JP5644342B2 - Control device for multi-cylinder internal combustion engine - Google Patents

Description

  The present invention relates to a control device for a multi-cylinder internal combustion engine.

  Conventionally, the air-fuel ratio of the gas (mixed exhaust gas) passing through the collective exhaust passage is determined based on the output value of the air-fuel ratio sensor disposed in the collective exhaust passage formed by collecting the exhaust passages extending from the plurality of cylinders. Air-fuel ratio control apparatuses that perform feedback control are widely known. The mixed exhaust gas is an exhaust gas obtained by mixing exhaust gases discharged from each cylinder. More specifically, in this air-fuel ratio control device, the air-fuel ratio feedback amount common to the plurality of cylinders is based on the output value of the air-fuel ratio sensor so that the air-fuel ratio of the mixed exhaust gas matches the stoichiometric air-fuel ratio. Calculated. The air-fuel ratio of the mixed exhaust gas is feedback-controlled by adjusting the amount of fuel injected to each of the plurality of cylinders based on the air-fuel ratio feedback amount.

  In recent years, in response to the stricter regulations on the amount of emission of hazardous substances (emission amount) emitted from vehicles equipped with an internal combustion engine due to the internal combustion engine, control for reducing the emission amount has also been implemented. Various proposals have been made. Specifically, purge control, EGR control, AI increase control, cold VVT control, catalyst warm-up delay control, and the like can be given.

  By the way, in a multi-cylinder internal combustion engine, a plurality of cylinders having an EGR gas amount recirculated to an intake system by an EGR mechanism, a variation among cylinders of an injection amount from a fuel injection valve, a variation between cylinders of a maximum lift amount of an intake valve, Variations in distribution to the device may occur. When the characteristic variation between the cylinders occurs, the air-fuel ratio variation (air-fuel ratio imbalance among cylinders, air-fuel ratio variation among cylinders, non-uniform air-fuel ratio among cylinders) may occur between the cylinders. Therefore, conventionally, control for reducing the above-described emission amount in accordance with the variation in the air-fuel ratio has been performed.

  For example, in Patent Document 1 below, a first air-fuel ratio sensor and a second air-fuel ratio sensor are provided on the upstream and downstream sides of the catalyst element, respectively. The main air-fuel ratio control is executed based on the fuel-fuel ratio sensor output, and the auxiliary air-fuel ratio control is executed based on the second air-fuel ratio sensor output. It is described that it is determined that a variation abnormality in the air-fuel ratio between cylinders has occurred when the determination value is reached. Further, for example, in Patent Document 2 below, it is determined that the variation in the air-fuel ratio between the cylinders has occurred by comparing a measured value of the trajectory length by the air-fuel ratio sensor with a reference value of a preset trajectory length. Is described.

JP 2009-74388 A US Pat. No. 7,152,594

  In order to appropriately execute the control for reducing the various emission amounts described above, it is important to accurately detect the variation in the air-fuel ratio (air-fuel ratio imbalance among cylinders). However, in a situation where EGR control is performed as one of the controls for reducing the emission amount, the detection accuracy of the air-fuel ratio imbalance among cylinders may be lowered due to the influence of the introduced EGR gas. In this case, if the introduction of EGR gas is simply stopped, the detection accuracy of the air-fuel ratio imbalance among cylinders can be improved, while the effect of reducing the emission amount may be impaired.

  The present invention has been made to address the above-described problems, and an object of the present invention is to improve the detection accuracy of the air-fuel ratio imbalance among cylinders while ensuring the effect of reducing the emission amount. It is to provide a control device.

  A control device (this control device) for a multi-cylinder internal combustion engine according to the present invention for achieving such an object is applied to a multi-cylinder internal combustion engine having a plurality of cylinders. The present control device includes an air-fuel ratio sensor, a plurality of fuel injection valves, a feedback amount calculation means, a feedback control means, and an exhaust gas recirculation control execution means.

  The air-fuel ratio sensor is disposed in the collective exhaust passage and generates an output value corresponding to the air-fuel ratio of the mixed exhaust gas.

  The plurality of fuel injection valves are disposed corresponding to each of the plurality of cylinders. The plurality of fuel injection valves respectively inject fuel contained in the air-fuel mixture supplied to the combustion chambers of the plurality of cylinders. That is, one or more fuel injection valves are provided for each cylinder. Each fuel injection valve injects fuel into the cylinder corresponding to the fuel injection valve.

  The feedback amount calculating means calculates a common air-fuel ratio feedback amount for the plurality of cylinders. The air-fuel ratio feedback amount is calculated based on the output value of the air-fuel ratio sensor so that the air-fuel ratio of the mixed exhaust gas matches the stoichiometric air-fuel ratio.

  The feedback control means adjusts the amount of fuel injected from each of the plurality of fuel injection valves based on the air-fuel ratio feedback amount. Thereby, the air-fuel ratio of the mixed exhaust gas is feedback controlled.

  The exhaust gas recirculation control execution means executes control for guiding the exhaust gas in the exhaust passage to the intake passage of the internal combustion engine. As a result, the ratio of the inert gas among the gases in the combustion chambers of the plurality of cylinders is increased to lower the maximum combustion temperature to suppress the generation of nitrogen oxides (NOx) due to combustion, and the exhaust gas is discharged from the combustion chambers. The amount of nitrogen oxides in the exhaust gas, that is, the amount of emissions is reduced.

  One of the features of the present control device is that it includes an imbalance index value acquisition means. The imbalance index value acquisition unit acquires an imbalance index value. The imbalance index value is a degree of difference between “a plurality of cylinder air-fuel ratios” which is “the air-fuel ratio of the air-fuel mixture supplied to the respective combustion chambers of the plurality of cylinders” (difference, degree of imbalance). ) Is a value that increases or decreases as the value increases (monotonically increases or decreases monotonically), and is a value obtained based on the output value of the air-fuel ratio sensor. Hereinafter, the degree of difference (difference, degree of imbalance) between “a plurality of cylinder-by-cylinder air-fuel ratios” is also referred to as “degree of air-fuel ratio imbalance among cylinders”.

  The imbalance index value includes the locus length of the output value of the air-fuel ratio sensor, the locus length of the air-fuel ratio (detected air-fuel ratio) represented by the output value of the air-fuel ratio sensor, and the like. On the other hand, it is preferable that the imbalance index value is configured to acquire a value based on a time differential value of the detected air-fuel ratio. The time differential value of the detected air-fuel ratio is less affected by the engine speed than the locus length of the detected air-fuel ratio. Therefore, according to the above configuration, it is possible to obtain an imbalance index value having characteristics that hardly change depending on the rotational speed of the engine. As a result, the degree of air-fuel ratio imbalance among cylinders can be stably acquired regardless of the engine speed.

  Another feature of the present control device is that the exhaust gas recirculation control execution means has a predetermined value when the degree of difference represented by the imbalance index value is large compared to when the degree of difference is small. The time difference from when the condition is satisfied to when the exhaust gas in the exhaust passage is guided to the intake passage is set large. Examples of the predetermined condition include a condition in which fuel cut control is terminated and fuel injection by the plurality of fuel injection valves is restored, a condition in which the engine rotational speed exceeds a preset threshold rotational speed, and the like.

  Normally, after the fuel cut control is completed or when the engine speed is equal to or lower than a preset threshold speed, control for guiding the exhaust gas in the exhaust passage to the intake passage of the internal combustion engine is stopped until a preset time difference elapses. Is done. On the other hand, according to the above configuration, for example, the additional time is set so that the preset time difference becomes large when the degree of air-fuel ratio imbalance among cylinders is large. As a result, when the degree of air-fuel ratio imbalance among cylinders acquired at the time of execution of the control for guiding the exhaust gas in the exhaust passage to the intake passage of the internal combustion engine is large, the exhaust gas in the exhaust passage that is normally executed is converted to the internal combustion engine. The duration (time difference) of the control stop state leading to the intake passage can be set slightly longer.

  Another feature of the present control device is that the imbalance index value acquisition means acquires the imbalance index value within the large time difference. According to this, the degree of air-fuel ratio imbalance among cylinders in the state where the control for guiding the exhaust gas in the exhaust passage to the intake passage of the internal combustion engine is stopped, that is, the influence of the exhaust gas being recirculated is eliminated is acquired. can do. Therefore, it is possible to improve the detection accuracy of the air-fuel ratio imbalance among cylinders while ensuring the effect of reducing the emission amount.

  The present control device may be configured such that the exhaust gas recirculation control execution means sets the time difference larger as the degree of the difference represented by the imbalance index value is larger. According to this, the duration (time difference) of the stop state of the control for guiding the exhaust gas in the exhaust passage to the intake passage of the internal combustion engine is set more appropriately according to the degree of the air-fuel ratio imbalance among cylinders, and as a result Thus, the detection accuracy of the air-fuel ratio imbalance among cylinders can be further improved while ensuring the effect of reducing the emission amount.

1 is a diagram showing a schematic configuration of a multi-cylinder internal combustion engine to which a control device according to an embodiment of the present invention is applied. It is a figure for demonstrating the inside of the intake passage near SCV shown in FIG. It is a figure for demonstrating the purge control mechanism with which the internal combustion engine shown in FIG. 1 is provided. It is a figure for demonstrating the AI increase control mechanism with which the internal combustion engine shown in FIG. 1 is provided. FIG. 2 is a view showing a state in which a catalyst, an upstream air-fuel ratio sensor, and a downstream air-fuel ratio sensor shown in FIG. 1 are arranged in a collective exhaust passage. 2 is a graph showing the relationship between the output of the upstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. 3 is a graph showing the relationship between the output of the downstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. FIG. 5 is a diagram showing an example of the air-fuel ratio of each cylinder when an air-fuel ratio imbalance among cylinders occurs and the air-fuel ratio of the mixed exhaust gas matches the stoichiometric air-fuel ratio. 5 is a time chart showing the behavior of each value related to an imbalance index value when an air-fuel ratio imbalance among cylinders occurs and when it does not occur. It is the flowchart which showed the routine which CPU shown in FIG. 1 performs. It is a graph which shows the relationship between the imbalance ratio (degree of imbalance between air-fuel ratio cylinders) and delay time (time difference).

  Hereinafter, a control apparatus for a multi-cylinder internal combustion engine according to an embodiment of the present invention (hereinafter also simply referred to as “this apparatus”) will be described with reference to the drawings.

(Constitution)
FIG. 1 shows a schematic configuration of a system in which the present apparatus is applied to a 4-cycle, spark ignition type, multi-cylinder (in-line 4-cylinder) internal combustion engine 10. FIG. 1 shows only a cross section of a specific cylinder, but the other cylinders have the same configuration.

  The internal combustion engine 10 includes a cylinder block 20 including a cylinder block, a cylinder block lower case, an oil pan, and the like, a cylinder head 30 fixed on the cylinder block 20, and a gasoline mixture in the cylinder block 20. An intake system 40 for supplying and an exhaust system 50 for releasing exhaust gas from the cylinder block unit 20 to the outside are included.

  The cylinder block unit 20 includes a cylinder 21, a piston 22, a connecting rod 23 and a crankshaft 24. The piston 22 reciprocates in the cylinder 21, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 through the connecting rod 23, whereby the crankshaft 24 rotates. The wall surface of the cylinder 21 and the upper surface of the piston 22 form a combustion chamber 25 together with the temporary surface of the cylinder head portion 30.

  The cylinder head portion 30 includes an intake port 31 communicating with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake camshaft that drives the intake valve 32, and continuously changes the phase angle of the intake camshaft. A variable intake timing control device 33, an actuator 33 a of the variable intake timing control device 33, an exhaust port 34 communicating with the combustion chamber 25, an exhaust valve 35 that opens and closes the exhaust port 34, and an exhaust camshaft that drives the exhaust valve 35. A variable exhaust timing control device 36 that continuously changes the phase angle of the exhaust camshaft, an actuator 36a of the variable exhaust timing control device 36, a spark plug 37, and an igniter 38 that includes an ignition coil that generates a high voltage applied to the spark plug 37. And fuel intake A fuel injection valve for injecting the over preparative 31 (fuel injection means, fuel supply means) 39. As described above, the internal combustion engine 10 includes the “variable valve (VVT) system” that changes the opening / closing timing of the intake valve 32 and the exhaust valve 35.

  One fuel injection valve 39 is provided for each fuel chamber 25. The fuel injection valve 39 is provided in the intake port 31. Thus, each of the plurality of cylinders includes the fuel injection valve 39 that supplies fuel independently of the other cylinders.

  The intake system 40 includes an intake manifold 41, an intake pipe 42, a throttle valve 43, and a swirl control valve (SCV) 44. The intake manifold 41 includes a plurality of branch portions 41a and a surge tank 41b. One end of each of the plurality of branch portions 41 a is connected to each of the plurality of intake ports 31. The other ends of the plurality of branch portions 41a are connected to the surge tank 41b. One end of the intake pipe 42 is connected to the surge tank 41b. The intake port 31, the intake manifold 41, and the intake pipe 42 constitute an intake passage.

  The throttle valve 43 is provided in the intake pipe 42 so that the opening cross-sectional area (throttle valve opening) of the intake passage is variable. The throttle valve 43 is rotationally driven in the intake pipe 42 by a throttle valve actuator 43a (a part of the throttle valve driving means).

  The SCV 44 is in each branch portion 41a and is rotationally driven by the SCV actuator 44a. As shown in FIG. 2, each intake port 31 is actually composed of intake ports 31a and 31b. The intake port 31a is formed in a helical shape so as to generate a swirl (swirl flow) in the combustion chamber 25 and constitutes a so-called swirl port, and the intake port 31b constitutes a so-called straight port.

  Each branch portion 41a is formed with a partition wall 41aa extending along the longitudinal direction of the intake manifold 41, whereby each branch 41a communicates with the first intake manifold 41ac communicating with the intake port 31a and the intake port 31b. The second intake manifold 41ad is partitioned. The SCV 44 is rotatably supported in the second intake manifold 41ad, and the opening cross-sectional area (SCV opening) of the second intake manifold 44ad can be changed.

  A communication passage 41ab that communicates the first and second intake manifolds 41ac and 41ad is formed at an appropriate location of the partition wall 41aa. The fuel injection valve 39 is fixed at a position near the communication path 41ab, and injects fuel toward the intake ports 31a and 31b. Thus, the internal combustion engine 10 includes an “intake flow adjustment system” that adjusts the intake flow by adjusting the opening of the SCV 44.

  As shown in FIGS. 1 and 3, the internal combustion engine 10 includes a fuel tank 45 that stores liquid gasoline fuel, and a canister (charcoal canister) that can store fuel gas generated by evaporation of fuel stored in the fuel tank 45. 46, a vapor collection pipe 47 for guiding the fuel gas from the fuel tank 45 to the canister 46, a purge flow path pipe 48 and a purge flow path pipe 48 for guiding the fuel gas separated from the canister 46 to the surge tank 41b A purge control valve 49 is provided. The purge control valve 49 changes the opening cross-sectional area of the purge flow path pipe 48.

  The canister 46 discharges the fuel gas occluded in the adsorbent 46a accommodated in the housing to the surge tank 41b through the purge passage pipe 48 during the period when the purge control valve 49 is open. . In addition, an atmospheric port 46b is formed in the casing of the canister 46, and fuel gas leaked (separated) from the adsorbent 46a can be opened to the atmosphere through the atmospheric port 46b. As described above, the internal combustion engine 10 includes a “purge system” that guides the fuel gas generated by the evaporation of the fuel stored in the fuel tank 45 to the intake passage.

  Referring again to FIG. 1, the exhaust system 50 includes an exhaust manifold 51 including a plurality of branches connected at one end to the exhaust port 34 of each cylinder, and the other ends of the branches of the exhaust manifold 51. An exhaust pipe 52 connected to a collecting portion (exhaust collecting portion of the exhaust manifold 51) where all branches are gathered, an upstream catalyst (three-way catalyst) 53 disposed in the exhaust pipe 52, and an upstream A downstream catalyst (three-way catalyst) (not shown) disposed in the exhaust pipe 52 downstream of the side catalyst 53 is provided. The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage. Thus, the upstream catalyst 53 is disposed in a collective exhaust passage formed by collecting exhaust passages extending from a plurality of cylinders.

  Further, the internal combustion engine 10 includes an exhaust gas recirculation pipe 54 that constitutes an external EGR passage, and an EGR valve 55. One end of the exhaust gas recirculation pipe 54 is connected to a collecting portion of the exhaust manifold 51. The other end of the exhaust gas recirculation pipe 54 is connected to the surge tank 41b. The EGR valve 55 is disposed in the exhaust gas recirculation pipe 54. The EGR valve 55 changes the opening cross-sectional area of the exhaust gas recirculation pipe 54. As described above, the internal combustion engine 10 includes the “exhaust gas recirculation (EGR) system”.

  As shown in FIGS. 1 and 4, the internal combustion engine 10 includes a secondary air supply device 60. The secondary air supply device 60 includes a secondary air supply passage 61 that connects an intake passage upstream of the throttle valve 53 and a collective exhaust passage upstream of the catalyst 53, and an air pump 62 interposed in the secondary air supply passage 61. An air switching valve (ASV) 63 interposed in the secondary air supply passage 61 downstream of the air pump 62, and a reed valve 64 (from the upstream) interposed in the secondary air supply passage 61 downstream of the ASV 63. And a check valve that allows only downstream flow). The secondary air supply device 60 also includes a negative pressure introduction passage 65 for introducing the negative pressure in the surge tank 41 b to the ASV 63, and an electromagnetic valve 66 interposed in the negative pressure introduction passage 65.

  The ASV 63 is opened when the electromagnetic valve 66 is open and negative pressure is introduced into the surge tank 41b, and is closed when the electromagnetic valve 66 is closed and no negative pressure is introduced. It becomes. That is, in the secondary air supply device 60, air is introduced into the collective exhaust passage upstream of the catalyst 53 by operating the air pump 62 and opening the electromagnetic valve 66. As described above, the internal combustion engine 10 includes the “secondary air supply system”.

  On the other hand, the internal combustion engine 10 includes an air flow meter 71, a throttle position sensor 72, a water temperature sensor 73, a crank position sensor 74, an intake cam position sensor 75, an exhaust cam position sensor 76, an upstream air-fuel ratio sensor 77, as shown in FIG. A downstream air-fuel ratio sensor 78, an accelerator opening sensor 79, an SCV opening sensor 81, and a pressure sensor 82 (see FIG. 4).

  The air flow meter 71 detects a mass flow rate (intake air flow rate) Ga of intake air flowing through the intake pipe 42. The throttle position sensor 72 detects the opening degree of the throttle valve 43 (throttle valve opening degree). The water temperature sensor 73 detects the temperature of the cooling water of the internal combustion engine 10. The crank position sensor 74 detects the phase (change) of the rotation angle of the crankshaft 24. This detection result represents the engine speed NE.

  The intake cam position sensor 75 detects the phase (change) of the rotation angle of the intake camshaft. Based on the signals from the crank position sensor 74 and the intake cam position sensor 75, the absolute crank angle CA based on the compression top dead center of the reference cylinder (for example, the first cylinder) is acquired. The absolute crank angle CA is set to “0 ° crank angle” at the compression top dead center of the reference cylinder, and increases to “720 ° crank angle” according to the rotation angle of the crank angle. Set to the crank angle. The exhaust cam position sensor 76 detects the phase (change) of the rotation angle of the exhaust cam shaft.

  As shown in FIG. 5, the upstream air-fuel ratio sensor 77 (air-fuel ratio sensor in the present invention) is upstream of the upstream catalyst 53 in the collective exhaust passage downstream of the collective portion HK (exhaust collective portion) of the exhaust manifold 51. It is arranged. The upstream air-fuel ratio sensor 77 is disclosed in, for example, “Limit current type equipped with a diffusion resistance layer” disclosed in JP-A-11-72473, JP-A-2000-65782, JP-A-2004-69547, and the like. "Wide area air-fuel ratio sensor".

  Hereinafter, the exhaust gas passing through the collective exhaust passage is referred to as “mixed exhaust gas”. The mixed exhaust gas is an exhaust gas obtained by mixing exhaust gases discharged from each cylinder. The upstream air-fuel ratio sensor 77 generates an output value Vabyfs (V) corresponding to the air-fuel ratio of the mixed exhaust gas flowing into the upstream catalyst 53. This output value Vabyfs is converted into an air-fuel ratio (hereinafter referred to as “detected air-fuel ratio”) abyfs represented by the output value Vabyfs using the air-fuel ratio conversion table (map) Mapabyfs shown in FIG. .

  Referring again to FIGS. 1 and 5, the downstream air-fuel ratio sensor 78 is disposed downstream of the upstream catalyst 53 in the collective exhaust passage and upstream of the downstream catalyst. The downstream air-fuel ratio sensor 78 is a known electromotive force type oxygen concentration sensor (a well-known concentration cell type oxygen concentration sensor using stabilized zirconia). The downstream air-fuel ratio sensor 78 generates an output value Voxs (V) corresponding to the air-fuel ratio of the mixed exhaust gas flowing out from the upstream catalyst 53 (and therefore the temporal average value of the air-fuel ratio of the air-fuel mixture supplied to the engine). To do.

  As shown in FIG. 7, the output value Voxs becomes the maximum output value max (for example, about 0.9 V) when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and becomes the minimum when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. The output value is min (for example, about 0.1 V), and when the air-fuel ratio is the stoichiometric air-fuel ratio, the voltage Vst is approximately halfway between the maximum output value max and the minimum output value min (for example, about 0.5 V). Further, this output value Voxs suddenly changes from the maximum output value max to the minimum output value min when the air-fuel ratio changes from an air-fuel ratio richer than the stoichiometric air-fuel ratio to a lean air-fuel ratio. When the air-fuel ratio leaner than the fuel ratio changes to a rich air-fuel ratio, it suddenly changes from the minimum output value min to the maximum output value max.

  Again, referring to FIG. 1, accelerator opening sensor 79 detects an operation amount (accelerator pedal operation amount) of accelerator pedal AP operated by the driver. The SCV opening sensor 81 detects the opening (SCV opening) of the SCV 44. The pressure sensor 82 (see FIG. 4) detects the pressure in the secondary air supply passage 61 upstream of the ASV 63.

  As shown in FIG. 1, the electric control device 90 is connected to each other by a bus “a CPU 91, a program executed by the CPU 91, various tables (maps, functions), constants, etc. This is a known microcomputer comprising a RAM 93 for temporarily storing data, a backup RAM 94, and various interfaces 95 including an AD converter.

  The interface 95 is connected to the sensors 71 to 82 and supplies signals from these sensors to the CPU 91. Further, the interface 95 includes an actuator 33a, an actuator 36a, an igniter 38 for each cylinder, a fuel injection valve 39 provided for each cylinder, a throttle valve actuator 43a, an SCV actuator 44a, and a purge control valve in accordance with instructions from the CPU 91. 49, a drive signal (instruction signal) is sent to the EGR valve 55, the electromagnetic valve 66, and the like.

(Air-fuel ratio feedback control)
Next, the outline of the air-fuel ratio feedback control by this apparatus will be described. This apparatus performs feedback control based on the output value Vabyfs of the upstream air-fuel ratio sensor 77 and the output value Voxs of the downstream air-fuel ratio sensor 78 so that the air-fuel ratio of the mixed exhaust gas matches the stoichiometric air-fuel ratio.

  Examples of this feedback control include the following. That is, the feedback correction value (sub feedback correction amount) is obtained by performing PID processing on the deviation between the output value Voxs of the downstream air-fuel ratio sensor 78 and the target value Vst corresponding to the theoretical air-fuel ratio. A value obtained by correcting the output value Vabyfs of the upstream air-fuel ratio sensor 77 by this sub-feedback correction amount is applied to the air-fuel ratio conversion table Mapabyfs shown in FIG. 6 to obtain the apparent air-fuel ratio. A PID process is performed on the difference between the apparent air-fuel ratio and the stoichiometric air-fuel ratio to obtain an air-fuel ratio feedback amount. This air-fuel ratio feedback amount is a value common to all cylinders.

  With this air-fuel ratio feedback amount, an amount of fuel obtained by correcting the “basic fuel injection amount obtained based on the engine speed NE, the intake air flow rate Ga, and the theoretical air-fuel ratio” is the fuel injection valve 39 of each cylinder. Each is injected from. In this manner, the air-fuel ratio of the mixed exhaust gas is feedback-controlled by adjusting the amount of fuel injected from each fuel injection valve 39 based on the air-fuel ratio feedback amount common to all cylinders.

(Emission reduction control)
Next, an outline of the emission amount reduction control by this apparatus will be described. This apparatus executes purge control, EGR control, AI increase control, cold VVT control, catalyst warm-up delay angle control, and SCV control as emission amount reduction control. Hereinafter, each control will be briefly described in order.

<Purge control>
The purge control is performed using the above-described “purge system” (see FIG. 3). In the purge control, by opening the purge control valve 49 under a predetermined condition, the fuel gas generated by the evaporation of the fuel stored in the fuel tank 45 is guided to the intake passage, and from each fuel injection valve 39 In this control, the amount of injected fuel is reduced (from the amount adjusted by the air-fuel ratio feedback amount described above).

  The reason why the fuel gas is guided to the intake passage is to prevent the fuel gas (that is, unburned matter, HC, etc.) from leaking outside from the canister 46 through the atmospheric port 46b. The fuel injection amount is reduced by the amount of fuel gas introduced into the intake passage. The amount of fuel gas introduced into the intake passage can be estimated using one of well-known techniques. Thus, according to the purge control, the amount of unburned matter (such as HC) discharged from the canister 46 can be reduced while maintaining the air-fuel ratio at the theoretical air-fuel ratio (near).

<EGR control>
The EGR control is performed using the above-described “EGR system”. The EGR control is control that guides the exhaust gas in the exhaust passage to the intake passage by opening the EGR valve 55 under a predetermined condition. This operation is also called external EGR.

  The exhaust gas (EGR gas) in the exhaust passage is guided to the intake passage by increasing the proportion of inert gas in the gas in the combustion chamber 25 and lowering the maximum combustion temperature, thereby reducing the nitrogen oxide (NOx) due to combustion. This is to suppress generation. Thus, according to EGR control, the amount of nitrogen oxides in the exhaust gas discharged from the combustion chamber 25 can be reduced.

<AI increase control>
The AI increase control is performed using the above-described “secondary air supply system” (see FIG. 4). In the AI increase control, the electromagnetic valve 66 is opened (ie, the ASV 63 is opened) under a predetermined condition, and the air pump 62 is operated to allow air to flow into the upstream collective exhaust passage of the upstream catalyst 53. This is a control that is introduced and increases the amount of fuel injected from each fuel injection valve 39 (from the amount adjusted by the air-fuel ratio feedback amount described above).

  The reason for introducing air to the upstream exhaust passage of the upstream catalyst 53 is to promote the warm-up of the upstream catalyst 53 by burning unburned matter (HC or the like) in the exhaust gas at this portion. . The fuel injection amount is increased by an amount necessary for burning the air guided to the upstream side of the upstream catalyst 53 (for example, a value obtained by dividing the amount of guided air by the stoichiometric air-fuel ratio). The amount of air introduced can be estimated using one of the well-known techniques. As described above, according to the AI increase control, when the temperature of the catalyst such as immediately after the cold start of the internal combustion engine 10 is low, the catalyst is activated early and unburned matter (HC) in the exhaust gas discharged from the catalyst. , CO, etc.) and nitrogen oxides (NOx) can be reduced.

<Cold VVT control>
Cold VVT control is performed using the above-described “VVT system”. In the cold VVT control, the opening / closing timing of the intake valve 32 and / or the opening / closing timing of the exhaust valve 35 is adjusted (compared to the normal non-cold VVT control) under predetermined conditions. The amount of burned gas that is blown back to the intake passage through the periphery of the intake valve 32 (combusted gas blowback amount) is increased (compared to the normal non-cold VVT control), and each fuel injection valve 39 Is a control for reducing the amount of fuel injected from the fuel (from the amount adjusted by the air-fuel ratio feedback amount described above). The operation of increasing the burned gas blowback amount is also referred to as internal EGR. The opening / closing timing of the intake valve 32 and / or the opening / closing timing of the exhaust valve 35 during non-cold VVT control is determined based on the operating state of the internal combustion engine 10 (based on the output results of the various sensors described above). The

  The reason why the burned gas in the combustion chamber is guided to the intake passage is to promote warming of the intake passage and promote atomization of the liquid fuel adhering to the intake passage. The fuel injection amount is decreased by the increase of the atomized fuel gas. The increase in atomized fuel gas can be estimated using one of the well-known techniques. Thus, according to the cold VVT control, when the temperature of the intake passage such as immediately after the cold start of the internal combustion engine 10 is low, atomization of the injected fuel is promoted, and the air-fuel ratio is set to the stoichiometric air-fuel ratio (nearby ), The amount of unburned matter (HC, CO, etc.) in the exhaust gas discharged from the combustion chamber 25 can be reduced.

<Catalyst warm-up delay angle control>
The catalyst warm-up delay angle control is a control for retarding the ignition timing of the spark plug 37 (compared to the normal non-catalyst warm-up delay angle control) under a predetermined condition. The ignition timing at the time of non-catalyst warm-up delay angle control is determined based on the operating state of the internal combustion engine 10 (based on the output results of the various sensors described above).

  The reason for retarding the ignition timing is to promote warm-up of the upstream catalyst 53 by delaying the combustion timing of the fuel and increasing the temperature of the exhaust gas flowing into the catalyst. As described above, according to the catalyst warm-up delay angle control, when the temperature of the catalyst such as immediately after the cold start of the internal combustion engine 10 is low, the catalyst is activated early and unburned in the exhaust gas discharged from the catalyst. The amount of substances (HC, CO, etc.) and nitrogen oxides (NOx) can be reduced.

<SCV control>
The SCV control is performed using the “intake flow adjustment system” described above. The SCV control is a control for opening and closing the SCV 44 in accordance with the operating state of the internal combustion engine 10. The reason why the SCV 44 is closed is to promote atomization of the injected fuel by increasing the intake flow velocity and increasing the swirl flow velocity. The reason why the SCV 44 is in the open state is to reduce the intake resistance and to suck more air into the combustion chamber 25. Thus, according to the SCV control, when the fuel in the idling state immediately after the cold start of the internal combustion engine 10 is difficult to atomize and the swirl flow rate is small, the SCV 44 is closed to close the injected fuel. Atomization can be promoted, and the amount of unburned matter (HC, CO, etc.) in the exhaust gas discharged from the combustion chamber 25 can be reduced. At other times, by opening the SCV 44, more air can be sucked into the combustion chamber 25 and the maximum output of the internal combustion engine 10 can be improved.

(Air-fuel ratio imbalance between cylinders)
Next, a description will be given of the occurrence of an air-fuel ratio imbalance among cylinders. “Air-fuel ratio imbalance among cylinders” refers to variations in air-fuel ratio among cylinders. The air-fuel ratio imbalance among cylinders is, for example, variation between cylinders in the actual injection amount from the fuel injection valve 39, variation between cylinders in the actual maximum lift amount of the intake valve 32, and recirculation to the intake passage by the EGR system. It may be generated due to variation in distribution of the amount of exhaust gas (EGR gas) to each cylinder.

  As shown in FIG. 8, when “air-fuel ratio imbalance among cylinders” occurs, the cylinder in which the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio even if the air-fuel ratio of the mixed exhaust gas matches the stoichiometric air-fuel ratio. (Rich cylinder) and a cylinder (lean cylinder) in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio always occur. FIG. 8 shows a case where the fourth cylinder is a “rich mechanism” and the first to third cylinders are “lean cylinders” as an example.

  In the air-fuel ratio imbalance among cylinders shown in FIG. 8, for example, the fuel injection valves 39 of the first to third cylinders are in a normal state of “injecting an amount of fuel equal to the instructed fuel injection amount”. This may occur when only the fuel injection valve 39 of the cylinder is in an abnormal state of “injecting an injection amount that is larger than the instructed fuel injection amount”. That is, in this case, only the air-fuel ratio of the fourth cylinder greatly changes to the rich side. Thereby, the air-fuel ratio of the mixed exhaust gas passing through the collective exhaust passage (the average of the air-fuel ratios of all cylinders) becomes richer than the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio of the fourth cylinder is changed to the lean side so as to approach the stoichiometric air-fuel ratio by the above-described “air-fuel ratio feedback amount” common to all the cylinders, and at the same time, the air-fuel ratio of the other three cylinders The fuel ratio is changed to the lean side so as to be away from the stoichiometric air-fuel ratio. As a result, the air-fuel ratio of the mixed exhaust gas that passes through the collective exhaust passage is substantially matched with the stoichiometric air-fuel ratio.

  However, the air-fuel ratio of the fourth cylinder is still kept richer than the stoichiometric air-fuel ratio, and the air-fuel ratios of the other three cylinders are kept leaner than the stoichiometric air-fuel ratio. From the above, the fourth cylinder is a “rich cylinder” and the first to third cylinders are “lean cylinders”.

  Thus, when the air-fuel ratio imbalance among cylinders occurs, the fuel state of the air-fuel mixture in each cylinder becomes a combustion state different from complete combustion. As a result, the amount of emissions discharged from each cylinder (the amount of unburned matter and the amount of nitrogen oxides) increases. For this reason, even if the air-fuel ratio (average of the air-fuel ratios of all cylinders) of the mixed exhaust gas that passes through the collective exhaust passage is the stoichiometric air-fuel ratio, the three-way catalyst cannot fully purify the increased emission, resulting in the exhaust gas as a result. Increasing the amount of emissions included.

(Detection of air-fuel ratio imbalance between cylinders)
Next, detection of occurrence of an air-fuel ratio imbalance among cylinders will be described. In order to detect the air-fuel ratio imbalance among cylinders, it is necessary to acquire an index value that represents the difference (degree of imbalance, degree of difference) between the air-fuel ratios for each cylinder. The air-fuel ratio for each cylinder refers to the air-fuel ratio of the air-fuel mixture supplied to each cylinder. Hereinafter, this index value is referred to as an “imbalance index value”. Further, for convenience of explanation, “a period during which the crank angle required for completing each one combustion process in all cylinders (all cylinders exhausting exhaust gas reaching the upstream air-fuel ratio sensor 77)” is expressed. , Called “unit combustion cycle period”. In the case of a 4-cylinder, 4-cycle engine, the unit combustion cycle period is 720 ° crank angle.

  FIG. 9B is obtained by applying the detected air-fuel ratio abyfs (the output value Vabyfs of the upstream air-fuel ratio sensor 77 to the air-fuel ratio conversion table Mapabyfs shown in FIG. 6 in the case of a 4-cylinder, 4-cycle engine. An example of the transition of the air / fuel ratio). The exhaust gas from each cylinder reaches the upstream air-fuel ratio sensor 77 in the ignition order (hence, the exhaust order). When the air-fuel ratio imbalance among cylinders does not occur, the cylinder-by-cylinder air-fuel ratios of all the cylinders are substantially the same. Therefore, the detected air-fuel ratio abyfs when the air-fuel ratio imbalance among cylinders is not generated changes as indicated by the broken line C1 in FIG. 9B, for example. That is, when the air-fuel ratio imbalance among cylinders does not occur, the waveform of the detected air-fuel ratio abyfs is substantially flat.

  On the other hand, when the air-fuel ratio imbalance among cylinders occurs, a “rich cylinder” and a “lean cylinder” always exist, so that a difference occurs between the air-fuel ratios of all cylinders. Therefore, the detected air-fuel ratio abyfs when the air-fuel ratio imbalance among cylinders is generated is equal to, for example, a 720 ° crank angle (that is, a unit combustion cycle period) as shown by a solid line C2 in FIG. 9B. It varies greatly as a cycle.

  As understood from the above, when the air-fuel ratio imbalance among cylinders occurs, the detected air-fuel ratio abyfs greatly fluctuates with the unit combustion cycle period as one cycle. Further, the amplitude of the detected air-fuel ratio abyfs increases as the difference between the cylinder-by-cylinder air-fuel ratios increases. For example, when the detected air-fuel ratio abyfs has a larger difference between the cylinder-by-cylinder air-fuel ratios than when the detected air-fuel ratio abyfs changes as indicated by the solid line C2 in FIG. 9B, the detected air-fuel ratio abyfs is represented by the one-dot chain line C2a in FIG. Transition as shown.

  Therefore, the imbalance index value may be a value that reflects such a fluctuation state of the detected air-fuel ratio abyfs. That is, the imbalance index value is a value that increases or decreases as the difference between the cylinder-by-cylinder air-fuel ratios increases, and is based on the output value Vabyfs of the upstream air-fuel ratio sensor 77 (accordingly, the detected air-fuel ratio abyfs). Any value can be used. As an example of the imbalance index value, the locus length of the output value Vabyfs (detected air-fuel ratio abyfs) of the upstream air-fuel ratio sensor 77 can be considered.

  Further, as the imbalance index value, for example, a value based on “amount of change in the detected air-fuel ratio abyfs per unit time” can be used. “The amount of change in the detected air-fuel ratio abyfs per unit time” can be said to be the time differential value d (abyfs) / dt of the detected air-fuel ratio abyfs when the unit time is an extremely short time of about 4 milliseconds, for example. it can. Therefore, “the amount of change in the detected air-fuel ratio abyfs per unit time” is also referred to as “the detected air-fuel ratio change rate ΔAF”.

  As shown by the broken line C3 in FIG. 9C, when the air-fuel ratio imbalance among cylinders does not occur, the absolute value of the detected air-fuel ratio change rate ΔAF is small, whereas it is shown by the solid line C4 in FIG. As described above, when the air-fuel ratio imbalance among cylinders occurs, the absolute value of the detected air-fuel ratio change rate ΔAF increases. Furthermore, the absolute value of the detected air-fuel ratio change rate ΔAF increases as the difference between the cylinder-by-cylinder air-fuel ratios increases.

  In this apparatus, as an imbalance index value, a value based on the detected air-fuel ratio change rate ΔAF (for example, the absolute value of the detected air-fuel ratio change rate ΔAF obtained every time the sampling time ts elapses, or a plurality of detected air-fuel ratio change rates) The average value of the absolute values of ΔAF, the maximum value among the absolute values of the plurality of detected air-fuel ratio change rates ΔAF, and the like) are used. This is based on the fact that the detected air-fuel ratio change rate ΔAF is less affected by the engine speed NE than the locus length of the detected air-fuel ratio abyfs.

(Detection accuracy of air-fuel ratio imbalance among cylinders)
Usually, it is detected by the EGR gas (exhaust gas) introduction state. However, since the inclination of the detected air-fuel ratio change rate ΔAF, that is, the time differential value d (abyfs) / dt of the detected air-fuel ratio abyfs tends to become smaller (becomes slower) with the introduction of EGR gas, the imbalance index value In other words, the detection accuracy of the air-fuel ratio imbalance among cylinders may decrease. In the following description, detecting the air-fuel ratio imbalance among cylinders in the EGR gas introduction state is referred to as “primary detection”. On the other hand, in order to improve the detection accuracy of the air-fuel ratio imbalance among cylinders in the “primary detection”, the “EGR control” in the emission amount reduction control described above is limited. The imbalance index value may be detected in a stopped state, but it is not preferable to restrict EGR control unnecessarily from the viewpoint of reducing the emission amount. In the following description, detecting the air-fuel ratio imbalance among cylinders in the EGR gas introduction stop state is referred to as “secondary detection”.

  FIG. 10 is a flowchart showing an example of the flow of processing related to “improvement of detection accuracy of air-fuel ratio imbalance among cylinders” executed by the CPU 91 of the present apparatus. In this example, first, in step 1005, it is determined whether or not the imbalance ratio Y1 is calculated and learned (updated) using the imbalance index value X1 detected by “primary detection”.

  Specifically, a new detected air-fuel ratio abyfs is acquired every time a sampling time ts (for example, 4 milliseconds) elapses. Each time a new detected air-fuel ratio abyfs is calculated (that is, every time the sampling time ts elapses), the detected air-fuel ratio change rate ΔAF is acquired by subtracting the previous detected air-fuel ratio from the current detected air-fuel ratio. The An average value ΔAFave of absolute values of a plurality of detected air-fuel ratio change rates ΔAF acquired within a predetermined period is calculated. The predetermined period is preferably the above-described unit combustion cycle period (720 ° crank angle in the case of a four-cylinder, four-cycle engine).

  This average value ΔAFave can also be described as “the average value of the absolute value of the detected air-fuel ratio change rate ΔAF in one unit combustion cycle period”. This average value ΔAFave is acquired for each of a plurality of unit combustion cycle periods. The average value of the plurality of average values ΔAFave acquired in this way is acquired as the imbalance index value X1. The imbalance index value X1 is a value that increases as the difference between the cylinder-by-cylinder air-fuel ratios increases.

  Next, an imbalance ratio Y1 is calculated, and stored in a predetermined storage position of the RAM 93, for example, and learned (updated). In this example, P1 and “empty index value X1 when the air-fuel ratio imbalance among cylinders does not occur (when the difference between the cylinder-by-cylinder air-fuel ratios is zero)” are calculated in advance. When the value of the imbalance index value X1 when the degree of imbalance between cylinders is the maximum (when the difference between the cylinder-by-cylinder air-fuel ratio is the maximum) is Q1 (Q1> P1), for example, Y1 = ( The imbalance ratio Y1 (%) is obtained according to the formula of (X1-P1) / (Q1-P1). That is, the imbalance ratio Y1 is “0%” when no air-fuel ratio imbalance among cylinders is occurring, and is “100%” when the degree of air-fuel ratio imbalance among cylinders is maximum.

  Subsequently, in step 1010, it is determined whether the imbalance ratio Y1 calculated in “primary detection” is equal to or greater than a predetermined value A (%), and if Y ≧ A is satisfied (“Yes” in step 1010). In step 1015, the time difference from the end of the fuel cut control to the introduction of EGR gas by the EGR control, that is, the delay time is set large. On the other hand, if Y <A is satisfied (“No” in step 1010), in step 1030, the delay time from the end of the fuel cut control to the introduction of EGR gas by the EGR control is set to a normal time difference. Here, the determination of “No” in step 1010 means that it is determined that the air-fuel ratio imbalance among cylinders has not occurred in “primary detection”, and the determination is “Yes”. Means that it is determined in the “primary detection” that an air-fuel ratio imbalance among cylinders has occurred or an occurrence of an air-fuel ratio imbalance among cylinders is suspected.

  The “delay time setting” in step 1015 will be specifically described below. In this case, since the air-fuel ratio imbalance among cylinders has occurred or is suspected in the “primary detection”, the delay time is set so that the time from the end of fuel cut control to the introduction of EGR gas becomes longer. Set. As shown in FIG. 11, if the imbalance ratio Y1 is equal to or greater than a predetermined value A (%), the delay time is normally Tbase which is determined in advance as a time difference from the end of the fuel cut control to the introduction of EGR gas. On the other hand, an additional time Tadd that changes to a larger value as the imbalance ratio Y1 increases is added and set. That is, in step 1015, the delay time Tbase + Tadd (Tadd ≠ 0) is set.

  The fuel cut control stops fuel injection from the fuel injection valve 39 when a preset fuel cut start condition is satisfied, and fuel injection when a preset fuel cut end condition (fuel cut return condition) is satisfied. This is control for returning the fuel injection from the valve 39. Here, as the fuel cut start condition, for example, the opening of the throttle valve 43 (throttle valve opening) is “zero” (or less than a predetermined opening), and the engine speed NE is a predetermined fuel. It can be set as a condition that the rotation speed is equal to or higher than the cut rotation speed. On the other hand, as the fuel cut end condition (fuel cut return condition), the opening degree of the throttle valve 43 (throttle valve opening degree) is “zero” (or a predetermined opening degree) or more, and the engine speed NE is It can be set as a condition that it is less than a predetermined fuel cut rotational speed. The fuel cut control is started when any of the fuel cut start conditions is satisfied, and the fuel cut control is ended when at least one of the fuel cut end conditions (fuel cut return conditions) is satisfied. .

  When the delay time Tbase + Tadd is set in step 1015, step 1020 is subsequently executed. In step 1020, it is determined whether the set delay time Tbase + Tadd has elapsed after the fuel cut control is completed (that is, after the fuel injection from the fuel injection valve 39 is restored). If the delay time Tbase + Tadd has not yet elapsed (“No” at step 1020), the EGR gas introduction by the EGR control is not performed at step 1025 (with the EGR gas introduction stopped). Detection of the imbalance index value X1 and calculation of the imbalance ratio Y1 are executed. That is, in step 1025, the detection of the imbalance index value X1 and the calculation of the imbalance ratio Y1 (detection of the air-fuel ratio imbalance among cylinders) by “secondary detection” are executed a plurality of times until the delay time Tbase + Tadd has elapsed. The

  Next, the setting of “delay time” in step 1030 will be specifically described. In this case, since the air-fuel ratio imbalance among cylinders does not occur in the “primary detection”, Tbase which is determined in advance as a delay time (time difference) from the end of the fuel cut control to the EGR gas introduction in the normal time. Is set. That is, in step 1015, the additional time Tadd is set to “0”, and the delay time Tbase is set.

  When the delay time Tbase is set at step 1030, step 1035 is subsequently executed. In step 1035, it is determined whether or not the set delay time Tbase has elapsed after the fuel cut control is completed (that is, after the fuel injection from the fuel injection valve 39 is restored). If the delay time Tbase has not yet elapsed, the determination of “No” is repeated in step 1035 repeatedly until the delay time Tbase has elapsed.

  When it is determined that the set delay time Tbase + Tadd has elapsed after the fuel cut control is completed in step 1020 (that is, after the fuel injection from the fuel injection valve 39 is restored), “Yes in step 1020” ”), Or when it is determined that the set delay time Tbase has elapsed after the fuel cut control is completed in Step 1035 (that is, after the fuel injection from the fuel injection valve 39 is restored) (Step S35). In Step 1040, EGR control is executed and EGR gas introduction is started. That is, in step 1040, the EGR valve 55 is changed from the closed state to the open state, and the exhaust gas (EG gas) in the exhaust passage is introduced into the intake passage.

  As described above, according to the embodiment (specifically, the processing shown in FIG. 10) according to the present invention, it is determined that the air-fuel ratio imbalance among cylinders is occurring in “primary detection” ( “Yes” in step 1010), a delay time Tbase + Tadd from the end of the fuel cut control to the EGR gas introduction by the EGR control is set (step 1015), and the “secondary detection” is empty until the delay time Tbase + Tadd elapses. Detection of the imbalance between cylinders is executed (steps 1020 and 1025). Therefore, it is possible to detect a very accurate air-fuel ratio imbalance among cylinders from which the influence of EGR gas introduction has been eliminated.

  In addition, this invention is not limited to the said embodiment, A various modification can be employ | adopted within the scope of the present invention. For example, in the above embodiment, the imbalance index value X1 based on the time differential value (detected air-fuel ratio change rate ΔAF) of the detected air-fuel ratio abyfs as the imbalance index value (a value that increases as the difference between the cylinder-by-cylinder air-fuel ratios increases). ) Is used, but a value based on the second-order differential value with respect to the time of the detected air-fuel ratio abyfs may be used. Further, the locus length of the output value Vabyfa of the upstream air-fuel ratio sensor 77 or the locus length of the detected air-fuel ratio abyfs may be used. These values are all “values that increase as the difference between the cylinder-by-cylinder air-fuel ratios increases”.

  Further, as an imbalance index value, an imbalance index value X2 obtained as follows may be used. A new detected air-fuel ratio abyfs is acquired every time the sampling time ts (for example, 4 milliseconds) elapses. The minimum MIN is selected from a plurality of detected air-fuel ratios abyfs acquired within a predetermined period. The predetermined period is preferably the above-described unit combustion cycle period (720 ° crank angle in the case of a four-cylinder, four-cycle engine).

  This minimum MIN can also be described as “the minimum value in one unit combustion cycle period of the detected air-fuel ratio abyfs”. This minimum value MIN is acquired in each of a plurality of unit combustion cycle periods. The average value of the plurality of minimum MINs acquired in this way is acquired as the imbalance index value X2. The imbalance index value X2 is a value that decreases as the difference between the cylinder-by-cylinder air-fuel ratios increases.

  Thus, when the imbalance index value X2 is used, the imbalance ratio Y2 is calculated as the imbalance ratio. That is, the previously determined “value of the imbalance index value X2 when the air-fuel ratio imbalance among cylinders does not occur (when the difference between the cylinder-by-cylinder air-fuel ratio is zero)” is set to P2, “air-fuel ratio cylinder When the value of the imbalance index value X2 when the degree of the imbalance between the cylinders is the maximum (when the difference between the cylinder-by-cylinder air-fuel ratios is the maximum) is Q2 (P2> Q2), for example, Y2 = (P2− The imbalance ratio Y2 (%) is obtained according to the formula of (X2) / (P2-Q2). That is, the imbalance ratio Y2 is “0%” when the air-fuel ratio imbalance among cylinders is not generated, and is “100%” when the degree of air-fuel ratio imbalance among cylinders is maximum.

  Further, in the above embodiment, the imbalance ratio is calculated based on the imbalance index value, and the delay time until EGR gas introduction by EGR control based on the magnitude of the imbalance ratio, more specifically, the additional time Tadd is calculated. Although the magnitude is determined, the magnitude of the additional time Tadd may be determined based on the magnitude of the imbalance index value itself without calculating the imbalance ratio.

  Furthermore, in the above embodiment, the delay time Tbase + Tadd until the EGR gas introduction by the EGR control is determined as the time difference after the fuel injection by the fuel injection valve 39 is restored after the fuel cut control is completed. In this case, the time difference after the engine rotational speed NE exceeds a predetermined threshold rotational speed set in advance (for example, after the engine rotational speed NE increasing from the idle state exceeds the predetermined threshold rotational speed), that is, a delay time. It is also possible to determine as Tbase + Tadd.

  When the engine speed NE is used in this way, if the imbalance ratio Y1 (%) is less than the predetermined value A (%) (“No” in step 1010), the additional time Tadd is determined in step 1030. The normal delay time Tbase is set to “0”. Then, in step 1035, it is determined that the delay time Tbase has elapsed after the engine rotational speed NE exceeds the threshold rotational speed, and then in step 1040, EGR gas introduction by EGR control is started.

  On the other hand, when the imbalance ratio Y1 (%) is equal to or greater than the predetermined value A (%) (“Yes” in step 1010), in step 1015, the additional time Tadd is increased according to the imbalance ratio Y1 (%). The delay time Tbase + Tadd is set by setting the value. Then, in step 1020, after it is determined that the delay time Tbase + Tadd has elapsed after the engine rotational speed NE exceeds the threshold rotational speed, introduction of EGR gas by EGR control is started in step 1040. Accordingly, since the EGR gas introduction is stopped until the delay time Tbase + Tadd elapses after the engine rotational speed NE exceeds the threshold rotational speed, in step 1025, the influence due to the EGR gas introduction is eliminated and the imbalance index is removed. The value X1 (that is, the imbalance ratio Y1) can be detected (calculated) with extremely high accuracy.

  25 ... Combustion chamber, 37 ... Spark plug, 39 ... Fuel injection valve, 33 ... Variable intake timing control device, 36 ... Variable exhaust timing control device, 44 ... SCV, 44a ... SCV actuator, 49 ... Purge control valve, 54 ... Exhaust Reflux pipe, 55 ... EGR valve, 63 ... ASV, 66 ... solenoid valve, 53 ... upstream catalyst, 77 ... upstream air-fuel ratio sensor, 90 ... electric control device, 91 ... CPU

Claims (3)

A control device applied to a multi-cylinder internal combustion engine having a plurality of cylinders,
An air-fuel ratio sensor that is disposed in a collective exhaust passage formed by collecting exhaust passages extending from the plurality of cylinders and generates an output value corresponding to an air-fuel ratio of mixed exhaust gas that is exhaust gas that passes through the exhaust exhaust passage. When,
A plurality of fuel injection valves that are arranged corresponding to each of the plurality of cylinders and inject fuel contained in the air-fuel mixture supplied to the respective combustion chambers of the plurality of cylinders;
Feedback amount calculation means for calculating an air-fuel ratio feedback amount common to the plurality of cylinders based on an output value of the air-fuel ratio sensor so that an air-fuel ratio of the mixed exhaust gas matches a stoichiometric air-fuel ratio;
Feedback control means for feedback-controlling the air-fuel ratio of the mixed exhaust gas by adjusting the amount of fuel injected from each of the plurality of fuel injection valves based on the air-fuel ratio feedback amount;
Exhaust recirculation control execution means for executing control for guiding exhaust gas in the exhaust passage of the internal combustion engine to the intake passage of the internal combustion engine;
A control device for a multi-cylinder internal combustion engine, comprising:
The air-fuel ratio sensor indicates an imbalance index value that increases or decreases as the degree of difference between the plurality of cylinder-by-cylinder air-fuel ratios, which is the air-fuel ratio of the air-fuel mixture supplied to the respective combustion chambers of the plurality of cylinders, increases. and the imbalance index value acquisition means for acquiring, based on the output value of,
Fuel cut means for executing fuel cut control for stopping injection of the fuel by the plurality of fuel injection valves when a predetermined fuel cut condition is satisfied;
With
The exhaust gas recirculation control execution means includes:
When the degree of difference represented by the imbalance index value is large, the fuel cut control by the fuel cut means is finished and the fuel by the plurality of fuel injection valves is compared to when the degree of difference is small. injection established conditions for returning to take the exhaust gas of the exhaust passage is set larger the difference in time leads to the intake passage from,
The imbalance index value acquisition means includes
A control device for a multi-cylinder internal combustion engine configured to acquire the imbalance index value within the largely set time difference. A control device applied to a multi-cylinder internal combustion engine having a plurality of cylinders,
An air-fuel ratio sensor that is disposed in a collective exhaust passage formed by collecting exhaust passages extending from the plurality of cylinders and generates an output value corresponding to an air-fuel ratio of mixed exhaust gas that is exhaust gas that passes through the exhaust exhaust passage. When,
A plurality of fuel injection valves that are arranged corresponding to each of the plurality of cylinders and inject fuel contained in the air-fuel mixture supplied to the respective combustion chambers of the plurality of cylinders;
Feedback amount calculation means for calculating an air-fuel ratio feedback amount common to the plurality of cylinders based on an output value of the air-fuel ratio sensor so that an air-fuel ratio of the mixed exhaust gas matches a stoichiometric air-fuel ratio;
Feedback control means for feedback-controlling the air-fuel ratio of the mixed exhaust gas by adjusting the amount of fuel injected from each of the plurality of fuel injection valves based on the air-fuel ratio feedback amount;
Exhaust recirculation control execution means for executing control for guiding exhaust gas in the exhaust passage of the internal combustion engine to the intake passage of the internal combustion engine;
A control device for a multi-cylinder internal combustion engine, comprising:
The air-fuel ratio sensor indicates an imbalance index value that increases or decreases as the degree of difference between the plurality of cylinder-by-cylinder air-fuel ratios, which is the air-fuel ratio of the air-fuel mixture supplied to the respective combustion chambers of the plurality of cylinders, increases. An imbalance index value acquisition means for acquiring based on the output value of
Engine rotation speed acquisition means for acquiring the rotation speed of the internal combustion engine;
With
The exhaust gas recirculation control execution means includes:
When the degree of the difference represented by the imbalance index value is large, the rotation speed of the internal combustion engine acquired by the period rotation speed acquisition unit is set in advance as compared to when the degree of difference is small. Set a large time difference from when the condition exceeding the rotational speed is established until the exhaust gas in the exhaust passage is led to the intake passage,
The imbalance index value acquisition means includes
A control device for a multi-cylinder internal combustion engine configured to acquire the imbalance index value within the largely set time difference. The control apparatus for a multi-cylinder internal combustion engine according to claim 1 or 2 ,
The exhaust gas recirculation control execution means includes:
A control device for a multi-cylinder internal combustion engine configured to set the time difference to be larger as the degree of the difference represented by the imbalance index value is larger.

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