JP2006299992A - Control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique which can increase supercharging pressure suitably in an internal combustion engine including a supercharger. <P>SOLUTION: In the internal combustion engine including a plurality of cylinders, fuel injection valves for injecting fuel into the cylinders and the supercharger, when increasing the supercharging pressure by the supercharger, blow-by air is generated in one cylinder, and further when the blow-by air is being generated in the cylinder, sub fuel injection is performed in the other cylinders the exhaust valves of which are opened. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control system for an internal combustion engine, and more particularly to a control system for an internal combustion engine having a supercharger that supercharges intake air by the energy of exhaust gas.

  In an internal combustion engine having a supercharger (hereinafter simply referred to as a supercharger) that supercharges intake air by the energy of exhaust gas, intake is performed during a valve overlap period in which both the intake valve and the exhaust valve are open. When the atmospheric pressure is higher than the exhaust pressure, a technique for making the valve overlap period longer is known (for example, see Patent Document 1).

Further, in an internal combustion engine having a supercharger, when the engine rotational speed and the rotational speed of the turbocharger turbine are low, the exhaust passage in the combustion chamber or in the vicinity of the combustion chamber is the time after the main fuel injection. A technique is known in which auxiliary fuel injection is performed from an in-cylinder injection valve at a time when fuel can be combusted inside (see, for example, Patent Document 2).
JP 2003-120361 A JP 2000-345889 A JP 2000-54894 A Japanese Patent Publication No. 7-101101 JP 2002-266686 A

  In an internal combustion engine having a supercharger, when the supercharging pressure is increased by the supercharger, an auxiliary fuel injection is performed at a time after the main fuel injection by a fuel injection valve that injects fuel into the cylinder, thereby exhaust passage May cause fuel to be discharged. When the fuel is discharged into the exhaust passage and the fuel burns in the exhaust passage, the energy of the exhaust increases, so that the supercharging pressure can be increased more quickly by the supercharger.

  However, even when the fuel is discharged into the exhaust passage, if the oxygen for burning the fuel is insufficient in the exhaust passage, the fuel does not burn and the boost pressure is increased more quickly. There is a possibility that it cannot be made. Further, in such a case, the fuel discharged into the exhaust passage is released into the atmosphere without being burned, which may lead to deterioration of fuel consumption and exhaust emission.

  This invention is made | formed in view of the said problem, Comprising: It aims at providing the technique which can raise a supercharging pressure more suitably in the internal combustion engine which has a supercharger.

  In an internal combustion engine having a plurality of cylinders, a fuel injection valve for injecting fuel into the cylinders, and a supercharger, when the supercharging pressure is increased by the supercharger, The blow-by air is generated, and further, when the blow-by air is generated in the one cylinder, the auxiliary fuel injection is executed in the other cylinder in which the exhaust valve is opened.

More specifically, the control system for an internal combustion engine according to the present invention is:
Multiple cylinders,
A fuel injection valve for injecting fuel into the cylinder;
A supercharger that supercharges intake air by the energy of exhaust gas flowing through the exhaust passage;
An internal combustion engine control system comprising:
Blow-through air generating means for generating blow-through air flowing out from the intake port to the exhaust port,
When the supercharging pressure is increased by the supercharger, blow-by air is generated by the blow-by air generating means in one cylinder, and further, an exhaust stroke is performed when the one cylinder is in the intake stroke. In the other cylinders, when the exhaust valve is open and when blow-by air is generated in the one cylinder, the fuel injection valve performs sub fuel injection.

  In the present invention, when the supercharging pressure is increased by the supercharger, blow-by air is generated in one cylinder. When blow-by air is generated, the amount of air in the exhaust passage increases.

  Further, in the present invention, when blow-by air is generated in one cylinder, that is, when the amount of air in the exhaust passage is increased, sub fuel injection is performed in another cylinder in which the exhaust valve is open. Execute. The fuel injected by the sub fuel injection is discharged into the exhaust passage in an unburned state together with the burned gas discharged from the cylinder. In the other cylinders, main fuel injection for injecting fuel to be used for combustion in the cylinder is executed before the auxiliary fuel injection is executed.

  That is, according to the present invention, when the supercharging pressure is increased by the supercharger, the amount of air in the exhaust passage is increased and the fuel is discharged into the exhaust passage. Therefore, it is possible to suppress a shortage of oxygen used for fuel combustion in the exhaust passage. That is, the fuel discharged into the exhaust passage is more easily combusted. Therefore, it is possible to increase the exhaust energy more reliably when the supercharging pressure is increased by the supercharger. Therefore, the supercharging pressure can be increased more quickly.

  Further, according to the present invention, the fuel discharged into the exhaust passage is more easily combusted, so that the fuel is not easily released into the atmosphere in an unburned state. Therefore, deterioration of fuel consumption and exhaust emission can be suppressed.

  Thus, according to the present invention, it is possible to increase the supercharging pressure more suitably.

  In the present invention, the blow-by air generating means may include overlap control means for controlling a valve overlap period in which both the intake valve and the exhaust valve of the internal combustion engine are in the open state. In this case, the blow-by air generating means generates blow-by air by controlling the valve overlap period by the valve overlap control means.

  When the supercharging pressure is increased by the supercharger, the pressure in the intake passage becomes higher than the pressure in the exhaust passage, that is, the pressure in the intake port becomes higher than the pressure in the exhaust port. Therefore, at this time, by controlling the valve overlap period, at least a part of the air flowing into the cylinder from the intake port can be discharged to the exhaust port. That is, it is possible to generate blow-by air.

  In the present invention, in the other cylinders, the auxiliary fuel injection is performed when the exhaust valve is open and the blow-off air is generated by controlling the valve overlap period in one cylinder. When the engine speed of the internal combustion engine is higher, the sub fuel injection execution timing may be delayed.

Even when the valve overlap period is controlled to generate blow-by air in one cylinder, there is a response delay until the valve overlap period changes, until the air amount in the exhaust passage actually increases Takes some time. On the other hand, the higher the engine speed of the internal combustion engine, the faster the exhaust flow velocity in the exhaust port and the exhaust passage. Therefore, the fuel injected by the auxiliary fuel injection in the other cylinders is discharged to the exhaust passage faster as the engine speed of the internal combustion engine is higher, and flows faster downstream in the exhaust passage. .

  Therefore, when the auxiliary fuel injection is executed at an excessively early time in the other cylinders, the fuel injected by the auxiliary fuel injection increases the amount of blow-through air in one cylinder, thereby increasing the amount of air in the exhaust passage. There are cases where the exhaust passage is reached before and flows downstream through the exhaust passage. In this case, there is a risk that oxygen used for fuel combustion in the exhaust passage is insufficient.

  Therefore, as described above, the higher the engine speed of the internal combustion engine, the slower the execution timing of the auxiliary fuel injection in the other cylinders. As a result, before the amount of air in the exhaust passage increases, it is possible to suppress the fuel injected by the auxiliary fuel injection in the other cylinders from reaching the exhaust passage and flowing downstream in the exhaust passage. . That is, it is possible to secure oxygen used for fuel combustion in the exhaust passage. Therefore, the fuel discharged into the exhaust passage can be more reliably burned in the exhaust passage.

  The present invention may further include a blow-by air amount estimation unit that estimates a blow-through air amount during a valve overlap period, and a cylinder air-fuel ratio estimation unit that estimates an air-fuel ratio in the cylinder. In such a case, when the exhaust valve is open in another cylinder and the blow-off air is generated by controlling the valve overlap period in one cylinder, the fuel injection valve When sub fuel injection is performed, the amount of blow-by air in one cylinder estimated by the blow-by air amount estimation means and the air-fuel ratio in other cylinders before execution of sub fuel injection estimated by the cylinder air-fuel ratio estimation means The sub fuel injection amount may be determined based on the above.

  According to such control, when the supercharging pressure is increased by the supercharger, even when the fuel is discharged to the exhaust passage while increasing the air amount in the exhaust passage, the air-fuel ratio of the exhaust gas is increased. Can be controlled to a desired air-fuel ratio. Therefore, deterioration of exhaust emission can be suppressed. In addition, the air-fuel ratio of the exhaust gas can be controlled to a value such that the energy of the exhaust gas increases as much as possible when the fuel injected by the auxiliary fuel injection burns in the exhaust passage.

  ADVANTAGE OF THE INVENTION According to this invention, a supercharging pressure can be raised more suitably in the internal combustion engine which has a supercharger.

  Hereinafter, specific embodiments of a control system for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Schematic configuration of internal combustion engine and its intake / exhaust system>
In this embodiment, the case where the present invention is applied to a gasoline engine for driving a vehicle will be described. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a four-cylinder gasoline engine having four cylinders 2.

A piston 4 is slidably provided in the cylinder 2. In the upper combustion chamber 5 in the cylinder 2,
An intake port 6 and an exhaust port 7 are connected. Openings of the intake port 6 and the exhaust port 7 to the combustion chamber 5 are opened and closed by an intake valve 8 and an exhaust valve 9, respectively. The intake valve 8 and the exhaust valve 9 are provided with an intake side variable valve mechanism 10 and an exhaust side variable valve mechanism 11, respectively, and the opening / closing timings thereof are variable. The cylinder 2 is provided with a fuel injection valve 3 for injecting fuel into the combustion chamber 5 and a spark plug 15 for igniting the air-fuel mixture in the combustion chamber 5.

  The intake port 6 and the exhaust port 7 are connected to an intake passage 12 and an exhaust passage 13, respectively. A compressor 14 a of a turbocharger (supercharger) 14 is installed in the middle of the intake passage 12. On the other hand, a turbine 14 b of the turbocharger 14 is installed in the middle of the exhaust passage 13. An air flow meter 25 is provided in the intake passage 12 upstream of the compressor 14a, and an electric signal corresponding to the pressure in the intake passage 12 is output to the intake passage 12 downstream of the compressor 14a. An intake pressure sensor 24 is provided. The exhaust passage 13 upstream of the turbine 14b is referred to as an upstream exhaust passage 13a.

  Further, the internal combustion engine 1 outputs an accelerator opening sensor 21 that outputs an electric signal corresponding to the accelerator opening, and an electric signal corresponding to the rotation angle of the crankshaft that rotates in conjunction with the reciprocating motion of the piston 4. A crank position sensor 22 is provided.

  The internal combustion engine 1 configured as described above is provided with an ECU 20 for controlling the internal combustion engine 1. The ECU 20 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver. An air flow meter 25, an intake pressure sensor 24, an accelerator opening sensor 21, and a crank position sensor 22 are electrically connected to the ECU 20. These output signals are input to the ECU 20.

  Further, the fuel injection valve 3, the spark plug 15, the intake side variable valve mechanism 10, and the exhaust side variable valve mechanism 11 are electrically connected to the ECU 20. These are controlled by the ECU 20. For example, the ECU 20 controls the opening / closing timings of the intake valve 8 and the exhaust valve 9 by controlling the intake side variable valve mechanism 10 and the exhaust side variable valve mechanism 11, respectively. As a result, the valve overlap period during which both the intake valve 8 and the exhaust valve 9 are open is controlled.

<Open / close timing of intake / exhaust valve>
Here, the opening and closing timings of the intake and exhaust valves 8 and 9 according to the present embodiment will be described with reference to FIG. FIG. 2 is a diagram showing opening and closing timings of the intake and exhaust valves 8 and 9 according to the present embodiment. In FIG. 2, the horizontal axis represents the rotation angle of the crankshaft, and −180 to 0 ° is the exhaust stroke, and 0 to 180 ° is the intake stroke. In FIG. 2, the vertical axis represents the opening degrees of the intake valve 8 and the exhaust valve 9.

  As shown in FIG. 2, in this embodiment, the intake valve 8 is opened at a time before the exhaust valve 9 is closed. Therefore, the period ΔTov is a valve overlap period. When the supercharging pressure is increased by the turbocharger 14 such as during acceleration, the pressure in the intake passage 12 becomes higher than the pressure in the exhaust passage 13. Therefore, by controlling this valve overlap period, it is possible to generate blow-through air that flows out from the intake port 6 to the exhaust port 7 without being used for combustion in the cylinder 2.

  Further, in this embodiment, as shown in FIG. 2, the exhaust valve 9 opens before the start of the exhaust stroke, that is, before the end of the expansion stroke.

<Valve overlap period and auxiliary fuel injection timing when boost pressure rises>
Next, the valve overlap period and the auxiliary fuel injection timing when the boost pressure is increased in this embodiment will be described with reference to FIG. FIG. 3 is a diagram showing a combustion stroke in each cylinder 2 in the present embodiment. In FIG. 3, a region a represents a valve overlap period, and a region b represents a sub fuel injection execution timing. In addition, # 1 to # 4 represent the first to fourth cylinders, respectively.

  In this embodiment, when the supercharging pressure is increased by the turbocharger 14, blow-by air is generated by controlling the valve overlap period in each cylinder 2. Further, when a certain cylinder 2 is in the valve overlap period, sub fuel injection is executed by the fuel injection valve 3 in the other cylinder 2 in which the exhaust valve 9 is open.

  For example, in this embodiment, as shown in FIG. 3, when the second cylinder is in the intake stroke, the first cylinder is in the exhaust stroke. Therefore, when the second cylinder is in the overlap period, the exhaust valve 9 of the first cylinder is opened. Therefore, in this case, when the exhaust valve 9 of the first cylinder is open and the second cylinder is in the overlap period (the period b in FIG. 3), the fuel of the first cylinder Sub fuel injection is performed by the injection valve 3. As shown in FIG. 3, when the supercharging pressure is increased, the auxiliary fuel injection is executed at the same time in each of the first to fourth cylinders.

  When blow-by air is generated by controlling the valve overlap period, the amount of air in the upstream side exhaust passage 13a increases. Further, if the sub fuel injection is executed by the fuel injection valve 3 while the exhaust valve 9 is open, the fuel injected by the sub fuel injection is in an unburned state together with the burned gas discharged from the cylinder 2. It is discharged to the upstream side exhaust passage 13a.

  That is, according to the present invention, when the boost pressure is increased by the turbocharger 14, the amount of air in the upstream exhaust passage 13a is increased and the fuel is discharged into the upstream exhaust passage 13a. For this reason, it is possible to suppress the shortage of oxygen used for fuel combustion in the upstream side exhaust passage 13a. That is, the fuel discharged to the upstream side exhaust passage 13a is more easily combusted. Therefore, it is possible to increase the energy of the exhaust gas more reliably when the supercharging pressure is increased by the turbocharger 14. Therefore, the supercharging pressure can be increased more quickly.

  Further, according to the present invention, the fuel discharged to the upstream side exhaust passage 13a is more easily combusted, so that the fuel is not easily released into the atmosphere in an unburned state. Therefore, deterioration of fuel consumption and exhaust emission can be suppressed.

  Thus, according to the present embodiment, the boost pressure can be increased more suitably.

<Supercharging pressure increase control>
Hereinafter, the control routine of the boost pressure increase control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 20, and is a routine that is repeated at specified intervals during the operation of the internal combustion engine 1.

  In this routine, the ECU 20 first determines whether or not the accelerator opening has increased in S101 based on the detected value of the accelerator opening sensor 21. If an affirmative determination is made in S101, the ECU 20 determines that there is a request to increase the supercharging pressure, and proceeds to S102. On the other hand, if a negative determination is made in S101, the ECU 10 once ends the execution of this routine.

  In S102, the ECU 20 calculates a target blown air amount Qat, which is a target blown air amount. Here, the target blow-through air amount Qat is a value determined according to the accelerator opening, and the amount of air necessary for fuel combustion in the cylinder 2 is an amount that can be secured in the cylinder 2. The relationship between the target blow-through air amount Qat and the accelerator opening may be obtained in advance through experiments or the like and stored in the ECU 20 as a map.

  Next, the ECU 20 proceeds to S103, and calculates a target valve overlap period ΔTovt in which the blown air amount becomes the target blown air amount Qat. The target valve overlap period ΔTovt is determined based on the target blow-through air amount Qat, the engine speed of the internal combustion engine 1 calculated from the output value of the crank position sensor 22, and the intake air amount detected by the air flow meter 25. Is the value to be Here, the target valve overlap period ΔTovt is lengthened as the engine speed is lower and the intake air amount is smaller. The relationship between the target valve overlap period ΔTovt, the target blow-through air amount Qat, the engine speed, and the intake air amount may be obtained in advance by experiments or the like and stored in the ECU 20 as a map.

  Next, the ECU 20 proceeds to S104, where the intake valve 8 is opened by the intake side variable valve mechanism 10 and the exhaust side variable valve mechanism 11 so that the valve overlap period becomes the target valve overlap period ΔTovt. The closing timing of the exhaust valve 9 is controlled.

  Next, the ECU 20 proceeds to S105, and calculates the current blown air amount Qa. Even in the case where the control of the opening timing of the intake valve 8 and the closing timing of the exhaust valve 9 is executed in S104, there is a response delay until the valve overlap period reaches the target valve overlap period ΔTovt. Therefore, in S105, based on the current valve opening timing of the intake valve 8 and the valve closing timing of the exhaust valve 9, the pressure in the intake passage 12 detected by the intake pressure sensor 24, and the engine speed, The blown air amount Qa at is calculated. The relationship between the blow-through air amount Qa, the opening timing of the intake valve 8 and the closing timing of the exhaust valve 9, and the pressure in the intake passage 12 and the engine speed is obtained in advance through experiments and stored in the ECU 20 as a map. You can leave it.

  Next, the ECU 20 proceeds to S106, and calculates the sub fuel injection amount Qf injected by the sub fuel injection so that the exhaust air fuel ratio in the upstream side exhaust passage 13a becomes the target exhaust air fuel ratio. Here, the target exhaust air-fuel ratio is a value capable of increasing the energy of the exhaust as much as possible by burning the fuel injected by the auxiliary fuel injection in the upstream side exhaust passage 13a, and This is a value that can suppress the deterioration of exhaust emission. This target air-fuel ratio may be determined based on the operating state of the internal combustion engine 1 or the like.

  Further, the auxiliary fuel injection amount Qf is determined based on the target exhaust air-fuel ratio, the in-cylinder air-fuel ratio of the cylinder 2 that performs the auxiliary fuel injection before the auxiliary fuel injection is executed, and the blow-by air amount Qa calculated in S105. Is done.

  Note that the amount of air in the cylinder 2 in which the sub fuel injection is performed is detected by the intake valve 8 and the exhaust valve 9 at the present time, and the intake pressure sensor 24, as with the blow-through air amount Qa. This is calculated based on the pressure in the intake passage 12 and the engine speed. Then, the air-fuel ratio in the cylinder before the execution of the sub fuel injection in the cylinder 2 that performs the sub fuel injection is calculated from the air amount in the cylinder calculated by these and the main fuel injection amount injected by the main fuel injection.

Next, the ECU 20 proceeds to S107 and calculates the execution time Tf of the auxiliary fuel injection. As described above, the execution timing Tf of the auxiliary fuel injection is when the exhaust valve of the cylinder 2 that performs the auxiliary fuel injection is open and the other cylinders 2 are in the valve overlap period. When you are. Further, in S107, the execution time Tf of the auxiliary fuel injection is set to a later time as the engine speed is higher. The relationship between the engine speed and the execution timing Tf of the auxiliary fuel injection may be obtained in advance by experiments or the like and stored in the ECU 20 as a map.

  Next, the ECU 20 proceeds to S108, executes sub fuel injection, and then temporarily ends the execution of this routine.

  According to the control routine described above, when the boost pressure is increased, blow-by air is generated, and when the blow-through air is generated, the auxiliary fuel injection is executed. Thereby, fuel can be discharged to the upstream exhaust passage 13a while increasing the amount of air in the upstream exhaust passage 13a.

  Further, the sub-fuel injection amount Qf is set to the target air-fuel ratio based on the air-fuel ratio in the cylinder before the sub-fuel injection is performed in the cylinder 2 that performs sub-fuel injection and the blow-through air amount Qa in the cylinder that is in the valve overlap period. The air / fuel ratio is determined. Therefore, even when the amount of air in the upstream side exhaust passage 13a is increased and fuel is discharged to the upstream side exhaust passage 13a, the exhaust energy is increased as much as possible, and deterioration of exhaust emission is suppressed. I can do it.

  Further, even when the valve overlap period is controlled to generate blow-through air in a certain cylinder 2, there is a response delay until the valve overlap period changes, so the amount of air in the upstream exhaust passage 13a is reduced. It takes some time to actually increase. Further, the fuel injected by the auxiliary fuel injection is discharged to the exhaust passage 13 earlier as the engine speed is higher, and flows faster downstream in the exhaust passage 13. Therefore, if the auxiliary fuel injection is executed at an excessively early time, the fuel injected by the auxiliary fuel injection reaches the upstream exhaust passage 13a before the amount of air in the upstream exhaust passage 13a increases, and further downstream May flow toward the exhaust passage 13.

  However, according to the control routine, the execution timing Tf of the auxiliary fuel injection is made slower as the engine speed is higher. As a result, before the amount of air in the upstream side exhaust passage 13a increases, the fuel injected by the auxiliary fuel injection reaches the upstream side exhaust passage 13a and is further prevented from flowing toward the downstream side exhaust passage 13. I can do it. That is, it is possible to secure oxygen used for fuel combustion in the upstream side exhaust passage 13a. Accordingly, the fuel discharged to the upstream exhaust passage 13a can be more reliably burned in the upstream exhaust passage 13a.

  In the present embodiment, the control for performing the auxiliary fuel injection while generating the blow-by air may be executed only during a predetermined period during which the boost pressure is increased.

The figure which shows schematic structure of the internal combustion engine which concerns on the Example of this invention, and its intake / exhaust system. The figure which shows the opening / closing timing of the intake / exhaust valve which concerns on the Example of this invention. The figure which shows the combustion stroke in each cylinder in the Example of this invention. The flowchart which shows the control routine of the supercharging pressure raise control which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 6 ... Intake port 7 ... Exhaust port 8 ... Intake valve 9 ... Exhaust valve 10 .... Intake side variable valve Mechanism 11 ..Exhaust side variable valve mechanism 12 ..Intake passage 13 ..Exhaust passage 14 ..Turbocharger 14a ..Compressor 14b ..Turbine 20 ..ECU
21 Accelerator opening sensor 22 Accelerator position sensor 24 Intake pressure sensor 25 Throttle valve

Claims (4)

Multiple cylinders,
A fuel injection valve for injecting fuel into the cylinder;
A supercharger that supercharges intake air by the energy of exhaust gas flowing through the exhaust passage;
An internal combustion engine control system comprising:
Blow-through air generating means for generating blow-through air flowing out from the intake port to the exhaust port,
When the supercharging pressure is increased by the supercharger, blow-by air is generated by the blow-by air generating means in one cylinder, and further, an exhaust stroke is performed when the one cylinder is in the intake stroke. An internal combustion engine that performs sub fuel injection by the fuel injection valve when an exhaust valve is open in another cylinder and when blow-by air is generated in the one cylinder Control system.   The blow-by air generating means has overlap control means for controlling a valve overlap period in which both the intake valve and the exhaust valve of the internal combustion engine are open, and the valve overlap control means 2. The control system for an internal combustion engine according to claim 1, wherein blow-by air is generated by controlling a lap period.   In the other cylinder, when the exhaust valve is open and the blow-in air is generated by controlling the valve overlap period in the one cylinder, the sub fuel injection is performed by the fuel injection valve. 3. The control system for an internal combustion engine according to claim 2, wherein the execution timing of the sub fuel injection is delayed as the engine speed of the internal combustion engine increases. Blowing air amount estimation means for estimating the amount of blown air during the valve overlap period;
An in-cylinder air-fuel ratio estimating means for estimating an air-fuel ratio in the cylinder, and
In the other cylinder, when the exhaust valve is open and the blow-in air is generated by controlling the valve overlap period in the one cylinder, the sub fuel injection is performed by the fuel injection valve. Is executed, the blow-by air amount in the one cylinder estimated by the blow-by air amount estimation means and the other cylinder before the sub fuel injection execution estimated by the in-cylinder air-fuel ratio estimation means are performed. 4. The control system for an internal combustion engine according to claim 2, wherein the auxiliary fuel injection amount is determined based on the air-fuel ratio.

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