JPH04187819A - Cylinder direct injection type spark ignition engine - Google Patents

Abstract

PURPOSE:To form an excellent mixture so as to obtain preferable combustion by providing a whirling flow controller for controlling strength of whirling flow generated inside a cylinder, and strengthening the whirling flow at a low temperature of the cylinder by the whirling flow controller. CONSTITUTION:A intake pipe 5 is divided into a straight intake port 50 and a helical intake port 51, and intake values 52, 53 are disposed corresponding to the intake ports 50, 51, respectively. A pair of exhaust valves 56, 57 are arranged corresponding to a pair of confluent exhaust ports 54, 55. In the straight intake port 50, there is provided an intake control valve 59 driven by a step motor 58. At the time of full closure of the intake control valve 59, air is supplied into a cylinder only from the helical intake port 51 so that strong flow whirling clockwise in the drawing is formed inside the cylinder. Control of an opening degree of the intake control valve 59 allows the strength of the whirling flow to be controlled. Therefore, it is possible to develop vaporization and atomization of fuel injected into the cylinder so as to form an excellent 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 is disclosed in which fuel is injected to perform weak stratified combustion (see Japanese Patent Laid-Open No. 2-16.9834).

[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 and ignited by a spark plug, a A swirl flow control means is provided, and the swirl flow is strengthened by the swirl flow control means when the temperature inside the cylinder is low.

[For production]

When the temperature inside the cylinder is low, the swirl flow is strengthened by the swirl flow control means. Thereby, it is possible to promote evaporation and atomization of the fuel injected into the cylinder, and it is possible to form a good air-fuel mixture.

〔Example〕

Referring to FIG. 1, 1 is a cylinder block, 2 is a cylinder head, 3 is a piston, 4 is a cylinder chamber, 5 is an intake pipe, and 6 is 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 to the cylinder chamber 4 and can directly inject fuel 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 igniter 1 via a distributor 13.
Connected to 4.

FIG. 2 shows a bottom view of the cylinder head 2.

Referring to FIG. 2, the intake pipe 5 is branched into a straight intake boat 50 and a helical intake boat 51, and intake valves 52, 53 are arranged corresponding to each intake boat 50, 51. A pair of exhaust valves 56 and 57 are arranged corresponding to the pair of exhaust boats 54 and 55 that merge. An intake control valve 59 driven by a step motor 58 is arranged on the straight intake boat 50 .

When the intake control valve 59 is fully opened, air flows into the cylinder only from the helical intake boat 51, so that a strong swirling flow clockwise in the figure is formed inside the cylinder. When the intake control valve 59 is opened, air also flows into the cylinder from the straight intake boat 50, thereby forming a swirling flow in the opposite direction to the swirling flow formed by the air flowing in from the helical intake boat 51. , the clockwise swirl flow is weakened.

When the intake control valve 59 is fully opened, the clockwise swirl flow becomes the weakest. By controlling the opening degree of the intake control valve 59 in this manner, the strength of the swirling flow can be controlled.

The opening degree of the intake control valve 59 is controlled depending on the load, as shown in FIG. 3, for example. It is fully closed when the load is low, the degree of opening increases stepwise as the load increases, and it is fully opened when the load is high.

Referring again to FIG. 1, the electronic control unit 30 consists of a digital computer and includes ROMs (IJ-only memory) 3 interconnected by a bidirectional bus 31.
2, RAM (Random Access Memory) 33, CPU
(microprocessor) 34, an input port 35, and an output port 36. A crank angle sensor 25 for detecting the engine speed is built into the distributor 13, and an output signal of the crank angle sensor 25 is input to the human-powered boat 35. A water temperature sensor 26 for detecting engine cooling water temperature is connected to the human-powered boat 35 via an AD converter 37. The accelerator opening sensor 27 for detecting the amount of depression of the accelerator pedal (not shown) is connected to an AD converter 38.
The input port 35 is connected to the input port 35 via the input port 35.

On the other hand, the output port 36 is connected to the fuel injection valve 9, the igniter 14, the step motor 58 of the intake control valve 59, and the step motor 8 of the throttle valve 7 through drive circuits 39, 40, 41, 42, respectively.

FIG. 4 shows an enlarged sectional view of the engine body shown in FIG. 1. Fourth
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 boat (not shown) is a swirl boat.
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 obliquely 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. 5 shows control patterns for compression stroke injection and intake stroke injection. Referring to FIG. 5, the horizontal axis represents the load on the engine, and in FIG. 5, 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 Q5, fuel is injected only in the compression stroke. The compression stroke fuel injection amount is gradually increased up to Q5. In the fuel injection amount Q, the compression stroke fuel injection amount is rapidly decreased to QIll, and the intake stroke fuel injection amount is rapidly increased to Q. Qs
is the fuel injection amount near medium load, and is expressed as the sum of Qn and Q by the following equation.

Q s = Q o + Q p Here, QIll is the minimum compression stroke fuel injection amount that can form a mixture that can be ignited by the spark plug 12, and Q,
is the minimum intake stroke fuel injection amount at which an ignition fire caused by the spark plug 12 can propagate when the fuel injected during the intake stroke is uniformly diffused into the cylinder chamber 4.

In a load region where the fuel injection amount is larger than Q and smaller than Qa, 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 kept constant regardless of the load during the intake stroke. The fuel 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 intake stroke injection is high enough for ignition due to the large fuel injection amount, so compression stroke injection is performed for ignition. Instead, the entire required fuel injection amount is injected during the intake stroke. Q
□ 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.

Referring again to FIG. 4, in the vicinity of the medium load Q and in the lower load region, 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 the load region higher than O5 and lower than QH near medium load, as shown in FIG.
Intake stroke injection is executed in a)), and fuel is injected from the fuel injection valve 9 toward the combustion chamber 20 . The injected fuel F mainly collides with the shallow dish part 21, a part of which is reflected into the cylinder 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 are absorbed by the suction vortex S
A premixture P is formed between the intake stroke and the compression stroke due to W and the turbulence R of the intake air flow (FIG. 6(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.

Note that if the intake stroke injection timing is advanced and the fuel is injected when the piston 3 is closer to the top dead center, most of the fuel will be injected into the deep dish portion 22; The mixture is pre-vaporized in the section 22.

Subsequently, compression stroke injection is performed in the latter half of the compression stroke (FIG. 6(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 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. 6(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 Squissini 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 the following embodiment, when the temperature inside the cylinder is low, the degree of opening of the intake control valve 59 is reduced to strengthen the swirling flow inside the cylinder.

This promotes evaporation and atomization of the fuel injected into the cylinder and forms a good air-fuel mixture, thereby making it possible to obtain good combustion.

FIG. 7 shows a first embodiment of the opening degree control of the intake control valve 59 when the temperature inside the cylinder is low. In this example, the opening degree of the intake control valve is controlled to be 20% even under high load, and under normal conditions (when the inside of the cylinder is not low temperature).
On the other hand, the opening degree of the intake control valve 59 is reduced in the middle and high load ranges.

A routine for executing the first embodiment is shown in FIG. This routine is executed by interrupts at regular intervals. First, in step 70, the total fuel injection amount Q is calculated from a map of the accelerator depression amount and the engine speed.

Next, in step 71, the opening degree R, cv of the intake control valve 59 is calculated from a map of the total fuel injection amount Q and the engine speed. In step 72, it is determined whether the RS CV is greater than 20%.

If R3° is 520%, this routine is ended and the Rscv calculated in step 71 is used. R8°.

> If it is 20%, proceed to step 73 and check the engine cooling water temperature T.
It is determined whether W is 70° C. or higher, that is, whether the engine is cold. When TW<70°C, that is, when the engine is cold, the process proceeds to step 76, and the intake control valve opening degree Rscv
is reduced to 20%. On the other hand, if it is determined that TW≧70°C, the process proceeds to step 74, where the average fuel injection amount QA
is calculated by the following formula.

QA=ΣQ,,/n Here, ΣQ,, indicates the sum of all fuel injection amounts Q for the past n times closest to the present, and therefore, calculate the average fuel injection amount for the past n times by ΣQ,/n. be able to.

The cylinder internal temperature becomes higher as the fuel injection amount increases, so QA indirectly indicates the cylinder internal temperature. In other words, a small QA indicates that the cylinder internal temperature is low. Next, in step 75, the difference between the current total fuel injection amount Q and the average fuel injection amount QA is calculated. Q
- When QA reaches a predetermined value, for example 15 plates 3 or more, it indicates that the cylinder internal temperature is relatively low. For example, when accelerating operation is started 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. Therefore, if Q-QA>15, the process proceeds to step 76, and the intake control valve opening RSCV is reduced to 20%. On the other hand, if Q-QA≦15, this routine is ended and the R3CV calculated in step 71 is used.

FIG. 9 shows a second embodiment of the opening degree control of the intake control valve 59 when the temperature inside the cylinder is low. In this embodiment, the opening degree of the intake control valve 59 is reduced in almost the entire load range compared to normal times, and when the normal opening degree is 20% or less, the opening degree is set to 0% in all cases, and the normal opening degree is reduced to 0%. When the opening is more than 20% and less than 70%, the opening is reduced by 20% from the normal opening, and when the opening is 70% or more, the opening is set to 50%.

FIG. 10 shows a routine for executing the second embodiment. This routine is executed by interrupts at regular intervals. Steps that are the same as those in the routine shown in FIG. 8 are given the same step numbers and their explanations will be omitted. If it is determined in step 73 that TW<70° C., the process proceeds to step 80, where it is determined whether the intake control valve opening degree R3°7 is greater than 20%. If R8° is 520%, the process proceeds to step 83, where R8CV is set to 0%. on the other hand,
If Rscv > 20%, proceed to step 81 and R
It is determined whether or not it is 3°7<70%. Rscv <70%
If so, in step 82 R5°7 calculated in step 71 is subtracted by 20%. On the other hand, R3CV≧
If it is 70%, proceed to step 84, and R8° is 50%.
It is said that

On the other hand, if it is determined in step 75 that Q-QA>15, R3° is corrected to decrease in steps 80 to 84. On the other hand, Q-QA ≦
In the case of 15, this routine is ended and the RSCV calculated in step 71 is used as is.

FIG. 11 shows the intake control valve 59 when the temperature inside the cylinder is low.
A third example of opening degree control is shown. In FIG. 11, the horizontal axis represents time, and the vertical axis represents the opening degree of the intake control valve 59. When opening the intake control valve 59, a delay time is provided when the temperature inside the cylinder is low compared to normal times. This also results in reducing the opening of the intake control valve, resulting in good combustion.

FIG. 12 shows a routine for executing the third embodiment. This routine is executed by interrupts at regular intervals. Referring to FIG. 12, first, in step 90, the total fuel injection amount Q is calculated.

Next, in step 91, the average fuel injection amount QA is calculated. In step 92, it is determined whether the difference between the total fuel injection amount Q and the average fuel injection amount QA is greater than 15 mm3. For example, if we consider a case where the engine is operating at a substantially steady state with a low load, Q-Q^≦15, and the process proceeds to step 93, where the intake control valve opening degree R5CV is calculated. In this case, since low-load operation is assumed, the intake control valve 59 is almost fully closed. Next, let us consider the case of accelerating operation from low load operation to high load operation. In this case, a large amount of fuel is injected into the cylinder when the temperature inside the cylinder is low due to low load operation, and the temperature inside the cylinder is low. This causes the problem of worsening combustion as described above.

In this case, since Q-QA>15, the process proceeds to step 94, where it is determined whether flag F=1. Since the flag F is initially 0, the process proceeds to step 98 and a predetermined value C8 is entered into the counter C. Next, in step 99, flag F is set to 1. In the next processing cycle, an affirmative determination is made in step 94 and the process proceeds to step 95. In step 95, counter C is decremented by one.

In step 96, it is determined whether the counter C has reached 0 or not. When the counter C is not 0, this routine is ended, and when the counter C is 0, the routine proceeds to step 97 and the flag F is reset to O. During this time, R3° is not calculated, so R5° remains small. Next, in step 92, if Q-Q is still >15, the counting operation of the counter C is repeated in steps 94 to 99. Then, near the end of acceleration, Q-QA≦15
When this happens, the process proceeds to step 93, where the intake control valve opening
is calculated. At this time, since the load is high, R5° = 100%, and the intake control valve 59 is fully opened.

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〕

Even when the temperature inside the cylinder is low, a good air-fuel mixture can be formed by strengthening the swirling flow, so that good combustion can be achieved.

[Brief explanation of drawings]

Fig. 1 is an overall view of the internal combustion engine, Fig. 2 is a bottom view of the cylinder head, Fig. 3 is a diagram showing the opening control of the intake control valve under normal conditions, and Fig. 4 is a longitudinal sectional view of the engine body. Fig. 5 is a diagram showing an example of a control pattern for compression stroke injection and intake stroke injection, Fig. 6 is an explanatory diagram showing the state of fuel injection, and Fig. 7 is a diagram showing the first implementation of intake control valve opening control. Diagram showing examples, No. 8
The figure is a flowchart for calculating the valve opening degree of the intake control valve in the first embodiment, FIG. 9 is a diagram showing the second example of controlling the opening degree of the intake control valve, and FIG. FIG. 11 is a flowchart for calculating the valve opening of the intake control valve in the third embodiment, FIG. 11 is a diagram showing the third embodiment of the intake control valve opening control, and FIG. It is a flowchart for calculating the valve opening degree of an intake control valve. 4... Cylinder chamber, 9... Fuel injection valve, 12...
...Spark plug, 26...Water temperature sensor, 59...
・Intake control valve. Figure 2 Load 3rd Figure 4 Early intake stroke (a) Late compression stroke (C) (b) (d) Figure 3 Figure 8 Figure 9 Figure 10 Figure 110

Claims (1)

[Claims] An internal combustion engine in which fuel is directly injected into a cylinder and ignited by a spark plug is equipped with a swirl flow control means for controlling the strength of swirl flow generated in the cylinder, and when the temperature inside the cylinder is low, the swirl flow An in-cylinder direct injection spark ignition engine that uses control means to intensify the swirling flow.