JPH0565840A - Abnormality detection method for air-fuel ratio sensor - Google Patents

Abstract

PURPOSE:To detect whether or not an air-fuel ratio sensor is abnormal in operation by setting a first and a second condition to detect a short-circuited condition and a disconnected condition respectively with respect to the output value of an air-fuel ratio sensor, and concurrently providing a means judging whether the air-fuel ratio sensor is in a disconnected condition or in a non-active condition based on relation among the output value of the air-fuel ratio sensor, the first and second conditions. CONSTITUTION:When time that has elapsed after an engine was started, is equal to or more than a set value TO2SHC or less than a set value TO2SHD, it is judged whether or not a first O2 sensor is short-circuited or disconnected with its activation completed, if the time elapsed is between the set value TO2 SHC and TO2SHD, the value of FLAGCL12 is referred. When FLAGCL12 1, the O2 sensor is moved for judging and processing a close loop condition 2, so that it is judged whether or not the sensor is disconnected. And when FLAGCL12 =O, the output voltage VO2 of the first O2 sensor is compared with the set value O2SHIN so as to be judged and processed. By this constitution, an abnormal air-fuel ratio sensor is detected by a condition set in response to time that has elapsed right after an engine was started.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio sensor abnormality detection method for preventing erroneous determination in air-fuel ratio sensor abnormality detection.

[0002]

As is well known, in air-fuel ratio feedback control of an engine, a basic fuel injection amount determined by an intake air amount and an engine speed is controlled by an air-fuel ratio sensor such as an O2 sensor provided in an exhaust system. The air-fuel ratio is corrected to the target air-fuel ratio (theoretical air-fuel ratio) by correcting the air-fuel ratio feedback correction coefficient.

Therefore, if there is an abnormality in the air-fuel ratio sensor, the feedback control will be misaligned and the air-fuel ratio will be inadequate to cause engine malfunction. Therefore, various methods for detecting an abnormality in the air-fuel ratio sensor have been conventionally proposed. For example, in JP-A-60-173332, when the internal combustion engine is in a specific operating state, the reduction correction value for the basic fuel injection amount is zero and the increase correction value for the basic fuel injection amount is zero. Instead, when the output signal of the air-fuel ratio sensor is lean, it is judged that the air-fuel ratio sensor is abnormal, so that even if the actual air-fuel ratio is lean, accurate air-fuel ratio sensor abnormality detection is performed. Techniques capable of doing so have been disclosed.

[0004]

However, when the actual air-fuel ratio is lean, such as when the engine is warmed up and restarted, before the air-fuel ratio actually becomes rich due to an increase in the amount of fuel for starting. Has a time delay, and if an abnormality detection of the air-fuel ratio sensor is performed from the fuel increase / decrease correction value and the output signal of the air-fuel ratio sensor, an erroneous determination may occur.

The present invention has been made in view of the above circumstances, and it is possible to reliably detect an abnormality of the air-fuel ratio sensor even when the actual air-fuel ratio immediately after the engine is started is lean regardless of the fuel increase correction. An object of the present invention is to provide a method of detecting an abnormality in an air-fuel ratio sensor that can be performed.

[0006]

A method for detecting abnormality of an air-fuel ratio sensor according to the present invention is a first method for detecting a short-circuit state with respect to an output value of an air-fuel ratio sensor for detecting an air-fuel ratio of engine exhaust gas. A condition and a second condition for detecting a disconnection state are provided, and the output value of the air-fuel ratio sensor is the set value or more and the second If the conditions are not satisfied, the procedure for determining that the air-fuel ratio sensor is in a broken state or inactive, and if the elapsed time after engine start is outside the set range, or even if it is within the set range, When the output value of the fuel ratio sensor is less than the set value and when the output value of the air-fuel ratio sensor does not satisfy the first condition, it is determined that the air-fuel ratio sensor is in the short-circuited state or inactive, while Air fuel When the output value of the sensor does not satisfy the second condition, characterized in that a procedure for determining the air-fuel ratio sensor is disconnected state or the deactivated.

[0007]

In the air-fuel ratio sensor abnormality detecting method of the present invention, when the output value of the air-fuel ratio sensor does not satisfy the first condition until a predetermined time or more has elapsed after the engine is started, the air-fuel ratio sensor is in a short circuit state or When it is determined that the air-fuel ratio sensor is inactive and the output value of the air-fuel ratio sensor does not satisfy the second condition, it is determined that the air-fuel ratio sensor is in the disconnected state or inactive.

Then, when a predetermined time elapses and falls within the set range, the output value of the air-fuel ratio sensor is equal to or more than the set value and is not in a short circuit state, and when the second condition is not satisfied, the air-fuel ratio sensor is in a disconnection state. Alternatively, it is determined that the air-fuel ratio sensor is inactive, and when the output value of the air-fuel ratio sensor is less than the set value, or after that, when the elapsed time after engine start is out of the set range,
The abnormality of the air-fuel ratio sensor is detected depending on whether the output value of the air-fuel ratio sensor satisfies the first condition or the second condition.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. The drawing shows an embodiment of the present invention, in which FIG.
FIG. 3 is a flowchart of a sensor-side feedback control condition determination procedure (No. 1), and FIG. 2 is a flowchart of a first O2 sensor-side feedback control condition determination procedure (No. 2).
Is a flowchart of the first O2 sensor side feedback control condition determination procedure (Part 3), FIG. 4 is a flowchart of the second O2 sensor side feedback control condition determination procedure (Part 1), and FIG. 5 is a flowchart of the second O2 sensor side feedback control condition determination procedure (Part 2), Figure 6 shows the second O2
FIG. 7 is a flowchart of a fuel injection amount setting procedure, FIG. 8 is a flowchart of an engine speed calculation / cylinder determination procedure, and FIG. 9 is a flowchart of a fuel injection start setting procedure. 10 is a flowchart of a fuel injection procedure, FIG. 11 is a flowchart of an air-fuel ratio feedback correction coefficient setting procedure, FIG. 12 is a flowchart of a first air-fuel ratio feedback correction coefficient calculation procedure (part 1), and FIG. 13 is a first air-fuel ratio feedback correction. FIG. 14 is a flow chart (No. 2) of the coefficient calculation procedure, FIG. 14 is a flow chart (No. 1) of the second air-fuel ratio feedback correction coefficient calculation procedure, and FIG.
16 is a flowchart of the air-fuel ratio feedback correction coefficient calculation procedure (No. 2), FIG. 16 is a flowchart of the air-fuel ratio feedback correction coefficient initial setting and timer setting procedure (No. 1), and FIG. 17 is the air-fuel ratio feedback correction coefficient initial setting and timer setting procedure. Flow chart (Part 2), Figure 1
8 is a flowchart of an air-fuel ratio feedback correction coefficient initial setting and timer setting procedure (No. 3), FIG. 19 is a schematic diagram of an engine control system, FIG. 20 is a front view of a crank rotor and a crank angle sensor, and FIG. 21 is a side view of FIG. FIG. 22, FIG. 22 is a front view of the first crank rotor and the first crank angle sensor, FIG. 23 is a front view of the second crank rotor and the second crank angle sensor, and FIG. 24 is a front view of the cam rotor and the cam angle sensor. FIG. 25 is a circuit configuration diagram of the control device, and FIG. 26 is O 2
27 is an output characteristic diagram of the sensor, FIG. 27 is an explanatory diagram showing the relationship between the O2 sensor output voltage and the air-fuel ratio feedback correction coefficient, FIG. 28 is an explanatory diagram showing the control condition determination at the engine cold start, and FIG. 29 is the engine warm-up. 30 is an explanatory diagram showing control condition determination at restart, FIG. 30 is an explanatory diagram showing control condition determination in the O2 sensor system short circuit state, FIG. 31 is an explanatory diagram showing control condition determination in the O2 sensor system disconnection state, and FIG. 32 is fuel It is a timing chart of injection and ignition.

[Structure of Engine Control System] In FIG. 19, reference numeral 1 in the drawing is an engine, and in the drawing, a 4-cycle 6-cylinder horizontally opposed engine is shown. In this engine 1, a cylinder block 2 is divided into two banks (a left bank on the right side and a right bank on the left side) on both sides of a crankshaft 1a as a center.
Cylinder groups of 1, # 3, # 5 cylinders are arranged, and # on the left bank
A cylinder group of 2, # 4 and # 6 cylinders is arranged.

In each cylinder head 3 of each bank,
Each intake port 4 is formed, and an intake manifold 5 is connected to each intake port 4. Resonance tubes 6a and 6b are connected to the upstream side of the intake manifold 5 corresponding to the banks, and a variable intake valve 11c is provided in a passage 6c connecting the resonance tubes 6a and 6b. The resonance pipes 6a and 6b, the passage 6c, and the variable intake valve 11c constitute a variable resonance supercharging system.

Further, the surge tank 7 is provided upstream of the resonance tubes 6a and 6b via the throttle chambers 11a and 11b.
An air cleaner 9 is attached to an upstream side of the surge tank 7 via an intake pipe 8, and an intake air amount sensor (a hot film type air flow meter in the drawing) 10 is provided immediately downstream of the air cleaner 9. Is installed.

In addition, each of the throttle chambers 11a,
Throttle valves 11c and 11d (so-called twin throttle valves) are provided in 11b, and one throttle valve 11d is provided with a throttle opening sensor 12a and an idle switch 12 for detecting the throttle valve fully closed.
and b are connected.

Further, the throttle chamber 11a,
A downstream side of the throttle valves 11c and 11d of 11b is communicated with a passage 6d, and an idle speed control (ISC) valve 13 is provided in an air bypass passage 6e which communicates the passage 6d with the surge tank 7.

An injector 14 is arranged immediately upstream of each intake port 4 of each cylinder of the intake manifold 5, and the tip of each injector of each cylinder head 3 is exposed to the combustion chamber. A spark plug 15 is attached. The ignition coil 15 a is directly attached to the terminal portion of the ignition plug 15 and connected to the igniter 16.

The injector 14 includes a fuel tank 1
Fuel is pressure-fed from an in-tank type fuel pump 18 provided inside 7 through a fuel filter 19 and regulated by a pressure regulator 20.

A cooling water temperature sensor 21 is exposed to a cooling water passage (not shown) formed in the cylinder block 2, and a right bank knock sensor 22a and a left bank knock sensor 22a are provided in the banks of the cylinder block 2, respectively. A bank knock sensor 22b is attached, and the exhaust ports 23 of the cylinder heads 3 communicate with the exhaust pipes 24a and 24b provided for each bank.

Each of the knock sensors 22a and 22b includes, for example, a vibrator having substantially the same natural frequency as the knock vibration,
This is a resonance type knock sensor composed of a piezoelectric element that detects the vibration acceleration of this vibrator and converts it into an electric signal, and detects the vibration transmitted to the cylinder block etc. by the combustion pressure wave in the explosion stroke of the engine. The detection signal according to the vibration waveform is output.

The exhaust pipes 24a and 24b are provided with
First and second O2 sensors 25a as air-fuel ratio sensors,
25b respectively, the oxygen concentration in the exhaust gas from the cylinder group of the right bank is detected by the first O2 sensor 25a, and the exhaust gas from the cylinder group of the left bank is detected by the second O2 sensor 25b. The oxygen concentration is detected. Further, these first and second O2 sensors 25a,
On the downstream side of 25b, the catalytic converter 26
a, 26b are interposed, and each catalytic converter 26a, 26
A catalytic converter 27 is provided at the downstream merging portion of b.

The first and second O 2 sensors 25a, 25
For example, b is a well-known zirconia tube with platinum electrodes coated on the inner and outer surfaces. The value of the output voltage VO2 changes abruptly on the side.

The first and second O 2 sensors 25a, 25
b, PTC pills (Positi
A heater (not shown) including a ve Temperature Coefficient Pill) is built in.

On the other hand, a crank sprocket 1b is axially mounted on the crank shaft 1a of the engine 1, and a timing belt 28 is stretched around the crank sprocket 1b (see FIG. 21). Then, the rotation of the crankshaft 1a is transmitted to the camshaft 1c via the timing belt 28, and the camshaft 1c rotates 1/2 of the crankshaft 1a.

The crankshaft 1a has a first crank rotor 29 for detecting a crank angle and groups (# 1, # 2 cylinders, # 3, # 4 cylinders, # 5, # 6).
(3 groups of cylinders) A second crank rotor 30 for cylinder discrimination and a first crank rotor 29,
Around the outer periphery of 30, first and second crank angle sensors 3 composed of an electromagnetic pickup or the like for detecting a protrusion, which is an object to be detected.
1 and 32 are provided opposite to each other. A cam rotor 33 is attached to the cam shaft 1c, and a cam angle sensor 34 including an electromagnetic pickup is provided on the outer periphery of the cam rotor 33 so as to be opposed thereto.

As shown in FIG. 21, the crank rotors 29 and 30 are axially mounted close to each other with a predetermined distance L2, and the crank angle sensors 31 and 32 are provided on the outer circumferences of the crank rotors 29 and 30, respectively. Are opposed to each other through a predetermined clearance S. Further, the distance L2 between the crank rotors 29, 30 is equal to the crank angle sensor 31,
It is smaller than the interval L1 of 32 (the interval in the axial direction of the crankshaft 1a), and therefore the axial center of the first crank angle sensor 31 is located at the first crank rotor 29.
It is slightly offset to the crank sprocket 1b side with respect to the plate thickness center of (crank rotor for crank angle detection), and the axial center of the second crank angle sensor 32 is the second crank rotor 30. It is slightly offset toward the main body of the engine 1 with respect to the center of the plate thickness of the (crank rotor for group cylinder discrimination).

Further, as shown in FIG. 20, each of the crank angle sensors 31 and 32 includes the crankshaft 1a.
Are arranged at a predetermined opening angle θ 0 (for example, 25 °) with respect to the axis center of the above, and noise is not generated due to mutual influence by the change in magnetic flux generated when the object to be detected passes through the crank angle sensors 31 and 32. Thus, a predetermined spatial distance is maintained.

That is, each of the crank rotors 29, 3 described above
The axial mounting length of 0 is minimized, mutual interference between the crank angle sensors 31 and 32 is prevented, and compactness can be achieved.
The configurations of 9 and 30 can be simplified.

Further, as shown in FIG. 22, the first crank rotor 29 for detecting the crank angle has a protrusion 29a formed on the outer periphery thereof, and the second crank rotor for discriminating the group cylinders. As shown in FIG. 23, the protrusion 30a of the group 30 for group cylinder discrimination is formed on the outer periphery thereof.

Then, each of the crank angle sensors 31, 3
2, the magnetic flux is changed when each of the protrusions 29a and 30a passes through, and as a result, a signal train of an AC voltage is output from each of the crank angle sensors 31 and 32 by electromagnetic induction, and a crank pulse and a group discrimination pulse, respectively. Is converted to.

In the first crank rotor 29 for detecting the crank angle, specifically, the projection 29a is, for example, 30 ° starting from 10 ° before compression top dead center (BTDC) of each cylinder.
The signals from the first crank angle sensor 31 for detecting the protrusions 29a are formed at equal intervals, and the waveform of the signal from the first crank angle sensor 31 is shaped so that crank pulses can be obtained at every crank angle of 30 °.

As shown in FIG. 32, for example, BTDC1
The crank pulse indicating 00 ° indicates the reference crank angle when the fuel injection timing is set, and the crank pulse indicating BTDC 70 ° indicates the calculation of the engine speed NE and the ignition timing A.
The reference crank angle when setting DV is shown. BTDC
The crank pulse indicating 10 ° indicates the crank angle of the fixed ignition timing at the time of starting.

Further, the protrusions 30a of the second crank rotor 30 for discriminating the group cylinder are, for example, # 1 and # 2.
One is formed at the BTDC 55 ° position of the cylinder.
Two at every 30 ° from the position of BTDC55 ° of 4 cylinders, #
3 every 30 ° from the BTDC 55 ° position of the 5th and 6th cylinders
The second is formed individually and detects the protrusion 30a.
The signal from the crank angle sensor 32 is similarly shaped to obtain a group discrimination pulse.

On the other hand, as shown in FIG. 24, in order to determine the compression top dead center of the specific cylinder, the cam rotor 33 is placed at a position 43.2 ° after the compression top dead center (ATDC) of the # 1 cylinder, for example. One protrusion 33a is formed, and each cylinder can be discriminated by the cam pulse from the cam angle sensor 34 and the group discrimination pulse.

Incidentally, the first and second crank rotors 2
9, 30, or on the outer circumference of the cam rotor 33,
Slits may be provided instead of the protrusions, and the first and second crank angle sensors 31, 32 and the cam angle sensor 34 are not limited to magnetic sensors such as electromagnetic pickups, but may be optical sensors or the like. good.

[Circuit Configuration of Control Device] In FIG.
Reference numeral 40 denotes a control device (ECU) including a microcomputer. The ECU 40 includes, for example, a main computer 41 that performs ignition timing control, fuel injection control, and the like, and a dedicated sub computer 42 that performs knock detection processing, for example. It is composed of two computers.

Further, the constant voltage circuit 4 is provided in the ECU 40.
3 is built in, and a stabilizing voltage is supplied from this constant voltage circuit 43 to each part. This constant voltage circuit 43
Is directly connected to the battery 45 via the relay contact of the ECU relay 44, and the relay coil of the ECU relay 44 is connected to the battery 4 via the key switch 46.
Connected to 5. Further, the fuel pump 18 is connected to the battery 45 via a relay contact of the fuel pump relay 47.
Are connected.

The main computer 41 is a main C
PU48, ROM49, RAM50, backup RA
M50a, timer 51, serial interface (S
The CI) 52 and the I / O interface 53 are connected to each other via a bus line 54. The backup RAM 50a also includes the constant voltage circuit 43.
The backup voltage is always applied via the.

The input port of the I / O interface 53 has an intake air amount sensor 10, a throttle opening sensor 12a, a cooling water temperature sensor 21, and a first O2 sensor 2.
5a, the second O2 sensor 25b, the atmospheric pressure sensor 55, and the vehicle speed sensor 56 are connected via an A / D converter 57a, and an idle switch (idle SW) 1
2b, the first and second crank angle sensors 31, 32, and the cam angle sensor 34 are connected, and the battery 45 is connected to monitor the battery voltage.

Further, the I / O interface 5
A power steering steering switch 58 for detecting the steering state, a neutral switch 59 for determining whether the select lever of the automatic transmission is set to neutral, and a determination for whether or not parking is set to the input port 3 A parking switch 60 and a starter switch 61 for detecting a starting state are connected.

An igniter 16 is connected to the output port of the I / O interface 53, and a radiator fan relay 63 for controlling the drive of the ISC valve 13, the injector 14 and the radiator fan 62 is further provided via a drive circuit 57b. The relay coil, the relay coil of the air conditioner clutch relay 65 that operates the connection and disconnection of the magnetic clutch 64a of the variable capacity compressor 64, and the relay coil of the fuel pump relay 47 are connected.

On the other hand, the sub computer 42 is a sub CP.
U66, ROM67, RAM68, timer 69, SCI
70 and an I / O interface 71 are connected to each other via a bus line 72.

The input port of the I / O interface 71 has first and second crank angle sensors 31, 32,
The cam angle sensor 34 is connected, and the right bank knock sensor 22a and the left bank knock sensor 22b are connected.
, Respectively, an amplifier 73, a frequency filter 74, and A /
It is connected through the D converter 75.

The detection signals from the knock sensors 22a and 22b are amplified to a predetermined level by the amplifier 73, then the necessary frequency components are extracted by the frequency filter 74, and are analogized by the A / D converter 75. Data is converted to digital data, and the sub computer 4
At 2, it is determined whether knock has occurred.

The main computer 41 and the sub computer 42 are connected by a serial line via the SCIs 52 and 70, and the output port of the I / O interface 71 of the sub computer 42 is the I / O of the main computer 41. It is connected to the input port of the interface 53, and the result of determining whether knock has occurred in the sub computer 42, that is, knock determination data, is read into the main computer 41 via the I / O interfaces 71 and 53.

If a knock occurs, SCI7
Knock data is transmitted from the sub computer 42 to the main computer 41 through a serial line via 0, 52, and as a result, in the main computer 41,
Based on this knock data, the ignition timing of the corresponding cylinder is immediately delayed to avoid knock.

The air-fuel ratio control in the ECU 40 having the above configuration is executed by the main CPU 48 of the main computer 41 in accordance with the control program stored in the ROM 49. That is, the main CPU 48 calculates the intake air amount from the output signal of the intake air amount sensor 10,
Based on various data stored in the RAM 50 and the backup RAM 50a, the fuel injection amount corresponding to the intake air amount is calculated, and the ignition timing is calculated.

Then, a drive pulse width signal corresponding to the fuel injection amount is output to the injector 14 of the corresponding cylinder at a predetermined timing via the drive circuit 57b to inject fuel, and the igniter 16 at a predetermined timing. An ignition signal is output to the ignition plug 15 of the corresponding cylinder.

As a result, the air-fuel mixture supplied to the corresponding cylinder explodes and burns and is discharged by the first O2 sensor 25a facing the exhaust pipe 24a or the second O2 sensor 25b facing the exhaust pipe 24b. The oxygen concentration contained in the gas is detected. After this detection signal is waveform-shaped, it is compared with the reference voltage signal by the CPU 48, it is determined whether the air-fuel ratio state of the engine is on the rich side or the lean side with respect to the target air-fuel ratio, and the air-fuel ratio is determined. Feedback control is performed so that the target air-fuel ratio is achieved.

Further, reference numeral 81 is an air conditioner control unit, which is connected to a CPU 82, a ROM 83, a RAM 84, an I / O interface 85 via a bus line 86, and a battery 45 via an ignition switch 87.
The stabilizing voltage is supplied to each part from the constant voltage circuit 88 connected to the.

An air conditioner switch 89 and an I / O interface 53 of the main computer 41 are connected to an input port of the I / O interface 85, and the variable capacity compressor is transferred from the main computer 41 to the air conditioner control unit 81. The required capacity signal (DUTY signal) for 64 is output.

A variable capacity control valve (not shown) provided in the variable capacity compressor 64 is connected to the output port of the I / O interface 85 to output a capacity signal signal (DUTY signal). Is connected to the input port of the I / O interface 53 of the main computer 41 and the air conditioner switch 89 is turned on.
A signal (A / C SW signal) indicating whether or not it is output.

[Operation] Next, the air-fuel ratio control operation of the ECU 40 will be described, and the first and second O 2 sensors 25 will be described.
The abnormality detection processing for a and 25b will be described.

In the main computer 41 of the ECU 40, as shown in FIG. 8, first, the crank pulse input causes the routine of the engine speed calculation and the cylinder discrimination procedure to be interrupted, and the first crank angle sensor 31 is started in step S201. The crank pulse input interval time T0 from is measured by the timer 51, and the engine speed NE is calculated according to the cycle obtained from the input interval time T0.
At 2, the cylinder is discriminated based on the output signals of the first and second crank angle sensors 31, 32 and the cam angle sensor 34, and the routine is exited.

In this cylinder discrimination, as shown in the timing chart of FIG. 32, 0 to 1 group discrimination pulses from the second crank angle sensor 32 are output between the crank pulses at every 30 ° CA, and the BTDC 100. ° and BT
There is no group discrimination pulse in any cylinder between DC 70 °, and the group discrimination pulse is
The crank pulse after the pattern with or without is always B
TDC 40 °, next crank pulse is BTDC1
Since it indicates 0 °, for example, BTDC10 of a certain cylinder
First, # 1 and # 2 cylinders, # 3 and # 4 cylinders, # 3 and # 4 cylinders are examined by checking the pattern of the group discrimination pulse existing between 0 ° and BTDC100 ° of the next cylinder.
Cylinder discrimination is performed for each group of the fifth and sixth cylinders, and further, individual cylinders are discriminated by the cam pulse from the cam angle sensor 34.

The main computer 41 takes in the output signals from the first and second O2 sensors 25a and 25b corresponding to each bank, and feedback-controls the air-fuel ratio for the cylinder determined by the cylinder.

At this time, the fuel injection amount is set to two corresponding to the left and right banks by the fuel injection amount setting routine shown in the flowchart of FIG. 7, and the cylinder of the right bank based on the output from the first O2 sensor 25a. The air-fuel ratio learning result of the group is taken in.

First, in step S101, the engine speed N
Based on E and intake air amount Q, basic fuel injection pulse width TP
Is calculated (TP ← K × Q / NE; where K is an injector characteristic correction coefficient), and in step S102, the cooling water temperature sensor 21
Based on the cooling water temperature TW from the engine, the throttle opening θ from the throttle opening sensor 12a, the output from the idle switch 12b, etc. The minute correction coefficient COEF is set.

Next, in step S103, the first and second air-fuel ratio feedback correction coefficients α1 and α2 for the cylinder groups of each bank, which are set in the air-fuel ratio feedback correction coefficient setting routine described later, are read from the RAM 50 at predetermined addresses. When the learning correction coefficient KBLRC is set in step S104, the voltage correction coefficient T for interpolating the invalid injection time of the injector 14 based on the battery voltage is set in step S105.
Set S.

Regarding the learning correction coefficient KBLRC,
It is described in detail in Japanese Patent Application No. 1-293276 by the applicant.

After that, the routine proceeds to step S106, where the basic fuel injection pulse width TP set at step S101 is air-fuel ratio corrected by various increasing amount correction coefficient COEF and the first air-fuel ratio feedback correction coefficient α1 and learning correction coefficient KB.
The first fuel injection pulse width Ti1 for the cylinder group (# 1, # 3, # 5 cylinders) in the right bank is set (Ti1 ← TP) after learning correction by LRC and voltage correction by the voltage correction coefficient TS.
X COEF x α1 x KBLRC + TS).

Further, the above steps S106 to S1
When proceeding to 07, the basic fuel injection pulse width TP is air-fuel ratio corrected by the various increase amount correction coefficient COEF and the second air-fuel ratio feedback correction coefficient α2 and learning correction coefficient KB
The second fuel injection pulse width Ti2 for the cylinder group (# 2, # 4, # 6 cylinders) of the left bank is set by learning correction by LRC and voltage correction by the voltage correction coefficient TS (Ti2 ← TP
X COEF x α2 x KBLRC + TS).

Then, in step S108, the injection start timing TMSTART is set based on the engine speed NE, and the routine exits. The injection start timing TMSTART
Is set to the advanced side as the engine rotation speed increases.

Next, the first and second fuel injection pulse widths T
i1 and Ti2 are set as the fuel injection pulse width Ti for the corresponding cylinder by the routine of FIG. 9 in which the interrupt start is started by the crank pulse of BTDC 100 °.

In this BTDC 100 ° interrupt routine, the injection target cylinders are # 1, # 3, # in step S301.
It is checked whether or not the cylinder belongs to the cylinder group of the right bank No. 5 and the injection target cylinder belongs to the cylinder group of the right bank # 1, # 3, # 5. The injection pulse width Ti1 is set as the fuel injection pulse width Ti for the corresponding cylinder (Ti ← Ti1), and the injection target cylinders are # 2, # 4, # 6.
If it belongs to the cylinder group of, branch to step S303,
The second fuel injection pulse width Ti2 is set as the fuel injection pulse width Ti for the corresponding cylinder (Ti ← Ti2).

Then, the process proceeds from step S302 or step S303 to step S304, and this BTDC is 100 °.
Then, the timer starts counting, the interruption of the injection start timing TMSTART is permitted, and the routine exits.

After that, when the timing of the timer started at BTDC 100 ° becomes the injection start timing TMSTART, the routine of the fuel injection procedure shown in FIG. 10 is interrupted and started, and in step S401, the fuel injection to the injector 14 of the fuel injection target cylinder is performed. A driving pulse signal having a pulse width Ti is output and the routine exits.

That is, as shown in FIG. 32, in the 4-cycle 6-cylinder engine of this embodiment, the combustion stroke is # 1 → #.
6 → # 3 → # 2 → # 5 → # 4, fuel injection is started from the fuel injection start timing TMSTART based on BTDC 100 ° CA to the fuel injection target cylinder, and 720
Sequential injection is performed once for each CA (every two engine revolutions).

Next, the procedure for setting the air-fuel ratio feedback correction coefficient will be described. The air-fuel ratio feedback correction coefficient setting routine shown in FIG. 11 is a program executed by interruption every engine revolution.
In S501, the value of the first O2 sensor side feedback control determination flag FLAGF / B1 is referred to.

This first O2 sensor side feedback control condition discrimination flag FLAGF / B1 is set in the first O2 sensor 25.
It is set to 1 when the feedback condition by a is satisfied, and FLAGF / B1 is set in step S501.
When = 0, it is determined that the right bank cylinder group is currently under open loop control, and the process proceeds to step S502 to call the first O2 sensor side feedback control condition determination subroutine.

In this first O2 sensor side feedback control condition judging subroutine, the first O2 sensor 25a is activated without any failure such as short circuit or disconnection by the closed loop condition 1 judging process and the closed loop condition 2 judging process described later. Is completed and it is determined whether or not it is possible to shift to the closed loop control, that is, the feedback control.

On the other hand, in step S501, FLAGF / B1
When = 1, it is determined that the cylinder group in the right bank is currently in feedback control and the process branches to step S503 to call the first air-fuel ratio feedback correction coefficient calculation subroutine to call the first air-fuel ratio feedback correction for the cylinder group in the right bank. Set the coefficient α1.

Thereafter, the process proceeds from step S502 or step S503 to step S504, and the value of the second O2 sensor side feedback control condition determination flag FLAGF / B2 is set to 1 when the feedback condition by the second O2 sensor 25b is satisfied. Refer to.

When FLAGF / B2 = 0, it is determined that the cylinder group of the left bank is currently under open loop control, and the process proceeds from step S504 to step S505.
The 2 sensor side feedback control condition judging subroutine is called, and the second O 2 sensor 25b is called in the same manner as the first O 2 sensor side feedback control condition judging subroutine.
It is judged whether or not there is no failure such as short circuit or disconnection, activation is completed and it is possible to shift to the feedback control, and the routine is exited.

On the other hand, when FLAGF / B2 = 1, it is determined that the cylinder group in the left bank is currently in the feedback control, the process branches from step S504 to step S506, and the second air-fuel ratio feedback correction coefficient calculation subroutine is called. The second air-fuel ratio feedback correction coefficient α2 for the cylinder group in the left bank is set and the routine exits.

Here, prior to the explanation of each subroutine in the above-mentioned air-fuel ratio feedback correction coefficient setting routine, the first and second air-fuel ratio feedback correction coefficients α1, α2
The initial setting and timer setting procedure will be described.

The routine of the air-fuel ratio feedback correction coefficient initial setting and the timer setting procedure shown in FIGS. 16 to 18 is executed every predetermined time, and in steps S1001 and S1002,
It is checked whether or not the engine speed NE is 0 and whether or not the starter switch 61 is ON.

In steps S1001 and S1002, when NE = 0, the engine is not rotating, or when NE ≠ 0 and the starter switch 61 is in the cranking state, the process branches to step S1036, and after engine start (starter switch). The elapsed time after start count value COUNT for measuring the elapsed time (after 61 has changed from the ON state to the OFF state)
When ST is cleared (COUNTST ← 0), step S103
In 7 and S1038, the first and second air-fuel ratio feedback correction coefficients α1 and α2 are fixed to 1.0 (α1 ← 1.0, α2 ← 1.
0), in step S1039, clear each flag and exit the routine.

On the other hand, NE ≠ 0 and the starter switch 61
Is OFF, the process proceeds to step S1003 through steps S1001 and S1002, and the elapsed time count value CO after starting CO
UNSTST is the set value TO2SHC (for example, equivalent to 30 sec)
It is determined whether or not the above. And COUNTST
When ≧ TO2SHC, jump to step S1006 from step S1003. When COUNTST <TO2SHC, step S1003.
Proceed to step 1004 from 1003.

In step S1004, the post-start elapsed time count value COUNTST is counted up (COUNTSTST
← COUNTST + 1), in step S1005, whether the counted up elapsed time after start count value COUNTST is less than or equal to the predetermined time INLSDS, that is, whether the elapsed time after the starter switch 61 is turned from ON to OFF is less than or equal to the predetermined time INLDS. Determine whether or not.

However, INLDS <TO2SHD <TO2SHC, and the set value TO2SHD (corresponding to 1 sec) is the first value described later.
Branch condition for closed loop condition 1 determination process and closed loop condition 2 determination process in O2 sensor side feedback control condition determination subroutine and second O2 sensor side feedback control condition determination subroutine
Is one.

Then, in step S1005, C
When OUNTST ≦ INLDS, the above step S1 is executed.
Exit the routine through 037, S1038, S1039, and complete the COUNTST
When> INLDS, the process proceeds from step S1005 to step S1006 and thereafter.

After step S1006, step S1006
S1023 is each timer count value (first timer count value COUNTTIM1, second timer count value COUNTTIM2, first O2 sensor side control cycle timer count value COUNTTIMTO21) used in the first O2 sensor side feedback control condition determination subroutine, the second O2 sensor Each timer count value used in the side feedback control condition determination subroutine (third timer count value COU
NTTIM3, 4th timer count value COUNTTIM4, 2nd
O2 sensor side control cycle timer count value COUNTTIMTO
22) is a process of counting up or clearing according to the value of the flag, and step S1024 and subsequent steps are first and first for activating the monitor function in the first and second air-fuel ratio feedback correction coefficient calculation subroutines described later. Two
O2 sensor side monitor function operation flag FLAGMP1, FLA
This is a process of setting GMP2.

That is, in step S1006, the value of the first timer operation flag FLAGTIM1 is referred to, and FLAGTIM1 =
When it is 1, in step S1007 the first timer count value COUNTTIM1 is incremented (COUNTTIM1 ← C
COUNTTIM1 + 1) while FLAGTIM1 = 0, the first timer count value COUNT in step S1008.
Clear TTIM1 (COUNTTIM1 ← 0).

Next, in step S1007 or step S1008, the flow advances to step S1009 to refer to the value of the second timer operation flag FLAGTIM2, and FLAGTIM2 =
If 1, the second timer count value CO is output in step S1010.
Count up UNTTIM2 (COUNTTIM2 ← CO
(UNTTIM2 + 1) and FLAGTIM2 = 0, the second timer count value COUNTTIM2 is cleared in step S1011 (COUNTTIM2 ← 0).

Further, when the process proceeds from step S1010 or step S1011 to step S1012, the value of the third timer operation flag FLAGTIM3 is referred to. When FLAGTIM3 = 1, the third timer count value COUNT is determined in step S1013.
Count up TTIM3 (COUNTTIM3 ← COU
NTTIM3 + 1) While proceeding to step S1015, FLAGTIM
When 3 = 0, in step S1014 the third timer count value C
Clear COUNTTIM3 (COUNTTIM3 ← 0) and proceed to step S1015.

In step S1015, the value of the fourth timer operation flag FLAGTIM4 is referred to. If FLAGTIM4 = 1, then in step S1016 the fourth timer count value COUNTT.
Count up IM4 (COUNTTIM4 ← COUNT
TTIM4 + 1) While proceeding to step S1018, FLAGTIM4
= 0, the fourth timer count value C in step S1017
Clear COUNTTIM4 (COUNTTIM4 ← 0) and proceed to step S1018.

Thereafter, in step S1018, the value of the first O2 sensor side control cycle timer operation flag FLAGTIMTO21 is referred to. When FLAGTIMTO21 = 1, step S1019
Then, the first O2 sensor side control cycle timer count value CO for counting the control cycle of the first O2 sensor 25a
Count up UNTTIMTO21 (COUNTTIMTO
21 ← COUNTTIMTO21 + 1) Proceed to step S1021, F
When LAGTIMTO21 = 0, in step S1020, the first O2
Sensor side control cycle timer count value COUNTTIMTO21
Is cleared (COUNTTIMTO21 ← 0) Step S1021
Go to.

In step S1021, the value of the second O2 sensor side control cycle timer operation flag FLAGTIMTO22 is referred to,
When FLAGTIMTO22 = 1, in step S1022, the second count for counting the control cycle of the second O2 sensor 25b is performed.
O2 sensor side control cycle timer count value COUNTTIMTO
Count up 22 (COUNTTIMTO22 ← COU
NTTIMTO22 + 1) Proceed to step S1024, and FLAGTIMT
When O22 = 0, the second O2 sensor side control cycle timer count value COUNTTIMTO22 is cleared (COUNTTIMTO22 ← 0) in step S1023, and the process proceeds to step S1024.

At step S1024, the first O 2 sensor 25
Referring to the value of the first O2 sensor side feedback control condition determination flag FLAGF / B1 which is set to 1 when the feedback condition by a is satisfied, when FLAGF / B1 = 0, the process jumps to step S1029 and FLAGF / B1 =
When it is 1, in step S1025, it is checked whether or not the monitor function is already in operation by referring to the value of the first O2 sensor side monitor function operation flag FLAGMP1.

If FLAGMP1 = 1 in step S1025, the process jumps to step S1030 and FLAGMP1 =
When it is 0, in step S1026, the timer count value COUNT for measuring the time from the start of the feedback control
Count up TTIMF / B1 (COUNTTIMF / B1 ← C
OUNTTIMF / B1 + 1), and in step S1027, it is determined whether or not this count value has reached the set value MONT.

Then, in step S1027, COUNT
If TTIMF / B1 <MONT and the set time has not elapsed from the start of the feedback control, step S103
Jump to 0, COUNTTIMF / B1 ≧ MONT,
When the set time has elapsed from the start of the feedback control, in step S1028, the first O2 sensor side monitor function operation flag FLAGMP1 is set (FLAGMP1 ←
1), in step S1029, the timer count value COUNTT
Clear IMF / B1 (COUNTTIMF / B1 ← 0) and proceed to step S1030.

In step S1030, the second O 2 sensor 25
Referring to the value of the second O2 sensor side feedback control condition determination flag FLAGF / B2 which is set to 1 when the feedback condition by b is satisfied, when FLAGF / B2 = 0, the process jumps to step S1035 and FLAGF / B2 = 0 At this time, in step S1031, it is checked with reference to the value of the second O2 sensor side monitor function operation flag FLAGMP2 whether or not the monitor function is already in operation.

Then, in the above step S1031, FLAGM
When P2 = 1, the routine is exited, and when FLAGMP2 = 0, in step S1032, the timer count value COUNT for measuring the time from the start of feedback control.
Count up TIMF / B2 (COUNTTIMF / B2 ← C
OUNTTIMF / B2 + 1).

After that, the process proceeds to step S1033, it is determined whether or not the timer count value COUNTTIMF / B2 has reached the set value MONT, and if COUNTTIMF / B2 <MONT and the set time has not elapsed from the start of the feedback control, Exit the routine, COUNTTIMF / B2 ≧ MON
If T is set and the set time has elapsed from the start of feedback control, the second O2 sensor side monitor function operation flag FLAGMP2 is set in step S1034 (F
LAGMP2 ← 1), in step S1035, clear the timer count value COUNTTIMF / B2 (COUNTTIMF / B2 ←
0), exit the routine.

On the other hand, the first O2 sensor side feedback control condition judging subroutine and the second O2 sensor side feedback control condition judging subroutine in the above-mentioned air-fuel ratio feedback correction coefficient setting routine are shown in FIGS. 1 to 3 and 4 to 6, respectively. Shown.

These sub-routines are functionally similar, and the step S6 ... Of the first O2 sensor side feedback control condition judging subroutine is the same as the step S8 of the second O2 sensor side feedback control condition judging subroutine.
Corresponding to.

Hereinafter, the subroutine for determining the feedback control condition of the first O 2 sensor will be mainly described, and the second O 2 sensor side feedback control condition determination subroutine will be described.
In the O2 sensor side feedback control condition determination subroutine, the first O2 sensor 25a is read as the second O2 sensor 25b, and its output voltage VO21 is read as VO22.

In the second O 2 sensor side feedback control condition judging subroutine, the first O 2 sensor side feedback control condition judging subroutine is
The air-fuel ratio feedback correction coefficient α1 and the integration constant I1 are respectively set as the second air-fuel ratio feedback correction coefficient α2 and the integration constant I2, and the first monitor open loop control determination flag FLAGMONI1 and the first O2 sensor side monitor function operation flag FLAGMP1 and the first O2 are set. The first side of each flag of the sensor side closed loop condition 2 shift determination flag FLAGCL21 and the first O2 sensor side feedback control condition determination flag FLAGF / B1 is replaced with the second ...
Replace 1 with 2.

Further, in the second O2 sensor side feedback control condition judging subroutine, instead of the first timer operating flag FLAGTIM1 and the second timer operating flag FLAGTIM2 in the first O2 sensor side feedback controlling condition judging subroutine, respectively, the third O3 Timer operation flag FLAGTIM3, fourth timer operation flag FLAGTIM4
In place of the first timer count value COUNTTIM1 and the second timer count value COUNTTIM2, the third timer count value COUNTTIM3 and the fourth timer count value COUNTTIM4 are used.

First, in step S601 of the first O2 sensor side feedback control condition determination subroutine, the value of the first monitor open loop control determination flag FLAGMONI1 is referred to, and it is determined whether or not the control is shifted to open loop control.

The first monitor open loop control discrimination flag FLAGMONI1 is set when the control cycle of the first O2 sensor 25a monitored by the monitor function of the first air-fuel ratio feedback correction coefficient calculation subroutine described later exceeds the set value. This is set in order to shift from the closed loop control to the open loop control. When FLAGMONI1 = 0 in step S601, the control is still in closed loop control, so the process jumps to step S610, and when FLAGMONI1 = 1, it opens. Since the control is shifted to the loop control, the process proceeds to step 602.

In step S602, the first O2 sensor side monitor function operation flag FLAGMP1 is cleared (FLAGMP1
← 0), in steps S603 to S606, the first air-fuel ratio feedback correction coefficient α1 is converged to the center value 1.0. That is,
In step S603, the first air-fuel ratio feedback correction coefficient α
If 1 is greater than 1.0, and if it is greater than 1.0, then in step S604, the first air-fuel ratio feedback correction coefficient α1 is reduced by the integral constant I1 in the proportional integral control (α1 ← α1-I1) in step S607. If it is not larger than 1.0, the process branches to step S605 to determine whether or not the first air-fuel ratio feedback correction coefficient α1 is smaller than 1.0.

When α1 <1.0 in step S605, the first air-fuel ratio feedback correction coefficient α1 is increased by the integral constant I1 in proportional-plus-integral control (α1 ← α1 + I1) in step S606, and the process proceeds to step S607. In step S605, when α1 = 1.0, the process jumps to step S607.

Next, in step S607, it is determined whether or not the idle switch 12b is OFF, and the idle switch 1
When 2b is ON, in steps S608 and S609,
The first timer operation flag FLAGTIM1 used in the closed loop condition 1 determination process and the second timer operation flag FLAGTIM2 used in the closed loop condition 2 determination process are cleared (FLAGTIM1 ← 0,
The FLAGTIM2 ← 0) routine is exited, and if the idle switch 12b is OFF in step S607, the process proceeds to step S610 and subsequent steps.

That is, when the closed loop control is switched to the open loop control by the monitor function,
As long as the idle switch 12b is in the ON fully closed throttle state, the process of determining whether or not it is possible to shift to the closed loop control again is not performed, and the closed monitor control of the first monitor open loop control determination flag FLAGMONI1 is cleared. Time, or after shifting to open loop control by the monitor function, the idle switch 12
When the throttle open state in which b is OFF is continued, the process proceeds to step S610 and the subsequent steps.

In step S610, the value of the elapsed time after start count value COUNTST is set to the set value TO2SHC (for example, 30
(equivalent to sec) or more, COUNTST <TO2
In the case of SHC, it is further determined in step S611 whether the value of the post-start elapsed time count value COUNTST is less than the set value TO2SHD (for example, 1 sec).

When the elapsed time after engine start is equal to or greater than the set value TO2SHC or less than the set value TO2SHD, step S610 or step S611 to step S6.
When the flow branches to 15 and the second timer operation flag FLAGTIM2 is cleared (FLAGTIM2 ← 0), the process proceeds to the closed loop condition 1 determination process after step S616, and the set value TO2SH
If D or more and less than the set value TO2SHC, steps S610, S61
After passing through 1, the process proceeds to step S612 to refer to the value of the first O2 sensor side closed loop condition 2 shift determination flag FLAGCL21.

In step S612, FLAGCL21 = 1
In the case of, the process jumps to step S624 to clear the first timer operation flag FLAGTIM1 (FLAGTIM1 ← 0), and the process proceeds to the closed loop condition 2 determination process of step S625 and thereafter, and when FLAGCL21 = 0 (initial value),
In step S613, it is determined whether or not the output voltage (first O2 sensor output voltage) VO21 of the first O2 sensor 25a is equal to or higher than a set value O2SHIN (for example, 200 mV).

As a result, when VO21 <O2SHIN, in step S615, the second timer operation flag FLAGTIM2 is cleared (FLAGTIM2 ← 0), and the process proceeds to the closed loop condition 1 determination process in step S616 and thereafter, VO21 ≧ O2SH
When it is IN, it can be regarded that the first O2 sensor 25a is not in the short-circuit state thereafter, so in step S614, the first O2 sensor side closed loop condition 2 shift determination flag FLAG.
CL21 is set (FLAGCL21 ← 1) to force the jump from step S612 to step S624 at the time of the next routine execution, and when the first timer operation flag FLAGTIM1 is cleared in step S624, step S6
The processing shifts to the closed loop condition 2 determination processing after 25.

Next, the closed loop condition 1 determination processing will be described. The closed loop condition 1 determination process includes a first condition including steps S616 to S618 for detecting a short-circuit state of the first O2 sensor 25a and a disconnection state of the first O2 sensor 25a. Step S
The second condition consisting of 616 to S619 is provided. First, in step S616, the cooling water temperature TW is set to the set value WOPN.
(For example, 22 ° C) or more is determined.

When TW <WOPN in step S616, the first O2 sensor 25a is not activated, the closed loop condition is not satisfied, and the process jumps to step S623 to clear the first timer operation flag FLAGTIM1 (FLAGTIM1 ← 0) Exit the routine, TW ≧ WOP
If N, it is assumed that the first O2 sensor 25a is activated by a built-in heater (not shown)
The process proceeds from step S616 to step S617, where the first O2 sensor output voltage VO21 is the rich determination reference voltage VE (for example, 650 mV).
It is determined whether or not the above.

As a result, when VO21 ≧ VE and the air-fuel ratio is completely rich, the routine proceeds from step S617 to step S620, and when VO21 <VE, step S618.
Then, it is determined whether or not the first O2 sensor output voltage VO21 is equal to or higher than the failure determination voltage O2SHRT (for example, 100 mV). When VO21 ≧ O2SHRT, in step S619, the first
It is determined whether the O2 sensor output voltage VO21 is lower than the lean determination reference voltage VL (for example, 350 mV).

Then, in the above step S619, VO21 <VL
, That is, when O2SHRT ≦ VO21 <VL and the air-fuel ratio is lean, or in step S617,
When VO21 ≧ VE and the air-fuel ratio is completely rich, at step S620, the first timer operation flag FLAG.
TIM1 is set (FLAGTIM1 ← 1) to start counting the first timer count value COUNTTIM1 by the above-described air-fuel ratio feedback correction coefficient initial setting and timer setting routine, and in step S621, the first timer count value COUNTTIM1 is set to the set value INLD. (For example, 0.5s
(corresponding to ec) is determined.

At step S621, COUNTTIM1 <I
When NLD, exit the routine as it is and
When TTIM1 ≧ INLD, VO21 ≧ VE or O2S
Since the state of HRT ≦ VO21 <VL has continued for the predetermined time corresponding to the set value INLD or more, it is determined that the closed loop condition is satisfied, the process proceeds to step S622, and the first O2 sensor side feedback control condition determination flag FLAGF / B1 is set (FLAGF / B1 ← 1), exits the routine through step S623 described above.

On the other hand, when VO21 <O2SHRT in step S618, a part of the wiring of the first O2 sensor 25a is short-circuited and grounded to the vehicle body, or the activation is not completed, so the first O2 sensor output It is determined that the voltage VO21 is near 0V, and VO21 is determined in step S619.
When ≧ VL (when VE> VO21 ≧ VL), the first O
2 It is determined that the output voltage has an intermediate value because a part of the wiring of the sensor 25a is broken or the activation has not been completed.
Jump to 23 to clear the first timer operation flag FLAGTIM1 and exit the routine.

That is, when the O2 sensor system is short-circuited and grounded to the vehicle body, its output voltage VO2 becomes approximately 0V, but even when the air-fuel ratio is excessively lean, the output voltage VO2 becomes approximately 0V. Become. Therefore, it is impossible to distinguish whether the O2 sensor system is defective due to a short circuit or whether the O2 sensor system is normal and the air-fuel ratio is lean.

Therefore, in the closed loop condition 1 determination processing, the air-fuel ratio immediately after the engine cold start is adjusted by the water temperature correction,
Taking advantage of the fact that the fuel amount is corrected by the fuel amount increase correction after the start and becomes rich, the O2 sensor (first O2 sensor 2
5a, the second O2 sensor 25b) is above the cooling water temperature that can be considered to have been activated by an internal heater (not shown), and FIG.
As shown in, a predetermined time (set value TO2
O2 sensor output voltage VO2
The setting value INLD is a state where (first O2 sensor output voltage VO21, second O2 sensor output voltage VO22) is V02 ≧ O2SHRT.
When the O2 sensor system is normal for a predetermined time or more corresponding to the above, it is determined that the O2 sensor system is normal, and the control is shifted to the closed loop control, that is, the feedback control.

As shown in FIG. 30, when the O2 sensor output voltage VO2 is near 0V (VO2 <O2SHRT), it is determined that the O2 sensor system is short-circuited and grounded or inactive. , As shown in FIG.
When the intermediate value (VE> VO2≥VL), the open loop control is continued by discriminating that the O2 sensor system is open or inactive.

On the other hand, in the closed loop condition 2 determination processing, only the second condition consisting of steps S625 to S627 for detecting the disconnection state of the first O2 sensor 25a is provided, and the cooling is performed in step S625. It is determined whether or not the water temperature TW is equal to or higher than the set value WOPN. When TW <WOPN, it is determined that the closed loop condition is not satisfied, the process jumps to step S632, the second timer operation flag FLAGTIM2 is cleared (FLAGTIM2 ← 0), and the routine exits.

In step S625, TW ≧ WOP
When it is N, the routine proceeds to step S626, where it is judged whether or not the first O2 sensor output voltage VO21 is equal to or higher than the rich judgment reference voltage VE. When VO21 <VE, the routine branches to step S627 and the first O2 sensor output voltage VO21 is judged. It is determined whether it is lower than the lean determination reference voltage VL.

When VO21 ≧ VE in step S626 and the air-fuel ratio is completely rich, or when VO21 <VL in step S627 and the air-fuel ratio is lean, step S628 is executed. Set the second timer operation flag FLAGTIM2 (FLAGTIM2 ← 1)
Second timer count value COUNT by the above-mentioned air-fuel ratio feedback correction coefficient initial setting and timer setting routine
Start counting TIM2, and in step S629, set the second
It is determined whether or not the timer count value COUNTTIM2 has reached the set value INLD.

As a result, in the step S629, the COUNT
When TTIM2 <INLD, the routine is exited as it is, and when COUNTTIM2 ≧ INLD, it is determined that the activation of the first O2 sensor 25a is completed and the closed loop condition is satisfied, and in step S630, the first O2 sensor side feedback control is performed. When the condition determination flag FLAGF / B1 is set (FLAGF / B1 ← 1), after the first monitor open loop control determination flag FLAGMONI1 is cleared (FLAGMONI1 ← 0) in step S631, the above-mentioned step S63 is performed.
Exit the routine via 2.

On the other hand, when VO21 <VL in step S627, it is determined that the first O2 sensor 25a is disconnected or inactive, and the process jumps to step S632 to clear the second timer operation flag FLAGTIM2. , Exit the routine.

That is, in the case of engine warm-up restart, the actual air-fuel ratio may be lean, and although the O2 sensor has already been activated, the O2 sensor output voltage VO
2 may be approximately 0V. Therefore, there is a possibility that an erroneous determination cannot be made and feedback control cannot be performed only by the closed-loop condition 1 determination processing described above, and the air-fuel ratio becomes inadequate, causing engine malfunction.

In this case, since the air-fuel ratio due to the increase correction becomes rich immediately after the engine starts, as shown in FIG. 29, the elapsed time after the engine starts becomes the set value TO2SHD.
If the O2 sensor output voltage VO2 becomes equal to or higher than the set value O2SHIN even once from the set value to the set value TO2SHC, it can be determined that the O2 sensor system is not short-circuited.

Thereafter, the first O2 sensor side closed loop condition 2 shift determination flag FLAGCL21 (second O2
Sensor side closed loop condition 2 transition determination flag FLA
GCL22) is always set, and the closed loop condition 2 determination process after step S625 (S825) is forced to always be performed. Is there any abnormality such as disconnection in the O2 sensor system in this closed loop condition 2 determination process? Is determined.

Further, the air-fuel ratio feedback correction coefficient in the case of shifting from the open loop control to the feedback control is the first air-fuel ratio feedback correction coefficient calculation subroutine shown in FIGS. 12 and 13, and FIGS.
It is calculated and set by the second air-fuel ratio feedback correction coefficient calculation subroutine shown in FIG.

In each of these subroutines, steps S7 ... S9 ... Correspond to each other and are functionally equivalent. Therefore, similarly, the first air-fuel ratio feedback correction coefficient calculation subroutine will be mainly described below. In the second air-fuel ratio feedback correction coefficient calculation subroutine, the first O2 sensor 25a Is read as the second O2 sensor 25b, and its output voltage VO21 is changed to VO2.
Read as 2. Then, the slice level SL1, the set value VS1, the first air-fuel ratio feedback correction coefficient α1, the correction value α1NEW, the integration constant I1, and the proportional constant P1 are respectively set as the slice level SL2, the set value VS2, and the second air-fuel ratio feedback correction coefficient α2. , Correction value α2NEW, integration constant I2, proportionality constant P2, first O2 sensor rich / lean determination flag FLAGAF1, first O2 sensor side control cycle timer operation flag FLAGTIMTO21, first O2 sensor side monitor function operation flag FLAGMP1, first 1O2 sensor side feedback control condition determination flag FLAGF / B1 and first monitor open loop control determination flag FLAGMONI1 flags, first O2 sensor side control cycle timer count value COU
For NTTIMTO21, the first ... Is replaced with the second ..., and the subscript ... 1 at the end of the code is replaced with 2.

In the first air-fuel ratio feedback correction coefficient calculation subroutine, first, in step S701, it is determined whether or not the first O2 sensor side clamp condition for clamping the first air-fuel ratio feedback correction coefficient α1 to the set value is satisfied. To determine.

This clamping condition is, for example, when the basic fuel injection pulse width TP is at a high load of a predetermined value or more, when the engine speed NE is at a high speed of a predetermined speed or more, during fuel cut, during deceleration, and full-open acceleration. It is determined that the condition is satisfied during fuel increase, during acceleration / deceleration at low water temperature, or during fuel increase due to air conditioner operation. In step S702, the first air-fuel ratio feedback correction coefficient α1 is clamped to the set value, and the routine exits. ..

On the other hand, if it is determined in step S701 that the clamp condition is not satisfied, the steps from step S701 to step
In step S703, the value of the first O2 sensor rich / lean determination flag FLAGAF1 is referred to. The first O2 sensor rich / lean determination flag FLAGAF1 is cleared to 0 when the first O2 sensor output voltage VO21 is on the air-fuel ratio rich side, and is set to 1 when it is on the air-fuel ratio lean side. It is possible to determine whether the air-fuel ratio of the cylinder group in the right bank is on the rich side or the lean side during the execution of the routine.

Therefore, in the above step S703, FLAGAF
When 1 = 0, the air-fuel ratio of the cylinder group of the right bank was on the rich side last time, so in step S704, the predetermined value VS1 is set to the slice level SL1 (SL1 ← VS1), FLAGAF
When 1 = 1, since the air-fuel ratio of the cylinder group in the right bank was on the lean side last time, the process branches to step S705 and the hysteresis level HIS is added to the predetermined value VS1 to set the slice level SL1 (SL1 ← VS1 + HIS).

When the slice level SL1 is set in step S704 or step S705, step S
Proceeding to 706, the first O2 sensor output voltage VO21 is compared with the slice level SL1 to determine whether the air-fuel ratio of the cylinder group in the right bank is currently on the rich side or the lean side, and V
When O21 ≧ SL1, that is, when the air-fuel ratio is judged to be on the rich side, the routine proceeds from step S706 to step S707, where it is judged if the first O2 sensor rich / lean judgment flag FLAGAF1 is set.

In step S707, when FLAGAF1 = 1, that is, when the previous routine is executed, the air-fuel ratio is lean, and this time when the air-fuel ratio is rich,
From step S707 to step S708, the correction value α1NEW is set by skipping the first air-fuel ratio feedback correction coefficient α1 in the negative direction by the proportional constant P1 (α1N
EW ← α1-P1).

Then, the process proceeds to step S709, and when the first O2 sensor side control cycle timer count value COUNTTIMTO21 is cleared (COUNTTIMTO21 ← 0), step S71
At 0, the first O2 sensor side control cycle timer operation flag FLA
GTIMTO21 is set (FLAGTIMTO21 ← 1), and counting of the first O2 sensor side control cycle timer count value COUNTTIMTO21 by the above-described air-fuel ratio feedback correction coefficient initial setting and timer setting routine is started.

After that, the routine proceeds to step S712, where the first O2 sensor rich / lean determination flag FLAGAF1 is cleared (FLAGAF1 ← 0) to indicate that the current first O2 sensor output voltage VO21 is on the air-fuel ratio rich side. , Go to step S717.

In step S707, FLAGAF1
= 0, that is, when the air-fuel ratio is on the rich side from the previous routine execution to this time, the process branches from step S707 to step S711, and the first air-fuel ratio feedback correction coefficient α1 is reduced by the integration constant I1 to obtain the correction value α1NEW. Is set (α1NEW ← α1-I1), and the first O2 sensor rich / lean determination flag FLA is similarly set in step S712 described above.
After clearing GAF1 (FLAGAF1 ← 0), step S7
Proceed to 17.

On the other hand, in the above step S706, VO21 <SL
If 1, that is, if the air-fuel ratio is determined to be lean, the process branches from step S706 to step S713, and the first rich /
It is determined whether or not the lean determination flag FLAGAF1 is set.

In step S713, FLAGAF1 = 0,
That is, when the air-fuel ratio is on the rich side when the previous routine is executed, and when the air-fuel ratio is on the lean side this time, the routine proceeds from step S713 to step S714, and the first air-fuel ratio feedback correction coefficient α1 is increased by the proportional constant P1 in the plus direction. Skip to and set the correction value α1NEW (α1NEW ← α1 +
P1), in step S716, the current first O2 sensor 25a
Of the first O2 sensor rich / lean determination flag FLA to indicate that the output voltage VO21 of the is on the lean side of the air-fuel ratio.
After setting GAF1 (FLAGAF1 ← 1), step S7
Proceed to 17.

In step S713, FLAGAF1
= 1, that is, when the air-fuel ratio is lean from the previous routine execution to this time, the process branches from step S713 to step S715, and the first air-fuel ratio feedback correction coefficient α1 is increased by the integration constant I1 to obtain the correction value α1NEW. If (α1NEW ← α1 + I1) is set, the process proceeds to step S717 via step S716 described above.

That is, as shown in FIG. 27, the O2 sensor output voltage VO2 (first O2 sensor output voltage VO21, second O2 sensor output voltage VO21,
2 The sensor output voltage VO22 is at the slice level SL (first
Slice level SL for O2 sensor output voltage VO21
1, when the slice level SL2) for the second O2 sensor output voltage VO22) is crossed to the rich side, the air-fuel ratio feedback correction coefficient α (first air-fuel ratio feedback correction coefficient α1, second air-fuel ratio feedback correction coefficient α2) is set to a proportional constant P. (The proportional constant P1 for the first air-fuel ratio feedback correction coefficient α1 and the proportional constant P2 for the second air-fuel ratio feedback correction coefficient α2) are used to skip in the negative direction, and then the integration constant I (for the first air-fuel ratio feedback correction coefficient α1 The integration constant I1 and the integration constant I2) for the second air-fuel ratio feedback correction coefficient α2) are used to gradually correct in the negative direction.

As a result, when the O2 sensor output voltage VO2 is inverted and the slice level SL set with the hysteresis HIS is crossed to the lean side, this time, the air-fuel ratio feedback correction coefficient α is skipped in the plus direction by the proportional constant P. , The integration constant I is gradually corrected in the positive direction to prevent control hunting and improve controllability.

When the O2 sensor output voltage VO2 crosses the slice level SL from the lean side to the rich side, the first O2 sensor side control cycle timer count value COUNTTIM.
TO21 (second O2 sensor side control cycle timer count value CO
When counting from the rich side to the lean side and then to the rich side again, the first O2 sensor side control cycle timer count value COUNTTIMTO21
(Second O2 sensor side control cycle timer count value COUNT
By referring to the value of TTIMTO22), the control cycle TO2 of the first O2 sensor 25a (second O2 sensor 25b) can be obtained.

Then, when proceeding from step S712 or step S716 to step S717, it is checked whether or not the correction value α1NEW is smaller than the lower limit value LMDMIN, and α1NEW <L
If MDMIN, the process branches to step S721 and the lower limit value L
Using MDMIN as a limiter, set the first air-fuel ratio feedback correction coefficient α1 (α1 ← LMDMIN) Step S722
If α1NEW ≧ LMDMIN, go to step S above.
From 717, proceed to step S718.

In step S718, it is checked whether or not the correction value α1NEW exceeds the upper limit value LMDMAX, and α1NEW ≦ LMDM.
In the case of AX, in step S719 the correction value α1NEW is set as the first air-fuel ratio feedback correction coefficient α1 (α1 ← α1NEW) and the process proceeds to step S722. When α1NEW> LMDMAX, in step S720 the upper limit LMDMAX is set as the first limiter. Set the air-fuel ratio feedback correction coefficient α1 (α1 ← LM
DMAX), and proceeds to step S722.

After step S722, the first O 2 sensor 2
This is a process for realizing the monitor function for monitoring the control cycle of 5a and shifting from the feedback control to the open loop control, and whether or not the first O2 sensor side monitor function operation flag FLAGMP1 is set in step S722, that is, It is determined whether or not the set time has elapsed from the start of the feedback control, and when FLAGMP1 = 0 and the set time has not elapsed, the routine exits as it is.

On the other hand, in step S722 described above, FLAGMP1
= 1, that is, when the set time has elapsed from the start of the feedback control, the routine proceeds to step S723, where the first O2 sensor side control cycle timer count value COU
It is determined whether or not NTTIMTO21 exceeds the set value MONT, and it is checked whether or not the control cycle TO2 is longer than usual.

As a result, COUNTTIMTO21 ≦ MONT
If, then the routine is exited and COUNTTIMTO2
When 1> MONT, as shown in FIG. 28, the air-fuel ratio is stuck to the rich side or the lean side, so feedback control on the first O2 sensor side is stopped and open loop control is performed. In order to shift, in step S724, the first O2 sensor side feedback control discrimination flag FLAGF / B1 is cleared (FLAG
F / B1 ← 0).

Next, in step S725, the above-mentioned first
The first monitor open loop control determination flag FLAGMONI1 is set (FLAGMONI1 ← to notify the O2 sensor side feedback control condition determination subroutine that the monitor function has shifted to open loop control.
1) In step S726, the first O2 sensor side control cycle timer operation flag FLAGTIMTO21 is cleared (FLAGT
IMTO21 ← 0) Exit the routine.

[0149]

As described above, according to the present invention, according to the condition set according to the elapsed time after the engine is started,
Since the abnormality of the air-fuel ratio sensor is detected, even if the actual air-fuel ratio is lean immediately after the engine starts regardless of the fuel increase correction, erroneous determination is prevented and the abnormality of the air-fuel ratio sensor is surely detected. It is possible to obtain an excellent effect such as being able to detect

[Brief description of drawings]

FIG. 1 is a flowchart of a feedback control condition determination procedure for the first O2 sensor (part 1).

FIG. 2 is a flowchart (part 2) of the first O2 sensor side feedback control condition determination procedure.

FIG. 3 is a flowchart (part 3) of the first O 2 sensor side feedback control condition determination procedure.

FIG. 4 is a flowchart (part 1) of a second O 2 sensor side feedback control condition determination procedure.

FIG. 5 is a flowchart (part 2) of a second O 2 sensor side feedback control condition determination procedure.

FIG. 6 is a flowchart (part 3) of the second O 2 sensor side feedback control condition determination procedure.

FIG. 7 is a flowchart of a fuel injection amount setting procedure,

FIG. 8 is a flowchart of an engine speed calculation and cylinder discrimination procedure.

FIG. 9 is a flowchart of a fuel injection start setting procedure.

FIG. 10 is a flowchart of a fuel injection procedure.

FIG. 11 is a flowchart of an air-fuel ratio feedback correction coefficient setting procedure.

FIG. 12 is a flowchart of a first air-fuel ratio feedback correction coefficient calculation procedure (part 1).

FIG. 13 is a flowchart of a first air-fuel ratio feedback correction coefficient calculation procedure (part 2).

FIG. 14 is a flowchart of a second air-fuel ratio feedback correction coefficient calculation procedure (part 1).

FIG. 15 is a flowchart of a second air-fuel ratio feedback correction coefficient calculation procedure (part 2).

FIG. 16 is a flowchart of an air-fuel ratio feedback correction coefficient initial setting and timer setting procedure (part 1).

FIG. 17 is a flowchart of an air-fuel ratio feedback correction coefficient initial setting and timer setting procedure (No. 2).

FIG. 18 is a flowchart of an air-fuel ratio feedback correction coefficient initial setting and timer setting procedure (part 3).

FIG. 19 is a schematic diagram of an engine control system.

FIG. 20 is a front view of a crank rotor and a crank angle sensor.

FIG. 21 is a side view of FIG. 20.

FIG. 22 is a front view of a first crank rotor and a first crank angle sensor.

FIG. 23 is a front view of a second crank rotor and a second crank angle sensor.

FIG. 24 is a front view of a cam rotor and a cam angle sensor.

FIG. 25 is a circuit configuration diagram of the control device.

FIG. 26: Output characteristic diagram of O2 sensor

FIG. 27 is an explanatory diagram showing the relationship between the O2 sensor output voltage and the air-fuel ratio feedback correction coefficient.

FIG. 28 is an explanatory diagram showing control condition determination at the time of engine cold start.

FIG. 29 is an explanatory diagram showing control condition determination at the time of engine warm-up restart.

FIG. 30 is an explanatory diagram showing control condition determination in the O2 sensor system short-circuited state.

FIG. 31 is an explanatory diagram showing control condition determination in the O2 sensor system disconnection state.

FIG. 32 is a timing chart of fuel injection and ignition.

[Explanation of symbols]

 1 engine 25a first O2 sensor 25b second O2 sensor VO21 first O2 sensor output voltage VO22 second O2 sensor output voltage O2SHIN set value

Claims (1)

[Claims] 1. A first condition for detecting a short-circuit state and a second condition for detecting a disconnection state are provided for an output value of an air-fuel ratio sensor for detecting an air-fuel ratio of engine exhaust gas. After the engine is started, within the setting range when a predetermined time has passed,
When the output value of the air-fuel ratio sensor is equal to or greater than the set value and does not satisfy the second condition, the procedure for determining that the air-fuel ratio sensor is in the disconnected state or inactive, and the elapsed time after the engine is started. When the output value of the air-fuel ratio sensor does not satisfy the first condition, when the output value of the air-fuel ratio sensor is less than the set value even if it is outside the set range or even within the set range It is determined that the air-fuel ratio sensor is short-circuited or inactive, while
A method for detecting an abnormality in an air-fuel ratio sensor, comprising: a step of determining that the air-fuel ratio sensor is in a disconnected state or inactive when the output value of the air-fuel ratio sensor does not satisfy the second condition. ..