JP2012097636A - Control device of multi-cylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change an air-fuel ratio of an engine in such a manner that it matches a changed target air-fuel ratio with sufficient responsiveness and to maintain a share between port injection and in-cylinder injection as much as possible.SOLUTION: A control device of a multi-cylinder internal combustion engine determines whether or not a target air-fuel ratio is inverted from a ratio in a lean side to a ratio in a rich side based on an output value of an air-fuel ratio sensor disposed downstream from a catalyst. When the target air-fuel ratio is inverted to an air-fuel ratio in a rich side, the control device determines completion of fuel injection by a port injection valve of the next combustion cylinder in an intake stroke in the current combustion cycle, and determines whether or not the intake valve is closed. When the intake valve is closed, the control device corrects an injection amount of the fuel by the in-cylinder injection valve based on the inverted (changed) target air-fuel ratio; and when the intake valve is open, the device corrects both of an injection amount of the fuel by the port injection valve and an injection amount of the fuel by the in-cylinder injection valve based on the changed air-fuel ratio.

Description

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

  Conventionally, an output value generated according to the air-fuel ratio of the gas (mixed exhaust gas) passing through the collective exhaust passage by the air-fuel ratio sensor disposed in the collective exhaust passage formed by collecting the exhaust passages extending from the plurality of cylinders. Based on the above, a control device for an internal combustion engine that performs feedback control of an air-fuel ratio of an internal combustion engine (hereinafter also simply referred to as “engine”) is widely known. The mixed exhaust gas is an exhaust gas obtained by mixing exhaust gases discharged from each cylinder. Specifically, in this control device, the air-fuel ratio common to a plurality of cylinders is set so that the air-fuel ratio of the engine (more specifically, the air-fuel ratio of the air-fuel mixture in the combustion chamber of each cylinder) matches the stoichiometric air-fuel ratio. A feedback correction amount is calculated based on the output value of the air-fuel ratio sensor. By adjusting the amount of fuel injected to each of the plurality of cylinders based on the air-fuel ratio feedback correction amount, the air-fuel ratio of the engine, in other words, the air-fuel ratio of the mixed exhaust gas is feedback-controlled.

  In recent years, in order to improve combustion efficiency, reduce fuel consumption, and the like, port injection means (port injection valve) for injecting fuel into the intake passage upstream of the intake valve, and fuel is directly injected into the combustion chamber of the cylinder. An internal combustion engine having both in-cylinder injection means (in-cylinder injection valve) has been developed. Hereinafter, a system including two fuel injection valves, that is, a port injection valve and an in-cylinder injection valve for each of a plurality of cylinders will be referred to as a “dual injection system”. In such a “dual injection system”, fuel injection by the port injection means (port injection valve) is referred to as “port injection”, and fuel injection by the in-cylinder injection means (in-cylinder injection valve) is referred to as “cylinder injection”. This is referred to as “inner injection”.

  And regarding the control apparatus which controls the air fuel ratio of an engine provided with such a "dual injection system", for example, in the following patent document 1, an air fuel ratio feedback system calculates the deviation between a target air fuel ratio and an air fuel ratio sensor value. Calculate the feedback correction amount by multiplying the deviation by a proportional gain, and multiply the calculated feedback correction amount by the basic injection amount multiplied by the share ratio of the in-cylinder injector (in-cylinder injection valve). It is described that it is added to the calculated injection amount of the in-cylinder injector (in-cylinder injection valve) and no feedback correction amount is added to the injection amount of the intake manifold injector (port injection valve). Further, for example, in Patent Document 2 below, a main air-fuel ratio sensor and a sub O2 sensor are arranged above and below the catalyst, and main feedback control based on the output of the main air-fuel ratio sensor is reflected in in-cylinder injection, and the output of the sub O2 sensor It is described that sub-feedback control based on the above is reflected in port injection.

JP 2006-258209 A JP 2007-32514 A

  In the control device described in Patent Document 1 described above, the target air-fuel ratio is realized by always adding the feedback correction amount only to the injection amount by the in-cylinder injector (in-cylinder injection valve). Here, the optimal value of the sharing rate changes every moment depending on the operating state of the engine. For this reason, in a situation where the feedback correction amount is always added only to the injection amount by the in-cylinder injector (in-cylinder injection valve), the optimum sharing ratio cannot always be maintained. On the other hand, in the control device described in Patent Document 2 described above, the sub feedback control based on the output of the sub O2 sensor arranged downstream of the catalyst is reflected only in the port injection. Here, in the port injection, the fuel injected only when the intake valve is open is sucked into the combustion chamber of the cylinder. For this reason, even if the sub feedback control based on the output of the sub O2 sensor is reflected in the port injection, the fuel is sucked into the cylinder combustion chamber only when the intake valve is open, and the fuel is injected into the port injection. After that, it takes time to be sucked into the combustion chamber of the cylinder, and as a result, there is a possibility that good responsiveness cannot be obtained with respect to the change of the air-fuel ratio.

  The present invention has been made in order to address the above-described problems. The object of the present invention is to change the air-fuel ratio of the engine so as to match the changed target air-fuel ratio with good responsiveness, and to perform port injection and in-cylinder injection. It is an object of the present invention to provide a control device for a multi-cylinder internal combustion engine that can maintain the sharing ratio with the engine as much as possible.

  In order to achieve such an object, a control device (this control device) for a multi-cylinder internal combustion engine according to the present invention includes a port injection means (port injection valve) and a cylinder injection means (cylinder injection valve) for each of a plurality of cylinders. And is applied to a multi-cylinder internal combustion engine having The present control device includes an air-fuel ratio sensor, a target air-fuel ratio setting unit, an injection amount setting unit, and a feedback control unit.

  The port injection means is disposed corresponding to each of the plurality of cylinders. The port injection means injects fuel (port injection) in an intake passage upstream of the intake valves of the plurality of cylinders. The in-cylinder injection means is disposed corresponding to each of the plurality of cylinders. The in-cylinder injection means injects fuel (in-cylinder injection) in each combustion chamber of the plurality of cylinders. That is, one or more port injection means and in-cylinder injection means are provided for each cylinder, and fuel is injected into the cylinders corresponding to these injection 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 target air-fuel ratio setting means sets a target air-fuel ratio that is a target value of the air-fuel ratio of the air-fuel mixture in the combustion chambers of the plurality of cylinders. Thereby, the target air-fuel ratio can be set to an air-fuel ratio leaner than the stoichiometric air-fuel ratio (hereinafter also referred to as “lean air-fuel ratio”) depending on the situation. In addition, the target air-fuel ratio can be set to an air-fuel ratio richer than the stoichiometric air-fuel ratio (hereinafter also referred to as “rich air-fuel ratio”) depending on the situation. Alternatively, the target air-fuel ratio can be set to the stoichiometric air-fuel ratio depending on the situation.

  The injection amount setting means sets the fuel injection amount by the port injection means and the fuel injection amount by the in-cylinder injection means based on the operating state of the internal combustion engine and the set target air-fuel ratio. Examples of the “operating state” here include the engine operating speed (engine speed), the amount of air sucked into the combustion chamber (intake air amount), the engine coolant temperature (cooling water temperature), and the like. . As a result, the fuel injection amount by the port injection means and the fuel injection amount by the in-cylinder injection means are appropriate values corresponding to the operating state of the engine that can change from moment to moment while realizing the target air-fuel ratio, that is, In principle, the sharing rate will be set.

  The feedback control means includes a fuel injection amount by the port injection means based on an output value from the air-fuel ratio sensor so that an air-fuel ratio of the air-fuel mixture in the combustion chambers of the plurality of cylinders matches the target air-fuel ratio. The fuel injection amount by the in-cylinder injection means is feedback-controlled. As a result, the air-fuel ratio of the air-fuel mixture in the combustion chambers of the plurality of cylinders is feedback-controlled based on the output value from the air-fuel ratio sensor.

  One of the features of this control apparatus is that it includes an intake valve closing determination means. The intake valve closing determination means is the time when the target air-fuel ratio is changed from the air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio by the target air-fuel ratio setting means. In the combustion cycle, the port injection means arranged corresponding to the next combustion cylinder in the intake stroke has finished injection of the fuel injection amount set by the injection amount setting means, and the intake of the next combustion cylinder It is determined whether or not the valve is closed.

  In an engine having a dual injection system, in the next combustion cylinder in the intake stroke in the combustion cycle, first, the port injection means is located upstream of the intake valve immediately before entering the intake stroke, specifically immediately before the intake valve is opened. Port injection is performed in the intake passage. Subsequently, the intake valve is opened and the piston strokes from the intake top dead center to the intake bottom dead center, so that the atomized fuel in the intake passage enters the combustion chamber of the next combustion cylinder together with air. Inhaled. Then, immediately after the piston strokes to the intake bottom dead center, the intake valve is closed and the next combustion cylinder enters the compression stroke with the exhaust valve closed. That is, the fuel injected by the port injection means can be sucked into the combustion chamber only when the intake valve of the next combustion cylinder is opened and in the intake stroke.

  Therefore, at the time when the target air-fuel ratio is changed from the lean-side air-fuel ratio to the rich-side air-fuel ratio, if it is before fuel injection by the port injection means disposed corresponding to the next combustion cylinder, By injecting the fuel in which the port injection means is set in order to make the air-fuel ratio of the air-fuel mixture at the target air-fuel ratio coincide with the target air-fuel ratio, the port was injected into the combustion chamber of the next combustion cylinder along with the opening of the intake valve Fuel can be inhaled. Further, when the target air-fuel ratio is changed from the lean-side air-fuel ratio to the rich-side air-fuel ratio, if the next combustion cylinder is still in the intake stroke and the intake valve is opened, the port injection means, for example, After injecting the fuel set by the injection amount setting means in order to make the air-fuel ratio of the air-fuel mixture in the combustion chamber coincide with the target air-fuel ratio, the fuel was additionally injected into the combustion chamber of the next combustion cylinder. Fuel can be inhaled. However, in this case, if the lift amount of the intake valve is small, the fuel additionally injected by the port injection means is hardly sucked into the combustion chamber of the next combustion cylinder. Therefore, at least when the next combustion cylinder is in the compression stroke, when the target air-fuel ratio is changed from the lean-side air-fuel ratio to the rich-side air-fuel ratio by the target air-fuel ratio setting means, the port injection is already performed at the time of the change. Since the means has finished the fuel injection set by the injection amount setting means and the intake valve of the next combustion cylinder is closed, even if the port injection means additionally injects fuel, the combustion chamber Thus, it becomes impossible to make the air-fuel ratio of the air-fuel mixture coincide with the target air-fuel ratio.

  Thus, various restrictions are imposed when the port injection means additionally injects fuel in order to make the air-fuel ratio of the air-fuel mixture in the combustion chamber coincide with the target air-fuel ratio. On the other hand, the in-cylinder injection means has a compression stroke in which the intake valve is closed, not to mention the intake stroke in which the intake valve is opened, regardless of whether the intake valve of the next combustion cylinder is opened or closed. Even fuel can be injected. Therefore, the intake valve closing determination means at least performs the next combustion after the port injection means injects fuel when the target air-fuel ratio is changed from the lean air-fuel ratio to the rich air-fuel ratio by the target air-fuel ratio setting means. By determining whether or not the intake valve of the cylinder is closed, the in-cylinder injection means performs in-cylinder injection so that the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder quickly matches the target air-fuel ratio. Determine when to do. In other words, the intake valve closing determination means determines when port injection by the port injection means is impossible in order to quickly match the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder with the target air-fuel ratio. The case where the in-cylinder injection means in-cylinder injection is determined.

  Another feature of the present control device is that it includes an injection amount correction means. When the intake valve of the next combustion cylinder is closed, the injection amount correction means calculates the fuel injection amount set by the injection amount setting means with respect to the in-cylinder injection means. Correction is performed based on the output value and the changed target air-fuel ratio.

  As described above, when the intake valve of the next combustion cylinder is at least closed, the fuel injected by the port injection means is not sucked into the combustion chamber of the next combustion cylinder. Therefore, the injection amount correcting means determines the injection amount that is injected into the combustion chamber by the in-cylinder injection means that can inject fuel even when the intake valve of the next combustion cylinder is closed by the target air-fuel ratio setting means. Correction is made so as to correspond to the changed target air-fuel ratio (specifically, change from the lean-side air-fuel ratio to the rich-side air-fuel ratio). As a result, the in-cylinder injection means injects the fuel into the combustion chamber of the next combustion cylinder by the corrected injection amount, thereby changing the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder to the changed target air-fuel ratio. It can be matched quickly. It should be noted that, in the cylinders that will be the next combustion cylinders in the subsequent combustion cycles, the fuel injection amount by the port injection means and the fuel injection amount by the in-cylinder injection means based on the target air-fuel ratio that has been changed by the injection amount setting means Can be set. Thereby, the air-fuel ratio of the air-fuel mixture in the combustion chambers of all cylinders can be matched with the target air-fuel ratio.

  Another feature of the present control device is that the injection amount correction means is changed so that the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder matches the changed target air-fuel ratio. Based on the target air-fuel ratio and the output value of the air-fuel ratio sensor, a feedback correction amount for correcting the fuel injection amount for the in-cylinder injection unit set by the injection amount setting unit is calculated, and the feedback correction amount The in-cylinder injection means corrects the amount of fuel injected into the combustion chamber of the next combustion cylinder. Thereby, the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder can be made to coincide with the changed target air-fuel ratio more quickly and appropriately.

  Another feature of the present control device is that the air-fuel ratio sensor is disposed at least in the collective exhaust passage downstream of the catalyst disposed in the collective exhaust passage, and flows out of the catalyst. The air-fuel ratio sensor is configured to generate an output value corresponding to the air-fuel ratio of the mixed exhaust gas, and the target air-fuel ratio setting means changes the output value of the air-fuel ratio sensor disposed downstream of the catalyst. Accordingly, the target air-fuel ratio is changed from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio. According to this, the target air-fuel ratio setting means can change the target air-fuel ratio from the lean-side air-fuel ratio to the rich-side air-fuel ratio according to the state inside the catalyst disposed in the collective exhaust passage.

  In this case, specifically, the change in the output value of the air-fuel ratio sensor disposed downstream of the catalyst flows into the catalyst from the reducing atmosphere in which the exhaust gas flowing into the catalyst is reduced. The target air-fuel ratio setting means can change the target air-fuel ratio from the lean-side air-fuel ratio to the rich-side air-fuel ratio when the change is caused by an oxidizing atmosphere that oxidizes the mixed exhaust gas. As a result, the target atmosphere in the combustion chamber of the next combustion cylinder is changed as the atmosphere inside the catalyst changes, more specifically, from the reducing atmosphere that reduces the mixed exhaust gas flowing into the catalyst to the oxidizing atmosphere that oxidizes the mixed exhaust gas. The fuel ratio can be changed from the lean air-fuel ratio to the rich air-fuel ratio. Therefore, the air-fuel ratio of the mixed exhaust gas flowing into the catalyst can be quickly made to the rich-side air-fuel ratio, and HC, CO, etc. that are unburned can be oxidized with a high purification rate by the catalyst that has become an oxidizing atmosphere. it can.

  Further, in this case, specifically, the injection amount correction means may change the changed target air-fuel ratio so that the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder matches the changed target air-fuel ratio. A feedback correction amount for correcting the fuel injection amount for the in-cylinder injection means set by the injection amount setting means based on the fuel ratio and the output value of an air-fuel ratio sensor disposed downstream of the catalyst. The amount of fuel injected by the in-cylinder injection means in the combustion chamber of the next combustion cylinder can be corrected using the calculated feedback correction amount. Thereby, the target air in which the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder is changed more quickly and appropriately with respect to the internal state of the catalyst (specifically, the change from the reducing atmosphere to the oxidizing atmosphere). It can be made to coincide with the fuel ratio (specifically, the rich air-fuel ratio).

  Another feature of the present control device is that it comprises catalyst temperature detecting means for detecting the catalyst temperature of the catalyst disposed in the collective exhaust passage, and the target air-fuel ratio setting means is detected by the catalyst temperature detecting means. The target air-fuel ratio may be changed from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio when the set catalyst temperature is equal to or higher than a preset temperature. . Thus, the target air-fuel ratio can be changed from the lean air-fuel ratio to the rich air-fuel ratio as the catalyst temperature of the catalyst increases, more specifically, as the catalyst temperature becomes equal to or higher than a predetermined temperature. . Therefore, the air-fuel ratio of the mixed exhaust gas flowing into the catalyst can be quickly changed to the rich-side air-fuel ratio, and unburnt substances (HC, CO, etc.) can be flowed into the catalyst to suppress an increase in the catalyst temperature, As a result, deterioration of the catalyst can be suppressed.

  In the present control device, when the target air-fuel ratio is changed from the lean air-fuel ratio to the rich air-fuel ratio by the target air-fuel ratio setting means, the intake valve closing determination means closes the intake valve of the next combustion cylinder. If the valve is closed, the injection amount correction means can correct the fuel injection amount by the in-cylinder injection means based on the changed target air-fuel ratio. As a result, the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder can be quickly brought close to the changed target air-fuel ratio. On the other hand, if the valve is not closed, the fuel injection amount by the port injection means and the fuel injection amount by the in-cylinder injection means can be set based on the target air / fuel ratio changed by the injection amount setting means. Thereby, for example, the fuel injection amount by the port injection means and the fuel injection amount by the in-cylinder injection means appropriately according to the operating state of the engine which can change from moment to moment, more specifically, the fuel by the port injection means The fuel injection amount by the port injection means and the fuel by the in-cylinder injection means with respect to the basic fuel injection amount for realizing the target air-fuel ratio expressed by the sum of the fuel injection amount and the fuel injection amount by the cylinder injection means Therefore, the air fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder can be quickly matched with the changed target air fuel ratio.

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. 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. It is a figure for demonstrating the relationship between the upstream air fuel ratio in a basic air fuel ratio control, and a downstream air fuel ratio. It is the flowchart which showed the routine which CPU shown in FIG. 1 performs. Corresponding to the change in the output value of the downstream air-fuel ratio sensor accompanying the change in the atmosphere in the catalyst shown in FIG. 1 and the change in the output value of the downstream air-fuel ratio sensor shown in FIG. 1 with respect to the intake and compression strokes in the combustion cylinder FIG. 2 is a diagram for explaining a change (reversal) of a target air-fuel ratio, fuel injection timing by a port injection valve shown in FIG. 1, and fuel injection timing by a cylinder injection valve shown in FIG. 6 is a flowchart showing a routine executed by the CPU shown in FIG. 1 according to a modification of the present invention. According to the modification of the present invention, the change in the catalyst temperature of the catalyst shown in FIG. 1 and the change in the target air-fuel ratio corresponding to the increase in the catalyst temperature of the catalyst shown in FIG. FIG. 2 is a diagram for explaining the fuel injection timing by the port injection valve shown in FIG. 1 and the fuel injection timing by the in-cylinder injection valve shown in FIG. 1.

  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 four-cycle, spark-ignition, multi-cylinder (in-line four-cylinder) internal combustion engine 10 equipped with a dual injection system. FIG. 1 shows only a cross section of a specific cylinder, but the other cylinders have the same configuration. Here, in this embodiment, an in-line four-cylinder gasoline engine is shown as the internal combustion engine, but the present invention is not limited to such an engine.

  The internal combustion engine 10 includes a cylinder block portion 20 including a cylinder block, a cylinder block lower case, an oil pan, and the like, a cylinder head portion 30 fixed on the cylinder block portion 20, and a gasoline mixture to the cylinder block portion 20. An intake system 40 for supplying and an exhaust system 50 for releasing exhaust gas from the cylinder block 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 lower 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 a phase angle of the intake camshaft and the intake valve 32. The variable valve mechanism 33 that continuously changes the maximum lift amount, the actuator 33a of the variable valve mechanism 33, the exhaust port 34 that communicates with the combustion chamber 25, the exhaust valve 35 that opens and closes the exhaust port 34, and the exhaust valve 35 are driven. A variable exhaust timing control device 36 that includes an exhaust camshaft and continuously changes the phase angle of the exhaust camshaft, an ignition plug 37, an igniter 38 that includes an ignition coil that generates a high voltage to be applied to the ignition plug 37, and an intake valve 32 Port injection valve for injecting fuel in intake port 31 upstream of 9P, and a direct injection to in-cylinder injection valve 39C fuel in the combustion chamber 25. Therefore, the internal combustion engine 10 includes a dual injection system having the port injection valve 39P and the in-cylinder injection valve 39C.

  One port injection valve 39P and one in-cylinder injection valve 39C are provided for each combustion chamber 25. Accordingly, each of the plurality of cylinders includes a port injection valve 39P and an in-cylinder injection valve 39C that supply fuel independently of the other cylinders. In the present embodiment, an internal combustion engine in which the two injection valves of the port injection valve 39P and the in-cylinder injection valve 39C are provided separately will be described, but the present invention is not limited to such an internal combustion engine. Absent. For example, it may be an internal combustion engine having one injection valve that has both an in-cylinder injection function and a port injection function.

  The intake system 40 includes an intake pipe 41 including an intake manifold connected to the intake port 31 of each cylinder, an air filter 42 provided at an end of the intake pipe 41, and an intake opening area within the intake pipe 41. A variable throttle valve 43 and an actuator 43a for the throttle valve 43 are provided. The intake port 31 and the intake pipe 41 constitute an intake passage.

  The exhaust system 50 includes an exhaust manifold 51 connected to the exhaust port 34 of each cylinder, an exhaust pipe 52 connected to a collection portion of the exhaust manifold 51, and a catalyst 53 (three-way catalyst) disposed in the exhaust pipe 52. I have. The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage.

  On the other hand, this system includes an air flow meter 61, a throttle position sensor 62, a cam position sensor 63, a crank position sensor 64, a water temperature sensor 65, an upstream air-fuel ratio sensor 66, a downstream air-fuel ratio sensor 67, and an accelerator opening sensor 68. ing.

  The air flow meter 61 outputs a signal corresponding to the mass flow rate (intake air flow rate) Ga of intake air flowing through the intake pipe 41. The throttle position sensor 62 detects the opening degree of the throttle valve 43 and outputs a signal representing the throttle valve opening degree TA.

  The cam position sensor 63 generates a signal (G2 signal) having one pulse every time the intake camshaft rotates 90 ° (that is, every time the crankshaft 24 rotates 180 °). The crank position sensor 64 outputs a signal having a wide pulse every time the crankshaft 24 rotates 360 °. This signal represents the engine speed NE. Further, based on the signals from the cam position sensor 63 and the crank position sensor 64, the absolute crank angle CA with reference to 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 water temperature sensor 65 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW.

  As shown in FIG. 2, the upstream air-fuel ratio sensor 66 is disposed upstream of the catalyst 53 in a collective exhaust passage formed by collecting exhaust passages extending from the cylinders. The upstream air-fuel ratio sensor 66 is disclosed in, for example, “Limit current type with diffusion resistance layer” disclosed in JP-A-11-72472, 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 66 is the air-fuel ratio of the mixed exhaust gas flowing into the catalyst 53 (and therefore the air-fuel ratio of the air-fuel mixture supplied to the engine, more specifically, the air-fuel ratio in the combustion chamber 25 of each cylinder). An output value Vabyfs (V) corresponding to the (fuel ratio) is generated. 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. .

  Further, as shown in FIG. 2, the downstream air-fuel ratio sensor 67 is disposed downstream of the catalyst 53 in the collective exhaust passage. The downstream air-fuel ratio sensor 67 is a known electromotive force type oxygen concentration sensor (a known concentration cell type oxygen concentration sensor using stabilized zirconia). The downstream air-fuel ratio sensor 67 is an air-fuel ratio of the mixed exhaust gas flowing out from the catalyst 53 (thus, the air-fuel ratio of the air-fuel mixture supplied to the engine (more specifically, the air-fuel ratio in the combustion chamber 25 of each cylinder). An output value Voxs (V) corresponding to the temporal average value) of the fuel ratio) is generated.

  As shown in FIG. 4, the output value Voxs is 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 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 of the mixed exhaust gas changes from an air-fuel ratio richer than the stoichiometric air-fuel ratio to a lean air-fuel ratio, and the mixed exhaust gas When the air-fuel ratio of the engine changes from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to a rich air-fuel ratio, it suddenly changes from the minimum output value min to the maximum output value max.

  The accelerator opening sensor 68 outputs a signal representing the operation amount Accp of the accelerator pedal 81 operated by the driver.

  The electric control device 70 includes a CPU 71 connected to each other by a bus, a routine (program) executed by the CPU 71, a ROM 72 pre-stored with tables (maps, functions), constants, and the like, and the CPU 71 temporarily stores data as necessary. The microcomputer includes a RAM 73 for storing data, a backup RAM 74 for storing data while the power is turned on, and retaining the stored data while the power is shut off, and an interface 75 including an AD converter.

  The interface 75 is connected to the sensors 61 to 68, supplies signals from the sensors 61 to 68 to the CPU 71, and in response to instructions from the CPU 71, the actuator 33a of the variable valve mechanism 33, the igniter 38 of each cylinder, and each cylinder. Drive signals are sent to the port injection valve 39P, the cylinder injection valve 39C, and the throttle valve actuator 43a provided corresponding to the above.

(Outline of air-fuel ratio feedback control)
Next, the air-fuel ratio of the air-fuel mixture supplied to the engine performed by the apparatus configured as described above, that is, the air-fuel ratio in the combustion chamber 25 of each cylinder (hereinafter simply referred to as “engine air-fuel ratio”). The outline of the feedback control will be described.

<Catalyst purification capacity>
A three-way catalyst such as the catalyst 53 (hereinafter also simply referred to as “catalyst”) is an air-fuel ratio (hereinafter referred to as upstream air-fuel ratio) of mixed exhaust gas flowing into the catalyst, that is, an engine air-fuel ratio. When the fuel ratio is the stoichiometric air-fuel ratio, unburnt substances (HC, CO, etc.) in the mixed exhaust gas are oxidized and nitrogen oxides (NOx) are reduced, and these harmful components are purified with high efficiency. Further, the catalyst normally stores the oxygen depleted from the NOx by reducing NOx in the mixed exhaust gas when the upstream air-fuel ratio (the air-fuel ratio of the engine) is a lean air-fuel ratio, and the upstream air-fuel ratio. Has a function of oxidizing HC, CO, etc. in the mixed exhaust gas with oxygen stored when the air / fuel ratio is rich (hereinafter referred to as an oxygen storage function). For this reason, even if the upstream air-fuel ratio (engine air-fuel ratio) has shifted from the stoichiometric air-fuel ratio to a certain extent, the oxygen storage function for storing and releasing oxygen can purify HC, CO, and NOx. That is, when the air-fuel ratio of the engine is lean (that is, the upstream air-fuel ratio is lean) and the mixed exhaust gas flowing into the catalyst contains a large amount of NOx, the catalyst deprives the oxygen molecules from NOx and reduces it. Occludes molecules and purifies NOx. In addition, when the air-fuel ratio of the engine is rich (that is, the upstream air-fuel ratio is rich) and the mixed exhaust gas flowing into the catalyst contains a large amount of HC, CO, etc., the catalyst absorbs oxygen molecules stored in these. Apply (release) and oxidize, thereby purifying HC, CO, etc.

  Therefore, in order to efficiently purify (oxidize) a large amount of HC, CO, etc. into which the catalyst continuously flows, the catalyst must store a large amount of oxygen, and conversely flows continuously. In order to efficiently purify (reduce) a large amount of NOx, the catalyst must be in a state where oxygen can be sufficiently stored. From the above, the purification capacity of the catalyst depends on the maximum oxygen amount (maximum oxygen storage amount) that the catalyst can store.

  On the other hand, a three-way catalyst such as the catalyst 53 deteriorates due to poisoning by lead, sulfur, etc. contained in the fuel, or heat applied to the catalyst, and the maximum oxygen storage amount gradually decreases accordingly. In addition, if the catalyst continuously purifies (oxidizes) a large amount of HC, CO, etc., the stored oxygen becomes insufficient and the purification capacity decreases, and the catalyst continuously purifies (reduces) a large amount of NOx. If it continues, purification capacity will fall without being able to store oxygen. In order to suppress such a decrease in the maximum oxygen storage amount and a decrease in purification capacity, the upstream air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio and to a lean air-fuel ratio. It is necessary to repeatedly occlude and release oxygen molecules.

<Determination of the atmosphere inside the catalyst>
As described above, in order to suppress the decrease in the maximum oxygen storage amount and the purification capacity, the upstream air-fuel ratio is repeatedly changed so that the air-fuel ratio is richer and leaner than the stoichiometric air-fuel ratio. Is effective. By the way, the catalyst 53 stores oxygen up to the vicinity of the maximum oxygen storage amount and the inside of the catalyst 53 is in an oxidizing atmosphere, or the catalyst 53 releases oxygen to the oxygen storage amount near “0” and releases the same catalyst. Whether or not the inside of 53 has a reducing atmosphere can be determined based on the output value Voxs of the downstream air-fuel ratio sensor 67.

  If the upstream air-fuel ratio is lean, the NOx flowing into the catalyst 53 is purified (reduced) by storing oxygen molecules. For this reason, the output value Voxs of the downstream air-fuel ratio sensor 67 is larger than the voltage Vst and less than or equal to the maximum output value max, and the air-fuel ratio of the mixed exhaust gas flowing out from the catalyst 53 (hereinafter referred to as the downstream air-fuel ratio) is rich. The air / fuel ratio becomes low. If the NOx continuously flowing into the catalyst 53 is continuously purified (reduced), the oxygen molecules stored in the catalyst 53 reach the maximum oxygen storage amount, and the NOx purification capacity beyond that decreases. Therefore, the inside of the catalyst 53 that has stored oxygen molecules up to the maximum oxygen storage amount becomes an oxidizing atmosphere, and the output value Voxs of the downstream air-fuel ratio sensor 67 changes from the maximum output value max to the minimum output value min due to the outflowing NOx. It changes suddenly. That is, when the downstream air-fuel ratio changes from a rich air-fuel ratio to a lean air-fuel ratio, the output value Voxs of the downstream air-fuel ratio sensor 67 changes suddenly from the maximum output value max to the minimum output value min. It can be determined whether or not the reducing atmosphere is changed to the oxidizing atmosphere.

  On the other hand, if the upstream air-fuel ratio is rich, the stored oxygen molecules are released, so that HC, CO, etc. flowing into the catalyst 53 are purified (oxidized). For this reason, the output value Voxs of the downstream air-fuel ratio sensor 67 is smaller than the voltage Vst and is not less than the minimum output value min, and the downstream air-fuel ratio becomes a lean air-fuel ratio. If HC, CO, etc., continuously flowing into the catalyst 53 are continuously purified (oxidized), the oxygen storage amount of the catalyst 53 becomes substantially “0”, and the purification capacity of HC, CO, etc. further decreases. . For this reason, the inside of the catalyst 53 with a small oxygen storage amount becomes a reducing atmosphere, and the output value Voxs of the downstream air-fuel ratio sensor 67 suddenly changes from the minimum output value min to the maximum output value max due to HC, CO, etc. flowing out. . That is, when the downstream air-fuel ratio changes from a lean air-fuel ratio to a rich air-fuel ratio, the output value Voxs of the downstream air-fuel ratio sensor 67 changes suddenly from the minimum output value min to the maximum output value max. It can be determined whether or not the atmosphere has changed from an oxidizing atmosphere to a reducing atmosphere.

<Basic air-fuel ratio control>
Next, an outline of basic air-fuel ratio control by this apparatus will be described. In this apparatus, when the engine is in a steady operation state, the output value Voxs of the downstream air-fuel ratio sensor 67 changes suddenly, that is, according to whether the inside of the catalyst 53 is an oxidizing atmosphere or a reducing atmosphere. Thus, the upstream air-fuel ratio (the air-fuel ratio of the engine) is controlled to be forcibly leaner than the stoichiometric air-fuel ratio or forcibly rich air-fuel ratio. Specifically, as shown in FIG. 5, when the downstream air-fuel ratio is rich based on the output value Voxs of the downstream air-fuel ratio sensor 67, the upstream air-fuel ratio (that is, the engine air-fuel ratio) is lean. When the downstream air-fuel ratio is a lean air-fuel ratio based on the output value Voxs of the downstream air-fuel ratio sensor 67, the upstream air-fuel ratio (that is, the engine air-fuel ratio) is rich. Control to achieve an air-fuel ratio. When the output value Voxs of the downstream air-fuel ratio sensor 67 suddenly changes from the maximum output value max to the minimum output value min, the upstream air-fuel ratio (that is, the engine air-fuel ratio) is changed from a lean air-fuel ratio to a rich air-fuel ratio. When the output value Voxs of the downstream air-fuel ratio sensor 67 suddenly changes from the minimum output value min to the maximum output value max, the upstream air-fuel ratio (that is, the engine air-fuel ratio) is made rich. Control is performed by changing from an air-fuel ratio to a lean air-fuel ratio (with a large amplitude).

  In view of this, in the present apparatus, the output values of the upstream air-fuel ratio sensor 66 and the downstream air-fuel ratio sensor 67 correspond to sensor target values (specifically, the output values Voxs of the downstream air-fuel ratio sensor 67 are less than the stoichiometric air-fuel ratio. The fuel injection amount by the port injection valve 39P and the in-cylinder injection valve 39C is controlled so as to match the rich air-fuel ratio or the air-fuel ratio leaner than the stoichiometric air-fuel ratio, respectively, and the air-fuel ratio of the engine is fed back. Control.

<Determination of basic fuel injection amount>
First, an example of determining the basic fuel injection amount Fbase will be described. When determining the basic fuel injection amount Fbase, it corresponds to the target value (upstream target value) of the upstream air-fuel ratio sensor output based on the engine speed NE and the throttle valve opening TA, etc., which are the operating state of the internal combustion engine 10 The upstream target air-fuel ratio abyfr (that is, the target air-fuel ratio of the engine) is determined. The upstream target air-fuel ratio abyfr is set to a value corresponding to an air-fuel ratio richer than the stoichiometric air-fuel ratio or an air-fuel ratio leaner than the stoichiometric air-fuel ratio according to the output value Voxs of the downstream air-fuel ratio sensor 67 as described above. It is preset so that it can be changed. Further, the upstream target air-fuel ratio abyfr is stored in the RAM 73 while corresponding to the intake stroke of each cylinder.

  When the upstream target air-fuel ratio abyfr is determined in this way, a predetermined table using as arguments the intake air flow rate Ga measured by the air flow meter 61 and the engine rotational speed NE obtained based on the output of the crank position sensor 64 is used. By dividing the in-cylinder intake air amount Mc, which is the intake air amount of the cylinder (that is, the next combustion cylinder) that reaches the current intake stroke determined based on the above, by the determined upstream target air-fuel ratio abyfr, the basic fuel Obtain the injection amount Fbase. That is, the basic fuel injection amount Fbase is a total amount of fuel injection amounts from the port injection valve 39P and the in-cylinder injection valve 39C corresponding to the next combustion cylinder necessary for realizing the upstream target air-fuel ratio abyfr.

<Calculation of in-cylinder injection amount and port injection amount>
Next, calculation of the in-cylinder injection amount Fid and the port injection amount Fip will be described. In calculating the in-cylinder injection amount Fid and the port injection amount Fip, the engine rotational speed NE that is the operating state of the internal combustion engine 10, the in-cylinder intake air amount Mc, and the coolant temperature THW are used as predetermined arguments. Based on the table, the ratio of the in-cylinder injection amount Fid to the sum of the in-cylinder injection amount Fid and the port injection amount Fip (more precisely, the sum of the basic in-cylinder injection amount Fbased described later and the basic port injection amount Fbasep described later) The in-cylinder injection ratio R (hereinafter also referred to as the sharing ratio R), which is a ratio of the basic in-cylinder injection amount Fbased), is determined. As a result, the in-cylinder injection ratio R can be appropriately changed according to the operating state of the engine.

  When the in-cylinder injection ratio R (that is, the sharing ratio R) is determined in accordance with the engine operating state in this way, the basic in-cylinder injection ratio R is multiplied by the obtained basic fuel injection amount Fbase. The injection amount Fbased (= Fbase × R) is determined. Similarly, the basic port injection amount Fbasep (= Fbase × (1-R)) is determined by multiplying the obtained basic fuel injection amount Fbase by a value (1-R). Then, the basic in-cylinder injection amount Fbased is multiplied by the sub feedback correction amount to determine the final in-cylinder injection amount Fid, and the basic port injection amount Fbasep is multiplied by the sub feedback correction amount and the main feedback correction amount to be finally obtained. A proper port injection amount Fip is determined.

  As for the sub feedback correction amount, as an example, the downstream side air-fuel ratio is based on the output value Voxs of the downstream side air-fuel ratio sensor 67, the engine speed NE, the throttle valve opening TA, etc., which are the operating states of the internal combustion engine 10. The deviation from the downstream target value Voxsref, which is the sensor output target value, is obtained by PID processing. Here, the downstream target value Voxsref is set so that the downstream target air-fuel ratio corresponding to the downstream target value Voxsref always coincides with the above-described upstream target air-fuel ratio abyfr. As for the main feedback correction amount, as an example, the detected air-fuel ratio abyfs at the present time by the upstream air-fuel ratio sensor 66 based on the output value Vabyfs of the upstream air-fuel ratio sensor 66 and the air-fuel ratio conversion table Mapabyfs shown in FIG. And a PID process for the deviation between the detected air-fuel ratio abyfs and the upstream target air-fuel ratio abyfr.

  In this way, the present system provides the in-cylinder injection valve for in-cylinder injection amount Fid obtained by correcting the basic in-cylinder injection amount Fbased with the sub-feedback correction amount for the next combustion cylinder in the current combustion cycle. In-cylinder injection is performed by 39C. Further, the fuel of the port injection amount Fip obtained by correcting the basic port injection amount Fbasep by the sub feedback correction amount and the main feedback correction amount is injected by the port injection valve 39P to the next combustion cylinder in the current combustion cycle. . Thus, the present apparatus can feedback control the air-fuel ratio of the engine so that the air-fuel ratio is richer than the stoichiometric air-fuel ratio or the air-fuel ratio leaner than the stoichiometric air-fuel ratio.

<Change from lean to rich upstream air-fuel ratio>
As described above, particularly when the upstream air-fuel ratio is a lean air-fuel ratio, the amount of oxygen stored in the catalyst 53 is increased to the maximum oxygen storage amount by purifying (reducing) NOx flowing into the catalyst 53. May result in an oxidizing atmosphere. Thus, when the inside of the catalyst 53 is in an oxidizing atmosphere, the NOx purification ability (reduction ability) may be reduced and NOx may flow out. In this case, the upstream air-fuel ratio is quickly changed from a lean air-fuel ratio to a rich air-fuel ratio, and HC, CO, etc. are caused to flow into the catalyst 53, and the HC, CO, etc. that have flowed in are purified (oxidized). Therefore, it is necessary to release (consume) the stored oxygen molecules to reduce the amount of stored oxygen.

  Incidentally, in the internal combustion engine 10 equipped with the dual injection system, as described above, the port injection by the port injection valve 39P is performed on the cylinder before the intake valve 32 of the next combustion cylinder is closed. Need to be For this reason, the output value Voxs of the downstream air-fuel ratio sensor 67 changes suddenly from the maximum output value max to the minimum output value min, and the upstream air-fuel ratio (that is, the engine air-fuel ratio) is changed from a lean air-fuel ratio to a rich air-fuel ratio. If the intake valve 32 of the next combustion cylinder in the intake stroke is open at the time of the change, as described above, it is determined based on the changed rich air-fuel ratio (that is, the upstream target air-fuel ratio). The port injection amount Fip is injected from the port injection valve 39P, and the in-cylinder injection amount Fid is injected from the in-cylinder injection valve 39C. Therefore, the upstream air-fuel ratio (that is, the air-fuel ratio of the engine) can be quickly changed from the lean air-fuel ratio to the rich air-fuel ratio, so that NOx can be prevented from flowing out and HC flowing into the catalyst 53 can be prevented. , CO and the like can be purified (oxidized) at a high purification rate.

  However, if the upstream side air-fuel ratio (that is, the engine air-fuel ratio) is changed from the lean air-fuel ratio to the rich air-fuel ratio, if the intake valve 32 of the next combustion cylinder in the intake stroke is closed, that is, If the port injection by the port injection valve 39P has already been completed and the next combustion cylinder has shifted to the compression stroke, the port injection from the port injection valve 39P becomes impossible, and the port is set against the changed rich air-fuel ratio. The injection amount Fip will be insufficient. Here, the in-cylinder injection valve 39C can perform in-cylinder injection even when the intake valve 32 of the next combustion cylinder in the compression stroke is closed. For this reason, it is possible to increase the in-cylinder injection amount Fid so as to quickly cope with the changed rich air-fuel ratio by using the in-cylinder injection valve 39C.

  However, as described above, in the dual injection system, the sharing ratio R between the port injection amount Fip by the port injection valve 39P and the in-cylinder injection amount Fid by the in-cylinder injection valve 39C is optimal according to the operating state of the engine. Is set. Therefore, in principle, the share ratio R is changed from moment to moment according to the operating state of the engine such as the engine speed NE and the coolant temperature THW. For this reason, when the upstream air-fuel ratio (that is, the air-fuel ratio of the engine) is changed from a lean air-fuel ratio to a rich air-fuel ratio, always responding by increasing the in-cylinder injection amount Fid by the in-cylinder injection valve 39C. The share ratio R may change, which may affect the operating state of the engine.

(Actual operation)
Next, the actual operation of the control device according to this embodiment will be described. FIG. 6 is a flowchart showing an example of a flow of a processing routine executed by the CPU 71 of the present apparatus to “change the air-fuel ratio of the engine from a lean air-fuel ratio to a rich air-fuel ratio as the catalyst is oxidized”. is there. In this example, first, in step 1005, based on the output value Voxs of the downstream air-fuel ratio sensor 67, is the downstream air-fuel ratio reversed (changed) from a rich air-fuel ratio to a lean air-fuel ratio? Determine whether or not.

  Specifically, the output value Voxs of the downstream air-fuel ratio sensor 67 is acquired every time a predetermined short sampling time ts (for example, 4 milliseconds) elapses. Then, if the output value Voxs of the downstream air-fuel ratio sensor 67 acquired at each sampling time ts is abruptly changed from the maximum output value max to the minimum output value min as shown in FIG. It is determined that the air-fuel ratio is reversed from a rich air-fuel ratio to a lean air-fuel ratio (“Yes” in step 1005), and in step 1010, it is determined whether or not the intake valve 32 in the next combustion cylinder is closed. To do. On the other hand, if the output value Voxs of the downstream air-fuel ratio sensor 67 acquired every sampling time ts does not change abruptly from the maximum output value max to the minimum output value min, the downstream air-fuel ratio becomes richer from the air-fuel ratio. It is determined that the air-fuel ratio has not been reversed ("No" in step 1005), and the execution of the processing routine is terminated.

  In step S1010, based on the G2 signal from the cam position sensor 63, it is determined whether or not the port injection valve 39P in the next combustion cylinder has already finished the port injection and the intake valve 32 is closed. Specifically, based on the G2 signal from the cam position sensor 63, the next combustion cylinder has shifted from the intake stroke to the compression stroke and the intake valve 32 is closed, or the next combustion cylinder is the intake stroke. If the intake valve 32 is just before closing (“Yes” in step 1010), in-cylinder injection by the in-cylinder injection valve 39C is executed in step 1015. On the other hand, based on the G2 signal from the cam position sensor 63, the port injection valve 39P in the next combustion cylinder has not finished the port injection, and the next combustion cylinder is in the intake stroke and the intake valve 32 has a sufficient lift amount. If the valve is opened ("No" in step 1010), port injection by the port injection valve 39P is executed in step 1020.

  Hereinafter, first, “in-cylinder injection by the in-cylinder injection valve 39C” in step 1015 will be specifically described. As shown in FIG. 7, in the next combustion cylinder, the port injection amount Fip has already been port-injected by the port injection valve 39P immediately before the intake top dead center, and the intake valve 32 is immediately after the intake bottom dead center in the intake stroke. If the valve is closed, the port injection valve 39P cannot additionally inject fuel into the combustion chamber 25 even if the air-fuel ratio of the air-fuel mixture in the combustion chamber 25 is changed to a rich air-fuel ratio thereafter. Alternatively, even if the air-fuel ratio of the air-fuel mixture in the combustion chamber 25 is changed to a rich air-fuel ratio immediately before the intake valve 32 closes in the vicinity of the intake bottom dead center in the intake stroke in the next combustion cylinder, Even if the port 32 has a small lift amount and the port injection valve 39P additionally performs port injection, the fuel cannot be properly supplied into the combustion chamber 25.

  In such a case, the in-cylinder injection valve 39C, which in-cylinder injects even when the intake valve 32 is closed, uses the in-cylinder injection amount Fid corrected so as to correspond to the change to the rich air-fuel ratio. Is injected into the combustion chamber 25. In this case, the in-cylinder injection amount Fid is the deviation between the downstream target value Voxsref corresponding to the downstream target air-fuel ratio that always matches the rich upstream target air-fuel ratio abyfr and the output value Voxs of the downstream air-fuel ratio sensor 67. It is determined by multiplying the basic in-cylinder injection amount Fbased by the sub feedback correction amount obtained by the PID processing. That is, the in-cylinder injection amount Fid determined in this way is an injection amount that satisfies the change to a rich air-fuel ratio. The in-cylinder injection valve 39C in-cylinder-injects the corrected in-cylinder injection amount Fid. In this case, the sharing rate R is forcibly changed exceptionally (temporarily).

  On the other hand, with respect to “port injection by the port injection valve 39P” in step 1020, in the next combustion cylinder, when the port injection by the port injection valve 39P is not completed, or the intake valve 32 opened in the intake stroke Is performed when the port injection valve 39P can perform port injection in response to changing the air-fuel ratio of the air-fuel mixture in the combustion chamber 25 to a rich air-fuel ratio.

  In this case, in response to the change to the rich air-fuel ratio, the port injection amount Fip and the in-cylinder injection amount Fid are determined as described above and injected by the port injection valve 39P and the in-cylinder injection valve 39C, respectively. . Thus, the basic fuel injection amount Fbase that satisfies the change to the rich air-fuel ratio is supplied in the cylinder. In this case, the sharing ratio R corresponding to the operating state of the engine is appropriately maintained.

  As described above, according to the embodiment of the present invention (specifically, the process shown in FIG. 6), the atmosphere inside the catalyst 53 becomes an oxidizing atmosphere and the upstream target air-fuel ratio abyfr (target air-fuel ratio). When it is necessary to change the air-fuel ratio from the lean air-fuel ratio to the rich air-fuel ratio (“Yes” in step 1005), it is determined whether or not the intake valve 32 in the next combustion cylinder is closed (step 1010). If the intake valve 32 is closed, the in-cylinder injection amount Fid corresponding to the change to the rich air-fuel ratio is injected by the in-cylinder injection valve 39C (step 1015), and if the intake valve 32 is opened, the port Port injection amount Fip and in-cylinder injection amount Fid corresponding to the change to the rich air-fuel ratio are injected by injection valve 39P and in-cylinder injection valve 39C (step 1020). Therefore, the upstream target air-fuel ratio abyfr can be quickly changed according to the atmosphere inside the catalyst 53 (specifically, the oxidizing atmosphere based on the oxygen storage amount), and thus the upstream target air-fuel ratio abyfr can be quickly changed. By changing, the purification rate of the catalyst 53 can be improved.

  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, in order to ensure a good purification rate of the catalyst 53, the upstream target air-fuel ratio abyfr is set to a lean air-fuel ratio in accordance with the change of the atmosphere inside the catalyst 53 from the reducing atmosphere to the oxidizing atmosphere. The air-fuel ratio was changed quickly to a rich air-fuel ratio. In this case, the upstream target air-fuel ratio abyfr can be changed rapidly from a lean air-fuel ratio to a rich air-fuel ratio in accordance with the temperature of the catalyst 53.

  Here, as described above, the catalyst 53 has a function of storing oxygen molecules (hereinafter referred to as oxygen storage capacity), and a substance that exhibits this oxygen storage capacity (hereinafter referred to as oxygen storage material). ) Can easily move oxygen within the material when its temperature is above a predetermined temperature. However, if the catalyst temperature is maintained at a predetermined temperature or higher for a long time, for example, the maximum oxygen storage amount may decrease, and so-called catalyst deterioration may occur.

  In order to prevent such deterioration of the catalyst, the upstream target air-fuel ratio abyfr is set to a rich air-fuel ratio, and unburnt substances (HC, CO, etc.) are allowed to flow into the catalyst 53 to suppress an increase in the catalyst temperature. . FIG. 8 is a flowchart showing an example of a flow of a processing routine executed by the CPU 71 of the present apparatus to “change the air / fuel ratio of the engine from a lean air / fuel ratio to a rich air / fuel ratio as the catalyst temperature rises”. . In the processing routine, only step 1005 of the processing routine in the above embodiment is changed to step 1050. Therefore, in the following description, only step 1050 will be described in detail.

  In this example, in step 1050, for example, the cooling water temperature THW is acquired based on the output value of the water temperature sensor 65, and the relationship between the acquired cooling water temperature THW and the catalyst temperature is acquired in a predetermined catalyst temperature estimation function. By applying the cooling water temperature THW, the catalyst temperature of the catalyst 53 is estimated and acquired. In this case, when a catalyst temperature sensor is provided in the catalyst 53, the catalyst temperature detected by this sensor may be used. Subsequently, as shown in FIG. 9, it is determined whether or not the obtained catalyst temperature of the catalyst 53 is equal to or higher than a predetermined temperature. Specifically, if the acquired catalyst temperature is equal to or higher than a predetermined temperature, it is determined that the upstream target air-fuel ratio abyfr needs to be changed from a lean air-fuel ratio to a rich air-fuel ratio (in step 1050, “ Yes "), each step process after step 1010 is executed in the same manner as in the above embodiment.

  Thus, according to the modification of the present invention, when the catalyst temperature of the catalyst 53 rises to a predetermined temperature or higher, it is necessary to change the upstream target air-fuel ratio abyfr from a lean air-fuel ratio to a rich air-fuel ratio. (“Yes” in step 1005), it is determined whether or not the intake valve 32 in the next combustion cylinder is closed (step 1010). If the intake valve 32 is closed, the in-cylinder injection valve 39C performs rich processing. When the in-cylinder injection amount Fid corresponding to the change to the correct air-fuel ratio is injected (step 1015) and the intake valve 32 is open, the change to the rich air-fuel ratio is performed by the port injection valve 39P and the in-cylinder injection valve 39C. The port injection amount Fip and the in-cylinder injection amount Fid corresponding to are injected (step 1020). Therefore, the upstream target air-fuel ratio abyfr can be quickly changed in accordance with the catalyst temperature of the catalyst 53, and the excessive increase in the temperature of the catalyst 53 is suppressed by rapidly changing the upstream air-fuel ratio in this way. Therefore, the deterioration of the catalyst 53 can be suppressed and the purification ability can be maintained for a long period.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 39P ... Port injection valve, 39C ... In-cylinder injection valve, 52 ... Exhaust pipe, 53 ... Three-way catalyst, 66 ... Upstream air-fuel ratio sensor, 67 ... Downstream air-fuel ratio sensor, 70 ... electric control device, 71 ... CPU

Claims (6)

Port injection means disposed corresponding to each of the plurality of cylinders and injecting fuel in an intake passage upstream of each intake valve of the plurality of cylinders;
Applied to a multi-cylinder internal combustion engine that is disposed corresponding to each of the plurality of cylinders and has in-cylinder injection means for injecting fuel in the combustion chamber of each of the 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 collective exhaust passage. When,
Target air-fuel ratio setting means for setting a target air-fuel ratio that is a target value of the air-fuel ratio of the air-fuel mixture in the combustion chambers of the plurality of cylinders;
An injection amount setting means for setting the fuel injection amount by the port injection means and the fuel injection amount by the in-cylinder injection means based on the operating state of the internal combustion engine and the set target air-fuel ratio;
The fuel injection amount by the port injection means and the in-cylinder injection means based on the output value from the air-fuel ratio sensor so that the air-fuel ratio of the air-fuel mixture in the combustion chambers of the plurality of cylinders matches the target air-fuel ratio. Feedback control means for feedback control of the fuel injection amount;
A control device for a multi-cylinder internal combustion engine comprising:
When the target air-fuel ratio is changed from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio by the target air-fuel ratio setting means, the next in the intake stroke in the current combustion cycle Whether or not the port injection means arranged corresponding to the combustion cylinder has finished injection of the fuel injection amount set by the injection amount setting means and the intake valve of the next combustion cylinder is closed An intake valve closing determining means for determining whether or not
When the intake valve of the next combustion cylinder is closed, the fuel injection amount set by the injection amount setting means with respect to the in-cylinder injection means is changed to the output value of the air-fuel ratio sensor and the change. A control apparatus for a multi-cylinder internal combustion engine, comprising: an injection amount correction unit that corrects based on a target air-fuel ratio. The control apparatus for a multi-cylinder internal combustion engine according to claim 1,
The injection amount correcting means includes
The injection amount is set based on the changed target air-fuel ratio and the output value of the air-fuel ratio sensor so that the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder matches the changed target air-fuel ratio. A feedback correction amount for correcting the fuel injection amount for the in-cylinder injection unit set by the unit is calculated, and the in-cylinder injection unit injects the fuel into the combustion chamber of the next combustion cylinder using the feedback correction amount. A control apparatus for a multi-cylinder internal combustion engine, which corrects the amount of fuel injected. In the control apparatus for a multi-cylinder internal combustion engine according to claim 1 or 2,
The air-fuel ratio sensor is at least
An air-fuel ratio sensor is provided which is disposed in the collective exhaust passage downstream of the catalyst disposed in the collective exhaust passage and generates an output value corresponding to the air-fuel ratio of the mixed exhaust gas flowing out from the catalyst. Has been
The target air-fuel ratio setting means includes
The target air-fuel ratio is changed from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio in response to a change in the output value of an air-fuel ratio sensor disposed downstream of the catalyst. A control device for a multi-cylinder internal combustion engine. The control apparatus for a multi-cylinder internal combustion engine according to claim 3,
The change in the output value of the air-fuel ratio sensor disposed downstream of the catalyst is
In the multi-cylinder internal combustion engine, the inside of the catalyst is a change that occurs as a result of changing from a reducing atmosphere that reduces the mixed exhaust gas flowing into the catalyst to an oxidizing atmosphere that oxidizes the mixed exhaust gas flowing into the catalyst. Control device. In the control device for a multi-cylinder internal combustion engine according to claim 3 or 4,
The injection amount correcting means includes
The changed target air-fuel ratio and the output of the air-fuel ratio sensor disposed downstream of the catalyst so that the air-fuel ratio of the air-fuel mixture in the combustion chamber of the next combustion cylinder matches the changed target air-fuel ratio. A feedback correction amount for correcting the fuel injection amount for the in-cylinder injection unit set by the injection amount setting unit is calculated based on the value, and the in-cylinder injection unit uses the feedback correction amount to calculate the feedback correction amount. A control apparatus for a multi-cylinder internal combustion engine, which corrects an injection amount of fuel injected in a combustion chamber of a next combustion cylinder. In the control apparatus for a multi-cylinder internal combustion engine according to claim 1 or 2,
Comprising catalyst temperature detecting means for detecting the catalyst temperature of the catalyst disposed in the collective exhaust passage,
The target air-fuel ratio setting means includes
When the catalyst temperature detected by the catalyst temperature detecting means becomes equal to or higher than a preset temperature, the target air-fuel ratio is changed from an air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio richer than the stoichiometric air-fuel ratio. A control apparatus for a multi-cylinder internal combustion engine, characterized in that

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