JPH08232731A - Control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To ensure sufficient accuracy ad stability of control of an air-fuel ratio even when the combustion state of an engine is deviated from a steady state and to maintain excellent operability and exhaust gas characteristics. CONSTITUTION: When an engine is in a combustion unsteady state, for example, an engine water temperature TW is outside of an specified engine water temperature range, or when vehicle operation is in a non-steady state, for example, before a lapse of a given time after completion of execution of traction control at a step 511, it is decided at a step S520 that the engine is in a low response feedback control region. Instead of feedback control of an air-fuel ratio through adaptive control based on an LAF sensor output feedback control of an air-fuel ratio through PID control is added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for feedback-controlling an air-fuel ratio of an air-fuel mixture supplied to the engine by feedback control applying an adaptive control theory.

[0002]

2. Description of the Related Art One of modern control theories is a method of feedback control of an air-fuel ratio of an air-fuel mixture supplied to an engine based on a wide-range air-fuel ratio sensor provided in an exhaust system of an internal combustion engine. An optimum regulator is applied to this air-fuel ratio feedback control, and an air-fuel ratio feedback control method using the output of the wide-range air-fuel ratio sensor and the optimum feedback gain calculated based on the dynamic model of the engine has already been proposed. (For example, Japanese Patent Laid-Open No. 3-1
85244).

In the air-fuel ratio feedback control to which the above-mentioned optimum regulator is applied, the measured result and the past control amount are related in the form of a recurrence formula, and the optimum value obtained thereby is controlled as the next control amount. The control response is high, and it is a very effective control means when the combustion state of the engine is continuously in a steady state.

However, when the engine decelerates, combustion becomes unstable and the detected air-fuel ratio fluctuates greatly, so in order to suppress this, an optimal feedback gain, which is inferior in response, is used when decelerating the engine, or from adaptive control. An air-fuel ratio control device for an internal combustion engine is already known in which proportional-integral control is switched to feedback-control the air-fuel ratio (Japanese Patent Laid-Open No. 4-209940).

[0005]

However, since the air-fuel ratio feedback control to which the above-mentioned optimum regulator is applied is a control that uses the result of past control, the continuity of control is performed even when the engine is decelerated as described above. If it is not possible to maintain, the incorrect control amount may be calculated.For example, if the combustion state of the engine deviates from the steady state, hunting will occur due to its high-speed control response. there is a possibility. Therefore, for example, when the air-fuel ratio suddenly changes, the combustion state of the engine deteriorates, when it is difficult to accurately detect the air-fuel ratio, or when the fuel amount corresponding to the calculated control amount is not accurately supplied to the engine, the control is performed. Since there is a decrease in the accuracy and stability of the engine, there is room for improvement from the viewpoint of improving engine operability and exhaust gas characteristics. This problem is particularly large in the recursive type adaptive controller, which has a higher response than the optimum regulator.

The present invention has been made to solve this problem, and ensures sufficient accuracy and stability of the air-fuel ratio control even when the combustion state of the engine deviates from the steady state. An object of the present invention is to provide a control device for an internal combustion engine that can maintain good drivability and exhaust gas characteristics.

[0007]

In order to achieve the above object, a control device for an internal combustion engine according to a first aspect of the present invention adopts a recursive formula based on an output of an air-fuel ratio sensor provided in an exhaust system of the internal combustion engine. First control means for feedback-controlling the fuel supplied to the engine so that the air-fuel ratio of the engine is converged to a target value using a controller, and more than the first control means depending on the output of the air-fuel ratio sensor. A control device for an internal combustion engine, comprising: a second control means for controlling the air-fuel ratio by feedback control with a slow response speed; and an operating condition detecting means for detecting an operating condition of at least one of the engine and a vehicle equipped with the engine. An unsteady state determination unit that determines an engine combustion unsteady state in which the combustion state of the engine changes based on the output of the operating state detection unit; and at least the engine combustion unsteady state. When the determination is characterized by having a selection means for selecting said second control means.

In order to achieve the same object, a control device for an internal combustion engine according to a second aspect of the present invention has the structure of the first aspect,
The adaptive controller includes a parameter adjusting mechanism for adjusting an adaptive parameter used in the adaptive controller.

Further, in order to achieve the same object, claim 3
The control device for an internal combustion engine according to claim 2, wherein the second control means sets an air-fuel ratio of the engine by using an adaptive controller of a recurrence type based on the output of the air-fuel ratio sensor. Feedback control of the fuel supplied to the engine so as to converge to a value, the adaptive controller of the second control means is provided with a parameter adjusting mechanism for adjusting the adaptive parameter used in the adaptive controller, and the parameter is adjusted. The parameter adjustment speed in the adjustment mechanism is the first
It is characterized in that it is slower than the parameter adjusting speed in the parameter adjusting mechanism of the control means.

In order to achieve the same object, a control device for an internal combustion engine according to a fourth aspect is the control device according to the first or second aspect, wherein the second control means has at least one of a proportional term, an integral term and a derivative term. It is characterized in that it is a control means for performing feedback control using one.

Further, in order to achieve the same object, claim 5
The control device for an internal combustion engine according to any one of claims 1 to 4, wherein the selection means determines that the engine combustion unsteady state has returned to the engine combustion steady state by the unsteady state determination means. It is characterized in that the first control means is selected after a lapse of a predetermined time from the point of time.

Further, in the structure according to any one of claims 1 to 5, specifically, it is preferable that the operating state detecting means detects the deceleration state of the engine.

The operating condition detecting means may detect the temperature of the engine.

Further, it is preferable that the operating condition detecting means detects a retard angle of the ignition timing of the engine.

Further, the operating condition detecting means may detect a fuel supply stop condition of the engine.

Further, it is preferable that the driving state detecting means detects the operation of the traction control means for suppressing excessive slip of the drive wheels of the vehicle.

Further, the operating condition detecting means may detect the operation of the engine output characteristic control means of the engine.

Further, it is preferable that the driving state detecting means detects that the transmission of the vehicle is in a shifting operation.

Further, the operating state detecting means may detect a change in the target air-fuel ratio of the air-fuel mixture supplied to the engine.

[0020]

According to the control apparatus for an internal combustion engine of the present invention, the engine combustion unsteady state in which the combustion state of the engine changes is determined based on the operating states of at least one of the engine and the vehicle equipped with the engine. At least when determining the engine combustion unsteady state, the second control means having a slower response speed than the first control means is selected.

According to the control device of the internal combustion engine of claim 5,
The first control means is selected after a lapse of a predetermined time from the time when it is determined that the combustion state of the engine has returned from the engine combustion unsteady state to the engine combustion steady state.

According to the control device for an internal combustion engine of claim 6,
The engine combustion unsteady state is determined by the deceleration state of the engine.

According to the control device for the internal combustion engine of claim 7,
The engine combustion unsteady state is determined by the temperature of the engine.

According to the control device for an internal combustion engine of claim 8,
The engine combustion unsteady state is determined by the retard of the ignition timing of the engine.

According to the control device for the internal combustion engine of claim 9,
The engine combustion unsteady state is determined depending on whether the engine fuel supply is stopped.

According to the control device for an internal combustion engine of the tenth aspect, the engine combustion unsteady state is determined by whether or not the traction control means of the vehicle is operating.

According to the eleventh aspect of the control device for the internal combustion engine, the engine combustion unsteady state is determined by whether or not the engine output characteristic control means of the engine is operating.

According to the twelfth aspect of the control device for the internal combustion engine, the engine combustion unsteady state is determined depending on whether or not the gear shifting operation of the transmission of the vehicle is being performed.

According to the thirteenth aspect of the control apparatus for the internal combustion engine, the engine combustion unsteady state is determined by changing the target air-fuel ratio of the air-fuel mixture supplied to the engine.

[0030]

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

(First Embodiment) 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 a first embodiment of the present invention. In the figure, 1 is an engine.

The intake pipe 2 of the engine 1 communicates with a combustion chamber of each cylinder of the engine 1 via 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 the 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.

An automatic transmission (not shown) including a fluid clutch or the like is provided between the engine 1 and wheels (not shown).
The shift position (P range, N range, D range, etc.) can be changed by operating a shift lever (not shown).

A shift position (SPN) sensor 70 is attached to the automatic transmission, the shift position of the automatic transmission is detected by the SPN sensor 70, and an output signal thereof is supplied to the ECU 5.

Further, a wheel speed sensor (not shown) for detecting the driving wheel speed and the driven wheel speed of the vehicle equipped with the engine 1 is provided, and the detection signal is supplied to the ECU 5. The ECU 5 determines the excessive slip state of the drive wheels based on the detected drive wheel speed and the driven wheel speed, and when the excessive slip state is detected, the air-fuel ratio becomes lean or the fuel supply to some cylinders is stopped. Or a control for retarding the ignition timing (traction control).

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 the high speed rotation region of the engine and a low speed valve timing suitable for the 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 even when the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio. I try to secure the combustion.

The valve timing switching mechanism 60 switches the valve timing via hydraulic pressure, and an electromagnetic valve and a hydraulic sensor (not shown) for switching the hydraulic pressure are set to E.
CU5 is connected. The detection signal of the hydraulic sensor is ECU
5, the ECU 5 controls the solenoid valve to control valve timing switching.

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.

[0046]

[Equation 1] TOUT = TIMF × KTOTAL × KCMD
M × KFB FIG. 2 is a functional block diagram for explaining the calculation method of the fuel injection time TOUT according to the above formula 1, and the outline of the calculation method of the fuel injection time TOUT in the present embodiment will be described with reference to this. 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. 2, 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 B4 are multiplication blocks, which multiply the input parameters of the block and output it. With these blocks, the calculation of the above formula 1 is performed and the fuel injection amount TOUT 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 for 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 22. 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 stoichiometric air-fuel ratio, it is also called a target equivalent 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 B1
8 and B23. Block B23 is KCMD
The final target air-fuel ratio coefficient KC
Calculate MDM 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 processing), and the block B18 is passed through the low-pass filter blocks B16 and B17.
And B19. 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.

A 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. Block B19 is adaptive control (Self Tunin) based on the detected air-fuel ratio.
g) and calculate the adaptive correction coefficient KSTR and input it to block B20. In this adaptive control, if the target air-fuel ratio coefficient KCMD (KCMDM) is simply multiplied by the basic fuel amount TIMF, the target air-fuel ratio becomes a blunted detected air-fuel ratio because of the response delay of the engine. It was introduced to compensate dynamically and improve toughness against disturbance.

The block B20 selects one of the input PID correction coefficient KLAF and adaptive correction coefficient KSTR according to the engine operating state, and inputs it to the block B4 as a feedback correction coefficient KFB. this is,
It is considered that it is better to use the KLAF value calculated by the conventional PID control instead of the adaptive control depending on the engine operating state.

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 fuel injection amount TOUT is calculated by switching the ID correction coefficient KLAF and the adaptive correction coefficient KSTR calculated by the adaptive control and applying it as the correction coefficient KFB to the above mathematical expression 1. With the adaptive correction coefficient KSTR, it is possible to improve the followability to the detected air-fuel ratio change and the toughness to the disturbance, improve the purification rate of the catalyst, and obtain good exhaust gas characteristics in various engine operating conditions.

In the present embodiment, the function of each block in FIG. 2 described above is realized by the arithmetic processing by the CPU of the ECU 5, so the content of the processing will be specifically described with reference to the flowchart of this processing.

FIG. 3 is a flow chart of a process of calculating the PID correction coefficient KLAF and the adaptive correction coefficient KSTR according to the output of the LAF sensor 17, and finally calculating the feedback correction coefficient KFB. 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 engine is in the starting mode, 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.

Then, it is determined whether or not 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 is 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
The D correction coefficient KLAF, the adaptive correction coefficient KSTR, and the feedback correction coefficient KFB are all set to "1.0", and the integral term KLAFI of the PID control is set to "0".
Then, this process ends. Also, FKLAFRE
When SET = 0, the feedback correction coefficient KFB is calculated (step S9), and this processing ends.

Hereinafter, the above steps S2 to S4, S6 and S
Details of the processing in 9 will be sequentially described.

FIG. 4 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 the 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, in 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 if 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 subsequent step S27, the target air-fuel ratio coefficient KCMD is calculated, and then the limit processing of the calculated KCMD value (processing to make it fall within the range of predetermined upper and lower limit values)
I do. 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 correction term DKCMDO2 of the target air-fuel ratio coefficient KCMD is calculated according to the output VMO2 of the O2 sensor 18. This process is carried out according to the deviation between the O2 sensor output VMO2 and the reference value VREFM.
The correction term DKCMDO2 is calculated by control.

In 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 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. 5 shows K in step S27 of FIG.
It is a flow chart of CMD calculation processing.

First, in step S51, the after-start lean flag FASTLEAN set in step S24 of FIG. 4 is set.
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. 4 (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 S59.

In step S59, it is determined whether or not an abnormality has been detected in the O2 sensor 18, and if no abnormality is detected, the process immediately proceeds to step S61. KCMDOFFSE
T is set to the adjustment value KCMDOFFSETFS for abnormal conditions (step S60), and the process proceeds to step S61.

Here, the adjustment KCMDOFF for abnormal conditions is used.
SETFS is set to a value such that the air-fuel ratio is biased in the slightly rich direction. This makes it possible to prevent torque fluctuation and knocking due to lean air-fuel ratio when the O2 sensor is abnormal.

Then, in step S61, the KCMD value is corrected by the following equation and the process proceeds to step S62. The adjustment addition term KCMDOFFSET is used for the engine exhaust system and LA.
This is a parameter for finely adjusting the target air-fuel ratio coefficient KCMD so as to take the optimum position of the window zone of the three-way catalyst by reflecting the influence of the variation in the characteristics of the F sensor and the change over time.

KCMD = KCMD + KCMDOFFSET In step S62, it is determined whether or not the WOT flag FWOT set in step S25 of FIG. 4 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 in FIG. 4, and when the KCMD value is smaller than these coefficient values, the KCMD value is multiplied by the correction coefficient KWOT or KXWOT to correct the value. It is something to do.

Next, the LAF sensor output selection processing in step S3 of FIG. 3 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. 6, the air-fuel ratio recognized by the ECU 5 has a completely different value depending on the sample timing as shown in FIG. 7. 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.

Further, the change in the air-fuel ratio also differs depending on the arrival time of the exhaust gas to the sensor and the reaction time of the sensor. 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 this embodiment, as shown in FIG.
CRK signal pulse (generated every 30 degrees of crank angle)
The LAF sensor output sampled each time the occurrence of is sequentially stored in the ring buffer (which has 18 storage locations in this embodiment), and the output value at the optimum timing (the optimum value from the value 17 times before to the current value) is stored. The value) is converted into the detected equivalent ratio KACT and is used for feedback control.

FIG. 9 shows the LA in step S3 of FIG.
It is a flow chart of F 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. 10, 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 reason for setting in this way is that the LAF sensor output is sampled at a position as close as possible to the maximum value or minimum value (hereinafter referred to as “extreme value”) of the actual air-fuel ratio, as shown in FIG. At its best, its extreme value, for example, the first peak value, occurs at a crank angle position that is faster as the engine speed NE decreases, as shown in FIG. 11, assuming that the reaction time of the sensor is constant. The higher the load, the more the exhaust gas pressure and the exhaust gas volume increase, the flow velocity of the exhaust gas increases, and the arrival time at the sensor is shortened.

The high speed valve timing map is as follows:
For the same engine speed NE or the intake pipe absolute pressure PBA, the timing is set to be earlier than the low speed valve timing map. This is because the valve opening start timing of the exhaust valve is earlier in the high speed valve timing than in the low speed valve timing.

As described above, according to the processing of FIG. 9, the sensor output VLAF sampled at the optimum timing is selected according to the engine operating state, so that the detection accuracy of the air-fuel ratio can be improved.

Next, the calculation processing of the detected equivalent ratio KACT in step S4 of FIG. 3 will be described. FIG. 12 is a flowchart of this KACT calculation process.

First, in step S101, as shown in FIG.
Sensor output selection value VLAFSE selected by the process
The sensor output center value VCENT is subtracted from L to calculate the temporary value VLAFTEMP. Here, the central value V
CENT is LA when the air-fuel ratio of the air-fuel mixture is the theoretical air-fuel ratio.
F 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 a succeeding step S105, the table output center value VOUTCNT is added to the temporary value VLAFTEMP to calculate a 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. 13 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, a 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. When any of the answers in steps S121 to S125 is affirmative (YES), the PID correction coefficient KLAF
The KLAF reset flag FKLAFRESET, which indicates by "1" that the value should be reset to 1.0 (uncorrected value), is set to "1" (step S132).

On the other hand, if the answers to steps S121 to S125 are all negative (NO), the KLAF reset flag FKLAFRESET is set to "0" (step S).
131).

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 feedback correction coefficient KFB in step S9 of FIG. 3 will be described.

The feedback correction coefficient KFB is the PID correction coefficient KL depending on the engine operating state as described above.
The AF or adaptive correction coefficient KSTR is set. Therefore,
First, a method of calculating these correction coefficients will be described with reference to FIGS. 14 and 15.

FIG. 14 is a flowchart of the PID correction coefficient KLAF calculation process.

In step S301 of the figure, it is determined whether or not the hold flag FKLAFHOLD is "1", and FK
When LAFHOLD = 1, this processing is immediately terminated,
When FKLAFHOLD = 0, it is determined whether or not the KLAF reset flag FKLAFRESET is "1" (step S302). As a result, FKLAFRESE
When T = 1, the process proceeds to step S303, the PID correction coefficient KLAF is set to 1.0, and the integral control gain KI, the target equivalent ratio KCMD, and the detected equivalent ratio KACT are set.
The deviation DKAF between and is set to "0", and this processing 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.

At 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 adaptive correction coefficient KSTR calculation processing will be described with reference to FIG.

FIG. 15 is a block diagram showing the configuration of the block B19 shown in FIG. 2, that is, the adaptive control (STR (Self Tuning Regulator)) block. This STR block has a target air-fuel ratio coefficient (target equivalent ratio) KCMD (k ) And the detected equivalent ratio KACT (k) are matched, the STR controller that sets the adaptive correction coefficient KSTR, and the STR
It consists of a parameter adjustment mechanism that sets the parameters used in the controller.

One of the adjustment rules for adaptive control in this embodiment is the parameter adjustment rule proposed by Landau et al. This method transforms an adaptive system into an equivalent feedback system consisting of a linear block and a non-linear block. For the non-linear block, Popov's integral inequality for input and output is established, and the linear block is adjusted to be strongly positive. Is a method that guarantees the stability of the adaptive system. This technique is described in, for example, “Compute Roll” (published by Corona Publishing Co.) No. This is a known technique as described on pages 27, 28 to 41 or "Automatic Control Handbook" (Ohm Co., Ltd.), pages 703 to 707.

In this example, the adjustment rule of Landau et al. Was used. Explaining below, according to the adjustment law of Landau et al., When the polynomial of the denominator numerator of the transfer function A (Z- ¹ ) / B (Z- ¹ ) of the controlled object of the discrete system is set as in Equation 2,
The adaptive parameter θ hat (k) and the input ζ (k) to the adaptive parameter adjusting mechanism are determined by the following equation (2). In Equation 2, when m = 1, n = 1, and d = 3,
That is, a plant having a dead time of 3 control cycles in the primary system is taken as an example. Here, k indicates a time, more specifically, a control cycle. Further, in Expression 2, u (k) and y (k) are respectively KSTR (k) in this embodiment.
And KACT (k).

[0112]

[Equation 2] Here, the adaptive parameter θ hat (k) is represented by Expression 3. Further, Γ (k) and e asterisk (k) in Expression 3 are a gain matrix and an identification error signal, respectively, and are represented by recurrence expressions such as Expression 4 and Expression 5.

[0113]

(Equation 3)

[0114]

[Equation 4]

[0115]

(Equation 5) Further, various concrete algorithms are given depending on how to select λ1 (k) and λ2 (k) in Expression 4. λ1
When (k) = 1, λ2 (k) = λ (0 <λ <2), the taper gain algorithm (when λ = 1, the least squares method),
λ1 (k) = λ1 (0 <λ1 <1), λ2 (k) = λ2
(0 <λ2 <2), the variable gain algorithm (when λ2 = 1, the weighted least squares method), λ1 (k)
When / λ2 (k) = σ is set and λ3 is expressed by Expression 6, when λ1 (k) = λ3 is set, a fixed trace algorithm is obtained. Further, λ1 (k) = 1, λ2 (k) = 0
When it becomes a fixed gain algorithm. In this case, as is clear from Equation 4, Γ (k) = Γ (k−1), and thus Γ (k) = Γ is a fixed value.

[0116]

(Equation 6) Here, in FIG. 15, the STR controller (adaptive controller) and the adaptive parameter adjusting mechanism are placed outside the fuel injection amount calculation system, and the detected equivalent ratio KACT (k) is the target equivalent ratio KCMD (k. -D ') (where d'is KCMD
To be adaptively matched with (dead time until is reflected in KACT) to calculate an adaptive correction coefficient KSTR (k).

In this way, the adaptive correction coefficient KSTR (k)
And the detected equivalent ratio KACT (k) is calculated and input to the adaptive parameter adjusting mechanism, where the adaptive parameter θ hat (k) is calculated and input to the STR controller. The target equivalence ratio KC is input to the STR controller.
MD (k) is given, and the adaptive correction coefficient KSTR (k) is calculated using a recurrence formula so that the detected equivalent ratio KACT (k) matches the target equivalent ratio KCMD (k).

The adaptive correction coefficient KSTR (k) is specifically calculated as shown in Expression 7.

[0119]

(Equation 7) Next, the PID correction coefficient KLAF calculated as described above
And the adaptive correction coefficient KSTR are switched, that is, PI
A method of calculating feedback correction coefficient KFB by switching between D control and adaptive control will be described.

FIG. 16 is a flowchart of the calculation process of the feedback correction coefficient KFB in step S9 of FIG.

First, in step S401, whether the previous execution of the process of FIG. 3 was open loop control (FKLA
If it is not the open loop control, the change amount DKCMD (= | KCMD (k) -KCMD (k-) of the target equivalent ratio KCMD is determined.
1) It is determined whether or not |) is larger than the reference value DKCMDREF (step S402). Then, when the previous time was the open loop control, or when the previous time was the feedback control and the change amount DKCMD is the reference value DKCMDRE.
When it is larger than F, it is determined to be a region in which low-response feedback control should be executed (hereinafter referred to as "low-response F / B region"), and the counter C is reset to "0" (step S403). Feedback control processing (described later) is performed (step S411), and this processing ends.

When the previous time was the open loop control, it is determined that the low response F / B region is, for example, in the case of returning from the fuel cut state, LAF
This is because the detection value does not always show a true value due to the detection delay of the sensor, etc., and the control may become unstable. For the same reason, the target equivalent ratio KCM
When the change amount DKCMD of D is large, for example, when returning from the throttle full-opening increase state, or when returning from lean burn control to stoichiometric air-fuel ratio control, low response F /
It is determined to be the B area.

When the answers to Steps S401 and S402 are both negative (NO), that is, the feedback control is also performed the previous time, and the change amount DKCM of the target equivalent ratio KCMD is DKCM.
When D is less than or equal to the reference value DKCMDREF, the counter C
Is incremented by "1" (step S40
4), it is determined whether or not the value of the counter C is less than or equal to a predetermined value CREF (for example, 5) (step S405), and C ≦ CREF.
If so, step S411 is executed, while C>
If it is CREF, the process proceeds to step S406. In step S406, the F / B discrimination process, that is, the region in which high response feedback control is to be executed (hereinafter referred to as “high response F / B”).
Area)) or a low response F / B area is determined by the processing described later. Next in step S407.
Then, it is determined whether or not the control region determined in step S406 is the high response F / B region, and when it is not the high response F / B region, the step S411 is executed, while in the high response feedback control region, If there is, a high response feedback control process (described later) is performed to adjust the adaptive correction coefficient KST.
R is calculated (step S408), and the adaptive correction coefficient KST is calculated.
Absolute value of the difference between R and 1.0 | KSTR (k) -1.0 |
Is greater than the reference value KSTRREF (step S409), | KSTR (k) -1.0 |> KS
When TRREF, the process proceeds to step S411, while when | KSTR (k) -1.0 | ≦ KSTRREF, the feedback correction coefficient KFB is set to KSTR.
The value is set (step S410), and this processing ends.

Here, the reason why "low response feedback processing" is selected when the absolute value of the difference between the adaptive correction coefficient KSTR and 1.0 is larger than the reference value KSTRREF is to ensure control stability.

When the value of the counter C is equal to or less than the CREF value, the low response F / B region is defined as the fuel response immediately after the return from the open loop control or immediately after the target equivalent ratio KCMD changes greatly. Delay until combustion is completed or L
This is because the influence of the detection delay of the AF sensor cannot be absorbed.

Next, in step S406 of FIG.
A process for selecting the response speed of the air-fuel ratio feedback control will be described. FIG. 17 is a flowchart of the determination process of this feedback process.

First, in step S501, the LAL sensor 1
It is determined whether or not the response of No. 7 is deteriorated, and if it is not deteriorated, the process proceeds to step S502.

Next, in step S502, the LAF sensor 17
Of the crank angle position sensor 14 (cylinder discriminating sensor, TDC sensor, CRK sensor) is discriminated whether or not an abnormality is detected. S503), when no abnormality is detected in any of the sensors, it is determined whether or not an abnormality in the valve opening θTH sensor 4 is detected (step S504). When no abnormality is detected, the valve timing mechanism It is determined whether or not an abnormality is detected (step S505).

As a result, when no deterioration or abnormality is detected in steps S501 to S505, step S5
When any one of the deteriorations or abnormalities is detected in step 06, it is determined to be in the low response F / B area (step S520), and this processing is ended.

The reason why the feedback control with low response is selected when each sensor is abnormal is to prevent deterioration of air-fuel ratio controllability.

Next, in step S506, it is determined whether or not the engine water temperature TW is lower than a predetermined water temperature TWSTRON (step S504). When TW ≧ TWSTRON, the engine water temperature TW is the predetermined water temperature TWSTROFF.
(For example, 100 ° C.) or more is determined (step S507). If TW ≧ TWSTROFF, it is determined whether the intake air temperature TA is equal to or higher than a predetermined temperature TASTROFF (step S508). As a result, when TW <TWSTROFF is satisfied in step S507, TW ≧ TWSTROFF is satisfied in step S507, and TA <TASTROFF is satisfied in step S508, the routine proceeds to step S509, where the engine speed NE is the predetermined engine speed. It is determined whether the engine speed is equal to or more than NESTRMT, and when NE <NESTRMT, it is determined whether the engine is in the idle state (step S51).
0) When not in the idle state, it is determined whether or not a timer for measuring the time after the traction control system (TCS) returns to operation (end of execution of traction control) is in operation (step S511). It should be noted that this timer is composed of a down-count timer and is set during the TCS operation, and the countdown is started from the time point when the TCS operation is resumed.

If the result of determination in step S511 is that the timer after returning to TCS operation is not operating, it is determined whether the timer after returning from the fuel cut state of the engine (end of fuel cut) is operating. (Step S512). Here, the fuel cut of the engine is executed in a predetermined deceleration state of the engine, and the fuel cut flag FFC is set to "1" during the execution.
This timer is also composed of a down count timer,
It is set during the fuel cut of the engine, and the countdown starts when it returns from the fuel cut state.

As a result of the above determination, when the answer to step S506 or any of steps S509 to S512 is affirmative (YES), and steps S507 and S508.
If both answers are affirmative (YES), it is determined to be in the low response F / B area (step S520), and this processing ends. Further, the answer in step S512 is negative (NO).
If so, the process proceeds to step S550.

In step S550, it is determined whether the engine has misfired. As a method for judging misfire, for example, Japanese Patent Application Laid-Open No. 6-
There is a method known as 146998 or the like, which determines that an engine misfire has occurred when the engine rotation fluctuation exceeds a predetermined value. When the engine is misfired in step S550, the process proceeds to step S520, while when the engine is not misfired, the process proceeds to step S513.

In step S513, it is determined whether or not there is an instruction to switch the valve timing between high speed / low speed.
If there is no switching instruction, it is determined whether or not control for retarding the ignition timing of the engine by a large amount (retard) has been executed (step S514). If not, the process proceeds to step S516. If the answer in any of steps S513 and S514 is affirmative (YES), the down-count timer tmKCMDCHNG is set to the predetermined period TC.
Set HNG and start (step S51
5) Determined to be a low response F / B area. Here, the predetermined period T
CHNG is set to a period sufficient to stabilize the combustion state after a valve timing switching command is issued or after a large amount of ignition timing retard control is executed.

In step S516, it is determined whether or not the value of the down count timer tmKCMDCHNG has reached 0. If it has not reached 0 yet, a low response F /
It is determined that the region is the B region (step S520), and 0
When the detected equivalent ratio KACT reaches the predetermined upper limit value KACTLMTH (for example, 1.01), KACTLMT
It is determined whether or not it is within the range of L (for example, 0.99) (steps S517 and S518), and KACT <KACT.
If LMTL or KACT> KACTLMTH, the process proceeds to step S520, while KACTLM.
When TL ≦ KACT ≦ KACTLMTH, it is determined to be the high response F / B area (step S519), and this processing is ended.

By steps S517 and S518, the switching from the low response feedback control to the high response feedback control is performed when the detected equivalent ratio KACT is a value near 1.0, and the switching can be performed smoothly. The stability of can be secured.

Here, the reason why the low response feedback control is selected depending on the results of the determinations in steps S506 to S516 is as follows.

First, at low water temperature (TW <TWSTRON)
The reason is that combustion is not stable due to deterioration of atomization of fuel and increase of engine friction, and there is a risk of misfire, and a stable detected equivalent ratio KACT cannot be obtained. Also,
This is because when the engine water temperature is high (TW ≧ TWSTROFF) and when the intake air temperature is high (TA ≧ TASTROFF), the vapor injection in the fuel supply line may cause the actual injection amount of the fuel injection valve 6 to decrease. Further, at high rotation speed (NE ≧ NESTRLMT), the calculation time of the ECU tends to be short, and the combustion is not stable. Also, when the engine is idle, the operating state is almost stable, and high-response feedback control is not required. Further, after returning from the temporary ignition timing retard control or fuel cut control by executing traction control for the purpose of torque reduction for avoiding drive wheel slip, the combustion state becomes temporarily unstable for a predetermined period. This is because the feedback control of high response may rather increase the air-fuel ratio fluctuation. For the same reason, the feedback control with low response is also selected for the predetermined period after the fuel cut is returned.
Similarly, when the engine is misfiring, the combustion state is obviously unstable, so feedback control with low response is selected. Further, after the valve timing is switched, a predetermined period T
This is because in CHNG, the combustion state changes abruptly due to changes in the valve opening time of the intake and exhaust valves due to valve timing switching. Also, after the ignition timing is retarded by a large amount, a predetermined period T
This is because the combustion state inside CHNG is not stable and a stable detected equivalent ratio KACT cannot be expected.

When executing a large amount of ignition timing retard control, in addition to the traction control described above, torque shock reduction control during automatic transmission gear shifting, knocking avoidance control during engine high load, and after engine start An example is when executing ignition timing control for the purpose of increasing the catalyst temperature early.

Next, the high response / low response feedback control according to this embodiment will be described.

FIG. 19 is a flowchart of the high response feedback control processing in step S408 of FIG. First, in step S601, the adaptive correction coefficient KSTR
It is determined whether or not the flag FKSTR, which is indicated by "1" indicating that the feedback control is to be executed in the area (hereinafter referred to as "adaptive control area"), was "0" last time. As a result, when FKSTR = 1 the previous time, the process immediately proceeds to step S603, the adaptive correction coefficient KSTR is calculated by the above-described method, the flag FKSTR is set to “1”, and this processing ends.

On the other hand, when FKSTR = 0 the previous time, the adaptive parameter (scalar amount that determines the gain) b0
Is replaced by a value obtained by dividing the previous value KLAF (k-1) of the PID correction coefficient (step S602), and step S602 is performed.
603 and subsequent steps are executed.

At step S602, the adaptive parameter b0
By substituting b0 / KLAF (k-1) for
Switching from PID control to adaptive control can be performed more smoothly, and control stability can be ensured. This is for the following reasons. B0 in Equation 7 is replaced with b0
When it is replaced with / KLAF (k−1), it becomes as shown in the first expression of the expression 8, but the first term of the first expression becomes 1 because KSTR (k) = 1 while PID control is being executed. . Therefore, the KSTR (k) value at the beginning of adaptive control is KLA
It becomes equal to F (k-1), and the correction coefficient value is smoothly switched.

[0145]

(Equation 8) FIG. 20 is a flowchart of the low response feedback control process in step S411 of FIG. In step S621, it is determined whether or not the previous flag FKSTR has been set to "1". As a result, the last time was FKST
When R = 0, the PID correction coefficient KLAF is immediately calculated by the process of FIG. 14 described above (step S62).
3) Then, the flag FKSTR is set to "0" (step S624), the feedback correction coefficient KFB is set to the PID correction coefficient KLAF (k) calculated in step S623 (step S625), and this processing ends.

On the other hand, when FKSTR = 1 the previous time, the previous value kALFI (k-1) of the integral term of PID control
Is set to the previous value KSTR (k−1) of the adaptive correction coefficient (step S622), and steps S623 and thereafter are executed.

Here, at the time of switching from the adaptive control to the PID control (when FKSTR = 1 last time and this time is the low response F / B region), the integral term KLAFI of the PID control may suddenly change. By step S622, KLAF
(K-1) = KSTR (k-1). As a result, the difference between the adaptive correction coefficient KSTR (k-1) and the PID correction coefficient KLAF (k) can be kept small, the switching can be smoothed, and the control stability can be ensured.

According to the processing of FIGS. 16 to 20, the air-fuel ratio feedback control is switched from the adaptive control to the PID control at least during the period when the combustion state of the engine is in the unsteady state. Sufficient accuracy and stability of the fuel ratio control can be secured, and good drivability and exhaust gas characteristics can be maintained.

(Second Embodiment) Next, a control device for an internal combustion engine according to a second embodiment of the present invention will be described. In the above-described first embodiment, it is determined whether the region of the air-fuel ratio feedback control is the high response F / B region or the low response F / B region according to the combustion state of the engine 1 and the like, and the high response feedback is performed. Adaptive control is adopted as the control, and PID control is adopted as the low response feedback control. In the present embodiment, as the low response feedback control, the control response speed is reduced as it is in the adaptive control instead of the PID control. Therefore, since the same parts as those in the first embodiment are used in FIGS. 1 to 18, the description thereof will be omitted, and the description will be made with reference to FIGS. 21 and 22 instead of FIGS.

FIG. 21 is a flowchart of the high response feedback control processing in step S408 of FIG. 16 according to this embodiment. First, in step S641, the gain matrix Γ is used as the gain matrix Γ for high response feedback control.
And the dead time cycle number d is set to a value dH for high response feedback control, and the adaptive correction coefficient K
STR is calculated by the method described above (step S64
2) Then, this process ends.

FIG. 22 is a flow chart showing the process for low response feedback control in step S411 of FIG. 16 according to this embodiment.

In step S661, the low response feedback control gain matrix ΓL is selected as the gain matrix Γ, and the cycle number d of the dead time is set to the low response feedback control value dL. Here, the cycle number dL for low response feedback control is set to a value larger than the cycle number dH for high response feedback control. Next, in step S662, the adaptive correction coefficient KSTRL for low response feedback control is calculated, and the feedback correction coefficient KFB is set to the KSTRL value (step S66).
3) Then, this process ends.

Here, the low response feedback control gain matrix ΓL is the high response feedback control gain matrix Γ.
For H, a matrix with a smaller gain is determined in advance. Specifically, it is determined as follows by the following equation (9).

[0154]

[Equation 9] Expression 9 represents the gain matrix Γ in the present embodiment, which is composed of 5 parameters in each of the vertical and horizontal directions, and the size of the parameters g ₁ , g ₂ , g ₃ , g ₄ , g ₅ depends on the parameter adjustment mechanism. The level of change rate of the adaptive parameters b ₀ , r ₁ , r ₂ , r ₃ , s ₀ is determined. Therefore, for the gain matrix ΓH for high response feedback control, its parameters g ₁ ,
By setting g ₂ , g ₃ , g ₄ , and g ₅ to smaller values, it is possible to obtain the low response feedback control gain matrix ΓL with a low adaptive parameter adjustment speed in the parameter adjustment mechanism. In this case, all of g _{1 to} g ₅ may be set to small values, or some of them may be changed.
For example, g ₁ to g ₄ corresponding to the changing speeds of r ₁ to r ₃ corresponding to the control gain are changed, or g ₁ and g ₅ corresponding to the changing speeds of s ₀ and b ₀ that determine the responsiveness are changed. Both or one may be changed.

Since the responsiveness is determined by the entire gain matrix Γ, when changing each parameter independently, for example, an adjustment such that g ₅ is decreased and g ₂ to g ₄ are increased a little. It is also possible to reduce the responsiveness.

16 to 18 and FIG. 2 according to this embodiment.
22. By the processing of FIG. 1 and FIG. 22, it is possible to obtain the same effect as the first embodiment of suppressing the air-fuel ratio fluctuation in the unsteady state of engine combustion.

In the present embodiment, the gain matrix Γ
Parameter g₁, G₂, G₃, G_Four, G _FiveHigh response and low response
I set it for feedback control in advance,
Not only this, the degree of deterioration of engine combustion is detected and
G depending on the case₁~ G_FiveMay be set.

Further, in this embodiment, the parameter of the gain matrix Γ and the cycle number d of the dead time are changed as means for changing the control speed of the adaptive control. However, either the gain matrix Γ or the cycle number d is changed. One of them may be changed.

Further, as the air-fuel ratio feedback control which is switched when the engine combustion is unsteady, a mode in which the adaptive control is changed to the PID control in the first embodiment and the response speed of the adaptive control is changed in the second embodiment has been described. Two unsteady control means may be provided so that either one can be selected according to the situation.

(Third Embodiment) Next, a control device for an internal combustion engine according to a third embodiment of the present invention will be described. In this embodiment, combustion of the engine becomes unstable even when the engine is decelerated, and the LA
In view of the fact that the change in the output of the F sensor 17 also increases the change in the air-fuel ratio, in order to prevent this from being further promoted, the control speed is reduced as in the first embodiment. Since the basic configuration of the control device for the internal combustion engine of this embodiment is the same as that of the control device of the first embodiment, FIGS. 1 to 16, 19 and 20 are used as they are, and the description thereof is omitted. Step S51 of the flowchart
Description will be made using the one in which the flowchart shown in FIG. 23 is inserted between step 4 and step S516. Therefore, FIG. 17 and FIG. 18 in which the flowcharts of FIG. 23 are inserted show the flowchart of the discrimination processing of the feedback processing. Further, in FIGS. 17 and 18, the description of the same steps as those in the first embodiment will be omitted.

FIG. 23 is a part of the flow chart of the feedback process discrimination process as described above. Step S5
In step 31, it is determined whether or not the amount of change ΔTH in the throttle valve opening θTH per predetermined time is less than or equal to a predetermined value ΔTHDEC. It is determined whether or not (step S532). As a result, ΔTH> ΔTHDE
When C is satisfied and PBA> PBALO is satisfied, it is determined that the engine is not in the deceleration region, and step S516 is performed.
While proceeding to ΔTH ≦ ΔTHDEC or PBA ≦ OBA
When LO is satisfied, it is determined that the engine is in the deceleration region, and the process proceeds to step S515.

By this processing, fluctuations in the air-fuel ratio during deceleration of the engine can be suppressed.

In this embodiment, the PID control is adopted as the low response feedback control at the time of deceleration of the engine, but the present invention is not limited to this, and the adaptive control is maintained and the control speed is reduced as in the second embodiment. You may

In the above-mentioned first to third embodiments,
Abnormality detection of the sensor is performed by, for example, determining whether the output values of the various sensors are out of the predetermined upper and lower limit values or whether the sensor output value does not change for a predetermined time or longer. Further, the LAF sensor 17 determines that the label resistance value is abnormal when the label resistance value cannot be read or the response is deteriorated.

The response deterioration of the LAF sensor 17 is determined as follows, for example. That is, the LAF sensor output is the air-fuel ratio A from the time when the fuel cut is started.
The time TFC until the value corresponding to / F = 30 is measured, and when the difference between the reference time TFCREF and the TFC value measured in advance at the start of use of the LAF sensor is equal to or more than a predetermined value, it is determined that the response is deteriorated.

Further, the abnormality of the valve timing switching is determined by, for example, comparing the hydraulic pressure of the valve timing switching mechanism with the switching command signal output from the ECU 5.

[0167]

As described in detail above, the control device for an internal combustion engine according to claim 1 uses an adaptive controller of a recurrence type based on the output of the air-fuel ratio sensor provided in the exhaust system of the internal combustion engine. Control means for feedback-controlling the fuel supplied to the engine so that the air-fuel ratio of the engine converges to a target value, and a response speed slower than that of the first control means according to the output of the air-fuel ratio sensor. A second control means for controlling the air-fuel ratio by feedback control, and an engine combustion unsteady state of the engine is determined based on an operating state of at least one of the engine and a vehicle equipped with the engine, and at least the engine. When determining the combustion unsteady state, the second control means is selected. Therefore, even in the unsteady state of the combustion state of the engine, the accuracy and stability of the feedback control are ensured to change the air-fuel ratio. The can be suppressed, as a result, it is possible to maintain good engine driveability and exhaust emission characteristics.

According to another aspect of the control apparatus for an internal combustion engine of the present invention, the second control means controls the air-fuel ratio of the engine by using an adaptive controller of a recurrence type based on the output of the air-fuel ratio sensor. Fuel is fed back to the engine so as to converge to a target value, and the adaptive controller of the second control means includes a parameter adjusting mechanism for adjusting an adaptive parameter used in the adaptive controller. The parameter adjustment speed in the parameter adjustment mechanism is the first
Since it is slower than the parameter adjusting speed in the parameter adjusting mechanism of the control means, it is possible to suppress the fluctuation of the air-fuel ratio while maintaining the adaptive control even when the engine combustion is unsteady.

Further, according to the control device for an internal combustion engine of claim 5, the first control means is selected after a lapse of a predetermined time from the time when it is determined that the engine combustion unsteady state is returned to the engine combustion steady state. The feedback control by the first control means is performed after the combustion state is actually stabilized, and it is possible to prevent the control from becoming unstable in the transient state.

Further, according to the control device of the internal combustion engine of the sixth aspect, the engine combustion unsteady state is judged by the deceleration state of the engine, so that the air-fuel ratio fluctuation in the engine deceleration state can be suppressed.

According to the control device for an internal combustion engine of claim 7,
Since the engine combustion unsteady state is determined based on the temperature of the engine, it is possible to suppress fluctuations in the air-fuel ratio at low temperatures or abnormally high temperatures of the engine.

According to the control device for the internal combustion engine of claim 8,
Since the engine combustion unsteady state is determined by the retard of the ignition timing of the engine, it is possible to suppress the air-fuel ratio fluctuation caused by the retard of the ignition timing.

According to the control device for an internal combustion engine of claim 9,
Since the engine combustion unsteady state is determined by the fuel supply stop state of the engine, it is possible to suppress the air-fuel ratio variation due to the fuel supply stop.

According to the control apparatus for an internal combustion engine of the tenth aspect, the engine combustion unsteady state is judged depending on whether the traction control means of the vehicle is operating or not. Therefore, the fluctuation of the air-fuel ratio due to the execution of the traction control is suppressed. Can be suppressed.

According to the control apparatus for an internal combustion engine of the eleventh aspect, the engine combustion unsteady state is judged depending on whether the engine output characteristic control means of the engine is operating or not. Therefore, it is caused by the operation of the engine output characteristic control means. Fluctuations in the air-fuel ratio can be suppressed.

According to the twelfth aspect of the control apparatus for the internal combustion engine, the engine combustion unsteady state is determined depending on whether the gear shift operation of the transmission of the vehicle is being performed. Can be suppressed.

According to the control apparatus for an internal combustion engine of the thirteenth aspect, the engine combustion unsteady state is detected by changing the target air-fuel ratio of the air-fuel mixture supplied to the engine, so that it is stable even when the target air-fuel ratio is changed. It becomes possible to control.

[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 functional block diagram for explaining an air-fuel ratio control method in the embodiment of the present invention.

FIG. 3 is a flowchart of a process of calculating an air-fuel ratio correction coefficient based on an LAF sensor output.

FIG. 4 is a flowchart of a final target air-fuel ratio coefficient (KCMDM) calculation process.

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

FIG. 6 is a diagram showing a relationship between a TDC signal pulse and a LAF sensor output.

FIG. 7 is a diagram for explaining an optimum sampling timing of the LAF sensor output.

FIG. 8 is a diagram for explaining a LAF sensor output selection process.

FIG. 9 is a flowchart of a LAF sensor output selection process.

FIG. 10 is a diagram showing a timing map for LAF sensor output selection.

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

FIG. 12 is a flowchart of a detection equivalence ratio (KACT) calculation process.

FIG. 13 is a flowchart of a LAF feedback area determination process.

FIG. 14 is a flowchart of a PID correction coefficient (KLAF) calculation process.

FIG. 15 is a block diagram for explaining a process of calculating an adaptive correction coefficient (KSTR).

FIG. 16 is a flowchart of a feedback correction coefficient (KFB) calculation process.

FIG. 17 is a flowchart of feedback processing determination processing.

FIG. 18 is a flowchart of feedback processing determination processing.

FIG. 19 is a flowchart showing a high response feedback control process according to the first embodiment.

FIG. 20 is a flowchart showing low response feedback control processing according to the first embodiment.

FIG. 21 is a flowchart showing a high response feedback control process according to the second embodiment.

FIG. 22 is a flowchart showing a low response feedback control process according to the second example.

FIG. 23 is a part of a flowchart of feedback processing determination processing according to the third embodiment.

[Explanation of symbols]

 1 Internal Combustion Engine (Main Body) 4 Valve Opening (θTH) Sensor 5 Electronic Control Unit (ECU) 10 PBA Sensor 12 Fuel Injection Valve 13 Engine Water Temperature (TW) Sensor 14 Crank Angle Position Sensor 17 Wide Range Air-Fuel Ratio Sensor 60 Valve Timing Switching Mechanism 70 shift position (SPN) sensor

Claims (13)

[Claims] 1. An engine is provided so that the air-fuel ratio of the engine converges to a target value using an adaptive controller of a recurrence type based on the output of an air-fuel ratio sensor provided in an exhaust system of the internal combustion engine. Internal combustion engine having first control means for feedback-controlling the fuel to be controlled, and second control means for controlling the air-fuel ratio by feedback control whose response speed is slower than that of the first control means according to the output of the air-fuel ratio sensor. In the control device, an operating state detecting means for detecting an operating state of at least one of the engine and a vehicle equipped with the engine, and an engine combustion unsteady state in which a combustion state of the engine changes based on an output of the operating state detecting means. An unsteady state determining means for determining a state; and a selecting means for selecting the second control means at least when determining the engine combustion unsteady state. Control device for internal combustion engine. 2. The control device for an internal combustion engine according to claim 1, wherein the adaptive controller includes a parameter adjusting mechanism that adjusts an adaptive parameter used in the adaptive controller. 3. The second control means supplies the engine so that the air-fuel ratio of the engine converges to a target value using an adaptive controller of a recurrence type based on the output of the air-fuel ratio sensor. Fuel is feedback-controlled, and the adaptive controller of the second control means includes a parameter adjusting mechanism for adjusting an adaptive parameter used in the adaptive controller, and the parameter adjusting speed in the parameter adjusting mechanism is the first control. 3. The speed is slower than the parameter adjusting speed in the parameter adjusting mechanism of the means.
A control device for an internal combustion engine as described. 4. The control means for performing feedback control using at least one of a proportional term, an integral term and a derivative term, as the second control means.
A control device for an internal combustion engine as described. 5. The selecting means selects the first control means after a lapse of a predetermined time from a time point when it is determined by the unsteady state determination means that the engine combustion unsteady state has returned to the engine combustion steady state. The control device for an internal combustion engine according to any one of claims 1 to 4, characterized in that: 6. The control device for an internal combustion engine according to claim 1, wherein the operating state detecting means detects a deceleration state of the engine. 7. The control device for an internal combustion engine according to claim 1, wherein the operating state detecting means detects a temperature of the engine. 8. The control device for an internal combustion engine according to claim 1, wherein the operating state detecting means detects a retard angle of the ignition timing of the engine. 9. The control device for an internal combustion engine according to claim 1, wherein the operating state detecting means detects a fuel supply stop state of the engine. 10. The internal combustion engine according to claim 1, wherein the driving state detecting means detects an operation of a traction control means for suppressing excessive slip of driving wheels of the vehicle. Control device. 11. The control device for an internal combustion engine according to claim 1, wherein the operating state detecting means detects an operation of the engine output characteristic control means of the engine. 12. The control device for an internal combustion engine according to claim 1, wherein the operating state detecting means detects that the transmission of the vehicle is undergoing a gear shift operation. 13. The control device for an internal combustion engine according to claim 1, wherein the operating state detecting means detects a change in a target air-fuel ratio of an air-fuel mixture supplied to the engine.