JPH0559952A - Control of combustion control device of engine and method thereof - Google Patents

Abstract

PURPOSE:To reduce HC and NOx by providing a control means to uniform a combustion ratio until flame ignited by an ignition gap reaches a peripheral part. CONSTITUTION:That which control an air-fuel ratio distribution state of an air-fuel mixture as a means to uniform combustion ratio are a first fuel injection valve 11 and a second fuel injection valve 12. The first fuel injection valve 11 supplies fuel to the central part of a combustion chamber 2 by way of injecting fuel in the neighbourhood of the upstream edge of a bulkhead 5. The second fuel injection valve 12 supplies fuel to the outer peripheral part of the combustion chamber 2 through the edge part on the side far from the bulkhead 5 of an air intake port 3A. Ignition by an ignition gap 10 is carried out at the richest central part, fire is restrained from extension by a lean intermediate territory and thereafter, fire reaches a rich peripheral part, but as the wall surface is cooled down, the combustion ratio does not increase and comes to be almost the same as the ratio in the intermediate territory. Consequently, it is possible to uniformize the combustion ratio and to restrain generation of HC and NOx.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine combustion control device and control method.

[0002]

2. Description of the Related Art Some engines include a multi-point ignition type in which a plurality of ignition gaps are provided for one combustion chamber. In Japanese Unexamined Patent Publication (Kokai) No. 57-148021, an annular holding plate is interposed between a cylinder head and a cylinder block, and a large number of spark plugs are held by the holding plate, and a cylinder is provided at an outer peripheral edge of a combustion chamber. It is disclosed that a plurality of ignition gaps are arranged at intervals in the circumferential direction. As a result, rapid combustion is performed by simultaneous ignition with a large number of ignition gaps, and an ideal equivolume combustion is obtained in the Otto-type engine.

[0003]

[Problems to be Solved by the Invention] By the way, recently,
From the viewpoint of exhaust gas purification and the like, it is desired to position a plurality of ignition gaps at the outer peripheral edge of the combustion chamber at intervals in the circumferential direction of the combustion chamber. By igniting from the periphery of the combustion chamber, the combustibility at the outer peripheral edge of the combustion chamber is improved to reduce HC, and the flame is first matched in the circumferential direction of the combustion chamber and then matched at the center of the combustion chamber. By suppressing the growth of flame by this, the combustion ratio within a predetermined period is made as uniform as possible, that is, the peak value of the combustion speed is made as small as possible,
This is intended to reduce NOx.

As described above, providing a plurality of ignition gaps at the outer peripheral edge of the combustion chamber and at intervals in the circumferential direction of the combustion chamber is not a good idea because the number of spark plugs increases. Therefore, if an ignition gap is provided at the center of the combustion chamber, which is a very common combustion chamber structure, if the combustion ratio can be made uniform, it is preferable for reducing HC and NOx.

Therefore, an object of the present invention is to provide an engine combustion control device and control method capable of significantly reducing both HC and NOx in an engine having an ignition gap arranged in the center of a combustion chamber. is there.

[0006]

To achieve the above object, the present invention has the following configuration. That is, in an engine in which the ignition gap is located in the center of the combustion chamber,
A control unit that controls a factor that contributes to the combustion of the air-fuel mixture is provided so that the combustion ratio of the flame generated by the ignition by the ignition gap reaches the outer peripheral edge of the combustion chamber is uniform. It has such a structure.

More specifically, the control means is configured so that the flame spread in the combustion center portion and the outer peripheral edge portion of the combustion chamber is accelerated, and the flame spread portion in the intermediate region between the center portion of the combustion chamber and the outer peripheral edge portion is increased. Can be configured to control the factors that contribute to combustion. In this case, the flame spread at the center of the combustion chamber may be faster than the flame spread at the outer peripheral edge of the combustion chamber.

The factor contributing to combustion is the air-fuel ratio of the air-fuel mixture, and in this case, the distribution state of the air-fuel ratio in the combustion chamber is controlled to a predetermined state. More specifically, the air-fuel ratio between the center of the combustion chamber and the outer peripheral edge of the combustion chamber may be made rich, while the intermediate region between them may be made lean. The distribution state of the air-fuel ratio can be set in consideration of the intake swirl, the combustion chamber shape, and the combustion chamber wall surface temperature. EGR gas is a factor that contributes to combustion, and in this case, the distribution state of EGR gas in the combustion chamber is controlled to a predetermined state.

[0009]

According to the present invention, the factors contributing to combustion are controlled so that the combustion ratio of the air-fuel mixture ignited by the ignition gap arranged in the center of the combustion chamber becomes uniform. In other words, since the peak value of the combustion speed is reduced to control the combustion ratio to be uniform over the entire combustion period, NOx is significantly reduced and sufficient combustion is achieved even at the outer peripheral edge of the combustion chamber. Is performed, and HC is significantly reduced.

When controlling the air-fuel ratio distribution state of the air-fuel mixture in the combustion chamber, the central portion of the combustion chamber and the outer peripheral edge portion are made rich, and the intermediate region thereof is made lean. As a result, after the reliable ignition by the ignition gap is obtained, the combustion proceeds while being suppressed in the intermediate region, and sufficient combustion is also performed in the outer peripheral edge of the combustion chamber. In this case, by making the air-fuel ratio of the center of the combustion chamber richer than that of the outer peripheral edge of the combustion chamber, it is preferable for more reliable ignition and prevention of abnormal combustion in the outer peripheral edge of the combustion chamber (prevention of knocking).

When EGR gas is selected as a factor contributing to combustion, the distribution state of EGR gas in the combustion chamber is
The distribution state of the air-fuel ratio is set to the opposite state, that is, the EGR gas is lean in the central portion of the combustion chamber and the outer peripheral edge portion,
The EGR gas is rich in the intermediate region. Preferred aspects and advantages of the invention will be apparent from the description of the examples below.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, 1 is a cylinder head, 2 is a combustion chamber, and the cylinder head 1 has two intake ports 3A and 3B and two exhaust ports 4A which open into the combustion chamber 2, respectively. 4B are formed. Intake / exhaust port 3A,
As is known, 3B, 4A, and 4B are opened / closed at known timing by intake / exhaust valves (not shown) in synchronization with the rotation of the crankshaft. An ignition gap 10 is arranged in the center of the combustion chamber 2.

The two intake ports 3A and 3B are connected to the combustion chamber 2
Are opened in the combustion chamber 2 on one side surface side of the cylinder head 1 with respect to the straight line L1 passing through the center of the cylinder and parallel to each other in the crank axis direction. Also, 2
The two exhaust ports 4A, 4B open into the combustion chamber 2 on the other side surface side of the cylinder head 1 with respect to the straight line L1,
They are formed in parallel with each other in the crankshaft direction. The intake ports 3A, 3B open on one side of the cylinder head,
The exhaust ports 4A, 4B are opened to the other side surface side of the cylinder head 1, and the cylinder head 1 is of a so-called cross flow type.

The two intake ports 3A, 3B have their downstream end portions, that is, the portions near the combustion chamber 2 as branch portions 3a, 3b defined by a partition wall 5, and their upstream portions gather together. It is a collecting unit 3c. Intake port 3A
From the upstream side to the downstream side, that is, the collecting portion 3c
From the to the branch portion 3a, it is formed in a substantially straight shape so as to be substantially orthogonal to the crankshaft.

The intake port 3B is curved from its branch portion 3b toward the collecting portion 3c. Explaining this curve, consider a straight line L2 that passes through the center of the combustion chamber 2 and is orthogonal to the crankshaft (orthogonal to the straight line L1). At this time, the upstream end of the partition wall 5 is on the straight line L2, and therefore the branch portion 3b is curved so as to be offset toward the intake port 3A side.

A swirl valve 6 is arranged in the collecting portion 3c. The swirl valve 6 is swingable around a rotary shaft 7 provided at the upstream end thereof. The state shown by the solid line in FIG. 1 is the fully closed state, and the state shown by the one-dot chain line is the fully opened state. is there. The rotating shaft 7 is located near the side wall of the collecting portion 3c on the side opposite to the intake port 3B.
The downstream end (free end) of the valve 6 is located at a small distance from the upstream end of the partition wall 5. Further, when the swirl valve 6 is fully opened, the swirl valve 6 is in a state of being substantially orthogonal to the crankshaft, that is, in a state of extending substantially parallel to the intake port 3A having a substantially straight shape. In the embodiment, the swirl valve 6 is fully closed when the load is low, the opening increases as the load increases when the load is medium, and is fully opened when the load is high.

As shown in FIG. 2, a first fuel injection valve 11 is arranged in the collecting portion 3c, and a second fuel injection valve 12 is arranged in the branch portion 3b. Each fuel injection valve 1
The fuel injection widths of 1 and 12 are set to be quite narrow, and the fuel injection is executed at a predetermined timing when the intake valve is opened. The position of the first fuel injection valve 11 in the height direction may be set at either the position shown by the solid line in FIG. 2 or the position shown by the alternate long and short dash line.

The first fuel injection valve 11 is oriented so as to inject fuel near the upstream end of the partition wall 5 and supply the fuel to the center of the combustion chamber. That is, the first fuel injection valve 11
The fuel injected from the both intake ports 3A, 3B is further prevented from interfering with the intake valve in the open state,
It reaches the center of the combustion chamber 2. The second fuel injection valve passes through an end of the intake port 3A on the side far from the partition wall 5,
The fuel is directed to the outer peripheral edge of the combustion chamber. That is, the fuel injected from the second fuel injection valve 12 reaches the outer peripheral edge of the combustion chamber from the intake port 3A so as not to interfere with the intake valve in the open state.

By the fuel injection as described above, the combustion chamber 2
Immediately before ignition by the ignition gap 10,
An air-fuel ratio distribution state of the air-fuel mixture as shown in FIG. 4 is formed. That is, the center of the combustion chamber is made rich (this is indicated by symbol α in FIG. 4), the outer peripheral edge of the combustion chamber is also made rich (this is indicated by symbol β in FIG. 4), and the intermediate region is made lean. (This is indicated by the symbol γ in FIG. 4). In this case, the air-fuel ratio at the center of the combustion chamber is richer than the air-fuel ratio at the outer peripheral edge of the combustion chamber. The process by which such an air-fuel ratio distribution state is formed is shown in FIGS. 11 to 13. In addition,
A general stratified air-fuel ratio distribution state is shown by a broken line in FIG.

According to the distribution state of the air-fuel ratio as described above,
Since the air-fuel ratio is particularly rich in the center of the combustion chamber, good ignitability can be obtained. The flame generated by ignition spreads to the outer peripheral edge of the combustion chamber centering on the ignition gap, but since the air-fuel ratio in the middle region is lean, flame spread is suppressed (inhibition of increase in combustion ratio). And, since the air-fuel ratio becomes rich again at the outer peripheral edge of the combustion chamber,
Although the flame spread tends to become faster, the wall ratio of the outer peripheral edge of the combustion chamber is cold, so that the combustion ratio does not increase extremely, and the combustion ratio is almost the same as in the intermediate region. A state of such combustion is schematically shown in FIG. 23, and in FIG. 23, a state of conventional general combustion is shown by a broken line.

Due to such combustion, the combustion ratio changes toward the peak value during combustion in the center of the combustion chamber, but the flame surface immediately moves to the lean intermediate region, so the peak is concerned. The black value becomes small, and NOx is greatly reduced. Further, since the combustion ratio at the outer peripheral edge of the combustion chamber is much larger than that in the conventional case, the calorific value becomes sufficient and HC is significantly reduced.

The above-mentioned air-fuel ratio distribution state is preferably set in consideration of the intake swirl as shown in FIG. In FIG. 5, the air-fuel ratio distribution state when the intake swirl is strong is shown by a solid line, and the air-fuel ratio distribution state when the intake swirl is weak is shown by a broken line. As described above, when the intake swirl is strong, as compared with when it is weak, the regions of the combustion chamber center portion and the outer peripheral edge portion, which are considered to be rich, are each narrow, that is, the combustion chamber intermediate region is set wide, and the rich region is set. The portion to be filled is made richer and the portion to be leaned is made leaner. By doing so, appropriate combustion can be obtained in consideration of the fact that the fuel is about to be moved in the radial direction of the combustion chamber 2 by the intake swirl. FIG. 16 shows an example in which the air-fuel ratio distribution state at the time of a weak swirl is a pentorf type combustion chamber. In order to allow the fuel to smoothly flow in the swirl direction, it is preferable to dispose the first fuel injection valve 11 as shown by the alternate long and short dash line in FIG.

The combustion chamber 2 may have a squish area in a part of its outer peripheral edge, and the squish flow is shown by an arrow Y1 in FIG. In this case, the distribution state of the air-fuel ratio is set so that the lean region γ is narrow in the squish flow direction and
It is recommended to widen and β so that each area becomes an ellipse as a whole (promotion of flame spread against squish flow). Since the influence of the squish becomes remarkable when the intake swirl is weak, it may be considered only when the intake swirl is weak. FIG. 14 shows a relationship between a specific setting example of the squish area and the air-fuel ratio distribution state. FIGS. 15 and 16 show an example in which the air fuel consumption distribution state at the time of a weak swirl is a pentorf type combustion chamber (without a squish area). At the time of weak swirl, the left and right ends in FIG. 15 become narrow near the compression top dead center, and there is a flow toward the center where it is difficult for the air-fuel mixture to enter this part. Thus, when there is a flow toward the radial center of the combustion chamber 2, the distribution state of the air-fuel ratio is set so as to narrow the intermediate region γ in this flow direction (the radial flow direction is the major axis). Set the areas α and β in an elliptical shape.

The air-fuel ratio distribution state shown in FIG. 6 can be obtained by intermittently injecting fuel from the fuel injection valves 11 and 12. That is, as shown in FIG. 18, in the case of a weak swirl, the injection pulse is intermittent as shown by the solid line (second fuel injection valve 12) and the broken line (first fuel injection valve 11), and the strong swirl is performed. In case of -le, continuous injection may be performed as indicated by the alternate long and short dash line. When the continuous injection and the intermittent injection are selectively used, it is preferable to adjust the fuel pressure in accordance with the relationship of the minimum injection pulse width (the fuel pressure during the continuous injection is small).

FIG. 7 shows a preferable distribution state of the air-fuel ratio according to the combustion shape. In FIG. 7, the solid line indicates the cone combustion chamber,
The case where the height of the combustion chamber becomes lower toward the outer peripheral edge of the combustion chamber is shown, and the broken line shows the case where the height of the combustion chamber is substantially the same in the radial direction of the combustion chamber. The distribution of the air-fuel ratio considering the height of the combustion chamber is made rich in the low part and lean in the high part (combustion velocity increase / decrease adjustment by changing the flame surface area). FIG. 17 shows the state of air-fuel ratio distribution when the combustion chamber is of the Pentorf type as shown in FIG. Note that FIG.
As shown in, when the region β is set to be considerably wide, both the injection angle of the second fuel injection valve 12 and the fuel pressure may be increased.

FIG. 8 shows the EGR gas distribution state in the combustion chamber when EGR gas is supplied. Since the EGR gas has a combustion suppressing effect, the distribution state is basically the reverse of the air-fuel ratio distribution state. When performing combustion control using this EGR gas, as shown in FIG. 20, the EGR gas introduction passage 41 directed toward the intermediate region (region indicated by γ in FIG. 4) of the combustion chamber 2 is provided to the intake port 3B. The control valve 42, which is an on-off valve, is connected to the introduction passage 41.
Then, the opening timing of the control valve 42 may be opened at a timing that does not interfere with the intake valve in the open state (FIG. 2).
2). Of course, such an introduction passage 41 and a control valve 42
And are provided for each cylinder. In addition, in the early stage of intake, EGR
Even if the gas is introduced, the intake swirl prevents the EGR gas from diffusing toward the center of the combustion chamber and causes no problem in terms of ignitability.

The widths of the regions α and β can be changed by changing the injection angle (width) of the fuel injection valves 11 and 12, as described above. In order to change this injection angle, for example, as shown in FIG.
It may be carried out by adjusting the amount of assist air from the air port 13 provided in 12, and the relationship between the swirl strength and the amount of assist air is shown in FIG. Of course,
When setting the distribution state of the air-fuel ratio, two fuel injection valves 1
Instead of using 1 and 12, as shown in FIG. 19, one fuel injection valve 51 of two injection hole type may be used.

When there is a difference in the wall temperature of the combustion chamber, considering that the higher the wall temperature, the faster the flame spread,
The distribution state of the air-fuel ratio may be determined. More specifically, when the wall surface temperature changes in the radial direction of the combustion chamber, the air-fuel ratio of the portion where the wall surface temperature is low may be made rich, and the higher the wall surface temperature, the leaner it may be.

[Brief description of drawings]

FIG. 1 is a diagram showing a setting example of an intake port, an ignition gap, and a fuel injection direction with respect to a combustion chamber.

FIG. 2 is a view showing the fuel injection direction shown in FIG. 1 from the side.

FIG. 3 is a diagram showing a basic form of an air-fuel ratio distribution state.

FIG. 4 is a plan view more specifically showing a basic form of an air-fuel ratio distribution state.

FIG. 5 is a diagram showing an air-fuel ratio distribution state according to swirl strength.

FIG. 6 is a diagram showing an air-fuel ratio distribution state in which a squish flow is added.

FIG. 7 is a diagram showing an air-fuel ratio distribution state according to the height of a combustion chamber.

FIG. 8 is a diagram showing a distribution state of EGR gas.

FIG. 9 is a view showing an example of a fuel injection valve in which the injection angle can be adjusted by assist air.

FIG. 10 is a diagram showing a relationship between an assist air amount and a swirl strength.

FIG. 11 is a diagram showing an air-fuel ratio distribution state in the early stage of intake.

FIG. 12 is a diagram showing an air-fuel ratio distribution state at the end of intake.

FIG. 13 is a diagram showing an air-fuel ratio distribution state at the final stage of compression.

FIG. 14 is a diagram showing a relationship between a specific setting example of a squish area and an air-fuel ratio distribution state.

FIG. 15 is a view showing the shape of a cone type combustion chamber.

FIG. 16 shows a swirl in the case of a cone type combustion chamber.
FIG. 6 is a diagram showing an air-fuel ratio distribution state when the flow is weak in the combustion chamber and a flow in the radial direction of the combustion chamber exists.

17 is a diagram showing an air-fuel ratio distribution state set in consideration of a change in the height of the combustion chamber in the case of the cone type combustion chamber shape shown in FIG.

FIG. 18 is a diagram showing an example in which the fuel injection timing is changed to change the air-fuel ratio distribution state.

FIG. 19 is a diagram showing an example in which an air-fuel ratio distribution state is obtained by a two-hole injection type fuel injection valve.

FIG. 20 is a diagram showing an example of setting an EGR gas introduction path.

FIG. 21 is a view showing an intake swirl.

FIG. 22 is a diagram showing an EGR gas introduction timing.

FIG. 23 is a diagram showing how the combustion ratio changes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder head 2 Combustion chamber 3A Intake port 3B Intake port 4A Exhaust port 4B Exhaust port 10 Ignition gap 11 First fuel injection valve 12 Second fuel injection valve α Rich region β in the center of combustion chamber Rich region at the outer peripheral edge of the combustion chamber γ Lean region between the center of the combustion chamber and the outer peripheral edge

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display area F02D 41/04 305 Z 9039-3G 43/00 301 U 8109-3G E 8109-3G 45/00 301 J 8109-3G F02P 13/00 301 A 8923-3G (72) Inventor Noriyuki Ota 3-3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Motor Corporation

Claims (14)

[Claims] 1. An engine in which an ignition gap is located at the center of a combustion chamber, so that the combustion ratio is uniform until the flame generated by ignition by the ignition gap reaches the outer peripheral edge of the combustion chamber. A combustion control device for an engine, further comprising: control means for controlling a factor that contributes to combustion of the air-fuel mixture. 2. The flame spreader according to claim 1, wherein the control means accelerates the flame spread in the combustion center part and the outer peripheral edge part of the combustion chamber, and in the intermediate region between the center part of the combustion chamber and the outer peripheral part. The thing that makes the bats slow down. 3. The flame spreader according to claim 2, wherein the flame spread at the center of the combustion chamber is faster than the flame spread at the outer peripheral edge of the combustion chamber. 4. The control system according to claim 2, wherein the control means sets a distribution state of the air-fuel ratio of the air-fuel mixture in the combustion chamber. 5. The control device according to claim 4, wherein the control means sets the distribution state of the air-fuel ratio according to the intake swirl. 6. The control device according to claim 5, wherein the control means sets an air-fuel ratio distribution state in the combustion chamber circumferential direction according to the intake swirl. 7. The device according to claim 5, wherein the control means sets an air-fuel ratio distribution state in the combustion chamber radial direction according to the intake swirl. 8. The device according to claim 2, wherein the pre-control means sets the distribution state of the air-fuel ratio according to the shape of the combustion chamber. 9. The control device according to claim 8, wherein the control means sets the distribution state of the air-fuel ratio according to the height of the combustion chamber. 10. The device according to claim 2, wherein the control means sets the distribution state of the air-fuel ratio according to the temperature of the wall surface of the combustion chamber. 11. The device according to claim 2, wherein the control means sets a distribution state of EGR gas in the combustion chamber. 12. In an engine having an ignition gap located in the center of a combustion chamber, a combustion ratio is uniform until a flame generated by ignition by the ignition gap reaches an outer peripheral edge of the combustion chamber. A method for controlling combustion of an engine, comprising: controlling a factor that contributes to combustion of an air-fuel mixture. 13. The flame spread according to claim 12, wherein the flame transfer speeds of the combustion center part and the outer peripheral edge part of the combustion chamber are respectively high, and the flame transfer speed of the intermediate region between the center part of the combustion chamber and the outer peripheral part is delayed. To control like. 14. The method according to claim 13, wherein the flame transfer rate at the center of the combustion chamber is higher than the flame transfer rate at the outer peripheral edge of the combustion chamber.