JP4449603B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to a fuel injection control device for an internal combustion engine suitable for accurately controlling an air-fuel ratio of exhaust gas.

  In-vehicle internal combustion engines generally include a catalyst for purifying exhaust gas in an exhaust passage. This type of catalyst exhibits an excellent purification capability by maintaining the air-fuel ratio of the exhaust gas in the vicinity of the theoretical air-fuel ratio. For this reason, in an in-vehicle internal combustion engine, control for setting the air-fuel ratio of exhaust gas to the target air-fuel ratio is widely performed.

  As the most general configuration, an airflow meter for measuring the intake air amount is provided in the intake passage, and an air-fuel ratio sensor for measuring the air-fuel ratio of exhaust gas is provided in the exhaust passage. Further, as a control executed in the internal combustion engine having such a configuration, the basic fuel injection amount is calculated by dividing the intake air amount by the theoretical air fuel ratio, and the basic fuel injection amount is calculated by the air fuel ratio sensor. An air-fuel ratio feedback control that corrects based on the output is known as a typical one.

  According to the control method as described above, the air-fuel ratio of the gas newly sucked into the cylinder can be accurately controlled to the stoichiometric air-fuel ratio. In the steady state, the air-fuel ratio of the exhaust gas can be accurately set to the stoichiometric air-fuel ratio. However, burned gas may exist in the cylinder in addition to newly sucked gas. In a transient state where the operating state of the internal combustion engine changes, it is normal that the air-fuel ratio of the burned gas does not match the air-fuel ratio of the new gas.

  Under such circumstances, even if the air-fuel ratio of the new gas is controlled to the stoichiometric air-fuel ratio, the air-fuel ratio of the gas existing in the cylinder cannot be made the stoichiometric air-fuel ratio as a whole. Therefore, in this case, exhaust gas having an air-fuel ratio that deviates from the stoichiometric air-fuel ratio is discharged from the cylinder to the exhaust passage. As described above, it is difficult to maintain the accuracy of the exhaust air-fuel ratio during the transient operation of the internal combustion engine, depending on the typical control method described above.

  Japanese Patent Application Laid-Open No. 2002-21615 discloses a method of estimating the air-fuel ratio of in-cylinder gas and performing feedback control of the fuel injection amount based on the estimation result. More specifically, here, the air-fuel ratio of the in-cylinder gas is estimated based on the air-fuel ratio of the new gas sucked into the cylinder and the air-fuel ratio of the residual gas remaining in the cylinder. A method for feedback control of the fuel injection amount based on the value is disclosed. Further, here, a method for correcting the estimated value of the in-cylinder gas air-fuel ratio based on the output of the air-fuel ratio sensor disposed in the exhaust passage is disclosed.

  According to the technique disclosed in the above publication, the difference between the air-fuel ratio of the in-cylinder gas and the target air-fuel ratio can be reflected in the fuel injection amount. For this reason, according to this method, the control accuracy of the in-cylinder gas can be increased as compared with the typical method described above. Therefore, according to this method, it is possible to improve the air-fuel ratio accuracy of the exhaust gas exhausted from the cylinder and create a favorable situation for realizing good emission characteristics.

Japanese Patent Laid-Open No. 2002-21615 JP 2002-30968 A

  However, the technique disclosed in the above publication is based on the fuel injection by multiplying the basic injection amount for setting the new gas sucked into the cylinder to the target air-fuel ratio by the feedback correction coefficient set according to the deviation. The injection amount is calculated. That is, in this method, the air-fuel ratio of the new gas is enriched or leaned according to a certain rule according to the deviation between the air-fuel ratio of the in-cylinder gas and the target air-fuel ratio.

  The ratio of burned gas and the ratio of new gas in the cylinder change according to the operating state of the internal combustion engine. When the ratio of the new gas is large, the air-fuel ratio of the in-cylinder gas greatly varies due to the above enrichment or leaning. On the other hand, when the ratio of the new gas is small, only a small change occurs in the air-fuel ratio of the in-cylinder gas with the above enrichment or leaning. For this reason, even with the technique disclosed in the above publication, it is difficult to accurately match the air-fuel ratio of the in-cylinder gas, that is, the air-fuel ratio of the exhaust gas, to the target air-fuel ratio during the transient operation of the internal combustion engine.

  The present invention has been made to solve the above-described problems, and is capable of accurately controlling the air-fuel ratio of exhaust gas discharged from the cylinder to the target air-fuel ratio even during transient operation of the internal combustion engine. An object of the present invention is to provide a fuel injection control device for an internal combustion engine.

In order to achieve the above object, a first invention is a fuel injection control device for an internal combustion engine,
A residual fuel amount calculating means for calculating an in-cylinder residual fuel amount at the time when intake starts,
An inflow required fuel amount calculating means for calculating an in-cylinder inflow required fuel amount based on the in-cylinder residual fuel amount so that an air-fuel ratio of exhaust gas discharged from the cylinder becomes a target air-fuel ratio;
Fuel injection amount calculating means for calculating a fuel injection amount by the fuel injection valve based on the in-cylinder inflow required fuel amount;
A residual gas amount detecting means for calculating a residual gas amount in the cylinder at the time when intake is started;
A target air-fuel ratio storage means for storing the latest target air-fuel ratio for at least one cycle,
The residual fuel amount calculating means calculates the in-cylinder residual fuel amount by dividing the in-cylinder residual gas amount in the current cycle by the target air-fuel ratio in the previous cycle .

The second invention is the first invention, wherein
In-cylinder gas amount calculating means for calculating the in-cylinder gas amount at the end of intake,
In-cylinder required fuel amount calculating means for calculating a value obtained by dividing the in-cylinder gas amount in the current cycle by the target air-fuel ratio in the current cycle as a required cylinder fuel amount,
The inflow required fuel amount calculation means calculates the in-cylinder inflow required fuel amount by subtracting the in-cylinder residual fuel amount in the current cycle from the in-cylinder required fuel amount.

The third invention is the second invention, wherein
A residual gas amount detecting means for calculating a residual gas amount in the cylinder at the time when intake is started;
An intake air amount detecting means for detecting an intake air amount sucked into the cylinder,
The in-cylinder gas amount calculating means calculates the in-cylinder gas amount by adding the in-cylinder residual gas amount in the current cycle and the intake air amount in the current cycle.

Moreover, 4th invention is set in 1st invention,
An exhaust gas amount calculating means for calculating an exhaust gas amount discharged from the cylinder;
A required exhaust fuel amount calculating means for calculating the required fuel amount by dividing the exhaust gas amount in the current cycle by the target air-fuel ratio in the current cycle,
The inflow required fuel amount calculation means calculates the in-cylinder inflow required fuel amount by adding the in-cylinder residual fuel amount in the next cycle to a value obtained by subtracting the in-cylinder residual fuel amount in the current cycle from the required discharge fuel amount. It is characterized by doing.

The fifth invention is the fourth invention, wherein
A residual gas amount calculating means for calculating an in-cylinder residual gas amount at the time when intake starts,
An intake air amount detecting means for detecting an intake air amount sucked into the cylinder,
The exhaust gas amount calculating means calculates the exhaust gas amount by subtracting the in-cylinder residual gas amount in the next cycle from a value obtained by adding the in-cylinder residual gas amount in the current cycle to the intake air amount in the current cycle. Features.

According to a sixth invention, in any one of the first to fifth inventions,
Intake air amount detection means for detecting the amount of intake air sucked into the cylinder;
Stoichiometric judgment means for judging whether or not the target air-fuel ratio of the previous cycle was the stoichiometric air-fuel ratio,
The inflow required fuel amount calculation means calculates, as the in-cylinder inflow required fuel amount, a value obtained by dividing the intake air amount by the target air fuel ratio of the current cycle when the target air fuel ratio of the previous cycle is the stoichiometric air fuel ratio. It is characterized by doing.

According to a seventh invention, in any one of the first to sixth inventions,
Intake air amount detection means for detecting the amount of intake air sucked into the cylinder;
Air-fuel ratio determining means for determining whether or not the target air-fuel ratio of the previous cycle and the target air-fuel ratio of the current cycle are the same,
When the target air-fuel ratio in the previous cycle and the target air-fuel ratio in the current cycle are the same, the inflow required fuel amount calculation means calculates a value obtained by dividing the intake air amount by the target air-fuel ratio in the current cycle. It is calculated as a fuel amount.

Further, an eighth invention is any one of the first to seventh inventions,
Intake air amount detection means for detecting the amount of intake air sucked into the cylinder;
And a state determining means for determining whether or not a combustion priority state that should give priority to the air-fuel ratio accuracy of the fresh gas sucked into the cylinder is prior to the air-fuel ratio accuracy of the exhaust gas discharged from the cylinder is provided. ,
The inflow required fuel amount calculation means calculates, as the in-cylinder inflow required fuel amount, a value obtained by dividing the intake air amount by the target air-fuel ratio of the current cycle when the formation of the combustion priority state is recognized. And

  According to the first aspect of the present invention, it is possible to calculate the in-cylinder residual fuel amount generated at the time when intake is started. If the in-cylinder residual fuel amount is known, it is possible to accurately calculate the in-cylinder inflow required fuel amount necessary for setting the air-fuel ratio of the exhaust gas discharged from the cylinder to the target air-fuel ratio even during transient operation. . According to the present invention, since the fuel injection amount is calculated based on the in-cylinder inflow requested fuel amount, the air-fuel ratio of the exhaust gas can be accurately set to the target air-fuel ratio even during transient operation.

Further, according to this invention, it is possible to calculate the in-cylinder residual gas quantity at the time when the intake air is initiated. The air-fuel ratio of the in-cylinder residual gas is controlled to the target air-fuel ratio of the previous cycle. According to the present invention, the in-cylinder residual fuel amount can be accurately calculated by dividing the value calculated as the in-cylinder residual gas amount in the current cycle by the target air-fuel ratio in the previous cycle.

According to the second aspect of the present invention, the amount of fuel required to bring the in-cylinder gas to the target air-fuel ratio by calculating the in-cylinder gas amount at the end of intake and dividing the value by the target air-fuel ratio; That is, the in-cylinder required fuel amount can be calculated. Further, according to the present invention, the in-cylinder inflow required fuel amount can be accurately calculated by subtracting the in-cylinder residual fuel amount already existing in the cylinder from the in-cylinder required fuel amount.

According to the third aspect of the present invention, by adding the intake air amount sucked into the cylinder during the intake process to the cylinder residual gas amount already existing in the cylinder at the time when the intake is started, The amount of gas can be calculated accurately.

According to the fourth aspect of the present invention, the amount of fuel required to make the exhaust gas the target air-fuel ratio is calculated by calculating the amount of exhaust gas discharged from the cylinder and dividing the value by the target air-fuel ratio of the current cycle. That is, it is possible to calculate the required amount of fuel to be discharged. The amount of fuel discharged from the cylinder is a value obtained by subtracting the amount of fuel remaining in the cylinder and becoming the in-cylinder residual fuel quantity in the next cycle from the total fuel quantity existing in the cylinder. On the other hand, the total fuel amount in the cylinder is a value obtained by adding the fuel amount flowing into the cylinder in the current cycle and the in-cylinder residual fuel amount in the current cycle. Therefore, the in-cylinder inflow required fuel amount that realizes the required fuel amount is a value obtained by adding the in-cylinder residual fuel amount in the next cycle to the value obtained by subtracting the in-cylinder residual fuel amount in the current cycle from the required exhaust fuel amount. . According to the present invention, the amount of fuel required for emission can be accurately calculated by following the above calculation rules.

According to the fifth aspect of the present invention, the in-cylinder residual gas amount (the in-cylinder residual gas amount in the current cycle) that already exists at the time when intake is started is added to the intake air amount that is drawn into the cylinder during the intake process. The amount of exhaust gas from the cylinder can be accurately calculated by subtracting the amount that becomes the cylinder residual gas amount in the next cycle from the value obtained by adding (the total gas amount in the cylinder).

According to the sixth invention, when the target air-fuel ratio of the previous cycle is the stoichiometric air-fuel ratio, a value obtained by dividing the intake air amount by the target air-fuel ratio, that is, a value for setting the new gas as the target air-fuel ratio is obtained. The fuel injection amount can be calculated as the in-cylinder inflow required fuel amount. If the current cycle requirement for the internal combustion engine is to reduce exhaust emissions, the target air-fuel ratio for the current cycle is also the stoichiometric air-fuel ratio. In this case, according to the above calculation method, the fuel injection amount in which the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio can be accurately calculated. When the demand for the current cycle for the internal combustion engine is not the reduction of exhaust emission but the realization of a desired operating state, the target air-fuel ratio of the current cycle is set to a value corresponding to the operating state. At this time, according to the above calculation method, the fuel injection amount is determined so that the influence of the burned gas is ignored and the air-fuel ratio of the new gas becomes the target air-fuel ratio. Since burnt gas does not contribute much to combustion, in order to bring the internal combustion engine into a desired operating state, rather than accurately controlling the air-fuel ratio of the in-cylinder gas, the air-fuel ratio of the new gas is accurately controlled. It is desirable. According to the present invention, good control accuracy can be achieved by satisfying the above requirements under a situation where the target air-fuel ratio deviates from the stoichiometric air-fuel ratio.

According to the seventh invention, when the target air-fuel ratio of the previous cycle and the target air-fuel ratio of the current cycle are the same, the value obtained by dividing the intake air amount by the target air-fuel ratio, that is, the new gas is set to the target air-fuel ratio. The amount of fuel injection can be calculated using the in-cylinder inflow requested fuel amount. When the target air-fuel ratio has not changed from the previous cycle to the current cycle, the fuel injection amount with the exhaust gas as the target air-fuel ratio can be calculated by the above calculation method. Therefore, according to the present invention, it is possible to reduce the calculation load for setting the air-fuel ratio of the exhaust gas to the target air-fuel ratio.

According to the eighth invention, when it is determined that the combustion priority state in which the air-fuel ratio accuracy of the fresh air gas should be prioritized over the air-fuel ratio accuracy of the exhaust gas is determined, the new gas is set to the target air-fuel ratio. It is possible to calculate the fuel injection amount for the purpose. Therefore, according to the present invention, the internal combustion engine can be brought into a desired operating state without being trapped by the exhaust air-fuel ratio under the formation of the combustion priority state.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. The configuration shown in FIG. 1 includes an internal combustion engine 10. An intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10. An air flow meter 16 for detecting an intake air amount Ga is disposed in the intake passage 12. A throttle valve 18 is provided downstream of the air flow meter 16. A throttle sensor 20 that detects the throttle opening degree TA is disposed in the vicinity of the throttle valve 18. A fuel injection valve 24 for injecting fuel into the intake port 22 of the internal combustion engine 10 is further disposed in the intake passage 12.

  The internal combustion engine 10 includes an intake valve 26 and an exhaust valve 28. The intake valve 26 and the exhaust valve 28 are connected to variable valve timing (VVT) mechanisms 30 and 32 as their drive sources, respectively. The VVT mechanisms 30 and 32 can change the valve opening timing VT of the intake valve 26 or the exhaust valve 28, respectively, according to a command supplied from the outside.

  A catalyst 34 for purifying exhaust gas is disposed in the exhaust passage 14. The catalyst 34 can purify the exhaust gas stably for a long period of time by maintaining the air-fuel ratio AFRe of the exhaust gas at a value close to the theoretical air-fuel ratio. An air-fuel ratio sensor 36 is disposed upstream of the catalyst 34. The air-fuel ratio sensor 36 is a sensor that emits an output corresponding to the air-fuel ratio AFRe of the exhaust gas discharged from the internal combustion engine 10.

  The system of this embodiment includes an ECU (Electronic Control Unit) 40. In addition to the various sensors described above, the ECU 40 is connected to a water temperature sensor 42 that detects the cooling water temperature THW, a rotation speed sensor 44 that detects the engine rotation speed Ne, and the like. The ECU 40 can drive actuators such as the fuel injection valve 24 and the VVTs 30 and 32 based on the outputs of these sensors.

[Concept of fuel injection control in Embodiment 1]
Next, the concept of fuel injection control in Embodiment 1 of the present invention will be described with reference to FIG. FIG. 2 is a diagram for explaining a phenomenon when the target air-fuel ratio AFR of the internal combustion engine 10 changes from the rich air-fuel ratio (12.5) to the stoichiometric air-fuel ratio (14.5).

  More specifically, FIG. 2 (A) is for explaining the phenomenon when the fuel injection amount fi is changed so that the air-fuel ratio AFRc of the new gas flowing into the cylinder matches the target air-fuel ratio AFR. FIG. On the other hand, FIG. 2B is a diagram for explaining a phenomenon when the fuel injection amount fi is changed so that the air-fuel ratio AFRe of the exhaust gas discharged from the cylinder matches the target air-fuel ratio AFR. .

  As a method for calculating the fuel injection amount fi, the basic in-cylinder inflow required fuel amount fcbase = Ga / AFR is calculated by dividing the measured value of the intake air amount Ga by the target air-fuel ratio AFR, and the value is corrected. A method of obtaining the fuel injection amount fi by adding is common. According to this method, when the target air-fuel ratio changes from the rich air-fuel ratio to the stoichiometric air-fuel ratio, a phenomenon as shown in FIG.

  That is, FIG. 2A shows a state in which the rich air-fuel ratio residual gas remains in the cylinder of the internal combustion engine 10 when the target air-fuel ratio AFR changes from the rich air-fuel ratio to the stoichiometric air-fuel ratio. . When the residual gas remains in the cylinder, the air-fuel ratio AFRe of the exhaust gas becomes the air-fuel ratio of the mixed gas of the new gas and the residual gas in the cylinder. Therefore, in this case, even if the air-fuel ratio AFRc of the new gas is the stoichiometric air-fuel ratio, the air-fuel ratio of the exhaust gas becomes a richly biased value (for example, 13.0).

  In the internal combustion engine 10, the target air-fuel ratio is set to the stoichiometric air-fuel ratio in order to maintain the purification ability of the catalyst 34 stably for a long period of time and obtain good emission characteristics. For this reason, in a situation where the target air-fuel ratio is the stoichiometric air-fuel ratio, it is often desirable to make the air-fuel ratio AFRe of the exhaust gas coincide with the target air-fuel ratio, that is, the stoichiometric air-fuel ratio. In addition, the above-described general method cannot always satisfy this requirement accurately.

  FIG. 2B is a diagram showing an example of conditions for setting the air-fuel ratio AFRe of the exhaust gas to the stoichiometric air-fuel ratio immediately after the target air-fuel ratio AFR changes from the rich air-fuel ratio to the stoichiometric air-fuel ratio. That is, FIG. 2 (B) shows that the air-fuel ratio AFRc of the new gas is set to the lean air-fuel ratio (here, immediately after the target air-fuel ratio changes from the rich air-fuel ratio to the stoichiometric air-fuel ratio, assuming the presence of rich in-cylinder residual gas. Shows the state of 15.5).

  If the air-fuel ratio of the new gas can be appropriately made lean when the rich in-cylinder residual gas exists, the air-fuel ratio of the in-cylinder gas can be made the stoichiometric air-fuel ratio as a whole, and as a result, As shown in FIG. 2B, the air-fuel ratio AFRe of the exhaust gas can be made the stoichiometric air-fuel ratio. Therefore, in the system of the present embodiment, the air-fuel ratio AFRe of the exhaust gas becomes the target air-fuel ratio AFR in consideration of the influence of the residual gas in the cylinder and, more strictly, in consideration of the amount of fuel remaining in the cylinder. In principle, the fuel injection amount fi is calculated.

[Calculation method of fuel injection amount fi]
(Calculation method of in-cylinder inflow required fuel amount fc)
The system of the present embodiment calculates the amount of fuel to be flown into the cylinder in order to realize a desired operating state (hereinafter referred to as “cylinder inflow required fuel amount fc”), and then requests the inflow in the cylinder. The fuel amount necessary to generate the fuel amount fc is calculated as the fuel injection amount fi. Here, first, a method of calculating the in-cylinder inflow requested fuel amount fc will be described.

  FIG. 3 is a diagram for explaining a method for calculating the in-cylinder inflow requested fuel amount fc in the present embodiment. In FIG. 3, the symbol “fw” represents the amount of injected fuel that adheres to the intake port 22 and the intake valve 26 and is not sucked into the cylinder. The symbols “Gr” and “fr” represent the gas amount and fuel amount remaining in the cylinder at the start of intake of each cycle, respectively. These are hereinafter referred to as “cylinder residual gas amount Gr” and “cylinder residual fuel amount fr”, respectively.

The amount of new gas flowing into the cylinder of the internal combustion engine 10 can be detected as the intake air amount Ga. Therefore, the air-fuel ratio AFRc of the new gas can be expressed by the following equation using the in-cylinder inflow required fuel amount fc.
AFRc = Ga / fc (1)

From the above equation (1), the in-cylinder inflow required fuel amount fc for setting the air-fuel ratio AFRc of the new gas to the target air-fuel ratio AFR is expressed by the following equation.
fc = Ga / AFRc
= Ga / AFR (2)

It can be considered that the air-fuel ratio AFRe of the exhaust gas discharged from the cylinder is equal to the air-fuel ratio of the cylinder gas at the time when the intake is completed. At the end of intake, the amount of fuel existing in the cylinder becomes fc + fr, and the amount of gas existing in the cylinder becomes Ga + Gr. For this reason, the air-fuel ratio AFRe of the exhaust gas can be expressed as the following equation.
AFRe = (Ga + Gr) / (fc + fr) (3)

From the above equation (3), the in-cylinder inflow required fuel amount fc for setting the air-fuel ratio AFRe of the exhaust gas to the target air-fuel ratio AFR is expressed as follows.
fc = (Ga + Gr) / AFRe-fr
= (Ga + Gr) / AFR-fr (4)

  The in-cylinder inflow required fuel amount fc calculated by the equation (4) and the in-cylinder inflow required fuel amount fc calculated by the equation (2) are different values unless AFR = Gr / fr is satisfied. In other words, fc obtained by equation (4) and fc obtained by equation (2) have the same value when the target air-fuel ratio AFR is constant, but different values during transient operation where the value changes. It becomes. Hereinafter, in order to distinguish between them, the in-cylinder inflow request amount calculated by the equation (4) is represented by a symbol “fc ′”.

  According to the above equation (4), the in-cylinder inflow required fuel amount fc ′ is calculated if the in-cylinder residual gas amount Gr and the in-cylinder residual fuel amount fr are known in addition to the intake air amount Ga and the target air-fuel ratio AFR. be able to. Both the in-cylinder residual gas amount Gr and the in-cylinder residual fuel amount fr have a correlation with the operation state of the internal combustion engine 10. Therefore, for example, if the relationship between them and the operating state of the internal combustion engine 10 is grasped in advance, both the in-cylinder residual gas amount Gr and the in-cylinder residual fuel amount fr can be estimated on the vehicle. is there. If these are estimated, it is possible to calculate the in-cylinder inflow requested fuel fc ′ for setting the air-fuel ratio AFRe of the exhaust gas to the target air-fuel ratio AFR according to the above equation (4).

(Calculation method of fuel injection amount fi)
Next, an example of a method for calculating the fuel injection amount fi based on the in-cylinder inflow requested fuel amount fc will be described. FIG. 4 is a diagram for explaining a fuel behavior model representing the relationship between the fuel injection amount fi and the in-cylinder inflow requested fuel amount fc. The system of the present embodiment calculates the fuel injection amount fi corresponding to the in-cylinder inflow requested fuel amount fc on the assumption of this model.

  Part of the fuel injected from the fuel injection valve 24 adheres to the wall surface of the intake port 22 and the intake valve 26, and the remaining part flows into the cylinder. Assuming that the rate at which the injected fuel adheres to the wall surface, etc., is “attachment rate R”, the amount of fuel that adheres to the wall surface etc. among the newly injected fuel will be represented by “R * fi”. . On the other hand, of the injected fuel, the amount of fuel sucked into the cylinder is represented by “(1-R) * fi”.

  In addition to the fuel “(1-R) × fi” directly supplied from the fuel injection valve 24, vaporized fuel generated by vaporization of the wall-attached fuel flows into the cylinder of the internal combustion engine 10. Assuming that the rate of remaining fuel adhering to the wall surface etc. is `` residual rate P '', the amount of wall adhering amount fw that occurred in the previous cycle is expressed as `` P * fw '' On the other hand, the amount of fuel represented by “(1-P) * fw” is sucked into the cylinder.

Accordingly, when the wall surface adhesion amount at the start of the kth cycle (for example, at the start of the intake stroke) is fw (k) and the fuel injection amount at the kth cycle is fi (k), the (k + 1) th cycle The wall surface adhesion amount fw (k + 1) in can be expressed as the following equation (5). Further, the amount of fuel fc (k) flowing into the cylinder in the k-th cycle can be expressed as the following equation (6).
fw (k + 1) = P * fw (k) + R * fi (k) (5)
fc (k) = (1-P) * fw (k) + (1-R) * fi (k) (6)

According to the above equation (6), the fuel injection amount fi (k) necessary for flowing the fuel of fc (k) into the cylinder can be expressed as follows.
fi (k) = {fc (k)-(1-P) * fw (k)} / (1-R) (7)

  The fuel adhesion rate R and the residual rate P have a correlation with the operating state of the internal combustion engine 10. Therefore, for example, if the relationship between them and the operating state of the internal combustion engine 10 is grasped in advance, both the adhesion rate R and the residual rate P can be estimated on the vehicle. If these are estimated, the fuel injection amount fi for generating the in-cylinder inflow requested fuel amount fc can be calculated according to the above equation (7).

  In the transient operation of the internal combustion engine 10, the system according to the present embodiment calculates the in-cylinder inflow required fuel amount fc ′ for setting the air-fuel ratio AFRe of the exhaust gas to the target air-fuel ratio according to the above equation (4). The fuel injection amount fi (k) is calculated by substituting the inflow required fuel amount fc ′ into the above equation (7). Therefore, according to the system of the present embodiment, it is possible to accurately control the air-fuel ratio AFRe of the exhaust gas to the target air-fuel ratio AFR even during the transient operation of the internal combustion engine 10.

[Specific Processing in Embodiment 1]
FIG. 5 is a flowchart of a routine executed in the present embodiment in order to realize the above function. The routine shown in FIG. 5 is executed for each cylinder of the internal combustion engine 10. The routine for each cylinder is started every time the internal combustion engine 10 operates for one cycle, more specifically, every time a predetermined crank angle is realized before fuel injection is started in the target cylinder. Shall be.

  In the routine shown in FIG. 5, first, various parameters representing the current state of the internal combustion engine 10 are acquired (step 100). Specifically, here, engine load KL (calculated from Ga, Ne, TA, etc.), engine speed Ne, intake valve 26 opening / closing timing VT, port inner wall surface temperature Tw (estimated from THW), and target air-fuel ratio AFR etc. are acquired.

  In the routine shown in FIG. 5, next, calculation of the residual rate P and calculation of the adhesion rate R are executed. The ECU 40 stores a map in which the residual rate P of the wall-attached fuel is determined in relation to the engine load KL, the engine speed Ne, the intake valve 26 opening / closing timing VT, and the port inner wall surface temperature Tw. Here, the residual rate P corresponding to the current operating state is calculated with reference to the map (step 102).

  The ECU 50 also stores a map in which the fuel adhesion rate R is determined in relation to the engine load KL, the engine speed Ne, the intake valve 26 opening / closing timing VT, and the port inner wall surface temperature Tw. Here, by referring to the map, the adhesion rate R corresponding to the current operating state is calculated (step 104).

  Next, it is determined whether or not the target air-fuel ratio AFR (k-1) of the previous cycle (referred to as "k-1 cycle") was the stoichiometric air-fuel ratio (step 106). As a result, if it is determined that the target air-fuel ratio AFR (k-1) of the previous cycle is the stoichiometric air-fuel ratio, what value is the target air-fuel ratio AFR (k) of the current cycle (referred to as “k cycle”)? Regardless of whether or not there is, the processing after step 108 is executed.

  Here, when the target air-fuel ratio AFR (k) in the current cycle is the stoichiometric air-fuel ratio, it can be determined that the target air-fuel ratio AFR has not changed from the previous cycle to the current cycle. That is, in this case, the target air-fuel ratio AFR is constant, and the ratio between the in-cylinder residual gas amount Gr (k) and the in-cylinder residual fuel amount fr (k) in the current cycle, that is, the in-cylinder residual gas in the current cycle. Therefore, it can be determined that the air-fuel ratio Gr (k) / fr (k) of the engine is equal to the target air-fuel ratio AFR (k) of the current cycle. In this case, if the air-fuel ratio AFRc of the new gas is set to the target air-fuel ratio AFR (k), the air-fuel ratio of the in-cylinder gas, that is, the air-fuel ratio AFRe of the exhaust gas is set to the target air-fuel ratio AFR (k). (Refer to the above formulas (2) and (4)).

  On the other hand, when the target air-fuel ratio AFR (k) in the current cycle is not the stoichiometric air-fuel ratio, it can be determined that a request for controlling the operating state without considering emissions is generated for the internal combustion engine 10. In the burned gas controlled to the stoichiometric air-fuel ratio, no unburned components of fuel and oxygen remain. Therefore, when the target air-fuel ratio AFR (k-1) of the previous cycle is the stoichiometric air-fuel ratio, the in-cylinder residual gas does not contribute to combustion at all. In order to quickly realize a desired operating state under such circumstances, it is appropriate to control the air / fuel ratio AFRc of the new gas to the target air / fuel ratio AFR (k).

  As explained above, when the target air-fuel ratio AFR (k-1) of the previous cycle is the stoichiometric air-fuel ratio, no matter what the target air-fuel ratio AFR (k) of the current cycle is, There is a need to control the gas air-fuel ratio AFRc to the target air-fuel ratio AFR (k). Therefore, if it is determined in step 106 that the target air-fuel ratio AFR (k-1) of the previous cycle is the stoichiometric air-fuel ratio, the air-fuel ratio AFRc of the new gas is set to the target air-fuel ratio according to the above equation (2). The in-cylinder inflow required fuel amount fc (k) = Ga (k) / AFR (k) for calculating AFR (k) is calculated (step 108).

  Thereafter, the fuel injection amount fi (k) for realizing the in-cylinder inflow required fuel amount fc (k) in the current cycle is calculated according to the above equation (7) (step 110). Next, the wall-attached fuel amount fw (k + 1) for the next cycle is calculated according to the above equation (5) (step 112). The ECU 40 controls the fuel injection valve 24 so that the fuel injection amount fi (k) calculated by the above processing is realized. As a result, the air / fuel ratio AFRc of the new gas becomes the target air / fuel ratio AFR (k), and a desired operation state is realized.

  In the routine shown in FIG. 5, if it is determined in step 106 that the target air-fuel ratio AFR (k-1) of the previous cycle is not the stoichiometric air-fuel ratio, the target air-fuel ratio AFR (k) of the current cycle is It is determined whether the cycle is the same as the target air-fuel ratio AFR (k-1) (step 114). If they are the same, the air-fuel ratio Gr (k) / fr (k) of the in-cylinder residual gas is equal to the target air-fuel ratio AFR (k) of the current cycle, and the air-fuel ratio AFRc of the new gas is set to the target air-fuel ratio. If AFR (k) is set, it can be determined that the air-fuel ratio AFRe of the exhaust gas is equal to the target air-fuel ratio AFR (k). Therefore, also in this case, the processing after step 108 is executed.

  According to the above processing, the air-fuel ratio AFRe of the exhaust gas can be accurately set to the target air-fuel ratio AFR by simple processing during the steady operation of the internal combustion engine 10. For this reason, according to the system of the present embodiment, excellent emission characteristics can be realized without unduly excessively increasing the calculation load of the ECU 40.

  In the routine shown in FIG. 5, if it is determined in step 114 that the target air-fuel ratio AFR (k) of the current cycle is not the same as the target air-fuel ratio AFR (k-1) of the previous cycle, the internal combustion engine 10 is in a transient state. Therefore, it can be determined that the air-fuel ratio Gr (k) / fr (k) of the in-cylinder residual gas does not match the target air-fuel ratio AFR (k) of the current cycle. That is, in this case, even if the air-fuel ratio AFRc of the new gas is set to the target air-fuel ratio AFR (k), it can be determined that the air-fuel ratio AFRe of the exhaust gas does not become the target air-fuel ratio AFR (k).

  Under such circumstances, the system of the present embodiment achieves good emission characteristics by matching the air-fuel ratio AFRe of the exhaust gas to the target air-fuel ratio AFR. Therefore, if a negative determination is made in 114 above, first, the intake air amount Ga (k), the in-cylinder residual gas amount Gr (k), and the target air-fuel ratio AFR (k) in the current cycle are detected. (Step 116).

  The intake air amount Ga (k) and the target air-fuel ratio AFR (k) can be detected by reading the values acquired in step 100 above. The ECU 40 stores a map that defines the relationship between the operating state of the internal combustion engine and the in-cylinder residual gas amount Gr. Therefore, the in-cylinder residual gas amount Gr (k) can be detected by referring to the map.

Next, the in-cylinder residual fuel amount fr (k) in the current cycle is calculated (step 118). It can be considered that the air-fuel ratio of the in-cylinder residual gas in the current cycle is equal to the target air-fuel ratio AFR (k-1) of the previous cycle. Therefore, the in-cylinder residual gas amount fr (k) in the current cycle is expressed by the following equation using the in-cylinder residual gas amount Gr (k) in the current cycle and the target air-fuel ratio AFR (k-1) in the previous cycle. Can be expressed as
fr (k) = Gr (k) / AFR (k-1) (8)

  The ECU 40 has a function of storing at least the latest target air-fuel ratio AFR in the past, and can read the target air-fuel ratio AFR (k-1) of the previous cycle in the current cycle. In step 118, the in-cylinder residual fuel amount fr (k) of the current cycle is substituted by substituting the AFR (k-1) read out in this way and the Gr (k) read out from the map into the equation (8). ) Is calculated.

  In the routine shown in FIG. 5, next, in-cylinder inflow required fuel amount for setting the air-fuel ratio AFRe of the exhaust gas to the target air-fuel ratio AFR (k) in consideration of the influence of the in-cylinder residual fuel amount fr (k). fc ′ (k) is calculated (step 120). Specifically, here, the intake air amount Ga (k), the in-cylinder residual gas amount Gr (k), the target air-fuel ratio AFR (k), and the in-cylinder residual fuel amount fr (k) are expressed by the above equation (4). By substituting into, the in-cylinder inflow required fuel amount fc ′ (k) = (Ga (k) + Gr (k)) / AFR (k) −fr (k) in the current cycle is calculated.

  When the process of step 120 is executed, the in-cylinder inflow requested fuel amount fc ′ (k) calculated there is substituted into the above equation (7) in step 110 thereafter. As a result, a fuel injection amount fi (k) that can match the air-fuel ratio AFRe of the exhaust gas with the target air-fuel ratio AFR (k) is calculated. In particular, according to the above processing, when the target air-fuel ratio AFR is returned to the stoichiometric air-fuel ratio from a value that is not the stoichiometric air-fuel ratio, the air-fuel ratio AFRe of the exhaust gas can be quickly returned to the stoichiometric air-fuel ratio. For this reason, according to the system of the present embodiment, it is possible to sufficiently suppress the deterioration of the emission characteristics during the transient operation.

  In the first embodiment described above, the method for calculating the fuel injection amount fi based on the in-cylinder inflow requested fuel amount fc or fc ′ is based on the fuel behavior model (PR model) shown in FIG. However, the present invention is not limited to this. In other words, any method may be used for calculating the fuel injection amount fi based on the in-cylinder inflow required fuel amount fc or fc ′. This also applies to other embodiments described below.

  In Embodiment 1 described above, the fuel injection method is limited to the port injection method, but the present invention is not limited to this. That is, the present invention can also be applied to the cylinder injection internal combustion engine 10. This also applies to other embodiments described below.

  In Embodiment 1 described above, if a negative determination is made in step 114, the fuel injection amount fi (k) for always setting the air-fuel ratio AFRe of the exhaust gas to the target air-fuel ratio AFR (k) is set. Although the calculation is made, the present invention is not limited to this. That is, the process for setting the air-fuel ratio AFRe of the exhaust gas to the target air-fuel ratio AFR (k) may be executed only when the target air-fuel ratio AFR (k) in the current cycle is the stoichiometric air-fuel ratio. The points that can be modified as described above are the same in other embodiments described below.

  In the first embodiment described above, the ECU 40 executes the process of step 118, so that the “residual fuel amount calculating means” in the first invention executes the process of step 120. By executing the processing of step 110, the “fuel injection amount calculating means” according to the first aspect of the present invention is realized by the “inflow required fuel amount calculating means” according to the present invention.

Further, in the first embodiment described above, the ECU 40 executes the process of step 116, whereby the “residual gas amount detecting means” in the first aspect of the invention is the target air-fuel ratio AFR (k−1) of the previous cycle. By storing the above, the “target air-fuel ratio storage means” in the first invention is realized, and the “residual fuel amount calculation means” in the first invention is realized by executing the processing of step 118. Yes.

In the first embodiment described above, the ECU 40 performs the calculation “Ga (k) + Gr (k)” in step 120, whereby the “in-cylinder gas amount calculating means” in the second invention is By calculating “{Ga (k) + Gr (k)} / AFR (k)” using the calculated value, the “in-cylinder required fuel amount calculating means” in the second aspect of the invention further calculates the value. By performing the calculation “{Ga (k) + Gr (k)} / AFR (k) −fr (k)” using the values, the “inflow required fuel amount calculating means” in the second invention is It has been realized.

In the first embodiment described above, the ECU 40 executes the processing of step 116, whereby the “residual gas amount detecting means” and the “intake air amount detecting means” in the third aspect of the invention are changed to “ By performing the calculation “Ga (k) + Gr (k)”, the “in-cylinder gas amount calculating means” in the third aspect of the present invention is realized.

In the first embodiment described above, the by ECU40 is, the "intake air amount detection means" in the invention of the sixth by executing the processing in step 100, performs the process of step 106 Sixth The “stoichiometric judgment means” in the present invention implements the “inflow required fuel amount calculating means” in the sixth invention by executing the processing of step 108.

Further, in the first embodiment described above, ECU 40 is, the second by the "intake air amount detection means" in the invention of the seventh by executing the processing in step 100, performs the process of step 114 7 The “air-fuel ratio determining means” in the present invention implements the “inflow required fuel amount calculating means” in the seventh aspect by executing the processing of step 108.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 6 and FIG. The system according to the present embodiment is the same as the system according to the first embodiment except that the calculation method of the in-cylinder inflow required fuel amount fc ′ for making the air-fuel ratio AFRe of the exhaust gas coincide with the target air-fuel ratio AFR is different. is there. This system can be realized by causing the ECU 40 to execute a routine shown in FIG. 7 described later in the system configuration shown in FIG.

[Calculation Method for In-Cylinder Inflow Required Fuel Amount fc ′ in Embodiment 2]
FIG. 6 is a diagram for explaining a method for calculating the in-cylinder inflow requested fuel amount fc ′ in the present embodiment. In FIG. 6, the symbol “Gex” is the flow rate of the exhaust gas discharged from the cylinder during one cycle of operation. Further, the symbol “fex” is the amount of fuel discharged together with the exhaust gas when desired injection control is realized. Hereinafter, these are referred to as “exhaust gas amount Gex” and “required exhaust fuel amount fex”, respectively.

In-cylinder residual gas amount represented by Gr (k) occurs at the start of the current cycle (k cycle), and the air amount represented by Ga (k) is inhaled during the intake stroke of the current cycle. Then, the in-cylinder total gas amount at the end of the intake stroke of the current cycle is an amount represented by Ga (k) + Gr (k). In the exhaust stroke of the internal combustion engine 10, a part of the total cylinder gas amount Ga (k) + Gr (k) is discharged as the exhaust gas amount, and the remaining part is the cylinder residual gas amount Gr (k + 1) in the next cycle. It becomes. Therefore, the exhaust gas amount Gex (k) in the current cycle can be expressed as the following equation.
Gex (k) = Ga (k) + Gr (k) -Gr (k + 1) (9)

On the other hand, the in-cylinder residual fuel amount at the start of the current cycle is fr (k), and the in-cylinder residual fuel amount at the end of the current cycle, that is, the in-cylinder residual fuel amount in the next cycle is fr (k + 1). If so, the relationship between the fuel amount fc ′ (k) flowing into the cylinder during the current cycle and the required fuel amount fex (k) during the current cycle can be expressed as the following equation. .
fex (k) = fc´ (k) + fr (k) -fr (k + 1) (10)

Further, the air-fuel ratio AFRe (k) of the exhaust gas in the current cycle can be expressed as follows using the exhaust gas amount Gex (k) and the required fuel amount fex (k).
AFRe (k) = Gex (k) / fex (k) (11)

Therefore, the conditions for setting the air-fuel ratio AFRe (k) of the exhaust gas in the current cycle to the target air-fuel ratio AFR (k) can be expressed as follows.
AFR (k) = Gex (k) / fex (k)
= {Ga (k) + Gr (k) -Gr (k + 1)} / {fc '(k) + fr (k) -fr (k + 1)} (12)

The above equation (12) can be organized as follows.
fc ′ (k) = {Ga (k) + Gr (k) −Gr (k + 1)} / AFR (k) −fr (k) + fr (k + 1) (13)

  That is, the condition for setting the air-fuel ratio AFRe (k) of the exhaust gas in the current cycle to the target air-fuel ratio AFR (k) is that the fuel amount fc ′ (k) flowing into the cylinder during the current cycle is the above (13). It will be a value represented by an expression. In other words, if the in-cylinder inflow required fuel amount fc ′ (k) in the current cycle is calculated according to the above equation (13), the air-fuel ratio AFRe (k) of the exhaust gas in the current cycle becomes the target air-fuel ratio AFR (k). It is possible to match.

  In the above equation (13), the intake air amount Ga (k) can be obtained by actual measurement. The target air-fuel ratio AFR (k) is a value determined according to a request for the internal combustion engine 10. Further, the in-cylinder residual gas amounts Gr (k) and Gr (k + 1) and the in-cylinder residual fuel amounts fr (k) and fr (k + 1) can be estimated based on the operating state of the internal combustion engine 10. it can. Therefore, the ECU 40 uses the above equation (13) to calculate the in-cylinder inflow required fuel amount fc ′ (k) for setting the air-fuel ratio AFRe (k) of the exhaust gas in the current cycle to the target air-fuel ratio AFR (k). Can be calculated accurately.

[Specific Processing in Second Embodiment]
FIG. 7 is a flowchart of a routine executed by the ECU 40 in the present embodiment in order to realize the above function. The routine shown in FIG. 7 is the same as the routine shown in FIG. 5 except that steps 116 to 120 are replaced with steps 122 to 126, respectively.

  That is, according to the routine shown in FIG. 7, in the case where the condition in step 114 is not satisfied, in addition to Ga (k), Gr (k), and AFR (k), the in-cylinder residual gas amount in the next cycle Gr (k + 1) is acquired (step 122). The cylinder residual gas amount Gr (k + 1) in the next cycle defines the relationship between the operating state of the internal combustion engine 10 and the cylinder residual gas amount Gr, as in the cylinder residual gas amount Gr (k) in the current cycle. Can be obtained by referring to the map.

  Next, in-cylinder residual fuel amount fr (k + 1) in the next cycle is calculated in addition to the in-cylinder residual fuel amount fr (k) in the current cycle (step 124). The in-cylinder residual fuel amount fr (k + 1) in the next cycle is calculated by dividing the in-cylinder residual gas amount Gr (k + 1) in the next cycle by the target air-fuel ratio AFR (k) in the current cycle according to the above equation (8). (Fr (k + 1) = Gr (k + 1) / AFR (k)).

  Next, the in-cylinder inflow required fuel amount fc ′ (k) is calculated by substituting the parameters acquired by the processing of steps 122 and 124 into the above equation (13) (step 126).

  According to the above processing, the in-cylinder residual fuel amount fr generated for each cycle is taken into account to accurately grasp the required fuel amount fex for each cycle, and then, the exhaust gas amount Gex and the required fuel amount fex The in-cylinder inflow required fuel amount fc ′ can be obtained so that the ratio becomes the target air-fuel ratio AFR. Therefore, also in the system of the present embodiment, as in the case of the first embodiment, the fuel injection for accurately matching the air-fuel ratio AFRe of the exhaust gas with the target air-fuel ratio AFR during the transient operation of the internal combustion engine 10 The quantity fi can be calculated.

In the second embodiment described above, the ECU 40 calculates the in-cylinder residual gas amounts Gr (k) and Gr (k + 1) in step 122, whereby the “exhaust gas amount calculating means in the fourth aspect of the invention”. ”Is calculated as“ Ga (k) + Gr (k) −Gr (k + 1)} / AFR (k) ”in step 126 to obtain“ required exhaust fuel amount calculation means ”in the fourth aspect of the invention. However, the “required inflow required fuel amount calculating means” in the fourth aspect of the present invention is realized by completing the calculation of equation (13) using the value obtained as a result.

In the second embodiment described above, the ECU 40 detects Gr (k) and Gr (k + 1) in step 122, so that the “residual gas amount calculating means” in the fifth aspect of the invention is step 122. In step 126, the “intake air amount detecting means” in the fifth aspect of the invention detects Ga (k) in step 126, and calculates “Ga (k) + Gr (k) −Gr (k + 1)”. Thus, the “exhaust gas amount calculating means” in the fifth aspect of the invention is realized.

Embodiment 3 FIG.
[Features of Embodiment 3]
Next, Embodiment 3 of the present invention will be described with reference to FIG. 8 and FIG. FIG. 8 is a diagram for explaining the characteristics of the system configuration of the present embodiment and the concept of fuel injection control in the present embodiment. More specifically, FIG. 8A is a diagram for explaining a phenomenon when the air-fuel ratio AFRc of the new gas is controlled to the target air-fuel ratio AFR in the system of the present embodiment. FIG. 8B is a diagram showing a state when the air-fuel ratio AFRe of the exhaust gas is controlled to the target air-fuel ratio AFR in the system of the present embodiment.

  As shown in FIGS. 8A and 8B, the system of this embodiment includes an EGR (Exhaust Gas Recirculation) passage 50 and an EGR valve 52. Except for this point, the system of the present embodiment has the same hardware configuration as the system of the first embodiment. The EGR passage 50 has one end communicating with the exhaust passage 14 and the other end communicating with the intake passage 12. The EGR valve 52 is arranged in the middle of the EGR passage 50, and can achieve a desired opening degree by being controlled by the ECU 40 (see FIG. 1).

  During operation of the internal combustion engine 10, the pressure in the exhaust passage 14 is higher than the pressure in the intake passage 12. For this reason, when the EGR valve 52 is opened, the burned gas in the exhaust passage can be recirculated to the intake passage 12. When the burned gas is recirculated to the intake passage 12, the burned gas can flow into the cylinder together with the new gas. When an appropriate amount of burned gas is mixed in the new gas, the in-cylinder combustion temperature can be lowered appropriately to suppress the amount of NOx generated. The ECU 40 controls the EGR valve 52 so that the applied burned gas flows into the cylinder as needed during operation of the internal combustion engine 10.

  As described above, according to the EGR passage 50 and the EGR valve 52, the burned gas in the exhaust passage 14 can be circulated into the cylinder 10 through the outside of the internal combustion engine 10. In the internal combustion engine 10, burned gas that has not been discharged into the exhaust passage 14, burned gas that has been once discharged into the exhaust passage 14, but is sucked back into the cylinder during the valve overlap, and the like. May remain. Hereinafter, in order to distinguish these, the former is referred to as “external EGR” and the latter is referred to as “internal EGR”.

  The system of the first embodiment described above is intended to improve the air-fuel ratio accuracy of exhaust gas by taking into consideration the influence of the in-cylinder residual fuel amount fr caused by the internal EGR. On the other hand, in the system having the function of the external EGR, as in the case of the first embodiment, if the air-fuel ratio of the exhaust gas is to be controlled with high accuracy, the in-cylinder EGR supplied into the cylinder by the external EGR It is necessary to perform fuel injection control in consideration of the fuel amount fegr.

  That is, FIG. 8A shows that when the target air-fuel ratio AFR changes from the rich air-fuel ratio (for example, 12.5) to the stoichiometric air-fuel ratio, the influence of the in-cylinder EGR fuel amount fegr is not taken into consideration. The case where the air-fuel ratio AFRc is made to follow the target air-fuel ratio is illustrated. In this case, even if the air-fuel ratio AFRc of the new gas is the stoichiometric air-fuel ratio, since the rich EGR gas flows into the cylinder together with the new gas, the air-fuel ratio AFRe of the exhaust gas is richly biased (for example, 13.0).

  On the other hand, FIG. 8B shows that immediately after the target air-fuel ratio AFR changes from the rich air-fuel ratio to the stoichiometric air-fuel ratio, the air-fuel ratio AFRc of the new gas becomes the lean air-fuel ratio in consideration of the influence of the in-cylinder EGR fuel amount fegr. The case where the fuel injection amount fi is controlled to be (here 15.5) is illustrated. Here, the lean new gas and the rich EGR gas are mixed in the cylinder, so that the air-fuel ratio AFRe of the exhaust gas is the stoichiometric air-fuel ratio. The system of the present embodiment is characterized in that, in principle, the fuel injection amount fi is calculated so that the state is formed.

[Specific Processing in Embodiment 3]
FIG. 9 is a flowchart of a routine executed in the present embodiment in order to realize the above function. The routine shown in FIG. 9 is the same as the routine shown in FIG. 5 except that steps 116 to 120 are replaced with steps 130 to 134, respectively.

  That is, according to the routine shown in FIG. 9, in the case where the condition in step 114 is not satisfied, the cylinder in the current cycle is added to the intake air amount Ga (k) and the target air-fuel ratio AFR (k) in the current cycle. The internal EGR gas amount Gegr (k) is acquired (step 130). The in-cylinder EGR gas amount Gegr (k) is a value determined according to a predetermined rule based on the operating state of the internal combustion engine 10. Here, the in-cylinder EGR gas amount Gegr (k) determined according to the rule is acquired.

Next, the amount of burned fuel that flows into the cylinder due to the external EGR, that is, the in-cylinder EGR fuel amount fegr (k) in the current cycle is calculated (step 132). The in-cylinder EGR fuel amount fegr (k) is obtained by dividing the in-cylinder EGR gas amount Gegr (k) by the air-fuel ratio AFRegr (k) of the EGR gas flowing into the cylinder during the current cycle as follows: Can be calculated.
fegr (k) = Gegr (k) / AFRegr (k) (14)

  Here, the air-fuel ratio AFRegr (k) of the EGR gas in the current cycle is discharged from the cylinder to the exhaust passage 14 in a cycle (k-degr cycle) retroactive from the present time by the number of cycles required for the EGR gas transfer. Exhaust gas. Therefore, the air-fuel ratio AFRegr (k) can be regarded as the target air-fuel ratio AFR (k-degr) in the k-degr cycle.

The number of cycles degr required for transporting the EGR gas can be accurately estimated from the operating state history of the internal combustion engine 10. Further, the ECU 40 in the present embodiment stores a sufficient number of past target air-fuel ratios AFR (ki). For this reason, the ECU 40 reads the target air-fuel ratio AFR (k-degr) in the k-degr cycle in the above step 132, and then uses the AFR (k-degr) to determine the in-cylinder EGR gas amount Gegr ( By dividing k), the in-cylinder EGR fuel amount fegr (k) in the current cycle can be calculated as follows.
fegr (k) = Gegr (k) / AFR (k-degr) (15)

  In the routine shown in FIG. 9, next, the in-cylinder required fuel amount fc ′ (k) for setting the air-fuel ratio AFRe of the exhaust gas to the target air-fuel ratio AFR (k) is calculated (step 134). The total in-cylinder gas amount at the end of intake of the current cycle can be expressed as Ga (k) + Gegr (k). Further, if the injected fuel flowing into the cylinder during the current cycle is fc ′ (k), the total in-cylinder fuel amount at the end of intake of the current cycle is fc ′ (k) + fegr (k). Can be represented.

Therefore, the conditions for setting the air-fuel ratio AFRe (k) of the exhaust gas discharged from the cylinder to the target air-fuel ratio AFR (k) can be expressed as follows.
AFR (k) = AFRe (k)
= {Ga (k) + Gegr (k)} / {fc´ (k) + fegr (k)} (16)

If the above equation (16) is rearranged, the amount fc ′ (k) of the injected fuel to be flown into the cylinder in order to set the air-fuel ratio AFRe (k) of the exhaust gas to the target air-fuel ratio AFR (k), that is, The in-cylinder inflow required fuel amount fc ′ (k) to be set in the current cycle in order to satisfy the condition can be expressed as follows.
fc´ (k) = {Ga (k) + Gegr (k)} / AFR (k) -fegr (k) (17)

  In step 134, the ECU 40 adds the intake air amount Ga (k), the in-cylinder EGR gas amount Gegr (k), the target air-fuel ratio AFR (k), and the in-cylinder EGR fuel amount in the current cycle to the above equation (17). By substituting fegr (k), the in-cylinder inflow required fuel amount fc ′ (k) is calculated. According to the above processing, the in-cylinder inflow required fuel amount fc ′ for making the air-fuel ratio AFRe of the exhaust gas coincide with the target air-fuel ratio AFR by considering the in-cylinder EGR fuel amount fegr during execution of the external EGR. Can be calculated accurately. Therefore, according to the system of the present embodiment, the air-fuel ratio AFRe of the exhaust gas is accurately set during the transient operation of the internal combustion engine 10 even during execution of the external EGR, as in the case of the first or second embodiment. It is possible to calculate the fuel injection amount fi for making it coincide with the target air-fuel ratio AFR.

Embodiment 4 FIG.
[Features of Embodiment 4]
Next, a fourth embodiment of the present invention will be described with reference to FIG. 10 and FIG. FIG. 10 is a diagram showing the air-fuel ratio AFRc of the new gas and the air-fuel ratio AFRe of the exhaust gas in comparison with the transient operation of the internal combustion engine 10. More specifically, FIG. 10A shows that the target air-fuel ratio is changed from the rich air-fuel ratio to the lean air-fuel ratio, and the fuel injection amount fi is controlled so that the air-fuel ratio AFRc of the new gas follows the change. It is a figure for demonstrating the phenomenon at the time of doing. On the other hand, FIG. 10B shows a phenomenon when the target air-fuel ratio is changed from the rich air-fuel ratio to the stoichiometric air-fuel ratio and the fuel injection amount fi is controlled so that the air-fuel ratio AFRe of the exhaust gas follows the change. It is a figure for demonstrating.

  As shown in FIG. 10 (A), during the transient operation of the internal combustion engine 10, the air-fuel ratio AFRc of the new gas and the air-fuel ratio AFRe of the exhaust gas are different with respect to the change of the target air-fuel ratio AFR. Specifically, they eventually converge to the same value, but in the process of change, the air-fuel ratio AFRc of the new gas changes more rapidly than the air-fuel ratio AFRe of the exhaust gas. Therefore, as shown in FIG. 10B, when the fuel injection amount fi is controlled so that the air-fuel ratio AFRe of the exhaust gas follows the target air-fuel ratio AFR, the air-fuel ratio AFRc of the new gas becomes the target air-fuel ratio AFR. It is easy to show a large overshoot.

  In the systems of the first to third embodiments described above, during the transient operation of the internal combustion engine 10, in principle, the fuel injection amount fi is calculated so that the air-fuel ratio AFRe of the exhaust gas matches the target air-fuel ratio AFR. However, the internal combustion engine 10 may be required to improve the air-fuel ratio accuracy of the new gas in preference to the air-fuel ratio accuracy of the exhaust gas. Hereinafter, this request is referred to as “combustion priority request”. Further, a request opposite to the request, that is, a request to increase the air-fuel ratio accuracy of the exhaust gas in preference to the air-fuel ratio accuracy of the new gas is referred to as an “exhaust priority request”.

  The combustion priority request is generated under a situation where the combustion in the cylinder is to be stabilized, or under a situation where the combustion state in the cylinder is to be accurately controlled. Specifically, a combustion priority request is generated when the internal combustion engine 10 is started, immediately after returning from a fuel cut, during operation in the drive priority mode, and during operation in the fuel efficiency priority mode.

  On the other hand, the exhaust priority request is generated under a situation where the emission characteristics should be kept good, or under a situation where an exhaust gas controlled to have a desired air-fuel ratio should flow into the catalyst 34. Specifically, an exhaust priority request is generated at the time of warming up of the internal combustion engine 10 for which emission reduction is desired, at the time of rich spike control executed for releasing the poisoning of the catalyst 34, or the like.

  In the systems of the first to third embodiments, the fuel injection amount fi is calculated in principle by the exhaust priority method during transient operation even under the situation where the combustion priority request occurs. For this reason, according to these systems, the operating state of the internal combustion engine 10 becomes unstable at the time of starting or immediately after returning from the fuel cut, and a good response cannot be obtained under a situation where driving is prioritized. Can occur.

  Therefore, in the system of the present embodiment, during the operation of the internal combustion engine 10, whether or not the combustion priority request is generated is successively monitored, and the calculation method of the fuel injection amount fi is switched according to the presence or absence of the generation. did. More specifically, when there is a combustion priority request, the fuel injection amount fi is always calculated by a method in which the air-fuel ratio AFRc of the new gas matches the target air-fuel ratio AFR. As long as the calculation method for matching the air-fuel ratio AFRe of the exhaust gas with the target air-fuel ratio AFR is used.

[Specific Method in Embodiment 4]
FIG. 11 is a flowchart of a routine executed in the present embodiment in order to realize the above function. The routine shown in FIG. 11 is the same as the routine shown in FIG. 5 except that step 140 is inserted after steps 102 and 104.

  That is, according to the routine shown in FIG. 11, after the residual rate P and the adhesion rate R are calculated by the processing of steps 102 and 104, it is determined whether or not a combustion priority request has occurred (step 140). The ECU 40 stores in advance operation states in which a combustion priority request is generated, and here, it is determined whether or not those operation states are realized.

  If the generation of the combustion priority request is recognized as a result of the above determination, the processing after step 108 is executed unconditionally. In this case, the fuel injection amount fi for setting the air-fuel ratio AFRc of the new gas to the target air-fuel ratio AFR is calculated (steps 108 to 112), and as a result, the combustion-priority operating state is realized.

  On the other hand, if it is determined in step 140 that the combustion priority request has been made, it is determined that the process after step 106 is executed. In this case, thereafter, the fuel injection amount fi is calculated in the same procedure as in the first embodiment.

  According to the above processing, when the combustion priority request has occurred, the fuel injection amount fi is calculated by a method that satisfies the request, while when the combustion priority request has not occurred, the fuel injection amount fi of the first embodiment is calculated. According to the same rules as in the case, the fuel injection amount fi can be calculated according to the exhaust priority procedure as necessary. For this reason, according to the system of this embodiment, the characteristic of the internal combustion engine 10 can be switched appropriately, and the operation characteristic can be improved comprehensively.

  By the way, in Embodiment 4 mentioned above, it is supposed that the control which switches the calculation method of fuel injection quantity fi is combined with the control method of Embodiment 1, but the object of the combination is the control method of Embodiment 1. It is not limited to. That is, the control for switching the calculation method of the fuel injection amount fi may be combined with the control method in the second or third embodiment.

  Further, in Embodiment 4 described above, only the generation of the combustion priority request is monitored and the generation of the exhaust priority request is not monitored, but the present invention is not limited to this. That is, after the generation of the exhaust priority request is monitored, if the generation is recognized, the processing after step 116 may be executed unconditionally.

In the above-described fourth embodiment, the ECU 40 executes the process of step 100 shown in FIG. 11 so that the “intake air amount detecting means” in the eighth invention executes the process of step 140. wherein the "state determining means" in the eighth aspect, the "inflow demand fuel amount calculation means" in the eighth aspect of the present invention by following the process of step 140 executes the processing of steps 108 and 110, respectively implemented by Has been.

It is a figure for demonstrating the structure of Embodiment 1 of this invention. It is a figure for demonstrating the concept of the fuel-injection control in Embodiment 1 of this invention. It is a figure for demonstrating the calculation method of the cylinder inflow request | requirement fuel amount fc in Embodiment 1 of this invention. It is a figure for demonstrating the fuel behavior model showing the relationship between fuel injection quantity fi and in-cylinder inflow request | requirement fuel amount fc. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure for demonstrating the calculation method of in-cylinder inflow required fuel amount fc 'in Embodiment 2 of this invention. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a figure for demonstrating the characteristic on the structure of the system of Embodiment 3 of this invention, and the concept of the fuel-injection control in Embodiment 3 of this invention. It is a flowchart of the routine performed in Embodiment 3 of the present invention. FIG. 6 is a diagram showing a comparison between an air-fuel ratio AFRc of a new gas and an air-fuel ratio AFRe of exhaust gas during a transient operation of the internal combustion engine. It is a flowchart of the routine performed in Embodiment 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Intake passage 14 Exhaust passage 16 Air flow meter 24 Fuel injection valve 26 Intake valve 28 Exhaust valve 40 ECU (Electronic Control Unit)
AFR target air-fuel ratio
AFRc Air-fuel ratio of new gas
AFRe exhaust gas air-fuel ratio
Ga intake air volume
fi Fuel injection amount
fw Fuel on the wall
fc, fc´ In-cylinder inflow required fuel amount
Gr In-cylinder residual gas volume
fr Residual fuel amount in cylinder
P Residual rate
R adhesion rate
Gex emissions
fex required fuel amount
Gegr EGR gas amount in cylinder
fegr EGR fuel amount in cylinder

Claims (8)

A residual fuel amount calculating means for calculating an in-cylinder residual fuel amount at the time when intake starts,
An inflow required fuel amount calculating means for calculating an in-cylinder inflow required fuel amount based on the in-cylinder residual fuel amount so that an air-fuel ratio of exhaust gas discharged from the cylinder becomes a target air-fuel ratio;
Fuel injection amount calculating means for calculating a fuel injection amount by the fuel injection valve based on the in-cylinder inflow required fuel amount;
A residual gas amount detecting means for calculating a residual gas amount in the cylinder at the time when intake is started;
A target air-fuel ratio storage means for storing the latest target air-fuel ratio for at least one cycle,
The fuel injection control for an internal combustion engine, wherein the residual fuel amount calculation means calculates the in-cylinder residual fuel amount by dividing the in-cylinder residual gas amount in the current cycle by a target air-fuel ratio in the previous cycle. apparatus. In-cylinder gas amount calculating means for calculating the in-cylinder gas amount at the end of intake,
In-cylinder required fuel amount calculating means for calculating a value obtained by dividing the in-cylinder gas amount in the current cycle by the target air-fuel ratio in the current cycle as a required cylinder fuel amount,
2. The in-cylinder inflow required fuel amount is calculated by subtracting the in-cylinder residual fuel amount in a current cycle from the in-cylinder required fuel amount, wherein the inflow required fuel amount calculation unit calculates the in-cylinder inflow required fuel amount. A fuel injection control device for an internal combustion engine. A residual gas amount detecting means for calculating a residual gas amount in the cylinder at the time when intake is started;
An intake air amount detecting means for detecting an intake air amount sucked into the cylinder,
The in-cylinder gas amount calculation means calculates the in-cylinder gas amount by adding the in-cylinder residual gas amount in the current cycle and the intake air amount in the current cycle. A fuel injection control device for an internal combustion engine. An exhaust gas amount calculating means for calculating an exhaust gas amount discharged from the cylinder;
A required exhaust fuel amount calculating means for calculating the required fuel amount by dividing the exhaust gas amount in the current cycle by the target air-fuel ratio in the current cycle,
The inflow required fuel amount calculation means calculates the in-cylinder inflow required fuel amount by adding the in-cylinder residual fuel amount in the next cycle to a value obtained by subtracting the in-cylinder residual fuel amount in the current cycle from the required discharge fuel amount. The fuel injection control device for an internal combustion engine according to claim 1, wherein: A residual gas amount calculating means for calculating an in-cylinder residual gas amount at the time when intake starts,
An intake air amount detecting means for detecting an intake air amount sucked into the cylinder,
The exhaust gas amount calculating means calculates the exhaust gas amount by subtracting the in-cylinder residual gas amount in the next cycle from a value obtained by adding the in-cylinder residual gas amount in the current cycle to the intake air amount in the current cycle. 5. The fuel injection control device for an internal combustion engine according to claim 4, wherein the fuel injection control device is an internal combustion engine. Intake air amount detection means for detecting the amount of intake air sucked into the cylinder;
Stoichiometric judgment means for judging whether or not the target air-fuel ratio of the previous cycle was the stoichiometric air-fuel ratio,
The inflow required fuel amount calculation means calculates, as the in-cylinder inflow required fuel amount, a value obtained by dividing the intake air amount by the target air fuel ratio of the current cycle when the target air fuel ratio of the previous cycle is the stoichiometric air fuel ratio. The fuel injection control device for an internal combustion engine according to any one of claims 1 to 5 , wherein: Intake air amount detection means for detecting the amount of intake air sucked into the cylinder;
Air-fuel ratio determining means for determining whether or not the target air-fuel ratio of the previous cycle and the target air-fuel ratio of the current cycle are the same,
When the target air-fuel ratio in the previous cycle and the target air-fuel ratio in the current cycle are the same, the inflow required fuel amount calculation means calculates a value obtained by dividing the intake air amount by the target air-fuel ratio in the current cycle. the fuel injection control device according to any one of the internal combustion engine according to claim 1 to 6, characterized in that calculated as the amount of fuel. Intake air amount detection means for detecting the amount of intake air sucked into the cylinder;
And a state determining means for determining whether or not a combustion priority state that should give priority to the air-fuel ratio accuracy of the fresh gas sucked into the cylinder is prior to the air-fuel ratio accuracy of the exhaust gas discharged from the cylinder is provided. ,
The inflow required fuel amount calculation means calculates, as the in-cylinder inflow required fuel amount, a value obtained by dividing the intake air amount by the target air-fuel ratio of the current cycle when the formation of the combustion priority state is recognized. A fuel injection control device for an internal combustion engine according to any one of claims 1 to 7 .

Images