JP2007291977A - Combustion control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion control device of an internal combustion engine capable of quickly stabilizing the change of combustion. <P>SOLUTION: This combustion control device of an internal combustion engine comprises a means for detecting the cylinder pressure of each cylinder of the internal combustion engine, a means for detecting the crank angle of the internal combustion engine, a means for estimating the combustion state of the internal combustion engine according to the detected cylinder pressure, and a means for controlling the ignition timing of each cylinder of the internal combustion engine according to the estimated combustion state. When the combustion state is determined to be stable, the means for controlling the ignition timing so controls the ignition timing of each cylinder that the crank angle at which the cylinder pressure is maximum matches the target crank angle at which the output torque is maximum. When the combustion state is determined to be instable, it so controls the ignition timing of each cylinder that the output torques of the cylinders are uniformized. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for controlling the combustion state of an internal combustion engine.

Japanese Patent Application Laid-Open No. 2004-228867 discloses a technique for performing combustion stability determination and allowing correction of the ignition timing and executing MBT (Minimum spark advance for Best Torque) control when stable. The technique of Patent Document 1 can improve both torque and fuel consumption by controlling the ignition timing by MBT and controlling the air-fuel mixture state (EGR amount, air-fuel ratio, etc.) when the combustion state is stable. It is.
Patent No. 3419113

  However, in the method of Patent Document 1, when the combustion state is unstable, the control of the ignition timing is stopped and only the mixture control is performed to continue the stabilization control. Actually, the combustion fluctuation is affected by the output torque between the cylinders, and this output torque depends on the variation in the intake air amount. Therefore, there is a possibility that the combustion fluctuation cannot be suppressed only by controlling the air-fuel mixture (fuel).

  An object of the present invention is to provide a combustion control device for an internal combustion engine that can quickly stabilize combustion fluctuations.

  The combustion state control apparatus for an internal combustion engine provided by the present invention includes: a means for detecting an in-cylinder pressure of each cylinder of the internal combustion engine; a means for detecting a crank angle of the internal combustion engine; and an internal combustion engine based on the detected in-cylinder pressure. And means for controlling the ignition timing of each cylinder of the internal combustion engine in accordance with the estimated combustion state. The means for controlling the ignition timing controls the ignition timing of each cylinder so that when the combustion state is determined to be stable, the crank angle that maximizes the in-cylinder pressure matches the target crank angle that maximizes the output torque. When it is determined that the combustion state is unstable, the ignition timing of each cylinder is controlled so that the output torque of each cylinder is uniform.

  According to the present invention, even when the combustion state is unstable due to combustion fluctuations, the ignition timing is controlled so that the output torque of each cylinder becomes uniform, so that the combustion of the internal combustion engine can be stabilized quickly.

  According to one embodiment of the present invention, the means for estimating the combustion state is based on the detected in-cylinder pressure, the indicated mean effective pressure, the maximum value of the in-cylinder pressure, the crank angle that takes the maximum value of the in-cylinder pressure, and the ignition delay time. Alternatively, the degree of combustion is detected, and these fluctuation amounts are calculated. When the fluctuation amount is within the predetermined range, the combustion state is determined to be stable, and when the fluctuation amount is not within the predetermined range, the combustion state is not determined. Judge as stable. With this configuration, it is possible to accurately estimate the combustion state of the internal combustion engine.

  According to one embodiment of the present invention, the means for controlling the ignition timing controls the ignition timing of each cylinder so that the indicated mean effective pressures of the respective cylinders match when it is determined that the combustion state is unstable. With this configuration, the combustion state of the internal combustion engine can be stabilized.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an overall configuration of a combustion state control apparatus according to an embodiment of the present invention.

  The electronic control unit (ECU) 10 is a computer having a central processing unit (CPU). The electronic control unit includes a read only memory (ROM) that stores computer programs and a random access memory (RAM) that provides a work area for the processor and temporarily stores data and programs. The input / output interface 11 receives detection signals from various parts of the engine, performs A / D (analog / digital) conversion, and passes them to the next stage. Further, the input / output interface 11 sends a control signal based on the calculation result of the CPU to each part of the engine. In FIG. 1, the electronic control unit is shown by functional blocks showing functions related to the present invention.

  First, the principle of the sensor output correction method according to the embodiment of the present invention will be described with reference to FIG. FIG. 2 shows the pressure in the combustion chamber of the cylinder in the range of the crank angle from -180 degrees to 180 degrees. The range of the crank angle from -180 degrees to 0 degrees is the compression stroke, and from 0 degrees to 180 degrees. Expansion (combustion) stroke. Curve 1 shows the transition of the motoring pressure (pressure at the time of misfire) of one cylinder of the engine, and curve 3 shows the transition of the in-cylinder pressure when normal combustion is performed in the same cylinder. The crank angle of 0 degrees is the top dead center, the motoring pressure peaks at the top dead center, and the in-cylinder pressure during combustion (curve 3) peaks near the ignition time after the top dead center.

  In this embodiment, a correction formula for correcting the detection output of the pressure detection means (in-cylinder pressure sensor 12 in FIG. 1) in a period before reaching top dead center in the compression stroke, for example, a period indicated by “a” in FIG. Identify the parameters. A black dot 5 indicates a detection output by the in-cylinder pressure sensor 12. The in-cylinder pressure sensor 12 is placed in a harsh environment such as an engine combustion chamber, and its characteristics change due to the influence of temperature, aging, and the like. In this embodiment, the detection output is corrected so that the detection output of the in-cylinder pressure sensor 12 is substantially on the curve 1 of the motoring pressure. The detection output corrected in this way is indicated by white dots 7.

The detection output is corrected by applying the correction expression PS = PD (θ) k ₁ + C ₁ to the detection output PD (θ) of the in-cylinder pressure sensor. k ₁ is a correction coefficient, and C ₁ is a constant. θ is a crank angle. The two parameters k ₁ and C ₁ of this correction formula are the above-described correction of the estimated value PM of the motoring pressure and the detection output of the in-cylinder pressure sensor during the compression stroke, for example, the period indicated by “a” in FIG. Calculation is performed by the least square method so that the square of the difference (PM−PS) from the value PS corrected by the equation is minimized.

  Referring to FIG. 1 again, the in-cylinder pressure sensor 12 is a piezoelectric element and is provided in the vicinity of a spark plug of each cylinder (cylinder) of the engine. The pressure sensor 12 outputs a charge signal corresponding to the pressure in the cylinder. This signal is converted into a voltage signal by the charge amplifier 31 and outputted, and then outputted to the input / output interface 11 through the low-pass filter 33. The input / output interface 11 sends a signal from the pressure sensor 12 to the sampling unit 13. The sampling unit 13 samples this signal at a predetermined period, for example, a period of 1/10 kHz, and passes the sample value to the sensor output detection unit 15.

The sensor output correction unit 17 corrects the sensor output PD (θ) according to the above-described correction formula PS = PD (θ) k ₁ + C ₁ . The sensor output correction unit 17 passes the sensor output value PS corrected at a predetermined crank angle interval to the combustion pressure detection unit 41.

On the other hand, the combustion chamber volume calculation unit 19 calculates the cylinder combustion chamber volume V _c according to the crank angle θ using the following equation.

In the above equation, m represents the displacement from the top dead center of the piston 8 calculated from the relationship of FIG. λ = l / r where r is the crank radius and l is the connecting rod length. V _dead is the volume of the combustion chamber when the piston is at top dead center, and _Apstn is the cross-sectional area of the piston.

In general, it is known that the state equation of the combustion chamber is expressed by the following equation (3).

   In Equation (3), G is an air flow meter or intake air amount obtained based on the engine speed and intake pressure, R is a gas constant, T is an operating state such as an intake air temperature sensor or engine water temperature, for example. This is the intake air temperature obtained based on this. k is a correction coefficient, and C is a constant.

In this embodiment, the pressure in the combustion chamber is measured in advance using a quartz piezoelectric pressure sensor that is not affected by the temperature change of the sensor mounting portion in advance, and this measured value is made to correspond to the equation (3) to The value k ₀ and the value C ₀ of C are obtained. The motoring pressure is estimated using the following equation (4) obtained by substituting this into equation (3).

The motoring pressure estimation unit 20 includes a basic motoring pressure calculation unit 21 and a motoring pressure correction unit 22. The basic motoring pressure calculator 21 calculates a basic motoring pressure GRT / V, which is a basic item in the equation (3). The motoring pressure correction unit 22 corrects the basic motoring pressure using the parameters k ₀ and C ₀ obtained in advance as described above. The parameters k ₀ and C ₀ are prepared as a table that can be referred to according to a parameter representing the engine load state such as the intake pipe pressure or the engine speed.

  The motoring pressure estimation unit 20 may alternatively be configured by only the basic motoring pressure calculation unit 21. In this case, the motoring pressure PM is the basic motoring pressure GRT / V calculated by the basic motoring pressure calculator 21.

The parameter identification unit 23 determines an error (PM−) between the estimated motoring pressure value PM calculated by the motoring pressure estimation unit 20 and the in-cylinder pressure PS output from the sensor output correction unit 17 in the compression stroke. The parameters k ₁ and C ₁ of the correction formula for correcting the sensor output by the least square method are identified so that (PS) is minimized. The sensor output detection unit 15 samples the output of the pressure sensor at a period of, for example, 1/10 kHz, and sets the average value of the sample values as the sensor output value PD (θ) at the timing synchronized with the crank angle. hand over. The parameter identification unit 23 executes a calculation for identifying parameters of the correction formula in the compression stroke of the cylinder. The correction formula PS = PD (θ) k ₁ + C ₁ is applied to the estimated motoring pressure value PM (θ) corresponding to the crank angle obtained from the motoring pressure correction unit and the sensor output value PD (θ) at the same crank angle. The square of the difference from the applied value PS, that is, k ₁ and C _{1 at} which (PM (θ) −PD (θ) k ₁ −C ₁ ) ² is minimized is obtained by a known least square method.

When the discrete value of PM is represented by y (i) and the sample value (discrete value) of the in-cylinder pressure PD obtained from the in-cylinder pressure sensor is represented by x (i), X (i) ^T = [x (0) , x (1),..., x (n)], Y (i) ^T = [y (0), y (1),..., y (n)]. The sum of the squares of the discrete values of errors is expressed by the following equation (5). The sample value is taken at a period of 1/10 kHz, and the value of i is up to 100, for example.

In order to obtain k and C that minimize the value of F, it is only necessary to obtain k and C at which the partial differentiation of F (k, C) with respect to k and C is zero. This can be expressed as follows:

The right side of Equations (6) and (7) is organized as follows.

This can be expressed as a matrix as follows.

When this equation is transformed using an inverse matrix, it becomes as follows.

Here, the inverse matrix on the right side is expressed by the following equation.

  The sensor output correction unit 17 corrects the sensor output PD (θ) in the combustion stroke using the parameters thus identified. The corrected sensor output PS (θ) for each predetermined crank angle is passed to the combustion pressure detector 41.

  The combustion pressure detection unit 41 calculates a pressure PC (θ) generated by pure combustion when the air-fuel mixture burns in the cylinder of the engine. Referring to FIG. 2, the pressure PS (θ) (curve 3) detected based on the output of the in-cylinder pressure sensor 12 is changed to the motoring pressure PM (θ), which is the cylinder pressure when there is no combustion, by combustion. The resulting pressure PC (θ) is added. Therefore, it is possible to calculate PC (θ) by an arithmetic expression of PC (θ) = PS (θ) −PM (θ).

  Referring to FIG. 4, the combustion start time point detection unit 43 searches the determination value DP_C for determining the combustion start point from a table using the intake air pressure PB as a parameter (S101), and is calculated as described above. When the combustion pressure PC (θ) (S103) exceeds this judgment value (S105), the ignition flag is set to 1 (S107). Since the calculated combustion pressure PC (θ) oscillates near the combustion start time of the air-fuel mixture, the crank angle when PC (θ) first exceeds the judgment value DP_C is used as the combustion start time. The angle is represented by θ_DLY_bs (S111).

  The ignition delay calculation unit 44 in FIG. 1 calculates an ignition delay D_θ_DLY (n) by subtracting the ignition time θ_DLY_bs from the crank angle IG (θ) ignited on the spark plug (FIG. 4, S113). When the ignition delay is larger than a predetermined maximum value (S115), the maximum value is set as a parameter D_θ_DLY_IG (n) for calculating an average value (S123). When the ignition delay D_θ_DLY (n) is smaller than a predetermined minimum value (S117), the minimum value is set in the parameter D_θ_DLY_IG (n) (S121). When the ignition delay D_θ_DLY_ (n) is between the maximum value and the minimum value, this is set in the parameter D_θ_DLY_IG (n) (S119). The 16 moving averages of the parameter D_θ_DLY_IG (n) are set as the average ignition delay θ_DLY_av (S125).

  Next, the function of the indicated mean effective pressure calculation unit 45 of FIG. 1 will be described with reference to FIG. The indicated mean effective pressure (IMEP) indicates the work in one combustion cycle of the engine divided by the stroke volume. The indicated mean effective pressure can be used as an evaluation index for comparing the performance of engines having different stroke volumes (displacements).

  Generally, the indicated mean effective pressure is obtained by dividing the total work over a section corresponding to a crank angle of 720 degrees as a whole combustion cycle by the stroke volume of the piston. In this embodiment, first, the indicated mean effective pressure IMEP_bs in the section after the ignition start point in the combustion stroke is calculated, and then a map is searched based on the calculated indicated mean effective pressure IMEP_bs, and the entire one combustion cycle is indicated. Average effective pressure IMEP is required. Details will be described below.

  Referring to FIG. 5, the indicated mean effective pressure calculation unit 45 sets the combustion start time θ_DLY_bs obtained by the combustion start time calculation unit 43 as an integration start point (S133). Further, a crank angle at the end of combustion, which is empirically obtained in advance, for example, 480 degrees (when the intake top is 0 degree) is set as the integration end point (S135).

A combustion chamber volume V (θ) at a predetermined crank angle θ is obtained by calculation (equations (1) and (2)) by the combustion chamber volume calculation unit 19 in FIG. (Θ) is obtained (S137).
ΔV (θ) = V (θ + Δθ) −V (θ) (11)
Here, Δθ is the crank angle interval at which the sensor output correction unit 17 calculates the in-cylinder pressure PS. That is, ΔV (θ) is calculated for each predetermined crank angle at which the sensor output correction unit 17 calculates the in-cylinder pressure PS.

Subsequently, the indicated mean effective pressure IMEP_bs in the combustion stroke is obtained (S139). This indicated mean effective pressure IMEP_bs is defined by the combustion pressure PC (the average value of the combustion pressure at the crank angles θ and θ + Δθ in the equation (12)) and the combustion chamber volume over the integral interval in the combustion stroke set in steps S133 and S135. It is obtained by integrating the product with the increment ΔV and dividing the integrated value by the sum of the increments of the combustion chamber volume. The indicated mean effective pressure IMEP_bs is calculated by the following equation, for example.

  When the calculated indicated mean effective pressure IMEP_bs exceeds a predetermined maximum value, this maximum value is set as the indicated mean effective pressure estimated value IMEP_ht (S141, S149). The value is set as IMEP_ht (S143, S145). When IMEP_bs is between the maximum value and the minimum value, IMEP_bs is set as IMEP_ht (S147).

  A table is searched using IMEP_ht obtained in this way as a parameter, and IMEP (n) in one combustion cycle is obtained (S151). This table shows the indicated mean effective pressure IMEP for one entire combustion cycle, and the corresponding IMEP (n) is obtained by referring to this table based on the IMEP_ht calculated in the combustion stroke. The 16 moving averages of IMEP (n) are set as the indicated mean effective pressure IMEP (S153).

  1 discriminates the combustion state of each cylinder of the engine based on the indicated mean effective pressure IMEP of each cylinder. Referring to FIG. 6, upon receiving the indicated average effective pressure IMEP of each cylinder, the combustion state determination unit 47 obtains a fluctuation amount ΔIMEP of the indicated average effective pressure IMEP of each cylinder (S201). The fluctuation amount ΔIMEP is obtained, for example, by calculating the deviation between the current value and the previous value of IMEP and integrating the square of this deviation a predetermined number of times. An average value ΔIMEP_ave of all the cylinders of this variation ΔIMEP is calculated (S203).

Further, this average value ΔIMEP_ave is smoothed (smoothed), and the calculated value is set as a combustion fluctuation parameter for determining the combustion state of the engine (S205). The annealing calculation is performed according to, for example, the equation (13).
Combustion fluctuation parameter =
C × ΔIMEP_ave + (1−C) × Combustion fluctuation parameter (previous value) (13)
Here, C is an annealing coefficient, for example, 0.008.

  Note that the combustion fluctuation parameter in the combustion state determination unit 47 may be an index that correlates with the combustion fluctuation of the engine, and instead of the indicated mean effective pressure IMEP, for example, based on the output PS (θ) of the in-cylinder pressure sensor, The maximum value Pmax of the in-cylinder pressure or the crank angle θPmax that takes the maximum value Pmax of the in-cylinder pressure may be detected, and the fluctuation amount of these values may be used as the combustion fluctuation parameter. Similarly, the fluctuation amount of the ignition delay θ_DLY_av obtained by the ignition delay calculation unit 44 may be used as a combustion fluctuation parameter. Further, the ratio (combustion degree) of the output PS (θ) of the in-cylinder pressure sensor to the motoring pressure PM (θ) over a predetermined section of the combustion stroke is detected, and the fluctuation amount of the combustion degree is used as a combustion fluctuation parameter. good.

  Subsequently, the combustion fluctuation parameter is compared with a predetermined threshold value to determine the combustion state of the engine (S207). When the parameter is equal to or greater than a predetermined threshold, it indicates that the engine output torque is fluctuating, and it is determined that the combustion state of the engine is unstable, and the process proceeds to step S211. When the parameter is smaller than the predetermined threshold, it indicates that the fluctuation of the engine output torque is relatively small, and it is determined that the combustion state of the engine is stable, and the process proceeds to step S209.

  The ignition timing control unit 49 of FIG. 1 controls the ignition timing by selecting a control mode based on the combustion state of the engine determined by the combustion state determination unit 47. The processing performed by the ignition timing control unit 49 will be described below with reference to FIG.

  If the combustion state determination unit 47 determines that the combustion state of the engine is stable (NO in S207), MBT control is performed so as to improve fuel efficiency while maintaining the stability of the output torque (S209). . In the MBT control, a target crank angle that outputs the maximum torque is set according to the operating state, and the ignition timing is corrected so that the crank angle θPmax that takes the maximum value Pmax of the in-cylinder pressure matches the target crank angle. This is a control method. For details of the MBT control, see, for example, Patent Document 1.

  On the other hand, if the combustion state determining unit 47 determines that the combustion state is unstable (YES in S207), the output torque of each cylinder is kept constant in order to suppress the engine output fluctuation and stabilize the combustion state. Torque stabilization control is performed to control the ignition timing so as to achieve (S211). Details of the torque stabilization control will be described later with reference to FIG.

  And the ignition timing control part 49 of FIG. 1 calculates the ignition timing correction amount suitable for each control by the control mode selected according to the combustion state. The ignition timing of each cylinder corrected by this correction amount is sent to the ignition plug 51 of each cylinder.

  Next, with reference to FIG. 7 and FIG. 8, torque stabilization control performed in the ignition timing control unit 49 when the combustion state is unstable will be described.

  First, an overview of torque stabilization control will be described with reference to FIG. FIG. 8 is a graph showing changes in output torque corresponding to changes in ignition timing. The horizontal axis of FIG. 8 represents the ignition timing. The left side from the basic ignition timing (A in the figure) is the retard direction, and the right side is the advance direction. The vertical axis in FIG. 8 represents the rate of change of the output torque, the upper side from 0 on the axis is the increasing direction of the output torque, and the lower side is the decreasing direction of the output torque.

  Referring to FIG. 8, the output torque increases as the ignition timing changes in the advance direction. Further, the output torque decreases as the ignition timing changes in the retarding direction. By utilizing this relationship, the output torque can be controlled by controlling the ignition timing in the advance or retard direction.

  In the present embodiment, the PID control is performed so that the illustrated effective in-cylinder pressure IMEP of each cylinder correlated with the output torque is uniform among the cylinders. By correcting the ignition timing of each cylinder according to the feedback amount by PID control, the output torque of each cylinder is made uniform, and the combustion state of the engine is stabilized. Note that the target engine in the present embodiment is a V-type engine that can divide a plurality of cylinder groups into banks, and the output torque of the cylinders is made uniform for each bank.

  FIG. 7 is a flowchart of torque stabilization control according to this embodiment.

First, from the indicated average effective pressure IMEP # (# is the cylinder number) of each cylinder calculated by the indicated average effective pressure calculation unit 45, an average value IMEP_obj of the indicated average effective pressure for each bank is obtained. It is set as another control target value (S221). A deviation ERROR # between the indicated mean effective pressure IMEP # of each cylinder and the control target value IMEP_obj is calculated from Expression (14) (S223).
ERROR # = IMEP #-IMEP_obj (i) (14)
However, # is a cylinder number and i is a bank number. The control target value IMEP_obj (i) is calculated for each bank, and the deviation ERROR # is calculated for each cylinder.

ここで、Kp、Ki、Kdは、それぞれフィードバックゲインである。式（１５）の右辺の第１項は比例項であり、第２項は積分項であり、第３項は微分項である。つまり、式（１５）は、入力を図示平均有効圧の偏差ERROR#としたＰＩD制御のフィードバック量を計算している。 Based on the deviation ERROR # of the indicated mean effective pressure of each cylinder, the ignition timing correction amount Kpid # for each cylinder is calculated as shown in Expression (15) (S225).

Here, Kp, Ki, and Kd are feedback gains, respectively. The first term on the right side of Equation (15) is a proportional term, the second term is an integral term, and the third term is a differential term. In other words, the equation (15) calculates the feedback amount of the PID control using the input as the deviation ERROR # of the indicated mean effective pressure.

  Here, PI control obtained by removing the differential term from the equation (15) may be applied to the calculation of the ignition timing correction amount Kpid #. Other feedback control methods can also be applied.

Further, the ignition timing correction amount Kpid # is subjected to limit processing (S227), and this correction amount is added to the basic ignition timing to calculate the ignition timing IG # for each cylinder (S229). The ignition timing IG # is calculated from the equation (16).
IG # = Basic ignition timing + Kpid # (16)

  The calculated ignition timing IG # is sent to the ignition plug 51 of each cylinder, and the ignition timing is controlled for each cylinder.

  According to the present embodiment, the ignition timing of each cylinder is controlled to suppress the torque fluctuation between the cylinders, whereby the output torque of each cylinder in the bank is made uniform and the combustion state of the engine is stabilized.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment. The present invention can be used for both gasoline engines and diesel engines. In the case of a diesel engine, it is possible to stabilize the combustion state of the engine by controlling the fuel injection timing instead of the ignition timing, as in the above-described embodiment.

1 is a block diagram illustrating an overall configuration of a combustion state control device according to an embodiment of the present invention. It is a figure which shows the curve of the correction value of a motoring pressure curve and the in-cylinder pressure sensor output at the time of combustion. It is a conceptual diagram for calculating one piston. It is a flowchart which shows the process which calculates a combustion start time. It is a flowchart which shows the process which calculates illustrated effective in-cylinder pressure IMEP. It is a flowchart which shows the process which controls ignition timing. It is a flowchart of torque stabilization control by this embodiment. It is a figure which shows the relationship between ignition timing and a torque change.

Explanation of symbols

10 Electronic control unit (ECU)
12 In-cylinder pressure sensor 18 Crank angle sensor 45 Illustrated effective in-cylinder pressure calculation unit 47 Combustion state determination unit 49 Ignition timing control unit

Claims (3)

Means for detecting the in-cylinder pressure of each cylinder of the internal combustion engine;
Means for detecting a crank angle of the internal combustion engine;
Means for estimating a combustion state of the internal combustion engine based on the detected in-cylinder pressure;
Means for controlling the ignition timing of each cylinder of the internal combustion engine in accordance with the estimated combustion state,
The means for controlling the ignition timing is:
When the combustion state is determined to be stable, the ignition timing of each cylinder is controlled so that the crank angle that maximizes the in-cylinder pressure matches the target crank angle that maximizes the output torque,
When the combustion state is determined to be unstable, the ignition timing of each cylinder is controlled so that the output torque of each cylinder is uniform.
A combustion state control device for an internal combustion engine.   Based on the detected in-cylinder pressure, the means for estimating the combustion state includes an indicated mean effective pressure, a maximum value of the in-cylinder pressure, a crank angle at which the maximum value of the in-cylinder pressure is obtained, an ignition delay time, or a degree of combustion. Detecting and calculating these fluctuation amounts, determining that the combustion state is stable when the fluctuation amount is within a predetermined range, and determining that the combustion state is unstable when the fluctuation amount is not within the predetermined range The combustion state control device according to claim 1. The combustion according to claim 1, wherein the means for controlling the ignition timing controls the ignition timing of each cylinder so that the indicated mean effective pressures of the respective cylinders coincide with each other when it is determined that the combustion state is unstable. State control device.

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