JP2018123768A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine, for improving manufacturing efficiency, enhancing the accuracy of determining the combustion stability of the internal combustion engine, and maintaining stable combustion as well.SOLUTION: A control device 3 includes a washer sensor 32 contacting a cylinder 11 at its outside so as to detect a combustion pressure in a combustion chamber 12 of the cylinder 11 of an internal combustion engine 1 for outputting a pressure signal according to the combustion pressure, and a crank angle acquisition part 43 for acquiring a crank angle, whereby the internal combustion engine 1 can be controlled in response to the stability of combustion in the combustion chamber 12. The control device 3 further includes an angle-pressure signal calculation part 44 for calculating an angle-pressure signal associating the pressure signal with a detection value θ for the crank angle, a combustion state estimation part 46 using the angle-pressure signal for calculating a combustion estimation parameter to estimate a combustion state in the combustion chamber 12, and a stability determination part 47 using the combustion estimation parameter for determining the stability of the combustion.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an internal combustion engine control apparatus configured to be able to control an internal combustion engine according to combustion stability in a combustion chamber of a cylinder.

  In an internal combustion engine, in particular, an HCCI (Homogeneous Charge Compression Ignition) engine, it is required to stably burn fuel in a combustion chamber. For example, in a vehicle equipped with an internal combustion engine, if the combustion in the combustion chamber becomes unstable, the output of the internal combustion engine becomes unstable, and as a result, the drivability of the vehicle may deteriorate. Further, if unstable combustion continues, in the worst case, misfire, partial combustion, etc. may occur, and as a result, catalyst poisoning, afterfire, etc. may occur. For this reason, when the combustion becomes unstable, the control device for the internal combustion engine detects this, and immediately after the detection, controls the internal combustion engine so that the combustion becomes stable.

  Generally, in a control device for an internal combustion engine, the combustion stability is determined based on the combustion pressure in the combustion chamber. For example, a reciprocating engine among internal combustion engines employs a pressure sensor (hereinafter referred to as “in-cylinder pressure sensor”) mounted on a cylinder head so as to directly detect the combustion pressure. However, in order to mount the cylinder pressure sensor on the cylinder head, it is necessary to form a hole in the cylinder head for inserting the cylinder pressure sensor. Furthermore, an additional process for sealing between the hole and the cooling water path formed in the cylinder head is required, and the additional process needs to be performed particularly strictly. Additional work is also required to seal between the cylinder pressure sensor and the peripheral surface of the hole with the cylinder pressure sensor inserted into the hole. In order to improve manufacturing efficiency, it is desirable to omit such additional processing. In-cylinder pressure sensors are expensive because they require durability against combustion pressure, high combustion pressure detection accuracy, and the like. In order to reduce the manufacturing cost, it is desirable to use a cheaper pressure sensor.

  Therefore, in order to improve manufacturing efficiency and reduce manufacturing costs, an inexpensive washer-type pressure sensor (hereinafter referred to as “washer sensor”) is used as an example of a control device for an internal combustion engine between an ignition plug and a cylinder head. And a technique for determining combustion stability based on variations in combustion pressure detected by such a washer sensor. (For example, see Patent Document 1.)

JP-A-6-74079

  However, in an example of the control device, the washer sensor may detect not only the combustion pressure but also noise such as vibration of the internal combustion engine and vibration accompanying abnormal combustion. For this reason, variations in combustion pressure cannot be accurately extracted, and as a result, there is a risk that the accuracy of determination of combustion stability is lowered. Furthermore, there is a possibility that stable combustion cannot be maintained.

  Therefore, in an internal combustion engine control device, it is desired to improve manufacturing efficiency, reduce manufacturing cost, increase the accuracy of determination of combustion stability of the internal combustion engine, and maintain stable combustion.

  In order to solve the problem, according to the control device for an internal combustion engine according to an aspect of the present invention, the cylinder is brought into contact with the cylinder from outside so as to be able to detect the combustion pressure in the combustion chamber of the cylinder in the internal combustion engine, and A pressure sensor of a washer type configured to output a pressure signal according to the combustion pressure, and a crank angle acquisition unit configured to acquire a crank angle of a crankshaft of the internal combustion engine, A control device for an internal combustion engine configured to be able to control the internal combustion engine in accordance with the stability of combustion in a room, wherein the control device is configured to calculate an angle-pressure signal in which the pressure signal is associated with the crank angle. An angle-pressure signal calculating unit; a combustion state estimating unit configured to calculate a combustion estimation parameter for estimating a combustion state in the combustion chamber using the angle-pressure signal; Using combustion estimation parameters, and a stability determination unit configured to determine the stability of combustion in the combustion chamber.

  According to the control apparatus for an internal combustion engine according to one aspect of the present invention, the manufacturing efficiency can be improved, the accuracy of determining the combustion stability of the internal combustion engine can be increased, and stable combustion can be maintained. be able to.

It is a schematic diagram which shows the control system containing the control apparatus of the HCCI engine which concerns on 1st Embodiment of this invention. It is the A section enlarged view of FIG. It is a block diagram of the control apparatus which concerns on 1st Embodiment of this invention. FIG. 2 is a diagram schematically showing a typical angle-pressure signal obtained in one cylinder of the HCCI engine in the first embodiment of the present invention. It is a flowchart for demonstrating the control method which concerns on 1st Embodiment of this invention. Angle-pressure obtained by using the washer sensor in the first and second settings of the first embodiment when the rotational speed of the engine is 3000 rpm and BMEP is 600 kPa in the combustion stroke of one cylinder. It is a figure which shows a signal and the angle-pressure signal obtained using a cylinder pressure sensor in the 1st and 2nd setting of the comparative example 1. FIG. FIG. 10 is a correlation diagram between the maximum change rate obtained in the first case of Example 2 and IMEP obtained in the first case of Comparative Example 2. 6 is a graph showing the relationship between the maximum rate of change obtained in the first case of Example 2 and IMEP obtained in the first case of Comparative Example 2 in 100 consecutive combustion cycles. 10 is a correlation diagram between the maximum change rate obtained in the second case of Example 2 and IMEP obtained in the second case of Comparative Example 2. FIG. 6 is a graph showing the relationship between the maximum rate of change obtained in the second case of Example 2 and IMEP obtained in the second case of Comparative Example 2 in 100 consecutive combustion cycles. In Example 3, when the rotational speed of an engine is 3000 rpm and BMEP is 600 kPa, it is a graph which shows the variation coefficient obtained by 100 continuous combustion cycles.

  A control system including the control device for an internal combustion engine according to the first and second embodiments of the present invention will be described below. As a preferred example, the internal combustion engine controlled by the control devices according to the first and second embodiments is an NVO (Negative Valve Overlap) type HCCI engine mounted on an automobile. However, the present invention is not limited to this, and the HCCI engine may be other than the NVO system. For example, the HCCI engine may be a port injection system. The internal combustion engine may be a reciprocating engine. For example, the reciprocating engine may be a spark ignition type engine, a PFI (Port Fuel Injection) type gasoline engine, a gasoline direct injection engine, a diesel engine, It may be a CNG (Compressed Natural Gas) engine.

  The reciprocating engine is particularly preferably a 4-stroke type. However, the reciprocating engine may be of a two-stroke type. In particular, the reciprocating engine preferably has a plurality of cylinders. However, the reciprocating engine can be of a single cylinder. The internal combustion engine may be mounted on a vehicle other than an automobile. For example, the internal combustion engine may be mounted on a motorcycle. The internal combustion engine may also be an internal combustion engine for power generation, a general-purpose engine mounted on various work machines, an inboard motor, an outboard motor, an inboard / outboard motor, or the like.

[First Embodiment]
A control system including a control device according to the first embodiment of the present invention will be described.

[Outline of control system]
First, an outline of the control system will be described. As shown in FIG. 1, the control system according to the present embodiment can control an HCCI engine (hereinafter simply referred to as “engine”) 1, an accelerator pedal 2 configured as an accelerator operation unit of an automobile, and the engine 1. And a control device 3 configured. The engine 1 has a plurality of cylinders 11, and FIG. 1 schematically shows a cross section of one of the plurality of cylinders 11 in the engine 1.

  The accelerator operation unit may be other than the accelerator pedal. In particular, in the case of a motorcycle, the accelerator operation unit may be an accelerator grip. The control device 3 includes an ECU (Engine Control Unit) 31 configured as a control unit used for controlling the engine 1 and a washer-type pressure sensor (hereinafter referred to as a “washer sensor”) 32 attached to each cylinder 11. Have.

  The ECU 31 is preferably configured to include an electronic component such as a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a flash memory, and an electric circuit in which such an electronic component is arranged. . The washer sensor 32 has a piezoelectric element (not shown), and the washer sensor 32 is formed in a substantially ring shape as shown in cross section in FIG. The washer sensor 32 is attached to each cylinder 11 in contact with the cylinder 11 from the outside so that the combustion pressure in the combustion chamber 12 of each cylinder 11 can be detected. The washer sensor 32 only needs to be attached to at least one of the plurality of cylinders 11. In particular, the washer sensor 32 is preferably attached to all of the plurality of cylinders 11.

  Such a control system and the control device 3 use the combustion pressure detected by the washer sensor 32 so that the determination accuracy of manufacturing efficiency and combustion stability can be improved and stable combustion can be maintained. It is configured to detect unstable combustion in the combustion chamber 12. Further, the control system and its control device 3 are configured to control the engine 1 so that an unstable combustion state can be resolved.

[About engine details]
Here, the details of the engine 1 will be described with reference to FIG. The plurality of cylinders 11 of the engine 1 are defined by cylinder blocks 13. The engine 1 includes a piston 14 configured to reciprocate in each cylinder 11 in the axial direction thereof. A cylinder head 15 is disposed on the top side of each cylinder 11. The combustion chamber 12 is surrounded by the cylinder 11, the piston 14, and the cylinder head 15.

  A crankcase 16 is disposed on the bottom side of the cylinder 11 with respect to the cylinder block 13, and a crankshaft 17 is disposed in the crankcase 16. The piston 14 in each cylinder 11 is connected to a crankshaft 17 via a connecting rod 18. The reciprocating motion of the piston 14 is converted into the rotational motion of the crankshaft 17.

  A spark plug 19 configured to enable spark discharge in the combustion chamber 12 is attached to the cylinder head 15. An intake port 20 and an exhaust port 21 are connected to the cylinder head 15. The intake port 20 has an intake opening 20 a that opens toward the combustion chamber 12 at a connection portion with the cylinder head 15, and the exhaust port 21 faces the combustion chamber 12 at a connection portion with the cylinder head 15. The exhaust opening 21a is open. The intake port 20 defines a path for sending air to the combustion chamber 12, and the exhaust port 21 defines a path for sending exhaust gas generated after combustion in the combustion chamber 12 toward a catalyst (not shown). Yes. However, the present invention is not limited to this, and in the case of a PFI engine, the intake port may define a path for sending a premixed gas containing fuel and air to the combustion chamber. Further, the intake opening 20 a can be opened and closed by an intake valve 22, and the exhaust opening 21 a can be opened and closed by an exhaust valve 23.

  A throttle valve 24 is arranged on the upstream side of the air flow with respect to the intake port 20, and the throttle valve 24 is configured to be able to adjust the flow rate of air sent from the intake port 20 to the combustion chamber 12. Yes. A direct injection injector 25 is also attached to the cylinder head 15, and the direct injection injector 25 is configured to inject fuel directly into the combustion chamber 12.

  In the engine 1, an air-fuel mixture suitable for HCCI combustion can be generated in the combustion chamber 12 by the air sent from the intake port 20 and the fuel injected from the direct injection injector 25. In the combustion chamber 12 filled with air, self-ignition can be generated without using the spark plug 19. Further, the engine 1 burns using the spark plug 19 in an operation state in which the ignition timing is likely to be unstable, such as during a low load operation, or in an operation state in which HCCI combustion is difficult such as during a high load operation. It may be configured to generate a flame kernel for combustion by generating a spark discharge in the chamber 12.

  In particular, in one combustion cycle of the engine 1 that is a four-stroke system, the combustion stroke ST1, the exhaust stroke ST2, the intake stroke ST3, and the compression stroke ST4 are performed in this order. In one combustion cycle, the crankshaft 17 rotates twice. Therefore, in one combustion cycle, the crank angle of the crankshaft 17 changes in principle by 720 °, and the crankshaft 17 cranks in each of the combustion stroke ST1, the exhaust stroke ST2, the intake stroke ST3, and the compression stroke ST4. The angle changes in principle by 180 °.

[Details of control device]
Next, details of the control device 3 will be described. In particular, as shown in FIG. 2, the washer sensor 32 is clamped between the cylinder head 15 and the spark plug 19. Therefore, when vibration is generated due to combustion in the combustion chamber 12, the tightening load of the washer sensor 32 is changed in the compression direction or the relaxation direction by the vibration, and the surface potential of the piezoelectric element is changed by the change of the tightening load. Change. The washer sensor 32 outputs a charge signal (hereinafter referred to as “pressure signal”) corresponding to a change in the surface potential of the piezoelectric element. However, the present invention is not limited to this, and the washer sensor may be clamped between the cylinder head and a member other than the spark plug as long as the combustion pressure in the combustion chamber of the cylinder can be detected. The washer sensor 32 can generate a pressure signal according to the combustion pressure in the combustion chamber 12.

  As shown in FIG. 1, the control device 3 also includes a crank angle sensor 33 configured as a crank angle detector that can detect the crank angle of the crankshaft 17. The crank angle sensor 33 can also detect the rotational speed of the crankshaft 17, that is, the rotational speed of the engine 1. The crank angle sensor 33 is particularly preferably configured to be able to detect the rotation angle and rotation speed of a timing rotor (not shown) attached to the crankshaft 17 in a non-contact manner and arranged around the timing rotor. .

  Further, the control device 3 is configured as a throttle opening degree sensor 34 configured as a throttle opening degree detection unit capable of detecting the opening degree of the throttle valve 24 and an accelerator operation amount detection unit capable of detecting an operation amount of the accelerator pedal 2. The accelerator sensor 35 is provided. The control device 3 also includes an intake pressure sensor 36 configured as an intake pressure detection unit capable of detecting the pressure of air in the intake port 20, an oxygen concentration in the exhaust gas sent from the combustion chamber 12 to the exhaust port 21, and It has a LAF sensor (Linear Air-Fuel ratio sensor) 37 configured as an air-fuel ratio detection unit capable of detecting the air-fuel ratio of the air-fuel mixture in the combustion chamber 12 based on the unburned gas concentration. The intake pressure sensor 36 is disposed on the intake port 20 between the intake valve 22 and the throttle valve 24. The LAF sensor 37 is disposed on the exhaust port 21.

[Details of ECU]
Details of the ECU 31 of the control device 3 will be described with reference to FIG. Since the pressure signal sent from the washer sensor 32 is weak, the ECU 31 has a pressure signal amplifier 41 configured to receive this pressure signal and amplify the pressure signal. The pressure signal amplifying unit 41 is electrically connected to the washer sensor 32.

  The ECU 31 includes a pressure signal acquisition unit 42 configured to be able to acquire a pressure signal amplified by the pressure signal amplification unit 41, and a crank configured to acquire a crank angle detection value θ sent from the crank angle sensor 33. And a corner acquisition unit 43. The ECU 31 is also configured to calculate an angle-pressure signal in which the pressure signal acquired by the pressure signal acquisition unit 42 is associated with the crank angle detection value θ acquired by the crank angle acquisition unit 43. A calculation unit 44 is included.

  The angle-pressure signal calculation unit 44 preferably calculates the angle-pressure signal within the range of the detected value θ of the crank angle corresponding to the state where both the intake valve 22 and the exhaust valve 23 are closed. Typically, both the intake valve 22 and the exhaust valve 23 are closed between the intake bottom dead center and the exhaust bottom dead center. Furthermore, it is preferable that the angle-pressure signal calculation unit 44 calculates the angle-pressure signal within the range of the detected crank angle value θ calculated from the combustion start timing. More preferably, the angle-pressure signal is calculated in the range of the detected value θ of the crank angle corresponding to the period from the first to the inflection point or the maximum peak of the angle-pressure signal appearing thereafter.

  Here, an outline of a typical angle-pressure signal is shown in FIG. In FIG. 4, the horizontal axis θ represents the detected value θ (°) of the crank angle, the vertical axis I represents the intensity I (V) of the angle-pressure signal, and the solid line L1 represents the angle-pressure signal. In the cylinder 11, the combustion stroke ST1 is performed when the crank angle detection value θ is basically in the range of 0 ° to 180 °, and the crank angle detection value θ is basically 180 ° to 360 °. The exhaust stroke ST2 is performed when it is within the range, the intake stroke ST3 is performed when the crank angle detection value θ is basically in the range of 360 ° to 540 °, and the crank angle detection value θ is principally The compression stroke ST4 is performed when the angle is in the range of 540 ° to 720 °. In this case, a state in which the detected value θ of the crank angle is in principle 180 ° corresponds to the exhaust bottom dead center, and a state in which the detected value θ of the crank angle is in principle 540 ° corresponds to the intake bottom dead center. . Such an angle-pressure signal has a pulse waveform protruding in a period from the compression stroke ST4 to the combustion stroke ST1. Such a pulse waveform reaches a maximum peak in the combustion stroke ST1.

  Referring to FIG. 3 again, the ECU 31 is configured to apply a filter process for gradually decreasing a frequency component higher than a predetermined cutoff frequency to the angle-pressure signal sent from the angle-pressure signal calculation unit 44. 45 is preferred. The filter unit 45 is configured to perform low-pass filter processing or band-pass filter processing. The cutoff frequency may be set after confirming the frequency band of a noise signal caused by engine drive vibration, knocking, or the like using a technique such as FFT analysis (Fast Fourier Transform Analysis). As an example, the cut-off frequency may be about 5 kHz, and particularly preferably about 1 kHz. However, the present invention is not limited to this, and the cutoff frequency may be other values as long as the noise signal can be removed and the angle-pressure signal resulting from the combustion in the combustion chamber can be extracted with high accuracy.

  The ECU 31 calculates a combustion estimation parameter for estimating the combustion state in the combustion chamber 12 of each cylinder 11 using the angle-pressure signal sent from the angle-pressure signal calculation unit 44 via the filter unit 45. The combustion state estimation unit 46 configured as described above, and the stability determination unit configured to determine the combustion stability in each combustion chamber 12 using the combustion estimation parameter calculated by the combustion state estimation unit 46 47. Further, the ECU 31 is configured to be able to adjust the air-fuel ratio of the air-fuel mixture filled in the combustion chamber 12 of the cylinder 11 and the direct injection control unit 48 configured to be able to adjust the fuel injection from the direct injection injector 25. And an air-fuel ratio adjustment unit 49.

  Further, with reference to FIG. 1, the ECU 31 sends a detected value of the rotational speed of the engine 1 sent from the crank angle sensor 33, a detected value of the throttle opening sent from the throttle opening sensor 34, and a sent value from the accelerator sensor 35. The flow rate of the air is adjusted based on at least one of the required torque determined according to the detected value of the accelerator operation amount, the detected value of the pressure of the air sent from the intake pressure sensor 36, and the like. . The air flow rate can be adjusted by controlling the opening / closing timing of the intake valve 22, the opening degree of the throttle valve 24, and the like.

[Details of combustion state estimation unit]
Details of the combustion state estimation unit 46 of the ECU 31 will be described with reference to FIG. The combustion state estimation unit 46 has a plurality of angle-pressure signal intensity I ratios that change in a certain section of the crank angle detection value θ in each combustion cycle in the combustion chamber 12 on the angle-pressure signal. A change rate calculation unit 51 configured to calculate the change rate C (= dI / dθ) is included. The change rate calculation unit 51 can store the calculated change rate C. In addition, the constant interval of the detected value θ of the crank angle that determines the rate of change C may be determined according to the resolution of the digitized angle-pressure signal. For example, such a fixed interval can be a unit angle, ie about 1 °. However, the present invention is not limited to this, and the constant interval of the detected value θ of the crank angle may be determined within a range of about 0.05 ° or more and about 5 ° or less.

  The combustion state estimation unit 46 selects a maximum value (hereinafter referred to as “maximum change rate”) M from among a plurality of change rates C calculated by the change rate calculation unit 51 in each combustion cycle in the combustion chamber 12. The change rate selection unit 52 is configured. Specifically, the change rate selection unit 52 selects the maximum change rate M from the plurality of change rates C stored by the change rate calculation unit 51 in one combustion cycle. Further, the change rate selection unit 52 can store the calculated maximum change rate M. However, the present invention is not limited to this, and the change rate selection unit may select a change rate C other than the maximum change rate M as long as a value substantially equal to the maximum change rate M is obtained. For example, the change rate selection unit may select the nth largest one of the plurality of change rates C. Note that n is an integer of 2 or more, and in particular, n is preferably 2 or 3. Further, the change rate selection unit 52 can store the calculated maximum change rate M.

  Here, the maximum change rate M has a high correlation with IMEP (Indicated Mean Effective Pressure) generally used as an evaluation item of combustion stability. Specifically, the maximum change rate M can be obtained in a period from the combustion start timing to the maximum peak of the angle-pressure signal that appears first thereafter, and the maximum change rates M and IMEP obtained in such a period are High correlation with each other. Therefore, the combustion stability in the combustion chamber 12 can be evaluated using the maximum change rate M as described later.

  The combustion state estimation unit 46 is configured to calculate a combustion estimation parameter using a plurality of maximum change rates M calculated by the change rate selection unit 52 in a plurality of combustion cycles, respectively. Have The combustion estimation parameter calculation unit 53 includes a standard deviation calculation unit 61 and an average value calculation unit 62 configured to calculate a standard deviation σ and an average value μ of a plurality of maximum change rates M, respectively. The standard deviation calculation unit 61 and the average value calculation unit 62 are based on the standard deviation σ and the average value based on a plurality of maximum change rates M stored in the change rate selection unit 52 in the latest combustion cycle and the previous combustion cycle. Calculate μ. Furthermore, the combustion estimation parameter calculation unit 53 uses the standard deviation σ and the average value μ calculated by the standard deviation calculation unit 61 and the average value calculation unit 62 as the combustion estimation parameters, respectively, and the variation coefficient V (= (σ / μ ) × 100 (%)).

  However, the present invention is not limited to this, and the combustion estimation parameter calculation unit includes a minimum value calculation unit configured to calculate the minimum values of the plurality of maximum change rates M instead of the standard deviation calculation unit. Furthermore, the variation coefficient calculation unit of the combustion estimation parameter calculation unit may calculate the variation coefficient using the minimum value calculated by the minimum value calculation unit instead of the standard deviation σ. Further, the combustion estimation parameter calculation unit estimates IMEP from the maximum change rate M, calculates a variation coefficient from the estimated plurality of IMEPs, and the stability determination unit determines combustion stability based on the variation coefficient. May be. In this case, a calculation formula or map defining the relationship between the maximum change rate M and IMEP is obtained in advance, and the calculation formula or map is stored in the combustion estimation parameter calculation unit, and the calculation formula or map is used. Thus, IMEP may be estimated from the maximum rate of change M. The relationship between the maximum change rate M and IMEP is preferably obtained in advance by an experiment such as a conformance test according to operating conditions, a numerical simulation, or the like.

[Details of Stability Determination Unit]
Details of the stability determination unit 47 of the ECU 31 will be described with reference to FIG. The stability determination unit 47 determines that the combustion in the combustion chamber 12 is unstable when the variation coefficient V calculated by the variation coefficient calculation unit 63 is greater than a predetermined stability determination threshold value T, and this is applied. When the variation coefficient V is equal to or less than the stability determination threshold T, it is determined that the combustion in the combustion chamber 12 is stable. Here, the stability determination threshold is preferably determined in advance as follows. That is, the coefficient of variation V is obtained in a state where combustion is stable in an engine having the same combustion characteristics as the engine 1 of the present embodiment by experiment, numerical simulation, and the combustion chamber is further obtained by experiment, numerical simulation, and the like. In order to stabilize the combustion in the combustion chamber 12, in particular, in order to reliably avoid the occurrence of misfires or partial combustion in the combustion chamber 12, it is greater than 0% and less than 40% with respect to the obtained coefficient of variation. The stability determination threshold value T may be determined within the range.

  The stability determination threshold value T can be changed according to the specifications of the engine 1. Further, the stability determination threshold value T can be constant under all operating conditions of the engine 1. However, the present invention is not limited to this, and the stability determination threshold value may be changeable according to the operating condition of the engine. For example, when the engine combustion is difficult to stabilize, especially when the engine is in a low rotation and low load state, the stability determination threshold value is decreased with respect to the stability determination threshold value when the engine is in a steady operation state. The stability determination threshold value when the engine combustion is likely to be stable may be increased with respect to the stability determination threshold value when the engine is in a steady operation state.

[Details of direct injection control section]
The details of the direct injection adjusting unit 48 of the ECU 31 will be described with reference to FIG. The direct injection adjusting unit 48, based on the detected value of the rotational speed of the engine 1 sent from the crank angle sensor 33 and the detected value of the throttle opening sent from the throttle opening sensor 34, respectively, the fuel from the direct injection injector 25. The target injection amount calculation unit 71 and the target injection timing calculation unit 72 calculate the target values of the injection amount and the injection timing. Each of the target injection amount calculation unit 71 and the target injection timing calculation unit 72 is electrically connected to the crank angle sensor 33 and the throttle opening degree sensor 34.

  The target injection amount calculation unit 71 preferably stores an injection amount map, and the target injection amount calculation unit 71 performs injection based on the detected values of the rotational speed of the engine 1 and the throttle opening based on the injection amount map. It is preferable to calculate a target value for the quantity. Specifically, the target value of the injection amount is preferably calculated using a correction coefficient corresponding to the detected value of the rotational speed of the engine 1 and the throttle opening on the injection amount map. The target injection timing calculation unit 72 preferably stores an injection timing map, and the target injection timing calculation unit 72 further detects detected values of the rotational speed of the engine 1 and the throttle opening based on the injection timing map. From this, it is preferable to calculate the target value of the injection timing. Specifically, the target value of the injection timing is preferably calculated using a correction coefficient corresponding to the detected value of the rotational speed of the engine 1 and the throttle opening on the injection timing map.

  The direct injection adjusting unit 48 is supplied from the direct injection injector 25 in accordance with the target value of the injection amount calculated by the target injection amount calculating unit 71 and the target value of the injection timing calculated by the target injection timing calculating unit 72. A direct injection injector control unit 73 configured to control fuel injection is provided. The direct injection injector control unit 73 is configured to send a control signal including a pulse waveform to the direct injection injector 25, and the direct injection injector 25 may inject fuel based on the control signal. In this case, the fuel injection amount from the direct injection injector 25 may be determined according to the pulse amplitude and pulse width of the control signal. The fuel injection timing of the direct injection injector 25 may be determined according to the pulse interval of the control signal.

[Details of air-fuel ratio adjustment unit]
The details of the air-fuel ratio adjusting unit 49 will be described with reference to FIG. The air-fuel ratio adjustment unit 49 is mixed in the combustion chamber 12 based on the detected value of the rotational speed of the engine 1 sent from the crank angle sensor 33 and the detected value of the throttle opening sent from the throttle opening sensor 34. A target air-fuel ratio calculating unit 81 configured to calculate a target value of the air-fuel ratio of the air; The target air-fuel ratio calculation unit 81 is electrically connected to the crank angle sensor 33 and the throttle opening sensor 34. It is preferable that an air-fuel ratio map is stored in the target air-fuel ratio calculation unit 81. Further, the target air-fuel ratio calculation unit 81 further determines the air-fuel ratio based on the detected values of the rotational speed of the engine 1 and the throttle opening based on the air-fuel ratio map. It is preferable to calculate the target value of the fuel ratio. Specifically, the target value of the air-fuel ratio is preferably calculated using a correction coefficient corresponding to the detected value of the rotational speed of the engine 1 and the throttle opening on the air-fuel ratio map.

  Further, the target air-fuel ratio calculation unit 81 determines that misfire or partial combustion can occur particularly in the combustion chamber 12 when the stability determination unit 47 determines that the combustion in the combustion chamber 12 is unstable. In this case, the target value of the air-fuel ratio is corrected to the rich side. In this case, it is preferable that the target air-fuel ratio calculation unit 81 corrects the air-fuel ratio map so as to increase the target value of the air-fuel ratio of the air-fuel mixture in a part or the entire region of the air-fuel ratio map. In particular, in the target air-fuel ratio calculation unit 81, the air-fuel ratio map may be rewritten to the one corrected in advance so as to increase the target value of the air-fuel ratio.

  The air-fuel ratio adjusting unit 49 controls the engine 1 so that the detected value of the air-fuel ratio of the air-fuel mixture sent from the LAF sensor 37 substantially matches the target value of the air-fuel ratio of the air-fuel mixture calculated by the target air-fuel ratio calculating unit 81. An air-fuel ratio correction unit 82 is provided. The air-fuel ratio correction unit 82 is electrically connected to the LAF sensor 37. For example, the air-fuel ratio correction unit 82 sets the target value of the injection amount calculated by the target injection amount calculation unit 71 so that the detected value of the air-fuel ratio of the air-fuel mixture substantially matches the target value of the air-fuel ratio of the air-fuel mixture. Correct it. Specifically, the air-fuel ratio correction unit 82 may correct the injection amount map of the target injection amount calculation unit 71, and the control signal sent from the direct injection injector control unit 73 to the direct injection injector 25 by this correction. The pulse width may be changed.

[About control method]
With reference to FIG. 5, the control method of the engine 1 which concerns on this embodiment is demonstrated below. The pressure signal acquisition unit 42 acquires the pressure signal, and the crank angle acquisition unit 43 acquires the detected value θ of the crank angle (step S1). The angle-pressure signal calculation unit 44 calculates an angle-pressure signal in which the pressure signal is associated with the crank angle detection value θ (step S2). The filter unit 45 performs a filtering process for gradually decreasing the frequency component higher than the cutoff frequency with respect to the angle-pressure signal (step S3).

  The change rate calculation unit 51 has a plurality of ratios of the intensity I of the angle-pressure signal that changes in a certain section of the detected value θ of the crank angle in each combustion cycle in the combustion chamber 12 on the angle-pressure signal. The change rate C is calculated and stored (step S4). The change rate sorting unit 52 sorts and stores the maximum change rate M of the plurality of change rates C in each combustion cycle (step S5). The standard deviation calculation unit 61 calculates the standard deviation σ of the plurality of maximum change rates M, and the average value calculation unit 62 calculates the average value μ of the plurality of maximum change rates M (step S6). The variation coefficient calculating unit 63 calculates the variation coefficient V using the standard deviation σ and the average value μ (step S7). The stability determination unit 47 determines whether or not the variation coefficient V is equal to or less than the stability determination threshold T (step S8).

  When the stability determination unit 47 determines that the variation coefficient V is greater than the stability determination threshold T (NO), it is determined that the combustion in the combustion chamber 12 is unstable (step S9). In this case, the target air-fuel ratio calculation unit 81 corrects the target value of the air-fuel ratio of the air-fuel mixture to the rich side (step S10). The target value of the injection amount set by the target injection amount calculation unit 71 is corrected so that the detected value of the air-fuel ratio of the air-fuel mixture detected by the LAF sensor 37 substantially matches the corrected target value of the air-fuel ratio. Further, the fuel injection amount from the direct injection injector 25 is increased according to the corrected target value of the injection amount (step S11). On the other hand, when the stability determination unit 47 determines that the coefficient of variation V is equal to or less than the stability determination threshold T (NO), it is determined that the combustion in the combustion chamber 12 is stable (step S12). . In this case, the conventional operation state related to the cylinder 11 is maintained (step 13). Such a control method may be implemented in a feedback control mode that is repeated until combustion is stabilized.

  However, the present invention is not limited to this, and in the control method of the present invention, the steps may be changed in accordance with the modified example of the control system.

  As described above, according to the control device 3 according to the present embodiment, the cost of the washer sensor 32 attached to the cylinder 11 so as to come into contact with the cylinder 11 from the outside is that the cylinder head 15 detects the combustion pressure directly in the combustion chamber. Since it can be made lower than the cost of a conventional pressure sensor (hereinafter referred to as “in-cylinder pressure sensor”), the manufacturing cost can be reduced. Further, since the washer sensor 32 is a washer mold and is attached so as to be in contact with the cylinder 11 from the outside, the attachment is easy. In particular, since the washer sensor 32 is tightened between the cylinder head 15 and the spark plug 19, the attachment becomes easier. As a result, manufacturing efficiency can be improved. Furthermore, a combustion estimation parameter for estimating the combustion state in the combustion chamber 12 is calculated using an angle-pressure signal in which the pressure signal of the combustion pressure is related to the crank angle of the crankshaft 17, and combustion is performed using the combustion estimation parameter. Since the stability is determined, the accuracy of determining the combustion stability can be improved, and consequently stable combustion can be maintained.

  According to the control device 3 according to the present embodiment, the pressure signal corresponding to the combustion pressure detected with the intake valve 22 and the exhaust valve 23 being closed is influenced by the vibration generated when the intake valve 22 and the exhaust valve 23 are seated. Therefore, the determination accuracy of combustion stability can be improved. Incidentally, since the pressure signal used for the calculation process is limited, the calculation load can be reduced.

  According to the control device 3 according to the present embodiment, noise included in the frequency component higher than the cutoff frequency in the angle-pressure signal, for example, vibration of the engine 1 and vibration generated when the intake valve 22 and the exhaust valve 23 are seated. Since vibration associated with knocking can be removed by the filter unit 45, the angle-pressure signal can be accurately detected so that the combustion state can be accurately grasped from the angle-pressure signal. As a result, the accuracy of determining combustion stability can be increased.

  According to the control device 3 according to the present embodiment, the maximum change rate M between the plurality of change rates C, which is the ratio of the angle-pressure signal intensity I that changes in a constant section of the crank angle detection value θ, is the combustion rate. Since it has a high correlation with IMEP that is generally used as an evaluation item of stability and combustion stability is determined based on the combustion estimation parameter calculated using the maximum change rate M, The determination accuracy of combustion stability can be made extremely high. Note that the same effect can be obtained when a plurality of change rates C that are substantially equal to the maximum change rate M are used instead of the maximum change rate M.

  According to the control device 3 according to the present embodiment, the coefficient of variation V based on the standard deviation σ and the average value μ of the plurality of maximum change rates M has a high correlation with the IMEP. Since the combustion stability is determined based on such a variation coefficient V, the determination accuracy of the combustion stability can be made extremely high.

  According to the control device 3 according to the present embodiment, the air-fuel ratio of the air-fuel mixture is made rich in order to stabilize the combustion in the combustion chamber 12 based on the accurate determination as described above regarding unstable combustion in the combustion chamber 12. Therefore, stable combustion can be reliably maintained. In particular, when the engine 1 is of the HCCI type as in the present embodiment, misfire or partial combustion in the combustion chamber 12 can be avoided, so that HCCI combustion can be reliably maintained.

[Second Embodiment]
A control system including a control device according to a second embodiment of the present invention will be described. The control system according to the present embodiment is the same as the control system according to the first embodiment except for control for stabilizing combustion when combustion in the combustion chamber is unstable.

[Regarding stabilization control of combustion in the combustion chamber]
The combustion stabilization control in the combustion chamber in the present embodiment will be described. In the control system according to the present embodiment, when the target injection timing calculation unit 72 determines that the combustion in the combustion chamber 12 is unstable by the stability determination unit 47, in particular, a misfire or a part in the combustion chamber 12. When it is determined that combustion can occur, the timing for directly injecting fuel into the combustion chamber 12 by the direct injection injector 25 in each combustion cycle is advanced. In this case, it is preferable that the target injection timing calculation unit 72 corrects the injection timing map so as to advance the injection timing in a part or the whole region of the injection timing map. In particular, in the target injection timing calculation unit 72, the injection timing map may be rewritten to the one that has been corrected in advance so as to increase the target value of the injection timing.

  In the control method according to the present embodiment, when the stability determination unit 47 determines that the coefficient of variation V is greater than the stability determination threshold T (NO), it is determined that the combustion in the combustion chamber 12 is unstable. Is done. In this case, the target injection timing calculation unit 72 advances the timing at which the fuel is directly injected into the combustion chamber 12 by the direct injection injector 25.

  As mentioned above, according to the control system which concerns on this embodiment, the effect similar to the control system which concerns on 1st Embodiment can be acquired except the following effects based on the stabilization control of the combustion in the combustion chamber 12. FIG. The direct injection injector for stabilizing the combustion in the combustion chamber 12 based on the above accurate determination regarding the unstable combustion in the combustion chamber 12 with respect to the effect based on the stabilization control of the combustion in the combustion chamber 12. 25, the timing for directly injecting fuel into the combustion chamber 12 is advanced, so that stable combustion can be reliably maintained. In particular, when the engine 1 is of the HCCI type as in the present embodiment, misfire or partial combustion in the combustion chamber 12 can be avoided, so that HCCI combustion can be reliably maintained.

  Although the embodiment of the present invention has been described so far, the present invention is not limited to the above-described embodiment, and the present invention can be modified and changed based on its technical idea.

[Example 1]
Example 1 will be described. In Example 1, in addition to the washer sensor 32, the engine 1 of the first embodiment in which a cylinder pressure sensor was attached to the cylinder head 15 was used. Furthermore, in the first embodiment, in the engine 1, when the ATDC (After Top Dead Center) is 9 °, the setting so that the MBF (Mass Burned Fraction) is 50% (hereinafter referred to as “first The maximum change rate M was calculated for each of a setting (hereinafter referred to as “second setting”) and an MBF of 50% when the ATDC was 15.5 ° (hereinafter referred to as “second setting”). Specifically, in each of the first and second settings, the rotational speed of the engine 1 is 3000 rpm, the BMEP (Break Mean Effective Pressure) in the combustion chamber 12 of the cylinder 11 is 600 kPa, and Under the conditions for generating HCCI combustion, a pressure signal is acquired from the washer sensor 32, an angle-pressure signal based on the pressure signal is calculated, and a certain interval of the detected value θ of the crank angle is further determined on the angle-pressure signal. The maximum change rate M in the case of 1 ° was calculated.

[Comparative Example 1]
Comparative Example 1 will be described. In Comparative Example 1, the same engine as in Example 1 was used. Further, in the first comparative example, the pressure signal is acquired in the first example under the same conditions as in the first example in each of the first and second settings similar to the first example, and at the same time from the in-cylinder pressure sensor. An internal pressure signal is acquired, and an in-cylinder angle-pressure signal is calculated based on the in-cylinder pressure signal. Further, on the in-cylinder angle-pressure signal, a constant section of the detected crank angle θ is set to 1 °. The in-cylinder maximum change rate N was calculated.

  In Example 1 and Comparative Example 1, an angle-pressure signal and an in-cylinder angle-pressure signal as shown in FIG. 6 were obtained. In FIG. 6, the horizontal axis θ represents the detected value θ (°) of the crank angle, and the vertical axis P on the left side of the drawing represents the detected value P (bar) of the in-cylinder combustion pressure obtained from the in-cylinder pressure sensor. The vertical axis I on the right side of the drawing shows the intensity I (V) of the angle-pressure signal obtained by the washer sensor 32. Furthermore, in FIG. 6, the solid line L2a and the broken line L3a indicate the first and second setting angle-pressure signals in the first embodiment, respectively, and the solid line L2b and the broken line L3b indicate the first and second in the comparative example 1, respectively. The set in-cylinder angle-pressure signal is shown.

  In FIG. 6, for convenience of comparison between Example 1 and Comparative Example 1, the angle-pressure signal of the first and second settings in Example 1 is shown by reversing the sign of the intensity I of the angle-pressure signal. Yes. In FIG. 6, the timing at which the first maximum peak after the crank angle of 0 ° appears in the first set angle-pressure signal in the first embodiment is the combustion start timing. Also, IMEP is obtained by integrating the in-cylinder angle-pressure signals of the first and second settings in Comparative Example 1.

  The maximum change rate M and the in-cylinder maximum change rate N in the first and second settings in Example 1 and Comparative Example 1 were compared. As a result, in the combustion stroke ST1, the maximum change rate M and the in-cylinder maximum change rate N in the first setting in Example 1 and Comparative Example 1 tend to be the same, and the maximum change rate in these second settings. It was confirmed that M and the maximum in-cylinder change rate N also had the same tendency. In particular, the first setting in the first embodiment and the first comparative example will be described. In FIG. 6, the maximum change rate M in the first embodiment is an angle in a constant section of the detected crank angle value θ indicated by Δθ. -An angle at which the maximum change amount ΔI of the intensity I of the pressure signal is obtained. -The maximum in-cylinder change rate N in Comparative Example 1 is the maximum of the detected value P of the in-cylinder combustion pressure. The change amount ΔP was calculated in the in-cylinder angle-pressure signal region.

[Example 2]
Example 2 will be described. In Example 2, in addition to the washer sensor 32, the engine 1 of the first embodiment in which a cylinder pressure sensor was attached to the cylinder head 15 was used. Furthermore, in Example 2, the rotation speed of the engine 1 is set to 1000 rpm, the BMEP in the combustion chamber 12 of the cylinder 11 is set to 600 kPa, and HCCI combustion is generated (hereinafter referred to as “first case”); In each of the cases where the rotational speed of the engine 1 is 3000 rpm, the BMEP in the combustion chamber 12 of the cylinder 11 is 600 kPa, and HCCI combustion is generated (hereinafter referred to as “second case”), the maximum change rate M is Calculated. Specifically, a pressure signal was acquired from the washer sensor 32, an angle-pressure signal based on the pressure signal was calculated, and a maximum change rate M between a plurality of change rates C was calculated from the angle-pressure signal. The maximum change rate M was calculated in 100 continuous combustion cycles. The fixed interval of the detected crank angle value θ used for calculating the rate of change C was 1 °.

[Comparative Example 2]
Comparative example 2 will be described. In Comparative Example 2, the same engine as in Example 2 was used. Furthermore, in the second comparative example, in the first and second cases similar to the second embodiment, the pressure signal is acquired in the second embodiment, and at the same time, the detected value of the combustion pressure is acquired from the in-cylinder pressure sensor. Furthermore, IMEP was calculated using the detected value of the combustion pressure. Such IMEP was calculated in 100 continuous combustion cycles.

  When comparing the first case of Example 2 and Comparative Example 2, the correlation between the maximum change rate M and IMEP as shown in FIG. 7 and the relationship between the maximum change rate M and IMEP as shown in FIG. The graph shown was obtained. Further, when comparing the second case of Example 2 and Comparative Example 2, the correlation diagram between the maximum change rate M and IMEP as shown in FIG. 9 and the maximum change rate M and IMEP as shown in FIG. A graph showing the relationship was obtained.

  In FIG. 7, the horizontal axis M indicates the maximum change rate M (V / °), and the vertical axis IMEP indicates IMEP (kPa). Further, on the correlation diagram of FIG. 7, the calculation results of 100 combustion cycles obtained by the first case of Example 2 and Comparative Example 2 are plotted. In FIG. 8, the horizontal axis CC indicates the combustion cycle (cycle), the vertical axis IMEP on the left side of the paper indicates IMEP (kPa), and the vertical axis M on the right side of the paper indicates the maximum change rate M (V / °). Indicates. In FIG. 8, the solid line L4a indicates the calculation result in the first case of Example 2, and the solid line L4b indicates the calculation result in the first case of Comparative Example 2. In FIG. 9, the horizontal axis M indicates the maximum rate of change M (V / °), and the vertical axis IMEP indicates IMEP (kPa). Further, on the correlation diagram of FIG. 9, the calculation results of 100 combustion cycles obtained by the second case of Example 2 and Comparative Example 2 are plotted. In FIG. 10, the horizontal axis CC indicates the combustion cycle (cycle), the vertical axis IMEP on the left side of the paper indicates IMEP (kPa), and the vertical axis M on the right side of the paper indicates the maximum change rate M (V / °). Indicates. In FIG. 10, the solid line L5a indicates the calculation result in the second case of Example 2, and the solid line L5b indicates the calculation result in the second case of Comparative Example 2.

  As shown in FIGS. 7 and 8, the correlation coefficient R between the maximum change rate M and IMEP for the first case of Example 2 and Comparative Example 2 is 0.8, and FIGS. As shown, the correlation coefficient for the second case of Example 2 and Comparative Example 2 was 0.85. Therefore, in any of the above cases, the correlation coefficient R was 0.8 or more, and it was confirmed that the maximum change rate M and IMEP were highly correlated. That is, it was confirmed that the combustion stability can be determined with high accuracy using the maximum change rate M.

[Example 3]
Example 3 will be described. In Example 3, the variation coefficient V was calculated based on the maximum change rate M of 100 combustion cycles under the same conditions as in Example 2, and the combustion stability was evaluated based on the variation coefficient V. Under such conditions, the combustion unstable state was reproduced in the 50th and subsequent combustion cycles, and the reliability of the combustion stability determination based on the coefficient of variation V was confirmed.

  In Example 3, the relationship between the combustion cycle and the coefficient of variation V as shown in FIG. 11 was obtained. In FIG. 11, the horizontal axis CC indicates the combustion cycle (cycle), the vertical axis V indicates the coefficient of variation V (%), and the solid line L6 indicates the calculation result of the third embodiment. As shown in FIG. 11, the coefficient of variation V increased in the 50th and subsequent combustion cycles, and particularly increased rapidly in the 80th and subsequent combustion cycles. Therefore, it was confirmed that the unstable combustion state can be determined by the variation coefficient V. For example, the stability determination threshold value T can be set larger than the variation coefficient V in a state where combustion is stable, as shown in FIG. The amount of increase in the stability determination threshold value T with respect to the coefficient of variation V when the combustion is stable reliably determines the coefficient of variation V when the combustion is stable and the coefficient of variation V when the combustion is unstable. It should be determined to be possible.

1 HCCI engine (engine)
11 Cylinder 12 Combustion chamber 13 Cylinder block 17 Crankshaft 22 Intake valve 23 Exhaust valve 25 Direct injection injector 3 Control device 31 ECU
32 Washer pressure sensor (washer sensor)
43 Crank angle acquisition unit 44 Angle-pressure signal calculation unit 45 Filter unit 46 Combustion state estimation unit 47 Stability determination unit 48 Direct injection control unit 49 Air-fuel ratio adjustment unit 51 Change rate calculation unit 52 Change rate selection unit 53 Calculation of combustion estimation parameters Unit 61 Standard deviation calculation unit 62 Average value calculation unit 63 Variation coefficient calculation unit θ Crank angle detection value I Angle-pressure signal intensity C Change rate M Maximum value of multiple change rates (maximum change rate)
σ Standard deviation μ Average value V Coefficient of variation T Stability judgment threshold

Claims (8)

A washer-type pressure sensor configured to come into contact with the cylinder from outside so as to be able to detect a combustion pressure in a combustion chamber of the cylinder in the internal combustion engine and to output a pressure signal in accordance with the combustion pressure;
A crank angle acquisition unit configured to acquire a crank angle of a crankshaft of the internal combustion engine,
A control device for an internal combustion engine configured to be able to control the internal combustion engine according to the stability of combustion in the combustion chamber,
An angle-pressure signal calculator configured to calculate an angle-pressure signal associated with the crank angle of the pressure signal;
A combustion state estimation unit configured to calculate a combustion estimation parameter for estimating a combustion state in the combustion chamber using the angle-pressure signal;
A control device for an internal combustion engine, comprising: a stability determination unit configured to determine the stability of combustion in the combustion chamber using the combustion estimation parameter.   2. The angle-pressure signal calculation unit is configured to calculate the angle-pressure signal within a range of the crank angle in a state where both an intake valve and an exhaust valve of the internal combustion engine are closed. Control device for internal combustion engine. A filter unit configured to subject the angle-pressure signal to a filtering process that reduces a frequency component higher than a predetermined cutoff frequency;
The internal combustion engine according to claim 1, wherein the combustion state estimation unit is configured to calculate the combustion estimation parameter using the angle-pressure signal subjected to the filter processing by the filter unit. Control device. The combustion state estimation unit,
Based on the angle-pressure signal, a plurality of change rates, which are ratios of the intensity of the angle-pressure signal that changes in a certain section of the crank angle, are calculated in each combustion cycle in the combustion chamber. A rate-of-change calculating unit,
A change rate selecting unit configured to select one selected change rate among the plurality of change rates in each combustion cycle in the combustion chamber;
The internal combustion engine according to claim 1, further comprising: a combustion estimation parameter calculation unit configured to calculate the combustion estimation parameter using a plurality of the selection change rates in the plurality of combustion cycles. Engine control device.   The control device for an internal combustion engine according to claim 4, wherein the selection change rate is a maximum value of the plurality of change rates. The combustion estimation parameter calculation unit,
A standard deviation calculation unit and an average value calculation unit configured to calculate a standard deviation and an average value of the plurality of selection change rates, respectively;
A variation coefficient calculation unit configured to calculate a variation coefficient using the standard deviation and the average value as the combustion estimation parameter;
The abnormality determination unit determines that the combustion in the combustion chamber is unstable when the variation coefficient is greater than a predetermined stability determination threshold, and the variation coefficient is equal to or less than the stability determination threshold. The control device for an internal combustion engine according to claim 4, wherein the control unit is configured to determine that combustion in the combustion chamber is stable.   When the stability determination unit determines that the combustion in the combustion chamber is unstable, the air-fuel ratio of the air-fuel ratio in the combustion chamber is changed to the rich side so as to stabilize the combustion in the combustion chamber. The control device for an internal combustion engine according to any one of claims 1 to 5, further comprising a fuel ratio adjusting unit.   When the stability determination unit determines that the combustion in the combustion chamber is unstable, fuel is directly injected into the combustion chamber by a direct injection injector in each combustion cycle so as to stabilize the combustion in the combustion chamber. The control device for an internal combustion engine according to any one of claims 1 to 6, further comprising a direct injection adjusting portion that is configured to advance the timing.

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