JP3603979B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel injection control device for controlling a fuel injection amount of each cylinder of a two-cylinder internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a fuel injection control device for a vehicle such as a motorcycle equipped with a two-cylinder internal combustion engine detects a throttle opening and an engine speed, and sets a fuel injection amount (a fuel injection amount (a fuel injection amount) set in advance using the throttle opening and the engine speed as parameters. From the two-dimensional map of the fuel injection time), the fuel injection amount according to the throttle opening and the engine speed at that time is calculated.
[0003]
[Problems to be solved by the invention]
In a general internal combustion engine, the fuel injection amount is calculated in accordance with the amount of air drawn into the cylinder and the target air-fuel ratio in one intake stroke, but the intake system of a two-cylinder internal combustion engine mounted on a motorcycle is Is a configuration in which air is introduced into each cylinder from the air box that takes in air through the intake manifold of each cylinder.Since there is no intake manifold upstream of the intake manifold, it is difficult to measure the amount of intake air. For this purpose, the throttle opening and the engine speed are used as parameters in place of the intake air amount, and the fuel injection amount is calculated from the throttle opening and the engine speed.
[0004]
However, depending on the engine load, the correspondence between the operating state determined by the throttle opening and the engine speed and the amount of intake air may deviate, and this may lower the calculation accuracy of the fuel injection amount and cause a deviation in the air-fuel ratio. This causes an increase in exhaust emissions and a decrease in drivability.
[0005]
In order to solve this drawback, it is conceivable to provide an intake pressure sensor in each intake manifold of each cylinder and calculate the fuel injection amount from the intake pressure of each cylinder and the engine speed. However, this configuration has a drawback in that the number of parts increases and the cost increases.
[0006]
Therefore, a communication pipe communicating with the intake manifolds of both cylinders of the two-cylinder internal combustion engine is provided, and an intake pressure sensor is provided in the communication pipe. The intake pressure sensor detects the average intake pressure of both cylinders, and detects the average intake pressure. It is conceivable to calculate the fuel injection amount from the pressure difference between the atmospheric pressure and the atmospheric pressure and the engine speed.
[0007]
However, when the intake manifolds of the two cylinders are communicated with the communication pipe, the intake pressures of the intake manifolds of the two cylinders affect each other through the communication pipe, and, particularly, in a low load region, the intake manifold on one side is connected to the other through the communication pipe. The influence of the airflow flowing into the intake manifold on the side becomes relatively large. For this reason, simply calculating the fuel injection amount from the output value of the intake pressure sensor (average intake pressure), the pressure difference between the atmospheric pressure, and the engine speed cannot necessarily calculate the fuel injection amount accurately. The air-fuel ratio may deviate, leading to an increase in exhaust emissions and a decrease in drivability.
[0008]
The present invention has been made in view of such circumstances, and therefore has as its object to accurately calculate the fuel injection amount of each cylinder of a two-cylinder internal combustion engine using the output signal of one intake pressure detecting means. It is an object of the present invention to provide a fuel injection control device for an internal combustion engine, which can reduce exhaust emissions and improve drivability.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the fuel injection control device for an internal combustion engine of the first aspect of the present invention, the average intake pressure of both cylinders is absorbed through a communication pipe communicating with the intake manifolds of both cylinders of the two-cylinder internal combustion engine. The first cylinder injection amount calculating means, which is detected by the atmospheric pressure detecting means, calculates the fuel of the first cylinder based on the differential pressure between the average intake pressure and the atmospheric pressure, which decrease due to the intake stroke of the second cylinder, and the internal combustion engine speed. An injection amount is calculated, and the second cylinder injection amount calculation means calculates the fuel injection amount of the second cylinder based on the differential pressure between the average intake pressure and the atmospheric pressure, which decreases due to the intake stroke of the first cylinder, and the internal combustion engine speed. Calculate the amount. As a result, when calculating the fuel injection amount of the two cylinders, the fuel injection amount can be accurately calculated in consideration of the influence of the intake pressure of the intake manifold on the opposite side, thereby reducing exhaust emissions and improving drivability. Can be realized. In addition, only one intake pressure detecting means is required, and it is possible to satisfy the demands of reducing the number of parts and reducing the cost.
[0010]
By the way, according to the test results of the present inventors, the influence of the intake pressure of the intake manifold on the opposite side becomes large in the low load region, and the influence of the intake pressure of the intake manifold on the opposite side in the medium load region and the high load region. Turned out to be relatively small.
[0011]
Therefore, as in claim 2, the first and second cylinder injection amount calculating means performs the calculation of the fuel injection amount by the calculation method of claim 1 only in a low load region, and in other load regions (medium). In the load / high load region), the fuel injection amount of the first cylinder is calculated using the average intake pressure that decreases due to the intake stroke of the first cylinder, and the average intake pressure that decreases due to the intake stroke of the second cylinder is used. Alternatively, the fuel injection amount of the second cylinder may be calculated. Even in this case, substantially the same effect as the first aspect can be obtained.
[0012]
Further, as in claim 3, the first and second cylinder injection amount calculating means performs the calculation of the fuel injection amount by the calculation method of claim 1 only in a low load region, and in other load regions (medium load). In a (high load region), the fuel injection amounts of the first and second cylinders may be calculated based on the throttle opening and the internal combustion engine speed. In other words, in the medium load / high load range, the relationship between the operating state determined by the throttle opening and the engine speed and the intake air amount is well established. By calculating the fuel injection amount based on the rotation speed, it is possible to calculate an appropriate fuel injection amount that matches the actual intake air amount of each cylinder, and reduce the deviation of the air-fuel ratio in the medium load and high load regions. can do.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
[Embodiment (1)]
Hereinafter, an embodiment (1) in which the present invention is applied to a motorcycle will be described with reference to FIGS. An intake manifold 12 is connected to an intake port 10 of each cylinder of a two-cylinder engine 11 which is a two-cylinder internal combustion engine, and an air box 13 is connected to an upstream side of the intake manifold 12 of each cylinder. The air sucked into the cylinder is sucked into the intake manifold 12 of each cylinder. An air cleaner 33 is mounted in the air box 13, and an intake air temperature sensor 14 for detecting an intake air temperature is attached to the air box 13. A throttle valve 15 is attached in the middle of the intake manifold 12 of each cylinder, and the opening of the throttle valve 15 (throttle opening) is detected by a throttle opening sensor 16 (throttle opening detecting means). Further, a fuel injection valve 18 is attached to the intake manifold 12 on the downstream side of the throttle valve 15.
[0014]
On the other hand, the fuel pumped from the fuel tank 19 by the fuel pump 20 is sent to the fuel pipe 21 → the fuel filter 22 → the fuel pipe 23 → the delivery pipe 24 and distributed to the fuel injection valve 18 of each cylinder. Excess fuel in the delivery pipe 24 is returned to the fuel tank 19 through a path from the pressure regulator 25 to the return pipe 26. The pressure regulator 25 adjusts the fuel pressure in the delivery pipe 24 so that the differential pressure between the fuel pressure in the delivery pipe 24 and the intake pressure becomes constant.
[0015]
An ignition plug 27 is attached to the cylinder head of the engine 11 for each cylinder, and a high voltage generated on the secondary side of the ignition coil 28 is applied to the ignition plug 27 of each cylinder at each ignition timing to ignite. The engine 11 includes an engine speed sensor 29 (rotation speed detection means) for outputting a pulse signal (crank angle signal) at every predetermined crank angle in order to detect the engine speed, and a cylinder discrimination sensor for discriminating a specific cylinder. 30 and a water temperature sensor 31 for detecting a cooling water temperature are attached. At a predetermined position of the vehicle body, an atmospheric pressure sensor 32 (atmospheric pressure detecting means) for detecting the atmospheric pressure is attached.
[0016]
As shown in FIG. 2, a thin communication pipe 34 is connected to the downstream side of the throttle valve 15 in the intake manifold 12 of both cylinders, and the communication pipe 34 connects the downstream side of the throttle valve 15 of the intake manifold 12 of both cylinders. Are in communication. An intake pressure sensor 17 (intake pressure detection means) such as a semiconductor pressure sensor is provided in the middle of the communication pipe 34, and the average value of the intake pressures of the intake manifolds 12 of the two cylinders (the intake pressure sensor 17) is provided by the intake pressure sensor 17. Average intake pressure) is detected.
[0017]
The output signal of the intake pressure sensor 17 and the output signals of various sensors such as the aforementioned throttle opening sensor 14 are input to an engine control circuit 35 (see FIG. 1). The engine control circuit 35 is mainly composed of a microcomputer, and a built-in ROM 45 (storage medium) stores an ignition control routine, a fuel injection control routine of FIG. 4, map data of FIGS. 5 and 6, and the like. Is stored.
[0018]
The engine control circuit 35 executes the fuel injection control routine of FIG. 4 to calculate the bottom pressure P2 of the average intake pressure that decreases due to the intake stroke of the second cylinder when calculating the fuel injection amount of the first cylinder. The fuel injection amount of the first cylinder is calculated using the bottom pressure P1 of the average intake pressure that is reduced by the intake stroke of the first cylinder when calculating the fuel injection amount of the second cylinder. Calculate the injection amount.
[0019]
Here, the relationship between the operation stroke of each cylinder of the two-cylinder engine 11 and the behavior of the intake pressure will be described with reference to FIG. The actual intake pressure of each cylinder repeats such a change that it decreases during the intake stroke of each cylinder and increases from the compression to the exhaust stroke. On the other hand, the pressure in the communication pipe 34 detected by the intake pressure sensor 17, that is, the average value (average intake pressure) of the intake pressures of the two cylinders is reduced by the intake stroke of the first cylinder, and the compression stroke of the first cylinder is reduced. , But again decreases during the intake stroke of the second cylinder and increases during the compression stroke of the second cylinder. Therefore, the average intake pressure detected by the intake pressure sensor 17 decreases in both the intake stroke of the first cylinder and the intake stroke of the second cylinder, and the lowest points thereof are the bottom pressures P1 and P2.
[0020]
According to the test results of the present inventors, in the low load region, when the actual intake pressure of the first cylinder decreases, the average cylinder intake pressure of the second cylinder becomes smaller than the decrease width of the bottom pressure P1 of the average intake pressure due to the intake stroke of the first cylinder. The decrease in the bottom pressure P2 of the average intake pressure due to the intake stroke becomes larger, and conversely, when the actual intake pressure of the second cylinder decreases, the decrease in the bottom pressure P2 of the average intake pressure due to the intake stroke of the second cylinder decreases. A test result was obtained that the decrease width of the bottom pressure P1 of the average intake pressure due to the intake stroke of the first cylinder was larger than that of the first cylinder. This is because the intake pressures of the intake manifolds 12 of both cylinders affect each other through the communication pipe 34, and in particular, in a low load region, air flowing from the one intake manifold 12 to the other intake manifold 12 through the communication pipe 34. It is considered that the influence of the flow is relatively large.
[0021]
In consideration of such characteristics, in the present embodiment (1), when calculating the fuel injection amount of the first cylinder, the bottom pressure P2 of the average intake pressure and the atmospheric pressure Pa that decrease due to the intake stroke of the second cylinder are calculated. The fuel injection amount of the first cylinder (basic injection time TP1) is calculated based on the pressure difference of the engine and the engine speed NE, and the fuel injection amount of the second cylinder is reduced by the intake stroke of the first cylinder when calculating the fuel injection amount of the second cylinder. The fuel injection amount (basic injection time TP2) of the second cylinder is calculated based on the differential pressure between the bottom pressure P1 of the average intake pressure and the atmospheric pressure Pa and the engine speed NE. Hereinafter, the processing content of the fuel injection control routine of FIG. 4 for performing the fuel injection amount calculation processing will be described.
[0022]
The fuel injection control routine of FIG. 4 is executed immediately before the fuel injection timing of the first cylinder and the second cylinder. When this routine is started, first, in step 100, the engine speed NE obtained from the output signal of the engine speed sensor 29 is read. In the next step 101, the atmospheric pressure Pa obtained from the output signal of the atmospheric pressure sensor 32 is read. Read. Thereafter, in step 102, it is determined which fuel injection time of the first cylinder or the second cylinder is to be calculated. In this determination method, for example, the output signal (crank angle signal) of the engine speed sensor 29 is counted by a counter, and the cylinder for which the fuel injection time is calculated is determined based on the count value and the output signal of the cylinder determination sensor 30.
[0023]
If it is determined in step 102 that the fuel injection time of the first cylinder is to be calculated, the process proceeds to step 103, in which the bottom pressure P2 of the average intake pressure that decreases due to the intake stroke of the second cylinder is read. Thereafter, in step 104, the first cylinder basic pressure is determined based on the differential pressure (Pa-P2) between the bottom pressure P2 of the average intake pressure and the atmospheric pressure Pa, which is reduced by the intake stroke on the second cylinder side, and the engine speed NE. The injection time TP1 is calculated. In this calculation method, the relationship between the differential pressure (Pa−P2), the engine speed NE, and the first cylinder basic injection time TP1 is determined in advance by an experiment or simulation, and the first cylinder basic injection time TP1 shown in FIG. A two-dimensional map is created, and this map is stored in the ROM 45 of the engine control circuit 35. At step 104, this map is searched, and the map is retrieved according to the differential pressure (Pa-P2) at that time and the engine speed NE. The calculated first cylinder basic injection time TP1 is calculated.
[0024]
On the other hand, if it is determined in step 102 that the fuel injection time of the second cylinder is to be calculated, the routine proceeds to step 105, where the bottom pressure P1 of the average intake pressure that decreases due to the intake stroke of the first cylinder is read. Thereafter, the routine proceeds to step 106, where the second pressure is determined based on the differential pressure (Pa-P1) between the bottom pressure P1 of the average intake pressure and the atmospheric pressure Pa, which is reduced by the intake stroke on the first cylinder side, and the engine speed NE. The cylinder basic injection time TP2 is calculated from the two-dimensional map of the second cylinder basic injection time TP2 in FIG. The map of FIG. 6 is set in the same manner as the map of FIG.
[0025]
After calculating the basic injection time TP1 or TP2 of the first cylinder or the second cylinder as described above, the routine proceeds to step 107, where the warm-up increase correction coefficient corresponding to the output signal (cooling water temperature) of the water temperature sensor 31 Various correction coefficients K, such as an increase correction coefficient and an intake temperature correction coefficient corresponding to an output signal (intake temperature) of the intake temperature sensor 14, are calculated.
[0026]
Thereafter, in step 108, a response delay time of the fuel injection valve 18, that is, an invalid injection time TV is calculated based on the power supply voltage. In the next step 109, the pulse of the injection pulse output to the fuel injection valve 18 of each cylinder is calculated. The width of the final injection time TAU1 or TAU2 is calculated. In step 109, if the first cylinder basic injection time TP1 has been calculated in step 104, the first cylinder final injection time is calculated using the first cylinder basic injection time TP1, various correction coefficients K, and the invalid injection time TV. The injection time TAU1 is calculated by the following equation.
TAU1 = TP1 × K + TV
[0027]
On the other hand, if the second cylinder basic injection time TP2 has been calculated in step 106, then in step 109, the second cylinder basic injection time TP2, various correction coefficients K, and the invalid injection time TV are used to determine the second cylinder final injection time TP2. The injection time TAU2 is calculated by the following equation.
TAU2 = TP2 × K + TV
[0028]
In this case, the processing of steps 103 → 104 → 107 → 108 → 109 functions as the first cylinder injection amount calculating means described in the claims, and the processing of steps 105 → 106 → 107 → 108 → 109 is described in the claims. It functions as the second cylinder injection amount calculation means.
[0029]
In the fuel injection amount calculation method described above, when calculating the fuel injection amount (fuel injection time) of each of the first and second cylinders, the influence of the intake pressure of the intake manifold 12 on the opposite side is taken into account, The fuel injection amount can be calculated with high accuracy, the deviation of the air-fuel ratio can be reduced, and the reduction of exhaust emission and improvement of drivability can be realized. In addition, only one intake pressure sensor 17 is required, and it is possible to satisfy the demands of reducing the number of parts, reducing the number of assembling steps, and reducing the cost.
[0030]
[Embodiment (2)]
In the above embodiment (1), the fuel injection amount of each of the first and second cylinders is calculated by the same method in the full load range. However, according to the test results of the present inventors, the intake air on the opposite side is calculated. It has been found that the influence of the intake pressure of the manifold 12 is large in a low load region, and that the influence of the intake pressure of the intake manifold 12 on the opposite side is relatively small in a medium load region and a high load region.
[0031]
Therefore, in the embodiment (2) of the present invention shown in FIGS. 7 to 9, the calculation of the fuel injection amount (final injection time TAU1, TAU2) of each of the first and second cylinders by the method of the embodiment (1). Is performed only in the low load range, and in the medium load / high load range, the final injection time TAU1 of the first cylinder is calculated using the bottom pressure P1 of the average intake pressure reduced by the intake stroke on the first cylinder side. The final injection time TAU2 of the second cylinder is calculated using the bottom pressure P2 of the average intake pressure reduced by the intake stroke of the two cylinders.
[0032]
Hereinafter, processing contents of each routine of FIGS. 7 to 9 executed in the present embodiment (2) will be described. The fuel injection control routine of FIG. 7 is executed immediately before the fuel injection timing of the first cylinder and the second cylinder. When this routine is started, first, in steps 201 to 203, the engine speed NE, the atmospheric pressure Pa, and the throttle opening VTA are read. Thereafter, in step 204, it is determined whether the operating state of the engine 11 is in the low load region. This determination is made, for example, if the engine speed NE is equal to or lower than a predetermined engine speed and the throttle opening VTA is equal to or lower than the predetermined opening, it is determined that the engine is in a low load area. I do. In addition, instead of the throttle opening VTA, an average intake pressure detected by the intake pressure sensor 17 may be used as a parameter for load determination, and, of course, both the throttle opening VTA and the average intake pressure may be used. good.
[0033]
If it is determined in step 203 that the region is in the low load region, the process proceeds to step 205, where a low load basic injection time calculation routine shown in FIG. 8 is executed. In the low-load basic injection time calculation routine, the intake of the second cylinder is performed when the first cylinder basic injection time TP1 is calculated by the same processing as in steps 102 to 106 in FIG. The first cylinder basic injection time TP1 is calculated based on the engine pressure NE and the pressure difference between the bottom pressure P2 of the average intake pressure and the atmospheric pressure Pa reduced by the stroke (step 301 → 302 → 303), and the second cylinder When calculating the basic injection time TP2, the second cylinder basic injection time TP2 is based on the differential pressure between the bottom pressure P1 of the average intake pressure and the atmospheric pressure Pa, which is reduced by the intake stroke on the first cylinder side, and the engine speed NE. Is calculated (step 301 → 304 → 305).
[0034]
On the other hand, if it is determined in step 206 in FIG. 7 that the region is a medium-load / high-load region, the process proceeds to step 206 to execute a medium-load / high-load basic injection time calculation routine shown in FIG. In the medium load / high load basic injection time calculation routine, the bottom pressure of the average intake pressure used for calculating the basic injection time is opposite to that at low load, and the first cylinder basic injection time TP1 is calculated when calculating the first cylinder basic injection time TP1. The first cylinder basic injection time TP1 is calculated based on the engine pressure NE and the pressure difference between the bottom pressure P1 of the average intake pressure and the atmospheric pressure Pa, which decrease due to the intake stroke on the cylinder side, and the engine speed NE (steps 311 → 312 → 313). When calculating the basic injection time TP2 for the second cylinder, the second cylinder based on the differential pressure between the bottom pressure P2 of the average intake pressure and the atmospheric pressure Pa, which is reduced by the intake stroke on the second cylinder side, and the engine speed NE. The basic injection time TP2 is calculated (steps 311 → 314 → 315).
[0035]
After calculating the basic injection time TP1 or TP2 of the first cylinder or the second cylinder as described above, the process returns to step 207 of FIG. 7, and after calculating the various correction coefficients K as in the embodiment (1), The invalid injection time TV is calculated (step 208), and the final injection time TAU1 or TAU2, which is the pulse width of the injection pulse output to the fuel injection valve 18 of each cylinder, is calculated (step 209).
In the embodiment (2) described above, the same effect as in the embodiment (1) can be obtained.
[0036]
[Embodiment (3)]
In the above embodiment (2), the basic injection time of each cylinder is calculated from the average intake pressure and the engine speed even in the medium load / high load region. However, in the medium load / high load region, the throttle opening and the engine speed are calculated. The basic injection time of each cylinder may be calculated based on the number. In other words, in the medium-load / high-load region, the operating state determined by the throttle opening and the engine speed and the intake air amount are well-correlated, so that the throttle opening and the engine speed at medium-load / high load are good. By calculating the basic injection time of each cylinder based on the above, it is possible to calculate an appropriate fuel injection amount corresponding to the actual intake air amount of each cylinder, and to calculate the deviation of the air-fuel ratio in the medium load / high load region. Can be reduced.
[0037]
FIG. 10 shows a routine for calculating the basic injection time at medium load / high load executed in the embodiment (3) that embodies this. Except for the routine for calculating the basic injection time at medium load / high load, the routine is the same as that of the above-described embodiment (2). Therefore, also in this embodiment (3), each routine of FIGS. In this embodiment (3), if it is determined in step 206 in FIG. 7 that the vehicle is in the medium load / high load region, the routine executes the medium injection / high load basic injection time calculation routine in FIG. The basic injection times TP1 and TP2 for each cylinder are calculated based on the engine speed NE and the engine speed NE (step 321). In this calculation method, a relationship between the throttle opening degree VTA, the engine speed NE, and the basic injection time TP1 is obtained in advance by an experiment or simulation, and a two-dimensional map of the basic injection time is created. The basic injection time TP1 corresponding to the throttle opening VTA and the engine speed NE at that time is calculated (in this case, TP2 = TP1).
[0038]
In the embodiment (1), the atmospheric pressure is detected by the atmospheric pressure sensor 32. However, the output value of the intake pressure sensor 17 immediately after the start of the engine or the output value of the intake pressure sensor 17 after a predetermined time has elapsed since the engine was stopped. The atmospheric pressure Pa may be taken into the engine control circuit 35 and stored in a backup RAM (not shown), and the stored value may be used as the atmospheric pressure Pa 2. In this case, the atmospheric pressure sensor 32 becomes unnecessary.
[0039]
In addition, the present invention is not limited to two-wheeled vehicles, but can be applied to four-wheeled vehicles.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an entire engine control system showing an embodiment (1) of the present invention; FIG. 2 is a schematic diagram of an intake system; FIG. 3 is an operation process of each cylinder and an actual intake pressure of each cylinder; FIG. 4 is a flowchart showing a flow of a fuel injection control routine executed in the embodiment (1). FIG. 5 is a conceptual diagram showing a first cylinder basic injection time map. FIG. 6 is a diagram conceptually showing a second cylinder basic injection time map. FIG. 7 is a flowchart showing a flow of a fuel injection control routine executed in an embodiment (2). FIG. 8 is an embodiment (2). FIG. 9 is a flowchart showing the flow of a low-load basic injection time calculation routine executed in the embodiment. FIG. 9 is a flowchart showing the processing flow of a medium-load / high load basic injection time calculation routine executed in the embodiment (2). 10) Real Embodiment (3) Flowchart [EXPLANATION OF SYMBOLS] showing the flow of processing load and high load basic injection time calculation routine in running on
11: engine (internal combustion engine), 12: intake manifold, 15: throttle valve, 16: throttle opening sensor (throttle opening detection means), 17: intake pressure sensor (intake pressure detection means), 18: fuel injection valve, 29: engine speed sensor (rotation speed detecting means), 32: atmospheric pressure sensor (atmospheric pressure detecting means), 34: communication pipe, 35 ... engine control circuit (first cylinder injection amount calculating means, first cylinder injection amount calculation) Means), 45 ... ROM.

Claims (3)

In a fuel injection control device for controlling a fuel injection amount of each cylinder of a two-cylinder internal combustion engine,
Rotation speed detection means for detecting the rotation speed of the internal combustion engine,
Atmospheric pressure detecting means for detecting atmospheric pressure;
Intake pressure detecting means for detecting the average intake pressure of both cylinders through a communication pipe communicating with the intake manifolds of both cylinders;
When calculating the fuel injection amount of the first cylinder, the fuel injection amount of the first cylinder is calculated based on the pressure difference between the average intake pressure and the atmospheric pressure, which decrease due to the intake stroke of the second cylinder, and the internal combustion engine speed. A first cylinder injection amount calculating means,
When calculating the fuel injection amount of the second cylinder, the fuel injection amount of the second cylinder is calculated based on the differential pressure between the average intake pressure and the atmospheric pressure, which decrease due to the intake stroke of the first cylinder, and the internal combustion engine speed. A fuel injection control device for an internal combustion engine, comprising: The first cylinder injection amount calculation means calculates the fuel injection amount of the first cylinder using the average intake pressure reduced by the intake stroke of the second cylinder only in a low load region, and in other load regions. A fuel injection amount of the first cylinder is calculated using an average intake pressure that is reduced by an intake stroke of the first cylinder,
The second cylinder injection amount calculation means calculates the fuel injection amount of the second cylinder using the average intake pressure reduced by the intake stroke of the first cylinder only in a low load region, and in other load regions. 2. The fuel injection control device for an internal combustion engine according to claim 1, wherein the fuel injection amount of the second cylinder is calculated using an average intake pressure reduced by an intake stroke of the second cylinder. A throttle opening detecting means for detecting a throttle opening;
The first cylinder injection amount calculation means calculates the fuel injection amount of the first cylinder using the average intake pressure reduced by the intake stroke of the second cylinder only in a low load region, and in other load regions. Calculating the fuel injection amount of the first cylinder based on the throttle opening and the internal combustion engine speed;
The second cylinder injection amount calculation means calculates the fuel injection amount of the second cylinder using the average intake pressure reduced by the intake stroke of the first cylinder only in a low load region, and in other load regions. 2. The fuel injection control device for an internal combustion engine according to claim 1, wherein a fuel injection amount of the second cylinder is calculated based on a throttle opening and an internal combustion engine speed.

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