JPH08232726A - Control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To suppress worsening of exhaust gas characteristics and lowering of operability to a minimum limit by continuing an air-fuel ratio feedback control as far as possible even when abnormality of a sensor is detected. CONSTITUTION: When abnormality (S172) of switching of a valve timing, abnormality (S173) of a sensor for each cylinder or a TDC sensor, or dispersion of adaptive control is detected (at S174), feedback control of an air-fuel ratio by PID control is carried out at S186 instead of feedback control of an air-fuel ratio by adaptive control based on an LAF sensor. When the abnormality is not detected, air-fuel ratio feedback by adaptive control is executed at S185 if other conditions, such as a water temperature, the number of revolutions, a high speed valve timing, and an idle state, are satisfied at S175-S178.

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 modern control theory.

[0002]

2. Description of the Related Art In an air-fuel ratio control device for feedback-controlling the air-fuel ratio of an air-fuel mixture supplied to an engine on the basis of the output of an oxygen concentration sensor for detecting the oxygen concentration in the exhaust gas of an internal combustion engine, an abnormal oxygen concentration sensor is detected. It is conventionally known that the feedback control is stopped when the determination is made (Japanese Patent Publication No. 60-56253).

Further, an optimum regulator, which is one of modern control theories, is applied to this air-fuel ratio feedback control, and is calculated based on the output of a wide range air-fuel ratio sensor provided in the exhaust system of the engine and a dynamic model of the engine. In the air-fuel ratio control device for feedback controlling the air-fuel ratio based on the optimum feedback gain, when the wide-range air-fuel ratio sensor is in a semi-warm state (a state before reaching a complete warm-up state),
The one in which the feedback control of the air-fuel ratio is performed by the PID control instead of the adaptive control has already been proposed (JP-A-5-52140).

[0004]

However, in the former air-fuel ratio control device, when the abnormality of the oxygen concentration sensor is detected, the feedback control is stopped, so that the exhaust gas characteristics and drivability during that period are stopped. There was room for improvement in terms of.

In the latter air-fuel ratio control device, the semi-warm state of the wide-range air-fuel ratio sensor is taken into consideration, but abnormal states of the wide-range air-fuel ratio sensor and other sensors are not taken into consideration. There was room for improvement.

The present invention has been made by paying attention to the above-mentioned points. The feedback control is continued as much as possible even when an abnormality of a sensor or the like is detected, and deterioration of exhaust gas characteristics and deterioration of drivability are minimized. An object is to provide a control device for an internal combustion engine that can be stopped.

[0007]

To achieve the above object, the present invention includes an engine operating state detecting means for detecting an operating state of the engine, which includes an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine, and First feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture to be supplied to the engine by using a controller of the recurrence type based on the output of the air-fuel ratio sensor, and the air-fuel ratio according to the detected engine operating state. A control device for an internal combustion engine, comprising: a feedforward control means for performing feedforward control of a fuel ratio, wherein the air-fuel ratio is controlled by feedback control having a response speed slower than that of the first feedback control means according to the output of the air-fuel ratio sensor. Based on the outputs of the second feedback control means and the engine operating state detection means, an abnormality of the engine or the control device is detected. And an abnormality processing means for prohibiting the operation of the first feedback control means or the operation of the first and second feedback control means in accordance with the detected abnormal state. Is.

The second feedback control means feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine by using a controller of a recurrence type based on the output of the air-fuel ratio sensor. Therefore, it is desirable that the adjustment speed of the feedback gain used in the recurrence type controller is slower than the adjustment speed of the feedback gain of the first feedback control means.

The second feedback control means may perform feedback control using at least one of a proportional term, a derivative term and an integral term.

[0010]

The abnormality of the engine or the control device is detected based on the output of the engine operating state detecting means, and the operation of the first feedback control means or the first and second feedback is performed according to the detected abnormal state. The operation of the control means is prohibited.

[0011]

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 an embodiment of the present invention. In the figure, 1 is an engine.

An 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 body of the engine 1 has an 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 (EGR) for controlling the amount of exhaust gas recirculation provided in the middle of the exhaust gas recirculation passage 31. 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, the evaporated fuel generated in the fuel tank 41 pushes the positive pressure valve of the two-way valve 44 open when it reaches a predetermined set pressure, flows 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 timing 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 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 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.

[0027]

[Equation 1] TOUT = TIMF × KTOTAL × KCMD
M × KFB FIG. 3 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. 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 B4 are multiplication blocks, which multiply the input parameters of the block and output the result. 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 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 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 an adaptive control (Self Tun) based on the detected air-fuel ratio.
ing Regulation), the adaptive correction coefficient KSTR is calculated and input to block B20. This adaptive control uses the target air-fuel ratio coefficient KCMD (KCMDM) as the basic fuel amount TIMF.
By simply multiplying by, the target air-fuel ratio becomes the blunted detected air-fuel ratio due to the response delay of the engine.
This is introduced in order to dynamically compensate for this and to 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 between 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 expression 1. With the adaptive correction coefficient KSTR, it is possible to improve the followability when the target air-fuel ratio is changed and the toughness with respect to 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. 3 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. 4 is a flow chart of a process for 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 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 LAF sensor 17 indicates the engine operating state.
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. 5 is a flowchart of the process for calculating the final target air-fuel ratio coefficient KCMDM in step S2 of FIG.

In step S21, it is determined whether or not the abnormality in the intake pipe absolute pressure sensor 10 is detected. If not detected, the process immediately proceeds to step S23. When the abnormality is detected, the throttle valve opening degree θTH is determined. The substitute value thus calculated is set as the intake pipe absolute pressure PBA, and the process proceeds to step S23.

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 a succeeding 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 a range of predetermined upper and lower limit values)
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, it is determined whether or not the abnormality of the O2 sensor 18 is detected (step S30). When the abnormality is not detected, the process proceeds to step S32, and the target air-fuel ratio coefficient KCMD is determined according to the output VMO2 of the O2 sensor 18. Correction term DK
Calculate CMDO2. This processing is performed by the O2 sensor output V
The correction term DKCMDO2 is calculated by PID control according to the deviation between MO2 and the reference value VREFM.

When the abnormality of the O2 sensor 18 is detected in step S30, the correction term DKCMDO2 is set to "0" (step S31), and the process proceeds to step S33.

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 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 S59.

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 S59. 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 of the O2 sensor 18 is detected. If no abnormality is detected, the process immediately proceeds to step S61. On the other hand, if an abnormality is detected, the adjustment addition term is used. KCMDOFFSE
T is set to the adjustment value KCMDOFFSETFS for abnormal conditions (step S60), and the process proceeds to step S61.

Here, the adjustment value KCMDOFF for abnormality 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. 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.

When an abnormality in the intake pipe absolute pressure (PBA) sensor is detected, the target equivalence ratio KCMD may be set to a fixed value.

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. 7, the air-fuel ratio recognized by the ECU 5 becomes 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.

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. 10 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. 11, the above 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 why the LAF sensor output is set as described above is that the LAF sensor output is sampled at a position as close as possible to a maximum value or a 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. 12, if the reaction time of the sensor is constant, and 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 process of FIG. 10, 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.

When the abnormality of the CRK sensor is detected, the LAF sensor output when the TDC signal pulse is generated is adopted. Thereby, the feedback control can be continued.

Next, the process of calculating the detected equivalent ratio KACT in step S4 of FIG. 4 will be described. FIG. 13 is a flowchart of this KACT calculation process.

First, in step S101, as shown in FIG.
Sensor output selection value VLAFS selected by processing 0
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.

Then, 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 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 which eliminates the influence of the characteristic variation of the LAF sensor.

FIG. 14 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 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, when all the answers in steps S121 to S125 are negative (NO), the LAF sensor 17 is further added.
Of the label resistance is detected (step S126). When the answer is affirmative (YES), whether stoichiometric feedback control is being performed, that is, the target equivalent ratio KCMD = 1.0. It is determined whether or not (step S127). Then, when the abnormality of the label resistance is not detected, or during the stoichiometric feedback even if the abnormality of the label resistance is detected, it is determined whether or not the abnormality of the engine water temperature sensor is detected (step S128). When the answer is negative (NO), it is determined whether or not an abnormality in the intake pipe absolute pressure sensor is detected (step S129). As a result, step S127
Is answered in the negative (NO) or step S128 or S
If any of the answers in 129 is affirmative (YES), the process proceeds to step S132 and steps S126 to S129.
If all the answers are negative (NO), the KLAF 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.

According to this processing, when the LAF sensor 17, the engine water temperature sensor 13 or the intake pipe absolute pressure sensor 10 is detected to be abnormal, the feedback control based on the LAF sensor output is stopped. It is possible to prevent the controllability of the air-fuel ratio from being deteriorated by executing it.

Next, the process of calculating the feedback correction coefficient KFB in step S9 of FIG. 4 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.

FIG. 15 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.

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

FIG. 16 is a block diagram showing the configuration of the block B19 shown in FIG. 3, 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 expressed by the following equation,
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).

[0098]

[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.

[0099]

(Equation 3)

[0100]

[Equation 4]

[0101]

(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.

[0102]

(Equation 6) Here, in FIG. 16, the STR controller (adaptive controller) and the adaptive parameter adjustment 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.

[0105]

(Equation 7) When it is detected that the response characteristic of the LAF sensor 17 is deteriorated (the response delay is increased), the order d of the dead time is increased or the gain matrix Γ is changed to a matrix having a smaller gain. It is desirable to lower the adjustment (identification) speed of the adaptive parameter. As a result, even when the response characteristic of the LAF sensor 17 is deteriorated, the adaptive control can be continued, and deterioration of the exhaust gas characteristic and deterioration of drivability can be minimized. When the response characteristic of the LAF sensor 17 is deteriorated, the adaptive control is changed to PI.
You may make it switch to D control.

Next, the PID correction coefficient KLAF calculated as described above and the adaptive correction coefficient KSTR are switched,
That is, a method of calculating the feedback correction coefficient KFB by switching the PID control and the adaptive control will be described.

FIG. 17 is a flow chart of the calculation process of the feedback correction coefficient KFB in step S9 of FIG.

First, in step S151, whether the previous execution of the process of FIG. 4 was the 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. When the previous time was the open loop control, or the previous time was the feedback control and the change amount D
When KCMD is larger than the reference value DKCMDREF,
It is determined that the feedback control by the PID correction coefficient KLAF is in an operating region (hereinafter referred to as “PID control region”), the counter C is reset to “0” (step S153), the process proceeds to step S164, and PI
The D correction coefficient KLAF calculation process (FIG. 19A) is executed.

In step S201 of FIG. 19A, it is determined whether or not the STR flag FKSTR was "1" in the previous control. The STR flag FKSTR indicates by "1" that it is an operating region (hereinafter referred to as "adaptive control region") in which feedback control by the adaptive correction coefficient KSTR is to be executed, and is set after calculation of the feedback correction coefficient (step S204, FIG. 19B, step S
213).

In step S201, last time FKSTR =
When it is 0, the process immediately proceeds to step S203, and when FKSTR = 1 last time, the previous value KALFI (k-1) of the integral term of the PID control is changed to the previous value KSTR (k-1) of the adaptive correction coefficient. ) (Step S20)
2) The process proceeds to step S203. In step S203, the PID correction coefficient KLA is obtained by the processing of FIG.
F is calculated, then the process proceeds to step S204, the STR flag FKSTR is set to "0", and the process of FIG.

At the time of switching from the adaptive control to the PID control (when FKSTR = 1 last time), there is a possibility that the integral term KLAFI of the PID control may suddenly change.
From 202, KLAFI (k−1) = KSTR (k−
1). As a result, the adaptive correction coefficient KSTR
The difference between (k-1) and the PID correction coefficient KLAF (k) can be kept small and the switching can be smoothed to ensure control stability.

Returning to FIG. 17, in the following step S165, the feedback correction coefficient KFB is set in step S164.
The PID correction coefficient KLAF (k) calculated in step S165 is set (step S165), and this processing ends.

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

When the answers to steps S151 and S152 are both negative (NO), that is, the previous feedback control is also performed, 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 S15
4), the value of the counter C is set to a predetermined value CR in step S155.
Compare with EF (eg 5). Here, if the value of the counter C is less than or equal to the CREF value, the process proceeds to step S164.

When the value of the counter C is less than or equal to the CREF value, P
The ID control area is set immediately after returning from the open loop control or immediately after the target equivalent ratio KCMD has changed significantly.
This is because it is not possible to absorb the influence of the delay until the combustion of the fuel is completed or the detection delay of the LAF sensor.

Next, proceeding to step S156, a discrimination process (FIG. 18) as to whether or not it is an adaptive control region is executed. The process of FIG. 18 determines whether the feedback correction coefficient KFB is obtained according to the adaptive control law or the PID control law according to the current engine operating state and whether the sensor or the like is abnormal.

That is, it is judged whether or not an abnormality in valve timing switching is detected (step S172),
If not detected, it is determined whether or not an abnormality of the CYL sensor or TDC sensor is detected (step S17).
3) If no abnormality of any sensor is detected,
It is determined whether the adaptive control has diverged (step S17).
4). Then, if any of the answers in steps S172 to S174 is affirmative (YES), it is determined to be the PID control area (step S186) and the present process is terminated, while all the answers in steps S172 to S174 are negative (NO). In the case of), the determinations of steps S175 to S179 are further performed. Whether or not the adaptive control has diverged is determined by, for example, whether or not the value of the adaptive correction coefficient KSTR falls outside the predetermined upper and lower limit values.

That is, the engine water temperature TW is equal to the predetermined water temperature T.
It is determined whether it is lower than WSTRON (step S17).
5) When TW ≧ TWSTRON, it is determined whether the engine speed NE is equal to or higher than a predetermined speed NESTRLMT (step S176), and NE <NESTRL.
When it is MT, it is determined whether or not the current valve timing is the high-speed valve timing (step S177), and when it is not the high-speed valve timing, it is determined whether the engine is in the idle state (step S178). As a result, if any of the answers in steps S175 to S178 is affirmative (YES), it is determined to be the PID control area (step S186), the present process is terminated, and steps S175 to S175.
When all the answers in S178 are negative (NO), the process proceeds to step S179.

In step S179, it is determined whether or not an abnormality in the throttle valve opening sensor 4 is detected. If no abnormality is detected, the process immediately proceeds to step S182. Further, when the abnormality of the throttle valve opening sensor is detected, the PBTHFS is changed according to the engine speed NE.
The table is searched to determine the STR stoppage determination value PBTHFS (step S180). Here, as shown in FIG. 20, the PBTHFS table is set so that the PBTHFS value decreases as the engine speed NE increases. Next, this PBTHFS value is set to the low load judgment value P.
As BLOW (step S181), step S18
Go to 2.

In step S182, the intake pipe absolute pressure P
It is determined whether BA is in a low load state lower than the low load determination value PBLOW, and when PBA <PBLOW, the PID
While it is determined to be the control area (step S186) and the present process is terminated, when PBA ≧ PBLOW, the process proceeds to step S183.

Here, the low load judgment value PBLOW is set to a predetermined value when the throttle valve opening sensor is normal, and only when there is an abnormality, the engine speed NE is set in step S180.
The STR stop determination value PBTHFS calculated according to This is because when the throttle valve opening sensor is abnormal, it is not possible to accurately determine the idle state based on the throttle valve opening θTH (when the throttle valve opening sensor is abnormal, the answer in step S178 is always negative ( This is because the idle state is determined by the absolute intake pipe pressure PBA.

When the throttle valve opening sensor abnormality is detected, both the adaptive control and the PID control may be prohibited (flag FKLAFRESET = 1). In that case, the throttle valve opening sensor abnormality is detected. If this is not detected, this processing is executed, and step S
The answer of 179 is always negative (NO).

In step S183, the detected equivalent ratio KAC
It is determined whether or not T is smaller than the predetermined value a. When it is equal to or larger than the predetermined value a, it is determined whether or not the detected equivalent ratio KACT is larger than the predetermined value b (> a) (step S184). Then, the answer in step S183 or S184 is affirmative (YE
If S), it is determined to be the PID control area (step S
186), and this processing ends. Also, step S183
If both answers in S184 and S184 are negative (NO), it is determined to be an adaptive control area (step S185), and this processing ends.

Here, the PID control area is determined, and the PID
The reason why the feedback correction coefficient KFB is calculated by the control is as follows. At low water temperature (TW <T
This is because in the case of (WSTRON), combustion is not stable, there is a risk of misfire, and a stable detection equivalent ratio KACT cannot be obtained. Even when the engine water temperature TW is abnormally high, the feedback correction coefficient KFB is calculated by the PID control for the same reason. Also, at high rotation speed (NE ≧ NE
This is because the calculation time of STRLMT) tends to be short and the combustion is not stable. Also, when high-speed valve timing is selected, the intake and exhaust valves are both open for a long overlap period, so intake air may pass through the exhaust valve as it is and be discharged, so-called blow-through may occur. This is because the equivalence ratio KACT cannot be expected. Also, when the engine is idle, the operating condition is almost stable, and high gain control such as adaptive control is not required.

When the detected equivalent ratio KACT is smaller than the predetermined value a or larger than the predetermined value b, it means that the air-fuel ratio of the engine is lean or rich, and high gain control such as adaptive control is not performed. Because it is better. In this embodiment, this determination is based on the detection equivalent ratio KA.
Although it was performed by CT, it may be performed by using the target equivalent ratio KCMD.

Returning to FIG. 17, in step S157, the feedback correction coefficient KFB is determined from the result of the processing in FIG.
Is determined by adaptive control. Step S1
When the answer to 57 is negative (NO), the above step S16
If the answer to step S157 is affirmative (YES), the process proceeds to step S158, and the previous STR flag FK
It is determined whether the STR is "0".

As a result, if FKSTR = 1 last time, the process immediately proceeds to step S161, and last time FKSTR = 1.
= 0, the detected equivalent ratio KACT is a predetermined upper and lower limit value KACTLMTH (for example, 1.01), KACTLM.
TL (for example, it is determined whether or not it is within the range of 0.99 (steps S159 and S160), and KACT <KACT
If LMTL or KACT> KACTLMTH, the process proceeds to step S164, and the PID correction coefficient K
Calculate LAF. In addition, KACTLMTL ≦ KACT
If ≦ KACTLMTH, the process proceeds to step S161 to execute the KSTR calculation process (FIG. 19B).

PI is set in steps S158 to S160.
Switching from the D control to the adaptive control is performed in the adaptive control region and when the detected equivalent ratio KACT is a value near 1.0. As a result, the PID control can be smoothly switched to the adaptive control, and the control stability can be ensured.

In step S210 of FIG. 19B, it is determined whether or not the previous flag KSTR was "0".
As a result, if FKSTR = 1 the previous time, the process immediately proceeds to step S212, the adaptive correction coefficient KSTR is calculated by the above-described method, and then the flag FKSTR is set to “1”, and the flag FKSTR shown in FIG. The process ends.

On the other hand, when FKSTR = 0 the previous time, the adaptive parameter (scalar amount for determining the gain) b0
Is replaced with a value obtained by dividing the PID correction coefficient by the previous value KLAF (k-1) (step S211), and the process proceeds to step S212.

In step S211, 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 equation of the equation 8, but the first term of the first equation is 1 because KSTR (k) = 1 while PID control is being executed. Become.
Therefore, the KSTR (k) value at the beginning of adaptive control is KL
It becomes equal to AF (k-1), and the correction coefficient value is smoothly switched.

[0132]

(Equation 8) Returning to FIG. 17, the absolute value of the difference between the value of the adaptive correction coefficient KSTR obtained in step S161 and 1.0 | KSTR (k)
It is determined whether -1.0 | is larger than the reference value KSTRREF (step S162), and | KSTR (k) -1.
If 0 |> KSTRREF, then step S1
While proceeding to 64, | KSTR (k) -1.0 | ≦ KST
When RREF, the feedback correction coefficient KFB
To the KSTR (k) value (step S163),
This process ends.

Here, when the absolute value of the difference between the adaptive correction coefficient KSTR and 1.0 is larger than the reference value KSTRREF, the PID control area is set in order to ensure control stability.

As described above, in the process of FIG. 18, the feedback correction coefficient KFB is set to the PID correction coefficient KLAF when an abnormality such as a sensor is detected in steps S172 to S174 and steps S179 to S181. Even when an abnormality occurs, air-fuel ratio feedback control, which has a slower response speed than adaptive control, is executed, and deterioration of exhaust gas characteristics and drivability can be minimized.

In the above-described embodiment, the sensor abnormality is detected by, for example, whether the sensor output value is outside the predetermined upper and lower limit values, or whether the sensor output value does not change for a predetermined time or longer. It is performed by determining whether or not. The label resistance of the LAF sensor 17 is determined to be abnormal when its value cannot be read.

The stoichiometric deviation of the LAF sensor 17 (FIG. 14, step S125) is detected as follows, for example. That is, when the output of the O2 sensor 18 is at a low level, the target equivalent ratio KCMD is gradually increased to
When the sensor output is at a high level, the control for gradually reducing the target equivalent ratio KCMD is continued for a predetermined time, and the average value KAC of the detected equivalent ratios KACT at the time of reversing the O2 sensor output.
TAV (however, the number of KACT values obtained when the O2 sensor output is inverted from low level to high level is made equal to the number of KACT values obtained when it is inverted in the opposite direction) is calculated. Then, when the average value KACTAV is outside the range of the predetermined upper and lower limit values (for example, outside the range of 1.0 ± 0.5), it is determined that the stoichiometric deviation has occurred.

The determination of the response deterioration of the LAF sensor 17 is made as follows, for example. That is, the LAF sensor output is the air-fuel ratio A / 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 becomes a predetermined value or more, it is determined that the response has deteriorated.

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

[0139]

As described in detail above, according to the present invention, an abnormality of the engine or the control device is detected based on the output of the engine operating state detecting means, and the abnormality detection unit detects the abnormality according to the detected abnormal state. 1 Since the operation of the feedback control means or the operation of the first and second feedback control means is prohibited, the feedback control is continued as much as possible even when the abnormality of the sensor or the like is detected, and the deterioration of the exhaust gas characteristics and the drivability are reduced. The drop can be minimized.

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

FIG. 8 is a diagram for explaining an optimum sampling timing of the LAF sensor output.

FIG. 9 is a diagram for explaining a LAF sensor output selection process.

FIG. 10 is a flowchart of a LAF sensor output selection process.

FIG. 11 is a diagram showing a timing map for LAF sensor output selection.

FIG. 12 is a diagram for explaining a setting tendency of the map of FIG. 11.

FIG. 13 is a flowchart of a detection equivalence ratio (KACT) calculation process.

FIG. 14 is a flowchart of a LAF feedback area determination process.

FIG. 15 is a flowchart of a PID correction coefficient (KLAF) calculation process.

FIG. 16 is a block diagram for explaining a process of calculating an adaptive correction coefficient (KSTR).

FIG. 17 is a flowchart of a feedback correction coefficient (KFB) calculation process.

FIG. 18 is a flowchart of a process for determining an adaptive control area.

FIG. 19 is a flowchart of a KLAF calculation process and a KSTR calculation process.

FIG. 20 is a diagram showing a table for calculating an abnormality determination reference value (PBTHFS).

[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 19, 20 Three-way Catalyst

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G05B 13/02 9131-3H G05B 13/02 B

Claims (3)

[Claims] 1. An engine operating state detecting means for detecting an operating state of the engine, which includes an air-fuel ratio sensor provided in an exhaust system of an internal combustion engine, and control of a recurrence type based on an output of the air-fuel ratio sensor. Feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture to be supplied to the engine, and feed-forward control means for feed-forward controlling the air-fuel ratio according to the detected engine operating state In an engine control device, a second feedback control unit that controls the air-fuel ratio by feedback control that has a response speed slower than that of the first feedback control unit according to the output of the air-fuel ratio sensor; An abnormality detecting means for detecting an abnormality of the engine or the control device based on the output, and And an abnormality processing means for prohibiting the operation of the first feedback control means or for prohibiting the operation of the first and second feedback control means. 2. The second feedback control means feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine by using a controller of a recurrence type based on the output of the air-fuel ratio sensor. Thus, the adjustment speed of the feedback gain used in the controller of the recurrence type is the first
The control device for an internal combustion engine according to claim 1, wherein the control speed is slower than the adjustment speed of the feedback gain of the feedback control means. 3. The control device for an internal combustion engine according to claim 1, wherein the second feedback control means performs feedback control using at least one of a proportional term, a derivative term and an integral term.