JP2012255398A - Internal combustion engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect an A/F imbalance between cylinders even if an alcohol concentration is high in fuel.SOLUTION: An ECU 50 detects rotation fluctuations based on an output of a crank angle sensor 40, and executes imbalance detection control that detects the A/F imbalance between the cylinders based on the rotation fluctuations. Moreover, when the alcohol concentration in the fuel is not lower than a specific value B during the execution of the imbalance detection control, the ECU drives a variable valve mechanism 38 to reduce torques of the respective cylinders. As a result, as the torques increase according to the alcohol concentration in the fuel, the torques are reduced, so that the torques (rotation fluctuations) can be maintained to be almost equal to a level when a gasoline is used. Accordingly, the rotation fluctuations when lean imbalance occurs can be sufficiently differentiated from those in a normal state, and the lean imbalance can be stably detected with high accuracy.

Description

  The present invention relates to a control device for an internal combustion engine mounted on a vehicle such as an FFV (Flexible-Fuel Vehicle), and more particularly to a control device for an internal combustion engine using alcohol fuel.

  As a conventional technique, for example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2009-257245), a control device for an internal combustion engine using alcohol fuel is known. The prior art has a function of detecting the alcohol concentration in the fuel and a function of detecting variations in the air-fuel ratio (A / F imbalance) between the cylinders.

JP 2009-257245 A JP-A-6-050202 JP 2007-113513 A JP 2006-220133 A

  In general, in an internal combustion engine using alcohol fuel, for example, when an A / F imbalance in which only one cylinder is leaner than other cylinders occurs, a difference in torque generated between the lean cylinders and the other cylinders is a gasoline difference. There is a tendency to become smaller than when using. This tendency becomes remarkable when the alcohol concentration in the fuel is high. For this reason, in the prior art, for example, when the A / F imbalance is detected based on a change (rotational fluctuation) in the engine speed, the detection accuracy of the A / F imbalance decreases due to the use of alcohol fuel, and the exhaust gas is exhausted. There is a problem of worsening emissions.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to stably and accurately maintain the A / F imbalance between cylinders even when the alcohol concentration in the fuel is high. It is an object of the present invention to provide a control device for an internal combustion engine that can detect the exhaust emission and can maintain the exhaust emission well.

1st invention, the alcohol concentration detection means which detects the alcohol concentration in the fuel,
An imbalance detection means for executing imbalance detection control for detecting an A / F imbalance among a plurality of cylinders based on a rotational fluctuation of the engine speed;
Torque reduction means for reducing the torque by an amount corresponding to an increase in the torque of each cylinder due to the alcohol component in the fuel when the alcohol concentration in the fuel is equal to or higher than a predetermined value when the imbalance detection control is performed. It is characterized by.

  The second invention includes a variable valve mechanism that can variably set the valve opening characteristic of the intake valve, and the torque reducing means changes the valve opening characteristic of the intake valve by the variable valve mechanism. The torque is reduced.

  A third invention includes an intake control valve that controls a flow of gas sucked into the cylinder by opening and closing at least a part of the intake passage, and the torque reducing means opens the intake control valve to the valve opening side. It is configured to drive and reduce torque.

  According to a fourth aspect of the invention, the imbalance detection means detects a lean imbalance in which the air-fuel ratio of only one cylinder among the plurality of cylinders shifts to the lean side.

  According to the first invention, the torque reducing means reduces the torque increased in accordance with the high alcohol concentration even when the alcohol concentration in the fuel is high when performing imbalance detection control. ) Can be maintained at the same level as when using gasoline. As a result, even when high-concentration alcohol fuel is used, a sufficient difference in rotational fluctuation can be secured between when the A / F imbalance occurs and when it is normal, and the A / F imbalance can be stabilized with high accuracy. Can be detected automatically.

  According to the second invention, the torque reducing means reduces the torque quickly compared to the case of using another mechanism or the like by changing the valve opening characteristic of the intake valve using the variable valve mechanism. High responsiveness can be obtained.

  According to the third invention, the torque reducing means can drive the intake control valve such as a swirl control valve or a tumble control valve to the valve opening side to reduce the torque. Thereby, torque reduction can be realized with a relatively simple structure.

  According to the fourth aspect of the invention, when lean imbalance occurs, the rotational fluctuation increases or decreases due to the balance between combustion deterioration due to lean air-fuel ratio and combustion improvement due to high alcohol concentration. For this reason, when the alcohol concentration in the fuel is high, the difference in rotational fluctuation between the occurrence of lean balance and the normal time becomes small, but the lean imbalance can be accurately detected by using the torque reducing means. .

It is a whole block diagram for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is explanatory drawing which shows a mode that exhaust emission deteriorates by generation | occurrence | production of A / F imbalance. It is a characteristic diagram which shows the relationship between the alcohol concentration in a fuel, and rotation fluctuation. It is a characteristic diagram which shows the sensitivity of the torque with respect to the alcohol concentration in a fuel. It is a characteristic diagram which shows the relationship between the disturbance of the air flow in a cylinder, the cylinder temperature before ignition, and a combustion speed. It is explanatory drawing which shows the valve opening characteristic of the intake valve changed by torque reduction control. In Embodiment 1 of this invention, it is a flowchart of the control performed by ECU. In Embodiment 2 of this invention, it is sectional drawing which shows TCV provided in the intake passage of the engine. It is sectional drawing which fractured | ruptured the intake passage at the position of TCV perpendicularly to the length direction. In Embodiment 2 of this invention, it is a flowchart of the control performed by ECU.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is an overall configuration diagram for explaining a system configuration according to the first embodiment of the present invention. The system of the present embodiment includes a multi-cylinder engine 10 as an internal combustion engine mounted on a vehicle such as an FFV (Flexible Fuel Vehicle). FIG. 1 exemplifies one cylinder among a plurality of cylinders mounted on the engine 10, and gasoline and alcohol fuel can be used in each cylinder. Each cylinder of the engine 10 has a combustion chamber 14 formed by a piston 12, and the piston 12 is connected to a crankshaft 16. Further, the engine 10 includes an intake passage 18 that sucks intake air into each cylinder. The intake passage 18 is provided with an electronically controlled throttle valve 20 that adjusts the amount of intake air.

  On the other hand, the engine 10 is provided with an exhaust passage 22 through which the exhaust gas of each cylinder flows, and an upstream side thereof is constituted by an exhaust passage manifold 24. The exhaust manifold 24 branches on the upstream side and is connected to the exhaust port of each cylinder, and joins on the downstream side. The exhaust passage 22 is provided with a catalyst 26 that purifies exhaust gas downstream of the exhaust manifold 24. Each cylinder of the engine has, for example, two fuel injection valves 28 and 30 for injecting fuel into the intake port and the cylinder, an ignition plug 32 for igniting the air-fuel mixture, and an intake passage 18 with respect to the cylinder. An intake valve 34 that opens and closes and an exhaust valve 36 that opens and closes the exhaust passage 22 with respect to the inside of the cylinder are provided. In the present invention, it is not always necessary to provide the two fuel injection valves 28 and 30, and it is sufficient that at least one fuel injection valve is mounted.

  The engine 10 also includes a variable valve mechanism 38 that variably sets the valve opening characteristics of the intake valve 34. The variable valve mechanism 38 has a known configuration as described in, for example, Japanese Patent Application Laid-Open No. 2008-45460, and has two arms supported so as to be swingable and a control driven to rotate by an actuator. And a shaft. In a state where the arms are connected, when a cam force is input to one arm from the drive cam for the intake valve, the cam force is transmitted to the other arm, and the intake valve 34 opens and closes. Further, the swing amount of the other cam with respect to the cam force changes according to the rotation angle of the control shaft, and the valve opening characteristics (opening / closing timing and lift amount) of the intake valve 34 change accordingly. Yes. In the present invention, the variable valve mechanism 38 is described in, for example, an electromagnetically driven valve mechanism described in Japanese Patent Laid-Open No. 2007-16710, or in Japanese Patent Laid-Open No. 2000-87769. VVT (Variable Valve Timing system) or the like may be used.

  The system of the present embodiment includes a sensor system including various sensors necessary for engine control, and an ECU (Engine Control Unit) 50 that controls the operating state of the engine. First, the sensor system will be described. The crank angle sensor 40 outputs a signal synchronized with the rotation of the crankshaft 16, and the air flow sensor 42 detects the intake air amount. The air-fuel ratio sensor 44 detects the exhaust air-fuel ratio, and is provided in the exhaust passage 22 at a position downstream of the joining portion of the exhaust manifold 24 and upstream of the catalyst 26. The alcohol concentration sensor 46 detects the alcohol concentration (ethanol concentration) in the fuel, and constitutes the alcohol concentration detection means of the present embodiment. In addition to this, the sensor system includes a water temperature sensor for detecting the temperature of the engine cooling water (engine water temperature), a throttle sensor for detecting the opening of the throttle valve 20, an accelerator sensor for detecting the operation amount of the accelerator pedal, and the like. It is. These sensors are connected to the input side of the ECU 50. On the output side of the ECU 50, actuators such as the throttle valve 20, the fuel injection valves 28 and 30, the spark plug 32, and the variable valve mechanism 38 are connected.

  Then, the ECU 50 drives each actuator based on engine operation information detected by the sensor system, and performs operation control. Specifically, the engine speed (engine speed) and the crank angle are detected based on the output of the crank angle sensor 40, and the intake air amount is detected by the air flow sensor 42. The engine load (load factor) is calculated based on the engine speed and the intake air amount, the fuel injection amount is calculated based on the intake air amount, the load factor, the alcohol concentration in the fuel, etc., and the crank angle is calculated. Based on this, the fuel injection timing and ignition timing are determined. The fuel injection valves 28 and 30 are driven when the fuel injection timing comes, and the spark plug 32 is driven when the ignition timing comes. Thereby, the air-fuel mixture is combusted in each cylinder, and the engine can be operated. Further, the ECU 50 executes air-fuel ratio control that feedback-controls the fuel injection amount so that the exhaust air-fuel ratio matches the target air-fuel ratio (for example, the theoretical air-fuel ratio) based on the output of the air-fuel ratio sensor 44 or the like.

[Features of Embodiment 1]
In general, it is known that when A / F imbalance between cylinders occurs during air-fuel ratio control, exhaust emission is deteriorated. Here, the A / F imbalance is defined as a state in which the air-fuel ratio of at least one cylinder deviates beyond the allowable range with respect to the air-fuel ratio of other cylinders due to, for example, abnormality of the fuel injection valve. FIG. 2 is an explanatory diagram showing how exhaust emission deteriorates due to the occurrence of A / F imbalance. First, FIG. 2A illustrates a state where the air-fuel ratio of each cylinder is equal to 14.7 (normal time) in a four-cylinder engine having # 1 to # 4 cylinders. As shown in this figure, since the air-fuel ratio sensor 44 detects the exhaust air-fuel ratio at the position where the exhaust gases of the cylinders merge, the air-fuel ratio control is performed by the average value of the air-fuel ratios of all the cylinders (example shown in the figure). Then, the air-fuel ratio is controlled so that 14.7) becomes the target air-fuel ratio.

  On the other hand, FIG. 2B shows a state where the air-fuel ratio of one cylinder (# 1 cylinder) has become lean to 15.8 and an A / F imbalance has occurred (during an abnormality). In the following description, the A / F imbalance in which only the air-fuel ratio of one cylinder exceeds the allowable range and becomes lean will be referred to as “lean imbalance”. As shown in FIG. 2B, when lean imbalance occurs, if air-fuel ratio control is performed so that the average value of the overall air-fuel ratio becomes the target air-fuel ratio, the other cylinders that are not leaned The air-fuel ratio is controlled to a richer side (for example, 14.0) than the target air-fuel ratio, and exhaust emission deteriorates.

(Imbalance detection control)
In order to avoid the above phenomenon, in the present embodiment, the imbalance detection control described below is executed, and the A / F imbalance is detected based on engine rotation fluctuation (torque difference between cylinders). Specifically, in the imbalance detection control, for example, every time a predetermined timing corresponding to the ignition timing of each cylinder arrives, the crank angle (or the elapsed time between the timings) is detected, and the detection result is Based on this, the rotational fluctuation, which is the temporal change in the engine speed, is quantitatively calculated. In general, since there is a correlation between the rotational fluctuation and the A / F imbalance, the occurrence of the A / F imbalance can be detected based on the rotational fluctuation. That is, in the imbalance detection control, when the rotation fluctuation is within the allowable range, it is determined that no A / F imbalance has occurred.

  On the other hand, when the rotational fluctuation exceeds the allowable range, the A / F imbalance occurs because the air-fuel ratio of one of the cylinders (abnormal cylinders) deviates from that of the other cylinders (normal cylinders). judge. For example, when lean imbalance occurs, only the torque generated in the abnormal cylinder decreases. As a result, the engine rotational speed decreases at the torque generation timing of the abnormal cylinder, and the rotational fluctuation increases beyond the allowable range, so that the lean imbalance can be detected. The imbalance detection control is executed in a state where a predetermined execution condition is satisfied (stable operation state), for example, during idle operation after the engine warm-up is completed and the catalyst 26 is activated.

  By the way, when alcohol fuel is used, the behavior of rotational fluctuation is different from that when gasoline is used, and the rotational fluctuation changes according to the alcohol concentration in the fuel. FIG. 3 is a characteristic diagram showing the relationship between the alcohol concentration in the fuel and the rotational fluctuation. This characteristic diagram is obtained during idle operation after the completion of warm-up, and the lower (normal) characteristic line shows the rotational fluctuation when no A / F imbalance occurs, and the upper ( The characteristic line at the time of abnormality shows the rotation fluctuation when the lean imbalance occurs. Further, “reference” in the figure indicates rotational fluctuation when the alcohol concentration in the fuel is zero (= gasoline).

  In the imbalance detection control, for example, when the rotational fluctuation is smaller than the predetermined abnormality determination value A shown in FIG. 3, it is determined that the A / F imbalance has not occurred, and the rotational fluctuation is equal to or higher than the abnormality determination value A. If this happens, it is determined that lean imbalance has occurred. Here, the abnormality determination value A is set, for example, according to the minimum value of the rotational fluctuation when the lean imbalance occurs when using gasoline. Further, the rotational fluctuation (characteristic line at the time of abnormality) caused by the lean imbalance changes with the alcohol concentration in the fuel. However, when the alcohol concentration is lower than a predetermined value (upper limit determination value B in FIG. 3), the difference in rotational fluctuation between the normal time and the abnormal time becomes sufficiently large, and the rotational fluctuation occurs only when the lean imbalance occurs. Since it becomes larger than the abnormality determination value A, the lean imbalance can be detected based on the rotational fluctuation.

  On the other hand, when the alcohol concentration in the fuel is higher than the upper limit determination value B, as shown in FIG. 3, the rotational fluctuation at the occurrence of lean imbalance decreases, and the difference in rotational fluctuation between normal and abnormal is reduced. Tends to be smaller. In this case, the rotational fluctuation at the time of occurrence of lean imbalance is less than the abnormality determination value A, or the rotational fluctuation at normal time and abnormal time is difficult to discriminate, so the detection accuracy of lean imbalance is lowered. This tendency is considered to be caused by a balance between combustion deterioration due to lean air-fuel ratio and combustion improvement due to high alcohol concentration. FIG. 4 is a characteristic diagram showing the sensitivity of torque to the alcohol concentration in the fuel. In general, the higher the alcohol concentration in the fuel, the higher the combustion speed, so the torque increases with the alcohol concentration. However, the increasing tendency of the torque becomes slower as the lean imbalance rate becomes higher. For this reason, as shown in FIG. 4, the difference between the torque at the normal time and the torque at the time of abnormality is larger than when using gasoline on the low alcohol concentration side, but the difference between the two is small on the high alcohol concentration side. A trend arises.

(Torque reduction control)
Therefore, in the present embodiment, when imbalance detection control is executed, the combustion speed is controlled based on the alcohol concentration in the fuel and the operating conditions (engine water temperature, engine speed, load factor, etc.), and lean imbalance is achieved. Rotational fluctuation caused by is adjusted to the same level as when using gasoline. More specifically, if the alcohol concentration in the fuel is equal to or higher than the upper limit determination value B when the imbalance detection control is executed, torque reduction control is executed to reduce the torque of each cylinder. In this case, in the torque reduction control, the torque is reduced by an amount corresponding to the increase in the torque according to the alcohol concentration in the fuel, and the torque that is actually output is controlled to be equivalent to the torque when using gasoline.

  Next, a specific example of torque reduction control will be described. FIG. 5 is a characteristic diagram showing the relationship between the combustion speed and the turbulence in the cylinder (turbulence in the cylinder), the in-cylinder temperature before ignition, and the combustion speed. As described above, there is a correlation between the combustion speed of the air-fuel mixture and the torque, but the combustion speed is greatly influenced by in-cylinder turbulence and in-cylinder temperature before ignition, as shown in FIG. As a method for controlling the combustion speed, for example, as shown in FIG. 6, there is a method of controlling the valve opening characteristics (opening / closing timing, lift amount) of the intake valve 34 using a variable valve mechanism 38.

  For example, in the torque reduction control, the intake valve closing timing (IVC) may be retarded. As a result, the actual compression ratio is lowered, and the in-cylinder temperature (compression end temperature) and the combustion speed are reduced, so that the torque can be reduced. In the torque reduction control, the intake valve lift amount may be increased, or the intake valve opening timing (IVO) may be advanced. As a result, the flow velocity of the intake air is lowered and the in-cylinder turbulence is reduced, so that the torque can be reduced. In this way, by changing the valve opening characteristics of the intake valve 34 using the variable valve mechanism 38, the torque can be quickly reduced and high responsiveness can be obtained compared to the case where an intake flow control valve or the like is used. Can do.

  Therefore, according to the torque reduction control, even if the alcohol concentration in the fuel is high when performing imbalance detection control, the torque corresponding to the increased alcohol concentration is reduced and the torque (rotational fluctuation) is used in gasoline. It can be held at the same level as time. As a result, even when high-concentration alcohol fuel is used, a sufficient difference in rotational fluctuation can be secured between when the lean imbalance occurs and when it is normal, and the lean imbalance can be detected stably with high accuracy. it can. Note that when the torque reduction control is executed, the combustion becomes slow, and the emission of gas discharged from the cylinder deteriorates. However, since the torque reduction control is executed when the imbalance detection control is executed, that is, in a state where the catalyst 26 is activated, the exhaust emission can be favorably maintained on the downstream side of the catalyst 26.

[Specific Processing for Realizing Embodiment 1]
Next, specific processing for realizing the above-described control will be described with reference to FIG. FIG. 7 is a flowchart of control executed by the ECU in the first embodiment of the present invention. The routine shown in this figure is repeatedly executed during operation of the engine. In the routine shown in FIG. 7, first, in step 100, the alcohol concentration in the fuel is acquired based on the output of the alcohol concentration sensor 46.

  In step 102, it is determined whether or not a predetermined execution condition for executing imbalance detection control is satisfied. That is, at step 102, the engine water temperature is equal to or higher than a predetermined value corresponding to the completion of warm-up, the engine speed is within a predetermined range, air-fuel ratio control is being performed, and the air is returned to the intake system. When the concentration of the evaporated fuel (purge concentration) is less than or equal to the predetermined value and the execution condition for the idle operation is satisfied, the engine rotation is stable, so the execution condition for the imbalance detection control is satisfied Judge that it is. When the determination in step 102 is established, in step 104, the above-described imbalance detection control (lean imbalance monitor) is started. On the other hand, if the determination in step 102 is not established, the process waits until it is established.

  Next, in step 106, it is determined whether the alcohol concentration in the fuel is equal to or higher than the upper limit determination value B. If this determination is satisfied, torque reduction control is executed in steps 108-112. More specifically, in step 108, the required values of IVC, IVO and intake valve lift amount are calculated based on the engine operating state, alcohol concentration in the fuel, etc., and in step 110, the required values are calculated based on the calculation result. The control target value of the actuator of the variable valve mechanism 38 is determined. In step 112, the valve opening characteristic of the intake valve 34 is changed by driving the actuator of the variable valve mechanism 38, so that the torque of each cylinder is reduced to the same level as when using gasoline. . On the other hand, if the determination in step 106 is not satisfied, the alcohol concentration in the fuel is not so high that torque reduction control is necessary, and therefore, the process proceeds to step 114 without executing steps 108 to 112.

  Next, in step 114, rotation fluctuation is detected by imbalance detection control, and in step 116, it is determined whether or not the detected rotation fluctuation is smaller than the abnormality determination value A. If this determination is established, it is determined in step 118 that the lean imbalance is not in a normal state, and in step 120, after the opening characteristic of the intake valve 34 is returned to the state before the change, this routine is executed. To end normal control. On the other hand, if the determination in step 116 is not established, it is determined in step 122 that the lean imbalance has occurred, and in step 124, it is determined that the A / F imbalance has occurred due to lighting of the MIL or the like. Notify the driver.

  In the first embodiment, steps 104, 114 and 116 in FIG. 7 show a specific example of the imbalance detecting means in claim 1, and steps 106 to 112 are steps of the torque reducing means in claims 1 and 2. A specific example is shown.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. The present embodiment is characterized in that an intake control valve is used in place of the variable valve mechanism of the first embodiment. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

[Features of Embodiment 2]
In the present embodiment, an intake control valve is used as an actuator for reducing torque. The intake control valve controls the flow of gas sucked into the cylinder by opening and closing at least a part of the intake passage 18, and includes a swirl control valve (SCV) that forms a swirl flow in the cylinder, A tumble control valve (TCV) for forming a tumble flow is included therein. In the present embodiment, TCV will be described as an example of the intake control valve.

  FIG. 8 is a cross-sectional view showing TCV 60 provided in engine intake passage 18 in Embodiment 2 of the present invention. In this figure, the TCV 60 is broken along the length direction of the intake passage 18. FIG. 9 is a cross-sectional view in which the intake passage 18 is broken perpendicularly to the length direction at the position of the TCV 60. As shown in these drawings, the TCV 60 is configured by a valve plate that opens and closes at least a part of the intake passage 18 and is driven by the ECU 50.

  Next, the operation of the TCV 60 will be described. First, when the TCV 60 is driven to the valve closing side, as shown by a solid line in FIG. 8 and FIG. It is formed. The intake air flows into the cylinder through this opening, thereby forming a tumble flow in the cylinder. As a result, in-cylinder turbulence increases due to the tumble flow, and the combustion speed is improved, so that the torque can be increased. On the other hand, when the TCV 60 is driven to the valve opening side, the opening of the intake passage 18 becomes larger as indicated by the dotted line. As a result, the tumble flow in the cylinder becomes weak and the combustion speed decreases, so that the torque can be reduced.

  In the present embodiment, when the alcohol concentration in the fuel is equal to or higher than the upper limit determination value B when the imbalance detection control is executed, the torque is reduced by driving the TCV 60 to the valve opening side. Thereby, it is possible to obtain substantially the same operational effects as those of the first embodiment using a relatively simple structure including a valve plate or the like. Moreover, in this Embodiment, it is good also as a structure which drives SCV to the valve opening side by torque reduction control, weakens the swirl flow in a cylinder, and reduces torque by this.

[Specific Processing for Realizing Embodiment 2]
Next, specific processing for realizing the above-described control will be described with reference to FIG. FIG. 10 is a flowchart of control executed by the ECU in the second embodiment of the present invention. The routine shown in this figure is obtained by replacing steps 108, 110, 112, and 120 of the first embodiment (FIG. 7) with steps 208, 210, 212, and 220, and only these steps will be described.

  First, in step 208, the required opening of the TCV 60 is calculated based on the operating state of the engine, the alcohol concentration in the fuel, etc., and in step 210, the control target value for the actuator of the TCV 60 is determined based on this calculation result. In step 212, the actuator of the TCV 60 is driven to change the valve opening of the TCV 60 and reduce the torque so that the torque of each cylinder is equivalent to that when using gasoline. Further, in step 220, after the valve opening of the TCV 60 is returned to the state before the change, this routine is terminated and the normal control is started.

  In the second embodiment, steps 104, 114 and 116 in FIG. 10 show a specific example of the imbalance detecting means in claim 1, and steps 106, 208 to 212 are torque reducing means in claims 1 and 3. A specific example is shown.

  In the first and second embodiments, the alcohol concentration sensor 46 is used as the alcohol concentration detection means. However, the present invention is not limited to this, and the air-fuel ratio sensor 44 is employed as the alcohol concentration detection means. The alcohol concentration may be estimated based on the output of the fuel ratio sensor 44.

  In each of the above embodiments, the ethanol fuel is described as an example of the alcohol fuel. However, the present invention is not limited to this, and can be widely applied to other alcohol components other than ethanol.

DESCRIPTION OF SYMBOLS 10 Engine 12 Piston 14 Combustion chamber 16 Crankshaft 18 Intake passage 20 Throttle valve 22 Exhaust passage 24 Exhaust manifold 26 Catalyst 28, 30 Fuel injection valve 32 Spark plug 34 Intake valve 36 Exhaust valve 38 Variable valve mechanism 40 Crank angle sensor 42 Air flow Sensor 44 Air-fuel ratio sensor 46 Alcohol concentration sensor (alcohol concentration detection means)
50 ECU
60 Tumble control valve (intake control valve)

Claims (4)

Alcohol concentration detection means for detecting the alcohol concentration in the fuel;
An imbalance detection means for executing imbalance detection control for detecting an A / F imbalance among a plurality of cylinders based on a rotational fluctuation of the engine speed;
Torque reduction means for reducing the torque by an amount corresponding to an increase in torque of each cylinder due to an alcohol component in the fuel when the alcohol concentration in the fuel is equal to or higher than a predetermined value when the imbalance detection control is performed;
A control device for an internal combustion engine, comprising: Equipped with a variable valve mechanism that can variably set the valve opening characteristics of the intake valve,
2. The control device for an internal combustion engine according to claim 1, wherein the torque reduction unit is configured to reduce a torque by changing a valve opening characteristic of the intake valve by the variable valve mechanism. An intake control valve for controlling the flow of gas sucked into the cylinder by opening and closing at least a part of the intake passage;
The control device for an internal combustion engine according to claim 1, wherein the torque reduction means is configured to reduce the torque by driving the intake control valve to a valve opening side.   4. The control device for an internal combustion engine according to claim 1, wherein the imbalance detection unit is configured to detect a lean imbalance in which an air-fuel ratio of only one cylinder among a plurality of cylinders shifts to a lean side. 5.

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