JP5511504B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more specifically to detecting and controlling variation in air-fuel ratio between cylinders of the internal combustion engine.

  Patent Document 1 discloses a control device that suppresses output fluctuation between cylinders of an internal combustion engine. This control device suppresses fluctuations in output between cylinders using a torque parameter calculated based on a detection value of a crank angle sensor.

  Patent Document 2 discloses a starting device for an internal combustion engine. This starter estimates the air-fuel ratio based on the engine generated torque.

JP 2008-215338 A Japanese Patent No. 4107184

  However, in the invention described in Patent Document 2, the friction torque caused by deviation in the shaft end torque amount calculated due to variation in accuracy of the sensor used when estimating the torque, or due to variation in manufacturing of the internal combustion engine. When the estimated deviation occurs, the calculated generated torque amount is deviated, so that the air-fuel ratio is erroneously estimated.

  Therefore, the present invention estimates the air-fuel ratio for each cylinder without being affected by variations in accuracy of sensors used for estimating torque and variations in friction caused by variations in the manufacture of internal combustion engines, and provides torque between cylinders. An object is to improve the merchantability and emission performance of an internal combustion engine by reducing the level difference.

  The present invention provides a control device for an internal combustion engine including a variable valve mechanism for an intake valve. The control device includes control means for controlling the output of the internal combustion engine so that the detected value of the air-fuel ratio sensor converges to the target air-fuel ratio, and torque for calculating torque based on the detected value of the crank angle sensor for each cylinder. Calculating means, first target air-fuel ratio setting means for setting the first target air-fuel ratio according to the operating state, and changing the first target air-fuel ratio by a predetermined amount according to the valve timing of the intake valve, Second target air-fuel ratio setting means for setting the fuel ratio, first torque for each cylinder when the output of the internal combustion engine is controlled to converge to the first target air-fuel ratio, and convergence to the second target air-fuel ratio Air-fuel ratio variation detecting means for detecting variations in the air-fuel ratio between the cylinders based on the second torque for each cylinder when such control is performed.

  According to the present invention, it is possible to improve the estimation accuracy of the inter-cylinder air-fuel ratio without being affected by sensor deviation or manufacturing variation.

  According to one aspect of the present invention, the second target air-fuel ratio setting means sets the second target air-fuel ratio so as to be lean with respect to the first target air-fuel ratio.

  According to an embodiment of the present invention, shifting the air-fuel ratio to the lean side rather than shifting the air-fuel ratio to the lean side increases the amount of torque fluctuation because the inclination of the torque fluctuation is larger, so the estimation accuracy of the inter-cylinder air-fuel ratio is improved. Can be made.

  According to an aspect of the present invention, the variable valve means sets the lift amount of the intake valve to be variable, and the predetermined amount is set to a larger value as the lift amount becomes smaller.

  According to one aspect of the present invention, by reducing the lift amount, the in-cylinder flow becomes faster and the combustion limit air-fuel ratio shifts to the lean side. Therefore, by setting the fluctuation range of the air-fuel ratio according to the lift amount, setting the fluctuation range of the air-fuel ratio to the maximum width makes it easy to detect the torque fluctuation amount and increases the estimation accuracy of the inter-cylinder air-fuel ratio. Can be improved.

  According to one aspect of the present invention, the variable valve mechanism sets the phase angle of the intake valve to be variable, and the predetermined amount is set to a larger value as the phase angle is retarded.

  According to one aspect of the present invention, by retarding the phase angle of the intake valve, the amount of EGR remaining in the cylinder decreases, and increases according to the density of fresh air sucked into the cylinder. The combustion limit air-fuel ratio shifts to the lean side. Therefore, by setting the fluctuation range of the air-fuel ratio according to the phase angle of the intake valve, it is possible to set the fluctuation range of the air-fuel ratio to the maximum width, and as a result, it becomes easy to detect the amount of torque fluctuation, and between cylinders. The estimation accuracy of the air-fuel ratio can be improved.

  According to one aspect of the present invention, the air-fuel ratio variation detecting means detects the variation in the air-fuel ratio between the cylinders from the air-fuel ratio for each cylinder estimated based on the difference between the first torque and the second torque. Air-fuel ratio control for each cylinder is performed so that the torque difference becomes smaller than a predetermined difference.

  According to one aspect of the present invention, variation in air-fuel ratio among cylinders can be suppressed, so that it is possible to improve the emission performance and merchantability of an internal combustion engine.

1 schematically shows an engine and its control device according to an embodiment of the invention. FIG. It is a functional block diagram of the control apparatus according to one Example of this invention. It is a figure which shows the torque calculation flow according to one Example of this invention. It is a figure which shows the relationship between the torque for every cylinder according to one Example of this invention, and an air fuel ratio. It is a figure which shows the control flow by a control apparatus according to one Example of this invention. It is a table which shows the relationship between the lift amount and the air fuel ratio amount according to one embodiment of the present invention. It is a figure which shows the relationship between the phase angle of an intake valve, and an air fuel ratio amount according to one Example of this invention. It is a figure which shows the relationship between the amount of torque changes for every cylinder, and an air fuel ratio according to one Example of this invention.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter referred to as an engine) and its control device according to an embodiment of the present invention.

  Referring to FIG. 1A, an electronic control unit (hereinafter referred to as “ECU”) 1 is a computer including a central processing unit (CPU) and a memory. The memory can store a computer program for realizing various controls of the vehicle and data, tables, and maps necessary for executing the program. The ECU 1 receives data sent from each part of the vehicle, performs calculation, and generates a control signal for controlling each part of the vehicle.

  The engine 2 includes six cylinders in this embodiment. The engine 2 includes an intake pipe 3 and an exhaust pipe 4. The EGR passage 5 connects the intake pipe 3 and the exhaust pipe 4. The exhaust gas in the exhaust pipe 4 returns to the intake pipe 3 via the EGR passage 5. An EGR valve 6 provided in the EGR passage 5 adjusts the amount of exhaust gas that is recirculated. The opening degree of the EGR valve 6 is changed according to a control signal from the ECU 1.

  The intake pipe 3 includes an air flow meter (AFM) 7 that detects the amount of air passing through the intake pipe 3, an intake air temperature sensor 8 that detects the temperature TA of the intake pipe 3, and an intake air that detects the pressure PB of the intake pipe 3. A tube pressure sensor 9 is provided. Detection values of these sensors are sent to the ECU 1. The ECU 1 calculates a gauge pressure (a differential pressure of the intake pipe pressure with respect to the atmospheric pressure) from the detection value of the intake pipe pressure sensor 9. The intake pipe 3 is branched toward each cylinder downstream of the intake pipe pressure sensor 9.

  The engine 2 is provided with a water temperature sensor 10 and a crank angle sensor 11 that detect the temperature TW of the cooling water of the engine 2. The crank angle sensor 11 outputs a CRK signal and a TDC signal to the ECU 1 in accordance with the rotation of the crankshaft 26 (see FIG. 1B). The CRK signal is output at every predetermined crank angle. The ECU 1 calculates the engine speed NE of the engine 2 from the CRK signal. The TDC signal is output as a crank angle corresponding to the top dead center (TDC) position of the piston 25 (see FIG. 1B). A PA sensor 12 that detects the atmospheric pressure PA is connected to the ECU 1.

  An air-fuel ratio (LAF) sensor 13 is provided upstream of a device (not shown) for purifying exhaust gas in the exhaust pipe of the engine 1. The air-fuel ratio sensor 13 linearly detects the air-fuel ratio in a region ranging from lean to rich of the engine 2. The detection value of the air-fuel ratio sensor 13 is sent to the ECU 1.

  Referring to FIG. 1 (b), one of the cylinders mounted on the engine 2 is shown. The cylinder combustion chamber 15 is connected to the intake pipe 3 via an intake valve 16 and is connected to the exhaust pipe 4 via an exhaust valve 17. A fuel injection valve 18 is attached to the intake pipe 3. The fuel injection mechanism 21 drives the fuel injection valve 18 in accordance with a control signal from the ECU 1 to inject fuel into the combustion chamber 15. The fuel injection valve 18 and the fuel injection mechanism 21 are called a fuel supply device.

  A spark plug 19 is attached to the upper portion of the combustion chamber 15. The ignition mechanism 22 drives the ignition plug 19 according to a control signal from the ECU 1 to generate a spark. Due to the spark, the injected fuel / air mixture burns in the combustion chamber 15. The spark plug 19 and the ignition mechanism 22 are called an ignition device. Combustion increases the volume of the air-fuel mixture, thereby pushing the piston 25 downward. The reciprocating motion of the piston 25 is converted into the rotational motion of the crankshaft 26.

  In this embodiment, the variable valve mechanism 23 includes a variable lift mechanism and a variable phase mechanism. The variable lift mechanism is a mechanism that can continuously change the lift amount of the intake valve of each cylinder in accordance with a control signal from the ECU 1 (see, for example, Japanese Patent Application Laid-Open No. 2004-36560). The variable phase mechanism is a mechanism that can continuously change the phase of the intake valve of each cylinder in accordance with a control signal from the ECU 1 (see, for example, Japanese Patent Laid-Open No. 2000-227033). The present invention is not limited to a mechanism that continuously changes the lift amount and phase, and the present invention can also be applied to a mechanism that can change the lift amount and phase stepwise (stepwise).

  The variable valve mechanism 23 is provided with a lift amount sensor (not shown) for detecting the lift amount of the intake valve 16 of each cylinder. The lift sensor is implemented by any suitable technique (eg, using a potentiometer). The detection result of the sensor is sent to the ECU 1.

  In this embodiment, a throttle valve 27 is provided in the intake pipe 3 in addition to the variable valve mechanism 23 as shown in FIG. The throttle valve 27 is connected to a throttle mechanism (not shown) that controls the opening degree of the throttle valve by a control signal from the ECU 1. By controlling the opening degree of the throttle valve 27, the amount of intake air taken into the combustion chamber 15 is controlled. The intake air amount is mainly controlled by the variable valve mechanism 23, but it can also be controlled by adjusting the opening of the throttle valve 27 in accordance with the operation region (output or load state) of the engine 2. A throttle valve opening (θTH) sensor 28 that detects the opening of the throttle valve is connected to the throttle valve 27. The detected throttle valve opening is sent to the ECU 1.

  FIG. 2 is a functional block diagram of a control device according to one embodiment of the present invention. These functional blocks are implemented in the ECU 1 in FIG.

  The torque calculation unit 101 calculates torque for each cylinder based on the detected value of the crank angle sensor. Details of this torque calculation will be described later. The first target air-fuel ratio setting unit 102 sets a first target air-fuel ratio according to the driving state of the vehicle. Details of the setting of the first target air-fuel ratio will be described later. The second target air-fuel ratio setting unit 103 sets the second target air-fuel ratio by changing the set first target air-fuel ratio by a predetermined amount corresponding to the valve timing of the intake valve. Details of the setting of the second target air-fuel ratio will be described later. The air-fuel ratio variation detection unit 104 controls the first torque for each cylinder when the engine output is controlled to converge to the first target air-fuel ratio and the second target air-fuel ratio. Based on the second torque for each cylinder, the variation in the air-fuel ratio between the cylinders is detected. Details of the air-fuel ratio variation detection will be described later. The output control unit 105 controls the output of the engine so that the detection value of the air-fuel ratio sensor 13 converges to the target air-fuel ratio. At that time, the output control unit 105 creates a control signal for controlling, for example, the fuel injection amount by the fuel injection mechanism 21, the ignition timing by the ignition mechanism 22, the intake air amount by the variable valve mechanism 23, etc. Send to.

  FIG. 3 shows an example of a process executed by the CPU of the ECU 1 according to an embodiment of the present invention, more specifically, executed by the torque calculation unit 101 of FIG. This process is performed every 1 TDC period.

In step S10, the rotational speed OMG (i) (rad / s) is calculated according to the equation (1). The rotational speed OMG is obtained by converting the CRK signal generation time interval of the crank angle sensor 11 into an angular speed, and represents the speed at which the crankshaft 26 rotates. Here, Dθ is an angular interval of 4π / ND for measuring the time parameter CRME, and in this embodiment is π / 30 (rad).

OMG (i) = Dθ / CRME (i) (1)

In step S12, a 720 degree filter process is executed according to the equation (2), and a post-filter process rotation speed OMGR (i) is calculated.

OMGR (i) = OMG (i) − (OMG (ND) −OMG (0)) × Dθ × i / 4π (2)

The 720 degree filter process cancels the linear change in one cycle period (crank angle 720 degrees), and extracts a fluctuation with a relatively short cycle. This processing is performed to remove rotational fluctuation components caused by torque applied to the engine from the engine load side (torque applied to the tires and accessories driven by the engine, torque due to friction of sliding parts of the engine, etc.). Done.

In step S14, the relative rotational speed OMGREF is calculated according to the equation (3).

OMGREF (i) = OMGR (i) −OMGR ((k-1) NTDC) (3)

Here, OMGR ((k−1) NTDC) is a reference rotational speed, and corresponds to the post-filtering rotational speed at the compression top dead center (TDC) of the target cylinder.

  Preferably, before calculating the integrated value, steps S16 and S18 are performed to remove the influence of inertia torque from the relative rotational speed. The inertia torque is a torque based on the inertial force of rotating parts on the load side of the engine, such as the mass of the reciprocating parts (piston and connecting rod) of the engine 2, the length of the connecting rod, the crank radius, the crank pulley, the torque converter, and the lockup clutch. It is. The relative rotational speed includes a component based on an inertial force, but the inertial torque does not contribute to the output torque generated by combustion, and therefore it is preferable to remove this.

In step S16, the inertial force rotational speed OMGI (k) at the compression top dead center of each cylinder is calculated according to the equation (4).

OMGI (k) = K.OMG ((k-1) NTDC) / 3I (4)

Here, K is a proportional constant, and I indicates the moment of inertia of a rotating component such as a crank pulley or a torque converter. In addition, it is preferable to change the value of the moment of inertia I according to whether or not the lockup clutch of the automatic transmission (not shown) is engaged. Thus, more accurate torque parameters can be calculated regardless of whether the lockup clutch is engaged or not.

In step S18, the corrected relative rotational speed OMGREFM (i) is calculated according to the equation (5). The corrected relative rotational speed is a relative rotational speed from which the influence of inertia torque is removed.

OMGREFM (i) = OMGREF (i) + OMGI (k) (5)

In step S20, the corrected relative rotational speed OMGREFM is integrated according to the equation (6) to calculate the torque parameter MFJUD (k).

  In step S22, it is determined whether or not the cylinder identification number k is equal to the number N of cylinders. When the answer is No, the cylinder identification number k is incremented by 1 (S24), and when the answer is Yes, the cylinder identification number k is returned to 1 (S26). Thus, the torque parameter MFJUD, that is, the output torque for each cylinder is calculated for each cylinder in synchronization with the generation of the TDC pulse.

  Next, the concept of setting the first and second target air-fuel ratios of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing a relationship between torque and air-fuel ratio for each cylinder according to one embodiment of the present invention. The horizontal axis is KACT (theoretical air-fuel ratio (= 14.7) / detected air-fuel ratio) obtained as the output of the LAF sensor 13, the left vertical axis is the torque ratio P, and the right vertical axis is the torque ratio P. Change rate (differential value). The curve P in the figure shows the torque ratio P, and the curve (dP / dt) shows the rate of change (differential value) of the torque ratio P.

  Now, it is assumed that the air-fuel ratio varies between cylinders during operation of the vehicle. First, the engine output control is performed with the average air-fuel ratio between the cylinders as the first target air-fuel ratio. At this time, it is assumed that the air-fuel ratio varies at the positions indicated by the symbols A and B in FIG. 4 in a certain cylinder. However, these positions cannot actually be specified. The torque tr1 is calculated for each cylinder by the method shown in the flow of FIG.

  Next, the torque tr2 for each cylinder when the average air-fuel ratio is shifted by ΔAF is calculated. In FIG. 4, the torque for each cylinder when KACT is shifted by 0.05 corresponding to ΔAF is calculated. A difference Δtr between the torques tr1 and tr2 before and after shifting the air-fuel ratio is obtained. In FIG. 4, it is assumed that the torque ratio P is shifted from the positions of the symbols A and B to the positions indicated by the symbols C and D, respectively, and the differences ΔP1 and ΔP2 of the torque ratio P are obtained. At this time, whether the corresponding cylinder is lean or rich can be recognized from the magnitude of Δtr, in other words, the magnitude of the difference ΔP of the torque ratio P. That is, in the example of FIG. 4, since the difference ΔP1 is larger than ΔP2, it can be recognized that the cylinder indicating the position of the symbol A is lean. Conversely, it can be recognized that the cylinder indicating the position of symbol B is rich. The magnitude relationship of the torque change amount Δtr (ΔP) can be recognized more clearly by using the curve (dP / dt) of the differential value of the torque ratio P in FIG.

  FIG. 5 shows a control flow by the control device according to one embodiment of the present invention. This flow is executed by the ECU 1 for each cylinder.

  In step S31, the average air-fuel ratio between the cylinders is set as the target air-fuel ratio, and the engine output is feedback-controlled so that the detection value of the air-fuel ratio sensor 13 converges to the target air-fuel ratio. This feedback control method is performed using a conventional method (for example, see Japanese Patent Application Laid-Open No. 2008-215338).

  In step S32, it is determined whether or not the operating state of the internal combustion engine is an idle state. Specifically, for example, the rotational speed NE of the engine 2 is calculated from the CRK signal of the crank angle sensor 11, and the presence / absence of the idle state is determined based on whether the rotational speed NE is smaller than a predetermined rotational speed. The reason for making this determination is that the fluctuation (variation) in the air-fuel ratio between the cylinders can be detected more stably when the output of the internal combustion engine is low and stable. Furthermore, in the idle operation state, the air-fuel ratio between the cylinders and the torque are likely to vary due to variations in the lift amount of the intake valve between the cylinders. If this determination is No, the process ends. If this determination is Yes, the process proceeds to the next step S33.

  In step S33, the air-fuel ratio amount ΔAF to be changed is calculated. The air-fuel ratio amount ΔAF here is set in order to calculate the amount of torque change in the same manner as ΔAF described with reference to FIG. For example, there are the following two methods for calculating the air-fuel ratio amount ΔAF.

  In the first method, the air-fuel ratio amount ΔAF that is changed from the lift amount for each cylinder is calculated. Specifically, the lift amount is acquired from the lift amount sensor of the intake valve 16 for each cylinder, and an air-fuel ratio amount ΔAF corresponding to the lift amount is obtained by referring to a table set in advance and stored in the memory.

  FIG. 6 is an example of a table showing the relationship between the lift amount and the air-fuel ratio amount. For example, if 1 mm is obtained as the lift amount (LIFT) from the lift amount sensor, 2.0 is obtained as the corresponding air-fuel ratio amount ΔAF. In the table of FIG. 6, the air-fuel ratio amount ΔAF is set large on the low lift side and small on the high lift side. In any case, as is apparent from the relationship of FIG. 4, shifting the target air-fuel ratio by ΔAF means that each cylinder is leaned.

  In the second method, the air-fuel ratio amount ΔAF is calculated according to the phase angle of the intake valve 16. Specifically, the phase angle of the intake valve 16 is detected for each cylinder, and an air-fuel ratio amount ΔAF corresponding to the phase angle is obtained by referring to a table set in advance and stored in the memory. FIG. 7 is a graph showing the relationship between the phase angle Θ of the intake valve and the air-fuel ratio amount ΔAF. In the relationship of FIG. 7, the air-fuel ratio amount ΔAF increases as the phase angle Θ is retarded. For example, if Θ1 (deg) is obtained as the phase angle Θ of the intake valve 16, ΔAF1 can be obtained as the corresponding air-fuel ratio amount ΔAF from the figure.

  In step S34, the base torque TRQ1 is calculated. Here, the base torque TRQ1 corresponds to the torque at the positions of symbols A and B when the average air-fuel ratio is controlled as the target air-fuel ratio in the example of FIG. Specifically, the torque for each cylinder is calculated by the method described in the flow of FIG.

  In step S35, the torque TRQ2 for each cylinder at the air-fuel ratio obtained by adding the air-fuel ratio amount ΔAF obtained in step S33 to the average air-fuel ratio between cylinders set in step S31 is calculated. Specifically, the torque for each cylinder when the air-fuel ratio obtained by adding ΔAF is controlled as the target air-fuel ratio is calculated by the method described in the flow of FIG. 3 as in step S34.

In step S36, first, a torque change amount ΔTRQ for each cylinder is calculated according to the equation (7). TRQt in equation (7) means torque at the stoichiometric air fuel ratio (14.7).

ΔTRQ = (TRQ1-TRQ2) / TRQt (7)

Next, the air-fuel ratio is estimated from the calculated ΔTRQ for each cylinder. Specifically, the air-fuel ratio corresponding to ΔTRQ is obtained by referring to a table set in advance and stored in the memory.

  FIG. 8 is a diagram showing the relationship between the amount of torque change for each cylinder and the air-fuel ratio according to one embodiment of the present invention. Curve A in the figure shows the relationship between the two when the air-fuel ratio amount ΔAF is large, and curve B shows the relationship between the two when the air-fuel ratio amount ΔAF is small. In the figure, only two curves are drawn, but actually, data of a plurality of curves are stored in a memory as a table. From this relationship (table), for example, when ΔTRQ becomes TR1 when a large air-fuel ratio amount ΔAF is set, the corresponding air-fuel ratio AF1 can be obtained from the curve A. This air-fuel ratio AF1 is an estimated value of the air-fuel ratio in the corresponding cylinder. Thus, according to one embodiment of the present invention, each cylinder is determined from the torque variation (deviation) calculated from the CRK signal of the crank angle sensor 11 when the air-fuel ratio is shifted from the average air-fuel ratio between cylinders by ΔAF. The air-fuel ratio can be estimated. At the same time, variations in air-fuel ratio among cylinders can be detected.

  In step S37, the air-fuel ratio control state for each cylinder is returned to the base state. That is, the target air-fuel ratio is returned to the average air-fuel ratio before shifting by ΔAF, and the engine output is feedback controlled so that the detected value of the air-fuel ratio sensor 13 converges to the target air-fuel ratio. That is, the same state as step S34 is set so that the air-fuel ratio obtained in step S36 can be controlled.

  In step S38, the theoretical air-fuel ratio (14.7) is set as the target air-fuel ratio, and each cylinder is feedback-controlled so that the air-fuel ratio (estimated value) for each cylinder obtained in step S36 becomes this target air-fuel ratio. .

  In step S39, it is determined whether or not the difference in ΔTRQ between the cylinders is smaller than a predetermined value. This determination is performed in order to eliminate the torque step between the cylinders. If this determination is Yes, the process ends. If No, the process returns to step S33, and a series of steps S33 to S39 are repeated until the difference in ΔTRQ between the cylinders becomes smaller than a predetermined value.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and can be modified and used without departing from the spirit of the present invention. For example, in the above-described embodiment, a six-cylinder engine has been described as an example, but the present invention can be applied to an engine having an arbitrary number of cylinders. The present invention is also applicable to engines such as direct injection engines and diesel engines.

1 ECU
2 Engine 11 Crank angle sensor 13 Air-fuel ratio sensor 16 Intake valve

Claims (4)

A control device for an internal combustion engine comprising a plurality of cylinders and a variable valve mechanism for intake valves,
Control means for controlling the output of the internal combustion engine so that the detection value of the air-fuel ratio sensor converges to the target air-fuel ratio;
Torque calculating means for calculating torque based on a detection value of a crank angle sensor for each cylinder;
First target air-fuel ratio setting means for setting a first target air-fuel ratio according to the operating state;
A second target air-fuel ratio setting for setting the second target air-fuel ratio by changing the first target air-fuel ratio to be lean with respect to the first target air-fuel ratio by a predetermined amount corresponding to the valve timing of the intake valve Means,
The first torque for each cylinder when the output of the internal combustion engine is controlled to converge to the first target air-fuel ratio, and the time when the output is controlled to converge to the second target air-fuel ratio Air-fuel ratio variation detecting means for detecting variations in air-fuel ratio between cylinders based on the second torque for each cylinder ,
When detecting variations in the air-fuel ratio among the plurality of cylinders,
The control means performs feedback control with an average air-fuel ratio of the plurality of cylinders as a target air-fuel ratio,
The air-fuel ratio variation detecting means estimates the air-fuel ratio between the cylinders based on a first torque for each cylinder and a second torque for each cylinder in a stable state of the internal combustion engine. Detects variation in air-fuel ratio,
The stoichiometric air-fuel ratio is set to the third target air-fuel ratio, and each cylinder is controlled so that the air-fuel ratio for each cylinder becomes the third target air-fuel ratio, and the difference in torque variation between the cylinders is predetermined. Perform air-fuel ratio control for each cylinder to be smaller than the difference,
Control device. The first target air-fuel ratio setting means sets an average air-fuel ratio of the plurality of cylinders to a first target air-fuel ratio,
The air-fuel ratio variation detecting means has calculation means for calculating a torque change amount for each cylinder based on the first torque, the second torque, and the torque at the theoretical air-fuel ratio, and the torque change The control device according to claim 1 , wherein a variation in the air-fuel ratio between the cylinders is detected by estimating an air-fuel ratio for each of the cylinders based on an amount and the predetermined amount .   The control device according to claim 1, wherein the variable valve mechanism sets the lift amount of the intake valve to be variable, and the predetermined amount is set to a larger value as the lift amount becomes smaller.   3. The control device according to claim 1, wherein the variable valve mechanism sets the phase angle of the intake valve to be variable, and the predetermined amount is set to a larger value as the phase angle is retarded.

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