JP2008025511A - Air fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air fuel ratio control device for an internal combustion engine provided with a dual injection system capable of inhibiting exhaust gas air fuel ratio from getting leaner than value of a target air fuel ratio while controlling combustion air fuel ratio to a value of the target air fuel ratio when blow by of intake air exists. <P>SOLUTION: The air fuel ratio control device for the internal combustion engine is provided with a cylinder fuel injection means 5a injecting fuel into a combustion chamber 5 and an intake port fuel injection means 8a injecting fuel in an intake port 8. When blow by of intake air exists, combustion air fuel ratio is controlled with adjusting quantity of fuel injected from the cylinder fuel injection means 5a with taking the blow by into account, and exhaust gas air fuel ratio is controlled by injecting fuel from the intake port fuel injection means 8a if air fuel ratio calculated based on quantity of intake air and quantity of fuel injected from the cylinder injection means 5a is leaner than the predetermined target air fuel ratio of exhaust gas air fuel ratio. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine.

  In recent years, a fuel injection valve that directly injects fuel into a combustion chamber (hereinafter referred to as “in-cylinder fuel injection valve”) and a fuel injection valve that injects fuel into an intake port upstream of the intake valve (hereinafter referred to as “inside port”). An internal combustion engine equipped with both of them is being developed. Hereinafter, a system including two fuel injection valves, the in-cylinder fuel injection valve and the in-port fuel injection valve, will be referred to as a “dual injection system”. An internal combustion engine having such a dual injection system Thus, it is possible to improve combustion efficiency and reduce fuel consumption, and to ensure startability at the time of engine start.

  In addition, for example, in an internal combustion engine with a supercharger, what is known as valve overlap in which both an intake valve and an exhaust valve are simultaneously opened when acceleration or high output is required is known. In other words, by performing valve overlap, the intake air is blown out to the exhaust side by using the supercharging pressure, etc., and the residual gas in the combustion chamber is scavenged to improve the combustibility and output, and The amount of exhaust gas supplied to the turbocharger turbine is increased to increase the supercharging effect and to improve the output.

  On the other hand, if the intake air is blown out to the exhaust side by performing valve overlap in this way, the amount of air charged in the combustion chamber becomes smaller than the intake air amount measured by an air flow meter or the like. Therefore, when an amount of fuel determined based on the intake air amount measured by an air flow meter or the like is injected, the air-fuel ratio in the combustion chamber (hereinafter referred to as “combustion air-fuel ratio”) becomes richer than a desired value. If the internal combustion engine generates an output different from the desired output, good control cannot be performed.

  In order to solve such a problem, Patent Document 1 obtains the amount of air blown to the exhaust side (hereinafter referred to as “blow-off air amount”), and based on the intake air amount detected by the intake air amount detection means such as an air flow meter. The amount of air charged into the combustion chamber (hereinafter referred to as “in-cylinder charged air amount”) is obtained by subtracting the amount of blown-off air, and the fuel injection amount is determined based on that value. A technique for achieving a desired value is disclosed.

JP 63-297746 JP-A-11-36994

However, when the combustion air-fuel ratio is set to a desired value in this way, the entire air-fuel ratio including the blow-by air amount, that is, the exhaust gas air-fuel ratio (hereinafter referred to as “exhaust air-fuel ratio”). Will be leaner than the combustion air-fuel ratio. That is, for example, when the combustion air-fuel ratio is set to the stoichiometric air-fuel ratio, the exhaust air-fuel ratio becomes lean. When the exhaust air-fuel ratio becomes lean in this way, the exhaust gas contains a large amount of oxygen, so that the exhaust purification catalyst provided in the exhaust system is likely to deteriorate or overheat, and the ternary When a catalyst is used, the purification rate is lowered and the emission is deteriorated.
Such a problem may normally occur in an internal combustion engine provided with the dual injection system.

  The present invention has been made in view of the above points, and an object of the present invention is an air-fuel ratio control apparatus for an internal combustion engine equipped with a dual injection system. An air-fuel ratio control apparatus for an internal combustion engine that can suppress the exhaust air-fuel ratio from becoming leaner than the target air-fuel ratio while controlling the air-fuel ratio to the target air-fuel ratio.

  The present invention provides an air-fuel ratio control apparatus for an internal combustion engine described in each claim as a means for solving the above problems.

  The invention according to claim 1 is an air-fuel ratio control device for an internal combustion engine comprising in-cylinder fuel injection means for injecting fuel into a combustion chamber and intake port fuel injection means for injecting fuel into an intake port. When the intake air is blown through, the amount of fuel injected from the in-cylinder fuel injection means is adjusted in consideration of the blow-through and the combustion air-fuel ratio is controlled, and the intake air amount and the in-cylinder fuel injection means are controlled. When the air-fuel ratio calculated based on the amount of fuel injected from the air-fuel ratio is leaner than the target air-fuel ratio of a predetermined exhaust air-fuel ratio, the fuel is injected from the fuel injection means in the intake port and exhausted. An air-fuel ratio control apparatus for an internal combustion engine for controlling an air-fuel ratio is provided.

  In order to scavenge the residual gas in the combustion chamber and improve the combustibility and output, the internal combustion engine may be operated by blowing the intake air to the exhaust side. However, in such a case, since there is an amount of air blown through, if the combustion air-fuel ratio is controlled to the target air-fuel ratio value, the exhaust air-fuel ratio becomes leaner than the target air-fuel ratio value, resulting in exhaust purification. There is a risk that the catalyst is likely to be deteriorated or excessively heated, and the emission is deteriorated.

  On the other hand, according to the first aspect of the present invention, when there is a blow-through of intake air, the amount of fuel injected from the in-cylinder fuel injection means is adjusted in consideration of the blow-through and the combustion air-fuel ratio is controlled. When the air-fuel ratio calculated based on the intake air amount and the amount of fuel injected from the in-cylinder fuel injection means is leaner than the target air-fuel ratio of the predetermined exhaust air-fuel ratio, the intake-port fuel The exhaust air / fuel ratio is controlled by injecting fuel from the injection means.

  Therefore, according to the first aspect of the present invention, when there is a blow-in of intake air, the exhaust air-fuel ratio becomes leaner than the target air-fuel ratio while controlling the combustion air-fuel ratio to the target air-fuel ratio. It can be suppressed. As a result, it is possible to prevent the exhaust purification catalyst from being easily deteriorated or excessively heated, and to suppress emission deterioration.

According to a second aspect of the present invention, in the first aspect of the present invention, the air-fuel ratio calculated based on the intake air amount and the amount of fuel injected from the in-cylinder fuel injection means is the predetermined exhaust air-fuel ratio. When the target air-fuel ratio is equal to or richer than the target air-fuel ratio, fuel injection from the intake port fuel injection means for controlling the exhaust air-fuel ratio is prohibited. Yes.
According to the second aspect of the invention, inappropriate control of the exhaust air-fuel ratio can be prevented.

  The invention according to claim 3 is an air-fuel ratio control apparatus for an internal combustion engine comprising in-cylinder fuel injection means for injecting fuel into the combustion chamber and intake port fuel injection means for injecting fuel into the intake port. Thus, when there is a blow-through of intake air, the amount of fuel injected from the in-cylinder fuel injection means is adjusted in consideration of the blow-through, and the combustion air-fuel ratio is controlled and provided in the exhaust passage of the internal combustion engine. When the air-fuel ratio detected by the air-fuel ratio sensor is leaner than the target air-fuel ratio of the predetermined exhaust air-fuel ratio, fuel is injected from the intake port fuel injection means to control the exhaust air-fuel ratio; An air-fuel ratio control apparatus for an internal combustion engine is provided.

  As described above, according to the third aspect of the present invention, when there is a blow-through of intake air, the amount of fuel injected from the in-cylinder fuel injection means is adjusted in consideration of the blow-through and the combustion air-fuel ratio is controlled. When the air-fuel ratio detected by the air-fuel ratio sensor is leaner than a predetermined target air-fuel ratio of the exhaust air-fuel ratio, fuel is injected from the intake port fuel injection means to control the exhaust air-fuel ratio It is supposed to be.

  Therefore, according to the third aspect of the present invention, when there is blow-in of intake air, the exhaust air-fuel ratio is leaner than the target air-fuel ratio while controlling the combustion air-fuel ratio to the target air-fuel ratio. Can be suppressed. As a result, it is possible to prevent the exhaust purification catalyst from being easily deteriorated or excessively heated, and to suppress emission deterioration.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the air-fuel ratio detected by an air-fuel ratio sensor provided in the exhaust passage of the internal combustion engine is equal to the target air-fuel ratio of the predetermined exhaust air-fuel ratio. In this case, or when the air-fuel ratio is richer than the target air-fuel ratio, fuel injection from the intake port fuel injection means for controlling the exhaust air-fuel ratio is prohibited.
According to the fourth aspect of the invention, inappropriate control of the exhaust air-fuel ratio can be prevented.

According to a fifth aspect of the invention, in the first aspect of the invention according to any one of the first to fourth aspects, the amount of fuel injected from the fuel injection means in the intake port in order to control the exhaust air / fuel ratio is: It is determined based on the amount of fuel injected from the in-cylinder fuel injection means.
According to the fifth aspect of the present invention, the exhaust air-fuel ratio can be accurately controlled to the target air-fuel ratio.

  According to a sixth aspect of the present invention, in the first aspect of the present invention, the amount of fuel injected from the intake port fuel injection means to control the exhaust air-fuel ratio is the in-cylinder fuel. It is determined based on the amount of fuel injected from the injection means and the air-fuel ratio detected by the air-fuel ratio sensor provided in the exhaust passage of the internal combustion engine.

According to a seventh aspect of the invention, in the invention according to any one of the first to fourth aspects, the amount of fuel injected from the intake port fuel injection means for controlling the exhaust air-fuel ratio is: It is determined based on the air-fuel ratio detected by an air-fuel ratio sensor provided in the exhaust passage of the internal combustion engine.
According to the sixth and seventh aspects of the invention, the exhaust air-fuel ratio can be accurately controlled to the target air-fuel ratio.

According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects, when there is means for obtaining an in-cylinder charged air amount and there is a blow-in of the intake air, the in-cylinder filling is performed. The combustion air-fuel ratio is controlled by adjusting the amount of fuel injected from the in-cylinder fuel injection means based on the amount of air.
When the intake air is blown through, the combustion air-fuel ratio can be accurately controlled.

  According to a ninth aspect of the present invention, in the invention according to any one of the first to eighth aspects, the fuel injection from the intake port fuel injection means for controlling the exhaust air-fuel ratio is performed asynchronously. It has become.

  According to the ninth aspect of the present invention, the fuel injected from the fuel injection means in the intake port blows through to the exhaust side, that is, flows into the exhaust side together with the intake air that blows through. Therefore, according to the ninth aspect of the present invention, the exhaust air-fuel ratio can be controlled without affecting the combustion air-fuel ratio by the fuel injection from the intake port fuel injection means.

  In the invention described in each claim, in an internal combustion engine having a dual injection system, when there is blow-in of intake air, the exhaust air-fuel ratio is controlled to the target air-fuel ratio while the combustion air-fuel ratio is controlled to the target air-fuel ratio. There is a common effect that leaner than the value of can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a case where an air-fuel ratio control apparatus according to an embodiment of the present invention is applied to a spark ignition type internal combustion engine. The present invention can also be applied to other types of internal combustion engines such as diesel engines.

  Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 5a is a cylinder fuel injection valve, 6 is a spark plug, 7 is an intake valve, and 8 is An intake port, 9 is an exhaust valve, and 10 is an exhaust port. A water temperature sensor 50 for detecting the temperature of cooling water for cooling the internal combustion engine is attached to the cylinder block 2. A cavity extending from the lower side of the in-cylinder fuel injection valve 5 a to the lower side of the spark plug 6 is formed on the top surface of the piston 4.

  The intake valve 7 and the exhaust valve 9 are provided with variable valve timing mechanisms 7a and 9a for changing the opening / closing timing of the valves, respectively, so that the valve overlap amount can be adjusted. In this internal combustion engine, the intake port 8 is also provided with a fuel injection valve (in-port fuel injection valve) 8 a that injects fuel into the intake port 8. That is, this internal combustion engine is an internal combustion engine provided with a so-called dual injection system.

  The intake port 8 is connected to the surge tank 12 via a corresponding intake branch pipe 11. The surge tank 12 is connected to the outlet of the compressor 15 of the exhaust turbocharger 14 via the intake duct 13, and the inlet of the compressor 15 is connected to the air cleaner 21. An air flow meter 22 is provided between the air cleaner 21 and the compressor 15 to detect the amount of intake air.

  A throttle valve 17 driven by a step motor 16 is disposed in the intake duct 13. Further, a cooling device 18 for cooling the intake air flowing through the intake duct 13 is disposed around the intake duct 13. In the internal combustion engine shown in FIG. 1, engine cooling water is guided into the cooling device 18, and the intake air is cooled by the engine cooling water.

  On the other hand, the exhaust port 10 is connected to an exhaust turbine 23 of the exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20. An exhaust gas purification device 24 is connected to the outlet side of the exhaust turbine 23 in order to purify the exhaust gas. In the internal combustion engine shown in FIG. 1, a three-way catalyst is built in the exhaust gas purification device 24. An air-fuel ratio sensor 25 for detecting the air-fuel ratio of the exhaust gas is provided between the exhaust turbine 23 and the exhaust gas purification device 24.

  The electronic control unit (ECU) 30 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a known type digital computer in which input / output ports are connected by a bidirectional bus. Various controls such as control of the fuel injection amount and fuel injection timing are performed by exchanging signals with each component of the engine. The air flow meter 22, the air-fuel ratio sensor 25, and the water temperature sensor 50 described above are connected to the ECU 30, and these output signals are supplied to the ECU 30.

  Connected to the accelerator pedal 40 is a load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 (hereinafter referred to as “accelerator depression amount”) L. The load sensor 41 is connected to the ECU 30, and its output voltage is input to the ECU 30. The ECU 30 is also connected with a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. Further, the ECU 30 is also connected with an in-cylinder fuel injection valve 5a, an in-port fuel injection valve 8a, a spark plug 6, variable valve timing mechanisms 7a and 9a, a throttle valve driving step motor 16, and the like. The components can be controlled by signals from the ECU 30.

  By the way, in air-fuel ratio control in a general internal combustion engine, a map for obtaining an appropriate air-fuel ratio is obtained in advance based on the engine operating state (for example, required torque determined from the accelerator depression amount L and the engine speed). The target air-fuel ratio is obtained using the map stored in the ECU. Then, in order to make the actual air-fuel ratio coincide with the target air-fuel ratio, the fuel injection amount is determined based on at least one of the intake air amount and the detected value of the air-fuel ratio sensor provided in the exhaust system, and the determined amount The fuel is injected and the air-fuel ratio is controlled.

  Further, for example, in an internal combustion engine with a supercharger, there is one in which valve overlap is performed when acceleration or high output is required. In other words, by performing valve overlap, the intake air is blown out to the exhaust side by using the supercharging pressure, etc., and the residual gas in the combustion chamber is scavenged to improve the combustibility and output, and The amount of exhaust gas supplied to the turbocharger turbine is increased to increase the supercharging effect and to improve the output, and such control is also performed in the internal combustion engine shown in FIG. ing.

  However, if the intake air is blown out to the exhaust side by performing valve overlap in this way, the amount of air charged into the combustion chamber (in-cylinder charged air amount) becomes the intake air amount (more specifically, Here, the total air amount taken into the internal combustion engine) is smaller. For this reason, when the amount of fuel determined based on the intake air amount is injected, the air-fuel ratio (combustion air-fuel ratio) in the combustion chamber becomes richer than the target air-fuel ratio, and the internal combustion engine generates an output different from the desired output. For example, good control cannot be performed.

  In such a case, for example, the amount of air blown to the exhaust side (blow-through air amount) is obtained, the amount of blow-through air is subtracted from the amount of intake air to obtain the amount of air charged in the cylinder, and the fuel injection amount is calculated based on the value. By determining, it is possible to control the combustion air-fuel ratio to the target air-fuel ratio. Alternatively, by calculating a blow-through rate that is a ratio of the blow-through air amount to the intake air amount, correcting the target air-fuel ratio obtained from the map based on the blow-through rate, and performing control based on the corrected target air-fuel ratio. The combustion air-fuel ratio can be set to the target air-fuel ratio before correction.

  However, when the combustion air-fuel ratio is set to the target air-fuel ratio in this way, the total air-fuel ratio including the blow-through air amount, that is, the exhaust gas air-fuel ratio (exhaust air-fuel ratio) is the combustion It becomes leaner than the air-fuel ratio. That is, for example, when the combustion air-fuel ratio is set to the stoichiometric air-fuel ratio, the exhaust air-fuel ratio becomes lean. When the exhaust air-fuel ratio becomes lean in this way, the exhaust gas contains a large amount of oxygen, so that the exhaust purification catalyst provided in the exhaust system is likely to deteriorate or overheat, and the ternary When a catalyst is used, the purification rate is lowered and the emission is deteriorated.

  Such a problem may normally occur in an internal combustion engine equipped with a dual injection system as shown in FIG. Therefore, in the present embodiment, when the intake air blows through by performing the control described below, the exhaust air / fuel ratio is controlled to the target air / fuel ratio while the exhaust air / fuel ratio is set to the target air / fuel ratio. The leaner than the air-fuel ratio value is suppressed.

  That is, the control performed in the present embodiment is simply described. When there is a blow-through of intake air, the amount of fuel injected from the in-cylinder fuel injection valve 5a is adjusted in consideration of the blow-through, and the combustion air-fuel ratio is adjusted. When the air-fuel ratio calculated based on the intake air amount and the amount of fuel injected from the in-cylinder fuel injection valve 5a is leaner than the target air-fuel ratio of the predetermined exhaust air-fuel ratio, The exhaust air fuel ratio is controlled by injecting fuel from the intake port fuel injection valve 8a.

  FIG. 2 is a flowchart showing a control routine of control executed to determine the fuel injection amount in the air-fuel ratio control apparatus for the internal combustion engine of the present embodiment. When this control routine is started, first, in step 101, the in-cylinder charged air amount Mc and the blow-by air amount Me are calculated. In the present embodiment, the in-cylinder charged air amount Mc and the blow-through air amount Me are calculated by a known method using a model in the ECU 30, and the detected value of the air flow meter 22 is used for error correction. It has become.

When the in-cylinder charged air amount Mc and the blow-by air amount Me are calculated in step 101, the process proceeds to step 103. In step 103, a blow-through rate P which is a ratio of the blow-through air amount Me to the intake air amount Ma (= Mc + Me) is calculated. That is, here, the blow-through rate P is calculated by the following equation (1) using the in-cylinder charged air amount Mc and the blow-through air amount Me calculated in step 101.
P = Me / (Mc + Me) (1)

  When the blow-through rate P is calculated in step 103, the process proceeds to step 105. In step 105, the target air-fuel ratio AFt is determined. In the present embodiment, a map for obtaining an appropriate air-fuel ratio (that is, a target air-fuel ratio AFt) based on the engine operating state is obtained in advance and stored in the ECU 30, and here, the target air-fuel ratio AFt is determined based on the map. Desired. Note that the air-fuel ratio obtained from this map is more specifically an air-fuel ratio appropriate as the air-fuel ratio in the combustion chamber with respect to the engine operating state at that time, so the target air-fuel ratio of the combustion air-fuel ratio (target combustion air-fuel ratio) It can be said that.

  When the target air-fuel ratio AFt is determined in step 105, the routine proceeds to step 107. In step 107, it is determined whether or not the blow-through rate P calculated in step 103 is greater than 0 (zero). In other words, this determination is a determination as to whether there is a blow-in of the intake air. Therefore, in another embodiment, instead of the determination in step 107, the presence / absence of blow-in of the intake air may be determined by another method, for example, using the relationship between the engine operation state and the presence / absence of the blow-through. Good. Further, as can be understood from the above description, since the blow-through rate P is a value of 0 (zero) or more, the determination in step 107 is substantially whether the blow-through rate P is 0 (zero) or not. It can be said that it is a judgment whether it is larger.

  If it is determined in step 107 that the blow-through rate P is 0 (zero) or less (that is, the blow-through rate P is 0 (zero)), that is, there is no blow-in of the intake air. The fuel injection amount Fa is calculated based on the intake air amount Ma and the target air-fuel ratio AFt. That is, in this case, air-fuel ratio control based on the target air-fuel ratio AFt determined in step 105 is performed. In this case, the fuel may be injected from either the in-cylinder fuel injection valve 5a or the in-port fuel injection valve 8a according to the engine operating state, and the in-cylinder fuel injection valve 5a or the in-port fuel injection valve. The fuel may be injected from both injection valves so that the total injection amount from 8a becomes the fuel injection amount Fa.

On the other hand, if it is determined in step 107 that the blow-through rate P is greater than 0 (zero), that is, if there is blow-in of the intake air, the process proceeds to step 109 in this case. In step 109, the target air-fuel ratio AFt determined in step 105 is corrected based on the blow-through rate P calculated in step 103, and a corrected target air-fuel ratio AFtc is calculated. More specifically, the corrected target air-fuel ratio AFtc is calculated by the following equation (2).
AFtc = AFt / (1-P) (2)

  When the corrected target air-fuel ratio AFtc is calculated at step 109, the routine proceeds to step 111, where the in-cylinder fuel injection amount Fc is calculated based on the intake air amount Ma (= Mc + Me) and the corrected target air-fuel ratio AFtc. That is, in this case, air-fuel ratio control based on the corrected target air-fuel ratio AFtc is performed, and thereby the combustion air-fuel ratio is controlled. As can be understood from the above equation (2) and the above description, the corrected target air-fuel ratio AFtc is a target value set to set the combustion air-fuel ratio to the target air-fuel ratio AFt. By performing air-fuel ratio control based on AFtc, the combustion air-fuel ratio is controlled to the target air-fuel ratio AFt.

  When the in-cylinder fuel injection amount Fc is calculated in step 111, the process proceeds to step 113. In step 113, it is determined whether or not the corrected target air-fuel ratio AFtc is greater than a predetermined target air-fuel ratio (target exhaust air-fuel ratio) AFte, that is, whether or not the corrected target air-fuel ratio AFtc is leaner than the target exhaust air-fuel ratio AFte. Determined. Here, the target exhaust air-fuel ratio AFte is, for example, the stoichiometric air-fuel ratio. Alternatively, the target air-fuel ratio AFt determined in step 105 may be set.

  As described above, the in-cylinder fuel injection amount Fc is calculated based on the intake air amount Ma (= Mc + Me) and the corrected target air-fuel ratio AFtc. It can be said that the air-fuel ratio is calculated based on the air amount and the in-cylinder fuel injection amount Fc. Therefore, in step 113, it is determined whether the air-fuel ratio calculated based on the intake air amount and the in-cylinder fuel injection amount Fc is larger than the target exhaust air-fuel ratio AFte, that is, whether the air-fuel ratio is leaner than the target exhaust air-fuel ratio AFte. It can be said that it has been judged.

If it is determined in step 113 that the corrected target air-fuel ratio AFtc is greater than the target exhaust air-fuel ratio AFte, that is, it is determined that the corrected target air-fuel ratio AFtc is leaner than the target exhaust air-fuel ratio AFte, the routine proceeds to step 115. In step 115, the in-port fuel injection amount Fp is calculated based on the intake air amount Ma (= Mc + Me) and the in-cylinder fuel injection amount Fc calculated in step 111. More specifically, the in-port fuel injection amount Fp is calculated by the following equation (3).
Fp = ((Mc + Me) / AFte) −Fc (3)

As understood from the equation (3), the in-port fuel injection amount Fp is the amount of fuel that needs to be added in order to set the exhaust air-fuel ratio to the target exhaust air-fuel ratio AFte. Further, the above equation (3) is expressed by the following equations (4) and (5) using the relationship between the corrected target air-fuel ratio AFtc, the intake air amount Ma (= Mc + Me), and the in-cylinder fuel injection amount Fc. Can be rewritten.
Fp = ((Mc + Me) / AFte) − ((Mc + Me) / AFtc) (4)
Fp = (Fc · AFtc / AFte) −Fc (5)

  These equations (4) and (5) can be further rewritten using the above equation (2). The in-port fuel injection amount Fp can be calculated using the above equation (3) and any equation obtained by rewriting it.

  On the other hand, if it is determined in step 113 that the corrected target air-fuel ratio AFtc is equal to or less than the target exhaust air-fuel ratio AFte, that is, the corrected target air-fuel ratio AFtc is the same as the target exhaust air-fuel ratio AFte or rich, step 117 The in-port fuel injection amount Fp is set to 0 (zero). That is, when the corrected target air-fuel ratio AFtc is the same as or richer than the target exhaust air-fuel ratio AFte, the exhaust air-fuel ratio cannot be brought close to the target exhaust air-fuel ratio AFte by adding fuel, and fuel is added. If this is the case, the exhaust air-fuel ratio is kept away from the target exhaust air-fuel ratio AFte. In this case, in-port fuel injection is prohibited.

  In the present embodiment, a map that can determine the appropriate fuel injection timing for each of the in-cylinder fuel injection and the in-port fuel injection based on the engine operating state is obtained in advance and stored in the ECU 30, as described above. Thus, the amount of fuel calculated according to the control routine shown in FIG. 2 is injected at the fuel injection timing determined from the map. In this embodiment, in particular, the in-port injection of the fuel of the amount Fp calculated in step 115 performed for controlling the exhaust air-fuel ratio is performed asynchronously with the intake air.

  As described above, in the present embodiment, when there is a blow-through of intake air, the amount of fuel injected from the in-cylinder fuel injection valve 5a is adjusted in consideration of the blow-through, and the combustion air-fuel ratio is controlled. When the air-fuel ratio AFtc calculated based on the air amount Ma (= Mc + Me) and the fuel amount Fc injected from the in-cylinder fuel injection valve 5a is leaner than the target air-fuel ratio AFte of the exhaust air-fuel ratio, The exhaust air fuel ratio is controlled by injecting fuel from the intake port fuel injection valve 8a.

  Therefore, according to the present embodiment, when there is blow-in of intake air, the combustion air-fuel ratio is controlled to the target air-fuel ratio value, and the exhaust air-fuel ratio is prevented from becoming leaner than the target air-fuel ratio value. can do. As a result, it is possible to prevent the exhaust purification catalyst from being easily deteriorated or excessively heated, and to suppress emission deterioration.

  In this embodiment, the amount of fuel Fp injected from the intake port fuel injection valve 8a in order to control the exhaust air-fuel ratio is determined from the intake air amount Ma (= Mc + Me) and the in-cylinder fuel injection valve 5a. It is determined based on the fuel amount Fc to be injected. Therefore, in this embodiment, the exhaust air / fuel ratio can be accurately controlled to the target air / fuel ratio AFte.

  Further, in this embodiment, when the air-fuel ratio calculated based on the intake air amount and the fuel amount Fc injected from the in-cylinder fuel injection valve 5a is equal to the target air-fuel ratio AFte of the exhaust air-fuel ratio, or When it is richer than the fuel ratio AFte, fuel injection from the intake port fuel injection valve 8a for controlling the exhaust air-fuel ratio is prohibited. Thereby, in the present embodiment, inappropriate control of the exhaust air-fuel ratio is prevented.

  In the present embodiment, fuel injection from the intake port fuel injection valve 8a for controlling the exhaust air-fuel ratio is performed asynchronously with intake air. This is because when fuel is injected from the intake port fuel injection valve 8a asynchronously with intake air, the injected fuel blows through to the exhaust side, that is, flows into the exhaust side together with the intake air that blows through. This is because the fuel injection from the fuel injection valve 8a makes it possible to control the exhaust air / fuel ratio without affecting the combustion air / fuel ratio.

  FIG. 3 shows an intake air amount Ma, a cylinder charge air amount Mc, a blow-through air amount Me, a blow-through rate P, a combustion air-fuel ratio AFc, and an exhaust air-fuel ratio when air-fuel ratio control is performed by the air-fuel ratio control apparatus of the present embodiment. It is the figure shown about an example of the time-dependent change of AFe, in-cylinder fuel injection amount Fc, and in-port fuel injection amount Fp. In the figure, these changes with time are indicated by solid lines.

  In the example of this figure, at the time t1, for example, an operation state in which intake air is blown through, such as valve overlap is performed. In the figure, AFt is a target air-fuel ratio (more specifically, a target combustion air-fuel ratio) in operation after time t1, AFtc is a corrected target air-fuel ratio, and AFte is a target exhaust air-fuel ratio.

  Further, the changes over time in the fuel injection amount (more specifically, the in-cylinder fuel injection amount) and the combustion air-fuel ratio indicated by the alternate long and short dash lines X and Y are those when the air-fuel ratio control is performed without taking the blow-through into consideration. In this case, the combustion air-fuel ratio is richer than the target air-fuel ratio AFt. Further, the time-dependent change in the exhaust air-fuel ratio indicated by the two-dot chain line Z is performed when the control considering the blow-through is performed only with respect to the combustion air-fuel ratio, that is, the control regarding the exhaust air-fuel ratio as in the present embodiment is not performed. In this case, the exhaust air-fuel ratio is leaner than the target exhaust air-fuel ratio AFte.

  From this figure, when the air-fuel ratio control is performed by the air-fuel ratio control apparatus of the present embodiment, when the intake air is blown through, the exhaust air-fuel ratio is controlled while the combustion air-fuel ratio is controlled to the target air-fuel ratio value. It can be seen that leaner than the target air-fuel ratio value can be suppressed, and that the exhaust air-fuel ratio can be controlled to the target air-fuel ratio value.

  In another embodiment of the present invention, the in-cylinder fuel injection amount Fc when there is intake air blow-off is directly calculated based on the in-cylinder charged air amount Mc and the target air-fuel ratio AFt. May be.

  In another embodiment of the present invention, the detected value of the air-fuel ratio sensor 25 may be used for controlling the exhaust air-fuel ratio. That is, for example, in the above-described embodiment, the corrected target air-fuel ratio AFtc and the target exhaust air-fuel ratio AFte are compared in step 113 of the control routine shown in FIG. The detected value (hereinafter referred to as “detected air / fuel ratio”) AFs and the target exhaust air / fuel ratio AFte may be compared.

  That is, in this case, it is determined in step 113 whether or not the detected air-fuel ratio AFs is larger than the target exhaust air-fuel ratio AFte, that is, whether or not the detected air-fuel ratio AFs is leaner than the target exhaust air-fuel ratio AFte. If it is determined in step 113 that the detected air-fuel ratio AFs is greater than the target exhaust air-fuel ratio AFte, that is, it is determined that the detected air-fuel ratio AFs is leaner than the target exhaust air-fuel ratio AFte, the routine proceeds to step 115 and fuel injection amount in the port On the other hand, if it is determined that the detected air-fuel ratio AFs is equal to or less than the target exhaust air-fuel ratio AFte, that is, the detected air-fuel ratio AFs is the same as the target exhaust air-fuel ratio AFte, or is rich, while Fp is calculated. Then, the in-port fuel injection amount Fp is set to 0 (zero).

  That is, in this embodiment, when there is a blow-through of intake air, the amount of fuel injected from the in-cylinder fuel injection valve 5a is adjusted in consideration of the blow-through, and the combustion air-fuel ratio is controlled. When the air-fuel ratio AFs detected by the air-fuel ratio sensor 25 provided in the exhaust passage is leaner than the target air-fuel ratio AFte of the exhaust air-fuel ratio, fuel is injected from the intake port fuel injection valve 8a. The exhaust air-fuel ratio is controlled.

  As can be understood from the above description, the combustion air-fuel ratio is controlled to the value of the target air-fuel ratio in the case where there is a blow-through of intake air as in the above-described embodiment, as can be understood from the above description. However, it is possible to suppress the exhaust air-fuel ratio from becoming leaner than the target air-fuel ratio, and as a result, it is possible to prevent the exhaust purification catalyst from being easily deteriorated or excessively heated, and to deteriorate emissions. Can be suppressed.

  In this embodiment, when the air-fuel ratio AFs detected by the air-fuel ratio sensor 25 is equal to the target air-fuel ratio AFte of the exhaust air-fuel ratio or richer than the target air-fuel ratio AFte, fuel injection in the port is performed. The amount Fp is set to 0 (zero), that is, fuel injection from the intake port fuel injection valve 8a for controlling the exhaust air-fuel ratio is prohibited. By doing so, inadequate control of the exhaust air-fuel ratio can be prevented as in the embodiment described above.

Further, the detected air-fuel ratio AFs may be used in the calculation of the in-port fuel injection amount Fp in step 115 of the control routine shown in FIG. That is, for example, the in-port fuel injection amount Fp is calculated by the following equation (6).
Fp = (Fc · AFs / AFte) −Fc (6)

In this case, that is, the in-port fuel injection amount Fp is determined based on the fuel amount Fc injected from the in-cylinder fuel injection valve 5a and the detected air-fuel ratio AFs. Alternatively, the in-port fuel injection amount Fp may be calculated by the following equation (7).
Fp = ((Mc + Me) / AFte) − ((Mc + Me) / AFs) (7)

  In this case, the in-port fuel injection amount Fp is determined based on the intake air amount Ma (= Mc + Me) and the detected air-fuel ratio AFs. The exhaust air / fuel ratio can be accurately controlled to the target air / fuel ratio when either of the equations (6) and (7) is used.

FIG. 1 is a diagram showing a case where an air-fuel ratio control apparatus according to an embodiment of the present invention is applied to a spark ignition type internal combustion engine. FIG. 2 is a flowchart showing a control routine of control executed to determine the fuel injection amount in the air-fuel ratio control apparatus for an internal combustion engine according to the embodiment of the present invention. FIG. 3 shows an intake air amount Ma, an in-cylinder charged air amount Mc, a blow-through air amount Me, a blow-through rate P, a combustion air-fuel ratio AFc, when the air-fuel ratio control is performed by the air-fuel ratio control apparatus of one embodiment of the present invention. It is the figure shown about an example of the time-dependent change of exhaust air fuel ratio AFe, in-cylinder fuel injection amount Fc, and in-port fuel injection amount Fp.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine body 2 Cylinder block 3 Cylinder head 4 Piston 5 Combustion chamber 5a In-cylinder fuel injection valve 6 Spark plug 7 Intake valve 7a Variable valve timing mechanism 8 Intake port 8a In-port fuel injection valve 9 Exhaust valve 9a Variable valve timing mechanism 10 Exhaust Port 14 Exhaust turbocharger 25 Air-fuel ratio sensor

Claims (9)

An air-fuel ratio control apparatus for an internal combustion engine comprising in-cylinder fuel injection means for injecting fuel into a combustion chamber and intake port fuel injection means for injecting fuel into an intake port,
When there is blow-in of intake air, the amount of fuel injected from the in-cylinder fuel injection means is adjusted in consideration of the blow-through and the combustion air-fuel ratio is controlled, and the intake air amount and injection from the in-cylinder fuel injection means are controlled. When the air-fuel ratio calculated based on the amount of fuel to be discharged is leaner than the target air-fuel ratio of the predetermined exhaust air-fuel ratio, fuel is injected from the fuel injection means in the intake port and the exhaust air-fuel ratio is An air-fuel ratio control apparatus for an internal combustion engine that controls the engine.   The air-fuel ratio calculated based on the intake air amount and the amount of fuel injected from the in-cylinder fuel injection means is equal to the target air-fuel ratio of the predetermined exhaust air-fuel ratio or richer than the target air-fuel ratio. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein fuel injection from the fuel injection means in the intake port for controlling the exhaust air-fuel ratio is prohibited. An air-fuel ratio control apparatus for an internal combustion engine comprising in-cylinder fuel injection means for injecting fuel into a combustion chamber and intake port fuel injection means for injecting fuel into an intake port,
When there is blow-in of intake air, the amount of fuel injected from the in-cylinder fuel injection means is adjusted in consideration of the blow-through to control the combustion air-fuel ratio, and the air-fuel ratio provided in the exhaust passage of the internal combustion engine An internal combustion engine for controlling the exhaust air-fuel ratio by injecting fuel from the fuel injection means in the intake port when the air-fuel ratio detected by the sensor is leaner than a target air-fuel ratio of a predetermined exhaust air-fuel ratio Air-fuel ratio control device.   When the air-fuel ratio detected by the air-fuel ratio sensor provided in the exhaust passage of the internal combustion engine is equal to the target air-fuel ratio of the predetermined exhaust air-fuel ratio or richer than the target air-fuel ratio, the exhaust gas The air-fuel ratio control apparatus for an internal combustion engine according to claim 3, wherein fuel injection from the intake port fuel injection means for controlling the air-fuel ratio is prohibited.   The amount of fuel injected from the intake port fuel injection means for controlling the exhaust air-fuel ratio is determined based on an intake air amount and an amount of fuel injected from the in-cylinder fuel injection means. The air-fuel ratio control apparatus for an internal combustion engine according to any one of 1 to 4.   In order to control the exhaust air / fuel ratio, the amount of fuel injected from the intake port fuel injection means includes the amount of fuel injected from the in-cylinder fuel injection means and an air / fuel ratio sensor provided in the exhaust passage of the internal combustion engine. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the air-fuel ratio control apparatus is determined based on an air-fuel ratio detected by the engine.   The amount of fuel injected from the intake port fuel injection means for controlling the exhaust air-fuel ratio is based on the intake air amount and the air-fuel ratio detected by the air-fuel ratio sensor provided in the exhaust passage of the internal combustion engine. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4, which is determined by: Having means for determining the amount of air filled in the cylinder;
8. The combustion air-fuel ratio is controlled by adjusting the amount of fuel injected from the in-cylinder fuel injection means based on the in-cylinder charged air amount when there is a blow-in of intake air. An air-fuel ratio control apparatus for an internal combustion engine according to any one of the preceding claims.   The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 8, wherein fuel injection from the intake port fuel injection means for controlling the exhaust air-fuel ratio is performed asynchronously with intake air.

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