JP2006194112A - Fuel injection amount control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection amount control device applied to an internal combustion engine having a supercharger and directly injecting fuel in a combustion chamber, making the air-fuel ratio as close as possible to the target air-fuel ratio regardless of the engine load state. To provide something that can be maintained.
This device is based on an engine speed NE and a throttle valve opening TA, which are factors that affect the amount of air blown from the intake side to the exhaust side during a valve overlap period during operation of the supercharger. The presence or absence of a blow-through is determined. If no blow-through occurs, the air flow meter outputs Vg (air flow rate Ga1). Based on the in-cylinder pressure Pa (air flow rate Ga2), the in-cylinder charged air amount Ma is determined, and the fuel injection amount Fi is determined from the in-cylinder charged air amount Ma and the target air-fuel ratio AFstoich.
[Selection] Figure 5

Description

  The present invention relates to a fuel injection amount control device for an internal combustion engine, and more particularly, to a direct fuel injection type internal combustion engine that includes a supercharger and directly injects fuel in a combustion chamber.

  Conventionally, in order to improve the output of an internal combustion engine, an internal combustion engine having a supercharger that boosts intake pressure to atmospheric pressure or higher and supplies high-density air into a combustion chamber is known. On the other hand, in recent years, the direct fuel injection type internal combustion engine has been developed in order to improve combustion efficiency and reduce fuel consumption.

For example, the engine control device described in Patent Document 1 below is applied to a direct fuel injection internal combustion engine equipped with a supercharger, and the amount of air (cylinder) charged into a combustion chamber based on the output of an air flow meter. The amount of injected fuel (fuel injection amount) required to obtain the target air-fuel ratio is calculated with respect to the calculated cylinder charge air amount.
JP 11-62639 A

  Incidentally, in general, in an internal combustion engine, a period during which both the exhaust valve and the intake valve are opened by opening the intake valve before closing the exhaust valve in the transition process from the exhaust stroke to the intake stroke (that is, the valve Overlap period) is provided.

  FIG. 6 shows an example of the actual measurement results of the intake pressure and the exhaust pressure with respect to the crank angle at the time of operation of the supercharger for one bank side of the V-type 6-cylinder engine with a supercharger (that is, for three cylinders). It is a graph. As shown in FIG. 6, this engine also has a valve overlap period (intake valve open (IVO) to exhaust valve close (EVC)) in the transition process from the exhaust stroke to the intake stroke.

  Here, as shown in FIG. 6, when the intake pressure is maintained at a pressure sufficiently higher than the atmospheric pressure by the operation of the supercharger (that is, when the engine is in a high load state), the valve overlap is performed. During this period, the intake pressure becomes higher than the exhaust pressure, and as a result, a phenomenon in which air blows from the intake side to the exhaust side during the valve overlap period (hereinafter referred to as “blow-through”) may occur. is there.

  FIG. 7 is a graph showing the relationship between the engine rotational speed and the blow-through rate obtained by measuring the blow-through rate with respect to the engine rotational speed when the engine is in a predetermined high load state. . Here, the blow-through rate is the amount of air blown to the exhaust side due to blow-through (that is, the amount of air that has passed through the exhaust valve and flowed into the exhaust system during the valve overlap period. Hereinafter, referred to as “blow-through amount”. )) (Ie, the amount of air that has passed through the intake valve and entered the combustion chamber during the period in which the intake valve is open (intake valve open (IVO) to intake valve close (IVC))). ). As shown in FIG. 7, the blow-through rate becomes higher as the engine speed is lower, and may be a large value exceeding 10 percent in the low speed region.

  When such a blow-through occurs, the actual in-cylinder charged air amount decreases by the amount of the blow-through. On the other hand, the in-cylinder charged air amount calculated based on the output of the air flow meter is a value including the above-described blow-through amount. Therefore, the in-cylinder charged air amount calculated by the apparatus described in the above document is larger than the actual value by the amount of blow-through.

  On the other hand, in a direct fuel injection type internal combustion engine, in general, fuel is injected after the end of the valve overlap period (after EVC). Therefore, the injected fuel is not discharged to the exhaust system before combustion. From the above, in the apparatus described in the above document, when the engine is in a high load state and the blow-by occurs, the fuel injection amount corresponds to the blow-through amount rather than an appropriate value for obtaining the target air-fuel ratio. It is calculated and set to a value that is as large as possible. As a result, there is a problem that the air-fuel ratio in the combustion chamber becomes richer than the target air-fuel ratio, which can cause engine output reduction, fuel consumption deterioration, and the like.

  The present invention has been made to cope with the above-described problem, and an object of the present invention is to provide a fuel injection amount that is applied to an internal combustion engine of a direct fuel injection system that includes a supercharger and directly injects fuel in a combustion chamber. An object of the present invention is to provide a control device that can maintain the air-fuel ratio to the target air-fuel ratio as much as possible regardless of the load state of the engine.

  A fuel injection amount control apparatus according to the present invention includes a direct fuel injection means for directly injecting fuel in a combustion chamber, a supercharger for increasing the intake pressure of the internal combustion engine to an atmospheric pressure or higher, and air sucked into an intake system And an in-cylinder pressure sensor for detecting the pressure in the combustion chamber.

  Here, examples of the supercharger include a mechanical supercharger (supercharger) driven by the power of the engine itself, and an exhaust turbine supercharger (turbocharger) driven by the power of the exhaust turbine. .

  The fuel injection amount control apparatus according to the present invention includes an acquisition unit, a selection unit, and a fuel injection instruction unit. Hereinafter, these actions will be described in order.

  The acquisition means acquires the value of a factor that affects the blow-through amount, which is the amount of air that blows from the intake side to the exhaust side during the valve overlap period in the transition process from the exhaust stroke to the intake stroke. The blow-through amount depends on the intake pressure, the exhaust pressure, the length of the valve overlap period, and the like. Accordingly, the “value of the factor that affects the blow-through amount” is, for example, the intake pressure, the exhaust pressure, the length of the valve overlap period, and the like.

  Furthermore, the engine operating speed is a factor that greatly affects the exhaust pressure and the length of the valve overlap period. The throttle valve opening is a factor that greatly affects the intake pressure. Further, in order to perform various controls and the like, an internal combustion engine is generally provided with sensors for detecting the engine operating speed and the throttle valve opening. From the above, it is preferable that the acquisition means is configured to acquire the engine operating speed and the throttle valve opening as the “value of the factor affecting the blow-by amount”.

  The selection means determines a fuel injection amount, which is the amount of fuel to be injected from the direct fuel injection means, based on the output of the air flow meter, or from the time when the intake valve is closed until the start of combustion in the combustion chamber. Whether to determine based on the output of the in-cylinder pressure sensor is selected based on the value of the acquired factor.

  More specifically, the selection means is an operation state in which the internal combustion engine is so small that the blow-by amount is negligible in determining the fuel injection amount based on the acquired factor value (or an operation in which no blow-through occurs). The air flow meter output is selected when it is determined that the engine is in a state), and the internal combustion engine is operated based on the acquired factor value so that the blow-through amount is not negligible in determining the fuel injection amount. It is preferable that the output of the in-cylinder pressure sensor is selected when it is determined that it is in a state.

  According to this, when it is determined that the internal combustion engine is in an operating state in which the blow-by amount is negligibly small in determining the fuel injection amount (or an operating state in which no blow-through occurs) (that is, the engine is in a low load state). In some cases, the fuel injection amount is determined based on the output of the air flow meter. Therefore, in this case, the fuel injection amount is a desired value (for example, a target air-fuel ratio) based on a value (for example, a flow rate of air sucked into the intake system) related to the cylinder charge air amount directly measured by an air flow meter. Can be calculated and determined accurately to the value necessary to obtain

  Here, “when the internal combustion engine is determined to be in an operating state in which the blow-by amount is negligibly small in determining the fuel injection amount” specifically refers to, for example, a value obtained by subtracting the exhaust pressure from the intake pressure Is determined to be equal to or less than a predetermined value (for example, “0” or a positive minute value), or the intake pressure is determined to be equal to or lower than atmospheric pressure.

  On the other hand, when it is determined that the internal combustion engine is in an operating state in which the blow-through amount is so large that it cannot be ignored in determining the fuel injection amount (that is, when the engine is in a high load state), the fuel injection amount is when the intake valve is closed. To the start of combustion in the combustion chamber (hereinafter referred to as “after IVC”).

  Here, “when the internal combustion engine is determined to be in an operating state in which the amount of blow-through is so large that it cannot be ignored in determining the fuel injection amount” specifically refers to, for example, a value obtained by subtracting the exhaust pressure from the intake pressure. Is determined to be greater than a predetermined value (for example, “0” or a positive minute value), or the intake pressure is determined to be greater than atmospheric pressure.

  As described above, in this case, if the fuel injection amount is determined based on the output of the air flow meter, the fuel injection amount is calculated to be larger than the appropriate value by the amount corresponding to the blow-through amount. It cannot be calculated or determined accurately.

  On the other hand, the total gas amount existing in the combustion chamber after IVC can be obtained from the pressure (in-cylinder pressure) in the combustion chamber after IVC. However, in the combustion chamber after IVC, not only the air sucked this time but also residual gas due to the previous combustion exists. Therefore, the sum of the cylinder charge air amount and the residual gas amount can be obtained from the cylinder pressure after IVC, but the cylinder charge air amount cannot be directly and accurately calculated. In other words, if the amount of residual gas can be obtained accurately, the amount of air charged in the cylinder can be accurately calculated from the pressure in the cylinder after IVC.

  Here, the residual gas amount cannot be directly detected. However, it is possible to estimate the residual gas amount to some extent accurately through experiments conducted in advance. Therefore, if the in-cylinder pressure after IVC and the estimation result of the residual gas amount are used, the in-cylinder charged air amount (accordingly, the fuel injection amount) can be calculated and determined with a certain degree of accuracy.

  Therefore, when the blow-through amount is so large that it cannot be ignored in determining the fuel injection amount, the fuel injection amount is calculated and determined based on the output of the in-cylinder pressure sensor after IVC as in the above configuration. For example, the fuel injection amount can be calculated and determined more accurately than when the fuel injection amount is calculated and determined based on the output of the air flow meter.

  Then, the fuel injection instruction means determines the fuel injection amount based on the output selected by the selection means, and issues an instruction to inject the determined amount of fuel to the direct fuel injection means. Specifically, the fuel injection instructing means, for example, the amount of air that is filled in the combustion chamber when the intake valve is closed based on the output selected by the selecting means (that is, the in-cylinder charged air) The fuel injection amount is determined on the basis of the in-cylinder charged air amount and the target air-fuel ratio.

  As a result, the fuel injection amount can be accurately calculated and determined not only when the engine is in a low load state but also in a high load state. As a result, the air-fuel ratio is set to the target air-fuel ratio regardless of the engine load state. It is possible to maintain as much as possible.

  In this case, when the fuel injection instruction means determines the fuel injection amount based on the output of the in-cylinder pressure sensor, the output of the in-cylinder pressure sensor at a time corresponding to a predetermined crank angle after the IVC. Preferably, the fuel injection amount is determined based on Here, the “predetermined crank angle” is, for example, a crank angle immediately after the intake valve closing (IVC).

  According to this, for example, the fuel injection instruction means uses a table (map) in which the output of the in-cylinder pressure sensor (and hence the in-cylinder pressure) is used as an argument (part of it) as an argument (part of it). ) In the data related to the output of the in-cylinder pressure sensor after the IVC (and hence the in-cylinder pressure), the value at the “time corresponding to the predetermined crank angle” is used. The table concerned can be produced by paying attention only, and the table can be produced easily.

  Even if the fuel injection instructing means is configured to perform fuel injection (that is, compression stroke injection) after IVC, it is before the intake valve closing (IVC) (and after the end of the valve overlap period ( The fuel injection (that is, the intake stroke injection) may be performed in the post-EVC)).

  However, considering that the fuel injection amount cannot be determined before IVC (and therefore during the intake stroke) when the fuel injection amount is determined based on the output of the in-cylinder pressure sensor after IVC, the intake stroke injection is performed. When executed, the fuel injection instruction of the fuel injection amount determined this time is given to the cylinder in which combustion occurs this time (that is, the cylinder after IVC. The cylinder that has already finished the intake stroke and has shifted to the compression stroke). It is impossible to do. Therefore, in this case, the fuel injection instruction means is configured to issue an instruction to inject the fuel of the fuel injection amount determined this time to the cylinder where the next combustion occurs.

  On the other hand, when the compression stroke injection is executed, it is also possible to issue an instruction to inject fuel of the fuel injection amount determined this time to the cylinder in which the current combustion occurs. Accordingly, in this case, even if the fuel injection instructing means is configured to issue an instruction to inject fuel of the fuel injection amount determined this time to the cylinder in which the current combustion occurs, it performs it to the cylinder in which the next combustion occurs. It may be configured as follows.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a fuel injection amount control device for an internal combustion engine according to the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a system in which a fuel injection amount control device according to an embodiment of the present invention is applied to a four-cycle spark ignition type four-cylinder direct fuel injection type internal combustion engine 10 with a supercharger.

  This system includes an engine main body 20 including a fuel supply system, an intake system 30 for introducing gas into a combustion chamber (in a cylinder) of each cylinder of the engine main body 20, and an exhaust system for discharging exhaust gas from the engine main body 20. 40, an EGR device 50 for performing exhaust gas recirculation, and an electric control device 60.

  A fuel injection valve (injector) 21 (direct fuel injection means) for directly injecting fuel in the combustion chamber is disposed above each cylinder of the engine body 20. Each fuel injection valve 21 is connected to a fuel injection pump 22 connected to a fuel tank (not shown) via a fuel pipe 23. The fuel injection pump 22 is electrically connected to the electric control device 60, and adjusts the fuel injection pressure by a drive signal from the electric control device 60.

  The fuel injection valve 21 is electrically connected to the electric control device 60, and is opened only for a predetermined time by a drive signal (command signal corresponding to the fuel injection amount Fi) from the electric control device 60. Thus, the fuel is directly injected into the combustion chamber by the fuel injection amount Fi. In this example, the fuel is injected immediately after the intake valve is closed (that is, the compression stroke injection is executed).

  The intake system 30 includes an intake manifold 31 connected to a combustion chamber of each cylinder of the engine body 20, an intake pipe 32 connected to an upstream side assembly of the intake manifold 31 and constituting an intake passage together with the intake manifold 31, an intake pipe A throttle valve 33 rotatably held in the throttle 32, a throttle valve actuator 33a for rotating the throttle valve 33 in response to a drive signal from the electric control device 60, and an intake pipe 32 upstream of the throttle valve 33. It includes a mounted intercooler 34, a compressor 35 a of a supercharger (turbocharger) 35, and an air cleaner 36 disposed at the tip of the intake pipe 32.

  The exhaust system 40 includes an exhaust manifold 41 connected to each cylinder of the engine body 20, an exhaust pipe 42 connected to a downstream gathering portion of the exhaust manifold 41, and a turbine of the supercharger 35 disposed in the exhaust pipe 42. 35b, a supercharger throttle valve 35c, and a three-way catalyst 43 interposed in the exhaust pipe 42. The exhaust manifold 41 and the exhaust pipe 42 constitute an exhaust passage.

  The supercharger throttle valve 35c is electrically connected to the electric control device 60, and flows into the turbine 35b so that the capacity of the supercharger 35 can be made substantially variable by a drive signal from the electric control device 60. It is a valve that makes the passage area of exhaust gas to be variable. As a result, the supercharging pressure is adjusted.

  The EGR device 50 includes an exhaust gas recirculation pipe 51 constituting a passage for recirculating exhaust gas, an EGR control valve 52 interposed in the exhaust gas recirculation pipe 51, and an EGR cooler 53. The exhaust gas recirculation pipe 51 communicates the upstream exhaust passage (exhaust manifold 41) of the turbine 35b and the downstream intake passage (intake manifold 31) of the throttle valve 33. The EGR control valve 52 can change the amount of exhaust gas to be recirculated (exhaust gas recirculation amount, EGR gas flow rate) in response to a drive signal from the electric control device 60.

  The electrical control device 60 is connected to each other via a bus 61, a ROM 62 that stores programs executed by the CPU 61, tables (look-up tables, maps), constants, and the like, and the CPU 61 temporarily stores data as necessary. The microcomputer includes a RAM 63, a backup RAM 64 that stores data while the power is on, and holds the stored data while the power is shut off, an interface 65 including an AD converter, and the like.

  The interface 65 is disposed in the intake passage downstream of the hot-wire air flow meter 71, the accelerator opening sensor 72, and the throttle valve 33 disposed in the intake pipe 32 and downstream of the portion to which the exhaust gas recirculation pipe 51 is connected. Intake pipe pressure sensor 73, crank position sensor 74 (acquisition means), in-cylinder pressure sensor 75 disposed above each cylinder, throttle position sensor 76 (acquisition means), and three-way catalyst 43 upstream The air-fuel ratio sensor 77 disposed in the exhaust passage is connected to supply signals to the CPU 61 from these sensors.

  The interface 65 is connected to the fuel injection valve 21, the fuel injection pump 22, the throttle valve actuator 33a, the supercharger throttle valve 35c, and the EGR control valve 52. In response to an instruction from the CPU 61, a drive signal is supplied to these. Is sent out.

  The air flow meter 71 measures the mass flow rate of the intake air passing through the intake passage (intake air amount per unit time, fresh air amount per unit time), and outputs Vg representing the same mass flow rate Ga1 (air flow rate Ga1). Is supposed to occur. The relationship between the output Vg and the air flow rate Ga1 is as shown in FIG. 2, and the ROM 62 stores a table MapGa1 that defines the relationship.

  The accelerator opening sensor 72 detects an operation amount of the accelerator pedal AP and generates a signal representing the accelerator operation amount Accp. The intake pipe pressure sensor 73 detects the pressure of gas taken into the cylinder of the engine 10 (that is, the intake pipe pressure) and generates a signal representing the intake pipe pressure Pb.

  The crank position sensor 74 detects the absolute crank angle of each cylinder and generates a signal that represents the crank angle CA and also represents the engine rotation speed NE that is the rotation speed of the engine 10. The in-cylinder pressure sensor 75 detects the pressure in the combustion chamber of each cylinder and generates a signal representing the in-cylinder pressure Pa for each cylinder.

  The throttle position sensor 76 detects the opening of the throttle valve 33 (throttle valve opening) and generates a signal representing the throttle valve opening TA. The air-fuel ratio sensor 77 detects the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 43, and generates a signal corresponding to the air-fuel ratio abyf.

(Determination of fuel injection amount Fi)
Next, a method of determining the fuel injection amount Fi by the fuel injection amount control device (hereinafter also referred to as “this device”) configured as described above will be described. In this apparatus, the crank angle of a certain cylinder (hereinafter referred to as “compression stroke cylinder”) is a predetermined crank angle immediately after the intake valve closing (IVC) (specifically, before the compression top dead center). Every time it matches 100 deg (hereinafter referred to as “BTDC 100 deg”), the air-fuel ratio of the engine (that is, the air-fuel ratio of the air-fuel mixture to be burned) matches the target air-fuel ratio AFstoich (for example, the stoichiometric air-fuel ratio). And the fuel of the determined fuel injection amount Fi is directly injected into the compression stroke cylinder (compression stroke injection).

  In order to accurately match the air-fuel ratio of the engine to the target air-fuel ratio AFstoich, it is necessary to accurately determine the fuel injection amount Fi. For this purpose, the amount of air charged in the compression stroke cylinder after IVC ( That is, it is necessary to accurately obtain the in-cylinder charged air amount Ma). The in-cylinder charged air amount Ma is basically the amount of air (all the air taken into the combustion chamber from the intake system 30 via the intake valve between the intake valve open (IVO) and the intake valve close (IVC). It matches the intake air volume.

  However, since the internal combustion engine 10 is an internal combustion engine with a supercharger, as described above, the blow-through can occur during a valve overlap period at a high load. When such blow-through occurs, the cylinder filling air amount Ma becomes smaller than the total intake air amount by the amount of blow-through.

  On the other hand, when the cylinder charge air amount Ma is determined based on the output Vg of the air flow meter 71 (and hence the air flow rate Ga1 measured by the air flow meter 71), the cylinder charge air amount Ma is determined regardless of whether there is a blow-through. It is determined to be equal to the total intake air amount.

  In addition, in the internal combustion engine 10, since the fuel is directly injected into the combustion chamber after the valve overlap period (after EVC, specifically, BTDC 100 deg), the injected fuel is discharged into the exhaust system 40 before combustion. Will not be discharged.

  Therefore, if the cylinder charge air amount Ma is determined based on the air flow rate Ga1 measured by the air flow meter 71 regardless of whether there is a blow-through, the fuel injection amount Fi is the target when no blow-through has occurred. While it can be calculated to an appropriate value for obtaining the air-fuel ratio AFstoich, if a blow-through has occurred, it is calculated to a value that is larger than the appropriate value for obtaining the target air-fuel ratio AFstoich by an amount corresponding to the above-described blow-through amount It will be done.

  From the above, in order to accurately obtain the cylinder air charge amount Ma regardless of the presence or absence of blow-through, it is first necessary to determine the presence or absence of blow-through. The blow-through occurs when the internal combustion engine 10 is in an operating state (high load state) in which the intake pressure exceeds the exhaust pressure during the valve overlap period.

  Here, the exhaust pressure increases as the engine speed NE increases. The intake pressure increases as the throttle valve opening TA increases. That is, the lower the engine speed NE and the greater the throttle valve opening TA, the easier the blow-through occurs. In other words, the engine rotation speed NE and the throttle valve opening degree TA are “factors affecting the blow-through amount”.

  FIG. 3 shows an example of the relationship between the presence or absence of blow-through, the engine rotational speed NE, and the throttle valve opening TA. The operation region where the blow-by occurs (that is, the operation region where the intake pressure is larger than the exhaust pressure) corresponds to the region indicated by dots in FIG.

  This relationship is determined, for example, whether or not the intake pressure exceeds the exhaust pressure during the valve overlap period in the steady operation state in which the engine speed NE and the throttle valve opening TA are fixed (thus, whether or not there is a blow-through). The experiment can be obtained by repeating the experiment while changing various combinations of the engine speed NE and the throttle valve opening TA. Therefore, by using the relationship shown in FIG.

  Therefore, this apparatus (ROM 62) stores a table MapBTH corresponding to the relationship shown in FIG. 3, and whether or not a blow-through has occurred from the engine speed NE, the throttle valve opening TA, and this table MapBTH. Determine.

  If it is determined that no blow-through has occurred (corresponding to the case where the blow-through amount is negligibly small in determining the fuel injection amount Fi), the present apparatus uses the air flow rate Ga1 measured by the air flow meter 71. Based on this, the cylinder filling air amount Ma (and hence the fuel injection amount Fi) is determined. Thereby, when the blow-by does not occur, the fuel injection amount Fi can be determined to an appropriate value for obtaining the target air-fuel ratio AFstoich.

  On the other hand, when it is determined that a blow-through has occurred (corresponding to a case where the blow-through amount is so large that it cannot be ignored in determining the fuel injection amount Fi), the air flow rate Ga1 measured by the air flow meter 71 as described above. If the in-cylinder charged air amount Ma is determined based on the above, the in-cylinder charged air amount Ma (accordingly, the fuel injection amount Fi) cannot be accurately determined. Therefore, in this case, it is necessary to adopt another method that can determine the cylinder filling air amount Ma more accurately than when the air flow rate Ga1 is used.

By the way, assuming that the in-cylinder temperature at a predetermined crank angle after IVC (and before the start of combustion) is a predetermined temperature T1, the combustion chamber volume V1 at the predetermined crank angle is known. In-cylinder pressure Pa at the same predetermined crank angle after IVC and gas state equation (Pa · V1 = Mall · R · T1
: R is the gas constant) and the total gas amount Mall existing in the combustion chamber can be obtained.

  On the other hand, the gas in the combustion chamber after IVC contains residual gas from the previous combustion. That is, the total gas amount Mall is the sum of the in-cylinder charged air amount Ma and the residual gas amount. Therefore, if the amount of residual gas can be acquired, the cylinder charge air amount Ma can be obtained by acquiring the cylinder pressure Pa at the predetermined crank angle after IVC.

  Here, the residual gas amount can be estimated to some extent accurately through experiments and the like. Therefore, using the in-cylinder pressure Pa at the predetermined crank angle after IVC and the estimation result of the residual gas amount, the in-cylinder charged air amount Ma can be determined to some extent accurately.

  FIG. 4 employs BTDC 100 deg as the predetermined crank angle, and the cylinder charge air amount Ma determined by using the cylinder pressure Pa at BTDC 100 deg and the estimation result of the residual gas amount is expressed in units of the engine speed NE. An example of the relationship between the air flow rate Ga2, the in-cylinder pressure Pa, and the engine rotation speed NE when converted into the air flow rate Ga2 that is the amount of air per hour is shown.

  This device (ROM 62) stores a table MapGa2 corresponding to the relationship shown in FIG. 4, and when it is determined that a blow-through has occurred, the compression stroke cylinder BTDC of 100 deg obtained from the in-cylinder pressure sensor 75 is used. The air flow rate Ga2 is determined from the in-cylinder pressure Pa, the engine rotational speed NE, and the table MapGa2, and the in-cylinder charged air amount Ma (accordingly, the fuel injection amount Fi) is determined based on the air flow rate Ga2.

  As a result, when the blow-through has occurred, the fuel injection amount Fi is more accurate for obtaining the target air-fuel ratio AFstoich than when the fuel injection amount Fi is determined based on the air flow rate Ga1 measured by the air flow meter 71. An appropriate value can be determined.

  In this way, the air-fuel ratio of the engine can be maintained as much as possible at the target air-fuel ratio AFstoich regardless of whether there is a blow-by (and therefore regardless of the engine load state). The above is the outline of the method for determining the fuel injection amount Fi by the present apparatus.

(Actual operation)
Next, the actual operation of the fuel injection amount control device configured as described above will be described with reference to FIG. 5 showing a routine (program) executed by the CPU 61 of the electric control device 60 in a flowchart.

  The CPU 61 repeatedly executes a routine for calculating the fuel injection amount Fi and instructing fuel injection shown in FIG. 5 for each cylinder every predetermined time. Accordingly, when the predetermined timing is reached, the CPU 61 starts the process from step 500 and proceeds to step 505 to determine whether or not the crank angle of an arbitrary cylinder (the compression stroke cylinder) matches BTDC 100 deg. If YES, the process proceeds immediately to step 595 to end the present routine tentatively. In this case, fuel injection is not executed.

  Assuming that the crank angle of the compression stroke cylinder coincides with BTDC 100 deg, the CPU 61 determines “Yes” when the process proceeds to step 505, proceeds to step 510, and obtains the current engine speed obtained from the crank position sensor 74. Based on the speed NE, the current throttle valve opening degree TA obtained from the throttle position sensor 76, and the table MapBTH shown in FIG. 3, the value of the blow-off flag BTH is set to “0” or “1”. To do. Here, the value of the blow-through flag BTH is set to “1” when the blow-through occurs, and to “0” when the blow-through does not occur.

  Next, the CPU 61 proceeds to step 515 to determine whether or not the value of the blow-through flag BTH is “1”. When determining “Yes” (that is, when blow-through occurs), the CPU 61 proceeds to step 520. Thus, the air flow rate Ga2 based on the in-cylinder pressure Pa at the present time (ie, BTDC 100 deg) of the compression stroke cylinder obtained from the in-cylinder pressure sensor 75, the current engine speed NE, and the table MapGa2 shown in FIG. And the value of the air flow rate Ga is set equal to the air flow rate Ga2.

  On the other hand, when the value of the blow-through flag BTH is “0” (that is, when the blow-through does not occur), the CPU 61 determines “No” in step 515 and proceeds to step 525 to output the air flow meter 71 at the present time. The air flow rate Ga1 is determined based on Vg and the table MapGa1 shown in FIG. 2, and the value of the air flow rate Ga is set equal to the air flow rate Ga1. Here, steps 510 and 515 correspond to selection means.

  Subsequently, the CPU 61 proceeds to step 530 to obtain the air flow rate Ga set in step 520 or 525, the current engine speed NE, and the cylinder charge air amount Ma using Ga and NE as arguments. The in-cylinder charged air amount Ma is obtained from the table MapMa.

  Next, the CPU 61 proceeds to step 535, obtains the basic fuel injection amount Fbase by dividing the obtained cylinder air charge amount Ma by the target air-fuel ratio AFstoich, and in step 540, sets the basic fuel injection amount Fbase. The fuel injection amount Fi is obtained by multiplying the coefficient K. Here, the coefficient K is a value set based on the air-fuel ratio abyf of the exhaust gas obtained from the air-fuel ratio sensor 77 and the like. Thereby, air-fuel ratio feedback control based on the output of the air-fuel ratio sensor 77 is achieved.

  Then, the CPU 61 proceeds to step 545, gives an instruction for injecting the fuel of the calculated fuel injection amount Fi to the fuel injection valve 21 of the compression stroke cylinder, proceeds to step 595, and once ends this routine. In this way, every time the crank angle of the compression stroke cylinder coincides with BTDC 100 deg, immediately after that, fuel of the fuel injection amount Fi for making the engine air-fuel ratio coincide with the target air-fuel ratio AFstoich is supplied to the compression stroke cylinder. On the other hand, direct injection (compression stroke injection) is performed. Steps 520 to 545 correspond to fuel injection instruction means.

  As described above, the fuel injection amount control device according to the embodiment of the present invention is applied to a direct fuel injection internal combustion engine with a supercharger. According to this device, it is determined whether or not a blow-through has occurred based on the engine speed NE and the throttle valve opening TA, which are factors that affect the blow-through amount during the valve overlap period. When it is determined that no blow-through has occurred, the output Vg (air flow rate Ga1) of the air flow meter 71 is used. The cylinder charge air amount Ma is determined based on the cylinder pressure Pa (air flow rate Ga2), and the fuel injection amount Fi is determined from the cylinder charge air amount Ma and the target air-fuel ratio AFstoich.

  Thereby, when the blow-through occurs, the fuel injection amount Fi becomes an appropriate value for obtaining the target air-fuel ratio AFstoich more accurately than when the fuel injection amount Fi is determined based on the output Vg of the air flow meter 71. Can be determined. Therefore, the engine air-fuel ratio can be maintained as much as possible at the target air-fuel ratio AFstoich regardless of the presence or absence of the blow-through (thus, regardless of the load state of the engine).

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, in the above embodiment, the presence or absence of the blow-through (and therefore the magnitude relationship between the intake pressure and the exhaust pressure) is determined based on the engine speed NE and the throttle valve opening TA. Instead, the accelerator operation amount Accp obtained from the accelerator opening sensor 72 may be used.

  In the above embodiment, it is determined that a blow-through occurs when the intake pressure is larger than the exhaust pressure, and it is determined that no blow-through occurs when the intake pressure is equal to or lower than the exhaust pressure. It is determined that a blow-through occurs when the value obtained by subtracting the exhaust pressure from the pressure exceeds a predetermined positive value, and it is determined that no blow-through occurs when the value obtained by subtracting the exhaust pressure from the intake pressure is equal to or less than the predetermined positive value. You may comprise as follows.

  Further, it may be configured to determine that a blow-through occurs when the intake pressure exceeds the atmospheric pressure and to determine that no blow-through occurs when the intake pressure is equal to or lower than the atmospheric pressure. In this case, it is preferable to use the intake pipe pressure Pb obtained from the intake pipe pressure sensor 73 as the intake pressure compared with the atmospheric pressure. Further, as the intake pressure, a value (Ga1 / NE) obtained by dividing the air flow rate Ga1 measured by the air flow meter 71 by the engine rotational speed NE may be used. This is because the value (Ga1 / NE) corresponds to the in-cylinder charged air amount when no blow-through occurs, and the in-cylinder charged air amount and the intake pressure in this case have a close relationship (proportional relationship). Based on that.

  Further, in the above embodiment, the air flow rate Ga is acquired based on the output Vg of the air flow meter 71 or the in-cylinder pressure Pa obtained from the in-cylinder pressure sensor 75, and from this air flow rate Ga (and the engine rotation speed NE). The in-cylinder charged air amount Ma is obtained, and the fuel injection amount Fi is determined from the in-cylinder charged air amount Ma. The output Vg (and engine speed NE) of the air flow meter 71 or the in-cylinder pressure is configured. The in-cylinder charged air amount Ma may be directly obtained based on the in-cylinder pressure Pa obtained from the sensor 75, and the fuel injection amount Fi may be determined from the in-cylinder charged air amount Ma. Further, the air flow rate Ga is acquired based on the output Vg of the air flow meter 71 or the in-cylinder pressure Pa obtained from the in-cylinder pressure sensor 75, and the fuel injection amount Fi is directly determined from the air flow rate Ga (and the engine speed NE). You may comprise.

  Further, in the above embodiment, the fuel of the fuel injection amount Fi determined this time at BTDC 100 deg of the current compression stroke cylinder is configured to be injected in the compression stroke immediately after BTDC 100 deg to the current compression stroke cylinder. However, the fuel of the fuel injection amount Fi determined this time may be injected in the compression stroke to the cylinder in which combustion occurs next to the current compression stroke cylinder.

  Moreover, in the said embodiment, although comprised so that compression stroke injection may be carried out, you may comprise so that intake stroke injection (injection after IVC and before IVC) may be carried out. In this case, the fuel of the fuel injection amount Fi determined this time at a predetermined crank angle (BTDC 100 deg) after IVC of the current compression stroke cylinder is the intake stroke with respect to the cylinder in which combustion occurs next to the current compression stroke cylinder. Configured to be injected.

  Moreover, in the said embodiment, although applied to the spark-injection type internal combustion engine of a super injection with a supercharger, you may apply to the diesel engine of a direct injection type with a supercharger.

It is the figure which showed the outline of the fuel injection amount control apparatus which concerns on embodiment of this invention applied to the internal combustion engine. It is the graph which showed the table which prescribes | regulates the relationship between the output of an air flow meter, and the air flow rate which CPU shown in FIG. 1 refers. 2 is a graph showing a table that defines the relationship between presence / absence of blow-through, engine rotation speed and throttle valve opening, which is referred to by the CPU shown in FIG. 1. 2 is a graph showing a table that defines the relationship between in-cylinder pressure, engine rotation speed, and air flow rate, which is referred to by the CPU shown in FIG. 1. 2 is a flowchart showing a routine executed by the CPU shown in FIG. 1 for calculating a fuel injection amount and performing fuel injection. It is the graph which showed the example of the actual measurement result of the intake pressure and the exhaust pressure with respect to the crank angle at the time of supercharger operation in an engine with a supercharger. It is the graph which showed an example of the relationship between an engine speed and a blow-through rate in an engine with a supercharger.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 ... Fuel injection valve, 33 ... Throttle valve, 35 ... Supercharger, 35a ... Compressor, 35b ... Turbine, 60 ... Electric control device, 61 ... CPU, 71 ... Air flow meter, 74 ... Crank position sensor, 75 ... In-cylinder Pressure sensor, 76 ... Throttle position sensor

Claims (5)

Direct fuel injection means for directly injecting fuel in the combustion chamber;
A supercharger that boosts the intake pressure of the internal combustion engine to an atmospheric pressure or higher;
An air flow meter that measures the flow rate of air drawn into the intake system;
An in-cylinder pressure sensor for detecting the pressure in the combustion chamber;
A fuel injection amount control device applied to an internal combustion engine comprising:
An acquisition means for acquiring a value of a factor that influences the amount of air blown from the intake side to the exhaust side during the valve overlap period in the transition process from the exhaust stroke to the intake stroke;
The fuel injection amount, which is the amount of fuel to be injected from the direct fuel injection means, is determined based on the output of the air flow meter, or from the time when the intake valve is closed until the start of combustion in the combustion chamber Selection means for selecting whether to determine based on the output of the pressure sensor based on the value of the acquired factor;
Fuel injection instruction means for determining the fuel injection amount based on the output selected by the selection means, and for instructing the fuel injection of the determined amount to the direct fuel injection means;
A fuel injection amount control device for an internal combustion engine comprising: The fuel injection amount control apparatus for an internal combustion engine according to claim 1,
The fuel injection instruction means includes
Based on the output selected by the selection means, the amount of air filled in the combustion chamber when the intake valve is closed is obtained, and the fuel injection amount is obtained based on the obtained amount of air and the target air-fuel ratio. A fuel injection amount control apparatus for an internal combustion engine configured to determine The fuel injection amount control device for an internal combustion engine according to claim 1 or 2,
The selection means includes
When the internal combustion engine determines that the blow-by amount is in an operating state that is negligibly small in determining the fuel injection amount based on the obtained factor value, the output of the air flow meter is selected, and The output of the in-cylinder pressure sensor is selected when the internal combustion engine determines that the blow-through amount is in an operating state that is so large that it cannot be ignored in determining the fuel injection amount based on the obtained factor value. A fuel injection amount control device for an internal combustion engine configured. The fuel injection amount control device for an internal combustion engine according to any one of claims 1 to 3,
The acquisition means includes
A fuel injection amount control device for an internal combustion engine configured to acquire at least an operation speed of the internal combustion engine and an opening degree of a throttle valve as the value of the factor. The fuel injection amount control device for an internal combustion engine according to any one of claims 1 to 4,
The fuel injection instruction means includes
When determining the fuel injection amount based on the output of the in-cylinder pressure sensor, the in-cylinder at the time corresponding to a predetermined crank angle from when the intake valve is closed to when combustion is started in the combustion chamber. A fuel injection amount control device for an internal combustion engine configured to determine the fuel injection amount based on an output of a pressure sensor.

Images