JPH04183924A - Direct injection in-cylinder type spark ignition engine - Google Patents

Abstract

PURPOSE:To sufficiently form a mixture necessary for ignition and flame propagation for satisfactory combustion by advancing fuel injection timing in compression stroke injection and ignition timing a low temperature in a cylinder. CONSTITUTION:A throttle valve 7 is controllably opened and closed by a step motor 8. A fuel injection valve 9 injects fuel directly into a cylinder chamber 4. An ignition plug 12 is connected through a distributor 13 to an ignitor 14. An electronic control unit 30 has a crank angle sensor 25, water temperature sensor 26 and accelerator opening sensor 27 connected to input ports 35. On the other hand, an output ports 36 are connected through respective drive circuits 39, 40, 41 respectively to the fuel injection valve 9, ignitor 14 and step motor 8. Thus, when a temperature is low in a cylinder, the fuel injection timing in a compression stroke injection is advanced and ignition timing is advanced. Thus, a fire nucleus is early formed to raise the temperature in the cylinder, promote the evaporation of fuel and form satisfactory mixture.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an in-cylinder direct injection spark ignition engine.

[Conventional technology]

Equipped with a fuel injection valve to directly inject fuel into the cylinder, at low loads, the spark plug is directed to inject fuel in the latter half of the compression stroke to perform stratified combustion, and at medium and high loads, the fuel is injected during the intake stroke and the latter half of the compression stroke. An in-cylinder direct injection spark ignition engine has been disclosed in which fuel is injected to perform weak stratified combustion (see Japanese Patent Laid-Open No. 2-169834).

[Problem to be solved by the invention]

However, in this internal combustion engine, when the engine is cold, the temperature inside the cylinder, for example, the wall temperature of the combustion chamber, is low.
Evaporation of the fuel injected into the cylinder deteriorates, resulting in insufficient formation of the air-fuel mixture necessary for ignition and flame propagation, resulting in a problem that good combustion cannot be achieved.

Furthermore, for example, during acceleration from low-load operation, the same problem occurs because the temperature inside the cylinder is relatively low.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, in an internal combustion engine in which fuel is directly injected into the cylinder during the compression stroke and ignited by the ignition plug, when the temperature inside the cylinder is low, the fuel injection timing of the compression stroke injection is At the same time, the ignition timing must be advanced.

[For production]

When the temperature inside the cylinder is low, the fuel injection timing for compression stroke injection must be advanced, and the ignition timing must also be advanced. As a result, a flame kernel is formed at an early stage, and as a result, the temperature inside the cylinder becomes higher, which promotes fuel evaporation and forms a good air-fuel mixture.

〔Example〕

Referring to FIG. 1, ▪ indicates a cylinder block, 2 indicates a cylinder head, 3 indicates a piston, 4 indicates a cylinder chamber, 5 indicates an intake pipe, and 6 indicates an exhaust pipe. A linkless throttle valve 7 is arranged in the intake pipe 5.

This throttle valve 7 is controlled to open and close by a step motor 8, and is kept substantially fully open except during idle operation and deceleration operation.

The tip of the fuel injection valve 9 extends into the cylinder chamber 4, and fuel can be directly injected into the cylinder chamber 4.

The fuel injection valves 9 of each cylinder are connected to a pressure accumulation chamber 10 common to each fuel injection valve 9, and this pressure accumulation chamber 10 is filled with high-pressure fuel at a substantially constant pressure by a fuel pump 11. The spark plug 12 is connected to the Eve knife 14 via an IJ computer 13.

The electronic control unit 30 consists of a digital computer with ROMs interconnected by a bidirectional bus 31.
(read only memory) 32 , RAM (random access memory! J) 33 , CP[I (microprocessor) 34 , a human power port 35 and an output port 36 .

A crank angle sensor 25 for detecting the engine speed is built into the distributor 13.
The output signal of 5 is inputted to the input port 35.

A water temperature sensor 26 for detecting engine cooling water temperature is connected to an input port 35 via a ΔD converter 37.

An accelerator opening sensor 27 for detecting the amount of depression of an accelerator pedal (not shown) is connected to the human power port 35 via an AD converter 38.

On the other hand, the output port 36 is connected to the fuel injection valve 9, the Eve knife 14, and the step motor 8 via respective drive circuits 39, 40, 4].

FIG. 2 shows an enlarged sectional view of the engine body shown in FIG. 1. Second
Referring to the figure, the concave combustion chamber 20 formed at the top of the piston consists of a large-diameter shallow dish part 21 on the upper side and a deep dish part 22 on the lower side formed at the center of the shallow dish part 21. It has a heavy structure, and the deep dish part 22 is formed to have a smaller diameter than the shallow dish part 21.

The intake port (not shown) is a swirl port,
The fuel injection valve 9 has a multi-hole nozzle. Therefore, the fuel injection valve 9 injects rod-shaped fuel with a relatively strong penetration force and a small spread angle.

The fuel injection valve 9 is arranged at the top of the cylinder chamber 4 so as to face diagonally downward. Further, the fuel injection direction and fuel injection timing of the fuel injection valve 9 are determined so that the injected fuel is directed into the combustion chamber 20. The ignition plug 12 is arranged so as to be located within the concave combustion chamber 20 when the piston 3 is at its top dead center.

FIG. 3 shows control patterns for compression stroke injection and intake stroke injection. Referring to FIG. 3, the horizontal axis represents the load on the engine, and in FIG. 3, the load is the fuel injection amount Q, and the vertical axis is the fuel injection amount Q. Up to a load range corresponding to the fuel injection amount Q, fuel is injected only in the compression stroke. The compression stroke fuel injection amount is gradually increased to Q. In the fuel injection amount Q, the compression stroke fuel injection amount is rapidly decreased to Q, and the intake stroke fuel injection amount is rapidly increased to Q. Q is the fuel injection amount near medium load;

It is expressed as the sum of and Q by the following equation.

Q, -Q. +Q.

Here, QIl is the minimum compression stroke fuel injection amount that can form an air-fuel mixture that can be ignited by the spark plug 12, and Q is the minimum amount of fuel injected during the intake stroke when the fuel injected in the intake stroke is uniformly diffused into the cylinder chamber 4. This is the minimum intake stroke fuel injection amount at which a fire ignited by the spark plug 12 can propagate.

In a load region where the fuel injection amount is larger than QS and smaller than Qu, the total fuel injection amount Q is divided into the compression stroke and the intake stroke and injected, and the compression stroke fuel injection amount is constant regardless of the load, and the intake stroke fuel is The injection amount is increased as the load increases.

In a load region where the fuel injection amount is Q or larger, the concentration of the premixture in the cylinder chamber formed by the intake stroke injection with a large fuel injection amount is rich enough for ignition, so the compression stroke for ignition is The injection is stopped and the entire required fuel injection amount is injected during the intake stroke. Q
I+ is the minimum intake stroke fuel injection amount that can form a homogeneous mixture that can be ignited by the spark plug even when the fuel is uniformly diffused in the cylinder chamber.

FIG. 4 shows a diagram showing the fuel injection control pattern of FIG. 3 in terms of the relationship between load and crank angle.

Referring again to FIG. 2, in a load region lower than the medium load vicinity Q3, the entire required injection amount is injected from the fuel injection valve 9 toward the combustion chamber 20 in the latter half of the compression stroke. The fuel injection timing is delayed, so most of the fuel is in the deep dish section 2.
It is injected into 2. The fuel adhering to the inner wall surface of the deep dish portion 22 is evaporated and atomized to form a mixed gas layer containing a flammable region within the combustion chamber 20. A part of this air-fuel mixture layer is ignited by the spark plug 12, and good combustion is completed mainly within the deep dish portion 22.

In a load region higher than Qs near medium load and lower than Q+□, as shown in FIG. Fuel is injected toward the chamber 20. The injected fuel F mainly collides with the shallow dish part 21, a part of which is reflected into the shilling chamber 4, and the other part adheres to the wall surface of the shallow dish part 21 and is evaporated and atomized by heating from the wall surface. These fuels form a premixture P during the period from the intake stroke to the compression stroke due to the intake swirl SW and the turbulence R of the intake flow (Fig. 5(b)).
.

The air-fuel ratio of this premixture P is set to a level that allows the ignition flame to propagate. When the suction vortex SW is strong, a premixture is formed that is rich near the outer periphery of the cylinder chamber 4 and thin near the center.

In addition, by advancing the intake stroke injection timing, piston 3 will be more effective.
- When fuel is injected at a position close to the dead center, most of the fuel is injected into the deep dish part 22, and most of the fuel is premixed in the deep dish part 22.

Subsequently, compression stroke injection is performed in the latter half of the compression stroke (FIG. 5(C)), and most of the fuel is injected into the deep dish portion 22.

The fuel adhering to the inner wall surface of the deep dish portion 22 is vaporized by heating from the wall surface and compressed air, and is diffused and mixed by the vortex SW, forming a heterogeneous mixture layer with a rich and light concentration including a flammable region. A part of this mixture layer is ignited by the spark plug 12, and combustion of the heterogeneous mixture layer proceeds (FIG. 5(d)). As the flame B formed by this combustion develops within the deep dish section 22, it propagates into the surrounding premixture, and further, the combustion progresses to the outside of the deep dish section 22 due to the reverse gas flow S.

In addition, when the compression stroke injection timing is advanced and the fuel is injected into both the shallow dish part 21 and the deep dish part 22, the flame is widely distributed in the shallow dish part 21 and the deep dish part 22, and the premixture is affected. Flame propagation can be made easier.

By the way, in such an internal combustion engine, when the engine is cold, the temperature inside the cylinder, for example, the wall temperature of the combustion chamber 20, is low, which worsens the evaporation of the fuel injected into the cylinder, which reduces ignition and flame propagation. This results in insufficient formation of the air-fuel mixture necessary for combustion, resulting in the problem that good combustion cannot be obtained.

Further, since the temperature inside the cylinder decreases as the fuel injection amount decreases, during acceleration from low-load operation, the temperature inside the cylinder becomes relatively low, causing the same problem as described above.

Therefore, in this embodiment, when the temperature inside the cylinder is low,
The fuel injection timing of the compression stroke injection is advanced, and the ignition timing is also advanced. That is, as shown in Fig. 4, when the temperature inside the cylinder is low, the compression stroke injection timing and ignition timing are advanced, as shown by the solid line, compared to when the inside of the cylinder is not low temperature (shown by the dotted line). It is being

As a result, a flame kernel is formed at an early stage, which, together with the heat generated by gas compression in the compression stroke, increases the temperature inside the cylinder, thereby promoting fuel evaporation. As a result, a good mixture can be formed,
In this way, good combustion can be obtained.

FIG. 6 shows a routine for executing this embodiment.

This routine is partially executed by an interrupt every crank angle. Referring to FIG. 6, first in step 60, a total fuel injection amount of 0 is calculated from a map of the accelerator depression amount and the engine speed. Next, in step 61, the compression stroke fuel injection amount Q is determined from a map of the total fuel injection amount Q and the engine speed.

is calculated. Next, in step 62, the compression stroke fuel injection amount Q is determined. Compression stroke fuel injection timing A is determined from the map of engine speed and engine speed. is calculated. Next, in step 63, the ignition timing I9 is calculated from the map of the total fuel injection IQ and the engine speed. In step 64, it is determined whether the engine cooling water temperature TW is 70° C. or higher, that is, whether the engine is cold. T.W.
If <70°C, that is, when the engine is cold, the process proceeds to step 67, where the compression stroke fuel injection amount Q is determined. It is determined whether or not is O.

In the case of Q, key 0, that is, when compression stroke injection is to be executed, the process advances to step 68 and the compression stroke fuel injection timing A is determined.

The advance angle amount X is calculated. Next, in step 69, the compression stroke fuel injection timing A is determined. X is added to , and the angle is advanced by the amount of advance X. Here, the compression stroke fuel injection timing A. is the angle measured from compression top dead center to intake bottom dead center. Next, in step 70, an advance amount Y of the ignition timing I is calculated. Next, in step 71, the ignition timing is changed to ■, Y.
is added, and the angle is advanced by the advance amount Y.

On the other hand, if it is determined in step 67 that Qc'=0, and the Zunawa compression stroke injection is not executed,
In step 70 and step 71, the ignition timing ■,
is advanced.

On the other hand, if it is determined in step 64 that TW≧70° C., the process proceeds to step 65 and the average fuel injection amount QA is calculated using the following equation.

QA-ΣQゎ/η Here, ΣQ,, indicates the sum of all fuel injection amounts Q for the past n times closest to the present, and therefore, the average fuel injection amount for the past one time can be calculated by ΣQ, /n. I can do it. The larger the fuel injection amount, the higher the temperature inside the cylinder. Therefore, QA indirectly indicates the temperature inside the cylinder. In other words, a small QA indicates that the temperature inside the cylinder is low. Next, step 66 Now, calculate the difference between the current total fuel injection amount O and the average fuel injection amount QA.When OQA exceeds a predetermined value, for example 15 mm3, it indicates that the cylinder internal temperature is relatively low. For example, when accelerating from low-load operation, Q-QA>15. In this case as well, there is a problem that good ignition and combustion cannot be obtained, as in the case when the engine is cold. - If QA〉15, step 67
Proceeding below, when compression stroke injection is executed, the compression stroke fuel injection timing Ac and ignition timing I are advanced, and when compression stroke injection is not executed, only the ignition timing is advanced.

On the other hand, if it is determined that Q QA ≦15, this routine ends. That is, if the inside of the cylinder is not at low temperature, the compression stroke fuel injection timing is A. and ignition timing ■, cannot be advanced.

In this embodiment, one fuel injection valve 9 is used to perform intake stroke injection and compression stroke injection, but there are two fuel injection valves, and one fuel injection valve is used to perform intake stroke injection. At the same time, the compression stroke injection may be performed by the other fuel injection valve.

〔Effect of the invention〕

Since a good air-fuel mixture can be formed even when the temperature inside the cylinder is low, good combustion can be achieved.

[Brief explanation of drawings]

Figure 1 is an overall view of the internal combustion engine, Figure 2 is a vertical cross-sectional view of the engine body, Figure 3 is a diagram showing an example of control patterns for compression stroke injection and intake stroke injection, and Figure 4 is the same as Figure 3. FIG. 5 is an explanatory diagram showing the state of fuel injection, and FIG. 6 is a flowchart for calculating the compression stroke fuel injection timing and ignition timing. 4... Cylinder chamber, 9... Fuel injection valve, 1
2... Spark plug, 26... Water temperature sensor. Figure 2 Figure 3 Early intake stroke (a) (b) Late compression stroke (C) Fierce combustion stroke (d) Figure 5

Claims (1)

[Claims] In an internal combustion engine in which fuel is directly injected into the cylinder during the compression stroke and ignited by the ignition plug, when the temperature inside the cylinder is low, the fuel injection timing of the compression stroke injection is advanced and the ignition timing is advanced. In-cylinder direct injection spark ignition engine.