JPH0222223B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection timing control method for an internal combustion engine.

In conventional multi-cylinder internal combustion engines, each cylinder is provided with a fuel injection valve, and fuel is injected into the intake passage of each cylinder.The fuel injection method used in conventional multi-cylinder internal combustion engines is simultaneous injection in all cylinders, group injection, or independent injection in each cylinder. It depends on one of the methods. Among these, simultaneous injection in all cylinders and group injection cannot select the best injection timing for each cylinder. On the other hand, for each cylinder independent injection, it is possible to select any injection timing for each cylinder. However, at present, the technical meaning of setting a specific injection timing for each cylinder has not been sufficiently considered, and this independent injection for each cylinder is expensive, so it is not used in products. This is the current situation.

The present invention completes fuel injection in the latter half of the intake stroke when the engine is running at low load, and stratifies the inside of the combustion chamber by using the swirling flow around the cylinder axis generated in the combustion chamber. To provide an internal combustion engine in which fuel injection is completed and the injection start timing is earlier than during low load operation to form a uniform air-fuel mixture in a combustion chamber.

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

Referring to FIGS. 1 to 3, 1 is an engine body of a so-called open chamber internal combustion engine that does not have a subchamber, 2 is a cylinder block, 3 is a piston, 4 is a cylinder head, 5 is a combustion chamber, 6 is an intake valve, 7 is an intake port, 8 is an exhaust valve, 9 is an exhaust port, 10 is a spark plug, 11 is an intake branch pipe, and 12 is an exhaust manifold. As shown in FIG. 3, this intake branch pipe 11 is connected to an air cleaner (not shown) via a surge tank 13 and an air flow meter 14, and furthermore, this intake branch pipe 11 is connected to a fuel injection valve 15 independently for each cylinder. is provided. On the other hand, as shown in FIG.
is connected to a three-way catalytic converter 17 via an exhaust pipe 16, and an oxygen concentration detector 18 is attached to the exhaust pipe 16 upstream of the three-way catalytic converter 17. As is well known, this oxygen concentration detector 18 outputs about 0.1 volt when the exhaust gas is in an oxidizing atmosphere, that is, when the air-fuel mixture supplied into the combustion chamber 5 is on the lean side with respect to the stoichiometric air-fuel ratio. emits voltage,
When the exhaust gas is in a reducing atmosphere, that is, when the air-fuel mixture supplied into the combustion chamber 5 is on the rich side with respect to the stoichiometric air-fuel ratio, an output voltage of about 0.9 volts is generated.

On the other hand, as shown in FIG. 3, an engine rotation speed detection disk 20 made of gears, for example, is attached to the crankshaft 19, and an engine rotation speed detection sensor 21 made of, for example, an electromagnetic pickup is mounted near the disk 20. It will be established. This sensor 21 generates a number of pulses proportional to the rotational speed of the crankshaft 19. On the other hand, the camshaft 22 has 4
Discs 23 for detecting a reference crank angle, for example, for detecting top dead center, are attached, and top dead center detecting sensors 24 made of, for example, an electromagnetic pickup are provided adjacent to each disc 23, respectively. Each sensor 24 detects the crank angle of the first to fourth cylinders, and generates a pulse when the piston of the corresponding cylinder reaches top dead center at the beginning of the intake stroke. The engine rotation speed detection sensor 21 is connected to an input terminal of a counter 25 , and an output terminal of the counter 25 is connected to an input terminal of a DA converter 26 . The output terminal of the D-A converter 26 is connected to the input terminal of the divider circuit 27 on the one hand, and the injection time calculation circuit 2 on the other hand.
8 input terminals. The air flow meter 14 and the oxygen concentration detector 18 are connected to the remaining input terminals of the injection time calculation circuit 28. The output terminal of the division circuit 27 is connected to one input terminal of the subtraction circuit 29, and the injection time calculation circuit 28
The output terminal of is connected to the other input terminal of the subtraction circuit 29. The output terminal of the subtraction circuit 29 is connected to one input terminal of four fuel injection pulse generators 30 provided corresponding to each cylinder, and the other input terminal of each fuel injection pulse generator 30 corresponds to each cylinder. It is connected to the top dead center detection sensor 24. The output terminal of each fuel injection pulse generator 30 is connected to the corresponding fuel injection valve 15, and the output terminal of each injection time calculation circuit 28 is further connected to the input terminal of the fuel injection pulse generator 30.

FIG. 4 shows the valve timing of the intake valve. In FIG. 4, arrow A indicates the opening period of the intake valve. According to the present invention, the injection end crank angle B of the fuel injection valve 15 is preset to a constant value that is slightly smaller than the intake valve closing crank angle C of the corresponding cylinder by θ.

Referring again to FIG. 3, as described above, the engine speed detection sensor 21 generates a number of pulses proportional to the engine speed. This pulse is counter 2
5, a predetermined time is counted, and this count value is therefore proportional to the engine speed. This count value is converted by the DA converter 26 into a voltage proportional to the count value, and therefore the output voltage of the DA converter 26 is proportional to the engine speed. The output voltage of this DA converter 26 is supplied to a division circuit 27 and an injection time calculation circuit 28.

As shown in Fig. 4, if the crank angle from top dead center TDC to fuel injection end crank angle B is φ, and the engine speed is Nr.pm, then the time from top dead center TDC to the end of fuel injection is assumed to be φ. The time τ ₁ msec is expressed as τ ₁ =60000·φ/360·1/N.

As mentioned above, the crank angle φ is set in advance, and this crank angle φ is applied to the divider circuit 27 in the form of a constant voltage. Therefore, in this division circuit 27, 60000・φ/360 is divided by the engine speed N, that is, 60000・φ/360・1/N is calculated, and thus the division circuit 27 uses the top dead center as the reference. As a result, an output voltage representing the time τ ₁ until the end of fuel injection is generated. This output voltage is
Sent to 9th.

On the other hand, the three-way catalytic converter 17 has the function of simultaneously reducing harmful components HC, CO, and _NO Purification rate increases. Therefore, when the three-way catalytic converter 17 is used, it is necessary to match the air-fuel mixture supplied into the engine combustion chamber to the stoichiometric air-fuel ratio. On the other hand, the air flow meter 14 generates an output voltage proportional to the amount of intake air per unit time, and this output voltage is supplied to the injection time calculation circuit 28. Furthermore, the output voltage of the oxygen concentration detector 18 and the output voltage of the DA converter 26 are supplied to the injection time calculation circuit 28. When the air-fuel mixture supplied into the engine combustion chamber is always set at a constant predetermined air-fuel ratio, the required fuel amount Q is proportional to the intake air amount, and thus the output voltage of the air flow meter 14 is proportional to the required fuel amount Q. It represents. The amount q of one injection to be injected from the fuel injection valve 15 is expressed as the value obtained by dividing the required fuel amount Q by the engine speed N, that is, q=Q/N. However, the injection amount from the fuel injection valve 15 is proportional to the injection time, and therefore, the injection amount q represents one injection time τ ₂ of the fuel injection valve 15. The injection time calculation circuit 28 generates an output voltage representing this injection time τ ₂ , and this output voltage is sent to the subtraction circuit 29 and the fuel injection pulse generation circuit 30 . Note that the fuel amount q to be injected from the fuel injection valve 15 at one time is corrected based on the output voltage of the oxygen concentration detector 18 so that the air-fuel mixture supplied into the engine combustion chamber has a stoichiometric air-fuel ratio.

In the subtraction circuit 29, the injection time τ ₂ is subtracted from the time τ ₁ , and as a result, the subtraction circuit 29 calculates the top dead center TDC.
An output signal is generated representing the time τ ₃ up to when fuel injection is started with reference to τ 3 . This output signal is supplied to each fuel injection pulse generator 30.
Furthermore, the output signal of the top dead center detection sensor 24 is supplied to the fuel injection pulse generator 30. Each of these fuel injection pulse generators 30 has an internal reference clock. Each fuel injection pulse generator 30
Then, when the piston of the corresponding cylinder reaches the top dead center, a countdown is started by the output signal of the top dead center detection sensor 24, and when time τ ₃ elapses, a fuel injection start pulse is emitted and the fuel is injected from the fuel injection valve 15. Start injection. On the other hand, when the fuel injection start pulse occurs, the countdown of the injection time starts, and the injection time τ ₂
After , the injection of fuel from the fuel injection valve 15 is stopped. The crank angle at which fuel injection stops corresponds to point B in FIG. In this way, the fuel injection end timing is set to the predetermined crank angle B.

When the engine is operated at low-medium speed and low-medium load, the fuel injection time τ ₂ is in the latter half of the intake stroke, as shown in FIG. Note that the fuel injection start timing becomes later as the engine speed decreases and as the engine load decreases. Therefore, referring to FIG. 1, since fuel is not injected from the fuel injection valve 15 for a while after the intake valve 6 is opened, air flows into the combustion chamber 5 from the intake port 7 via the intake valve 6. As shown in FIG. 2, the longitudinal axis of the intake port 7 is arranged eccentrically with respect to the center of the combustion chamber 5, so that the air flowing into the combustion chamber 5 from the intake port 7 is directed toward the cylinder as shown by arrow K. Generates swirling flow around the axis. Next, when the piston 3 descends, the air swirls and descends together with the piston 3. Next, when the piston 3 further descends and enters the second half of the intake stroke, fuel injection from the fuel injection valve 15 is started, and as a result, the air-fuel mixture flows into the combustion chamber 5. This air-fuel mixture also generates a swirling flow around the cylinder axis within the combustion chamber 5. As a result, when the piston ₃ descends, as shown in FIG. The upper area within is arrow K ₂
As shown, the combustion chamber 5 is filled with a rich air-fuel mixture swirling around the cylinder axis, and the inside of the combustion chamber 5 is thus stratified. Since the air-fuel mixture continues to swirl in the upper region of the combustion chamber 5 in this way, the air-fuel mixture does not diffuse much into the lower region of the combustion chamber 5, and thus the stratified state continues until the end of the compression stroke. Therefore, at the end of the compression stroke, a rich air-fuel mixture exists around the spark plug 10, so that the air-fuel mixture can be easily ignited. On the other hand, during high-speed, high-load engine operation, the fuel injection start timing approaches top dead center or comes before top dead center. At this time as well, the fuel injection is stopped at the crank angle B in FIG. 4, so the air-fuel mixture is supplied from the intake port 7 into the combustion chamber 5 throughout the period when the intake valve 6 is open. At this time, combustion chamber 5
There is no stratification inside the combustion chamber 5, and the mixture inside the combustion chamber 5 is almost uniform. Note that during engine high-speed, high-load operation, the fuel injection start timing becomes later as the engine speed decreases and as the engine load decreases, as in the case of engine low-medium speed and low-medium load operation. Further, it is preferable that the fuel injected from the fuel injection valve 15 is completely sucked into the combustion chamber 5 during the intake stroke, and the fuel injected from the fuel injection valve 15 flies within the intake port 7 and enters the combustion chamber 5. Because it takes time to reach the 4th
As shown in the figure, the fuel injection end crank angle B is smaller than the intake valve closing crank angle C by the crank angle θ. This crank angle θ varies depending on the combustion chamber shape, intake system type, cam profile, valve timing, etc., and therefore needs to be set to an optimal value for each engine.

When an oxidation catalytic converter is used in place of the three-way catalytic converter 17 as shown in FIG. It is preferable to set the fuel injection amount so that the air-fuel ratio shifts to the lean side as the engine speed decreases and as the engine load decreases. In this case, even if the average air-fuel ratio of the air-fuel mixture supplied into the combustion chamber becomes lean during engine operation at low-medium speeds and low-medium load, stable ignition is ensured because a concentrated mixture is formed around the spark plug. Can be done. Therefore, the average air-fuel ratio can be increased during low-medium-speed and low-medium-load operations, which have a large effect on actual fuel efficiency, improving the fuel consumption rate, and the average air-fuel ratio becomes smaller during high-speed, high-load operations that require even more output. Therefore, high output can be obtained.

As described above, according to the present invention, the inside of the combustion chamber can be stratified during low-load engine operation, making it easier to ignite the air-fuel mixture, and the combustion chamber can be filled with a substantially uniform air-fuel mixture during high-load engine operation. Therefore, high output can be obtained while ensuring good combustion.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an internal combustion engine according to the present invention;
Figure 2 is a bottom view of the cylinder head in Figure 1, and Figure 3 is a bottom view of the cylinder head in Figure 1.
This figure is an overall view of the fuel injection timing control device, FIG. 4 is a valve timing diagram, and FIG. 5 is a side sectional view of the internal combustion engine showing the position where the piston is lowered. 5... Combustion chamber, 6... Intake valve, 7... Intake port, 14... Air flow meter, 15... Fuel injection valve, 18... Oxygen concentration detector, 21... Engine speed detection sensor, 24... …TDC detection sensor,
25... Counter, 26... D-A converter,
27... Division circuit, 28... Injection time calculation circuit,
29... Subtraction circuit, 30... Fuel injection pulse generator.

Claims (1)

[Claims] 1. A fuel injection valve is disposed in an intake passage configured to communicate with a combustion chamber via an intake valve and generate a swirling flow around a cylinder axis in the combustion chamber, and the fuel injection valve is inserted into the intake passage from the fuel injection valve. inject fuel,
In an open chamber spark ignition internal combustion engine in which the amount of fuel injected from the fuel injection valve is varied according to the engine load, all the injected fuel enters the combustion chamber before the intake valve closes during low engine load operation. Fuel injection is completed in the latter half of the intake stroke before the intake valve closes, creating stratification within the combustion chamber, so that during high-load engine operation, all injected fuel flows into the combustion chamber before the intake valve closes. A fuel for an internal combustion engine in which fuel injection is completed in the latter half of the intake stroke before the intake valve closes, and the fuel injection start timing is earlier than during low-load operation so that a uniform air-fuel mixture is formed in the combustion chamber. Injection timing control method.