JPS6157458B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection control device for an internal combustion engine (hereinafter referred to as an engine), and particularly relates to a single-point fuel injection control device having one fuel injection valve for a plurality of cylinders. .

Conventionally, a fuel injection control device for a gasoline engine generally has a fuel injection valve installed in each cylinder to individually supply fuel to a plurality of cylinders. This type of multi-point fuel injection system is effective in reducing the difference in the amount of fuel supplied to each cylinder and increasing the responsiveness of fuel supply during acceleration/deceleration operation, but it requires as many fuel injection valves as there are cylinders. As a result, electrical wiring and fuel piping became complicated, and maintenance and inspection became complicated, leading to high costs.

As a means to eliminate the drawbacks of such multi-point fuel injection systems, one fuel injection valve is provided in the intake pipe gathering part of the engine to inject fuel in the form of fine particles.
A single-point fuel injection system has come into use in which a mixture of fuel mist and intake air is distributed to each cylinder.
However, this single-point fuel injection system has a drawback that the air-fuel ratio of the air-fuel mixture supplied to each cylinder is different, that is, the distribution ratio is poor compared to the multi-point fuel injection system.

A fuel injection control device disclosed in Japanese Patent Application Laid-open No. 115411/1983 is known as a means for solving these drawbacks. However, this fuel injection control device attempts to distribute fuel uniformly by changing the fuel injection timing based on the crank angle of each cylinder, and has a limit on the amount of fuel injected at one time, which limits the accuracy of fuel control. No consideration was given to improving the performance.

An object of the present invention is to improve the fuel control accuracy of an internal combustion engine by increasing the amount of fuel injected at one time, as well as improving the fuel distribution ratio in this single-point fuel injection system. To provide fuel injection equipment.

In order to achieve such an objective, the present invention
An internal combustion engine that performs the intake stroke in the order of the first, third, fourth, and second cylinders, and distributes the air-fuel mixture to each cylinder by injecting fuel at a single point with one fuel injection valve for each of the four cylinders. In the fuel injection control device, the first and second cylinders are set as a first group, and the third and fourth cylinders are set as a second group, and the mixture is branched to each group and further branched to each cylinder. At the same time, means is provided for determining whether the engine rotational speed is high or low, and by this means, fuel is supplied synchronously to the first and fourth cylinders when the engine is rotating at a low speed, and when the engine is rotating at a high speed, the fuel is supplied to the first and fourth cylinders in synchronization. A means for supplying fuel to the third cylinder in synchronization is provided.

Incidentally, Japanese Patent Application Laid-Open No. 50-90826 discloses controlling fuel injection timing.
In this known example, each shilling was provided with an injector, so there was no interval between distributions.

Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

FIG. 1 shows a control device for the entire engine system. In the figure, intake air passes through an air cleaner 2, a throttle chamber 4, an intake pipe 6, and is supplied to a cylinder 8. The gas burned in the cylinder 8 passes through the exhaust pipe 10 from the cylinder 8 and is discharged into the atmosphere.

The throttle chamber 4 is provided with a fuel injection valve 12 (hereinafter referred to as the injector 12) for injecting fuel, and the fuel injected from the injector 12 is atomized within the air passage of the throttle chamber 4. is mixed with intake air to form a mixture, and this mixture passes through the intake pipe 6 and enters the intake valve 2.
When the valve 0 is opened, the fuel is supplied to the combustion chamber of the cylinder 8.

A throttle valve 14 is located near the outlet of the injector 12.
16 are provided. The throttle valve 14 is configured to mechanically interlock with the accelerator pedal and is driven by the driver. On the other hand, the throttle valve 16 is arranged so as to be driven by the diaphragm 18, and is fully closed when the air flow rate is small.As the air flow rate increases, the negative pressure on the diaphragm 18 increases, so that the throttle valve 16 It begins to open and suppresses the increase in inhalation resistance.

An air passage 22 is provided upstream of the throttle valves 14 and 16 of the throttle chamber 4.
2 is an electric heating element 2 that constitutes an air flow rate detector.
4 is arranged, and a periodic electric signal that changes according to the air flow rate determined from the relationship between the air flow rate and the amount of heat transfer of the heating element 24 is extracted. Since the heating element 24 is provided within the air passage 22, it is protected from high-temperature gas generated when the cylinder 8 backfires, and is also protected from being contaminated by dust in the intake air. The outlet of the air passage 22 is opened near the narrowest part of the bench lily, and the inlet thereof is opened on the upstream side of the bench lily.

Fuel supplied to the injector 12 is supplied from a fuel tank 30 to a fuel pressure regulator 38 via a fuel pump 32, a fuel damper 34, and a filter 36. On the other hand, pressurized fuel is supplied from the fuel pressure regulator 38 to the injector 12 via a pipe 40.
From the fuel pressure regulator 38 to the fuel tank 3 so that the difference between the pressure in the intake pipe 6 where fuel is injected from the fuel tank 3 and the fuel pressure to the injector 12 is always constant.
Fuel is returned to zero via a return pipe 42.

The air-fuel mixture taken in from the intake valve 20 is transferred to the piston 5.
0 and is combusted by a spark from the ignition plug 52, and this combustion is converted into kinetic energy. The cylinder 8 is cooled by cooling water 54, and the temperature of this cooling water is measured by a water temperature sensor 56, and this measured value is used as the engine temperature. A high voltage is supplied to the spark plug 52 from an ignition coil 58 in accordance with the ignition timing.

Further, the crankshaft (not shown) is provided with a crank angle sensor that outputs a reference angle signal and a position signal at every reference crank angle and every fixed angle (for example, 0.5 degrees) according to the rotation of the engine.
The output of this crank angle sensor is 60, and the water temperature sensor is 5.
6 output 56A and electrical signal 2 from heating element 24
The signal 4A is input to a control circuit 70 consisting of a microcomputer or the like, where it is subjected to arithmetic processing, and the output of the control circuit 70 drives the injector 12 and the ignition coil 58.

The operation of the engine described above will be explained with reference to FIG. 2. FIG. 2A shows the timing of fuel injection from the injector in a four-cylinder engine. The horizontal axis is the rotation angle of the engine crankshaft, and the intake stroke of each cylinder is indicated by hatching. As is clear from the figure, the crank angle
There is an intake stroke every 180 degrees, 0 degrees to 180 degrees is the 1st cylinder, 180 degrees to 360 degrees is the 3rd cylinder, 360 degrees to 540 degrees is the 4th cylinder, 540 degrees to 720 degrees Between degrees is the second cylinder.

As shown in FIG. 2B, a reference crank angle pulse is generated every 180 degrees of the crank angle, the injector 12 is opened based on this pulse, and the calculation is processed by the control circuit 70 based on the already measured data. Based on the result, the opening time of the injector 12 is determined. The fuel injection time, which is the valve opening time of the injector 12, is shown in FIG. 2C.

Next, the control circuit 70 will be explained based on FIG. 3. FIG. 3 shows a concrete block of the control circuit 70, and in the figure, the input signals can be roughly classified into three types. That is, first, the output 24A of the heating element 24 that detects the amount of intake air;
Output 56 of a sensor 56 that detects engine cooling water
There is an analog input sent from A, etc. These analog inputs are multiplexed (MPX)
) 100, the output of each sensor is selected in parts from time to time, and sent to an analog-to-digital converter (denoted as ADC) 102.
It is converted into a digital value at 102. The second information is input as an on/off signal, which is, for example, a signal θ representing the fully closed state of a throttle valve.
Switch 10 that operates in conjunction with the throttle valve at TH
There is a signal 104A sent from 4. This signal can be handled as a 1-bit digital signal.

Furthermore, the third possible input signal is a signal input as a pulse train, such as a reference crank angle signal (hereinafter referred to as CRP) or a position pulse signal (hereinafter referred to as CPP).
These signals are sent from 06.

CRP is output every 180 degrees of crank angle for 4 cylinders, every 120 degrees for 6 cylinders, and 90 degrees for 8 cylinders.
output every time. CPP is, for example, the crank angle
Output every 0.5 degrees.

The CPU 108 is a central processing unit that performs digital arithmetic processing, and the ROM1
10 is a storage element for storing control programs and fixed data, and RAM 112 is a readable and writable storage element. The input/output interface circuit 114 inputs the input signal to the ADC1.
02 and sensors 104 and 106, and sends the signal to the CPU 108. Also, CPU10
The signal from 8 is sent to the injector 12 and the ignition coil 58 as a signal INJ or IGN. Note that voltage is applied from the power supply terminal 116 to each circuit and element constituting the control circuit 70, but their description is omitted in the drawing. Further, the injector 12 and the ignition coil 58 are each provided with an electromagnetic coil for driving the valve and a primary coil for accumulating electromagnetic energy, one end of which is connected to the power supply terminal 116, and the other end of the coil. It is connected to the input/output interface circuit 114, and the current flowing into the injector 12 and the ignition coil 58 is controlled. Note that 162 is a data bus, 164 is a control bus, and 166 is an address bus.

Next, the fuel injection control device of the present invention will be explained. The fuel injection control device of the present invention is configured as a part of the control circuit 70 shown in FIG. 3 described above. That is, the CPU 108 performs digital arithmetic processing for fuel injection control, and the ROM 110 stores a fuel injection control program and optimum injection timing characteristic data necessary for executing the program. Here, the optimal injection timing characteristic is an injection timing characteristic that is optimal for improving the distribution ratio that allows the injection fuel corresponding to the operating state of the engine to be supplied to the engine in a well-distributed manner. This injection timing characteristic data is stored in the ROM 110 so that it can be retrieved by map search based on the input of the operating state.

In addition, the input/output interface circuit 114 takes in the operating state of the engine, ie, an air flow velocity signal from the heating element 24, and sends it to the CPU 108.
A control signal INJ consisting of a pulse having injection timing and injection time for improving the fuel distribution ratio calculated by the CPU 108 is output to the injector 12. That is, the CPU 108 uses a map search to find, for example, the optimum injection timing corresponding to the required amount of injected fuel from the ROM 110 based on the engine operating state signal. Here, the operating state of the engine, which is a prerequisite for determining the injection timing, is data obtained from, for example, the intake flow rate, that is, the air flow rate AF, the cooling water temperature TW, and the like. Therefore, the valve opening timing of the injector 12 is the injection start timing, and the valve closing timing is the end timing of the injection time.

In the case of this embodiment, the injection timing characteristic data necessary to improve the distribution ratio is obtained from the ROM 110 by map search, but instead of this, the optimum injection timing may be obtained by calculation from the required fuel injection amount. The effect of this can be obtained.

The injection start timing and injection time (injector 12
The control operation with respect to the valve opening period) will be explained.

Figure 4 is a diagram showing the relationship between the crank angle of the engine in Figure 1 and the intake flow velocity at the bench lily.
The engine speed is shown as a parameter.
The solid line a shows the state when the engine rotates at low speed, and the dashed line b shows the state when the engine rotates at high speed. In this way, the flow rate of intake air changes depending on the engine speed and crank angle, and the amount of intake air in one intake stroke is proportional to the area of one mountain. Therefore, the intake flow velocity at a constant crank angle of the engine is detected by the heating element 24, and the output of the heating element 24 and the engine rotation speed detected by the crank angle sensor 106 are sent from the input/output interface circuit 114 to the CPU 108. input. On the other hand, the ROM 110 stores in advance the optimal fuel injection period for improving the fuel distribution ratio corresponding to two variables, intake flow rate and engine speed, so the distribution ratio can be improved according to the injection control program. The optimum injection timing and injection time are determined, and the opening/closing control of the injector 12 is performed based on these.

Note that the intake flow velocity signal at a constant crank angle is likely to change due to irregularities in the opening/closing timing of the engine's intake and exhaust valves, fluctuations in the internal pressure of the exhaust pipe 10, etc.
The oxygen ratio in the exhaust gas may be detected by an exhaust gas sensor (not shown) provided in the exhaust pipe 10, and the injection timing and injection time may be corrected based on this detection signal.

Next, determination of fuel injection start timing and injection time will be explained. The first thing to consider is that if the fuel is simply injected in synchronization with the crank angle, the intake flow velocity will fluctuate as shown in Figure 4, so some of the fuel injected into the intake pipe 6 will The air-fuel mixture will not be able to ride the intake air flow and will form a flow along the wall surface, which may cause the air-fuel mixture sucked into each cylinder to become non-uniform. Therefore, in order to avoid this, the injection should be performed at a time when the air flow velocity is high. This requires control similar to ignition advance control that adjusts the ignition timing of each cylinder, and this has been confirmed through experiments. In other words, it has become clear that by controlling the injection timing, uniform fuel distribution can be achieved over the entire operating range of the engine.

Figure 5 is a diagram showing the relationship between the crank angle and fuel injection speed of a 4-stroke, 4-cylinder, single-point fuel injection engine, where the intake order is 1st, 3rd, 4th, and 2nd cylinders per crank revolution. This is based on experimental values obtained when fuel injection is performed twice. That is, the crank rotates twice during one intake stroke of the four cylinders, but fuel injection is performed when the first and fourth cylinders are in the intake stroke.

FIG. 5a shows a case where fuel injection is started at the beginning of the intake stroke of the first and fourth cylinders. As is clear from the shaded area ratio in the figure, a large amount of fuel is supplied to the first and fourth cylinders, and only a small amount of fuel is supplied to the third and second cylinders. However,
In FIG. 5b, fuel is injected midway between the intake strokes of the first and fourth cylinders, so the amount of fuel supplied to each cylinder is approximately equal. That is, by adjusting the injection start timing, it is possible to equalize the fuel distribution to each cylinder.

The above is a case where the engine speed is relatively low, but as the engine speed increases, a large amount of fuel is required, so the injection period (time width) increases. Therefore, the fuel injected at one time flows over the intake strokes of multiple cylinders. Figure 5c shows a case where fuel injection is started at the beginning of the intake stroke of the first and fourth cylinders during such high-speed operation.
At first glance, it can be seen that the fuel distribution among the cylinders is uneven. In FIG. 5d, as in FIG. 5b, the fuel injection start timing is delayed, so that the fuel is evenly distributed to each cylinder. In the figure, the broken line shows the distribution of fuel introduced at one time, and the solid line shows the fuel distribution including the overlapping portion.

This shows that by adjusting the timing of starting fuel injection to the first and fourth cylinders, it is possible to distribute fuel equally to each cylinder over the entire operating range of the engine.

FIG. 6 is a diagram simulating the flow of fuel in the intake pipe 2. In this case as well, the order of the intake strokes is first,
The order is the third, fourth, and second cylinders. FIG. 6a shows a case where fuel is injected during the intake stroke of the first and fourth cylinders, and FIG. 6b shows a case where fuel is injected during the intake stroke of the second and third cylinders. That is, since each cylinder is actually separated into the second group and communicated with each other as shown in the figure, we are trying to examine which one is more reasonable.

The intake strokes of this four-cylinder engine are the first, third,
Since the injection is performed in the order of the fourth and second cylinders, in the case of FIG. 6a, fuel is injected in synchronization with the intake strokes of the first and fourth cylinders. A portion of the fuel injected during the intake stroke of the first cylinder also flows into the third cylinder. Next, a portion of the fuel injected during the intake stroke of the fourth cylinder also flows into the second cylinder. That is, the fuel (more precisely, the air-fuel mixture) is divided at the entrance of the intake pipe 2. However, in the case of Figure 2b, part of the fuel injected during the intake stroke of the second cylinder also flows to the first cylinder, and part of the fuel injected during the intake stroke of the third cylinder also flows to the fourth cylinder. , division will be performed between adjacent cylinders.

When the air-fuel mixture is reversely split at the branch portion of the intake pipe 2 as shown in FIG. 6a, this is suitable when the engine speed is relatively low, and sufficient steam time for the fuel can be ensured. On the other hand, when the air-fuel mixture is divided between adjacent cylinders as shown in FIG. 6b, this is an effective fuel injection pattern when the engine is operated at high speed where fuel followability is a problem. To summarize the above, it is best to synchronize the fuel injection pattern with the intake strokes of the 1st and 4th cylinders depending on the driving conditions, but it is best to select whether to synchronize it with the intake strokes of the 2nd and 3rd cylinders. This is the method.

Such a selection can be made when the engine speed reaches a predetermined number of rotations or higher, but it is also possible to make the selection when the intake pipe pressure or throttle valve opening degree related to the engine speed reaches a predetermined value. You can also do it. Alternatively, the detection signal of the electric heating element 24 for detecting the amount of intake air shown in FIG. 1 can also be used. By comparing these detected values with setting switching values stored in advance in the control device 17, the high/low operating range is determined, and the injection pattern is changed from the 1st and 4th cylinder type to the 2nd and 3rd cylinder type. can be done. However, the distribution characteristics also differ depending on the shape of the intake pipe 6, the shape of the combustion chamber of each cylinder, the shape of the intake valve, etc., and must be determined taking these into consideration. As mentioned above, in the four-cylinder engine of this embodiment, the intake stroke is performed in the order of the first, third, fourth, and second cylinders, and if the order of the cylinders changes, the I have to decide. Figure 7 is a diagram showing the relationship between the crank angle and the fuel concentration of the mixture for a 4-stroke, 4-cylinder, single-point fuel injection engine. It is changed from the stage of starting injection to synchronizing with the ignition explosion stroke of the second and third cylinders. That is, since the ignition explosion stroke and the intake stroke shown in FIG. 5 differ by 180 degrees in terms of crank angle, the density of the air-fuel mixture is opposite to the relationship shown in FIG. The solid line f1 is the experimental result showing the mixture concentration in the first cylinder, the thick broken line f2 is the second cylinder, the dashed line f3 is the third cylinder, and the thin broken line f4 is the fourth cylinder.
~There are two points where the air-fuel mixture concentrations supplied to the fourth cylinder are almost the same, and these are indicated by arrows. However, the reason why the two locations are different and no periodicity is observed is due to the difference in shape and length of the intake pipe that distributes fuel and the order of the intake stroke, etc., as explained in Figure 6. It is.

In addition, the crank angle at which the mixture concentration between each cylinder matches as described above is unique to the engine and is determined by the shape of the engine's combustion chamber, the shape of the intake pipe, the amount of overlap between the intake and exhaust valves, the engine speed, the pressure inside the intake pipe, etc. belongs to. Therefore, such a crank angle is determined in advance by experiment and the control circuit 70 shown in FIG.
It is stored in the ROM 110, and when the actual operating conditions reach this crank angle, it is called from the ROM 110 to determine the injection start timing.

Next, an injection control circuit for setting the fuel injection start timing and injection time in the injector 12 will be explained based on FIGS. 8 and 9. The injection control circuit shown in FIG. 8 is provided in the input/output interface circuit 114 in the control circuit 70 shown in FIG. 3 described above.

In FIG. 8, an address decoder 202 is connected to the CPU 108 via an address bus 166, and by inputting an address signal output from the CPU 108 to the address decoder 202, an injection start register 204 and an injection time register 206 are specified. It is becoming more and more common. Injection start register 204 and injection time register 206
is connected to the CPU 108 via a data bus 162,
The injection start register 204 is set with the optimum injection timing to improve the distribution rate determined by the CPU 108 based on the operating conditions, and the injection time register 2 is set with the injection start register 204.
In 06, an injection time for a predetermined amount of fuel to be injected determined based on the operating conditions is set.

On the other hand, the initial pulse generation circuit 208 is a circuit for generating an initial pulse to create a reference time serving as a reference for the injection start timing, and is a circuit shown in FIG. 9C from the CRP shown in FIG. 9A input to the input terminal 210. Create an initial pulse (hereinafter referred to as INTL). This initial pulse is the signal corresponding to the top dead center of the piston in the cylinder.

The injection start timer 212 counts the CPP shown in FIG. 9B input to the input terminal 214 and calculates the CPP shown in FIG. 9D.
This timer 21 is a circuit that generates the time signal E shown in
2, the output of the initial pulse generation circuit 208 is input as a reset signal.

The output E of the injection start timer 212 is input to the comparator 216 together with the output F of the injection start register 204, and the output E of the injection start register 204 is input to the comparator 216 as shown in F in FIG.
is set as a comparison reference value. Therefore, while the count output E of the injection start timer 212 exceeds the output E of the injection start register 204, the comparator 216
generates the output pulse shown in FIG. 9G. This output G is the RS that creates one condition that determines the injection time.
It is input to a set terminal S of a flip-flop circuit 218 and an RS flip-flop circuit 220 that outputs control pulses for injection start timing and injection time. In response to this input G, the RS flip-flop circuit 220 outputs a high level output (hereinafter referred to as H output) shown in FIG. 9N from a terminal Q. This H
The leading edge of the output is the injection start time, and the opening operation of the drive solenoid of the injector 12 starts.

Further, the RS flip-flop circuit 218 generates an H output from the terminal Q in response to the set input, and generation of this H output becomes the start of the injection time. This H output is applied to the AND gate 224 along with the clock pulse shown in FIG. 9I of the clock pulse generating circuit 222.
When both inputs are satisfied, the AND gate 224 sends the clock pulse output I to the injection time timer 22.
Enter 6. Note that the RS flip-flop circuit 218 receives the output INTL of the initial pulse generation circuit 208.
will be reset.

The injection time timer 226 counts the clock pulses shown in FIG. 9I and generates the time signal K shown in FIG. 9J.
This is a circuit that generates a pulse generator, and is placed in a reset state by the output of the initial pulse generator circuit 208. The output K of the injection time timer 226 is input to the comparator 228 together with the output of the injection time register 206, that is, the output L shown in FIG.
8, the output L of the injection time register 206 is set as a comparison reference value. Therefore, when the count output K of the injection time timer 226 exceeds the output L of the injection time register 206, the comparator 228
generates the output pulse shown in FIG. 9M. This output M is input to the reset terminal R of the RS flip-flop circuit 220, whereby the RS flip-flop 220 is reset. That is, the RS flip-flop 220 generates an H output based on the setting value of the injection start register 204,
The duration of the H output is until the end of the set value of the injection time register 206, as shown in FIG. 9N.
Output terminal 23 of RS flip-flop circuit 220
The H output generated at 0 is the valve opening time of the injector 12 corresponding to the optimal fuel injection start timing and injection time to improve the fuel distribution ratio.

The output pulse shown in FIG. 9N is input to the base of a drive transistor of an injector drive circuit (not shown), and the injector 12 opens for fuel injection based on the ON operation of the transistor.

As described above, the fuel injection timing and injection time sufficient to improve the fuel distribution ratio determined by the CPU 108 are stored in the injection start register 204 and injection time register 208 provided correspondingly. is set, and based on this setting, the count outputs of the injection start timer 212 and the injection time timer 226 determine the comparator 21 provided respectively.
Obtain the time signal or angle signal from 6,228,
As a result, an injection control signal is sent from the output terminal 230 of the RS flip-flop circuit 220 that has the optimum injection timing at the leading edge portion and the injection time is determined by the duty.
INJ is created. The injection control signal INJ generated in this way always corresponds to the operating state and is controlled with enough fuel injection timing and injection time to improve the fuel distribution ratio required by the CPU 108.
Valve opening control of the injector 12 is always necessary to improve the distribution ratio optimally.

As explained above, according to the present invention, the optimal injection timing for improving the fuel distribution ratio according to the operating conditions in single-point fuel injection is determined, and the predetermined fuel can be injected from this timing. Fuel distribution is improved and engine efficiency can be increased.

Furthermore, since fuel for two cylinders is injected at once, by lengthening the fuel injection interval, the amount of fuel injected at one time can be increased, and fuel control accuracy can be improved.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the control device for the entire engine system, Figure 2 is a time chart showing the operation of the engine, Figure 3 is a block diagram showing the specific configuration of the engine control circuit, and Figure 4 is the engine crank. Graphs showing the relationship between crank angle and intake flow rate, Figures 5a to 5d are graphs showing the relationship between crank angle and fuel injection speed, Figures 6a and b are explanatory diagrams showing the flow of fuel in the intake pipe, FIG. 7 is a graph showing the relationship between crank angle and mixture concentration, FIG. 8 is a block diagram showing the specific configuration of the output circuit of the fuel injection control device for an internal combustion engine of the present invention, and FIG. FIG. 12...Injector, 70...Control circuit, 1
08...CPU, 110...ROM, 112...
RAM, 114...input/output interface circuit,
204...Register for injection start, 208...Register for injection time, 212...Timer for injection start,
226...Timer for injection time.

Claims (1)

[Claims] 1 Internal combustion in which fuel is single-point injected with one fuel injection valve to four cylinders in which the intake stroke is performed in the order of the first, third, fourth, and second cylinders, and the mixture is distributed to each cylinder. In a fuel injection control device for an engine, the first and second cylinders are set as a first group, the third and fourth cylinders are set as a second group, and the mixture is branched into each group, and the mixture is further branched and supplied to each cylinder. In addition, a means for determining the high or low speed of the engine is provided, and by this means, fuel is supplied synchronously during the intake stroke of each of the first and fourth cylinders when the engine is rotating at low speed, and the engine is A fuel injection control device for an internal combustion engine, comprising means for supplying fuel synchronously during the intake stroke of each of the second and third cylinders during high-speed rotation.