JPH1130148A - Method for controlling air-fuel ratio of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the air-fuel ratio from being erroneously corrected when a driven device or a power transmission means is abnormal. SOLUTION: In a method for controlling the air-fuel ratio of an internal combustion engine, the elapsed time of the 30 deg. crank angle near the top dead center of compression and the elapsed time of the 30 deg. crank angle near 90 deg. after the top dead center of compression are found. The difference between the elapsed times of 720 deg. crank angles is found in relation to a first cylinder and a second cylinder in which combustion is to be performed next the first cylinder. The virtual elapsed time obtained when that torque fluctuation is not generated is assumed from the elapsed time difference between the first cylinder and the second cylinder is found, and the torque fluctuation amount is calculated by using the virtual elapsed time. Whether a driven device 32 such as an accessory to be driven by a crankshaft 13 through a power transmission device 31 such as a belt or the power transmission device 31 is abnormal or not is judged from the torque fluctuation amount. When it is judged that the device is abnormal, correction of the air-fuel ratio, based on the torque fluctuation amount is prohibited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for detecting output fluctuation in a multi-cylinder internal combustion engine.

[0002]

2. Description of the Related Art Crankshaft is 30 ° after compression top dead center
The first angular velocity of the crankshaft at this time is determined from the time required to rotate from 60 ° to 60 °, and the time required for the crankshaft to rotate from 90 ° to 120 ° after the compression top dead center is determined from the time required to rotate the crankshaft during this time. An internal combustion engine that obtains a second angular velocity, obtains a torque generated by a cylinder from the square of the first angular velocity and the square of the second angular velocity, and calculates a torque variation from the variation of the generated torque. It is known. (See Japanese Patent Publication No. 7-33809).

That is, when combustion is performed in each cylinder, the angular velocity of the crankshaft is increased from the first angular velocity ωa to the second angular velocity ωb by the combustion pressure. At this time, assuming that the rotational inertia moment of the engine is I, the kinetic energy is changed from (1/2) · Iωa ² to (1 /
2) It is raised to Iωb ² . Roughly speaking, the amount of increase in kinetic energy (1/2) · I · (ωb ² −ω
a ² ), the generated torque is (ω
b ² −ωa ² ). Therefore, the generated torque is obtained from the difference between the square of the first angular velocity ωa and the square of the second angular velocity ωb. Therefore, in the above-described internal combustion engine, the amount of torque fluctuation is calculated from the generated torque thus obtained. I am trying to do it.

[0004]

When the amount of torque fluctuation can be calculated in this way, the air-fuel ratio can be controlled to the lean limit based on the amount of torque fluctuation. That is, when the air-fuel ratio is richer than the lean limit, the torque variation is small, and when the air-fuel ratio is leaner than the lean limit, the torque variation increases. If the air-fuel ratio is corrected based on the torque fluctuation amount, the air-fuel ratio can be controlled to the lean limit. However, such air-fuel ratio control is possible when the torque fluctuation calculated based on the first angular velocity ωa and the second angular velocity ωb indicates a torque fluctuation due to a fluctuation in combustion pressure.

[0005] However, when the pulley attached to, for example, an accessory driven by the crankshaft through a belt, for example, is not on the same plane as the pulley of the crankshaft, or when the belt tension is reduced, the rotation speed of the crankshaft is reduced. A large fluctuation occurs, and as a result, the torque calculated based on the first angular velocity ωa and the second angular velocity ωb largely fluctuates. As described above, when the torque fluctuation not caused by the combustion pressure fluctuation occurs, a large torque fluctuation occurs, so that when the air-fuel ratio is corrected, the air-fuel ratio largely deviates from the lean limit. It is necessary to prohibit the correction of the air-fuel ratio when a large torque fluctuation occurs due to an abnormality of the accessory or the belt.

However, in the above-mentioned internal combustion engine, there is no suggestion of the occurrence of torque fluctuation due to an abnormality of an auxiliary machine or a belt. There is a problem that it deviates from the air-fuel ratio.

[0007]

According to the present invention, a first crank angle range is set within a crank angle range from the end of a compression stroke to the beginning of an explosion stroke. A second crank angle range is set within a crank angle region in the middle stage of the explosion stroke separated by a certain crank angle from the crank angle range, and a first angular velocity of the crankshaft within the first crank angle range is detected and a second crank angle is detected. A second angular velocity of the crankshaft within a crank angle range of 2 to obtain a variation in output of each cylinder based on the first angular velocity and the second angular velocity, and a driven device driven by the crankshaft via power transmission means. Alternatively, it is determined whether or not the power transmission means is abnormal based on the output fluctuation, and when it is determined that the driven device or the power transmission means is abnormal, the output fluctuation is determined. So that to prohibit the correction of the air-fuel ratio based. That is, if the driven device or the power transmission means is abnormal, the output fluctuation increases, and this abnormality can be detected. At this time, the correction of the air-fuel ratio based on the output fluctuation is prohibited.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes an engine main body having four cylinders including a first cylinder # 1, a second cylinder # 2, a third cylinder # 3, and a fourth cylinder # 4. . Each cylinder #
The fuel tanks # 1, # 2, # 3, and # 4 are connected to the surge tank 3 through the corresponding intake branch pipes 2 and inject fuel into the corresponding intake ports in the respective intake branch pipes 2. The injection valve 4 is attached. The surge tank 3 is connected to an air cleaner 7 via an intake duct 5 and an air flow meter 6, and a throttle valve 8 is arranged in the intake duct 5. On the other hand, the cylinders # 1, # 2, # 3, # 4 is connected to the casing 12 with a built-in _the NO _x absorbent 11 via an exhaust manifold 9 and an exhaust pipe 10. This NO _x absorbent 11 contains N contained in exhaust gas when the air-fuel ratio is lean.
It has a function of absorbing O _x and releasing and reducing the absorbed NO _x when the air-fuel ratio becomes stoichiometric or rich.

The electronic control unit 20 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 22, a RAM (Random Access Memory) 23, a CPU (Microprocessor) 24, and a power supply connected to each other by a bidirectional bus 21. Backup RAM connected
25, an input port 26 and an output port 27. A rotor 14 with external teeth is attached to the output shaft 13 of the engine, and a crank angle sensor 15 composed of an electromagnetic pickup is arranged facing the external teeth of the rotor 14. In the embodiment shown in FIG. 1, external teeth are formed on the outer periphery of the rotor 14 at every 30 ° crank angle. For example, some external teeth are deleted in order to detect the compression top dead center of the first cylinder. ing. Therefore, the crank angle sensor 15 generates an output pulse every time the output shaft 13 rotates by 30 ° crank angle except for the portion where the external teeth are deleted, that is, the missing tooth portion, and the output pulse is input to the input port 26. You.

The air flow meter 6 generates an output voltage proportional to the amount of intake air, and the output voltage is input to an input port 26 via a corresponding AD converter 28. An idle switch 16 for detecting that the throttle valve 8 is at the idling opening is attached to the throttle valve 8, and an output signal of the idle switch 16 is input to an input port 26. An air-fuel ratio sensor (O ₂ sensor) 1 for detecting the air-fuel ratio is provided in the exhaust manifold 9.
The output signal of the air-fuel ratio sensor 17 is input to the input port 26 via the corresponding AD converter 28. On the other hand, the output port 27 is connected to the corresponding drive circuit 2
9 is connected to each fuel injection valve 4 and the warning device 30. The warning device 30 is activated when the engine is abnormal and informs the vehicle driver of the abnormality, and includes, for example, a display device such as a lamp or a buzzer.

Referring to FIG. 1, the engine body 1 includes a driven device 32 driven by a crankshaft 13 via a power transmission device 31. The driven device 32 includes, for example, a cooling water pump, an alternator, an auxiliary device such as an air conditioner, a camshaft, an idler, or a tension adjusting device. On the other hand, the power transmission device 31 is formed of, for example, a belt, a chain, or a gear, but as shown in FIG.
1 is formed from a belt, the crankshaft 13
Pulleys 33 are attached to the rotating shafts of the driven devices 32, respectively, and a belt 34 is stretched around these pulleys 33.

In the internal combustion engine shown in FIG. 1, the fuel injection time TA
U is calculated based on the following equation. TAU = TP ・ FLEAN ・ FLLFB ・ FAF + TA
UV Here, TP indicates a basic fuel injection time, FLEAN indicates a lean correction coefficient, FLLFB indicates a lean limit feedback correction coefficient, FAF indicates a stoichiometric air-fuel ratio feedback correction coefficient, and TAUV indicates an invalid injection time.

The basic fuel injection time TP indicates the injection time required for setting the air-fuel ratio to the stoichiometric air-fuel ratio. The basic fuel injection time TP is obtained by an experiment. The basic fuel injection time TP is a function of the engine load Q / N (intake air amount Q / engine speed N) and the engine speed N in the form of the map shown in FIG. Is stored in the ROM 22 in advance. The lean correction coefficient FLEAN is a correction coefficient for making the air-fuel ratio a lean air-fuel ratio. The lean correction coefficient FLEAN is stored in the ROM 22 in advance as a function of the engine load Q / N and the engine speed N in the form of a map shown in FIG. Is stored in

Lean limit feedback correction coefficient F
LLFB is a correction coefficient for maintaining the air-fuel ratio at the lean limit. In the embodiment according to the present invention, a learning region for the lean air-fuel ratio feedback control is divided into, for example, nine regions with respect to the intake air amount Q and the engine speed N as shown in FIG. Lean limit feedback correction coefficients FLLFFB _{11 to} FLLFB, respectively
₃₃ is set.

The stoichiometric air-fuel ratio feedback correction coefficient FAF
Is a coefficient for maintaining the air-fuel ratio at the stoichiometric air-fuel ratio. The stoichiometric air-fuel ratio feedback correction coefficient FAF is controlled based on the output signal of the air-fuel ratio sensor 17 when the air-fuel ratio is to be maintained at the stoichiometric air-fuel ratio. Move up and down.

As shown in FIG. 4, a lean correction coefficient FLEAN is determined in accordance with the operating state of the engine in an operation region surrounded by a broken line, and the air-fuel ratio is maintained at a lean air-fuel ratio in this operation region. Is done. On the other hand, the air-fuel ratio is maintained at the stoichiometric air-fuel ratio in the operation region outside the region surrounded by the broken line in FIG. When the air-fuel ratio should be maintained at the stoichiometric air-fuel ratio, the lean correction coefficient FLEAN and the lean limit feedback correction coefficient FLLFB are fixed to 1.0, and the stoichiometric air-fuel ratio feedback correction coefficient FAF is controlled based on the output signal of the air-fuel ratio sensor 17. You.

On the other hand, when the air-fuel ratio should be maintained at the lean air-fuel ratio, the stoichiometric air-fuel ratio feedback correction coefficient FAF is fixed at 1.0, that is, the feedback control based on the output signal of the air-fuel ratio sensor 17 is stopped, and the lean correction coefficient FLEAN and lean limit feedback correction coefficient F
The air-fuel ratio is controlled to a lean air-fuel ratio by the LLFB.
Next, the lean limit feedback control will be described with reference to FIG. Figure 3 shows the relationship between the engine output torque variation amount and NO _x generation amount and the air-fuel ratio. Fuel consumption rate as the air-fuel ratio is lean becomes small, and the generation amount of the more NO _x air-fuel ratio becomes lean is reduced. Therefore, from these points, it is preferable that the air-fuel ratio be as lean as possible. However, when the air-fuel ratio becomes lean to a certain degree or more, combustion becomes unstable, and as a result, the amount of torque fluctuation increases as shown in FIG. Therefore, in the embodiment according to the present invention, as shown in FIG. 3, the air-fuel ratio is maintained within the air-fuel ratio control region where the torque fluctuation starts to increase.

That is, specifically, the lean correction coefficient FLE
AN is the lean limit feedback correction coefficient FLLF
When B is set to FLLFFB = 1.0, the air-fuel ratio is determined to be at the center of the air-fuel ratio control region shown in FIG. On the other hand, the lean limit feedback correction coefficient F
LLFB is controlled in the torque fluctuation control region shown in FIG. 3 in accordance with the torque fluctuation amount, and when the torque fluctuation amount becomes large, the lean limit feedback correction coefficient FLL
When FB is increased, that is, the air-fuel ratio is reduced, and the torque fluctuation amount is reduced, the lean limit feedback correction coefficient FLLFB is reduced, that is, the air-fuel ratio is increased. Thus, the air-fuel ratio is controlled within the air-fuel ratio control region shown in FIG.

Note that the lean limit feedback correction coefficient FLLFB is set so as to cover the engine operating region in which the lean correction coefficient FLEAN is determined. Can amount of torque fluctuation is reduced by a large margin the generation amount of the fuel consumption rate and NO _x while ensuring the operation of the good vehicle when it is controlled to within the torque fluctuation control region shown in FIG. However, in order to control the amount of torque fluctuation within the torque fluctuation control region, the amount of torque fluctuation must be detected.

By the way, various methods for calculating the amount of torque fluctuation have been conventionally proposed. A typical example is a method of mounting a combustion pressure sensor in a combustion chamber and calculating a torque fluctuation amount based on an output signal of the combustion pressure sensor,
Alternatively, as described at the beginning, there is a method of calculating the torque fluctuation amount based on the difference between the square of the first angular velocity ωa and the square of the second angular velocity ωb.

The use of a combustion pressure sensor has the advantage that the torque generated by the cylinder to which the combustion pressure sensor is attached can be reliably detected, but has the disadvantage that a combustion pressure sensor is required. On the other hand, the angular velocities ωa, ω
b can be calculated from the output signal of the crank angle sensor provided in the internal combustion engine, so that the angular velocities ωa, ω
When the output torque is calculated based on b, there is an advantage that it is not necessary to provide a new sensor. However, in this case, as described at the beginning, when the power transmission device 31 or the driven device 32 becomes abnormal, there is a problem that the torque fluctuation amount cannot be accurately detected. However, it is clear that a torque calculation method based on angular velocity that does not require a new sensor is preferable as long as this problem is solved. Therefore, in the present invention, the generated torque is calculated based on the angular velocity, and when it is determined that the power voltage device 31 or the driven device 32 is abnormal, the correction of the air-fuel ratio is prohibited.

The output fluctuation and the torque fluctuation of the engine may be obtained in any manner as long as it is based on the angular velocity of the crankshaft 13. However, when the engine drive system generates torsional vibration, when the crankshaft itself generates torsional vibration, When the vehicle travels on a rough road or when there are variations in the external teeth of the rotor, the output fluctuation and torque fluctuation of the engine cannot be accurately calculated. Therefore, in the embodiment according to the present invention, even if the engine drive system or the crankshaft itself generates torsional vibration, the vehicle runs on a rough road, or the external teeth of the rotor vary, the output fluctuation and torque fluctuation of the engine can be accurately determined. A new calculation method of these output fluctuations and torque fluctuations is adopted in order to detect the fluctuations.

Next, a method for calculating the output fluctuation and the torque fluctuation of the engine will be described. First, FIG. 6 shows a time of steady operation in which the engine drive system does not generate torsional vibration.
A method of calculating the driving force generated by each cylinder and the torque generated by each cylinder will be described with reference to (A) and (B). As described above, the crank angle sensor 15 generates an output pulse every time the crankshaft rotates by 30 ° crank angle.
The output pulses are generated at the compression top dead center TDC of # 2, # 3, and # 4. Therefore, the crank angle sensor 15 generates an output pulse every 30 ° crank angle from the compression top dead center TDC of each of the cylinders # 1, # 2, # 3, and # 4. The ignition sequence of the internal combustion engine used in the present invention is 1-3-4-2.

6 (A) and 6 (B), the vertical axis T30 represents the elapsed time of a 30 ° crank angle from the time when the crank angle sensor 15 generates an output pulse to the time when the next output pulse is generated. Further, Ta (i) indicates the elapsed time from the compression top dead center (hereinafter, referred to as TDC) of the i-th cylinder to 30 ° after the compression top dead center (hereinafter, referred to as ATDC),
Tb (i) is from ATDC60 ° of the i-th cylinder to ATDC9
The elapsed time up to 0 ° is shown. Therefore, for example, Ta
(1) indicates the elapsed time from TDC of the first cylinder to 30 ° ATDC, and Tb (1) indicates the ATDC of the first cylinder.
This indicates the elapsed time from 60 ° to ATDC 90 °. On the other hand, the 30 ° crank angle is changed to the elapsed time T3.
When divided by 0, the result of the division represents the angular velocity ω. In the embodiment according to the present invention, 30 ° crank angle / Ta
(I) is referred to as a first angular velocity ωa in the i-th cylinder, and 3
0 ° crank angle / Tb (i) is set to the second
Is referred to as the angular velocity ωb. Therefore, 30 ° crank angle / T
a (1) represents the first angular velocity ωa of the first cylinder,
° Crank angle / Tb (1) represents the second angular velocity ωb of the first cylinder.

Focusing on the first cylinder in FIGS. 6A and 6B, when the combustion starts and the combustion pressure increases, the elapsed time decreases from Ta (1) to Tb (1), and then. Tb
It rises again from (1). In other words, the angular velocity ω of the crankshaft is changed from the first angular velocity ωa to the second angular velocity ωb
And then fall again from the second angular velocity ωb. That is, the angular velocity ω of the crankshaft is determined by the combustion pressure.
Has been increased from the first angular velocity ωa to the second angular velocity ωb. FIG. 6A shows a case where the combustion pressure is relatively high, and FIG. 6B shows a case where the combustion pressure is relatively low. 6A and 6B, when the combustion pressure is high, the amount of decrease in the elapsed time (Ta (i) −Tb (i)) is greater than when the combustion pressure is low, and therefore the angular velocity ω is increased. The large amount (ωb−ωa) increases. When the combustion pressure increases, the driving force generated by the cylinder increases. Therefore, when the increase amount (ωb−ωa) of the angular velocity ω increases, the driving force generated by the cylinder increases. Therefore the first
(Ωb−ωa) between the second angular velocity ωb and the second angular velocity ωa
, The driving force generated by the cylinder can be calculated.

On the other hand, assuming that the rotational inertia moment of the engine is I, the kinetic energy is (1/2) Iωa ^{2 due} to the combustion pressure.
From () Iωb ² . Increased amount of kinetic energy (1/2) · I · (ωb 2 -ωa 2)
It is capable of calculating the square and the torque generated by the cylinder from the difference (ωb ² -ωa ²⁾ of the square of the second angular velocity [omega] b for represents the torque that cylinder will occur, thus the first angular velocity ωa Become.

As described above, if the first angular velocity ωa and the second angular velocity ωb are detected, the driving force generated by the corresponding cylinder and the torque generated by the corresponding cylinder can be calculated from these detected values. The changes in the elapsed time T30 shown in FIGS. 6 (A) and 6 (B) are slightly different depending on the engine. The range is set so that (ωb−ωa) best represents the driving force generated by the engine, or (ωb ² −ωa) depending on the engine.
² ) is determined to best represent the torque generated by the engine. Therefore, depending on the engine, the crank angle range in which the first angular velocity ωa should be detected is the BTDC 30 before the compression top dead center.
° to TDC, and the crank angle range for detecting the second angular velocity ωb is from ATDC 90 ° to ATDC 120 °.
It is possible that

Therefore, if the method of detecting the angular velocities ωa and ωb is generally expressed, the first crank angle range is set within the crank angle range from the end of the compression stroke to the beginning of the explosion stroke, and the first crank angle range is set. A second crank angle range is set in a crank angle region in a middle stage of an explosion stroke separated by a certain crank angle from the first crank angle range, a first angular velocity ωa of the crankshaft in the first crank angle range is detected, and a second This means that the second angular velocity ωb of the crankshaft within the crank angle range is detected.

As described above, if the angular velocities ωa and ωb are detected, the driving force and torque generated by the corresponding cylinder can be calculated based on the detected values. However, in the engine drive system, torsional vibration oscillating at the natural frequency of the drive system is generated by the explosion effect sequentially performed in each cylinder, and when the torsional vibration is generated in the engine drive system, the angular velocity ωa , Ωb, the driving force and torque generated by the cylinder cannot be accurately calculated. Next, this will be described with reference to FIGS.

FIG. 7 shows an elapsed time Ta sequentially calculated for each cylinder when torsional vibration occurs in the engine drive system.
The change of (i) is shown. When torsional vibration occurs in the engine drive system, the torsional vibration causes the angular velocity of the crankshaft to periodically increase and decrease, so that the elapsed time Ta
(I) periodically increases and decreases as shown in FIG.

FIG. 8 shows the elapsed time Ta in FIG.
The portion where (i) is decreasing is shown in an enlarged manner. FIG.
The elapsed time Ta (i) is equal to Ta (1) and T as shown in FIG.
a (3) decreases by ho time.
It is considered that the decrease in time is due to an increase in the amount of torsion due to torsional vibration. In this case, between Ta (1) and Ta (3), the amount of decrease in the elapsed time due to the torsional vibration is considered to increase almost linearly with the passage of time, and therefore, the amount of decrease in the elapsed time due to this torsional vibration. Are Ta (1) and Ta
It is represented by the difference between the dashed line connecting (3) and the horizontal line passing through Ta (1). Therefore, between Ta (1) and Tb (1), the elapsed time is reduced by h due to torsional vibration.

As described above, when torsional vibration occurs in the engine drive system, the elapsed time of Tb (1) is reduced with respect to Ta (1). This includes the decrease amount h of the elapsed time due to the vibration. Therefore, in order to obtain only the elapsed time Tb (1) reduced by the combustion pressure, h must be added to Tb (1). That is, even if the driving force or torque generated by each cylinder is obtained based on the detected elapsed times Ta (i) and Tb (i), the true driving force or torque cannot be obtained, and thus the true driving force or torque cannot be obtained. The engine output fluctuation or torque fluctuation cannot be determined.

Further, in a multi-cylinder internal combustion engine, in addition to such torsional vibration of the engine drive system, torsional vibration of the crankshaft itself is generated. Output fluctuation or torque fluctuation cannot be obtained. Next, this will be described with reference to FIG. In a multi-cylinder internal combustion engine, for example, a four-cylinder internal combustion engine as shown in FIG. 1, a large torsional vibration of the crankshaft itself occurs in the first and second cylinders. That is, in the cylinder in which the torsional vibration of the crankshaft itself hardly occurs, for example, the third cylinder # 3, the elapsed time gradually decreases from Ta (3) to Tb (3) as shown in FIG. In the cylinder # 1, the elapsed time does not gradually decrease from Ta (1) to Tb (1), and the time elapses due to torsional vibration of the crankshaft itself.
The elapsed time of b (1) becomes long. As a result, 1
Regarding the # 1 cylinder, even if the driving force or torque generated by the # 1 cylinder # 1 is determined based on the detected elapsed times Ta (1) and Tb (1), the true driving force or torque can be determined. Therefore, it is not possible to obtain the true engine output fluctuation or torque fluctuation.

Therefore, in the embodiment according to the present invention, even if torsional vibration of the engine drive system or torsional vibration of the crankshaft itself occurs, it is possible to calculate the true engine output fluctuation or torque fluctuation. Calculation method is adopted. Next, this new calculation method will be described with reference to FIG. In FIG. 10, Ta (1) _j-1 and T
b (1) _j-1 represents the elapsed time of the first cylinder # 1 during the preceding combustion, and Ta (1) _j and Tb (1) _j represent the elapsed time of the first cylinder # 1 during the next combustion. Represents time. On the other hand, Ta (3) _j-1 represents the elapsed time at the time of combustion of the third cylinder # 3, which is performed subsequent to the combustion of the first cylinder # 1, and Ta (3) _j is 3 This represents the elapsed time of the next cylinder # 3 during the next combustion.

First, Ta (1)_jAnd Ta (1)_j-1 
DTa (1) (= Ta (1) _j-Ta (1)
_j-1 ), And Ta (3)_jAnd Tb (3)_j-1 And the difference D
Ta (3) (= Ta (3)_j-Ta (3)_j-1 ) And
Confuse. Next, the output torque of the first cylinder # 1 during the preceding combustion and
Assuming that the output torque during the next combustion is the same
ATDC at the time of the next combustion of the first cylinder # 1
Is the virtual elapsed time from Tb 'to ATDC 90 °
(1)_jAnd Tb '(1)_jAnd Tb (1)_j-1 When
Difference Kb (1) (= Tb '(1)_j-Tb (1)_j-1 )
Ask for. These differences DTa (1), Kb (1) and
When DTa (3) is rewritten as a height on a straight line,
As shown in FIG.

As shown in FIG. 11, the elapsed time difference DTa
The elapsed time difference between (1) and DTa (3) is reduced by _I0 time. Even if torsional vibration occurs in the crankshaft itself, the effect of the torsional vibration does not appear in the elapsed time difference, and therefore, the decrease in the _I0 time of the elapsed time difference is due to the torsional vibration of the engine drive system. In this case, DTa
It is considered that the amount of decrease in the elapsed time difference between (1) and DTa (3) due to torsional vibration of the engine drive system increases almost linearly with time. Therefore, assuming that the output torque of the first cylinder # 1 during the previous combustion is the same as the output torque during the next combustion, the elapsed time difference DTa (1) and Kb
It is considered that the elapsed time difference decreases by I due to the torsional vibration of the engine drive system between (1). Therefore, FIG.
As can be seen from the above, the elapsed time difference Kb (1) is expressed by the following equation, assuming that the output torque of the first cylinder # 1 during the previous combustion and the output torque during the next combustion are the same.

Kb (1) = (2DTa (1) + DTa
(3)) / 3 By the way, when it is assumed that the output torque of the first cylinder # 1 during the previous combustion and the output torque during the next combustion are the same, 1
The virtual elapsed time Tb ′ (1) _j of the cylinder # 1 is expressed by the following equation. Tb '(1) _j = Tb (1) _j-1 + Kb (1) Accordingly, when the output torque of the first cylinder # 1 during the previous combustion is assumed to be the same as the output torque during the next combustion, 1 Virtual output torque D during the next combustion of cylinder # 1
NS (1) is represented by the following equation. DNS (1) = {30 ° / Tb ′ (1) _j ｝ ² − {30 ° / Ta (1) _j ｝ ² = {30 ° / (Tb (1) _j−1 + Kb (1))} ² − {30 ° / Ta (1) _j } ² ATDC60 at the time of the next combustion of the first cylinder # 1
Actual elapsed time Tb (°) to ATDC 90 ° (1)
_When the actual output torque is calculated using _j , this output torque DN (1) is expressed by the following equation.

DN (1) = {30 ° / Tb (1) _j } ²
− {30 ° / Ta (1) _j } ^{2 In} this case, the virtual output torque DNS of the first cylinder # 1
The difference between (1) and the actual output torque DN (1) indicates the amount of torque fluctuation of the first cylinder # 1, and therefore, the first cylinder # 1
The torque fluctuation amount DLN (1) is expressed by the following equation. DLN (1) = DNS (1) −DN (1) = {30 ° /
Tb ′ (1) _j ｝ ² − {30 ° / Tb (1) _j ｝ ² Generally, the torque fluctuation amount DLN (i) of the i-th cylinder can be expressed by the following equation.

DLN (i) = DNS (i) -DN (i)
= {30 ° / Tb '(i)} ^2- {30 ° / Tb
(I)｝ ² That is, the torque fluctuation amount of the i-th cylinder is the virtual second
And the square of the actual second angular velocity. By calculating the amount of torque fluctuation by such a method, it is possible to accurately detect the amount of torque fluctuation of each cylinder even if torsional vibration occurs in the engine drive system or even if torsional vibration occurs in the crankshaft itself. Become.

On the other hand, when calculating the torque fluctuation amount by such a method, if there is a variation in the interval between the external teeth formed along the outer periphery of the rotor 14 (FIG. 1), the torque fluctuation amount of each cylinder is calculated. It cannot be detected accurately. Therefore, in the embodiment according to the present invention, even if the interval between the external teeth of the rotor 14 varies, the respective elapsed times Ta (i), Tb detected so that the amount of torque fluctuation of each cylinder can be accurately detected.
(I) is corrected. Next, the elapsed time Ta
The correction method (i) will be described with reference to FIG.

In the embodiment according to the present invention, the elapsed time Ta
(I) is calculated based on the following equation. Ta (i) = (time required from TDC of cylinder i to 30 ° ATDC). (1 + KTa (i)) where KTa (i) represents a correction coefficient for the i-th cylinder, and these correction coefficients KTa ( i) is calculated when fuel supply is stopped during deceleration operation in which no torsional vibration of the engine drive system occurs and no torsional vibration of the crankshaft itself occurs.

FIG. 12 shows the elapsed time Ta during the deceleration operation.
The change of (i) is shown. Since the rotation speed of the crankshaft gradually decreases during the deceleration operation, the elapsed time Ta
(I) is Ta (1) _j−1 , Ta (3) _j−1 , Ta (4)
_j-1 , Ta (2) _j-1 , Ta (1) _j , Ta (3) _j ,
It gradually increases as represented by Ta (4) _j and Ta (2) _j . At this time, if the intervals between the external teeth of the rotor 14 are the same, each elapsed time Ta (i) is considered to change along the solid line in FIG. 12, and the detected elapsed time Ta
When (i) deviates from the solid line in FIG. 12, it is considered that the interval between the external teeth for detecting the elapsed time Ta (i) deviating from the solid line in FIG. 12 deviates from the regular interval. . Therefore, in the embodiment according to the present invention, the elapsed time Ta
When (i) deviates from the straight line shown in FIG. 12, the elapsed time Ta (i) is corrected by the correction coefficient KTa (i) such that the elapsed time Ta (i) is located on the solid line in FIG. Like that.

More specifically, in the embodiment according to the present invention, the average value TaAV _j-1 of the elapsed time Ta (i) of the four cylinders in the 720 ° crank angle range (j-1), (j).
(Ta (1) _j-1 + Ta (3) _j-1 + Ta (4) _j-1 +
Ta (2) _j-1 ) / 4}, TaAV _j } = (Ta (1)
_j + Ta (3) _j + Ta (4) _j + Ta (2) _j ) /
Are sequentially calculated. Next, each elapsed time Ta (4)
_j-1 , Ta (2) _j-1 , Ta (1) _j , Ta (3) _j are considered to have increased from the average value TaAV _{j -1} to the average value TaAV _j at an average constant increase rate; Elapsed time AAV (4), AAV (2), AAV for each cylinder when considered to have increased at an average constant increase rate
(1), AAV (3) is obtained from the following equation.

AAV (4) = (TaAV_j-TaAV
_j-1 ) ・ (1/8) + TaAV_j-1 AAV (2) = (TaAV_j-TaAV_j-1 ) ・ (3 /
8) + TaAV_j-1 AAV (1) = (TaAV_j-TaAV_j-1 ) ・ (5 /
8) + TaAV_j-1 AAV (3) = (TaAV_j-TaAV_j-1 ) ・ (7 /
8) + TaAV_j-1 Next, the elapsed time AA for each cylinder is calculated based on the following equation.
V (4), AAV (2), AAV (1), AAV (3)
Elapsed time Ta (4) actually detected with respect to _j-1 , T
a (2)_j-1 , Ta (1)_j, Ta (3)_jDeviation ratio
KAFC (4), KAFC (2), KAFC (1), K
Find AFC (3).

KAFC (4) = ｛Ta (4) _j−1 −AA
V (4)｝ / AAV (4) KAFC (2) = {Ta (2) _j−1 −AAV (2)} /
AAV (2) KAFC (1) = {Ta (1) _j −AAV (1)} / A
AV (1) KAFC (3) = {Ta (3) _j −AAV (3)} / A
AV (3) Next, a basic correction coefficient KTaB (i) is obtained for each cylinder using the following equation.

KTaB (i) = KTa (i) _j-1 -KA
FC (i) / 4 That is, the previous correction coefficient KTa (i) for each cylinder
_The basic correction coefficient KTaB (i) is calculated by subtracting 1/4 of the deviation ratio KAFC (i) from _j-1 .
Next, the average value tKTaM of the basic correction coefficient KTaB (i)
Is calculated based on the following equation.

TKTaM = ｛KTaB (1) + KTaB
(2) + KTaB (3) + KTaB (4)｝ / 4 Then, as shown in the following equation, each basic correction coefficient KTaB
The correction coefficient KTa (i) for each cylinder is calculated by subtracting the average value tKTaM from (i).

KTa (i) = KTaB (i) −tKTaM As described above, the correction coefficient KTa (i) _{j−1 is set} to the deviation ratio K
The reason why the basic correction coefficient KTaB (i) is once obtained without directly correcting based on AFC (i) is as follows. For example, the deviation ratio KA only for the first cylinder # 1
It is assumed that FC (1) exists and only the correction coefficient KTa (1) of the first cylinder # 1 is corrected based on the deviation ratio KAFC (1). In this case, the elapsed time T of only the first cylinder # 1
a (1) is increased or decreased. However 1
When the elapsed time Ta (1) of only the cylinder # 1 is increased or decreased, the correction coefficients KTa (2), KTa (3), and KTa (4) of the remaining cylinders # 2, # 3, and # 4 are increased. A shift will occur.

In order to prevent such a problem from occurring, a basic correction coefficient KTaB (i) is once obtained, and an average value tKT of the basic correction coefficient is calculated from the basic correction coefficient KTaB (i).
The final correction coefficient KTa is obtained by subtracting aM.
(I) is obtained. That is, for example, when the basic correction coefficient KTaB (1) of the first cylinder # 1 is increased, the basic correction coefficient KTaB (i) of all the cylinders # 1, # 2, # 3, and # 4 is calculated. Average value of tKTa
M is subtracted. As described above, when tKTaM is subtracted from the basic correction coefficient KTaB (i) of all cylinders, the correction coefficient KTa (1) of the first cylinder # 1 increases, but the remaining cylinders ##
2, # 3, # 4 correction coefficients KTa (2), KTa
(3), KTa (4) is reduced and KTa
(1), KTa (2), KTa (3) and KTa
The sum of (4) is always maintained at zero. Thus, KTa
(1), KTa (2), KTa (3) and KTa
Each correction coefficient KTa is such that the sum of (4) is always zero.
When (i) is corrected, one of the correction coefficients KTa
Even if (i) is corrected, other correction coefficients KTa (i) do not shift.

In the embodiment shown in FIG. 12, for example, the elapsed time AAV (1) when the elapsed time Ta (1) _{j of the} first cylinder # 1 is considered to have increased at an average constant increasing rate.
Is larger than the displacement ratio K with respect to the first cylinder # 1.
AFC (1) has a positive value. As a result, the correction coefficient KTa
(1) is decreased until the deviation ratio KAFC (1) becomes zero, and when the deviation ratio KAFC (1) becomes zero, the value of the correction coefficient KTa (1) becomes a constant value.
At this time, the elapsed time Ta (1) matches the elapsed time AVV (1). Correction coefficient KTa (i) for all cylinders
Reaches a constant value, when the rotation speed of the rotor 14 is constant, the elapsed time Ta (i) of each cylinder corrected using the correction coefficient KTa (i) becomes equal. Therefore, even if the interval between the external teeth of the rotor 14 varies, the torque variation of each cylinder can be accurately detected.

Returning again to the calculation of the torque fluctuation, when the torsional vibration occurs in the engine drive system, the elapsed time difference DTa
(I) varies as shown in FIG. However, the elapsed time difference DTa (i) also fluctuates when the vehicle travels on an uneven road, and at this time, the fluctuation width of DTa (i) may become extremely large. FIG. 13 shows the fluctuation of DTa (i) when the vehicle travels on an uneven road, and the AMP of FIG.
a (i), that is, the amplitude. This amplitude AM
When P is small, the output fluctuation and torque fluctuation of each cylinder can be accurately detected by the method described above.

However, when the amplitude AMP increases, D
The output fluctuation or torque fluctuation of the cylinder in which Ta (i) becomes maximum or minimum cannot be detected accurately. That is, assuming that, for example, in FIG. 13, for example, the first cylinder having the maximum DTa (i) is the first cylinder # 1, the decrease I due to the torsional vibration of the virtual elapsed time difference Kb (1) of the first cylinder # 1 is shown in FIG. 11 D
It is determined from the inclination of the chain line connecting Ta (1) and DTa (3). However, near the time when DTa (1) becomes maximum, the amount of increase or decrease of the elapsed time due to torsional vibration is DTa (1).
(2), DTa (1), and a smooth curve passing through DTa (3). Therefore, when Kb (1) of the first cylinder # 1 is obtained from DTa (1) and DTa (3), Kb (1) is obtained. The value of 1) is calculated to be much smaller than the actual value. As a result, Kb (1) does not show a regular value, and thus the output fluctuation amount and the torque fluctuation amount cannot be accurately detected. When the amplitude AMP increases, the same occurs in a cylinder in which DTa (i) is minimized.

Further, the DT of the cylinder in which combustion was performed immediately before
Even in a cylinder in which DTa (i) suddenly changes with respect to a (i), the value of Kb (i) deviates from the actual value, so that output fluctuation and torque fluctuation cannot be detected accurately. Therefore, in the embodiment according to the present invention, when the amplitude AMP is large, D
The output fluctuation amount or the torque fluctuation amount is not obtained for the cylinder in which Ta (i) becomes the maximum or the minimum, and DTa (i) changes abruptly with respect to DTa (i) of the cylinder in which the combustion was performed immediately before. Also, the output fluctuation amount or the torque fluctuation amount is not calculated for the set cylinder.

Further, in the embodiment according to the present invention, it is determined whether the power transmission device 31 or the driven device 32 is abnormal based on the obtained output fluctuation amount or torque fluctuation amount, and the power transmission device 31 or the driven device When it is determined that 32 is abnormal, the correction of the air-fuel ratio is prohibited and the lean operation is prohibited. First, the driven device 32 will be described. When the driven device 32 is normal, for example, the rotation axis of the accessory extends parallel to the crankshaft, the pulleys 33 are mounted perpendicular to the corresponding rotation axes, and all the pulleys 33 are aligned in the same plane. ing. However, if the assembly is incorrect, for example, the rotation axis of the accessory will not be parallel to the crankshaft, the pulley 33 will not be perpendicular to the corresponding rotation axis, or
3 are not aligned on the same plane, and the rotation speed of the pulley 33 greatly varies. The fluctuation of the rotation speed of the pulley 33 is transmitted to the crankshaft 13 via the belt 34. As a result, the rotation speed of the crankshaft 13 largely fluctuates, and the amount of torque fluctuation increases. In other words, if the driven device 32 is abnormal, the amount of torque fluctuation increases. On the other hand, when the combustion pressure fluctuates, the amount of torque fluctuation also increases, and it is not known whether the large amount of torque fluctuation is due to an abnormality in the driven device 32 or to fluctuation in the combustion pressure.

However, when the driven device 32 is abnormal, a large amount of torque fluctuation is maintained even in an engine operating state in which fluctuations in combustion pressure should be kept small. on the other hand,
In the internal combustion engine of FIG. 1, the combustion is particularly stable at this time because the air-fuel ratio is set to the stoichiometric air-fuel ratio during engine idle operation.
Fluctuations in combustion pressure are kept small. Therefore, when the torque fluctuation amount is large during the idling operation, it can be determined that the driven device 32 is abnormal. Therefore, in the embodiment according to the present invention, when the average value of the torque fluctuation amount exceeds a certain value for a certain time or more during the idling operation, it is determined that the driven device 32 is abnormal and the correction of the air-fuel ratio is prohibited, and the lean operation is performed. They are banned. At this time, the warning device 30 is operated.

On the other hand, when the power transmission device 31 is abnormal, for example, when the tension of the belt 34 deviates from the optimum value,
Especially when the crankshaft 1 drops below the optimum value.
The rotation speed of No. 3 fluctuates, but in this case, the torque fluctuation value greatly fluctuates. On the other hand, even when the combustion pressure fluctuates, a large variation occurs in the torque variation. Therefore, it is not known whether the large variation in the torque variation is due to an abnormality of the power transmission device 31 or a variation in the combustion pressure.

However, when the power transmission device 31 is abnormal, the variation in the torque variation is largely maintained even in the engine operating state where the variation in the combustion pressure should be kept small. On the other hand, in the internal combustion engine of FIG. 1, as described above, the fluctuation of the combustion pressure is kept small during the engine idle operation. Therefore, when a large variation occurs in the torque fluctuation amount during the idling operation, it can be determined that the power transmission device 31 is abnormal. Therefore, in the embodiment according to the present invention,
When the variation of the torque variation exceeds a certain value during the idling operation, it is determined that the power transmission device 31 is abnormal, and the correction of the air-fuel ratio is prohibited and the lean operation is prohibited. At this time, the warning device 30 is operated.

Next, a routine for obtaining the torque fluctuation amount of each cylinder will be described with reference to FIGS. FIG. 25 shows the calculation timing of each value performed in each routine. FIG. 14 shows an interrupt routine performed every 30 ° crank angle. FIG.
First, the process proceeds to a routine (step 100) for calculating the elapsed time difference DTa (i) and the elapsed time Tb (i). This routine is shown in FIGS. Next, the routine proceeds to a routine (step 200) for checking whether calculation of torque fluctuation is permitted. This routine is shown in FIGS. Next, the routine proceeds to a routine (step 300) for calculating the torque fluctuation. This routine is shown in FIG. Next, a counter CD used for calculating the torque fluctuation value
The process proceeds to the LNIX processing routine (step 400). This routine is shown in FIG.

Elapsed time difference DTa (i) and elapsed time T
Referring to FIGS. 15 to 18 showing the calculation routine of b (i), first, at step 101, the time TIM
E is set to TIMEO. The electronic control unit 20 includes a free-run counter that indicates the time, and the time TIME is calculated from the count value of the free-run counter. Next, at step 102, the current time TIME is taken. Therefore, the TIMEO of step 101 is 30 °
This indicates the time before the crank angle.

Next, at step 103, it is determined whether the i-th cylinder is at ATDC 30 ° or not. If the ATDC of the i-th cylinder is not 30 °, the process jumps to step 111 to determine whether or not the ATDC of the i-th cylinder is 90 °. If the current i-th cylinder is not at 90 ° ATDC, the elapsed time difference DTa (i) and the elapsed time Tb
The calculation routine of (i) is completed.

On the other hand, if it is determined in step 103 that the ATDC of the i-th cylinder is currently 30 °, the routine proceeds to step 104, where the elapsed time Ta (i) calculated before the 720 ° crank angle is TaO (i). Is done. Next, at step 105, the TD of the i-th cylinder is calculated based on the following equation.
Final elapsed time Ta from C to ATDC 30 °
(I) is calculated.

Ta (i) = (TIME-TIMEO).
(1 + KTa (i)) That is, for example, if it is the ATDC 30 ° of the first cylinder # 1 now, the final elapsed time Ta (1) from TDC of the first cylinder # 1 to ATDC 30 ° is (TIME−TIME)
O) · (1 + KTa (1)). Here, (TIME-TIMEO) represents the elapsed time Ta (1) actually measured by the crank angle sensor 15, and KT
a (1) is a correction coefficient for correcting an error due to the external tooth interval of the rotor 13, and accordingly, (TIME-TIME)
The final elapsed time Ta (1) obtained by multiplying (O) by (1 + KTa (1)) accurately represents the elapsed time during which the crankshaft rotates by 30 ° crank angle.

Next, at step 106, the elapsed time difference DTa (i) (= Ta (i) is obtained by subtracting the elapsed time TaO (i) calculated 720 ° crank angle before from the currently calculated elapsed time Ta (i). -TaO (i))
Is calculated. Next, at step 107, it is determined whether or not the ATDC of the second cylinder # 2 is 30 °. When the ATDC of the second cylinder # 2 is not 30 °, the process jumps to step 110, and the combustion is performed immediately before (i-
1) A flag XCAL (i-1) indicating that the torque variation of the cylinder No. should be calculated is set (XCAL (i-1) ←
"1"). Next, the routine proceeds to step 111. In the embodiment according to the present invention, as described above, the ignition order is set to 1-3-4.
Assuming that the ATDC of the first cylinder # 1 is 30 ° at present, the flag XCAL (2) indicating that the torque fluctuation amount of the second cylinder # 2 in which combustion was performed immediately before should be calculated.
Is set. Similarly, when the final elapsed time Ta (3) is calculated as shown in FIG.
When (1) is set and the final elapsed time Ta (4) is calculated, the flag XCAL (3) is set. When the final elapsed time Ta (2) is calculated, the flag XCAL is set.
(4) is set.

On the other hand, if it is determined in step 111 that the ATDC of the i-th cylinder is 90 °, the process proceeds to step 112, where the elapsed time Tb (i) calculated before the 720 ° crank angle is set to TbO (i). . Next, at step 113, the ATDC6 of the i-th cylinder is determined based on the following equation.
Final elapsed time Tb from 0 ° to 90 ° ATDC
(I) is calculated.

Tb (i) = (TIME-TIMEO).
(1 + KTb (i)) That is, for example, if the ATDC of the first cylinder # 1 is currently 90 °, the ATDC of the first cylinder # 1 is 60 ° to ATDC9.
The final elapsed time Tb (1) up to 0 ° is (TIME-
TIMEO) · (1 + KTb (1)).
Also in this case, the value (1 + KTb (1)) for correcting the error due to the external tooth interval of the rotor 13 is (TIME-TIM).
EO), the final elapsed time Tb
(1) accurately represents the elapsed time during which the crankshaft rotates by 30 ° crank angle. Next, at step 114, the ATDC 90 of the current second cylinder # 2
° is determined. AT of current cylinder # 2
If DC is not 90 °, the calculation routine of the elapsed time difference DTa (i) and the elapsed time Tb (i) is completed.

On the other hand, if it is determined in step 107 that the ATDC of the second cylinder # 2 is currently 30 ° ATDC, the routine proceeds to step 108, where the elapsed time Ta (i) in the 720 ° crank angle range (j) of FIG. average TaAV _j of) is calculated. TaAV _j = (Ta (1) + Ta (3) + Ta (4) +
Ta (2)) / 4 where Ta (1), Ta (3), Ta (4), Ta
(2) is Ta (1) _j , Ta (3) _j ,
Ta (4) _j and Ta (2) _j respectively. Next, the routine proceeds to a routine for calculating the correction coefficient KTa (i) in step 109. This routine is shown in FIG.

Referring to FIG. 17, first, in step 1
In 20 whether or not the fuel supply is stopped during deceleration operation
Is determined. When fuel supply is not stopped during deceleration operation
Completes the processing cycle and stops fuel supply during deceleration operation
Sometimes the process proceeds to step 121. Step 121
Of the elapsed time Ta (i) calculated in step 108
Average value TaAV_jAnd 720 of FIG. 12 which has already been calculated.
° Elapsed time Ta in crank angle range (j-1)
Average value TaAV of (i)_j-1 (= (Ta (1) + Ta
(3) + Ta (4) + Ta (2)) / 4) (where Ta
(1), Ta (3), Ta (4), Ta (2)
Ta (1) shown in 12_j-1 , Ta (3) _j-1 , Ta
(4)_j-1 , Ta (2)_j-1 Is equivalent to)
FIG. 12 when it is considered that the increase has occurred at a certain constant increase rate.
Elapsed time AAV (4), AAV (2), AAV
(1), AAV (3) is calculated as follows.

AAV (4) = (TaAV _j −TaAV
_j-1 ). (1/8) + TaAV _j-1 AAV (2) = (TaAV _j -TaAV _j-1 ). (3 /
8) + TaAV _j−1 AAV (1) = (TaAV _j −TaAV _j−1 ) · (5 /
8) + TaAV _j−1 AAV (3) = (TaAV _j −TaAV _j−1 ) · (7 /
8) + TaAV _j-1 Next, at step 122, these elapsed times AAV (4), AAV (2), AAV (1), AAV
Elapsed time TaO actually detected for (3)
(4), TaO (2), Ta (1), Ta (3) deviation ratio KAFC (4), KAFC (2), KAFC
(1), KAFC (3) is calculated. Here TaO
(4), TaO (2), Ta (1), Ta (3) are Ta (4) _j−1 , Ta (2) _j−1 , T
a (1) _j and Ta (3) _j .

KAFC (4) = ｛TaO (4) -AAV
(4)｝ / AAV (4) KAFC (2) = {TaO (2) −AAV (2)} / A
AV (2) KAFC (1) = {Ta (1) -AAV (1)} / AA
V (1) KAFC (3) = {Ta (3) -AAV (3)} / AA
V (3) Next, in step 123, it is determined whether or not the learning condition of the correction coefficient KTa (i) is satisfied. For example, when a certain time has elapsed since the fuel supply was stopped, the engine speed is within a predetermined range, and the vehicle is not traveling on a rough road, for example, the elapsed time difference DTa shown in FIG.
When the amplitude AMP in (i) does not exceed the set value, it is determined that the learning condition is satisfied. If the learning condition is not satisfied, the routine proceeds to step 128, where the deviation amount KAFC
The integrated value KAFCI (i) of (i) is set to zero, and then at step 129, the integrated count value CKAFC is cleared.

On the other hand, if the learning condition is satisfied, the routine proceeds to step 124, where the deviation KA for each cylinder is determined.
FC (i) is added to the corresponding integrated value KAFCI (i), and then at step 125, the integrated count value CK
AFC is incremented by one. Next, at step 126, it is determined whether or not the integrated count value CKAFC has reached 8. When the accumulated count value CKAFC is not 8, the processing cycle is completed, and the accumulated count value CKA
When FC becomes 8, the routine proceeds to step 127, where the correction coefficient KT
a (i) is calculated. That is, the deviation amount K for each cylinder
When AFC (i) is integrated eight times, the routine proceeds to step 127, where the correction coefficient KTa (i) is calculated.

In step 127, the correction coefficient KTa (i) is calculated as follows. That is, first, each integrated value KAFCI (i) is replaced with KAFCE (i). Next, a basic correction coefficient KTaB (i) is calculated based on the following equation. KTaB (i) = KTa (i)-(KAFCI (i) /
8) / 4 That is, when the elapsed time Ta (i) actually detected is shifted from the elapsed time AAV (i) when it is considered that the elapsed time Ta (i) increases at an average constant increase rate. Is the basic correction coefficient KTaB obtained by correcting the current correction coefficient KTa (i) by ４ of the average value of the integrated value KAFCI (i).
(I). Next, the average value tKTaM of the basic correction coefficient KTaB (i) for all cylinders is calculated based on the following equation.

TKTaM = (KTaB (1) + KTaB
(2) + KTaB (3) + KTaB (4)) / 4 Then, as shown in the following equation, the basic correction coefficient KTaB
By correcting (i) with its average value tKTaM, the correction coefficient KTa (i) is updated. KTa (i) = KTaB (i) -tKTaM In this way, the correction coefficient KTa (i) for each cylinder is updated when fuel injection is stopped during deceleration operation.

On the other hand, if it is determined in step 114 of FIG. 16 that the ATDC of the second cylinder # 2 is 90 ° at present, the routine proceeds to step 115, where the 720 ° crank angle is obtained by the same method as when TaAV _j is obtained, based on the following equation. average TbAV _j of the elapsed time in the angular range Tb (i) is calculated. TbAV _j = (Tb (1) + Tb (3) + Tb (4) +
Tb (2)) / 4 Next, the routine proceeds to a routine for calculating the correction coefficient KTb (i) in step 116. This routine is shown in FIG.

Referring to FIG. 18, first, in step 1
At 30, it is determined whether or not the fuel supply is stopped during the deceleration operation. When the fuel supply is not stopped during the deceleration operation, the processing cycle is completed. When the fuel supply is stopped during the deceleration operation, the process proceeds to step 131. The average value TbAV _j in step 131 the elapsed time Tb which is calculated in step 115 (i), the average value of the time elapsed in 720 ° crank angle range immediately preceding _{Tb (i) TbAV j-1} (=
(Tb (1) + Tb (3) + Tb (4) + Tb (2))
/ 4), the elapsed times BAV (4), BAV (2), B
AV (1) and BAV (3) are calculated.

BAV (4) = (TbAV _j −TbAV
_j-1 ). (1/8) + TbAV _j-1 BAV (2) = (TbAV _j -TbAV _j-1 ). (3 /
8) + TbAV _j−1 BAV (1) = (TbAV _j −TbAV _j−1 ) · (5 /
8) + TbAV _j−1 BAV (3) = (TbAV _j −TbAV _j−1 ) · (7 /
8) + TbAV _j-1 Next, at step 132, these elapsed times BAV (4), BAV (2), BAV (1), BAV
Elapsed time TbO actually detected for (3)
(4), deviation ratio of TbO (2), Tb (1), Tb (3) KBFC (4), KBFC (2), KBFC
(1), KBFC (3) is calculated.

KBFC (4) = {TbO (4) -BAV
(4)｝ / BAV (4) KBFC (2) = {TbO (2) -BAV (2)} / B
AV (2) KBFC (1) = {Tb (1) -BAV (1)} / BA
V (1) KBFC (3) = {Tb (3) -BAV (3)} / BA
V (3) Next, at step 133, it is determined whether or not the learning condition of the correction coefficient KTb (i) is satisfied. As described above, for example, when a certain time has elapsed since the fuel supply was stopped, the engine speed is within a predetermined range, and the vehicle is not traveling on a bad road, for example, the elapsed time difference shown in FIG. When the amplitude AMP of DTa (i) does not exceed the set value, it is determined that the learning condition is satisfied. If the learning condition is not satisfied, the routine proceeds to step 138, where the integrated value KBFCI (i) of the deviation amount KBFC (i) is made zero, and then at step 139, the integrated count value CK
BFC is cleared.

On the other hand, if the learning condition is satisfied, the routine proceeds to step 134, where the deviation KB for each cylinder is determined.
FC (i) is added to the corresponding integrated value KBFCI (i), and then at step 135, the integrated count value CK
BFC is incremented by one. Next, at step 136, it is determined whether or not the integrated count value CKBFC has reached 8. When the accumulated count value CKBFC is not 8, the processing cycle is completed, and the accumulated count value CKB
When FC becomes 8, the routine proceeds to step 137, where the correction coefficient KT
b (i) is calculated. That is, the deviation amount K for each cylinder
When BFC (i) is integrated eight times, the routine proceeds to step 137, where the correction coefficient KTb (i) is calculated.

In step 137, the correction coefficient KTb (i) is calculated as follows. That is, first, each integrated value KBFCI (i) is replaced with KBFCE (i). Next, the basic correction coefficient KTbB (i) is calculated based on the following equation. KTbB (i) = KTb (i)-(KBFCI (i) /
8) / 4 That is, when the actually detected elapsed time Tb (i) is shifted from the elapsed time BAV (i) when it is considered that the elapsed time Tb (i) increases at an average constant increase rate. Is the basic correction coefficient KTbB obtained by correcting the current correction coefficient KTb (i) by ４ of the average value of the integrated value KBFCI (i).
(I). Next, an average value tKTbM of the basic correction coefficients KTbB (i) for all cylinders is calculated based on the following equation.

TKTbM = (KTbB (1) + KTbB
(2) + KTbB (3) + KTbB (4)) / 4 Then, as shown in the following equation, the basic correction coefficient KTbB
By correcting (i) with its average value tKTbM, the correction coefficient KTb (i) is updated. KTb (i) = KTbB (i) -tKTbM In this manner, when the fuel injection is stopped during the deceleration operation, the correction coefficient KTb (i) for each cylinder is updated.

Next, the torque fluctuation calculation permission check routine shown in FIGS. 19 to 21 will be described with reference to FIG. In this routine, the amplitude AMP of the fluctuation of the elapsed time difference DTa (i) due to the vehicle traveling on the uneven road
It is provided to prohibit calculation of the amount of torque fluctuation for a specific cylinder when (FIG. 13) becomes large.

That is, referring to FIG. 19 to FIG. 21, first, in step 201, it is determined whether or not the ATDC of any of the cylinders is currently 30 °. If the ATDC of any of the cylinders is not 30 °, the processing cycle is completed. If the ATDC of any of the cylinders is currently 30 °, the process proceeds to step 202. In steps 202 to 204, the maximum elapsed time difference DT30max when the elapsed time difference DTa (i) increases and then decreases is calculated. That is, in step 202, step 10 in FIG.
6, the DTa (i) calculated is the maximum elapsed time difference D
It is determined whether it is larger than T30max. DT3
If 0max> DTa (i), the routine jumps to step 205, whereas DT30max ≦ DTa (i)
In the case of, the routine proceeds to step 203, where DTa (i) is DT
30 max. Next, at step 204, DTa
An increase flag XMXRE indicating that (i) is increasing
C is set (XMXREC ← “1”), and then the routine proceeds to step 205.

In steps 205 to 207, the minimum elapsed time difference DT30min when the elapsed time difference DTa (i) decreases and then increases is calculated. That is, in step 205, it is determined whether or not DTa (i) calculated in step 106 in FIG. 15 is smaller than the minimum elapsed time difference DT30min. DT30min <DTa
In the case of (i), the process jumps to step 208. On the other hand, when DT30min ≧ DTa (i), the process proceeds to step 206, where DTa (i) is set to DT30min. Next, at step 207, a decrease flag XMNREC indicating that DTa (i) is decreasing is set (XM
NREC ← “1”), and then proceed to step 208.

In steps 208 to 214, D
The amplitude AMP of the fluctuation of Ta (i) (FIG. 13) is equal to the set value A _0.
Is exceeded, a prohibition flag is set to prohibit the calculation of the amount of torque fluctuation for the cylinder in which DTa (i) is maximized. That is, in step 208, DT30max>
It is determined whether or not DTa (i) and XMXREC = "1". DT30max ≦ DTa (i) or the increase flag XMXREC is reset (XMXR
If EC = “0”), the process jumps to step 215, where DT30max> DTa (i)
And if XMXREC = "1", step 209
Proceed to.

[0084] That is, the No. 1 cylinder # 1 of the difference of elapsed times DTa at time t ₁ as shown in FIG. 22 (1) is to become the maximum. In this case, in the interruption routine performed at the time t ₁ proceeds from step 202 to step 203 DTa (1) is a DT30max, then the maximum flag XMXREC is set in step 204. On the other hand, in the interruption routine performed at the time t ₂ in FIG. 22 jumps from step 202 to step 205. At this time, in step 208, DT30ma
Since it is determined that x> DTa (3) and XMXREC = "1", the flow proceeds to step 209. That is, the time t ₂ the flow proceeds to step 209 where the elapsed time DTa (i) starts to decrease.

In step 209, the maximum elapsed time difference DT3
0max is set to TMXREC. Then step 21
At 0, the minimum elapsed time difference TMNREC from the maximum elapsed time difference TMXREC (determined in step 216 described later)
Is subtracted to obtain the amplitude AM of the variation of DTa (i).
P is calculated. Next, at step 211, the initial value of the minimum elapsed time difference DT30min is set to DTa (i).
Next, at step 212, the increase flag XMXREC is reset (XMXREC ← “0”). Next, at step 213 whether the amplitude AMP is greater than the set value A ₀ is judged. Step 21 when AMP <A ₀
Jump to 5. On the other hand, when AMP ≧ A _0, the routine proceeds to step 214, where the torque fluctuation calculation prohibition flag X
NOCAL is set (XNOCAL ← “1”).
That is, 1st amount of torque fluctuation of the cylinders # 1, as described above in the interruption routine performed at the time t ₂ in FIG. 22 is calculated. Therefore, in this interrupt routine, AMP ≧
A ₀ becomes, when the torque fluctuation calculation prohibition flag XNOCAL is set determining of the first cylinder # 1 of the amount of torque fluctuation, i.e., DTa (i) to calculate the amount of torque fluctuation of the cylinder giving the maximum is prohibited.

In steps 215 to 221, D
Amplitude AMP of the variation of ta (i) is set prohibition flag for prohibiting calculation of the amount of torque fluctuation for cylinder DTa (i) is minimized when it exceeds the set value A _0.
That is, in step 215, DT30min <DTa
It is determined whether or not (i) and XMNREC = "1". DT30min ≧ DTa (i) or the decrease flag XMNREC is reset (XMREC =
If "0"), the process jumps to step 222, whereas if DT30min <DTa (i) and XMNREC = "1", the process proceeds to step 216.

[0087] That is, the first cylinder # 1 of the difference of elapsed times DTa at time t ₃ as shown in FIG. 22 (1) is minimized. In this case, in the interruption routine performed at the time t ₃ proceeds from step 205 to step 206 DTa (1) is a DT30min, then decrease flag XMNREC is set in step 207. On the other hand, in the interruption routine performed at the time t ₄ in FIG. 22 jumps from step 205 to step 208. At this time, in step 215, DT30mi
Since it is determined that n <DTa (3) and XMNREC = "1", the process proceeds to step 216. That is, the time t ₄ when the elapsed time difference DTa proceed to step 216 (i) starts to increase.

At step 216, the minimum elapsed time difference DT3
0 min is set as TMNREC. Then step 21
In step 7, the amplitude AMP of the fluctuation of DTa (i) is calculated by subtracting the minimum elapsed time difference TMNREC from the maximum elapsed time difference TMXREC. Next, at step 218, the initial value of the maximum elapsed time difference DT30max is set to DTa.
(I). Next, at step 219, the decrease flag XMNREC is reset (XMNREC ← “0”). Next, at step 220, the amplitude AMP is set to the set value A _0.
It is determined whether or not it is greater than At the time of the AMP <A ₀ jumps to step 222. AM
When P ≧ A _0, the routine proceeds to step 221, and the torque fluctuation calculation prohibition flag XNOCAL is set (XNOCAL ←
"1"). That is, the torque variation of the first cylinder # 1 is in the interruption routine performed at the time t ₄ in FIG. 22 is calculated. Therefore, in this interrupt routine, AMP
≧ A ₀ and the torque fluctuation calculation prohibition flag XNOCAL
Is set, the torque fluctuation amount of the first cylinder # 1 is calculated,
That is, calculation of the torque fluctuation amount of the cylinder in which DTa (i) is minimized is prohibited.

In steps 222 and 223, the calculation of the torque fluctuation amount for the cylinder in which the elapsed time difference DTa (i) has suddenly changed is prohibited. That is, at step 222 | DTa (i-2) -DTa (i-1) | is K _o · |
DTa (i-1) -DTa (i) | is determined. Here, the constant _Ko is a value of about 3.0 to 4.0. In step 222, | DTa (i−
2) -DTa (i-1) | <K o · | DTa (i-1)
-DTa (i) |, the processing routine is completed, and | DTa (i-2) -DTa (i-1).
_{| ≧ K o · | DTa (} i-1) -DTa (i) | a is judged to be the torque fluctuation calculation prohibition flag XNOCAL proceeds to step 223 when the are set.

[0090] That is, when an interrupt routine at time t ₃ now Figure 22 at this time | DTa (4) -
DTa (2) | ≧ K _o · | DTa (2) −DTa (1)
| Is determined. As shown in FIG. 22, when DTa (2) changes rapidly with respect to DTa (4), | DT
a (4) -DTa (2) | is _{K o · | DTa (2)} -D
Ta (1) |. At this time, the torque fluctuation calculation prohibition flag is set, and the calculation of the torque fluctuation amount of the second cylinder # 2 in which the elapsed time difference DTa (i) has suddenly changed is prohibited.

Next, the torque fluctuation calculation routine shown in FIG. 23 will be described. Referring to FIG. 23, first, in step 301, combustion was performed immediately before (i-
1) It is determined whether or not a flag XCAL (i-1) indicating that the torque variation of the cylinder No. should be calculated is set. When the flag XCAL (i-1) = "0", that is, when the flag XCAL (i-1) is not set, the processing cycle is completed. On the other hand, the flag XC
When AL (i-1) = "1", that is, when the flag XCAL
When (i-1) is set, step 302
The flag XCAL (i-1) is reset, and then the routine proceeds to step 303.

In step 303, a prohibition flag XNOCAL for prohibiting the calculation of the amount of torque fluctuation for the cylinder in which combustion was performed immediately before is reset (XNOCAL = "0").
It is determined whether or not it has been performed. When this prohibition flag is set (XNOCAL = "1"), the routine proceeds to step 311 where the prohibition flag XNOCAL is reset. On the other hand, when the prohibition flag has been reset, the routine proceeds to step 304. That is, the process proceeds to step 304 only when the flag XCAL is set and the prohibition flag XNOCAL is reset.

In step 304, a virtual elapsed time difference Kb (i-1) of the (i-1) th cylinder in which combustion was performed immediately before.
(See FIG. 10 and FIG. 11) is calculated based on the following equation. Kb (i−1) = ｛2 · DTa (i−1) + DTa
(I)｝ / 3 Next, at step 305, based on the following equation, the actual output torque DN of the (i-1) th cylinder in which combustion was performed immediately before:
(I-1) is calculated.

DN (i-1) = {30 ° / Tb (i-
1) { ^2- {30 ° / Ta (i-1)} ² Next, at step 306, the virtual output torque DNS of the (i-1) th cylinder in which combustion was performed immediately before based on the following equation.
(I-1) is calculated. DNS (i-1) = {30 ° / (TbO (i-1) + K
b (i-1)) ^2- {30 / Ta (i-1)} ² Then, in step 307, as shown in the following equation, the virtual output torque DNS (i-1) is converted to the actual output torque DN (i
By subtracting -1), the torque fluctuation amount DLN (i-1) of the (i-1) th cylinder in which combustion was performed immediately before is calculated.

DLN (i-1) = DNS (i-1) -D
N (i-1) That is, for example, if the flag XCAL (1) is set at 30 ° ATDC of the third cylinder # 3 and the flag XCAL (1) is set, the virtual elapsed time difference Kb (1) with respect to the first cylinder # 1 in step 304 Is calculated, then in step 305, the actual output torque DN (1) of the first cylinder # 1 is calculated, and in step 306, the virtual output torque DNS (1) of the first cylinder # 1 is calculated, and then, in step 30
At 7, the torque fluctuation amount DLN (1) of the first cylinder # 1 is calculated.

Note that the output fluctuation amount GLN (i−
When determining 1), steps 305 to 30
7, the following calculation may be performed. That is, in step 305, instead of obtaining the actual torque fluctuation DN (i-1), the actual output fluctuation GN (i-
1) is calculated. GN (i-1) = {30 ° / Tb (i-1)}-{30
° / Ta (i-1)｝ Next, at step 306, the virtual torque fluctuation amount DNS
Instead of obtaining (i-1), the virtual output fluctuation amount GNS (i-1) is calculated based on the following equation.

GNS (i-1) = {30 ° / (TbO)
(I-1) + Kb (i-1))｝-｛30 ° / Ta (i
−1)｝ Next, at step 307, the torque fluctuation amount DLN (i−
Instead of obtaining 1), the output fluctuation amount GLN is calculated based on the following equation.
(I-1) is calculated. GLN (i-1) = GNS (i-1) -GN (i-1) In step 307, the torque fluctuation amount DLN (i
When -1) is calculated, the routine proceeds to step 308, where it is determined whether or not the torque fluctuation amount DLN (i-1) is positive.
If DLN (i−1) ≧ 0, the routine jumps to step 310 and the torque fluctuation amount DL of the cylinder in which combustion was performed immediately before is performed.
Integration request flag X indicating that N (i-1) should be integrated
DLNI (i-1) is set (XDLNI (i-1) ←
"1"). On the other hand, if DLN (i-1) <0, the routine proceeds to step 309, where DLN (i-1) is set to zero, and then proceeds to step 310. Note that the torque of each cylinder repeatedly increases and decreases. In this case, the amount of torque fluctuation may be obtained by integrating either the increase in torque or the decrease in torque. In the routine shown in FIG. 23, only the decrease in torque is integrated, and therefore, when DLN (i-1) <0, as described above, DLN (i-1)
Is set to zero.

Next, the counter CDLN will be described with reference to FIG.
IX processing will be described. This counter CDLNI
The count value of X is used when calculating an engine torque fluctuation value described later. Referring to FIG. 24, first, at step 401, the ATDC of the current third cylinder # 3
It is determined whether it is 30 °. If the current ATDC of the third cylinder # 3 is not 30 °, the processing cycle is completed.
If it is currently ATDC 30 ° of the third cylinder # 3, the routine proceeds to step 402. In step 402, it is determined whether a torque fluctuation value calculation condition for calculating a torque fluctuation value of the engine is satisfied. For example, the condition for making the air-fuel ratio lean is not satisfied, or the variation ΔQ / N of the engine load Q / N per unit time is equal to or greater than a set value, or the variation of the engine speed per unit time. When ΔN is equal to or larger than the set value, it is determined that the torque fluctuation value calculation condition is not satisfied. Otherwise, it is determined that the torque fluctuation value calculation condition is satisfied.

If it is determined in step 402 that the torque fluctuation value calculation condition is satisfied, step 40
Proceeding to 8, the count value CDLNIX is incremented by one. The increment operation of the count value CDLNIX is performed every time the third cylinder # 3 reaches ATDC 30 °.
That is, it is performed every 720 ° crank angle. Next, at step 409, the average value N _AVE of the engine speed and the average value Q _AVE of the intake air amount Q from the start of the increment operation of the count value CDLNIX until the count value CDLNIX is cleared are calculated.

On the other hand, when it is determined in step 402 that the torque fluctuation value calculation condition is not satisfied, the routine proceeds to step 403, where the count value CDLNIX is cleared. Next, at step 404, the integrated value DLNI (i) of the torque fluctuation amount DLN (i) for each cylinder (this integrated value is calculated in a routine described later) is cleared, and then at step 405, the integrated count value CDLNI for each cylinder. (I) (this integrated count value is calculated in a routine described later) is cleared.

Next, at step 406, the target torque fluctuation value LVLLFB is calculated. In the embodiment according to the present invention, the air-fuel ratio is feedback-controlled so that the torque fluctuation value calculated as described later becomes the target torque fluctuation value LVLLFB. This target torque fluctuation value LVLLLF
B increases as the engine load Q / N increases, and increases as the engine speed N increases, as shown in FIG. The target torque fluctuation value LVLLFB is stored in the ROM 22 in advance in the form of a map as a function of the engine load Q / N and the engine speed N as shown in FIG. Next, at step 407, the torque fluctuation value DLNISM (i) of each cylinder
(This torque fluctuation value is calculated in a routine to be described later) is set as a target torque fluctuation value LVLLFB calculated from the map of FIG.

FIG. 28 shows a main routine that is repeatedly executed. In this main routine, first, a torque fluctuation value calculation routine (step 600) is executed. This routine is shown in FIGS. 29 and 30. Next, an abnormality determination routine of power transmission device 31 (step 650) is executed. This routine is shown in FIG. Next, a calculation routine (step 700) of the lean limit feedback correction coefficient FLLFB is executed. This routine is shown in FIG. Next, when a predetermined crank angle is reached, an injection time calculation routine (step 800) is executed. This routine is shown in FIG. Next, another routine (step 900) is executed.

Next, a description will be given of a torque variation calculation routine shown in FIGS. 29 and 30. Referring to FIGS. 29 and 30, first, at step 601, an integration request flag XDLNI (i) indicating that the torque variation DLN (i) should be integrated is set (XDLNI).
(I) = “1”) is determined. If the integration request flag XDLNI (i) has not been set, the process jumps to step 616, where the integration request flag XD
Step 60 when LNI (i) is set
Proceed to 2. In step 602, the integration request flag XDLN
I (i) is reset. Next, at step 603, the torque variation DLN (i) is changed to the torque variation integrated value DLN.
It is added to I (i). Next, at step 604, the integrated count value CDLNI (i) is incremented by one. That is, for example, assuming that the integration request flag XDLNI (1) for the first cylinder is set in step 601, this flag XDLN is set in step 602.
I (1) is reset, and in step 603, the torque variation integrated value DLNI (1) is calculated.
At 04, the integrated count value CDLNI (1) is incremented by one.

Next, at step 605, it is determined whether or not the integrated count value CDLNI (i) has become "8". When CDLNI (i) is not "8", the routine jumps to step 616. When CDLNI (i) becomes "8", the routine proceeds to step 606, where the torque fluctuation value DLNISM (i) of each cylinder is calculated from the following equation. DLNISM (i) = DLNISM (i) + ｛DLNI
(I) -DLNISM (i)｝ / 4 Next, in step 607, the torque variation integrated value DLNI (i) for each cylinder is cleared, and then step 6
At 08, the integrated count value CDLNI (i) is reset.

That is, the calculated torque variation integrated value DL
NI (i) and torque fluctuation value DL used so far
When there is a difference from NISM (i), this difference ｛DL
NI (i) -DLNISM (i)} multiplied by 1/4 is added to torque fluctuation value DLNISM (i). Therefore, for example, the integrated count value CD for the first cylinder # 1
When LNI (1) becomes “8”, the torque fluctuation value DLNISM (1) is calculated in step 606.

The following steps 609 to 615 are for judging whether or not the driven device 32 is abnormal. First, in step 609, it is determined whether an abnormality determination condition for the driven device 32 is satisfied. In the present embodiment, it is determined that the abnormality determination condition is satisfied when the engine is idling, the air-fuel ratio is the stoichiometric air-fuel ratio, and the variation ΔN per unit time of the engine speed is smaller than the set value, Otherwise, it is determined that the abnormality determination condition is not satisfied.

When it is determined that the abnormality determination condition is satisfied, the process proceeds to step 610. When it is determined that the abnormality determination condition is not satisfied, the process proceeds to step 61.
Proceed to 2. In step 610, the torque fluctuation amount D of each cylinder
It is determined whether LNISM (i) is greater than a fixed value LVLAUX. This LVLAUX is set so that DLNISM (i) does not exceed if the driven device 32 is normal. If DLNISM (i)> LVLAUX, then the process proceeds to step 611, where DLNISM (i)
The count value CFAIL (i) representing the time during which the state of> LVLAUX is continued is incremented by one. Next, the routine proceeds to step 613. On the other hand, DLNISM
When (i) ≦ LVLAUX, it is determined that the driven device 32 is normal, and the process proceeds to step 612. After the count value CFAIL (i) is reset, the process proceeds to step 616.
Jump to

At step 613, the count value CFAIL
Whether (i) is greater than a fixed value CAUX, ie, DL
It is determined whether the state of NISM (i)> LVLAUX has been continued for a time represented by CAUX. CFA
When IL (i)> CAUX, it is determined that the driven device 32 is abnormal, and then the routine proceeds to step 614, where the abnormal flag XFAILA is set (XFAILA ← “1”). This abnormality flag XFAILA is reset (XF
AILAＩＬ “0”), and is set (XFAILA ← “1”) when it is determined that the driven device 32 is abnormal. Next, the routine proceeds to step 615, where the warning device 30 is operated (ON), and then the routine proceeds to step 616. on the other hand,
If CFAIL (i) ≦ CAUX in step 613, it is determined that the driven device 32 is normal, and the process jumps to step 616.

In some cases, when the driven device 32 is abnormal, only the torque fluctuation value of a specific cylinder increases.
In this case, if the abnormality of the driven device 32 is detected based on the average torque fluctuation value DLNISM described later, the abnormality of the driven device 32 cannot be accurately detected. Therefore, in the present embodiment, the torque fluctuation value DLNISM (i) of each cylinder
The abnormality of the driven device 32 is detected based on the following.

Next, at step 616, it is determined whether or not the count value CDLNIX calculated in the routine shown in FIG. 24 has become "8". When CDLNIX is not "8", the processing cycle is completed and CDLNIX is not executed.
When IX becomes “8”, the routine proceeds to step 617, where the average torque fluctuation value DLNISM (= ｛DLNISM (1) + D), which is the average of the torque fluctuation values DLNISM (i) of each cylinder.
LNISM (2) + DLNISM (3) + DLNISM
(4)｝ / 4) is calculated. Next, at step 618, the count value CDLNIX is cleared. In this way, the value DLNISM representing the torque fluctuation amount of the engine is calculated.

As described above, the count value CDLN
IX is incremented by 1 every 720 ° crank angle, and unless the calculation of torque is prohibited for any cylinder, when the count value CDLNIX becomes “8”, the integrated count value CDL for all cylinders
NI (1), CDLNI (2), CDLNI (3), C
DLNI (4) is already "8". Therefore, in this case, the torque fluctuation value DLNISM for all cylinders
(I) is calculated. On the other hand, for example, if the calculation of the torque fluctuation amount is prohibited for the first cylinder # 1, when the count value CDLNIX becomes "8", only the integrated count value CDLNI (1) of the first cylinder # 1 becomes "8". As a result, a new integrated torque variation amount DLNI (1) is not calculated for the first cylinder # 1. Therefore, in this case, in step 617, the average torque fluctuation value D
When obtaining the LNISM, the torque fluctuation value DLNISM (1) previously calculated is used for only the first cylinder # 1.

Next, the power transmission device 31 will be described with reference to FIG.
Will be described. Referring to FIG. 31, first, at step 651, the power transmission device 31
It is determined whether or not the abnormality determination condition is satisfied. In the present embodiment, it is determined that the abnormality determination condition is satisfied when the engine is idling, the air-fuel ratio is the stoichiometric air-fuel ratio, and the variation ΔN per unit time of the engine speed is smaller than the set value, Otherwise, it is determined that the abnormality determination condition is not satisfied.

When it is determined that the abnormality determination condition is not satisfied, the process proceeds to step 660 to initialize MAXB (MAXB ← “0”), and then to step 661 to initialize MINB (MINB ← MIN0, where MIN0 is a constant value that is larger than the average torque flat value DLNISM can normally take), and then the processing cycle is completed. On the other hand, when it is determined that the abnormality determination condition is satisfied, the process proceeds to step 652. In step 652, the average torque flat value DLNISM is set to MAX.
It is determined whether it is larger than B or not. This MAXB is the value of DLN when the abnormality determination condition of the power transmission device 31 is satisfied.
Indicates the maximum value of ISM, DLNISM> MAXB
In step 653, proceed to step 653 to set DLNISM to MA.
XB, then go to step 654. On the other hand, DLN
If ISM ≦ MAXB, the process jumps to step 654. In step 654, it is determined whether DLNISM is smaller than MINB. This MINB is DLNISM when the abnormality determination condition of the power transmission device 31 is satisfied.
, And when DLNISM <MINB, DLNISM is set to MINB.
Proceed to 56. On the other hand, when DLNISM ≧ MINB, the routine jumps to step 656.

In step 656, the difference (MAXB-MINB) between the maximum value MAXB and the minimum value MINB is set to HENDO representing the variation of the average torque fluctuation value DLNISM. Next, at step 657, HENDO is set to a constant value L.
It is determined whether it is larger than VLBLT. HEND
When O> LVLBLT, it is determined that the power transmission device 31 is abnormal, and the routine proceeds to step 658, where the abnormality flag XFAILB is set (XFAILB ← “1”), and then the routine proceeds to step 659 to activate the warning device 30 (O
N). The abnormality flag XFAILB has been reset (XFAILB ← “0”) in advance, and the power transmission device 3
1 (XFAIL
B ← “1”). On the other hand, HENDO ≦ LVLBLT
In this case, the power transmission device 31 is determined to be normal, and the processing cycle is completed.

Next, the FLLFB calculation routine will be described with reference to FIG. Referring to FIG. 32, first, at step 701, it is determined whether or not the condition for updating the lean limit feedback correction coefficient FLLFB is satisfied. In this embodiment, when the abnormality flag XFAILA of the driven device 32 is set (XFAILA ← “1”), the abnormality flag XFAIL of the power transmission device 31 is set.
When B is set (XFAILB ← “1”),
It is determined that the update condition is not satisfied when the engine is in the warm-up operation or when the operating state of the engine is not in the learning region surrounded by the broken line in FIG. 5, and otherwise it is determined that the update condition is satisfied. Is done. When the update condition is not satisfied, the processing cycle is completed, and when the update condition is satisfied, the process proceeds to step 702.

In step 702, a target torque fluctuation value LVLLFB is calculated from the engine load Q / N and the engine speed N based on the map shown in FIG. Next, at step 703 and step 704, the target torque fluctuation value L
Variation discrimination value DH (n), DL according to VLLFB
Based on (n), the torque fluctuation level LV represented by the following equation
LH (n) and LVLL (n) are calculated.

LVLH (n) = LVLLFB + DH (n) LVLL (n) = LVLLFB + DL (n) Here, the fluctuation amount determination values DH (n) and DL (n) are predetermined as shown in FIG. 27 (A). Have been. That is, as can be seen from FIG. 27A, three positive values are defined for DH (n), and DH (3)> DH
(2)> DH (1) Furthermore, these DH
(1), DH (2), DH (3) are the target torque fluctuation values L
It gradually increases as VLLFB increases. On the other hand, three negative values are defined for DL (n), and have a relationship of DL (1)> DL (2)> DL (3). Further, DL (1), DL (2), DL (3)
Of the target torque fluctuation value LVLLFB gradually increases.

Now, suppose that the target torque fluctuation value LVLLFB calculated in step 702 is a value indicated by a broken line. In this case, in step 703, the values obtained by adding the DH (1), DH (2), and DH (3) on the broken line to the target torque fluctuation value LVLFB are the torque fluctuation levels LVLH (1), LVLH (2), LVLH ( 3), and in step 704, DL (1), DL on the broken line
The values obtained by adding (2) and DL (3) to the target torque fluctuation value LVLLFB are the torque fluctuation levels LVLL (1) and LLL, respectively.
VLL (2) and LVLL (3).

On the other hand, as shown in FIG.
Area between the torque fluctuation levels LVLH (n) and LVLL (n)
Feedback correction value + a₁ , + A_Two , + A
_Three , + A_Four , -B₁ , -B_Two , -B_Three , -B_Four Is predetermined
For example, when the torque fluctuation level is LVLH
Feed for the area between (1) and LVLH (2)
The back correction value is + a_Two Becomes These feedback supplements
Positive value is + a_Four > + A_Three > + A_Two > + A₁ And -b
₁ > -B_Two > -B_Three > -B_Four It is. As shown in FIG.
Each feedback correction value + a₁ , + A_Two , + A_Three , +
a_Four , -B₁ , -B _Two , -B_Three , -B_Four Is shown in FIG.
In the corresponding area.

At steps 703 and 704, the torque fluctuation levels LVLH (n) and LVLL are respectively
When (n) is calculated, the routine proceeds to step 705, where the average torque fluctuation value DLNISM calculated by the torque fluctuation value calculation routine shown in FIG. 29 and FIG.
Which torque fluctuation level LVLH (n), LV
It is determined whether it is between LL (n). Next, at step 706, the corresponding feedback correction value DLFB is calculated. For example, now, the target torque fluctuation value LVLLFB is a value indicated by a broken line in FIG. 27 (A), and the calculated average torque fluctuation value DLNISM is represented by L in FIG.
In the case between VLH (1) and LVLH (2), that is, the deviation of the average torque fluctuation value DLNISM from the target torque fluctuation value LVLLFB is indicated by DH (1) and DH (2) on the broken line in FIG. If it is between them, the feedback correction value DLFB is set to + a ₂ .

Next, at step 707, C shown in FIG.
Average engine speed N _AVE and intake air amount Q obtained in step 409 of the processing routine of DLNIX
The lean limit feedback correction coefficient FLFBBij to be updated is determined based on the average value Q _AVE of the learning region in FIG. Next, at step 708, the feedback correction value DLFB is added to the lean limit feedback correction coefficient FLLFBij determined at step 707.

That is, as described above, for example, DLNISM
> LVLLFB and LVLH (1) <DLNIS
When M <LVLH (2), + a ₂ is added to the lean limit feedback correction coefficient FLLFBij. As a result, the air-fuel ratio becomes smaller, so that the torque fluctuation amount of each cylinder is reduced. On the other hand, DLNISM <LV
LLFB and LVLL (1)>DLNISM> LV
-B ₂ is added to the lean limit feedback correction coefficient FLLFBij when a LL (2). As a result, the air-fuel ratio increases, so that the amount of torque fluctuation in each cylinder is increased. In this way, the air-fuel ratio during the lean operation is controlled such that the average torque fluctuation value DLNISM of all cylinders becomes the target torque fluctuation value LVLLFB.

When the calculation condition of the torque fluctuation value is not satisfied, as shown in the routine shown in FIG.
(I) is LVLLFB, and thus the average torque fluctuation value DLNISM is also the target torque fluctuation value LVLLFB. Therefore, at this time, the lean limit feedback correction coefficient FLLFBij is not updated.

Next, a routine for calculating the fuel injection time will be described with reference to FIG. Referring to FIG. 33, first, at step 801, the basic fuel injection time TP is calculated from the map shown in FIG. Then step 8
01a, both the abnormality flags XFAILA and XFAILB of the driven device 32 and the power transmission device 31 are reset (X
It is determined whether FAILAＩＬ “0”, XFAILB ← “0”). Error flags XFAILA, XF
If both AILBs have been reset, then the routine proceeds to step 802, where it is determined whether or not the operating state is such that lean operation should be performed. When the vehicle is in the operating state in which the lean operation is to be performed, the routine proceeds to step 803, where the value of the stoichiometric air-fuel ratio feedback correction coefficient FAF is fixed at 1.0. Next, at step 804, the lean correction coefficient F is obtained from the map shown in FIG.
LEAN is calculated, and then at step 805, the lean limit feedback correction coefficient FLLFFB is read from the map shown in FIG. Next, at step 809, the fuel injection time TAU is calculated based on the following equation.

TAU = TP / FLEAN / FLLFFB /
FAF + TAUV On the other hand, at step 801a, the abnormal flag XF
Either AILA or XFAILB is set (XFAI
If (LA ← “1”, XFAILB ← “1”), or if it is determined in step 802 that the operating state is not such that lean operation should be performed, that is, if the air-fuel ratio should be set to the stoichiometric air-fuel ratio, the process proceeds to step 806. , The lean correction coefficient FLEAN is fixed at 1.0, and then at step 807, the lean limit feedback correction coefficient FLLFB is fixed at 1.0. Then step 80
At 8, the stoichiometric air-fuel ratio feedback correction coefficient FAF is controlled based on the output signal of the air-fuel ratio sensor 17 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Next, the routine proceeds to step 809, where the fuel injection time TAU is calculated.

Next, another embodiment of a method for determining an abnormality of the driven device 32 will be described. As described above, when the torque fluctuation amount is large in the engine operating state in which the fluctuation of the combustion pressure is to be kept small, it can be determined that the driven device 32 is abnormal. On the other hand, when the fuel injection is stopped during the deceleration operation, the combustion pressure does not fluctuate. Therefore, in this embodiment, when the average value of the torque fluctuation amount exceeds the set value for a certain period of time or more when the fuel injection is stopped during the deceleration operation, it is determined that the driven device 32 is abnormal.

FIGS. 34 and 35 show a routine for calculating the torque fluctuation value in this embodiment. In this routine, steps 601 to 608 and steps 616 to 618 are the same as the routine shown in FIGS. This routine is executed in a main routine as shown in FIG.

Referring to FIGS. 34 and 35, in step 609, it is determined whether or not the abnormality determination condition of the driven device 32 is satisfied. In this embodiment, when the fuel injection is stopped during the deceleration operation, it is determined that the abnormality determination condition is satisfied, and otherwise, it is determined that the abnormality determination condition is not satisfied.
When it is determined that the abnormality determination condition is satisfied, the process proceeds to step 609a, and when it is determined that the abnormality determination condition is not satisfied, the process proceeds to step 612.
In step 609a, the set value LVLAUX2 is calculated using the map of FIG. This set value LVLAUX2
36 is set in advance so as to become larger as the engine operating state, for example, the average value N _AVE of the engine speed becomes smaller.
Are stored in the ROM 22 in advance in the form of a map shown in FIG. Next, the routine proceeds to step 610a, where it is determined whether or not the torque fluctuation value DLNISM (i) of each cylinder is larger than the set value LVLAUX2. DLNISM (i)> LV
If it is LAUX2, then the process proceeds to step 611, where D
The count value CFAIL (i) representing the time during which the state of LNISM (i)> LVLAUX2 is continued is incremented by one. Next, the routine proceeds to step 613a.
On the other hand, when DLNISM (i) ≦ LVLAUX2, it is determined that the driven device 32 is normal, and then step 6
Proceeding to 12, the program jumps to step 616 after resetting the count value CFAIL (i).

At the step 613a, the count value CFAI
Whether L (i) is larger than a fixed value CAUX2, that is, if DLNISM (i)> LVLAUX2 is CAUX
It is determined whether or not the operation has been continued for the time represented by 2. When CFAIL (i)> CAUX2, it is determined that the driven device 32 is abnormal, and then the routine proceeds to step 614, where the abnormality flag XFAILA is set (XFAILA ←
"1"). When the abnormality flag XFAILA is set, the updating of the lean limit feedback correction coefficient FLLFB is prohibited and the lean operation is prohibited, as in the above-described embodiment. Next, the routine proceeds to step 615, where the warning device 30 is operated (ON), and then the routine proceeds to step 616. On the other hand, in step 613, CFAIL (i) ≦
In the case of CAUX2, it is determined that the driven device 32 is normal, and the routine jumps to step 616.

Next, another embodiment of a method for determining an abnormality of the power transmission device 31 will be described. As described above, the power transmission device 31
Is abnormal, the rotation speed of the crankshaft 13 fluctuates, and as a result, a large variation occurs in the output torque obtained. On the other hand, even if the combustion is stable, the variation in the output torque increases as the lean degree of the air-fuel ratio increases, so that the large variation in the output torque is due to an abnormality in the power transmission device 31 or I do not know if it is due to the large lean degree of the air-fuel ratio.

However, as shown in FIG. 37A, as long as the power transmission device 31 is normal, the frequency distribution of the calculated output torque in the region of the output torque larger than the average value of the output torque indicates the lean degree of the air-fuel ratio. It is almost constant regardless of On the other hand, as shown in FIG. 37 (B), when the power transmission device 31 is abnormal (broken line), the calculated output torque frequency distribution in the output torque region larger than the average value of the output torque is normal (solid line). Spread than).
Therefore, when the deviation between the maximum value and the average value of the output torque is large, it can be determined that the power transmission device is abnormal. Therefore, in the present embodiment, when the deviation between the obtained maximum value and the average value of the output torque exceeds a certain value, it is determined that the power transmission device 31 is abnormal.

FIG. 38 shows an interruption routine executed at every 30 ° crank angle in the present embodiment. This routine is a routine for calculating a torque fluctuation (step 300) and a processing routine for the counter CDLNIX (step 400). The difference from the interrupt routine in FIG. 14 is that the abnormality determination routine (step 350) of the power transmission device 31 is executed between the two. This abnormality determination routine is shown in FIG.

Referring to FIG. 39, first, at step 351, it is determined whether or not the abnormality determination condition of power transmission device 31 is satisfied. In this embodiment, when the variation ΔN per unit time of the engine speed is smaller than the set value, it is determined that the abnormality determination condition is satisfied, and otherwise, it is determined that the abnormality determination condition is not satisfied. . If it is determined that the abnormality determination condition is satisfied, then step 3 is performed.
Proceeding to 52, the output torque DN (i-1) of the (i-1) th cylinder calculated by the torque fluctuation calculation routine shown in FIG.
Is added to the output torque integrated value DNI (i-1). Next, at step 353, the integrated count value CDNI (i−
1) is incremented by one. Then step 3
At 54, the output torque DN (i-1) of the (i-1) th cylinder
Is larger than the maximum value DNMAX (i-1) of the output torque of the (i-1) th cylinder during the current output torque integration period. DN (i-1)> DNMAX
In the case of (i-1), the process then proceeds to step 355, where D
N (i-1) is set to the maximum value DNMAX (i-1), and then the routine proceeds to step 356. On the other hand, DN (i-
1) When ≤ DNMAX (i-1), step 356
Jump to

In step 356, the integrated count value CDN
It is determined whether or not I (i-1) has become "n". C
When DNI (i-1) is not "n", the processing cycle is completed. When CDNI (i-1) is "n", the routine proceeds to step 357, where the average value of the output torque of the (i-1) th cylinder is obtained. A certain average output torque DNAV (i-1)
(= {DNI (i-1) / n}) is calculated. Next, at step 358, the maximum value DNMAX (i-1) of the output torque of the (i-1) th cylinder and the average output torque DNAV
Deviation from (i-1) (= DNMAX (i-1) -DNA
V (i-1)) is DDN (i-1). This DD
N (i-1) represents a variation in the output frequency calculation frequency distribution in an output torque region larger than the average output torque. Next, at step 359, DDN (i-1)
Is larger than the constant value LVLBLT2. When DDN (i−1) ≦ LVLBLT2, it is determined that the power transmission device 31 is normal, and the processing cycle is completed. When DDN (i−1)> LVLBLT2, the power transmission device 31 is determined to be abnormal. Next, the routine proceeds to step 360, where after setting the abnormality flag XFAILB, the routine proceeds to step 361, where the warning device 30 is operated. When the abnormality flag XFAILB is set, the updating of the lean limit feedback correction coefficient FLLFB is prohibited,
Lean operation is prohibited.

On the other hand, when it is determined in step 351 that the abnormality determination condition is not satisfied, the routine proceeds to step 362, where the output torque integrated value DNI (i-1) is reset (DNI (i-1) ← “0”). ), Then, in step 363, the integrated count value CDNI (i-1) is also reset (CDNI (i-1) ← "0"), and then in step 364, the maximum output torque value DNMAX (i)
-1) is also reset (DNMAX (i-1) ← “0”).

[0136]

The air-fuel ratio can be prevented from being erroneously corrected when the driven device or the power transmission means is abnormal.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing a map of a basic fuel injection time.

3 is a diagram showing a generation amount and the torque fluctuation of the NO _x.

FIG. 4 is a diagram showing a map of a lean correction coefficient.

FIG. 5 is a diagram showing a map of a lean limit feedback correction coefficient.

FIG. 6 shows elapsed times Ta (i) and T of a 30 ° crank angle.
It is a time chart which shows the change of b (i).

FIG. 7 is a time chart showing a change in elapsed time Ta (i) at a 30 ° crank angle.

FIG. 8 shows elapsed times Ta (i) and T of a 30 ° crank angle.
It is a time chart which shows the change of b (i).

FIG. 9 shows elapsed times Ta (i) and T of a 30 ° crank angle.
It is a time chart which shows the change of b (i).

FIG. 10 is a time chart showing changes in elapsed time Ta (i) at a 30 ° crank angle.

FIG. 11 is a diagram showing a relationship between elapsed time differences DTa (i) and Kb (i).

FIG. 12 is a time chart showing changes in elapsed time Ta (i) during deceleration operation.

FIG. 13 is a time chart showing changes in the elapsed time difference DTa (i).

FIG. 14 is a flowchart showing an interrupt routine.

FIG. 15 shows an elapsed time difference DTa (i) and an elapsed time Tb.
It is a flowchart for calculating (i).

FIG. 16 shows an elapsed time difference DTa (i) and an elapsed time Tb.
It is a flowchart for calculating (i).

FIG. 17 is a flowchart for calculating KTa (i).

FIG. 18 is a flowchart for calculating KTb (i).

FIG. 19 is a flowchart for checking permission for calculating a torque fluctuation amount.

FIG. 20 is a flowchart for checking permission for calculating a torque fluctuation amount.

FIG. 21 is a flowchart for checking permission of calculation of a torque fluctuation amount.

FIG. 22 shows changes in elapsed time difference DTa (i) and flag XM.
It is a time chart which shows a change of XREC and XMREC.

FIG. 23 is a flowchart for calculating a torque fluctuation amount.

FIG. 24 is a flowchart for processing a counter CDLNIX.

FIG. 25 is a diagram showing calculation timings of various values.

FIG. 26 is a diagram showing a target torque fluctuation value.

FIG. 27 is a diagram showing fluctuation amount determination values DH (n) and DL (n) and torque fluctuation levels LVLH (n) and LVLL (n).

FIG. 28 is a flowchart showing a main routine.

FIG. 29 is a flowchart for calculating a torque fluctuation value.

FIG. 30 is a flowchart for calculating a torque fluctuation value.

FIG. 31 is a flowchart for determining an abnormality of the power transmission device.

FIG. 32 is a flowchart for calculating a lean limit feedback correction coefficient.

FIG. 33 is a flowchart for calculating a fuel injection time.

FIG. 34 is a flowchart for calculating a torque fluctuation value in another embodiment.

FIG. 35 is a flowchart for calculating a torque fluctuation value in another embodiment.

FIG. 36 is a diagram showing a setting value LVLAUX2.

FIG. 37 is a diagram showing a frequency distribution of the calculated output torque.

FIG. 38 is a flowchart showing an interrupt routine in another embodiment.

FIG. 39 is a flowchart for determining an abnormality of the power transmission device in another embodiment.

[Explanation of symbols]

 3 ... Surge tank 4 ... Fuel injection valve 8 ... Throttle valve 13 ... Crankshaft 14 ... Rotor 15 ... Crank angle sensor 31 ... Power transmission device 32 ... Moving device

Claims (1)

[Claims] 1. A first crank angle range is set within a crank angle range from the end of a compression stroke to the beginning of an explosion stroke.
A second crank angle range is set in a middle crank angle range of an explosion stroke separated by a certain crank angle from the first crank angle range, and a first angular velocity of the crankshaft in the first crank angle range is set. And detecting a second angular velocity of the crankshaft within the second crank angle range to obtain an output variation of each cylinder based on the first angular velocity and the second angular velocity. It is determined based on the output fluctuation whether the driven device or the power transmission means driven via the output is abnormal, and when it is determined that the driven device or the power transmission means is abnormal, the air-fuel ratio based on the output fluctuation is determined. An air-fuel ratio control method for an internal combustion engine, wherein the correction of the air-fuel ratio is prohibited.