JP2013181486A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine, which can prevent the degradation in exhaust cleaning performance of a catalytic converter due to an influence of cylinders having air-fuel ratio deviation at start warming-up or the like.SOLUTION: A control device for an internal combustion engine detects an exhaust air-fuel ratio by an air-fuel ratio sensor on an exhaust passage of a multiple cylinder internal combustion engine which is provided with a catalytic converter for exhaust cleaning, corrects the fuel supply amount to each cylinder based on a detection value by the air-fuel ratio sensor to execute feedback control for allowing a combustion air-fuel ratio in each cylinder to follow a target air-fuel ratio and selectively executes fuel cut processing for stopping fuel supply to the each cylinder according to an operation condition of the internal combustion engine. The control device increases (step S13) an execution period of the fuel cut processing according to the required load of the internal combustion engine to the execution period in the operation condition in which the cylinders having air-fuel deviation are not generated on condition that the deviation amount of the combustion air-fuel ratio to the target air-fuel ratio is out of a specific range and the cylinders having air-fuel ratio deviation which are dispersed in a lean side are generated (step S11, S12).

Description

  The present invention relates to an internal combustion engine control apparatus, and more particularly to an internal combustion engine control apparatus suitable for executing air-fuel ratio feedback control of a multi-cylinder internal combustion engine and suppressing variations in air-fuel ratio among cylinders.

  In an internal combustion engine mounted on a vehicle or the like, in order to maximize the performance of a catalytic converter such as a three-way catalyst that performs exhaust purification processing, an air-fuel ratio (hereinafter, referred to as a mixture ratio of intake air and fuel in a cylinder) A change in the combustion air-fuel ratio is detected from a change in residual oxygen concentration or unburned gas concentration in the exhaust gas (hereinafter also referred to as the exhaust air-fuel ratio), and the combustion air-fuel ratio is set to the target air-fuel ratio based on the detected value. Many perform air-fuel ratio feedback control that feedback-controls the fuel supply amount to each cylinder so as to follow.

  In addition, air-fuel ratio sensors are provided on the upstream side and downstream side of the catalytic converter, respectively, and main feedback control of the air-fuel ratio based on the detected value of the upstream air-fuel ratio sensor is executed, and at the same time, the upstream air-fuel ratio sensor The control accuracy is improved by executing sub-feedback control for correcting the output of the upstream air-fuel ratio sensor based on the output of the downstream air-fuel ratio sensor so that the detected value matches the actual exhaust air-fuel ratio. is there.

  However, in a multi-cylinder internal combustion engine, not only the characteristics of the injector and the degree of deterioration thereof vary among the cylinders, but also the variation of the intake characteristics among the cylinders. In some cases, the accuracy of air-fuel ratio control by air-fuel ratio feedback control as described above may be reduced. In view of this, a control apparatus for an internal combustion engine that executes control for suppressing variations in air-fuel ratio among cylinders of a multi-cylinder internal combustion engine has been proposed.

  As such a control device for an internal combustion engine, for example, when an abnormality in air-fuel ratio variation is estimated from detection information of an air-fuel ratio sensor, it is determined whether or not there is a possibility that the catalyst is overheated. When the air-fuel ratio is lean and the possibility that the catalyst is overheated is high, the air-fuel ratio of the normal cylinders other than the abnormal cylinder is controlled in the rich direction so that the air-fuel ratio of the exhaust gas flowing into the catalyst is close to the theoretical air-fuel ratio. A catalyst that is controlled to the rich side to prevent overheating of the catalyst is known (see, for example, Patent Document 1).

  Further, when the degree of variation in the air-fuel ratio between cylinders is large, as a control for suppressing deterioration of the catalyst due to a temperature rise, the fuel cut prohibition rotation number for prohibiting fuel cut processing for stable combustion is set to the degree of variation in the air-fuel ratio. A control that executes a control to decrease in accordance with this to facilitate the prohibition of fuel cut processing is known (for example, see Patent Document 2).

  Further, by identifying cylinders having a large deviation between the peak value and the average value of the air-fuel ratio and correcting the fuel injection amount of the specific cylinder according to the average value of the deviations during the specification, the air-fuel ratio between the cylinders is made uniform. There is known one that is designed to be realized (see, for example, Patent Document 3).

  In addition, the difference in engine rotation speed between the explosion cylinder of this time and the previous explosion cylinder is calculated, and the average injection amount of all cylinders is adjusted according to the difference in rotation speed between the explosion cylinders after the cold start. The difference between the rotational speeds of the cylinders and the previous explosion is averaged for each cylinder, and the injection amount of each cylinder is adjusted so that the average value of the rotational speed differences between the cylinders approaches zero (see, for example, Patent Document 4) It has been known.

JP 2008-064078 A JP 2009-264287 A JP 2002-332895 A JP 2009-281236 A

  However, in the conventional control device for an internal combustion engine as described above, the air-fuel ratio corresponding to a specific cylinder or cylinder group can be corrected, but the combustion air-fuel ratio of each cylinder generated during the air-fuel ratio feedback control Therefore, there is a problem in that variations in the combustion air-fuel ratio among the cylinders cannot be accurately suppressed.

  In addition, if an abnormal air / fuel ratio cylinder is generated in which the combustion air / fuel ratio is greatly deviated to the lean side due to a shortage of fuel injection amount with respect to the target air / fuel ratio, the exhaust gas in the exhaust gas may be exhausted due to misfiring, etc. In addition to an increase in the amount of unburned hydrocarbons (HC), the exhaust air-fuel ratio of exhaust gas flowing into the catalytic converter from other cylinders also becomes rich, and the purification rate of unburned hydrocarbons during start-up warm-up, etc. decreases There was a possibility that.

  Further, depending on the shape of the exhaust pipe and the arrangement of the catalytic converter, in an internal combustion engine in which sub-feedback control is executed, exhaust gas from a cylinder having a large deviation of the combustion air-fuel ratio with respect to the target air-fuel ratio may differ from exhaust gas from other cylinders. There is a possibility that the air-fuel ratio sensor on the downstream side will be strongly hit without being sufficiently mixed. In that case, if an abnormality occurs in the air / fuel ratio in which the fuel injection amount becomes insufficient due to some problem and the combustion air / fuel ratio shifts to the lean side, the detected value on the lean side exceeds the actual exhaust air / fuel ratio from the downstream air / fuel ratio sensor. May be output and the accuracy of air-fuel ratio control may be reduced.

  Accordingly, the present invention provides a control device for an internal combustion engine that can reliably prevent the exhaust gas purification performance of the catalytic converter from deteriorating due to the influence of exhaust gas from a cylinder with a large air-fuel ratio deviation during start-up warm-up or the like. Is to provide.

  In order to achieve the above object, the control apparatus for an internal combustion engine according to the present invention (1) detects an exhaust air / fuel ratio by an air / fuel ratio sensor on an exhaust path of a multi-cylinder internal combustion engine equipped with a catalytic converter for exhaust purification. Feedback control for correcting the fuel supply amount to each cylinder of the internal combustion engine based on the detected value of the air-fuel ratio sensor to cause the combustion air-fuel ratio in each cylinder to follow the target air-fuel ratio, and A control device for an internal combustion engine that selectively executes a fuel supply stop process for stopping the fuel supply to each cylinder of the internal combustion engine in accordance with an operating state, the deviation of the combustion air-fuel ratio from the target air-fuel ratio The execution period of the fuel supply stop process according to the required load of the internal combustion engine, on the condition that an air-fuel ratio deviation cylinder that the amount deviates from within a certain range and varies on the lean side has occurred, Wherein the ratio shift cylinder increases to execution period of at operating conditions do not occur.

  According to the present invention, when an air-fuel ratio shift cylinder in which the deviation amount of the combustion air-fuel ratio with respect to the target air-fuel ratio deviates from a predetermined range and varies on the lean side occurs, the fuel supply stop selectively executed according to the required load of the internal combustion engine A process for increasing the execution period of the process relative to the execution period in an operating state in which no air-fuel ratio deviation cylinders are generated is performed. Therefore, while the amount of fuel supplied to each cylinder by feedback control increases due to the influence of the air-fuel ratio shift cylinder, the fuel supply stop process accurately reduces the combustion opportunity in each cylinder, and misfires in the air-fuel ratio shift cylinder It is possible to reliably reduce the amount of fuel supplied to each cylinder while avoiding the influence of the above. As a result, the exhaust gas flowing into the catalytic converter can be prevented from becoming rich in the exhaust air-fuel ratio, and the reduction in the purification rate of unburned hydrocarbons by the catalytic converter can be effectively suppressed. It is possible to reliably prevent the performance from deteriorating.

  The control apparatus for an internal combustion engine of the present invention is preferably configured to execute (2) the fuel supply stop process under a first fuel supply stop execution condition on condition that the air-fuel ratio deviation cylinder does not occur, and the air-fuel ratio This is executed under the second fuel supply stop execution condition in which the execution frequency of the fuel supply stop process is higher than that of the first fuel supply stop execution condition on condition that a shift cylinder is generated.

  With this configuration, the fuel supply stop process is performed under the second fuel supply stop execution condition that is executed more frequently than the first fuel supply stop execution condition, on condition that an air-fuel ratio shift cylinder has occurred. Therefore, in response to the increase in the fuel supply amount in each cylinder due to the influence of the air-fuel ratio deviation cylinder, the fuel supply amount in each cylinder is reduced by the fuel supply stop process, so that the fuel injection amount becomes too low. It is possible to suppress the exhaust air / fuel ratio of exhaust gas flowing into the catalytic converter from becoming rich while reducing misfires in the cylinder with a deviation in the fuel ratio, and the purification rate of unburned hydrocarbons in the catalytic converter is reduced. Can be effectively suppressed.

  In the control apparatus for an internal combustion engine having the configuration of (2), (3) the air-fuel ratio deviation is based on the amount of change in the rotational speed of the internal combustion engine when the fuel supply amount of the internal combustion engine is changed for each cylinder. Provided that an air-fuel ratio deviation cylinder detection mechanism for detecting the occurrence of a cylinder is provided, and that the occurrence of the air-fuel ratio deviation cylinder is detected by the air-fuel ratio deviation cylinder detection mechanism during start-up and warm-up of the internal combustion engine. The fuel supply stop process is preferably executed under the second fuel supply stop execution condition.

  In this case, it becomes possible to detect the air-fuel ratio deviation cylinder with relative accuracy by using existing sensors such as a fuel injection amount control unit and a crank angle sensor that detects the engine rotation speed, and moreover, It is possible to reliably increase the frequency of executing the fuel supply stop process when the fuel ratio deviation cylinder is generated.

  In the control apparatus for an internal combustion engine having the configuration of (3), (4) the fuel for each cylinder of the internal combustion engine is provided on the condition that the rotational fluctuation amount during start-up warming of the internal combustion engine deviates from a target rotational speed range. The air-fuel ratio shift by the air-fuel ratio shift cylinder detection mechanism is executed on the condition that the cylinder-by-cylinder increase correction for increasing the supply amount and reducing the rotation fluctuation amount is selectively executed. It is preferable to execute a cylinder detection process.

  As a result, the air-fuel ratio shift cylinder detection mechanism is reliably operated when a significant rotation fluctuation occurs due to the influence of the air-fuel ratio shift cylinder, while the air-fuel ratio shift cylinder does not occur and no significant rotation fluctuation due to the influence occurs. The processing load for detecting the air-fuel ratio deviation cylinder can be reduced, and the hardware resources mounted on the vehicle can be effectively utilized. Note that the air-fuel ratio shift cylinder detection mechanism can determine whether or not only a specific cylinder that has been subject to cylinder-by-cylinder increase correction is an air-fuel ratio shift cylinder.

  In the control apparatus for an internal combustion engine according to the present invention, (5) the fuel supply stop process is executed on condition that the required load on the internal combustion engine has reached a threshold value or less, and the required load has reached the threshold value or less. The fuel supply to each cylinder is stopped when a delay time set according to the operating state of the internal combustion engine elapses, and the delay time is shortened when the execution period of the fuel supply stop process is increased. Is preferred.

  As a result, the execution period of the fuel supply stop process can be realized easily and reliably with a simple process.

  In the control apparatus for an internal combustion engine according to the present invention, (6) when the internal combustion engine is installed in a hybrid vehicle that constitutes a hybrid drive apparatus for driving driving together with an electric motor, and the fuel supply stop process is executed, the hybrid drive apparatus It is preferable to increase the frequency of intermittent stop of the internal combustion engine in the hybrid drive device by decreasing the power load ratio of the internal combustion engine while increasing the power load ratio of the electric motor among the power required for the motor.

  In this case, by increasing the frequency of intermittent stop of the internal combustion engine, the exhaust air / fuel ratio of the exhaust gas flowing into the catalytic converter becomes rich while reducing misfires and the like in the air / fuel ratio shift cylinder where the fuel injection amount becomes excessive. It can be suppressed, and the reduction of the purification rate of unburned hydrocarbons in the catalytic converter can be effectively suppressed.

  In the control apparatus for an internal combustion engine according to the present invention, (7) when performing the fuel supply stop process, it is preferable to temporarily stop the fuel injection to each cylinder during the engine rotation of the internal combustion engine.

  In this case, by simply adding a simple processing step to the existing fuel cut processing means, it is possible to prevent a reduction in the exhaust gas purification performance of the catalytic converter at a low cost.

  According to the present invention, when an air-fuel ratio deviation cylinder in which the deviation amount of the combustion air-fuel ratio with respect to the target air-fuel ratio deviates from a predetermined range and varies toward the lean side occurs, the execution period of the fuel supply stop process according to the required load of the internal combustion engine Is increased with respect to the execution period in the normal operation state in which no air-fuel ratio shift cylinders are generated, so that the amount of fuel supplied to each cylinder and the combustion empty by feedback processing are influenced by the influence of exhaust gas from the air-fuel ratio shift cylinders. Even if the fuel ratio deviates to the rich side, it is possible to prevent the exhaust air / fuel ratio in the catalytic converter from being overcorrected to the rich side at the time of start-up warm-up, etc., and the exhaust gas purification performance of the catalytic converter will deteriorate. It is possible to provide a control device for an internal combustion engine that can reliably prevent this.

1 is a schematic configuration diagram of a control device for an internal combustion engine according to an embodiment of the present invention. 1 is a graph showing output characteristics of air-fuel ratio sensors arranged upstream and downstream (before and after the catalyst) of a catalytic converter in an internal combustion engine according to an embodiment of the present invention, where the vertical axis represents each sensor output, and the horizontal axis represents empty air. Indicates the fuel ratio. FIG. 3 is a time chart illustrating an engine rotational speed fluctuation pattern when an air-fuel ratio deviation cylinder is generated in an internal combustion engine according to an embodiment of the present invention. FIG. ) Shows the fluctuation state of each crank rotation speed. 6 is a graph showing changes in crank rotation angular velocity when cylinder-by-cylinder increase correction is performed for an air-fuel ratio shift cylinder in an internal combustion engine according to an embodiment of the present invention, and the vertical axis represents the combustion state of the air-fuel ratio shift cylinder. The angular velocity difference between the front and rear is shown, and the horizontal axis shows the imbalance rate, which is an index value of the air-fuel ratio deviation of the air-fuel ratio deviation cylinder. In the internal combustion engine according to an embodiment of the present invention, the amount of change in rotation before and after combustion of the air-fuel ratio shift cylinder changes by the cylinder-by-cylinder increase correction for the air-fuel ratio shift cylinder. It is a graph explaining the principle which specifies a shift | offset | difference direction, a vertical axis | shaft shows the said variation | change_quantity before and behind combustion of an air fuel ratio shift cylinder, and a horizontal axis shows the imbalance rate of the air fuel ratio shift cylinder. It is a flowchart which shows the general | schematic flow of the exhaust gas deterioration suppression control program performed when the air-fuel ratio deviation cylinder generate | occur | produces with the control apparatus of the internal combustion engine which concerns on one Embodiment of this invention. It is a flowchart which shows the general | schematic flow of the detection processing program which detects an air-fuel ratio deviation abnormal cylinder with the control apparatus of the internal combustion engine which concerns on one Embodiment of this invention. 6 is a time chart showing changes in a vehicle speed, an execution correction flag for cylinder-by-cylinder increase correction, an engine speed, and a fuel cut execution flag set when fuel cut is executed in a hybrid vehicle equipped with an internal combustion engine according to an embodiment of the present invention. .

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(One embodiment)
1 to 8 show an embodiment of a control device for an internal combustion engine according to the present invention.

  In the present embodiment, the present invention is applied to an in-line four-cylinder four-cycle gasoline engine (hereinafter simply referred to as an engine) that is a multi-cylinder internal combustion engine. A hybrid travel drive device is configured together with an electric motor and is mounted on a hybrid vehicle.

  First, the configuration will be described.

  As shown in FIG. 1, the engine 10 of this embodiment includes an engine body 12 in which a plurality of cylinders 11 (indicated by # 1, # 2, # 3, and # 4 in FIG. 1) are formed. . Although not shown in detail, the engine body 12 is provided with a cylinder block in which cylinder bores corresponding to the plurality of cylinders 11 are formed, a cylinder head and a head cover provided on the upper side of the cylinder block, and a lower side of the cylinder block. A crankcase and an oil pan.

  Although not shown in detail, the engine body 12 includes a plurality of pistons that form combustion chambers 14 in a plurality of cylinders 11 and a crankshaft in which the plurality of pistons are connected via a connecting rod. doing. The engine body 12 includes an intake valve and an exhaust valve that open and close on the upper side of the combustion chamber 14, a spark plug 16 that sparks and ignites the compressed mixed gas in the combustion chamber 14, and an intake valve and an exhaust valve that are connected to the crankshaft. And a valve mechanism that opens and closes according to the stroke position of the piston accompanying the rotation of the valve.

  Further, a plurality of intake ports (no reference numerals) corresponding to the plurality of cylinders 11 are formed on one side of the cylinder head of the engine body 12 in the short direction, and an intake valve is provided on the inner end side of each intake port. Is provided. The cylinder head of the engine body 12 has a plurality of intake ports so that a mixed gas of air and fuel can be sucked (intake) into the combustion chamber 14 corresponding to the intake valve when each intake valve is opened. An intake manifold 20 having a plurality of intake branch pipes 18 and a surge tank 19 forming an intake passage connected to the intake manifold 20 is mounted.

  An intake pipe 22 that forms an intake passage 21 on the upstream side is connected to the intake manifold 20, and an air cleaner 23 having a filter that can remove foreign matter in the intake air is attached to the most upstream end of the intake pipe 22. Has been. In addition, an air flow meter 24 that measures the flow rate Qa of the air that has passed through the air cleaner 23 and a part of the intake passage 21 in the intake pipe 22 downstream of the intake pipe 22 are throttled to an arbitrary opening thv. An electronically controlled throttle valve 25 capable of performing the above is mounted. Further, a plurality of injectors 26 (fuel injection valves) are attached to the cylinder head of the engine body 12 corresponding to the plurality of intake ports and the intake branch pipes 18.

  On the other hand, on the other side in the short direction of the cylinder head of the engine body 12, a plurality of exhaust branch pipes 32 and collecting pipes are provided so that exhaust gas can be discharged from the corresponding combustion chamber 14 when the exhaust valves are opened. An exhaust manifold 30 having a portion 34 is mounted.

  An exhaust pipe 36 on the downstream side is connected to the collecting pipe portion 34 of the exhaust manifold 30, and a catalytic converter 40 that purifies harmful components contained in the exhaust gas of the engine 10 is attached to the exhaust pipe 36. ing. The catalytic converter 40 incorporates a known three-way catalyst, and NOx (nitrogen oxide), which is a harmful component in the exhaust gas, when the air-fuel ratio in the combustion chamber 14 is within a certain range near the stoichiometric air-fuel ratio. HC (hydrocarbon) and CO (carbon monoxide) can be highly purified respectively. The catalytic converter 40 may be of a type that can purify unburned components and nitrogen oxides even if the air-fuel ratio deviates from the stoichiometric air-fuel ratio by the oxygen storage function.

  A first air-fuel ratio sensor 42 for detecting the exhaust air-fuel ratio is mounted upstream of the catalytic converter 40 in the collecting pipe portion 34 of the exhaust manifold 30 or in the exhaust pipe 36 near the catalytic converter 40. A second air-fuel ratio sensor 44 that detects the exhaust air-fuel ratio downstream of the catalytic converter 40 is attached to the pipe 36.

  FIG. 2 illustrates the output characteristics of the first and second air-fuel ratio sensors 42 and 44.

The first air-fuel ratio sensor 42 is a wide area on the known limit current side in which an atmosphere side electrode is provided on one surface side of an oxygen ion conductor such as zirconia (ZrO ₂ ) and a diffusion resistance layer and an exhaust side electrode are provided on the other surface side. It is an air-fuel ratio sensor. The first air-fuel ratio sensor 42 outputs a limit current (pump current accompanying O ₂ movement) corresponding to the unburned gas partial pressure (unburned gas concentration) in the exhaust gas at the time of rich combustion. In the exhaust gas, a limit current corresponding to the oxygen partial pressure (O ₂ concentration) is output. That is, the output characteristic of the first air-fuel ratio sensor 42 is a characteristic illustrated by a black circled line in FIG.

The second air-fuel ratio sensor 44 is, for example, a known concentration cell type exhaust oxygen concentration sensor (O ₂ sensor), and has a characteristic that the electromotive force rises sharply on the rich side where unburned gas remains with the theoretical air-fuel ratio as a boundary. have. In the second air-fuel ratio sensor 44, the outer electrode functions as a catalyst in the rich state, and reacts so that HC, CO, and O ₂ in the exhaust gas reach a chemical equilibrium state, so that the air side and the exhaust gas side An electromotive force corresponding to the oxygen concentration difference is generated. That is, the output characteristic of the second air-fuel ratio sensor 44 is a characteristic exemplified by a line with a black square in FIG.

  Information detected by the first air-fuel ratio sensor 42 and the second air-fuel ratio sensor 44 is taken into an electronic control unit (hereinafter referred to as ECU) 50, respectively.

  The ECU 50 includes a crank angle sensor 52 that detects the operating state of the engine 10 (including the engine speed Ne and the cooling water temperature tw shown in FIG. 1) in addition to the detection information of the air-fuel ratio sensors 42 and 44 and the air flow meter 24. Further, based on the sensor information of the water temperature sensor 54 and the like, a request operation signal from the accelerator opening sensor 56 and the like (including the accelerator opening Acc shown in FIG. 1) and a request signal from other in-vehicle ECU (not shown) Based on this, the engine 10 has a function of electronic control.

  Although ECU 50 does not illustrate a specific hardware configuration, ECU 50 includes a CPU, a ROM, a RAM, and a backup memory, and further includes an input interface circuit including an A / D converter and the like, an output interface circuit including a driver and a relay switch, The communication interface with other in-vehicle ECUs is included.

  The ECU 50 realizes outputs (torque and engine speed) required for the engine 10 while executing so-called multitask processing, for example, according to a control program stored in a ROM or a backup memory (hereinafter referred to as a ROM or the like). Thus, the opening degree of the throttle valve 25 of the engine 10, the ignition timing, the fuel injection timing, the fuel injection amount, and the like are each controlled.

  The control of the fuel injection amount by the ECU 50 includes a fuel cut process which is a fuel supply stop process according to the present invention. That is, the ECU 50 determines the fuel for each cylinder 11 during the rotation of the engine 10 according to the operating state of the engine 10 according to the control program stored in the ROM or the like, in particular according to the required load specified by the accelerator opening or the like. Cut processing is executed.

  The fuel cut processing referred to here is a deceleration request state in which the required load of the engine 10 is smaller than a preset threshold load, for example, the accelerator opening Acc detected by the accelerator opening sensor 56 is fully closed or a low opening range close thereto. When the fuel cut condition that the engine speed Ne (engine speed) is higher than the preset fuel cut region lower limit speed N1 is satisfied, the injector 26 This is a process for temporarily stopping fuel injection into each cylinder 11. This fuel cut processing is executed in an operating speed region between the fuel cut region lower limit rotational speed N1 and the fuel cut region upper limit rotational speed N2 that is higher than the fuel cut region lower limit rotational speed N1. The number N1 is set to about 1000 rpm, for example, and the fuel cut region upper limit rotation speed N2 is set to about 2000 rpm, for example. Of course, the fuel cut condition can be changed depending on the type of the vehicle and the engine 10.

  Further, in this fuel cut process, when the required load on the engine 10 reaches the threshold value or less, for example, the accelerator opening Acc detected by the accelerator opening sensor 56 reaches a fully closed or close low opening range. When a fuel cut delay time (referred to as “F / C delay” in FIG. 8) set in accordance with the required load and the operating state (for example, vehicle speed) of the engine 10 has elapsed since The fuel supply to 11 is stopped. The fuel cut delay time here is, for example, equal to or longer than the lower limit delay time during deceleration that can prevent the vehicle occupant from feeling a deceleration shock by a decrease in the output torque of the engine 10 in a very short time. Thus, it is set as a time equal to or shorter than the upper limit delay time during deceleration that can prevent the deterioration of the HC emission amount due to misfire.

  The ECU 50 also executes main feedback control and sub-feedback control so as to control the combustion air-fuel ratio in each cylinder 11 to the theoretical air-fuel ratio that is the target air-fuel ratio in accordance with a control program stored in a ROM or the like. ing. That is, the ECU 50 performs the functions described in detail below, thereby enabling main feedback control means, sub feedback control means, main feedback learning control means, and sub feedback learning control, which are main parts of the air-fuel ratio control apparatus. It is designed to function as a means.

  Here, the main feedback control is based on the detection value of the first air-fuel ratio sensor 42, correcting the fuel supply amount by port injection to each cylinder 11 of the engine 10, and thus the combustion air-fuel ratio in each cylinder 11, that is, This is feedback control in which the air-fuel ratio, which is the mixing ratio of intake air and fuel in each cylinder 11, follows the target air-fuel ratio.

  The sub feedback control is a sub feedback correction amount for making the detected value of the first air / fuel ratio sensor 42 coincide with the actual exhaust air / fuel ratio in the catalytic converter 40 based on the detected value of the second air / fuel ratio sensor 44. In this control, the calculated value of the first air-fuel ratio sensor 42 is corrected using the sub feedback correction amount. That is, the sub-feedback control increases the detection accuracy of the first air-fuel ratio sensor 42 by correction, so that the combustion air-fuel ratio in each cylinder 11 that is subjected to main feedback control based on the detection value of the first air-fuel ratio sensor 42. Is made to accurately follow the theoretical air-fuel ratio which is the target air-fuel ratio.

  The ECU 50 further detects a steady deviation between the output value of the first air-fuel ratio sensor 42 and the exhaust air-fuel ratio in the catalytic converter 40 based on the sub-feedback correction amount calculated during the execution of the sub-feedback control. A sub-feedback learning value for correction is calculated. The sub-feedback learning value is written and stored in a predetermined memory area of a backup memory including a backup RAM or the like (which may be a nonvolatile memory).

  The sub-feedback learning value here is obtained by, for example, performing proportional / integral / differential processing on the deviation between the output value of the second air / fuel ratio sensor 44 and the target exhaust air / fuel (theoretical air / fuel ratio) downstream of the catalytic converter 40. Calculated.

  Then, the ECU 50 sets the sub feedback amount to the cylinder from the start period before the second air-fuel ratio sensor 44 is activated and from the time when the sub-feedback control is started by the activation of the second air-fuel ratio sensor 44. In the period until the convergence value corresponding to the variation in the air-fuel ratio during the period, the control value for correcting the output value of the first air-fuel ratio sensor 42 using the learned value of the sub feedback amount obtained during the previous operation is performed. (Hereinafter, referred to as sub-feedback learning control).

  Further, during the operation of the engine 10, the ECU 50 calculates by the proportional / integral / derivative processing or the like based on the deviation between the output value of the second air-fuel ratio sensor 44 and the target exhaust air / fuel on the downstream side of the catalytic converter 40. The learning value written in the predetermined memory area is updated using the feedback learning value.

  In addition, the ECU 50 detects an air-fuel ratio deviation cylinder (hereinafter referred to as “air-fuel ratio deviation”) that is out of a certain range (a range in which the control for suppressing the air-fuel ratio deviation is not necessary) and is on the lean side. Exhaust gas deterioration suppression control, which will be described later, is executed on the condition that the lean imbalance cylinder) is generated.

  Specifically, as will be described in detail below, the ECU 50 first has a function of calculating an imbalance rate that is an index value of variation in the combustion air-fuel ratio for each cylinder 11 of the engine 10 and an object having a large imbalance rate. A function of determining the amount of change in the crank rotational angular speed when the fuel injection amount is increased for the cylinder, that is, the direction of the air-fuel ratio deviation (either the rich side or the lean side) from the rotational fluctuation mode. Yes. Therefore, the ECU 50 detects an air-fuel ratio deviation cylinder detection that detects the occurrence of a lean imbalance cylinder in which the deviation amount of the combustion air-fuel ratio with respect to the target air-fuel ratio deviates from a predetermined range and varies to the lean side based on the rotational fluctuation of the engine 10. Can function as a mechanism.

  The imbalance rate referred to here is a value that serves as an index of variation when the variation in the combustion air-fuel ratio between the cylinders 11 becomes large. This imbalance rate is such that the combustion air-fuel ratio is constant when, for example, the injector 26 is clogged (deposit accumulation, clogging due to foreign matter, etc.) or a failure occurs in a part of all the cylinders 11 of the engine 10. The combustion air-fuel ratios of some of the cylinders (lean imbalance cylinders; hereinafter simply referred to as imbalance cylinders) that are shifted to the lean side beyond the allowable range are set to the combustion air of all other normal cylinders (hereinafter referred to as balance cylinders). This is expressed as an average value of the fuel ratio or a deviation ratio of the air-fuel ratio with respect to the target air-fuel ratio.

  More specifically, when the imbalance rate is IB (%), the fuel injection amount (actual injection amount) of the imbalance cylinder is Qib, and the fuel injection amount of the balance cylinder is Qs, the imbalance rate IB is, for example, IB = (Qib−Qs) / Qs × 100 (%).

  In this case, the imbalance rate IB represents the rich imbalance as a positive value and the lean imbalance as a negative value. In any case, the larger the absolute value, the greater the degree of variation.

  By the way, with respect to the cylinder 11 having a large imbalance rate, the mode of rotational fluctuation of the engine 10 when the fuel injection amount is increased differs depending on the direction of the air-fuel ratio deviation. The ECU 50 uses this property to grasp the aspect of the rotational fluctuation of the engine 10 when the fuel injection amount is increased based on the detection information of the crank angle sensor 52, and determines the direction of the air-fuel ratio deviation from the fluctuation aspect. It is possible to determine whether or not a lean imbalance cylinder has occurred.

  Although not shown in detail, the crank angle sensor 52 includes a toothed crank angle detection rotor that rotates integrally with the crankshaft, and an electromagnetic pickup disposed in the vicinity thereof. A plurality of teeth are formed at a predetermined angular pitch (for example, at an interval of 10 ° CA) on the outer peripheral portion, and a missing tooth portion is provided. The electromagnetic pickup generates a voltage pulse when the teeth of the crank angle detection rotor accompanying the rotation of the crankshaft pass in the vicinity. Therefore, when the missing tooth portion passes in the vicinity of the electromagnetic pickup, the generation interval of the voltage pulse becomes long, but in other cases, the voltage pulse is generated every 10 ° CA, for example.

The ECU 50 calculates the time required for the crank angle to change by a predetermined angle (for example, 10 ° CA) based on the voltage pulse from the crank angle sensor 52 as the crank rotation time T [s], and further, Every time the rotation time T is calculated, a time difference (hereinafter referred to as a rotation time difference) ΔT from the previous crank rotation time T is calculated. Therefore, assuming that the crank rotation time T calculated this time is T _n and the previous crank rotation time T is T _n−1 , the rotation time difference ΔT is calculated as ΔT = T _n −T _n−1 .

  As shown in FIG. 3A, the crankshaft of the engine 10 rotates twice (720 ° CA rotation) during one cycle of the engine cycle. Therefore, the crank angle of the engine 10 indicated by the solid line A in FIG. [° CA] changes in a sawtooth shape as shown in FIG. Further, the crank rotation time T [s] and the rotation time difference ΔT calculated by the ECU 50 change within a relatively narrow fluctuation range at the normal time as shown by a thin two-dot chain line in FIG. As shown by a solid line B in (a), when a lean imbalance cylinder is generated, the cylinder fluctuates greatly. Note that the crank rotation time T indicates that the crank rotation speed becomes slower as it is positioned higher in FIG. 3A (the rotation time becomes longer), and is positioned lower in FIG. 3A (rotation). This shows that the shorter the time), the faster the crank rotation speed.

  The ECU 50 calculates an angular velocity ω [rad / s] and an angular velocity difference Δω [rad / s] corresponding to the crank rotation time T [s] and the rotation time difference ΔT instead of the crank rotation time T [s] and the rotation time difference ΔT. May be. In this case, the crank angle of the engine 10, the angular speed ω of the crank rotation, and the angular speed difference Δω change as shown in FIG.

  Since the piston in each cylinder 11 reaches the top dead center twice in one cycle of the engine cycle of the engine 10, accurate cylinder discrimination cannot be performed only with the detection signal of the crank angle sensor 52. In addition to the crank angle sensor 52, cylinder detection is performed by using a detection signal of a cam angle sensor (not shown). However, since such a technique itself is known, it will not be described in detail here.

  Next, a method for calculating the imbalance rate and a method for determining the direction of the air-fuel ratio deviation from the mode of rotational fluctuation when the fuel injection amount is increased will be described.

The ECU 50 has a remarkable timing difference suitable for measuring the variation of the crank rotation speed (rotation time T or angular velocity ω) for each combustion of each cylinder 11, for example, the difference in crank rotation speed due to the variation of the combustion air-fuel ratio. At a specific crank angle position near an easy compression top dead center (indicated by TDC in FIGS. 3A and 3B), a crank rotation speed for each combustion of each cylinder 11, for example, an angular speed ω _n is acquired. An angular velocity difference Δω that is a rotational fluctuation amount between the cylinders 11 in the order of explosion (for example, the order of # 1, # 3, # 4, and # 2) is calculated. Assuming that the cylinder number of the current speed measurement target cylinder is n and the previous speed measurement target cylinder number is n-1, the rotation time Δωn here is the current measured angular speed ω _n −the last measured angular speed. The difference is ω _n−1 .

  FIG. 4 shows the relationship between the angular velocity difference Δω between the cylinders 11 before and after such explosion order and the imbalance ratio of the air-fuel ratio in each cylinder 11, where α is an air-fuel ratio abnormality. This is a determination threshold value for determining whether or not to determine.

  As shown in FIG. 4, on the lean side, the angular velocity difference Δω representing the amount of variation in rotation between cylinders exceeds the determination threshold α even if the absolute value of the imbalance rate IB is relatively small. On the rich side, Even if the imbalance rate is such that a certain amount of air-fuel ratio deviation occurs, there is a low fluctuation range in which the determination threshold value α is not exceeded and rotation fluctuation does not occur so much. Further, in the range on the lean side and the rich side exceeding the low fluctuation range, the rotational fluctuation increases as the absolute value of the imbalance rate IB increases.

  Here, as shown by a right-pointing thick arrow in FIG. 4, by increasing the fuel supply amount (port injection amount) to one target cylinder 11 within these three ranges by a certain amount, the imbalance rate IB Is shifted to the plus side. In that case, on the lean side, the rotational fluctuation decreases from the state in which the rotational fluctuation exceeding the determination threshold value α occurs in the target cylinder 11 until the angular speed difference Δω falls below the determination threshold value α, and in the low fluctuation range, the angular speed difference Δω is much smaller. Without change, on the rich side exceeding the low fluctuation range, the rotation fluctuation due to the rich deviation that has not been manifested in the target cylinder 11 before the increase is generated as the rotation fluctuation exceeding the determination threshold value α.

  Therefore, for the target cylinder 11 whose fuel supply amount has been increased due to the change in the angular velocity difference Δω before and after increasing the fuel supply amount to the target cylinder 11, is the imbalance rate on the lean side without increasing the fuel supply amount? It is possible to determine whether the engine is on the rich side, whether the imbalance rate in the state where there is no increase is within the low fluctuation range (whether the air-fuel ratio deviation is within the normal range), and further, a lean imbalance cylinder is generated. It can be determined whether or not.

  FIG. 5 shows the relationship between the amount of change dΔω in the angular velocity difference Δω before and after the increase in the fuel supply amount to the target cylinder 11 and the imbalance rate IB, and also from this figure, before and after the increase in the fuel injection amount. From the change amount dΔω of the angular velocity difference Δω, it can be determined whether the imbalance rate of the cylinder 11 is on the lean side or the rich side, that is, the direction of the air-fuel ratio shift, and the air-fuel ratio shift is in the normal range (in the figure). It can be seen that it is also possible to determine whether it is within the range of the difference in rotational fluctuation from δ to γ. Here, the difference values δ and γ of the variation amount may or may not be equal to each other in absolute value.

  The ECU 50 stores and holds information necessary for determining the determination threshold value α and the air-fuel ratio deviation direction as design data or map information created based on the experimental data in advance, and the air-fuel ratio deviation direction based on the map or the like. Determination and air-fuel ratio deviation abnormality determination are executed.

  On the other hand, the ECU 50 executes idle-up control (hereinafter also referred to as start-first idle operation) for increasing the engine speed to a constant speed during the first warm-up after the engine 10 is started. When there is a cylinder 11 that causes rotational fluctuation due to a failure, the cylinder-by-cylinder increase correction is executed in stages, and the cylinder-by-cylinder increase correction execution flag indicating the occurrence of the process is set to “1 (ON)”. It has become.

  The cylinder-by-cylinder increase correction referred to here is based on the condition that the fluctuation amount of the rotational speed (engine speed [rpm]) during start-up first idle operation of the engine 10 deviates from the target rotational speed range. The fuel injection amount is increased to reduce the fluctuation amount of the engine rotation speed. In this cylinder-by-cylinder increase correction, for example, one target cylinder 11 (hereinafter referred to as a target cylinder) 11 is switched in order of the cylinder number in order to converge the variation amount of the engine rotational speed to the target rotational speed range. This is a correction process for increasing the fuel supply amount so as to increase the fuel injection amount this time, and the discharge of unburned fuel gas from the cylinder 11 in which misfire or deterioration of combustion has increased, resulting in HC (hydrocarbon in the catalytic converter 40). ) Is prevented from decreasing.

  The ECU 50 detects an air-fuel ratio shift cylinder in which the rotational speed drops by a certain level or more due to misfire or deterioration of combustion, and executes cylinder-by-cylinder increase correction for increasing the fuel injection amount for the cylinder 11. In addition to that, the ECU 50 as the air-fuel ratio deviation cylinder detection mechanism estimates the imbalance rate from the amount of change in rotational fluctuation before and after the increase of the fuel injection amount for the target cylinder 11 that is the target of the cylinder-by-cylinder increase correction. At the same time, it is determined whether or not the vehicle is in a lean imbalance cylinder. Depending on the operating state of the engine 10, it may be preferable that the cylinder-by-cylinder increase correction cannot be performed or not executed. In this case, the cylinder-by-cylinder increase correction execution flag is reset to “0 (OFF)”. The cylinder-by-cylinder increase correction is not executed.

  Further, the ECU 50 confirms that the cylinder-by-cylinder increase correction processing at the time of start first idling is executed by setting the cylinder-by-cylinder increase correction execution flag (a state set to 1), and the lean imbalance cylinder is When it is determined that the exhaust gas has occurred, the exhaust gas deterioration suppression control including switching of the execution condition of the fuel cut processing described above is executed. That is, the ECU 50 functions as exhaust gas deterioration suppression control means.

  Specifically, when it is determined that the cylinder-by-cylinder increase correction execution flag is “1” and the lean imbalance cylinder is generated, the ECU 50 performs the fuel cut execution period according to the operating state of the engine 10. Is increased more than usual. That is, the ECU 50 increases the cylinder-by-cylinder increase with respect to the fuel cut execution period under a normal operating state in which it is determined that the cylinder-by-cylinder increase correction execution flag is “0” or that a lean imbalance cylinder has not occurred. The execution period of the fuel cut when the correction execution flag is “1” and the air-fuel ratio abnormality is determined as the occurrence of the lean imbalance cylinder is increased to a long period. Further, when it is determined that the cylinder-by-cylinder increase correction execution flag is “1” and the lean imbalance cylinder is generated during the start first idle operation, the ECU 50 determines the current trip of the hybrid vehicle equipped with the engine 10. During the operation continuation period of the hybrid drive device including the engine 10 (hereinafter referred to as the current trip), the fuel supply stop condition for increasing the fuel cut execution period than usual is maintained. The current trip here includes a period in which the engine 10 is in an intermittent stop state when the motor is driven and an idling stop period in which the operation of the hybrid drive apparatus is intermittently stopped. Corresponds to the duration.

  In this way, the ECU 50 sets the required load of the engine 10 on the condition that the deviation amount of the combustion air-fuel ratio with respect to the target air-fuel ratio at the start-up first idling is out of a certain range and varies to the lean side. The execution period of the corresponding fuel cut process is increased with respect to the execution period in the operation state in which the air-fuel ratio deviation cylinder does not occur.

  More specifically, the ECU 50 performs the above-described fuel cut processing according to a control program stored in a ROM or the like under the first fuel supply stop condition on the condition that a lean imbalance cylinder (air-fuel ratio deviation cylinder) does not occur. This is executed under the second fuel supply stop condition where the execution frequency of the fuel cut process is higher than that of the first fuel supply stop condition.

  In the first fuel supply stop condition, the fuel cut region lower limit rotational speed N1 is set to 1000 rpm, for example, and the fuel cut region upper limit rotational speed N2 is set to 2000 rpm, for example. The fuel cut delay time described above is set as the first delay time Tdf1 according to the vehicle speed under the first fuel supply stop condition.

  On the other hand, in the second fuel supply stop condition, the fuel cut region lower limit rotational speed N1 is set to 950 rpm, for example, and the fuel cut region upper limit rotational speed N2 is set to 2100 rpm, for example. The fuel cut delay time described above is set according to the vehicle speed as a second delay time Tdf2 (<Tdf1) that is shorter than the first delay time Tdf1.

  That is, the ECU 50 executes the fuel cut process on the condition that the required load on the engine 10 has reached the threshold value or less, and the delay set according to the operating state of the engine 10 from the time when the required load has reached the threshold value or less. When the fuel supply to each cylinder is stopped when the time Tdf elapses and the execution period of the fuel cut processing is increased, the delay time Tdf is changed from the first delay time Tdf1 to a second delay time Tdf2 shorter than that. It has come to be shortened.

  The ECU 50 further controls the operation of the engine 10 in accordance with a command value from the HVECU which is an electronic control unit for hybrid drive control (not shown).

  The HVECU is a hybrid drive including the engine 10 and the electric motor based on the required accelerator opening Acc (driver's requested output) from the accelerator opening sensor 56 and various sensor information on the vehicle speed at that time and other vehicle running conditions. A target vehicle speed is set for each control cycle of the apparatus. Further, the HVECU stores in advance in a memory such as a ROM a specific vehicle speed range in which the target vehicle speed makes the hybrid vehicle run with electric motor output by intermittently stopping the output of the engine 10 and becomes highly efficient as a whole hybrid drive device. In addition, the intermittent permission vehicle speed that is the upper limit vehicle speed in the specific vehicle speed range is set to any one of the first intermittent permission vehicle speed V1 (see FIG. 8) and the second intermittent permission vehicle speed V2 set on the higher speed side. It can be switched.

  The first intermittently permitted vehicle speed V1 here is an intermittently permitted vehicle speed under a normal driving state in which it is determined that the cylinder-by-cylinder increase correction execution flag is “0” or no lean imbalance cylinder is generated. The second intermittently permitted vehicle speed V2 is set to be switchable as the intermittently permitted vehicle speed when the cylinder-by-cylinder increase correction execution flag is “1” and it is determined that the lean imbalance cylinder is generated. Is done.

  That is, the ECU 50 cooperates with the HVECU to increase the power load ratio of the motor among the power required for the hybrid drive device on the condition that a lean imbalance cylinder has occurred, while the power load ratio of the engine 10 Is reduced, the frequency of intermittent stop of the engine 10 in the hybrid drive device is increased, and the operating time of the engine 10 is reduced. Further, the HVECU compensates for the shortage of power due to an increase in the intermittent stop frequency (stop count and stop time) of the engine 10 by increasing the output frequency of the electric motor in the hybrid drive device.

  Here, the switching process from the first intermittent permission vehicle speed V1 to the second intermittent permission vehicle speed V2 on the higher speed side switches the intermittent stop time of the engine 10 to a longer time, and the fuel cut processing time described above. Similar to the process of increasing the exhaust gas, the process contributes to suppressing the exhaust air-fuel ratio of the exhaust gas flowing into the catalytic converter 40 from becoming rich while reducing misfire in the lean imbalance cylinder. That is, the process of stopping the engine 10 during the intermittent stop period corresponds to the fuel supply stop process according to the present invention.

  The HVECU determines which of the engine 10 and the electric motor is operated as a prime mover, a required output value, a storage state of the secondary battery for hybrid drive, an EV travel selection switch, an eco switch, and a sports travel mode selection (not shown). It is determined according to the ON / OFF state of the switch. Therefore, the hybrid vehicle has an engine traveling that travels using only the power from the engine 10, an HV traveling that travels using both the engine 10 and the electric motor (hybrid traveling), and an EV traveling that travels only using the power from the electric motor (electric vehicle traveling). You can run either

  Next, the operation will be described.

  In the control apparatus for an internal combustion engine of the present embodiment configured as described above, there is a cylinder 11 that causes a rotational fluctuation due to misfire or combustion failure during the start-up first idle operation of the engine 10, and the engine speed Ne is the target. When out of the rotational speed range, correction for increasing the fuel injection amount for each cylinder in a stepwise manner is executed, and the cylinder-by-cylinder increase correction execution flag indicating the occurrence of the cylinder-specific increase correction is set to “1”.

  Assuming that the vehicle speed of the hybrid vehicle is in a specific vehicle speed range, the start fast idle operation of the engine 10 can be executed while the hybrid vehicle is running on the motor, and the learning control of the air-fuel ratio feedback is also executed during the operation time. It is easy to secure time for performing the cylinder-by-cylinder increase correction, the generation detection process of the lean imbalance cylinder (air-fuel ratio deviation cylinder), and the like.

  FIG. 6 shows a schematic flow of the exhaust gas deterioration suppression control that is executed when the ECU 50 detects a lean imbalance cylinder.

  In this control, first, it is determined from the set state of the execution flag for the cylinder-by-cylinder increase correction whether or not the cylinder-by-cylinder increase correction has been executed during the start fast idle operation (step S11).

  At this time, if the cylinder-by-cylinder increase correction execution flag is not set (NO in step S11), then, the first fuel supply stop condition is set or the set state is maintained ( Step S14), the current process ends.

  In this state, as described above, the fuel cut region lower limit rotational speed N1 is set to 1000 rpm, for example, and the fuel cut region upper limit rotational speed N2 is set to 2000 rpm, for example. Further, the fuel cut delay time is set as the first delay time Tdf1 according to the vehicle speed.

  On the other hand, if the execution flag for the cylinder-by-cylinder increase correction is set (in the case of YES at step S11), it is then determined whether or not a lean imbalance cylinder has occurred (step S12).

  At this time, if the lean imbalance cylinder is not generated (NO in step S12), then, the first fuel supply stop condition is set or the set state is maintained (step S14). This process ends.

  On the other hand, if a lean imbalance cylinder has occurred (YES in step S12), then, after the second fuel supply stop condition is set, the current process ends.

  In this state, as described above, the fuel cut region lower limit rotational speed N1 is set to 950 rpm, for example, and the fuel cut region upper limit rotational speed N2 is set to 2100 rpm, for example. The fuel cut delay time is set according to the vehicle speed as a second delay time Tdf2, which is shorter than the first delay time Tdf1. Further, the ECU 50 and the HVECU increase the power load ratio of the motor among the power required for the hybrid drive device, while decreasing the power load ratio of the engine 10, and the above-described intermittent permission vehicle speed is set to the first intermittent permission. The vehicle speed is switched from the vehicle speed V1 to the second intermittent permission vehicle speed V2 set on the higher speed side.

  FIG. 7 shows an air-fuel ratio shift that can determine whether or not a lean imbalance cylinder has occurred while determining the direction of the air-fuel ratio shift from the rotational fluctuation mode when the fuel injection amount is increased for each cylinder 11 of the engine 10. The flow of detection processing is shown. This process may be executed only for a specific cylinder 11 suspected of being a lean imbalance cylinder, or may be executed sequentially for all cylinders 11.

  First, the cylinder counter CT is set to a counter value corresponding to the cylinder 11 of the cylinder number n that is the current determination target, for example, zero corresponding to the first cylinder (cylinder indicated by # 1 in FIG. 1) (step S21). ).

  Next, the engine 10 is in a predetermined operating state after starting, for example, the cooling water temperature is equal to or lower than a predetermined temperature (for example, 70 ° C.), and within a predetermined load range (the intake amount per second is about 15 to 50 g, for example). In addition, it is determined whether or not the engine speed is within a predetermined speed range (for example, about 1500 to 2000 rpm). This determination corresponds to determination of whether or not air-fuel ratio feedback correction has been started so that the combustion air-fuel ratio in the cylinder 11 follows the stoichiometric air-fuel ratio for exhaust gas purification by the catalytic converter 40.

  At this time, if the engine 10 is in a predetermined operation state after starting (YES in step S22), then, for the first cylinder that is the current target cylinder under an operation state in which the cylinder-by-cylinder increase correction is not executed. Specific data such as the output value of the crank angle sensor 52 related to the operation data, in particular, the rotational fluctuation is collected (step S23).

  Next, under the operation state in which the cylinder-by-cylinder increase correction for the current target cylinder 11 is performed, the operation data for the target cylinder, for example, the first cylinder, particularly the specific data such as the output value of the crank angle sensor 52 related to the rotation fluctuation Are collected (step S24).

  Then, Δωna, which is the rotational speed difference Δωn for the target cylinder 11 in the operating state where the cylinder-by-cylinder increase correction is not executed, and Δωnb, which is the rotational speed difference Δωn for the target cylinder 11 in the operating state where the cylinder-by-cylinder increase correction is executed. Are calculated (step S25), the change amount dΔωn of the angular velocity difference Δωn before and after the fuel supply amount increase correction is calculated from the difference value (Δωna−Δωnb) (step S26).

  Next, it is determined whether or not the change amount dΔωn of the angular velocity difference Δωn is equal to or smaller than a first predetermined value γ (step S27). If the determination result is YES, then the change amount dΔωn is the first change amount dΔωn. It is determined whether or not it is equal to or less than a predetermined value γ (step S28).

  Then, if the change amount dΔωn of the angular velocity difference Δωn exceeds the first predetermined value γ, it is determined that the air-fuel ratio deviation is out of the rich side (“rich abnormality” in FIG. 7) (step 7). S29) If the amount of change dΔωn of the angular velocity difference Δωn exceeds the first predetermined value γ, it is determined that the air-fuel ratio deviation is outside the lean side (“lean abnormality” in FIG. 7). (Step S30).

  Next, the cylinder counter CT is set to the counter value CT + 1 corresponding to the next target cylinder from the counter value corresponding to the cylinder 11 of the cylinder number n which is the current determination target (step S31). When the counter value CT becomes 4 and the process of lean imbalance detection for the total number of cylinders of the engine 10 is completed (in the case of YES in step S32), the current series of detection processes ends.

  FIG. 8 shows the vehicle speed of the hybrid vehicle when the control as described above is executed, the engine speed of the engine 10, the setting timing of the cylinder-specific increase correction execution flag of the engine 10, and the setting timing of the fuel cut execution flag. Is illustrated.

  The hybrid vehicle on which the engine 10 is mounted can be driven by only the electric motor constituting the hybrid drive device together with the engine 10, and the engine 10 is intermittently stopped, but the power-on state of the ECU 50 is maintained during the current trip.

  In the case shown in FIG. 8, after the engine 10 is started, first, an execution flag for cylinder-by-cylinder increase correction is set on condition that the engine speed Ne during start-up fast idle operation deviates from the target rotation speed range, and cylinder-by-cylinder increase correction is performed. Is executed. Then, on the condition that the exhaust gas deterioration suppression control process shown in FIG. 6 is executed and the cylinder-by-cylinder increase correction is executed, it is checked whether or not a lean imbalance cylinder is generated, and a lean imbalance cylinder is generated. If so, the fuel supply stop condition is switched from the first fuel supply stop condition to the second fuel supply stop condition. Furthermore, the intermittent permission vehicle speed, which is the upper limit vehicle speed in the specific vehicle speed range in which the engine 10 can be intermittently stopped, is switched to the second intermittent permission vehicle speed V2 set on the higher speed side than the first intermittent permission vehicle speed V1.

  Here, if a command for intermittently stopping the engine 10 is output at time tc in FIG. 8 according to a command from the HVECU, the intermittent permission vehicle speed is set higher than the first intermittent permission vehicle speed V1 at this time. In this embodiment (in the case indicated by the solid line PI in the figure), the intermittent stop condition of the engine 10 is normal (conventional system indicated by the dotted line PA in the figure). (In the case of the comparative example), it is established earlier.

  Further, at time td in FIG. 8, if the accelerator opening from the accelerator opening sensor 56 is fully closed or close to a low opening range, the fuel supply stop condition is the first fuel supply stop condition at this time. Since the condition is switched to the second fuel supply stop condition, the fuel cut processing condition is established earlier than usual (in the case of the comparative example of the conventional method indicated by the dotted line PA in the figure), and the fuel cut The execution frequency of processing will also increase.

  As described above, in the present embodiment, when a lean imbalance cylinder is generated in which the deviation amount of the combustion air-fuel ratio with respect to the target air-fuel ratio of the engine 10 deviates from a certain range and varies toward the lean side, the selection is made according to the required load of the engine 10. The fuel supply stop condition is switched so as to increase the execution period of the fuel cut process that is executed in an automatic manner with respect to the execution period in the operation state in which the lean imbalance cylinder does not occur.

  Accordingly, in terms of driving comfort (drivability) and suppression of deterioration of the catalytic converter 40 due to fuel cut when the catalyst is hot, it is somewhat inferior to normal, but under the condition of air-fuel ratio abnormality generated by the lean imbalance cylinder, An increase in the amount of fuel supplied to each cylinder 11 by feedback control due to the influence of the lean imbalance cylinder is suppressed by the fuel cut process, and the fuel supply to each cylinder 11 is avoided while avoiding the influence of misfire etc. in the lean imbalance cylinder. The amount can be reliably reduced. As a result, the exhaust air-fuel ratio of the exhaust gas flowing into the catalytic converter 40 is prevented from becoming rich, and the exhaust gas deterioration caused by the reduction of the unburned hydrocarbon (HC) purification rate by the catalytic converter 40 is effectively suppressed. It is possible to reliably prevent the exhaust gas purification performance of the catalytic converter 40 from being deteriorated.

  That is, in the present embodiment, the fuel cut process is executed under the first fuel supply stop condition on the condition that no lean imbalance cylinder is generated, and the first fuel supply stop is performed on the condition that the lean imbalance cylinder is generated. It is executed under the second fuel supply stop condition where the frequency of execution of the fuel cut process is higher than the condition. Therefore, the lean fuel supply amount in each cylinder 11 due to the influence of the lean imbalance cylinder is reduced by the fuel cut process to reduce the fuel injection amount, thereby reducing the fuel injection amount. It is possible to suppress the exhaust air / fuel ratio of the exhaust gas flowing into the catalytic converter 40 from becoming rich while reducing misfiring in the cylinder, and the purification rate of unburned hydrocarbons in the catalytic converter 40 is reduced. Can be effectively suppressed.

  In particular, in the present embodiment, the lean imbalance cylinder detection mechanism in which the ECU 50 detects the occurrence of a lean imbalance cylinder based on the amount of change in the rotational speed of the engine 10 when the fuel supply amount of the engine 10 is changed for each cylinder. The fuel cut processing is executed under the second fuel supply stop condition on the condition that the lean imbalance cylinder is detected when the engine 10 is warmed up.

  Therefore, it is possible to detect the lean imbalance cylinder with relative accuracy by using the existing sensors such as the crank angle sensor 52 for detecting the fuel injection amount and the engine rotational speed Ne, and moreover, It is possible to reliably increase the frequency of execution of the fuel cut process when the balance cylinder is generated.

  Further, the ECU 50 performs cylinder-by-cylinder increase correction that increases the fuel supply amount for each cylinder of the engine 10 and reduces the rotation variation amount on condition that the rotation variation amount during the warm-up of the engine 10 deviates from the target rotation speed range. The detection process of the lean imbalance cylinder by the lean imbalance cylinder detection mechanism is executed under the condition that it is selectively executed and the cylinder-by-cylinder increase correction is executed. Therefore, when a remarkable rotational fluctuation occurs during the start first idle operation and the cylinder-by-cylinder increase correction is executed, the ECU 50 is operated as a lean imbalance cylinder detection mechanism, while a lean imbalance cylinder is not generated, and the influence is significant. When the rotation fluctuation does not occur, the processing load for detecting the lean imbalance cylinder can be reduced, and the ECU 50 that is a hardware resource mounted on the vehicle can be effectively used.

  Further, in the present embodiment, the fuel cut processing is executed on condition that the required load on the engine 10 has reached the threshold value or less, and is set according to the operating state of the engine 10 from the time when the required load has reached the threshold value or less. When the delay time Tdf elapses, the fuel supply to each cylinder 11 is stopped, and when the execution period of the fuel cut processing is increased, the delay time Tdf is shortened. Therefore, it is possible to easily and surely extend the execution period of the fuel cut processing, for example, by adding a simple processing step to the existing fuel cut processing means.

  In addition, the control device for the internal combustion engine of the present embodiment is equipped with a hybrid vehicle that constitutes a hybrid drive device for driving driving with the electric motor 10 and a lean imbalance cylinder (abnormal air-fuel ratio deviation cylinder) is generated. As a result, the ECU 50 and the HVECU cooperate to increase the power share of the motor among the power required for the hybrid drive device, while decreasing the power share of the engine 10 to increase the intermittent permission vehicle speed. To the side, the frequency of intermittent stop of the engine 10 in the hybrid drive device is increased. Therefore, by increasing the intermittent stop period of the engine 10, the exhaust air-fuel ratio of the exhaust gas flowing into the catalytic converter 40 is enriched while reducing misfire and the like in the lean imbalance cylinder where the fuel injection amount has become excessive. Can be suppressed, and the reduction in the purification rate of unburned hydrocarbons in the catalytic converter 40 can be effectively suppressed.

  Thus, according to the present embodiment, even when the fuel supply amount to each cylinder 11 and the combustion air-fuel ratio shift to the rich side due to the feedback processing due to the influence of the exhaust gas from the lean imbalance cylinder, the start-up warm-up, etc. Of the engine 10 in which the exhaust air-fuel ratio in the catalytic converter 40 can be prevented from being excessively corrected to the rich side, and the exhaust purification performance of the catalytic converter 40 can be reliably prevented from deteriorating. An apparatus can be provided.

  In the above-described one embodiment, the imbalance rate is calculated for at least one target cylinder of the engine 10 and when the fuel injection amount increase correction is executed for the target cylinder and when the increase correction is not executed. The determination of whether or not the engine has fallen into a lean imbalance cylinder with an abnormal air-fuel ratio is performed selectively based on the difference in rotational fluctuation of the engine, but the imbalance rate is limited to such an estimation method. Instead, it may be estimated from, for example, the periodic fluctuation of the output of the first air-fuel ratio sensor 42 and the slope of the fluctuation of the output value in the specific section.

  Further, in the above-described embodiment, when switching from the first fuel supply stop condition to the second fuel supply stop condition, the hybrid vehicle may be driven by the motor output by intermittently stopping the output of the engine 10. The intermittent permission vehicle speed, which is the upper limit vehicle speed of the specific vehicle speed range that is highly efficient as a whole device, is switched from the first intermittent permission vehicle speed V1 to the second intermittent permission vehicle speed V2 on the higher speed side, and the engine 10 is intermittently stopped. However, the intermittent start permission vehicle speed, which is the lower limit vehicle speed of a specific hybrid drive vehicle speed range in which the engine 10 is intermittently operated and the hybrid vehicle is driven by the outputs of both the engine 10 and the electric motor, It may be switched from the first intermittent start permission vehicle speed V1 ′ to the second intermittent start permission vehicle speed V2 ′ on the lower speed side. Needless to say.

  Further, by reducing the tightening speed of the throttle opening when the engine 10 is stopped, a process for leaning the exhaust air / fuel ratio of the exhaust gas flowing into the catalytic converter 40 is added, and the exhaust gas at the time of abnormal air / fuel ratio is added. Deterioration suppression control can also be achieved.

  Further, in the above-described embodiment, the target cylinder of the fuel cut for temporarily stopping the fuel injection during the engine rotation of the engine 10 is each one of all the cylinders of the engine 10. In the case of having a plurality of banks such as a V-type internal combustion engine, each cylinder in a specific bank including an air-fuel ratio deviation cylinder may be used. That is, the target cylinders for fuel cut need not be all cylinders.

  As described above, according to the present invention, even when the fuel supply amount to each cylinder and the combustion air-fuel ratio shift to the rich side due to feedback processing due to the influence of exhaust gas from the air-fuel ratio shift cylinder, Provided is a control device for an internal combustion engine that can prevent the exhaust air-fuel ratio in the catalytic converter from being overcorrected to the rich side and can reliably prevent the exhaust gas purification performance of the catalytic converter from deteriorating. can do. The present invention as described above is useful for all internal combustion engine control devices suitable for executing air-fuel ratio feedback control of a multi-cylinder internal combustion engine and suppressing variation in air-fuel ratio among cylinders.

10 Engine (Internal combustion engine)
11 cylinders (target cylinder, specific cylinder)
DESCRIPTION OF SYMBOLS 12 Engine main body 14 Combustion chamber 16 Spark plug 18 Intake branch pipe 19 Surge tank 20 Intake manifold 21 Intake passage 22 Intake pipe 23 Air cleaner 24 Air flow meter 25 Throttle valve 26 Injector (fuel injection valve)
30 Exhaust manifold 32 Exhaust branch pipe 34 Collecting pipe section 36 Exhaust pipe 40 Catalytic converter 42 First air-fuel ratio sensor (upstream air-fuel ratio sensor, pre-catalyst sensor)
44 Second air-fuel ratio sensor (downstream air-fuel ratio sensor, post-catalyst sensor)
50 ECU (air-fuel ratio deviation cylinder detection mechanism, exhaust gas deterioration suppression control means, main feedback control means, sub-feedback control means)
52 Crank angle sensor 54 Water temperature sensor 56 Accelerator opening sensor (load detection means)
N1 Fuel cut region lower limit rotation speed N2 Fuel cut region upper limit rotation speed Tdf1 First delay time Tdf2 Second delay time V1 First intermittent permission vehicle speed V2 Second intermittent permission vehicle speed

Claims (7)

An exhaust air / fuel ratio is detected by an air / fuel ratio sensor on an exhaust path of a multi-cylinder internal combustion engine equipped with a catalytic converter for purifying exhaust gas, and a fuel supply amount to each cylinder of the internal combustion engine based on a detection value of the air / fuel ratio sensor The feedback control is performed so that the combustion air-fuel ratio in each cylinder follows the target air-fuel ratio is corrected, and the fuel supply to each cylinder of the internal combustion engine is stopped according to the operating state of the internal combustion engine A control device for an internal combustion engine that selectively executes a fuel supply stop process,
The fuel supply stop process according to the required load of the internal combustion engine is performed on the condition that a deviation amount of the combustion air-fuel ratio with respect to the target air-fuel ratio deviates from a predetermined range and varies toward the lean side. A control apparatus for an internal combustion engine, wherein an execution period is increased with respect to an execution period in an operating state in which the air-fuel ratio deviation cylinder does not occur.   The fuel supply stop process is executed under a first fuel supply stop execution condition on the condition that the air-fuel ratio shift cylinder does not occur, and on the condition that the air-fuel ratio shift cylinder is generated The control apparatus for an internal combustion engine, which is executed under a second fuel supply stop execution condition where the execution frequency of the fuel supply stop process is higher than the stop execution condition. An air-fuel ratio deviation cylinder detection mechanism for detecting that the air-fuel ratio deviation cylinder is generated based on the amount of change in the rotational speed of the internal combustion engine when the fuel supply amount of the internal combustion engine is changed for each cylinder;
The fuel supply stop process is performed under the second fuel supply stop execution condition on the condition that the air / fuel ratio shift cylinder detection mechanism detects that the air / fuel ratio shift cylinder is generated when the internal combustion engine is warmed up. The control device for an internal combustion engine according to claim 2, wherein the control device is executed. Selection of cylinder-by-cylinder increase correction that reduces the rotation fluctuation amount by increasing the fuel supply amount for each cylinder of the internal combustion engine on the condition that the rotation fluctuation amount during warm-up of the internal combustion engine deviates from the target rotation speed range Run
4. The control device for an internal combustion engine according to claim 3, wherein the detection processing of the air-fuel ratio shift cylinder by the air-fuel ratio shift cylinder detection mechanism is executed on condition that the cylinder-by-cylinder increase correction is executed. The fuel supply stop process is executed on condition that the required load on the internal combustion engine has reached a threshold value or less, and a delay set in accordance with the operating state of the internal combustion engine from the time when the required load has reached the threshold value or less. When the time elapses, the fuel supply to each cylinder is stopped,
The control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the delay time is shortened when the execution period of the fuel supply stop process is increased. The internal combustion engine is equipped with a hybrid vehicle that constitutes a hybrid drive device for traveling drive together with an electric motor,
When executing the fuel supply stop process, the power load ratio of the electric motor among the power required for the hybrid drive apparatus is increased, while the power load ratio of the internal combustion engine is decreased, and the hybrid drive apparatus The control device for an internal combustion engine according to any one of claims 1 to 5, wherein the frequency of intermittent stop of the internal combustion engine is increased.   7. The fuel injection system according to claim 1, wherein when the fuel supply stop process is executed, fuel injection to each of the cylinders is temporarily stopped during engine rotation of the internal combustion engine. The control apparatus of the internal combustion engine described in 1.

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