JPH05223015A - Combustion control device for engine - Google Patents

Abstract

PURPOSE:To restrain the generation of detrimental components which cause atmospheric pollution while improving the fuel consumption by providing ternary catalyst for purifying exhaust gas in an exhaust passage, and by providing a fuel supply means for feeding a mixture having a stoichiometric air-fuel ratio into a combustion chamber so as to open its introduction port at a position around an intake port. CONSTITUTION:A spark plug 9 is provided in a substantially center part of a combustion chamber, and a ternary catalyst 19 for purifying exhaust gas in an exhaust passage 17. Of three intake ports 5a to 5c communicated with the combustion chamber, the center one 5b is opened toward the position of the spark plug 9. A fuel supply means 15 for feeding a mixture having a stoichiometric airfuel ratio is provided in an intake-air passage 11b communicated with the center intake port 5b. Two intake-air passages 11a, 11c on opposite sides of the center intake-air passage 11b are formed with introduction ports 21, respectively, for introducing at least a part of exhaust gas which is inert components at least during low load operation. With this arrangement, the quantity of unburnt fuel components can be reduced, thereby it is possible to prevent incomplete combustion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gasoline engine having three intake valves, and more particularly to a combustion control device for suppressing the generation of harmful substances which cause air pollution while improving the fuel consumption thereof.

[0002]

2. Description of the Related Art Exhaust gas from an automobile engine contains a wide variety of harmful components. Of these, hydrocarbons (HC ), Carbon monoxide (CO), and nitrogen oxides (NOx).

Conventionally, in order to purify the three kinds of harmful components contained in the exhaust gas, a mixture having a stoichiometric air-fuel ratio is used as the intake air, and a three-way catalyst is provided in the exhaust passage of the engine to introduce the exhaust gas into the exhaust gas. A catalyst purification system has been widely adopted in which the oxidation reaction of unburned components contained and the reduction reaction of nitrogen oxides are simultaneously performed.

On the other hand, recently, in an engine having a plurality of intake valves per cylinder, when the engine is operating under a low load, lean combustion is performed by using an air-fuel mixture much thinner than the theoretical air-fuel ratio to improve fuel economy. It is known to do so. In this lean burn engine, intake air is sucked in through two intake valves, and fuel is injected into the intake air sucked in from one intake valve. A spark plug is placed at a position facing the intake valve where this fuel is injected. Is provided. For this reason, a layer of a rich air-fuel mixture is formed around the spark plug even in one combustion chamber,
The rich mixture is ignited via a spark plug.

[0005]

By the way, in the case of the lean burn engine of this type, since the two intake valves are opened and closed at the same time, the intake air amount flowing into the combustion chamber through these intake valves is substantially equal. .. Therefore, even when the air-fuel ratio of the entire combustion chamber is 22 to 23, there is a possibility that a mixture region extremely richer than the stoichiometric air-fuel ratio exists in the vicinity of the spark plug, which causes the exhaust stroke. By the end, it may be difficult to burn all of the air-fuel mixture sucked into the combustion chamber.

As a result, the unburned or incompletely burned fuel components are discharged as they are with the combustion gas, and as a result, the emission concentrations of CO and HC increase, and the burden on the three-way catalyst increases. is there.

Further, in a lean burn engine that burns in an excessive oxygen state, a sufficient amount of oxygen remains in the exhaust gas to oxidize CO and HC, and NOx is decomposed by a three-way catalyst. Oxygen can be easily obtained without doing so. Moreover, the amount of NOx generated becomes maximum in a lean region where the air-fuel ratio is 16-18, which is thinner than the stoichiometric air-fuel ratio. Therefore, NOx generated in the combustion process is discharged as it is without being decomposed by the three-way catalyst. I will end up.

Therefore, in the conventional lean burn engine described above, although it is possible to improve the fuel consumption, it is difficult to efficiently remove the harmful substances contained in the exhaust gas with the three-way catalyst.

The present invention has been made under these circumstances, and particularly in a low-load operating region, it is possible to improve the fuel efficiency and suppress the generation of harmful components that cause air pollution. An object of the present invention is to provide a combustion control device for an engine that can effectively utilize the original catalyst for purifying harmful components.

[0010]

In view of the above, according to the present invention, an ignition plug is provided substantially in the center of the combustion chamber, and the ignition plug is located in the combustion chamber around the ignition plug and individually opened and closed by intake valves. In an engine in which three intake ports are provided, the intake passages are respectively communicated with these intake ports, and an exhaust passage communicating with the combustion chamber is provided with a three-way catalyst for exhaust gas purification,

Of the three intake ports connected to the combustion chamber,
The central intake port is opened in the direction of the position of the above-mentioned spark plug, and in one intake passage connected to the central intake port,
A fuel supply means for supplying the air-fuel mixture of the stoichiometric air-fuel ratio to the combustion chamber is provided, and the intake passages on both sides of the central intake passage are provided with exhaust gas which is an inactive component at least during low load operation. It is characterized by having an inlet for introducing some of them. According to a second aspect of the present invention, an introduction port for guiding a part of the exhaust gas to the intake passage is opened near the intake port by directing the intake port.

Further, according to a third aspect of the present invention, the opening timing of the intake valves corresponding to the intake passages on both sides having the introduction port is set earlier than the opening timing of the intake valves corresponding to the central intake passage. There is.

[0013]

According to the configurations described in claims 1 and 2,
At least in the low load range, some of the exhaust is
It is introduced into the two intake passages on both sides through the introduction port, and this exhaust gas is filled in the intake passage during the period when the intake valve is closed. In this case, since the inlet is opened in the vicinity of the intake port, the exhaust gas recirculated to the intake passage is sequentially stored from the open end of the intake port toward the upstream side. Then, when the intake valve is opened in the intake stroke, the exhaust gas filled in the intake passage flows into the combustion chamber, and the air-fuel mixture having the theoretical air-fuel ratio flows into the combustion chamber through the central intake passage. The intake port connecting the central intake passage is open toward the spark ignition position by the spark plug, so that the air-fuel mixture of the stoichiometric air-fuel ratio is surely introduced near this spark plug, and ignition at the spark ignition position is easy. It is possible to form a mixed gas layer.

Therefore, a recirculated exhaust gas flow and a stoichiometric air-fuel mixture flow are formed in one combustion chamber, and these two flows are large in the combustion chamber even after reaching the compression stroke. After being compressed in a substantially layered state without being agitated, it is ignited through an ignition plug.

Therefore, the air-fuel mixture in the combustion chamber is ignited after being compressed in a state of a substantially stoichiometric air-fuel ratio, so that flame propagation in the combustion chamber is stably performed and the air-fuel mixture is generated like a conventional lean-burn engine. There is no fear that a rich mixture region will be formed in the combustion chamber. Therefore, unburned fuel components are reduced, incomplete combustion can be prevented, and HC and CO emissions to the exhaust passage are reduced.

Since most of the exhaust gas, which is an inert component, is supplied into the combustion chamber together with the air-fuel mixture, the oxygen component contained in the exhaust gas is reduced. Therefore, NOx can be decomposed by the three-way catalyst, and the three-way catalyst can be effectively used for purification of harmful components.

Further, since the air-fuel mixture is burned under a large amount of exhaust gas recirculation, pumping loss due to rise in intake pressure can be reduced, and fuel consumption can be improved accordingly.

According to the third aspect of the present invention, at least in a low load operation range, a part of the exhaust gas is introduced into the intake passages on both sides through the introduction port, and the exhaust gas is in a period in which the intake valve is closed. It is filled in the intake passage. At the same time, the intake valve corresponding to the intake passage through which the exhaust gas recirculates opens earlier than the intake valve corresponding to the central intake passage, so that the communication between the combustion chamber and the intake passages on both sides during the exhaust stroke is increased. Since it is performed from an early stage before the dead point, at the end of the exhaust stroke, the high-pressure burned gas remaining in the combustion chamber flows back into the intake passage through the intake port.

From this fact, since the exhaust gas and the burnt gas are recirculated in the two intake passages on both sides, the inactive component stored in the intake passages on both sides can be made sufficient, and When the valve is opened, fresh air can be suppressed from flowing into the combustion chamber from these two intake passages as much as possible.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

FIG. 1 shows a four-cylinder gasoline engine for automobiles, in which reference numeral 1 is a cylinder head.
On the mating surface of the cylinder head 1 and the cylinder block 2,
Four combustion recesses 3 are formed. The combustion recess 3 forms a combustion chamber 4 between itself and a piston (not shown) housed in the cylinder block 2.
As shown in, it has a pent roof shape.

The combustion recess 3 has three intake ports 5a, 5a.
b, 5c and two exhaust ports 6a, 6b are formed.
The intake ports 5a, 5b, 5c and the exhaust ports 6a, 6b are arranged facing each other with respect to a line X ₁ passing through the center of the combustion chamber 4 and parallel to the crankshaft (not shown). These intake ports 5a, 5b, 5c are individually opened and closed by three intake valves 7, and the exhaust ports 6a, 6b are individually opened and closed by two exhaust valves 8.

In the case of this embodiment, the intake ports 5 on both sides are provided.
The intake valve 7 that opens and closes a and 5c has a central intake port 5c.
4 ° to 10 before top dead center than the intake valve 7 that opens and closes
Start opening at an early timing of about ° (crank angle),
It is designed to close 4 ° to 10 ° (crank angle) early after bottom dead center.

A spark plug 9 is arranged in the combustion chamber 4. The spark plug 9 is located at the center of the combustion recess 3 surrounded by the intake ports 5a, 5b, 5c and the exhaust ports 6a, 6b. As shown in FIG. 1, the spark plug 9 is located on an extension of the central intake port 5b among the three intake ports 5a, 5b, 5c. For this reason,
The central intake port 5b is opened toward the position of the spark plug, that is, the direction of the spark ignition position in the combustion chamber 4.

The intake ports 5a, 5b, 5c of each combustion chamber 4 are
The intake passages 11a, 11b and 11c are connected to each other.
The intake passages 11a, 11b, 11c are provided independently of each other, and these three intake passages 11a, 11b,
The volume of 11c is set to 25% or more of the stroke volume. The three intake passages 11a, 11b, 11c are arranged in parallel with each other, and these intake passages 11a, 11b,
The end of 11c on the side connected to the intake ports 5a, 5b, 5c is
As shown in FIG. 2, it is curved downward. And
The curvature of the curved portion of the central intake passage 11b is smaller than the curvature of the curved portions of the intake passages 11a and 11c on both sides.

Intake passages 11a connected to the four combustion chambers 4,
The upstream ends of 11b and 11c are opened to a single intake chamber 12. The intake chamber 12 includes a throttle body 13 connected to an air cleaner (not shown).
A throttle valve 14 is provided in the throttle body 13, and the throttle valve 14 is manually opened / closed.

Three intake passages 11a connected to the combustion chamber 4
A fuel injection valve 15 is provided in the central intake passage 11b of the 11b and 11c. The fuel injection valve 15 injects fuel into the intake air flowing through the intake passage 11b at a certain timing during the intake stroke, preferably immediately before the intake valve 7 is closed, and when the engine is in a low / medium load operating state, A stoichiometric air-fuel mixture is supplied to the combustion chamber 4 through the intake passage 11b.

The exhaust ports 6a and 6b of each combustion chamber 4 are
It is connected to the exhaust passage 17. The exhaust passages 17 are gathered into one, and a three-way catalyst 19 for exhaust purification is provided downstream of the exhaust gathering portion 18.

An exhaust gas recirculation path 20 for returning a part of the exhaust gas to the intake system is connected to the exhaust gas collecting portion 18. The exhaust gas recirculation passage 20 has an inlet 21 for introducing exhaust gas into the two intake passages 11a and 11c on both sides of the central intake passage 11b. As shown in FIG. 2, the introduction port 21 is opened immediately before the intake ports 5a and 5c in a posture that directs the intake ports 5a and 5c.

An EGR valve 22 for controlling the flow rate of exhaust gas returned to the intake system is provided in the exhaust gas recirculation path 20. The EGR valve 22 is opened and closed according to the intake negative pressure proportional to the intake air amount.
The drive unit of the valve 22 is connected to the intake chamber 12 via the negative pressure introduction passage 23. In this negative pressure introduction path 23, E
A negative pressure control valve 24 is provided to control the intake negative pressure introduced to the drive section of the GR valve 22. This negative pressure control valve 2
4 is controlled by a command from the EGR control device 25. To the EGR control device 25, various signals indicating the actual operating condition of the engine during engine operation, such as signals indicating the engine speed, the coolant temperature and the throttle opening, are input. Determines the operating condition of the engine based on various input signals, and controls the opening / closing of the negative pressure control valve 24 based on the result of the determination.

Therefore, the EGR valve 22 of the present embodiment is opened when the engine is in the low / medium load operating range excluding the idling range, and exhaust gas of 10 to 20% of the intake air amount is recirculated to the combustion chamber 4. It has become so. Next, the operation of the above configuration will be described.

When the engine is operated under a low load, the intake air throttled by the throttle valve 14 is
As indicated by the white arrows, the air is introduced into the three intake passages 11a, 11b, 11c through the intake chamber 12.

Since the EGR valve 22 is opened in this operating range, a part of the exhaust gas, which is an inactive component, is introduced into the exhaust gas recirculation passage 20 through the inlet 21 as shown by the black arrow in FIG. Is introduced into the two intake passages 11a and 11c on both sides. In this case, the inlet 21 is opened immediately before the intake ports 5a and 5c so as to be directed toward the intake ports 5a and 5c, so that the exhaust gas from the introduction port 21 does not flow as shown in FIG. It flows toward the intake ports 5a and 5c. At the same time, as shown in FIG. 2B, the intake valve 7 corresponding to the intake passages 11a and 11c in which the exhaust gas is recirculated is an intake valve corresponding to the intake passage 11b to which the air-fuel ratio mixture is supplied. Since it starts to open at a timing earlier than 7, the communication between the combustion chamber 4 and the intake passages 11a and 11c during the exhaust stroke is performed from an early stage before top dead center, and remains in the combustion chamber 4. The high-pressure burnt gas that flows therein flows back into the intake passages 11a and 11c through the intake ports 5a and 5c. Moreover, the volumes of the intake passages 11a and 11c are
Since it is set to a large value of 25% or more of the stroke volume, during the period when the intake valve 7 is closed, the intake passages 11a, 11a
A sufficient amount of inactive ingredients will be stored in c.

When the engine reaches the intake stroke and the intake valve 7 is opened near the top dead center, the intake passages 11a, 1 on both sides are opened.
The inactive component filled in 1c flows into the combustion chamber 4 through the intake ports 5a and 5c, and the stoichiometric air-fuel ratio mixture flows into the combustion chamber 4 through the central intake port 5b. Since the central intake port 5b is opened toward the spark ignition position by the spark plug 9, the air-fuel mixture having the stoichiometric air-fuel ratio is surely guided to the vicinity of the spark plug 9, and the combustion chamber 4
An air-fuel mixture layer that can easily be ignited can be formed at the spark ignition position inside.

From the above, a flow of the recirculated inert component and a flow of the air-fuel mixture having the stoichiometric air-fuel ratio are formed in the combustion chamber 4, and these two flows are large until the end of the compression stroke. It is compressed without being agitated while maintaining a substantially layered state. Then, at the end of the compression stroke, the air-fuel mixture is ignited via the spark plug 9.

In this case, from the intake ports 5a, 5c to the combustion chamber 4
Since most of the inactive components stored in the intake passages 11a and 11c when the intake valve 7 is closed, the air-fuel mixture in the combustion chamber 4 is compressed at a substantially stoichiometric air-fuel ratio. It is ignited after being done.

Moreover, in this embodiment, the fuel injection valve 1
5 indicates that the fuel is introduced into the intake passage 11 immediately before the intake valve 7 is closed.
Since the fuel is injected into b, the air-fuel mixture layer having the stoichiometric air-fuel ratio is reliably formed around the spark plug 9.

Therefore, the air-fuel mixture is reliably ignited, and the flame is stably propagated in the combustion chamber 4, so that the combustion chamber 4 is overheated like the conventional lean burn engine. No dense mixture layer is formed.

From this, it becomes possible to burn all of the air-fuel mixture sucked into the combustion chamber 4 by the end of the exhaust stroke, and it is possible to prevent generation of unburned fuel components and incomplete combustion. it can. Therefore, the amount of HC and CO discharged to the exhaust passage 17 is reduced, and the load on the three-way catalyst 19 is reduced.

Further, during the intake stroke, the intake passages 11a, 11
Exhaust gas, which is an inactive component, occupies most of the flow from c to the combustion chamber 4, so that the excess oxygen contained in the exhaust gas decreases. Therefore, NOx produced in the combustion process can be decomposed by the three-way catalyst 19, and the three-way catalyst 19 can be effectively utilized for purifying harmful components in addition to the reduction in the amount of HC and CO emissions. ..

Moreover, since combustion in the low load operation range is performed under a large amount of exhaust gas recirculation, pumping loss due to increase in intake pressure can be reduced. Therefore, it is possible to improve the fuel consumption even though the air-fuel mixture having the stoichiometric air-fuel ratio is supplied.

Further, in this embodiment, the intake valve 7 for supplying the inactive component to the combustion chamber 4 at the end of the intake stroke.
Is closed earlier, the flow of the air-fuel mixture supplied from the central intake port 5b is less likely to be affected by the flow of the inert component. Therefore, the air-fuel mixture easily flows around the ignition plug 9, and a layer of the air-fuel mixture can be formed more reliably there, and the ignitability of the air-fuel mixture is improved.

When the burned gas in the combustion chamber is made to flow backward from the intake port into the intake passage as in the above-described embodiment, the introduction port for guiding the exhaust gas to the intake passage is not necessarily the intake air. It need not be provided near the mouth, but may be provided, for example, in the middle portion of the intake passage.

Further, in the above-described embodiment, the intake valves on both sides for supplying the inert component to the combustion chamber are closed earlier than the central intake valve for supplying the air-fuel mixture to the combustion chamber. However, the timing at which the intake valves on both sides close may be the same as or later than that at the central intake valve.

Further, the engine according to the present invention is not specified for automobiles but can be applied as a drive source for motorcycles and other fields, and the number of cylinders is not specified in the above embodiment.

[0046]

According to the present invention, it is possible to reliably form an air-fuel mixture layer that is easily ignited at the spark ignition position in the combustion chamber, and the air-fuel mixture flowing into the combustion chamber is substantially Since ignition is performed after being compressed in the state of the stoichiometric air-fuel ratio, flame propagation in the combustion chamber is performed stably, and there is no fear that a rich mixture region is formed in the combustion chamber. Therefore, unburned fuel components are reduced, and incomplete combustion can be prevented, and accordingly, the amount of HC and CO emissions is reduced, and the burden on the three-way catalyst is reduced.

Further, since the combustion is carried out under a large amount of exhaust gas recirculation, the surplus oxygen in the exhaust gas is reduced. Therefore,
NOx generated in the combustion process can be decomposed by the three-way catalyst, and the three-way catalyst can be effectively used as a harmful component for purification together with the reduction of the emission amount of HC and CO.

Further, since the combustion during the low load operation is performed under a large amount of exhaust gas recirculation, it is possible to reduce the pumping loss due to the rise of the intake pressure, and to supply the air-fuel mixture of the stoichiometric air-fuel ratio. However, the fuel efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of an engine in an embodiment of the present invention.

FIG. 2A is a cross-sectional view showing the flow of exhaust gas recirculated to the intake passage when the intake valve is closed. FIG. 6B is a cross-sectional view showing the flow of exhaust gas recirculated to the intake passage when the central intake valve is opened.

[Explanation of symbols]

4 ... Combustion chamber, 5a, 5b, 5c ... Intake port, 7 ... Intake valve, 9 ... Spark plug, 11a, 11b, 11c ... Intake passage, 15 ... Fuel injection means (fuel injection valve), 17 ... Exhaust passage, 19 … Three-way catalyst, 21… Inlet.

Claims (3)

[Claims] 1. A spark plug is provided substantially in the center of a combustion chamber, and three intake ports that are located around the spark plug and that are individually opened and closed by intake valves are provided in the combustion chamber. In an engine in which the intake passage is communicated and an exhaust passage communicating with the combustion chamber is provided with a three-way catalyst for exhaust purification, the central intake port among the three intake ports communicating with the combustion chamber is the spark plug. A fuel supply means for supplying the air-fuel mixture of the stoichiometric air-fuel ratio to the combustion chamber is provided in one intake passage which is opened toward the position of the central intake port and is connected to the central intake port. A combustion control device for an engine, characterized in that the intake passages on both sides of the passage are provided with inlets for introducing at least a part of exhaust gas which is an inactive component at the time of low load operation. 2. The combustion control device for an engine according to claim 1, wherein the introduction port is opened near the intake port so as to be directed toward the intake port. 3. The method according to claim 1, wherein the opening timing of the intake valves corresponding to the intake passages on both sides having the introduction port is set earlier than the opening timing of the intake valves corresponding to the central intake passage. Characteristic engine combustion control device.