JP4325517B2 - Fuel injection control method for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection method in an internal combustion engine.

  In Patent Document 1, in order to recirculate the exhaust gas to the combustion chamber by introducing the exhaust gas discharged from the combustion chamber into the exhaust passage, the exhaust gas is exhausted from the exhaust passage downstream of the catalyst to the downstream of the throttle valve. An internal combustion engine is disclosed that includes a passage (indicated by reference numeral 28 in the same document, hereinafter referred to as “EGR passage”) extending to an intake passage upstream of the compressor of the turbocharger. In the internal combustion engine described in this document, the exhaust gas is recirculated to the combustion chamber through the EGR passage according to the engine operating state.

  By the way, in the internal combustion engine described in Patent Document 1, when the required load (the load required for the internal combustion engine) increases, the throttle opening (throttle valve) is increased in order to increase the intake air amount (the amount of air sucked into the combustion chamber). And the fuel injection amount (amount of fuel injected from the fuel injection valve) is also increased.

JP 2000-008835 A JP 09-257518 A JP 09-088704 A JP 09-151761 A JP 2000-205055 A

  However, as in the internal combustion engine described in Patent Document 1, when there is a certain distance from the throttle valve to the combustion chamber, even if the throttle opening is increased, the actual intake air amount (actually sucked into the combustion chamber) The amount of air that is produced does not increase immediately. When the exhaust gas is recirculated to the combustion chamber via the EGR passage, particularly when the amount of exhaust gas recirculated to the combustion chamber is large, it is effective after the throttle opening is increased. It takes a relatively long time for the intake air amount to increase.

  Therefore, even if the required load increases, the throttle opening increases, and at the same time the fuel injection amount increases, the actual intake air amount does not increase (or hardly increases) at the same time. In this case, the required load cannot be achieved, and the fuel consumption is deteriorated by the amount of fuel injection.

  Accordingly, an object of the present invention is to reduce fuel consumption when the required load increases in an internal combustion engine that can recirculate exhaust gas in the exhaust passage to the intake passage in order to recirculate exhaust gas into the combustion chamber. It is to achieve the required load without making it happen.

In order to solve the above problems, in the first invention, a throttle valve for controlling the amount of air sucked into the combustion chamber and an exhaust gas in the exhaust passage for recirculating the exhaust gas to the combustion chamber are provided. In a fuel injection control method for an internal combustion engine having an exhaust gas recirculation passage that is recirculated to an intake passage, the fuel injection amount is maintained constant as the intake air amount increases while the exhaust gas is recirculated to the combustion chamber. However, the engine is operated in a specific air-fuel ratio range where the engine speed increases, and when the required engine load increases during operation in this specific air-fuel ratio range, the throttle valve is opened while maintaining the fuel injection amount at that time. The fuel injection amount is increased when the engine speed increases after exceeding a predetermined value.

  In the second invention, in the first invention, after increasing the fuel injection amount, the fuel injection amount is continuously increased while the engine speed is increasing, and then the engine speed is determined in advance. When the value becomes larger than the value and becomes substantially constant, the fuel injection amount at that time is maintained.

  According to a third aspect, in the first or second aspect, the internal combustion engine includes an exhaust turbocharger, and the exhaust recirculation passage extends from an exhaust passage downstream of the exhaust turbocharger to an upstream side of the compressor of the exhaust turbocharger. It extends to the intake passage.

In a fourth aspect of the invention, in any one of the first to third aspects, when the amount of exhaust gas recirculated to the combustion chamber by the internal combustion engine is increased, the amount of soot generated gradually increases and peaks. The first combustion in which the amount of exhaust gas recirculated to the combustion chamber is larger than the amount of exhaust gas at which soot generation peaks, and soot is hardly generated, and the amount of soot generation is An internal combustion engine capable of selectively switching between the second combustion in which the amount of exhaust gas recirculated to the combustion chamber is smaller than the peak amount of exhaust gas, and the engine is operated when performing the first combustion. Operate in a specific air-fuel ratio range.

  According to the present invention, when the required load increases when the exhaust gas is recirculated to the combustion chamber and combustion is performed with an air-fuel ratio richer than the stoichiometric air-fuel ratio, the engine speed is predetermined. When the fuel pressure rises above the value, that is, when the amount of air actually taken into the combustion chamber starts to increase, the fuel injection amount is increased, so that the required load is achieved without deteriorating the fuel consumption. be able to.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a four-stroke compression ignition type internal combustion engine. In 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, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, and 9 is Exhaust valves 10 represent exhaust ports, respectively. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11. The surge tank 12 is connected to an outlet portion of a compressor 16 of a supercharger (for example, an exhaust turbocharger) 15 via an intake duct 13 and an intercooler 14. An inlet portion of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17. A throttle valve 20 driven by a step motor 19 is disposed in the air suction pipe 17. A mass flow rate detector 21 for detecting the mass flow rate of the intake air is disposed in the air suction pipe 17 upstream of the throttle valve 20.

  On the other hand, the exhaust port 10 is connected to an inlet portion of the exhaust turbine 23 of the exhaust turbocharger 15 via an exhaust manifold 22. The outlet of the exhaust turbine 23 absorbs NOx when the average air-fuel ratio in the combustion chamber 5 is lean through the exhaust pipe 24 (three-way catalyst or a catalyst having an oxidation function), and the average in the combustion chamber 5 The air-fuel ratio is connected to a catalytic converter 26 containing a NOx absorbent 25 having a function of releasing NOx when the air-fuel ratio becomes rich. An air-fuel ratio sensor (hereinafter referred to as “upstream air-fuel ratio sensor”) 27 a is disposed in the exhaust manifold 22 on the upstream side of the catalytic converter 26. On the other hand, an air-fuel ratio sensor (hereinafter referred to as “downstream air-fuel ratio sensor”) 27 b is disposed in the exhaust pipe 28 on the downstream side of the catalytic converter 26.

  The exhaust pipe 28 connected to the outlet of the catalytic converter 26 and the air suction pipe 17 downstream of the throttle valve 20 and upstream of the compressor 16 are connected to each other via an exhaust gas recirculation (hereinafter referred to as “EGR”) passage 29. ing. An EGR control valve 31 driven by a step motor 30 is disposed in the EGR passage 29. Further, an EGR cooler 32 for cooling exhaust gas (hereinafter also referred to as “EGR gas”) flowing in the EGR passage 29 is disposed in the EGR passage 29. In the example shown in FIG. 1, the engine cooling water is guided into the EGR cooler 32, and the EGR gas is cooled by the engine cooling water.

  On the other hand, the fuel injection valve 6 is connected to a fuel reservoir (so-called common rail) 34 via a fuel supply pipe 33. Fuel is supplied into the common rail 34 from an electrically controlled fuel pump 35 with variable discharge amount. The fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 through each fuel supply pipe 33. A fuel pressure sensor 36 for detecting the fuel pressure in the common rail 34 is attached to the common rail 34. The discharge amount of the fuel pump 35 is controlled based on the output signal of the fuel pressure sensor 36 so that the fuel pressure in the common rail 34 becomes the target fuel pressure.

  The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41. A ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45, and an output A port 46 is provided. The output signal of the mass flow rate detector 21 is input to the input port 45 via the corresponding AD converter 47. Output signals of the upstream air-fuel ratio sensor 27a, the downstream air-fuel ratio sensor 27b, and the fuel pressure sensor 36 are also input to the input port 45 via the corresponding AD converters 47, respectively. A load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50. The output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, 30 °. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EGR control valve control step motor 30, and the fuel pump 35 via a corresponding drive circuit 48.

  By the way, in the present embodiment, the first combustion (hereinafter also referred to as “low temperature combustion”) and the second combustion (hereinafter also referred to as “normal combustion”) are selectively performed according to the engine operating state. To be done. Here, low temperature combustion means combustion in which the amount of exhaust gas recirculated in the combustion chamber 5 is larger than the amount of exhaust gas at which soot generation peaks, and soot is hardly generated. Means combustion in which the amount of exhaust gas recirculated into the combustion chamber 5 is smaller than the amount of exhaust gas at which the amount of generated soot reaches a peak. For details of these low-temperature combustion and normal combustion, see Patent Document 1.

  Next, the engine operation control of this embodiment will be described with reference to FIG. FIG. 2 shows the opening of the throttle valve 20 with respect to the required load L (hereinafter referred to as “throttle opening”), the opening of the EGR control valve 31 (hereinafter referred to as “EGR opening”), the EGR rate, the air-fuel ratio, the injection timing, and the like. The injection amount is shown. As shown in FIG. 2, in the first operation region I where the required load L is low, low temperature combustion is performed. In this region I, the throttle opening is gradually increased from near fully closed to about 2/3 as the required load L increases, and the EGR opening is fully closed as the required load L increases. It is gradually increased from near to full open. In the example shown in FIG. 2, in the first operating region I, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.

  In other words, in the first operating region I, the throttle opening and the EGR opening are controlled so that the EGR rate becomes approximately 70% and the air / fuel ratio becomes a slightly lean air / fuel ratio. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the required load L is increased, and the injection completion timing θE is also delayed as the injection start timing θS is delayed.

  During the idling operation, the throttle valve 20 is closed to near full close, and at this time, the EGR control valve 31 is also closed to close to full close. When the throttle valve 20 is closed close to being fully closed, the pressure in the combustion chamber 5 at the start of compression becomes low, so the compression pressure becomes low. When the compression pressure is reduced, the compression work by the piston 4 is reduced, so that the vibration of the engine body 1 is reduced. That is, at the time of idling operation, the throttle valve 20 is closed to almost fully closed in order to suppress vibration of the engine body 1.

  On the other hand, in the second operation region II where the required load L is high, normal combustion (diffusion combustion) is performed. When the engine operating state changes from the first operating region I to the second operating region II, the throttle opening is increased stepwise from about 2/3 opening to the fully open direction. At this time, in the example shown in FIG. 2, the EGR rate is decreased stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, since the EGR rate exceeds the EGR rate range in which a large amount of smoke is generated, a large amount of smoke does not occur when the engine operating state changes from the first operating region I to the second operating region II. .

  In the second operation region II, the throttle valve 20 is held in a fully open state except for a part thereof, and the opening degree of the EGR control valve 31 is gradually reduced as the required load L increases. In this operation region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is made a lean air-fuel ratio even when the required load L increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

  FIG. 3 shows the target air-fuel ratio A / F when low-temperature combustion is performed. In FIG. 3, the curves indicated by A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 have target air-fuel ratios of 15.5, 16, 17, The air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 3, the air-fuel ratio is lean in the first operating region I. Further, in the first operating region I, the target air-fuel ratio A / F becomes leaner as the required load L becomes lower. It is said.

  That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, low temperature combustion can be performed even if the EGR rate is reduced as the required load L decreases. When the EGR rate is decreased, the air-fuel ratio increases. Therefore, as shown in FIG. 3, the target air-fuel ratio A / F increases as the required load L decreases. As the target air-fuel ratio A / F increases, the fuel consumption rate improves. Therefore, in order to make the air-fuel ratio as lean as possible, in the embodiment of the present invention, the target air-fuel ratio A / F decreases as the required load L decreases. Is increased.

  FIG. 4 shows the target air-fuel ratio A / F when normal combustion is performed. In FIG. 4, the curves indicated by A / F = 24, A / F = 35, A / F = 45, and A / F = 60 indicate the target air-fuel ratios 24, 35, 45, and 60, respectively. ing. Further, when normal combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N.

  By the way, in the embodiment of the present invention, when the required load increases (that is, when acceleration is required), the fuel injection amount is roughly controlled according to the control described with reference to FIG. The control is performed according to a control slightly different from this control. Next, this control will be described with reference to the time chart of FIG.

  In FIG. 5, DT in (A) shows the throttle opening, DE in (B) shows the EGR opening, A / F in (C) shows the air-fuel ratio, and in (C), L is lean, S is stoichiometric (theoretical air-fuel ratio), R is rich, Ga in (D) is the intake amount (the amount of air sucked into the combustion chamber 5), and in (D), Ga1 is the mass flow detector 21. , Ga2 indicates the amount of air actually taken into the combustion chamber 5 (hereinafter referred to as “actual intake amount”), and NE in (E) indicates the engine. The rotation speed is indicated, Q in (F) indicates the fuel injection amount, and T in (G) indicates the output torque.

  FIG. 5 shows a case where the required load is a constant value which is relatively small before time T0 and low temperature combustion is performed, and the required load becomes large at time T0. Therefore, in the example shown in FIG. 5, before time T0, the throttle opening DT is maintained at a relatively small constant opening, the EGR opening DE is maintained at a relatively large constant opening, and the fuel injection amount Q is also maintained at a relatively small constant amount. At this time, the air-fuel ratio A / F is slightly leaner than the theoretical air-fuel ratio (hereinafter also referred to as “weak lean”). Further, at this time, the detected intake air amount Ga1 and the actual intake air amount Ga2 are the same constant value, the engine speed is also increased and decreased, but the substantially constant value is maintained, and the output torque T is also a constant value. ing.

  Here, in the example shown in FIG. 5, the required load increases at time T0. At this time, the throttle opening DT is increased and the EGR opening DE is decreased. However, since there is a certain distance (more precisely, a certain volume) from the throttle valve 20 to the combustion chamber 5 and from the EGR control valve 31 to the combustion chamber 5, the throttle opening degree Even if the EGR opening is decreased and the EGR opening is decreased, the actual intake air amount Ga2 does not increase immediately. Further, before the time T0, the air-fuel ratio A / F is weakly lean, so that of the air sucked into the combustion chamber 5, there is very little excess air that is not consumed for combustion. For this reason, even if the fuel injection amount Q is increased at the time T0, an increase in the output torque T cannot be expected, and the fuel consumption is deteriorated as much as the fuel injection amount Q is increased.

  Therefore, in the embodiment of the present invention, at time T0, the fuel injection amount Q is not increased and the amount at that time is maintained. Therefore, immediately after time T0, the engine speed NE changes in the same manner as before time T0, and the output torque T also changes in the same way as before time T0.

  On the other hand, the detected intake air amount Ga1 starts to increase at a time T1 when a certain time has elapsed from the time T0. However, since there is a certain distance from the mass flow detector 21 to the combustion chamber 5, the actual intake air amount Ga2 does not increase even at this time. For this reason, also at time T1, the amount at that time is maintained without increasing the fuel injection amount Q.

  Then, the actual intake air amount Ga2 starts increasing at a time T2 when a certain time has elapsed from the time T1. At this time, since combustion is performed with a weak lean air-fuel ratio, that is, an air-fuel ratio extremely close to the stoichiometric air-fuel ratio, a small amount of the fuel injected from the fuel injection valve 6 does not burn. There is fuel that will remain. Here, if the actual intake air amount increases, the remaining fuel burns, and the engine speed NE begins to increase. That is, when the actual intake air amount Ga2 starts to increase at time T2, the engine speed NE starts to increase.

  Therefore, in the example shown in FIG. 5, when the engine speed NE begins to increase (or when the engine speed NE increases and exceeds a predetermined value), the fuel injection amount Q is increased. start. As a result, the engine speed NE further increases and the output torque T also increases. As long as the engine speed NE increases, the actual intake air amount Ga2 is considered to increase. Therefore, the fuel injection amount Q continues to increase while the engine speed NE continues to increase.

  Basically, after the required load increases, the fuel injection amount Q increases toward the target fuel injection amount as described above. However, the increase in the actual intake amount Ga2 and the fuel injection amount Q are increased. Depending on the relationship between the increase in the actual intake air amount Ga2 and the increase in the fuel injection amount Q, the air-fuel ratio may become excessively rich (in the example shown in FIG. 5). At time T3, the air-fuel ratio has become excessively rich). In this case, if the fuel injection amount Q is continuously increased, the fuel is wasted.

  Therefore, when the air-fuel ratio becomes excessively rich, the increase in the engine speed NE is stopped. Therefore, in the embodiment of the present invention, the fuel injection amount Q is set to the target after the engine speed NE starts to increase. Before reaching the fuel injection amount (or after the engine speed NE starts to increase and exceeds a certain value larger than the predetermined value and before the fuel injection amount Q reaches the target fuel injection amount) ), When the increase of the engine speed NE is stopped (that is, when the engine speed NE becomes a constant value), the increase of the fuel injection amount Q is stopped and the fuel injection amount Q is set at that time. Keep the value. Then (after the time T4 in the example shown in FIG. 5), when the engine speed NE starts to increase again, the fuel injection amount Q is increased again.

  In the embodiment of the present invention, the fuel injection amount Q is increased to the target fuel injection amount TQ while repeating such control. Thereby, the output torque T becomes the target torque TT, and the required load is achieved.

  According to this, when low temperature combustion is performed and the required load becomes large, the required load can be achieved without deteriorating fuel consumption. Conventionally, there is a fuel injection amount that is corrected by the intake air temperature (the temperature of the air taken into the combustion chamber 5), the supercharging pressure by the exhaust turbocharger 15 or the like. In addition, it is not necessary to correct the fuel injection amount based on the supercharging pressure by the exhaust turbocharger 15.

  In the description with reference to FIG. 5, the fuel injection control in the case where the required load is increased when the low temperature combustion is performed with weak lean has been described. However, according to the present invention, the stoichiometric air-fuel ratio is increased. The same fuel injection control is also applied when the required load is increased during low temperature combustion or rich low temperature combustion. In this case, since the fuel injected from the fuel injection valve 6 remains more unburned than the case where low-temperature combustion is performed with weak lean before the required load increases. When the required load increases and the actual intake air amount begins to increase, the engine speed increases more.

  In the above-described embodiment, the control of the fuel injection amount according to the present invention is applied when the required load becomes large during low-temperature combustion. For example, a relatively large amount of exhaust gas is emitted. The present invention is also applied to a case where the required load becomes large when the gas is recirculated to the combustion chamber 5 and combustion is performed with a weak lean air-fuel ratio, a stoichiometric air-fuel ratio, or a rich air-fuel ratio. Is possible.

  In the above-described embodiment, the fuel injection amount Q continues to increase while the engine speed NE continues to increase. At this time, the increase rate of the fuel injection amount Q is proportional to the fluctuation amount of the engine speed NE. The predetermined increase rate may be stored in a table or the like in advance, and the increase rate may be read from this table.

  FIG. 6 shows an example of a routine for controlling the fuel injection amount when low-temperature combustion is performed according to the present invention. In the routine of FIG. 6, first, at step 10, it is determined whether or not acceleration is required (that is, whether or not the required load has increased). Here, when it is determined that acceleration is not requested, the routine ends. On the other hand, when it is determined in step 10 that acceleration is required, the throttle opening degree DT is increased in step 11, and then in step 12, the EGR opening degree DE is decreased.

  Next, at step 13, it is determined whether or not the increase amount ΔNE of the engine speed NE has become equal to or greater than a predetermined value α (ΔNE ≧ α) (that is, whether or not the actual intake air amount has started increasing). The Here, when it is determined that ΔNE <α (when it is estimated that the actual intake air amount has not started to increase), the routine ends. On the other hand, when it is determined in step 13 that ΔNE ≧ α (when it is estimated that the actual intake air amount has started to increase), in step 14, the fuel injection amount Q is increased.

  Next, at step 15, it is judged if the fuel injection amount Q has reached the target fuel injection amount TQ (Q = TQ). Here, when it is determined that Q = TQ, the increase in the fuel injection amount Q is terminated in step 16. On the other hand, when it is determined in step 15 that Q ≠ TQ, it is determined in step 17 whether or not the increase amount ΔNE of the engine speed NE is equal to or smaller than a predetermined value β (ΔNE ≦ β) (ie, It is determined whether or not the air-fuel ratio is excessively rich. Here, β is a value smaller than α.

  When it is determined in step 17 that ΔNE ≦ β (that is, when it is estimated that the air-fuel ratio is excessively rich), the increase in the fuel injection amount Q is temporarily stopped in step 18. The routine returns to step 17 again. Thereafter, steps 17 and 18 are repeated until it is determined in step 17 that ΔNE> β.

  When it is determined in step 17 that ΔNE> β (that is, when it is estimated that the air-fuel ratio is not excessively rich), the routine returns to step 14. Then, in step 15 again, it is determined whether or not Q = TQ. Here, if it is determined that Q = TQ, the increase of the fuel injection amount Q is terminated in step 16, and if it is determined that Q ≠ TQ, the routine proceeds to step 17 again.

1 is an overall view of an internal combustion engine to which the present invention is applied. It is a figure for demonstrating the engine operation control in embodiment of this invention, and the throttle opening etc. with respect to the request | requirement load L are shown. It is the figure which showed the target air fuel ratio when low temperature combustion is performed. It is the figure which showed the target air fuel ratio when normal combustion is done. It is the figure which showed the time chart for demonstrating fuel-injection control when acceleration is requested | required in embodiment of this invention. It is the figure which showed an example of the control routine of the fuel injection amount when the low temperature combustion is performed according to this invention.

Explanation of symbols

5 Combustion chamber 6 Fuel injection valve 15 Exhaust turbocharger 16 Compressor 17 Intake passage 18 Exhaust passage 20 Throttle valve 23 Exhaust turbine 29 EGR passage 31 EGR control valve DT Throttle opening DE EGR opening A / F Air-fuel ratio Ga Intake amount Ga1 detection Intake amount Ga2 Actual intake amount NE Engine speed Q Fuel injection amount T Output torque

Claims (4)

A throttle valve for controlling the amount of air taken into the combustion chamber, and an exhaust gas recirculation passage for recirculating the exhaust gas in the exhaust passage to the intake passage to recirculate the exhaust gas to the combustion chamber. In a fuel injection control method for an internal combustion engine, the engine is operated in a specific air-fuel ratio range in which the engine speed increases even when the fuel injection amount is kept constant as the intake air amount increases while the exhaust gas is recirculated to the combustion chamber. When the engine demand load increases during operation in this specific air-fuel ratio range, the throttle valve opening is increased while maintaining the fuel injection amount at the fuel injection amount at that time, and then the engine speed is determined in advance. A fuel injection control method for increasing a fuel injection amount when the fuel consumption exceeds a predetermined value.   After the fuel injection amount is increased, the fuel injection amount is continuously increased while the engine speed is increasing, and then the engine speed exceeds the predetermined value and becomes substantially constant. 2. The fuel injection control method according to claim 1, wherein the fuel injection amount at that time is maintained.   2. The internal combustion engine includes an exhaust turbocharger, and the exhaust recirculation passage extends from an exhaust passage downstream of the exhaust turbocharger to an intake passage upstream of a compressor of the exhaust turbocharger. Or the fuel-injection control method of 2. When the internal combustion engine increases the amount of exhaust gas recirculated to the combustion chamber, the amount of soot generation gradually increases and peaks, and the amount of exhaust gas at which soot generation amount peaks The amount of exhaust gas recirculated to the combustion chamber is larger than that of the first combustion in which soot is hardly generated, and the amount of exhaust gas recirculated to the combustion chamber rather than the amount of exhaust gas in which the amount of soot generation is peak The internal combustion engine capable of selectively switching between the second combustion with a small amount of fuel, and operating the engine in the specific air-fuel ratio range when performing the first combustion. The fuel-injection control method as described in any one.

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