JPS647226Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a fuel injection control device for an internal combustion engine.

It is equipped with a negative pressure sensor that detects the negative pressure in the intake passage and a rotation speed sensor that detects the engine speed, and the fuel injection time is determined based on the output signals of these negative pressure sensors and the rotation speed sensor. Internal combustion engines are known. In such an internal combustion engine, the relationship between negative pressure, engine speed, and fuel injection time is stored in the ROM in advance in the form of a map, and the fuel injection time is determined based on the data stored in this ROM. I have to.

By the way, recently it has become necessary to make the air-fuel ratio as lean as possible in order to improve fuel consumption.
By improving the combustion chamber and intake system, the air-fuel ratio can be improved.
It is becoming possible to use ultra-lean mixtures of 20 or more. However, even if such an ultra-lean mixture can be used, the operating range in which it can be used is limited, and during high-load engine operation, it is necessary to use a rich mixture to ensure high engine output. .
Therefore, in order to improve the fuel consumption rate as much as possible while ensuring high engine output, it is necessary to gradually change the air-fuel mixture from an ultra-lean air-fuel mixture to a rich air-fuel mixture as the engine load increases.

However, when the engine is operated under high load, the negative pressure changes only slightly even if the throttle valve opening changes. Therefore, if the fuel injection time is determined based on negative pressure and engine speed as described above, the air-fuel ratio of the mixture will gradually change from ultra-lean to rich in response to slight changes in negative pressure. Therefore, there is a problem in that fine control of the air-fuel ratio is practically difficult.

An object of the present invention is to provide a fuel injection control device that can finely control the air-fuel ratio even during high-load engine operation.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, 1 is a cylinder block;
2 is a piston that reciprocates within the cylinder block 1, 3 is a cylinder head fixed on the cylinder block 1, and 4 is a piston 2 and a cylinder head 3.
5 is an intake valve, 6 is an intake port formed in the cylinder head 3, 7 is a fuel injection valve arranged in the intake port 6, 8 is an exhaust valve, and 9 is an exhaust port. Show each. Although not shown in the figure, an ignition plug is disposed within the combustion chamber 4.

As shown in FIGS. 1 and 2, the fuel injection valve 7 has an injection angle of θ, and the injection axis a of the fuel injection valve 7 passes through the center of the back surface of the intake valve 5.
Now, the radius of the back surface of the intake valve 5, that is, the intake valve 5
If the radius of the intake port 6 around the bulk part is R, and the distance from the back surface of the intake valve 5 to the nozzle hole 10 of the fuel injection valve 7 is l, then the fuel injected from the fuel injection valve 7 will flow into the intake valve 5. In order to directly reach the entire area on the back surface of the umbrella, the relationship R=l·tanθ/2 must be satisfied. Therefore, the fuel injection valve 7 must be placed at a distance of 1=R/tanθ/2 from the back surface of the bulk part of the intake valve 5. In reality, the density of the injected fuel is high at the center of the injection area, so the distance L between the actual fuel injection valve 7 and the back of the intake valve bulk is set to L.
= 1.4l, most of the fuel reaches directly onto the back surface of the bulk part of the intake valve 5. On the other hand, if the injected fuel is too concentrated at one point on the back surface of the intake valve bulk, sufficient heat will not be transferred to the injected fuel from the intake valve 5, so the distance L should be larger than L=0.9l. . In this way, the actual distance L is compared to the ideal distance l.
If approximately 0.9lL and 1.4l are selected, the fuel injected from the fuel injection valve 7 will directly collide with the back surface of the intake valve 5, absorb heat from the intake valve 5, and quickly vaporize.

Referring again to FIG. 1, the intake port 6 is connected to a surge tank 12 common to each cylinder via a branch pipe 11, and this surge tank 12 is connected to the air duct 1.
3 to the air cleaner 14. A throttle valve 15 connected to an accelerator pedal (not shown) is disposed within the air duct 13, and a potentiometer 16 is attached to the throttle valve 15. This potentiometer 16 consists of a slider 16a connected to the throttle valve 15 and rotating together with the throttle valve 15, and a fixed resistor 16b.The slider 16a has an output voltage proportional to the opening degree of the throttle valve 15. Occur. Therefore, this potentiometer 16 constitutes a throttle valve opening degree detector that detects the opening degree of the throttle valve 15.

The electronic control unit 20 consists of a digital computer, including a microprocessor (MPU) 21 that performs various calculation processes, a random access memory (RAM) 22, and a read-only memory (ROM) in which control programs, calculation constants, etc. are stored in advance. 23, an input port 24, and an output port 25 are connected to each other via a bidirectional bus 26. Furthermore, a clock generator 27 is provided within the electronic control unit 20 for generating various clock signals. Input port 24 has surge tank 1
A negative pressure sensor 28 for detecting negative pressure within the
A potentiometer 16 is connected to the input port 24 via the AD converter 29, and a potentiometer 16 is connected to the AD converter 3.
Connected via 0. Further, a rotation speed sensor 31 is connected to the input port 24 . Negative pressure sensor 2
8 generates an output voltage proportional to the negative pressure inside the surge tank 12, and this voltage is converted into a corresponding binary number in the AD converter 29, and this binary number is input to the MPU 21 via the input port 24 and bus 26. be done. As described above, the potentiometer 16 generates an output voltage proportional to the opening degree of the throttle valve 15, and this voltage is converted into a corresponding binary number by the AD converter 30, and this binary number is sent to the input port 24 and the bus 26. The signal is input to the MPU 21 via the . On the other hand, the rotation speed sensor 31 generates a pulse every time the engine crankshaft rotates by a predetermined crank angle, and this pulse is input to the MPU 21 via the input port 24 and the bus 26.

The output port 25 is provided to output data for operating the fuel injection valve 7, and the binary data is sent to the MPU 21.
from the bus 26. Output port 2
The output terminal of 5 is connected to the corresponding input terminal of the down counter 32. This down counter 32
This down counter 32 is provided to convert the binary data written from the MPU 21 into the corresponding time length.
A down count of the data sent from the clock generator 27 is started by the clock signal of the clock generator 27, and when the count value reaches 0, the count is completed and a count completion signal is generated at the output terminal. S-R
The reset input terminal R of the flip-flop 33 is connected to the output terminal of the down counter 32, and the S-R
A set input terminal S of flip-flop 33 is connected to clock generator 27. This S-R flip-flop 33 is set by the clock signal of the clock generator 27 at the same time as the down count starts, and when the down count is completed, the down counter 32 is set.
It is reset by the count completion signal. Therefore, the output terminal Q of the S-R flip-flop 33 is at a high level while the down count is being performed. The output terminal Q of the S-R flip-flop 33 is connected to the fuel injection valve 7 via the power amplification circuit 34, so that the fuel injection valve 7 is energized while the down counter 32 is counting down. I understand.

Figure 3 shows the negative pressure P (-mmH) inside the surge tank 12.
g) and air-fuel ratio A/ for engine speed N (rpm)
It shows F. In Figure 3, the numbers written in the figure indicate the air-fuel ratio, but in reality, Figure 3 is a map in which the fuel injection time that will result in the air-fuel ratio written in the figure is written. There is. Therefore, when the engine speed N and the negative pressure P are determined, the fuel injection time is determined from FIG. 3, and the air-fuel ratio supplied into the engine cylinder at that time becomes the numerical value shown in FIG. The fuel injection time map shown in FIG. 3 is stored in advance in a predetermined area of the ROM 23 forming the first storage means. As can be seen from Figure 3, the fuel injection amount is determined when the engine speed N is between approximately 1400r.pm and approximately 3200r.pm and the negative pressure P is approximately 350mm.
The air-fuel ratio is set to 22 when it is smaller than Hg. Furthermore, the engine speed N is approximately
From 600r.pm to approximately 1400r.pm, as the engine speed N decreases, the air-fuel ratio decreases to 1.25 per 100r.pm.
It is set to decrease by ~2.75. This is because when the engine speed N decreases and the air-fuel ratio is large, torque fluctuations occur, and in order to suppress this torque fluctuation, the air-fuel ratio is made smaller as the engine speed N decreases. On the other hand, when the negative pressure P is greater than -350 mmHg, the air-fuel ratio is set to decrease by 1 to 2 per 100 mmHg as the negative pressure P increases. This is because when the negative pressure P increases and the air-fuel ratio is large, torque fluctuations occur, and in order to suppress this torque fluctuation, the air-fuel ratio is made smaller as the negative pressure P increases. Also, the engine speed N is approximately 3200r.
pm or more, the air-fuel ratio is set to decrease by 0.5 to 1.5 per 100 rpm, thereby making it possible to obtain high output when the engine speed N is high.

Control of the fuel injection amount using the map shown in FIG. 3 is performed when the opening degree of the throttle valve 15 is smaller than θ ₀ shown in FIG. 4, and when the opening degree of the throttle valve 15 is larger than θ ₀ shown in FIG. The amount of fuel injection is controlled by the opening degree of the throttle valve 15. In FIG. 4, the vertical axis θ indicates the opening θ of the throttle valve 15, and a throttle opening of 80° indicates a fully open state. As can be seen from FIG. 4, the opening degree θ ₀ is 30° to 40° when the engine speed N is 1000 rpm, and is 50° to 60° when the engine speed N is 4000 rpm. The negative pressure P corresponding to this opening degree θ ₀ is indicated by a broken line T in FIG. Therefore, when the negative pressure P is smaller than the broken line T in FIG. 3, that is, when the opening θ of the throttle valve 15 is larger than the opening θ ₀ in FIG. is controlled. When the negative pressure P is smaller than the broken line T in FIG. 3, the air-fuel ratio is rapidly decreased as the negative pressure P becomes smaller in order to obtain high output. Therefore, when the negative pressure P changes slightly, the air-fuel ratio changes greatly, so if the air-fuel ratio is changed in accordance with the negative pressure P, fine control becomes difficult. Thus, when the negative pressure P is smaller than the broken line T in FIG. 3, the fuel injection amount is controlled by the opening degree θ of the throttle valve 15. The relationship between the engine speed N and the throttle valve opening θ, which is indicated by the solid line θ ₀ in FIG. 4, is stored in advance in a predetermined area of the ROM 23 forming the second storage means.

FIG. 5 shows the air-fuel ratio A/F with respect to the opening degree θ of the throttle valve 15 and the engine speed N. In Figure 5, the numbers written in the figure indicate the air-fuel ratio, but in reality, Figure 5 is a map in which the fuel injection time that will result in the air-fuel ratio written in the figure is written. There is. Therefore, when the engine speed N and throttle valve opening θ are determined, the fuel injection time is determined from Figure 5, and the air-fuel ratio supplied to the engine cylinder at that time becomes the numerical value shown in Figure 5. . Fifth
The fuel injection time map shown in the figure is stored in the ROM23 in advance.
stored within. As can be seen from Fig. 5, the fuel injection amount is set so that the air-fuel ratio decreases as the throttle valve opening θ increases.
When the throttle valve 15 is fully opened, the air-fuel ratio is
It will be about 12.5.

Next, fuel injection control will be explained with reference to FIG. Referring to FIG. 6, first, in step 40, the output signal of the rotation speed sensor 31 is
The engine speed N is inputted to the MPU 21 and calculated. Next, in step 41, the output signal of the potentiometer 16 representing the throttle valve opening degree θ is
The output signal of the negative pressure sensor 28 representing the negative pressure P is inputted to the MPU 21 and then in step 42.
It is input to MPU21. Next, in step 43, it is determined whether the point Q(N) in FIG. 4, which is determined by the throttle opening .theta. and the engine speed N, is larger than the opening _{.theta..sub.0} in FIG. If it is determined in step 43 that Q(N) is not greater than the opening degree θ ₀ , the process proceeds to step 44 where the fuel injection time T is calculated from the map shown in FIG. 3, and then the process proceeds to step 45. On the other hand, in step 43, Q
When it is determined that (N) is larger than the opening degree θ ₀ , the process proceeds to step 46 where the fuel injection time T is calculated from the map shown in FIG. 5, and then the process proceeds to step 45. In step 45, drive data corresponding to the fuel injection time T obtained in step 44 or step 46 is written to the output port 25, and fuel is injected from the fuel injection valve 7 for this fuel injection time T. Therefore, an air-fuel mixture having an air-fuel ratio as shown in FIG. 3 or 5 is supplied into the engine cylinder.

As described above, according to the present invention, when the throttle valve opening is less than a predetermined opening, the fuel injection time is determined based on the negative pressure and the engine speed. At this time, the fuel injection time is determined to form a lean mixture in a predetermined operating range determined by the negative pressure and engine speed, but as the engine speed becomes lower than this operating range or the negative pressure becomes larger. Since the fuel injection time is set so that the air-fuel ratio decreases as the engine speed increases, torque fluctuations are suppressed.Furthermore, the fuel injection time is set so that the air-fuel ratio decreases as the engine speed becomes higher than this operating range. Because of this, high output can be obtained. On the other hand, when the throttle valve opening is greater than or equal to a predetermined opening, the fuel injection time is determined based on the throttle valve opening and the engine speed, and the fuel injection is performed so that the air-fuel ratio decreases as the throttle valve opening increases. Since the time is fixed, high output can be obtained. Additionally, by determining the fuel injection time based on the throttle opening when the throttle valve opening is greater than or equal to a predetermined opening, the air-fuel ratio can be changed in response to a fairly large change in the throttle valve opening. Therefore, fine control of the air-fuel ratio becomes possible.

[Brief explanation of the drawing]

Figure 1 is an overall view of the intake device according to the present invention, Figure 2
The figure is an enlarged side sectional view of the intake port in Figure 1, and
The figure shows the air-fuel ratio determined by the negative pressure in the surge tank and the engine speed, Figure 4 shows the throttle opening when switching to throttle valve opening control, and Figure 5 shows the throttle opening when switching to throttle valve opening control.
The figure shows the air-fuel ratio determined by the throttle valve opening and the engine speed, and FIG. 6 is a flowchart showing the operation of fuel injection control. 5... Intake valve, 6... Intake port, 7... Fuel injection valve, 10... Nozzle hole.

Claims (1)

[Scope of utility model registration request] It is equipped with a throttle valve opening detector that detects the opening of the throttle valve provided in the intake passage, a negative pressure sensor that detects the negative pressure in the intake passage, and a rotational speed sensor that detects the engine rotational speed. , in an internal combustion engine in which the fuel injection time is determined based on the output signals of the throttle valve opening detector, negative pressure sensor, and rotation speed sensor, the relationship between the negative pressure, the engine speed, and the fuel injection time is memorized. It comprises a first storage means and a second storage means that stores the relationship between the throttle valve opening, the engine speed, and the fuel injection time, and the first storage means is determined from the negative pressure and the engine speed. In a predetermined operating range, the fuel injection time to form a lean mixture is memorized, and as the engine speed becomes higher or lower than the operating range, or the negative pressure increases. The second storage means stores the fuel injection time such that the air-fuel ratio decreases as the throttle valve opening increases, and the second storage means stores the fuel injection time such that the air-fuel ratio decreases as the throttle valve opening increases. When the valve opening is less than a predetermined opening, the fuel injection time is determined based on the first storage means, and when the throttle valve opening is more than the predetermined opening, the fuel injection time is determined based on the second storage means. A fuel injection control device for an internal combustion engine that determines the injection time.