JPH0968080A - Control device for internal combustion engine - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] Controlling the air-fuel ratio and ignition timing to the combustion stability limit without being affected by variations in combustion pressure detection values between cylinders, and making the combustion pressure fluctuations for all cylinders an allowable level. Avoid exceeding and growing. SOLUTION: The in-cylinder pressure is integrated in a predetermined integration section for each cylinder, and the in-cylinder pressure integrated value Pi is obtained for each cylinder (S
1) The fluctuation rate ΔPi of the integrated value Pi is calculated for each cylinder (S2). Then, the ignition timing is retarded within a range in which the fluctuation pressure ΔPi does not exceed a predetermined value for each cylinder (S3),
Alternatively, the air-fuel ratio is made lean (S4). Further, the leaning amount or the retarding amount for each cylinder is limited by a limiter set based on the combustion pressure variation in all cylinders (S6, 7).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine, and more particularly to a technique for controlling the air-fuel ratio and ignition timing of the engine to a combustion stability limit.

[0002]

2. Description of the Related Art Conventionally, engine output fluctuations have been detected, and the air-fuel ratio and ignition timing have been adjusted to combustion stability limits based on the detection results. Specifically, the engine output fluctuation (combustion pressure fluctuation rate in all cylinders) is calculated based on the combustion pressure sensor provided for each cylinder, and the fluctuation rate does not exceed a predetermined value (combustion stability limit). Within the range, the air-fuel ratio is made lean and the ignition timing is retarded.

[0003]

By the way, if the output characteristic of the combustion pressure sensor provided for each cylinder varies, the combustion pressure detected for each cylinder also varies (see FIG. 9). Even if combustion is stable in each cylinder, the variation in combustion pressure detection value between cylinders is erroneously detected as engine output fluctuation, and the air-fuel ratio becomes lean even though the combustion stability limit has not actually been reached. , In some cases, the ignition timing could not be retarded.

In particular, when a ring-shaped piezoelectric element is mounted as a washer of a spark plug and a combustion pressure sensor for detecting a combustion pressure as a relative pressure with respect to a tightening load of the spark plug is used, a sensor is generated due to the variation of the tightening load. There is a possibility that the output characteristics will vary greatly between the two, and it may not be possible to control the air-fuel ratio and ignition timing to the combustion stability limit.

As a technique for solving such a problem, the present applicant calculates a combustion pressure fluctuation for each cylinder based on the combustion pressure detected for each cylinder, and calculates each combustion pressure fluctuation based on the calculated combustion pressure fluctuation. Proposed a configuration that controls the ignition timing and air-fuel ratio for each cylinder to the combustion stability limit

[0006] Japanese Patent Application No. 7-

[Enter the application number of 95-00385 separately] (see issue). However, the combustion stability limit of each cylinder is different for each cylinder due to the distribution performance of fuel and air, the variation of parts for each cylinder, etc. Therefore, the combustion stability limit for each cylinder is controlled by the control for each cylinder. The ignition timing and the air-fuel ratio are varied among the cylinders (see FIGS. 6 and 7), which causes variation in the combustion pressure between the cylinders, which may cause an output fluctuation exceeding an allowable level for the entire engine. There was (Fig. 8
reference).

The present invention has been made in view of the above-mentioned problems, and the output fluctuation exceeding the permissible level occurs in the engine as a whole while controlling near the combustion stability limit for each cylinder without being affected by variations in the combustion pressure sensor. An object of the present invention is to provide a control device for an internal combustion engine that can avoid such a situation.

[0008]

Therefore, the invention according to claim 1 is constructed as shown in FIG. In FIG.
The combustion pressure detecting means detects the combustion pressure for each cylinder of the engine,
The combustion pressure fluctuation calculating means calculates the combustion pressure fluctuation for each cylinder based on the combustion pressure for each cylinder detected by the combustion pressure detecting means.

The cylinder-by-cylinder combustion control means controls the cylinder-by-cylinder combustion control independently of each other and is controlled by the combustion pressure fluctuation calculating means. Feedback control is performed based on fluctuations in combustion pressure so that the combustion stability limit is reached for each cylinder. Further, the feedback limiting means limits the feedback control of the controlled object by the cylinder-by-cylinder combustion control means to within a predetermined limit value.

With this configuration, the combustion pressure fluctuation is calculated not for all cylinders but for each cylinder. Therefore, even if the absolute value of the combustion pressure detection value varies among the cylinders, it is substantially correct for each cylinder. The combustion pressure fluctuation can be calculated. That is, even if there is an error in the absolute value of the combustion pressure detected for each cylinder, the fluctuation of the combustion pressure is calculated and controlled for each cylinder, so that the shift of the absolute value has no effect. It is possible to correctly detect the combustion pressure fluctuations in the cylinders and control the combustion stability limit for each cylinder.

Here, in order to prevent variations in the combustion pressure among the cylinders due to variations in the combustion stability limit among the cylinders, and thus to prevent the engine output variations from increasing, the individual cylinders based on the combustion pressure variations for the individual cylinders. A limit value is set for the control to prevent a large combustion pressure variation between cylinders. In the invention according to claim 2, the feedback limiting means sets the predetermined limit value uniformly for each cylinder based on the output fluctuation in the entire engine.

According to this structure, the combustion stability limit control for each cylinder sets the limit value based on whether or not the engine output fluctuation actually exceeds the allowable value. It is possible to avoid over-limiting the limit control. According to a third aspect of the invention, the feedback limiting means detects the output fluctuation in the entire engine based on the combustion pressure of each cylinder detected by the combustion pressure detecting means.

According to this structure, the combustion pressure fluctuations in all the cylinders are calculated based on the combustion pressure detected for each cylinder, and it is determined whether the engine output fluctuation exceeds the allowable value. Thus, the limit value in the combustion stability limit control for each cylinder is set. According to the invention of claim 4,
The feedback limiting means is configured to detect the output fluctuation in the entire engine based on the fluctuation in the engine rotation speed.

According to this structure, the variation in the combustion pressure among the cylinders causes the fluctuation in the engine rotation speed. Therefore, the engine output fluctuation is detected based on the fluctuation in the engine rotation speed, and the combustion stability limit control for each cylinder is performed. Set the limit value in. According to the invention of claim 5, a fuel supply unit is provided for each cylinder of the engine, and the combustion control unit for each cylinder independently controls the fuel supply amount in the fuel supply unit as the control target for each cylinder, The air-fuel ratio of each cylinder is controlled to the combustion stability limit of each cylinder, and the feedback limiting means limits the lean margin of the air-fuel ratio to within a predetermined limit value.

According to this structure, the air-fuel ratio of each cylinder can be made lean to the combustion stability limit of each cylinder, while it is possible to prevent the engine output fluctuation from increasing due to the variation of the air-fuel ratio among the cylinders. . In the invention according to claim 6, the cylinder-by-cylinder combustion control means independently controls the ignition timing in each cylinder as the control target to the combustion stability limit for each cylinder, and the feedback limiting means is provided. The configuration is such that the retard amount of ignition timing is limited within a predetermined limit value.

According to this structure, it is possible to retard the ignition timing of each cylinder to the combustion stability limit of each cylinder to suppress the amount of HC, and on the other hand, due to the variation of the ignition timing among the cylinders, It is possible to avoid a large output fluctuation.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. In FIG. 2 showing the system configuration, air is taken into the internal combustion engine 1 through an air cleaner 2, an intake duct 3, and an intake manifold 4. In the intake duct 3,
A butterfly-type throttle valve 5 that interlocks with an accelerator pedal (not shown) is interposed, and the throttle valve 5 adjusts the intake air amount of the engine.

Further, an electromagnetic fuel injection valve 6 (fuel supply means) is provided for each cylinder in each branch portion of the intake manifold 4, and the amount of fuel injected and supplied from the fuel injection valve 6 is adjusted. A mixture having a predetermined air-fuel ratio is formed by electronic control. Here, by individually controlling the fuel injection valve 6 provided for each cylinder, it is possible to form an air-fuel mixture having a different air-fuel ratio for each cylinder.

The air-fuel mixture sucked into the cylinder through the intake valve 7 is ignited and burned by the spark ignition by the spark plug 8 provided for each cylinder, and the combustion exhaust gas is discharged through the exhaust valve 9 and the exhaust manifold. Catalyst not shown by 10,
Guided by the muffler. The control unit 11 for controlling the fuel injection amount by the fuel injection valve 6 and the ignition timing of the spark plug 8 is constituted by including a microcomputer, and the intake air amount signal Q from the hot wire type air flow meter 12 and the throttle sensor 13 The throttle valve opening signal TVO, the crank angle signal from the crank angle sensor 14, the cooling water temperature signal Tw from the water temperature sensor 15, the cylinder pressure signal P from the cylinder pressure sensor 16, and the like are input.

The hot-wire type air flow meter 12 directly detects the intake air amount of the engine 1 as a mass flow rate based on the resistance change of the temperature-sensitive resistance due to the intake air amount.
The throttle sensor 13 is an opening TV of the throttle valve 5.
O is detected by a potentiometer. The crank angle sensor 14 outputs a unit angle signal for each unit crank angle and a reference angle signal for each predetermined piston position. Here, the engine rotation speed Ne can be calculated by measuring the number of generations of the unit angle signal within a predetermined time or the generation cycle of the reference angle signal.

The water temperature sensor 15 detects the cooling water temperature Tw in the water jacket of the engine 1 as a temperature representing the engine temperature. In-cylinder pressure sensor 16
The (combustion pressure detecting means) is composed of a ring-shaped piezoelectric element mounted as a washer of the spark plug 8 as disclosed in Japanese Utility Model Laid-Open No. Sho 63-17432, and is relative to the tightening load of the spark plug. This is a sensor that detects combustion pressure as pressure, and by mounting it on each spark plug 8 of each cylinder, the in-cylinder pressure P (combustion pressure) can be detected for each cylinder.
The in-cylinder pressure sensor 16 is of a type that is mounted as a washer of the spark plug 8 as described above, and is of a type that directly detects the in-cylinder pressure in the combustion chamber and detects the in-cylinder pressure as an absolute pressure. Is also good.

The control unit 11 determines the basic ignition timing (basic ignition advance value) based on engine operating conditions such as engine load and engine speed, and controls the ignition timing by the spark plug 8. The control of the injection amount of the fuel injection valve 6 by the control unit 11 is performed as follows.

Based on the intake air amount Q detected by the hot-wire air flow meter 12 and the engine speed Ne calculated from the detection signal from the crank angle sensor 14, the basic fuel injection amount Tp (corresponding to the target air-fuel ratio = K × Q / Ne: K is a constant), and the cooling water temperature T is added to the basic fuel injection amount Tp.
A final fuel injection amount Ti is obtained by performing a correction according to an operating condition such as w. Then, a drive pulse signal having a pulse width corresponding to the fuel injection amount Ti is output to the fuel injection valve 6 at a predetermined timing. The fuel, which is adjusted to a predetermined pressure by a pressure regulator (not shown), is supplied to the fuel injection valve 6, and an amount of fuel proportional to the pulse width of the drive pulse signal is injected and supplied to a predetermined space. A fuel-air mixture is formed.

In addition to the basic ignition timing and air-fuel ratio (fuel injection amount) control, the control unit 11 also determines the cylinder internal pressure for each cylinder based on the cylinder internal pressure detected by the cylinder internal pressure sensor 16. The combustion pressure fluctuation is calculated (combustion pressure fluctuation calculation means), and based on the calculation result, feedback control for retarding the ignition timing and leaning the air-fuel ratio is independently provided for each cylinder within a range where the combustion pressure fluctuation does not exceed the allowable limit. Is executed (cylinder combustion control means), and the state of such control will be described in detail with reference to the flowchart of FIG.

The flow chart of FIG. 3 shows the ignition timing and the air-fuel ratio control in the # 1 cylinder, but in the other cylinders, the same control as the control shown in the flow chart of FIG. 3 is independent. The ignition timing and the air-fuel ratio (fuel injection amount) are individually controlled for each cylinder. In the flowchart of FIG. 3, first, step 1 (S1 in the figure; the same applies hereinafter).
Then, the detection signal of the in-cylinder pressure sensor 16 provided in the # 1 cylinder is A / D converted and read, and the read in-cylinder pressure is integrated in a predetermined integration section (for example, compression TDC to ATDC 100 °) to obtain an integrated value Pi. Get (# 1).

In step 2, the ratio ΔPi (# 1) between the latest value of the integrated value Pi (# 1) and the previous value is calculated as the combustion pressure fluctuation rate in the # 1 cylinder. In step 3, the combustion pressure fluctuation rate ΔPi (# 1) in the # 1 cylinder is compared with a predetermined value that is preset as a value corresponding to the combustion stability limit. Then, when the combustion pressure fluctuation rate ΔPi (# 1) exceeds the predetermined value, the routine proceeds to step 4 to restore combustion stability, or the air-fuel ratio is made rich.
Alternatively, the ignition timing is advanced.

To enrich the air-fuel ratio, for example, the multiplication correction term of the basic fuel injection amount Tp is increased by a predetermined value,
This is performed by increasing the fuel injection amount Ti. Further, the ignition timing is advanced by, for example, increasing the addition correction term for the basic ignition timing by a predetermined value to increase the ignition advance value. On the other hand, when the combustion pressure fluctuation rate ΔPi (# 1) is less than the predetermined value, it is possible that the lean air-fuel ratio or the ignition timing retard correction can be advanced without exceeding the combustion stability limit. Therefore, the routine proceeds to step 5, where the air-fuel ratio is made lean, or the ignition timing is retarded.

To make the air-fuel ratio lean, for example, the multiplication correction term of the basic fuel injection amount Tp is decreased by a predetermined value,
This is performed by reducing the fuel injection amount Ti. The ignition timing is retarded by, for example, reducing the addition correction term for the basic ignition timing by a predetermined value to reduce the ignition advance value. Further, when the combustion pressure fluctuation rate ΔPi (# 1) and the predetermined value are substantially equal to each other and it is considered that the ignition timing or the air-fuel ratio is controlled near the combustion stability limit, the air-fuel ratio and the ignition timing are controlled. Step 6 without modifying
Proceed to.

In step 6, whether or not the leaning amount or the retarding amount based on the combustion pressure fluctuation rate ΔPi (# 1) exceeds the all-cylinder limiter (limit value) set as a uniform value for all the cylinders. To determine. Then, if the leaning margin or the retarding margin based on the combustion pressure fluctuation rate ΔPi (# 1) is equal to or more than the all cylinder limiter, the process proceeds to step 7 to limit the leaning margin or the retarding margin to the all cylinder limiter. And proceed to step 8.

In step 8, the combustion pressure fluctuation rate ΔPi
The correction items of the air-fuel ratio (fuel injection amount) and the ignition timing, which are controlled based on the comparison between (# 1) and a predetermined value, are stored as data corresponding to the # 1 cylinder, for example, for each operating condition, and the stored items are stored. The actual injection amount correction and ignition timing correction are performed based on the data. By the above control, the ignition timing or the air-fuel ratio in the # 1 cylinder is accurately controlled to near the combustion stability limit. For example, the cylinder pressure sensor
Since 16 is to be fastened together with the spark plug 8, variations in the tightening torque of the spark plug will affect the sensor output. However, as described above, the variation rate of the integrated value Pi is calculated. If so, since the absolute level shift does not affect, the combustion pressure fluctuation of the # 1 cylinder is accurately detected, and thus the air-fuel ratio is made lean to the maximum and the ignition timing is retarded to the maximum. Is something that can be done.

Since the same control is performed in the other cylinders, the air-fuel ratio and the ignition timing of each cylinder can be controlled accurately near the combustion stability limit. here,
When the lean control of the air-fuel ratio or the retard control of the ignition timing is performed for each cylinder based on the combustion pressure fluctuation rate ΔPi for each cylinder as described above, each combustion stability limit of each cylinder varies (see FIG. 6). There are cases where the leaning amount or the retarding amount (see FIG. 7) differs for each cylinder, and although the combustion pressure fluctuation is suppressed for each cylinder, the combustion pressure varies among the cylinders (FIG. 8). reference). Then, when the combustion pressure variation between the cylinders is large, the engine output is changed. Therefore, in step 6,
In 7 (feedback limiting means), the leaning margin and the retarding margin are limited within the all-cylinder limiter so as to prevent the total combustion pressure fluctuation (engine output fluctuation) from increasing beyond the allowable level. I am doing it.

The all-cylinder limiter is set according to the flow chart of FIG. In the flowchart of FIG. 4, in step 11, an in-cylinder pressure sensor provided in each cylinder
The 16 detection signals are A / D converted and read, and the read in-cylinder pressure is converted into a predetermined integration section (for example, compression TDC to ATDC).
Integral value Pi (#
1 to #n) are obtained.

In step 12, the integrated value P for each cylinder is
The average value ΣPi of i (# 1 to #n) is calculated. Steps
At 13, the variation rate ΔΣPi of the average value ΣPi is obtained as the ratio between the current value ΣPi and the previous value ΣPi ₋₁ (ΔΣPi
= ΣPi / ΣPi ₋₁ ). In step 14, the fluctuation rate Δ
ΣPi is compared with a predetermined value as a preset allowable value of combustion pressure fluctuation (engine output fluctuation) in all cylinders.

When the fluctuation rate ΔΣPi exceeds the predetermined value and combustion pressure fluctuations exceeding the allowable level occur in all cylinders in total, the process proceeds to step 15 and the all cylinders limiter is decreased by a predetermined value. Make lean or retard charges smaller. As a result, even if there is a cylinder that can be greatly leaned or retarded within the combustion stability limit among the cylinders, the fluctuation rate ΔΣ
When Pi exceeds a predetermined value, the leaning margin and the retarding margin are limited, thereby suppressing the variation in the combustion pressure due to the large difference in the leaning margin and the retarding margin between the cylinders, and reducing the total cylinder total. It is possible to suppress the fluctuation of the combustion pressure, that is, the fluctuation of the engine output within the allowable level.

On the other hand, when the fluctuation rate ΔΣPi is below a predetermined value and the total combustion pressure fluctuations of all cylinders are low, even if the leaning margin or the retarding margin of each cylinder is expanded, the total cylinder total is reduced. Since there is a possibility that the fluctuation of the combustion pressure can be suppressed within the allowable level, the routine proceeds to step 16, where the all-cylinder limiter is increased by a predetermined value so that leaning or retarding can be further advanced.

This makes it possible to avoid the lean limit and the retard being unnecessarily limited by the all-cylinder limiter in a cylinder which can be greatly leaned or retarded within the combustion stability limit. Further, when the fluctuation rate ΔΣPi and the predetermined value are substantially equal to each other, this routine is ended without increasing or decreasing the all-cylinder limiter.

The all-cylinder limiter may be set on the basis of the combustion pressure detected for each cylinder as shown in the flow chart of FIG. 4, but the combustion pressure fluctuation as a total of all cylinders, that is, the engine output. Since it suffices to detect the fluctuation, as shown in the flowchart of FIG. 5, the configuration may be set based on the fluctuation rate of the engine rotation speed. In the flowchart of FIG. 5, in step 21, the engine rotation speed Ne is detected based on the detection signal from the crank angle sensor 14.

In step 22, the fluctuation rate ΔNe (= Ne / Ne _-1 ) of the engine rotation speed Ne is calculated based on the ratio between the current value of the engine rotation speed Ne and the previous value (Ne _-1 ). In step 23, the fluctuation rate ΔNe is compared with a predetermined value corresponding to a preset allowable value of engine output fluctuation. Then, as in the case of using the fluctuation rate ΔΣPi, when the fluctuation rate ΔNe exceeds a predetermined value and combustion pressure fluctuations exceeding the allowable level occur in all cylinders, the process proceeds to step 24, and all cylinders are processed. The limiter is reduced by a predetermined value so that the leaning margin or the retarding margin is restricted to a smaller value.

On the other hand, when the fluctuation rate ΔNe is below the predetermined value and the total combustion pressure fluctuation of all cylinders is low,
Even if the lean amount or the retard amount for each cylinder is expanded, there is a possibility that the combustion pressure fluctuations in all cylinders can be suppressed within the allowable level, so proceed to step 25, and set the all cylinder limiter to the predetermined value. To increase leanness or retard further.

Note that, instead of the integrated value Pi, the cylinder pressure (combustion pressure) at a predetermined crank angle position may be detected, but by using the integrated value Pi, combustion pressure detection with less noise influence is possible. Becomes Further, it is preferable that the all-cylinder limiter (limit value) is set based on ΔΣPi or ΔNe indicating the engine output fluctuation as described above, but it may be set as a fixed value in advance.

[0041]

As described above, according to the first aspect of the present invention, even if there is an error in the absolute value of the combustion pressure detected for each cylinder, the combustion pressure fluctuation of each cylinder is correctly detected,
In addition to being able to control the combustion stability limit for each cylinder, as a result of the cylinder-by-cylinder control, it is possible to prevent large combustion pressure variations between cylinders and suppress engine output fluctuations within an allowable level. is there.

According to the second aspect of the present invention, by setting the limit value based on the actual engine output fluctuation, it is possible to prevent the combustion stability limit control for each cylinder from being excessively limited. According to the third aspect of the present invention, the combustion pressure variation in all the cylinders is calculated based on the combustion pressure detected for each cylinder, and thereby the limit value in the combustion stability limit control for each cylinder is set appropriately. There is an effect that can be done.

According to the invention as set forth in claim 4, there is an effect that the engine output fluctuation can be detected based on the fluctuation of the engine rotation speed and the limit value in the combustion stability limit control for each cylinder can be appropriately set. . According to the invention described in claim 5, it is possible to make the air-fuel ratio of each cylinder lean to the combustion stability limit of each cylinder, while ensuring that the engine output fluctuation becomes large due to the variation of the air-fuel ratio among the cylinders. There is an effect that can be avoided.

According to the sixth aspect of the present invention, the ignition timing of each cylinder is retarded to the respective combustion stability limit, and H
While it is possible to suppress the C amount and the like, there is an effect that it is possible to reliably prevent the engine output fluctuation from increasing due to the variation in the ignition timing between the cylinders.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an apparatus according to the first aspect of the invention.

FIG. 2 is a system configuration diagram of the engine in the embodiment.

FIG. 3 is a flowchart showing a state of feedback control of air-fuel ratio and ignition timing in the embodiment.

FIG. 4 is a flowchart showing limiter setting control in cylinder-by-cylinder feedback control.

FIG. 5 is a flowchart showing limiter setting control in cylinder-by-cylinder feedback control.

FIG. 6 is a diagram showing variations in ignition timing at the combustion stability limit between cylinders.

FIG. 7 is a diagram showing ignition timing variation as a result of combustion stability limit control for each cylinder.

FIG. 8 is a diagram showing how the combustion pressure varies in all cylinders due to variations in combustion pressure among the cylinders.

FIG. 9 is a diagram showing how combustion pressure detection varies.

[Explanation of symbols]

 1 Internal Combustion Engine 4 Intake Manifold 5 Throttle Valve 6 Fuel Injection Valve 8 Spark Plug 10 Exhaust Manifold 11 Control Unit 12 Hot Wire Air Flow Meter 13 Throttle Sensor 14 Crank Angle Sensor 15 Water Temperature Sensor 16 Cylinder Pressure Sensor

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[Procedure amendment]

[Submission date] December 7, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

(See Japanese Patent Application No. 7-202441 ).
However, the combustion stability limit of each cylinder is different for each cylinder due to the distribution performance of fuel and air, the variation of parts for each cylinder, etc. Therefore, the combustion stability limit for each cylinder is controlled by the control for each cylinder. The ignition timing and the air-fuel ratio are varied among the cylinders (see FIGS. 6 and 7), which causes variation in the combustion pressure between the cylinders, which may cause an output fluctuation exceeding an allowable level for the entire engine. There was (see FIG. 8).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display F02P 5/153

Claims (6)

[Claims] 1. A combustion pressure detecting means for detecting a combustion pressure for each cylinder of an engine, and a combustion for calculating a combustion pressure fluctuation for each cylinder based on the combustion pressure for each cylinder detected by the combustion pressure detecting means. A pressure fluctuation calculating unit and a control target that is independently controlled for each cylinder, and is a control target that correlates with combustion stability, based on the combustion pressure fluctuation of each cylinder calculated by the combustion pressure fluctuation calculating unit. A cylinder-by-cylinder combustion control means for performing feedback control so that a combustion stability limit is reached for each cylinder; An internal-combustion-engine control device configured to include. 2. The control device for an internal combustion engine according to claim 1, wherein the feedback limiting means sets the predetermined limit value uniformly for each cylinder based on an output variation in the entire engine. 3. The internal combustion engine according to claim 2, wherein the feedback limiting means detects the output fluctuation in the entire engine based on the combustion pressure of each cylinder detected by the combustion pressure detecting means. Control device. 4. The control device for an internal combustion engine according to claim 2, wherein the feedback limiting means detects an output variation in the entire engine based on a variation in the engine rotation speed. 5. A fuel supply means is provided for each cylinder of the engine, and the combustion control means for each cylinder independently controls the fuel supply amount in the fuel supply means as the control target for each cylinder, and the empty space of each cylinder is controlled. 5. A structure for controlling a fuel ratio to a combustion stability limit for each cylinder, respectively, and the feedback limiting means limits a lean margin of the air-fuel ratio within a predetermined limit value. 1. A control device for an internal combustion engine according to any one of the above. 6. The cylinder-by-cylinder combustion control means independently controls the ignition timing of each cylinder to be controlled to the combustion stability limit of each cylinder, and the feedback limiting means controls the ignition timing. 5. The control device for the internal combustion engine according to claim 1, wherein the retard amount is limited within a predetermined limit value.