45 communicates with the chamber 9 of the intake pipe 2 via the purge passage 43. The canister 45 contains an adsorbent 46 that adsorbs the evaporated fuel generated in the fuel tank 41, and has an outside air intake port 47. A two-way valve 44 composed of a positive pressure valve and a negative pressure valve is arranged in the middle of the passage 42, and a purge control valve 48 and a purge passage 43 which are duty control type electromagnetic valves flow in the middle of the purge passage 43. A flow rate sensor 49 for detecting the flow rate of the air-fuel mixture containing fuel vapor and an HC concentration sensor 50 for detecting the HC concentration in the air-fuel mixture are provided. The purge control valve 48 and the sensors 49, 50 are
The purge control valve 48 is connected to the ECU 5 and is connected to the ECU.
The detection signals of the sensors 49 and 50 are supplied to the ECU 5 by being controlled according to the signal from the ECU 5.

According to the evaporated fuel processing device 40, when the evaporated fuel generated in the fuel tank 41 reaches a predetermined set pressure, the positive pressure valve of the two-way valve 44 is opened to flow into the canister 45 and the canister 45. It is adsorbed and stored by the adsorbent 46 inside. The purge control valve 48 is the ECU 5
The valve is opened / closed by the duty signal from the fuel vapor, and the vaporized fuel temporarily stored in the canister 45 during the valve opening time is sucked from the outside air intake port 47 of the canister 45 due to the negative pressure of the chamber 9. It is sucked into the chamber 9 through the purge control valve 48 together with the outside air and sent to each cylinder. Further, when the fuel tank 41 is cooled by the outside air and the negative pressure in the fuel tank increases, the negative pressure valve of the two-way valve 44 opens, and the evaporated fuel temporarily stored in the canister 45 is transferred to the fuel tank 41. Will be returned. In this way, it is possible to prevent the fuel vapor generated in the fuel tank 41 from being released to the atmosphere.

The engine 1 is capable of switching the valve timings of the intake valve and the exhaust valve in two stages, a high speed valve timing suitable for a high speed rotation region of the engine and a low speed valve timing suitable for a low speed rotation region of the engine. It has a mechanism 60. This switching of the valve timing includes switching of the valve lift amount. Further, when the low speed valve timing is selected, one of the two intake valves is deactivated to stabilize the air-fuel ratio leaner than the stoichiometric air-fuel ratio. I try to ensure the burning.

The valve timing switching mechanism 60 switches the valve timing via hydraulic pressure, and the solenoid valve and hydraulic sensor for switching the hydraulic pressure are connected to the ECU 5. The detection signal of the hydraulic pressure sensor is supplied to the ECU 5, and the ECU 5 controls the solenoid valve to control the switching of the valve timing.

Further, an atmospheric pressure (PA) sensor 21 for detecting the atmospheric pressure is connected to the ECU 5, and the detection signal is supplied to the ECU 5.

The ECU 5 shapes the input signal waveforms from the various sensors described above, corrects the voltage level to a predetermined level, changes an analog signal value to a digital signal value, and the like, and a central processing circuit. (CPU), various arithmetic programs executed by the CPU, storage circuits including ROM and RAM for storing various maps and arithmetic results to be described later, drive signals for various solenoid valves such as the fuel injection valve 12 and ignition plugs. And an output circuit for outputting.

The ECU 5 determines various engine operating states such as a feedback control operating region and an open control operating region according to the outputs of the LAF sensor 17 and the O2 sensor 18 based on the various engine operating parameter signals described above. According to the engine operating state, the fuel injection time TOUT of the fuel injection valve 12 is calculated by the following formula 1,
A signal for driving the fuel injection valve 12 is output based on the calculation result.

[0029]

[Formula 1] TOUT (N) = TIMF × KTOTAL × K
CMDM × KLAF × KOBSV # N FIG. 3 is a functional block diagram for explaining the calculation method of the fuel injection time TOUT (N) according to the above-mentioned mathematical expression 1, and the fuel injection time TOUT in the present embodiment with reference to this.
The outline of the calculation method of (N) will be described. Here, N represents a cylinder number, and the parameter with this is calculated for each cylinder. In the present embodiment, the fuel supply amount to the engine is calculated as the fuel injection time. Since this corresponds to the injected fuel amount, TOUT is also called the fuel injection amount or the fuel amount.

In FIG. 3, block B1 calculates the basic fuel amount TIMF corresponding to the intake air amount. The basic fuel amount TIMF is basically set according to the engine speed NE and the absolute pressure PBA in the intake pipe, but the intake system from the throttle valve 3 to the combustion chamber of the engine 1 is modeled, and the intake system model It is desirable to make a correction considering the delay of the intake air based on the above. In that case, the throttle valve opening θTH and the atmospheric pressure PA are detected parameters.
Is further used.

Blocks B2 to B8 are multiplication blocks, which multiply the input parameters of the block and output it. The calculation of Equation 1 is performed by these blocks, and the fuel injection amount T for each cylinder is output as the output of blocks B5 to B8.
OUT (N) is obtained.

Block B9 is an engine water temperature correction coefficient KTW set according to the engine water temperature TW, and an EGR correction coefficient K set according to the exhaust gas recirculation amount during execution of exhaust gas recirculation.
A purge correction coefficient KPUG set according to the amount of purged fuel when the EGR / evaporated fuel processing device 40 executes the purge.
The correction coefficient KTOTAL is calculated by multiplying all the feedforward system correction coefficients such as
Enter 2.

Block B21 is the engine speed NE,
Target air-fuel ratio coefficient KCM according to the intake pipe absolute pressure PBA, etc.
D is determined and input to block B22. The target air-fuel ratio coefficient KCMD is the reciprocal of the air-fuel ratio A / F, that is, the fuel-air ratio F
Since it is proportional to / A and takes a value of 1.0 at the theoretical air-fuel ratio,
Also called the target equivalence ratio. The block B22 corrects the target air-fuel ratio coefficient KCMD based on the O2 sensor output VMO2 input through the low pass filter 23, and the block B22
18 and B23. Block B23 is KCM
The fuel cooling correction is performed according to the D value, and the final target air-fuel ratio coefficient K
Calculate CMDM and enter in block B3.

The block B10 is a low-pass filter 22.
The LAF sensor output value that is input via is sampled each time a CRK signal pulse is generated, the sample value is sequentially stored in the ring buffer memory, and the sample value sampled at the optimum timing is selected according to the engine operating state. (LAF sensor output selection process), block B1
1 and the low-pass filter block B16 and input to the block B18. This LAF sensor output selection processing cannot accurately detect the air-fuel ratio that changes depending on the sampling timing, and the time until the exhaust gas discharged from the combustion chamber reaches the LAF sensor 17 and LA
This is because the reaction time of the F sensor itself changes depending on the engine operating state.

Block B18 is a PID correction coefficient K by PID control according to the deviation between the detected air-fuel ratio and the target air-fuel ratio.
The LAF is calculated and input to the block B20.

The block B11 has a function as a so-called observer, and is a collecting unit (mixed gas of exhaust gas discharged from each cylinder) detected by the LAF sensor 17.
The air-fuel ratio of each cylinder is estimated on the basis of the air-fuel ratio of the above, and is input to the blocks B12 to B15 corresponding to the four cylinders. In FIG. 3, block B12 corresponds to cylinder # 1, block B13 corresponds to cylinder # 2, and block B1
4 corresponds to cylinder # 3, and block B15 corresponds to cylinder # 4. In blocks B12 to B15, the cylinder-by-cylinder correction coefficient KOBSV # N (N = 1 to 4) is set by PID control so that the air-fuel ratio of each cylinder (the air-fuel ratio estimated by the observer block B12) matches the collective air-fuel ratio. It is calculated and input to blocks B5 to B8, respectively.

As described above, in this embodiment, P calculated by the normal PID control according to the output of the LAF sensor 17 is used.
The ID correction coefficient KLAF is applied to the above equation 1, and the cylinder-by-cylinder correction coefficient KOBSV # N set according to the air-fuel ratio of each cylinder estimated based on the LAF sensor output is further applied to the above equation 1 Fuel injection amount TO for each
UT (N) is calculated. Cylinder correction coefficient KOBSV #
By using N, the variation in the air-fuel ratio among the cylinders can be eliminated, the purification rate of the catalyst can be improved, and good exhaust gas characteristics can be obtained in various engine operating conditions.

In the present embodiment, the function of each block in FIG. 3 described above is realized by the arithmetic processing by the CPU of the ECU 5, and therefore the contents of the processing will be specifically described with reference to the flowchart of this processing.

FIG. 4 shows the PID correction coefficient KLAF and the cylinder-specific correction coefficient KOBSV according to the output of the LAF sensor 17.
9 is a flowchart of a process of calculating #N. This process is executed every time a TDC signal pulse is generated.

In step S1, it is determined whether or not the engine is in the starting mode, that is, whether or not the cranking is being performed. If the starting mode is selected, the process proceeds to the starting mode. If it is not the start mode, calculation of the target air-fuel ratio coefficient (target equivalent ratio) KCMD and the final target air-fuel ratio coefficient KCMDM (step S2) and L
The AF sensor output selection process is performed (step S3), and the detected equivalent ratio KACT is calculated (step S4).
The detected equivalence ratio KACT is obtained by converting the output of the LAF sensor 17 into an equivalence ratio.

Next, it is determined whether the LAF sensor 17 has been activated (step S5). this is,
For example, the difference between the output voltage of the LAF sensor 17 and its center voltage is compared with a predetermined value (for example, 0.4 V), and when the difference is smaller than the predetermined value, it is determined that the activation is completed.

Next, the engine operating state indicates the LAF sensor 17
It is determined whether or not it is in the operation region (hereinafter, referred to as "LAF feedback region") in which the feedback control is executed based on the output (step S6). This is for example L
When the activation of the AF sensor 17 is completed and the fuel cut or the throttle fully open operation is not being performed, it is determined to be the LAF feedback region. As a result of this determination, L
Reset flag F when not in AF feedback area
KLAFRESET is set to "1" and set to "0" when in the LAF feedback area.

In the following step S7, the reset flag F
It is determined whether KLAFRESET is "1", and FKLA
When FRESET = 1, the process proceeds to step S8 and PI
D correction coefficient KLAF is "1.0", cylinder-specific correction coefficient KO
The cylinder-by-cylinder correction coefficient learning value KOBSV described below is used for BSV # N.
#Nsty and the integral term K of PID control
The LAFI is set to "0", and this processing ends. By setting the cylinder-by-cylinder correction coefficient KOBSV # N to the cylinder-by-cylinder correction coefficient learning value KOBSV # Nsty, misfire of the internal combustion engine due to a change in the fuel supply state due to secular change or the like during feedforward control or engine rotation The stability of the organization against fluctuations can be secured.

When FKLAFRESET = 0, the cylinder-specific correction coefficient KOBSV # N and the PID correction coefficient KLAF are calculated (steps S9 and S10), and this processing ends.

FIG. 5 is a flowchart of the process for calculating the final target air-fuel ratio coefficient KCMDM in step S2 of FIG.

In step S23, the engine speed NE
And a map is searched according to the intake pipe absolute pressure PBA to calculate a basic value KBS. The value for idle time is also set in the map.

In a succeeding step S24, it is determined whether or not a condition for executing the lean burn control immediately after the engine is started is satisfied, and when the condition is satisfied, the post-start lean flag FASTLEAN is set to "1". When the condition is not satisfied, it is set to "0". The lean burn control execution condition is, for example, within a predetermined period after the engine is started, the engine water temperature TW, the engine speed NE, and the intake pipe absolute pressure P.
It is established when BA is within a predetermined range. The lean burn control immediately after the start is performed for the purpose of preventing an increase in the amount of discharged HC while the catalyst is inactive immediately after the engine is started.

Next, at step S25, it is determined whether or not the throttle valve is in the fully open (WOT) state. When the throttle valve is fully opened, the WOT flag FWOT is set to "1", and when not fully opened, it is set to "0". Next, the increase correction coefficient KWOT is calculated according to the engine water temperature TW (step S26). At this time, the correction coefficient KXWOT at high water temperature is also calculated.

In the following step S27, the target air-fuel ratio coefficient KCMD is calculated, and then the calculated KCMD value is limited (processing to bring it within a predetermined upper and lower limit range).
Is performed (step S28). The process of step S27 will be described later with reference to FIG.

In the following step S29, the O2 sensor 18
The activation flag FMO2 is set to "1" when the activation is completed, and is set to "0" when the activation is not completed. For example, when a predetermined period of time has passed after the engine was started, it is determined that the activation is completed. Next, in step S32, the output V of the O2 sensor 18
The correction term DKC of the target air-fuel ratio coefficient KCMD according to MO2
Calculate MDO2. This process is performed by the O2 sensor output VM
The correction term DKCMDO2 is calculated by PID control according to the deviation between O2 and the reference value VREFM, which will be described later with reference to FIG.

In the following step S33, the target air-fuel ratio coefficient KCMD is corrected by the following equation.

KCMD = KCMD + DKCMDO2 As a result, the target air-fuel ratio coefficient KCMD can be set so as to compensate for the deviation of the output of the LAF sensor 17.

In the following step S34, the calculated KCM
The KCMD-KETC table is searched according to the D value to calculate the correction coefficient KETC, and the final target air-fuel ratio coefficient KCMDM is calculated by the following equation.

KCMDM = KCMD × KETC The correction coefficient KETC is to correct the effect in consideration that the fuel cooling effect by injection increases as the KCMD value increases and the fuel injection amount increases. KC
It is set to a larger value as the MD value increases.

Next, while limiting the KCMDM value (step S35), the KCMD value obtained in step S33 is stored in the ring buffer (step S36), and this processing ends.

FIG. 6 shows K in step S27 of FIG.
It is a flow chart of CMD calculation processing.

First, at step S51, the post-start lean flag FASTLEAN set at step S24 of FIG.
Is FASTLEAN = 1, and when FASTLEAN = 1, the KCMDASTLEAN map is searched and the lean target value KCM corresponding to the center air-fuel ratio during lean control is searched.
DASTLEAN is calculated (step S52). Here, KCMDASTLEAN map is the engine water temperature T
A lean target value KC according to W and the absolute pressure PBA in the intake pipe
It is a map in which MDASTLEAN is set. Then, the target air-fuel ratio coefficient KCMD is set to the lean target value KCMDA.
It is set to STLEAN (step S53) and the process proceeds to step S61.

On the other hand, in step S51, FASTLAE
When AN = 0 and the lean burn control execution condition is not satisfied after the start, the engine water temperature TW is the predetermined water temperature TWC.
It is determined whether the temperature is higher than MD (for example, 80 ° C.). When TW> TWCMD is established, the KCMD value is set to the basic value KBS calculated in step S23 of FIG. 5 (step S57), and the process proceeds to step S61. Also, T
When W ≦ TWCMD is established, the map set according to the engine water temperature TW and the intake pipe absolute pressure PBA is searched to calculate the low water temperature target value KTWCMD (step S55), and the basic value KBS is the KTWCMD. It is determined whether or not the value is larger than the value (step S56). As a result K
If BS> KTWCMD, the above step S57.
And if KBS ≤ KTWCMD, the basic value K
The BS is replaced with the low water temperature target value KTWCMD (step S58), and the process proceeds to step S61.

In step S61, KCM is calculated by the following equation.
The D value is corrected and the process proceeds to step S62. Adjustment addition term K
CMDOFFSET is to finely adjust the target air-fuel ratio coefficient KCMD to reflect the influence of variations in the characteristics of the engine exhaust system and LAF sensor and changes over time, and to take the optimum position of the window zone of the three-way catalyst. Parameter and is calculated in the process of FIG. 7 described later.

KCMD = KCMD + KCMDOFFSET In step S62, it is determined whether or not the WOT flag FWOT set in step S25 of FIG. 5 is “1”, and FWO
If T = 0, this process is immediately terminated, and if FWOT = 1, a KCMD value setting process for high load is performed (step S63), and this process is terminated. This process is based on KCM
The D value is compared with the high load amount increase correction coefficients KWOT and KXWOT calculated in step S26 of FIG. 5, and when the KCMD value is smaller than these coefficient values, the KCMD value is multiplied by the correction coefficient KWOT or KXWOT to perform the correction. It is something to do.

FIG. 7 is a flowchart of the calculation process of the correction term DKCMDO2 executed in step S32 of FIG.

First, in step S161, it is determined whether the thinning-out variable NIVRM is "0". This decimation variable NIVRM is a variable that is decremented by the decimation TDC number NIM set according to the engine operating state every time a TDC signal pulse is generated, as will be described later, and is initially "0", so step The answer to S61 is affirmative (YES).
Then, the process proceeds to step S162.

In the subsequent loop, step S161
When the answer is negative (NO), the process proceeds to step S170.

In step S162, the KVPM map,
The KVIM map, the KVDM map, and the NIVRM map are searched to change the rate of feedback control based on the output of the O2 sensor 18, that is, the proportional term (P term) coefficient K.
VPM, integral term (I term) coefficient KVIM, differential term (D term)
The coefficient KVDM and the thinning-out variable NIVRM are calculated. The KVPM map, KVIM map, KVDM map and NIVRM map are given predetermined map values for each of a plurality of engine operating regions determined by the engine speed NE and the intake pipe absolute pressure PBA. The map value according to the operating state of is read or calculated by an interpolation method.

Next, in step S163, the thinning-out variable NI
VRM is the NIVRM calculated in step S162.
The value is set, and the VRREFM table is searched to calculate the reference value VRREFM of the output voltage of the O2 sensor 18 (step S164). Next, the reference value VRREFM and the O2 sensor 18 in the current loop are calculated by the following equations.
The deviation ΔVM (k) from the output voltage VMO2 is calculated (step S165).

ΔVM (k) = VRREFM-VMO2 Next, in step S166, the target correction values VREFPM of the respective correction terms, that is, the P term, the I term, and the D term are calculated by the following equations.
After calculating (k), VREFIM (k), and VREFDM (k), these correction terms are added to calculate the target correction value VREFM (k) in O2 feedback.

VREFPM (k) = ΔVM (k) × KVPM VREFIM (k) = VREFIM (k−1) + ΔVM
(K) × KVIM VREFDM (k) = (ΔVM (k) −ΔVM (k−
1)) × KVDM + VREFDM (k) Next, in step S167, the target correction value VREFM
(K) Limit check is performed and target correction value VRE
The FM and the I term VREFIM are set within the predetermined upper and lower limit values.

After the VREFM (k) limit check is completed, the flow proceeds to step S168, and the correction term DK
Calculate CMDO2.

The correction term DKCMDO2 is specifically shown in FIG.
As shown in, it is calculated by searching the DKCMDO2 table. That is, the DKCMDO2 table is DK
The CMDO2 value is set to a larger value as VREFM has a larger value. Further, since the VREFM value is subjected to the limit check in step S167, the DKCMDO2 value is also set to a value within a predetermined upper and lower limit value.

Then, in step S169, the adjustment term KCMDOFFSET is set to the correction term D by the following equation.
KCMDO2 is averaged and calculated.

KCMDOFFSET = α × DKCMDO
2+ (1−α) × KCMDOFFSET Here, KCMDOFFSET on the right side is a previously calculated value, and α is a smoothing coefficient set to a value between 0 and 1.

Adjustment addition term KC calculated in this way
By adding MDOFFSET to the target equivalent ratio KCMD, it is possible to suppress the influence of variations in the characteristics of the exhaust system of the engine and the LAF sensor and aging.

On the other hand, in step S161, the NIVRM
When> 0 holds, the counter NIVRM is thinned out T
Decrement by the DC number NIM (step S17
0), deviation ΔVM, target correction value VREFM and correction term D
KCMDO2 is held as the previous value (step S171,
(S172, S173), and this processing ends.

Next, the LAF sensor output selection processing in step S3 of FIG. 4 will be described.

Since the exhaust gas of the engine is discharged in the exhaust stroke, the behavior of the air-fuel ratio in the exhaust system collecting portion of the multi-cylinder engine is clearly synchronized with the TDC signal pulse. Therefore, it is necessary to detect the air-fuel ratio by the LAF sensor 17 in synchronization with the TDC signal pulse. However, the behavior of the air-fuel ratio may not be accurately grasped depending on the sampling timing of the sensor output. For example, when the air-fuel ratio of the exhaust system collecting portion with respect to the TDC signal pulse is as shown in FIG. 9, the air-fuel ratio recognized by the ECU 5 has a completely different value depending on the sample timing, as shown in FIG. In this case, it is desirable to sample at a timing at which the actual output change of the LAF sensor can be grasped as accurately as possible.

Furthermore, 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. Of these, the time to reach the sensor is the exhaust gas pressure,
It changes depending on the exhaust gas volume. Furthermore, T
Since sampling in synchronization with the DC signal pulse means sampling based on the crank angle,
It is inevitably affected by the engine speed NE. As described above, the optimum timing of detecting the air-fuel ratio largely depends on the engine operating state.

Therefore, in the present embodiment, as shown in FIG. 11, the LAF sensor output sampled at every occurrence of the CRK signal pulse (generated every 30 degrees of the crank angle) is stored in the ring buffer (in this embodiment, 18 pieces are stored. Sequentially stored in a location), and the output value at the optimum timing (the optimum value from the value 17 times before to the current value) is detected.
It is converted to CT and used for feedback control.

FIG. 12 shows L in step S3 of FIG.
6 is a flowchart of AF sensor output selection processing.

First, in step S81, the engine speed NE and the intake pipe absolute pressure PBA are read out, and then it is determined whether or not the current valve timing is the high speed valve timing (step S82). As a result, the timing map for the high speed valve timing is searched for the high speed valve timing (step S83), and the timing map for the low speed valve timing is searched for the low speed valve timing (step S84), according to the search result. The LAF sensor output VLAF stored in the ring buffer is selected (step S85), and this processing ends.

As shown in FIG. 13, the timing map shows that the lower the engine speed NE or the higher the intake pipe absolute pressure PBA, the faster the crank angle position, depending on the engine speed NE and the intake pipe absolute pressure PBA. It is set to select the value sampled in. Here, “early” means a value sampled at a position closer to the previous TDC position (in other words, an old value).
The LAF sensor output is set as shown in FIG.
As shown in, it is best to sample at a position that is as close as possible to the maximum or minimum value of the actual air-fuel ratio (hereinafter referred to as "extreme value"), but the extreme value, for example, the first peak value is Assuming that the reaction time of the sensor is constant, as shown in FIG.
As shown in Fig. 5, the lower the engine speed NE, the faster the crank angle position occurs, and the higher the load, the higher the exhaust gas pressure and the exhaust gas volume. Because it will be earlier.

As described above, according to the processing of FIG. 12, the sensor output VLAF sampled at the optimum timing is selected according to the engine operating state, so that the accuracy of detecting the air-fuel ratio can be improved. As a result, the accuracy of the air-fuel ratio estimation for each cylinder by the observer is improved, and the accuracy of the air-fuel ratio feedback control for each cylinder can be improved.

When it is detected that the response characteristic of the LAF sensor 17, which will be described later, is deteriorated, that is, when the detection delay of the sensor becomes larger than a predetermined value, the sensor output value selected by the above-mentioned processing is set at a later time. Change to the one sampled in.

Next, the calculation processing of the detected equivalent ratio KACT in step S4 of FIG. 4 will be described. FIG. 15 is a flowchart of this KACT calculation process.

First, in step S101, the process shown in FIG.
Sensor output selection value VLAFS selected by the process 2
The sensor output center value VCENT is subtracted from EL to calculate the temporary value VLAFTEMP. Here, the central value VCENT is L when the air-fuel ratio of the air-fuel mixture is the theoretical air-fuel ratio.
AF sensor output value.

Next, it is judged whether or not the VLAFTEMP value is a negative value (step S102), and VLAFTEMP <
When it is 0 and the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the lean correction coefficient KLBLL is multiplied to obtain VLAFT.
The EMP value is corrected (step S103), while the VL
When AFTEMP ≧ 0 and the air-fuel ratio is richer than the theoretical air-fuel ratio, the VLAFTEMP value is corrected by multiplying by the rich correction coefficient KLBLR (step S10).
4). Here, the lean correction coefficient KLBLL and the rich correction coefficient KLBLR are correction coefficients for variation correction calculated according to the value of the label resistance attached to the LAF sensor. The label resistance value is set in advance by measuring the characteristics of the LAF sensor and is set according to the result, and the ECU 5 reads the value and determines the correction coefficients KLBLL and KLBLR.

In the following step S105, the table output center value VOUTCNT is added to the temporary value VLAFTEMP to calculate the corrected output value VLAFE, and then VLA is calculated.
The KACT table is searched according to the FE value to calculate the detected equivalent ratio KACT (step S106). here,
The KACT table is a table for calculating the detected equivalent ratio KACT according to the corrected output value VLAFE, and the table center value VOUTCNT is the theoretical air-fuel ratio (KACT =
It is grid point data (corrected output value) corresponding to 1.0).

By the above processing, it is possible to obtain the detection equivalence ratio KACT in which the influence of the characteristic variation of the LAF sensor is eliminated.

FIG. 16 shows L in step S6 of FIG.
7 is a flowchart of AF feedback area determination processing.

First, in step S121, it is determined whether or not the LAF sensor 17 is in the inactive state. When the LAF sensor 17 is in the inactive state, the flag FFC indicating "1" indicating that the fuel cut is in progress is "1" or not. Is determined (step S12
2) When FFC = 0, it is determined whether or not the flag FWOT, which indicates by "1" that the throttle valve is fully open, is "1" (step S123), and when FWOT = 1 is not shown. It is determined whether or not the battery voltage VBAT detected by the sensor is lower than a predetermined lower limit value VBLOW (step S124), and when VBAT ≧ VBLOW, a deviation of the LAF sensor output corresponding to the stoichiometric air-fuel ratio (LAF sensor stoichiometric deviation). It is determined whether or not there is. If any of the answers in steps S121 to S125 is affirmative (YES), K indicating that feedback control based on the LAF sensor output should be stopped is indicated by "1".
The LAF reset flag FKLAFRESET is set to "1" (step S132).

On the other hand, if the answers to steps S121 to S125 are all negative (NO), it is determined that feedback control based on the LAF sensor output can be executed, and KLAF is executed.
The reset flag FKLAFRESET is set to "0" (step S131).

In the following step S133, the O2 sensor 1
8 is in the inactive state, and when it is in the active state, the engine water temperature TW is the predetermined lower limit water temperature TWLOW.
It is determined whether the temperature is lower than (for example, 0 ° C.) (step S
134). When the O2 sensor 18 is inactive or TW <TWLOW, the hold flag FKLAFHOLD indicating "1" indicating that the PID correction coefficient KLAF should be maintained at the current value is set to "1" ( In step S136), this process ends. On the other hand, when the O2 sensor 18 is in the active state and TW ≧ TWLOW, FKLAFHOLD = 0 is set (step S13).
5) Then, this process ends.

Next, the calculation process of the cylinder specific correction coefficient KOBSV # N in step S9 of FIG. 4 will be described.

First, the method for estimating the cylinder-by-cylinder air-fuel ratio will be described, and then the method for calculating the cylinder-specific correction coefficient KOBSV # N according to the estimated cylinder-by-cylinder air-fuel ratio will be 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 consider the detection response delay of the LAF sensor. So LA
When the F sensor was modeled assuming a first-order lag system and the model shown in FIG. 17 was created, it was confirmed by experiments that the air-fuel ratio obtained based on this model agrees well with the true air-fuel ratio. Here, LAF (t) is the LAF sensor output, A / F (t) is the input A / F, and α is the gain, and the state equation of this model can be expressed by Equation 2.

[0095]

[Equation 2] When this is discretized with the period ΔT, it becomes as shown in Expression 3, and when it is expressed in a block diagram, it becomes as shown in FIG. 18.

[0096]

(Equation 3) When this Equation 3 is modified, it becomes as shown in Equation 4,
The value at the time (k−1) can be calculated backward from the value at the time k as in Expression 5.

[0097]

[Equation 4]

[0098]

(Equation 5) Specifically, since Z is converted from Expression 3 and expressed by a transfer function, Expression 6 is obtained. Therefore, by multiplying the inverse transfer function by the LAF sensor output LAF (k) of this time, the previous input air-fuel ratio A / F (k-1) can be estimated in real time. FIG. 19 shows a block diagram of the real-time A / F estimator.

[0099]

(Equation 6) 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 described.

The air-fuel ratio of the exhaust system collecting portion is considered to be a weighted average in consideration of the temporal contribution of the air-fuel ratio of each cylinder, and the value at time k is expressed as in Equation 7. Note that the fuel-air ratio F / A is used in Equation 7 because the fuel amount (F) is the manipulated variable. The fuel-air ratio F / A in Expression 7 means a true value obtained by correcting the response delay of the sensor obtained by Expression 5.

[0101]

(Equation 7) That is, the air-fuel ratio of the collecting portion is represented by the sum of the past combustion history of each cylinder multiplied by the weight C (for example, 40% for the cylinder that burned immediately before, 30% before that, ...). When this model is represented by a block diagram, it becomes as shown in FIG. 20, and its equation of state becomes as shown in Equation 8.

[0102]

(Equation 8) Further, if the fuel-air ratio of the collecting portion is set to y (k), the output equation can be expressed as Equation 9.

[0103]

[Equation 9] In Expression 9, since u (k) cannot be observed, x (k) cannot be observed even if an observer is designed from this equation of state. Therefore, assuming that the air-fuel ratio before 4TDC (that is, the same cylinder) is in a steady operation state where it does not change rapidly, and x (k + 1) = x (k-3), then Equation 9 becomes Equation 10. .

[0104]

[Equation 10] FIG. 21 shows the air-fuel ratio of the three cylinders of the four cylinder engine is 14.7.
When the air-fuel ratio of one cylinder is 12.0,
It is a diagram showing the transition of the output value and the measured value of the model,
It was confirmed that the above model well models the exhaust system of a 4-cylinder engine. Therefore, the problem of estimating the cylinder-by-cylinder air-fuel ratio from the collecting portion A / F results in the problem of a normal Kalman filter that observes x (k) in the state equation and the output equation shown in Expression 11. When the Riccati's equation is solved for the weighting matrices Q and R as in Expression 12, the gain matrix K becomes as in Expression 13.

[0105]

[Equation 11]

[0106]

(Equation 12)

[0107]

(Equation 13) From this, when (A-KC) is obtained, it becomes as shown in Expression 14.

[0108]

[Equation 14] Here, a general structure of the observer is as shown in FIG. 22, but since there is no input u (k) in the model of the present embodiment, as shown in FIG. 23, only y (k) is input. When this is expressed by a mathematical formula, a mathematical formula 15 is obtained.

[0109]

(Equation 15) Therefore, the estimated value x hat (k) of the fuel-air ratio for each cylinder can be calculated from the fuel-air ratio y (k) of the collecting portion and the estimated value X-hat (k) of the fuel-air ratio for each cylinder in the past. .

Here, the observer to which y (k) is input, that is, the system matrix S of the Kalman filter, is expressed as in Expression 16.

[0111]

[Equation 16] Then, in the model of this embodiment, the weight distribution R of the Riccati equation is
When the elements of Q: elements of Q = 1: 1, the system matrix S is
It is given by Equation 17.

[0112]

[Equation 17] FIG. 24 is a block diagram in which the model and the observer are combined, and a simulation result is obtained in which the cylinder-by-cylinder air-fuel ratio obtained by this is in good agreement with the actually measured value. As described above, in this embodiment, the response delay of the LAF sensor is taken into consideration and the observer is introduced, so that the air-fuel ratio for each cylinder can be accurately extracted from the air-fuel ratio of the collecting portion.

Next, a method of calculating the cylinder-specific correction coefficient KOBSV # N based on the estimated cylinder-specific air-fuel ratio will be described with reference to FIG.

First, as shown in Equation 18, the gathering part A /
The detected equivalent ratio KACT corresponding to F is divided by the previous calculated value of the average value of the cylinder-by-cylinder correction coefficients KOBSV # N for all cylinders to obtain the target value KCMDOB as the equivalent ratio corresponding to the target A / F.
SV (k) is calculated, and the cylinder-by-cylinder correction coefficient KOB of the # 1 cylinder is calculated.
The SV # 1 has its target value KCMDOBSV (k) and # 1.
Deviation DKAC from the estimated equivalent ratio KACT # 1 (k) of the cylinder
T # 1 (k) (= KACT # 1 (k) -KCMDOBS
It is determined by PID control so that V (k)) becomes zero.

[0115]

(Equation 18) More specifically, according to Equation 19, the proportional term KOBSVP #
1, integral term KOBSVI # 1 and derivative term KOBSVD #
1 is calculated, and the correction coefficient KOB for each cylinder is calculated according to the equation 20.
Calculate SV # 1.

[0116]

[Formula 19] KOBSVP # 1 (k) = KPOBSV × D
KACT # 1 (k) KOBSVI # 1 (k) = KIOBSV × DKACT #
1 (k) + KOBSV # 1 (k−1) KOBSVD # 1 (k) = KDOBSV × (DKACT
# 1 (k) -DKACT # 1 (k-1))

[0117]

(20) KOBSV # 1 (k) = KOBSVP # 1
(K) + KOBSVI # 1 (k) + KOBSVD # 1
(K) +1.0 Similar calculations are performed for cylinders # 2 to # 4 to calculate KOBSV # 2 to # 4.

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 by the PID correction coefficient KLAF. As a result, the air-fuel ratios of all cylinders are targeted. It can be converged to the air-fuel ratio.

Further, this cylinder-by-cylinder correction coefficient KOBSV #
Cylinder-based correction coefficient learning value KOBSV # N which is a learning value of N
sty is calculated by the following formula and stored.

KOBSV # Nsty = C × KOBSV #
N + (1-C) × KOBSV # Nsty where C is a weighting factor and KOBSV # Nsty (n−
1) is the previously learned value.

FIG. 26 is a flowchart of the cylinder-by-cylinder correction coefficient KOBSV # N calculation processing in step S10 of FIG.

First, in step S331, it is determined whether or not the lean deterioration of the LAF sensor 17 is detected. If not detected, the process immediately proceeds to step S336, while if it is detected, the target equivalent ratio KCMD is detected. Is 1.0
Or not, that is, whether or not the target air-fuel ratio is the stoichiometric air-fuel ratio (step S332). Here, the lean deterioration of the LAF sensor means a state in which the deviation of the output corresponding to the air-fuel ratio on the lean side of the stoichiometric air-fuel ratio is equal to or more than a predetermined value, and the detection method will be described later. When KCMD = 1.0, the process proceeds to step S336, while KCMD ≠ 1.
When it is 0, the cylinder-by-cylinder correction coefficient KOB of all cylinders
The SV # N is set to 1.0 (step S344), that is, the cylinder-by-cylinder air-fuel ratio feedback control is not performed, and this processing is ended.

In step S336, the cylinder-by-cylinder air-fuel ratio estimation processing is performed by the above-described observer, and then it is determined whether or not the hold flag FKLAFHOLD is "1".
When FKLAFHOD = 1, this processing is immediately terminated.

In a succeeding step S338, it is determined whether or not the reset flag FKLLAFRESET is "1", and FK is determined.
When LAFRESET = 0, the engine speed N
It is determined whether E is higher than a predetermined rotation speed NOBSV (eg, 3500 rpm) (step S339), and NE ≦ N.
If it is OBSV, it is judged whether or not the absolute intake pipe absolute pressure PBA is higher than a predetermined upper limit pressure PBOBSVH (for example, 650 mmHg) (step S340), and PBA ≦ PBO.
If it is BSVH, the PBOBSVL table set as shown in FIG. 28 according to the engine speed NE is searched to determine the lower limit pressure PBOBSVL (step S
341), the absolute pressure PBA in the intake pipe is the lower limit pressure PBOBSV
It is determined whether it is lower than L (step S342).

As a result of the above determination, steps S338 to S338
The answer to either 340 or S342 is affirmative (YES).
If so, the process proceeds to step S344, and the cylinder-by-cylinder air-fuel ratio feedback control is not performed. On the other hand, step S33
When all the answers of 8 to S340 and S342 are negative (NO), the engine operating state is in the region shown by the diagonal lines in FIG. 28, it is determined that the cylinder-by-cylinder air-fuel ratio feedback control is feasible, and the cylinder is determined by the method described above. Other correction coefficient KOBSV
The calculation of #N is performed (step S343), and this processing ends.

FIG. 27 is a flowchart of the cylinder-by-cylinder air-fuel ratio estimation processing in step S336 of FIG.

In the figure, in step S361, observer calculation for high-speed valve timing (that is, estimation calculation of the cylinder-by-cylinder air-fuel ratio) is performed, and in the following step S362,
Performs observer calculation for low speed valve timing. Then, it is determined whether or not the current valve timing is the high speed valve timing (step S363), when the high speed valve timing is selected, the observer calculation result for the high speed valve timing is selected (step S364), and when the low speed valve timing is selected. , An observer calculation result for low speed valve timing is selected (step S365).

Thus, regardless of the current valve timing, the observer calculation for the high speed valve and the low speed valve timing is performed, and according to the current valve timing,
The reason why the calculation result is selected is that the estimation calculation of the cylinder-by-cylinder air-fuel ratio requires calculation several times before it converges. As a result, it is possible to improve the estimation accuracy of the cylinder-by-cylinder air-fuel ratio immediately after switching the valve timing.

Next, the PID in step S10 of FIG.
The correction coefficient KLAF calculation process will be described with reference to FIG.

First, in step S301, it is determined whether the hold flag FKLAFHOLD is "1", and FKL
When AFHOLD = 1, this process is immediately terminated and F
When KLAFHOLD = 0, it is determined whether or not the KLAF reset flag FKLAFRESET is "1" (step S302). As a result, FKLAFRESET =
If it is 1, the process proceeds to step S303, the PID correction coefficient KLAF is set to 1.0, and the deviation DKAF between the integral control gain KI and the target equivalent ratio KCMD and the detected equivalent ratio KACT is set to "0". This process ends.

In step S302, FKLAFRESET
When = 0, the process proceeds to step S304, and the proportional control gain KP, the integral control gain KI, and the differential control gain KD are searched from a map set according to the engine speed NE and the intake pipe absolute pressure PBA. However, the gain for idle is adopted in the idle state. Next, the deviation DKAF between the target equivalent ratio KCMD and the detected equivalent ratio KACT
(K) (= KCMD (k) -KACT (k)) is calculated (step S305), the deviation DKAF (k) and the control gains KP, KI, KD are applied to the following equation to calculate the proportional term K.
LAFP (k), integral term KLAFI (k) and derivative term K
LAFD (k) is calculated (step S306).

KLAFP (k) = DKAF (k) × KP KLAFI (k) = DKAF (k) × KI + KLAF
(K-1) KLAFD (k) = (DKAF (k) -DKAF (k-
1)) × KD In the subsequent steps S307 to S310, the integral term KLAF
Perform limit processing of I (k). That is, KLAFI
(K) Value is a predetermined upper and lower limit value KLAFILMTH, KLAF
It is determined whether or not it is within the range of ILMTL (step S
307, S308), KLAFI (k)> KLAFIL
When MTH, KLAFI (k) = KLAFLM
TH (step S310), KLAFI (k) <K
When LAFILMTL, KLAFI (k) = K
It is set to LAFILMTL (step S309).

In the following step S311, the PID correction coefficient KLAF (k) is calculated by the following formula.

KLAF (k) = KLAFP (k) + KL
AFI (k) + KLAFD (k) +1.0 Then, the KLAF (k) value is the predetermined upper limit value KLAFLMT.
It is determined whether or not it is larger than H (step S312), and K
If LAF (k)> KLAFLMTH, then KLA
F (k) = KLAFMTH (step S31
6) Then, this process ends.

In step S312, KLAF (k) ≤K
When it is LAFLMTH, it is determined whether or not the KLAF (k) value is smaller than the predetermined lower limit value KLAFLMTL (step S314), and KLAF (k) ≧ KLALMTL.
If this is the case, this processing is immediately terminated, while KLAF (k)
<KLAFMLTL, KLAF (k) = K
As LAFLMTL (step S315), this processing ends.

By this processing, PID control is performed so that the detected equivalent ratio KACT matches the target equivalent ratio KCMD.
The ID correction coefficient KLAF is calculated.

Next, the deterioration determination processing of the LAF sensor 17 and the fail-safe processing when the deterioration is detected will be described.

FIG. 30 is a diagram showing the overall structure of these processes. In step S401, the deterioration of the LAF sensor is determined. Here, the deterioration to be determined is stoichiometric deterioration,
Response deterioration and lean deterioration. The stoichiometric deterioration is a state in which the LAF sensor output corresponding to the stoichiometric air-fuel ratio deviates by a predetermined amount or more, the response deterioration is a state in which the detection delay of the sensor is more than a predetermined value, and the lean deterioration is the lean side from the stoichiometric air-fuel ratio. The state in which the LAF sensor output corresponding to the air-fuel ratio of 1 is deviated by a predetermined amount or more. These deterioration determination processes are shown in FIGS.
2, which will be described later.

In a succeeding step S403, it is determined whether or not the deterioration is detected, and if not detected, this processing is immediately ended.

When the deterioration is detected, it is judged whether it is the response deterioration or not (step S403), and if it is not the response deterioration, it is judged whether it is the lean deterioration or not (step S40).
5). As a result, when the response is degraded, as described above, L
The sample value selected in the AF sensor output selection processing is changed to that sampled at a later timing (step S404). As a result, the cylinder-by-cylinder air-fuel ratio can be accurately estimated even when the response is deteriorated, and good exhaust gas characteristics can be maintained.

When the lean deterioration is detected, the label resistance cannot be read and the sensor output value cannot be corrected according to the label resistance value. The detected value on the rich side may also have a large deviation. Therefore, as described above (FIG. 26), feedback control (correction coefficient KOBS for each cylinder) on the rich side and the lean side of the theoretical air-fuel ratio is performed.
Feedback control by V # N and PID correction coefficient K
The feedback control by LAF) is stopped, and only the so-called stoichiometric feedback control in which the target equivalent ratio KCMD is 1.0 is executed (step S407). Thus, when the target air-fuel ratio is other than the stoichiometric air-fuel ratio, feedback control is performed to an air-fuel ratio different from the originally target air-fuel ratio, and it is possible to prevent deterioration of exhaust gas characteristics.

When neither response deterioration nor lean deterioration is occurring, that is, stoichiometric deterioration, the reset flag FKLAFRESET is set to "1" and the cylinder-by-cylinder air-fuel ratio feedback is stopped, as described in the processing of FIG. . In this case, the feedback control by the PID correction coefficient KLAF is also stopped (FIG. 4). This allows
Feedback control is performed to an air-fuel ratio different from the originally target air-fuel ratio, and it is possible to prevent deterioration of exhaust gas characteristics.

Next, the outline of the deterioration determination process will be described with reference to FIGS.

FIG. 31 is a diagram for explaining the stoichiometric deterioration determination processing. When the deterioration determination processing is executed, the output of the O2 sensor 18 is at a high level (the air-fuel ratio is richer than the theoretical air-fuel ratio). The target equivalence ratio KCMD is gradually decreased while the target equivalence ratio KCMD is gradually decreased, while the target equivalence ratio KCMD is gradually decreased at a low level (indicating that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio). Reversal point B,
Average value KAC of detection equivalent ratio KACT in C, D, E
TAV (= (KACT (B) + KACT (C) + KAC
T (C) + KACT (D)) / 4) is calculated. When the KACTAV value deviates from 1.0 by a predetermined amount or more,
Judge as stoichiometric deterioration. Note that the number of KACT values used to calculate the average value KACTAV is not limited to four, but the number of detection values on the lean side and the rich side needs to be the same.

FIG. 32 is a diagram for explaining the response deterioration determination processing. When this determination processing is executed, the normal PID feedback control is stopped and the target equivalent ratio KC is reached.
MD is fixed to 1.0, and the value of the PID correction coefficient KLAF is gradually decreased when the detected equivalent ratio KACT is larger than 1.0, while it is gradually increased when the detected equivalent ratio KACT is smaller than 1.0. Integral term and KACT value to be set to 1.
PI feedback control is performed using a proportional term that is added or subtracted when the magnitude relationship with 0 is reversed. Then, a predetermined number of times M ×
Measure the time TMWAVE required to invert by 2,
The cycle tmCYCL (= TMWAVE / M) is calculated, and t
When the mCYCL value exceeds a predetermined value, it is determined that the response has deteriorated.

FIG. 33 is a diagram for explaining the lean deterioration determination processing. This determination processing corresponds to the atmosphere at the time when a predetermined time or more has elapsed from the start of the fuel cut, that is, the exhaust gas does not contain fuel. LAF sensor output VLA
When the state in which F is outside the range of the predetermined upper and lower limit values VLAFFCH and VLAFFCL continuously occurs, it is determined as lean deterioration. Here, the predetermined upper and lower limit value VLAFF
CH and VLAFFCL are the allowable range R when the LAF sensor output shows a value equivalent to A / F22 as shown in FIG.
It is decided based on.

FIG. 34 is a flow chart showing the overall structure of the above-mentioned deterioration determination processing, and this processing is executed every predetermined time (for example, 10 msec).

First, in step S501, it is determined whether or not the engine is in the starting mode, that is, whether or not the cranking is being performed. If it is in the starting mode, this process is immediately terminated. If it is not the start mode, the stoichiometric deterioration determination process (step S502), the response deterioration determination process (step S503), and the lean deterioration determination process (step S504) are sequentially executed. Then, it is determined whether or not the stoichiometric deterioration flag FLFSTNG, which indicates that the stoichiometric deterioration is detected by "1", is "1" (step S505). When FLFSTNG = 0, it is determined that the response deterioration is detected by "1". Response deterioration flag FLFR indicated by
It is determined whether PNG is "1" (step S506),
When FLFRPNG = 0, it is determined whether or not the lean deterioration flag FLFLNNG indicating "1" that the lean deterioration is detected is "1" (step S507).

As a result, if the answer to any of steps S505 to S507 is affirmative (YES) and some deterioration is detected, it indicates that the LAF sensor 17 is not deteriorated by "1". Set the flag FOK61 to "0"
(Step S511), the counter C61M is incremented by "1" (step S512),
This process ends.

On the other hand, if the answers to steps S505 to S507 are all negative (NO), the stoichiometric deterioration determination end flag FLF indicating "1" is the end of the stoichiometric deterioration determination process.
It is determined whether STEND is "1" (step S50).
8) When FLFSTEND = 1, the response deterioration determination end flag FLF that indicates the end of the response deterioration determination process by "1"
It is determined whether RPEND is "1" (step S50).
9). As a result, when the answer to step S508 or S509 is negative (NO), this processing is immediately terminated, while the answer to step S508 and S509 is affirmative (YE).
In the case of S), the OK flag FOK61 is set to "1" (step S510), and the process proceeds to step S512.

FIG. 35 is a flowchart of the stoichiometric deterioration determination process in step S502 of FIG.

First, in step S521, it is determined whether or not the stoichiometric deterioration determination end flag FLFSTEND is "1". When FLFSTEND = 0, the first monitoring condition is satisfied by the first flag "1". It is determined whether the monitor condition flag FLFMCHK is "1" (step S).
522). Here, the first monitor condition is an execution permission condition for the stoichiometric deterioration determination and the response deterioration determination, and the flag FL
FMCHK is set in the processing of FIG. 39 described later.

If the answer to step S522 is affirmative (YES), the O2 sensor output (VMO2) monitoring flag FSV is displayed.
It is determined whether O2HLD is "1" (step S52).
3). If the answer to step S523 is negative (NO), the process proceeds to step S527, while step S52.
1 or the answer of S523 is affirmative (YES), or the answer of step S522 is negative (NO), the VMO
2 The monitoring flag FSVO2HLD is set to "0" (step S524), and the stoichiometric deterioration determination execution flag FLFSTM is indicated by "1" indicating that the stoichiometric deterioration determination is being executed.
Is set to "0" (step S525), and the down-count timer tmLFSTM is set to the predetermined time TLFS.
TM is set (step S526), and this processing ends.

In step S527, the target equivalent ratio KCMD is calculated by the processing of FIG. 36, which will be described later, and in the following step S528, the stoichiometric deterioration determination execution flag FLFS.
TM is set to "1" and the process proceeds to step S529.

In step S529, it is determined whether or not the reversal flag FKACTT, which is set in the process of FIG. 36 to be described later and indicates by "1" that the predetermined time has elapsed after the O2 sensor output is reversed, is FKACTT = When it is 0, the step S526 (or step S532 described later) is performed.
It is determined whether or not the value of the timer tmLFSTM set in is 0 (step S530). As a result, tmLF
If STM> 0 and the predetermined time TLFSM has not elapsed, this process is immediately terminated, and tmLFSTM =
When it is 0, the VMO2 monitoring flag FSVO2HLD
Is set to "1" (step S531), and this processing ends.

When FKACTT = 1 in step S529 and the O2 sensor output is inverted, the downcount timer tmLFSTM is set to a predetermined time TLFSTM and started (step S532), and the value of the counter NKACT is "0". It is determined whether or not (step S533). Since NKACT = 0 at the beginning, the process proceeds to step S535, the counter NKACT is incremented by "1" (step S535), and it is determined whether or not the value is smaller than a predetermined value NKACTC (for example, 5) (step S535). Step S536). Initially NKACT <NK
Since this is ACTC, this processing is immediately terminated.

Next, when the output of the O2 sensor is inverted, the answer to step S533 is negative (NO), the integrated value KACTT of the detected equivalent ratio KACT is calculated by the following formula (step S534), and the process proceeds to step S535.

KACTT = KACTT + KACT Then, in step S536, NKACT = NKACTC.
Then, the process proceeds to step S537, and the average detection equivalent ratio KACTAV is calculated by the following formula.

KACTAV = KACTT / (NKACT-1) As a result, KAC at points B, C, D and E in FIG.
The KACTAV value is calculated as the average value of the T values.

In subsequent steps S538 and S539, it is determined whether or not the average value KACTAV is larger than a predetermined lower limit value KACTAVL and less than a predetermined upper limit value KACTAVH, and as a result, KACTAVL <KACTAV <
If it is KACTAVH, it is determined that there is no deterioration, the process immediately proceeds to step S541, the stoichiometric deterioration determination end flag FLFSTEND is set to "1", and this processing ends.

When KACTAV≤KACTAVL or KACTAV≥KACTAVH, it is determined that the stoichiometry is deteriorated, the flag FLFSTNG is set to "1" (step S540), and the process proceeds to step S541.

FIG. 36 is a flowchart of the calculation process of the target equivalent ratio KCMD during the execution of the stoichiometric deterioration determination in step S527 of FIG.

First, in step S801, it is determined whether or not the O2 sensor output VMO2 is larger than a predetermined reference value VMO2REF. If VMO2> VMO2REF and it is on the rich side of the stoichiometric air-fuel ratio, the first rich flag FA is set.
FR1 is set to "1" (step S803), VMO
When 2 <VMO2REF and leaner than the stoichiometric air-fuel ratio, the flag FAFR1 is set to "0" (step S802), and the process proceeds to step S804.

In step S804, it is determined whether or not the first rich flag FAFR1 is inverted. If not, the process immediately proceeds to step S808. If it is inverted, then the first rich flag FAFR1 is "1". It is determined whether or not (step S805). When FAFR1 = 1, the down-count timer tmDLYR that measures the time after reversal is set to the rich predetermined time TRD and started (step S807), while FAFR1
When = 0, the lean side predetermined time TLD is set in the timer tmDLYR (step S806), and the process proceeds to step S808.

In step S808, it is determined whether the stoichiometric deterioration determination execution flag FLFSTM is "1",
When FLFSTM = 0 and the determination is started from this time, the integrated value KACTT of the detection equivalence ratio KACT and FIG.
Counter N incremented in step S535 of
Both KACT are set to "0" (step S80
9), the second rich flag FAFR2 is set to the same value as the first rich flag FAFR1, and the target equivalent ratio KCMD is set to a predetermined value KCMCHK (for example, 1.0) (step S
810) and the process proceeds to step S813.

In step S813, the inversion flag FKA is set.
CTT is set to "0", then the second rich flag FA
It is determined whether FR2 is "0" (step S81).
4). As a result, when FAFR2 = 0, the rich side integral term IRSP is added to the target equivalent ratio KCMD (step S815), and when FAFR2 = 1, KCM is added.
The lean-side integral term ILSP is subtracted from the D value (step S816), and the process proceeds to step S822.

At step S808, FLFSTM =
When it is 1 and the stoichiometric deterioration determination is being executed, the process proceeds to step S811, and it is determined whether or not the first rich flag FAFR1 and the second rich flag FAFR2 are equal, and FA
When FR1 = FAFR2, the above step S81
Go to 3. When FAFR1 ≠ FAFR2, it is determined whether the value of the timer tmDLYR started in step S806 or S807 is "0" (step S812). Immediately after the inversion of the first rich flag FAFR1, since tmDYLR> 0, the step S81 is performed.
3, and when tmDYLR = 0, step S81
7 to set the second rich flag FAFR2 to the first rich flag F.
It is made equal to AFR1 and then the inversion flag FKACTT is set to "1" (step S818).

In a succeeding step S819, it is determined whether or not the first rich flag FAFR1 is "1", and FAFR1 =
When it is 0, the rich side proportional term PRSP is added to the target equivalent ratio KCMD (step S820), and FAFR1 =
When it is 1, the lean side proportional term PLS from the KCMD value
P is subtracted (step S821), and step S822
Proceed to.

In step S822, the limit check process shown in FIG. 37 is executed, and this process ends.

In the processing of FIG. 37, the KCMD value is compared with predetermined upper and lower limit values KCDMLMTH and KCDMLMTL (steps S831, S832), and when the KCMD value is equal to or larger than the predetermined upper limit value KCDMLMTH, KCMD = KCMDL
When MTH is set (step S833) and the KCMD value is equal to or lower than the predetermined lower limit value KCDMMLTL, KCMD = KCML
It is set to LMTL (step S834).

As described above, according to the process of FIG. 36, the target equivalence ratio KCMD is proportionally / integrally controlled according to the O2 sensor output VMO2 during the execution of the stoichiometric deterioration determination. Note that FIG. 31 shows the set time (TR) of the timer tmDLYR.
This corresponds to the case where D, TLD) is set to "0".

FIG. 38 is a flowchart of the response deterioration determination process in step S504 of FIG.

First, in step S551, it is determined whether or not the response deterioration determination end flag FLFRPEND is "1".
When FLAFRPEND = 0, it is judged whether or not the first monitor condition flag FLFMCHK is "1" (step S
552), when FLFMCHK = 1 and the first monitor condition is satisfied, the response deterioration determination start flag FLFRPMS set by the process in FIG. 39 and indicating “1” that the response deterioration determination start condition is satisfied is “ It is determined whether or not it is "1" (step S553). As a result, when the response deterioration determination is completed (FLFRPEND = 1), when the first monitoring condition is not satisfied (FLFMCHK = 0), or when the response deterioration determination start condition is not satisfied (FLFRPMS = 0), the response deterioration determination is executed. The response deterioration determination execution flag FLFRPM, which indicates "1" as being in the middle, is set to "0" (step S554), and this processing ends.

On the other hand, the answer to step S553 is affirmative (YE
In the case of S), it is determined whether or not the detected equivalent ratio KACT is inverted from a state smaller than 1.0 to a state larger than 1.0 (step S555), and if not reversed, this processing is immediately terminated, When inverted, the response deterioration determination execution flag FLFRPM is set to "1" (step S5).
57), and it is determined whether or not the previous flag FLFRPM was "1" (step S558). And last time it was FL
If FRPM = 0, the counter NWAVE and the up-count timer tmWAVE are set to "0" (steps S559 and S560), and this processing ends.

At step S558, FLFRPM is also last time.
= 1, the counter NWAVE is incremented by "1" (step S561), and the timer tm
It is determined whether or not the value of WAVE has exceeded the predetermined time TMWAVE (step S562). tmWAVE <TMW
If it is AVET, this processing is immediately terminated and tmW
When AVE> TMWAVET, the period tmCYCL is calculated by the following formula (step S563).

TmCYCL = tmWAVE / NWAVE In a succeeding step S564, it is determined whether or not the cycle tmCYCL is shorter than a predetermined cycle tmCYCLOK, and tmCY.
If CL <tmCYLOK, the end flag FLFRP
The END is set to "1" (step S566), the deterioration determination execution flag FLFRPM is set to "0" (step S567), and this processing is ended.

In step S564, tmCYCL ≧ tm
If it is CYCLOK, it is determined that the response is deteriorated, the response deterioration determination flag FLFRPNG is set to "1" (step S565), and the process proceeds to step S566.

During the response deterioration determination (FLFRPM
= 1), the normal PID feedback control is stopped, and as shown in FIG. 32, PI feedback control with KCMD (= 1.0) as the threshold value is executed.

FIG. 39 is a flowchart of the process for determining the above-mentioned first monitor condition. This process is executed in the so-called background in which the process with high priority is not executed.

First, in step S572, the O2 sensor 1
Active flag nO indicating "1" indicating that 8 is in the active state
It is determined whether or not 2R is “1”, and when nO2R = 1, it is determined whether or not the operating state of the engine 1 and the vehicle equipped with the engine 1 is within a predetermined range (step S5).
73).

That is, the engine water temperature TW is the predetermined upper and lower limit value T
Whether it is within the range of WLAFMH, TWLFML,
The intake air temperature TA is a predetermined upper and lower limit value TALAFMH, TALAF
Whether the engine speed NE is within the range of ML, whether the engine speed NE is within a range of predetermined upper and lower limit values NELAFMH, NELAFML, and the absolute intake pipe absolute pressure PBA is a predetermined upper and lower limit value PBL.
It is determined whether AFMH and PBLAFML are within the range and whether the vehicle speed V is within the predetermined upper and lower limit values VLAFMH and VLAFML, and all the answers are affirmative (YES).
At this time, it is determined that the operating state is in a predetermined area.

Then, in that case, it is further determined whether or not the flag FCRS, which indicates by "1" that the vehicle is in a cruise state in which the rate of change in vehicle speed is small, is "1" (step S574), and FCRS = 1. In case of, the reset flag F
It is determined whether KLAFRESET is "0" (step S575).

As a result of the above discrimination, steps S572-S
If any of the answers in 575 is negative (NO), it is determined that the first monitor condition is not satisfied, the process proceeds to step S580, and the purge cut flag FLAFPG, which indicates that the purge cut should be performed by "1", is set to "0", Next, the down count timer tmLFMCHK is set to a predetermined time TLFMCHK and started (step S581), and the first monitor condition flag FLFMCHK is set to "0" (step S581).
583), the down count timer tmLFRPMS is set to the predetermined time TLFRPMS and started (step S586), and the response deterioration determination start flag FLFRPM is set.
S is set to "0" (step S588), and this processing ends.

Further, in step S575, FKLAFRE
When SET = 0 and in the air-fuel ratio feedback control region, it is determined whether or not the first monitor flag FLFMCHK is "1" (step S576), and FLFM.
When CHK = 1, the process immediately proceeds to step S578, while when FLFMCHK = 0, the target equivalent ratio KCMD is a predetermined value KCMDZML (for example, a value corresponding to the stoichiometric air-fuel ratio, that is, set to 1.0). It is determined whether or not this is the case (step S577). And KCMD <
If KCMDZML, it is determined that the first monitor condition is not satisfied, and the process proceeds to step S580, where KCMD ≧ KC
If it is MDZML, the process proceeds to step S578.

In step S578, it is determined whether or not the response deterioration determination end flag FLFRPEND is "1", and FL is set.
When FRPEND = 1 and the determination is completed, the process proceeds to step S580. Also, FLFRPEND = 0
If so, the purge cut flag FLAFPG is set to "1" to perform the purge cut (step S57).
9), the timer tm started in step S581
It is determined whether the value of LFMCHK is "0" (step S582). At first, since tmLFMCHK> 0, the process proceeds to step S583, and when tmLFMCHK = 0, it is determined that the first monitor condition is satisfied and the flag FLFM is satisfied.
CHK is set to "1" (step S584), and it is determined whether or not the stoichiometric deterioration determination end flag FLFSTEND is "1" (step S585).

As a result, if FLFSTEND = 0 and the stoichiometric deterioration determination has not ended, the flow proceeds to step S586, and the stoichiometric deterioration determination ends and FLF is determined.
When STEND = 1, the process proceeds to step S587, and the timer tmLFRPMS started in step S586.
It is determined whether the value of is "0" (step S587).
At first, since tmLFRPMS> 0, the process proceeds to step S588, and when tmLFRPMS = 0, the response deterioration determination start flag FLFRPMS is set to "1" (step S589), and the start of the response deterioration determination is permitted.

FIG. 40 is a flowchart of the lean deterioration determination processing in step S504 of FIG.

First, in step S601, whether or not the lean deterioration determination permission flag FLFFCLN is "1", which indicates by "1" that the second monitor condition determined by the processing of FIG. 42, that is, the lean deterioration determination execution condition is satisfied. And FLF
When FCLN = 0 and the monitor condition is not satisfied, the lean deterioration determination end flag FL indicating the deterioration determination end by "1" is given.
It is determined whether NJG is "1" (step S602),
If FLNJG = 0, immediately step S605.
If FLNJG = 1, the flag FLN
JG is set to "0" (step S603), and a check flag FFCCHK indicating "1" to determine whether or not the LAF sensor output VLAF is within the predetermined upper and lower limit values.
Is set to "0" (step S604), and step S
Proceed to 605.

In step S605, the check counter CFCCHK for determining the monitoring cycle of the VLAF value is set to a predetermined value NFCCHK, and then the stable period counter CIPFCST for measuring the period after the fluctuation of the VLAF value falls within the predetermined range. Is set to a predetermined value NIPFCST (step S611), and the process proceeds to step S622.

In step S601, FLFFCLN
When = 1 and the monitor condition is satisfied, it is determined whether or not the value of the check counter CFCCHK set in step S605 is "0" (step S606). Since CFCCHK> 0 at first, the value is decremented by "1" in step S607, and the process proceeds to step S622. When CFCCHK = 0, the process proceeds to step S608, and the check counter CFCCHK is again set to the predetermined value NFC.
Set CHK. Next, check flag FFCCHK
Is determined to be "1" (step S609), the FFC
When CHK = 0, it is determined whether or not the fluctuation of the sensor output VLAF is greater than or equal to a predetermined value (step S610).

Then, when FFCCHK = 1 or when the fluctuation of the VLAF value is more than a predetermined value, the process proceeds to the step S611 without monitoring the VLAF value.
When FFCCHK = 0 and the fluctuation of the VLAF value is small, it is determined whether or not the value of the stable period counter CIPFCST set in step S611 is "0" (step S612). Since CIPFCST> 0 at first, the process proceeds to step S613, the count value is decremented by "1", and the process proceeds to step S622. Thereafter, when CIPFCST = 0, it is determined whether or not the VLAF value is within the range of the predetermined upper and lower limit values VLAFFCH and VLAFFCL (steps S614 and S61).
5), VLAF> VLAFFCH or VLAF <VLA
If FFCL is out of the allowable range, step S
In 616, the NG counter CIPFCNG is incremented by "1", and then it is determined whether or not the counter CIPFCNG overflows (step S617).
If it does not overflow, the process immediately proceeds to step S621, and if it overflows, the NG counter CIPFC
Set FF (hexadecimal number) to NG (step S61)
8) and proceeds to step S621.

On the other hand, as a result of the determination in steps S614 and S615, if VLAFFCL≤VLAF≤VLAFFCH and it is within the allowable range, the process proceeds to step S619 and N
It is determined whether or not the value of the G counter CIPFCNG is "0". Immediately when CIPFCNG = 0, and the CIPF
When CNG> 0, the count value is decremented by "1" (step S620), and step S6 is performed.
Proceed to 21.

In step S621, the check flag F
FCCHK is set to "1" and the process proceeds to step S622.

In step S622, the process of FIG. 41 is executed. That is, in step S631, it is determined whether the check flag FFCCHK is "1", and FFCCHK =
When it is 0, this processing is immediately terminated.

When FFCCHK = 1, the value of the NG counter CIPFCNG is NG judgment value NIPFCNG.
It is determined whether or not (for example, 2) (step S6
32), when CIPFCNG <NIPFCNG, it is determined that the deterioration has not occurred, and the lean deterioration flag FLF.
LNG is set to "0" (step S634), and CI is set.
When PFCNG ≧ NIPFCNG, it is determined that the deterioration has occurred, and the lean deterioration flag FLFLNNG is set to “1”.
Is set (step S633). Continued Step S63
In step 5, the determination end flag FLNJG is set to "1", and this processing ends.

According to the processing of FIGS. 40 and 41, the LAF sensor output VLAF is the predetermined upper and lower limit values VLAFFCH, VLA.
When it is out of the range of FFCL, NG counter CIPFCNG
Is incremented (step S616), is decremented when it is within the range (step S620), and when the count value is equal to or more than the NG determination value NIPFCNG, it is determined to be lean deterioration (step S633).

FIG. 42 is a flowchart of the process for determining the second monitor condition, that is, the lean deterioration determination execution condition, and this process is executed in the background like the process of FIG.

First, in step S641, it is determined whether or not the engine is in the start mode, and in the start mode, the lean region flag FLFFCLNZ which indicates by "1" that the operating conditions of the engine and the vehicle are in the lean region is set to "0". (Step S649) and the lean deterioration determination permission flag FLFFCLN is set to "0" (step S6).
53), the present process is terminated.

When not in the start mode, the LAF sensor 1
It is determined whether or not 7 is in the active state (step S64
2) If it is not in the active state, the process proceeds to step S649, and if it is in the active state, the deceleration fuel cut flag FDECFC, which indicates by "1" that the engine is in the deceleration operation and is in the fuel cut state, is "1". It is determined whether or not (step S643). When FDECFC = 0 and the deceleration fuel cut is not being performed, it is determined whether the engine water temperature TW is lower than the predetermined water temperature TWLFFC (step S644). When TW ≧ TWLFFC, the intake air temperature TA is the predetermined intake It is determined whether the temperature is higher than TALFFC (step S645), and TA ≦ TALFFC.
, The vehicle speed V is a predetermined upper and lower limit vehicle speed VLFFCH,
It is determined whether or not it is within the range of VLFFCL (steps S646 and S647), and VLFFCLV ≦ VLFFCH.
Engine speed NE is equal to the predetermined speed NLF,
It is determined whether it is higher than FCH (step S64).
8).

As a result, if any of the answers in steps S644 to S648 is affirmative (YES), it is determined that the region is not the lean region, the process proceeds to step S649, and step S649.
When all the answers from 644 to S648 are negative (NO),
Lean area flag FLFFCL
NZ is set to "1" (step S650), and the lean deterioration determination permission flag FLFFCLN is set to "0".
Is set (step S653), and the lean deterioration determination is not permitted.

In step S643, FDECFC =
When 1 and during deceleration fuel cut, it is determined whether or not the lean region flag FLFFCLNZ is "1" (step S651), and when FLFFCLNZ = 0, that is, immediately before shifting to deceleration fuel cut, the lean region is set. If not, the process proceeds to step S653, and the lean deterioration determination is not permitted. On the other hand, if FLFFCLNZ = 1, the lean deterioration determination permission flag FLFFCLN is set to "1" (step S652), and the lean deterioration determination is performed. Allow

As described above, according to the processing of FIG. 42, the lean deterioration determination is permitted when the lean area flag FLFFCLNZ is shifted to the deceleration fuel cut from the lean area set to "1".

In the above embodiment, when the response deterioration of the LAF sensor is detected, the sensor output selection timing is changed to a later one. However, the present invention is not limited to this. Feedback feedback gains KPOBSV, KIOBSV and K
At least one of DOBSV (formula 19) may be changed to a smaller value.

The stoichiometric deterioration determination processing of the LAF sensor may be performed as shown in FIG. 43, for example.

In step S701 of the figure, it is determined whether or not the above-described stoichiometric deterioration determination condition (monitor condition 1) is satisfied, and if not satisfied, this processing is immediately terminated. If so, the adjustment addition term KCMDOFFSET calculated in the process of FIG. 7 is the predetermined upper limit value KLAF.
It is determined whether FSH or more (step S702), KC
When MDOFFSET <KLAFFSH, KC
It is determined whether the MDOFFSET value is less than or equal to the predetermined lower limit value KLAFFSL (step S703). As a result, KC
MDOFFSET ≧ KLAFFSH or KCMDOF
When FSET ≧ KLAFFSL, the stoichiometric deterioration is determined and the stoichiometric deterioration flag FLFSTNG is set to “1”.
Is set (step S705). On the other hand, KCMDOF
When the FSET value is within the range of the upper and lower limits, it is determined that the stoichiometry is not deteriorated and the flag FLAFSTNG is set to "0" (step S704).

The adjustment addition term KCMDOFFSET is O
2 is an average value of the correction term DKCMDO2 of the target equivalent ratio KCMD set according to the sensor output, and the LAF sensor 1
Since the value becomes a value that compensates the influence of the stoichiometric deterioration of 8, the stoichiometric deviation of the LAF sensor output can be determined to be large when this value is outside the predetermined range.

The response deterioration may be detected as follows.

As shown in FIG. 44, when the target air-fuel ratio shifts from the stoichiometric air-fuel ratio to the fuel-cut state, the LAF sensor output corresponds to the air-fuel ratio A / F = 30 from the start of the fuel-cut execution. The detection time TDET until the value reaches the predetermined value is experimentally obtained in advance when the LAF sensor is in the normal stage, and this is calculated as the reference time TDETREF.
And Then, the detection time TDET is measured during the actual engine operation, and the delay time τ (= TDET-TDETREF) from the reference time TDETREF is calculated. This delay time τ becomes longer as the response characteristic of the LAF sensor deteriorates. Therefore, when the τ value exceeds a predetermined value, it is determined that the response has deteriorated.

[0209]

As described above in detail, according to the air-fuel ratio control device of the first aspect, when the deterioration of the response characteristic of the air-fuel ratio sensor is detected, the output of the air-fuel ratio sensor sampled at a later timing is output. Since the cylinder-by-cylinder air-fuel ratio feedback is performed by using the cylinder-by-cylinder air-fuel ratio, an accurate estimated value of the cylinder-by-cylinder air-fuel ratio can be obtained and good exhaust gas characteristics can be maintained even when the response characteristics of the air-fuel ratio sensor deteriorate.

According to the air-fuel ratio control device of the second aspect,
When the stoichiometric deterioration of the air-fuel ratio sensor is detected, the cylinder-by-cylinder air-fuel ratio feedback is prohibited. Therefore, it is possible to prevent the feedback from deteriorating the controllability of the air-fuel ratio.

According to the air-fuel ratio control device of claim 3,
When lean deterioration of the air-fuel ratio sensor is detected, feedback control is performed with the air-fuel ratio near the stoichiometric air-fuel ratio as the target air-fuel ratio, so in the operating range where the air-fuel ratio away from the theoretical air-fuel ratio is the target air-fuel ratio. Feedback control is not executed, and it is possible to prevent deterioration of the controllability of the air-fuel ratio in the operating region.

According to the air-fuel ratio control device of claim 4,
When the cylinder-by-cylinder air-fuel ratio feedback is performed using at least one of the proportional term, the integral term, and the derivative term, and when deterioration of the response characteristic of the air-fuel ratio sensor is detected, at least one of the proportional term, the integral term, and the derivative term. Is changed to a smaller value and the feedback control is executed, so that the same effect as that of the air-fuel ratio control device of the first aspect is achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control system therefor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a detailed configuration of part of FIG.

FIG. 3 is a functional block diagram for explaining an air-fuel ratio control method in this embodiment.

FIG. 4 is a flowchart of a process of calculating an air-fuel ratio correction coefficient based on the LAF sensor output.

FIG. 5 is a flowchart of a final target air-fuel ratio coefficient (KCMDM) calculation process.

FIG. 6 is a flowchart of a target air-fuel ratio coefficient (KCMD) calculation process.

FIG. 7 shows a target air-fuel ratio coefficient (KC
It is a flowchart of the process which calculates the correction term (DKCMDO2) of MD).

8 is a diagram showing a table used in the process of FIG. 7. FIG.

FIG. 9 is a diagram showing a relationship between a TDC signal pulse and a LAF sensor output.

FIG. 10 is a diagram for explaining an optimum sampling timing of the LAF sensor output.

FIG. 11 is a diagram for explaining a LAF sensor output selection process.

FIG. 12 is a flowchart of a LAF sensor output selection process.

FIG. 13 is a diagram showing a timing map for LAF sensor output selection.

FIG. 14 is a diagram for explaining a setting tendency of the map in FIG.

FIG. 15 is a flowchart of a detection equivalence ratio (KACT) calculation process.

FIG. 16 is a flowchart of LAF feedback area determination processing.

FIG. 17 is a block diagram showing an example of modeling the detection operation of the LAF sensor.

FIG. 18 is a block diagram of a model in which the model shown in FIG. 17 is discretized with a period ΔT.

FIG. 19 is a block diagram of a true air-fuel ratio estimator modeling a detection operation of a LAF sensor.

FIG. 20 is a block diagram of a model showing the behavior of the exhaust system of the internal combustion engine.

FIG. 21 is a diagram showing the air-fuel ratio output value and the actual measurement value of the collecting portion of the model of FIG. 20 in comparison.

FIG. 22 is a block diagram showing a configuration of a general observer.

FIG. 23 is a block diagram showing the structure of an observer in this embodiment.

24 is a block diagram showing a configuration in which the model shown in FIG. 20 and an observer are combined.

FIG. 25 is a block diagram for explaining cylinder-by-cylinder air-fuel ratio feedback control.

FIG. 26 is a flowchart of a process for calculating a correction coefficient for each cylinder (KOBSV # N).

FIG. 27 is a flowchart of cylinder-by-cylinder air-fuel ratio estimation processing.

FIG. 28 is a diagram showing an operating region in which cylinder-by-cylinder air-fuel ratio feedback control is executed.

FIG. 29 is a flowchart of a PID correction coefficient (KLAF) calculation process.

[Fig. 30] Fig. 30 is a flow chart for explaining the deterioration determination of the LAF sensor and the fail-safe processing at the time of detecting the deterioration.

FIG. 31 is a diagram illustrating a method for determining stoichiometric deterioration of a LAF sensor.

FIG. 32 is a diagram for explaining a method of determining response deterioration of a LAF sensor.

FIG. 33 is a diagram for explaining a method for determining lean deterioration of the LAF sensor.

FIG. 34 is a flowchart showing the overall configuration of LAF sensor deterioration determination processing.

FIG. 35 is a flowchart of stoichiometric deterioration determination processing.

FIG. 36 is a flowchart of a target equivalent ratio calculation process during determination of stoichiometric deterioration.

FIG. 37 is a flowchart of a process of performing a limit check of a target equivalent ratio.

FIG. 38 is a flowchart of a response deterioration determination process of the LAF sensor.

FIG. 39 is a flowchart of a process for determining a determination execution condition for stoichiometric deterioration and response deterioration of the LAF sensor.

FIG. 40 is a flowchart of lean deterioration determination processing of the LAF sensor.

41 is a flowchart showing in detail a part of the processing of FIG. 41. FIG.

FIG. 42 is a flowchart of a process of determining a lean deterioration determination execution condition of the LAF sensor.

FIG. 43 is a flowchart of stoichiometric deterioration determination processing of the LAF sensor.

[Fig. 44] Fig. 44 is a diagram for describing a method for determining a response deterioration of a LAF sensor.

[Explanation of symbols]

 1 Internal Combustion Engine (Main Body) 2 Intake Pipe 5 Electronic Control Unit (ECU) 12 Fuel Injection Valve 16 Exhaust Pipe 17 Wide Area Air-Fuel Ratio Sensor 18 Oxygen Concentration Sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location F02D 45/00 368 F02D 45/00 368G (72) Inventor Shusuke Akasaki 1-chome, Wako-shi, Saitama Prefecture No. 1 Stock Company Honda Technical Research Institute

Claims (4)

[Claims] 1. An air-fuel ratio sensor provided in an exhaust system of an internal combustion engine, and an observer for observing the internal state of the engine based on a model describing the behavior of the exhaust system of the engine are set, and the air-fuel ratio sensor Cylinder-by-cylinder air-fuel ratio estimation means for estimating the air-fuel ratio of each cylinder by using the output as input, and feedback control of the air-fuel ratio of the air-fuel mixture supplied to each cylinder so that the estimated air-fuel ratio of each cylinder converges to a target value. In an air-fuel ratio control device for an internal combustion engine, comprising: a cylinder-by-cylinder feedback control means for: an engine operating state detecting means for detecting an operating state of the engine; and an output of the air-fuel ratio sensor for each predetermined crank angle rotation of the engine. Sampling means for sequentially sampling the sampled values and selecting one of the stored sampled values according to the operating state of the engine. Selecting means, response deterioration detecting means for detecting deterioration of response characteristics of the air-fuel ratio sensor, and when deterioration of response characteristics of the air-fuel ratio sensor is detected,
Sample value changing means for changing the sample value selected by the selecting means to one sampled at a later timing, and the cylinder-by-cylinder feedback control means uses the changed sample value for the feedback control. An air-fuel ratio control device for an internal combustion engine, which is characterized. 2. An air-fuel ratio sensor provided in an exhaust system of an internal combustion engine and an observer for observing an internal state of the engine based on a model describing the behavior of the exhaust system of the engine are set, and the air-fuel ratio sensor Cylinder-by-cylinder air-fuel ratio estimation means for estimating the air-fuel ratio of each cylinder by using the output as input, and feedback control of the air-fuel ratio of the air-fuel mixture supplied to each cylinder so that the estimated air-fuel ratio of each cylinder converges to a target value. In an air-fuel ratio control device for an internal combustion engine, which comprises: An air-fuel ratio control device for an internal combustion engine, comprising: prohibiting means for prohibiting the operation of the feedback control means for each cylinder when the stoichiometric deterioration is detected. . 3. An air-fuel ratio sensor provided in an exhaust system of an internal combustion engine, capable of detecting at least an air-fuel ratio leaner than a stoichiometric air-fuel ratio, and an internal state thereof based on a model describing the behavior of the exhaust system of the engine. Set the observer to observe,
Cylinder-by-cylinder air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder by inputting the output of the air-fuel ratio sensor, and of the air-fuel mixture supplied to each cylinder so that the estimated air-fuel ratio of each cylinder converges to a target value. An air-fuel ratio control device for an internal combustion engine, comprising: a cylinder-by-cylinder feedback control means for feedback-controlling an air-fuel ratio, wherein a deviation of an output corresponding to an air-fuel ratio leaner than a theoretical air-fuel ratio of the air-fuel ratio sensor is a predetermined lean Providing lean deterioration detecting means for detecting deterioration, wherein the cylinder-by-cylinder feedback control means, when detecting the lean deterioration, executes feedback control with an air-fuel ratio near the theoretical air-fuel ratio as a target air-fuel ratio. Air-fuel ratio control device for internal combustion engine. 4. An air-fuel ratio sensor provided in an exhaust system of an internal combustion engine and an observer for observing an internal state of the engine based on a model describing the behavior of the exhaust system of the engine are set, and the air-fuel ratio sensor Using cylinder-by-cylinder air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder with the output as an input, and at least one of a proportional term, an integral term and a differential term calculated according to the estimated air-fuel ratio of each cylinder, An air-fuel ratio control device for an internal combustion engine, comprising: a cylinder-by-cylinder feedback control means for feedback-controlling an air-fuel ratio of an air-fuel mixture supplied to each cylinder so that the estimated air-fuel ratio of each cylinder converges to a target value. Response deterioration detecting means for detecting deterioration of response characteristics of the air-fuel ratio sensor is provided, and when the cylinder-specific feedback control means detects the response deterioration, the proportional term, integral term, and derivative term are small. Both air-fuel ratio control apparatus for an internal combustion engine and executes a to feedback control changing one to a smaller value.